Characterization of milled solid residue from cypress liquefaction in sub- and super ethanol

Cypress liquefaction in sub- and super ethanol was carried out in an autoclave at various temperatures. Milled solid residue (MSR) was isolated from solid residue remaining from the liquefaction process, and its chemical characteristics was comparatively investigated with milled wood lignin (MWL) of cypress by sugar analysis, elemental analysis, FT-IR analysis, gel permeation chromatography, and NMR analysis. Results showed that there were two reactions (de-polymerization and re-polymerization) during the cypress liquefaction in sub- and super ethanol and the re-polymerization reactions were the main reaction at 220–260 °C. Considering the stability of side-chain, the stability of lignin side-chain in cypress during liquefaction process in ethanol could be sequenced as follows: β-5 > β-β′ > β-O-4′. The MSR were mainly from the decomposition and re-polymerization of lignin. This study suggests that characterization of MSR provides a promising method to investigate the mechanisms of cypress liquefaction in ethanol.