Gas permeability coefficient

Typically, laboratory experiments for gas permeability are performed on one gas at a time to simplify the interpretation of results. The separating ability of the membrane for a particular gas pair is described by the ratio of the individual gases permeability coefficients and is called the separation factor (a), where a = PJ Pb- This differs from pervaporation experiments, where it is not possible to calculate the composition of the permeant from only a knowledge of the feed composition and the rates of permeation for pure components, because the membranes usually swell in the feed liquid mixture. Therefore, the membrane s condition when it is being permeated by individual compounds can differ from its condition during permeation by a mixture. For liquid separations, mixtures are generally measured to see which components selectively permeate the membrane. The relative composition of the permeant solution is a direct measure of the separating ability of the membrane. 

The gas-permeability coefficient K of the material is obtained by measuring the gas flow J through a flat sample with thickness L under a total pressure difference AP. The gas-permeability coefficient K is a two terms sum ... 

The dependence of the gas permeability coefficient on surfactant concentration in the bulk solution is studied by the method of diminishing bubble (see Chapter 2). Fig. 3.108 presents the K(C) dependence for NaDoS bubbles at four different temperatures. 

The unique molecular packing of rod-like chains in liquid crystalline polymers (LCP) closely resembles the extended chain structure of highly oriented flexible chain polymers, suggesting that these materials are good candidates for barrier applications. Thermotropic LCP s, first developed in the early 1970 s, have been the object of much interest because of their excellent mechanical properties and ease of product fabrication. Preliminary observations have shown that a commercially available wholly aromatic thermotropic copolyester has gas permeability coefficients that are lower than those of polyacrylonitrile (4.). These results raise some fundamental questions as to the nature of the mechanism for transport of small molecules through a matrix of ordered rigid rod-like chains. 

The gas permeability coefficient (usually permeabihty to air) is determined by measuring the flow of gas under pressure through a sample. In this case the fluid is compressible and the flow can be expressed by the equation ... 

Gas permeability coefficient of silica filled PMPS membrane, at... 

Gas-Permeability Coefficient A measure of gas permeability of a barrier wall such as plastic film. Gas permeability coefficient, P, is a coelficient in Pick s first law that states that the volume (V) of a substance that penetrates a barrier wall is directly proportional to the area (A) of the wall, partial pressure differential (p) of the penetrant, and time (t) and inversely proportional to the wall thickness (s), if the wall is homogeneous in the direction of penetration. Gas permeability coefficient depends on the test temperature. 

Figure 28 shows the relationships between the amount of inorganics in the clay and the gas permeability coefficient. The gas permeabiUty coefficient decreased as the amount of added clay increased. The gas barrier performance of PPCN-5 increased by 1.7 times. It has been reported that the barrier performance of the nylon-clay nanocomposites and polymer-clay nanocomposites was improved. This barrier effect is explained as being attributed to the geometrical detour effect of the dispersed nanosized silicates. The barrier effect of PPCN, however, was smaller than that of the nylon-clay nanocomposites. hi the case of the nylon-clay hybrid, the addition of 1.8 wt % of mont-morillonite caused its hydrogen permeability to decrease to 70%. In the case of PPCN, about 3 wt % of montmorillonite must be added to obtain the same... 

Table 1,3 Gas permeability coefficients (Barrer) and selectivity of UV cross-linked polyimides (Type II)... 

A feature of PTMSN is a relatively high gas permeability coefficient P, higher than those of other addition-type polynorbomenes and comparable with permeability coefficients of... 

Table 2.11 Gas Permeability Coefficients (P) and Permselectivities (a) Values of Poly(Arylene Ether) Membranes... 

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