Separation of ethylene/ethane mixtures by adsorption on small-pored titanosilicate molecular sieves

Adsorptive separation of ethylene and ethane may represent a less energy-intensive alternative to current sub-ambient distillation methods. In this approach, ethylene and ethane are separated by inverse-phase gas chromatographic and gravimetric isotherm techniques on ion-exchanged forms of ETS-4 and RPZ titanosilicate molecular sieves. Gas chromatography reveals that kinetic separation of ethylene from ethane is possible using ETS-4 and RPZ adsorbents exchanged with Zn and mixed Ca/H. Gas chromatographic selectivities of 4–40 for the adsorptive separation of ethylene and ethane were measured for these adsorbents, and the limiting selectivity calculated from gravimetric adsorption isotherms was between 4 and 12. In accordance with the ideal adsorbed solution theory, ethylene/ethane selectivity increases with pressure in all cases studied, especially for strontium- and barium-exchanged ETS-4. Due to the molecular sieving character of the adsorbents, steric effects were observed for the adsorption of ethylene and ethane, and contact time between the adsorbent and the gas mixture was the key factor in the separation of the gases. ETS-4 and RPZ materials exchanged with Zn or Ca/H are excellent candidates for the commercial adsorptive separation of ethylene and ethane.