Sustainable utilization of waste palm oil and sulfonated carbon catalyst derived from coconut meal residue for biodiesel production

Accepted Manuscript Short Communication Sustainable utilization of waste palm oil and sulfonated carbon catalyst derived from coconut meal residue for biodiesel production Indika Thushari, Sandhya Babel PII: DOI: Reference:

S0960-8524(17)31010-6 http://dx.doi.org/10.1016/j.biortech.2017.06.106 BITE 18343

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Bioresource Technology

Received Date: Revised Date: Accepted Date:

25 April 2017 19 June 2017 20 June 2017

Please cite this article as: Thushari, I., Babel, S., Sustainable utilization of waste palm oil and sulfonated carbon catalyst derived from coconut meal residue for biodiesel production, Bioresource Technology (2017), doi: http:// dx.doi.org/10.1016/j.biortech.2017.06.106

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Sustainable utilization of waste palm oil and sulfonated carbon catalyst derived from coconut meal residue for biodiesel production Indika Thushari, Sandhya Babel,* Sirindhorn International Institute of Technology, Thammasat University, Pathum Thani, Thailand * Tel: +669869009 Ext 2307, Fax: +669869112, E-mail: [email protected] Abstract: In this study, an inexpensive, environmental benign acid catalyst is prepared using coconut meal residue (CMR) and employed for biodiesel production from waste palm oil (WPO). The total acid density of the catalyst is found to be 3.8 mmolg-1. The catalyst shows a unique amorphous structure with 1.33 m2 g-1 of surface area and 0.31 cm3g-1 of mean pore volume. Successful activation is confirmed by Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The highest biodiesel yield of 92.7% was obtained from WPO in an open reflux system using the catalyst. Results show that biodiesel yield increases with increasing methanol:oil (molar ratio) and reaction time up to an optimum value. It is found that the catalyst can be reused for at least four cycles for >80% biodiesel yield. Fuel properties of the produced biodiesel meet international biodiesel standards. Key words: Biodiesel; Waste palm oil; Carbon based solid acid catalyst; Direct sulfonation; Coconut meal residue; 1 Introduction Biodiesel is a clean, renewable liquid fuel which is considered as a promising alternative for conventional diesel fuel. Among various types of biodiesel feedstocks, waste cooking oil (WCO) is attractive and economical, compared to expensive first generation edible oils/fats. Use of WCO as an alternative biodiesel feedstock reduces 1

the problems associated with food crises, environmental pollution, and waste treatment (Banani et al., 2015). Among various types of cooking oil, the demand for palm oil is increasing. According to the United States Department of Agriculture (USDA) (Foreign agricultural service 2017), 64.5 million metric tons of palm oil will be produced globally in 2016-2017, making it the most consumed oil in the world. This increases the available amount of used palm oil as a potential feedstock. However, use of WCO as a low cost biodiesel feedstock is challenging due to the presence of a high amount of free fatty acids (FFAs) and water. This limits the conventional alkali catalyzed trans-esterification reactions for biodiesel production (Banani et al., 2015; Zong et al., 2007). Also, applications of homogeneous acid catalysts and biocatalysts for biodiesel production are limited due to various associated drawbacks (Parthiban & Perumalsamy, 2015; Zong et al., 2007). Therefore, the use of a heterogeneous solid acid catalyst (SAC) has been considered as a promising method for biodiesel production from low quality feedstocks. A SAC can convert both FFA and TGs into their esters simultaneously by catalyzing esterification and trans-esterification reactions, respectively (Su & Guo, 2014). Use of a carbon based SAC for biodiesel production is popular due to the simplicity of catalyst preparation and its stability in the reaction medium (Nakajima et al., 2007). Use of biomass wastes for SAC preparation is recommended since they are largely available at low or no cost. Various studies have reported the use of waste biomass for SAC preparation and their successful use in biodiesel production (Fu et al., 2013; Li et al., 2014; Parthiban & Perumalsamy, 2015). However, most of these studies have reported the use of a SAC for direct esterification reactions or pre-treatment of acidic feedstocks only. Direct in-situ incomplete sulfuric carbonization under mild reaction conditions has gained more attention recently, as a simple, economical and environmental friendly 2

