Page 50 - Chemical and process design handbook

Speight_Part 1_N&O 11/7/01 3:02 PM Page 1.36

OXIDATION

Oxidation is the addition of oxygen to an organic compound or, conversely,
the removal of hydrogen.
Reaction control is the major issue during oxidation reactions. Only par-
tial oxidation is required for conversion of one organic compound into
another or complete oxidation to carbon dioxide and water will ensue.
The most common oxidation agent is air, but oxygen is frequently used.
Chemical oxidizing agents (nitric acid, dichromates, permanganates, chromic
anhydride, chlorates, and hydrogen peroxide) are also often used.
As examples of oxidation processes, two processes are available for the
manufacture of phenol, and both involve oxidation. The major process
involves oxidation of cumene to cumene hydroperoxide, followed by
decomposition to phenol and acetone. A small amount of phenol is also
made by the oxidation of toluene to benzoic acid, followed by decomposi-
tion of the benzoic acid to phenol.
Benzoic acid is synthesized by liquid-phase toluene oxidation over a
cobalt naphthenate catalyst with air as the oxidizing agent. An older
process involving halogenation of toluene to benzotrichloride and its
decomposition into benzoic acid is still used available.
Maleic acid and anhydride are recovered as by-products of the oxidation
of xylenes and naphthalenes to form phthalic acids, and are also made
specifically by the partial oxidation of benzene over a vanadium pentoxide
(V O ) catalyst. This is a highly exothermic reaction, and several modifi-
2 5
cations of the basic process exist, including one using butylenes as the
starting materials.
Formic acid is made by the oxidation of formamide or by the liquid-
phase oxidation of n-butane to acetic acid. The by-product source is
expected to dry up in the future, and the most promising route to replace it
is through carbonylation of methanol.
Caprolactam, adipic acid, and hexamethylenediamine (HMDA) are all
made from cyclohexane. Almost all high-purity cyclohexane is obtained
by hydrogenating benzene, although some for solvent use is obtained by
careful distillation of selected petroleum fractions.

1.36