Biodiesel production from waste cooking oil catalyzed ...

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Energy 158 (2018) 881e889

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Biodiesel production from waste cooking oil catalyzed by in-situ decorated TiO2 on reduced graphene oxide nanocomposite Manash Jyoti Borah a, *, Anuchaya Devi a, Raktim Abha Saikia b, Dhanapati Deka a a b

Biomass Conversion Laboratory, Department of Energy, Assam 784028, India Department of Chemical Sciences, Tezpur University, Assam 784028, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 18 October 2017 Received in revised form 6 June 2018 Accepted 12 June 2018 Available online 15 June 2018

Current research reports the synthesis of in-situ TiO2/RGO nanocomposite and used as a heterogeneous catalyst for the transesterification of waste cooking oil into biodiesel. The prepared catalyst was characterized viz. X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Transmission Electron Microscopy (TEM), Thermogravimetric analysis (TGA) techniques conforming the successful formation of nanocomposite. The effects of various reaction parameters used for transesterification were examined to optimize the reaction conditions. The best operational conditions were oil to methanol molar ratio of 1:12 at 65  C with 1.5 wt% catalyst loading and reaction time of 3 h. The catalyst showed good catalytic activity in biodiesel production and biodiesel conversion of 98% was obtained under optimum reaction conditions. Biodiesel conversion was confirmed by Proton Nuclear Magnetic Resonance (1H NMR), Carbon Nuclear Magnetic Resonance (13C NMR) and Gas Chromatography-Mass Spectroscopy (GC-MS) techniques. The excellent catalytic activity of TiO2/RGO could be attributed to the enhanced surface area of the composite. © 2018 Elsevier Ltd. All rights reserved.

Keywords: Biodiesel Nanocomposite Heterogeneous catalyst Transesterification

1. Introduction The current energy policies worldwide have focused on the development of sustainable renewable energy to reduce the level of greenhouse gas emissions due to fossil fuel burning. Moreover, the scarcity of petroleum reserves as well as the increasing oil costs also has created need for searching alternative clean environmentally benign fuel [1]. In the recent years, biodiesel has drawn attraction as a renewable and sustainable energy source with negligible emissions of pollutants as it is non-toxic and obtained from renewable precursors. The physical and chemical properties of biodiesel are similar and sometimes better than petroleum diesel such as high flash point, low sulphur concentration, superior lubricity and low pollutants produced [2,3]. Biodiesel is produced conventionally by transesterification of triglycerides such as animal fats and vegetable oil with short chain alcohols generally methanol and ethanol in presence of a catalyst [4,5]. The main drawbacks associated with the commercialization of biodiesel are the nonavailability of suitable feedstock. The use of edible oil feedstock

* Corresponding author. E-mail address: [email protected] (M.J. Borah). https://doi.org/10.1016/j.energy.2018.06.079 0360-5442/© 2018 Elsevier Ltd. All rights reserved.

not only generates food versus fuel conflict but also increases the total cost of biodiesel production [6]. This problem can be overcome by employing low quality non-edible feedstock as it is of low cost and have the potential of reducing the overall biodiesel production cost [7]. Hence, the selection of feedstock and catalyst should be based on technical and economic aspects for cost effective biodiesel production. The use of homogeneous catalyst produces high yield of biodiesel at mild temperature and shorter reaction time; but have some shortcomings related with catalyst separation, reusability and generation of excess waste water during the process [8]. To solve the limitations associated with homogeneous catalyst, the use of heterogeneous catalyst is preferred because it eliminates the cost associated with purification and separation and hence can be applied for commercial production [9e11]. Wide ranges of heterogeneous catalyst such as MgO loaded with KOH [12], MgeZn mixed metal oxide [13], Copper vanadium phosphate [14], sulfated zirconia [15], heteropolyacids [16], CaO, PbO, PbO2 and ZnO [17], Li incorporated CaO [18], ZnOe La2O3 [19] and hydrotalcites catalyst [20e22] have been developed and introduced in biodiesel production. Among the heterogeneous catalysts, CaO was found to have great potential for biodiesel production due to higher basicity, low price, close to environmental material and can be derived from

