Modeling of phase transition sI−sII in binary gas hydrates of methane and ethane in dependence on composition of gas phase

Calculations of phase transformations ‘structure sI–structure sII’ for binary methane–ethane hydrates were performed in the framework of molecular level model. The conditions of hydrate formation in equilibrium with gas phase and ice have been determined at different gas-phase compositions and pressures. It was shown that even at very low ethane concentration in the gas phase (about 0.5%) hydrate structure sII becomes more stable than sI. Regions of stability in T, P plane of sI and sII structures for mixed hydrates have been predicted. For mixed hydrates with ethane content about 5% in gas phase pressure-induced phase transformation at low temperatures is predicted.