Atomistic molecular dynamics simulations of H₂O diffusivity in liquid and supercritical CO₂

Abstract

Molecular dynamics simulations were employed for the calculation of diffusion coefficients of pure CO₂ and of H₂O in CO₂ over a wide range of temperatures (298.15 K < T < 523.15 K) and pressures (5.0 MPa < P < 100.0 MPa), that are of interest to CO₂ capture-and-sequestration processes. Various combinations of existing fixed-point-charge force-fields for H₂O (TIP4P/2005 and Exponential-6) and CO₂ (elementary physical model 2 [EPM2], transferable potentials for phase equilibria [TraPPE], and Exponential-6) were tested. All force-field combinations qualitatively reproduce the trends of the experimental data for infinitely diluted H₂O in CO₂; however, TIP4P/2005–EPM2, TIP4P/2005–TraPPE and Exponential-6–Exponential-6 were found to be the most consistent. Additionally, for H₂O compositions ranging from infinite dilution to $x_{{\mathrm{H}}_2\mathrm{O}}=0.36$, the Maxwell–Stefan diffusion coefficient is shown to have a weak non-linear composition dependence.

Keywords:

• diffusion coefficients
• CO₂
• H₂O
• force-fields
• molecular dynamics simulation

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Acknowledgements

This publication was made possible by NPRP [grant number 6-1157-2-471] form the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. We are grateful to the High Performance Computing Center of Texas A&M University at Qatar for generous resource allocation.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00268976.2015.1023224.

Additional information

Funding

NPRP [grant number 6-1157-2-471] form the Qatar National Research Fund (a member of Qatar Foundation).