No abstract

The conversion of biogas to biomethane is an interesting alternative for clean energy production. Although biogas separation by physical adsorption using activated carbons has many advantages, the selectivity for CH 4 /CO 2 adsorption is fairly low. In this work, the surface chemistry of a commercial activated carbon (CNR-115) was modified by a two-step process: oxidative thermal treatment followed by ammonia modification. The activated carbons resulting from each modification step (CNR-115 ox and CNR-115 am , respectively) were characterized texturally and chemically, and their CH 4 /CO 2 equimolar mixture adsorption behaviors were measured. The results showed a significant loss of both surface area and porosity after the modification steps. However, the increased amount of polar surface functionalities leads to a remarkable increase of the selectivity factor (max. selectivity: 2.7 for CNR-115 < 23.4 for CNR-115 ox < 129.0 for CNR-115 am ). The reasons behind the significantly enhanced selectivity are discussed on the basis of the surface chemistries and textural properties of the materials, in relation with molecule characteristics. We demonstrate herein a very efficient surface modification strategy, which allowed to obtain activated carbon adsorbents with oxygen and nitrogen groups that favor a superior CH 4 /CO 2 separation capacity. Furthermore, the stability of the added surface groups and the adsorption behavior was tested, proving the maintenance of the chemical characteristics and the adsorption performance after 10 adsorption/ desorption cycles.