Highly Efficient Liquefaction of Woody Biomass in Hot-Compressed Alcohol−Water Co-solvents

TLDR

FTIR and GC‑MS analyses of the bio‑oil revealed a predominance of phenolic compounds and their derivatives, along with aldehydes, ketones, alcohols, esters, acids, and ethers. Using a 50 wt % methanol–water or ethanol–water co‑solvent at 300 °C for 15 min, the process achieved ~65 wt % bio‑oil yield and >95 % biomass conversion, with hot‑compressed ethanol promoting lignin depolymerization to monomeric phenols, while temperatures above 300 °C led to significant char formation and complete conversion of cellulose to amorphous or crystalline carbon.

Abstract

Alcohol (methanol or ethanol) and water showed synergistic effects on biomass direct liquefaction, and the 50 wt % co-solvent of either methanol−water or ethanol−water was found to be the most effective solvent for the liquefaction of eastern white pine sawdust. The 50 wt % aqueous alcohol at 300 °C for 15 min produced a bio-oil yield at approximately 65 wt % and a biomass conversion of >95%. At a temperature higher than 300 °C, conversion of bio-oil to char was significant by repolymerization. The Fourier transform infrared spectroscopy (FTIR) and gas chromatography−mass spectrometry (GC−MS) analyses of the obtained bio-oils confirmed the presence of primarily phenolic compounds and their derivatives (such as benzenes), followed by aldehyde, long-chain (and cyclic) ketone and alcohol, ester, organic acid, and ether compounds. Gel permeation chromatography (GPC) results suggested that hot-compressed ethanol as the liquefaction solvent favored lignin degradation into monomeric phenols. The X-ray diffraction (XRD) patterns of sawdust before and after the liquefaction displayed that the cellulosic structure of the feedstock was completely converted into amorphous carbon at around 300 °C and into crystalline carbon at about 350 °C.