Chemical Liquid Deposition Modified 4A Zeolite as a Size-Selective Adsorbent for Methane Upgrading, CO ₂ Capture and Air Separation

Chemical liquid deposition (CLD) modified 4A zeolite is developed as a size selective sorbent at 0.01 nm resolution for gas separation. The silica layer formed by CLD modification is located on the external surface of 4A zeolite, resulting in reduced pore apertures while not altering internal cavities. With controllable pore aperture sizes, the sorbents were able to selectively adsorb carbon dioxide, hydrogen sulfide and oxygen while excluding methane, nitrogen and argon, for application to methane upgrading from biogas, CO ₂ capture and as an oxygen-selective sorbent for energy-saving air separation. The optimized CLD modified 4A zeolite samples achieved a CO ₂ /CH ₄ (pure-component) selectivity as high as 76, a CO ₂ /N ₂ selectivity of 44, an O ₂ /N ₂ selectivity of 1.6 and an O ₂ /Ar selectivity of 2, while preserving high adsorption capacities for the targeted molecules. It was shown that the hydroxyl groups on zeolites were essential in the CLD mechanism and that the deposited CLD layer offered no diffusion resistance to the small molecules studied. The success of pore confinement provides a strategy for the development of efficient and scalable sorbents for size-selective separations.