Permeability oxygen versus nitrogen

In the early 1990s Robeson (1993) found an upper limit to the performance of polymer membranes in the commercially important separation of oxygen and nitrogen from air. On a log-log plot of selectivity versus oxygen permeability (a Robeson plot), the upper bound plots as a straight line (see Problem 17.D17 for more details). Although theoretical reasons for this limit have not been found, very few new membranes have been developed that are able to perform better than Robeson s limit. Membrane research has focused on ways to do better than Robeson s upper limit. 

D17. On a Robeson plot (a log-log plot of selectivity versus oxygen permeability in Barrers) the upper bound for separation of oxygen from nitrogen plots as a straight line. Approximate values of the end points are for Pq2 = 0.0001 Barrers, 002. 2 = 42 and for Pq2 = 10,000 Barrers, ao2-N2 ... 

Figure 8.24 Oxygen/nitrogen selectivity as a function of oxygen permeability. This plot by Robeson [11] shows the wide range of combination of selectivity and permeability achieved by current materials. Reprinted from J. Membr. Sci. 62, L.M. Robeson, Correlation of Separation Factor Versus Permeability for Polymeric Membranes, p. 165. Copyright 1991, with permission from Elsevier...

Figures 1, 2 and 3 plot the oxygen permeability coefficients (Po2) versus the separation factor against nitrogen (Pq2/Pn2) of the present polymers dong with those of poly(DMS) and poly(TMSP).

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