Comparative study of the CH4/CO2 adsorption selectivity of activated carbons for biogas upgrading

This works provides a new insight on the adsorption of CH4/CO2 and its components on carbonaceous materials. The equimolar mixture adsorption isothemrs were obtained for 5 well characterized activated carbons at a temperature of 303 K on the pressure range of 0-3 MPa. A higher BET surface area in addition to a narrow pore size distribution centered at a pore size of 0.8 nm resulted in higher CH4/CO2 total adsorption capacity. Furthermore, whilst the presence of basic functionalities on the surface of the adsorbents enhanced the adsorption of carbon dioxide, the adsorption selectivity was influenced by both textural and chemical properties of the samples. The selectivity was determined to be higher for carbon ROx 0.8 (selectivity factor of up to 4.7), a microporous steam activated carbon with a mild surface area (1323 m(2) g(-1)), narrow pore size distribution with an average pore size of 0.84 nm. Higher BET surface areas and average pore sizes resulted in a detriment of the selectivity. In addition, the presence of sulfur surface groups increased resulted in a rise of the selectivity factor.