Clathrate Hydrate Crystal Growth at the Seawater/Hydrophobic−Guest−Liquid Interface

Abstract

This paper reports visual observations of clathrate hydrate crystals growth at the interface of water/seawater and a guest substance to reveal the effect of salts on the crystal growth. Cyclopentane was used as the guest substance to form a structure II hydrate. Cyclopentane hydrate crystals grew along the interface of cyclopentane and seawater to form a polycrystalline layer covering the entire interface. We visually analyzed the individual crystals and classified the morphology of the hydrate crystals according to the subcooling (ΔTsub) from the cyclopentane hydrate equilibrium temperature of atmospheric pressure. The results showed that the morphology of the individual cyclopentane hydrate crystals in water and seawater are qualitatively similar at similar subcooling. As a general trend, for ΔTsub < 2.0 K, the shape of the hydrate crystals is typically polygons, at ΔTsub = 2.0−4.5 K, the shape changes to small polygons or slender polygons, and for ΔTsub > 4.5 K, the crystals have triangular or swordlike shape.