Kinetic analysis of the catalytic hydrogenation of alkyl levulinates to γ-valerolactone

Abstract

γ-Valerolactone is considered as a promising platform chemical from lignocellulosic biomass. This study focusses on the kinetics of the production of γ-valerolactone from three different esters of levulinic acid using Ru supported on activated carbon as hydrogenation catalyst. Methyl, ethyl, and n-butyl levulinates are used as substrates. The transformation of these alkyl levulinates proceeds through a hydrogenation of the substrate to the intermediate γ-hydroxy valeriate followed by lactonization to form γ-valerolactone. Alkyl levulinates with shorter alkyl residue show an accelerated formation of γ-valerolactone. Nevertheless, an efficient transformation of all alkyl levulinates into γ-valerolactone is possible. The kinetic study indicates that at all reaction temperatures, lactonization occurs slower than hydrogenation and presents the rate-determining step. Analysis of the kinetic data shows the activation energies of hydrogenation and lactonization increase in the following order: methly levulinate<ethyl levulinate<butyl levulinate. Furthermore, activation energies for the hydrogenation and lactonization steps of the studied alkyl levulinates are in the range of 41–58kJmol-1 and 50–63kJmol-1, respectively, emphasizing the potential of alkyl levulinates as promising intermediates for γ-valerolactone formation.