Supported liquid membranes inorganic support

Carrier-facilitated transport is used successfully to extract various organic and inorganic substances from a feed mixture in liquid membranes. Liquid membranes are employed as bulk liquid membranes, emulsion liquid membranes, and supported liquid membranes. 

Dense inorganic or metallic membranes for gas separation are usually ion-conducting materials, while membranes with carriers are polymers or supported liquid membranes (SLM). For transport through these materials, different flux equations should be applied. Figure 4.2 sums up and generalizes the various types of transport, which may take place in gas-separation membranes [21]. 

In the SLM process, like in all membrane processes, the membrane plays a key role in the transport and separation efficiency. The permeation rate and separation efficiency depends strongly on the type of liquids and supports used for SLM construction. However, the transport properties depend on the type of liquids used as a membrane phase the hquid membrane stability and mechanical stability depend, to a large extent, on the microstructure like pore shape, size, and tortuosity of the membrane used as a support. Therefore, many types of polymeric and inorganic microporous membrane supports are studied for the liquid membrane phase immobilization. 

Catalytically active supported ionic liquid membranes were used for propylene/propane vapor mixture separation. In this case, the ionic Hquid was immobilized in the pores of an asymmetric ceramic support, displaying sufficient permeability, good selectivity, and long-term stabUity [51]. Porous inorganic membranes were also used as a support for chiral-selective liquid membranes. For this purpose, porous tubular ceramic membranes were impregnated with 3-cyclodextrin polymer. Such SLMs were used for separation of enantiomers of racemic pharmaceutical chlorthahdone [52]. 

Organic membrane reactions are best carried out in reactors made of inorganic membranes, such as from palladium, alumina, or ceramics. A recent trend has been to develop polymeric-inorganic composite-type membranes formed by the deposition of a thin dense polymeric film on an inorganic support. Another class of membranes under development for organic synthesis is the liquid membrane. The permselective barrier in this type of membrane is a liquid phase, often containing a dissolved carrier or transporter which selectively reacts with a specific permeate to enhance its transport rate through the membrane. 

The separations of inorganic cations can be provided by liquid-liquid extraction, the use of RTIL-based liquid membranes and supported membranes. It was observed, that the... 

A few other players in the nuclear membranes activity also developed inorganic membranes for the filtration of liquids. This was the case with Norton-USA who with the know-how of Euroceral developed MF membranes made of an 0-AI2O3 tubular support with an a-Al203 layer. The inner tube diameter was 3 mm and the outer diameter 5 mm. In 1988-1989, Norton also produced the multichannel membrane elements. These membranes produced by Norton are now sold by Millipore under the trademark Ceraflo . 

Inorganic membranes can be categorized as shown in Table 2.1. The dense inorganic membranes consist of solid layers of metals (Pd, Ag, alloys) or (oxidic) solid electrolytes which allow diffusion of hydrogen (or oxygen). In the case of solid electrolytes transport of ions takes place. Another category of dense membranes consist of a porous support in which a liquid is... 

Self-supporting inorganic membranes can be formed with or without a substrate. In either case the precursor sol, consisting of either a colloidal suspension or a polymeric solution, must be formed. To produce a membrane supported on a substrate (i.e. a supported membrane), a preformed porous support is dipped in the precursor sol and a gel forms at the surface of the support typically by the slipcasting method [48]. Another approach is spin coating, in which an excess amount of liquid is deposited onto a substrate and then thinned uniformly by centrifugal force [12]. To produce a non-supported membrane, the liquid is simply poured into a mold of appropriate shape and allowed to dry. All these processes need to be done before the gel point which is accompanied by a large increase in viscosity. 

The early preparations of mesoporous silica film were conducted by growth from solution.[20,276]. The basic principle for the synthesis of ordered mesoporous films by growth from solution is to bring the synthesis solution (including a solvent, surfactant, and inorganic precursor) into contact with a second phase, e.g. solid (ceramic), gas (air), or another liquid (oil). The two-phase system is kept under specific conditions and the ordered film is formed at the interface. When the second phase is solid, it is the support on which the ordered film or membrane is grown. When the second phase is air or oil, the solid films are self-standing. 

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