Reductive Depolymerization of Kraft and Organosolv Lignin in Supercritical Acetone for Chemicals and Materials

Kraft and organosolv lignin (KL and OL) were depolymerised efficiently in supercritical acetone in the presence of various hydrogenation catalysts (supported metal, e.g., Ni, Ru, Mo, W) and 100 bar hydrogen in the temperature range of 250-350 degrees C. Under the optimal conditions with Ru/C or FHUDS-2 catalysts at 350 degrees C for 1 h, the yield of depolymerised Kraft lignin (DKL) or depolymerised organosolv lignin (DOL) was over 95 wt%. The weight average molecular weight of the lignin was reduced significantly from 10200 (for KL) to 1020 gmol(-1) (DKL) and from 2600 (OL) to 900 gmol(-1) (DOL). The oxygen and sulfur contents of Kraft lignin were reduced by 24 and 96 %, respectively. The reductive depolymerisation treatment also decreased the amount of aliphatic hydroxyl groups and increased the amount of aromatic hydroxyl groups in the depolymerised lignin products.