Hydrophobic Imidazole-Based Ionic Liquids for Efficient Extraction of Furfural from Wood Pulp Waste Liquor: Extraction Study and Mechanism Analysis

There is a large amount of ethanol (EtOH) and a small amount of furfural (FF) in the ethanol pulping waste liquid. How to separate FF, a high value-added product, efficiently and cleanly and at the same time recover EtOH effectively and save energy is an urgent problem. This article describes the phase equilibrium process of extracting FF from wood pulp waste liquor by ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6])/1-pentyl-3-methylimidazolium hexafluorophosphate ([PMIM][PF6]) as the extractant. Two ILs have excellent distribution coefficients (D) and selectivity (S) for FF, which can separate EtOH and FF well. A set of extraction performance evaluation methods based on the COSMO-RS model, liquid–liquid extraction method, and NRTL simulation were proposed. Combined with quantum chemical calculations such as interaction energy (ΔE), electrostatic potential analysis, and interaction region indicator, analysis of internal interaction and extraction mechanism between different molecules is realized.