Wilson Non-random Factor Reference State Based Model for Prediction of Gas Hydrate Formation Conditions in the Presence of Electrolyte and/or Alcohol in Solution

Abstract

In this study, a new thermodynamic model is presented for prediction of hydrate formation conditions of different hydrate formers in solutions containing an electrolyte, alcohol and their mixtures. The developed model is based on the γ–φ approach for modeling the phase behavior. The theory of van der Waals–Platteeuw and the Valderama–Patel–Teja equation of state coupled with non-density dependent mixing rules were used to describe the hydrate and vapor phase, respectively. Also, the nonelectrolyte Wilson, non-random factor local composition model and Margules equation were adopted to determine the water activity in solutions containing electrolyte and alcohol, respectively. The effects of solubility of the components in the liquid and vapor phases were considered for prediction of hydrate formation conditions. The model was applied to a number of hydrate forming compounds and mixtures in different electrolyte and methanol solutions, including NaCl, KCl and CaCl2 and their mixtures, and results are compared with experimental data and/or existing models. It was found that hydrate formation conditions are better predicted by this model compared to existing models, especially for ethane and propane in electrolyte solutions, and C1/CO2/C3 gas mixture in solutions containing electrolyte and alcohol. The solubility of components in the liquid and vapor phases was found to have a considerable effect on the model predictions.