Abstract
Esters are a highly relevant class of compounds in the industrial context, and biocatalysis applied to ester syntheses is already a reality for some chemical companies. Their syntheses in solvent-free systems using immobilized lipases show many economic and environmental advantages. However, considering the complexity and the variety of the simultaneous phenomena involved, the optimization of reactions in these systems is challenging. In a solvent-free system, the molar ratio of the reagents is of utmost importance, defining the behavior of the reaction medium in terms of polarity, mutual solubility, and water activity. Furthermore, the molar ratio of reagents determines the environment in which the immobilized lipase will act, and the intensity of its influence depends on the biocatalyst loading. The variation of the molar ratio and biocatalyst loading, essential parameters to be determined in an optimization study, will significantly impact the thermodynamics and kinetics of the synthesis. In this context, this review intends to show the most relevant aspects for solvent-free enzymatic esterification from thermodynamic and kinetic perspectives.