Studying the kinetics of rapeseed oil reactions with methanol, methyl formate, and methyl acetate under mild conditions for biodiesel production

Abstract

The rate constants of the transesterification reactions of rapeseed oil with methanol, methyl formate, and methyl acetate at room temperature in the presence of homogeneous potassium tert-butoxide in tetrahydrofuran were investigated and mutually compared for the first time. The aim of this study is to ascertain which of these reactants is the most promising in terms of reaction rate and fuel product formation with higher biodiesel yield. As rapeseed oil and methanol are immiscible with each other, the use of tetrahydrofuran as a co-solvent was also investigated to improve the miscibility of the oil and reactant and to exclude mass transfer effects. The pseudo-first-order kinetic model best described the reaction of the oil with methanol, with a reaction rate constant of 1.49 min−1, whereas the second-order kinetic model best described the reactions with methyl acetate and methyl formate, with reaction rate constants of 6.66 and 4.05 L mol−1 min−1, respectively, at 25 °C. The best yield of biodiesel was obtained by the interesterification of triglycerides with methyl acetate (86.5%), and the properties of the obtained product conform closely to the biodiesel standard requirements despite the use of mild reaction conditions to save energy.