Thermodynamic and Molecular Properties of Gas Hydrates from Mixtures Containing Methane, Argon, and Krypton

Because hydrate formation in pipelines, processing operations, and reservoirs is generally undesirable, studies of gas-hydrate thermodynamics, particularly examinations of conditions where a second hydrate phase or a hydrocarbon-rich phase exists in addition to the water, hydrate, and gas phases, are important to the natural gas industry. In this study, analysts used experimental methane-krypton and methane-argon hydrate data to generate chemical-potential, enthalpy, and heat-capacity functions for Structure I hydrates for temperatures between -190/sup 0/ and 80/sup 0/F (150 and 300 K). These properties were based upon a modified statistical model where the gas-water interactions were calculated from the spherical-core Kihara intermolecular pair potential function. (The model does not use any adjustable parameters that depend upon the gas species present.) Estimates of the Kihara water-energy and water-distance parameters were -251.57/sup 0/F (115.46 K) and 375.06 pm, respectively. The mixing rules for the Kihara parameters are probably the weakest point of the model, but they are necessary to the corresponding-states approach for predicting the hydrate phase equilibrium. Although the model does not allow satisfactory predictions for larger or highly asymmetric hydrate-forming molecules (such as propane and isobutane), the results of this study can serve as a base for modificatins that account for bothmore » size and asymmetry.« less