Effect on gas permeabilities

Eqs. (3.139)-(3.141) suggest that the rate of diffusion is much lower than the rate of gas dissolution and gas evolution from both film surfaces and the adsorption surfactant layers do not affect gas transfer. However, it is known that monomolecular films from some insoluble surfactants (e.g. cetyl alcohol) considerably decrease the rate of evaporation of the water substrate [204]. At high surface pressures the rate of evaporation can be reduced 5 to 10 times. Lipid bilayers, water and electrolytes can exert a significant effect on gas permeability, as was found in the study of the properties of vesicles (lyposomes) and flat black hydrocarbon films in aqueous medium [479]. 

Structure Level n effects on gas permeability properties of the polyimides discussed in this paper are especially Interesting when considered with regard to the role of solubility and diffusion parameters on permeability properties. From segmental shape considerations it is clear that the solubility and diffusion... 

Extended immersion of the PIM-PI membrane in alcohol obviously affects the properties of permeation. After immersion in alcohol, the residual solvents can be removed and polymer chain relaxation may be achieved in the swollen state. It was observed that both ethanol and methanol treatment have similar effects on gas permeability. PIM-PI membranes treated with methanol or ethanol for several days show higher gas permeabilities than the films cast directly from chloroform, even though these films are subjected to removal of the chloroform in a vacuum at room temperature for a few days until a constant weight of the film is achieved (Table 5.3). These effects were also observed in PIM-1, though PIM-1 has the higher permeability coefficient of the films. These phenomena indicate local interactions between low molecular weight alcohol and some binding sites on the PIM structure. It should be noted that an increase of permeability is always accompanied by a decrease in permselectivity. 

Cebe and Rimt [56] used DSC to investigate the effect of inclusion size, shape and filler surface treatment with stearic acid on the crystallinity and gas permeability of HDPE composites filled with micron sized calcite or nanosized calcium carbonate or clay. It was foimd that spherical inclusions had no effect on gas permeability whereas the plate-like inclusions reduced gas permeability and that neither the calcium carbonate nor the clay nucleated the crystallisation of HDPE imder slow cooling conditions. 

The effect of copolymer composition on gas permeability is shown in Table 9. The inherent barrier in VDC copolymers can best be exploited by using films containing Htde or no plasticizers and as much VDC as possible. However, the permeabiUty of even completely amorphous copolymers, for example, 60% VDC—40% AN or 50% VDC—50% VC, is low compared to that of other polymers. The primary reason is that diffusion coefficients of molecules in VDC copolymers are very low. This factor, together with the low solubiUty of many gases in VDC copolymers and the high crystallinity, results in very low permeabiUty. PermeabiUty is affected by the kind and amounts of comonomer as well as crystallinity. A change from PVDC to 50 wt °/ VC or 40 wt % AN increases permeabiUty 10-fold, but has Httle effect on the solubiUty coefficient. 

Robinson AV. 1982. Effect of in vitro exposure to hydrogen sulfide on rabbit alveolar macrophages cultured on gas-permeable membranes. Environ Res 27 491-500. 

Solvent-drying. After annealing at lOO C, the absorbed water inside the membranes was removed by a proprietary procedure. Its effect on gas permeation is given in Table VI. No effect is observed on the.helium and carbon dioxide permeability rates. But the permeability rates of nitrogen and methane are considerably lowered so that the separations of both systems, helium/nltrogen and carbon dloxlde/methane, are enhanced. With a value of 44.1 for helium/ nitrogen, the ideal separation factor of the external reference membrane is slightly exceeded, whereas the separation factor for CO2/CK of more than 2500 is Improved by a factor of 600. 

Henderson, G.D., Danesh, A., Tehrani, D.H., Al-Kharasi, B., 2000. The relative significance of positive coupling and inertial effects on gas condensate relative permeabilities at high velocity. Paper SPE 62933 presented at the SPE Annual Technical Conference and Exhibition, Dallas, 1-4 October. 

S. A. Stem, F. J. Onoraio, and C. Libove, The Permeation of Gases through Hollow Silicone Rubber Fibers Effects of Fiber Elasticity on Gas Permeability, AIChEJ., 23, 567 (1977). 

FIGURE 4.14 (a-e) The effect of nanoparticles (FS, Ti02) content on gas permeabilities... 

Figure 1.2 presents the effects of UV irradiation time on gas permeability and selectivity for acryl-terminated telechelic polyimide, 6FDA-TeMPD-BEI [33]. It is seen that the gas permeability decreases, while the selectivity increases. 

S. Matsui, H. Sato, T. Nakagawa, Effects of low molecular weight photosensitizer and UV irradiation on gas permeability and selectivity of polyimide membrane, J. Membr. Sci., 141,... 

S. Matsui, T. Nakagawa, Effect of ultraviolet light irradiation on gas permeability in polyimide membranes. II. Irradiation of membranes with high-pressure mercury lamp, J. Appl. Polym. 

M. Kawakami, Y. Yamashita, M. Yamasaki, M. Iwamoto, S. Kagawa, Effects of dissolved inorganic salts on gas permeabilities of immobilized liquid polyethylene glycol membranes, J. Polym. ScL, Polym. Lett. Ed., 20, 251-257 (1982). 

A series of 6FDA-based polyimides containing laterally attached p-terphenyls and biphenyls moiety was synthesized by Chung and co-workers [178] to investigate the effect of noncoplanar components on gas permeability and selectivity. The chemical structures of the polyimides are shown in Scheme 3.14. They observed that only p-terphenyl... 

The separation factor or permselectivity between two penetrants A and B, axB, is important in membrane separation systems. This factor is equal to the ratio of the downstream (permeate) mole fractions of component A relative to component B divided by the ratio of the upstream mole fractions of A relative to B. Under conditions of negligible downstream pressiue, the permselectivity is simply equal to the ratio of the permeabilities of components A and B. In addition, since the presence of one component has a negligible effect on the permeability of the other at low pressiues in rubbery materials, pure component permeabilities can often be used as good estimates of mixed-gas permeabilities ... 

The operating pressure has no effect on the permeability defined by Equation 6.114 when the gas-phase flow (slip flow and the Knudsen flow) mechanism is dominant The permeability should increase with an increase in the operating pressure when the surface flow is dominant. 

Effect of Physical Aging on Gas Permeability. Literature values of the oxygen permeability coefficient of PTMSP are strikingly variable. At room temperature, the minimum and maximum values are 3,000 and 12,000 Barrers (11J2). The unusually... 

Effects of Physical Aging on Gas Permeability and Molecular Motion in Poly(l-trimethylsilyl-l-propyne)... 

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