Assessment of sepiolite as a carbon dioxide storage material

Abstract

Due to the dynamics of Earth’s natural carbon cycle, levels of carbon dioxide in the atmosphere have varied over geologic time. An analysis of the geologic record indicates that warm periods in Earth’s history are correlated with relatively high levels carbon dioxide in the atmosphere. Since the onset of the industrial revolution the natural rate of carbon dioxide accumulation in the atmosphere has been augmented by human activity. Several approaches have been proposed to offset the anthropogenic contribution to the rise in atmospheric carbon dioxide, including underground and ocean sequestration, and storage in synthetic porous materials such as zeolites and metal-organic-frameworks (MOFs). In this work we assess the possibility of utilizing natural porous materials for the storage of carbon dioxide; namely, the clay mineral sepiolite whose structure prominently features water filled pores. Molecular dynamics simulations are used to determine whether a thermodynamic driving force exists for replacing the water in these channels with carbon dioxide. Our results indicate that along the carbon dioxide liquid-vapor curve as much as 10% of the water in sepiolite may be replaced by carbon dioxide. We show that the incorporation of carbon dioxide into the mineral structure is primarily driven by favorable entropic terms at these concentrations. Based on this result we estimate that it may be possible to sequester up to 0.986 mmol of carbon dioxide per gram of sepiolite, which is approximately twice the experimental value reported for montmorillonite clay under similar conditions.