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renewable sources [23e25]. However, the activity of heterogeneous catalyst is lower as compared to homogeneous catalyst. Thus, the focus is to develop novel improved catalysts that can overcome the shortcomings associated with both homogeneous and heterogeneous catalysts. Nowadays, the use of nanoparticles as catalyst in transesterification process has gained a wide attention owing to its high surface to volume ratio of the nanomaterials. Nanocatalyst with high surface area and lower particle size are capable of accelerating the reaction rate due to increased number of molecules having the minimum required energy for reaction to occur [26,27]. Researchers have reported various nanocatalysts that have been utilized extensively for biodiesel production from different feedstocks. Moreover, the nanocatalyst can be reused for several reaction cycles [28e30]. Various reviews highlighted the application of graphene based materials in catalysis, but no attention has been paid in the area of biomass catalysis. Among different materials that can be used to prepare composite with TiO2, carbon based materials provides distinctive advantages, such as stability and chemical inertness both in acid and basic media along with tunable textural and chemical properties [31e33]. Graphene with 2D planar structure exhibit many extraordinary properties such as high chemical stability, notably high specific surface area, excellent mobility of charge carriers and good optical transparency [34,35]. Moreover, graphene, with a good interfacial interaction with the metal oxide facilitates charge transfer through the interface, resulting in synergistic effect which enhances the catalytic activity of the composite [36]. Additionally, the in-situ preparation of the composite makes it more stable system [37]. Hence, TiO2 coupled with graphene may provide the catalyst with additional characteristics which promises to make them a multifunctional hybrid class of materials for future applications including transesterification. Herein, we reported the in-situ preparation of TiO2/RGO nanocomposite and used it as a heterogeneous catalyst in the transesterification of waste cooking oil. The catalyst was prepared via hydrothermal method and analyzed using XRD, FT-IR, SEM, EDX, TEM and TGA techniques. The obtained biodiesel have been characterized using 1H NMR, 13C NMR and GC-MS techniques. Several reaction parameters, such as effect of catalyst loading, methanol/oil molar ratio, reaction temperature and reaction time were also examined. Moreover, the catalyst was successfully recycled for 3 times for biodiesel production. 2. Material and methods 2.1. Materials Natural graphite flakes, Titanium iso-propoxide [Ti{OCH(CH3)2}4] were purchased from Sigma-Aldrich. Potassium Permanganate [KMnO4], Sulphuric acid [H2SO4], Hydrogen Peroxide [H2O2], Hydrochloric acid [HCl] and Nitric acid [HNO3] were purchased from Merck (India) Ltd. All the reagents are of analytical grade and used without any further purification and doubled- distilled water was used throughout the experiments.

Table 1 Properties of waste cooking oil. Properties

Raw WCO

Pretreated WCO

Acid Value (mg KOH/g) Viscosity at 40 C (mm2/s) Density at 25  C (Kg/m3) Iodine Value (g/100 g)

18 46 e 148

1.23 31.95 916 132

35% H2O2 was added dropwise till the colour of the solution turned to bright yellow. Then 5% HCl solution was added to reduce the residual manganese ions. The product was washed several times with deionized water until the pH of solution becomes neutral to remove residual salts and acids. The resulting sample was vaccum dried at room temperature to get GO powder. The TiO2/RGO composite was prepared via hydrothermal method based on earlier reported method with slight modification [40]. In the synthesis process, two solutions namely A and B were prepared initially. Solution A was prepared by dissolving 100 mg of GO in 50 ml of deionized water. Solution B was prepared by mixing 2 ml of Titanium iso-propoxide with 20 ml of 2-propanol. Finally, both solution A and B were sonicated separately for 30 min and thereafter mixed and further sonicated for 15 min. Then, few drops of ammonia were added dropwise under constant stirring till the pH of the solution adjusted to 10. After that, the suspension was transferred into a 100 ml Teflon-lined sealed autoclave and maintained at 180  C for 8 h at a ramping rate of 4  C/min. The autoclave was allowed to cool to room temperature and the resulting product was then washed several times, and dried at 80  C under vacuum condition for 12 h. Finally, the product obtained was calcined at 450  C for 2 h. 2.3. Catalyst characterization The crystallinity and phase structure of the synthesized sample were analyzed using X-ray diffractometer (Rigaku Miniflex, Japan) using CuKa radiation at 30 KV in the 2Ɵ range of 10e70 . The presence of different functional groups in the prepared catalyst was determined using FT-IR spectrometer (Nicolet Impact 410, USA). The surface morphology and elemental analysis of the prepared composite were studied by Scanning Electron Microscope (SEM; JEOL, JSM-46390LV) in connection with Energy dispersive X-ray (EDX) spectroscopy. Transmission Electron Microscopy (TEM) images were obtained (Jeol, JSM-2100, 20 KV) for determining the structural and morphological characteristics of the prepared catalyst. The thermal stability of the synthesized catalyst was examined by thermogravimetric analysis (Model TGA-50 & DSC-60, Shimadzu) from room temperature to 600  C under N2 flow and at a ramping rate of 10  C min1. The 1H NMR and 13C NMR spectra were recorded on JEOL, ECS-400 spectrometer. The GCeMS analysis was performed in Agilent GC, 240 Ion Trap. The method of separation for FAME components in the biodiesel and oven temperature was optimized based on earlier reported literature [41].

