Page 368 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

P1: GLQ Final Pages
Encyclopedia of Physical Science and Technology EN009K-419 July 19, 2001 20:57

Membranes, Synthetic, Applications 303

FIGURE 13 Hydrogen separation applications in the refinery. [From S. Leeper et al. (1984). Report No. EGG-2282,
EG&G Idaho, Inc. (Report to U.S. Department of Energy), and D. L. MacLean et al. (1983). Hydrocarbon Processing
62, 47–51.]

other hydrogen-rich streams in the chemical process metal working operations; and retarding spoilage of foods
industry. during transport and storage.
Until the commercialization of membrane-based air
separation systems in the mid-1980s, oxygen and nitro-
2. Air Separation
gen have traditionally been supplied in bulk by cryogenic
The products of air separation are oxygen and nitrogen at systems via fractional distillation of liquified air, and by
various purities. Oxygen-enriched air containing 30–40% PSA. In many cases those conventional technologies re-
O 2 can be used to increase the efficiency of combustion main competitive, especially for large-scale installations
and other oxidation processes. Biochemical processes and where their cost per unit capacity is favorable. By compar-
organic chemical oxidations also benefit from the use of ison, membrane systems require lower capital investment
oxygen-enriched air to increase reaction rates and yields; and operate at high efficiency over a wider range of re-
an advantage of using membrane-processed air is that air- duced capacities. There are no expenses associated with
borne impurities are thoroughly removed, thus reducing storage and transportation of liquified gases. Mechanical
contamination. Nitrogen at 90–99% purity provides an problems or performance degradation due to inadequate
inert atmosphere useful for various purposes: blanketing feed air pretreatment are less likely to develop than in
fuel storage tanks and pipelines to minimize fire hazards; PSA. Recognizing the advantages of membrane systems,
reducing oxidation during annealing, sintering, and other major gas producers have collaborated with suppliers of