Molecular sieve carbons for CO2 capture

Abstract

With the current interest in controlling greenhouse gases, there is a new focus on materials that can discriminate between gas molecules by capturing those gases which must be curtailed and releasing those which pose no adverse effects to the atmosphere. Although zeolites can be applied to such tasks, molecular sieve (MS) carbons have an additional advantage in their ability to both adsorb and desorb molecules cyclically with comparatively little energy demand.This paper describes studies of commercial ATMI carbons obtained from polyvinylidene chloride pyrolysis that have experienced different levels of activation and additives to modify the sizes of pore ‘portals’ (i.e., those pores which orchestrate movement of molecules from the gas phase into the inner structure of the carbon). The structures are probed using molecules in the 0.3–0.68nm size range. One significant feature of these materials is that total pore volume for smaller molecules is maintained during the ‘tailoring’ of the portal pore size. These carbons have additional benefits such as high strength and high density, becoming ideal candidates for capturing CO2. Data for select carbons indicate capacities at ambient conditions for CO2 of >140v/v (∼20wt.%) and, in simulated power plant exhaust, Henry’s Law Separation Factors >6. Through collaboration with SRI International, ATMI has developed carbons that exhibit >97% capture of CO2 in such streams with subsequent desorption of 98% purity CO2 in the stripper section of a pilot-scale unit. In this application, these carbons outperform the claims made for MOFs and other similar materials.