A first order method of hydrate equilibrium estimation and its use with new structures

Lederhos, J.P.; Christiansen, Richard L.; Sloan, E. Dendy

doi:10.1016/0378-3812(93)87049-7

Cited by 20 publications

(16 citation statements)

References 11 publications

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“…It is well known that hydrate cavities are stabilized by the inclusion of guest molecules. According to previous research by Lederhos et al [42], a guest-to-cavity ratio between 0.75 and 1.0 is conducive to stabilizing clathrate cavities. In this case, the ratio for C 2 H 6, C 3 H 8 , and iso-C 4 H 10 were all within this range, according to the results shown in Table 3.…”

Section: Discussionmentioning

confidence: 84%

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates

Pan

Schicks

2021

Molecules

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Natural gas hydrate occurrences contain predominantly methane; however, there are increasing reports of complex mixed gas hydrates and coexisting hydrate phases. Changes in the feed gas composition due to the preferred incorporation of certain components into the hydrate phase and an inadequate gas supply is often assumed to be the cause of coexisting hydrate phases. This could also be the case for the gas hydrate system in Qilian Mountain permafrost (QMP), which is mainly controlled by pores and fractures with complex gas compositions. This study is dedicated to the experimental investigations on the formation process of mixed gas hydrates based on the reservoir conditions in QMP. Hydrates were synthesized from water and a gas mixture under different gas supply conditions to study the effects on the hydrate formation process. In situ Raman spectroscopic measurements and microscopic observations were applied to record changes in both gas and hydrate phase over the whole formation process. The results demonstrated the effects of gas flow on the composition of the resulting hydrate phase, indicating a competitive enclathration of guest molecules into the hydrate lattice depending on their properties. Another observation was that despite significant changes in the gas composition, no coexisting hydrate phases were formed.

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Section: Discussionmentioning

confidence: 84%

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates

Pan

Schicks

2021

Molecules

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“…The filling of the large sII cavity by nC4 is not particularly favourable. Its molecule/cavity size ratio of 1.081 makes it difficult for nC4 to experience attractive van der Waals forces in the cavity due to overlap of nC4 and the water molecules' van der Waals radii (Lederhos, et al, 1993). It can be concluded that the combination of nC4's size and the effect of lattice distortion with pressure, adding nC4 to C1 can inhibit the hydrate phase equilibria by acting as a non-former.…”

Section: Methane-n-butanementioning

confidence: 99%

“…Stabilization of C1 hydrates also manifests upon the addition of sI hydrate formers. Ethane, for example, is capable of entering the 5 12 6 2 cage of sI hydrates according to its van der Waals radius (Lederhos, et al, 1993). Early hydrate equilibrium studies performed by Deaton and Frost (1946) demonstrate the added stability provided by ethane.…”

Section: Introductionmentioning

confidence: 99%

Propane, n -butane and i-butane stabilization effects on methane gas hydrates

Smith

Pack²,

Barifcani

2017

The Journal of Chemical Thermodynamics

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The goal of this work is to analyse the hydrate equilibria of methane + propane, i-butane and n-butane gas mixtures. Experimental hydrate equilibrium data was acquired for various compositions of these components in methane, ranging from 0.5-6.8 mol%. Applying this information with the Clausius-Clapeyron equation, the extent of hydrate promotion was demonstrated quantitatively by calculating the slope of the equation and the dissociation enthalpy (ΔHd). Methane equilibria was found to be most sensitive towards propane and ibutane, where very small concentrations were sufficient to increase the thermodynamic conditions for hydrate equilibrium drastically. The degree of hydrate stabilisation, i.e. transition from sI to sII hydrate, was immediatethere was no detectable composition slightly above 0.0 mol% where propane or i-butane did not have a sII hydrate-promoting impact, although one was implied with the aid of Calsep PVTsim calculations. Addition of nbutane to methane was far less sensitive and was deemed inert from 0.0-0.5 mol%. It was concluded that the sII hydrate was favoured when the n-butane composition exceeded 0.5-0.75 mol%. The influence of composition on stability was quantified by determining the gradient of ΔHd versus mol% plots for the initial steep region that represents the increasing occupancy of the sII guests. Average gradients of 11.66, 26.64 and 43.50 kJ/mol.mol% were determined for n-butane, propane and i-butane addition to methane respectively. A hydrateinert range for propane/i-butane (in methane) was suspected according to the perceived inflection point when less 0.5 mol%, implying the gradient was very low at some minute concentration range starting at 0.0 mol%. Awareness of these sI to sII transition regions is beneficial to natural gas recovery and processing as a small percentage of these components may remain without being detrimental in terms of promoting the hydrate equilibria.

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“…Therefore, a gas with a higher solubility will likely have a greater driving force for hydrate formation resulting in a higher equilibrium temperature. Additionally, carbon dioxide is a larger molecule than both methane and nitrogen and offers more stability to its hydrate structure Lederhos et al (1993). Carbondioxide is more capable of filling and providing stability to the larger 5 12 6 2 cavities making methane-carbon-dioxide hydrate dissociation more energy intensive, and therefore requiring a higher temperature.…”

Section: Fig5 -Dissociation Temperature Profile For Carbon Dioxide Imentioning

confidence: 99%

Gas hydrate formation and dissociation numerical modelling with nitrogen and carbon dioxide

Smith

Barifcani

Pack³

2015

Journal of Natural Gas Science and Engineering

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This work aims at providing experimental data for various methane-based hydrates, namely nitrogen and carbon dioxide gas mixtures with varying concentrations to provide an empirically based hydrate equilibrium model. Acquired using a sapphire pressurevolumetemperature (PVT) cell, this data is used as the foundation for the derivation of a model able to calculate the equilibrium temperature of a nitrogen and/or carbon dioxide diluted methane gas is accomplished. There are several theoretical predictive models used in software which can provide hydrate formation and equilibrium data, however theoretical models appear to outnumber experimental data and empirical models for which a comparison can be made.The effect of nitrogen and carbon dioxide, an inhibitor and promotor respectively, on methane hydrate formation and dissociation and their associated pressure and temperature conditions are explored. The hydrate profiles for various gas mixtures containing the gases mentioned are presented at pressures ranging between 40-180 bara. These hydrate profiles and the model presented were compared to those predicted by hydrate computational software and experimental data from other studies for verification. The derived model proved to be reliable when applied to various gas mixtures at different pressure conditions and was consistent when compared to computational software based on theoretical models.Consistency of methane hydrate formation data was compared to dissociation data proved that the formation temperature is not an accurate representation of the equilibrium temperature. A simple statistical measure revealed the dissociation temperature measurements to be more precise and agreed to a much larger degree with literature.

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A first order method of hydrate equilibrium estimation and its use with new structures

Cited by 20 publications

References 11 publications

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates

Propane, n -butane and i-butane stabilization effects on methane gas hydrates

Gas hydrate formation and dissociation numerical modelling with nitrogen and carbon dioxide

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