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 °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.