Study of the Kinetics and Morphology of Gas Hydrate Formation

Abstract

The kinetics and morphology of ethane hydrate formation were studied in a batch type reactor at a temperature of ca. 270-280 K, over a pressure range of 8.83-16.67 bar. The results of the experiments revealed that the formation kinetics were dependant on pressure, temperature, degree of supercooling, and stirring rate. Regardless of the saturation state, the primary nucleation always took place in the bulk of the water and the phase transition was always initiated at the surface of the vortex (gas-water interface). The rate of hydrate formation was observed to increase with an increase in pressure. The effect of stirring rate on nucleation and growth was emphasized in great detail. The experiments were performed at various stirring rates of 110-190 rpm. Higher rates of formation of gas hydrate were recorded at faster stirring rates. The appearance of nuclei and their subsequent growth at the interface, for different stirring rates, was explained by the proposed conceptual model of mass transfer resistances. The patterns of gas consumption rates, with changing rpm, have been visualized as due to a critical level of gas molecules in the immediate vicinity of the growing hydrate particle. Nucleation and decomposition gave a cyclic hysteresis-like phenomena. It was also observed that a change in pressure had a much greater effect on the rate of decomposition than it did on the formation rate. Morphological studies revealed that the ethane hydrate resembles thread or is cotton-like in appearance. The rate of gas consumption during nucleation, with different rpm and pressures, and the percentage decomposition at different pressures, were explained precisely for ethane hydrate.

Modelling of hydrate formation kinetics: State-of-the-art and future directions

“…For carbon dioxide, nucleation at the gas-liquid interface started on the wall and the hydrate layer grew into the liquid bulk, which was confirmed by Takeya et al (2000) with a highspeed video camera. Additional data for nucleation in the interfacial region for quiescent systems are found in the literature for ethane (Hussain et al, 2006), propane (Gayet et al, 2005), dichlorofluoroethane (Li et al, 2005) and methane-propane hydrates, all formed from distilled water. Working with diluted SDS solutions, Lin et al (2004) and Gayet et al (2005) observed nucleation at the reactor wall, close to the gas-liquid interface, for pure methane and propane hydrates, respectively, with a rapid growth along the wall in the gas side.…”

Inhibition–Promotion: Dual Effects of Polyvinylpyrrolidone (PVP) on Structure-II Hydrate Nucleation

“…Similar to ice formation and melting, gas hydrate may undergo phase transitions of three stages, i.e., nucleation, , growth, , and dissociation. , Accumulated research efforts via experimental studies ,− and modeling/simulation work ,− have been made in attempt to gain more understanding of hydrate formation and dissociation phenomena for decades. It is relatively easy to monitor and study hydrate growth and dissociation on a macroscopic scale. ,,− During nucleation, the water–gas clustering process is an energy battle between the volume excess free energy (favorable, reduced enthalpy) and surface excess free energy (unfavorable, reduced entropy) in the metastable region. Nucleation is stochastic and intractable because initial embryos of hydrate clusters of different sizes would not obtain the critical size to form stable nuclei until the free energy barrier of pushing away the old phases is overcome. , Only a nucleus surpassing such energy barrier would reach critical size for sustainable nucleation and trigger macroscopic growth.…”

Effect of SDS/THF on thermodynamic and kinetic properties of formation of hydrate from a mixture of gases (CH4+C2H6+C3H8) for storing gas as hydrate

“…Several studies on the phase equilibrium and kinetics of gas hydrate formation and dissociation have been reported by many researchers, but most of them are on hydrate formation/dissociation in pure or binary gas mixture [3][4][5][6][7][8][9] . On the other hand, there are very limited experimental data of hydrate formation and dissociation conditions in ternary gas mixtures [10][11][12][13][14] .…”

“…The objective of this study is to see the effect of promoter for storing natural gas as hydrates. In this study, effect of sodium dodecyl sulfate (SDS) and tetrahydrofuran (THF) on phase equilibrium condition and formation kinetics of CH 4…”