Method for producing acetic acid

A method for producing acetic acid, comprising:

• a carbonylation reaction step of reacting methanol with carbon monoxide in a reaction vessel in the presence of a catalyst system containing a metal catalyst and methyl iodide as well as acetic acid, methyl acetate, and water to produce acetic acid;
• an evaporation step of introducing and heating a reaction mixture obtained in the carbonylation reaction step in an evaporator to separate the reaction mixture into a vapor stream and a residual liquid stream;
• a residual liquid stream recycle step of recycling the residual liquid stream to the reaction vessel;
• a lower boiling point component removal step of separating the vapor stream with a first distillation column into a first overhead stream rich in methyl iodide and acetaldehyde and a first acetic acid stream rich in acetic acid and of condensing and separating the first overhead stream to obtain an aqueous phase and an organic phase;
• a first overhead stream recycle step of recycling at least a portion of the aqueous phase and/or the organic phase to the reaction vessel;
• and
• an acetaldehyde separation and removal step of separating and removing acetaldehyde in a process stream,
• wherein the ratio between the vapor stream and the residual liquid stream to be separated in the evaporation step is 28/72 to 60/40 in terms of a mass ratio wherein evaporation rate is 28 to 60% by mass,
• wherein with regard to operation conditions of the first distillation column, when only the aqueous phase is refluxed to the first distillation column, a reflux ratio of the aqueous phase is not less than 2;
• when only the organic phase is refluxed, a reflux ratio of the organic phase is not less than 1;
• and when both the aqueous and organic phases are refluxed, a total reflux ratio of the aqueous and organic phases is not less than 1.5, and
• wherein with heating of the evaporator, (i) an acetaldehyde concentration in the aqueous phase is controlled to not less than 2340 ppm by mass;
• (ii) a methyl acetate concentration in the aqueous phase is controlled to less than 19.0% by mass;
• and (iii) a methyl acetate concentration in the organic phase is controlled to less than 38.0% by mass, and at least a portion of the aqueous phase is treated in the acetaldehyde separation and removal step to recycle a residual liquid after the acetaldehyde separation and removal to the reaction vessel and/or the acetaldehyde separation and removal step and/or other processes.