Sorption equilibrium and kinetics of CO2 on clay minerals from subcritical to supercritical conditions: CO2 sequestration at nanoscale interfaces

• The sorption isotherm and rate of high pressure CO2 among clay minerals were studied.
• Structural change of clay minerals was observed after supercritical CO2 sorption.
• Excess sorbed amount of CO2 on clay mineral showed a maximum near critical pressure.
• The absolute sorbed amount changed negligibly after the critical density of CO2.

CO2 sequestration in geological formations has attracted attention as a promising method to reduce anthropogenic CO2 emission. CO2 sorption at nanoscale interfaces of clay minerals were studied from subcritical to supercritical conditions because clay minerals are a constituent of various rocks such as a cap rock, reservoir rock and coal mineral matter. The sorption capacity and kinetics of CO2 on montmorillonite, illite, and sepiolite were measured by a gravimetric method. Sepiolite had the highest sorption capacity at all experimental conditions. After high CO2 pressure sorption, the desorption isotherm on montmorillonite showed significant hysteresis, but the hysteresis on illite and sepiolite was relatively weak. The excess sorption isotherms of all clay minerals showed a maximum near the critical pressure and the absolute sorption isotherms approached the saturation over the critical density value of CO2. The surface area changes of clay minerals by supercritical CO2 sorption were observed by comparing the N2 sorption isotherms between the raw material and post-experiment sample. The CO2 sorption rates on clay minerals were within a single order of magnitude (10−8 m2/s). The results at nanoscale interfaces can contribute to understanding the sorption capacity and sealing integrity of sedimentary rocks in CO2 geological storage.

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