Browsing by Subject "Membranes"

Now showing 1 - 5 of 5
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    Block polymer membranes for selective separations.
    (2009-06) Phillip, William A.
    Polymeric membranes are used for many separations. Some act as selective filters, separating viruses and other undesirable solutes from drinking water. Others perform chemical separations, separating air to make an atmosphere which extends fruit shelf-life. The ability of a membrane to perform a separation is determined by its chemistry and microstructure. Block polymers are macromolecules composed of two or more chemically incompatible polymers (blocks) covalently bonded together. Depending upon the relative amounts of each block, the polymer forms different ordered structures 5-50 nm in scale. This control over the constituent polymers and microstructure will be used to produce membranes with different transport properties. Ammonia selective membranes which retain selectivity in mixed gas systems are made from poly(cycloocetene-b-styrene sulfonate). Using poly(styrene-b-lactide) as a template, ultrafiltration membranes with a monodisperse pore size distribution are formed.
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    Development of Novel Porous Materials and Thin Membranes For Gas Separations
    (2020-01) Xue, Feng
    The development of high-flux, high-selectivity, and low-cost membranes has the potential to improve the energy efficiency in the chemical industry by reducing the reliance on energy-intensive separation processes, such as distillation. To achieve this goal, novel porous materials and membrane fabrication methods are being increasingly sought after. Metal-organic frameworks (MOFs) are a new type of microporous materials with tunable pore structures suitable for gas separations. However, the high manufacturing cost and industrially-unattractive throughput hinder the industrial applications of MOF membranes. Fabrication of thin membranes with high throughput has the potential to overcome this barrier. This dissertation focuses on developing synthesis methods for thin MOF membranes by using two-dimensional (2D) MOF nanosheets and an all-vapor-phase zeolitic imidazolate frameworks (ZIFs) membrane synthesis process named ligand-induced permselectivation (LIPS). Crystal growth strategies for 2D MOFs were developed that yield Zn(Bim)OAc MOF nanosheets with desirable aspect ratio and uniformity for membrane formation. Using the Zn(Bim)OAc nanosheets, uniform coatings were successfully prepared on porous supports by vacuum filtration. A novel vapor growth method combining the support surface modification and ligand vapor treatment was developed to transform the nanosheet deposits into thin propylene-selective membranes. In addition, in an effort to reduce the membrane cost by using low-cost polymers, porous Cu(BDC) MOF nanosheets were incorporated into polymer matrices to form mixed matrix membranes that exhibited significantly improved performance for CO2/N2 separation. Besides solution processing of MOF membranes, a novel, well-controlled and cost-effective all-vapor-synthesis LIPS method with a combination of atomic layer deposition (ALD) and ligand vapor treatment was investigated. It was demonstrated that an ALD processing condition allowing a thin non-permeable ZnO deposit formation, as well as efficient ZnO-to-ZIFs conversion during ligand vapor treatment are very critical to realize consistent high membrane performance. With optimized ALD parameters, support and ligand properties, the membranes exhibit superior separation performance, with propylene permeance above 1.3 ×10-7 mol m-2 s-1 Pa-1 and propylene/propane selectivity above 60, which is highly promising for industrial applications.
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    Morphology control of porous materials and molecular sieve membrane applications.
    (2010-12) Yoo, Won Cheol
    For advanced applications of porous materials, morphology control of porous materials is desired. Simultaneous dissolution and surfactant-induced re-assembly via micelle formation with dissolved species were performed to introduce mesoporosity in the amorphous silica spheres and zeolite crystals. Textural features of mesoporous silica spheres were controlled from corrugated to smooth. Mesoporous zeolite catalysts were synthesized via surfactant-induced re-assembly with dissolved crystal fragments of zeolite crystals. In addition, the concept of confined synthesis was used for control of morphologies of zeolite crystals. Using 3-D ordered macroporous (3DOM) carbon as a template, growth patterns and shape development of zeolite crystals were studied. Various shaped zeolite crystals, e.g., hollow interior (geode-like structure), corrugated/smooth surface of polycrystalline crystals, needle-shaped crystals and 3DOM imprinted single crystals, were produced by careful choice of reaction parameters during the confined synthesis. Polycrystalline aggregates produced by the confined synthesis were used as seed particles for zeolite membrane fabrication. Novel seeding techniques, rubbing and leveling methods, were applied to deposit the confinement product directly on the surface of porous alumina supports, and zeolite membranes were grown by secondary hydrothermal growth. Moreover, rapid thermal processing and conventional calcination were used to investigate the effect of thermal treatments on the overall membrane quality. To evaluate the membrane quality, permeation measurements to separate p-/o-xylene isomers based on the zeolite's intrinsic capability of size-selective molecular separations were conducted. A high separation factor and high permeance were observed.
