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 (1), acetoguaiacone (2) and iso-eugenol (3) (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.

Graphical abstractThe use of water-soluble homogeneous ruthenium catalysts (Ru–TPPTS, prepared in situ by reacting RuCl3·3H2O and tris(m-sulfonatophenyl)phosphine, TPPTS) to hydrogenate the dichloromethane soluble fraction of fast pyrolysis oil is reported. Significant reductions in the aldehyde content were observed at mild conditions (<70 °C, 45 bar hydrogen). Model studies with typical lignin derived compounds were performed and it was shown that vanillin (1) is hydrogenated to creosol (6) via the intermediate vanillylalcohol (5). Figure optionsDownload full-size imageDownload as PowerPoint slide