Page 38 - Chemical and process design handbook

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HYDRATION AND

HYDROLYSIS

Ethyl alcohol is a product of fermentation of sugars and cellulose but the
alcohol is manufactured mostly by the hydration of ethylene.
An indirect process for the manufacture of ethyl alcohol involves the dis-
solution of ethylene in sulfuric acid to form ethyl sulfate, which is
hydrolyzed to form ethyl alcohol (Fig. 1). There is always some by-product
diethyl ether that can be either sold or recirculated.

3CH =CH + 2H SO → C H HSO4 + (C H ) SO
2 2 2 4 2 5 2 5 2 4
C H HSO + (C H ) SO + H O → 3C H OH + 2H SO
2 5 4 2 5 2 4 2 2 5 2 4
C H OH + C H HSO → C H OC H
2 5 2 5 4 2 5 2 5
The conversion yield of ethylene to ethyl alcohol is 90 percent with a 5 to
10 percent yield of diethyl ether (C H OC H ).
2 5 2 5
o
A direct hydration method using phosphoric acid as a catalyst at 300 C
is also available (Fig. 2):
CH =CH + H O → C H OH
2 2 2 2 5
and produces ethyl alcohol in yields in excess of 92 percent. The con-
version per pass is 4 to 25 percent, depending on the activity of the cata-
lyst used.
In this process, ethylene and water are combined with a recycle stream
in the ratio ethylene/water 1/0.6 (mole ratio), a furnace heats the mixture
o
to 300 C, and the gases react over the catalyst of phosphoric acid absorbed
on diatomaceous earth. Unreacted reagents are separated and recirculated.
By-product acetaldehyde (CH CHO) is hydrogenated over a catalyst to
3
form more ethyl alcohol.
Iso-propyl alcohol is a widely used and easily made alcohol. It is used in
making acetone, cosmetics, chemical derivatives, and as a process solvent.
There are four processes that are available for the manufacture of iso-propyl
alcohol:

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