Competitive Adsorption Mechanism Study of CHClF2 and CHF3 in FAU Zeolite

Separating and recovering CHF3 and CHClF2 greenhouse gases from exhausted gases is quite important for avoiding adverse impacts to the environment. In synthesizing chlorofluorocarbons substitutes, faujasite (FAU) is proved to be effective in separating the hydrofluorocarbons. Grand canonical ensemble Monte Carlo simulations were used without precedent in analyzing the competitive adsorption mechanism of CHF3/CHClF2 in Na58Al58Si134O384 (58Al), Na88Al88Si104O384 (88Al), and Na96Al96Si96O384 (96Al) FAU zeolite model from infinite dilution to saturation adsorption, so as to explore the overall competitive relationship as the adsorption amount increases. As a result, it has been found that the sodium migration degree is affected by the guest–host effect in the 58A1 model. However, the sodium migration is not discovered in 88Al and 96Al models with diversified CHF3 or CHClF2 loadings. The preferred binding site in all FAU zeolite models involves CHClF2 and CHF3 anchored by cations in sites II and site III′. Adsorption enthalpy predicted is highly correlated upon the adsorption site and the geometry structure of CHClF2 and CHF3 in FAU zeolite. The CHF3 molecule is preferentially adsorbed via the short-range force of its hydrogen center with the lattice oxygens of the FAU supercage. In addition, the CHF3 selectivity would be enhanced to a certain degree with ratios of Si/Al and adsorption temperatures being lowered. Through this computational study, the inherent competitive adsorption mechanism at the molecular level is clearly illustrated, thus providing an effective strategy of designing and screening adsorptive materials, so as to have a better separation and recovery of CHF3–CHClF2.