This work deals with the desulfurization of model fuel at mild conditions with sulfur content of 100 to 500 and 300 to 3000 ppm using prepared nano titanium ...
Republic of Iraq Ministry of Higher Education and Scientific Research University of Baghdad College of Engineering Chemical Engineering Department
Oxidative Desulfurization of Model Liquid Fuel Using Prepared NanoTitanium Dioxides Catalyst A Thesis Submitted to the College of Engineering of the University of Baghdad in the Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Chemical Engineering
BY Fadhil Abed Allawi (B.Sc. in Chemical Engineering 1995) (M.Sc. in Chemical Engineering 2013)
December 2017
63
Summary
Oxidative Desulfurization of Model Liquid Fuel Using Prepared Nano -Titanium Dioxide Catalyst By Fadhil Abed Allawi Supervised by Prof Dr. Basma Abbas Abdulmajeed Assit Prof Dr. Sameera M. Hamad-Allah
This work deals with the desulfurization of model fuel at mild conditions with sulfur content of 100 to 500 and 300 to 3000 ppm using prepared nano titanium dioxide as catalyst in three crystalline forms (amorphous,
anatase
and
anatase-rutile)
with
and
without
phosophtungstic acid (PWA) and Octade cetyltrimethylammonium bromide (STAB). Nano titanium dioxide was successively synthesized by sol-gel and hydrothermal methods using titanium tetra-isopropoxide (TTIP), titanium ethoxide, (STAB) as surfactant, and different acids (hydrochloric, acetic, phosphoric, and phosphotungstic) as catalyst. The effect of different parameters on the synthesis of nano titanium dioxide was studied like; varied pH (1-9) by using acid and base, acid type (HCl, CH3COOH, H3PO4, and H3PW12O40) for sol-gel method and crystallization temperature (170-190)oC , crystallization time (12-24) hrs and acid type (acetic and phosphotungstic)for hydrothermal method and finally calcinations temperature (450- 900)oC for two methods. Characterization was made using X-ray Diffraction (XRD) for crystalline phase identification, BET surface area, Scanning Electron Microscopy (SEM) for surface morphology, X-ray Fluorescence (XRF)
64
for chemical analysis, (FTIR) and Atomic Force Microscopy (AFM) for particles size measurement. It was found that all the prepared samples at different conditions represent crystalline nano titanium dioxide. The best preparation conditions for preparing nano titanium dioxide were found at pH=1for sol-gel method ,(TTIP) as source materials and 120,450, 700oC calcination temperature with 1370, 77.5 and 28.9 m2/gm surface area for amorphous, anatase and anatase-rutile phases, 0.46, 0.15 and 0.048 cm3/gm pore volume, and 71.98 and 95.50 nm average particle size for anantase and anatase-rutile phases. In hydrothermal method best conditions by using (PWA) acid with (TTIP) as source materials and (STAB) as a structure directing agent were 180oC crystallization temperature, 24 hrs crystallization time, and 120,450, 800oC calcination temperature with 1923.8, 221and 153.99 m2/gm surface area for amorphous, anatase and anatase-rutile phases, 0.68, 0.32 and 0.25 cm3/gm pore volume and 77.92 and 96.70 nm average particle size for anantase and anatase-rutile phases. The activity of two types of catalysts with and without phosphotungstic acid for oxidative desulfurization of model fuel was examined. Several factors affecting the reduction of sulfur compounds were investigated .These factors were TiO2 crystalline forms, stirring rate 200 to1200 rpm, different reaction temperatures 40 to 80oC , different initial concentration of dibenzothiophene (DBT) from 100 to 500 and 300 to 3000 ppm, different catalyst amount 0.1 to 0.3 gm/ml, different oxidant amount (5:1to 20:1 mol ratio H2O2/DBT) , and different reaction time from 0 sec to 120 sec and 0 min to10 min. 65
It was concluded that the activity of nano TiO2 with phosphotungstic acid catalyst is higher than that obtained by nano TiO2 without phosphotungstic acid catalyst. In the case of nano TiO2 without phosphtungstic acid anatase nano-TiO2 exhibited high activity for the catalytic oxidation of DBT (100 ppm), and DBT as high as 100% was achieved at a reaction time of 40 s, 70oC, and 800 rpm. By contrast, the catalytic rates presented by anatase– rutile TiO2 and amorphous TiO2 were only 50% and 23.5%, respectively. TiO2 with phosphotungstic acid the DBT solution with an initial concentration of 3000 ppm, nano TiO2 (anatase) prepared showed the best catalytic reactivity 70% DBT conversion was achieved within 10 min. While nano TiO2 (anatase-rutile) and (amorphous) showed the least conversion to catalytic reactivity towards DBT and only 46.5% and 29% DBT conversion occurred after 10 min respectively. The oxidative desulfurization data fitted the first order kinetic model for two cases.The activation energy of oxidative desulfurization of model fuels estimated by Arrhenius equation were 57.66,and 52.8 kJ/mol using nano TiO2 without (PWA) acid and TiO2 with (PWA) acid respectivily.
66
Contents Contents
Page
Acknowledgement
I
Summary
II
Contents
V
Nomenclature
X
Chapter One Introduction
1.1 Introduction
1
1.2 The Aim of the Work
3
Chapter Two Literature survey 2.1 Nanoparticles
4
2.2 Titanium Dioxide
6
2.2.1 TiO2 Crystal Structures
7
2.2.1.1 Anatase
7
2.2.1.2 Rutile
8
2.2.1.3 Brookite
9
2.2.2 Phase transformation: Anatase to Rutile
10
2.3 Photocatalysis
12 67
2.3.1 Photocatalysis and Titanium Dioxide
13
2.4 Titania as a Catalyst and Catalyst Support
13
2.5 Methods of Preparation Nano TiO2
14
2.5.1 Sol-gel Process
14
2.5.2 Hydrothermal Process
17
2.5.2.1 Variables Hydrothermal Process
18
2.5.2.1.1 Effect of Starting Materials
18
2. 5.2.1.2 Effect of Time and Temperature
18
2.5.2.1.3 Effect of pH
19
2.5.3 Solvothermal Routes
19
2.5.4 Gas Phase Methods
19
2.5.4.1 Chemical Vapor Deposition (CVD)
20
2.5.4.2 Physical Vapor Deposition (PVD)
20
2.5.4.3 Spray Pyrolysis deposition (SPD)
20
2.6 Sulfur Compounds in Petroleum Fractions
24
2.7 Desulfurization Methods
27
2.7.1 Hydrodesulfurization (HDS) Process
27
2.7.2 Oxidation Desulfurization (ODS)
29
2.7.2.1 H2O2- Oxidation Method
31
2.7.2.2 H2O2- Organic Acid System
33
2.7.2.3 H2O2 -HetroPoly Acid System
33
2.7.3 Catalytic Oxidation Desulfurization
34
2.7.4 Photocatalytic Oxidation Desulfurization system
35
2.7.5 Ultrasound Oxidative Desulfurization system (UAOD)
36
2.7.6 Extraction Desulfurization
37
2.7.7 Adsorption Desulfurization
38
2.7.7 Biodesulfurization (BDS)
38
2.8 Previous Work
41 68
2.9 Kinetics of ODS Reactions
43
Chapter Three Experimental Work 3.1 Introduction
46
3.2 Materials
47
3.2.2 Chemicals
47
3.2.3 Equipment
48
3.3 Preparation of Nano Titanium Dioxide
48
3.3.1 Sol-Gel Method and Titanium Tetraisopropoxide as Source Material
3.3.2 Sol-Gel Method and Titanium Ethoxide as Source
48
52
Material 3.3.3 Preparation of Nano Titanium Dioxide by Hydrothermal Method
55
3.4 Oxidative Desulfurization Processes
58
3.5 Test methods
59
3.5.1 X-Ray Diffraction
59
3.5.2 Fourier –Transform Infrared Spectroscopy
60
3.5.3 Surface area and pore volume
60
3.5.4 Atomic Force Microscope
61
3.5.5 Scanning Electron Microscope
61
3.5.6 X-Ray Fluorescence
62
Chapter Four 69
Results and Discussion 4.1 Characterization of Prepared Nano titanium dioxide
63
4.1.1 X–Ray Diffraction (XRD)
63
4.1.1.1 X–Ray Diffraction (XRD) for Nano TiO2 Prepared by
64
sol-gel method and TTIP as Source Material 4.1.1.2 X–Ray Diffraction (XRD) for Nano TiO2 Prepared by
75
Sol-Gel Method and Titanium Ethoxide as Source Material 4.1.1.3 X–Ray Diffraction (XRD) for Nano TiO2 Prepared by
79
Hydrothermal Method 4.1.1.4 Effect of pH on the Syntheses TiO2 Nanoparticles
84
4.1.1.5 Effect of Calcination Temperatures on Crystalline Size
88
4.1.1.6 Effect of Acid Type
89
4.1.2 Fourier Transform Infrared Spectroscopy (FTIR)
92
4.1.3 Surface Area and Pore Volume
94 99
4.1.4 Atomic Force Microscope (AFM) Reports 4.1.5 Scanning Electron Microscopy (SEM)
110 122
4.1.6 X-Ray Fluorescence 4.2 Oxidative Desulfrazation of Model fuels by Prepared
122
NanoTiO2 Catalysts without PWA acid 4.2.1 Effect of the NanoTiO2 Form on Oxidative Desulfurization 4.2.2 Effect of Stirring Rate on Conversion
122 124
4.2.3 Effect of Temperature on DBT Oxidation
125
4.2.4 Effect of Initial Concentration on Conversion of DBT
126
4.2.5 Effect of Catalyst Amount on Conversion of DBT
127
4.2.6 Effect of Oxidant Amount on Conversion of DBT
128
4.2.7 Reaction Kinetic Model
129
4.3 Oxidative Desulfrazation of Model Fuel by Nano TiO2
132
70
Prepared with Phosphotungustic Acid and STAB 4.3.1 Catalytic Activity on Oxidation of Dibenzothiophene
132
(DBT) 4.3.2 Effect of Temperature on DBT Conversion
134
4.3.3 Effect of Initial Concentration of DBT on Conversion
135
4.3.4 Effect of Oxidant Amount on Conversion
137
4.3.5 Effect of DBT/H2O2 Molar Ratio on the Removal of DBT
139
4.3.6 Effect of TiO2 Prepared by PWA with and Without STAB 139
on DBT Conversion 4.3.7 Effect of Catalyst Amount on Conversion
141 142
4.3.8 Reaction Kinetic Model
Chapter Five Conclusions and Recommendations 5.1 Conclusions
145
5.2 Recommendations
148 References
149
Appendices Appendix A
(XRD sample)
Appendix B
(FTIR sample)
B1-B15
Appendix C
(AFM sample)
C1-C20
Appendix D
(XRF sample)
D1-D2
Appendix E
(BET sample)
E1-E4
Appendix F
( UV carve) 71
A1-A41
F1
1.1 Introduction Vehicle engines generate SOx as a consequence of sulfur presence in fuels, leading to air pollution (Murata et al. 2004). The reaction of these gases with water in the atmosphere produces sulfates and acid rain that causes damage buildings, affecting the vehicles paints. The acid present in soil, leads to loss of forests and other environmental systems. Different problems of human health such as, respiratory illnesses, asthma, heart disease, etc. can be caused by Sulfur emissions. They can contribute to atmospheric particulates formation, pollution of water and global warming (Alhooshani et al. 2015). Catalyst used in refining and cracking processes are poisoned by traces of sulfur in fuels causing breakdown of combustion engine, with reduced effectiveness of the oxidation of carbon monoxide, volatile organic materials, and hydrocarbons (Zuber et al. 2014). To refine crude oil to its final product, desulfurization is considered one of the important processes. Fuels used in transportation, specification are largely considers the sulfur content. The price of a crude oil is highly changed according to its sulfur content (Javadli et al. 2012). The strict regulation of environmental limited the sulfur level to a certain degree, eg. in USA: less than 15 ppm since 2006, less than 10 72
ppm since Europe 2005 in Europe , and in China less than 50 ppm since 2008 (Jiang et al.2011). These strict conditions, made refineries face a major problem to treat crude oil from sulfur and look for more effective desulfurization process. Hydrodesulfurization employs hydrogen at elevated pressure of (20100atm) with high temperatures of 300-400°C. This method treats highly the aliphatic and acyclic sulfur compound, but to a lesser degree aromatic compound. Hard operating conditions are needed to remove the last 100 ppm of sulfur by existing hydrodesulphurization method because of the presence of refractory sulfur compounds such as benzothiophenes (BT) and dibenzothiophene (DBT). These need higher hydrogen pressure, temperature, and contact time to reach sulfur concentration of less than 10 ppm of fuels. This will increase the initial and operating costs (Jarullah et al.2011). Oxidative desulfurization (ODS) is an alternative cost efficient method and its includes : 1. Oxidation of sulfur compounds. 2. Liquid extraction or adsorption. The organic sulfur present in fuels oil is oxidized by oxidant, and then it is removed by adsorption or extraction. "Clean oxidation catalysis", which involves catalysis and H2O2, is receiving much attention. Oxidation of organic substrates is promoted by catalytic system because of their content of oxygen. They are low in cost, safe to use and store, and H2O2 is environmentally friendly. Encouraged development of practical procedures for selective oxidation of sulfur compounds is important. This is because oxidative desulfurization (ODS) is very effective method to remove sulfur compounds from industrial effluents and fuels according to environmental regulations (Ezzat and Nasibeh 2015). ODS is considered a complementary technology to the process of hydrodesulfurization for deep desulfurization (Jiang et 73
al.2011). Amongst the advantages of this process is: mild conditions of reaction conditions i.e, low temperature and ambient pressure. It has high selectivity. Benzothiophene (BT) and dibenzothiophene (DBT) with their alkylated derivatives are oxidized to the corresponding sulfone or sulfoxide which are highly polar and can be removed using organic extractants (Imitaz et al.2013). Titanium dioxide has high surface area, low cost, and feasibility for production in large scale, made it used and examined in catalytic applications (Jun M.2011). Improving the efficiency and activity of desulfurization needed suitable catalyst (Lorencon et al.2014). Catalysts with Ti are widely examined in systems of oxidative desulfurization. The interaction between Ti (IV) sites and H2O2 produced active radical species giving good performance in Oxidative desulfurization system, in addition to being cheap and pollution-free (Jin et al.2008). 1.2 The Aim of the Work This work deals with: Preparation different crystalline forms of nano-TiO2 by using the sol-gel and hydrothermal methods and investigation the effect of various parameters on the synthesis process. Characterization the physical and chemical properties of TiO2 nanoparticles and morphology.
Oxidation desulfurization of model liquid fuel by using prepared nano- TiO2.
Study the effects of different crystalline forms of nano-TiO2 ,stirring rate, reaction temperature, catalyst amount, oxidant content and initial DBT concentration on the removal of sulfur compounds from model fuels. 74
Studying the kinetic model of oxidative desulfurization process to estimate the parameters of the kinetics.
2.1 Nanoparticles Nanomaterials characterize by its promoted physiochemical properties compared with the same material that has larger sizes of particles (Tiwari & Tiwari, 2014). Catalyst with nanostructure confers high activity and selectivity in comparing with conventional catalyst due to its texture characteristic that grants high surface area and small opening pores (Moqadam & Mahmoudi, 2008). Nano catalysts characterize by having the merits of both homogeneous and heterogeneous catalysts, i.e., improving contact between reactants and catalyst from one side (as for homogeneous catalyst), and facilitating its separation from mixture (like heterogeneous catalyst) (Singh & Tandon, 2014). Figure 2.1 shows a schematic comparison between nanomaterial, homogeneous and heterogeneous catalysts.
Homogeneous Catalysts
Nanomaterials High activity
High activity
High selectivity
High selectivity 75 Excellent stability
Difficult purification of products
Easily separable
Harder recovery of catalysts
Energy efficient
Heterogeneous Catalysts
Excellent stability Ease of accessibility Easily separable Last longer reaction time Inferior catalytic activity compared with homogeneous
Fig. 2.1: Basic differences between nanomaterials, homogeneous and heterogeneous catalysts (Singh & Tandon, 2014)
According to (Stankovich et al. 2007) 2-dimensional materials like graphene and silicene of 1- dimension less than 100 nm may be classed as nanosheets. According to (Teo et al. 2006) nanofibres are structures with 2-dimensions less than 100 nm in diameter. If all 3 dimensions of the material are in the 100 nm range, they are defined as a nanoparticle (Pileni,M.P . 1997). Nanostructured materials have been subjected a lot of interests and can be widely used in numerous applications due to the greatest advantageous that can be acquired by their use as shown in Fig. 2.2 (Sharma et al., 2015).
76
Minimum Chemical Waste Reduce Global Warming
Energy Efficient
Nanomaterials Super Catalyst & Reagents
Waste Water Treatment Improved Economy
Fig. 2.2: Advantageous of nanomaterials (Sharma et al., 2015)
Nanometrials are used to a large extent in the area of catalysis, since they have high surface areas, unique morphology and complex pore networks. (Fuishima and Honda. 1972).
2.2 Titanium Dioxide Titanium is a highly considerable metal and element. It has been detected on the sun, moon, and stars. TiO2 is used for white pigments, welding rod coatings, fluxes, Ti metals, and TiO2 (particularly nano TiO2 materials) for catalytic applications. TiO2 has high photocatalytic active and so it has attracted attention as a catalyst since the discovery of its high photocatalytic activity by (Fuishima and Honda. 1972).Other properties such as high thermal stability, low environmental effect, low cost and versatility, made TiO2 to be widely used as a catalyst and as a catalyst support. It is used in many applications, such as photovolatics, photocatalysis,
environmental
cleanup, 77
coatings,
pigments,
and
antibacterial agents, (Zou et al.2001), (Zhang et al.2012), (Tang et al.2012). TiO2 is a very good support material for noble metals such as Pt, Au, and Pd, in different of oxidative synthesis and pollution-control reactions. New applications, where well structured, high surface area, porous and complex types of titania based materials are used; depending on its properties and also its crystalline modifications. Some well-known properties of TiO2 are: • It is amphoteric in nature. • It is insoluble in water as well as acids. • It shows high room temperature resistivity. • It has a melting point of 1610oC and boiling point of 3000oC. • It shows temperature dependent paramagnetic susceptibility. Figure 2.3 shows the general applications of TiO2 fields.
Fig 2.3: Various applications of TiO2 (Tang et al.2012)
2.2.1 TiO2 Crystal Structures 78
Titania exists in both the crystalline and amorphous forms. There are three crystalline modifications which are mostly studied of titania and these are Anatase, Rutile and Brookite. Each crystalline structure has specific physical properties such as surface states, band gap, etc. (Lee.2003) that rules their applications and uses. Anatase and rutile are famous
photocatalysts, and
anatase generally shows very high
photocatalytic activity (Chen and Moa 2007),(Li et al.2010). Rutile is usually used as a white pigment in paints. Brookite has not yet been applied commercially but a dye sensitized solar cell (DSSC) has been used (Baur 1961). Anatase and rutile have both tetragonal structure while the brookite has orthorhombic structure Figure 2.4 shows the crystal structures of different types of titania.
2.2.1.1 Anatse The tetragonal structure of anatase is shown in Figure 2.4. This crystal is made up of chains of octahedrons of a Ti atom surrounded by six oxygen atoms. The octahedrons share four edges to form Eight-faced tetragonal dypyramids are formed due to the octahedrons sharing four edges. Anatase has no corner sharing and the TiO6 octahedra are linked together only through edge sharing. (Li et al 2010) Anatase contains twelve atoms per each cell. Information on the properties and crystal structure of anatase is shown in Table 2.1. Anatase is the stable phase when the crystallite sizes are less than (11 – 13) nm. (Zhang and Banfield 2000) Because of the stablility and high surface area of the obtained anatase it has traditionally been found as the best phase for catalysis. Slightly higher Fermi level, lower capacity of oxygen adsorbed, high hydroxylation and the longer photo-excited h+/e- carriers
79
lifetimes
present in the lattice of anatase, made anataseto exhibit a high photocatalytic reactivity compared to rutile. (Tanaka et al.1991)
2.2.1.2 Rutile Rutile is present in a tetragonal structure (Figure 2.4).The rutile structure has parallel chains of TiO6 octahedrons. Linear chains along the [001] direction are formed since two edges of each octahedron are shared, with the linking of chains together through corner connections (Li et al. 2010). TiO6 octahedrons are deformed in the rutile structure, with a lesser degree than that observed in the anatase structure. (Chen and mao. 2007) Rutile contains six atoms per unit cell. Properties of the crystal structure of rutile and some information are given in Table 2.1. The rutile phase has the highest density. It is widely used in pigments and coatings. Rutile considered
the stable phase at most
temperatures and pressures up to 60 kbar at sizes above (11 – 35) nm. (Zhang and Banfield. 2000) , (Zhang et al. 2000)
2.2.1.3 Brookite Brookite TiO2 belongs to the orthorhombic crystal system. It has a unit cell of 8 formula units of TiO2. It is formed by edge-sharing TiO6 octahedra. It has a larger cell volume, with less density than the other two types and it is also more complicated. Anatase and brookite structures often convert to rutile when calcined at high temperatures. Heating anatase and brookite gives rutile with large crystallites (100 nm or larger). A decrease in surface area, is accompanied the increase in particle size hence large rutile crystallites are not considered catalytically active.
80
a
b
(Brookite) c Fig 2.4 Crystal structures of TiO2; (a) anatase, (b) rutile, and (c) brookite (http://ruby.colorado.edu/~smyth/min/tio2.html).
Table 2.1 Some Bulk Properties of the Three Main Polymorphs of TiO2 (Anatase, Rutile, Brookite)
81
Phase
Refractiv
z
e Index
Density
Band
Light
Crystal
(g.cm-3)
Gap
wavelength
structure
(eV)
(nm)
Anatase
2.49
4
3.895
3.26
384
Tetragonal
Rutile
2.903
2
4.2743
3.02
410
Tetragonal
Brookite
2.583
8
4.123
2.96
401
Orthorhombic
2.2.2 Phase transformation: Anatase to Rutile The synthesis conditions affect the transformation behaviour from amorphous to anatase or rutile phase. Other factor affecting the phase transformation are :pressure, particle size, temperature, hydrothermal conditions, impurities and additives/dopants. Some of the factors affecting the phase transition are discussed below: (1) Temperature: The heat treatment of amorphous titania converts it to a crystalline anatase structure at temperature less than 400oC. It is converted to rutile form on further heated to 600oC- 1100oC (Zhang,H. 1999). The transformation of anatase to rutile phase is considered as a metastable state to stable state. (Li et al.2004) found that the anatase to rutile phase transformation happened in the temperature range of 700800oC. Increasing the temperature, increases both anatase and rutile particle sizes with different growth rate. Rutile had a much higher growth rate than anatase. The growth rate of anatase stops at 800°C. The temperature increasing causes an increased lattice compression of anatase. (Jagtap,N. et al.2005)
studied the start of transformation
temperature by heat treatment of anatase from 150 to 950oC. It was also 82
found that the anatase had higher stability in vacuum when compared to atmospheric air. The transformation of anatase to rutile is suppressed due to lack of oxygen and only 3% of anatase is transformed to rutile at 900oC.
