Abstract
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•New mixtures of [Ch][AA]-glycerol are biocompatible and cost-effective solvents.•50% [Ch][Ala]-glycerol is comparable to other solvents on wheat straw pretreatment.•The pH of [Ch][AA]-glycerol affects lignin removal and polysaccharide conversion.•[Ch][AA] can remove lignin while not remarkably dissolve and only swell cellulose.•Glycerol can inhibit xylan loss.
New solvents for pretreating wheat straw, mixtures of cholinium amino acids ionic liquids ([Ch][AA] ILs) and glycerol, were developed. As a typical result, 50% cholinium alanine-glycerol is capable of removing 67.6% lignin while reserving 95.1% cellulose (90°C, L/S mass ratio of 20:1, 6h) and the conversions of cellulose and xylan are 89.7% and 70.9%, respectively, which is comparable to the pretreatment capability of other solvents, while [Ch][AA]-glycerol mixtures have desirable advantages, e.g., biocompatibility, lower cost with adding glycerol than pure IL, much lower pretreatment temperature (typically <100°C) than that by glycerol (typically >200°C). Lignin removal and polysaccharide conversion are dependent on [Ch][AA] content and pH of pretreatment solvents. [Ch][AA] not only remove lignin in wheat straw effectively but also swell cellulose while not remarkably dissolve cellulose with high cellulose reservation, favoring the enzymatic hydrolysis. Such mixtures of ILs and co-solvents are potential solvents for pretreating biomass.