Biodiesel production from waste cooking oil catalyzed

Biodiesel production from waste cooking oil catalyzed by solid acid SO4 2−/TiO2/La3+ Kui Wang, Jianchun Jiang, Zhan Si, and Xinyu Liang Citation: Journal of Renewable and Sustainable Energy 5, 052001 (2013); doi: 10.1063/1.4820563 View online: http://dx.doi.org/10.1063/1.4820563 View Table of Contents: http://scitation.aip.org/content/aip/journal/jrse/5/5?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Comparative studies of thermal, oxidative and low temperature properties of waste cooking oil and castor oil J. Renewable Sustainable Energy 5, 063104 (2013); 10.1063/1.4830257 Diesel-like fuel production from catalytic cracking and esterification of waste oil J. Renewable Sustainable Energy 5, 052004 (2013); 10.1063/1.4822035 Kinetic study on lipase catalyzed trans-esterification of palm oil and dimethyl carbonate for biodiesel production J. Renewable Sustainable Energy 5, 033127 (2013); 10.1063/1.4803744 Brønsted-Lewis acidic ionic liquid for the “one-pot” synthesis of biodiesel from waste oil J. Renewable Sustainable Energy 5, 023111 (2013); 10.1063/1.4794959 The use of oil shale ash in the production of biodiesel from waste vegetable oil J. Renewable Sustainable Energy 4, 063123 (2012); 10.1063/1.4768544

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 54.210.20.124 On: Tue, 03 Nov 2015 10:23:45

JOURNAL OF RENEWABLE AND SUSTAINABLE ENERGY 5, 052001 (2013)

Biodiesel production from waste cooking oil catalyzed by solid acid SO422/TiO2/La31 Kui Wang,1,2 Jianchun Jiang,1,2,a) Zhan Si,1 and Xinyu Liang1 1

Institute of Chemical Industry of Forest Products, 210042 Nanjing, China National Engineering Laboratory for Biomass Chemical Utilization, 210042 Nanjing, China 2

(Received 15 January 2013; accepted 24 July 2013; published online 9 September 2013)

A solid acid catalyst SO42/TiO2/La3þ was prepared via sol-gel method using tetrabutyl titanate as TiO2 precursor. The catalyst simultaneously catalyzed esterification and transesterification resulting in the synthesis of biodiesel from waste cooking oil with high content of free fatty acids as feedstock. The optimization of reaction conditions was also performed. The maximum yield of more than 90% could be obtained under the optimized conditions that catalyst amount 5 wt. % of oil, 10:1 molar ratio (methanol to oil), temperature 110 C, and esterification of 1 h. The catalyst can be reused for five times by activation without observing the decrease of its catalytic performance. The final products were purified by molecular distillation and detected by GC-MS. The content of fatty acid methyl esters was 96.16%. C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4820563] V

I. INTRODUCTION

The current world energy demand and decrease of environmental pollution based on use of fossil fuels has been recognized as a top priority for both developed and developing nations. Fatty acid methyl esters (FAMEs) better known as biodiesel has attracted considerable attention as a renewable, biodegradable, environmental friendly and non-toxic fuel, and lots of research have been developed for its production.1–3 Different varieties of feedstock have been studied for biodiesel production, such as canola, palm, palm kernel, sunflower, and coconut. The major bottleneck concerning biodiesel production from these feedstocks is the high price of vegetable oils compared to that of fossil based diesel fuel. The search on ways to improve the economical feasibility of biodiesel has gained attraction for decades.4–6 One way to reduce the cost of biodiesel production is to employ low quality feedstock such as waste cooking oil instead of vegetable oil. However, the traditional alkali catalyzed transesterification reactions provide low biodiesel yields due to high free fatty acid (FFA) content in low cost feed stocks which reacts with alkali to form soap, resulting in serious emulsification and separation problems. To solve these problems, some initiative attempts have been made to use heterogeneous acid catalysts for the formation of biodiesel.7–10 In comparison with homogenous catalyst, heterogeneous acid catalysts have several advantages, such as easy separation, regeneration and recycling, and particularly, the heterogeneous acid can be easily incooperated into pack bed reactor in continuous processes. Apart from the above advantages, an ideal solid acid for biodiesel preparation should have high stability, numerous strong acid sites, large pores, and hydrophobic surface.11 Recently, sulfated metal oxides have been employed as an effective class of heterogeneous acid catalysts in biodiesel production. There have been several studies on the usage of zirconium oxide (ZrO2) as a solid acid catalyst for biodiesel production.12–17 In order to enhance the strong surface acidity, sulfated zirconia (SO42/ZrO2) was obtained by impregnating ZrO2 with sulfuric acid solution,

