Crystal Growth of Clathrate Hydrate in Liquid Water Saturated with a Simulated Natural Gas

Abstract

This paper reports the visual observation of the formation and growth of clathrate hydrate crystals in liquid water presaturated with a simulated natural gas (methane þ ethane þ propane mixture). The compositions of the methane þ ethane þ propane gas mixtures are (i) 90:7:3, (ii) 94.1:5.8:0.1, and (iii) 99.47:0.51:0.02 in molar ratio. A hydrate film first formed to intervene between the mixed gas and liquid water, and then hydrate crystals grew in the liquid water phase. The morphology of hydrate crystals grown in liquid water distinctly varied depending on the system subcooling ΔT sub . When ΔT sub is smaller than ∼7 K, hydrate crystal growth in liquid water was not observed. At ∼7 K < ΔT sub < ∼12 K, hydrate crystals with polygonal morphology were observed. At ΔT sub > ∼12 K, polygonal crystals were replaced by dendritic crystals. These changes in morphology were observed with all three gas mixtures. It was found that the morphology in the system with mixed gas of the molar ratio 99.47:0.51:0.02 was different from those of the other two systems. We also observed the hydrate crystals floating to the hydrate film from liquid water phase. Floating crystals formed in the bulk of liquid water, attached the hydrate film, and then continued to grow in liquid water. The morphology of floating crystals varied with ΔT sub and the gas composition.

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

“…4). The crystal morphology obtained in this study in the range 7.8 K < T sub < 12.1 K is similar to that of the system with mixed gas (94.1:5.8:0.1) reported by Watanabe et al 21 in the lower subcooling part, i.e. polygonal flat plate crystals.…”

“…Hydrate crystal morphology observed in the present study is arranged along the horizontal axis of T sub with mixture gas as reported by Watanabe et al 21 and with methane as reported by Ohmura et al 18 (Fig. 4).…”

Initial thickness measurements and insights into crystal growth of methane hydrate film

“…Study on the growth mechanism of hydrate crystals is also of great importance for modeling of macroscopic kinetics of hydrate formation with respect to different application fields of gas hydrate. Many theoretical and experimental studies about the hydrate crystal growth have been performed with respect to different subcoolings and compositions of gas mixtures. However, a further understanding of the growth patterns of hydrate crystals is necessary, in view that most of those investigations only examined the formation pattern of hydrate crystals in two dimension.…”

Methane Storage in a Hydrated Form as Promoted by Leucines for Possible Application to Natural Gas Transportation and Storage

“…We speculate that the promoting effect of L ‐leucines may come from their surface activity and surface adsorption (Figure S5, Supporting Information). Visual observations of methane hydrate growth in the quiescent water/methane system disclosed the formation of a rigid hydrate film at the liquid/gas interface, which would hinder further hydrate formation 8. In contrast, L ‐leucine, a typical amphiphilic molecule composed of hydrophilic amine and carboxylic acid groups, along with a hydrophobic aliphatic isobutyl side chain,9 can act as a surfactant to prevent hydrate particles from agglomerating and forming a rigid hydrate film at the liquid/gas interface.…”

“…That means the guest molecules may affect the formation kinetics of gas hydrates in the presence of promoters such as leucines. It is possible that gas hydrate crystal morphologies are affected by the gas composition,8 or that the same molecule can work as a promoter or an inhibitor depending on the particular conditions of the experiment,14 although a detailed mechanistic study is outside the scope of this first report.…”