The Protection of C−O Bond of Pine Lignin in Different Organic Solvent Systems

Abstract

The methods of extraction and degradation of lignin from biomass are very important for obtaining high value-added chemical precursors. In this paper, pine wood powder was selected as the feedstock to investigate the effect of different organic solvent systems (ethanol, ethylene glycol, 1, 4-butanediol and acetone) on the lignin extraction using different radio of H2SO4 and acetic acid. The extraction yields were calculated, the solvent lignin structure was analyzed by SEM, Elemental Analyzer, GPC, FT-IR, HSQC and the organosolv lignin was depolymerized over NaOH and Pd/C in ethanol. The results showed that the molecular weight of all lignin extracted from biomass by different organic solvents were lower than 2000 g mol−1. Among the organic solvents, acetic acid and glycol could react with the γ and ɑ position of the β-O-4 bond in lignin, which protect the C−O bond during the extraction treatment. The analysis of depolymerization products suggested that the ethylene glycol had the best ability of retaining the structures of lignin and dissolution. About 17.74 wt. % aromatic compounds were obtained from the ethylene glycol lignin in 2 MPa H2 at 240°C, which were mainly phenyl alcohol compounds. Ethylene glycol lignin could give more aromatic hydrocarbon compounds and phenols than the other two kinds of lignin. Ethylene glycol and 1,4-butanediol was also found in the depolymerization product respectively. The protection of the C−O bond offers effective strategies for directional depolymerization design.