Optimization of intermolecular potential parameters for the CO2/H2O mixture.

Area of Science:

• Physical Chemistry
• Chemical Engineering
• Computational Chemistry

Background:

• Accurate modeling of carbon dioxide (CO2) and water (H2O) mixtures is essential for advancing carbon capture and sequestration (CCS) technologies.
• Intermolecular potential parameters significantly influence the predicted phase behavior of fluid mixtures.

Purpose of the Study:

• To optimize intermolecular potential parameters for CO2/H2O mixtures using Monte Carlo simulations in the Gibbs ensemble.
• To evaluate the performance of Lennard-Jones (LJ) and exponential-6 (Exp-6) force fields in describing the phase behavior of CO2/H2O mixtures across relevant temperatures and pressures for CCS.

Main Methods:

• Utilized Monte Carlo simulations within the Gibbs ensemble framework.
• Employed fixed-point-charge force fields, specifically Lennard-Jones (LJ) 12-6 and exponential-6 (Exp-6) models, for CO2 and H2O interactions.
• Systematically varied intermolecular potential parameters, including unlike interaction terms and partial charges.

Main Results:

• Lennard-Jones (LJ) force fields showed limitations, with no combination of unlike interaction parameters accurately representing both CO2-rich and H2O-rich phases simultaneously.
• Adjusting H2O partial charges improved fits to experimental data for both phases but compromised pure H2O properties.
• The exponential-6 (Exp-6) model demonstrated superior performance, requiring only the optimization of the oxygen-oxygen unlike-pair interaction to accurately predict solubilities in both phases while maintaining pure component accuracy.

Conclusions:

• The exponential-6 (Exp-6) model offers a more robust and accurate approach for simulating CO2/H2O mixtures compared to traditional LJ models.
• Optimized Exp-6 parameters are recommended for future molecular simulation studies involving CO2/H2O mixtures in the context of carbon capture and sequestration.
• This study provides valuable insights into selecting appropriate force fields for accurate phase behavior predictions in critical industrial applications.