Crystal growth of clathrate hydrate in liquid water in contact with methane + ethane + propane gas mixture

BACKGROUND: Understanding the formation/dissociation characteristics of clathrate hydrates is required for the developments of hydrate-based novel energy technologies such as the transportation and storage of natural gas. Crystal morphology is one of the most important factors for the development of hydrate production facilities. RESULTS: Crystal growth of clathrate hydrate in liquid water presaturated with a methane + ethane + propane gas mixture was visually observed and analyzed. The molar ratio composition of the methane + ethane + propane gas mixture was 98.5:1.4:0.1. The composition is that of the gas phase at the steady state achieved during continuous natural gas hydrate production from the feed gas of molar ratio 90:7:3. First of all a hydrate film formed between the mixed gas and liquid water, and then hydrate crystals grew into the liquid water phase from the hydrate film. The morphology of hydrate crystals grown in liquid water varied distinctly depending on the system subcooling (ΔT_sub). CONCLUSION: Hydrate crystals with polygonal morphology were observed at ∼6 K <ΔT_sub < ∼12 K. At ΔT_sub > ∼12 K, polygonal crystals were replaced by dendritic crystals, whereas crystal growth was not observed at ΔT_sub < ∼6 K.