(633g) Time Dependent CO2 Sorption Hysteresis by Octahedral Molecular Sieves with Manganese Oxide Framework

Solvent-free technologies based on solid sorbents and membranes have been recognized as a potential solution for reducing operating costs of carbon capture technologies.[1]  In principle, solid sorbent and membrane materials can be tailored with specific physico-chemical characteristics to meet the CO₂ capture performance targets specific to a particular separation process.  However, systematic approaches for designing carbon capture materials with cost-effective capture efficiency, selectivity, adsorption/desorption cycle life, and scale-up potential require identification of the ‘active’ material structure and establishment of the CO₂ sorption or separation mechanism.  Promising CO₂ sorbent materials present an interesting challenge due to the dynamic nature of the material structure that may respond in a complex fashion to various stimuli[2] (e.g., temperature, pressure, and/or gas composition), making it difficult to establish the nature of the interaction between CO₂ and the sorbent structure 'in action'. 

To design new sorbent materials that meet such performance goals, we must have a detailed understanding of CO₂/sorbent interactions.[1]  In particular, an important feature in the development of novel CO₂ capture materials with engineered flexible architectures and pore sizes is the phenomenon of gas adsorption hysteresis, where the volume of gas molecules adsorbed by the porous host is larger on the desorption branch than on the adsorption.  High pressure hysteresis in gas sorption by rigid porous materials has been traditionally attributed to capillary condensation.[3]  Sorption hysteresis that persists down to very low pressures can be ascribed to a failure of the adsorptive system to reach equilibrium and is a reflection of specific dynamic that depend on temperature and maximum pressure achieved in the adsorption/desorption cycle.[4] 

We have evaluated the CO₂ sorption properties of octahedral molecular sieves with manganese oxide frameworks in which the nanopores (prior to contact with CO₂) appear to be of comparable size to the kinetic diameter of CO₂. We observe time dependant low pressure hysteretic CO₂ adsorption and desorption behavior at temperatures slightly below and above the supercritical temperature of CO₂.  Our results open up the possibility of hysteresis due to a combination of time dependent events involving physico-chemical interactions, structure dynamics, and kinetic CO₂ trapping, which may pave the way towards a comprehensive interpretation of hysteretic gas adsorption phenomena.

References

[1] R. Vaidhyanathan, S. S. Iremonger, G. K. H. Shimizu, P. G. Boyd, S. Alavi, T. K. Woo, Science, 330:650 (2010)

[2] C. Serre, S. Bourrelly, A. Vimont, N. A. Ramsahye, G. Maurin, P. L. Llewellyn, M. Daturi, Y. Filinchuk, O. Leynaud, P. Barnes, and G. Férey, Advanced Materials, 19:2246 (2007)

[3] Characterization of Porous Solids and Powders: Surface Area, Porosity and Density; S. Lowell, J. Shields, M.A. Thomas & M. Thommes, Springer, (2004)

[4] A. Bailey, D. A. Cadenhead, D. H. Davies, D. H. Everett and A. J. Miles, Transactions of the Faraday Society, 67:231 (1971)