Experimental measurement of phase equilibrium for gas hydrates of refrigerants, and thermodynamic modeling by SRK, VPT and CPA EOSs

Abstract

In this study, three-phase equilibrium conditions of hydrate-liquid–vapor, (VLWH), were experimentally determined for chlorodifluoromethane and 1,1,1,2-tetrafluoroethane gas hydrates at temperatures ranging from (278 to 290)K and (280 to 285)K respectively, at pressures ranging from (0.2 to 0.8)MPa. Then the different models were presented for estimating of the hydrate dissociation conditions of chlorodifluoromethane, 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane refrigerants. The cubic simple equations of state (SRK and VPT) and the cubic plus association equation of state (CPA) were employed for modeling the vapor and liquid phases, also van der Waals–Platteeuw statistical model was used for the solid hydrate phase. In this paper, the binary interaction parameters of classic and modified mixing rules were optimized by using two-phase equilibrium data (VLWH). The Kihara potential parameters in each refrigerant were estimated using obtained experimental equilibrium data (VLWH) and based on the optimization scheme by the Nelder Mead optimization method. The agreement between the experimental and the predicted pressure is acceptable by using these models. The average deviation of models for chlorodifluoromethane, 1,1,1,2-tetrafluoroethane, and 1,1-difluoroethane hydrates is about 3%, 4.3%, and 3.6%, respectively.