(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

Authors: 
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.