Readily available and cheap feedstocks such as waste cooking oils as supposed to fresh edible oils, represent a better feedstock option for sustainable biodiesel synthesis. However, these cheap feedstocks contain relatively high levels of free fatty acids. Heterogeneous solid acid catalysts are preferred for such low-cost feedstocks because these catalysts are insensitive to high levels of free fatty acids in the raw materials. In this work, we evaluated different solid catalysts such as β-zeolite, ZnO-β-zeolite and SO42−/ZnO-β-zeolite for the production of biodiesel from waste cooking oil. The catalysts were characterized by FTIR, pyridine-FTIR, N2 adsorption-desorption, XRD, thermogravimetric analysis (TGA), and SEM. The resulting biodiesel was analyzed using 1H and 13C NMR and GC-MS. The SO42−/ZnO-β-zeolite catalyst showed good catalytic performance, which was higher than that of β-zeolite and ZnO-β-zeolite. We ascribed this performance to the high pore size, and high acidity of SO42−/ZnO-β-zeolite. The existence of Lewis/Brønsted acid sites on the surface of this catalyst due to incorporation of sulfonate group could explain the increased activity of the catalyst and consequently higher catalytic performance. We also conducted kinetic studies, which showed that the esterification reaction follows a pseudo first-order kinetic model, with an activation energy (Ea) of 38.6 kJ/mol.

Evaluation of different β-zeolite catalysts for biodiesel production from waste cooking oil

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