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4.1 Introduction
Just after the termination of World War II, the CEO of one
of the largest industrial gas companies advised his engi-
neering department not to be too complacent in regard to
the expanding sales of industrial gases produced by cryo-
genic systems. Some day an enterprising engineer would
develop a machine in which air will be fed through one
end, and its components will come out separately from the
other. Little did he realize at the time that his off-the-cuff
statement was prophetic. About 5 years later, a young engi-
neer delivered a technical paper at an AIChE meeting in
New York City, demonstrating that it was possible to sepa ...