Permselectivity groups

While Freeman (79) has developed a theory about the upper bound line depending on gas size, condensability, and an adjustable parameter, another direction was taken by Robeson et al. (78), who developed a group contribution (80) approach to predict permselectivity. The intent of the latter is to maximize the proximity to the upper bound line based on a knowledge of the permeability contribution of each specific group in a wide variety of polymers. Ideally polymers synthesized on the basis of the most permselective groups would yield the best possibility to increase selectivity. 

Quantitative analytical treatments of the effects of mass transfer and reaction within a porous structure were apparently first carried out by Thiele (20) in the United States, Dam-kohler (21) in Germany, and Zeldovitch (22) in Russia, all working independently and reporting their results between 1937 and 1939. Since these early publications, a number of different research groups have extended and further developed the analysis. Of particular note are the efforts of Wheeler (23-24), Weisz (25-28), Wicke (29-32), and Aris (33-36). In recent years, several individuals have also extended the treatment to include enzymes immobilized in porous media or within permselective membranes. The important consequence of these analyses is the development of a technique that can be used to analyze quantitatively the factors that determine the effectiveness with which the surface area of a porous catalyst is used. For this purpose we define an effectiveness factor rj for a catalyst particle as... 

Besides Knudsen diffusion, permselective transport of gases can occur by various mechanisms involving molecular scale interactions of the sorption-diffusion type. These can be broadly classified into three groups as described below and pictured in Fig. 7. 

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