Biomethane can be isolated from biogas through selective CO2 adsorption. Faujasite-type zeolites are promising adsorbents for CO2 separation due to their high CO2 adsorption capacity. While commonly inert binder materials are used to shape zeolite powders into the desired macroscopic format for application in an adsorption column, here we report the synthesis of Faujasite beads without the use of a binder and their application as CO2-adsorbents. Three types of binderless Faujasite beads (d = 0.4-0.8 mm) were synthesized using an anion-exchange resin hard template. All the prepared beads consisted mostly of small Faujasite crystals, as demonstrated by characterization with XRD and SEM, which are interconnected through a network of meso- and macropores (10-100 nm), yielding a hierarchically porous structure, as shown by N2 physisorption and SEM. The zeolitic beads showed high CO2 adsorption capacity (up to 4.3 mmol g-1 at 1 bar and 3.7 mmol g-1 at 0.4 bar) and CO2/CH4 selectivity (up to 19 at the partial pressures mimicking biogas, i.e., 0.4 bar CO2 and 0.6 bar CH4). Additionally, the synthesized beads have a stronger interaction with CO2 than the commercial zeolite powder (enthalpy of adsorption -45 kJ mol-1 compared to -37 kJ mol-1). Therefore, they are also suitable for CO2 adsorption from gas streams in which the CO2 concentration is relatively low, such as flue gas.
Keywords: CO2 adsorption; hierarchical porosity; zeolites.