2.2. Catalyst preparation 2.4. Feedstock treatment Graphene oxide (GO) was prepared by modified Hummers method [38,39]. In this method, 2 g of graphite flakes were mixed with 46 ml concentrated H2SO4 in a round bottomed flask. To that, 6 g of KMnO4 was added slowly within a time span of 30 min and kept stirring for 2 h for homogeneous mixing. The temperature of the reaction mixture was maintained below 20  C (using ice bath). The reaction system was then transferred to an oil bath at 35  C under constant stirring for 12 h. Thereafter, 92 ml deionized water was added to it under constant stirring for another 1 h. After that,

The collected waste cooking oil was initially filtered to remove all the impurities followed by heating at 110  C for 30 min to remove the moisture. The acid value of the collected oil was analyzed and found to be quite high i.e, 18 mg KOH/g; hence direct transesterification cannot be performed to produce biodiesel. Therefore, an acid esterification was performed with conc. H2SO4 as catalyst to reduce its acid value. The acid value of waste cooking oil after pretreatment was found to be reduced to 1.23 mg KOH/g. The

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characteristics of waste cooking oil before and after pretreatment are represented in Table 1.

2.5. Reaction procedure The transesterification of waste cooking oil was performed in a 500 ml three necked round bottom flask with a reflux condenser and a magnetic stirrer. Initially, the catalyst was dispersed in methanol with magnetic stirring (at 600 rpm) followed by addition of above pretreated waste cooking oil. The reaction mixture was then refluxed at different temperature for different time period. After completion of reaction, excess methanol was evaporated using rotary evaporator and catalyst was separated by high speed centrifugation. After removal of glycerol layer, the biodiesel was collected and ready for analysis. The biodiesel conversion was identified by 1H NMR technique and oil conversions, as methyl ester content, CMester (%) was calculated by comparing the area of methoxy protons of the methyl ester (at 3.6 ppm) and a-methylene protons (at 2.3 ppm) using CDCl3 as solvent (eq. (1)) [42]

CMEster ð%Þ ¼ 100  ð2AME Þ=ð3ACH2 Þ

(1)

AME ¼ integral of methoxy protons of methyl ester peak at 3.6 ppm. ACH2 ¼ integral of a-methylene peak at 2.3 ppm.

2.6. Reaction mechanism Transesterification of triglycerides can be easily driven by both acid and base catalyzed pathways [43e45]. The reaction mechanism of triglyceride to methyl ester over TiO2/RGO nanocomposite is shown in Fig. 1. Prevailing the Lewis acidic character in Ti atoms of TiO2 nanoparticles [46], the oxygen atoms of triglycerides are prone to attach with the Ti atoms and enhances the electrophilicity on the carbonyl sites. This helps the methanol to attack at the carbonyl sites and forms tetrahedral intermediate. After the simultaneous proton shift and the triglycerides cleaves into one mole methyl ester and diglyceride. Similarly, further addition of methanol to the TiO2-activated carbonyl sites step-by-step, leads to one mole of glycerol and another two different methyl esters.

Fig. 2. XRD pattern of GO, TiO2 and TiO2/RGO.

3. Results and discussion 3.1. Characterization of TiO2/RGO composite The XRD pattern of GO, TiO2 and TiO2/RGO nanocomposite is shown in Fig. 2. The XRD pattern of GO displays a characteristics peak at ~10.89 corresponding to (002) reflection of GO, suggesting that major portion of the graphite powder was oxidized to form GO [47]. The diffraction peaks of TiO2 at 2Ɵ ¼ 25.27, 37.9 , 48.12 , 54.87, 62.73 and 68.91 are related to (101), (004), (200), (105), (211), (204), and (116) plane of anatase TiO2 (JCPDS No. 21-1272). The peak at 25.8 , corresponding to (002) plane confirms the reduction of GO to RGO. The spectrum of RGO is shown in ESI (Fig.S1). Furthermore, the XRD pattern of TiO2/RGO nanocomposite has similar diffraction peaks corresponding to that of anatase TiO2, indicating that RGO peak was overlapped by main (101) peak of TiO2 because of the presence of small amount of graphene. The average crystallite size was calculated using Scherrer's formula [48] and found to be 20.3 nm for TiO2 and 17.8 nm in case of TiO2/RGO composite. It is noticed that (101) plane of TiO2/RGO is broader as compared to anatase TiO2 indicating that large number of defects were introduced in the crystal structure of TiO2 during the interaction with RGO, hence distorting the crystal structure of TiO2 [49]. Moreover, the TEM result indicates that RGO affects the crystal structure of TiO2 nanoparticles. The FT-IR spectra of TiO2 and TiO2/RGO sample are shown in Fig. 3. The absorption band around 3400 cm1 was assigned to the

Fig. 1. Reaction mechanism of triglyceride to methyl ester over TiO2/RGO nanocomposite.

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Fig. 3. FT-IR spectra of TiO2 and TiO2/RGO.

