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Phase Behavior and Applications of Ionic Liquid/compressed Refrigerant Gases (R-134a & CO2)

Wei Ren and Aaron M. Scurto. Chemical and Petroleum Engineering & NSF-ERC Center for Environmentally Beneficial Catalysis, University of Kansas, 1530 W. 15th St., 4132 Learned Hall, Lawrence, KS 66045

This investigation presents the experimental and modeling of the phase behavior and equilibria of imidazolium ionic liquids with compressed refrigerant gases, 1,1,1,2-tetrafluoroethane (R-134a) and carbon dioxide. The global phase behavior has been measured for 1-n-alkyl-3-methyl-imidazolium ionic liquids with the hexafluorophosphate [PF6], tetrafluoroborate [BF4] and bis(trifluoromethylsulfonyl)imide [Tf2N] anions, and the refrigerant, 1,1,1,2-tetrafluoroethane (R-134a) from approximately 0C to 105C and pressure up to 330 bar in order to determine the optimal operational conditions. All of the ionic liquids studied with R-134a were of the Type V systems from the classification scheme of Scott-van Konynenburg. The effect of the alkyl chain length was investigated for ethyl- ([EMIm]), n-butyl- ([BMIm]) and n-hexyl- ([HMIm]). The phase behavior of carbon dioxide and imidazolium ionic liquids have also been measured and modeled.

Traditional air condition systems in automobiles utilize the common vapor compression process, which leads to lower gas mileage, higher fuel consumption and increased pollution. As an alternative, absorption refrigeration with ionic liquids may be able to use waste heat to power the air-conditioning system. The phase equilibria for a model ionic liquid and the refrigerant gases were used to simulate an absorption refrigeration system for a possible automotive application. The performance of the proposed system and the common vapor compression system for are compared.