Methane adsorbed in slit pores - low temperature mechanism of adsorption and phase diagram
Résumé
Properties of methane adsorbed in confined geometries are interesting from both fundamental and practical points of view. At ambient temperatures adsorption at the supercritical conditions is usually studied, as it is interesting from the point of view of methane storage. At the same time, the analysis of low temperature adsorption properties is essential for understanding the mechanism of adsorption, as a function of temperature and the pore size. In this work we study phase diagram of methane confined in carbon slit pores of the width between 1nm and 4nm. We analyze the mechanism of the layering transition(s) and capillary condensation at subcritical conditions, for temperatures between 80 K and 180 K, () then we study the capacity of storage up to the room temperature. The mechanism of the layers formation is strongly temperature dependent, and changes from a sharp adsorption at low temperature to more continuous one at higher temperatures. The size of pore defines the number of layers adsorbed: 1 nm pore allows adsorbing 2 layers of methane molecules. Capillary condensation is observed in 4 nm pores.