OeH stretching vibration of the hydroxyl groups on the surface of TiO2 [50]. The peak that appeared around 670 cm1 was due to the presence of TieOeTi bond [51]. The peak around 1630 cm1 originates from the presence of hydroxyl group of molecular water [52]. The appearance of peak at ~2300 cm1 can be ascribed to CO2 molecules in the atmosphere [50]. In the TiO2/RGO spectra the peak at 765 cm1 may be assigned to the presence of TieOeC bonds, indicating the formation of a strong chemical interaction between graphene and TiO2 nanoparticles during hydrothermal reaction [53]. From the spectra of TiO2/RGO composite the appearance of peak at 1569 cm1 is the indication for skeletal vibration of graphene sheets [54]. The characteristics peaks of GO at 1052 cm1 (CeO stretching vibration), 1720 cm1 (CeOH stretching vibration) and 1220 cm1(CeO stretching) respectively were not observed in the spectra, indicating that most of the oxygen containing functional groups were decomposed and successful reduction of GO in TiO2/RGO composite occurs [55]. The SEM image of the as prepared samples is shown in Fig. 4(A). It is observed that TiO2 nanoparticles were dispersed and grafted on the surface of the RGO sheets through TieOeC bonding between TiO2 and RGO during hydrothermal synthesis. The SEM image also exhibits the homogeneity of the composite in a large scale. Agglomerations of TiO2 particles could also be seen at some places. The layer of the RGO sheets also have strong affinity to agglomerate occurring due to van der Waals interaction but was prevented by

TiO2 particles deposited on RGO sheets [53,56]. Energy dispersive X-ray (EDX) analysis shows the elemental composition of the composite and confirms the presence of only Ti, O and C as shown in Fig. 4(B). The composition shows 39.06% of Ti, 34.25% of O and 26.59% of C in the composite. The structural and morphological features of the as synthesized GO and TiO2/RGO examined by TEM is depicted in Fig. 5(A, B & C). From the TEM image of exfoliated GO sheets as shown in Fig. 5(A) the presence of wrinkles and folds on the sheet could be noticed which were entangled with each other. In case of TiO2/RGO composite the uniform dispersion and coupling of spherical anatase TiO2 nanoparticles on the RGO sheets could be observed, indicating that TiO2 nanoparticles and RGO sheets are strongly chemically bonded. This strong chemical interaction between TiO2 nanoparticles and RGO sheets is important for achieving good catalytic activity. The average particle size of the TiO2 nanoparticles was found to be in the range of 25e30 nm. The TEM image also reveals the crystal lattice spacing of 0.352 nm in TiO2/RGO composite, and is related to the characteristic of (101) plane of perfect anatase TiO2. The thermal stability of the prepared catalyst was analyzed using TGA technique and is shown in Fig. 6. The TGA curve of TiO2 shows a weight loss of almost 1.5% up to 100  C while the curve of TiO2/RGO shows 1% weight loss up to 100  C. In both the case the loss is due to decomposition of surface adsorbed water. Beyond that, a weight loss of 5.5% was observed up to 550  C which could be due to the oxidation of RGO [57]. Above this temperature, the composite shows minor weight loss and is relatively stable. 3.2. Optimization of reaction parameters 3.2.1. Effect of catalyst loading Transesterification reaction was performed by varying the amount of catalyst concentration from 0.5 to 2.5 wt% (with respect to molecular weight of oil used) and oil to methanol molar ratio of 1:12 (Fig. 7). The reaction was carried out at 65  C for 3 h. At low catalyst concentration of 0.5 wt% biodiesel conversion of 64.22% was achieved, which increased gradually and attained a maximum of 98% with 1.5 wt% catalyst loading. The high conversion achieved with increasing catalyst concentration up to 1.5 wt% may be due to the presence of large number of highly active sites which favors the transesterification reaction. Further increase in catalyst loading beyond 1.5 wt% decreases the conversion due to the increased viscosity of the reaction

Fig. 4. SEM (A) and EDX (B) images of TiO2/RGO.

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Fig. 5. TEM image of (A) GO and (B & C) TiO2/RGO.

Fig. 6. TGA curve of TiO2 and TiO2/RGO.

mixture which resists the mass transfer of oil-methanol-catalyst system [58]. Hence 1.5 wt% catalyst concentration have been chosen for further optimization of reaction parameters. 3.2.2. Effect of oil to methanol ratio The optimal oil to methanol molar ratio was determined by varying the ratio of oil to methanol from 1:6 to 1:15 (Fig. 8). It is clear from the results that when molar ratio of oil to methanol was increased from 1:6 to 1:12 biodiesel conversion increases from 57.54% to 98%. Thus 1:12 oil to methanol ratio was sufficient to complete the reaction. Beyond, 1:12, no change in biodiesel conversion was observed which may be due to dissolution of glycerol by product in excess methanol that inhibits the reaction of methanol with catalyst and oil phase [23]. Thus the optimal oil to methanol ratio chosen for further study is 1:12. 3.2.3. Effect of reaction temperature The reaction temperature was optimized by carrying out

Fig. 7. Effect of catalyst concentration.

transesterification reaction in the temperature range of 45e75  C at constant oil to methanol molar ratio of 1:9 and catalyst concentration of 1.5 wt% for 3 h (Fig. 9). From the experiments, a steady increase in conversion was noticed with increasing reaction temperature up to 65  C beyond which the conversion starts decreasing. The decrease in conversion beyond 65  C was due to the methanol vaporization and formation of bubbles that slows down reaction on the three phase interface [45,59]. 3.2.4. Effect of reaction time To study the effect of reaction time on biodiesel conversion the reaction was carried out using optimum catalyst amount of 1.5 wt% and oil to methanol ratio of 1:12 at 65  C. The reaction was carried out for 4 h and biodiesel conversion was checked at regular interval of 1 h (Fig. 10). The results shows a steady increase in biodiesel conversion attaining a maximum of 97.93% at 3 h of reaction and thereafter the

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Fig. 8. Effect of oil to methanol ratio.

