Deep eutectic solvents’ ability to solubilize lignin, cellulose, and hemicellulose; thermal stability; and density

[Display omitted] •Preferential dissolution of lignin in 5 deep eutectic solvents (DESs).•TGA data shows DES are stable at 100°C–160°C, typical for biomass processing.•Pretreatment of loblolly pine by a DES gives glucose yield 7× that of controls.•Bulk density of DES-pretreated product is 40% higher than raw pine’s density. An environmentally-friendly method to separate cellulose and hemicelluloses from lignin in recalcitrant biomass for subsequent conversion is desirable to reduce greenhouse gas generation. Easily-prepared, deep eutectic solvents (DESs) have low volatility, wide liquid range, non-flammability, nontoxicity, biocompatibility, and biodegradability. This study shows the DESs (formic acid:choline chloride, lactic acid:choline chloride, acetic acid:choline chloride, lactic acid:betaine, and lactic acid:proline) to be capable of preferentially dissolving lignin at 60°C. Thermogravimetric analysis show DES to be stable at typical biomass processing temperatures. Pretreating loblolly pine in one DES increased glucose yield after enzymatic hydrolysis to more than seven times that of raw or glycerol-pretreated pine. The density of DES-pretreated biomass was found to be 40% higher than the untreated pine’s density.