Reaction Kinetics of Vanillin Hydrogenation in Aqueous Solutions Using a Ru/C Catalyst

Aqueous phase processing (APP) of bio-oil represents a candidate technique for the production of renewable hydrogen (H-2) in a fast pyrolysis-based biorefinery. Low temperature hydrogenation of the water-soluble portion of bio-oil is a useful intermediate step of APP. In this work, the reaction kinetics of mild aqueous-phase hydrogenation of vanillin (VL), a model compound of the bio-oil aqueous fraction, was studied using Ru/C catalyst. The investigated aromatic aldehyde was converted to vanillyl alcohol (VA) and creosol (CR). Catalytic runs were performed in a slurry reactor in the 318-338 K range using different catalyst loadings (0.2-0.8 kg/m(3)), initial VL concentrations (32.9 to 65.7 mM) and H-2 partial pressures (0.69-2.07 MPa). The initial rates varied linearly with respect to both initial VL concentration and H-2 partial pressure. Four Langmuir-Hinshelwood-Hougen-Watson (LHHW) type kinetic models were proposed assuming that surface reaction was rate-determining. These models were simplified to a second order reaction model based on bulk concentration of the reacting species. From the temperature dependence of the second order reaction rate constant, the activation energy was found to be 41.2 kJ/mol.