Carbon materials porosity analysis using DFT models for potential application in the recovery of methane from its low-concentration mixtures

Abstract

One of the key factors in the adsorption-based processes such as Pressure Swing Adsorption is the proper selection of the adsorbent material. The primary motivation of this work is the thorough analysis of the porous structure of selected carbon materials for this process. Considering that the pore size distribution (PSD) determines the specific part of the adsorbent structure that is accessible to probe molecules of N2 and CO2 used for the analysis, we discuss the optimal pore size for the adsorption of CH4 at 293 K having molecular diameter is larger than N2 and CO2. To perform a detailed textural characterization of our carbon samples using the N2 and CO2 adsorption isotherms, we apply the 2D-NLDFT and QSDFT/NLDFT models available in the SAIEUS and ASiQwin software packages, respectively. To discuss the relationship between the PSD and the CH4 adsorption of our samples, we chose to use PSDs derived by the dual gas N2 & CO2 analysis method (SAIEUS software). We show that it is possible to estimate the experimental CH4 adsorption isotherms at 293 K based on the porous texture characteristics derived from N2 at 77 K and CO2 at 273 K and the application of appropriate 2D-NLDFT models. Furthermore, we demonstrate that the described carbon PSD characterization and the following prediction methods constitute valuable links between the textural properties and CH4 adsorption isotherms of the carbon materials. We believe that the results of this work will be a practical guide for future research on the selection of adsorbents for the separation of mixtures containing low concentrations of methane.