Hollow-fiber separator composition-dependent permeability

The work of Pinnau and co-workers with asymmetric films was the first to show dramatic time-dependent gas transport properties (127,128). Later, Pfromm and co-workers showed similar behavior in free-standing polyimide and polysul-fone films (129). Figure 34 shows that for a 0.5-/xm thick polyimide film, the N2 permeability decreases by approximately 50% over a 6000-h period, while the He/N2 selectivity increases by approximately 25% in the same time period. The decrease in permeability is not nearly as dramatic for the thick films. Rezac and co-workers (130) and McCaig and co-workers (131) saw similar effects in pol5dmide/ceramic and polycarbonate/ceramic composite membranes, respectively. Chung and Teoh observed the same effects in asymmetric hollow fiber gas separation membranes (132). 

---