InterPore2023

Effect of Water on the Methane Adsorption on the Na-Montmorillonite Surface: Molecular Dynamics Study

24 May 2023, 16:10

1h 30m

Poster Presentation (MS06-B) Interfacial phenomena across scales Poster

Speaker

Dr Vasily Pisarev (HSE University)

Description

The study of methane adsorption on the surface and in the interlayer space of clay minerals is of great importance for the exploration and production of natural gas and shale hydrocarbons. Substantial part of the shale gas exists in the adsorbed state, so understanding the adsorption capacity as well as mechanisms of adsorption is important to properly estimate the amount of shale gas and to develop recovery strategies. Humidity is one of the key factors influencing gas adsorption. The goal of this work is to study the effect of the water coverage of a weakly charged clay mineral in slit-like pore on methane adsorption by the molecular dynamics method. An atomistic model of montmorillonite with the structural formula Na${}_{0.75}$(Al${}_{3.75}$Mg${}_{0.25}$)(Si${}_{7.75}$Al${}_{0.25}$)O${}_{20}$(OH)${}_4\cdot$2.5H${}_2$O was used as a surface model. The interaction between the clay mineral, metal ions, and water molecules was described by the ClayFF force field. The methane molecules were described by Trappe-UA and OPLS-AA models. It was shown that the choice of the force field has little effect on the results. At STP conditions methane molecules adsorb at the centers of free siloxane rings on the surface and water molecules do not affect the adsorption mechanism.

As higher pressures (>6 MPa), two peaks are observed in the methane density profile, indicating the presence of two methane adsorption layers near the pore walls. The first adsorption layer is always ordered and contains methane even with high amount of H${}_2$O molecules. The structure of the second adsorption layer depends on the pressure and amount of water.

Presentation materials

poster_interpore2023.pdf