(688a) Predicting the Solubility and Diffusivity of Gases (CO2, CH4, H2, Noble Gases) in Nano-Confined Interlayer Water and Bulk Water Using Molecular Dynamics Simulations

Gadikota, G., University of Wisconsin
Bourg, I., Princeton University
The chemistry of water films with dissolved gases confined between clay mineral surfaces has applications for a number of areas in energy and environment. For example, gas adsorption in solid-water interfaces impacts the formation of CH4 hydrates in fine-grained sediments, the behavior of CH4 in shale, CO2 leakage across caprocks of geologic CO2 sequestration sites, H2 leakage across engineered clay barriers of high-level radioactive waste repositories, and the use of noble gases as tracers for subsurface hydrocarbon migration. Here, we present molecular dynamics (MD) simulations of the solubility and diffusivity of a range of gases (CH4, CO2, H2, noble gases) in bulk water and in nano-confined interlayer water in clays. Our results indicate that the affinity of dissolved gases for clay mineral surfaces has a non-monotone dependence on the hydrated radius of the gas molecules. This non-monotone dependence arises from a combination of two effects: the enthalpic affinity of the gas solutes for the surrounding species and the entropic penalty of hydrophobic solvation.