Nano anatase can transform to the more stable rutile phase on heating, generally between 500-900°C. (Roy et al.2008), (Zhang et al.2009) observed the occurance of rutile when heating anatase at 600°C. The material had totally transformed to rutile by 900°C. In contrast (Zhu et al.2007) showed that heating samples for longer times at 600°C led to the formation of rutile. This shaved both calcination time and temperature affect product crystal phase. (2) Additives/Dopants: (Talavera et al.1996) confirmed the phase transformation of anatase to rutile depends strongly on the kind of cation (Li+, K+, Zn2+, Al3+) applied to dope the titania material. Using different metal ions, phase transition occurs at different temperatures. Presence of additives such as alumina, silica, zirconia, sulphate ions etc. in TiO2 can stabilise the anatase phase (Cheng et al.2003), (Calleja et al.2008) The anatase to rutile phase transformation under hydrothermal conditions is accelerated by the presence of chloride ions (Coronado et al.2008). (3) Particle size: The crystal structure of TiO2 nanoparticles depended largely on the preparation method. For less than 50 nm TiO2 nanoparticles, anatase is more stable and is transformed to rutile at >700oC. (Gribb et al.1997) showed that the formedTiO2 nanoparticles had structures anatase and/or brookite. These are transformed to rutile at a certain particle size. When the rutile is formed it grew much faster than anatase. ( Zhang and 83
Banfield 2000) showed that the sequence of transformation and the thermodynamic stability of state are affected by the sizes of anatase and brookite.
2.3 Photocatalysis It is catalysis under light radiation, and it is a reaction with the presence of a catalyst causing the acceleration of the as a whole process. The main difference between the catalyst and photocatalyst is that a catalyst has contains active sites, at which conversion of substrate to product is done, while there are no active sites on a photocatalyst (Fig.2. 5). Photocatalysis can be homogenous, i.e. it takes place in homogenous phase, or heterogeneous where it is carried out at the two phases boundary, or interfacial boundary. Two phases (solid-liquid, solid-gas) (Benedix et al.2005).
Fig 2.5 Difference in concepts of catalytic and photocatalytic reaction (Ohtani, B., 2010)
2.3.1 Photocatalysis and Titanium dioxide Photocatalysis and photoelectrochemistry are related. In 1970s, titanium (IV) oxide TiO2) was used as a semiconductor electrodes in photoelectrolysis of water and photocell (Frank et al., 1977). In 1977, Frank et al showed that TiO2 could be used in photocatalytic degradation of cynide as pollutant. Titanium (IV) oxide is one of the preferable photocatalysts because of its high availability, relatively low cost stable chemical structure, and it is high effective with oxidizing photogenerated holes on surface (Kaneko et al., 2002). 84
A corroding to (Robert et al., 2002), the principle of semiconductors is the excitation of the particles of semiconductor. On the surface of the particles conduction band electrons (e¯CB ) and valence band holes (h+VB) are formed under UV irradiation, where the energy state of electrons of the electrons of semiconductor is changed, (Robert et al., 2002). Radicals such as hydroxyl or superoxide from oxygen or water due to oxidation or other chemical reactions are generated at active sites of surface with conduction band electrons and valence band holes. Oxidizing the target pollutants is done by generated radicals. At valence band holes, direct oxidation of the target pollutants is also possible.
2.4 Titania as a catalyst and catalyst support Some of the important characteristics of titania as a catalyst are: chemical stability, low cost, non-toxicity and the highest oxidation rate as compared to other metal oxides (Redy et al.2004). During the synthesis, controlling the particle size, phase, morphology and the presence of defects must be considered. Using nanosized TiO2 , shows promising enhancement of surface area and optical properties. Titania supported catalysts are efficient as support or as active catalyst component. Surface compounds are formed from the interaction of the support as a carrier with active components (Retuert et al.2000). Higher dispersion of the active component happens because of the porous nature support, leading to use of small amount of the active component. The selectivity and overall conversion of the catalyst are also affected. The development of titania nanotubes was a consequence of the need to produce highly structured, high surface area, high porosity and complex forms of titania based materials (Antonelli and Ying 1995).
85
The catalytic activity is influenced by surface properties of catalyst. Some of these properties are particle size, surface area, and colloidal size.
2.5 Methods of preparation nano TiO2 There are many methods of synthesizing TiO2 nanostructures. Generally these methods can be divided to two main groups; (1) Solution routes: consists of sol-gel, hydrothermal and solvothermal. Solution route has the advantages of stoichiometry controlling, production of homogenous materials, coating complex shapes and composite materials preparation. Second group; (2) Gas phase methods: consists of chemical vapor deposition, physical vapor deposition, and spray pyrolysis. In gas phase methods, the synthesis can be of chemical or physical nature.
2.5 .1 Sol-gel process In this method, metal oxides are used as precursor. It is a wet chemical where nanostructured particles are made by a chemical reaction in solution. Sol-gel means transition from a liquid “sol” to solid “gel” phase. Fig.2.6 shows an overview of the sol-gel method. Inorganic metal salts or metal organic compounds are the starting materials to prepare the “sol”. A colloidal suspension or the “sol” are formed as the precursor is subjected to a series of hydrolysis and polymerization (condensation) reactions. Aerogel which is a high porous material with low density, is formed if the liquid in a wet “gel” is removed under a supercritical conditions. Ceramic fibers may be drawn from the “sol” if the viscosity of a “sol” is adjusted to a certain limit. (Chemat Technology, Inc.,1998). The easily controlled parameters, such as powder morphology, average size of nanocrystallite, surface area, crystallinity, and the phase 86
structure, which affect the activity of nanocrystalline TiO2, all made the sol-gel receive more attention,(Yoo, et al., 2005; Baiju, et al., 2007). Two simultaneous reactions, hydrolysis and condensation, take place in sol-gel synthesis .Here an alkoxide precursor reacts with water as shown in the following equeations (1)to(4). Hydrolysis: M (OR) z + xH2 O partially hydrolyzed → (HO) x −M (OR) z − x + xROH 0 < x < z (1)
M (OR) z + zH2 O completely hydrolyzed→M (OH ) z + zROH (2)
Condensation: (RO) z −1 M − OH + HO − M (OR) z −1→ (RO) z −1 M − O − M (OR) z −1 + H 2 O (3) (RO) z −1 M − OR + HO − M (OR) z −1→ (RO) z −1 M − O − M (OR) z −1 + ROH (4)
where R is typically an alkyl group, M is the required metallic cations and z is the valence of cations. Adjusting the process parameters, such as , pH conditions, reaction temperatures, acid or basic catalysts used, composition of raw materials , and H2O/M(OR)x molar ratios can control the above reactions, (Yu, et al., 2000; Caruso and Antonietti, 2001; Yoo, et al., 2005; Alapi, et al., 2006). The advantages of sol-gel method are (Liu, et al., 2005; Venkatachalam, et al., 2007) such as: ease of composition control. good homogeneity. low processing temperature. chemical purity. 87
accessibility of nanocrystalline materials. Strongly influenced by the synthesis conditions. low equipment cost. Table 2.2 showes a brief of the key steps in a sol-gel process with the aim of each step
Table 2.2 Important Parameters in the Various Steps of a SolGel Process ( Sanchez and Ribot, 1994). Purpose
Step Solution Chemistry
Important Parameters
To form gel
Type of Solvent, Type of Precursor Water Content, Precursor Concentration, Water Content, pH, Temperature Aging environment, Temperature, Composition of the pore liquid,Time
Aging
To allow a gel undergo changes in properties
Drying
To remove solvent from a gel (Areogel, Xreogel and Cryogel)
Pressure and pressurization rate, Temperature and heating rate, Drying method (evaporative super critical & freez drying), Time
Calcination
To change the physical /chemical properties of the solid, often resulting in crystallization and densification
Gaseous environment (inert, reactive gases), Temperature and heating rate, Time
88
Fig 2.6: Schematic representation of the different stages sol-gel process( Sanchez and Ribot, 1994).
2.5.2 Hydrothermal Process Ultra-fine powder and particles are manufactured industrially by hydrothermal systems. An autoclave with Teflon or glass liners under controlled temperature and /or pressure is used with the reaction in aqueous solutions. The temperature can be raised above water boiling point at standard conditions and the vapor pressure saturation is reached. The produced internal pressure in the autoclave largely depends on temperature and amount of added solution. Hydrothermal synthesis is used largely to produce small particles, or prepare TiO2 nanoparticles, (Chae et al.2003) nanowires (Yoshida et al.2005), or TiO2nanorods (Yang and Gao 2005), and nanotubes (Bavykin et al.2005). The phase transformation of the TiO2 powders is enhanced by hydrothermal treatment. This transformation is from amorphous to crystallite phase, by re-crystallization and restructuring. Precipitation of precursor solution containing titanium alkoxide or halide, is the initial step in hydrothermal synthesis. A surfactant is added to the prepared precipitate to be mixed into aqueous slurry, which is placed in an 89
autoclave to be heated for a period of time. Centrifugation or filtration is then used to collect the formed precipitate which is washed using a suitable solvent and dried. One of the advantages of hydrothermal method to prepare TiO2 particles is producing different crystalline phases but with no heat treatment after that. It provides good crystalline composition and quality. (Stride and Tuong 2010) Other advantages are decrease in particles agglomeration, phase homogeneity, controlled particle morphology, narrow particle size distributions, purity of the product,etc.
2.5.2.1Variables of Hydrothermal process 2.5.2.1.1 Effect of the starting materials A large amount of various compounds like Degussa TiO2 (P25) nanoparticles, Ti metal , TiOSO4, rutile or anatase TiO2, molecular TiIV alkoxide, layered titanate Na2Ti3O7, SiO2–TiO2 mixture, or TiOCl2, can be used as the precursor for the preparation of TiO2 by hydrothermal synthesis. Also titanium dioxide sol can also be used as the starting reactant in the hydrothermal process (Prescott and Arnold 2008).
2.5.2.1.2 Effect of time and temperature The morphological properties of the TiO2 particles are influence by hydrothermal treatment temperature. The nucleation and growth crystal of TiO2 nanoparticles are mostly promoted by temperature. Increasing the temperature increases the degree of crystallinity and the crystallite size. The range of temperature usually preformed in the hydrothermal synthesis is 110°C–250°C. The more dominant phase in the product is rutile, with small amounts of anatase persisted if the temperature is 90
almost 200°C. Another factor that influence morphology and crystallinty of final TiO2 is the duration of hydrothermal treatment. The average size of crystallite and average pore size are increased with increasing both time and temperature of hydrothermal treatment. The pore volume, porosity and BET specific surface area decreases continuously (Wang et al.2007). almost all researchers showed that at temperature less than 100°C no nanoparticles of TiO2 are formed (Seo et al.2008).
2.5.2.1.3 Effect of pH The proper selection of pH and crystallization temperature is required to create a pure phase of anatase and rutile. At pH of 1 and 2, only rutile is formed. At even lower pH, TiO2 produced contains small amounts of anatase. Increasing the pH, anatase is essentially produced with small amounts of rutile. The formation of anatase is favoured by adding KOH or NaOH. Only amorphous TiO2 is formed by further increase of pH, above 12 (Byrappa 2001).
2.5.3 Solvothermal routes The only difference between solvothermal and hydrothermal reactions is that is a non-aqueous medium is used as reaction mediums. Since a variety of organic solvents that have boiling points can be selected, the temperature can be elevated much higher than in hydrothermal method. A stainless steel autoclave is also used. Better control of size, shape distributions and crystallinity of TiO2 nanoparticles is more pronounced in the solvothermal method. Different shapes of TiO2 (e.g.; nanowires (Wen et al.2005), nanoparticles (Kim et al.2003), can be obtained by varying the synthesis initial parameters such as titanium precursors, presence or not of surfactant, reaction time, solvent, and temperature. 91
2.5.4 Gas Phase Methods Gas methods are popular ways to synthesize thin films TiO2. The most common techniques are given below.
2.5.4.1 Chemical vapor deposition (CVD) To form a metal or oxide product, CVD involves the decomposition of a gaseous precursor (Jones and Chalker 2003). This technique is widely used to synthesize coatings and thin films, such as ceramics and semiconductors because it is done fast and continuously.
2.5.4.2 Physical vapor deposition (PVD) CVD and PVD are similar, since they are used to form thin films, but PVD does not include a chemical reaction. The process involves thermal evaporation of TiO2 followed by deposition on substrates. To minimize collisions of gas molecules which leads to impurities in the deposited films, reduced pressures are used. PVD can be used to form TiO2 films with high purity, conductivity, crystallinity and smoothness although it is a slower and more difficult process (Carp et al.2004).
2.5.4.3 Spray pyrolysis deposition (SPD) SPD technique is used TiO2 thin films and powders on to substrates. SPD, is similar to CVD and PVD, an aerosol, not a vapor, is formed from the precursor solution. The substrates are usually at ambient pressures. Inorganic salts or metal-organic compounds are usually used as starting materials for the precursor solution, (Ahonen et al.2001). Controlling crystallite size and particle morphology in addition to obtaining mixed oxides is done by precursor composition, gas flow rates and substrate temperature reaction parameters. Different structure-direct-agent and dispersants like surfactant and alcohols are used to produce high purity, high surface area, and high pore volume nanoparticles, in the synthesis using room temperature (sol 92
gel) method and high temperature over 1000C (hydrothermal treatment by auto-clave reactors or microwave irradiation) (Mandana, et al., 2010, Faramawy, et al., 2014).
Previous work: (Santana et al. 2005)
used sol-gel techniques to prepare TiO2
nanoparticles. Titanuim alkoxide as source of titanuim, 2-propanol, distilled water, ammonium hydroxide and hydrochloric acid with different pH(3,7,and 9)were used. The particles sizes were between 12 nm and 20 nm. The thermal treatment was at 5500C, using pH=3the prepared catalyst, had best surface area of 80 m2/gm and total pore volume of 0.187 cm3/g. The effect of adding phosphoric acid on the surface area , pore size, pore volume and the phase structure of prepared mesoporouse titanium dioxide in a template- free syntheses process was studied by (Huang et al . 2005).
The sol-gel method was performed using phosphoric acid,
tetrabutyl titanate and deionized water. The surface area ranged from 41m2/gm to 294 m2/gm. The average pore size was from 5.4 nm to 9.4 nm while the total pore volume from 0.056 cm3/g to 0.545 cm3/g. The concentration of phosphoric acid is an important factor to control its distribution and the pore size. (Huang et al., 2008) used sol-gel method to produce mesoporouse titanium dioxide materials by tetrabutyl titanate as the precursor at ambient condition. The catalyst used was phosphotungstic acid (PWA) with four structure-directing agent (STAB,TTAB, DTAB, and CTAB). The best structure-directing found was STAB with high surface area 180 m2/gm and total pore volume 0.312cm3/gm at calcination temperature of 500oC for 3 hr.
93
(Thuy et al., 2009) used hydrothermal process to produce titanium dioxide nanoparticles. The precursor used was titanuim isopropoxide. The morphological/ crystallographic controlling agent was hydrochloric acid. The auto clave worked at 1800C for 36 hrs with drying in an oven for 1050C for 12 hr. The different morphologies of nano TiO2 were obtained on the acid medium including flower, cuboid, cauliflower, flower, raspberry, and ball-like shapes. Titanuim dioxide nanostructures
were produced by sol-gel
method with tianuim iopropoxide as the source of titanium. Hydrochloric
acid and ammonium hydroxide
were used
as
catalyst. pH ranged between 2 to 10. pH influence on the reaction morphology of using
a titanium tetra-isopropoxide was studied,
considering on the amounts of the catalyst. Using of NH4OH, the morphology of TiO2 particles was in powder form, while in the case of HCl, granular form was shown (Chang Sung Lim et al., 2010). Titanium isopropoxide, acetic acid, and water were used to synthesize TiO2 by hydrothermal treatment using auto-clave at different reaction times (6,12,24, and 36)hr with crystallization temperature of (1500C and 2000C), (Collazzo et al. 2011). precipitate was dried at 1000C for 12 hr in an oven. was
obtained
with
pure
anatase
crystalline
The
Nano TiO2
phase
for
all
conditions, of temperature and reaction times. The particle size was between 9 to 17 nm. The surface area ranged from 86 m2/gm to 186 m2/gm, (Wenbing and Tingying. 2011), titanium tetrachloride as starting material to synthesized nano TiO2 by sol-gel method,in addition to H2SO4, and NH4OH which was added later so the pH reached 7. Drying and calcination of the product was done at 4000C and 94
6000C for 2 hr. The hydrolysis of TiCl4 with H2SO4 solution ensured the
synthesis of titanai
nanostructures. H2SO4 presence
to a certain amount promotes the phase of anatase, while it inhibits the transformation of anatase to rutile at 6000C. Sol-gel method with titanium isopropoxide dissolved in ethanol were used to prepare TiO2. Water was then added for hydrolyses with different calcination temperatures from 250 0C to 8000C. In temperature range between 2500C to 6500C nano TiO2 was formed as anatse phase with particles size 6 nm. At 8000C anatase and rutile crystal structure of 100 nm and more, particle size were present (Andrej et al. 2012). (Vijayalakshmi and Rajendran., 2012), used sol-gel and hydrothermal techniques to prepared nano titanium dioxide,
by using titanium
isopropoxide and titanium tetrachloride. They were dissolved in ethanol. Water, nitric acid, and NaOH were added then at calcination temperature of 4500Cfor 2 hr. Compared with hydrothermal method, the prepared nanoparticles of TiO2 was highly crystalline and with smaller crystallite size of 7nm (for hydrothermal method 17nm). (Kavitha et al., 2013), synthesized TiO2 structures using both hydrothermal and sol-gel methods. They studied the growth, chemical, and physical characterization using titanium isopropoxide as source of titanium. The catalyst was acetic acid. Different calcination temperatures of (3000C and 6000C) were experimented and at aging time 24 hrs with autoclave for hydrothermal process. The nanoparticles prepared in the two methods the nanoparticles formed had good crystallinity and clear spherical like structure in hydrothermal process compered to powder produced from sol- gel route which was not uniform in shape. (Manasi. 2014), used titanium isopropoxide and titanium butoxide as precursor with a catalyst of HCl to synthesized nano titanium dioxide by 95
sol-gel technique. Aging time was 24 hrs. Calcination temperature of 4500C was used for 3 hrs.The anatase titania nanoparticles obtained were highly crystalline by controlling hydrolysis reaction rate. The size of produced particles was in range 5-13 nm. Choice of precursor did not affected the size of particles. Film-like structures were shown using titanium isopropoxide. Spherical granules were shown using titanium butoxide. (Liatang et al. 2016), prepared nano titanium dioxide by sol-gel method, with the use of titanium ethoxide, ethanol and water. Different calcination temperatures 100, 500, and 7000C were used. Different forms of TiO2 nanoparticles (amorphous, anatse, and anatse-rutile) were produced with surface area of (615.2, 24.5, and 15) m2/g respectively, while the total pore volume was (0.35, 0.07, and 0.02) cm3/g respectively. (Saja and Hydeir. 2016), synthesized nano titanium dioxide using solgel method with the aid of ultrasound. Titanium isopropoxide was the source of titanium, and it was dissolved in isopropyl alcohol and water added after at pH=3. Ultrasound was use for irradiation and then calcintion at 4500C for 3 hrs. Anatase phase of TiO2 nanoparticles were prepared with 11nm (small size of crystals). The shape was spherical with surface area of 64.041m2/gm.
2.6 Sulfur Compounds in Petroleum Fractions Sulfur compounds are some of the most hetero- atomic components of petroleum. They exist in petroleum as sulfides, thiophenes, benzothiophenes, and dibenzothiophenes. The fractions with higher sulfur have higher boiling point than the middle boiling fractions. The increase in boiling point during distillation of crude oil increase the sulfur compounds amounts. (Speight, 2006). 96
The presence of sulfur compounds in petroleum refinery has a destructive effect because it poisons the catalyst during the process. 0.1 to 3 % of sulfur in Petroleum is undesirable where it causes corrosion and atmospheric pollution. (Speight, 2002). Sulfur may be present in: elemental sulfur, inorganic forms, hydrogen sulfide, carbonyl sulfide, or positioned with organic molecules. Usually crude oil may contain the following sulfur compounds: Thiols or mercaptans CnH2n+1SH in fractions with low boiling point. Hydrogen bonded to sulfur shows acidic characteristic. Sulfides, here sulfur is considered as part of a saturated chain CH3-CH2-CH2-S-(CH2)4-CH3 (Propyl Pentyl Sulfide). Disulfides with the general formula R-S-S-R, they are found in light fractions. Thiophenes and their derivatives. They can be found in fractions having boiling point of 250 ºC. They are considered the most important sulfur compound. The sulfur atom is found in the aromatic ring (Wauqier j., 1995), some examples are: benzothiophene and dibenzothiophene. Fig.2.7 shows Some of these compounds.
97
Fig. 2.7 Some examples of sulfur compounds (Fox, 2011). There are different important reasons to remove sulfur from petroleum fractions; 1. The corrosion reduced or limited during handling, refining, and the use of different products. 2. Production of compounds an acceptable odor. 3. Increasing the stability and performance of gasoline. 4. Decreasing formation of smoke in kerosene. 5. Fuel oils burning characteristic and it environmental acceptance is done by reducing the content of sulfur. 6. Poisoning of catalyst.
2.7 Desulfurization methods 2.7.1 Hydrodesulfurization (HDS) Process Hydrodesulphurization (HDS) is a catalytic chemical process. It is widely used to remove sulfur from natural gas. Also, it is used to remove sulfur from jet fuel, gasoline, diesel fuel, keroseneand fuel oils (Gary, et al., 1984). In HDS, the light oil is heated, mixed with hydrogen and then it is fed to a reactor with pelleted catalyst. The range of temperature in the reactor is 300 to 3800C. Depending on the feed, its boiling range, and the 98
pressure all or some of the feed is vaporized. If the feed are heavier, most of the feed is liquid. Considering the difficulty of sulfur removing, the reaction pressure ranges 15 to 90 bar (Campos-Martin et al. 2010). 30 bar is commonly used in the production of light oil such as jet fuel or diesel. In the earlier processes, the flow of the mixture of feed and hydrogen is downward the reactor, or it passes through and around the catalyst. The flow is upward the reactor from its bottom in the newer processes (Synsat process), (Babich and Moulijn,2003). When the mixture of hydrogen and treated fuels leaves the reactor, it passes through a set of mechanical devices so that the hydrogen is separated or recycled, H2S is removed and the desulfurized product is recovered. The HDS is limited in benzothiophenes (BTs) and dibenzothiophenes (DBTs) treating, especially DBTs with alkyl substituents on 4 or 6 positions. (Song and Ma , 2004).The production of light oil, having very low levels of compounds continuing sulfur, therefore requires certainly hard operating conditions i.e., high temperatures, very low space velocities, and high pressures, as well as the use of highly active catalysts. An alternative process, under moderate conditions and without for H2 and catalysts, is therefore necessary required (Song ,2003). There two groups of organic sulfur compounds: one where cost-effective procedures like HDS can be used and the
other
is
recalcitrant.
This
part
must
be
also
desulfurized so that the low sulfur content regulations are met. Hydrodesulfurization can be used to treat refractory sulfur, but the process needs very high temperature and pressure. (Campos-Martin et al. 2010). According to the increase in fuel
consumption
and
the
utilization
of
petroleum
resources, the remaining part of petroleum shows high 99
viscosity and high sulfur content. This part needs a high cost to be desulfurized. If a mild desulfurization process is used, it will lower the price of the final fuel, it will reduce the energy consumption and the amounts of pollutants will be decreased. Using an alternative method or approaches that can be used after the HDS unit must be considered (Mehdizadeh et al., 2013). Gasoline and naphtha can be hydrodesulfurized efficiently. Heavier streams such as kerosene and gasoil have high boiling point with sulfur as benzothiophene and its complex alkylated derivatives encounter difficulties in hydrotreating compared to the lighter streams with sulfide, disulfide and thiols (Acton, 2013).
