Synergistic Mechanisms and Economic-Environmental Analysis of Novel Extractive Distillation Using [BMIM][NTf ₂ ]-Based Mixed Solvents for Enhanced Separation of Battery-Grade Dimethyl Carbonate

With the widespread application of dimethyl carbonate (DMC) in lithium-ion battery electrolytes, the efficient separation of a DMC/methanol/water mixture has become a critical challenge. Addressing the issues of high volatility, low mass transfer efficiency, and impurities caused by traditional entrainers, this work proposes a novel mixed solvent with synergistic effects in thermodynamics and process economics, consisting of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) and propylene carbonate (PC). A comprehensive method is proposed for evaluating mixed solvents from molecular to life cycle perspectives. Quantum chemical calculations assess the interaction energy at the molecular level, revealing enhanced separation mechanisms. Synergistic effects are analyzed at the phase equilibrium level. Process optimization for extractive distillation is achieved using a multiparticle parallel swarm optimization method. Finally, the environmental impact across the solvent production, usage, and recovery stages is evaluated throughout the entire life cycle. The extractive processes using single [BMIM][NTf2], PC, and their optimal blend are compared in terms of mass transfer efficiency, energy consumption, economic performance, and life cycle environmental impact. The results indicate that the separation of the DMC/methanol is governed by both electrostatic interactions and van der Waals forces between [BMIM][NTf2] and DMC, with PC playing a synergistic role. The mixed solvent exhibits significantly higher interaction energies with DMC compared with either solvent alone, enhancing the selectivity of DMC to methanol. The direct extractive distillation process using a mixed solvent of 69% [BMIM][NTf2] and 31% PC consistently achieves the lowest total annual cost (TAC) and environmental impacts, with TAC and global warming potential savings 10.06–10.08%, and 9.91–17.33% compared to using either [BMIM][NTf2] or PC alone. The mass transfer coefficient increases by 2.04% compared with single [BMIM][NTf2].