Modeling hydrate-containing phase equilibria for mixtures with sulfur dioxide or alkali halides

Gas hydrate-containing phase behaviors are essentially required for flow assurance in carbon dioxide sequestrations and resources recovery. To model effects of weak electrolyte such as SO2 and strong electrolytes such as alkali halides on phase equilibria of hydrate systems, an electrolyte equation of state is used, which is based on hydrogen-bonding nonrandom lattice fluid equation of state for fluid phases and van der Waals and Platteeuw model for hydrate phases. A guest gas of SO2 is modeled as partially dissociating component in aqueous solution. Various phase behaviors of water and SO2 mixtures for hydrate-free and hydrate-forming conditions are analyzed by comparing the model results with experimental data. An improvement in accuracy of liquid–liquid equilibria for the mixture is achieved by the inclusion of cross-association between water and SO2. The proposed model has been also found to provide with reliable predictions of hydrate-containing phase equilibria for a binary guest of CO2 and SO2. In the presence of NaCl or KCl as an inhibitor of formed hydrate, predicted incipient hydrate-forming conditions of single guests such as methane, ethane, propane, and CO2 are compared with experimental data and available models, showing good agreement with the data.