2.7.2 Oxidation Desulfurization (ODS) Oxidative desulfurization (ODS) has received more attention since it is considered as novel method for deep desulfurization of light oil. Reaching
a
lower
sulfur
content
in
fuels
with
known
hydrodesulphurization (HDS) technology needs the use of, larger reactor volume, higher reaction pressure, higher reaction temperature, or more active catalysts, or some combination of these (Liu, 2010; Guoxian et al., 2007). Potential problems for HDS in converting heterocyclic sulfur – containing compounds are encountered. Some of these compounds are methylated derivatives of DBT, 4- methyldibenzothiophene and 4,6– dimethyldibenzothiophene (4,6DMDBT). ODS is run at atmospheric pressure and temperature below 100⁰C. There are mild reaction conditions, and there is with minimum special operating conditions. ODS has high selectivity, and can remove nitrogen also. The BT, DBT, etc. 100
sulfur compounds can be removed easily by oxidation (Zhanga et al.,2009). A selective oxidant compounds are used to oxidize sulfur containing compounds. These can be extracted from light oil because of their increased relative polarity. These oxidants include hydroperoxides, peroxysalts, peroxyorganic acids, ozone, and nitrogen oxides, etc. Oxygen atoms can be denoted by these compounds to the sulfur in sulfides, disulfides, mercaptans (thiols), and thiophene forming sulfones or
sulfoxides. Light oil is contacted with an oxidant under certain
conditions, and the reaction continuous until oxidized sulfur compounds are formed. The formed sulfones are removed into aqueous phase, also they form insoluble precipitate which remains in light oil. Contacting oxidized light oil with a non-miscible solvent can extract the oxidized compounds. Fig. 2.8 shows ODS/extraction reaction (Campos-Martin et al., 2010).
Fig 2.8 Schematic biphasic simultaneous oxidation/extraction ODS reaction
The sulfones has greater polarity than that of the corresponding sulfides. Sulfones are highly soluble in polar solution, compared to that of sulfides. The efficiency of desulfurization by using either adsorption or extraction, can be increased after oxidizing sulfides into sulfones to a large extent. (Li, 2004).
101
An industrial flow system of oxidative desulfurization for hydrotreated crude oil figure 2.9. Catalyst in the crude oils are extracted and washed, the un-used oxidant can be separated. This is done before further processing in the separator section.
Sulfones and sulfoxides, i.e the oxidized compounds were liquidliquid extracted. This was done by contacting a non-miscible solvent with oxidized crude oil. The solvent is selective for the polar oxidized sulfur compounds (Hulea et al.2001), (Shiraishi et al. 2003).To produce a high clean sulfur free oil, the desulfurized crude oil is washed with water to get any traces of the dissolved extraction solvent. After that, absorption by silica gel and alumina is accomplished. (Campos-Martin et al. 2010).
Fig 2.9 Schematics of oxidative-desulfurization ODS process (Campos-Martin et al. 2010)
The advantages of ODS are: 102
(1) Low capital cost. The large hydro reactor is not needed. (2) Low operating cost. Comparing ODS and HDS, the forma operates at ambient temperature and pressure. (3) Hydrogen gas is not required (Cheng, 2008).
2.7.2.1 H2O2- Oxidation Method The essential objective is to oxidize sulfur compounds from a fuel sample to its relative sulfides or sulfones. The oxidant converts organic sulfur compounds (OSCs) and the resultants are more polar oxidized species. The common oxidants used are: peroxide compounds, permanganate salts, hypohalite compounds, ammonium cerium (IV) nitrate, chlorite, Tollen's Reagent, hexavalent chromium compounds, ozone, and oxygen (Cheng, 2008). The following must considered to select the optimum oxidant : (1) amount of active oxygen content. (2) selective ability (3 reaction by- product (4) its price. As shown in table (2.4) hydrogen peroxide (H2O2) gives the highest percentage of active oxygen. According to (Cheng, 2008), this percentage represents the ratio of oxygen weight that is transferred to a suitable substrate to the oxidant molecular weight of the oxidant. Table (2.4) Active oxygen from different oxidants Donor
Active Oxygen (wt%)
H2O2
47.0a
H2O
O3
33.3
O2
t-BuOOH
17.8
t-BuOH
N2O
36.4
N2
103
By-product
NaClO2
35.6
NaCl
NaClO
21.6
NaCl
NaBrO
13.4
NaBr
C5H11NO2d
13.7
C5H11NO
HNO3
25.4
NOx
KHSO5
10.5c
KHSO4
NaIO4
7.2b
NaIO3
PhIO
7.3
PhI
a: Calculated in 100% H2O2, b: Assuming only one oxygen atom is utilized, c:Stabilized and commercialized as the “triple salt”: 2KHSO5.KHSO4.K2SO4 (oxone), d: N-Methylmorpholine N-oxide (NMO).
H2O2 is reported as the main amongst many oxidizing agents after the desulfurization reaction. it can be considered as “green” reagent. Hydrogen peroxide can oxidize OSCs to their sulfones in ambient conditions with the help of catalyst. Water and oxygen are only byproducts, during reactions or degradation. These have inverse effect considering the environment. Equation (2.5) illustrate the degradation of H2O2 (Zhanga et al., 2009; Chan, 2010). 2H2O2→2H2O + O2
(5)
2.7.2.2 H2O2- Organic Acid System Used with acids, H2O2 is more effective. The main organic acids used are formic and acetic acids. In 1996, Petro star Inc. combined (conversion extraction) desulfurization (CED) to remove sulfur from diesel fuel. After mixing the fuel with peroxyacetic acid (H2O2/acetic acid), the oxidative reaction below 100ºC under atmospheric pressure. Liquid-liquid extraction is used after that to get a fuel with low sulfur content, and an extract with high sulfur content. Additional treatment is 104
needed for the low sulfur fuel. The extraction solvent can be removed from the extract, where can be reused.
2.7.2.3 H2O2 -HetroPoly Acid System British Petroleum Company introduced a new alternative oxidative desulfurization process so that the use of organic or inorganic acids is avoided. This is done by using phosphotungstic acid as the catalyst and tetraoctylanmonium
bromide as the phase transfer agent(PTA) in a
mixture of water and toluene (Zongxuan et al., 2011). (Sachdeva and Pant 2010) investigated the hetrocyclic sulfur compounds removal from diesel. This was done using phophotungstic acid as the catalyst in presence of H2O2 oxidant and tetraoctylammonium bromide as the phase transfer agent. Heteropoly acid (HPA) catalysts in H2O2 oxidation systems showed high catalytic activity in the oxidation of BTs and DBTs. HPA has been widely used because of high catalytic activity for the oxidation of benzothiophene and its derivatives (Li et al.,2013). (Angelo et al., 2016) investigated a mixed assisted oxidative desulfurization of DBT and BT. This was done using polyoxometalate/ H2O2 systems and phase transfer agent. The catalytic activity of the different catalyst showed H3PW12O40>H3PM12O40>H3SiW12O40 for both DBT and BT. (Huaming Li et al,.2009) studied oxidative desulfurization system composed of Phosphotungstic acid H3PW12O40 ,H2O2 and [ bmim] BF4 of ionic liquid as an extractant. 98.2% removal of DBT was at room temperature (300C) for 1 h. Increasing the temperature to 700C, 100% removal of sulfur compounds was given in 3 h when treating BT,DBT and 4,6-DMDBT. 105
2.7.3 Catalytic Oxidation Desulfurization Conversion of hydrocarbon feed stocks such as (olefins, alkanes and aromatics) to oxygenated derivatives are widely done using catalytic oxidations. For economic reasons, the primary oxidant choice is restricted to molecular oxygen (Sheldon, 1997). Different approaches are used. One, using oxidation catalysts to reduce the energy barrier of oxidation. This is done by extending the oxidation reaction on the surface which is catalytically active. Two, materials that serve as oxygen carriers. These can be considered more active oxidants. Three, catalysts that facilitate the hydroperoxides decomposition. This accelerates the oxidation reaction propagation step (Javadli and De Klerk, 2012). Different loading ratio (5, 10, and 15 wt.%) of tintanium silica matrix as a catalyst in ODS was studied, where DBT of 500ppm sulfur content was studied. 99% sulfur removal was shown after 3 h at 60oC and H2O2 as oxidant (Shah et al. 2009). Polyoxometalate with transition metal (W and Mo) catalyst was studied for ODS of gas oil. It had 5700 ppm of sulfur content and model fuel (BT, DBT and4,6-DMDBT dissolved in n-hexane) which have 640 ppm with sulfur content, H2O2 and acetic acid. The highest removal of 98% was shown using polyoxometalate with W (Trakarnpruk & Rujiraworawut 2009).
Tintanium silicate (0.507 wt. % Ti) which was homogenously dispersed on porous glass bed surface, showed complete conversion of (DBT and 4,6-DMDBT) in 70oC and 3 min using a 150 ppm sulfur content model fuel. The oxidant used was isopropanol and cumene
106
hydroperoxide. The activation energy was 60.5 kJ/mol and reaction is pseudo-first order (Shen et al. 2015).
2.7.4 PhotoCatalytic Oxidation Desulfurization System In this process high-pressure mercury lamp of ultra-violet radiation or visible light is used into the polar solvents sulfur compounds. The sulfur compounds can be photo-oxidized. It can be considered as photochemical reaction and liquid-liquid extraction combination. The temperature and pressure are normal. To begin the photocatalytic oxidation, both the oil and extractant are added at the same time. The oxidant can be oxygen, peroxide, etc. (Zhanga et al., 2009). The utilization of UV-light to remove pollutants via photocatalytic oxidation has been used widely as one of the ODS processes. Using titanium dioxide -based photo catalysis in environmental purification was widely used over the past decade. This was done so that organic compounds in air and wastewater are decomposed. The conditions used are mild.TiO2 has a strong oxidizing power (with UV light) and it is inert to chemical corrosion. Two
main
stages
are
encountered
in
the
photocatalytic
desulfurization: (1) photocatalytic oxidation is subjected to the sulfur containing compounds, where sulfoxides or sulfones are produced by oxygen donation to the sulfurous compounds, (2) extraction of higher polarity oxidized products by exposure to the phase of polar solventextracting. The successful removal of thiophenes and benzo-thiophene and dibenzothiophene derivatives, (which are considered as model of gasoline, light oil and diesel sulfur compounds) is done by application of photocatalysis for deep desulfurization (Trongkaew et al., 2011).
2.7.5 Ultrasound Oxidative Desulfurization System (UAOD) 107
One new technology for desulfurization is the Ultrasound oxidation desulfurization. In this process the mixing of oxidants, raw materials and surfactants in water, in a reactor. By this, a water phase and organic medium is formed (Zhanga et al., 2009). Oxidative reaction generates
organic phase which contains
sulfoxides and sulfones. Decantation or extraction can be used to separate the sulfones and sulfoxides because of their polarity. The UAOD is used to treat gasoline, diesel, kerosene and jet fuels. Also, it can be applied to bunker and residual fuels (Hielscher Ultrasonics, 2012). In a batch laboratory system, (Durate et al., 2011), used a combination of ultrasound irradiation with hydrogen peroxide and acetic acid to remove
sulfur from diesel oil and petroleum product
feedstock.These contained model sulfur compounds (benzothiophene, dibenzothiophene and dimethyldibenzothiophene). The percentage removal of sulfur was 98% for feedstocks enriched with DBT and 4,6DMDBT. For diesel, the removal was 75% and it was better than the case without ultrasound.
2.7.6 Extraction Desulfurization Organic sulfur compounds are more soluble than hydrocarbons in convient solvent. The Extractive desulfurization is based on this point. And it must be known that the chemical structure of the fuel oil compounds is not changed (Babich and Moulijn, 2003). Fig. 2.10 shows a general process flow of extractive desulfurization
108
Fig. (2.10) General Process for extractive desulfurization (Javadli and De Klerk,2012)
The cost of desulfurization is reduced to a large extent when using sulfur extraction technologies, because no hydrogen is used, and also for using atmospheric temperatures and pressure. Also, the process has the advantage of applying to all middle distillates types.
2.7.7 Adsorption Desulfurization Adsorptive desulfurization is an effective inexpensive method that can be used to remove cyclic sulfide from hydrocarbon fuel. It is characterized by its low energy consumption, ambient operational conditions without using hydrogen gas, availability of broad adsorbents as well as regeneration possibility of spent adsorbents. It is strongly dependent on the sorbent properties like adsorption capacity, selectivity for the organosulfuric compounds; durability as well as regenerability (Alhooshani et al., 2015). It can be divided into two types according to the way that adsorption process takes place: Physical adsorption and reactive adsorption. The later includes a chemical reaction between organosulfur compounds and solid sorbent surface, where sulfur is usually converted to sulfide.
2.7.8 BioDesulfurization (BDS) 109
BDS is used to remove sulfur from organsulfur compounds, because of selective splitting of carbon-sulfur bonds using a biocatalyst. The catalyst are desirable because of their selectivity to remove sulfur compounds without conversion of other components. BDS can happen as an oxidative process converting sulfur to sulfate, or as a reduction process converting sulfur to hydrogen sulfide. The reductive processes is elusive and rarely used. Reaction conditions are moderate for both (Delmon and Yates, 2007). The BDS process can be applied to a larger scale. It is based on using biocatalyst to convert sulfur organic compounds to sulfones or sulfoxides. In fig. (2.11) an example is shown, where DBT is converted to hydroxyl biphenyl (Zainab, 2010).
Fig. (2.11) Biodesulfurization pathway for DBT In refineries BDS is used as an alternative or a complimentary to hydrodesulphurization (Kareem et al., 2013), (Ishii et al., 2005) showed
110
that a BDS process was applied using mild conditions and microorganisms to get deeper desulfurization of diesel oil. BDS is an advantages process, because it operates at ambient temperature and pressure, has high selectivity, results in less cost, has low emission and no undesirable side products are generated (Mohebali and Bal, 2008). Table 2.4: Advantages and disadvantages of some desulfurization methods
Process
Hydrodesulfurization
Advantages
Disadvantages
Important and efficient methods.
Highly effective in removing sulfur
quality as a result of severe
from light petroleum fractions such as
conditions (Javadli & de Klerk,
gasoline and naphtha.
2012).
Successful
removing
of
sulfur,
Reduction in catalyst life and fuel
High
operational
cost
and
nitrogen, oxygen, and metals which
requirements of excess amounts of
impairs equipment, catalysts, and the
hydrogen gas.
final product (Simanzhenkov & Idem,
Difficulty
2003).
benzothiophenes and their alkylated
of
removing
derivatives (Acton, 2013). Oxidation
Desulfurization
Mild operational conditions with no
High cost of handling and storage
hydrogen requirements.
of
Economic and attractive process (Liu,
oxidants (Sundararaman et al.,
2010).
2010).
Can be utilized to remove nitrogen
Formation of biphasic two phase
compounds.
system as a result of extraction
Promising process efficiently employed
method
to remove refractory sulfur compounds
limits the mass transfer, decreases
which are difficult to be eliminated by
the oxidation rate and losses of the
HDS (Shiraishi et al., 2002).
fuel oil (Murata et al., 2004).
111
expensive
dangerous
followed
ODS;
liquid
which
Extraction
Attractive physical process.
desulfurization
Applied
in
many
organosulfuric compounds in the
industrial
solvent.
applications without requirements of
hydrogen.
Biodesulfurization
Limitation to the solubility of the
Requirements of low viscous fuel
Operated at almost ambient conditions.
and solvent to enhance mixing and
No changes in the chemical structure of
extraction.
the treated fuels (Babich & Moulijn,
High cost recovery of solvent
2003).
(Javadli & de Klerk, 2012).
Low capital (two times less).
Low operational costs (about 15 %
of microorganisms in a sanitary
less) (Soleimani et al., 2007).
environment.
Difficulty in handling and storage
Lasts longer process (Soleimani et al., 2007).
2.8 Previous Work
An effective catalyst of (Kong et al., 2006), organic sulfur using
Ag/TS-1 (0.06 wt%) was synthesized by
for the
oxidative desulfurization of gasoline
equal-volume impregnation. There was a high
dispersion of Ag with preferred
deposition
around Ti of the TS-1
catalyst. The performance of TS-1 is adversely influenced by large amount of Ag, because it may hinder the organic sulfur oxidation. The oxidative desulfurization of gasoline was accomplished over Ag/TS-1 catalyst with water as solvent and H2O2 as oxidant. The sulfur decreased from 136.5 to18.8 µg/g after 4 h. (Cheng et al., 2006) investigated an oxidative desulfurization process for model light oil over Ti-MWW. Benzothiophene and dibenzothiophene 112
are oxidized to their corresponding sulfoxides and sulfones, which can be removed
by
extraction
using
acetonitrile.
The
conversion
of
benzothiophene and dibenzothiophene is 100% and 95%, respectively, at 70oC. The effect of solvent was also studied. Under the same conditions, the conversion of benzothiophene in three solvents is in the order acetonitrile>methanol>water.
The oxidative desulfurization of a model diesel fuel was investigated by (Cui et al., 2007), with H2O2 as oxidizing agent and a catalyst of molecular sieving containing Ti. They investigated the sulfur removal considering TiO2/SiO2 ratio in hexagonal mesoporous molecular sieves containing Ti (Ti-HMS). They also investigated; reaction conditions such as temperature, time of reaction, and n(H2O2)/n(S). The results showed that the mesoporous catalyst such as Ti-MSU and Ti-HMS were efficient for the oxidation of BT and DBT. The titanium silicalite-1(TS-1) microporous is completely inactive. The conversion increased with increasing the
molar ratio of TiO2/SiO2.With the optimum ratio the
conversion of DBT reached 80.6%.
(Huang et al. 2008). TiO2 as a catalyst for ODS with H2O2 was examined, for model fuel of DBT with sulfur content 300 ppm, 98% removal in 2 min was reached, at 80oC, and the order of reaction is 0.75 with activation energy 4.7 kJ/mol . (Park et al.2009). Prepared mesoporous TS-1 catalysts by a nanocasting route using two different carbon template sources of CMK-3 and commercial carbon black. The catalytic performance of these samples for allylchloride
epoxidation
and
oxidative
desulfurization
of
the
representative refractory sulfur compounds, DBT, and 4,6-DMDBT were compared with those of conventional TS-1. While the allylchloride 113
epoxidation activity for the mesoporous TS-1 samples was similar, mesoporous TS-1 exhibited significantly higher catalytic activities than conventional TS-1 during oxidative desulfurization. (Campos-Marten et al. 2010) showed that the high removal of BT, DBT and 4,6 DMDBT had been achieved successfully using oxidation with H2O2 in liquid phase. The catalyst used was amorphous silicaloaded titanium dioxide. They showed that H2O2 and organosulfur concentration, and the nature of the solvent plays an important role in the removal of sulfur. (Wang et al. 2012) explored the photocatalytic activity of nano-TiO2 in desulfurization and found that nano-TiO2 can be prepared in ionic liquids and reduce sulfur contents to 8 and 26 ppm in model oil and actual diesel oil, respectively, after 10 h of UV irradiation. (Yan et al.2013) showed that to remove sulfur, oxidants and synthesized TiO2 with phosphotungstic acid (HPW) as a catalyst used for ODS. By increasing TiO2, a high conversion of 95.2% of DBT can be obtained. (Zhu et al.2014) The effect of TiO2 forms as photocatalysts was studied in the oxidative desulfurization by (Zhu et al.2014). They showed that these forms affect the photocatalytic oxidation of TiO2 significantly. The conversion of DBT was reaches 96.6% in model oil using amorphous TiO2, 23.6% using anatase TiO2 and 18.2% with anatase–rutile TiO2. In 2014, (Arellano et al) showed that 300ppm of DBT was removed at 10 wt% Fe using Fe–TiO2 as acatalyst. The authers showed that Ti and Fe work as active sites. The conversion 100% was achieved from the 300 ppm DBT initially present in the reaction mixture after 5 min. Porous glass supported with TiO2 nanoparticles as catalyst was designed and prepared in the ultra-deep oxidative desulfurization of DBT and 4,6DMDBT by (Shen et al.2015) in a green way. The catalyst had good 114
stability and high activity to produce ultr-clean fuels. Within 2 min a 100% was reached. Sol-gel method was usedto prepare different forms of TiO2 nanoparticles by (Liantang Li et al. 2016).It was shown that anatase nano-TiO2 is more active compared to anatase-rutile and amorphous forms. Complete conversion of DBT (100ppm) was reached within 50 seconds using a catalyst of anatase nano-TiO2. Increasing the temperature from 313K to 343K greatly increased the reaction rate. Also, it was shown that reaction rate increased with increasing DBT initial concentration. 2. 9 Kinetics of ODS reactions An important step of any kinetic study is mathematical model capable of predicting product yields for given feed rate, feed composition, and reaction conditions. It translates experimental data into parameters used as the basis of commercial reactor design (Weit et al., 1997). To make a material balance on component A in a batch reactor, at any time, the composition is uniform. Also, it is assumed that no fluid enters or leaves the reaction mixture during reaction. or Input and output= 0 or Disappearance= - accumulation Input = Output +Disappearance +Accumulation
(6)
Disappearance of A by reaction 𝑚𝑜𝑙𝑒 𝐴 𝑟𝑒𝑎𝑐𝑡𝑖𝑛𝑔 (Moles/time) = (−𝑟𝐴)𝑉 = ((𝑡𝑖𝑚𝑒)(𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑓𝑙𝑢𝑖𝑑))(𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑓𝑙𝑢𝑖𝑑) moles/time 𝑑𝑁𝐴 𝑑[𝑁𝐴0 (1−𝑋𝐴 )] 𝑑𝑋 Accumaltion of A (mol/time) = = = −𝑁𝐴0 𝐴 𝑑𝑡
𝑑𝑡
(7)
𝑑𝑡
(8) by replacing these two terms in Eq .1, we obtain
(−𝑟𝐴 )𝑉 = 𝑁𝐴0
𝑑𝑋𝐴
(9)
𝑑𝑡
Rearranging and Integration then 115
𝑋𝐴 𝑑𝑋𝐴
𝑡 = 𝑁𝐴0 ∫0
(10)
−𝑟𝐴
For first order the reaction rate of the chemical reaction –rA=k CA and by substitution 𝑑𝑋𝐴 =
−𝑑𝐶𝐴 𝐶𝐴ₒ
and the in Eq. 10 became: 𝑋𝐴 𝑑𝑋𝐴
𝑡 = 𝐶𝐴0 ∫0
−𝑟𝐴
𝐶𝐴 𝑑𝐶𝐴
= − ∫𝐶𝐴0
−𝑟𝐴
(11) 𝐶𝐴 𝑑𝐶𝐴
− ∫𝐶𝐴0
𝐶𝐴
𝑡
= 𝐾 ∫0 𝑑 𝑡
(12) Integration Eq.12 gives Eq.13
−𝑙𝑛 (
𝐶𝐴 𝐶𝐴ₒ
) = 𝐾𝑡
(13) For second order the reaction rate of the chemical reaction –rA=k CA2 and by sub 𝑑𝑋𝐴 = 𝑡
−𝑑𝐶𝐴 𝐶𝐴ₒ
and the in Eq. (10) became:
𝐶𝐴 − 𝑑𝐶𝐴
𝑘 ∫𝑜 𝑑𝑡 = ∫𝐶𝐴ₒ
(14)
𝐶𝐴2
Integration Eq. 14 gives Eq. 15 1 𝐶𝐴
−
1 𝐶𝐴0
=
1
𝑋𝐴
𝐶𝐴0 1−𝑋𝐴
= 𝐾𝑡
(15)
116
3.1 Introduction This chapter represents the following work:1. Preparation and characterization of nano titanium dioxide with four different structures (amorphous, anatase, anatase-rutile, and rutile) by solgel and
hydrothermal methods using two sources of titanium
tetraisopropoxide
(TTIP)
and
titanium
ethoxide,
and
octade
cetyltrimethylammonium bromide (STAB) as the structure-directing agent also, studying the effect of different variables on the properties of titanium dioxide nanoparticles like ; (A) Crystallization temperature of 170,180, and 190oC for hydrothermal method. (B) Aging time of 12, and 24 hrs for two methods. 117
(C) Aqueous solution with varied pH 1,2,3,4,7, and 9. (D)
Acid
type
using
phosphoric,
acetic,
hydrochloric,
and
phosphotungustic acids. (E) Base type using ammonium hydroxide. (F) Drying temperature 120oC. (G) Calcination temperature of 450,700, 800, and 900oC. 2. Study the effects of crystalline forms, stirring rate, reaction temperature, catalyst amount, oxidant content and initial DBT concentration on the removal of sulfur compounds from model fuel using the prepared nanoTiO2 catalysts. 3. Study the kinetic model of oxidative desulfurization process to estimate the parameters of the kinetics for model fuels.
