Page 70 - Chemical and process design handbook

Speight_Part II_A 11/7/01 3:16 PM Page 2.11

ACETIC ACID

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Acetic acid (ethanoic acid, vinegar acid, CH CO H, melting point 16.6 C,
3 2
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boiling point: 117.9 C, density: 1.0490, flash point: 43 C, ignition tem-
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perature 465 C) is a colorless, pungent liquid that is miscible with water,
alcohol, and ether in all proportions.
Acetic acid is available commercially in several concentrations: (1) glacial
acetic is approximately 99.7% glacial acetic acid with water the principal
impurity, (2) reagent grade acetic acid generally contains 36% acetic acid by
weight, and (3) commercial aqueous solutions are usually 28, 56, 70, 80, 85,
and 90% acetic acid.
Acetic acid is the active ingredient in vinegar, in which the content
ranges from 4 to 5% acetic acid. Acetic acid is classified as a weak,
monobasic acid (-CO H) but the three hydrogen atoms linked to the carbon
2
atom (CH ) are not replaceable by metals.
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Acetic acid is manufactured by three processes: acetaldehyde oxidation,
n-butane oxidation, and methanol carbonylation.Ethylene is the exclusive
organic raw material for making acetaldehyde, 70 percent of which is fur-
ther oxidized to acetic acid or acetic anhydride. The single-stage (Wacker)
process for making acetaldehyde involves cupric chloride and a small
amount of palladium chloride in aqueous solution as a catalyst.
CH =CH + H O + PdCl → CH CHO + 2HCl + Pd 0
2 2 2 2 3
The yield is 95 percent and further oxidation of the acetaldehyde produces
acetic acid (Fig. 1).
2CH CHO + O → 2CH CO H
3 2 3 2
A manganese or cobalt acetate catalyst is used with air as the oxidizing
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agent in the temperature and pressure ranges of 55 to 80 C and 15 to 75 psi;
the yield is 95 percent.
The second manufacturing method for acetic acid utilizes butane from
the C petroleum stream rather than ethylene. A variety of products is
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formed but conditions can be controlled to allow a large percentage of
acetic acid to be formed. Cobalt, manganese, or chromium acetates are cat-

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