Multicomponent Gas Hydrate Nucleation: The Effect of the Cooling Rate and Composition

Abay, Hailu K.; Svartaas, Thor M.

doi:10.1021/ef1011879

Cited by 31 publications

(29 citation statements)

References 42 publications

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“…However, experiments at ambient conditions give nucleation rates of 10 0 –10 –7 nuclei cm –3 s –1 . 30 − 37 30 − 37 Our predicted rate is 5–9 orders of magnitude higher, which is consistent with the higher pressure imposed in our work.…”

Section: Resultssupporting

confidence: 92%

Rate Prediction for Homogeneous Nucleation of Methane Hydrate at Moderate Supersaturation Using Transition Interface Sampling

Arjun

Bolhuis

2020

J. Phys. Chem. B

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The crystallization of methane hydrates via homogeneous nucleation under natural, moderate conditions is of both industrial and scientific relevance, yet still poorly understood. Predicting the nucleation rates at such conditions is notoriously difficult due to high nucleation barriers, and requires, besides an accurate molecular model, enhanced sampling. Here, we apply the transition interface sampling technique, which efficiently computes the exact rate of nucleation by generating ensembles of unbiased dynamical trajectories crossing predefined interfaces located between the stable states. Using an accurate atomistic force field and focusing on specific conditions of 280 K and 500 bar, we compute for nucleation directly into the sI crystal phase at a rate of ∼10 –17 nuclei per nanosecond per simulation volume or ∼10 2 nuclei per second per cm 3 , in agreement with consensus estimates for nearby conditions. As this is most likely fortuitous, we discuss the causes of the large differences between our results and previous simulation studies. Our work shows that it is now possible to compute rates for methane hydrates at moderate supersaturation, without relying on any assumptions other than the force field.

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Section: Resultssupporting

confidence: 92%

Rate Prediction for Homogeneous Nucleation of Methane Hydrate at Moderate Supersaturation Using Transition Interface Sampling

Arjun

Bolhuis

2020

J. Phys. Chem. B

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“…In cooling down the system, we used a constant cooling rate. Thus possible effects from cooling rate have been eliminated [40,80].…”

Section: Resultsmentioning

confidence: 99%

Gas Hydrate Growth Kinetics: A Parametric Study

Meindinyo

Svartaas

2016

Energies

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Gas hydrate growth kinetics was studied at a pressure of 90 bars to investigate the effect of temperature, initial water content, stirring rate, and reactor size in stirred semi-batch autoclave reactors. The mixing energy during hydrate growth was estimated by logging the power consumed. The theoretical model by Garcia-Ochoa and Gomez for estimation of the mass transfer parameters in stirred tanks has been used to evaluate the dispersion parameters of the system. The mean bubble size, impeller power input per unit volume, and impeller Reynold's number/tip velocity were used for analyzing observed trends from the gas hydrate growth data. The growth behavior was analyzed based on the gas consumption and the growth rate per unit initial water content. The results showed that the growth rate strongly depended on the flow pattern in the cell, the gas-liquid mass transfer characteristics, and the mixing efficiency from stirring. Scale-up effects indicate that maintaining the growth rate per unit volume of reactants upon scale-up with geometric similarity does not depend only on gas dispersion in the liquid phase but may rather be a function of the specific thermal conductance, and heat and mass transfer limitations created by the limit to the degree of the liquid phase dispersion is batched and semi-batched stirred tank reactors.

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“…The binary SNG2 has the same composition, thermodynamic properties, and equilibrium curve as that investigated by Abay and Svartaas. 43…”

Section: Methodsmentioning

confidence: 99%

“…This simplification is supported by the flash calculations of molar composition of hydrate–water–gas phases in previous work using SNG2 gas by Abay and Svartaas. 43…”

Section: Computational Modelmentioning

confidence: 99%

“…The non-stoichiometric factors, m, p , and w , are normalized values based on previous flash calculations by Abay and Svartaas. 43 Their calculation showed that the molar ratios of methane, propane, and water in the formed SNG2 hydrate phase were 0.0810, 0.0494, and 0.8696, respectively. The rate constants and factors used for numerical computations are summarized in Table 1.…”

Section: Computational Modelmentioning

confidence: 99%

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Methane–propane hydrate formation and memory effect study with a reaction kinetics model

Chen

2020

Progress in Reaction Kinetics and Mechanism

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Although natural gas hydrates and hydrate exploration have been extensively studied for decades, the reaction kinetics and nucleation mechanism of hydrate formation is not fully understood. In its early stage, gas hydrate formation can be assumed to be an autocatalytic kinetic reaction with nucleation and initial growth. In this work, a reaction kinetics model has been established to form structure II methane–propane hydrate in an isochoric reactor. The computational model consists of six pseudo-elementary reactions for three dynamic processes: (1) gas dissolution into the bulk liquid, (2) a slow buildup of hydrate precursors for nucleation onset, and (3) rapid and autocatalytic hydrate growth after onset. The model was programmed using FORTRAN, with initiating parameters and rate constants that were derived or obtained from data fitted using experimental results. The simulations indicate that the length of nucleation induction is determined largely by an accumulation of oligomeric hydrate precursors up to a threshold value. The slow accumulation of precursors is the rate-limiting step for the overall hydrate formation, and its conversion into hydrate particles is critical for the rapid, autocatalytic reaction. By applying this model, the memory effect for hydrate nucleation was studied by assigning varied initial amounts of precursor or hydrate species in the simulations. The presence of pre-existing precursors or hydrate particles could facilitate the nucleation stage with a reduced induction time, and without affecting hydrate growth. The computational model with the performed simulations provides insight into the reaction kinetics and nucleation mechanism of hydrate formation.

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Multicomponent Gas Hydrate Nucleation: The Effect of the Cooling Rate and Composition

Cited by 31 publications

References 42 publications

Rate Prediction for Homogeneous Nucleation of Methane Hydrate at Moderate Supersaturation Using Transition Interface Sampling

Rate Prediction for Homogeneous Nucleation of Methane Hydrate at Moderate Supersaturation Using Transition Interface Sampling

Gas Hydrate Growth Kinetics: A Parametric Study

Methane–propane hydrate formation and memory effect study with a reaction kinetics model

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