3.2 Materials 3.2.1 Chemicals The chemical materials used in the experimental work are listed in table 3.1.
Table 3.1 Chemicals used in catalyst preparation No 1
2
materials
function
Titanium
Source of
Tetraisopropoxide
titanium
Titanium ethoxide
Source of titanium
formula
company
purity
C12H28O4Ti
Himedia
pure
C32H80O16Ti4
Himedia
pure
C19H42BrN
Wuhan kemiWorks, Chemical Co.Ltd.
H3PW12O40
Riedel-De Haen
Octade 3
cetyltrimethylamm
structure-
onium bromide
directing agent
99%
(STAB) 4
Phosphotungustic
Catalyst
118
pure
acid 5
Acetic acid
CH3COOH (96%)
pure
6
Hydrochloric acid
HCl (34%)
99%
7
Phosphoric acid
H3PO4 (85%)
99%
Ammonium 8
hydroxide
9
Alkaline agent
NH4OH (28%)
Sigma
99%
Solvent
C2H6O
Sigma
99%
Ethanol
3.2.2 Equipment The equipment used for catalyst preparation are presented in Table 3.2. Table 3.2 Specifications of the equipment. No.
1
Apparatus Mechanical stirrer with digital display
Specification
Company Heidolph
Rotation speed(40-2000) rpm
instruments-RZR 2021-Germany)
2
Electrical furnace
Maximum temperature 1340 oC Power 6 kw
Nabertherm
3
Electrical oven
Maximum temperature 300 oC
Gallenkamb
4
Electronic balance
Maximum weight 210 gm Minimum weight 0.1 gm
Sartorius
3.3 Preparation of Nano-Titanium Dioxide 3.3.1 Sol-gel Method and Titanium Tetra-Isopropoxide as Source Material 119
The nano TiO2 was prepared by the following steps : 1. Titanium tetra-isopropoxide (TTIP) was mixed with ethanol in molar ratio of 1:10 and stirred for 1 hour (solution A). 2. 0.1g of octade cetyltrimethylammonium bromide (STAB) was added to the (solution A) for 1 step with stirring conditions. Chang et.al.2010. 3. Another solution was prepared from a mixture of water and ethanol with a molar ratio of 10:1 (Solution B). 4. (Solution B) was titrated into (solution A) and stirred for 2 hour until sol was produced. 5. Different molar ratio between (TTIP) and catalyst acid (HCL, or CH3COOH acid, or H3PO4 acid, and or PWA acid) or base was used to obtain various pH (1, 2,3,4,7, and 9). 6. After aging time for 12 and 24 hrs the sol transformed into gel. 7. The gel was dried at 120oC in an oven for 24 hrs to evaporate water and organic material to the maximum extent. 8. The powder obtained at 120oC was (amorphous phase of nano TiO2) 9. The powder obtained was calcined at 450, 700, 800, and 9000C. Table (3.3) gives the conditions of the prepared samples by sol-gel method with TTIP as a source material.
120
Table 3.3 Conditions of the prepared samples by sol-gel method and (TTIP) as a source material Sample code
Acid or base type
pH
Drying and Calcination temperature,0C
T1
HCl
1
120 450 700
T2
HCl
2
120 450 700
T3
HCl
3
120 450 700
T4
HCl
4
120 450 700
T5
NH4OH
7
120 450 700
T6
NH4OH
9
120 450 700
121
T7
H3PO4
120 450 700
T8
CH3COOH
120
3.8
450 700.800,900 T9
H3PW12O40
120
_
450 700,800
A flow diagram of the preparation of nano TiO2 by sol-gel method in figure 3.1. Titanium tetraisoprpoxide
Ethanol
STAB
Stirring (solution A) for 1 hrs
pH controlled by adding acid or base
Vigorous stirring at 800rpm for 2 hrs
Aging for 12and 24 hrs sol to gel
Drying at 1200C for 24 hrs
122
Water+Ethanol (Solution B)
Calcination at temperatures between (450 to 900) 0Cfor 3 hrs
NanoTiO2 powder to characterization Fig.3.1 Flow diagram of nano TiO2 preparation by sol-gel method (TTIP source material)
3.3.2 Sol-gel Method and Titanium Ethoxide as a Source Material The nano TiO2 was prepared by the following steps: 1. 14ml of titanium ethoxide was dissolved in 140ml of ethanol. 2. 0.1g of octade cetyltrimethylammonium bromide (STAB) was added to the solution for 1 step with stirring conditions. Liantang et.al.2016 3. After 15 min, 2ml of phosphotungustic acid (PWA) solution with concentration of 0.15 M or 2 ml of phosphoric acid was added. 4. The resulting suspension was stirred for 3 hr at room temperature. 5. After that 20ml of deionized water was added drop-wise, and then the solution was stirred for additional 2hrs. 6. The solution produced was dried in an oven at 120oC for 24 hrs. 7. The obtained solid product was washed thrice with deionized water and then thrice with ethanol. 8. The product was dried in an oven at 120oC for 12 hrs to produced amorphous phase. 9. The powder obtained was calcined at 450, 700, and 800 oC. Table (3.5) shows the conditions of the prepared samples by sol-gel method with titanium ethoxide as a source material. 123
Table 3.4 Conditions of the prepared samples by sol-gel method and titanium ethoxide as a source material Sample code
Acid type
Drying and Calcination temperature, 0C
T1E
120
-
450 700,800 T2E
H3PO4
120 450 700,800
T3E
H3PW12O40
120 450 700,800
Fig. (3.2) is a flow diagram for the preparation of nano TiO2 by sol-gel method and titanium ethoxide as a source material.
124
Titanium ethoxide
Ethanol
STAB
Vigorous stirring for 15 min
Phosphotungustic or phosphoric acids Vigorous stirring for 3 hrs Deionized water Vigorous stirring for 2 hrs
Drying at 120oC for 24 hrs
Washing with water and ethanol
The solid dried at 120oC for 24 hrs 125
Calcination at temperatures between (450 to 800) 0Cfor 3 hrs
NanoTiO2 powder to characterization Fig.3.2 Flow diagram of nano TiO2 preparation by sol-gel method (titanium ethoxide source material)
3.3.3
Preparation
of
Nano
Titanium
Dioxide
by
Hydrothermal Method The nano TiO2 was prepared by the following steps: 1. 10ml of Titanium tetra-isopropoxide (TTIP) was added to 20ml acetic acid with stirring (900 rpm). 2.
After stirring for 30min, 200ml distilled water was added dropwise from burette at a rate 1ml/min.
3. The stirring was continued without heating till clear solution was obtained. 4. After aging for 12 and 24 hrs the sol transformed into gel. 5. The gel was then transferred into a Teflon-Lined stainless steel autoclave (i.d =5.2 cm, o.d =10 cm, thickness =2.4 cm, L=11.6 cm) shown in fig 3.4 at crystallization temperature of either 170, or 180, or 1900C for either of 12, or 24hrs. 6. After crystallization the product was filtered using nano type filter papers, washed by deionized water and ethanol for several times to eliminate the contaminants, dried at temperature 100 0C for 24 hrs, and finally calcined at either of 450, or 700, or 800 ,or 9000C Kavithaet.al.2013. 7. The same procedure of prepared nano TiO2 with TTIP as source material was repeated but by using phosphotungsti acid instead of acetic acid. 126
Conditions for prepared samples by hydrothermal method are shown in table (3.5).
Table 3.5 Conditions of the prepared samples by hydrothermal method Sample
Acid type
code
Crystallization
Crystallization
Drying and
temperature,0C
time,hr
Calcination temperature,0C
T1H
Acetic acid
170
24
120 450 700,800,900
T2H
Acetic acid
180
24
120 500 700,800,900
T3H
Acetic acid
190
24
120 450 700,800,900
T4H
H3PW12O40
170
24
120 450 700
T5H
H3PW12O40
180
24
120 450 700
T6H
H3PW12O40
190
24
120 450 700
Fig. (3.3) shows a flow diagram of preparation of nano TiO2 by hydrothermal method. 127
Fig. (3.4) shows the twin- autoclave for preparation by hydrothermal method.
Titanium tetraisoprpoxide
Acetic or Phosphotungsti c
STAB
Vigorous stirring at 900rpm for 3 hrs
Distilled water
Crystallization at temperatures between (170190 0C) using stainless steel auto clave for (1224hrs)
Filtration
drying overnight at 120°C
Calcinations at temperatures between (450-9000C) for 3hrs
powder characterization Fig.3.3 FlowNanoTiO diagram2 of nano to TiO 2 preparation by hydrothermal method
128
Figure 3.4: Twin autoclaves for preparation by hydrothermal method
3.4 Oxidative desulfurization processes DBT was dissolved in octane solution and used as the model fuel. A 250 mL glass-stirred reactor was equipped with a water bath to maintain a stable reaction temperature. In a typical run: 1. A magnetic stirrer was set between (200,600, 800, and 1200) rpm to blend the reaction mixture. 2. Reaction times were (10 to 120) sec for nano TiO2 without PWA and (1 to 10) min for nano TiO2 with PWA. 3. Reaction temperatures were (40, 50, 60,70, and 80) o C 4. The prepared catalyst in different amount (0.05, 0.08 , 0.1, 0.2 ,0.3 ,0.4, and 0.5) gm/l and different forms (amorphous, anantse, and anatase-rutile) was used. 129
5. Different
concentration
of
model
fuel
(DBT)
(100,200,300,400,500,1000,and 3000) ppm. 6. H2O2 as oxidant was used to initiate the reaction, and in the molar ratio of H2O2 to S set to (5, 9, 10, 15, 18, and 20) respectively. The samples were collected at different times, centrifuged in a centrifugal separator, and then analyzed by UV-Spectroscopy the UV-carve calibration at different concentration of DBT as shown in appendix F.
3.5 Test Methods 3.5.1 X-Ray Diffraction The identity and crystinallity of all prepared samples was tested using X-ray diffractmeter type Shimadzu SRD 6000, Japan shown in fig. 3.5, with Cu wave length radiation 1.54060 cm-1 in the 2 theta range from10800, and fixed power source 40Kv, 30mA. X-ray diffraction was attempted in the Research Center of Materials/Ministry of Science and Technology.
Fig. 3.5 X-ray diffraction devic
3.5.2 Fourier –Transform Infrared Spectroscopy (FTIR) This test was applied using (IR-Affinity,Shimazdo,Japan) shown in fig. 3.6 with wave range between (400-4000)cm-1 at the Central 130
Environmental Laboratory/ College of Science / University of Baghdad. The sample was pressed to disk shape after adding 1% nano TiO2to 99% KBr.
Fig. 3.6 Fourier –transform infrared spectroscopy (FTIR) device
3.5.3 Surface area and pore volume The surface area, and pore volume of the samples were conducted at the Petroleum Research and Development Center / Ministry of Oil and in the Research Center of Materials/Ministry of Science and Technology. Using Brunauer, Emmett, and Teller (BET) method with Thermo Analyzer/USA shown in fig. 3.7 according to ASTM D1993.
Fig. 3.7 Surface area and pore volume device
3.5.4 Atomic Force Microscope Average particle size and the morphology of surface of each sample were tested at the Department of Chemistry/ College of Science/ 131
University of Baghdad using Atomic Force Microscope Device (type Angstrom, Scanning Probe Microscope, Advanced Inc, AA 3000, USA) shown in fig.3.8.The samples were dispersed in ethanol and dried before studying the morphology and the particle size.
Fig. 3.8 Atomic Force microscope (AFM) Device
3.5.5 Scanning Electron Microscope (SEM) The Scanning Electron Microscope SEM tests were done to study the morphology of the surface. The specimen of prepared nano TiO2was dispersed in ethanol and coated by gold using special cell. The tests were done in Research Center of Materials/Ministry of Science and Technology by FEI NOVA NANO SEM device (www.daypetronic.com) shown in fig. 3.9.
132
Fig. 3.9 Scanning Electron Microscope (SEM) Device
3.5.6 X-Ray Fluorescence The percentages of metal oxides on nano gamma alumina support were measured by X-Ray Fluorescence (SPECTRO XEROS, AMETEK, GERMANY) shown in fig. 3.10. The tests were done in Research Center of Materials/Ministry of Science and Technology. Each test needed at least 3 gm of sample pressed as disk shape, and contacted to Helium.
Fig. 3.10 X-Ray Fluorescence device
133
4.1 Characterization of Prepared Nano Titanium Dioxide 4.1.1 X–Ray Diffraction (XRD) The identity of the nano titanium dioxide prepared at various methods, crystallization temperature, crystallization time, acid type, and calcination temperature was determined by X-ray diffraction. The results of x-ray diffraction were shown in figures (4.1) to (4.9) for preparation by sol-gel method and titanium tetra-isoprpoxide as a source material, figures (4.10) to (4.12) for preparation by sol-gel method and titanium ethoxide as a source material, and figures (4.13) to (4.16) for preparation by hydrothermal method. 134
The phase and crystallinity of prepared TiO2 nanoparticles were analyzed by X-ray diffractometer. The results of XRD patterns for the synthesized titanium dioxide can be referred to the formation of amorphous, anatase, anatase –rutile and rutile phases through the comparison with the powder diffraction data [JCPS]; 21.1272 the standard XRD peaks of titanium dioxide (anatase) were presented at 2θ of 25.281, 37.8 and 48.575 respectively and standard XRD peaks of titanium dioxide (rutile) were presented at 2θ of 27.446, 36.085, and 41.225 respectively as shown in all Figures represented XRD. The purity of the prepared titanium dioxide was tested after comparison between 2Ɵ
and d-spacing of the prepared
samples with 2Ɵ and d-spacing of international titanium dioxide Card (JCPDS) files No. 21.1272 as shown in table 4.1, 4.2, 4.4,4.5, and 4.7. The relative
crystallinity percentage was calculated according to
equation 4.1 using the intensities in the tables mentioned above and shown in appendix A.
Average Crystallinity % =
∑ 𝐼𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑖𝑒𝑠 𝑜𝑓 𝑝𝑒𝑎𝑘𝑠 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒𝑠 𝐼𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑖𝑒𝑠 𝑜𝑓 𝑟𝑒𝑓𝑒𝑟𝑛𝑐𝑒 𝑝𝑒𝑎𝑘𝑠 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒𝑠
* 100
(4.1)
The content of anatase and rutile for all TiO2 samples was calculated in Eq.4.2 and as shown in appendix A: XA=100/ (1+1.265IR/IA)
(4.2)
Where, XA: weight fraction of rutile in the powders. 135
IA: X-ray integrated intensity of the strongest peaks of anatase (2θ = 25.3o, (101) plane). IR: X-ray integrated intensity of the strongest peaks of rutile (2θ = 27.5o, (110) plane) (Tao et.al.2015). The crystalline size (DP) of TiO2 nanoparticles was estimated according to the Scherrer equation (4.3) (Tao et.al.2015) and as shown in appendix A and sample of calculations of the crystalline size and crystallinity as shown in appendix G:
Dp=
0.94 λ β.Cosθ
(4.3) Where: Dp= Crystallite size, nm. λ = X-Ray wave length = 1.5418 Ao. 𝛽 = Line width at half maximum (FWHM), rad. θ = Bragg angle o.
4.1.1.1 X–Ray Diffraction (XRD) for Nano TiO2 Prepared by Sol-Gel Method and TTIP as Source Material Table (4.1) Comparison of 2Ɵ and d-spacing between prepared titanium dioxide (anatse) and standard titanium dioxide (anatse) for sol-gel method and TTIP as a source material Sample
Synthesis
code
conditions
Practical values of angle (2ɵ) deg and d,spacing (Å) 136
Standard values
2ɵ=25.40,d=3.50 2ɵ=37.89,d=2.36 0
T1
450 C ,HCl acid,
2ɵ=48.13,d=1.88
pH 1 2ɵ=27.53 2ɵ=25.32,d=3.51 2ɵ=37.94,d=2.37
T2
4500C,HCl acid,
2ɵ=48.04,d=1.89
2ɵ=25.281,d=3.52
pH 2 2ɵ=27.48 2ɵ=25.37, d=3. 51
T3
4500C, HCl acid,
2ɵ=37.86,d=2.37
pH 3
2ɵ=48.11,d=1.89
I/Io=100 2ɵ=37.8,d=2.378 I/Io=20 2ɵ=48.049,d=1.892 I/Io=35
2ɵ=25.3,d=3.51 2ɵ=37.79,d=2.37 T4
T5
Sample code
T6
4500C, HCl acid,
2ɵ=48.03,d=1.89
pH 4
4500C, NH4OH,pH 7
Synthesis conditions
4500C, NH4OH,pH 9
2ɵ=25.38,d=3.50 2ɵ=37.91,d=2.37 2ɵ=48.09,d=1.89
Practical values of angle(2ɵ) deg, and d,spacing(Å) 2ɵ=25.44,d=3.49
2ɵ=25.281,d=3.52
2ɵ=38.04,d=2.36
I/Io=100
2ɵ=48.15,d=1.88
2ɵ=37.8,d=2.378
137
Standard values
T7
T8
7000C, H3PO4 acid
2ɵ=25.47d=3.49
I/Io=20
2ɵ=38.07,d=2.36
2ɵ=48.049,d=1.892
2ɵ=48.17,d=1.88
I/Io=35
2ɵ=25.40,d=3.50
4500C, ,acetic acid,
2ɵ=37.94,d=2.36
pH3.8
2ɵ=48.09,d=1.89 2ɵ=25.41,d=3.50
T9
2ɵ=37.93,d=1.67
4500C,H3PW12O40
2ɵ=48.06,d=1.89 2ɵ=27.39
Table (4.2) Comparison of 2Ɵ and d-spacing between prepared titanium dioxide (anatase-rutile) and standard titanium dioxide (anatse) and (rutile) for sol-gel method and TTIP as a source material Sample
Synthesis
code
conditions
Practical values of angle (2ɵ) deg and d,spacing
Standard values
(Å) 2ɵ=27.097,d=3.288 2ɵ=36.209,d=2.478
T1
7000C ,HCl acid,
2ɵ=41.372,d=2.180
pH 1 2ɵ=25.52
T2
7000C,HCl acid, pH 2
2ɵ=27.446,d=3.247 I/Io=100 2ɵ=36.085,d=2.487 I/Io=50
2ɵ=27.62,d=3.486
2ɵ=41.225,d=2.188
2ɵ=36.252,d=2.475
I/Io=25
2ɵ=41.409,d=2.178 2ɵ=25.52
Sample code
Synthesis conditions
Practical values of angle (2ɵ) deg and d,spacing (Å) 138
Standard values
2ɵ=27.56,d=3.21 T3
7000C,HCl acid, pH 3
2ɵ=36.20,d=2.467 2ɵ=41.37,d=2.19 2ɵ=25.43 2ɵ=27.53,d=3.23
T4
T5
7000C,HCl acid, pH 4
0
700 C, NH4OH,pH 7
2ɵ=36.174,d=2.48 2ɵ=41.32,d=2.18
7000C, NH4OH,pH 9
I/Io=100
2ɵ=54.73
2ɵ=36.085,d=2.487
2ɵ=27.59,d=3.22
I/Io=50
2ɵ=36.22,d=2.477
2ɵ=41.225,d=2.188
2ɵ=41.38,d=2.17
I/Io=25
2ɵ=35.98
2ɵ=54.322,d=1.68
2ɵ=27.54,d=3.23 T6
2ɵ=27.446,d=3.247
I/Io=60
2ɵ=36.18,d=2.48 2ɵ=41.33,d=2.18 2ɵ=25.40 2ɵ=25.25,d=3.50
T9
8000C,H3PW12O40
2ɵ=37.84,d=1.67 2ɵ=47.98,d=1.89 2ɵ=54.94
From tables (4.1) and (4.2) it is clear that all the coordinates of the peaks of prepared samples were accepted the three strong standard peaks of titanium dioxide (anatase) (2θ of 25.281,3.52 d spacing), (2θ of 37.8 2.378 d spacing), and (2θ of 48.049 -1.8 d spacing) and four strong standard peaks of titanium dioxide (rutile) (2θ of 27.446 3.247 d spacing), (2θ of 36.085 2.487 d spacing), (2θ of 41.225 -2.188 d spacing), and (2θ of 54.322 -1.68 d spacing) which represents the pure substantial crystallization of titanium dioxide card (JCPDS) files No. (21.1272).
139
All the XRD-diffraction figures from (4.1) to (4.9) represented high crystalline titanium dioxide for different acids and pH in three different forms (amorphous, anatase, and anatase-rutile).
1600 1400
Intensity (Counts)
1200 1000 800
Amorphous
600
Anatase Anatase-Rutile
400 200 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.1) XRD diffraction of the three structures forms of nano titanium dioxide prepared using HCl acid pH=1 and at different calcination temperatures. Amorphous (120oC), anatase (450oC) and anatase- rutile (700oC).
140
1800 1600 Intensity (Counts)
1400 1200
1000
Amorphous
800
Anatase
600
Anatase-Rutile
400 200 0 0
20
40
60 2Ѳ (deg)
80
100
Fig. (4.2) XRD diffraction of the three structures forms of nano titanium dioxide prepared using hydrochloric acid pH=2 and at different calcination temperatures. Amorphous (120oC), anatase (450oC) and anatase -rutile (700oC). . 3000
Intensity (Counts)
2500 2000 Amorphous
1500
Anatase
1000
Anatase-Rutile
500 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.3) XRD diffraction of the three structures forms of nano titanium dioxide prepared using hydrochloric acid pH=3 and at different calcination temperatures. Amorphous (120oC), anatase (450oC) and anatase- rutile (700oC).
