(617d) Adsorption Separation of Methane and Carbon Dioxide for the Production of Renewable Natural Gas Using Activated Carbons

Activated carbons are a widely used in industry for different applications due to their low cost and low energy requirements. This study investigated commercially available activated carbons and carbon aerogel for CO₂ removal from biogas using adsorption, for the production of renewable natural gas. Pure component isotherms for methane were determined gravimetrically for temperatures of 10 to 90°C for pressures up to 6.5 atm. We also investigated the effect of some characteristics of the adsorbents such as pore size, surface, % oxidation, and ash content on this separation. It was observed that % oxidation had little effect on CH₄ adsorption, while ash content had a negative effect on CH₄ adsorption with these adsorbents. In the high-pressure region, pore size and surface area dominated the adsorption, whereas in the low pressure region, the heterogeneous nature of the carbon materials dominated adsorption, which has previously been observed for CO₂ adsorption with similar materials. Using previously obtained pure component CO₂ isotherms by the same materials, the Ideal Adsorbed Solution Theory (IAST) was used to predict binary isotherms for a CH₄-CO₂ mixture, and the Expected Working Capacity values (EWC) were calculated for different pressure swing adsorption applications. The most practical adsorbent used in this study for CO₂ separation from biogas was found to be OLC carbon.