a)

Author to whom correspondence should be addressed. Electronic mail: [email protected]

1941-7012/2013/5(5)/052001/8/$30.00

5, 052001-1

C 2013 AIP Publishing LLC V


052001-2

Wang et al.

J. Renewable Sustainable Energy 5, 052001 (2013)

Thiruvengadaravi et al. reported that SO42/ZrO2 showed well performance in esterification of high free fatty acid karanja oil.12 Park et al. found that WO3/ZrO2 showed higher stability than SO42/ZrO2 in esterification of waste cooking oil.13 Titanium dioxide (TiO2) has attracted attention for biodiesel production due to their acidic properties.18–21 In addition, introduction of sulfuric group on the surface of TiO2 will enhance the acid strength of catalyst. Chen et al.20 evaluated the catalytic activity of SO42/TiO2 and SO42/ZrO2 for transesterification of cotton seed oil high in FFAs content to FAME. The study indicated that SO42/TiO2 shows better performance than SO42/ZrO2 for its specific area of 99.5 m2/g, which is higher than SO42/ZrO2 with a specific area of 91.5 m2/g. Apart from TiO2 and ZrO2, SnO2 also has been reported as efficient catalyst in transesterification or esterification of waste cooking oil.22–24 Sarkar et al.23 developed mesoporous WO3/SnO2 with surface area of 130 m2/g and pore size of 3.9 nm exhibits up to 90% conversion of oleic acid with high yield (92%) to the ethyl oleate at 80 C for 2 h. The catalyst can be reused without losing its catalytic activity when treated at 400 C for 3 h. However, the catalyst showed poor performance when waste cooking oil was charged as feedstock due to its sulfate groups hydrolyzed. Researchers tried to combine Al2O3 or SiO2 with SO42/TiO2, SO42/SnO2, or WO3/ZrO2, the addition of Al2O3 or SiO2 further stabilizes the tetragonal phase of metal oxides support and also prevents the growth of acid particles, which not only provides high mechanical strength but also enhances the acidity of the catalyst.21,24 However, high reaction temperature (RT) and long reaction time are needed to carry out the esterification and transesterification catalyzed by these catalysts. In this study, rare earth elements are introduced into sulfated metal oxides. The prepared solid acid catalyst shows higher stability and activity in production of biodiesel from waste oils. The addition of lanthanum (rare earth) played an important part in the enhancement of catalytic stability and activity. The technical route for the synthesis of biodiesel from waste oil under lower temperature and shorter reaction time was established. II. EXPERIMENTAL A. Materials

The industrial waste oil was obtained from Jiangsu Qianglin Biology Energy Co., Ltd. in China. The composition of the waste oil was investigated using gas chromatography mass spectrometer (GC-MS) (Agilent 7890/5975) and Kari-Fisher moisture teller (Mettler Toledo V30). The moisture content of the waste oil was determined by Kari-Fisher moisture teller. The waste oil obtained after dehydration was analyzed by GC-MS and the target compounds were identified. The waste oil consists of free fatty acid (79.9%), fatty matter (14.4%), steroids (4.1%), and moisture content (1.6%). Tetrabutyl titanate, sulfate acid, nitric acid, silica, iso-propanol and methanol used for catalyst preparation and biodiesel production were of analytical reagent (AR) grade and were purchased from Sinopharm Co., respectively. B. Catalyst preparation

