Crystalline Membranes

In certain aspects, the invention features methods for forming crystalline membranes (e.g., a membrane of a framework material, such as a zeolite) by inducing secondary growth in a layer of oriented seed crystals. The rate of growth of the seed crystals in the plane of the substrate is controlled to be comparable to the rate of growth out of the plane. As a result, a crystalline membrane can form a substantially continuous layer including grains of uniform crystallographic orientation that extend through the depth of the layer

Synthesis of Porous Inorganic Membranes

Here we will attempt a brief overview of recent synthetic efforts for micropore and lower-end mesopore membranes. We will not address the very important classes of nonporous membranes, such as dense metals and solid electrolytes with applications in H_2 and O_2 separations, or meso- and macroporous membranes, which find applications in food processing and water treatment. Microporous materials provide high permselectivities for molecules encountered in the chemical-processing industry but suffer from low intrinsic permeabilities. Therefore, in order to bring microporous membrane materials to commercial applications, functional composites with small effective thicknesses (in the micron or submicron range) must be developed. For example, to achieve economical membrane-reactor sizes, fluxes as high as 0.1 mol/(m^2 s) are desirable. Approaches to microporous membranes include modification of mesoporous membranes by sol-gel and chemical-vapor-deposition (CVD) techniques, carbonization of polymers to form molecular-sieve carbon, and polycrystalline-film growth of zeolites and other molecular sieves

A New Concept for the Fabrication of Hydrogen Selective Silica Membranes

It was proposed to investigate a new concept for the synthesis of molecular sieve hydrogen selective membranes. This concept is based on the use of exfoliated layered zeolite precursors in coating processes to make nanocomposite films with inorganic or polymeric matrices. We discovered that creating exfoliated zeolite layers was much more difficult than anticipated because the methods originally proposed (based on existing literature reports) were not successful in providing exfoliated layers while preserving their porous structure. Although the original goals of fabricating high-selectivity-high-flux membranes that are stable under conditions present in a water-gas-shift reactor and that are able to selectively permeate hydrogen over all other components of the mixtures present in these reactors were not accomplished fully, significant progress has been made as follows: (1) Proof-of-concept hydrogen-selective nanocomposite membranes have been fabricated; (2) Methods to exfoliate layered zeolite precursors preserving the layer structure were identified; and (3) Unexpectedly, membranes exhibiting high ideal selectivity for carbon dioxide over nitrogen at room temperature were produced. The findings listed above provide confidence that the proposed novel concept can eventually be realized

Zeolite membranes - a review and comparison with MOFs

The latest developments in zeolite membranes are reviewed, with an emphasis on the synthesis techniques, including seed assembly and secondary growth methods. This review also discusses the current industrial applications of zeolite membranes, the feasibility of their use in membrane reactors and their hydrothermal stability. Finally, zeolite membranes are compared with metal–organic framework (MOF) membranes and the latest advancements in MOF and mixed matrix membranes are highlighted

Interplay between hydrophilicity and surface barriers on water transport in zeolite membranes

A comprehensive understanding of molecular transport within nanoporous materials remains elusive in a broad variety of engineering and biomedical applications. Here, experiments and atomistic simulations are synergically used to elucidate the non-trivial interplay between nanopore hydrophilicity and surface barriers on the overall water transport through zeolite crystals. At these nanometre-length scales, these results highlight the dominating effect of surface imperfections with reduced permeability on the overall water transport. A simple diffusion resistance model is shown to be sufficient to capture the effects of both intracrystalline and surface diffusion resistances, thus properly linking simulation to experimental evidence. This work suggests that future experimental work should focus on eliminating/overcoming these surface imperfections, which promise an order of magnitude improvement in permeability.MITOR ProjectNANO-BRIDGE (PRIN 2012, grant number 2012LHPSJC)NANOSTEP (Fondazione CRT, Torino) projectsScuola Interpolitecnica di Dottorato—SCUDOISCRA initiative (CINECA award)Center for Clean Water and Clean Energy at MIT and KFUP

Steam-Induced Coarsening of Single-Unit-Cell MFI Zeolite Nanosheets and Its Effect on External Surface Brønsted Acid Catalysis.