Fig. 11. Effect of catalyst reusability.

reaction attained equilibrium and conversion remain constant. This may be due to enough contact time for sufficient interaction between the reactants and catalyst [60].

Fig. 9. Effect of reaction temperature.

3.2.5. Reusability of the catalyst The reusability test of the prepared catalyst was conducted for 3 consecutive cycles under optimized reaction conditions discussed earlier in our study (Fig. 11). After completion of the reaction the catalyst particles was recovered by filtration followed by washing with methanol. The catalyst was dried in oven at 100  C for 2 h and used for the next cycles following the same reaction parameters. The conversion remains stable for the first two cycles and reaches 78.86% at the end of the 3rd cycle. The decrease in oil conversion may be due to leaching of the catalyst which reduces the active sites of the catalyst [61]. The loss of Ti and C from the catalyst due to leaching was confirmed by EDX analysis. The weight % of Ti & C present in fresh catalyst was 39.06% & 26.59% which get reduced to 37.66% and 20.83% at the end of 3rd cycle. The EDX pattern of the reused catalyst is shown in ESI (Fig.S2). 3.3. Characterization and fuel properties of biodiesel

Fig. 10. Effect of reaction time.

The biodiesel obtained by transesterification of waste cooking oil was confirmed as well as characterized by 1H NMR and 13C NMR techniques. The 1H NMR spectra of biodiesel produced from waste cooking oil is shown in Fig. 12. The formation of fatty acid methyl ester is confirmed by appearance of single peak at 3.6 ppm and multiplet peaks around ~2.3 ppm which is attributed to methoxy protons. As can be seen from figure the triplet that appears around 0.8 ppm is due to terminal methyl protons, peak around 1.2 ppm is attributed to methylene protons of carbon chain and multiplet at 1.6 ppm is assigned to b carbonyl methylene protons. The signal that appears at 5.3 ppm is ascribed to olefinic hydrogen [62e64]. The 13C NMR spectrum of biodiesel obtained is depicted in Fig. 13. The spectra shows the characteristic peak of ester carbonyl (eCOOe) and (eOCH3) at 174 ppm and 51.29 ppm respectively. The presence of unsaturated fatty acid in 13C NMR spectra of biodiesel is confirmed by presence of peaks around 130, 128 and 129 ppm. The appearance of peak around 22e34 ppm is related to eCH2eCH2 group of FAME and the signal at ~14 ppm arises due to CH3 group of methyl ester formed [62,65,66]. The conversion of oil to biodiesel has been further analyzed using GC-MS technique. Table 2 shows the composition of fatty acid

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Fig. 12. 1H NMR spectra of biodiesel.

Fig. 13.

13

C NMR spectra of biodiesel.

methyl ester identified in the biodiesel sample. The sample consisted of saturated as well as unsaturated fatty acid methyl esters. The GC-MS chromatograph is shown in ESI (Fig. S3). The various fuel properties of the prepared biodiesel were determined according to the standard methods of American Society

for Testing and Materials (ASTM) and the results are presented in Table 3. It is seen that the biodiesel produced has the fuel properties within the limits of ASTM D6751 standards.

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Table 2 Fatty acid methyl ester composition of waste cooking oil methyl ester. Retention Time

Name of the Compound

Total

8.301 11.958 11.997 12.971 13.244 13.334 14.561 15.220 16.192 17.414 18.963

Capric acid methyl ester 9-dodecenoic acid methyl ester Palmitic acid methyl ester 12-Methyltetradecanoic acid methyl ester Linoleic acid, methyl ester Oleic acid methyl ester Stearic acid methyl ester Heptafluorobutyric acid, n-tridecylester 7-hexadecenoic acid, methyl ester, (Z)15-Methylhexadecanoic acid methyl ester 1,2-Benzenedicarboxylic acid, diisooctyl ester

0.11 3.63 3.75 49.46 36.69 3.68 0.82 0.74 0.04 0.08 0.45

[8]

[9] [10]

[11] [12]

[13]

[14]

Table 3 Fuel properties of biodiesel.