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    Nanoporous thermosetting membranes using reactive block polymer templates.
    (2010-08) Amendt, Mark A.
    Pressure driven membrane filtrations are a facile means of performing aqueous separations. The efficiency of these processes depends on the permeability and selectivity of a membrane, which is determined by its structure. This dissertation describes research investigating nanoporous thermosets templated by reactive block polymers as alternatives to current ultrafiltration membranes. The goal of the research was to develop materials with narrow pore size distributions and high void fractions for forming membranes with increased selectivity and permeability. The flux, filtration and fouling characteristics of membranes formed by selective removal of poly(lactide) from crosslinked films of dicyclopentadiene (DCPD) and the reactive block polymer poly(norbornenylethyl styrene-s-styrene)-b-poly(lactide) (PNS-PLA) were first explored. The results suggest that thin film composite membranes could achieve permeabilities and selectivities greater than current ultrafiltration membranes without excessive fouling characteristics. Additionally, hydrophilic and stimuli responsive membranes templated by reactive triblock terpolymers exhibited environmentally dependent fluxes demonstrating the ease of creating functionalized membranes using reactive triblock terpolymers. Further investigation into the compositional influences on the morphology of nanostructured PNS-PLA/PDCPD materials revealed that nanoporous bicontinuous structures form over a wide composition range and that different pore sizes are achievable by varying the PLA block size. Extension of reactive block polymer templating to vinyl crosslinking systems was demonstrated by crosslinking a poly(lactide)-b-poly(cyclooctene-s-norbornenylmethacrylate)-b-poly(lactide) reactive triblock copolymer with a variety of vinyl monomers. Although the soft nature of the poly(cyclooctene) prevented removal of polylactide due to collapse of the pores, nanoporous vinyl thermosets were realized by crosslinking a polylactide-b-poly(styrene-s-hydroxyethyl methacrylate-s-ethylene glycol dimetacrylate) reactive diblock copolymer with styrene and divinyl benzene.
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    Ultra-thin MFI zeolite films: Synthesis, Characterization and Progress Toward Industrial Applications
    (2017-05) Rangnekar, Neel
    Separation processes account for 10-15% of US energy consumption. A large fraction of that energy is consumed by energy-inefficient thermal separation processes like distillation. If membranes could perform these separations, up to 90% of that energy could be saved. Zeolites have ideal properties for separations, which include their high thermal and chemical stability. However, there are currently very few examples of industrial zeolite membrane separation processes. This is due to the high cost associated with their manufacture, industrially unattractive throughput and lack of membrane separation experiments at industrially relevant conditions. This dissertation aims to make progress on some of these fronts. The recent advances in zeolite membranes are reviewed, with an emphasis on industrial applications. A membrane fabrication procedure using 3.2 nm-thick MFI zeolite “nanosheets” is reported, resulting in high-flux and high separation efficiency membranes. High performance membrane separations at industrially relevant conditions have also been achieved for the first time. Moreover, further progress towards synthesis of even thinner films and membranes has been made. The discovery of a novel deposition technique enables the transfer of monolayers of nanosheets to silicon wafers. By intergrowing them, the thinnest-ever MFI films have been synthesized. In future, this technique could be extended to fabricate even higher-flux membranes. An application of zeolite films on silicon wafers as a low-dielectric constant material is also described. Superior insulating properties and mechanical strength compared to previously reported MFI films is achieved. Such a film could save energy and promote the development of the next generation of computer chips.