A combined sorption and kinetic model for multiphasic ethyl esterification of fatty acids from soybean soapstock acid oil catalyzed by a fermented solid with lipase activity in a solvent-free system

Abstract

A low-cost enzymatic catalyst for biodiesel production can be produced by growing a lipase-producing organism in solid-state fermentation and then drying the solids after the fermentation. Recently, we cultivated Burkholderia cepacia on a mixture of sugar cane bagasse and sunflower seed meal and used the dried fermented solid to catalyze the esterification of fatty acids with ethanol in a solvent-free system (Soares et al., Fuel (2015) 159, 364–372). During the reaction, up to 30% of the reaction medium sorbed onto the dried fermented solid, with the sorbed medium having a composition different from that of the bulk phase. In the current work, we develop a combined sorption-kinetic model to describe the reaction kinetics in this system. The sorption of the medium components onto the fermented solid follows a multicomponent Langmuir isotherm, while the kinetic equation is expressed in terms of the composition of the sorbed phase. With a single set of parameters, the model adjusted well to the experimental results obtained by Soares et al. for three different ethanol to fatty acid molar ratios (1:1, 1.5:1 and 3:1), not only for the overall conversion profile, but also for the compositions of the bulk phase and the sorbed phase. The model has potential to be used to guide the scale-up of our system.