Experimental determination and thermodynamic modeling of clathrate hydrate stability conditions in methane + hydrogen sulfide + water system

Abstract

In the petroleum industry, it is essential to comprehend the hydrate equilibrium qualifications in order to prevent or defer this phenomenon. However, the thermodynamic equilibrium information on hydrogen sulfide containing systems reported in the literature is limited and discrepant in comparison with other gases. In this communication, new experimental investigations of hydrate dissociation conditions of methane (0.995 mole fraction) + hydrogen sulfide (0.005 mole fraction) + water system which forms stable structure I were carried out in temperature and pressure ranges from 282.1 to 288.3 K and 5.63 to 12.19 MPa, respectively. The experiments were carried out by using the stepwise heating method with an isochoric pressure search procedure in a 100 cm3 autoclave. The apparatus and method validity were confirmed by comparison of the methane hydrate equilibrium data from the current study with some selected data from the literature. In this study, a thermodynamic model was developed to estimate the dissociation conditions of the binary CH4+H2S hydrate system. For this purpose, a systematic comparison is made between results from PC-SAFT (Perturbed-Chain Statistical Associating Fluid Theory) and CPA (Cubic Plus Association) equations of state (EoS). In the present work, PC-SAFT and CPA equations of state are utilized to model the gas/vapor and water phases and van der Waals Platteeuw (vdW-P) is used for hydrate phase modeling. In this regard, the binary interaction parameters in PC-SAFT/CPA EoS for the aforementioned system were tuned using literature data on H2S/CH4 solubility in water. Model outcomes show that both models are entirely trustworthy over an extensive range of temperatures (273 to 350 K), pressure (2 to 22 MPa) and all H2S concentrations. In addition, a comparison between experimental data, the models results and HWHydrate (version 1.1) predictions ascertain that the PC-SAFT is relatively precise than CPA in the binary hydrate system of CH4-H2S.