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

Abstract

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 Tg/Ta/Tc/Te = 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 Tg = 350 K, but at Tg = 340 K, DME/[HMIM][Tf2N] shows better performance. The difference of optimal Tg 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.