Fabrication of b-Oriented MFI Zeolite Films under Neutral Conditions without the Use of Hydrogen Fluoride

Controllable Orientation Growth of ZSM-5 for Methanol to Hydrocarbon Conversion: Cooperative Effects of Seed Induction and Medium pH Control

The growth orientation of ZSM-5 zeolites strongly affects product selectivity in methanol conversion reaction. Here, we proposed a versatile synthetic strategy by introducing seeds and controlling medium pH to achieve controllable orientation growth of ZSM-5. The systematic analysis of the crystallization process indicated that the introduction of seeds ensured successful crystallization in a quasi-neutral solution and the dissolution rate of seeds and aluminosilicate determined the growth orientation of ZSM-5. In the quasi-neutral solution, the slow dissolution of seeds and aluminosilicate enhanced growth advantages along the c axis. The ratio between the length of the c axis and b axis (L_c/L_b) of the obtained ZSM-5 at pH of 7 could reach 8.1, much higher than 1.8 obtained at pH of 11. No obvious impact of seed added amount on growth orientation was found, while with increasing seed crystal size, the obtained ZSM-5 showed preferred growth along the c axis. The L_c/L_b of the sample adding seeds with a size of 355 nm reached 7.9, much higher than 2.1 of the sample adding seeds with a size of 70 nm. The obtained ZSM-5 with specific growth orientation exhibited potential shape selectivity in methanol to aromatics and olefin reaction. This work opens new possibilities to tailor the orientation growth of ZSM-5 based on the seed-induced strategy under mild conditions.

One-Step Scalable Fabrication of Highly Selective Monolithic Zeolite MFI Membranes for Efficient Butane Isomer Separation

The reproducible fabrication of large-area zeolite membranes for gas separation is still a great challenge. We report the scalable fabrication of high-performance zeolite MFI membranes by single-step secondary growth on the 19-channel alumina monoliths for the first time. The packing density and mechanical strength of the monolithic membranes are much higher for these than for tubular ones. Separation performance of the monolithic membranes toward the butane isomer mixture was comparably evaluated using the vacuum and Wicke-Kallenbach modes. The n-butane permeances and n-butane/i-butane separation factors for the three membranes with an effective area of ∼84 cm² were >1.0 × 10^-7 mol (m² s Pa)^-1 and >50 at 343 K for an equimolar n-butane/i-butane mixture, respectively. We succeeded in scaling up the membrane synthesis with the largest area of 270 cm² to date which has 1.3 times the area of an industrial 1 m long tubular membrane. Monolith supported zeolite MFI membranes show great potential for industrial n-butane/i-butane separation.

Twin-free, directly synthesized MFI nanosheets with improved thickness uniformity and their use in membrane fabrication

Zeolite nanosheets can be used for the fabrication of low-defect-density, thin, and oriented zeolite separation membranes. However, methods for manipulating their morphology are limited, hindering progress toward improved performance. We report the direct synthesis (i.e., without using exfoliation, etching, or other top-down processing) of thin, flat MFI nanosheets and demonstrate their use as high-performance membranes for xylene isomer separations. Our MFI nanosheets were synthesized using nanosheet fragments as seeds instead of the previously used MFI nanoparticles. The obtained MFI nanosheets exhibit improved thickness uniformity and are free of rotational and MEL intergrowths as shown by transmission electron microscopy (TEM) imaging. The nanosheets can form well-packed nanosheet coatings. Upon gel-free secondary growth, the obtained zeolite MFI membranes show high separation performance for xylene isomers at elevated temperature (e.g., p-xylene flux up to 1.5 × 10^-3 mol m^-2 s^-1 and p-/o-xylene separation factor of ~600 at 250°C).

Controlled release of siliceous species for the fabrication of highly b-oriented MFI zeolite films

Silicate precursor nanoparticles are complexed with 1,2-dihydroxybenzene and then gradually released to feed the secondary growth of b-oriented MFI zeolites.

One-Pot Synthesis of High-Flux b-Oriented MFI Zeolite Membranes for Xe Recovery

We demonstrate that b-oriented MFI (Mobil Five) zeolite membranes can be manufactured by in situ crystallization using an intermediate amorphous SiO₂ layer. The improved in-plane growth by using a zeolite growth modifier leads to fusion of independent crystals and eliminates boundary gaps, giving good selectivity in the separation of CO₂/Xe mixtures. The fast diffusion of CO₂ dominates the overall membrane selectivity toward the CO₂/Xe mixture. Because of the straight and short [010] channels, the obtained CO₂ permeation fluxes are several orders of magnitude higher than those of carbon molecular sieving membranes and polymeric membranes, opening opportunities for Xe recovery from waste anesthetic gas.

Thermal processing of zeolite seed layers for the fabrication of compact oriented MFI zeolite films

The formation of a close-packed oriented MFI zeolite film through thermal processing created a strong covalent linkage between the seed layer and the substrate.

A graphene oxide layer as an acid-resisting barrier deposited on a zeolite LTA membrane for dehydration of acetic acid

A graphene oxide layer (GO) was deposited as acid-resisting barrier to avoid the degradation of zeolite LTA membrane by acetic acid, leading to a high selectivity and stability of the zeolite LTA membrane for the dehydration of acetic acid.

Rapid fabrication of highly b-oriented zeolite MFI thin films using ammonium salts as crystallization-mediating agents

Highly b-oriented zeolite MFI films can be obtained by adding ammonium salts in the traditional secondary growth solution.