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

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 RuCl2(PPh3)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.

Biomass to Fuels. Upgrading of Flash Pyrolysis Oil by Reactive Distillation Using a High Boiling Alcohol and Acid Catalysts

We here report our studies on the upgrading of flash pyrolysis oil using an improved alcohol treatment method. The method consists of treating pyrolysis oil with a high boiling alcohol like n-butanol in the presence of a (solid) acid catalyst at 323–353 K under reduced pressure (<10 kPa). Using this approach, the water content of the pyrolysis oil is reduced significantly. Variables like the type of alcohol (n-butanol, ethylene glycol, 2-ethyl-hexyl-alcohol) and liquid and solid acids were explored and the product properties of the resulting upgraded pyrolysis oil (kinematics viscosity, water content, pH and heating value) were determined. On the basis of these screenings studies, n-butanol and the solid acid Nafion SAC13 seem to have the highest potential. The product properties of the upgraded pyrolysis oils, and particularly the heating value and the acidity are considerably improved. These improvements are not only due to blending effects but also the result of the occurrence of chemical reactions (a.o. esterification).

The application of water-soluble ruthenium catalysts for the hydrogenation of the dichloromethane soluble fraction of fast pyrolysis oil and related model compounds in a two phase aqueous–organic system

The hydrogenation of a dichloromethane soluble fraction of flash pyrolysis oil (bio-oil, BO), obtained by treatment of BO with a water–dichloromethane solvent mixture, was investigated using a water-soluble homogeneous ruthenium catalyst (RuCl3·3H2O/tris(m-sulfonatophenyl)phosphine, TPPTS). The catalyst is active at mild conditions (<70 °C, 45 bar hydrogen) and particularly the levels of aldehydes in the BO fraction are reduced considerably. Model studies using vanillin, acetoguaiacone and iso-eugenol (45 bar hydrogen and 45–70 °C) showed that vanillin is the most reactive and unexpectedly forms creosol (6) instead of the vanillylalcohol (5). An optimisation study was performed on the latter reaction and the highest TOF (36.4 mol/(mol h)) was obtained at 60 °C, 45 bar hydrogen and a NaI concentration of 0.08 M. Kinetic studies imply that the formation of 6 proceeds via the intermediate alcohol 5 in a series type of mechanism. TEM-EDX measurements suggest that the reactions are most likely catalyzed by single metal homogeneous Ru complexes and not by Ru nanoparticles/colloids.