Cs-RHO Goes from Worst to Best as Water Enhances Equilibrium CO2 Adsorption via Phase Change

Privileged zeolitic sites for humid CO2 adsorption: K+ in double eight-membered rings

Humid CO2 adsorption in K+-exchanged zeolites featuring double-eight membered ring (D8R) structures results in CO2 outcompeting and desorbing dimeric water under equilibrated conditions, which is not observed for either the H+-form of the same zeolites or larger-pore zeolites.

CO2 Desorbs Water from K-MER Zeolite under Equilibrium Control

Competitive adsorption by water in zeolites is so strongly prevalent that established gravimetric techniques for quantification have assumed that humid CO2 has no effect on preadsorbed water at the same relative humidity. Here, we demonstrate sites in small-pore zeolite K-MER, in which CO2 adsorption causes 20% of preabsorbed water to desorb under equilibrium control at 30 °C and 5% relative humidity. Diffuse reflectance IR spectroscopic data demonstrate that dimeric water species that are coordinated to cationic sites in K-MER zeolite are selectively displaced by CO2 under these humid conditions. Though Cs-RHO contains more weakly bound water than K-MER, we observe a lack of dimeric water species and no evidence of CO2 outcompeting water in Cs-RHO. We conclude that the desorption of water by CO2 in K-MER is driven by a highly desired site for CO2 adsorption as opposed to an intrinsically weak binding of water to the zeolite. Our demonstration that CO2 can outcompete water in a zeolite under wet conditions introduces new opportunities for the design of selective sites for humid CO2 adsorption and stresses the importance of independently characterizing adsorbed water and CO2 in these systems.

Preparation of a Fiber-Like 3D-Structured Adsorbent for CO2 Capture

Solid amine adsorbents are promising materials to mitigate global warming. In this study, a commercially available melamine-formaldehyde sponge was adopted as a support to prepare a kind of solid amine adsorbent using polyethylenimine as a functional component and ethylene glycol diglycidyl ether as a cross-linker. The adsorbent, with abundant tunnels and a high amine loading amount, had a high adsorption capacity. When the amine loading was 89.6 wt%, the as-prepared adsorbent showed a high adsorption capacity of 7.29 mmol/g at 20 °C in the presence of water. The spent adsorbent could be easily regenerated by heating it at 90 °C, resulting in lower energy consumption. It has been proved by the Avrami model that physical and chemical adsorption coexist in the adsorption of CO₂ on this adsorbent. Simulation with the intraparticle diffusion model has revealed that the rate-controlling step in the adsorption process was the gas film diffusion period when the adsorption temperature was below 30 °C, while it was the adsorption equilibrium period when the adsorption temperature was above 30 °C.

Carbon dioxide capture with zeotype materials

This review describes the application of zeotype materials for the capture of CO2 in different scenarios, the critical parameters defining the adsorption performances, and the challenges of zeolitic adsorbents for CO2 capture.