Approach to an efficient pretreatment method for rice straw by deep eutectic solvent for high saccharification efficiency.

Deep eutectic solvent comprising choline chloride (ChCl) and acetic acid (AA) was used for rice straw (RS) pretreatment. Effect of ChCl: AA molar ratio, time and temperature on lignin removal and retainment of total carbohydrate content (TCC) in pretreatment process were evaluated by central composite design (CCD) approach. The pretreatment temperature and molar ratio of AA to ChCl played a significant role in delignification. The optimized conditions for RS pretreatment were 1:3.59 (ChCl:AA molar ratio), 126 °C and 150 min. ChCl:AA pretreated RS (CApRS) gave 83.1% delignification, 679 mg/g TCC and 83.7% pretreatment efficiency. CApRS contained enriched cellulose content, 0.73 g/g as compared with 0.43 g/g in raw RS. CApRS showed 31% higher crystallinity index, 17-fold higher surface area than raw RS. The morphological study of CApRS displayed porous surface. Saccharification of CApRS by commercial cellulase gave total reducing sugar of 18.8 g/L in hydrolysate with saccharification efficiency, 92.2%.