Calculating the Phase Behavior of Gas-Hydrate-Forming Systems from Molecular Models

Wierzchowski, SJ; Monson, P. A.

doi:10.1021/ie050875s

Cited by 32 publications

(46 citation statements)

References 69 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…65 This work has shown that this simple model can reproduce all the qualitative features of the phase diagram. Phase diagram calculations for more realistic models with the goal of achieving more quantitative agreement with experimental phase behavior are underway.…”

Section: Discussionmentioning

confidence: 85%

“…The first model was chosen in answer to the question of what might be the simplest molecular model that could describe hydrate behavior. 65 This is a mixture of a hard spheres representing the methane molecule and associating hard spheres (primitive model of water, PW) representing waterswe refer to this as the PW/ HS model. This model has been used extensively by Nezbeda and co-workers 81,85 in applications to aqueous solutions of alkanes, and the solid-fluid equilibrium of the PW has been previously studied for two ice phases.…”

Section: Molecular Models and Monte Carlo Simulationsmentioning

confidence: 99%

See 1 more Smart Citation

Calculation of Free Energies and Chemical Potentials for Gas Hydrates Using Monte Carlo Simulations

2007

Self Cite

View full text Add to dashboard Cite

We describe a method for calculating free energies and chemical potentials for molecular models of gas hydrate systems using Monte Carlo simulations. The method has two components: (i) thermodynamic integration to obtain the water and guest molecule chemical potentials as functions of the hydrate occupancy; (ii) calculation of the free energy of the zero-occupancy hydrate system using thermodynamic integration from an Einstein crystal reference state. The approach is applicable to any classical molecular model of a hydrate. We illustrate the methodology with an application to the structure-I methane hydrate using two molecular models. Results from the method are also used to assess approximations in the van der WaalsPlatteeuw theory and some of its extensions. It is shown that the success of the van der Waals-Platteeuw theory is in part due to a cancellation of the error arising from the assumption of a fixed configuration of water molecules in the hydrate framework with that arising from the neglect of methane-methane interactions.

show abstract

Section: Discussionmentioning

confidence: 85%

Section: Molecular Models and Monte Carlo Simulationsmentioning

confidence: 99%

Calculation of Free Energies and Chemical Potentials for Gas Hydrates Using Monte Carlo Simulations

2007

Self Cite

View full text Add to dashboard Cite

show abstract

“…Here we demonstrate a method by which this chemical potential may be determined accurately. This method of calculation is in the same spirit as those employed in recent work by Monson et al 29,30 who tested the predictions of van der Waals theory against those of more accurate GCMC ͑Grand Canonical Monte Carlo͒ simulation to see what effect the various approximations of the van der Waals-Platteeuw theory had on the estimation of the hydrate guest occupancies.…”

Section: Introductionmentioning

confidence: 99%

The phase diagram of water at negative pressures: Virtual ices

Conde

Vega

Tribello

et al. 2009

The Journal of Chemical Physics

View full text Add to dashboard Cite

The phase diagram of water at negative pressures as obtained from computer simulations for two models of water, TIP4P/2005 and TIP5P is presented. Several solid structures with lower densities than ice Ih, so-called virtual ices, were considered as possible candidates to occupy the negative pressure region of the phase diagram of water. In particular the empty hydrate structures sI, sII, and sH and another, recently proposed, low-density ice structure. The relative stabilities of these structures at 0 K was determined using empirical water potentials and density functional theory calculations. By performing free energy calculations and Gibbs-Duhem integration the phase diagram of TIP4P/2005 was determined at negative pressures. The empty hydrates sII and sH appear to be the stable solid phases of water at negative pressures. The phase boundary between ice Ih and sII clathrate occurs at moderate negative pressures, while at large negative pressures sH becomes the most stable phase. This behavior is in reasonable agreement with what is observed in density functional theory calculations.

show abstract

“…5,6 For this reason, the possibility of recovering methane stored in the form of hydrates, for energetic purposes, is receiving increasing attention and simulation and theoretical studies of methane hydrates are becoming more and more popular in recent years. [7][8][9][10][11][12][13][14] A review of each of these areas may be found in two recent review papers. The first is by Chandler 15 and focuses on a molecular description of the hydrophobic effect, while the second is by Sloan 16 and deals with gas hydrates.…”

Section: Introductionmentioning

confidence: 99%

A potential model for methane in water describing correctly the solubility of the gas and the properties of the methane hydrate

Docherty

Galindo

Vega

et al. 2006

The Journal of Chemical Physics

148

149

View full text Add to dashboard Cite

We have obtained the excess chemical potential of methane in water, over a broad range of temperatures, from computer simulation. The methane molecules are described as simple Lennard-Jones interaction sites, while water is modeled by the recently proposed TIP4P/2005 model. We have observed that the experimental values of the chemical potential are not reproduced when using the Lorentz-Berthelot combining rules. However, we also noticed that the deviation is systematic, suggesting that this may be corrected. In fact, by introducing positive deviations from the energetic Lorentz-Berthelot rule to account indirectly for the polarization methane-water energy, we are able to describe accurately the excess chemical potential of methane in water. Thus, by using a model capable of describing accurately the density of pure water in a wide range of temperatures and by deviating from the Lorentz-Berthelot combining rules, it is possible to reproduce the properties of methane in water at infinite dilution. In addition, we have applied this methane-water potential to the study of the solid methane hydrate structure, commonly denoted as sI, and find that the model describes the experimental value of the unit cell of the hydrate with an error of about 0.2%. Moreover, we have considered the effect of the amount of methane contained in the hydrate. In doing so, we determine that the presence of methane increases slightly the value of the unit cell and decreases slightly the compressibility of the structure. We also note that the presence of methane increases greatly the range of pressures where the sI hydrate is mechanically stable.

show abstract

Calculating the Phase Behavior of Gas-Hydrate-Forming Systems from Molecular Models

Cited by 32 publications

References 69 publications

Calculation of Free Energies and Chemical Potentials for Gas Hydrates Using Monte Carlo Simulations

Calculation of Free Energies and Chemical Potentials for Gas Hydrates Using Monte Carlo Simulations

The phase diagram of water at negative pressures: Virtual ices

A potential model for methane in water describing correctly the solubility of the gas and the properties of the methane hydrate

Contact Info

Product

Resources

About