Carbon Dioxide Hydrate Growth Dynamics and Crystallography in Pure and Saline Water

Abstract

To develop the crucial concepts of clathrate hydrates toward the hydrate-based technological implications, it is indispensable to comprehend their formation and growth mechanisms and stability in pure and saline water environments. In this view, we provide fundamental insights into the gas hydrate dynamics by carefully conducting a molecular dynamics simulation in an extensive range of carbon dioxide (CO 2 ) gas (CO 2 /H 2 O from 1:5 to 1:18) and sodium chloride (NaCl) salt (from 0.0 to 18.0 wt %) concentrations. Using the F 4φ order parameter and the radial distribution function, we assess the important information about the time evolution of the visualization states and the formation and growth of small (5 12 ) and large (5 12 6 2 and 5 12 6 4 ) cages of hydrates along with their crystalline nature. We found that (1) CO 2 forms the pure S−I type of hydrate structure irrespective of guest gas and salt concentrations; (2) lower CO 2 gas concentration (CO 2 /H 2 O from 1:8 to 1:18) leads to fast but incomplete conversion of water to hydrate, while the higher CO 2 gas concentration (1:6) causes the phase separation and consequent sluggish hydrate growth; (3) 1:7 is an optimum CO 2 /H 2 O ratio for the rapid, complete, and properly ordered hydrate growth; (4) at the optimum amount of CO 2 and H 2 O, the lower range of salt concentrations (0.0−5.0 wt %) has a slight inhibition effect on the hydrate growth, while there is a notable inhibition effect for the higher salt concentrations (7.0−18.0 wt %); (5) the number of oxygen atoms of water present in the first coordination sphere remains constant for the lower salt concentrations (0.0−5.0 wt %), and they get reduced with the higher salt concentrations (7.0−18.0 wt %); (6) the inhibition effect is due to the reduction of CO 2 solubility in the aqueous phase in the presence of salt ions. These novel findings provide useful assistance for choosing an appropriate combination of the imperative elements of gas hydrate systems toward carbon dioxide separation, sequestration, storage, and transportation.

Intensified Carbon Dioxide Hydrate Formation Kinetics in a Simulated Subsea Sediment: Application in Carbon Capture and Sequestration

“…Another key conclusion that can be deduced from Figure 5b is that the presence of salts promotes the nucleation; IT in saline water is significantly low compared to that in the DI water systems, which corroborates well with the literature data. 53,54 Further, our future work will focus on acquiring the statistical number of data points to measure the actual probability distribution of the IT/ nucleation events. The shortest IT would help reduce the overall process time and support deploying the hydrate-based CCS approach at the field scale.…”

Review of Gas Hydrate Research in India: Status and Future Directions

“…Structural coexistence of both sI and sII methane hydrates was observed, and low methane concentration favored the formation of the sII structure. A similar MD simulation study was performed for CO 2 hydrate formation with varying CO 2 /water ratio (1:5 to 1:18) and NaCl content (0–18 wt%). It was reported that pure sI hydrate formed irrespective of guest gas/water ratio and salt concentration, with 1:7 being the optimal CO 2 /water ratio for rapid hydrate growth without salt.…”

Thermodynamic and Kinetic Effects of Quaternary Ammonium and Phosphonium Ionic Liquids on CO2 Hydrate Formation

“…61,71,72 In addition, the first peak of g H2O−H2O (r) in the [N 4 4 4 4 ]Br + H 2 O + CO 2 system locates at 2.75 Å, which corresponds to the distance between the O atoms of the hydrogen-bonded water molecules. 73 A shorter distance indicates a stronger hydrogen bond, and a higher peak means a larger probability of hydrogen bond formation between water molecules. The strong interaction forces between water molecules are favorable for adjusting the distance and angle between water molecules to According to DFT and MD calculations, it is found that the anion−cation interaction in [N 2 2 2 2 ]Br is stronger than that in [N 4 4 4 4 ]Br, which may lead to the weakening of the interaction between the anion and water for [N 2 2 2 2 ]Br.…”

“…61, 71,72 In addition, the first peak of g H2O−H2O (r) in the [N 4 4 4 4 ]Br + H 2 O + CO 2 system locates at 2.75 Å, which corresponds to the distance between the O atoms of the hydrogen-bonded water molecules. 73 A shorter distance indicates a stronger hydrogen bond, and a higher peak means a larger probability of hydrogen bond formation between water molecules. The strong interaction forces between water molecules are favorable for adjusting the distance and angle between water molecules to…”