Depolymerization of oak wood lignin under mild conditions using the acidic ionic liquid 1-H-3-methylimidazolium chloride as both solvent and catalyst

• Published in: Bioresource technology Vol. 118; pp. 584 - 588
• Main Authors: Cox, Blair J., Ekerdt, John G.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-08-2012
• Subjects: Biomass; Catalysis - drug effects; catalysts; Chlorides; Chromatography, Gel; Depolymerization; Ethers; Fragments; gel permeation chromatography; hydrolysis; Imidazoles - pharmacology; Ionic liquid; Ionic liquids; Ionic Liquids - pharmacology; Lignin; Lignin - chemistry; nuclear magnetic resonance spectroscopy; Oak; Polymerization - drug effects; Pretreatment; Quercus; Quercus - chemistry; Reference Standards; Solvents; Solvents - pharmacology; Wood; Wood - chemistry; Lignin; Biomass; Pretreatment; Ionic liquid
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2012.05.012

► Lignin extracted from wood in ionic liquid through dissolution and precipitation. ► Lignin reacted with 1-H-3-methylimidazolium chloride at mild temperatures. ► Hydrolysis of lignin ether linkages with acidic ionic liquid was demonstrated. ► Acidic ionic liquid could be used for biomass pretreatment by lignin degradation.
Oak wood lignin, which was separated from the wood using dissolution in the ionic liquid 1-methyl-3-ethylimidazolium acetate and subsequent precipitation, was successfully depolymerized in the acidic ionic liquid 1-H-3-methylimidazolium chloride under mild conditions (110–150°C). Based on gel permeation chromatography results, an increase in temperature from 110 to 150°C increased the rate of reaction, but did not significantly change the final size of the lignin fragments. Nuclear magnetic resonance and infrared spectroscopy were utilized to demonstrate that the depolymerization proceeded via a hydrolysis reaction that cleaved the alkyl–aryl ether linkages. Coupling of the lignin fragments was also shown to occur in the reaction mixture. These hydrolysis results are consistent with the literature on acid catalyzed depolymerization of lignin in conventional solvents and with recent model compound studies involving guaiacylglycerol-β-guaiacyl ether and veratrylglycerol-β-guaiacyl ether done in acidic ionic liquids.