Hydrogenation of fast pyrolyis oil and model compounds in a two-phase aqueous organic system using homogeneous ruthenium catalysts

Abstract

The use of homogeneous ruthenium catalysts to hydrogenate the water-soluble fraction of pyrolysis oil is reported. Pyrolysis oil, which is obtained by fast pyrolysis of lignocellulosic biomass at 450–600 °C, contains significant amounts of aldehydes and ketones (e.g. 1-hydroxy-2-propanone ( 1) and 1-hydroxy-2-ethanal ( 2)), that are known to have a negative effect on the product properties (a.o. storage stability) of pyrolysis oil. The hydrogenation experiments were performed at mild conditions (40 bar, 90 °C) using a biphasic system (water/toluene) and RuCl 2(PPh 3) 3 as the toluene soluble catalyst. Significant reductions in the amounts of ( 1) and ( 2) were observed, demonstrating the potential of homogeneous Ru-catalysts to upgrade pyrolysis oils. Model studies showed that ( 1) and ( 2) are selectively hydrogenated to 1,2-propanediol and 1,2-ethanediol, respectively. The influence of the temperature (50–90 °C), pressure (20–40 bar) and initial substrate concentration on the reaction rates were investigated. For ( 2), the reaction was shown to be first order in substrate and zero order in hydrogen. An overall kinetic model for the hydrogenation of ( 2) was developed including the rate of active catalyst formation and the kinetic parameters were determined.