Solvent effect investigation on the acid-catalyzed esterification of levulinic acid by ethanol aided by a Linear Solvation Energy Relationship

Abstract

When processing lignocellulosic biomass materials to obtain platform molecules such as levulinic acid (LA), alkyl levulinates or γ-valerolactone (GVL), the choice of solvent is of prime importance for kinetics. The knowledge of relationships between reaction kinetics and solvent serves as a decision tool for process design. To determine such relationships, esterification reactions was chosen because such reaction steps are present in several biomass conversion processes. In this work, kinetic models of LA esterification by ethanol over sulfuric acid in polar aprotic solvent (GVL) and polar protic solvents (water or ethanol) were developed and evaluated by Bayesian statistics. The apparent dissociation constants in solvents were estimated by ePC-SAFT approach to distinguish the proton concentration from the rate constants. The developed models can fit the experimental concentrations of ethyl levulinate and predict the proton concentration. Using the Kalmet-Abboud-Taft equation, linear relationships between estimated rate constants and solvent properties were established at different temperatures. We observed that solvents with low polarizability and high hydrogen-bond acceptor capacity should be favored for this reaction. Hence, the reaction of esterification is faster in ethanol solvent than in GVL solvent than in water solvent.