Selection of protic ionic liquids for the improved production of butanol from rice straw

Biomass pretreatment with protic ionic liquids (PILs) has been proved as an economically attractive method to enhance saccharification yield. This work evaluated the use of six PILs -based on acetate and hydrogen sulfate anions - using water as cosolvent for processing a high solid loading of rice straw (RS). Among the investigated PILs, the most promising results were obtained by 2-hydroxyethylammonium acetate [MEOA][OAc] containing 20 %w/w water, achieving 87.3 % of glucose and 68.6 % of xylose yield, respectively, and 98.3 % of delignification at 150 ◦C for 2 h with 15 %w/w solid loading. Five recovery and reuse cycles were successfully performed with [MEOA][OAc], obtaining a delignification degree of 69.5 % after the fifth reuse. Process viability was evaluated by enzymatic hydrolysis followed by acetone-butanol-ethanol (ABE) fermentation using Clostridium beijerinckii. Similar saccharification yields (89.9 ± 6.8 % glucose and 71.5 ± 4.7 % xylose) and butanol production (7.3 ± 0.1 g/L, 81.7 ± 1.7 g butanol per kg of RS) were achieved for fresh and recycled [MEOA] [OAc], demonstrating the feasibility of PIL reuse. This study showed the potential of [MEOA][OAc] as a costeffective pretreatment agent for rice straw valorization into an advanced biofuel such as butanol.