Page 370 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering
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Encyclopedia of Physical Science and Technology EN009K-419 July 19, 2001 20:57
Membranes, Synthetic, Applications 305
FIGURE 16 “Technology maps” showing feasibility of various air separation technologies for (a) nitrogen generation
and (b) oxygen enrichment, using membranes compared to competitive technologies.
leftinsidethefibersiscollectedatapressureslightlybelow
that of the feed. Increasing the residence time of the feed
air through the hollow fiber bundle reduces product out-
put, but also results in more thorough removal of oxygen.
By accepting a relatively low yield (<40% recovery), up
to 99.5%-pure nitrogen can be obtained. The membranes
available today are between three- to seven fold more per-
meable to oxygen than to nitrogen. With the most selective
of these membranes, both oxygen-enriched air and high-
purity nitrogen can be produced from the same system.
However, the purity of oxygen is limited to 45–50% with
present membranes because of the significant quantity of
nitrogen entering the permeate stream.
Considerable effort is being devoted to developing new
polymeric membrane materials. A special type of oxygen-
enrichment membrane has also been explored, which con-
FIGURE 17 Compact nitrogen enrichment membrane system. sists of a solvent immobilized within a microporous solid
(Courtesy Air Liquide.) support (Fig. 7D). Dissolved in the liquid is a carrier