Dynamic separation of binary ethene/ethane mixtures by Ba-ETS-4

• A small-pore, barium-exchanged ETS-4 titanosilicate was successfully synthesized and structurally characterized. • Time-dependent uptake measurements revealed that ethene diffuses 4.75 times faster than ethane at 30 °C. • A high ethene/ethane kinetic selectivity of 12.5 was achieved at 30 °C, driven by differences in intracrystalline diffusion rates. • Ethane exhibited a sharp breakthrough front, indicating its restricted diffusion and limited adsorption under binary mixture conditions. • Elevated temperatures led to sharper curves and delayed ethene breakthrough, indicating reduced diffusion resistance and enhanced separation. The dynamic adsorptive separation performance of the small pore Ba 2+ -exchanged ETS-4, titanosilicate zeotype material, for mixtures of ethene and ethane was investigated. Na-ETS-4 was ion-exchanged with Ba 2+ to form microporous Ba-ETS-4, and characterized using XRD, SEM and EDX spectroscopy. Adsorption isotherms and fractional uptakes were recorded at three different temperatures of 30, 50, and 70°C to evaluate the effect of temperature on adsorption capacity and kinetics. Time-dependent fractional uptake recorded at different temperatures confirmed that ethene diffuses significantly faster than ethane in Ba-ETS-4, which can be attributed to ethene’s smaller molecular size, i.e. at 30°C, the time-constant diffusivity of ethene was 4.75 times higher than ethane. Though diffusivity increases for both gases with temperature, ethane rises more, reducing the ethene/ethane diffusivity ratio from 3.58 to 3.09 between 50 °C and 70 °C. Moreover, a high ethene/ethane kinetic selectivity of 12.5 was observed at 30 °C. Breakthrough experiments further highlighted the impact of diffusion limitations on separation. A comprehensive analysis has been performed for ethene/ethane mixtures between 30 and 90°C, ethene/ethane compositions varying from 10/90 (vol/vol%) - 90/10 (vol/vol%) and different regeneration conditions. Ethane exhibited a sharp breakthrough front, as it was excluded from adsorption in mixture conditions. A broader profile was observed for ethene, which its adsorption is affected by diffusion limitations. At higher temperatures, ethene’s breakthrough became sharper and more delayed, indicating reduced diffusion limitations. Optimal separation was achieved at 70 °C based on ethene uptake and breakthrough time difference. Given the strong adsorption in Ba-ETS-4, a TSA process is required for complete desorption of the adsorbed hydrocarbons.