method for SAC preparation. Studies have reported successful carbon based heterogeneous catalyst preparation using glycerol (Devi et al., 2014) and bagasse powder (Savaliya & Dholakiya, 2015) by direct in-situ sulfuric carbonization and their use in biodiesel production. Coconut meal residue (CMR) is a food waste which is obtained after coconut milk extraction. According to Ng et al. (2010), only a small portion of CMR is used as fertilizer or fodder while a large quantity of CMR is left for open dumping. As reported by Ng et al. (2010), CMR consists of about 72.6% cellulose, 2% hemicellulose, and 1.8% lignin. The high cellulose content of CMR, comprised of D-glucose units, provides a rigid carbon support for SAC preparation. In addition, the presence of oxygen rich functional groups in the carbon framework may support a greater degree of sulfonation (Huang et al., 2016). Therefore, the use of CMR for catalyst preparation, using one-step direct concentrated H2SO4 carbonization, makes the overall biodiesel production from WPO more economical and sustainable. Waste utilization is necessary for sustainable development and to reduce environmental pollution. WPO and CMR are abundant food wastes. In this study, a sulfonated CMR derived SAC is prepared using a one-step direct in-situ concentrated H2SO4 impregnation method and employed for single step biodiesel production from WPO in a conventional reflux system. The effect of operating parameters, such as methanol:oil (molar ratio), reaction time, and catalyst loading on biodiesel yield are investigated. The produced biodiesel is compared with international biodiesel standards. 2 Experimental 2.1 Preparation of CMR-DS-SO3H catalyst CMR with elemental composition of 50.3, 7.7, 41.1, and 0.09 wt. % of C, H, O, and S, respectively, was collected from a local market at Pathum Thani, Thailand and selected as the carbon support for catalyst preparation. The oven dried (110 °C, 5 h) CMR 3

powder (10 g) and concentrated H2SO4 were mixed (1:5 wt/wt) at 100 °C for 1 h to facilitate in-situ incomplete sulfuric carbonization. After 24 h, the reaction mixture was diluted, filtered, and repeatedly washed with hot distilled water (>80 °C) until the excess H2SO4 acid was removed. Then, the resultant carbon based SAC was kept in an oven (120 °C, 2 h) to remove all moisture. The prepared catalyst was denoted as CMRDS-SO3H. 2.2 Characterization of CMR-DS-SO3H catalyst Total acid density of the catalyst was measured by standard acid base back titration. Sulfur content of the catalyst was determined by using energy dispersive X-ray spectroscopy (EDS) (HITACHI S-3400N), using Edax Genesis software. Elemental composition of the catalyst was determined by CHNS/O analyzer (628 series, Leco Corporation). Surface functional groups of the catalyst were analyzed by using a Fourier transform infrared (FT-IR) spectrometer (NICOLET iS50, FT-IR, Thermo scientific) with attenuated total reflectance (ATR) mode. The chemical state of the functional groups was analyzed by X-ray photoelectron spectroscopy (XPS) (PH15000 Versa Probe II @ Ulvac- PHI Inc, Japan) with Al Ka radiation. Surface morphology of the catalyst was examined by a scanning electron microscope (SEM-VE-8800, Keyence, Japan). The textural properties of the catalyst were studied by using N2 adsorption and desorption isotherm data, using liquid nitrogen at 77 K (BELSORP miniII, Japan). 2.3 Evaluation of catalytic activity WPO collected from Useful Food Co. Ltd, Thailand was used as received for biodiesel production without any pre-treatment. The experiments were carried out in a 500 ml three-neck round bottom flask, equipped with a reflux condenser and a thermometer, on a hot plate with a magnetic stirrer. An oil bath was used to maintain the reaction temperature. A mixture of WPO (20 g), methanol, and CMR-DS-SO3H catalyst was 4

