Ultrasound-assisted biodiesel production using heterogeneous base catalyst and mixed non-edible oils

In the present study, the ultrasound-assisted biodiesel production from mixed feedstock of non-edible oils in presence of KI impregnated ZnO as a catalyst in batch reactor was investigated. The production was optimized by using two approaches (1) feedstock optimization and (2) process parameters optimization. Various non-edible oils at optimum volumetric ratio were blended and used as feedstock for transesterification reaction. Biodiesel yield was optimized by Box-Behnken statistical design. The maximum triglyceride conversion of 92.35 ± 1.08% was achieved at optimized conditions of catalyst loading = 7% (w/w); alcohol/oil molar ratio = 11.68:1 and reaction temperature = 59 °C. Transesterification process with mechanical agitation was used as base case for identification of role of sonication in the process. The transesterification process was analysed for kinetic behaviour using pseudo first order kinetics and Eley-Rideal mechanism based model. Overall activation energy of transesterification process for mechanically agitated and ultrasound-assisted systems was calculated as 135.4 and 123.65 kJ/mol, respectively. However, the sum of activation energies of three reaction steps of Eley-Rideal mechanism (64.69 kJ/mol and 46.63 kJ/mol, for mechanically agitated and ultrasound-assisted system, respectively) was much lower. This discrepancy is attributed to mass transfer limitations in the system, even in presence of sonication.