La2O3 (1.14 g) was slowly added into sulfuric acid of 1.84 mol/l (200 ml) with vigorous stirring in order to obtain aqueous solution of La2 (SO4)3. Then the solution was dropwise added into a stirred solution of tetrabutyl titanate (100 ml) in iso-propanol (50 ml), followed by adding dropwise a solution of iso-propanol (100 ml) in deionized water (30 ml). The gel obtained after filtration was infrared dried and then activated in a muffle furnace at 550 C for 4 h to obtain SO42/TiO2/La3þ (STL). For comparison, the solid acid catalysts (SO42/TiO2 and SO42/TiO2-SiO2) were synthesized via sol-gel method, adapted from works reported by Almeida et al. and Peng et al., respectively.19,21 Briefly, into a stirred solution of tetrabutyl titanate in iso-propanol, HNO3 70% (v/v) was added, followed by dropwise addition of concentrated H2SO4. Then, a solution of iso-propanol in deionized water was dropwise added to the former solution. A gel was formed and allowed


052001-3

Wang et al.


to settle for 1.5 h. The solvent was evaporated and the gel was dried at 90 C for 4 h. SO42/ TiO2 (ST) was obtained after calcination at 300 C for 4 h. SiO2 powder was slowly added to 0.5 mol/l tetrabutyl titanate solution of iso-propanol, and was agitated under reflux for 4 h. After filtering and drying at 100 C for 2 h, the powder was calcined at 450 C for 4 h. The resulting TiO2-SiO2 particles were soaked in a 0.5 mol/l H2SO4 solution for 24 h, followed by filtering and drying. SO42/TiO2-SiO2 (STS) was finally obtained by calcining at 500 C for 4 h. C. Experimental procedure

Experiments were carried out using the prepared solid acid catalysts in a 250 ml laboratory-scale closed autoclave with constant stirring at 900 rpm. The endpoint of reaction was confirmed by the acid value titration method. The solid acid catalyst was mixed with waste oil and methanol, and then the mixtures were charged into the reactor. The autoclave was closed, followed by setting temperature and the rotating rate on the control board. The displayed pressure of autoclave increased due to the gasification of methanol and air expansion on heating the autoclave. When the set temperature was reached, it was timed under pressure (lower than 1.0 MPa). The products were withdrawn after stopping agitation and cooling the materials to room temperature. The solid catalyst was separated by filtration and the filtrate was transferred to a separatory funnel. The lower phase was separated and then distilled to recycle methanol. The upper phase was dried with sodium sulfate to obtain crude products. The crude products were purified by molecular distillation to get final products. D. Catalyst characterization

The Brunauer, Emmett, and Teller (BET) specific surface area of the catalyst was measured using a BET surface analyzer (Micromeritics ASAP2020M). NH3-TPD (Temperature Programmed Desorption) spectra were recorded using a temperature programmed desorption instrument (Micromeritics Auto chem. 2920) to characterize the acid site adsorption distribution for each solid acid catalyst. The catalyst was pretreated at 600 C for 1 h under a He flow, cooled to 100 C, followed by adsorption of NH3, and then treated under a He flow for 0.5 h, at last heated to 600 C at 10 C/min. E. FAMEs analysis

The products were analyzed by GC-MS (Agilent 7890/5975). The conditions of GC-MS were the following: HP-5 capillary column (30 m 0.25 mm 0.25 lm); diffluent ratio 50:1; carrier gas He; feed temperature 280 C; temperature programmed from 50 C to 280 C at 5 C/min, the temperature of 280 C was kept constant for 10 min, EI ionic source 230 C, interface temperature 280 C. The target compounds were identified by mass spectrometry in SCAN mode. Spectra of the compounds was obtained and compared with those in library. III. RESULTS AND DISCUSSIONS A. Catalyst activity

