Vapor–Liquid Equilibrium Experiment and Process Simulation Study of Tetrahydrofuran–Methanol Azeotrope Separation from Wastewater Using Ionic Liquid Mixed Solvent

Ionic liquids (ILs) have shown excellent performance in separating azeotropes, but they are sometimes limited by their high viscosity and low solubility. This paper proposes a separation method for tetrahydrofuran (THF)–methanol azeotrope in wastewater using an organic solvent–ionic liquid mixed extractant. Using the COSMO-SAC model, bis(2-hydroxyethyl)ammonium nitrate ([BHEA][NO3]) was selected as the IL extractant, and the reaction product of ethylene oxide and water, ethylene glycol (EG), was used as the organic solvent. The vapor–liquid equilibrium (VLE) data of the three-component and four-component mixtures, as well as the viscosity of the mixed extractant, were measured at 323.15 K, and the experimental data were correlated with the nonrandom two-liquids mode (NRTL) model. The experimental results showed that [BHEA][NO3] had better separation performance than EG, and adding EG enhances the separation performance of the mixed extractant in the high-concentration region of THF while also reducing system viscosity. Density functional theory (DFT) calculations showed that the mixed extractant had more interaction sites with the azeotrope. Finally, a genetic algorithm was used to optimize the separation process with the total annual cost (TAC) and CO2 emissions as the objective functions, and the results showed that compared with the EG process, TAC and CO2 emissions of [BHEA][NO3] extractive distillation process decreased by 56.34 and 59.14%, respectively, and that of [BHEA][NO3] + EG process decreased by 57.53 and 51.15%, respectively.