loaded into the reactor. To study the effect of operating parameters, the reaction conditions were varied as follows: methanol:oil (molar ratio)(6:1-16:1), reaction time (6-16 h), and catalyst loading as a weight percent of used WPO (5-20 wt.%), at 65-70 °C. Control experiments, without using the catalyst and using only non-activated dry CMR powder, were carried out to study the effect on fatty acid methyl ester (FAME) yield. The used catalyst was separated by vacuum filtration and dried at 105 °C for 2 h in an oven after washing with hexane for reuse. After complete phase separation, the crude methyl ester upper layer was washed with >80 °C hot distilled water in a separating funnel, until the pH of the effluent was neutral. An anhydrous Na2SO4 bed was used to absorb the remaining water in the ester layer. Finally, the FAME yield was determined by Gas Chromatography (PerkinElmer, Clarus 580, equipped with a flame ionization detector and HP-INNOWax capillary column), according to the standard method of EN 14103. Fuel properties, such as acid value, kinematic viscosity, density, heating value, flash point, pour point, ash content, and sulfur content of the prepared biodiesel were measured and compared with international biodiesel standards. 3 Results and Discussion 3.1 Characterization of CMR-DS-SO3H catalyst It is found that the C and S content of the catalyst increased to 56.9 and 3.89 wt. % while H and O content of the catalyst decreased to 3.3 and 35.4 wt. %, respectively, compared to the raw CMR powder. This is due to dehydration and de-oxygenation of the CMR in the presence of concentrated H2SO4 acid and production of sulfonated carbonaceous products. As stated by North (2016), it is expected that biomass, such as CMR, containing high cellulose content may be converted into a partially oxygenated aromatic carbon framework during sulfuric carbonization, while simultaneous sulfonation converts this structure into a sulfonated carbon catalyst. The total acid 5

density of the CMR-DS-SO3H catalyst is found to be 3.8 mmolg-1. The total acid density of biomass derived SACs is associated with sulfonic, carboxyl, and phenolic groups (Su & Guo, 2014). Among them, the highest contribution for both esterification and transesterification is shown by sulfonic acid groups (pka=-7) (Zong et al., 2007). Sulfur content of the CMR-DS-SO3H catalyst is found to be 2.26 wt. % in the EDS analysis and 3.89 wt.% as found in elemental analysis, contributing to the high acidity of the CMR-DS-SO3H catalyst. The SEM image indicates that the catalyst has a unique amorphous porous carbon structure. Nitrogen adsorption and desorption isotherms of the catalyst are found to be similar to type-III and/or type-IV isotherms at lower p/p 0 values, indicating the presence of nonporous and mesoporous phases of the catalyst (Brunauer et al., 1938), in line with scanning electron microscopy. The BET surface area and mean pore volume of the catalyst are 1.33 m2g-1 and 0.31 cm3 g-1, respectively. The mean pore diameter of the catalyst is 13.2 nm and the pore size distribution of the catalyst is found to be 2.4-200 nm. The lower surface area and lower pore volume of the catalyst, compared to the high acid density, may be due to the accumulation of SO3H groups in the pores of the CMR-DS-SO3H catalyst (Savaliya & Dholakiya, 2015). The presence of acidic functional groups in the catalyst is confirmed by FT-IR analysis. The strong and broad peak at around 3600-2800 cm-1 is attributed to alcoholic and phenolic OH groups in the raw CMR, fresh CMR-DS-SO3H catalyst, and used catalyst. As can be seen in the raw sample, the sharp peaks at around 2916-2800 cm-1 are recognized as anti-symmetric and symmetric vibrations of CH groups. The sharp peak at around 1800-1500 cm-1 is attributed to the carbonyl/carboxylic region in each sample. The peaks at around 1200-1100 cm-1 and 715-670 cm-1 in the CMR-DS-SO3H catalyst

