Temperature- and Pressure-Dependent Adsorption Equilibria and Diffusivities of Propylene and Propane in Pure-Silica Si-CHA Zeolite

Propylene/propane separation by an adsorption process based on pure-silica zeolites (such as Si-CHA) is an energy-efficient alternative for cryogenic distillation. High-pressure adsorption isotherms of propylene were obtained on large crystals of Si-CHA zeolite (11 μm) at 303–423 K up to 1000 kPa. As propane adsorption was very slow, equilibrium was not achieved on large crystals of Si-CHA and even on small crystals (1 μm) after 2.5 days at 303 K. Finally, real equilibrium isotherms of propane were measured on fine Si-CHA particles at 373–473 K and up to 500 kPa. This is the first time that the experimental isotherms of propane are reported. Kinetic adsorption data of propylene and propane were evaluated at different pressures and temperatures. The results showed that both temperature and pressure have positive effects on diffusivities. The results showed that Si-CHA zeolite is an excellent kinetic selective adsorbent having propylene diffusivity 3 orders of magnitude higher than propane.