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Keywords:

  • depolymerization;
  • heterogeneous catalysis;
  • Kraft lignin;
  • molybdenum carbide catalysts;
  • supercritical ethanol

Abstract

We report the complete ethanolysis of Kraft lignin over an α-MoC1−x/AC catalyst in pure ethanol at 280 °C to give high-value chemicals of low molecular weight with a maximum overall yield of the 25 most abundant liquid products (LP25) of 1.64 g per gram of lignin. The LP25 products consisted of C6–C10 esters, alcohols, arenes, phenols, and benzyl alcohols with an overall heating value of 36.5 MJ kg−1. C6 alcohols and C8 esters predominated and accounted for 82 wt % of the LP25 products. No oligomers or char were formed in the process. With our catalyst, ethanol is the only effective solvent for the reaction. Supercritical ethanol on its own degrades Kraft lignin into a mixture of small molecules and molecular fragments of intermediate size with molecular weights in the range 700–1400, differing in steps of 58 units, which is the weight of the branched-chain linkage C3H6O in lignin. Hydrogen was found to have a negative effect on the formation of the low-molecular-weight products.