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.
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