Imidazole: Prospect Solvent for Lignocellulosic Biomass Fractionation and Delignification

The future widespread production of biomass-derived fuels, chemicals, and materials requires cost-effective processing of sustainable feedstock. The use of imidazole as a solvent for biomass creates a novel approach that helps to accomplish this idea in a green fashion. This work proposes imidazole as a novel solvent for wheat straw pretreatment, which allowed the production of cellulose- and hemicellulose-rich fractions and added-value products from depolymerization of lignin. Various temperatures (110, 140, and 170 °C) and processing times (1, 2, and 4 h) of pretreatment were investigated. Both cellulose and hemicellulose recovery were highly dependent on reaction temperature. The best result for the recovery of cellulose-rich material was obtained at 170 °C for 2 h, achieving 62.4% w·w^-1, whereas native wheat straw is composed by only 38.8% w·w^-1 cellulose. For the same conditions, optimal results were also obtained regarding the enzymatic hydrolysis yield (99.3% w·w^-1 glucan to glucose yield) in cellulose-rich material. This result was possible to be obtained due to morphological and structural changes in cellulose-rich materials accompanied by extensive delignification (up to 92%). The presence of added-value phenolic compounds in recovered imidazole was analyzed by capillary electrophoresis and HPLC-MS. Vanillin and other lignin-based products were identified. Finally, the high purity of recovered imidazole was demonstrated by ¹H and ¹³C NMR.