(436d) Microporous Coating Modified 5A Zeolite for Propylene/Propane Separation

Separation of propylene/propane mixtures is a crucial processing step in the chemical industry. Compared with traditional cryogenic distillation, adsorptive separation, for example, by Pressure Swing Adsorption (PSA), may serve as a more energy-efficient separation alternative. So far, this process has yet been demonstrated industrially, and lack of high performance adsorbents is probably an important restricting factor. It is very challenging to prepare selective adsorbents for separating propylene/propane mixture because of their small size difference and similar chemical/physical properties.

In this study, Molecular Layer Deposition (MLD) and Atomic Layer Deposition (ALD) were combined to deposit uniform microporous coatings on 5A zeolite surface to tune the effective pore size for propylene/propane separation. The pore entrance of 5A zeolite was fine-tuned at the Angstrom scale by changing the MLD and ALD cycle numbers. In this process, MLD was first applied to form a conformal and uniform coating on the external surface of 5A zeolite, which was converted into microporous coating by calcination to remove the organic compound. We have shown that MLD coating effectively reduced the pore size of 5A zeolite due to pore misalignment. Then, ALD was applied to further fine tune the MLD coating pores and thus further reduce the pore size of 5A zeolite. The results showed that the propylene/propane adsorption selectivity increased to ~21 after optimizing MLD/ALD cycles. Meanwhile, diffusivity ratio of propylene/propane increased drastically from ~1 of bare 5A to ~75 for MLD/ALD modified 5A. Our research work suggests that MLD/ALD modified zeolites may have great potential for the adsorptive separation of propylene/propane mixtures.