New Observations and Insights into the Morphology and Growth Kinetics of Hydrate Films

Abstract

The kinetics of film growth of hydrates of methane, ethane, and methane-ethane mixtures were studied by exposing a single gas bubble to water. The morphologies, lateral growth rates, and thicknesses of the hydrate films were measured for various gas compositions and degrees of subcooling. A variety of hydrate film textures was revealed. The kinetics of two-dimensional film growth was inferred from the lateral growth rate and initial thickness of the hydrate film. A clear relationship between the morphology and film growth kinetics was observed. The shape of the hydrate crystals was found to favour heat or mass transfer and favour further growth of the hydrate film. The quantitative results on the kinetics of film growth showed that for a given degree of subcooling, the initial film thicknesses of the double hydrates were larger than that of pure methane or ethane hydrate, whereas the thickest hydrate film and the lowest lateral growth rate occurred when the methane mole fraction was approximately 0.6.

Crystallization Mechanisms and Rates of Cyclopentane Hydrates Formation in Brine

“…Therefore, when it rises, the speed of hydrate formation increases. This phenomenon has been described in details elsewhere , , .…”

“…It is worth mentioning here the early experimental studies that addressed the crystal growth rates and mass transfer rates through the hydrate layer , , provide models , , , , , , , or perform molecular dynamics (MD) simulations , . The pioneering work of Mori and co‐workers , explored theoretically the evolution of a hydrate layer thickness at the interface between water and another non‐miscible phase of guest molecules.…”

“…Li and co‐workers , reported the crystal growth of gas hydrates from methane and ethane by suspending a single gas bubble in water under different subcoolings. Their showed that, under low subcoolings, the growth of hydrate film is dominated by the film thickening, but not by lateral film growth.…”

Hydrate growth at the interface between water and pure or mixed CO2/CH4 gases: Influence of pressure, temperature, gas composition and water-soluble surfactants

“…These and other authors (Servio and Englezos, 2003;Ohmura et al, 2004) examined hydrate crust mor phologies: a more faceted aspect (individual crystals of millimeter sizes) is observed at low subcooling ΔT, while a smooth appearance is noted at intermediate and high ΔT. Extensive observations of hydrate crust texture and lateral growth at water/gas interfaces have been conducted over the past decade, most of them focused on water/CH 4 systems, using various configurations: a rising (gas) bubble in water (Peng et al, 2007;Sun et al, 2007;Li et al, 2013Li et al, , 2014, a water drop (in gas) either pendent (Zhong et al, 2011) or sitting on a substrate (Tanaka et al, 2009), or a planar water/gas interface (Kitamura and Mori, 2013). While there is some scatter in the published lateral growth rates, all observations show that the hydrate crust texture gets smoother with increasing subcooling and increasing time.…”

Self-preservation and structural transition of gas hydrates during dissociation below the ice point: an in situ study using Raman spectroscopy

“…Gas mixtures of methane and ethane, with methane content lower than 75 mol.% or higher than 99 mol.%, form sI hydrates. Otherwise, they form sII hydrate4142. Up to now, most structural transition studies have been performed during the formation process of hydrates374344, while there are limited studies focused on the dissociation process4345.…”