Valorization of Glycerol Into Short‐Chain Esters: Kinetic and Thermodynamic Aspects

Abstract

Latin America is the second-largest global biodiesel producer, making bio-derived glycerol—its by-product—an abundant and accessible chemical platform in the region. This study explores kinetic and thermodynamic aspects of the straightforward valorization route of glycerol into short-chain esters, furthering insights previously reported by our group on fatty-acid glycerol esterifications. Three carboxylic acids —formic, acetic, and levulinic—were mixed with glycerol in stoichiometric amounts. The performance of two acid catalysts, a lipase, and the addition of a nonpolar solvent was evaluated by initial rates, final conversions, and glyceride selectivities. Sulfuric acid and p-toluenesulfonic acid exhibited excellent catalytic properties for the esterification of levulinic acid, inhibiting the nonselective ketalization. The carboxylic acid reactivity can be correlated with their chain length even for fatty acids immiscible in glycerol, which showed significantly lower reaction rates. The esterifications with short-chain acids predominantly yielded monoglycerides, with low diglyceride content and no triglycerides. The commercial lipase Candida antarctica B immobilized on porous methacrylate was inactive in these systems but showed partial activity when toluene was added, yielding over 50% diglycerides. UNIFAC flash calculations confirmed that the partitioning of products from the reactive phase to the second phase shifted the equilibrium of glycerol esterifications toward more substituted glycerides, a phenomenon already observed in solvent-free esterifications with immiscible fatty acids. Chemical equilibrium constants based on activities are reported for mono- and di-glycerides formation with acetic and levulinic acids, a key parameter of thermodynamically limited reactions.