Adsorption of natural gas and biogas components on activated carbon

Experimental results are presented for the adsorption equilibria of methane, ethane, propane, butane, carbon dioxide, and nitrogen, as well as natural gas odorants tert-butyl mercaptan and tetrahydrothiophene, on an activated carbon with the desirable characteristics for use in a guard bed for adsorbed natural gas storage, but that can also be applied for separation of biogas components, such as carbon dioxide and nitrogen. The adsorption experiments were performed using both open- and closed-loop gravimetry over the pressure and temperature ranges of 0–9 MPa and 273–325 K, respectively. The two odorants were analyzed at the very low concentrations usually found in natural gas (0–25 mg/(N m³)). The experimental data were successfully correlated by the adsorption potential theory and collapsed into a single temperature-independent characteristic curve. This analysis allows for extrapolation of the adsorption data to higher alkanes, for which no experimental data are available, in order to span the global composition of a typical natural gas stream. The adsorption equilibrium data for methane, carbon dioxide and nitrogen were fitted to the Toth and Sips isotherm models and their isosteric heats of adsorption were determined. The preferential adsorption capacity for carbon dioxide indicates that the carbon can be used for methane purification from natural gas, carbon dioxide sequestration from flue gas, or biogas purification.