CO₂ As an Adsorptive To Characterize Carbon Molecular Sieves and Activated Carbons

Abstract

Adsorption of CO 2 at 273 K up to 4 MPa has been studied in activated carbons and carbon molecular sieves of different origins and pore size distribution. The materials selected for this study include carbon molecular sieves with a pore size (i.e., pore width) between 0.3 and 0.5 nm, activated carbons with supermicroporosity (pore size between 0.7 and 2 nm), and mesoporous and macroporous activated carbons. The relative fugacities covered in the experiments ranges from 10 - 4 to nearly 1. Additionally, N 2 adsorption at 77 K at subatmospheric pressures has been also done. The experimental conditions used allow us to compare both measurements at similar adsorption potentials, in which both gases adsorb in the different ranges of porosity. The results obtained show that CO 2 adsorbs at 273 K in the different ranges of porosity following a mechanism similar to that of N 2 at 77 K. CO 2 is sensitive to narrow micropores not accessible to N 2 at 77 K, and hence, it is an adequate complement to N 2 at 77 K. This is especially important for the characterization of the narrow micropores of carbonaceous solids and, especially, carbon molecular sieves. CO 2 adsorbs in mesopores according to the capillary condensation mechanism.