The interest in the development of efficient and environmentally benign catalysts for esters synthesis has increased exponentially, mainly due to the demand for biodiesel. In general, fatty esters are used as bioadditive, cosmetic ingredients, polymers, and, more recently, biofuel. Nevertheless, most of the production processes use nonrecyclable and homogenous alkaline catalysts, which results in the reactors corrosion, large generation of effluents, and residues on the steps of separation and catalyst neutralization. Heterogeneous acid catalysts can answer these demands and are an environmentally benign alternative extensively explored. Remarkably, solid acid catalysts based on tin have been shown highly attractive for the biodiesel production, mainly via FFA esterification reactions. This review describes important features related to be the synthesis, stability to, and activity of heterogeneous tin catalysts in biodiesel production reactions. 1. Introduction The recent demand by alternative energy sources has made the biodiesel production a concern worldwide. Biodiesel is a renewable, biodegradable, and less polluting fuel than mineral diesel. It consists of ethyl (FAEE) or methyl esters of fatty acids (FAME), which are obtained from the triglycerides (TG) transesterification reactions present in vegetal oil (Figure 1), such as showed in Figure 1 [1]. Figure 1: Transesterification of triglycerides with methyl or ethyl alcohol. Currently, most of the processes used for biodiesel production from the vegetable oils transesterification operating under homogeneous alkaline catalysis conditions (i.e., NaOH, KOH, or NaOCH3) [1]. However, if a high content of FFA is present, homogeneous acid catalysts (i.e., H2SO4) are commonly applied on the steps of preesterification [1]. Both processes result in a large generation of wastewaters, residues, and salts formed during the catalyst neutralization and products recovery. Currently, the greater part of the biodiesel consumed is produced by transesterification of expensive edible vegetable oils, which are responsible for 65% of the final price [2]. Alternative routes for the production of biodiesel where inexpensive feedstock such as animal fats, waste frying, and highly acid vegetable oil are an attractive option [3]. Nevertheless, these low cost raw materials are incompatible with alkaline catalysts due the formation of soaps, which hinders the separation of the FAME or FAEE from the glycerol, reducing consequently the biodiesel yields [4]. For these reasons, developing active catalysts for the FFA esterification
References
[1]
A. Corma and H. García, “Lewis acids: from conventional homogeneous to green homogeneous and heterogeneous catalysis,” Chemical Reviews, vol. 103, no. 11, pp. 4307–4365, 2003.
[2]
A. Demyrbas, “Comparison of transesterification methods for production of biodiesel from vegetable oils and fats,” Energy Conversion and Management, vol. 49, no. 1, pp. 125–130, 2008.
[3]
J. H. Michael, “Improving the economics of biodiesel production through the use of low value lipids as feedstocks: vegetable oil soapstock,” Fuel Processing Technology, vol. 86, no. 10, pp. 1087–1096, 2005.
[4]
M. J. Haas, K. M. Scott, W. N. Marmer, and T. A. Foglia, “In situ alkaline transesterification: an effective method for the production of fatty acid esters from vegetable oils,” Journal of the American Oil Chemists' Society, vol. 81, no. 1, pp. 83–89, 2004.
[5]
E. Lotero, Y. Liu, D. E. Lopez, K. Suwannakarn, D. A. Bruce, and J. G. Goodwin Jr., “Synthesis of biodiesel via acid catalysis,” Industrial and Engineering Chemistry Research, vol. 44, no. 14, pp. 5353–5363, 2005.
[6]
E. M. Shahid and Y. Jamal, “Production of biodiesel: a technical review,” Renewable and Sustainable Energy Reviews, vol. 15, no. 9, pp. 4732–4745, 2011.
[7]
S. Semwal, A. K. Arora, R. P. Badoni, and D. K. Tuli, “Biodiesel production using heterogeneous catalysts,” Bioresource Technology, vol. 102, no. 3, pp. 2151–2161, 2011.
