Global phase behavior of imidazolium ionic liquids and compressed 1,1,1,2‐tetrafluoroethane (R‐134a)

Abstract

in Wiley InterScience (www.interscience.wiley.com).Novel processes involving ionic liquids with refrigerant gases have recently been developed. Here, the complete global phase behavior has been measured for the refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a) and 1-n-alkyl-3-methyl-imidazolium ionic liquids with the anions hexafluorophosphate [PF 6 ], tetrafluoroborate [BF 4 ] and bis(trifluoromethylsulfonyl)imide [Tf 2 N] from ;08C to 1058C and to 33 MPa. All of the systems studied were Type V from the classification scheme of Scott-van Konynenburg with regions of vapor-liquid equilibrium, miscible/critical regions, vapor-liquid-liquid equilibrium, and upper and lower critical endpoints (UCEP and LCEP). The effect of the alkyl chain length has been investigated, for ethyl-([EMIm]), n-butyl-([BMIm]), and n-hexyl-([HMIm]). With increasing chain length, the temperature of the lower critical end points increases and pressure at the mixture critical points decrease. With a common cation, the temperature of the LCEP increased and the mixture critical point pressures decreased in the order of [BF 4 Keywords: imidazolium ionic liquids, R-134a, global phase behavior, high-pressure, mixture critical points IntroductionThe solubility and separation of refrigerant gases are important problems for several industries. Many refrigerants and their intermediates have very similar physical and chemical properties which can often render their separation costly by traditional distillation. The separation of the common azeotropes encountered among refrigerant mixtures usually requires additional components in extractive distillation. Ionic liquids (ILs) have been shown to provide efficient solutions to these problems.1 Absorption refrigeration with refrigerant gases uses a low-volatility solvent to first absorb the gas at low temperatures and then uses heat to liberate a highpressure gas for the refrigeration cycle. However, widespread application of absorption refrigeration has been impeded by the often bulky equipment that is needed to purify the high-pressure gas from the generator; the presence of any absorption liquid significantly decreases the efficiency. Non-volatile ILs in these systems with refrigerants may help solve these problems. 2The high-pressure phase behavior and equilibria are the most important data needed to utilize any of the novel applications with ILs and refrigerant gases. The phase behavior indicates the conditions (temperature and pressure) of the different equilibria and transitions, whether vapor-liquid, liquidliquid, etc. For instance, regions in which the IL and refrigerant are miscible would not be conducive to separations or absorption refrigeration. This study will investigate the phase behavior of a series of 1-n-alkyl-3-methyl imidazolium ILs with various alkyl groups and anions (see Figure 1.) with the

Phase equilibria of imidazolium ionic liquids and the refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a)

“…They used the regressed parameters from this low-pressure data and predicted that this system was a Type V of Scott-van Konynenburg. We have recently measured the high-pressure phase behavior and equilibria of this system and have confirmed the Type V behavior [3,4]. Shariati and Peters measured the high-pressure phase behavior of fluoroform (trifluoromethane (CHF 3 )), in [ [20].…”

“…have no reported miscibility with ILs [6][7][8][9]. For instance, Brennecke and coworkers [10] indicate that [BMIm][PF 6 ] and CO 2 represent a two-phase system even beyond 3.1 kbar at 40 • C. For comparison, we have measured the critical point of this IL with R-134a at approximately 110 bar at 50 • C [3]. Fig.…”

“…We have recently investigated the global phase behavior (pressure-temperature projection) of binary mixtures of R-134a and [ 4 ] between approximately 0 • C and 105 • C and pressures to 330 bar [3,4]. In all cases, the phase behavior is classified with reasonably certainty as Type V according to the classification of Scott and van Konynenburg [5].…”

“…Shiflett, Yokozeki and coworkers [11][12][13][14][15][16][17][18] have reported the majority of known low- [Tf2N] and R-134a adapted from the data of Ren and Scurto [3] and the vapor pressure of R-134a by Lemmon et al [37]. pressure equilibria data.…”

Perfect Composition Depth Profiling of Ionic Liquid Surfaces Using High-resolution RBS/ERDA

“…ILs are promising materials for a wide range of applications, such as electrolytes for energy-storage devices, 7 heterogeneous catalysis 8 and gas capture/separation media. 9,10 In these applications, the measurement and control of the surface adsorption sites is crucial. In this respect, hydrogen is a key element because of its important role in hydrogen bonding.…”