6

and used catalyst are assigned to symmetric and asymmetric stretching vibrations of SO2 and SO3H, and CS, respectively (Coates, 2000). The XPS spectra of CMR-DSSO3H catalyst reveal peaks at 168 eV, 284 eV, and 530 eV, corresponding to the S2p, C1s, and O1s binding energy (Russo et al., 2014). These peaks can be differentiated via de-convolution. The presence of S-C (168 eV) and S-O/S=O (169 eV) bonds in the CMR-DS-SO3H catalyst confirms the presence of SO3H on the catalyst surface (Nakajima & Hara, 2012). Further, the presence of C-O (286 eV) and C=O (287 eV) bonds at the C1s band and the presence of C-O/C-O-H (533 eV) bonds at the O1s band confirm the presence of OH and COOH groups on the catalyst surface (Liu et al., 2013; Nakajima & Hara, 2012). These data confirm the presence of sulfonic, carboxylic, and phenolic groups on the surface of the catalyst, in line with FTIR data. The presence of these hydrophilic functional groups, bonded to the flexible carbon sheets, can incorporate a large amount of hydrophilic molecules such as water and prevent poisoning of the catalysts. This creates good access of reactants to SO3H groups, which ultimately contributes to a high catalytic activity despite the relatively small surface area of the catalyst (Su & Guo, 2014). However, the peak intensity of the FT-IR spectrum of used catalyst after the fourth cycle is weakened, compared to the fresh catalysts. This implies a gradual deactivation or loss of active sites during the reaction. S2p spectra for the used catalysts gradually become weakened, confirming the loss of sulfonic acid groups in the catalyst during the reaction. 3.2 Catalytic activity of CMR-DS-SO3H for biodiesel production It is found that the major fatty acids found in the WPO are oleic acid (42.39 g/100 g), palmitic acid (36.63 g/100 g), and linoleic acid (9.85 g/100 g). Since, the used WPO contains 5.2% FFA more than the recommended value (<0.5%) for a base catalyzed

7

trans-esterification reaction (Su & Guo, 2014), a carbon based SAC for biodiesel production is employed in this study. As both esterification and trans-esterification reactions are reversible, there must be an excess of methanol in the reaction medium to shift the reaction equilibrium towards the formation of methyl esters, according to Le Chatelier’s principle. Thus, experiments are carried out to determine the optimum methanol:oil (molar ratio) for biodiesel production. It can be clearly seen that in the presence of the catalyst, the FAME yield is significantly higher compared to the experiments conducted without using the catalyst. It is observed that the FAME yield increases to 77.3% with increasing methanol:oil (molar ratio = 12:1), and a further increase causes a decrease to 69.5% (Fig. 1). These results can be explained according to Le Chatelier’s principle. Even though, excess methanol in the reaction medium accelerates the forward reaction, the presence of a very high amount of methanol beyond the requirements and the high ester content in the reaction medium may increase the rate of the reverse reaction, leading to a lower biodiesel yield after 12:1, methanol to oil molar ratio. Also, excess methanol may decrease the activity of the catalyst by binding to the active sites of the catalyst. Therefore, in this study, the optimum methanol:oil (molar ratio) is identified as 12:1 and used for further investigations. The amount of methanol:oil ratio is reported differently by different researchers. Parthiban and Perumalsamy (2015) have reported an increase of FAME yield (97%) with increase of methanol:Cebia pentandra oil (molar ratio) until 18:1and no further increase with increasing ratio. A high FAME yield of >99% with a higher methanol:oil (molar ratio) of 45:1 was reported by Devi et al. (2014) during biodiesel production from Karanja oil using a glycerol based SAC. The amount of methanol used in industrial/large scale biodiesel production varies. A 6:1 oil to methanol molar ratio was used in KOH/NaOH catalyzed batch biodiesel production 8

