مسعود مفرحی

In this work VTPR equation of state was used to describe vapor and liquid phases. The VTPR mixing rule was used that used LIFAC/LIQUAC activity coefficient for electrolyte solutions and combined it with VTPR equation of state. The one of the best property (characteristic) of VTPR-LIFAC model is that this model does not need critical properties of electrolyte, properties that they are limited and associated with uncertainty. For the hydrate phase the final Chen-Guo model was used. In addition to the original version that introduced new concept, in this final version the calculation was based on fugacity and host-host interaction was considered. At first, parameters of the hydrate phase were fitted for various gas and then by using these parameters the ability of this model was tested to calculate hydrate formation temperature and pressure of some binary and natural gases including Parsian refinery gas. Methane, ethane, propane, i-butane, n-butane, hydrogen sulfide, carbon dioxide and nitrogen gases were studied in this work. The results had good agreement with experimental data so that the average absolute error for 1282 experimental data of hydrate formation pressure without presence of electrolyte inhibitor was 5.98. In the final step hydrate formation pressure was calculated in the presence of electrolytes. Sodium chloride and potassium chloride were studied in this work. The interaction parameters between the ions of these electrolytes and water and between each other was fitted to experimental osmotic coefficient of water at low temperature in order to calculate activity of water well (accurately). The result showed that an average absolute deviation for 225 experimental data of hydrate formation pressure in the presence of electrolyte inhibitor was 9.36.