Dimethyl silicone membranes

Research on removal of noble gases by permeation method with dimethyl silicon membranes was carried out in Oak Ridge National Laboratory [160]. On the basis of experimental work, the calculations for different industrial cascades separating krypton and xenon from the space of molten salt and sodium cooled breeder reactor or from the off gas from a plant processing spent reactor fuel were performed. 

Water can be removed from methanol by a membrane of polyvinyl alcohol cross-linked with polyacrylic acid, with a separation factor of 465.204 A polymeric hydrazone of 2,6-pyridinedialdehyde has been used to dehydrate azeotropes of water with n- and /-propyl alcohol, s- and tort butyl alcohol, and tetrahydrofuran.205 The Clostridium acetobutylicum which is used to produce 1-butanol, is inhibited by it. Pervaporation through a poly(dimethyl-siloxane) membrane filled with cyclodextrins, zeolites, or oleyl alcohol kept the concentration in the broth lower than 1% and removed the inhibition.206 Acetic acid can be dehydrated with separation factors of 807 for poly(4-methyl-l-pentene) grafted with 4-vinylpyridine,207 150 for polyvinyl alcohol cross-linked with glutaraldehyde,208 more than 1300 for a doped polyaniline film (4.1 g/m2h),209 125 for a nylon-polyacrylic acid membrane (5400 g/m2h), and 72 for a polysulfone.210 Pyridine can be dehydrated with a membrane of a copolymer of acrylonitrile and 4-styrenesulfonic acid to give more than 99% pyridine.211 A hydrophobic silicone rubber membrane removes acetone selectively from water. A hydrophilic cross-linked polyvinyl alcohol membrane removes water selectively from acetone. Both are more selective than distillation.212... 

Gas diffusion from a donor stream—in which the analyte chemically is converted to a volatile species—into an acceptor stream, where the two streams run in parallel separated by a suitable gas-permeable membrane, is a highly selective technique particularly well suited for adaptation into FI A, because in nonsegmented streams the diffusion unit can be made extremely small and the flow rates may be considerably reduced. Although in the first FI A gas-diffusion method, developed by Baadenhuijsen and Seuren-Jacobs [57] for the determination of carbon dioxide in plasma, a nonporous dimethyl silicone rubber membrane was used, hydrophobic microporous membranes such as Teflon or isotactic polypropylene have proven to be more versatile diffusion barriers, since they can be used for a greater variety of gases. 

Figure 9-33. Selectivity of different polymer membranes to He-N2 separation as a function of nitrogen permeability (n, incm /(cm x atm x s)) (1) polyvinylidenechloride (2,4)polyethylene terephthalafe (3) polyvinylfluoride (5) polyvinylchloride (6) polyamide (7) plasfified polyvinylidene chloride (8) cellulose nitrate (9) polypropylene (lO)fluoroplast (26) (ll)co-polymer of isoprene (74%) and acryl-nitryl (26%) (12, 18, 20) different co-polymers of butadiene and acryl-rritryl (13) polyacrylate (14) polycarbonate (15) polyisobutylene (16) bulyl latex (17) co-polymer of vinyl chloride and vinyl acetate (19, 37) butyl acetate of cellulose (21) polyethylene vinyl acetate (22) polybutadiene (23) special polymer SKI-3 (24) natural latex (25) nitryl silicon latex (26) dimethyl silicon latex (27) special polymer SKS-30 (28) special polymer SKMS-50 (29) special polymer SKMS-30 (30, 34, 35) high-density, medium-densily, and low-density polyethylene (31) polyethylene with 5% soot (32) co-polymer of ethylene (90%) and propylene (10%) (33) co-polymer of ethylene (96.5%) and vinyl acetate (3.5%) (36) triacetate of cellulose (38) acetate cellulose (39) polystyrene.

Hydrophilic membranes have a higher difference in the flow due to pure solvent polarity when compared with hydro-phobic membranes. According to Bhannshali et al. [22], the permeation of pure solvents in hydrophilic membrane (composed of aromatic PA) shows that polar solvents (methanol, ethanol, and isopropanol) have significantly higher flow (8-10 times) than nonpolar solvents (pentane, hexane, and octane). In contrast, the flow of nonpolar solvents was two to four times greater than the flow of polar solvents on hydro-phobic membranes (consisting of dimethyl silicone). 

MEMBRANE SEPARATIONS TECHNOLOGY Table A1.6 Gas Selectivity for Dimethyl Silicone Polymer ... 

The DOPH membrane did not respond to picric acid, which is a strong bitter substance. We, therefore, studied a response by a different lipid membrane [12], The synthesized lipid is dialkyl-dimethyl-ammonium, which has two hydrocarbon chains and an ammonium group positively charged. This lipid was cast on a silicon film with one hole, 100 pm in diameter. It was shown that picric acid changes the membrane potential of this membrane largely. 

Thus, both elastomeric and nonelastomeric polymers are used as PV membrane for selective removal/recovery of organics from water. The polymers used for this class of application are listed in Table 8.3. Although some of the polymers listed in Table 8.3 are readily available and less expensive, the standard for hydrophobic membranes has been set by poly(dimethyl siloxane) a silicone rubber membrane popularly abbreviated as PDMS. This is a... 

Biomedical Applications. Dillon (114) synthesized IPN membranes from polytetrafluoroethylene (PTFE) and poly(dimethyl siloxane) (PDMS) (see Perfluorinated Polymers, Polytetrafluoroethylene Silicones). These flexible membranes are used for a variety of medical purposes, especially second-degree bum care. These materials are commercially available under the trade name Silon. The PDMS component rapidly transports body fluids away from the bum site, while the PTFE provides mechanical strength. The PTFE is also waterproof, so that when the woimd area is washed, water beads up on the film. An additional valuable feature is that the Aims are highly transparent, so that the doctor can observe the wound area easily, making early treatment of any infection or other problem possible. 

In liquid mixtures of type (2), the solutions of primary interest are azeotropic and other mixtures containing variable amounts of water in organics dehydration of organic solvents containing very small amounts of water. Removal of water from azeotropic mixtures of ethanol-water, isopropanol-water, etc., is extensively practiced using polymeric membranes (of crosslinked polyvinyl alcohol) that are highly polar and selective for water. On the other hand, the membranes that are used to remove VOCs selectively from aqueous solutions are usually highly nonpolar rubbery polymeric membranes, e.g. dimethyl siloxane (silicone rubber). 

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