Efficient pretreatment of lignocellulose in ionic liquids/co-solvent for enzymatic hydrolysis enhancement into fermentable sugars
Process biochemistry (2014) 49, 1144-1151
Ngoc Lan Mai, Sung-Ho Ha and Yoon-Mo Koo
Ionic liquids (ILs) have been widely used as alternative solvents for biomass pretreatment, however,efficient methods that enable economically use of ILs at large scale have not been established. In thisstudy, a new method in which ILs and polar organic solvents (ILs/co-solvent systems) was proposed forefficient pretreatment of lignocellulosic materials. The combination use of appropriate ILs and organicco-solvents can significantly enhance the solubility of lignocellulose due to the lower viscosity of ILs/co-solvent mixture as compared to those of pure ILs while the hydrogen bond basicity was maintained. Inaddition, the solubility of lignocellulosic materials in ILs/co-solvent system was found to be correlatedwith the Kamlet-Taft solvent parameters. Moreover, the use of microwave heating also enhances theefficiency of lignocellulose pretreatment. For example, the microwave-assisted [Emim][OAc]-DMSO (1:1volume ratio) treated-rice straw could be hydrolyzed at least 22 times faster than that of untreated-ricestraw by cellulase from Trichoderma reesei. This enhancement was attributed by several factors includingmore efficient lignin extraction, less crystalline cellulose and lower residual ILs in treated-rice straw.The produced sugars can be effectively fermented by Pichia stipitis for ethanol production. Moreover,[Emim][OAc]-DMSO mixture could be reused at least 5 times without significantly decrease in effec-tiveness demonstrated that the use of ILs/co-solvent was potential alternative method for large-scalebiomass pretreatment.