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Abstract
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Gas hydrate formation processes have considerable importance in petrochemical, oil and gas industry. Electrolytes are known as inhibitors in the hydrate formation process and are important components in the gas hydrates resources (e. g. Gulf of Oman and Caspian Sea) and saline aquifers. Thermodynamic modeles are strong tools for studying thermodynamic behavior of these processes. In this thesis, a thermodynamic model is used which composed of Peng- Robinson equation of state, Born and MSA equation. This electrolyte equation of state is in terms of Helmholtz free energy in which a Peng- Robinson term is for interactions between uncharged species, a Born term is for the charging free energy of ions and a MSA term for the electrostatic interactions between ions. At first, the volumetric properties (density, activity coefficient…) of electrolyte system are calculated. These results were in good agreement with available datas. It should be noted that when concentration of salt is increased, the accuracy of results is decreased. Then the solubility of CO2 in NaCl solution is calculated. In these calculations, the accuracy of results is gradually decreased when salinity is increased. Also, the Solubility of CO2 is predicted in saline aquifers. Afterwards, hydrate formation pressure of CO2 and CH4 is calculated in electrolyte solutions. Hydrate formation calculation is done in two different cases. The first one is done when the gas- water binary interaction parameters are adjusted and the second one is done when the gas- salt binary interaction parameters are adjusted according to the hydrate formation datas. These results are compared with each other and with the results of other themodynamic modeles. Those were in good agreement with available datas while in the high concentration of electrolytes, the accuracy is decreased. Finally, the gas hydrate formation process is studied according to these adjusted parameters in Gulf of Oman and Caspian Sea and the gas hydrate equil
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