An adsorption study on STA-16(Co)

• STA-16(Co) shows poor CO2 adsorption, but exceptionally high H2O uptake.
• The hydrothermal stability of STA-16(Co) appears good up to at least 60% RH.
• Decrease in CO2 uptake after H2O sorption at 90% RH is due to change in crystal structure.

Adsorption is considered a promising method for carbon capture. CO2 adsorbents take a variety of forms, but one approach is the use of metal-organic frameworks (MOFs). In this study, the potential of STA-16(Co) to selectively adsorb and separate CO2 is considered. Isotherms for CO2 and N2 were measured from 0 to 25 bar at temperatures between 25 and 105 °C to evaluate the potential application in high pressure separation processes. Low pressure CO2 pseudo-isotherms were measured from 0 to 0.5 bar at temperatures between 25 and 105 °C, together with dry and wet cycling experiments, to determine the applicability of STA-16(Co) in a vacuum swing adsorption (VSA) process. The presence of 1% H2O vapour during ten cycle experiments resulted in a decrease in CO2 working capacity obtained under dry cyclic conditions of ∼66% due to the high H2O uptake. In contrast to the majority of MOFs, STA-16(Co) exhibited a good H2O stability and maintained its CO2 adsorption capacity after adsorption/desorption of H2O vapour at 30 and 60% RH at 25 °C. However the treatment at 90% RH resulted in a small decrease in CO2 adsorption capacity, apparently due to the formation of a different crystal structure.

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