Catalytic conversion of waste cooking oils for the production of liquid hydrocarbon biofuels using in-situ coating metal oxide on SBA-15 as heterogeneous catalyst

Abstract

Liquid hydrocarbon biofuels obtained from the catalytic cracking of animal fats and plant oils have become attractive because of their possible environmental benefits, and the current concerns over the depletion of fossil-fuel sources. In this work, five different metal-oxide (ZnO, La2O3, CeO2, NiO and MgO) modified SBA-15 (MeO-SBA-15) samples were prepared by a simple one-pot synthesis method and were used in the catalytic cracking of waste cooking oils. The synthesized catalysts were characterized using X-ray diffraction, N2 physisorption, transmission electron microscopy and Fourier-transform infrared techniques, and their catalytic performances were investigated in detail in the cracking of waste cooking oils. To obtain high-quality biofuel, all the pyrolysis products were separated into two compounds by distillation: (a) liquid hydrocarbon biofuels including gasoline and diesel fractions (distillation temperature ≤ 350 °C); (b) heavy oils (distillation temperature >350 °C). The results indicated that the mesostructure of the SBA-15 was well preserved after metal oxide modification, and the MeO-SBA-15 catalysts improved the hydrocarbon biofuels yield and decreased the heavy oil yield. Among the catalysts, the ZnO-SBA-15 showed an excellent catalytic performance and produced the highest biofuel yield (37.3%) and the lowest yield of heavy oils (39.9%). The liquid hydrocarbon biofuels obtained using the ZnO-SBA-15 catalyst had a similar chemical composition to the diesel-based fuels and showed a lower density, lower viscosity and higher heating values than raw waste cooking oils. These results indicated that ZnO-SBA-15 can promote the chemical reactions, such as deoxygenation and decarbonylation.