Advanced pore characterization and adsorption of light gases over aerogel-derived activated carbon

Abstract

Abstract Activated carbon produced by etching with CO2 is an attractive adsorbent material because of its ultrahigh surface area above 1000 m2/g and substantial pore volume. This being stated, because etched carbon was only reported recently, many of its properties, such as its textural properties, high-pressure adsorption capacities towards CO2, N2, H2, CO, and CH4, and dynamic performance, have never been thoroughly investigated. Accordingly, this study explored these characteristics for the first time. The textural and adsorptive properties were also assessed for zeolite 5A, a metal-organic framework (Ni MOF-74), and activated carbon provided by Ingevity corporation to allow for comparison to established benchmarks. The textural properties were assessed by a combination of N2 physisorption at 77 K and CO2 adsorption at 273 K using a combination of t-plot, Dubinin–Radushkevich, 2D-NLDFT, and Horvath–Kawazoe models. Therein, it was determined that the etched carbon had a hierarchical porosity, with pores appearing in both the ultramicro- and meso-porous ranges. From the adsorption isotherms at 298 K and 0–20 bar, the etched carbon exhibited adsorption capacities of 20, 9, 5, 4.5, and 1 mmol g−1 for CO2, CH4, CO, N2, and H2 respectively, indicating that the samples high (i.e., 95%) pore volume made it selective towards multiple species at high pressure. Having said this, when the material was examined for dynamic CO2 adsorption from N2, H2, and CH4 mixtures at 25 °C and 1 bar, it achieved CO2/CH4, CO2/H2, and CO2/N2 selectivities of 2.4, 15.4, and 6.6 mol/mol, respectively, meaning that it can be used for kinetic separations. The high dynamic selectivity was retained for CO2/H2 at 20 bar, however, the CO2/CH4 breakthrough fronts were much broader compared to the low-pressure experiments, meaning that the two species' diffusivities were competitive. As such, EC-RF was concluded to be effective for low-pressure CO2 separations as well as for high pressure CO2/H2 separations. More importantly, this study provides an in-depth characterization and better understanding of EC-RF's properties, which is imperative to its use as an adsorbent material.