Catalytic depolymerization/degradation of alkali lignin by dual-component catalysts in supercritical ethanol

Depolymerization of lignin is an important step to obtain lignin monomer for the synthesis of functional bio-polymers. In this paper, catalytic degradation/depolymerization of an alkali lignin was investigated in a supercritical ethanol system. The process conditions were optimized in terms of lignin monomer yield, and the liquid products and solid residue were characterized. Results show that the conversion rate of the alkali lignin was improved in both the Ni₇Au₃ catalyzed and Nickel-catalyzed systems with supercritical ethanol as the solvent. The maximum lignin conversion rate was 69.57% and 68% respectively for the Ni₇Au₃ and Nickel-based catalysis systems. Gas chromatography/mass spectroscopy (GC/MS) analysis indicated that the catalytic depolymerization products of alkali lignin were mainly monomeric phenolic compounds such as 2-methoxyphenol. The highest yield of 2-methoxyphenol (84.72%) was achieved with Ni₇Au₃ as the catalyst.