Kinetic modeling, mechanistic, and thermodynamic studies of HPW-MAS-9 catalysed transesterification reaction for biodiesel synthesis

The kinetics and reaction mechanism of methanolysis of unrefined green seed canola oil using heterogeneous HPW-MAS-9 composite catalyst have been investigated. The activity coefficients of the reactant and product species were estimated using the UNIQUAC method. Eley-Rideal reaction pathway with the surface reaction of adsorbed methanol as the rate controlling step, was found to be a reliable representation of the observed kinetics. Other kinetic models deduced from pseudo-homogenous (PH) and Langmuir-Hinshelwood-Hougen-Watson (LHHW) were rejected based on statistical analysis. E-a (activation energy), Delta H double dagger (enthalpy of activation), Delta G double dagger (free energy of reaction), and Delta S* (entropy of activation) for the reaction were found to be 72.5 kJ mol(-1), 68.9 kJ mol(-1), 58.3 la mol(-1), and 0.04 kJ mol(-1), respectively. The positive values of Delta H double dagger and Delta G double dagger indicated that the reaction is endothermic and non-spontaneous. Intricate mechanistic details for the stepwise transesterification reactions were deduced from the kinetic and thermodynamic parameters. On the basis of the Delta S double dagger, the reaction of triglyceride to diglyceride followed the dissociative pathway (S-N 1 mechanism), whereas the reactions of diglyceride to monoglyceride and monoglyceride to glycerol proceeded via the associative pathway (S-N 2 mechanism).