Naoki WADA1, Takahiro HARA2, Tetsuo FUJIE1, Kenji TAKAHASHI1
1Faculty of Biological Science and Technology, Institute of Science and Engineering, Kanazawa University, Kanazawa, Japan
2Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan
1-Ethyl-3-methylimidazolium Acetate (EmimOAc) is an excellent solvent for cellulosic biomass and thus strongly expected to be utilized in the chemical conversion of biomass, for example, acetylation with acetic anhydride. The corresponding carboxylic acid, acetic acid (AcOH), can be quantitatively generated as a by-product, and therefore, we need to separate AcOH from EmimOAc for their recycling use. However, the strong interaction between EmimOAc and AcOH makes it difficult to separate them in moderate conditions. In this study, we focus on the effect of protic solvents to weaken this interaction by solvation and/or hydrogen bonding interaction. The separation efficiency of AcOH by distillation in the coexistence of various kinds of alcohols became greater and greater as the boiling point of alcohol increased. At a similar boiling point, water was more effective as an entrainer than alcohol, such as 1-propanol (bp.=97 oC) and 2-butanol (bp.=100 oC). The extraction of AcOH from EmimOAc by various kinds of organic solvents did not work well. When we added water to the mixture of AcOH and EmimOAc, AcOH became extractive by common organic solvents such as diisopropyl ether, diethyl ether, and ethyl acetate. The partition coefficient of AcOH between the water and organic phase increased as the permittivity of organic solvents became larger. On the contrary, the partition coefficient of EmimOAc was getting lower. Both in the case of distillation and extraction, repeated treatment by several times completely separated EmimOAc and AcOH. This work is funded by the Japan Science and Technology Agency (JST) (grant number JPMJPF2102).