High Phenol Yields from Catalytic Hydropyrolysis of Lignin and Phenolic-Rich Raffinate

In this work, fast pyrolysis of woody biomass for levoglucosan production was combined with reductive thermoca-talytic valorization of its two main side streams, being (i) pyrolytic lignin and (ii) a phenolic-rich raffinate. Pyrolytic lignin is the precipitate, obtained upon cold water precipitation of pyrolysis oil. The phenolic-rich raffinate is the organic phase that originates from subsequent solvent extraction of the former water and levoglucosan-rich stream. This organic raffinate contains water-soluble phenolic monomers and is as such an underexplored (co-)feed for hydropyrolysis. Hydropyrolysis was performed of (i) pyrolytic lignin, (ii) pyrolysis oil-derived phenolics from the organic raffinate, (iii) organosolv lignin as model technical lignin, and a combination of pyrolytic lignin and pyrolysis oil-derived phenolics. The effect of hydrogen pressure (4 and 30 bar) and the presence of a Pd/C catalyst on the product slate and yields were assessed. Without catalytic vapor-phase upgrading, many different low-concentration phenolics were obtained, with a total yield of ca. 10 wt % (for pyrolytic lignin) to 13 wt % (for pyrolysis oil-derived phenolics). The product slate positively decomplexified upon catalytic vapor-phase upgrading. The yield in phenolics decreased modestly to 7-10 wt %, mostly being phenol, cresol, and xylenol. Pyrolysis oil-derived phenolics had for these conditions the highest yield in phenolics; its application as co-feed thus always goes in tandem with a yield increase in phenolics. It was also calculated that conversion of all quantified monomers to either phenol or catechol, yielded ca. 5-6 wt % phenol or 5-7 wt % catechol. From pine wood to phenolics, the yield varied between 1.9 (catalytic hydropyrolysis) and 2.3 wt% (non-catalytic). Overall, this work demonstrates value creation from overlooked side streams of the pyrolysis refinery.