Moyer Preenaa, Smith Micholas Dean, Abdoulmoumine Nourredine, Chmely Stephen C, Smith Jeremy C, Petridis Loukas, Labbé Nicole
Center for Renewable Carbon, University of Tennessee, 2506 Jacob Drive, Knoxville, TN 37996-4542, USA.
Phys Chem Chem Phys. 2018 Jan 24;20(4):2508-2516. doi: 10.1039/c7cp07195g.
The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIM]Acetate) has been widely used for biomass processing, i.e., to pretreat, activate, or fractionate lignocellulosic biomass to produce soluble sugars and lignin. However, this IL does not achieve high biomass solubility, therefore minimizing the efficiency of biomass processing. In this study, [EMIM]Acetate and three other ILs composed of different 3-methylimidazolium cations and carboxylate anions ([EMIM]Formate, 1-allyl-3-methylimidazolium ([AMIM]) formate, and [AMIM]Acetate) were analyzed to relate their physicochemical properties to their biomass solubility performance. While all four ILs are able to dissolve hybrid poplar under fairly mild process conditions (80 °C and 100 RPM stirring), [AMIM]Formate and [AMIM]Acetate have particularly increased biomass solubility of 40 and 32%, respectively, relative to [EMIM]Acetate. Molecular dynamics simulations suggest that strong interactions between IL and specific plant biopolymers may contribute to this enhanced solubilization, as the calculated second virial coefficients between ILs and hemicellullose are most favorable for [AMIM]Formate, matching the trend of the experimental solubility measurements. The simulations also reveal that the interactions between the ILs and hemicellulose are an important factor in determining the overall biomass solubility, whereas lignin-IL interactions were not found to vary significantly, consistent with literature. The combined experimental and simulation studies identify [AMIM]Formate as an efficient biomass solvent and explain its efficacy, suggesting a new approach to rationally select ionic liquid solvents for lignocellulosic deconstruction.
离子液体（IL）1-乙基-3-甲基咪唑醋酸盐（[EMIM]醋酸盐）已被广泛用于生物质处理，即预处理、活化或分离木质纤维素生物质以生产可溶性糖和木质素。然而，这种离子液体不能实现高生物质溶解度，因此降低了生物质处理效率。在本研究中，分析了[EMIM]醋酸盐和其他三种由不同的3-甲基咪唑阳离子和羧酸盐阴离子组成的离子液体（[EMIM]甲酸盐、1-烯丙基-3-甲基咪唑（[AMIM]）甲酸盐和[AMIM]醋酸盐），以将它们的物理化学性质与其生物质溶解性能相关联。虽然所有四种离子液体都能够在相当温和的工艺条件（80°C和100 RPM搅拌）下溶解杂交杨树，但相对于[EMIM]醋酸盐，[AMIM]甲酸盐和[AMIM]醋酸盐的生物质溶解度分别特别提高了40%和32%。分子动力学模拟表明，离子液体与特定植物生物聚合物之间的强相互作用可能有助于这种增强的溶解作用，因为计算得出的离子液体与半纤维素之间的第二维里系数对[AMIM]甲酸盐最为有利，与实验溶解度测量趋势相符。模拟还表明，离子液体与半纤维素之间的相互作用是决定整体生物质溶解度的一个重要因素，而木质素-离子液体相互作用没有发现有显著变化，这与文献一致。综合实验和模拟研究确定[AMIM]甲酸盐是一种有效的生物质溶剂，并解释了其功效，为合理选择用于木质纤维素解构的离子液体溶剂提出了一种新方法。
