Hydrogenation of gluconolactones in equilibrium with gluconic acid on ruthenium catalyst

Water solutions of glucono-delta-lactone and glucono-gamma-lactone in equil ibrium with gluconic acid were hydrogenated with molecular hydrogen in the presence of a commercial carbon-supported ruthenium catalyst (5% Ru/C, Enge lhard Escat 40). Reactions were conducted batchwise on 20 wt% solutions und er 100 bar pressure in the temperature range 80-140 degrees C. Reaction rat es were unexpectedly high at moderate temperatures (e.g., 0.58 mol h(-1) g( Ru)(-1) at 100 degrees C) because lactones were probably the reactive speci es. The selectivity to sorbitol at total conversion was larger than 99% at temperatures lower than 100 degrees C. Kinetic study was done at different temperatures, pressures and concentrations. Modelling of the reaction kinet ics showed that the reaction followed a rate law corresponding either to th e Langmuir-Hinshelwood mechanism without H-2 dissociation, or to the Horiut i-Polanyi mechanism.