Dynamic Performance of Biomass-Based Carbons for CO₂/CH₄ Separation. Approximation to a Pressure Swing Adsorption Process for Biogas Upgrading

Physical adsorption-based processes such as pressure swing adsorption (PSA) constitute an alternative to selectively adsorb CO 2 from biogas streams. There is abundant work regarding the equilibrium of adsorption of pure CH 4 and CO 2 on different adsorbents. However, to design an adsorption process with a selected adsorbent it is very important to account for its dynamic behavior in a packed-bed. Thus, the performance of two biomass-based activated carbons (CS-CO 2 and CS-H 2 O) previously prepared in our laboratory to separate CO 2 /CH 4 has been evaluated. Full adsorption–desorption cycles were conducted at 30 °C (isothermal conditions) and different pressures (1, 3, 5, and 10 bar) feeding binary CO 2 /CH 4 (50/50 vol %) mixtures to a purpose-built fixed-bed setup. A commercial activated carbon, Calgon BPL, was also evaluated for reference purposes. CO 2 equilibrium uptakes were obtained from dynamic breakthrough curves and proved to be maximum at 10 bar (5.14, 4.48, and 4.14 mol kg –1 for CS-CO 2, CS-H 2 O, and Calgon BPL, respectively). However, the CO 2 /CH 4 separation efficiency, according to the difference in breakthrough times between CH 4 and CO 2, is very limited at 10 bar. A combined analysis of the productivity and purity of CH 4 along with CO 2 working capacity derived from dynamic experiments indicates that our biomass-based activated carbons would be better candidate materials for the CO 2 /CH 4 separation at a pressure of 5 bar than the commercial activated carbon Calgon BPL.