(Ouanji et al., 2016) while a 12:1 WCO:methanol molar ratio was used in a continuous flow type microwave reactor for large scale biodiesel production using SrO/SiO 2 as catalysts (Tangy et al., 2017). Additionally, as stated by Chai et al. (2014), a 19.8:1 methanol:FFA molar ratio was used for pre-treatment of acidic feedstocks in United States. Thus, it can be concluded that the amount of methanol required for biodiesel production varies based on the feed stock, catalyst used, and operating conditions. As the experiments are carried out in a conventional open reflux system at 65-70 °C, a longer time may be required to catalyze trans-esterification reactions. Thus, the effect of reaction time on FAME yield is studied. It is observed that the FAME yield increased to 92.6% after 12 h, and a further increase of the reaction time decreases the FAME yield. Results are in line with Chen and Fang (2011). They have reported about a 90% FAME yield after 12 h during biodiesel production from waste cotton seed oil. Also, Zong et al. (2007) have reported >90% FAME yield after 12 h using a sugar derived SAC under a reflux system. A decrease of the FAME yield after 12 h may be due to the accumulation of water due to the increased rate of the esterification reaction, causing deactivation of the catalyst. Also, deactivation of the active sites of the catalyst during a longer reaction time is possible, due to the binding of polar molecules in the reaction mixture and leaching of active acid sites, such as SO3H (Lou et al., 2008). When investigating the effect of catalyst loading, a slight decrease in the FAME yield with increasing catalyst loading after 5 wt.% is observed . In fact, an increase of catalyst loading increases the active acid sites available for esterification and trans-esterification reactions. Nevertheless, increasing the catalyst loading (wt. %) may decrease the rate of diffusion of reactants due to bulk mass fraction, causing a decrease in the FAME yield. Also, an increase of water content due to an increase in the rate of the esterification reaction can deactivate the catalyst, decreasing the final FAME yield. 9

Further, a low FAME yield of 12.3% was obtained from the control experiment using dry CMR powder as the catalyst at optimum reaction conditions, while a FAME yield of 20% was observed without catalyst at 12:1 methanol to oil molar ratio at 65-70 °C after 8 h. This may be because dry CMR can absorb methanol, which limits reactant diffusion. Thus, the results confirm that CMR-DS-SO3H is successfully functionalized, and the active sites of the catalyst are contributing to the reaction as can be seen by the higher FAME yield. The reusability of the catalyst is important and was investigated for five cycles. Even though the activity of the catalyst is slightly decreased after 5 consecutive runs, results show that the catalyst is relatively stable and capable of long time usage. As stated by Liu et al. (2015), high stability of the porous carbon structure and the strong attachment of sulfonic groups to the substrate are the main factors for relatively high reusability of a carbon catalyst. On the other hand, Konwar et al. (2016) mentioned that the non-porous carbon typically found in incompletely carbonized biomass, contains weakly bonded SO 3 H groups, which are likely to be leached out. Weakening of the peak intensities for active sites in the catalyst after usage in both XPS and FT-IR indicates the possible ways of activity loss as discussed above. Moreover, the fuel properties, such as acid value, kinematic viscosity, density, flash point, pour point, heating value, ash content, and sulfur content of the prepared biodiesel, are according to ASTM D 6751 and EN 14214 standards (Table 1). Insert Table 1 4 Conclusions Both WPO and CMR as food wastes are used for sustainable and economical biodiesel production. A SAC prepared from CMR following a simple protocol, was successfully

