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               304                                                                         Membranes, Synthetic, Applications
























































                      FIGURE 14  Hydrogen recovery scheme in ammonia synthesis. [From R. Rautenbach and R. Albrecht (1985). Chem.-
                      Ing.-Tech. 57, 119–130.]



                                                                 membranes to offer membrane systems for smaller users,
                                                                 and have successfully engineered hybrid cryogenic and
                                                                 PSA systems, which include membranes as an integral
                                                                 component. Figure 16 illustrates the complementary roles
                                                                 of different nitrogen- and oxygen-producing technologies
                                                                 for different purity and capacity requirements.
                                                                   A commercial nitrogen enrichment system is illustrated
                                                                 in Fig. 17. Hollow-fiber membrane modules are connected
                                                                 to a compressed air feed at 70–150 psi. The feed in usually
                                                                 to the bore side of the hollow fibers. Oxygen (and water va-
                                                                 por that may be present) permeate out of the fiber into the
               FIGURE 15  Hydrogen recovery scheme in methanol synthesis.  shell and exit at low pressure. Dry, nitrogen-enriched air
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