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 CO2 from biogas streams: There is' abundant work regarding the equilibrium of adsorption of pure CH4 and CO2 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-CO2 and CS-H2O), previously prepared in our laboratory to separate CO2/CH4 has been evaluated. Full adsorption-desorption-cycles were: conducted at 30 degrees C (isothermal conditions) and different pressures (1, 3, 5, and 10 bar) feeding binary CO2/CH4 (50/50 vol %) mixtures to a purpose-built fixed-bed setup. A commercial activated carbon; Calgon BPL, was also evaluated for reference purposes. CO2 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-CO2, CS-H2O, and Calgon BPL, respectively). However, the CO2/CH4 separation efficiency, according to the difference in breakthrough times between CH4 and CO2 is very limited at 10 bar. A combined analysis of the productivity and purity of CH4 along with CO2 working capacity-derived from dynamic experiments indicates that our biomass-based activated carbons would be better candidate materials for the CO2/CH4 separation at a pressure of 5 bar than the commercial activated carbon Calgon BPL.