The influence of C-F- and C-H-bonds on the adsorption of propane and perfluoropropane on FAU-type zeolites

This study aims to investigate the influence of carbon-fluorine- and carbon-hydrogen-bonds on adsorption. Therefore, we performed comparative experiments with perfluoropropane (C 3 F 8 ) and propane (C 3 H 8 ) on FAU-type zeolites (NaX and CaNaX) over a temperature range of −20 to 25 °C. Breakthrough curves measured by FTIR are used to obtain both pure component and mixture isotherms. Additionally, mixture isotherms were predicted using the Ideal Adsorbed Solution Theory (IAST). While in pure component adsorption at low relative pressure on NaX the loading of C 3 F 8 achieves higher values than the loading of C 3 H 8 the loadings of C 3 F 8 and C 3 H 8 on CaNaX are similar. Obviously, propane benefits from ion exchange (from sodium to calcium) which increases propane interactions while perfluoropropane interaction are not significantly affected due to its bulkier structure. Due to its larger molecular dimensions C 3 F 8 has lower saturation capacities. Electrostatic and steric effects are combined in mixed adsorption. Mixture data show that C 3 H 8 displaces C 3 F 8 more strongly, especially on zeolite NaX, as the degree of coverage increases and the temperature decreases. IAST predictions qualitatively reflect the experimental data but partly show significant deviations. These can be attributed to inaccuracies in fitting pure component isotherms and to non-idealities. The largest deviations between IAST predictions and experimental data occur at low relative pressure of the respective component, likely due to the lack of experimental data in particular in the low-pressure region, the limited representation of molecular size effects, interaction-specific effects and the lack of consideration for the energetic heterogeneity of the adsorption sites. The results of this study provide mechanistic insights into the role of C-F and C-H functionalities in influencing selectivity and capacity in competitive adsorption and support the development of selective separation processes for fluorinated hydrocarbons. • Systematic study on competitive adsorption of C 3 H 8 and C 3 F 8 on FAU-type zeolites. • Enthalpy of Adsorption of C 3 H 8 shows different pattern on NaX and CaNaX. • Steric limitations reduce saturation capacity of C 3 F 8 compared to C 3 H 8 . • C 3 H 8 displaces C 3 F 8 on NaX with increasing concentration, while CaNaX favors C 3 F 8 . • IAST delivers a qualitative prediction despite different size and electron distribution of C 3 H 8 and C 3 F 8 .