Investigation on Absorption and Separation Performance of R-32, R-125, R-134a, and R-1234yf Refrigerants Using EMIM-Based Ionic Liquids

As potent fluorinated greenhouse gases, refrigerants need to be recovered and reclaimed in a timely manner to reduce greenhouse gas emissions. R-410A (50 wt % R-32 (difluoromethane) + 50 wt % R-125 (pentafluoroethane)) and R-513A (44 wt % R-134a (1,1,1,2-tetrafluoroethane) + 56 wt % R-1234yf (2,3,3,3-tetrafluoroprop-1-ene)) were azeotropic refrigerant mixtures that were difficult to separate by conventional distillation. Two ionic liquids (ILs), 1-ethyl-3-methylimidazolium perchlorate ([EMIM][ClO4]) and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMIM][FSI]), had been considered as promising extractants in the extractive distillation. Solubilities of R-32, R-125, R-134a, and R-1234yf in [EMIM][ClO4] and [EMIM][FSI] were measured from 288.15 to 308.15 K and correlated well with the five-parameter nonrandom two-liquid (NRTL) activity coefficient model. Henry's law constants and ideal selectivities (SI) of [EMIM][ClO4] and [EMIM][FSI] were used to compare absorption and separation performance with ILs in the literatures. Surface shielding charge distributions of the refrigerants and anions were used to analyze the absorption and separation mechanism. R-410A and R-513A separation processes using four ILs ([EMIM][ClO4], [EMIM][FSI], 1-ethyl-3-methy-limidazolium thiocyanate ([EMIM][SCN]), and 1-ethyl-3-methy-limidazolium acetate ([EMIM][Ac])) were simulated and evaluated. Results showed that R-32 and R-134a formed higher peak heights in the hydrogen bond donor region than R-125 and R-1234yf, which resulted in higher solubilities of R-32 and R-134a than R-125 and R-1234yf in both ILs. At 298.15 K, the SI of [EMIM][ClO4] for R-32 + R-125 (11.30) and [EMIM][FSI] for R-134a + R-1234yf (8.01) were both the highest to date. [SCN] formed peaks in nonpolar and polar regions with only half the value of [ClO4], which led to the highest SI of [EMIM][ClO4] for R-32 + R-125. The total annual cost (TAC) using [EMIM][ClO4] (14.1362 × 104 $) in R-410A separation was less than that of [EMIM][SCN] (18.1249 × 104 $). Moreover, the TAC of [EMIM][FSI] (13.9365 × 104 $) and [EMIM][Ac] (13.5974 × 104 $) were close for R-513A separation, because the noncompetitive selectivity (Sp) of [EMIM][Ac] at high pressures was higher than that of [EMIM][FSI]. [EMIM][ClO4] and [EMIM][FSI] were proved to be efficient extractants for the separation of R-410A and R-513A, respectively.