Adsorption of carbon dioxide, methane, and their mixture by montmorillonite in the presence of water

• Molecular simulation study of adsorption of CO2, CH4, and their mixture in montmorillonite clays in the presence of water.
• Favorability of adsorption of CO2 by montmorillonite at low pressures, large basal spacings, and intermediate water contents.
• The ideal adsorbed solution theory agrees well with the observed adsorption capacities and selectivities of CO2/CH4 mixture.
• Atomistic model gives reasonable agreement with single-component experimental adsorption isotherms for CH4 and CO2 molecules.

Using grand canonical Monte Carlo (GCMC) simulations, we study the adsorption behavior of CH4, CO2, and their mixture at 298.15 K and pressures up to 50 bar in Na-, Cs-, and Ca-montmorillonite clays in the presence of water. Montmorillonite clays in the presence of preadsorbed water, preferentially adsorb CO2 over CH4 during both pure component and mixture adsorption. The atomistic model we have used, gives good agreement with available single-component experimental adsorption isotherms, for CH4 and CO2 molecules adsorbed onto montmorillonite clays in the presence of water. We observe the general trend that the presence of increasing preadsorbed water content in the clay interlayers, reduced adsorption amounts of pure CH4 and CO2 molecules. With a relatively large basal spacing (d = 30 Å), the favorability of adsorption of CO2 by montmorillonite at relatively low pressures and intermediate water contents has been demonstrated using simulations. GCMC simulation is also used to assess the effect of water on the adsorption of N2/CH4, H2S/CH4, CO2/N2, and CO2/H2S binary mixtures in Na-montmorillonite clay. The ideal adsorbed solution theory is shown to agree well with the observed adsorption capacities and selectivities of mixtures in Na-montmorillonite clay.

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