科研之友
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摘要
In the present work, zeolite membranes were for the first time evaluated for separations at cryogenic temperatures. MFI membranes were evaluated with a feed of synthetic air, at varying feed pressures between 1 and 5 bar and a sweep stream of helium at a constant pressure of 1 bar for temperatures in the range 77-1101K. When the feed pressure was 1 bar, the highest O-2/N-2 separation factor was 3.9, corresponding to a separation selectivity of 4.1, with an oxygen permeance of 6.7 x 10(-7) mol m(-2) S-1 Pa-1 at the optimum temperature 79 K. This membrane performance is just above the upper bound in the 2008 Robeson selectivity-permeability plot for polymeric membranes. As the feed pressure increased, the maximum separation factors for 02/N2 decreased while the optimum separation temperatures increased. It is inferred that the separation is governed by condensation and effective transport of oxygen in the zeolite pores under these conditions. However, the adsorption of nitrogen, and thereby the transport of nitrogen, likely increases as the pressure is increased, which reduce the selectivity. To test this hypothesis, the feed was diluted with 33% helium and the total feed pressure was maintained at I bar, corresponding to a partial pressure of air of 0.66 bar. In this case, the maximum separation factor increased to 4.3, which supports the proposed separation mechanism.
- 出版日期2014-7-1
