Single-stage membrane separations

Oxygen-Nitrogen Because of higher solubility, in many polymers, O2 is faster than N2 by a factor of 5. Water is much faster still. Since simple industrial single-stage air compressors provide sufficient pressure to drive an air-separating membrane, moderate purity N2 (95-99.5%) may be produced in low to moderate quantities quite... 

Figure 7. An example of the use of deuterated GA s as internal standards for the quantitation of GA s in plant extracts. [2a-zH1]GAts was added to an extract of young pea seeds in order to quantitate GA29 (cf. 25). Ions in the region of the molecular ion were scanned. The acidic fraction from the pea seed extract was run as the Me TMS derivative on a MS 30 coupled to a Pye 104 GC via a single-stage silicone membrane separator (34).

As a general rule, gas separation by membranes is most attractive in applications where a product purity of 95% or lower is acceptable or the feed flow-rate is not too high. As the required purity approaches 100%, the membranes become less cost effective than other separation processes. This is particularly true with single-stage units. For more stringent applications, some traditional separation processes are preferred or required to integrate with the membrane system. 

DERIVATIONS AND CALCULATIONS FOR SINGLE-STAGE MEMBRANE SEPARATIONS 685... 

Figure 19.17. Single-stage membrane separation with perfect mixing.

E.J. Hoffman, Membrane Separations Technology Single-Stage, Multistage, and Differential Permeation, Gulf Professional Publishing, an Imprint of Elsevier Science, Amsterdam, 2003. 

Walawender WP and Stem SA. Analysis of membrane separation parameters. 2. Countercurrent and cocurrent flow in a single permeation stage. Sep. Sci. 1972 7 553-584. 

With the proper choice of membrane material, a membrane separator can achieve significant separations in a single stage. Indeed, as we shall see, it usually turns out that multistage operations with membranes are not economical (compared to cryogenic distillation). Thus most industrial applications of membranes do not require very high purity products. 

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