141
2500
Intensity (Counts)
2000 1500 Amorphous 1000
Anatase
Anatase-Rutile 500 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.4) XRD diffraction of the three structures forms of nano titanium dioxide prepared using hydrochloric acid pH=4 and at different calcination temperatures. Amorphous (120oC), anatase (450oC) and anatase- rutile (700oC).
2500
Intensity (Counts)
2000 1500 Amorphous 1000
Anatase Anatase-Rutile
500 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.5) XRD diffraction of the three structures forms of nano titanium dioxide prepared using NH4OH pH=7 and at different calcination temperatures. Amorphous (120oC), anatase (450oC) and anatase -rutile (700oC).
142
3000
Intensity (Counts)
2500 2000 Amorphous
1500
Anatase
1000
Anatase-Rutile
500 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.6) XRD diffraction of the three structures forms of nano titanium dioxide prepared using NH4OH pH=9 and at different calcination temperature. Amorphous (120oC), anatase (450oC) and anatase- rutile (700oC).
2500
Intensity (Counts)e
2000 1500
Amorphous Anatase
1000
ANatase Anatase
500 0 0
20
40
60 2Ѳ (deg)
80
100
Fig. (4.7) XRD diffraction of the three structures forms of nano titanium dioxide prepared using acetic acid pH=3.8 and at different calcination temperatures. Amorphous (120oC), anatase (450oC), anatase (700oC) and anatase (900oC).
143
1200
Intensity (Counts)
1000 800 Amorphous
600
Amorphous
400
Anatase
200 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.8) XRD diffraction of the three structures forms of nano titanium dioxide prepared using phosphoric acid and at different calcination temperature. Amorphous (120oC), amorphous (450oC) and anatase (700oC)..
3000
Intensity (Counts)
2500 2000 Amorphous
1500
Anatase-Rutile
Anatase
1000
Anatase-Rutile
500 0 0
20
40 2Ѳ (deg)
60
80
Fig. (4.9) XRD diffraction of the three structures forms of nano titanium dioxide prepared using phosphotungstic acid and at different calcination temperatures. Amorphous (120oC), anatase-rutile (450oC), anatase (700oC) and anatase rutile (800oC).
It was obtained in 2θ range of 20-80°with Cu Kα radiation source (λ = 1.5406 A°) and the X-ray tube operated at 40 mA and 40 kV. XRD 144
pattern shows three distinct peaks at 2θ° = 25.53, 37.73, and 48.189 which corresponds to (101), (004), and (200) planes, respectively. The observed peaks correspond to the anatase crystalline phase of TiO2.Also, XRD pattern shows three distinct peaks at 2θ° = 27.446, 36.085, 41.225, and 54.322 which corresponds to (110), (101), (111), and (211) planes, respectively. The observed peaks correspond to the rutile crystalline phase of TiO2.The XRD pattern was compared with standard JCPDS database and good matching with formation of anatase and anatase-rutile TiO2 was confirmed. The average crystallite size, determined using Debye Scherrer equation from full width half maxima (FWHM) of the distinct peak (101) and (110) was determined as shown in table (4.3) for different conditions.
Table (4.3) Crystallite size of nano TiO2 at different conditions for sol-gel method and TTIP as a source material
Sample code
Synthesis conditions
Acid type
pH
Crystalline size (nm)
anatase, 4500C
1
11
anatase-rutile , 7000C
1
32
anatase, 4500C
2
11.5
2
30.4
anatase, 4500C
3
18.33
anatase-rutile , 7000C
3
39.5
anatase, 4500C
4
18.64
T1
T2 anatase-rutile , 7000C
HCl
T3
T4
145
anatase-rutile , 7000C
4
40.77
7
15.4
anatase-rutile , 7000C
7
43.61
anatase, 4500C
9
13.23
anatase-rutile , 7000C
9
42.96
-
-
-
11.05
3.8
12.17
3.8
21.94
_
7.22
_
15.16
anatase, 4500C T5
T6
Amorphous T7
H3PO4
anatase, 7000C anatase, 4500C
T8
CH3COOH
anatase-rutile , 7000C Anatase,450oC T9
H3PW12O40
Anatase-rutile ,800oC
Table (4.3) shows the crystallite size of samples for different acids and calcination temperatures. Nano TiO2 prepared with phosphotungstic acid had smaller crystallite size than other samples of produced TiO2. The crystallite size of nano TiO2 prepared with HCl in lower pH is smaller than higher pH values.
4.1.1.2 X–Ray Diffraction (XRD) for Nano TiO2 Prepared by Sol-Gel Method and Titanium Ethoxide as Source Material
146
Table (4.4) Comparison of 2Ɵ and d-spacing between prepared titanium dioxide (anatse) and standard titanium dioxide (anatse) for sol-gel method and titanium ethoxide as a source material Sample
Synthesis
code
conditions
Practical values of angle (2ɵ) deg and d,spacing
Standard values
(Å) 2ɵ=25.4,d=3.51
4500C
T1E
2ɵ=37.92,d=2.37 2ɵ=48.02,d=1.89 2ɵ=25.34,d=3.51
7000C
T1E
2ɵ=37.80,d=2.37
2ɵ=25.281,d=3.52
2ɵ=48.07,d=1.89
I/Io=100
2ɵ=27.46 2ɵ=25.42,d=3.49 T2E
0
700 C,H3PO4 acid
2ɵ=38.07,d=2.36 2ɵ=48.17,d=1.88
2ɵ=37.8,d=2.378 I/Io=20 2ɵ=48.049,d=1.892 I/Io=35
2ɵ=25.42, d=3. 51
T3E
4500C, H3PW12O40 acid,
2ɵ=37.99,d=2.37 2ɵ=48.03,d=1.89 2ɵ=29.96
Table (4.5) Comparison of 2Ɵ and d-spacing between prepared titanium dioxide (anatase-rutile) and standard titanium dioxide (anatse) and (rutile) for sol-gel method and titanium ethoxide as a source material Sample
Synthesis
code
conditions
Practical values of angle (2ɵ) deg and d,spacing (Å) 147
Standard values
2ɵ=27.544,d=3.235 2ɵ=36.182,d=2.480 T1E
0
800 C
2ɵ=54.409,d=1.684
2ɵ=27.446,d=3.247 I/Io=100 2ɵ=36.085,d=2.487
T3E
8000C
2ɵ=25.40
I/Io=50
2ɵ=25.35,d=3.245
2ɵ=41.225,d=2.188
2ɵ=37.90,d=2.485
I/Io=25
2ɵ=48.05,d=1.685
2ɵ=54.322,d=1.687
2ɵ=26.29
I/Io=60
From the table (4.4) and (4.5) it is clear that all the coordinates of the peaks of prepared samples were accepted the three strong standard peaks of titanium dioxide (anatase) (2θ of 25.281 3.5 d spacing), (2θ of 37.8 2.378 d spacing), and (2θ of 48.049 -1.8 d spacing) and three strong standard peaks of titanium dioxide (rutile) (2θ of 27.446 -3.247 d spacing), (2θ of 36.085 -2.487 d spacing), (2θ of 41.225 -1.88 d spacing) and (2θ of 54.322 -1.687 d spacing) which represents the pure substantial crystallization of titanium dioxide card (JCPDS) files No. (21.1272). The results of x-ray diffraction were shown in figures (4.10) to (4.13) for preparation by sol-gel method and titanium ethoxide as a source material.
148
6000
Intensity (Counts)
5000 4000 Amorphous
3000
Anatase Anatase-Rutile
2000
Rutile
1000 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.10) XRD diffraction of the four structures forms of nano titanium dioxide prepared at different calcination temperatures. Amorphous (120oC), anatase (450oC) anatase rutile (700oC) and rutile (800oC).
1200
Intensity (Counts)
1000 800 Amorphous
600
Amorphous
400
Anatase
200 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.11) XRD diffraction of the two structures forms of nano titanium dioxide prepared using phosphoric acid at different calcination temperature. Amorphous (120oC), amorphous (450oC) and anatase (700oC)..
149
3000
Intensity (Counts)
2500 2000 Amorphous
1500
Anatase-Rutile Anatase
1000
Anatase-Rutile
500 0 0
20
40 2Ѳ (deg)
60
80
Fig. (4.12) XRD diffraction of the three structures forms of nano titanium dioxide prepared using phosphotungstic acid at different calcination temperatures. Amorphous (120oC), anatase-rutile (450oC) anatase (700oC) and anatase-rutile (800oC).
Table (4.6) shows the crystallite size of samples at different acids and calcination temperatures. When titanium ethoxide was used to prepare nano TiO2 without acid bigger crystallite size was found compared with the samples prepared with phosphtungstic acid which had smaller crystallite size. Table (4.6) Crystallite size of nano TiO2 at different conditions for sol-gel method and titanium ethoxide as a source material Sample code
Synthesis conditions
Acid Type
Crystallite size (nm)
T1E
Anatase,450oC
11.04
Anatase-rutile,700oC
_
Rutile, 800oC Sample code
36.83 46.17
Synthesis conditions
Acid Type
Crystallite size (nm)
150
T2E
Amorphous,450oC
H3PO4
Anatase,700oC
_ 11.75
Anatase, 450oC 6.70
T3E Anatase-rutile, 800oC
H3PW12O40
14.89
4.1.1.3 X–Ray Diffraction (XRD) for Nano TiO2 Prepared by Hydrothermal Method Table (4.7) Comparison of 2Ɵ and d-spacing between prepared titanium dioxide (anatse) and standard titanium dioxide (anatse) for hydrothermal method Sample
Synthesis
code
conditions
Practical values of angle (2ɵ) deg and d,spacing (Å)
Standard values
2ɵ=25.48,d=3.49
T1H
4500C,170oC, acetic acid
2ɵ=38.03,d=2.36 2ɵ=48.20,d=1.88 2ɵ=27.29 2ɵ=25.39,d=3.50
T1H
7000C,170oC, acetic acid
2ɵ=25.281,d=3.52 I/Io=100
2ɵ=37.88,d=2.37
2ɵ=37.8,d=2.378
2ɵ=48.11,d=1.88
I/Io=20 2ɵ=48.049,d=1.892
2ɵ=26.29
I/Io=35
2ɵ=25.37,d=3.50
T2H
4500C,180oC, acetic acid
2ɵ=37.91,d=2.37 2ɵ=48.05,d=1.89 2ɵ=26.84
Sample
Synthesis
code
conditions
Practical values of angle (2ɵ) deg and d,spacing (Å)
151
Standard values
2ɵ=25.34,d=3.51 2ɵ=37.84,d=2.37 T2H
700oC,180oC
2ɵ=48.07,d=1.89
acetic acid 2ɵ=26.04 2ɵ=25.38,d=3.50
T3H
4500C,190oC,
2ɵ=37.96,d=2.36
acetic acid
2ɵ=48.05,d=1.89 2ɵ=25.40,d=3.50
T3H
7000C,190oC,
2ɵ=37.89,d=2.36
acetic acid
2ɵ=48.13,d=1.88
2ɵ=25.281,d=3.52 2ɵ=25.34,d=3.51 T3H
9000C,190oC,
2ɵ=53.93,d=1.69
acetic acid
2ɵ=48.07,d=1.89
I/Io=100 2ɵ=37.8,d=2.378 I/Io=20
T4H
450oC,180oC, H3PW12O40
2ɵ=25.26,d=3.52
2ɵ=48.049,d=1.892
2ɵ=37.85,d=2.37
I/Io=35
2ɵ=47.97,d=1.89 2ɵ=27.15 2ɵ=27.54, d=3.23 2ɵ=36.18,d=2.48
T4H
700oC,180oC,
2ɵ=54.41,d=1.68
H3PW12O40 2ɵ=25.15
The results of x-ray diffraction were shown in figures (4.13) to (4.16) for preparation by hydrothermal method. 152
1400
Intensity (Counts)
1200 1000 800 Amorphous 600
Anatase
400
Anatase
200 0 0
20
40 2Ѳ (deg)
60
80
Fig. (413) XRD diffraction of the three structures forms of nano titanium dioxide prepared by hydrothermal method using, 170oC crystallization temperature and at different calcination temperatures. Amorphous (120oC), anatase (450oC) and anatase (700oC).. 3500 3000
Intensity (Counts)
2500 2000
Amorphous
1500
Anatase
1000
Anatase
500
Anatase
0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.14) XRD diffraction of the two structures forms of nano titanium dioxide prepared by hydrothermal method using acetic acid , 180oC crystallization temperature and at different calcination temperatures. Amorphous (120oC), anatase (450oC), anatase (700oC) and anatase (900oC).
153
3500
Intensity (Counts)
3000 2500 2000
Amorphous
1500
Anatase Anatase
1000
Anatase 500 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.15) XRD diffraction of the two structures forms of nano titanium dioxide prepared by hydrothermal method using, 190oC crystallization temperature and at different calcination temperatures. Amorphous (120oC), anatase (450oC), anatase (700oC) and anatase (900oC).. 1800 1600 Intensity (Counts)
1400
1200 1000
Amorphous
800
Anatase
600
Anatase-Rutile
400 200 0 0
20
40 60 2Ѳ (deg)
80
100
Fig. (4.16) XRD diffraction of the three structures forms of nano titanium dioxide prepared by hydrothermal method using phosphotungstic acid, 180oC crystallization temperature and at different calcination temperatures. Amorphous (120oC), anatase (450oC), and anatase-rutile (700oC).
154
Table (4.8) shows the crystallite size of samples with different acids, calcination temperatures and crystallization temperatures. For samples prepared with acetic acid, the crystallite size was increased with increasing crystallization temperatures from 170 oC to 190oC. When using phosphotungstic acid in preparation, the crystallite size decreased more than in acetic acid. Table (4.8) Crystallite size of nano TiO2 at different conditions for hydrothermal method Sample code
Synthesis conditions
Acid Type
Crystallite size (nm)
T1H
T2H
Anatase,170oC,450oC
17.49
Anatase, 180oC,450oC
8.01 Acetic acid
16.77
Anatase, 180oC,900oC
27.2
Anatase,190oC,450oC
10.07
Anatase,190oC,700oC
Acetic acid
Anatase,190oC,900oC T4H
7.68
Anatase,170oC,700oC
Anatase, 180oC,700oC
T3H
Acetic acid
Anatase, 180oC,450oC
28.46
H3PW12O40
Anatase-rutile,180oC,700oC
4.1.1.4 Effect of pH on the Syntheses TiO2 Nanoparticles. 155
21.68
7.34 15.62
TiO2 nanoparticles were synthesized by using acid (HCl) and alkaline (NH4OH) routes. Fig.(4.1) to (4.6) shows the X-ray diffraction (XRD) patterns of the powder samples prepared in initial solution at different pH (1,2,3,4,7, and 9).As seen in Fig.1 distinct peaks were noted in the XRD patterns at 25.39o. A trace of rutile was found in sample prepared at pH=1 at 27.533o corresponding to rutile phase. In this case, it is found that high acidity in medium solution will favor the formation of rutile phase until pH=3 where the rutile phase disappeared while lower acidity favor anatase formation (Juha et al.2007).
This mechanism may be explained using the concept of partial charge model, (Sugimoto et al.2002). According to this model, hydrolysis of titanium cation occurred at strong acidity condition. In this condition, a stable species of [Ti(OH)(OH2)5]3+ will form, but due to the positive charge of hydroxo group , these species are not able to condense. When acidity is not sufficiently low to stabilize these precursor, deprotonation will takes place forming new species of [Ti(OH) 2(OH2 )5]2+. However, these species also do not condense probably because of spontaneous intramolecular oxolation to [TiO(OH2)5]2+, (Ellis and Sykes1973). Condensation to both anatase and rutile starts when the solution activity is sufficient enough to allow further deprotonation to [TiO(OH)(OH2)4]+, which can undergo intramolecular of deoxolation [TiO(OH)3(OH2)3]+ depending on exact pH. In lower pH region, deoxolation does not happen and oxolation leads to linear growth along the equatorial plane of cations. This reaction leads to rutile formation due to oxolation between resulting linear chains. Meanwhile, in higher pH values, when deoxolation occurs, condensation apical direction and leads to the skewed chain of 156
can proceed along anatase structure.
Therefore, based on this study, it is believed that the determination of resulting crystal structure is affected by pH values (Henry et al.1992), (Aruna and Tirosh 2000). The higher acidity promotes rutile formation and lower acidity will lead to anatase. The average crystallite size, determined using Debye Scherrer equation from full width half maxima (FWHM) of the distinct peak (101) and (110) was determined as shown in table.(4.9) for different pH.
Table (4.9) Crystallite size of nano TiO2 at different pH PH
Phase of TiO2
1
Anatase
11
Anatase-Rutile
32
Anatase
11.5
Anatase-Rutile
30.4
Anatase
18.33
Anatase-Rutile
39.5
Anatase
18.64
Anatase-Rutile
40.77
Anatase
15.4
Anatase-Rutile
43.61
Anatase
13.23
Anatase-Rutile
42.96
2
3
4
7
9
Crystalline size (nm)
The size of crystalline at lower pH values is smaller than other pH. According to several studies, the variety of TiO2 surface charge is pH dependent. TiO2 in sol possess electrical charge due to absorption of H+ or OH- in aqueous suspension. According to (Bahnemann et. al. 1987), the surface charge of TiO2 can be determined by chemisorptions of : For H+ 157
TiO2 + nH+
TiO2Hn n+
for pH< 3.5
(4.4)
For OHTiO2 + nOH-
TiO2(OH)n n-
for pH> 3.5
(4.5)
In acidic and alkaline media, the strong repulsive charge among particles reduces the probability to coalesce and more stable sol can be formed. (Su et al.2004) have indicated that isoelectric of TiO2 powder varies between the pH ranges 5-6.8. The hydrolysis and condensation of Ti alkoxide are controlled by the following factors: the concentration of reactant, the hydrolysis ratio, the nature of the alkyl group, and the catalyst Table (4.10) shows the arrangement of different phases for the TiO2 powders in the distinctive pH and the calcination temperature (Am: amorphous, An: anatase, R: rutile). At the point when the temperature was raised, the anatase phase was changed to the rutile phase, which could be credited to the thermally advanced crystallite development. Specifically, the phase change of amorphous Ti(OH)4 to anatase TiO2 and anatase to rutile were essentially activatied by the HCl catalyst.This uncovers nucleation and development of the rutile phase have been started at temperatures some place from 400-700°C. It might be accepted that the development of rutile crystallization was influenced by the pH value of acid.
Table (4.10) Development of different phases for the TiO2 powders in the distinctive pH and calcination temperature. pH
Dried
400
500 158
600
700
(120) 9
Am
A
A+R
A+R
A+R
7
Am
A
A+R
A+R
A+R
4
Am
A
A
A+R
A+R
3
Am
A
A
A+R
A+R
2
Am
A+R
A+R
A+R
A+R
1
Am
A+R
A+R
A+R
A+R
*Am : amorphous, A : anatase, R : rutile
As shown in Fig.(4.17) temperature and pH level function to transformation of anatase to rutile. It is noticed that the temperature of the rutile proportion is moved to a low temperature of 400-500oC in high acidity. This is ascribed to the high surface energy of the particles in strong acid. Consequently, the rutile proportion increases quickly relying upon the lower pH level and in addition at higher temperatures, while increases gradually at the higher pH level. It is expected that the anatase phase has been eliminated taking after large rutile particles with poor agglomeration, and collection happens amid the molecule development prepared at higher temperatures
159
1.3 400C 500 C 600 C
1.2 1.1
Rutile ratio (weigh t%)
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -0.1 0
2
4
6
8
10
pH
Fig.(4.17). Rutile weight fractions of the TiO2 powders calculated as a function of pH.
4.1.1.5 Effect of Calcination Temperatures on Crystalline Size The impact of calcination temperatures on the crystalline size of TiO2 was shown in Fig.(4.18). At the point when the temperature has been raised to 400°C, the extent of framed crystallites has expanded, which could be credited to the thermally advanced crystallite development. When calcination temperature has been elevated to 700°C the size of anatase crystallites increased. At 700°C, aside from anatase, sharp rutile pinnacles was additionally seen in the XRD result. The shaped rutile demonstrated very unique conduct having bigger size than the remained anatase particles. This, indeed, reveals nucleation and development of rutile phase would have been started at temperature some place from 400 to 700°C, (Li et al. 2002).
160
50 45
Partical size (nm)
40 35 30 25 20 15 10 5 0 0
100
200
300
400
500
600
700
Temperature ( C )
Fig.(4.18). Crystalline size variation of prepared powders at different calcination temperatures.
4.1.1.6 Effect of Acid Type Four types of acids (HCL, CH3COOH, H3PO4, and H3PW12O40) were used as catalyst in syntheses of nano TiO 2. The effect of varying the acid type on the XRD diffraction is shown in the figures (4.1) to (4.9). The nature of acid was found to substantially affect the crystalline phase composition, morphology and also the size of TiO2 nanoparticles. When hydrochloric acid was used only the powder prepared in a strongly acidic solution contained fine spherical particles of nano TiO2 obtained. It was shown that anatase to rutile transformation occurred at temperature 400oC. The used of phosphoric acid resulted in the formation of amorphous rather than crystalline phase until 600oC.When reached 700oC the amorphous phase transformed to anatase phase with bigger particles size as shown in Fig.(4.8). Presumably, this can be associated with different affinity of the anions with respect to Ti(IV) ions in aqueous solutions (Cl exhibited weak affinity, while PO4-2 demonstrated strong affinity). The strong affinity of PO4-2for titanium inhibits the titanium dioxide
161
rearrangement and, hence, the overall crystallization process, (Zhang et al.2002). Acetic acid often used in the hydrolysis of titanium containing precursors can also serve as an efficient stabilizer of anatase phase in the calcination. Thus the hydrolysis of an acetic acid solution of Ti(OPr i)4 with aqueous ammonia at pH 3-4 and 80oC afforded a gel that showed an anatase phase even 1000oC, (Suresh et al.1998).However, as the hydrolysis medium pH increased to 5, pure rutile was formed at 1000oC, whereas at pH 6, anatase to rutile transformation is complete at 800 oC as shown in table (4.11) below.
Table.(4.11). Phase composition of calcined TiO2 samples as a function of the pH of acetic acid- containing solution of titanium isopropoxide during the hydrolysis. Calcination temperature/oC
Hydrolysis medium pH 3
4
5
6
1000
A
A
R
R
800
A
A
A+R
R
600
A
A
A
A
400
A
A
A
A
A is anatase, R is rutile
In the case of prepared nano titanium dioxide with acetic acid by hydrothermal method which found that at the crystallization temperature 170oC and 180oC, the nano TiO2 formed anatase phase containing a trace of rutile. This trace will be disappeared when reaching calcination temperature 800oC. In the crystallization temperature 190oC the rutile phase not found until 900oC. 162
Table 4.12 shows the phase composition of prepared TiO2 at different crystallization and calcination temperatures in the pH range 3-4.
Table (4.12) phase composition of TiO2 samples at different crystallization and calcination temperatures in the pH range 3-4. Calcination temperature/oC
Crystallization temperature/oC
450
700
800
900
170
A+R
A+R
A
A
180
A+R
A+R
A
A
190
A
A
A
A
When phosphotungstic acid was used the formation of anatase phase with trace of rutile crystalline phase at 450oC.On reaching 700oC the rutile phase disappeared and only anatase phase found after that when the calcination temperature was raised to 800oC the anatase phase began to transform to the rutile phase as shown in Fig.(4.9).
