Process optimization, reaction kinetics, and thermodynamics studies of water addition on supercritical methyl acetate for continuous biodiesel production

Biodiesel production from rapeseed oil using supercritical methyl acetate with water addition has been developed to attain a higher biodiesel yield than that of supercritical methyl acetate without water. We newly constructed a plug flow reactor for the supercritical reaction usage system. We examined the effect of process variables by utilizing response surface methodology to optimize the process. As a result, the maximum biodiesel yield of 97 wt% was achieved at water addition of 8.2 wt%, reaction temperature of 578 K, and space time of 30 min. From the pseudo-first order reaction model, it was found that water addition under supercritical methyl acetate escalates reaction rate and reduces the activation energy of the reaction. The water addition improved the thermodynamics activation parameters, including enthalpy, entropy, Gibb’s energy, and equilibrium constant based on the transition-state theory. The thermodynamics activation parameters obtained show that the reaction was endothermic and unspontaneous.