Isothermal vapor-liquid equilibrium measurements and assessments of 1,1,1,3,3,3-hexafluoropropane + N,N-dimethylformamide/N-methyl-2-pyrrolidone working pairs for absorption power cycles

To develop novel working pairs for absorption power cycles, this study selected 1,1,1,3,3,3-hexafluoropropane (HFC236fa) + N,N-dimethylformamide (DMF) and HFC236fa + N-methyl-2-pyrrolidone (NMP) systems. In addition, the vapor-liquid equilibrium (VLE) data of the two systems were measured in a temperature range extending from 293.15 K to 353.15 K and a pressure range of 30-900 kPa. The five-parameter non-random two liquid (NRTL) model was chosen to regress the obtained VLE data. The results indicated that the NRTL model was suitable for the regression of the VLE data, and the maximum deviations of the pressure between the experimental and calculated values were 4.06% and 3.83%, and the average relative deviations were 1.55% and 1.90%, respectively. The regressed activity coefficients were both less than 1, which indicated that the two binary mixtures exhibit negative deviations from Raoult's law. Therefore, the two systems exhibit good affinity. However, the activity coefficient of HFC236fa + DMF is smaller than that of HFC236fa + NMP. Finally, the systems in the literature were compared to this work, and the affinity of the systems was analyzed based on the molecular structure and hydrogen bond.