The catalytic activities of the prepared solid acid catalysts were evaluated for the esterification of waste oil with methanol under the same reaction conditions, such as a reaction temperature of 110 C, alcohol to oil molar ratio of 10:1, and catalyst amounts 5 wt. % of oil. Table I shows the FFA conversion obtained under the conditions. The results suggest that the STL catalyst was the most active, exhibiting 92.3% FFA conversion. The addition of SiO2 and lanthanum both showed well performance in the enhancement of catalytic surface area. On the other hand, the increase in catalytic acid site density when the STL catalyst was employed could be justified as the illustration in Fig. 1. The introduction of La3þ in STL was believed to be responsible for the withdrawal of electrons from the framework hydroxyl and Ti-O groups, thus making the protons and titanium ion more acidic.


052001-4

Wang et al.


TABLE I. Catalyst activity and physical properties of catalyst. Catalyst

STa

STSb

STLc

Acid site density (lmol/g)

0.67

0.69

0.85

Surface area (m2/g) FFA conversion (%)

195 73.3

233 80.1

229 92.3

ST—SO42/TiO2. STS—SO42/TiO2-SiO2. c STL—SO42/TiO2/La3þ. a

b

B. Effect of reaction temperature

The synthesis of biodiesel from waste oil with methanol was carried out over the prepared catalysts of ST, STS, and STL. The yield of FAMEs from waste oil after 1 h of time on stream at 90–170 C are shown as a function of temperature in Fig. 2. The figure shows that the STL catalyst is quite effective for the reaction, the yield of FAMEs being more than 90% at temperature 110 C. Comparatively speaking, the yields of FAMEs were more than 90% at temperature 150 C when using ST and STS as catalyst, respectively. C. Effect of reaction time

Reaction time effects on the FAMEs yield over the solid acid catalysts at 110 C were shown in Fig. 3. At the first 1 h, the conversion takes place at a faster rate and the yield increases significantly due to the high concentration of reactants and small amount of products at first. As can be seen from Fig. 3, the STL catalyst shows better performance than ST and STS, and the yield of FAMEs could be more than 90% for only 1 h reaction time, extending the reaction further is of little use in improving the yield. Thus, 1 h was selected as the optimum reaction time for STL. In comparison with STL, the reaction should take 2 h to reach the equilibrium point when using ST and STS as catalyst, respectively. D. Effect of molar ratio of methanol to oil

With the catalyst amount of 5 wt. %, temperature 110 C, and reaction 1 h, the effects of methanol to oil ratio over the prepared catalysts were shown in Fig. 4. Normally, methanol is used in excess to push the reaction forward for formation of FAMEs. A higher methanol to oil ratio is beneficial to attain a higher conversion, however, using a lower methanol to oil ratio is preferred to minimize the cost for separation and recycling of the unreacted methanol. Fig. 4

FIG. 1. The framework structure of STL.


052001-5

Wang et al.


FIG. 2. FAMEs yield (%) at the different reaction temperature over catalysts. Reaction conditions: methanol to oil ratio 10:1, reaction time 1 h, catalyst amounts 5 wt. % of oil.

shows the effect of methanol to oil ratio on the yield of FAMEs using ST, STS, and STL as catalysts. From the figure, the yield of FAMEs catalyzed by STL increased abruptly from 60.5% to 92.5% as the methanol to oil ratio increased from 4 to 12. The maximum yield obtained by STL was 92.5% at ratio 10 whereas for ST and STS were 83.5% and 81.8% at 12, respectively.

E. Effect of catalyst loading

Fig. 5 shows the effect of catalyst amount on the yield of FAMEs. The value of catalyst amounts was varied from 0.5 to 10 wt. % (based on weight of waste oil). It can be observed

FIG. 3. FAMEs yield (%) at the different reaction time over catalysts. Reaction conditions: methanol to oil ratio 10:1, reaction temperature 110 C, catalyst amounts 5 wt. % of oil.


