Binderless Faujasite Beads with Hierarchical Porosity for Selective CO 2 Adsorption for Biogas Upgrading.

Biomethane can be isolated from biogas through selective CO 2 adsorption. Faujasite-type zeolites are promising adsorbents for CO 2 separation due to their high CO 2 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 CO 2 -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 N 2 physisorption and SEM. The zeolitic beads showed high CO 2 adsorption capacity (up to 4.3 mmol g -1 at 1 bar and 3.7 mmol g -1 at 0.4 bar) and CO 2 /CH 4 selectivity (up to 19 at the partial pressures mimicking biogas, i.e., 0.4 bar CO 2 and 0.6 bar CH 4 ). Additionally, the synthesized beads have a stronger interaction with CO 2 than the commercial zeolite powder (enthalpy of adsorption -45 kJ mol -1 compared to -37 kJ mol -1 ). Therefore, they are also suitable for CO 2 adsorption from gas streams in which the CO 2 concentration is relatively low, such as flue gas.