[8]
M. K. Lam, K. T. Lee, and A. R. Mohamed, “Homogeneous, heterogeneous and enzymatic catalysis for transesterification of high free fatty acid oil (waste cooking oil) to biodiesel: a review,” Biotechnology Advances, vol. 28, no. 4, pp. 500–518, 2010.
[9]
Y. C. Sharma, B. Singh, and J. Korstad, “Advancements in solid acid catalysts for ecofriendly and economically viable synthesis of biodiesel,” Biofuels, Bioproducts and Biorefining, vol. 5, no. 1, pp. 69–92, 2011.
[10]
M. di Serio, R. Tesser, L. Pengmei, and E. Santacesaria, “Heterogeneous catalysts for biodiesel production,” Energy and Fuels, vol. 22, no. 1, pp. 207–217, 2008.
[11]
Z. Helwani, M. R. Othman, N. Aziz, J. Kim, and W. J. N. Fernando, “Solid heterogeneous catalysts for transesterification of triglycerides with methanol: a review,” Applied Catalysis A, vol. 363, no. 1-2, pp. 1–10, 2009.
[12]
H. Hattori, “Solid acid catalysts: roles in chemical industries and new concepts,” Topics in Catalysis, vol. 53, no. 7–10, pp. 432–438, 2010.
[13]
J.-Y. Park, Z.-M. Wang, D.-K. Kim, and J.-S. Lee, “Effects of water on the esterification of free fatty acids by acid catalysts,” Renewable Energy, vol. 35, no. 3, pp. 614–618, 2010.
[14]
Y. Maeda, L. T. Thanh, K. Imamura et al., “New technology for the production of biodiesel fuel,” Green Chemistry, vol. 13, no. 5, pp. 1124–1128, 2011.
[15]
A. Sivasamy, K. Y. Cheah, P. Fornasiero, F. Kemausuor, S. Zinoviev, and S. Miertus, “Catalytic applications in the production of biodiesel from vegetable oils,” ChemSusChem, vol. 2, no. 4, pp. 278–300, 2009.
[16]
A. L. Cardoso, S. C. G. Neves, and M. J. da Silva, “Kinetic study of alcoholysis of the fatty acids catalyzed by tin chloride(II): an alternative catalyst for biodiesel production,” Energy and Fuels, vol. 23, no. 3, pp. 1718–1722, 2009.
[17]
W. Xie, H. Wang, and H. Li, “Silica-supported tin oxides as heterogeneous acid catalysts for transesterification of soybean oil with methanol,” Industrial & Engineering Chemistry Research, vol. 51, no. 1, pp. 225–231, 2012.
[18]
H. F. Guo, P. Yan, X. Y. Hao, and Z. Z. Wang, “Influences of introducing Al on the solid super acid SO42？/SnO2,” Materials Chemistry and Physics, vol. 112, no. 3, pp. 1065–1068, 2008.
[19]
M. K. Lam, K. T. Lee, and A. R. Mohamed, “Sulfated tin oxide as solid superacid catalyst for transesterification of waste cooking oil: an optimization study,” Applied Catalysis B, vol. 93, no. 1-2, pp. 134–139, 2009.
[20]
M. K. Lam and K. T. Lee, “Accelerating transesterification reaction with biodiesel as co-solvent: a case study for solid acid sulfated tin oxide catalyst,” Fuel, vol. 89, no. 12, pp. 3866–3870, 2010.
[21]
M. K. Lam and K. T. Lee, “Mixed methanol-ethanol technology to produce greener biodiesel from waste cooking oil: a breakthrough for SO42？/SnO2-SiO2 catalyst,” Fuel Processing Technology, vol. 92, no. 8, pp. 1639–1645, 2011.
[22]
J. Jitputti, B. Kitiyanan, P. Rangsunvigit, K. Bunyakiat, L. Attanatho, and P. Jenvanitpanjakul, “Transesterification of crude palm kernel oil and crude coconut oil by different solid catalysts,” Chemical Engineering Journal, vol. 116, no. 1, pp. 61–66, 2006.
