Biodiesel production in the presence of heterogeneous catalyst of alumina: Study of kinetics and thermodynamics

In the current research, biodiesel production was investigated in the presence of solid catalysts of K2CO3/Al2O3 by transesterification of rapeseed oil. The specifications of produced fatty acid methyl esters like viscosity and flash point were studied, and it was noted that they complied with the requirements of ASTM D6751. In addition, the kinetic and thermodynamic parameters were explored considering the temperature changes between 318.15 and 348.15 K. Mass transfer resistance (external diffusion or internal diffusion) over the catalyst was neglected with regard to theWeisz-Prater criterion and Mears criterion. The kinetic models containing Eley-Rideal, Langmuir-Hinshelwood, pseudo-first-order, pseudo-second-order, and alpha-order models were investigated. Corrected Akaike information criterion was utilized to find the best model fitted with the experimental data. The greatest illustration for the K2CO3/Al2O3-catalyzed reaction was the nonlinear model with an order of alpha = 1.287 and the activation energy of 12.12 kJ/mol. Using transition state theory (Eyring-Polanyi equation), the activation Gibbs free energy, activation enthalpy, and activation entropy were calculated at different temperatures. The equilibrium thermodynamic properties depicted that this process is endothermic and spontaneous toward biodiesel production and tends to be irreversible.