Adsorption of fluorinated greenhouse gases on activated carbons: evaluation of their potential for gas separation

Background The increasing awareness of the release of fluorinated gases (F-gases) into the atmosphere is instigating the development of techniques to capture them from refrigerants. In this work, the adsorption of difluoromethane (R-32), pentafluoroethane (R-125), and 1,1,1,2-tetrafluoroethane (R-134a) on four different activated carbons (ACs) is studied. Additionally, the selectivity of the ACs for the components of commercial refrigerants, R-410A and R-407F, is evaluated. Results The estimation of the density of the adsorbed phase as a function of temperature allows the experimental fractional loading of each F-gas on any of the ACs to be correlated as a temperature-independent function of its reduced pressure, which is described by Toth or dual-site Langmuir equations or as an exponential function of the adsorption potential under the framework of the Adsorption Potential theory (APT). It is shown that the APT can be generalized with excellent accuracy to the systems studied if an adsorbate-dependent affinity coefficient is used as a shifting factor to bring the characteristic curves of all F-gases into a single one for each AC. R-32 is the F-gas most adsorbed by all adsorbents, followed by R-134a, and by R-125. All ACs are selective for R-125 in R-410A commercial refrigerants, especially at lower pressures. Additionally, all ACs are selective for R-125 and R-134a over R-32 in R407-F commercial refrigerant. Conclusion The utilization of ACs for adsorption of the three most used F-gases is promising. By selecting ACs with different porous characteristics, it is possible to evaluate their influence on the selectivity for the components of different commercial refrigerants. (c) 2020 Society of Chemical Industry