Effect of Pd/C catalytic extraction on the hydrothermal depolymerization properties of ethanol organosolv lignin (EOL) in supercritical ethanol

Abstract

This study investigated the effect of a Pd/C catalytic extraction process on the hydrothermal depolymerization product properties of ethanol organosolv lignin (EOL) in supercritical ethanol. Phenolic products were separated and analyzed by gel permeation chromatography (GPC) and thermogravimetric (TG) analyses. The gas chromatography–mass spectrometry (GC-MS) analyses of obtained liquid oil products from depolymerized EOL confirmed the presence of value-added phenolics. Scanning electron microscopy (SEM) was used to observe the morphology of the char product. During ethanol organosolv lignin extraction, 90.5% purity of EOL was obtained. A high yield of EOL up to 39.6% from bamboo without catalysts and with higher yield of EOL up to 44.0% from 1% Pd/C catalyst under 200 °C. A high yield of liquid oil products, up to 65.4%, was recovered from EOL depolymerization under conditions of 240 °C, 240 min, 100 vol % ethanol, and 2% EOL, with only 24% solid residue. The main phenolic products were 2-methoxyphenol, 4-ethylphenol, 4-methoxy-2-methylphenol, 4-ethyl-2-methoxyphenol, 2,6-dimethoxy-phenol, and 2-methoxy-4-propylphenol.