Thermodynamic and Process Analyses of Extractive Distillation for Separating Refrigerant R-410A Using Imidazolium-Cyano-Based Ionic Liquids

Abstract

R-410A is a near-azeotropic refrigerant mixture of difluoromethane (HFC-32) and pentafluoroethane (HFC-125) that is scheduled to be phased out internationally due to a high Global Warming Potential (GWP). While conventional distillation cannot be used, extractive distillation using ionic liquids (ILs) has been proposed to separate and recycle HFC-32 (lower GWP) for future refrigerant blends and to repurpose HFC-125 (high GWP). Here, we present both a thermodynamic and process design analyses of various ILs using an equation of state method. From experimental binary vapor–liquid equilibrium data and equation of state modeling, 1-ethyl-3-methylimidazolium tricyanomethanide [C₂C₁im][tcm] and 1-ethyl-3-methylimidazolium dicyanamide [C₂C₁im][dca] were identified from 10 ILs as viable entrainers. Selectivity increases with temperature and decreases with pressure, while the solvent-to-feed (S/F) ratio did not have much effect. These effects were more pronounced for [C₂C₁im][tcm] than for [C₂C₁im][dca]. A sensitivity analysis reveals that the optimum operational parameters were solvent-to-feed ratio (S/F), reflux ratio (RR), and total number of stages (Nt) with values of 5, 3, and 20, respectively, for the case of [C₂C₁im][tcm] and 6, 3, and 20 for [C₂C₁im][dca]. High-purity products HFC-32 and HFC-125 (>99.5 wt %) were obtained with IL [C₂C₁im][tcm], providing the lowest energy consumption, compared to [C₂C₁im][dca] and other ILs.