Pretreatment and Fractionation of Wheat Straw by an Acetone-Based Organosolv Process

Abstract

Acetone-based organosolv fractionation of wheat straw was studied to produce sugars and lignin in a lignocellulose biorefinery. The influence of acetone-water ratio, reaction time, and temperature on fractionation degree, lignin yield, and enzymatic digestibility of the cellulose fraction was examined. The solvent-water ratio was found to influence delignification and hemicellulose hydrolysis by its effect on lignin solubility and pH. Organosolv treatment in 50:50% w/w acetone-water during 1 h at 205°C resulted in 82% hemicellulose hydrolysis, 79% delignification, and 93% cellulose recovery. A substantial part of the sugars formed upon hemicellulose hydrolysis seems to have reacted further including possible formation of lignin-furfural condensation products. Finally, aqueous acetone pretreatment was found to substantially improve the enzymatic digestibility of the cellulose fraction (glucose yield: up to 87% vs 16% for untreated wheat straw).

Pyrolysis of wheat straw-derived organosolv lignin

“…This type of residue seems only suited as fuel for heat and power generation. An alternative pretreatment technology is organosolv fractionation that uses organic solvents such as ethanol to delignify biomass prior to enzymatic hydrolysis [8,9]. Subsequently, the lignin can be recovered from the organosolv liquor with a high purity and essentially free of sulphur and ash.…”

“…No extractions were performed prior to hydrolysis. For more details about these analyses we refer to [9]. The elemental analysis (C, H, N, O) of the lignins was determined in duplicate using a Carlo-Erba analyzer.…”

“…Apparently, the furfural is formed from another source, possibly from 'pseudo lignin', a lignin-like substance resulting from polymerization reactions of (hemi)cellulose derivatives like furfural or condensation reactions between lignin and furfural that have been reported to occur during organosolv [9].…”

Pretreatments to Enhance the Digestibility of Wheat Straw

“…Ethanol is a renewable solvent and its volatility facilitates the extensive recycling required [87]. Wheat straw (Fig.6) has been successfully pulped and pretreated using aqueous ethanol in previous studies [82,90,91]. A maximum enzymatic digestibility of 86% with a lignin yield of 84% was reached without the use of a catalyst (organosolv at 210 C, 50% w/w aqueous EtOH) [77].…”

“…A maximum enzymatic digestibility of 86% with a lignin yield of 84% was reached without the use of a catalyst (organosolv at 210 C, 50% w/w aqueous EtOH) [77]. A drawback of the organosolv process is that the conditions required to delignify lignocellulosic feedstocks may lead to low yields of hemicelluloses sugars due to degradation and subsequent formation of humans and condensation products with lignin [82,87]. In earlier work on autocatalytic acetone-based organosolv pretreatment of wheat straw, were illustrated that, at conditions yielding maximum enzymatic digestibility (205C o ), the yield of the major hemicellulose sugar xylose was only 4% of its theoretical maximum or 1% w/w raw wheat straw [81].…”