In industry, propionic acid is prepared by hydroxycarboxylation of ethylene.
It is also formed as a result of propionic acid fermentation. Propionic acid is a by-product of many processes, which makes it possible to use them for its isolation.
Propionic acid can be obtained by twoBy means of propionic acid fermentation and hydrocarboxylation of ethylene. The second method is currently considered the most common in the industry. There are other less well known methods for the production of propionic acid, for example, recovery from oil, catalytic oxidation of propionic aldehyde, separation of hydrocarbons with a carbon number of 4-10 as a by-product in the vapor-phase oxidation of hydrocarbons.
Hydroxycarboxylation of ethylene
The production of propionic acid was first realized by BASF in this way. It was characterized by a high yield of the final product (about 95%), but had a number of drawbacks:
1) The process required stringent conditions: the pressure reached 25-30 MPa, the temperature was about 300 oC.
2) The catalysts were carcinogenic and strongly corrosive substances - nickel carbonyl and hydrogen iodide, respectively.
Later on the basis of VNIINeftekhimii this methodReceipt was finalized. As a result of the replacement of aggressive catalysts with the cobalt-pyridine complex [Co (Py) 6] [Co (CO) 4] 2, the synthesis conditions became softer, which were now carried out in one step. The temperature was lowered to 150-170 oC, and the pressure was reduced to 5-15 MPa. Disadvantages of this method are:
1); A slight decrease in the yield of the final product to 92%.
2) Formation of a by-product of diethyl ketone (5-7%). However, it has its own application.
The equation for the synthesis of propionic acid in a single step: CH2 = CH2 + CO + H2O? CH3CH2COOH
Propionic acid fermentation
Propionic acid fermentation is carried outPropionic acid anaerobic bacteria of the genus Propionibacterium. Acid is formed as the final product of their vital activity as a result of absorption of carbohydrates. In the presence of oxygen, fermentation does not occur, since an oxidative process is carried out.
First, bacteria metabolize carbohydrates into a wholeA number of products, among which is propionic acid. Here it is not the final product. The formed carbon dioxide is fixed and, when combined with pyruvic acid, it turns into oxaloacetic acid, which then turns into succinic acid. Succinic acid is decarboxylated to form propionic acid, the final fermentation product. The scheme of fermentation can be written as follows:
3C6H12O6? 4CH3CH2COOH + 2CH3COOH + 2CO2? + 2H2O + E.