Novel dihydrogen-bonding deep eutectic solvents: Pretreatment of rice straw for butanol fermentation featuring enzyme recycling and high solvent yield

Rice straw (RS) is one of the most abundant lignocellulosic biomasses in China, which contains mainly of cellulose, hemicellulose and lignin. In this study, a novel deep eutectic solvent (DES), foraceline, was prepared with choline chloride and double hydrogen bond donors (formic acid and acetic acid). By combining foraceline and sodium carbonate (1%), a two-stage pretreatment method was developed and applied in RS pretreatment to improve the biodegradability of lignocellulose. The highest glucose and total sugar of 37.3 g·L−1 and 42.8 g·L−1 were obtained after hydrolysis of 24 h using 50 FPU·gtotal solid-1 of cellulase. The cellulase attached to RS was reutilized for five continuous cycles in which enzyme loading was reduced from 50 FPU·gtotal solid-1 (Cycle I) to 30 FPU·gtotal solid-1 (Cycle V), resulting in total sugar of 41.3–42.6 g·L−1 for each cycle. RS hydrolysates (Cycle I and V) was utilized in butanol fermentation by Clostridium saccharobutylicum DSM 13864, achieving butanol titer and yield of 9.5 g·L−1 and 0.25 g·gtotal sugar-1, similar to those of glucose medium. This study demonstrated the feasibility of this newly developed biomass pretreatment by dihydrogen bonding DES featuring cellulase recycling and high butanol yield.