Phase Equilibria of Water/CO₂ and Water/n-Alkane Mixtures from Polarizable Models

Abstract

Phase equilibria of water/CO and water/n-alkane mixtures over a range of temperatures and pressures were obtained from Monte Carlo simulations in the Gibbs ensemble. Three sets of Drude-type polarizable models for water, namely the BK3, GCP, and HBP models, were combined with a polarizable Gaussian charge CO (PGC) model to represent the water/CO mixture. The HBP water model describes hydrogen bonds between water and CO explicitly. All models underestimate CO solubility in water if standard combining rules are used for the dispersion interactions between water and CO. With the dispersion parameters optimized to phase compositions, the BK3 and GCP models were able to represent the CO solubility in water, however, the water composition in CO-rich phase is systematically underestimated. Accurate representation of compositions for both water- and CO-rich phases cannot be achieved even after optimizing the cross interaction parameters. By contrast, accurate compositions for both water- and CO-rich phases were obtained with hydrogen bonding parameters determined from the second virial coefficient for water/CO. Phase equilibria of water/n-alkane mixtures were also studied using the HBP water and an exponenial-6 united-atom n-alkanes model. The dispersion interactions between water and n-alkanes were optimized to Henry's constants of methane and ethane in water. The HBP water and united-atom n-alkane models underestimate water content in the n-alkane-rich phase; this underestimation is likely due to the neglect of electrostatic and induction energies in the united-atom model.

Overview of the Adsorption and Transport Properties of Water, Ions, Carbon Dioxide, and Methane in Swelling Clays

“…The simulated binding energy of H 2 O–CH 4 was about −0.24 kcal/mol . The difference is probably because of the use of nonpolarizable models . These findings indicate the stronger interactions of water with CO 2 than with CH 4 .…”

Data-Driven Many-Body Models for Molecular Fluids: CO2/H2O Mixtures as a Case Study

“…Subsequent simulations carried out for CO 2 /H 2 O mixtures demonstrated current difficulties in determining CO 2 solubility in water as well as the water composition in CO 2 -rich phases using polarizable models. 56 Building upon recent progress in the development of explicit many-body potential energy functions (PEFs) capable of describing molecular interactions with chemical accuracy, [59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] 20 , the interactions between the water molecules were described by the manybody MB-pol PEF [62][63][64] that accurately reproduces the properties of water from the gas to the condensed phase. 74,75 More recently, a 2B PEF for CO 2 was developed from CCSD(T)-F12b/aug-cc-pVTZ reference data and used in the analysis of both structures and energetics of small (CO 2 ) N clusters with N ≤ 13 which were found to be in good agreement with results obtained using density functional theory (DFT) with the M06-2X and B2PLYP-D functionals.…”

Electrostatic and induction effects in the solubility of water in alkanes

“…As McDaniel and Yethiraj [11] subsequently noted in an insightful comment, the work by Ballal et al [7] "uncovered a wonderful example of where pure-component parameters fail for mixtures" and "a more accurate model must better describe the electrostatic, induction, and dispersion interactions, all of which are potentially important." Recent studies on water/CO 2 and water/n-alkane mixtures further support this idea [12].…”