ADSORPTION OF TETRAFLUOROMETHANE AND NITROGEN BY VARIOUS ADSORBENTS

Abstract Adsorption of tetrafluoromethane (CF4) and nitrogen (N2) was studied by various adsorbents for the possible separation of these gases by an adsorption process. Adsorbent screening was carried out for 13 different adsorbents by determining Henry's law constants at different temperatures and determining the adsorption selectivity for the separation of these gases. Heat of adsorption values were also determined for these adsorbents. This was accomplished by using the concentration pulse chromatographic technique. The adsorbents studied included one activated alumna, three different activated carbons, zeolites A, X, Y, and ZSM-5 at different SiO2/Al2O3 ratios. Among them, three ZSM-5 zeolites and three activated carbon adsorbents were chosen for the determination of pure component isotherms at 23°C, since they showed the highest selectivity for CF4–N2 separation. Furthermore, activated carbon F-400, ZSM-5-30 (with a SiO2/Al2O3 ratio of 30), and ZSM-5-280 (with a SiO2/Al2O3 ratio of 280) were chosen to be studied further. Pure adsorption isotherms for CF4 and N2 were determined for different temperatures between 23 and 100°C for these three adsorbents up to 140 kPa pressure. Standard volumetric technique was used for the determination of the adsorption isotherms. Freundlich isotherm equation was used to model the pure isotherms for N2. Temperature dependent Toth isotherm model was used for the pure isotherms for CF4 and using the parameters of the Toth isotherm, isosteres were determined for this adsorbate at different adsorption capacities. It was concluded that ZSM-5-280 was the best adsorbent for the separation of CF4 from N2 since it had the largest capacity for CF4 and the lowest capacity for N2 within the pressure and temperature range looked at in this study. ACKNOWLEDGMENTS The authors acknowledge the financial support received from Natural Sciences and Engineering Research Council (NSERC) of Canada during the course of this study.