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used for one-step biodiesel production from WPO with a high amount of FFA (5.2%). CMR-DS-SO3H had high total acid density (3.8 mmolg-1). FT-IR and XPS confirms the presence of acidic groups on the catalyst, resulting in a high FAME yield of 92.7% under optimum conditions in a reflux system. The catalyst shows relatively high stability, giving >80% FAME yield after four runs. The prepared biodiesel meets the international standards of fuel properties for biodiesel. Appendix A. Supplementary data E-supplementary data for this work can be found in e-version of this paper online. Acknowledgement The authors gratefully acknowledge the financial support provided by Sirindhorn International Institute of Technology, through an Excellent Foreign Students (EFS) doctoral scholarship. References 1. Banani, R., Youssef, S., Bezzarga, M., Abderrabba, M. 2015. Waste frying oil with high levels of free fatty acids as one of the prominent sources of biodiesel production. Journal of Materials and Environmental Sciences 6(4), 1178-1185. 2. Brunauer, S., Emmett, P.H., Teller, E. 1938. Adsorption of gases in multimolecular layers. Journal of the American Chemical Society, 60(2), 309319. 3. Chai, M., Tu, Q., Lu, M., Yang, Y.J. 2014. Esterification pretreatment of free fatty acid in biodiesel production, from laboratory to industry. Fuel processing technology, 125, 106-113. 4. Chen, G., Fang, B. 2011. Preparation of solid acid catalyst from glucose–starch mixture for biodiesel production. Bioresource Technology, 102(3), 2635-2640. 5. Coates, J. 2000. Interpretation of Infrared Spectra, a Practical Approach. John Wiley & Sons Ltd, Chichester. 6. Devi, B.P., Reddy, T.V.K., Lakshmi, K.V., Prasad, R. 2014. A green recyclable SO3H-carbon catalyst derived from glycerol for the production of biodiesel from

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FFA-containing karanja (Pongamia glabra) oil in a single step. Bioresource Technology, 153, 370-373. 7. Foreign agricultural service , F. 2017. Oil seeds: World Market and Trade, (Ed.) U.S.D.O. Agriculture, Government Printing Office. Washington. 8. Fu, X., Li, D., Chen, J., Zhang, Y., Huang, W., Zhu, Y., Yang, J., Zhang, C. 2013. A microalgae residue based carbon solid acid catalyst for biodiesel production. Bioresource Technology, 146, 767-770. 9. Huang, M., Luo, J., Fang, Z., Li, H. 2016. Biodiesel production catalyzed by highly acidic carbonaceous catalysts synthesized via carbonizing lignin in suband super-critical ethanol. Applied Catalysis B: Environmental, 190, 103-114. 10. Konwar, L.J., Wärnå, J., Mäki-Arvela, P., Kumar, N., Mikkola, J.-P. 2016. Reaction kinetics with catalyst deactivation in simultaneous esterification and transesterification of acid oils to biodiesel (FAME) over a mesoporous sulphonated carbon catalyst. Fuel, 166, 1-11. 11. Li, M., Zheng, Y., Chen, Y., Zhu, X. 2014. Biodiesel production from waste cooking oil using a heterogeneous catalyst from pyrolyzed rice husk. Bioresource Technology, 154, 345-348. 12. Liu, R.-L., Gao, X.-Y., An, L., Ma, J., Zhang, J.-F., Zhang, Z.-Q. 2015. Fabrication of magnetic carbonaceous solid acids from banana peel for the esterification of oleic acid. RSC Advances, 5(114), 93858-93866. 13. Liu, W.-J., Tian, K., Jiang, H., Yu, H.-Q. 2013. Facile synthesis of highly efficient and recyclable magnetic solid acid from biomass waste. Scientific Reports, 3. 14. Lou, W.-Y., Zong, M.-H., Duan, Z.-Q. 2008. Efficient production of biodiesel from high free fatty acid-containing waste oils using various carbohydratederived solid acid catalysts. Bioresource Technology, 99(18), 8752-8758. 15. Nakajima, K., Hara, M. 2012. Amorphous carbon with SO3H groups as a solid Brønsted acid catalyst. ACS Catalysis, 2(7), 1296-1304. 16. Nakajima, K., Hara, M., Hayashi, S. 2007. Environmentally benign production of chemicals and energy using a carbon‐based strong solid acid. Journal of the American Ceramic Society, 90(12), 3725-3734. 17. Ng, S., Tan, C.P., Lai, O.M., Long, K., Mirhosseini, H. 2010. Extraction and characterization of dietary fiber from coconut residue. Journal of Food Agriculture and Environment, 8(2), 172-177. 12

