Process for producing acetic acid

A process for producing acetic acid, which comprises:

• a reaction step for continuously allowing methanol to react with carbon monoxide in the presence of a catalyst system comprising a metal catalyst, a halide salt, and methyl iodide in a carbonylation reactor,
• a flash evaporation step for continuously feeding a flasher with a reaction mixture from the reactor and separating a lower boiling point component (2A) containing product acetic acid and methyl iodide and a higher boiling point component (2B) containing the metal catalyst and the halide salt,
• an acetic acid collection step for continuously feeding a distillation column with the lower boiling point component (2A), and separating a lower boiling point component (3A) containing methyl iodide and by-product acetaldehyde and a stream (3B) containing acetic acid to collect acetic acid,
• a condensation step for condensing and temporarily holding the lower boiling point component (3A) in a decanter and discharging the lower boiling point component (3A) from the decanter, and
• a separation and recycling step for separating the lower boiling point component (3A) discharged from the decanter into acetaldehyde and a liquid residue and recycling the liquid residue to a step from the reaction step to the acetaldehyde-separation step,
• wherein in the condensation step, the amount of the lower boiling point component (3A) to be held is adjusted or controlled based on a fluctuating flow rate of the lower boiling point component (3A) to be fed to the decanter, and the amount of the lower boiling point component (3A) to be fed to the separation and recycling step is adjusted or controlled.