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J. Izydorczyk, J. Sałwiński


Transport of CO2, H2, N2 and mixtures thereof through polyetherimide Ultem 1000 membranes


Polimery 1999, No 7-8, 541


DOI: dx.doi.org/10.14314/polimery.1999.541


Summary

Permeabilities of CO2, H2, N2 and mixtures thereof through polyetherimide Ultem 1000 membranes were measured at a temperature of 293 К and at pressure differences of 0—1.82 MPa. The transporting properties of the membranes were stabilized by long-term treatment with the penetrant gases. The penetrant's conditioning activity, which manifests itself as a hysteresis in the permeability vs. pressure plot, was found to occur with CO2, but not with N2. In the first cycle measurements conducted with first increasing and then decreasing pressure differences, the permeability of CO2 through unconditioned membranes was found to increase invariably. In subsequent cycles, the permeability hysteresis is seen to have progressively decreased and, with the time of membrane—carbon dioxide contact exceeding 24 hours (Fig. 2), to have completely disappeared. Again, in the first cycle of measurements carried out at increasing and then decreasing pressure differences, the permeability of hydrogen showed a hysteresis. This hysteresis differs in nature from the former: here the permeability decreases (Fig. 5). In the second cycle of measurements the hydrogen hysteresis did not occur any longer. The hydrogen's conditioning effect was unstable and could be completely eliminated by changing the gas in the diffusion chamber. Such an effect has not been reported before. The permeabilities of the gases examined were correlated by an empirical equation (eqn. 6, coefficients in Table 1). In binary mixtures, gas permeabilities were found to be essentially different from those of pure gas components. The real selectivity of membranes toward mixtures was found to be much inferior to that inferred from the individual-gas permeabilities (Fig. 8).


Keywords: permeability of pure gases and binary gas mixtures through membranes, polyetherimide membranes, hystereses of hydrogen and carbon dioxide permeabilities, ideal and real selectivity of membranes

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