Evaluation of the Performance of an Activated Carbon’s Family for Biogas Upgrading Using the Adsorption Performance Indicator

The ideal selection of adsorbents for a wide range of binary gas separations remains a critical challenge, but the combining of the primary key adsorption parameters, including adsorption capacity, selectivity, and heat of adsorption using the adsorption performance indicator (API), facilitates this selection. The study applies the API to choose the selective adsorbent for separating CO2 from an equimolar CO2/CH4 mixture, representing a biogas stream. Three activated carbons (ACs) of the CNR family (CNR-115, CNR-115-ox, and CNR-115-ox-am) are discussed, highlighting their ability to selectively adsorb the carbon dioxide molecules while preserving the valuable methane component. Also, the heat of adsorption of CO2 indicated that the three ACs are regenerative as they are in the range of physisorption. The addition of chemical groups on the surface of the ACs plays an essential role in varying the adsorption parameters. Although the three ACs belong to the same family, it was shown that the addition of the different chemical surfaces and varying the pressure changes the choice of the ideal adsorbent; CNR-115-ox showed a better overall performance than the others under the low-pressure region (< 1.5 MPa) due to the presence of oxygen groups, but CNR-115-ox-am is the preferred one for the separation of CO2 from CO2/CH4 mixtures under the high-pressure region due to the presence of nitrogen groups.