Strong and binder free structured zeolite sorbents with very high CO2-over-N2 selectivities and high capacities to adsorb CO2 rapidly

Abstract

Mechanically strong monoliths of zeolite NaKA with a hierarchy of pores displayed very high CO₂-over-N₂ selectivity. The zeolite monoliths were produced by pulsed current processing (PCP) without the use of added binders and with a preserved microporous crystal structure. Adsorption isotherms of CO₂ and N₂ were determined and used to predict the co-adsorption of CO₂ and N₂ using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic adsorbents of NaKA could reach an extraordinarily high CO₂-over-N₂ selectivity in a binary mixture with a composition similar to flue gas (15 mol% CO₂ and 85 mol% N₂ at 25 °C and 101 kPa). Structured NaKA monoliths with a K⁺ content of 9.9 at% combined a CO₂-over-N₂ selectivity of >1100 with a high CO₂ adsorption capacity (4 mmol g⁻¹) and a fast adsorption kinetics (on the order of one minute). Estimates of a figure of merit (F) based on IAST CO₂-over-N₂ selectivity, and time-dependent CO₂ uptake capacity, suggest that PCP-produced structured NaKA with a K⁺ content of 9.9 at% offers a performance far superior to 13X adsorbents, in particular at short cycle times.