[15]

Properties

ASTM D6751

Obtained Values

Acid Value (mg KOH/g) Viscosity at 40  C (mm2/s) Density at 25  C (Kg/m3) Cloud Point (0C) Flash Point (0C) Calorific Value (KJ/g) Pour Point Cetane Number Carbon residue (wt %) Fire Point (oC)

0.5 1.9e6.0 e 3.0 to 12 100e170 33e40 15 to 5 e 0.05 max e

0.18 4.57 870 4.5 138 38.43 3 52 0.027 143

[16]

[17] [18]

[19]

[20]

4. Conclusion TiO2/RGO nanocomposite was prepared via hydrothermal method and used in the transesterification of waste cooking oil for biodiesel synthesis. Under optimum reaction conditions of 65  C, oil to methanol ratio of 1:12, 1.5 wt% catalyst and 3 h of reaction time maximum biodiesel conversion of 98% was achieved. Biodiesel produced was characterized using 1H NMR, 13C NMR and GC-MS techniques and its fuel properties are found to be within the limit of ASTM D6751 standards. Thus, TiO2/RGO nanocomposite is a promising catalyst for transesterification of waste cooking oil to biodiesel, which can also be reused over 3 cycles.

[21]

[22] [23]

[24] [25]

[26] [27]

Acknowledgements

[28]

M. J. Borah thanks Tezpur University for financial support in the form of institutional fellowship to him.

[29]

Appendix A. Supplementary data

[30]

Supplementary data related to this article can be found at https://doi.org/10.1016/j.energy.2018.06.079.

[31]

References

[32]

[1] Demirbas A. Importance of biodiesel as transportation fuel. Energy Pol 2007;35(9):4661e70. [2] Macor A, Pavanello P. Performance and emissions of biodiesel in a boiler for residential heating. Energy 2009;34(12):2025e32. [3] Chen KS, Lin YC, Hsieh LT, Lin LF, Wu CC. Saving energy and reducing pollution by use of emulsified palm-biodiesel blends with bio-solution additive. Energy 2010;35(5):2043e8. [4] Boro J, Deka D. A review on biodiesel. J Biobased Mater Bioenergy 2012;6: 1e17. [5] Yusuf NN, Kamarudin SK, Yaakub Z. Overview on the current trends in biodiesel production. Energy Convers Manag 2011;52(7):2741e51. [6] Gui MM, Lee KT, Bhatia S. Feasibility of edible oil vs. non-edible oil vs. waste edible oil as biodiesel feedstock. Energy 2008;33(11):1646e53. [7] Atabani AE, Mahlia TM, Masjuki HH, Badruddin IA, Yussof HW, Chong WT,

[33]

[34] [35]

[36] [37]

[38]

