Permeability through polymers

The more permeable component is called the. st ga.s, so it is the one enriched in the permeate stream. Permeability through polymers is the product of solubihty and diffusivity. The diffusivity of a gas in a membrane is inversely proportional to its kinetic diameter, a value determined from zeolite cage exclusion data (see Table 22-23 after Breck, Zeolite Molecular Sieves, Wiley, NY, 1974, p. 636). 

The diffusion of oxygen through polymer films has been examined by a number of workers. Guruviah measured the permeability to oxygen of films cast from five paints (Tabic 14.4) and compared the results with the... 

Direct fluorination of polymer or polymer membrane surfaces creates a thin layer of partially fluorinated material on the polymer surface. This procedure dramatically changes the permeation rate of gas molecules through polymers. Several publications in collaboration with Professor D. R. Paul62-66 have investigated the gas permeabilities of surface fluorination of low-density polyethylene, polysulfone, poly(4-methyl-1 -pentene), and poly(phenylene oxide) membranes. 

When the crystallinity of polyethylenes is increased, the gas permeability through the film decreases. The factors involved are the tortuosity of the gas path through the amorphous phase, and the effect of the crystals in restricting the mobility of the amorphous polymer chains (chain immobilisation factor). The logarithm of the permeability of nitrogen, argon and carbon dioxide decreased almost linearly with increased crystallinity of PE, with the ratio of the gas values remaining almost constant for a particular PE. 

Part A of the scheme represents the initial state. Two parts of the system are separated by semi-permeable membrane. Polymer (represented by ) is surrounded by molecules of monomer, M, and molecules of solvent, S. Composition of mixed solvent (solvent and monomer) is initially uniform. If the interaction between monomer and polymer is stronger than that between polymer and solvent, the diffusion through the membrane takes place. Monomer molecules are associated with macromolecules while molecules of solvent are displaced to the right part of the vessel. 

The values of permeability coefficients for He, O2, N2, CO2, and CH4 in a variety of dense (isotropic) polymer membranes and the overall selectivities (ideal separation factors) of these membranes to the gas pairs He/N2,02/N2, and CO2/CH4 at 35°C have been tabulated in numerous reviews (Koros and Heliums, 1989 Koros, Fleming, and Jordan et al., 1988 Koros, Coleman, and Walker, 1992). Moreover, several useful predictive methods exist to allow estimation of gas permeation through polymers, based on their structural repeat units. The values of the permeability coefficients for a given gas in different polymers can vary by several orders of magnitude, depending on the nature of the gas. Thevalues oftheoverall selectivities vary by much less. Particularly noteworthy is the fact that the selectivity decreases with increasing permeability. This is the well-known inverse selectivity/permeability relationship of polymer membranes, which complicates the development of effective membranes for gas separations. 

Equation (6.173) implies that the release rate is governed by the porosity of the membrane, which influences the permeability the polymer material, which influences the semipermeability of the membrane the thickness and surface area of the membrane the solubility and osmotic pressure and the amount of drug in the core. Figure 6.41 shows the effect of osmotic pressure on the release of KC1 from MPOPS. By extrapolating the linear line to zero osmotic pressure, the release rate of drug by diffusion through the microporous membrane structure can be obtained. 

It will be clear that the diffusive transport (permeability) of water in and through polymers is of extreme importance, since all our clothes are made of polymeric materials and water vapour transport is one of the principal factors of physiological comfort. 

One of these properties is the replication of the catalyzing particle shape by the generated polymer. The product flakes produced are 15-20 times larger than the catalyst particles [216]. Various opinions exist concerning monomer permeability through the polymer layer towards the polymerization centres. 

Oxygen transport measurements were conducted at 25°C, 0% and 50% relative humidity RH, 1 atm partial oxygen pressure difference using the commercially manufactured diffusion apparatus OX-TRAN 2/20 (Modem Control Inc.). This apparatus employs a continuous-flow method (ASTM-D 3985-81) to measure oxygen flux, J(t), through polymer films or thin sheets. In order to obtain the diffusion coefficient and to accurately determine the permeability coefficient, the data, flux, J(t), were fitted to the solution of Fick s second law ... 

Fig. 7. Gas permeability through different types of polymers and substituted polyacetylenes (25 °C)...

The permeability data in Table 7.10 and other data show that the polarity of the substituent group on the polymer backbone (such as poly[bis(phenoxy)phosphazene] or PPOP) has a significant impact on the membrane permeability. The more polar gas (i.e. S02) the more easily it permeates a polar polymer (i.e., m-F-PPOP) and a less polar gas (i.e., CO2) exhibits a lower permeability through a more polar membrane (i.e., SO3-PPOP). This seems to provide a vast opportunity for chemically designing an inorganic polymer membrane for a particular separation application [Peterson et al., 1993]. 

Polymer films have been obtained by plasma polymerization of hexafluorobenzene, N-vinylpyrrolidine, and chloracrylonitrile (Munro). Higuchi et al. have shown that irradiation of an azobenzene-modified poly(Y-methyl-L-glutamate-CO-L-glutamic acid) in bilayer membrane vesicles of distearyldimethylammonium chloride leads to trans-cis isomerization of the polymer this leads to transfer of the polypeptide from the hydrophobic bilayer membrane interior to the hydrophilic surface. As a result, there was a decrease in the ion permeability through the bilayer membrane and the formation of intervesicular adhesion. Eisner and Ritter have prepared photosensitive membranes from an aromatic polyamide and a cinnamate that incorporates a liquid crystalline component. 

Patil, G.S., Bora, M. and Dutta, N.N. (1995). Empirical Correlations for Prediction of Permeability of Gases Liquids Through Polymers. J.Memb.ScL, 101,145-152. 

Post-water drive. The water cut continues increasing and injection pressure decreases. Water breaks through high permeability channels. Polymer concentration decreases and liquid offtake rate increases. About 11% of the cumulative oil is produced in this period. 

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