Immobilizing Phosphotungstic Acid on Al2O3-ZnO Nano Mixed Oxides as Heterogeneous Catalyst for Biodiesel Production by Esterification of Free Fatty Acids

In this study, esterification reaction of different carboxylic acids (Acetic acid, Palmitic acid, Oleic acid) with ethanol was investigated by ZnO, Al2O3-ZnO mixed oxide and phosphotungestic acid (10 %wt) immobilized on the Al2O3-ZnO mixed oxide. The heterogeneous catalysts were characterized by XRD, BET, FE-SEM and EDX techniques. Optimum yield was achieved by using 10% HPW/Al2O3-ZnO as the best catalyst and the effect of amount of catalyst, molar ratio of acid to alcohol, reaction temperature and time was investigated to get the ideal yield of esterification reaction of acetic acid and ethanol. The results showed that the esterification of acetic acid to its ethyl ester was carried out in 3.5 hours, alcohol to acid molar ratio equal to 2 and temperature of 80˚C with yield 98%. Also, the 10% HPW/Al2O3-ZnO catalyst showed well activity in biodiesel production by esterification of palmitic and oleic acids and the reaction yield didn’t decrease with increasing of alkyl chain length in acid molecules, remarkably.