Lee KT. A comparative evaluation of physical and chemical properties of biodiesel synthesized from edible and non-edible oils and study on the effect of biodiesel blending. Energy 2013;58:296e304. Lam MK, Lee KT, Mohamed AR. Homogeneous, heterogeneous and enzymatic catalysis for transesterification of high free fatty acid oil (waste cooking oil) to biodiesel: a review. Biotechnol Adv 2010;28(4):500e18. Semwal S, Arora AK, Badoni RP, Tuli DK. Biodiesel production using heterogeneous catalysts. Bioresour Technol 2011;102(3):2151e61. Yan S, DiMaggio C, Mohan S, Kim M, Salley SO, Ng KS. Advancements in heterogeneous catalysis for biodiesel synthesis. Top Catal 2010;53(11e12): 721e36. Endalew AK, Kiros Y, Zanzi R. Heterogeneous catalysis for biodiesel production from Jatropha curcas oil (JCO). Energy 2011;36(5):2693e700. Ilgen O, Akin AN. Transesterification of canola oil to biodiesel using MgO loaded with KOH as a heterogeneous catalyst. Energy Fuels 2008;23(4): 1786e9. Lee HV, Taufiq-Yap YH, Hussein MZ, Yunus R. Transesterification of jatropha oil with methanol over MgeZn mixed metal oxide catalysts. Energy 2013;49: 12e8. Chen L, Yin P, Liu X, Yang L, Yu Z, Guo X, Xin X. Biodiesel production over copper vanadium phosphate. Energy 2011;36(1):175e80. Garcia CM, Teixeira S, Marciniuk LL, Schuchardt U. Transesterification of soybean oil catalyzed by sulfated zirconia. Bioresour Technol 2008;99(14): 6608e13. Alsalme A, Kozhevnikova EF, Kozhevnikov IV. Heteropoly acids as catalysts for liquid-phase esterification and transesterification. Appl Catal A Gen 2008;349: 170e6. Singh AK, Fernando SD. Transesterification of soybean oil using heterogeneous catalysts. Energy Fuels 2008;22(3):2067e9. Boro J, Konwar LJ, Deka D. Transesterification of non-edible feedstock with lithium incorporated egg shell derived CaO for biodiesel production. Fuel Process Technol 2014;122:72e8. Yan S, Salley SO, Simon Ng KY. Simultaneous transesterification and esterification of unrefined or waste oils over ZnO- La2O3 catalysts. Appl Catal A Gen 2009;353(2):203e12. Gomes JF, Puna JF, Gonçalves LM, Bordado JC. Study on the use of MgAl hydrotalcites as solid heterogeneous catalysts for biodiesel production. Energy 2011;36(12):6770e8. Gao L, Xu B, Xiao G, Lv J. Transesterification of palm oil with methanol to biodiesel over a KF/hydrotalcite solid catalyst. Energy Fuels 2008;22(5): 3531e5. Dias AP, Bernardo J, Felizardo P, Correia MJ. Biodiesel production over thermal activated cerium modified Mg-Al hydrotalcites. Energy 2012;41(1):344e53. Farooq M, Ramli A, Naeem A. Biodiesel production from low FFA waste cooking oil using heterogeneous catalyst derived from chicken bones. Renew Energy 2015;76:362e8. Xie J, Zheng X, Dong A, Xiao Z, Zhang J. Biont shell catalyst for biodiesel production. Green Chem 2009;11(3):355e64. Buasri A, Rattanapan T, Boonrin C, Wechayan C, Loryuenyong V. Oyster and Pyramidella shells as heterogeneous catalysts for the microwave-assisted biodiesel production from Jatropha curcas oil. J Chem 2015;2015. Deng X, Fang Z, Liu YH, Yu CL. Production of biodiesel from Jatropha oil catalyzed by nanosized solid basic catalyst. Energy 2011;36(2):777e84. Thiele EW. Relation between catalytic activity and size of particle. Ind Eng Chem 1939;31(7):916e20. ANR R, Saleh AA, Islam MS, Hamdan S, Maleque MA. Biodiesel production from crude Jatropha oil using a highly active heterogeneous nanocatalyst by optimizing transesterification reaction parameters. Energy Fuels 2015;30(1): 334e43. Wang H, Covarrubias J, Prock H, Wu X, Wang D, Bossmann SH. Acid-functionalized magnetic nanoparticle as heterogeneous catalysts for biodiesel synthesis. J Phys Chem C 2015;119(46):26020e8. Banerjee M, Dey B, Talukdar J, Kalita MC. Production of biodiesel from sunflower oil using highly catalytic bimetallic goldesilver coreeshell nanoparticle. Energy 2014;69:695e9. Bell NJ, Ng YH, Du A, Coster H, Smith SC, Amal R. Understanding the enhancement in photoelectrochemical properties of photocatalytically prepared TiO2-reduced graphene oxide composite. J Phys Chem C 2011;115(13): 6004e9. Mahmoodi NM. Photocatalytic degradation of dyes using carbon nanotube and titania nanoparticle. Water, Air, Soil Pollut 2013;224(7):1612. Kim HI, Kim S, Kang JK, Choi W. Graphene oxide embedded into TiO2 nanofiber: effective hybrid photocatalyst for solar conversion. J Catal 2014;309: 49e57. Geim AK, Novoselov KS. The rise of graphene. Nat Mater 2007;6(3):183. Akhavan O, Ghaderi E. Photocatalytic reduction of graphene oxide nanosheets on TiO2 thin film for photoinactivation of bacteria in solar light irradiation. J Phys Chem C 2009;113(47):20214e20. Zhang H, Lv X, Li Y, Wang Y, Li J. P25-graphene composite as a high performance photocatalyst. ACS Nano 2009;4(1):380e6. Sharma A, Lee BK. Rapid photo-degradation of 2-chlorophenol under visible light irradiation using cobalt oxide-loaded TiO2/reduced graphene oxide nanocomposite from aqueous media. J Environ Manag 2016;165. 1e0. Srivastava M, Das AK, Khanra P, Uddin ME, Kim NH, Lee JH. Characterization of in situ grown ceria nanoparticles on reduced graphene oxide as a catalyst for