[23]
F. R. Abreu, M. B. Alves, C. C. S. Macêdo, L. F. Zara, and P. A. Z. Suarez, “New multi-phase catalytic systems based on tin compounds active for vegetable oil transesterificaton reaction,” Journal of Molecular Catalysis A, vol. 27, no. 1-2, pp. 263–267, 2005.
[24]
C. C. S. Macedo, F. R. Abreu, A. P. Tavares et al., “New heterogeneous metal-oxides based catalyst for vegetable oil trans-esterification,” Journal of the Brazilian Chemical Society, vol. 17, no. 7, pp. 1291–1296, 2006.
[25]
D. Zhai, Y. Nie, Y. Yue, H. He, W. Hua, and Z. Gao, “Esterification and transesterification on Fe2O3-doped sulfated tin oxide catalysts,” Catalysis Communications, vol. 12, no. 7, pp. 593–596, 2011.
[26]
H. Matsuhashi, H. Miyazaki, and K. Arata, “The preparation of solid superacid of sulfated tin oxide with acidity higher than sulfated zirconia,” Chemistry Letters, vol. 30, no. 5, pp. 452–453, 2001.
[27]
H. Matsuhashi, H. Miyazaki, Y. Kawamura, H. Nakamura, and K. Arata, “Preparation of a solid superacid of sulfated tin oxide with acidity higher than that of sulfated zirconia and its applications to aldol condensation and benzoylation,” Chemistry of Materials, vol. 13, no. 9, pp. 3038–3042, 2001.
[28]
S. Furuta, H. Matsuhashi, and K. Arata, “Catalytic action of sulfated tin oxide for etherification and esterification in comparison with sulfated zirconia,” Applied Catalysis A, vol. 269, no. 1-2, pp. 187–191, 2004.
[29]
A. S. Khder, E. A. El-Sharkawy, S. A. El-Hakam, and A. I. Ahmed, “Surface characterization and catalytic activity of sulfated tin oxide catalyst,” Catalysis Communications, vol. 9, no. 5, pp. 769–777, 2008.
[30]
A. Sarkar, S. K. Ghosh, and P. Pramanik, “Investigation of the catalytic efficiency of a new mesoporous catalyst SnO2/WO3 towards oleic acid esterification,” Journal of Molecular Catalysis A, vol. 327, no. 1-2, pp. 73–79, 2010.
[31]
J. I. Moreno, R. Jaimesa, R. Gómezb, and M. E. Nino-Gómeza, “Catalysis in Iberoamerica. Selected papers from XXII Iberoamerican congress on catalysis,” Catalysis Today, vol. 172, no. 1, pp. 34–40, 2011.
[32]
L. Qi, J. Ma, H. Cheng, and Z. Zhao, “Synthesis and characterization of mesostructured tin oxide with crystalline walls,” Langmuir, vol. 14, no. 9, pp. 2579–2581, 1998.
[33]
K. Nuithitikul, W. Prasitturattanachai, and J. Limtrakul, “Catalytic activity of sulfated iron-tin mixed oxide for esterification of free fatty acids in crude palm oil: effects of iron precursor, calcination temperature and sulfate concentration,” International Journal of Chemical Reactor Engineering, vol. 9, no. 1, p. A98, 2011.
[34]
V. M. Mello, G. P. A. G. Pousa, M. S. C. Pereira, I. M. Dias, and P. A. Z. Suarez, “Metal oxides as heterogeneous catalysts for esterification of fatty acids obtained from soybean oil,” Fuel Processing Technology, vol. 92, no. 1, pp. 53–57, 2011.
[35]
C. S. Cordeiro, F. R. da Silva, F. Wypych, and L. P. Ramos, “Heterogeneous catalysts for biodiesel production,” Quimica Nova, vol. 34, no. 3, pp. 477–486, 2011.
[36]
S. Yan, S. O. Salley, and K. Y. S. Ng, “Simultaneous transesterification and esterification of unrefined or waste oils over ZnO-La2O3 catalysts,” Applied Catalysis A, vol. 353, no. 2, pp. 203–212, 2009.
