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.