Crystal growth of clathrate hydrate at the interface between seawater and hydrophobic-guest liquid: Effect of elevated salt concentration

This paper reports the visual observations of the clathrate hydrate crystal growth and morphology at the interface of aqueous NaCl solutions and a guest-substance liquid. The hydrate crystal growth was visually characterized in the systems of a wide range of NaCl concentrations from 0.035 to 0.264 in mass fraction. The mass fraction 0.035 was corresponding to that of ordinary seawater, and the salt concentration tested was extended up to the saturation level, i.e., 0.264. Cyclopentane was used as the guest substance. Formation and growth of hydrate crystals at the cyclopentane-NaCl solution interface were observed. We visually analyzed the individual hydrate crystals and classified the morphology of the crystals according to ΔT _sub at atmospheric pressure. It was found that the size of the individual hydrate crystals decreased with increasing ΔT _sub. The results showed that the morphology of the individual hydrate crystals in any NaCl concentration is roughly similar at a given ΔT _sub. We also measured the lateral growth rates of the hydrate-film propagation. The hydrate film growth rate decreased with decreasing ΔT _sub in any of the systems and decreased with increasing concentration of NaCl at a given ΔT _sub.