Alumina membranes

Ceramic Membranes Alumina-based microfiltration membranes and porous carbon substrates are tightened for use as UF membranes usually by depositing a layer of zirconium oxide on the surface. 

Membranes UF membranes consist primarily of polymeric structures (polyethersulfone, regenerated cellulose, polysulfone, polyamide, polyacrylonitrile, or various fluoropolymers) formed by immersion casting on a web or as a composite on a MF membrane. Hydrophobic polymers are surface-modified to render them hydrophilic and thereby reduce fouling, reduce product losses, and increase flux [Cabasso in Vltrafiltration Membranes and Applications, Cooper (ed.). Plenum Press, New York, 1980]. Some inorganic UF membranes (alumina, glass, zirconia) are available but only find use in corrosive applications due to their high cost. 

Supported, multilayered (as5onmetric) - dense oxide or metal - porous ceramic membranes alumina, zirconia, titania, carbon - composite ceramic-metal, ceramic-ceramic layers on porous support tube, disk multilayers on porous support plate, disk, tube, monolith... 

Ceramic Membranes. Alumina membranes for UF have been introduced by Ceraver (Tarbes, France) (membrane division recently purchased by Alcoa). The Norton Co. (Worcester, MA) is reportedly about to introduce an alumina UF membrane in addition to its current MF membrane. 

A sol of metal alkoxides has been used to prepare inorganic ion exchange membranes. Metal alkoxides are easily hydrolyzed to form a metal hydroxide sol in the presence of acid. The sol is then repeatedly coated on a microporous inorganic membrane (alumina substrate) and heated to form a metal oxide on the substrate, which is an inorganic ion exchanger.139 Though this is also a heterogeneous membrane, some reported membranes show lithium ion permselectivity in electrodialysis.140... 

Examples of commercial porous inorganic membranes are ceramic membranes (alumina, silica), glass and porous metals (stainless steel and silver). 

MF and UF membranes can be polymeric or inorganic. Membrane materials must be chemical resistant to both feed and cleaning solutions, mechanically and thermally stable, and characterized by high selectivity and permeability. Polysulfone (PS), polyethersulfone (PES), polyamide (PA), cellulose acetate (CA), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), poly(vinylidene F ) (PVDF) and polypropylene (PP) are typical materials commonly used to cast the membrane. Alumina, zirconia and ceramic materials are usually used as inorganic materials. 

Track-etch membranes Alumina membranes Block copolymer membranes Silicon wafers... 

Inorganic membranes, such as purely molecular sieving zeohte membranes, carbon membranes, " alumina membranes," and silica membranes," have high thermal and chemical stabUities. Over the past 25 years, extensive work has been reported on the synthesis, characterization, and apphcation of inorganic membranes. 

Key words mesoporous ceramic membranes, alumina, titania, zirconia, membrane reactors for dehydrogenation reactions. 

The sol—gel technique has been used mosdy to prepare alumina membranes. Figure 18 shows a cross section of a composite alumina membrane made by sHp coating successive sols with different particle sizes onto a porous ceramic support. SiUca or titanium membranes could also be made by the same principles. Unsupported titanium dioxide membranes with pore sizes of 5 nm or less have been made by the sol—gel process (57). 

Fig. 18. Cross-sectional scanning electron micrograph of a three-layered alumina membrane/support (pore sizes 0.2, 0.8, and 12 p.m, respectively).

Membranes. Membranes comprised of activated alumina films less than 20 )J.m thick have been reported (46). These films are initially deposited via sol—gel technology (qv) from pseudoboehmite sols and are subsequently calcined to produce controlled pore sizes in the 2 to 10-nm range. Inorganic membrane systems based on this type of film and supported on soHd porous substrates have been introduced commercially. They are said to have better mechanical and thermal stabiUty than organic membranes (47). The activated alumina film comprises only a miniscule part of the total system (see Mel rane technology). 

Usually they are employed as porous pellets in a packed bed. Some exceptions are platinum for the oxidation of ammonia, which is in the form of several layers of fine-mesh wire gauze, and catalysts deposited on membranes. Pore surfaces can be several hundred mVg and pore diameters of the order of 100 A. The entire structure may be or catalytic material (silica or alumina, for instance, sometimes exert catalytic properties) or an active ingredient may be deposited on a porous refractory carrier as a thin film. In such cases the mass of expensive catalytic material, such as Pt or Pd, may be only a fraction of 1 percent. 

For inorganic contaminants removal membranes, ion exchange, activated alumina, and GAC. 

CASE STUDY INORGANIC ZIRCONIA y-ALUMINA-COATED MEMBRANE ON CERAMIC SUPPORT... 

In this case study, a zirconia-alumina membrane has been developed using the sol-gel technique with and without support.6-7 The porous ceramic was prepared to fabricate the membrane support. A thin film of aluminum and zirconium were formed on the porous ceramic support. Unsupported membrane was also prepared. The unsupported membrane was not strong enough to hold a high-pressure gradient it was very fragile and not useful... 

Fig. 16.25. Mixture of zirconia and alumina coated on the ceramic membrane.

Once the membrane was successfully produced, it was analysed for characterisation and scanning. The sol-gel technique was successfully used to obtain a crack-free unsupported membrane, which was expected to have pore size of 1-2 nm. The development of the crack-free membrane may not have the same strength without strong, solid support. The next stage of this work was to characterise the fabricated membrane. Hie objectives of this study were to develop a zirconia-coated 7-alumina membrane with inorganic porous support by the sol-gel method and to characterise the surface morphology of the membrane and ceramic support. 

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