Commonly used methods to assess crystallinity, micro-/mesoporosity, Brønsted acid site density and distribution (in micro- vs. mesopores), and catalytic activity suggest nearly invariant structure and function for aluminosilicate zeolite MFI two-dimensional nanosheets before and after superheated steam treatment. Yet, pronounced reaction rate decrease for benzyl alcohol alkylation with mesitylene, a reaction that cannot take place in the zeolite micropores, is observed. Transmission electron microscopy images reveal pronounced changes in nanosheet thickness, aspect ratio and roughness indicating that nanosheet coarsening and the associated changes in the external (mesoporous) surface structure are responsible for the changes in the external surface catalytic activity. Superheated steam treatment of hierarchical zeolites can be used to alter nanosheet morphology and regulate external surface catalytic activity while preserving micro- and mesoporosity, and micropore reaction rates

Zeolite ZSM-5 membranes grown on porous α-Al_2O_3

ZSM-5 membranes with good permeation selectivity for n-butane–isobutane are grown hydrothermally from a clear solution on horizontally-held porous α-Al_2O_3 disks

Self-Pillared, Single-Unit-Cell Sn-MFI Zeolite Nanosheets and Their Use for Glucose and Lactose Isomerization

Single-unit-cell Sn-MFI, with the detectable Sn uniformly distributed and exclusively located at framework sites, is reported for the first time. The direct, single-step, synthesis is based on repetitive branching caused by rotational intergrowths of single-unit-cell lamellae. The self-pillared, meso- and microporous zeolite is an active and selective catalyst for sugar isomerization. High yields for the conversion of glucose into fructose and lactose to lactulose are demonstrated

On stability and performance of highly c-oriented columnar AlPO4-5 and CoAPO-5 membranes

[EN] Continuous films comprised of highly c-oriented aluminophosphate AlPO4-5 or cobalt-substituted AlPO4-5 (CoAPO-5) were grown on porous supports and subjected to heat treatment in order to investigate the potential for membrane applications. A study in the early stages of in-plane crystalline intergrowth revealed a potential mechanism for flake-like crystal formation between the original oriented columnar crystals. Variations in metal substitution (AlPO4-5, CoAPO-5), support (glass, silicon, porous alumina), and calcination method (conventional, rapid thermal processing) were chosen to examine the conditions by which structural integrity was compromised following secondary (or tertiary) growth, resulting in reduced membrane functionality. Through the use of rapid thermal processing, the structure debilitation could be partially avoided. The membrane quality was inspected through pervaporation measurements consisting of a liquid hydrocarbon feed of n-heptane and 1,3,5-triisopropylbenzene. By investigating the effect of template removal on the oriented, columnar crystalline structure, useful insight is provided into the potential for the membranes to participate in applications such as molecular separations, catalysis, or host-guest assemblies. (C) 2011 Elsevier Inc. All rights reserved.Support by the American Chemical Society (ACS-PRF) and the European Community through the FP7 NextGTL project and a Marie Curie International Reintegration Grant (FP7, Grant agreement No. 210947) is greatly appreciated. M.P. thanks CSIC for a JAE doctoral fellowship. We would like to thank Kumar Varoon for assistance with membrane sectioning and imaging using the focused ion beam technique. Parts of this work were carried out in the Characterization Facility on the campus of the University of Minnesota-Twin Cities, which receives partial support from NSF through the MRSEC program.Stoeger, JA.; Veziri, CM.; Palomino Roca, M.; Corma Canós, A.; Kanellopoulos, NK.; Tsapatsis, M.; Karanikolos, GN. (2012). On stability and performance of highly c-oriented columnar AlPO4-5 and CoAPO-5 membranes. Microporous and Mesoporous Materials. 147(1):286-294. https://doi.org/10.1016/j.micromeso.2011.06.028286294147