052001-6

Wang et al.


FIG. 4. FAMEs yield (%) with various methanol to oil ratios over catalysts. Reaction conditions: reaction temperature 110 C, reaction time 1 h, catalyst amounts 5 wt. % of oil.

from the figure that the yield increases accordingly with catalyst amount increasing until a value in which higher increment no longer increased the yield. Trace enhancement in yield is detected if the STL catalyst amount exceeds 5%. According to ST and STS, the optimum value is 5% and 8%, respectively. F. Catalyst stability

Considering the economic and environmental friendly characteristics, the stability of prepared catalysts was studied. The recycled catalysts were washed with alcohol and then dried

FIG. 5. FAMEs yield (%) with various catalyst amounts over catalyst. Reaction conditions: methanol to oil ratio10:1, reaction temperature110 C, reaction time1 h.


052001-7

Wang et al.


TABLE II. FAMEs yield (%) with various catalyst reused times over catalysts. The reaction conditions were methanol to oil ratio10:1, reaction temperature 110 C, reaction time 1 h, catalyst amounts 5 wt. % of oil. RT1a

Catalyst

RT2b

RT3c

RT4d

RT5e

SO42/TiO2 (ST)

73.3

57.1

39.5

trace

Trace

SO42/TiO2-SiO2 (STS)

80.1

78.6

75.0

70.8

61.6

SO42/TiO2/La3þ (STL)

92.3

92.1

91. 7

91.1

90.2

a

RT1—The catalyst reused one time. RT2—The catalyst reused two times. c RT3—The catalyst reused three times. d RT4—The catalyst reused four times. e RT5—The catalyst reused five times. b

under infrared, followed by activation in a muffle furnace at 550 C for 2 h, the data of reusability of the catalysts were presented in Table II. It shows that STL can be reused for 5 times when the yield of FAMEs is still as high as 90 wt. %. However, obviously decrease of the catalytic performance was observed when using ST and STS as catalysts. The experiment results indicated that STL is a stable catalyst for biodiesel production from waste oil and suitable for long-term use. G. Analysis of product

The composition of biodiesel produced from waste oil under the optimized conditions was analyzed by GC-MS. The total ion chromatography (TIC) is shown in Fig. 6. Based on the library, the corresponding component of each peak is listed in Table III according to the analysis of retention time. The total content of FAMEs obtained from Table III through area normalization method was 96.16 wt. %.

FIG. 6. TIC of compositions of FAMEs measured by GC-MS.


052001-8

Wang et al.


TABLE III. Analysis of compositions of FAMEs. Retention time (min)

Compounds

Content (%)

1

24.096

Dodecanoic acid methyl ester

C13H26O2

1.16

2 3

28.309 32.818

Pentadec acid methyl ester Hexadecanoic acid methyl ester

C15H30O2 C17H34O2

1.43 10.06

4

36.057

9,12-Octadecadienoic acid methyl ester

C19H34O2

26.90

5 6

36.307 36.511

8-Octadecenoic acid methyl ester 9-Octadecenoic acid methyl ester

C19H36O2 C19H36O2

31.52 9.31

7

36.776

Octadecanoic acid methyl ester

C19H38O2

6.51

8 9

37.852 43.284

9,11-Octadecadienoic acid methyl ester 13-Docosenoic acid methyl ester

C19H34O2 C23H44O2

3.26 2.56

10

43.678

Docosanoic acid methyl ester

C23H46O2

2.06

11

46.794

Tetracosanoic acid methyl ester

C25H50O2

1.31

IV. CONCLUSIONS

It was demonstrated that SO42/TiO2/La3þ was an efficient catalyst for the synthesis of biodiesel from waste oil under low pressure in this study. The optimum reaction conditions were catalyst to oil amount of 5 wt. %, temperature of 110 C, and reaction time of 1.0 h, for which a maximum ester yield of more than 90 wt. % could be obtained. The solid superacid catalysts showed high activity and could be reused five times after simple treatment with no significant lose of activity. The FAMEs content of final products purified by molecular distillation was 96.16 wt. %. The strategy of using SO42/TiO2/La3þ as catalyst would be feasible for application of biodiesel industry. ACKNOWLEDGMENTS

