Growth Mechanisms and Phase Equilibria of Propane and Methane + Propane Hydrates

Gas hydrates of light hydrocarbons exhibit complex phase behavior, polymorphism, and diverse crystal morphology. We investigated phase equilibria and growth mechanisms of propane and methane + propane gas hydrates in the range of 0.25 to 2.1 MPa and 273.6 to 287.25 K. Clathrates formed from pure propane and the yCH4 = 0.90 methane + propane mixture exhibited similar morphologies at low subcoolings but differed considerably at higher subcoolings. The yCH4 = 0.98 methane + propane mixture formed crystals with radically different morphologies than those of pure propane and the yCH4 = 0.90 mixture. We report a new hydrate growth mechanism that proceeds via partial dissociation of the growing crystal in propane and propane + methane hydrates.