Glucose hydrogenation on ruthenium catalysts in a trickle-bed reactor

Glucose in 40 wt% aqueous solution was hydrogenated into sorbitol in a trickle-bed reactor over ruthenium catalysts supported on active charcoal pellets. The metal was loaded by cationic exchange or anionic adsorption. After reduction, ruthenium was under the form of 1-nm particles homogeneously distributed throughout the support. The reaction was conducted at 100 degrees C under 8 MPa of hydrogen at 20 L h(-1) flow rate. Conversion and selectivity to sorbitol were studied as a function of residence time. Whatever the mode of preparation, the catalysts give a total conversion of glucose with an initial specific activity of 1.1 mol h(-1) g(-1). The selectivity to sorbitol was higher than 99.2% at 100% conversion; however, the liquid flow rate should be adjusted very accurately because any increase in the residence time results in a loss of selectivity due to epimerization of sorbitol into mannitol. The catalyst activity was stable over several weeks and no leaching of ruthenium was detected. (C) 1998 Academic Press.