Characterization of size-selective kinetic-based Ba-ETS-4 titanosilicate for nitrogen/methane separation: Chlorine-enhanced steric effects

Barium exchanged ETS-4 is the promising size-selective and thermally stable adsorbent in nitrogen separation from methane. The halogen contained Ba-ETS-4, named Ba-RPZ, by upgrading the steric effect has superior performance in this separation process. In this work, the Na-ETS-4 was synthesized in two ways, chlorine halogen contained and halogen free medium, and the synthesized adsorbents (i.e., RPZ and HFZ, respectively) were ion exchanged with Ba²⁺. Equilibria and kinetic adsorption properties of nitrogen and methane were investigated on two types of Ba-ETS-4 adsorbents, i.e., Ba-RPZ and Ba-HFZ. The adsorption experimental data were measured at 30 ^◦C and 0–100 kPa pressure range by the static volume adsorption method. The experimental equilibrium data were correlated with the Toth isotherm. Also, the uptake rates of nitrogen and methane were correlated with Crank's method and diffusion time constant parameter was predicted for both gases at the aforementioned conditions above. A temperature range of 250–400 ^◦C was selected to study the impact of heat treatment on the Ba-ETS-4 adsorptive performance. Also, equilibrium and kinetic selectivities of Ba-HFZ were calculated for the first time. An acceptable equilibrium (i.e., 3.79) and kinetic (i.e., 67) nitrogen/methane selectivity have been obtained for Ba-HFZ at 375 ^◦C activation temperature. Moreover, chlorine halogen by creating an extra molecular exclusion property in Ba-RPZ framework leads to an improved nitrogen/methane equilibrium (i.e., 3.9) and kinetic selectivities (i.e., 290) at 375 ^◦C activation temperature.