18. North, M. 2016. Sustainable Catalysis. Royal Society of Chemistry, Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge, CB4 0WF, UK. 19. Ouanji, F., Khachani, M., Boualag, M., Kacimi, M., Ziyad, M. 2016. Large-scale biodiesel production from Moroccan used frying oil. International Journal of Hydrogen Energy, 41(45), 21022-21029. 20. Parthiban, K.S., Perumalsamy, M. 2015. Nano sized heterogeneous acid catalyst from Ceiba pentandra stalks for production of biodiesel using extracted oil from Ceiba pentandra seeds. RSC Advances, 5(15), 11180-11187. 21. Russo, P.A., Antunes, M.M., Neves, P., Wiper, P.V., Fazio, E., Neri, F., Barreca, F., Mafra, L., Pillinger, M., Pinna, N., Valente, A.A. 2014. Solid acids with SO3H groups and tunable surface properties: versatile catalysts for biomass conversion. Journal of Materials Chemistry A, 2(30), 11813-11824. 22. Savaliya, M.L., Dholakiya, B.Z. 2015. A simpler and highly efficient protocol for the preparation of biodiesel from soap stock oil using a BBSA catalyst. RSC Advances, 5(91), 74416-74424. 23. Su, F., Guo, Y. 2014. Advancements in solid acid catalysts for biodiesel production. Green Chemistry, 16(6), 2934-2957. 24. Tangy, A., Pulidindi, I.N., Perkas, N., Gedanken, A. 2017. Continuous flow through a microwave oven for the large-scale production of biodiesel from waste cooking oil. Bioresource Technology, 224, 333-341. 25. Zong, M.-H., Duan, Z.-Q., Lou, W.-Y., Smith, T.J., Wu, H. 2007. Preparation of a sugar catalyst and its use for highly efficient production of biodiesel. Green Chemistry, 9(5), 434-437.

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Fig. 1 Effect of methanol:oil (molar ratio) on FAME yield (%): 5 wt.% catalyst, at 65-70 °C, 8 h

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Table 1 Fuel properties

WPO

Biodiesel*

ASTM

EN

10.3

0.5

0.5 max

0.5 max

5.2

0.21

24.1

3.12

1.9-6.0

3.5-5.0

970

840

-

34.72

37.27

-

Flash point (°C) ASTM D92

300

260

> 93

> 101

Pour point (°C) ASTM D97

-23

-6.5

-15-10

-4

0.43

0.009

0.01

0.01

0.0015

0.0011

0.0015

0.001

Acid value (mg KOH g-1) (ASTM D664) % FFA Kinematic viscosity ( at 40 °C cSt) (ASTM D446) Density (kg/m3) Heating value (MJ/kg) ASTM D240-2

Ash content (wt. %) ASTM D482-13 Sulfur content (wt. %)

- 820-845

Remarks: * Fuel characteristics of biodiesel are tested for biodiesel produced under reaction conditions of 5 wt. % catalyst, 12:1 methanol:oil (molar ratio) at 65-70 °C, 10 h

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Highlights An economical, environmental benign sulfonated carbon catalyst is prepared from CMR Successful activation of the catalyst is confirmed by XPS and FTIR Catalyst can be employed for one-step biodiesel production from waste palm oil A FAME yield of >92% was obtained at optimum conditions in a reflux system Catalyst showed a good reusability for four consecutive cycles with >80% FAME yield

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Waste palm oil FFA

Triglyceride

O

Palm Oil

O

O

C R

OH

H2 C

C O

C H2

R1

H C

C O R3

C O

O R2

Biodiesel (esters) R1

R

O

O

Biomass

CO2 Emissions

O

O

C

C

R' R2

R' R3

O O

Carbon acid catalyst CMR-DS-SO3H

Coconut meal residue

Sustainable biodiesel from waste palm oil using CMR derived carbon acid catalyst

C

O R'

O C R'