Theoretical and experimental analysis of methane adsorption on activated carbon

The isosteric heat and the adsorption model of methane on activated carbon were determined for the further study on the adsorbed natural gas (ANG) storage system. Activated carbon Ajax was selected as an adsorbent, six adsorption isotherms of high purity methane were measured at temperature from 268 K to 338 K and pressure up to 12.8 MPa. Isosteric heats of adsorption at nine excess adsorption amounts and those at zero surface coverage were respectively plotted by adsorption isosteres and the temperature dependent of Henry law's constants. Ono-Kondo model was parameterized by adsorption data to predict the excess adsorption amount. Results show that the parameterized model can predict the isotherms with a relative error smaller than 2.5 %, and the isosteric heat of adsorption is about 17.25kJ·mol-1 ～21.5kJ·mol-1 with a mean valueat zero surface coverage. Results also reveal that adsorption isosteres of adsorption data at different temperature regions bring about a different isosteric heat of adsorption due to the variation in contributions from thermal motion of adsorbate molecules. Conclusions are drawn that adsorption isosteres on the adsorption data in correspondence with the lowest and highest temperatures of the ANG system during the typical charge or discharge process should be carried out to determine the isosteric heat of adsorption for effectively managing the thermal effect.