The authors acknowledge National Key Technology R&D Program of China (No. 2011BAD22B05) for their financial support in this study. 1

J. S. Lee and S. Saka, Bioresour. Technol. 101, 7191–7200 (2010). E. Santacesaria, G. M. Vicente, M. D. Serio, and R. Tesser, Catal. Today 195(1), 2–13 (2012). M. K. Lam, K. T. Lee, and A. R. Mohamed, Biotechnol. Adv. 28, 500–518 (2010). 4 A. Islam, Y. H. T. Yap, C. M. Chu, E. S. Chan, and P. Ravindra, Process Saf. Environ. Prot. 91(1), 131–144 (2013). 5 I. M. Atadashi, M. K. Aroua, A. R. A. Aziz, and N. M. N. Sulaiman, Renewable Sustainable Energy Rev. 16, 3456–3470 (2012). 6 I. M. Atadashi, M. K. Aroua, A. R. A. Aziz, and N. M. N. Sulaiman, Renewable Sustainable Energy Rev. 16, 3275–3285 (2012). 7 A. K. Endalew, Y. Kiros, and R. M. Zanzi, Biomass Bioenergy 35, 3787–3809 (2011). 8 S. Semwal, A. K. Arora, R. P. Badoni, and D. K. Tuli, Bioresour. Technol. 102, 2151–2161 (2011). 9 M. Zabeti, W. M. A. W. Daud, and M. K. Aroua, Fuel Process. Technol. 90, 770–777 (2009). 10 M. E. Borges and L. Diaz, Renewable Sustainable Energy Rev. 16, 2839–2849 (2012). 11 W. Y. Lou, M. H. Zong, and Z. Q. Duan, Bioresour. Technol. 99, 8752–8758 (2008). 12 K. V. Thiruvengadaravi, J. Nandagopal, P. Baskaralingam, V. S. S. Bala, and S. Sivanesan, Fuel 98, 1–4 (2012). 13 Y. M. Park, S. H. Chung, H. J. Eom, J. S. Lee, and K. Y. Lee, Bioresour. Technol. 101, 6589–6593 (2010). 14 W. N. N. W. Omar and N. A. S. Amin, Fuel Process. Technol. 92, 2397–2405 (2011). 15 K. F. Yee, J. C. S. Wu, and K. T. Lee, Biomass Bioenergy 35, 1739–1746 (2011). 16 M. Kim, C. D. Maggio, S. O. Salley, and K. Y. S. Ng, Bioresour. Technol. 118, 37–42 (2012). 17 S. Furuta, H. Matsuhashi, and K. Arata, Catal. Commun. 5, 721–723 (2004). 18 S. Furuta, H. Matsuhashi, and K. Arata, Biomass Biotechnol. 30, 870–873 (2006). 19 R. M. Almeida, L. K. Noda, N. S. Goncalves, S. M. P. Meneghetti, and M. R. Meneghetti, Appl. Catal., A 347, 100–105 (2008). 20 H. Chen, B. X. Peng, D. Z. Wang, and J. F. Wang, Front. Chem. Eng. China 1(1), 11–15 (2007). 21 B. X. Peng, Q. Shu, J. F. Wang, G. R. Wang, D. Z. Wang, and M. H. Han, Process Saf. Environ. Prot. 86, 441–447 (2008). 22 M. K. Lam, K. T. Lee, and A. R. Mohamed, Appl. Catal., B 93, 134–139 (2009). 23 A. Sarkar, S. Ghosh, and P. Pramanik, J. Mol. Catal. A: Chem. 327, 73–79(2010). 24 M. K. Lam and K. T. Lee, Fuel Process. Technol. 92, 1639–1645 (2011). 2 3
