A comparative study of several microporous materials to store methane by adsorption

Abstract

Methane adsorption was studied in microporous materials with differences in their pore geometry and surface chemistry in order to evaluate the characteristics that enhance methane storage in porous materials. The studied materials included metal-organic frameworks (Cu-BTC, MIL-53 and ZIF-8), zeolites (5A and 13X) and an activated carbon (Maxsorb). Textural properties such as pore volume and specific surface area were studied by nitrogen adsorption-desorption isotherms. Methane adsorption was analyzed by means of measurements at low and high pressures (0-5000 kPa) at various temperatures (278-323 K). The effect of the adsorbate-adsorbent interaction was evaluated by the determination of the Henry constant using the adsorption data of methane at low pressures and 298 K. In addition, the isosteric enthalpy of adsorption using data of adsorption at several temperatures was obtained. A linear trend was observed between the Henry constant, the enthalpy of adsorption and the pore size, indicating that the latter is the most influential factor in the interaction of a microporous adsorbent and methane at room temperature. Also, it was found that the textural properties (i.e. specific surface and micropore volume) are directly related with the methane storage capacity at 298 K and 3.5 MPa. However, we obtained a deviation of this behavior for ZIF-8 that is related to its geometry and pore size.