Structured Zeolite Nax Coatings on Ceramic Cordierite Monolith Supports for PSA Applications

Novel structured adsorbents in the form of thin zeolite films grown on substrates designed for low pressure drop have a great potential to improve pressure swing adsorption (PSA) processes. In the present work, template free films of NaX zeolite were grown on the walls of ceramic cordierite supports using a seeding technique. The supports had 400 parallel channels per square inch. Films were grown both from a gel and a clear synthesis solution. The materials were analyzed by scanning electron microscopy, X-ray diffraction, N₂ adsorption/desorption measurements, Hg-porosimetry as well as CO₂ breakthrough experiments. When a gel was used for film growth, a film consisting of well intergrown crystals with a thickness of about 1 μm was obtained. However, a large amount of sediments were deposited on top of the film, which resulted in a dispersed CO₂ adsorption breakthrough front. Zeolite films grown in one longer hydrothermal treatment in a clear solution were less intergrown and consisted of both NaX and hydroxysodalite crystals and, in addition, some sediments were deposited on top of the film, which again resulted in a dispersed breakthrough front. By using a multiple-step synthesis procedure and a clear synthesis solution, well intergrown NaX films, free from sediments and with only a very small fraction of hydroxysodalite crystals could be prepared. The CO₂ breakthrough front for the latter adsorbent was sharper than the front for an empty adsorption column and only shifted in time. This indicates that the flow distribution in the adsorbent is even and that the mass transfer resistance in the film is very low due to the small film thickness and high effective diffusivity for CO₂ in the NaX film and still, the adsorption capacity is considerable. The even flow distribution, very low mass transfer resistance and low pressure drop in combination with considerable adsorption capacity in this adsorbent indicates that it is a promising adsorbent for PSA applications. The findings from the present work will be important for the development of structured adsorbents to use as a competitive alternative to traditionally used adsorbents in PSA.