Kinetics of the catalytic hydrogenation of D-lactose on a carbon supported ruthenium catalyst

Catalytic hydrogenation of D-lactose to lactitol over various supported ruthenium catalysts was studied in a semi-batch slurry autoclave (300 ml, Paff Co.). 5% Ru/C (Johnson Matthey) had the best activity and gave the highest lactitol yield of the studied catalysts. Kinetic experiments of hydrogenation of aqueous D-lactose (1.31 mol/l) solutions on 5% Ru/C were performed at 40-60 bar hydrogen and 110-130 degrees C. The main hydrogenation product was lactitol, the selectivity varied between 96.5 and 98.5%, while small amounts of lactulose, lactulitol, sorbitol, galactitol and lactobionic acid were detected as by-products. The selectivity improved, as the hydrogen pressure increased and the reaction temperature decreased within the experimental range. The kinetic data were modelled by Langmuir-Hinshelwood-Hougen-Watson (LHHW) rate expressions, assuming surface reaction steps being rate determining. Non-competitive adsorption of molecular hydrogen and lactose on the catalyst surface was assumed. The kinetic model was fitted to the experimental data by a combined Simplex-Levenberg-Marquardt method. The model predicted the experimental concentrations of lactose and lactitol very well. A reasonable good description of the by-products was obtained. (C) 2007 Elsevier B.V. All rights reserved.