M.J. Borah et al. / Energy 158 (2018) 881e889 the electro oxidation of hydrazine. J Mater Chem A 2013;1(34):9792e801. [39] Humers WS, Offeman RE. Preparation of graphitic oxide. J Am Chem Soc 1958;80(6):1339. [40] Shen J, Shi M, Yan B, Ma H, Li N, Ye M. Ionic liquid-assisted one-step hydrothermal synthesis of TiO2-reduced graphene oxide composites. Nano Res 2011;4(8):795. [41] Flood ME, Connolly MP, Comiskey MC, Hupp AM. Evaluation of single and multi-feedstock biodieselediesel blends using GCMS and chemometric methods. Fuel 2016;186:58e67. [42] Gelbard G, Bres O, Vargas RM, Vielfaure F, Schuchardt UF. 1H nuclear magnetic resonance determination of the yield of the transesterification of rapeseed oil with methanol. J Am Oil Chem Soc 1995;72(10):1239e41. [43] Thanh LT, Okitsu K, Boi LV, Maeda Y. Catalytic technologies for biodiesel fuel production and utilization of glycerol: a review. Catalysts 2012;2(1):191e222. [44] Boey PL, Maniam GP, Hamid SA. Biodiesel production via transesterification of palm olein using waste mud crab (Scylla serrata) shell as a heterogeneous catalyst. Bioresour Technol 2009;100(24):6362e8. [45] Madhuvilakku R, Mariappan R, Jeyapal S, Sundar S, Piraman S. Transesterification of palm oil catalyzed by fresh water bivalve mollusk (margaritifera falcata) shell as heterogeneous catalyst. Ind Eng Chem Res 2013;52(49): 17407e13. [46] Bahrami K, Khodaei MM, Naali F. TiO2 nanoparticles catalysed synthesis of 2arylbenzimidazoles and 2-arylbenzothiazoles using hydrogen peroxide under ambient light. J Exp Nanosci 2016;11(2):148e60. [47] Li B, Cao H. ZnO@ graphene composite with enhanced performance for the removal of dye from water. J Mater Chem 2011;21(10):3346e9. [48] Verma R, Samdarshi SK. Correlating oxygen vacancies and phase ratio/interface with efficient photocatalytic activity in mixed phase TiO2. J Alloy Compd 2015;629:105e12. [49] Zhang S, Xu J, Hu J, Cui C, Liu H. Interfacial growth of TiO2-rGO composite by Pickering emulsion for photocatalytic degradation. Langmuir 2017;33: 5015e24. [50] Hasan MR, Hamid SB, Basirun WJ, Chowdhury ZZ, Kandjani AE, Bhargava SK. Ga doped RGOeTiO2 composite on an ITO surface electrode for investigation of photoelectrocatalytic activity under visible light irradiation. N J Chem 2015;39(1):369e76. [51] Yang N, Zhai J, Wang D, Chen Y, Jiang L. Two-dimensional graphene bridges enhanced photoinduced charge transport in dye-sensitized solar cells. ACS Nano 2010;4(2):887e94. [52] Tan LL, Ong WJ, Chai SP, Mohamed AR. Reduced graphene oxide-TiO2nanocomposite as a promising visible-light-active photocatalyst for the conversion

889

of carbon dioxide. Nanoscale Res Lett 2013;8(1):465. [53] Pan X, Zhao Y, Liu S, Korzeniewski CL, Wang S, Fan Z. Comparing grapheneTiO2 nanowire and graphene-TiO2 nanoparticle composite photocatalysts. ACS Appl Mater Interfaces 2012;4(8):3944e50. [54] Nethravathi C, Rajamathi M. Chemically modified graphene sheets produced by the solvothermal reduction of colloidal dispersions of graphite oxide. Carbon 2008;46(14):1994e8. [55] Murugan AV, Muraliganth T, Manthiram A. Rapid, facile microwavesolvothermal synthesis of graphene nanosheets and their polyaniline nanocomposites for energy storage. Chem Mater 2009;21(21):5004e6. [56] Perera SD, Mariano RG, Vu K, Nour N, Seitz O, Chabal Y, Balkus Jr KJ. Hydrothermal synthesis of graphene-TiO2 nanotube composites with enhanced photocatalytic activity. ACS Catal 2012;2(6):949e56. [57] Das M, Datta J, Dey A, Jana R, Layek A, Middya S, Ray PP. One step hydrothermal synthesis of a rGOeTiO2 nanocomposite and its application on a Schottky diode: improvement in device performance and transport properties. RSC Adv 2015;5(123):101582e92. [58] Chen G, Shan R, Shi J, Liu C, Yan B. Biodiesel production from palm oil using active and stable K doped hydroxyapatite catalysts. Energy Convers Manag 2015;98:463e9. [59] Feyzi M, Hassankhani A, Rafiee HR. Preparation and characterization of Cs/Al/ Fe3O4 nanocatalysts for biodiesel production. Energy Convers Manag 2013;71: 62e8. [60] Olutoye MA, Lee SC, Hameed BH. Synthesis of fatty acid methyl ester from palm oil (Elaeisguineensis) with Ky(MgCa)2xO3 as heterogeneous catalyst. Bioresour Technol 2011;102(23):10777e83. [61] Kouzu M, Hidaka JS. Purification to remove leached CaO catalyst from biodiesel with the help of cation-exchange resin. Fuel 2013;105:318e24. [62] Tariq M, Ali S, Ahmad F, Ahmad M, Zafar M, Khalid N, Khan MA. Identification, FT-IR, NMR (1H and 13C) and GC/MS studies of fatty acid methyl esters in biodiesel from rocket seed oil. Fuel Process Technol 2011;92:336e41. [63] Silverstein RM, Webster FX, Kiemle DJ, Bryce DL. Spectrometric identification of organic compounds. John wiley & sons; 2014 Sep 29. [64] Monteiro MR, Ambrozin AR, Liao LM, Ferreira AG. Determination of biodiesel blend levels in different diesel samples by 1H NMR. Fuel 2009;88:691e6. [65] Diehl B, Randel G. Analysis of biodiesel, diesel and gasoline by NMR spectroscopyea quick and robust alternative to NIR and GC. Lipid Technol 2007;19:258e60. [66] Pavia DL, Lampman GM, Kriz GS. Chapter 3: nuclear magnetic resonance: Part one: basic concept. Pavia-introduction to spectroscopy. third ed. USA: Thomson Learning Academic Resource Center; 2001. p. 152e4.