Kinetics of the production of alkyl esters by transesterification of soybean oil

Abstract

AbstractBiodiesel was produced by transesterification from soybean oil using methanol (methanolysis) and ethanol (ethanolysis) under conditions including NaOH/alcohol 0.50% wt, molar ratio alcohol:oil = 6:1, 600 rpm, 333 K. The evolution of biodiesel and glycerol esters concentrations were obtained by gas chromatography and liquid chromatography, respectively, as a basis for the evaluation of the kinetics of the process. A mathematical model was developed to represent the batch transesterification operations, referring to a mechanism including reactive acylglycerols and intermediates, esters, and glycerol. Considering the importance of the composition of fatty esters in biodiesel, their evolution during processing was quantified. The specific reaction rates for methanolysis and ethanolysis were 0.245 and 0.275 min−1, respectively. The concentration evolution of each fatty ester of the biodiesel was predicted by the solutions of the model equations, based on specific reaction rate constants quantified in the orders of magnitude k = 0.225–0.245 min−1 for methanolysis, and k = 0.225–0.275 min−1 for ethanolysis. Selectivity and yield values of the fatty esters were calculated: it was found Si = 23.5%–25.6% and Ri = 66.3%–89.1% for methanolysis and Si = 21.8%–26.7% and Ri = 74.1%–90.6% for ethanolysis. Based on the model, predictions of the kinetic behavior of acylglycerols reactants (triacylglycerois) and intermediates (monacylglycerois, diacylglycerois) were established.