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Evaluation of Gas Hydrate Formation Temperature for Gas/Water/Salt/Alcohol Systems: Utilization of Extended UNIQUAC Model and PC-SAFT Equation of State

Kondori, Javad, Zendehboudi, Sohrab, James, Lesley
Industrial & engineering chemistry process design and development 2018 v.57 no.41 pp. 13833-13855
butanes, calcium chloride, carbon cycle, carbon dioxide, climate change, coastal sediments, energy, equations, ethane, ethanol, gas hydrate, gases, glycerol, hydrogen sulfide, magnesium chloride, methane, methanol, potassium chloride, process design, propane, sodium chloride, temperature, thermodynamic models, thermodynamics, van der Waals forces
Naturally occurring gas hydrates are of great importance as a strategic energy source. Hydrates affect coastal sediment stability, global climate change, and ocean carbon cycling. It is vital to understand the thermodynamic conditions of gas hydrates to control/manage and inhibit hydrate formation. A variety of equations of state (EOSs) have been utilized to model the thermodynamic behaviors of gas hydrates. In this study, the perturbed chain statistical association fluid theory (PC-SAFT) equation of state combined with van der Waals and Platteuw model is employed to determine the clathrate hydrate formation temperature of pure gases (e.g., methane, ethane, propane, isobutane, carbon dioxide, and hydrogen sulfide) and binary and ternary systems of hydrate gases. In addition, the gas hydrate formation conditions are investigated where methanol, ethanol, glycerol, NaCl, KCl, CaCl₂, and MgCl₂ as inhibitors are present. The UNIQUAC model is utilized in this work to obtain the hydrate formation conditions in systems with inhibitors. The interaction parameters between water, alcohols, salts, and gases are considered in the thermodynamic modeling. The long-range interaction contribution term is also incorporated in the model to determine the hydrate formation temperature in the presence of salts and alcohols. To achieve more accurate results, the association contribution is taken into account to calculate the residual Helmholtz energy. It is found that the PC-SAFT equation of state is able to predict the hydrate formation conditions with high precision. The comparison between the calculated and experimental data reveals that the average absolute error in this study is generally lower lower than that in the earlier works. The modeling strategy employed in this research study can be applicable to forecast the thermodynamic behaviors of natural or synthetic gas hydrates within a broad range of process conditions.