Effects of fluorination on carbon molecular sieves for CH4/CO2 gas separation behavior

The surface of carbon molecular sieves (CMSs) was fluorinated to investigate the separation behavior of CH4/CO2. The fluorination of CMSs was carried out at various F2 partial pressures to determine the effect of the F2 content. Fluorine functional groups were effectively introduced on the surface of the CMSs, and the volume of pores in the CMSs was increased due to fluorination, especially those with a diameter less than 8 Å. As the fluorine partial pressure was increase, an increase in the CO2 adsorption capacity of CMSs was observed due to Lewis acid–base interactions between the functional groups of CMSs and CO2. Based on the selective CO2 adsorption results, the CO2 breakthrough with fluorinated CMS occurred at later stages of CH4/CO2 gas separation process compared to Raw-CMS. Therefore the presence of fluorine on the surfaces of CMSs affects the pore volumes of CMSs. According to the adsorption isotherms, the CO2 adsorption efficiency of CMSs was improved from 1.61 to 2.04 mmol/g at 298 K.

The effects of fluorination on interactions between functionalized surface molecules of CMSs and CO2 gas.Figure optionsDownload as PowerPoint slideHighlights
► Fluorinated CMSs were used to investigate the breakthrough behavior of CH4/CO2 separation.
► The pore width and number of fluorine functional groups on the surfaces of CMSs increased due to fluorination.
► The CO2 adsorption capacities of CMSs increased when fluorine functional groups were introduced via fluorination.
► A mechanism for the improvement in the CH4/CO2 separation behavior of fluorinated CMSs was suggested.