Fabrication, characterization, and application of zeolite inorganic membranes

It was demonstrated for the first time that a-out-of-plane oriented assembly of anisometric zeolite crystals on a porous support followed by secondary growth leads to continuous, thin, uniformly a-out-of-plane oriented zeolite films of the structure type MFI. These a-oriented films, along with the previously reported b-oriented ones, are the first set of thin molecular sieve membranes with uniform orientation. The a-oriented MFI membranes were expected to provide high separation performance comparable to that of b-oriented ones. However, a-oriented MFI films suffered from severe cracks and did not provide exceptionally high separation performance. Nevertheless, we attempted to make other types of a-oriented MFI films that exhibit high separation performance.;c-Oriented columnar MFI films made by secondary growth of randomly oriented seed monolayers exhibit n-hexane/2,2-dimethylbutane separation factor of up to 104, n-/i-butane separation factor of up to 50, and p-/o-xylene separation factor of up to 2. A MFI film grown from an a-oriented seed layer shows lower separation factors for the linear/branched isomers but higher separation factors for p-/o-xylene, consistent with that drawn from the membrane properties of b- and c-oriented MFI membranes. However, rapid thermal annealing of c-oriented MFI membranes resulted in dramatically improved separation performance for both aromatic compounds (∼130 p-/o-xylene) and linear/branched alkanes (∼30 n-/i-butane & ∼6x 103 n-hexane/2,2-dimethylbutane). To the best of knowledge, such c-oriented MFI membranes with unprecedentedly improved performance are reported for the first time. In an effort to address scale-up, we succeed in fabricating columnar MFI films on stainless steel tubes by secondary growth of globular seeds attached during a simple sonication.;A layer-by-layer deposition method is presented for the fabrication of compact c-oriented-MCM-22/Silica films on porous alpha-alumina discs. The film fabrication procedure combines deposition of plate-like MCM-22 crystals on substrates by sonication-assisted covalent attachment with evaporation-induced-self-assembly (EISA) of surfactant-templated silica. They exhibited hydrogen ideal selectivities up to H2/CO2 ∼8.2 and H2/N2 ∼ 28, above those expected by Knudsen diffusion (H2/CO2 ∼4.4 and H2/N2 ∼.3.7) indicating molecular sieving potential.