Catalytic Activity of KOH–CaO–Al2O3 Nanocomposites in Biodiesel Production: Impact of Preparation Method

Abstract

CaO–Al₂O₃ mixed oxides were prepared by different preparation methods–such as sol–gel, co-precipitation, impregnation, and MW-assisted solution combustion synthesis (M-SCS)–and then impregnated with KOH to examine their activity in transesterification of canola oil to biodiesel. Synthesized nanocomposites were characterized by XRD, FTIR, BET/BJH, and SEM/EDX. The mixed oxides, except those prepared by M-SCS method, exhibited a nearly amorphous structure with some diffraction peaks of calcium oxide. Due to high combustion temperature during the M-SCS process, Ca ions could diffuse into the alumina lattice to form CaAl₂O₄. But upon impregnation with KOH, the former transformed to Ca₁₂Al₁₄O₃₃. The KOH/Ca₁₂Al₁₄O₃₃ nanocatalyst prepared by M-SCS method exhibited better basicity, mean pore size, and activity, as well as highest Ca/Al and K/Al ratios. In the presence of this catalyst, around 86% of canola oil were converted to biodiesel in the transesterification reaction carried out at 65°C, methanol/oil molar ratio 12: 1, 4 wt% catalyst, 4 h. Such parameters seem appropriate for industrial application. The M-SCS method is technically simple, cost effective, time/energy saving and requires no further thermal treatment.