Propanoic production methods include chemical synthesis and microbial fermentation. At present, propionic acid is mainly produced by chemical synthesis in industry. Propionaldehyde oxidation, Rapa method and light hydrocarbon oxidation are the most commonly used methods in propionic acid production industry. In addition, acrylonitrile method, ethanol carbonyl method, n-propanol oxidation method, propane (butane, paraffin) liquid phase oxidation method, etc. can also be used in the production of propionic acid, but due to the large investment in equipment and other reasons, it has not been used in practice so far. .
Propionaldehyde Oxidation Method At present, in industrial production, ethylene, carbon monoxide and hydrogen are used as raw materials, and propionic acid is prepared by hydroformylation of ethylene under the catalysis of cobalt carbonyl or rhodium carbonyl. Propionaldehyde oxidation process is mature, and it is currently the production method of propionic acid with the largest output. The main disadvantage of this method is that the process is complicated, the equipment is various, and the requirements for equipment and pipeline materials are relatively high.
The Repper method, also known as the ethylene oxo method, is a patent of the German BASF company. It uses ethylene as raw material to react with carbon monoxide and water under the catalysis of nickel carbonyl to generate propionic acid. The reaction is carried out under the conditions of 250-320°C and 10-30MPa. Carbonyl complexes of cobalt, iron, rhodium, iridium, platinum, palladium, ruthenium, molybdenum-nickel, tungsten-nickel, etc. can also be used as catalysts.
The Rapa method has the characteristics of low raw material cost, simple process flow, high conversion rate, good selectivity, and simple operation. However, due to the severe corrosion of propionic acid under high temperature and high pressure, it is necessary to use a reactor whose inner wall is lined with silver. In view of this, many foreign companies have made many improvements to this method. In 1975, the low-pressure synthesis of butyraldehyde from propylene was successfully developed, which greatly promoted the development of the technology of direct carbonylation of ethylene to propionic acid. This new process has the potential to be the best method for Propanoic production.