Vapor-liquid equilibrium for dimethyl ether and three imidazolium ionic liquids as working pairs in absorption-refrigeration cycle

To overcome the shortcomings of traditional working pairs of H₂O/LiBr and NH₃/H₂O, the combination of dimethyl ether (DME) and ionic liquids (ILs) have been studied recently. The solubilities of DME in [HMIM][BF₄], [HMIM][PF₆] and [HMIM][Tf₂N] were firstly measured and correlated using NRTL equation. The thermodynamic performance of absorption refrigeration system (ARS) using those working pairs are compared with R152a/[HMIM][Tf₂N], R1234ze(E)/[HMIM][Tf₂N] and other DME/IL pairs which include [BMIM][BF₄], [BMIM][PF₆] and [BMIM][Tf₂N]. Under the studied condition T_g/T_a/T_c/T_e = 325–370 K/300 K/300 K/278 K, the maximum COPs of DME/[HMIM][Tf₂N], DME/[BMIM][PF₆] and R152a/[HMIM][Tf₂N] in ARS are 0.592, 0.531 and 0.648, respectively, while that of R1234ze(E)/[HMIM][Tf₂N] is only 0.345. DME/[BMIM][PF₆] performs best at T_g = 350 K, but at T_g = 340 K, DME/[HMIM][Tf₂N] shows better performance. The difference of optimal T_g between them is about 10 K. It shows that ARS of using DME/[HMIM][Tf₂N] can utilize lower-grade waste heat. Our studies prove that DME/ILs are good choices to balance the environmental protection property and energy efficiency improve.