Surface-Modified Activated Carbon with a Superior CH₄/CO₂ Adsorption Selectivity for the Biogas Upgrading Process
2022
Peredo-Mancilla, Deneb | Matei Ghimbeu, Camelia | Réty, Bénédicte | Hồ, Bích Ngọc | Pino, David | Vaulot, Cyril | Hort, Cécile | Bessières, D. (David)
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 CH₄/CO₂ 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-115ₒₓ and CNR-115ₐₘ, respectively) were characterized texturally and chemically, and their CH₄/CO₂ 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-115ₒₓ < 129.0 for CNR-115ₐₘ). 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 CH₄/CO₂ 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.
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