4.1.2 Fourier Transform Infrared Spectroscopy (FTIR) 163
FTIR spectra tests of the prepared nano titanium dioxide samples are shown in figures 4.19 to 4.21 and B-1 to B-15 in appendix B. In the FT-IR spectrum of the nano TiO2, a broad peak appearing at 3,100–3,600 cm-1 (precisely at 3,417.86 cm-1) is assigned to fundamental stretching vibration of O–H hydroxyl groups (free or bonded) (Gaoa, Y., et al.2002). The band at 2,927 cm-1 is assigned to C–H vibrations. The C–H can be attributed to the organic residues, which remain in TiO2 even after calcination (Yodyingyong, et al .2011). Also, the sharp peaks centred on 1,631, 1,492, and 1,172 cm-1 can be attributed to C = C (in unsaturated hydrocarbon dehydrated, such as butene, propene from precursors) stretching, –C–H (methyl or methylene) bending and –C–O stretching, respectively. (Chaudharier et al.2011). The shoulder observed at 690 cm-1 may have been due to the vibration of the Ti–O–O bond. The peak between 800 and 400 cm-1 is assigned to the Ti–O stretching bands (Ba-Abbad et al.2012).
Fig. (4.19) FTIR-spectra of the nano titanium dioxide prepared using acetic acid and at calcination temperature 4500C.
164
The structure of TiO2 in the case of prepared nano TiO2 with PWA and STAB was confirmed in the FTIR spectrum while no band characteristic of PWA was found in TiO2 materials, suggesting that there is no indication of PWA crystalline form in TiO2 materials.
Fig. (4.20) FTIR-spectra of phosphotungstic acid
Fig. (4.21) FTIR-spectra of the nano titanium dioxide prepared using phosphotungustic acid and STAB 165
4.1.3 Surface Area and Pore Volume The surface area and pore volume of the nano catalyst play a very important role for the activity of the nano catalyst, because high surface area leads to high active sites causing increase in activity. Table 4.13 shows the results of surface area and pore volume of the samples obtained at different conditions. TiO2 nanoparticles obtained by acid route (HCl acid) showed a larger surface area and slightly higher pore volume than the ones obtained with alkaline medium (NH4OH) as shown in table (4.13). In fact, acid pH hydrolysis results in a very transparent sol, different from the sol obtained by alkaline route, which is opaque due to the presence of larger particles and aggregates. Table (4.13) The values of surface area and pore volume at different pH (pH=1 to 4 HCl acid, pH 7 to 9 NH4OH base) Sample
PH
Phase of TiO2
Surface
Pore
area(m2/g)
volume(cm3/g)
Amorphous
1370
0.4631
Anatase
77.5
0.1582
Anatase-rutile
28.9
0.0487
Amorphous
1183
0.4212
Anatase
73.43
0.1564
Anatase-rutile
22.88
0.0445
Amorphous
938
0.4066
Anatase
49.5
0.0773
code T1
T2
T4
1
2
4
166
Anatase-rutile
Sample
pH
9.615
Phase of TiO2 Surface area(m2/g)
code T5
T6
7
9
0.0198
Pore volume(cm3/g)
Amorphous
289
0.2957
Anatase
24
0.0456
Anatase-rutile
6.7
0.0125
Amorphous
437
0.3310
Anatase
40
0.0654
Anatase-rutile
11.6
0.0221
Increasing the calcination temperature causes agglomeration of the particles with each other resulting in a reduction of the available open pores hence decreasing pore volume and surface area. Also it can be noticed that as the calcination temperatures increased particle sizes and hence pore size increased. This increasing can be ascribed to the agglomeration of crystallites as a result of material sintering (Regalbuto, 2007). It was concluded that the addition of different acids to the starting materials had very important role, because it represents the bridge between the surfactant and the source of titanium ions. The high surface area was obtained by using phosphotungstic acid and STAB compared to phosphoric and acetic acids as shown in table 4.14. Therefore, when STAB was used in the TiO2 preparation process, hydrogen bonds between PWA and TTIP as well as interaction between 167
surfactants and TTIP exist together, leading to the TiO2 nanoparticles. Thermal treatment is helpful to remove STAB from TiO2 materials, thus leading to larger pore volume. ( Huang et al. 2008). Table (4.14) The values of surface area and pore volume for different acids Sample
Acid type
Phase of TiO2
Surface
Pore
area(m2/g)
volume(cm3/g)
Amorphous
1401
0.4698
Anatase
95.8
0.1823
Amorphous
396
0.3267
Anatase
44.7
0.0724
Anatase-Rutile
9.3
0.0186
Amorphous
1457
0.5145
Anatase
143
0.2468
Anatase-Rutile
52
0.0912
code T7
T8
T9
H3PO4
CH3COOH
H3PW12O40
maximum surface areas were obtained from smaller crystallite sizes as shown in table (4.15). These crystallites contained high proportion of small pores. Increasing calcination temperatures led to the increase in the rate of evaporation of water and gases (OH bond and CO2 gas) entrapped in the small pores towards larger ones and then to the bulk causing a drop in pressure. This pressure drop would result in a partial loss of surface area due to the collapse of part of the pores (Chen et al., 2003 and Richardson, 1989). Table (4.15) Surface area, pore volume and crystallite size at different acid for nano TiO2 prepared in hydrothermal method 168
Sample
Acid type
Phase of TiO2
code
T1H
T2H
T3H
T4H
CH3COOH
CH3COOH
CH3COOH
H3PW12O40
Amorphous
Surface
Pore
Crystallit
area
volume
e
(m2/g)
(cm3/g)
(nm)
size
1875.11
0.6358
_
Anatase,170oC
192.5
0.2817
7.68
Amorphous
1612.6
0.5473
_
Anatase,180oC
174.96
0.2702
8.01
Amorphous
1419.3
0.4729
_
Anatase,190oC
148.5
0.2464
10.07
1890.25
0.5891
_
202
0.3016
7.45
147.2
0.2432
14.62
1923.8
0.6891
_
221
0.3216
7.34
153.99
0.2532
15.62
Amorphous
1715.6
0.5291
_
Anatase,190oC
189.1
0.2916
9.45
Anatase-
125.87
0.2132
18.62
Amorphous Anatase,170oC AnataseRutile,170oC
T5H
H3PW12O40
Amorphous Anatase,180oC AnataseRutile,180oC
T6H H3PW12O40
Rutile,190oC
The increasing of the crystallization temperature from 170 to 190oC will lead to decrease in surface area in the case of using acetic acid but in the case of phosphotungstic acid the surface area is higher than all samples of prepared nano TiO2 in hydrothermal method .Generally the surface area in the case of hydrothermal method is higher than sol gel method. The relationship between calcination temperature, surface area, and crystallization temperature was clear that the surface area decreased by increasing calcination temperature and crystallization temperature. A 169
maximum surface area of 192.5m2/g was obtained at calcination temperature of 450oC, and 170oC as the crystallization temperature. The highest surface area obtained was 221m2/g in the case of using phosphotungstic acid with 180oC crystallization temperature and 450oC calcination temperature. The
decrease
in
surface
area
may
be
due
to
the
dehydroxylation and hydrogen bonds elimination which will cause agglomeration of particles (Padmaja et al., 2004). The surface area tests are given in Appendix E. (Wang et al., (2008) concluded that the calcination temperature was the important factor in the surface area study. The crystal growth is increased at higher calcination temperatures; as a result the contact of crystallites between each other is increased. So that at higher temperatures smaller crystallites will be coalesced and form crystallite with larger size. This coalescing step will decrease pore volume and surface area of the sample by crystallite sintering or agglomeration phenomena. Table (4.16) The values of surface area and pore volume for different acids for nano TiO2 prepared by titanium ethoxide and sol-gel method
Sample code Acid type
Phase
of Surface area Pore volume (m2/g)
TiO2 T1E
T2E
T3E
-
H3PO4
H3PW12O40
( cm3/g)
Amorphous
385
0.3142
Anatase
40
0.0644
Anatase-rutile
12.5
0.0232
Amorphous
493
0.3497
Anatase
45
0.0731
Amorphous
618.6
0.3672
Anatase
77.5
0.1597
170
Anatase-rutile
16.7
0.0247
Table 4.16 shows that surface area of samples prepared without acid is less than others prepared with the assistance of acid. Samples prepared with phosphotungstic acid were higher surface area than others.
4.1.4 Atomic Force Microscope (AFM) Reports The atomic force microscopy (AFM) method was used to find the particle size distribution, average particle size, and the shape of the surface. The results of the particle size at different operating conditions are listed in table (4.17). Table (4.17) The values of particle size distribution and average particle size at different operating conditions for sol-gel method and TTIP as source material
Sample code
Synthesis conditions
Acid type
pH=1,anatase, 4500C T1
T2
particle size, nm 71.98
7000C
55-130
94.50
pH=2,anatase, 4500C
50-100
74.88
70-120
97.53
65-105
86.77
7000C
60-13-
97.40
pH=7,anatase, 4500C
25-95
60.44
pH=1,anatase-rutile ,
pH=2,anatase-rutile , HCl
pH=4,anatase, 4500C
T5
distribution, nm
Average
35-105
7000C
T4
Particle size
pH=4,anatase-rutile ,
171
pH=7,anatase-rutile ,
T6
7000C
50-140
95.89
pH=9,anatase, 4500C
35-110
75.85
60-125
90.48
-
-
75-150
115.62
0-95
79.74
60-150
105.75
40-100
71.43
40-115
80.55
pH=9,anatase-rutile , 7000C Amorphous, 4500C
T7
H3PO4
Anatase, 7000C pH=3.8, anatase, 4500C
T8
CH3COOH
pH=3.8,anatase, 7000C Anatase,500oC T9
H3PW12O40
Anatase-rutile ,800oC
As shown in table (4.17) the average particle size of the prepared nano TiO2 was in the nano scale catalyst for all experiments. At higher pH the average size particles of nano TiO2 prepared with HCl acid was smaller than other pH. For nano TiO2 prepared with acetic acid and phosphoric acid the average size of particles was larger than TiO2 prepared with phosphotungstic acid. The size of average particles for the phase of anatase-rutile for TiO2 with PWA was smaller than all phases of anataserutile for prepared nano TiO2 in all experiments. Increasing in the calcination temperature from 450 to 7000C leads to increase the particle size. This causes
decreasing in surface area and
pore volume. In the calcination temperatures 4500C the pores between the 172
particles may be opened causing high surface area and pore volume. The increasing in calcination temperature causes an increase the capillary forces coming from the gaseous products during calcinations in high temperatures making the particles close (agglomeration) associated with blockage in the pores reaching to the sintering. Table (4.18) shows that the average particles size of prepared nano TiO2 without acids was smaller than other samples prepared with acids (H3PO4, PWA). The used of phosphoric acid resulted in the formation of amorphous phase rather than crystalline phase as explained before with high sizes of average particles. Table (4.18) The values of particle size distribution and average particle size for different operating conditions for sol-gel method and titanium ethoxide as source material Sample code
Synthesis conditions
Acid type
Particle size distribution, nm
Average particle size, nm
Anatase, 4500C
T1E
35-80
60.36
60-110
88.25
60-130
101.75
_
_
70-150
113.83
65-115
90.37
70-115
94.25
Anatase-Rutile , 7000C
_
Rutile, 800oC Amorphous, 4500C H3PO4 T2E Anatase, 7000C Anatase, 4500C T3E
H3PW12O40
173
Anatase-Rutile , 8000C
Table (4.19) shows the average particle size of the prepared nano TiO2 was not in the nano scale catalyst for all experiments. The increasing in crystallization temperature from 170 to 180oC at constant calcination temperature of 450oC leads to increase the average particle size gradually from 79.14 to 81.43 nm. This behavior is due to gradual decreasing in pore volume of the prepared samples. Table (4.19) The values of particle size distribution and average particle size at different operating conditions for hydrothermal method Sample code
Synthesis conditions
Acid type
particle size distribution, nm
Average particle size, nm
170oC,anatase, 4500C T1H
170oC,anatase, 7000C
40-110
79.14
60-140
103.27
60-95
81.43
60-115
88.72
55-100
97.70
60-125
121.05
60-130
77.92
CH3COOH
180oC,anatase, 4500C CH3COOH T2H 180oC ,anatase, 7000C 190oC,anatase, 4500C T3H
CH3COOH
190oC,anatase, 7000C 180oC,anatase, 4500C T4H
H3PW12O40
174
60-170
180oC ,anatase- rutile ,
96.70
7000C
Increasing the crystallization temperatures from 180oC to 190oC at constant calcination temperatures 450oC causes increase in the
average
particle size from 81.43 to 97.70 nm. Using variable acids in the presence of the surfactant produced different
ranges
of
average
nano
titanium
dioxide
particles.
Phosphotungstic acid produced nano TiO2 with average particle size less than samples prepared by acetic acid, produced nano TiO2 with average particle size 77nm. Increasing the calcination temperature from 450 to 7000C leads to increase the particle size for all the samples. The bar charts of particle size distribution of all prepared samples are shown in appendix C. Figures (4.22 to 4.30), (4.31 to 4.33), and (4.34 to 3.36) represent the three dimension surface morphology of the prepared for sol-gel with TTIP, solgel with titanium ethoxide, and hydrothermal methods respectively.
175
Fig.(4.22a) Three-dimensional surface of T1
Fig.(4.22b)Three-dimensional surface of T1
Fig.(4.23a) Three-dimensional surface of T2
Fig.(4.23b) Three-dimensional surface of T2
Fig.(4.24a) Three-dimensional surface of T3
Fig.(4.24b) Three-dimensional surface of T3
176
Fig.(4.25a) Three-dimensional surface of T4
Fig.(4.25b) Three-dimensional surface of T4
Fig.(4.26a) Three-dimensional surface of T5
177
Fig.(4.26b) Three-dimensional surface of T5
Fig.4.(27a) Three-dimensional surface of T6
Fig.(4.27b)Three-dimensional surface of T6
Fig.(4.28a) Three-dimensional surface of T7
Fig.(4.28b) Three-dimensional surface of T7
178
Fig.(4.29a) Three-dimensional surface of T8
Fig.(4.29b) Three-dimensional surface of T8
64
Fig.(4.30a) Three-dimensional surface of T9
Fig.(4.30b) Three-dimensional surface of T9
Fig4.(31a) Three-.dimensional surface of T1E
Fig.(4.31b) Three-dimensional surface of T1E
Fig.(4.32a) Three-dimensional surface of T2E
Fig.(4.32b) Three-dimensional surface of T2E
64
Fig.(4.33a) Three-dimensional surface of T3E
Fig.(4.33b) Three-dimensional surface of T3E
Fig.(4.34a)Three-dimensional surface of T1H
Fig.(4.34b)Three-dimensional surface of T1H
Fig.(4.35a) Three-dimensional surface of T2H
Fig.(4.35b) Three-dimensional surface of T2H
65
Fig.(4.36a) Three-dimensional surface of T3H
Fig(.4.36b) Three-dimensional surface of T3H
4.1.5 Scanning Electron Microscopy (SEM) The morphology of the surface of prepared nano titanium dioxide by using titanium tetra-isopropoxide as source material and HCl acid, NH4OH as catalyst are shown in figures 4.37-4.43. The effect of calcination temperature at pH=1 is shown in figures 4.37and 4.39. When increasing temperature from 450 to 700oC the size of particles is increased and spherical in shape. In acidic and alkaline media, the strong repulsive charge among particles reduces the probability to coalesce and more stable sol can be formed. (Su et. al.2004) have indicated that isoelectric of TiO2 powder varies between the pH ranges (5-6.8).Based on this work samples prepared at pH=1 is away from the range of isoelectric point, less aggregates and bigger TiO2 particles is formed. The size of particles at higher pH=7 and 9 values is smaller and can agglomerate.
66
Fig. 4.37 SEM image of the nano titanium dioxide (amorphous) prepared using HCl acid at pH=1, TTIP, and calcination temperature 1200C
Fig. 4.38 SEM image of the nano titanium dioxide prepared using HCl acid at pH=1, TTIP, and calcination temperature 4500C
Fig. 4.39 SEM image of the nano titanium dioxide prepared using HCl acid at pH=1, TTIP, and calcination temperature 7000C
67
Fig. 4.40 SEM image of the nano titanium dioxide prepared using HCl acid at pH=2, TTIP, and calcination temperature 4500C
Fig. 4.41 SEM image of the nano titanium dioxide prepared using HCl acid at pH=4, TTIP, and calcination temperature 4500C
68
Fig. 4.42 SEM image of the nano titanium dioxide prepared using HCl acid at pH=7, TTIP, and calcination temperature 4500C
Fig. 4.43 SEM image of the nano titanium dioxide prepared using HCl acid at pH=9, TTIP, and calcination temperature 4500C
The morphology of the surface of prepared nano titanium dioxide by using titanium tetra-isopropoxide as source material and acetic and 69
phosphotungstic acids as catalysts by hydrothermal method are shown in figures 4.44-4.51. Non uniform shape of particles with low agglomeration is observed by using acetic acid and when increasing crystallization temperatures from 170 to 190oC the particles size will increase as shown in figures 4.44 to 4.49. Agglomeration and small particles size is observed by using phosphotungstic acid compared to other samples shown in figures 4.50 and 4.51 leading to high surface area and pore volume.
Fig. 4.44 SEM image of the nano titanium dioxide prepared using acetic acid at 1700C crystallization temperature, by hydrothermal method
70
Fig. 4.45 SEM image of the nano titanium dioxide prepared using acetic acid at 1700C crystallization temperature, by hydrothermal method
Fig. 4.46 SEM image of the nano titanium dioxide prepared using acetic acid at 1800C crystallization temperature, by hydrothermal method and 450oC calcination temperatures
71
Fig. 4.47 SEM image of the nano titanium dioxide prepared using acetic acid at 1800C crystallization temperature, by hydrothermal method and 450oC calcination temperatures
Fig. 4.48SEM image of the nano titanium dioxide prepared using acetic acid at 1900C crystallization temperature, by hydrothermal method and 450oC calcination temperatures
72
Fig. 4.49 SEM image of the nano titanium dioxide prepared using acetic acid at 1900C crystallization temperature, by hydrothermal method and 450oC calcination temperatures
Fig. 4.50 SEM image of the nano titanium dioxide prepared using phosphotungstic acid at 1900C crystallization temperature, by hydrothermal method and 450oC calcination temperatures
73
Fig. 4.51 SEM image of the nano titanium dioxide prepared using phosphotungstic acid at 1900C crystallization temperature, by hydrothermal method and 450oC calcination temperatures
The morphology of the surface of prepared nano titanium dioxide by using titanium ethoxide as source material and phosphoric and phosphotungstic acids as catalysts by sol-gel method are shown in figures 4.52-4.57. The use of phosphotungstic and phosphoric acids as catalyst in preparation of nano TiO2 resulted in the formation of amorphous phase rather than crystalline spherical TiO2 in the case of phosphoric acid, uniform small spheres particles for PWA and coarse spheres with bigger size for phosphoric acid.
74
Fig. 4.52 SEM image of the nano titanium dioxide prepared using titanium ethoxide as source material by sol-gel method and 450oC calcination temperatures
Fig. 4.53 SEM image of the nano titanium dioxide prepared using titanium ethoxide as source material by sol-gel method and 450oC calcination temperatures
75
Fig. 4.54 SEM image of the nano titanium dioxide prepared using titanium ethoxide as source material , phosphotungstic acid by sol-gel method and 450oC calcination temperatures
Fig. 4.55 SEM image of the nano titanium dioxide prepared using titanium ethoxide as source material , phosphotungstic acid by sol-gel method and 450oC calcination temperatures
76
Fig. 4.56SEM image of the nano titanium dioxide prepared using titanium ethoxide as source material , phosphoric acid by sol-gel method and 450oC calcination temperatures
Fig. 4.57 SEM image of the nano titanium dioxide prepared using titanium ethoxide as source material , phosphoric acid by sol-gel method and 450oC calcination temperature
4.1.6 X-Ray Fluorescence 77
Nano TiO2 prepared by sol-gel and hydrothermal method with phosphotungstic acid as catalyst and STAB as the structure-directing agent was characterized by X-Ray Fluorescence. The chemical compositions of prepared samples including Ti, W, P, etc. inside the calcined TiO2 materials are listed in Table 4.20. Both tungsten (W) and phosphorus (P) were detected, while no nitrogen (N) or bromine (Br) was detected. Therefore, it is proved that STAB does not exist in the calcined TiO2 material, suggesting that little STAB is in existence in the calcined materials and STAB was successfully removed during calcination, leading to larger pore volume. The XRF test is given in Appendix D. Table 4.20 Chemical composition of synthesized nano TiO2 Symbol
Element
Sol-gel Wt%
Hydrothermal Wt %
Ti
Titanium
41.88
44.03
W
Tungsten
11.45
10.10
P
phosphorus
0.0013
0.0013
4.2. Oxidative desulfrazation of model fuels by Prepared nanoTiO2 Catalysts without PWA acid The activity of nano TiO2 catalyst was tested for ODS process of model oil fuels with 100 to 500 ppm sulfur content at different parametres. 4.2.1. Effect of the NanoTiO2 Crystalline Form on Oxidative Desulfurization Three types of TiO2 were used as oxidative catalysts to remove the sulfur compounds in model fuels. Adding H2O2 to the model fuels generated a faint yellow product that was adsorbed on the catalyst surface. This result is consistent with the fact that DBT sulfone is easily 78
adsorbed on the catalyst, (Yang et al.2007).The experiments revealed that different TiO2 forms presented different influences on the resultant TiO2 properties. Fig. (4.58), shows the experimental results of anatase nano-TiO2, anatase–rutile nano-TiO2, and amorphous nano-TiO2 when used as catalysts in oxidative desulfurization. Anatase nano-TiO2 exhibited high activity for the catalytic oxidation of DBT, and DBT as high as 100% was achieved at a reaction time of 40 s. By contrast, the catalytic rates presented by anatase–rutile TiO2 and amorphous TiO2 were only 50% and 23.5%, respectively. Comparing the BET results of the different TiO2 catalysts, amorphous TiO2 exhibited the largest surface area but its oxidative activity was the worst. Therefore, the crystal form of TiO2, instead of its surface area, dictates the oxidative activity of the catalyst. Anatase TiO2 and rutile TiO2 present tetragonal structures, whereas amorphous TiO2 features hexagonal crystals. Ti functions as the active site of TiO2. The first step of catalytic oxidation is adsorption. (Guo et al.2010), shows that anatase (001) and rutile (110) surfaces are highly adsorptive for sulfur compounds. The results of oxidative desulfurization are consistent with this explanation. The BET results of anatase and anatase–rutile TiO2 show that the surface area and total pore volume are larger than those of the later; thus, the former shows improved oxidative activity.
79
120 anatase anatase-rutile amorphous
110 100
DBT conversion (%)
90 80 70 60 50 40 30 20 10 0 0
10
20
30
40
50
60
70
80
90
100
110
120
Time (t)
Fig.(4.58) Effect of different forms of catalyst on conversion, initial DBT concentration: 100 ppm; reaction temperature: 70oC; molar ratio of H2O2 to DBT: 10:1; stirring rate: 800 rpm; 0.3 g/ml of catalyst.
4.2.2. Effect of Stirring Rate on Conversion The effect of stirring rate on DBT conversion is shown in Fig. (4.59). When those blending rate might have been 200 rpm, those response rate might have been moderate also DBT transformation might have been just something like 54% toward 120 what's more. When those mixing rate might have been raised will 500 rpm, those response rate might have been clearly improved. Change rates of in 90% were got at 40 encountered with urban decay because of deindustrialization, engineering imagined. However, past this blending rate, the response rate indicated no further increment with expanding blending. Over fact, higher mixing rates could decrease the outside dispersion imperviousness. Dependent upon these results, those mixing rate will be set with 800 rpm on resulting analyses.
