Hydrogenation of gluconolactones in equilibrium with gluconic acid on ruthenium catalyst

Water solutions of glucono-δ-lactone and glucono-γ-lactone in equilibrium with gluconic acid were hydrogenated with molecular hydrogen in the presence of a commercial carbon-supported ruthenium catalyst (5% Ru/C, Engelhard Escat 40). Reactions were conducted batchwise on 20 wt% solutions under 100 bar pressure in the temperature range 80–140°C. Reaction rates were unexpectedly high at moderate temperatures (e.g., 0.58 mol h -1 g Ru -1 at 100°C) because lactones were probably the reactive species. The selectivity to sorbitol at total conversion was larger than 99% at temperatures lower than 100°C. Kinetic study was done at different temperatures, pressures and concentrations. Modelling of the reaction kinetics showed that the reaction followed a rate law corresponding either to the Langmuir–Hinshelwood mechanism without H 2 dissociation, or to the Horiuti–Polanyi mechanism.