Thermodynamic modeling of gas hydrate formation conditions in the presence of organic inhibitors, salts and their mixtures using UNIQUAC model

Gas hydrate formation conditions of CH4, C2H6, C3H8, CO2 and H2S in the presence of inhibitors are modeled in this study by applying a combination of Chen-Guo model, SRK-HV EoS and UNIQUAC model in conjunction with Henry's law. Methanol, ethanol, monoethylene glycol, diethylene glycol, triethylene glycol, glycerol, NaCl, KCl, CaCl2 and MgCl2 are considered as hydrate inhibitors. The predictions are performed in the presence of single inhibitors, mixed salts and mixture of alcohol and salts. All the possible interactions between components in the aqueous phase including water, salts, alcohol and gases are incorporated in the UNIQUAC model. The UNIQUAC interaction parameters are optimized directly through the hydrate data so that any dependence on various VLE data is eliminated. Also the parameters of both supercritical and condensable components are calculated. The strong salts are treated as molecular species in the aqueous phase so that no electrostatic model is used for long-range interaction. Based on this assumption, the original UNIQUAC model is easily extendable for electrolyte and mixture of electrolyte and non-electrolyte solutions. For the first time, the original UNIQUAC model is employed here to calculate the hydrate formation conditions in the presence of electrolytes. Despite the simplicity of the proposed approach, the results of this study are in good consistency with the experimental data, particularly for hydrate systems containing mixture of salts and alcohol.