Solubility of Methane in Water: Some Useful Results for Hydrate Nucleation

Grabowska, Joanna; Blazquez, S.; Sanz, Eduardo; Zerón, Iván M.; Algaba, Jesús; Mı́guez, José Manuel; Blas, Felipe J.; Vega, Carlos

doi:10.1021/acs.jpcb.2c04867

Cited by 29 publications

(19 citation statements)

References 92 publications

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“…Each of the salty solution phases contains 26 NaCl and 2304 water molecules (∼3.5 wt % of NaCl). A total of 1200 CO 2 molecules are present in the gas phase, which ensures that the gas phase does not become bubbled during the simulation process because the bubbles will affect the surface tension of the gas and liquid, thus further impacting the hydrate growth process. Water and CO 2 molecules were modeled with TIP4P/Ice and TraPPE force field parameters, , respectively.…”

Section: Methodsmentioning

confidence: 99%

Molecular Study on Carbon Dioxide Hydrate Formation in Salty Water

Zhao,

Zeng,

Zhao

et al. 2023

Crystal Growth & Design

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Clathrate hydrate-based seawater desalination has the potential to be a low-energy, environmentally friendly technique. However, the underlying hydrate growth and ion fractionation mechanism remains unclear. Hence, systematic molecular dynamics simulations were conducted to investigate the carbon dioxide hydrate growth process in the presence of salt. We find that hydrate growth slows with the increasing solution salinity, and the number of ions bound in the hydrate structure is related to the growth rate and the salinity. Ions can replace the water molecules at the vertex of the cages, which has been proven to be energetically unfavorable. The temperature dependence of the hydrate growth rate shows a maximum, while the pressure has a negligible impact on the growth rate of carbon dioxide hydrate under our conditions. The ion concentration in the hydrate phase decreases with an increase in temperature and is hardly affected by the pressure. Further examination indicates that the trapping of ions in the hydrate phase is kinetically controlled by the diffusion properties of the ions. Our study not only expands our understanding of the process of hydrate formation in seawater but also has great benefits for hydrate-based seawater desalination and seabed carbon sequestration.

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Section: Methodsmentioning

confidence: 99%

Molecular Study on Carbon Dioxide Hydrate Formation in Salty Water

Zhao,

Zeng,

Zhao

et al. 2023

Crystal Growth & Design

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“…All molecular models are rigid in this study. The model parameters for all species have been widely used in hydrate-related studies, ,,,− ,,− and more details are provided in Table S1. The temperature was controlled using a Nosé-Hoover thermostat with a time constant of 2.0 ps, and the pressure was controlled using an isotropic Parrinello-Rahman barostat with a time constant of 4.0 ps .…”

Section: Methodsmentioning

confidence: 99%

“…87 ■ RESULTS AND DISCUSSION Solubility within Water Nanodroplets. Since the nucleation events observed in this study involved H 2 S-filled cages almost exclusively, and since nucleation has a strong dependence on the guest concentration, 30,33,65,89 we initiate our investigation by measuring the concentration of H 2 S in the water nanodroplets. We note that for the current systems where a water nanodroplet is immersed in a non-aqueous liquid, the two phases (water/non-aqueous liquid) are in compositional equilibrium; thus, the concentrations of the guest species in the aqueous solution are essentially their saturated values, which represent their solubilities.…”