80
110
200 rpm 500 rpm 800 rpm 1200 rpm
100
DBT conversion (%)
90 80 70 60 50 40 30 20 10 0 0
10
20
30
40
50
60
70
80
90
100 110 120 130 140
Time (s)
Fig.(4.59) Effect of stirring rate on conversion: initial DBT concentration: 100 ppm; reaction temperature:; 70oC molar ratio of H2O2 to DBT: 10:1; 0.3 g/ml of TiO2.
4.2.3. Effect of Temperature on DBT Oxidation Temperature is an important factor influencing a reaction; thus, the effect of temperature on DBT oxidation was studied. As shown in Fig. (4.60), DBT change could be progressed eventually those response temperature starting with 40oC on 70oC. DBT transformation might have been just 75%. When the point when those response temperature might have been 40oC. Likewise temperature expanded with 70oC, DBT might a chance to be totally uprooted inside 40 sec. Therefore, helter skelter temperatures need aid valuable to the response.
81
110 40oC 50oC 60oC 70oC
100
DBT conversion (%)
90 80 70 60 50 40 30 20 10 0 0
20
40
60
80
100
120
140
160
180
Time (t)
Fig.(4.60) Effect of temperature on conversion: initial DBT concentration: 100 ppm; molar ratio of H2O2 to DBT: 10:1; stirring rate: 800 rpm; 0.3 g/ml of TiO2.
4.2.4. Effect of initial concentration on conversion of DBT The initial concentration of sulfur compounds cannot be neglected because this parameter can decide the range of catalyst application. As shown in Fig. (4.61), the conversion of DBT decreased as the DBT concentration increased. DBT conversion was highest when the initial DBT concentration was 100 ppm. However, when the initial sulfur concentration was 200 ppm, conversion was relatively lower than that at 100 ppm; the lowest conversion rate was achieved at an initial concentration of 500 ppm. Based on these results, TiO2 is suitable for deep oxidative desulfurization.
82
120
100 200 300 400 500
110 100
ppm ppm ppm ppm ppm
DBT conversion (%)
90 80 70 60 50 40 30 20 10 0 0
20
40
60
80
100
120
140
160
180
200
Time (t)
Fig.(4.61) Effect of initial DBT concentration on conversion: reaction temperature: 70oC ; molar ratio of H2O2 to DBT: 10:1; stirring rate: 800 rpm; 0.3 g/ml of TiO2.
4.2.5. Effect of catalyst amount on conversion of DBT The effect of catalyst amount on DBT conversion was explored, and the results are shown in Fig.(4.62). Conversion was improved as the catalyst amount increased from 0.1 g to 0.3 g. The reaction rate could not obviously be improved when the catalyst amount was increased from 0.3 g to 0.4 g. This likely because excess TiO2 causes easy agglomeration in the reaction system, thereby reducing the availability of active sites of TiO2.
83
110 0.1 0.2 0.3 0.4 0.5
100
DBT conversion (%)
90
g g g g g
80 70 60 50 40 30 20 10 0 0
10
20
30
40
50
60
70
80
90
100
110
120
Time (s)
Fig.(4.62). Effect of catalyst amount on conversion: initial DBT concentration: 100 ppm; reaction temperature:; 70oC molar ratio of H2O2 to DBT: 10:1; stirring rate: 800 rpm.
4.2.6. Effect of Oxidant Amount on Conversion of DBT The amount of oxidant has an important effect on a reaction. The effect of oxidant amount on DBT conversion is shown in Fig. (4.63). The reaction rate increased at first and then decreased as the mole ratio of H2O2 to DBT increased from 5:1 to 20:1. When the H2O2-to-DBT ratio was less than 10, the reaction rate was low. The reaction rate significantly increased with increasing H2O2 amount. However, further increase in H2O2 reduced the reaction rate. These phenomena may be explained as follows: First, increase in H2O2 provide more oxygen radicals to oxidize the DBT, hence the promoted reaction. However, when the amount of H2O2 reaches a certain level, adding more H2O2 may form a liquid film on TiO2, which affects DBT adsorption to active sites. Thus, the reaction is limited under high H2O2 contents.
84
110 5:1 10:1 15:1 20:1
100
DBT conversion (%)
90 80 70 60 50 40 30 20 10 0 0
10
20
30
40
50
60
70
80
90
100
110
120
Time (s)
Fig.(4.63).Effect of oxidant amount on conversion: initial DBT concentration: 100 ppm; reaction temperature: 70oC; stirring rate: 800 rpm; 0.3 g/ml of TiO2.
4.2.7. Reaction kinetic model A slight change in H2O2 is ignored in this study as it is ten times the amount of DBT in the reaction. Furthermore, the activity of the catalyst is assumed to be unchanged because it is in excess in the system. Thus, the kinetic equation was obtained as follows:
𝑟𝐴 = −
𝑑𝐶 𝑑𝑡
= 𝑘𝐶 ∝
(4.6)
where k is the apparent rate constant and C is the DBT concentration. Based on the experiment, the following values were obtained under a reaction temperature of 323 K: k = 0.02 and ∝= 0.885 as shown in table 4.21. Here, ∝ is approximately 1. Therefore, the reaction rate can be described as a pseudo-first-order reaction:
𝑟𝐴 = −
𝑑𝐶 𝑑𝑡
= 𝑘𝐶 ∝
As C = C0 (1-X), the equation can be written as: 85
ln(1 − 𝑋) = −𝑘𝑡
(4.7)
where X is the conversion of DBT and C0 is the initial DBT concentration. Fig. 4.64 shows the plot of ln (1-X) plots versus reaction times at 313, 323, and 333 K. The kinetic reaction can be described as a pseudofirst-order. Based on the Arrhenius formula, the following equation can be obtained:
𝑙𝑛𝑘 = 𝑙𝑛𝑘𝑜 −
𝐸𝑎
(4.8)
𝑅𝑇
where ln k0 is the pre-exponential factor, Ea is the apparent activation energy, R is the gas constant, and T is the reaction temperature in (K).The resulrs are listed in Table. 4.21. From the plot in Fig.4.65, the activation energy Ea is determined as 57.66 kJ/mol under the experimental conditions employed.
Table (4.21 ) The apparent rate constant of DBT oxidation under different temperatures.
Temperature (K)
Rate constant (k) (sec-1)
-ln k
313
0.01
4.6
323
0.02
3.91
333
0.028
3.5
86
0 -0.2 -0.4
ln (1-X)
-0.6 -0.8 -1
40o C 50o C 60o C y=0.01305-0.01439x y=0.0321-0.0209x y=0.06662-0.02849x
-1.2 -1.4 -1.6 -1.8 0
3
6
9
12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
Time (s)
Fig.(4.64) Model of the pseudo-first-order reaction
5 4.5 4 3.5
-lnK
3
y = 52.242x - 15.739 R² = 0.9973
2.5 2 1.5 1 0.5 0 3.6
3.65
3.7
3.75 3.8 1/RTx104
3.85
3.9
3.95
Fig.(4.65). Arrhenius activation energy for DBT oxidation.
Comparison of result obtains in these experimental and other studies shown in table 4.22 below. 87
Researcher
Catalyst
Initial
DBT Reaction
concentration
time
ppm Jun, 2010
TiO2/ionic
DBT
Condition
conversio n rate %
500
10 h
98.2
UV
liquid Guo et al.2010
TiO2/C3N4
500
2h
98.9
UV
Hussian and
TiO2/BC
1000
2.5 h
80
UV
MWNTs/TiO2
700
2h
98
UV
Thu et al.2012
PWA/TiO2
1000
2h
100
_
Yan et al.2013
Fe–TiO2
300
5 min
100
pH=0
Fadhil, 2017
Anatase TiO2
100
40 sec
100
_
Fadhil, 2017
Anatase
300
1.5 min
100
-
Tatarchuk, 2013 Xiao et al.2013
TiO2/PWA
4.3. Oxidative desulfrazation of model fuel by nano TiO2 prepared with phosphotungustic acid and STAB The activity of nano TiO2 catalyst was tested for ODS process of model fuels with 300 to 3000 ppm sulfur content at different parametres. 4.3.1 Catalytic activity on oxidation of dibenzothiophene (DBT) The calcined nanoTiO2 with different structure forms (amorphous, anantase, and anatase-rutile) were used as the catalyst for the oxidation of DBT. Fig.(4.66) shows DBT conversion as a function of the reaction time with TiO2 prepared at different temperatures (three structures forms). In case of the DBT solution with an initial concentration of 3000 ppm, nano TiO2 (anatase) prepared showed the best catalytic reactivity. About 70% DBT conversion was achieved within 10 min. While nano TiO2 (anatase88
rutile) and (amorphous) showed the least catalytic reactivity towards DBT and only 46.5% and 29% DBT conversion occured after 10 min respectively. However, the difference was not so obvious although TiO2 prepared (anatase) still exhibited the best performance compared to the other forms when decreasing the initial concentration to 300 ppm. It can be seen that 100% DBT was converted in 1.5 min in the case of anatase. However, in the cases of anatase-rutile and amorphous the catalytic activity of removal DBT decreases to 52% and 31% in 1.5 min respectively. DBT oxidation takes place at the surface of inner pores in nanoTiO2. This process can be divided into the following steps: (1) DBT mass transfer from organic media towards the surface of TiO2 particles, (2) DBT transfers into the pores of the TiO2 nanomaterials, contacts with the active site, and is oxidized into its sulfones, (3) DBT sulfones desorption from TiO2. Larger pores volume will facilitate DBT mass transfer within the pores, leading to higher reaction rate. DBT sulfones desorption is facilitated with larger pore sizes as well. Therefore, compared with surface area, pore size plays a more significant role in DBT oxidation.
89
80 anatase anatase-rutile amorphous
70
DBT conversion (%)
60 50 40 30 20 10 0 0
1
2
3
4
5
6
7
8
9
10
Time (min)
120 anatase anatase-rutile amorphous
110 100
DBT conversion (%)
90 80 70 60 50 40 30 20 10 0 0
0.25 0.5 0.75
1
1.25 1.5 1.75
2
2.25 2.5 2.75
3
3.25 3.5
Time (min)
Fig.(4.66) The catalytic oxidation of DBT prepared Conditions: 3000/300 ppm DBT in octane, 70oC, molar ratio of H2O2 to DBT: 18:1, 0.1 g/ml of TiO2.
4.3.2. Effect of Temperature on DBT Conversion The nanoTiO2 prepared was used as the catalyst to investigate the effect of temperature on the kinetics of DBT oxidation. The conversion profiles of DBT in the ODS reaction versus the reaction time at four 90
different temperatures (50, 60, 70 and 80oC) are shown in Fig.(4.67). The initial concentration of DBT was 3000 ppm and the H2O2 /DBT mole ratio was set at 18:1. A rise in the reaction temperature from 50 to 80oC led to a remarkable increase in the reaction rate. DBT conversion was substantially increased, from 31% at 50oC to 43% at 60oC for a 10 min reaction time. By further increasing reaction temperature to 80oC, DBT content of the oil was decreased from 3000 ppm to less than 700 ppm (more than 75% conversion) within 10 min.
80 50 oC 60 oC 70 oC 80 oC
72
DBT conversion (%)
64 56 48 40 32 24 16 8 0 0
1
2
3
4
5
6
7
8
9
10
Time (min)
Fig.(4.67). Effect of temperature on the conversion of DBT. Conditions: 3000 ppm DBT in octane, molar ratio of H2O2 to DBT: 18:1, 0.1 g/ml of TiO2 .
4.3.3. Effect of Initial Concentration of DBT on Conversion In order to examine the influence of the DBT concentration on the kinetics of the removal of S-containing compounds, additional 91
experiments were conducted by changing the DBT initial concentrations. Thus, DBT concentrations ranging from 300 ppm to 3000 ppm were selected while maintaining the other variables constant. Fig.(4.68) shows DBT conversion as a function of the reaction time for different DBT concentrations. The reaction rate with low DBT initial concentrations was much higher than that of a higher concentration. DBT removal from a 300 ppm DBT–octane mixture was as high as 100% within 1.5 min reaction. While DBT content of the oil was decreased from 3000 ppm to less than 900 ppm (more than 71% conversion) within 10 min. On the one hand, this indicates that the hydrogen peroxide concentration, or the molar ratio of H2O2 to DBT, is an important factor in the DBT oxidation process. Intuitively, this behavior can be explained as that the relative concentration of H2O2, or the molar ratio of H2O2 to DBT, for the DBT concentration of 300 ppm was much higher than for the reaction with 3000 ppm DBT. On the other hand, DBT was oxidized to the corresponding DBT sulfones, which are more polar than DBT. The sulfones adsorb onto the surface of TiO2 catalyst, leading to fewer active sites which have access to the reactant during oxidation. This is consistent with the BET results as listed in table 22. Catalyst was separated from the system
after
reaction
and
characterized
by
the
nitrogen
adsorption/desorption measurements. Compared with the fresh TiO2 materials, the separated catalyst after reaction exhibited smaller surface area and pore volume. With a high DBT concentration, more sulfone was produced and it was adsorbed onto the catalyst, leading to the decrease of the surface area. In case of the catalyst separated from 300 ppm DBT– octane solution, its BET surface area decreased from 221 m2/g to145 m2/g and the total pore volume from 0.297 cm3/g to 0.227cm3/g. In further 92
increase of
DBT concentration to 3000 ppm, surface area of the
separated catalyst was only 116 m2/g and the total pore volume 0.196 cm3/g as shown in Table.22. A practical conclusion to be drawn from these facts is that adsorption of DBT sulfones onto the solid catalyst results in less catalytic reactivity not only due to fewer active sites, but also the new resistance in DBT mass transfer.
110 100
DBT conversion (%)
90 80 70 60 50 40
3000 ppm 2400 ppm 1800 ppm 1200 ppm 600 ppm 300 ppm
30 20 10 0 0
1
2
3
4
5
6
7
8
9
10
11
12
Time (min)
Fig.(4.68). Effect of the initial concentration on the conversion of DBT. Conditions: 70oC, molar ratio of H2O2 to DBT: 18:1, 0.1 g/ml of TiO2.
Table.22. Properties of the TiO2 catalyst after DBT oxidation. Type of catalyst
Surface area (m2/g)
Total pore volume (cm3/g)
The fresh catalyst
221
0.321
Catalyst recycled from 300 ppm
145
0.227
Catalyst recycled from 3000 ppm
116
0.196
4.3.4. .Effect of Oxidant Amount on Conversion 93
The above experiments were carried out with an excess of hydrogen peroxide (octane: H2O2 = 50:1, or H2O2: DBT = 18:1 molar ratio). Experiment to study the influence of the hydrogen peroxide concentration on the kinetics of DBT conversion was carried out. The DBT conversion values as a function of the reaction time for H2O2 concentration of 0%, 10%, 15% and 30% are plotted in Fig.(4.69). As can be seen, the hydrogen peroxide concentration had a strong influence on the reaction rate. The reaction rate decreases when the H2O2 concentration was reduced. Working with a high H2O2 concentration, the reaction rate was very high. It also shows the blank test of DBT oxidation without the addition of H2O2, in which case DBT removal from the n-octane was attributed to the adsorption of DBT onto the solid catalyst. However, in this experiment, no DBT removal was detected at the absence of H2O2 as the sulfur concentration of the system was kept almost the same as the initial DBT concentration. It indicates TiO2 adsorptive removal of the sulfur species over the nanoTiO2 material does not happen although it has a large surface area and pore volume. Therefore DBT removal in this experiment was due to the catalytic oxidation with H2O2 as the oxidant. 105 0 10% 15% 30%
90
DBT conversion (%)
75 60 45 30 15 0 -15 -1.5
0
1.5
3
4.5
6
7.5
Time (sec)
94
9
10.5
12
Fig.(4.69) Effect of the H2O2 concentration on the conversion of DBT. Conditions: 3000 ppm DBT in octane, 70oC, 0.1 g/ml of TiO2.
4.3.5. Effect of H2O2/DBT Molar Ratio on the Conversion of DBT The effect of various H2O2/DBT molar ratios (O/S) on sulfur removal were given in Fig.(4.70). It was obvious that the sulfur removal increased fastly at first, and then turned to decrease slightly with the increasing reaction time as mol ratio of H2O2 to DBT increased from 9:1 to 25:1. This could be due to more superoxide radical (.O2-) generated and stabilized at titanium dioxide sites. Stoichiometrically, 2 mol of H2O2 was consumed for oxidation of 1 mol of DBT to DBT sulfone (DBTO2). When O/S was 9:1, the removal of DBT was 48% after10 min. While O/S was 18:1, sulfur removal reached 71% after 10 min.
100 9:1 18:1 25:1
90
DBT conversion (%)
80 70 60 50 40 30 20 10 0 0
1
2
3
4
5
6
7
8
9
10
11
12
Time (sec)
Fig.(4.70).Effect of oxidant amount on conversion: conditions: 3000 ppm DBT in octane, 70oC, 0.1 g/ml of TiO2. 95
4.3.6 Effect of TiO2 Prepared by PWA with and Without STAB on DBT Conversion Experiments showed that TiO2 catalysts had good catalytic activity because PWA is introduced into TiO2 structures. Furthermore, a comparative study was carried out using different TiO2 catalysts, prepared with and without STAB, respectively. As shown in Fig. (4.71),(4.72)
DBT oxidation was catalyzed less effectively by TiO2
nanomaterials prepared without STAB, and only 50% conversion of DBT was achieved within 10 min when initial concentration of DBT 3000 ppm and 42% conversion of DBT was achieved within 1.5 min when initial concentration of DBT 300 ppm . The difference in the catalytic reactivity of these TiO2 materials showed that the nanostructure has remarkable effect on DBT desulfurization. Larger pore volume will facilitate DBT mass transfer and therefore the rate of DBT oxidation. It facilitates DBT sulfones desorption as well. It is estimated that element W in TiO2 is the active site for DBT oxidation. Peroxide between W and hydrogen peroxide is formed and it further reacts with the sulfur compound by inserting oxygen into the Satom of the DBT molecule.
96
100 90 TiO2 prepared by PWA TiO2 prepared by PWA+STAB
DBT coversin (%)
80 70 60 50 40 30 20 10 0 0
1
2
3
4
5
6
7
8
9
10
Time (min)
Fig. 4.71 Reactivity of different catalysts on DBT oxidation, including TiO2+PWA catalyst prepared with and without STAB. Conditions: 3000 ppm DBT in octane, 70oC, 0.1 g of catalyst.
110 100
DBT conversion (%)
90 80 70 60 50 40 30 T iO2 prepared by PWA T iO2 prepared by PWA+ST AB
20 10 0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
Time (min)
Fig.
4.72
Reactivity of different catalysts on DBT oxidation, including TiO2+PWA catalyst prepared with and without STAB. Conditions: 300 ppm DBT in octane, 70oC, 0.1 g of catalyst.
4.3.7 Effect of Catalyst Amount on conversion 97
Increasing the amount of TiO2 catalyst increases the rate of oxidation as in Fig.(4.73). In comparison to the standard reaction conditions of 0.1 g of TiO2 (71% conversion, 10 min), a lower conversion of about 52% was achieved when decreasing the catalyst amount to 0.08 g. When the reaction is run with 0.05 g TiO2, only 46% DBT conversion occurs after 10 min. 100 0.05 gm 0.08 gm 0.1 gm
90
DBT conversion (%)
80 70 60 50 40 30 20 10 0 0
1
2
3
4
5
6
7
8
9
10
Time (min)
Fig.(4.73). Effect of the amount of TiO2 catalyst on the conversion of DBT. Conditions: 3000 ppm DBT in octane, 70oC, octane: H2O2 = 18:1 (mole ratio).
4.3.8. Reaction kinetic model Kinetics of DBT oxidation with TiO2 prepared by PWA with STAB was investigated. In the reaction system, it is assumed that the volume and mass of the reaction mixtures were constant, since only small amounts of liquid samples were withdrawn during the reaction. Furthermore, excessive amount of H2O2 was demonstrated and the little change of its concentration could be ignored. At the beginning of the reaction, the active catalyst was assumed to be unchanged. Then the rate equation can be simplified as: 98
𝑟𝐴 = −
𝑑𝐶 𝑑𝑡
= 𝑘𝐶 ∝
where rA is the rate of consumption of DBT, C is the concentration of DBT, k is the rate constant. Fig.(4.74) shows the ln (1-X) plots versus reaction temperatures at 333, 343, and 353 K. The kinetic reaction can be described as a pseudo-first-order. Based on the experimental results of different DBT initial concentrations, values for k and ∝ were obtained: K= 0.12, ∝=0.875 At a constant temperature, the rate constant k does not change when the catalyst concentration is varied. The results are listed in Table 4.23. Reaction rate increases when temperature rises from 333 to 353 K. It is obvious that the reactivity is increased with an increase in the temperature. A linear Arrhenius plot of the rate constants is demonstrated in Fig. (4.75). From the plot of -ln k
−
1 𝑅𝑇
, the apparent activation energy Ea is obtained as 52.8 kJ/mol under
the experimental conditions. The experimental results demonstrate that organic sulfur compounds in diesel oils, such as DBT, can be effectively oxidized by TiO2 nanomaterials using hydrogen peroxide as the oxidizing agent under mild conditions.
Table 4.23 The apparent rate constants of DBT oxidation under different temperatures Temperature (K)
Rate constant k (min-1)
-lnk
333
0.053
2.937
343
0.122
2.3
353
0.156
1.86
99
0 -0.25 -0.5
ln (1-X)
-0.75 -1 -1.25
60 oC 70oC 80oC y=-0.0002524-0.05386x y=-0.00631-0.1227x y=-0.02172-0.1568x
-1.5 -1.75 -2 0
1
2
3
4
5
6
7
8
9
10
11
12
Time (min)
-lnK
Fig.(4.74) Model of the pseudo-first-order reaction
y = 51.057x - 15.779 R² = 0.9944
3.4
3.45
3.5
3.55 1/(RT) x 104
3.6
Fig.(4.75) Arrhenius activation energy for DBT oxidation.
