Common Production of Acetic Acid

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Prior to the commercialization of the Monsanto process, most acetic acid was produced by acetaldehyde oxidation. This is still the second most important manufacturing method, although it is generally not competitive with the carbonylation of methanol. Acetaldehyde can be prepared by hydrat

Acetaldehyde oxidation

Prior to the commercialization of the Monsanto process, most acetic acid was produced by acetaldehyde oxidation. This is still the second most important manufacturing method, although it is generally not competitive with the carbonylation of methanol. Acetaldehyde can be prepared by hydration of acetylene. This was the dominant technology in the early 1900s.

 

Light naphtha components are easily oxidized to peroxides by oxygen or even air, which decompose into acetic acid according to the chemical equation, illustrated with butane:

2 C4H10 + 5 O2 → 4 CH3CO2H + 2 H2O

 

This oxidation requires metallic catalysts, such as manganese, cobalt, and chromium naphthenates.

 

The reaction typically takes place at temperatures and pressures designed to be as hot as possible, while still maintaining butane as a liquid. Typical reaction conditions are 150 °C (302 °F) and 55 ATM. Byproducts may also be formed, including butanone, ethyl acetate, formic acid, and propionic acid. These byproducts also have commercial value and can be modified to produce more when needed. However, the separation of acetic acid from these by-products increases the cost of the method.

 

Under conditions similar to butane oxidation and using similar catalysts, oxygen in air can oxidize acetaldehyde to produce acetic acid.

 

2 CH3CHO + O2 → 2 CH3CO2H

 

Using modern catalysts, the acetic acid yield of the reaction can be greater than 95%. The main by-products are ethyl acetate, formic acid and formaldehyde, which have lower boiling points than acetic acid and are easily separated by distillation.

 

Ethylene oxide

Acetaldehyde can be prepared from ethylene by the Wacker process and then oxidized as described above.

 

More recently, chemical company Showa Denko opened an ethylene oxidation plant in Oita, Japan, in 1997 to commercialize a cheaper single-stage conversion of ethylene to acetic acid. The process is catalyzed by palladium metal catalysts supported on heteropoly acids such as silicotungstic acid. Similar processes use the same metal catalysts on silicotungstic acid and silica:

C2H4 + O2 → CH3CO2H

 

For small plants (100-250 kt/a), it is considered competitive with methanol carbonylation, depending on the local price of ethylene. The method will be based on selective oxidation of ethylene and ethane to acetic acid using a novel selective photocatalytic oxidation technique. Unlike traditional oxidation catalysts, the selective oxidation process will use ultraviolet light to produce acetic acid at ambient temperature and pressure.