Section: ■ Methodsmentioning

confidence: 99%

Hydrate Nucleation in Water Nanodroplets: Key Factors and Molecular Mechanisms

2023

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Clathrate hydrate nucleation in heterogeneous systems, such as the water-in-oil emulsions found in pipeline environments, is of considerable technological importance and scientific interest. While there has been a number of experimental studies investigating hydrate nucleation in water-in-oil emulsions, there have been essentially no molecular simulations to provide important molecular insights into the hydrate nucleation process. Here, we report extensive molecular dynamics simulations of gas hydrate nucleation to examine nucleation behavior in water nanodroplets immersed in a non-aqueous liquid, probing key factors impacting nucleation, including guest species, guest compositions, size of the nanodroplets, and temperature. The nucleation behavior with pure-guest (i.e., H2S, C3H8, and CO2) and H2S-containing mixtures, where the second guest species is one of C3H8, CH4, C2H6, and CO2, has been studied. For the various systems examined in this study, we find that H2S always tends to initiate hydrate formation, with the only exception being the H2S/CO2 mixture, where the relatively high solubility of H2S compared to the other guest species is identified as an important factor for the current systems. Three different sizes of water nanodroplets at different temperatures are used to examine hydrate nucleation with pure-H2S guest systems, where the observed mechanism of hydrate nucleation within nanodroplets exhibits behavior similar to that found in bulk counterparts. Within water nanodroplets, the hydrate nucleation process features the initial formation of amorphous solids, which can then be annealed into more recognizable hydrate-like structures. Detailed cage analyses provide insights into the impacts of temperature and the size of the water nanodroplet on the initial location and the induction time of hydrate nucleation. Our simulations improve the understanding of the molecular mechanism of clathrate hydrate nucleation in water-in-oil emulsions, thus helping the development of hydrate-related applications and exploitation.

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“…34,36 Note that this strategy is successful only at low temperatures where the nucleation of gas bubbles occurs in a much larger timescale, as we have shown recently. 51 The second strategy is more subtle. One has a two phase system (water and gas), but instead of having a planar interface, methane molecules form a spherical bubble, which results in an increase of the solubility of methane molecules in the aqueous phase.…”

Section: Introductionmentioning

confidence: 99%

“…We shall use the TIP4P/ICE force field 65 for water and the single Lennard-Jones (LJ) site model 66,67 for methane, which are able to provide quite good estimates of T 3 as compared to experiments. 51 To determine J, we shall use the seeding technique. 68 Seeding studies started with the work of Bai and Li; 69,70 it is also in the spirit of the work of Carignano and co-workers 71 and was more officially presented in the work of Knott et al 35 and Sanz et al 14 In the paper of Knott et al, the nucleation rate for the formation of a hydrate was considered, while in the paper of Sanz et al, the nucleation rate for the formation of ice was determined.…”

Section: Introductionmentioning

confidence: 99%

Homogeneous nucleation rate of methane hydrate formation under experimental conditions from seeding simulations

Grabowska

Blazquez

Sanz

et al. 2023

The Journal of Chemical Physics

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In this work, we shall estimate via computer simulations the homogeneous nucleation rate for the methane hydrate at 400 bars for a supercooling of about 35 K. The TIP4P/ICE model and a Lennard-Jones center were used for water and methane, respectively. To estimate the nucleation rate, the seeding technique was employed. Clusters of the methane hydrate of different sizes were inserted into the aqueous phase of a two-phase gas–liquid equilibrium system at 260 K and 400 bars. Using these systems, we determined the size at which the cluster of the hydrate is critical (i.e., it has 50% probability of either growing or melting). Since nucleation rates estimated from the seeding technique are sensitive to the choice of the order parameter used to determine the size of the cluster of the solid, we considered several possibilities. We performed brute force simulations of an aqueous solution of methane in water in which the concentration of methane was several times higher than the equilibrium concentration (i.e., the solution was supersaturated). From brute force runs, we infer the value of the nucleation rate for this system rigorously. Subsequently, seeding runs were carried out for this system, and it was found that only two of the considered order parameters were able to reproduce the value of the nucleation rate obtained from brute force simulations. By using these two order parameters, we estimated the nucleation rate under experimental conditions (400 bars and 260 K) to be of the order of log10 ( J/(m3 s)) = −7(5).

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Solubility of Methane in Water: Some Useful Results for Hydrate Nucleation

Cited by 29 publications

References 92 publications

Molecular Study on Carbon Dioxide Hydrate Formation in Salty Water

Molecular Study on Carbon Dioxide Hydrate Formation in Salty Water

Hydrate Nucleation in Water Nanodroplets: Key Factors and Molecular Mechanisms

Homogeneous nucleation rate of methane hydrate formation under experimental conditions from seeding simulations

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