Experimental Measurements and Thermodynamic Modeling of the Dissociation Conditions of Clathrate Hydrates for (Refrigerant + NaCl + Water) Systems

Abstract

Experimental gas hydrate dissociation data for the refrigerants R134a, R410a, and R507 in the absence and presence of NaCl aqueous solutions at various molalities were measured. The binary systems, in this study, which consisted of {chloro(difluoro)methane (R22), 1,1,1,2-tetrafluoroethane (R134a), (0.5 mass fraction difluoromethane + 0.5 mass fraction 1,1,1,2,2-pentafluoroethane) (R410a), or (0.5 mass fraction 1,1,1-trifluoroethane + 0.5 mass fraction 1,1,1,2,2-pentafluoroethane) (R507)} + water were measured in the temperature range between (276.4 to 291.8) K and pressures ranging from (0.114 to 1.421) MPa. The ternary system R134a + water + NaCl, at three salt molalities of (0.900, 1.901, and 3.020) mol·kg–1, was measured in the temperature range between (268.1 to 280.6) K and pressures ranging from (0.086 to 0.383) MPa. For the ternary systems comprising of {R410a or R507} + water + NaCl, at two salt molalities of (0.900 and 1.901) mol·kg–1, measurements were undertaken in the temperature range between (273.9 to 290.9) K and pressures ranging from (0.226 to 1.345) MPa. The isochoric pressure-search method was used to undertake the measurements. The purpose of this study is to generate accurate hydrate phase equilibrium data which will be used to design wastewater treatment and desalination processes using gas hydrate technology. The results show that the presence of NaCl in the aqueous solutions has a thermodynamic inhibition effect on refrigerant gas hydrates. Modeling of the data measured was undertaken using a combination of the solid solution theory of van der Waals and Platteeuw for the hydrate phase, the Aasberg–Petersen et al. model for the electrolyte aqueous system, and the Peng–Robinson equation of state with classical mixing rules for the liquid and vapor phases. The correlated model results show good agreement with the experimental dissociation data.