(725f) Comparison of Narrow Pore Silicate and Phosphates Based CO2 Sorbents: The Good and The Bad

Effective carbon capture from flue gas requires sorbents with desirable properties, these properties include: high CO₂ capacity, high CO₂ selectivity over N₂, fast adsorption kinetics, and many others. Inorganic crystalline sorbents with narrow pore window apertures have significant advantages; the uptake of CO₂ on these materials is comparably very high at the partial pressures of CO₂ in flue gas, and that they potentially can be tuned into CO₂-selective molecular sieves. Hence, we study such sorbents and here we compared properties of the silicate and phosphate based sorbents we studied.  The sorbents include Zeolite LTA (and ZK-4), silico- and aluminophosphates (SAPOs and AlPOs) and titanium silicates (ETS-4 and CTS-1). We showed that zeolite NaKA (17% K⁺) and NaK-ZK-4 (25% K⁺) were both highly selective (with ideal CO₂-N₂ selectivity > 200). Silicoaluminosphoshpates (SAPO) had very high CO₂ capacity (SAPO-56 - 5.6 mmol/g, 273K, 101kPa) and retained over 95% of the original CO₂ capacity after cycling. Aluminophosphates (AlPO) and titanium silicates (CTS-1) were selective towards CO₂ sorption and offered reasonable CO₂ capacity. AlPOs also showed good cyclic capacity. AlPOs and Zeolite ZK-4 (with high Si/Al ratio) were relatively hydrophobic, which could be important for CO₂ capture from non-dried flue gas. In this work we rationalized and highlighted the advantages and the drawback of each of these narrow pore sorbents. This could be important for the research and development of good CO₂ sorbents.