Solubility of carbon dioxide in water: Some useful results for hydrate nucleation

Abstract

In this paper, the solubility of carbon dioxide (CO2) in water along the isobar of 400 bar is determined by computer simulations using the well-known TIP4P/Ice force field for water and the TraPPE model for CO2. In particular, the solubility of CO2 in water when in contact with the CO2 liquid phase and the solubility of CO2 in water when in contact with the hydrate have been determined. The solubility of CO2 in a liquid–liquid system decreases as the temperature increases. The solubility of CO2 in a hydrate–liquid system increases with temperature. The two curves intersect at a certain temperature that determines the dissociation temperature of the hydrate at 400 bar (T3). We compare the predictions with T3 obtained using the direct coexistence technique in a previous work. The results of both methods agree, and we suggest 290(2) K as the value of T3 for this system using the same cutoff distance for dispersive interactions. We also propose a novel and alternative route to evaluate the change in chemical potential for the formation of hydrates along the isobar. The new approach is based on the use of the solubility curve of CO2 when the aqueous solution is in contact with the hydrate phase. It considers rigorously the non-ideality of the aqueous solution of CO2, providing reliable values for the driving force for nucleation of hydrates in good agreement with other thermodynamic routes used. It is shown that the driving force for hydrate nucleation at 400 bar is larger for the methane hydrate than for the carbon dioxide hydrate when compared at the same supercooling. We have also analyzed and discussed the effect of the cutoff distance of dispersive interactions and the occupancy of CO2 on the driving force for nucleation of the hydrate.

Experimental Study on the Influence of the Temperature and Gas–Liquid Ratio on Hydrate-Based CO2 Separation from the CH4–CO2 Gas Mixture under Static Conditions

“…Because the nucleation of CO 2 hydrate is affected by the dissolution of carbon dioxide, 48 the higher the concentration of CO 2 is, the more favorable the nucleation of CO 2 hydrates. Therefore, when the gas−liquid ratio reaches its maximum value, the amount of CO 2 dissolved in water is the least, and the magnitude of the pressure drop is relatively low.…”

“…Furthermore, when the same molar amount of CO 2 was dissolved in water, the smaller the gas–liquid ratio, the more significant the pressure drop and the lower the CO 2 concentration in water. Because the nucleation of CO 2 hydrate is affected by the dissolution of carbon dioxide, the higher the concentration of CO 2 is, the more favorable the nucleation of CO 2 hydrates. Therefore, when the gas–liquid ratio reaches its maximum value, the amount of CO 2 dissolved in water is the least, and the magnitude of the pressure drop is relatively low.…”

Special Topic Preface: Nucleation—Current understanding approaching 150 years after Gibbs

“…Although energetics align (critical nucleus size and interfacial free energies), significant differences in dynamical properties (characteristic nucleation time and growth rate) impact the kinetics of crystallization, resulting in different characteristics of crystalline nuclei and methane concentration dependencies between the two models. Algaba et al 22 employ computer simulations to determine the solubility of carbon dioxide (CO 2 ) in water under conditions relevant to hydrate nucleation. Using the TIP4P/Ice and TraPPE models for water and CO 2 , respectively, the simulations show that the solubility of CO 2 in water when in contact with liquid CO 2 decreases with temperature, while it increases with temperature in a hydrate-liquid water system.…”