Composite membranes silicone rubber

Aneja (2006) reported that biocomponent/composite hfs have major potential for the separation of organic and aqueous-organic mixtures via PV. They investigated the transport of isopentane through a composite of silicone rubber and PSf asymmetric hf membrane. A one-parameter mathematical model of the PV process was developed. The parameter was related to the sorption and transport properties of the penetrant through the membrane layers. They claimed that the PV parameter is a useful tool for membrane characterization and process design. 

Jia and coworkers prepared thin-film composite zeolite-filled silicone rubber membranes by a dip-coating method [82]. The membranes have a thin silicalite-1/ silicone rubber mixed-matrix selective layer on top of a porous polyetherimide support. 

Bartels-Caspers, C., Tusel-Langer, E., and Lichtenthaler, R.N. (1992) Sorption isotherms of alcohols in zeolite-filled silicone rubber and in PVA-composite membranes./. Membr. Sci., 70 (1),... 

Recently developed blood oxygenators are disposable, used only once, and can be presterilized and coated with anticoagulant (e.g., heparin) when they are constructed. Normally, membranes with high gas permeabilities, such as silicone rubber membranes, are used. In the case of microporous membranes, which are also used widely, the membrane materials themselves are not gas permeable, but gas-liquid interfaces are formed in the pores of the membrane. The blood does not leak from the pores for at least several hours, due to its surface tension. Composite membranes consisting of microporous polypropylene and silicone rubber have also been developed. 

Figure 3.23 Schematic of the apparatus developed by Ward et al. [52] to prepare water-cast composite membranes. Reprinted from J. Membr. Sci., 1, W.J. Ward, HI, W.R. Browall and R.M. Salemme, Ultrathin Silicone Rubber Membranes for Gas Separations, p. 99, Copyright 1976, with permission from Elsevier...

Another type of gas separation membrane is the multilayer composite structure shown in Figure 8.9. In this membrane, a finely microporous support membrane is overcoated with a thin layer of the selective polymer, which is a different material from the support. Additional layers of very permeable materials such as silicone rubber may also be applied to protect the selective layer and to seal any defects. In general it has been difficult to make composite membranes with... 

For separating VOCs from water, silicone rubber composite membranes are the state-of-the-art material. Silicone rubber is easy to fabricate, is mechanically and... 

Figure 9.14 Pervaporation separation factor, /9pervap> as a function of the VOC evaporation separation factor, /3evaP- Data obtained with laboratory-scale spiral-wound modules containing a composite silicone rubber membrane and in laboratory cells with thick membranes...

Bessarabov s devices use composite membranes consisting of a thin silicone rubber polymer layer coated onto a microporous poly(vinylidene fluoride) support layer. These membranes have high fluxes and minimal selectivities for the hydrocarbon gases, but the dense silicone layer provides a more positive barrier to bleed-through of liquid than do capillary effects with simple micro-porous membranes. 

The types of polymeric membranes that have attracted much interest for analytical applications and are nowadays in common use are characterized as nonporous membranes such as low-density polyethylene (LDPE), dense PP and PDMS silicone rubbers, and asymmetric composite membranes... 

K. Kimura, T. Matsuba, Y. Tsujimura, M, Yokoyama, Unsymmetrical Calix[4]arene lonophore Silicone-Rubber Composite Membranes for High Performance Sodium ion Sensitive Field-Effect Transistors , Anal. Chem., 64, 2508 (1992)... 

Y.-C. Long, X. Chen, Z.-H. Ping, S.-K. Fu, and Y.-J. Sun, MFI-type zeolite filled silicone rubber membranes Preparation, composition, and performance. Zeolites and related microporous materials State of the art 1994 Part B. Proc. lOth Int. Zeol. Conf., Garmisch-Panenkirchen (J. Weitkamp, H.G. Karge, H. Pfeifer, and W. Holderich, eds.), Elsevier, Amsterdam, 1994, p. 1083. 

Other types of electrodes are listed in Table 8.9. The glass membrane is replaced by a synthetic single-crystal membrane (solid-state electrodes), by a matrix (e.g., inert silicone rubber) in which precipitated particles are imbedded (precipitate electrodes), or by a liquid ion-exchange layer (liquid-liquid membrane electrodes). The selectivity of these electrodes is determined by the composition of the membrane. All these electrodes show a response in their electrode potentials according to the Nemst equation. 

Membranes for vapor removal from air have a structure similar to the prism membrane, but they are prepared on a different principle.Aromatic PEI is used to produce a porous substrate membrane by the dry-wet phase inversion method. This polymer was chosen over PS/PES because of the higher durability of PEI to organic vapors. Unlike an asymmetric PS substrate for the prism membrane, the top layer of asymmetric PEI membrane has a large number of pores, the size of which is equivalent to those of UF membranes. When a layer of silicone rubber is coated on the top layer of the porous substrate membrane, the silicone rubber layer will govern the selectivity and the porous support will provide only mechanical strength to the composite membrane. Because the permeabilities of water and organic vapors through the silicone... 

