Dear Editor,
One of "the 12 Principles of Green Chemistry" (CEN, August 18,
2008,
p. 64) is concerned with "design for energy efficiency"
and says that "if possible, synthetic methods should
be conducted at ambient temperature and pressure".
I was also told the same when I studied chemistry more than 30 years
ago, but it is a myth. The correct is that, for
energy efficiency and heat integration purposes, an exothermic
reaction should be conducted at a high temperature, and an endothermic
reaction at a low temperature.
This follows from the laws of thermodynamics and the Carnot factor. For
gas phase reactions, it is often optimal to use high
pressure in order to increase reaction rates and reduce equipment
sizes.
Sigurd Skogestad
Professor of Chemical Engineering, NTNU, Trondheim, Norway
Comment
See also page 269-270 ("Choice of reaction conditions") in my recently
published textbook:
Sigurd Skogestad, "Chemical and Energy Process Engineering", CRC Press
(2009).
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