VLLE measurements and correlation for the pentafluoroethane (R125)+n-butane (R600) system

Hydrocarbon and hydrofluorocarbon mixtures are possible substitutes for chlorinated refrigerants. This family of mixtures, as pointed out in our studies on VLLE for the difluoromethane (R32) + propane (R290) and (R32) + n-butane (R600) systems, shows the possibility of liquid-liquid phase splitting. In this work, the liquid immiscibility of the pentafluoroethane (R125) + (R600) system has been measured with the cloud-point method down to 200 K in a sealed glass cell of about 30 cm(3) and equipped with magnetic stirrers. The temperature is maintained at +/-3 mK and measured to within +/-0.1 K. Uncertainty in pressure is estimated to be within +/-4 kPa. The bulk composition is gravimetrically measured with an uncertainty of +/-0.005 in mole fraction. Having measured P-T-x data, the VLLE parameters are derived using the Redlich-Kwong-Soave (RKS) and Peng-Robinson (PR) equations of state (EoS), both with the Huron-Vidal mixing rule with the NRTL equation for the excess Gibbs free energy at infinite pressures. (C) 2004 Elsevier B.V. All rights reserved.