5.1 CONCLUSIONS 100
3.65
3.7
This work has highlighted the following conclusions: 1) Nano sized titanium dioxide has been successfully produced in four crystalline forms (amorphous, anatase, anatase-rutile and rutile). 2) Sol-gel and hydrothermal methods was used to prepare nano TiO 2 with two source materials titanium tetra-isopropoxide and titanium etrhoxide. 3) X- Ray diffraction pattern showed the formation of four crystalline forms of titanium dioxide at whole studied calcination temperatures from 120 to 900oC. 4) Effect of pH was examined in preparation of TiO2, high acidity solution will favor the formation of rutile phase until pH=3 where the rutile phase disappeared while lower acidity favor anatase formation. Also the average particles size at higher pH values is smaller than other pH. 5) Effect of four acid types (HCl, CH3COOH, H3PO4 and H3PW12O40) was studied as a catalyst in syntheses of nano TiO 2. The nature of acid was found to substantially affect the crystalline phase composition, morphology and the size of TiO2 nanoparticles. A) HCl: In strongly acidic solution fine spherical particles of nano TiO2 was obtained, anatase to rutile transformation occurred at 400oC. B) H3PO4: The formation of amorphous rather than crystalline phase until 600oC.In 700oC the amorphous phase transformed to anatase phase with bigger particles size. C) CH3COOH: An efficient Stabilizer of anatase phase in the calcination. D) H3PW12O40: The formation of anatase phase with trace of rutile crystalline phase at 450oC.On reaching 700oC the rutile phase disappeared and only anatase phase found. 101
6) The peak between 800-400cm-1 is assigned to the Ti-O stretching bands obtained from FTIR spectra tests. The structure of TiO2 in the case of prepared TiO2 with PWA and STAB was confirmed in the FTIR spectrum no band of PWA was found. 7) In sol- gel method and TTIP as source materials TiO2 nanoparticles obtained by acid route showed a larger surface area and slightly higher porosity than the ones obtained with alkaline medium. The surface area at pH=1 in three crystalline forms was (amorphous=1370, anatase=77.5 and anatase-rutile=28.9 m2.g) higher than surface area in pH=9 in (amorphous=437, anatase=40 and anatase-rutile=11.6 m2.g). 8) Increasing the calcination temperature from 450 to 700oC causes decrease in surface area for anatase in pH=1 from 77.5 to 28.9 m2/g and pore volume from 0.1582 to 0.0487 cm3/g. 9) The high surface area was obtained by using phosphotungstic acid and STAB compared to other acids (phosphoric acetic, and hydrochloric) in sol-gel method and TTIP as source materials. The surface area for anatase by using PWA was 143 compared to 37and 112m2/g for anatase by using acetic and phosphoric acids respectively. 10) In hydrothermal method the increasing of the crystallization temperature from 170 to 190oC will lead to decrease in surface area in the case of using acetic acid but in the case of phosphotungstic acid the surface area is higher than all samples of prepared nano TiO2. 11) In sol-gel method and titanium ethoxide as source materials showed less surface area and pore volume with acid or without in preparation compared to all samples. 12) The morphology of prepared nano titanium dioxide obtained from AFM analysis and SEM images shows:
102
A. In sol-gel method with TTIP as source materials acidic and alkaline media the shapes of particles is spherical but in high acidity case the less aggregates and bigger TiO2 particles is formed. The size of particles at higher pH=7 and 9 values is smaller and can agglomerate. B. In hydrothermal method non uniform shape of particles with low agglomeration is observed by using acetic acid. Agglomeration and small
particles size is observed by using phosphotungstic acid.
C. In sol-gel method with titanium ethoxide as source materials uniform
small spheres particles for PWA and coarse spheres with
bigger size for phosphoric acid. 13) The chemical compositions of prepared samples including Ti, W, P, etc. inside the calcined TiO2 materials were examined by X-Ray Fluorescence. 14) Anatase nano –TiO2 is a promising catalyst for direct deep oxidative desulfurization of model fuel. The results showed that complete DBT conversion (100 ppm) was obtained within 40 sec in the case of nano TiO2 prepared without PWA. 15) nano TiO2 prepared with PWA and STAB exhibit good performance in DBT oxidation. DBT removal from 300ppm was 100% conversion in 1.5 min and in 3000 ppm was 71% conversion in 10 min. 16) The ODS results of both nano catalysts fitted first order kinetic model, and activation energies of ODS process are 57.66 kJ/mol in the case of nano TiO2 without PWA and 52.8 kJ/mol for nano TiO2 prepared with PWA and STAB.
5.2 RECOMMENDATIONS 103
The following recommendations are suggested for the future work:
1) Study the effect of using another solvent such as methanol instead of ethanol in the preparation of nano titanium dioxide.
2) Investigate the use of sulfuric, nitric and citric acid as a catalyst in the preparation of nano titanium dioxide.
3) Examine the influence of using another method in preparation nano TiO2 like precipitation method with titanium tetrachloride.
4) Studying the effect of using different petroleum product like kerosene or gasoil under different conditions in ODS process.
104
Fig.(A-1)XRD diffraction data list of sample T1(amorphous)
A-1
105
Fig.(A-2)XRD diffraction data list of sample T1(anatase)
A-2
106
Fig.(A-3)XRD diffraction data list of sample T1(anatase-rutile)
A-3
107
Fig.(A-4)XRD diffraction data list of sample T2(anatase)
A-4
108
Fig.(A-5)XRD diffraction data list of sample T2 (anatase-rutile)
A-5
109
Fig.(A-6)XRD diffraction data list of sample T3 (anatase)
A-6
110
Fig.(A-7)XRD diffraction data list of sample T3 (anatase-rutile)
A-7
111
Fig.(A-8)XRD diffraction data list of sample T4 (anatase)
A-8
112
Fig.(A-9)XRD diffraction data list of sample T4 (anatase-rutile)
A-9
113
Fig.(A-10)XRD diffraction data list of sample T5 (anatase)
A-10
114
Fig.(A-11)XRD diffraction data list of sample T5 (anatase-rutile)
A-11
115
Fig.(A-12)XRD diffraction data list of sample T6 (anatase)
A-12
116
Fig.(A-13)XRD diffraction data list of sample T6 (anatase-Rutile)
A-13
117
Fig.(A-14)XRD diffraction data list of sample T7 (amorphous)
A-14
118
Fig.(A-15)XRD diffraction data list of sample T7 (anatase)
A-15
119
Fig.(A-16)XRD diffraction data list of sample T8 (amorphous)
A-16
120
Fig.(A-17)XRD diffraction data list of sample T8 (anatase)
A-17
121
Fig.(A-18)XRD diffraction data list of sample T8 (anatase)
A-18
122
Fig.(A-19)XRD diffraction data list of sample T9 (anatase)
A-19
123
Fig.(A-20)XRD diffraction data list of sample T9 (anatase-rutile)
A-20 Table A-1 Crystallinity of the prepared samples for sol-gel method and TTIP as a source material Sample code Synthesis conditions Crystallinity % 124
T1 T2 T3 T4 T5 T6 T7 T8 T9
450oC, pH 1 700oC, pH 1 450oC, pH 2 700oC, pH 2 450oC, pH 3 700oC, pH 3 450oC, pH 4 700oC, pH 4 450oC, pH 7 700oC, pH 7 450oC, pH 9 700oC, pH 9 700oC,H3PO4 450oC, acetic acid
84.7 110.95 96.77 107.14 96.13 106.2 93.5 105.24 95.48 99.52 87.1 100 91.61 92.26
700oC,acetic acid 450oC,H3PW12O40
98.06 91
700oC,H3PW12O40 800oC,H3PW12O40
98 108.45
Table A-2 Crystallinity for the samples prepared by sol-gel and titanium ethoxide as a source material Sample code Synthesis conditions Crystallinity % o T1E 450 C 95 o 700 C 95.5 o 800 C 100 o T2E 700 C, H3PO4 91 o T3E 450 C,H3PW12O40 100.15 o 700 C, H3PW12O40 100.27 o 800 C, H3PW12O40 100.31
A-21 Table A-3 Crystallinity for the samples prepared by hydrothermal method Sample code Synthesis conditions Crystallinity % o o T1H 450 C, 170 C,acetic acid 98.1 o o 700 C, 170 C,acetic acid 106.9 o o T2H 450 C, 180 C,acetic acid 98.2 o o 700 C, 180 C,acetic acid 100.10 125
900oC, 180oC,acetic acid 100.25 o o T3H 450 C, 190 C,acetic acid 98.1 o o 700 C, 190 C,acetic acid 100.26 o o 900 C, 190 C,acetic acid 116.13 o o T4H 450 C,180 C,H3PW12O40 96.12 o o 700 C,180 C,H3PW12O40 96.77 o o T5H 450 C,190 C,H3PW12O40 100.11 o o 700 C,190 C,H3PW12O40 105.27 Table A-4 The content of anatase and rutile for the samples prepared by sol-gel and TTIP as a source material Sample code Synthesis condition Anatase % Rutile % T1 450oC, pH 1 58.84 42.16 o 700 C, pH 1 27.65 72.35 o T2 450 C, pH 2 57.87 42.13 o 700 C, pH 2 27.57 72.43 o 450 C, pH 3 T3 100 o 700 C, pH 3 49.3 50.7 o 450 C, pH 4 T4 100 o 700 C, pH 4 38.89 61.11 o 450 C, pH 7 T5 100 o 700 C, pH 7 49 51 o 450 C, pH 9 T6 100 o 700 C, pH 9 29.2 70.8 o 700 C,H3PO4 T7 100 o 450 C, acetic acid T8 100 o 700 C, acetic acid 100 o 450 C,H3PW12O40 T9 57.69 42.31 o 800 C, H3PW12O40 58.3 41.7 A-22 Table A-5 The content of anatase and rutile for the samples prepared by sol-gel and titanium ethoxide as a source material Sample code T1
Synthesis condition o
450 C 700oC 800oC 126
Anatase %
Rutile %
100 27.05 10.13
72.95 89.87
T2 T3
450oC, H3PO4 450oC 700oC 800oC
60 60 100 28.46
40 71.54
Table A-6 The content of anatase and rutile for the samples prepared by hydrothermal method Sample code Synthesis condition Anatase % Rutile % T1H 450oC,170oC,acetic acid 57.54 42.46 o o 700 C,170 C,acetic acid 56.7 43.3 o o T2 450 C, 180 C,acetic acid 57.24 42.76 o o 700 C, 180 C,acetic acid 56.5 43.5 o o 900 C, 180 C,acetic acid 100 o o 450 C, 190 C,acetic acid T3 100 o o 700 C, 190 C,acetic acid 100 o o 900 C, 190 C,acetic acid 100 o o 450 C, 180 C,H3PW12O40 T4 57.63 42.37 o o 700 C, 180 C,H3PW12O40 53.2 46.8 o o 450 C, 190 C,H3PW12O40 T5 100 o o 700 C, 190 C,H3PW12O40 61.4 38.6 A-23
127
Fig. B-1 FTIR-spectra of the nano titanium dioxide prepared using hydrochloric acid, pH=1, and at calcination temperature 4500C
Fig.B-2 FTIR-spectra of the nano titanium dioxide prepared using hydrochloric acid, pH=1, and at calcination temperature 7000C
(B1)
128
Fig. B-3 FTIR-spectra of the nano titanium dioxide prepared using hydrochloric acid, pH=4, and at calcination temperature 4500C
Fig. B-4 FTIR-spectra of the nano titanium dioxide prepared using hydrochloric acid, pH=4, and at calcination temperature 7000C
(B2)
129
Fig. B-5 FTIR-spectra of the nano titanium dioxide prepared using NH4OH, pH=7, and at calcination temperature 4500C
Fig. B-6 FTIR-spectra of the nano titanium dioxide prepared using NH4OH, pH=7, and at calcination temperature 7000C
(B3)
130
Fig. B-7 FTIR-spectra of the nano titanium dioxide prepared using NH4OH, pH=9, and at calcination temperature 4500C
Fig. B-8 FTIR-spectra of the nano titanium dioxide prepared using NH4OH, pH=9, and at calcination temperature 7000C
(B4)
131
Fig. B-9 FTIR-spectra of the nano titanium dioxide prepared using acetic acid and at calcination temperature 4500C
Fig B-10 FTIR-spectra of the nano titanium dioxide prepared using acetic acid and at calcination temperature 7000C
(B5)
132
Fig. B-11 FTIR-spectra of the nano titanium dioxide prepared using phosphotungustic acid and at calcination temperature 4500C
Fig. B-12 FTIR-spectra of the nano titanium dioxide prepared using phosphotungustic acid and at calcination temperature 7000C
Granularity Cumulation Distribution Reports: 133
Sample Code: T1 Avg. Diameter:71.98 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00
1.16 3.94 2.32 6.50 4.41 3.71 5.34 5.57 6.73
1.16 5.10 7.42 13.92 18.33 22.04 27.38 32.95 39.68
70.00 75.00 80.00 85.00 90.00 95.00 100.00 105.00 110.00
7.19 8.12 7.19 6.73 5.57 6.50 5.57 2.78 3.25
46.87 54.99 62.18 68.91 74.48 80.97 86.54 89.33 92.58
115.00 120.00 125.00 130.00 140.00 145.00 155.00
3.25 1.16 0.70 0.70 0.70 0.70 0.23
95.82 96.98 97.68 98.38 99.07 99.77 100.00
Fig. (C1) Bar chart of particle size distribution of sample T1 (450oC) (C1) Sample Code: T1 Avg. Diameter:94.50 nm Diamete Volu Cumulat Diamete Volu Cumulat Diamete Volu Cumulat r(nm)< me(%) ion(%) r(nm)< me(%) ion(%) r(nm)< me(%) ion(%) 30.00 35.00
0.32 0.65
0.32 0.97
75.00 80.00
6.13 4.19 134
26.77 30.97
120.00 125.00
5.16 6.77
78.06 84.84
40.00 45.00 50.00 55.00 60.00 65.00 70.00
2.26 1.61 2.26 2.90 2.58 4.19 3.87
3.23 4.84 7.10 10.00 12.58 16.77 20.65
85.00 90.00 95.00 100.00 105.00 110.00 115.00
7.74 5.81 8.39 7.10 2.90 4.52 5.48
38.71 44.52 52.90 60.00 62.90 67.42 72.90
130.00 135.00 140.00 145.00 150.00 155.00
2.90 2.90 2.26 2.58 2.58 1.94
87.74 90.65 92.90 95.48 98.06 100.00
Fig. (C2) Bar chart of particl size distribution of sampleT2 (700oC) Sample Code: T2 Avg. Diameter : 74.88 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 35.00 40.00 45.00 50.00 55.00 60.00
0.94 1.89 1.89 2.36 4.72 8.49
0.94 2.83 4.72 7.08 11.79 20.28
65.00 70.00 75.00 80.00 85.00 90.00
11.32 14.62 6.13 8.02 10.85 2.83 (C2)
135
31.60 46.23 52.36 60.38 71.23 74.06
95.00 100.00 105.00 110.00
9.43 6.13 6.60 3.77
83.49 89.62 96.23 100.00
Fig. (C3) Bar chart of particle size distribution of sampleT2 (450oC) Sample Code: T2 Avg. Diameter: 97.53 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 70.00 80.00 90.00 100.00
1.36 25.79 16.74 18.10
1.36 27.15 43.89 61.99
110.00 120.00 130.00 140.00
12.67 8.60 8.60 4.07
74.66 83.26 91.86 95.93
150.00 160.00 170.00 210.00
1.36 1.81 0.45 0.45
97.29 99.10 99.55 100.00
Fig. (C4) Bar chart of particle size distribution of sampleT2 (700oC) (C3) Sample Code: T4 Avg. Diameter: 86.77nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 136
50.00 55.00 60.00 65.00 70.00
0.43 0.86 2.58 3.00 6.87
0.43 1.29 3.86 6.87 13.73
75.00 80.00 85.00 90.00 95.00
9.01 11.59 9.01 14.59 11.16
22.75 34.33 43.35 57.94 69.10
100.00 105.00 110.00 115.00
10.30 6.87 7.73 6.01
79.40 86.27 93.99 100.00
Fig. (C5) Bar chart of particle size distribution of sampleT4 (450oC) Sample Code: T4 Avg. Diameter: 97.40 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 40.00 50.00 60.00 70.00
0.62 2.80 3.43 6.85
0.62 3.43 6.85 13.71
80.00 90.00 100.00 110.00
11.53 13.40 14.64 15.58
(C4)
137
25.23 38.63 53.27 68.85
120.00 130.00 140.00 150.00
10.28 9.35 9.03 2.49
79.13 88.47 97.51 100.00
Fig. (C6) Bar chart of particle size distribution of sampleT4 (700oC) Sample Code: T5 Avg. Diameter: 60.44 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00
0.34 1.68 3.86 5.03 5.70 7.72 8.22 6.04 10.40
0.34 2.01 5.87 10.91 16.61 24.33 32.55 38.59 48.99
60.00 65.00 70.00 75.00 80.00 85.00 90.00 95.00 100.00
6.54 5.37 4.87 5.20 5.54 6.04 2.52 2.85 4.03
138
55.54 60.91 65.77 70.97 76.51 82.55 85.07 87.92 91.95
105.00 110.00 115.00 120.00 125.00 130.00 135.00 150.00
2.35 1.51 1.68 0.50 1.17 0.50 0.17 0.17
94.30 95.81 97.48 97.99 99.16 99.66 99.83 100.00
Fig. (C7) Bar chart of particle size distribution of sampleT5 (450oC) Sample Code: T5 Avg. Diameter: 95.89 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 30.00 40.00 50.00 60.00 70.00
1.53 2.55 4.59 3.06 10.20
1.53 4.08 8.67 11.73 21.94
80.00 90.00 100.00 110.00 120.00
10.71 12.76 7.65 12.24 9.18
32.65 45.41 53.06 65.31 74.49
130.00 140.00 150.00 160.00
8.16 6.63 9.18 1.53
82.65 89.29 98.47 100.00
Fig. (B8) Bar chart of particle size distribution of sampleT5 (700oC) (C6) Sample Code: T6 Avg. Diameter:75.85nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 139
15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00
0.29 0.88 1.18 3.24 3.53 2.65 2.94 6.47 4.12 7.06
0.29 1.18 2.35 5.59 9.12 11.76 14.71 21.18 25.29 32.35
65.00 70.00 75.00 80.00 85.00 90.00 95.00 100.00 105.00 110.00
7.06 2.94 5.59 6.18 7.06 6.47 6.18 5.29 4.41 3.82
39.41 42.35 47.94 54.12 61.18 67.65 73.82 79.12 83.53 87.35
115.00 120.00 125.00 130.00 135.00 140.00 145.00 150.00
4.41 2.35 1.47 1.47 1.18 1.18 0.29 0.29
91.76 94.12 95.59 97.06 98.24 99.41 99.71 100.00
Fig. (C9) Bar chart of particle size distribution of sampleT6 (450oC) Sample Code: T6 Avg. Diameter: 90.48 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 60.00 65.00 70.00 75.00 80.00 85.00 90.00 95.00 100.00
5.73 10.75 9.68 7.89 9.32 6.45 6.81 7.89 5.73
5.73 16.49 26.16 34.05 43.37 49.82 56.63 64.52 70.25
105.00 110.00 115.00 120.00 125.00 130.00 135.00 140.00 145.00
3.58 3.94 5.02 1.43 4.30 4.66 0.36 2.15 0.72
140
73.84 77.78 82.80 84.23 88.53 93.19 93.55 95.70 96.42
150.00 155.00 160.00 180.00 190.00 195.00 220.00
1.08 0.36 0.72 0.36 0.36 0.36 0.36
97.49 97.85 98.57 98.92 99.28 99.64 100.00
Fig. (C10) Bar chart of particle size distribution of sampleT6 (700oC) Sample Code: T7 Avg. Diameter: 79.74 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 65.00 70.00 75.00
11.11 12.87 16.37
11.11 23.98 40.35
80.00 85.00 90.00
11.70 11.70 9.36
52.05 63.74 73.10
95.00 100.00
15.20 11.70
88.30 100.00
Fig. (C11) Bar chart of particle size distribution of sampleT7 (450oC) (C8) Sample Code: T7 Avg. Diameter: 105.75 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 30.00
0.47
0.47
100.00
11.32 141
48.58
170.00
1.42
94.34
40.00 50.00 60.00 70.00 80.00 90.00
1.42 1.89 4.72 9.91 9.43 9.43
1.89 3.77 8.49 18.40 27.83 37.26
110.00 120.00 130.00 140.00 150.00 160.00
8.96 7.55 7.55 8.96 7.08 4.25
57.55 65.09 72.64 81.60 88.68 92.92
180.00 190.00 200.00 210.00
1.89 1.89 1.42 0.47
96.23 98.11 99.53 100.00
Fig. (C12) Bar chart of particle size distribution of sampleT7 (700oC) Sample Code: T8 Avg. Diameter:71.43 nm Diamete Volum Cumulat Diamete Volum Cumulat Diamete Volum Cumulat r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) r(nm)< e(%) ion(%) 20.00 25.00 30.00 35.00 40.00 45.00 50.00
0.27 1.37 1.10 2.74 4.11 3.84 4.93
0.27 1.64 2.74 5.48 9.59 13.42 18.36
55.00 60.00 65.00 70.00 75.00 80.00 85.00
7.40 6.30 7.40 7.40 7.12 8.22 7.12
142
25.75 32.05 39.45 46.85 53.97 62.19 69.32
90.00 95.00 100.00 105.00 110.00
7.67 5.48 5.48 6.03 6.03
76.99 82.47 87.95 93.97 100.00
Fig. (C13) Bar chart of particle size distribution of sampleT8 (450oC) Sample Code: T8 Avg. Diameter: 80.55 nm Diameter( Volume Cumulatio Diameter( Volume Cumulatio Diameter( Volume Cumulatio nm)< (%) n(%) nm)< (%) n(%) nm)< (%) n(%) 20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00
0.38 0.95 2.10 1.72 2.48 3.24 4.58 5.53 4.58 6.87 4.96
0.38 1.34 3.44 5.15 7.63 10.88 15.46 20.99 25.57 32.44 37.40
75.00 80.00 85.00 90.00 95.00 100.00 105.00 110.00 115.00 120.00 125.00
8.21 5.53 8.40 5.53 5.53 4.77 3.44 4.58 3.63 3.24 2.29
45.61 51.15 59.54 65.08 70.61 75.38 78.82 83.40 87.02 90.27 92.56
130.00 135.00 140.00 145.00 150.00 160.00 170.00 175.00 180.00 190.00
0.76 1.91 1.34 1.91 0.38 0.38 0.19 0.19 0.19 0.19
Fig. (C14) Bar chart of particle size distribution of sampleT8 (700oC) (C10)
143
93.32 95.23 96.56 98.47 98.85 99.24 99.43 99.62 99.81 100.00
Fig.(D-1) Concentration of metal oxides for nano TiO2 prepared by sol-gel method and titanium ethoxide as source materials
D-1
144
Fig.(D-2) Concentration of metal oxides for nano TiO2 prepared by sol-gel method and TTIP as source materials
D-2
Appendix E 145
Surface Area Test
E-1
146
E-2
147
E-3
148
E-4
UV-Carve (1) 149
UV-Carve 0.8 0.7
y = 0.0002x + 0.0465 R² = 0.9887
Absorbency
0.6 0.5 0.4 0.3 0.2 0.1 0 0
500
1000
1500 2000 2500 DBT concentration ppm
3000
3500
UV-Carve (2)
Absorbency
UV-Carve 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 -0.02 0
y = 0.0003x - 0.0049 R² = 0.9975
100
200 300 400 DBT concentration ppm
500
F1
Sample of calculations Calculation of Relative Crystallinity (%) of samle T2:-
150
600
Average
Crystallinity
%
∑ 𝐼𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑖𝑒𝑠 𝑜𝑓 𝑝𝑒𝑎𝑘𝑠 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒𝑠
=𝐼𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑖𝑒𝑠 𝑜𝑓 𝑟𝑒𝑓𝑒𝑟𝑛𝑐𝑒 𝑝𝑒𝑎𝑘𝑠 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒𝑠
100…..4.1
Average Crystallinity %=
100+28+22 100+20+35
*100= 96.77%
Calculation of Crystal Size (nm) of samle T2:-
Dp=
Dp=
0.94 λ β.Cosθ
……………….4.3
0.94∗0.154 𝑛𝑚 1.032∗o.o175∗cos(12.66)
= 11.5 nm
151
*
