Cholinium carboxylate ionic liquids for pretreatment of lignocellulosic materials to enhance subsequent enzymatic saccharification

The present study is the first report demonstrating that ionic liquids consisting of cholinium cations and linear carboxylate anions ([Ch][CA] ILs) can be used for pretreatment of lignocellulosic materials to enhance subsequent enzymatic saccharification. Six variants of [Ch][CA] ILs were systematically prepared by combining cholinium cations with linear monocarboxylate anions ([CnH2n+1–COO]−, n = 0–2) or dicarboxylate anions ([HOOC–CnH2n+1–COO]−, n = 0–2). These [Ch][CA] ILs were analyzed for their toxicity to yeast cell growth and their ability to pretreat kenaf powder for subsequent enzymatic saccharification. When assayed against yeast growth, the EC50 for choline acetate ([Ch][OAc]) was 510 mM, almost one order of magnitude higher than that for 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]). The cellulose saccharification ratio after pretreatment at 110 °C for 16 h with [Ch][OAc] (100.6%) was almost comparable with that after pretreatment with [Emim][OAc]. Therefore, [Ch][OAc] is a biocompatible alternative to [Emim][OAc] for lignocellulosic material pretreatment.

► Cholinium carboxylate ionic liquids (ILs) were used to pretreat lignocellulose. ► Especially, choline acetate ([Ch][OAc]) was found to be promising cholinium IL. ► [Ch][OAc] was compared with 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]). ► [Ch][OAc] was more biocompatible than [Emim][OAc]. ► [Ch][OAc] could pretreat lignocellulosic biomass as [Emim][OAc] did.