Valorization of rapeseed straw through alkali-assisting deep eutectic solvent ChCl:Thiourea pretreatment at room temperature

Abstract

• NaOH-ChCl:TH treatment was established at room temperature. • Enzymatic hydrolysis efficiency increased to 82.2%. • Coproduction of reducing sugars, formic acid and acetic acid was achieved. • The structural change, lignin property and enzymatic saccharification were testified. A green and efficient biomass pretreatment strategy is essential for value-added conversion of lignocellulosic biomass into biofuel and biobased chemicals. This research aimed to develop a combination method for treatment of rapeseed straw (RS) by sodium hydroxide-choline chloride:thiourea (NaOH-ChCl:TH). The xylan elimination (51.1 %) and delignification (36.1 %) could be acquired by treatment at 25 °C for 120 min. NaOH-ChCl:TH destroyed the RS stubborn structure, improved the cellulose crystallinity, enhanced cellulose accessibility, reduced the surface lignin area, and declined hydrophobicity of lignin, and enhanced the enzymatic saccharification efficiency (82.2 %). Formic acid (0.8 g/L) and acetic acid (1.1 g/L) were acquired in pretreatment liquor. Mass and energy balance analysis manifested that the glucose yield and xylose yield were 69.2 % and 83.3 %, respectively, and 72.7 % of the energy in cellulose was effectively utilized after RS treatment. Finally, the economic analysis of biomass pretreatment-enzymolysis-ethanol production suggested that this research developed a mild and cost-effective pretreatment for bioethanol production. To sum up, this NaOH-ChCl:TH pretreatment strategy had potential application for valorization of biomass in the future.