A multi reaction kinetic model to describe the enzymatic transesterification reaction of jatropha oil using a fermented solid containing lipases

Abstract

The advancement of more precise tools for sustainable process design in enzymatic biodiesel synthesis from renewable sources is crucial. Kinetics of solvent-free transesterification reactions were conducted across a temperature spectrum from 30 °C to 60 °C, utilizing Jatropha curcas oil (T_G) and ethanol as substrates, alongside a fermented solid by Rhizopus homothallicus as the biocatalyst. The dynamics of chemical species concentrations were monitored through High-performance Thin-Layer Chromatography. Maximum productivities were achieved at 35 °C and 60 °C for biodiesel (293.24 and 299.02 g kg biocat⁻¹ h⁻¹, respectively), at 40 °C for diglycerides (1018.36 g kg biocat⁻¹ h⁻¹), and at 35 °C for monoglycerides (560.75 g kg biocat⁻¹ h⁻¹). Maximum yields were determined at 30 °C for fatty acid ethyl esters (0.56 g gT_G⁻¹), and at 40 °C for diglycerides (0.53 g gT_G⁻¹) and monoglycerides (0.30 g gT_G⁻¹). Based on the experimental findings, a kinetic model was formulated encompassing three reversible transesterification reactions. Individual reactions were structured following classical biochemical kinetics, inclusive of ethanol inhibition. Model fitting was executed through non-linear multivariable regression techniques, with the minimum of the average coefficient of variation of the residuals (ACV_R) serving as the objective function. The resulting fit of the kinetic model to the experimental data proved satisfactory, with an ACV_R of less than 5 % across all instances. Notably, the maximum biodiesel productivity, obtained in this work, represented the highest value, compared to other related studies, using a fermented solid as a biocatalyst.