Monsanto s Prism permeators for gas separation also employ composite membranes. Polyamide coatings are not used for the composite membrane in the Prism module. The Prism membrane consists of a coating of silicone rubber applied from an organic solvent on a porous polysulfone substrate. The Prism membrane is another good example of a composite membrane where Structure Level IV is used to obtain good membrane properties (22). 

Earlier papers on the continuous membrane column (28,29) have discussed the separation of CO2-N2, CO2-O2 and O2-N2 (air) mixtures in stripper, enricher and total column units composed of 35 silicone rubber capillaries. A characterization of the membrane column using a membrane unit concept (analogous to transfer unit concept — HTU, NTU) has also been presented. The purpose of this paper is to present some new data and discussions on the extended study of continuous membrane column. Specifically, the topics of multicomponent separations, Inherent simulation difficulties, composition minima in the enriching section, variation of experimental parameters, and local HMU variation along the column will be covered. 

As usual with membrane separations, the membrane is critical for success. Currently, two different classes of membranes are used commercially for pervaporation. To remove traces of organics from water a hydrophobic membrane, most commonly silicone rubber is used. To remove traces of water from organic solvents a hydrophilic membrane such as cellulose acetate, ion exchange men )rane, polyacrylic acid, polysulfone, pol5 inyl alcohol, composite membrane, and ceramic zeolite is used. Both types of membranes are nonporous and operate by a solution-diffusion mechanism Selecting a membrane that will preferentially permeate the more dilute conponent will usually reduce the membrane area required. Membrane life is typically about four years tBaker. 20041. 

The construction of ISEs used in clinical measurements is of the membrane electrode type, i.e., the ion-sensitive membrane separates the sample from an internal reference electrolyte, which is the site of the internal reference element, usually a silver wire covered by silver chloride. The membrane can be shaped to different forms such as flat, convex, tubular, etc. Sodium sensitive membranes are made from special composition glass, the other ion-sensitive membranes from a polymer matrix such as plasticized polyvinylchloride (PVC) or silicon rubber. The particular selectivity of polymer membranes is first of all due to a small percentage of active material, e.g., valinomycin, dissolved in the polymer. Important secondary effects have been attributed to the type and permittivity of the polymer. The useful lifetime of the sensors also depends on the polymer. The time response [13] may again depend on membrane composition. 

Another example is that of a mixture which consists of two components which are not miscible with each other over the whole composition range, e.g. trichloroethylene-water. Pervaporadon can be used to remove a small amount of water from trichloroethylene or to remove small amounts of trichloroethylene from water. If silicone rubber (polydimethylsiloxane) is used as a membrane material, good results are obtained if small amounts of trichloroethylene from water should be removed. When the same membrane material is used to remove water from almost pure trichloroethylene, the membrane becomes too highly swollen and the separation and mechanical properties are lost. Thus in order to remove traces of water anotherm eiial has to be chosen, e.g. poly(vinyl alcohol). These extreme examples indicate the influence of composition on the membrane performance. 

Calculate the membrane area required and the energy consumption for a product stream of 10 m /h of air enriched to 30% oxygen in a single-stage process at zero recovery (x = x ). The feed is air containing 21% oxygen. Composite membranes are available with polydimethylsiloxane (silicone rubber) top layer of thickness 1 pm polydimethylsiloxane has a Pq, value of 600 Barrer and a selectivity factor of 2.2.The... 

For the preparation of oxygen enriched air membranes can be applied with a relatively low selectivity and a high flux. Often the vacuum mo is applied in which the permeate flow rate is negligible to feed flow rate (qj q ). For the preparation of 30% of oxygen enriched air fiequently composite membranes are applied with a silicone rubber toplayer. 

Note that the ratio of the permeability coefficient of H2 and CO by the poly-sulfone polymer matrix is 4.019 x 10 Vl0.047xlO = 40 therefore, the selectivity of the composite membrane is close to that of the polysulfone polymer matrix. It should be also noted that two important assumptions were made in the above calculation. They are (1) the permeability coefficient of the void space was assumed to be the same as that of silicone rubber, and (2) the effective thickness of the void space was assumed to be the same as that of the polymer network. This implies that the void space was completely filled with silicone rubber, and its effective thickness is the same as that of the polymer network. Furthermore, we can calculate the loss in permeability by coating. The resistance without coating is that of the porous substrate, and therefore, it is designated as / ub- With respect to hydrogen gas, it becomes... 

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