Barrier, gaseous diffusion permeability

In subsequent analysis of the gaseous diffusion process, the diffusion barrier will be assumed to have the properties of the French barrier listed second in Table 14.6, made by anodic oxidation of aluminum, with Pc = 1500 Torr and 7 = 15.6 X 10. Over the range of operating conditions of economic interest, the specific permeability y will be treated as independent of pressure and temperature. 

Membrane separation. Here the separation takes place by a selective diffusion of one or more gaseous components across a semi-permeable barrier. In most applications, the membrane is a micro-porous solid, but there are also liquid membranes. The feasibility may be evaluated by using an index of perselectivity aq defined by means of solubility (S/) and diffusivity (D,) ratios as follows ... 

Membrane and Barrier Implications. In the case of typical rubbers, crankshaft and other related rotational motions of the repeat units are so large that little difference in diffusion coefficients exists for simple gaseous penetrants, the sizes of which differ by less than a few hundredths of a nanometer. Of course, since permeation is a solution-diffusion process, membranes or selective barriers do not operate strictly on the basis of size selection. Under a fixed partial pressure driving force for component i, the flux through a material of given thickness i is determined by the permeability, as can be seen by rearrangement of equation 24. 

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