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

Abstract

AbstractKraft 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 °C. Under the optimal conditions with Ru/C or FHUDS‐2 catalysts at 350 °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 10 200 (for KL) to 1020 g mol−1 (DKL) and from 2600 (OL) to 900 g mol−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.