Page 200 - Chemical and process design handbook

Speight_Part II_C 11/7/01 3:08 PM Page 2.140

2.140 MANUFACTURE OF CHEMICALS
becomes ammonium phosphate that can be sold as a fertilizer. The capro-
o
lactam can be extracted and vacuum distilled (boiling point: 139 C/12
mmHg) and the overall yield is 90 percent.
Caprolactam is also manufactured from toluene (Fig. 2) by oxidation of
o
toluene (with air) to benzoic acid at 160 C and 10 atm pressure. The ben-
o
zoic acid is then hydrogenated under pressure (16 atm) and 170 C in a
series of continuous stirred tank reactors. The cyclohexane carboxylic acid
is blended with oleum and fed to a multistage reactor, where it is converted
to caprolactam by reaction with nitrosyl sulfuric acid.
Another process utilizes a photochemical reaction in which cyclohexane
is converted into cyclohexanone oxime hydrochloride (Fig. 2), from which
cyclohexanone is produced. The yield of cyclohexanone is estimated at
about 86 percent by weight. Then, in a rearrangement reaction, the cyclo-
hexanone oxime hydrochloride is converted to e-caprolactam.
Caprolactam is used for the manufacture of nylon 6, especially fibers
and plastic resin and film. Nylon 6 is made directly from caprolactam by
heating with a catalytic amount of water.
In one process for nylon manufacture, the feedstock is nitration-grade
toluene, air, hydrogen, anhydrous ammonia (NH ), and sulfuric acid
3
(H SO ). The toluene is oxidized to yield a 30% solution of benzoic
2
4
acid, plus intermediates and by-products. Pure benzoic acid, after frac-
tionation, is hydrogenated with a palladium catalyst in stirred reactors
operated at about 170°C under a pressure of 147 psi (1013 kPa). The
product, cyclohexanecarboxylic acid, is mixed with sulfuric acid and
then reacted with nitrosylsulfuric acid to yield caprolactam.
The nitrosylsulfuric acid is produced by absorbing mixed nitrogen
oxides (NO + NO ) in sulfuric acid:
2
NO + NO + H SO → SO + 2NOHSO
2 2 4 3 4
The resulting acid solution is neutralized with ammonia to yield ammo-
nium sulfate [(NH ) SO ] and a layer of crude caprolactam that is purified
4 2
4
according to future use.