Measuring and modelling supercritical adsorption of CO2 and CH4 on montmorillonite source clay

J. Hwang, L. Joss, R. Pini

    Research output: Contribution to journalArticlepeer-review

    Abstract

    The porosity of clay minerals is dominated by nanoscale pores that provide a large surface area for physical and chemical interactions with the surrounding fluids, including gas adsorption. Measuring gas adsorption at subsurface conditions is difficult, because elevated pressures are required and the interactions between the supercritical gas and the clay are relatively weak. Here, we report on the measurement of adsorption isotherms of CO2 and CH4 on the source clay Na-montmorillonite (SWy-2) at different temperatures (25–115°C) over a wide range of pressures (0.02–25 MPa). The experimental observations are thoroughly analysed by considering both net and excess adsorbed amounts, and by extracting adsorption metrics, such as the Henry's constants and enthalpy of adsorption. The results consistently indicate that SWy-2 favours adsorption of CO2 over CH4 with selectivity, S≈5.5. The experimental data are successfully described using a Lattice Density Functional Theory (LDFT) model. The adsorption energetics estimated by the model compare well with the experimentally obtained enthalpy of adsorption. It is further shown that even at the highest pressure the pore space of the clay is only partially filled and that the degree of saturation increases upon approaching the critical temperature of the gas. The ability of the LDFT model to reveal pore-dependent adsorption behaviours demonstrates its potential against empirical models, such as the Langmuir equation, which fail at capturing the complexities of supercritical gas adsorption at subsurface conditions.

    Original languageEnglish
    Pages (from-to)107-121
    Number of pages15
    JournalMicroporous and Mesoporous Materials
    Volume273
    Early online date2 Jul 2018
    DOIs
    Publication statusPublished - 1 Jan 2019

    Keywords

    • Clay minerals
    • CO Sequestration
    • Gas adsorption
    • Porous materials
    • Shale gas

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