Production and purification of acetic acid

A process for producing acetic acid, comprising:

• (a) a reaction step of allowing methanol to continuously react with carbon monoxide in a reactor in the presence of a reactive system comprising a metal catalyst, an ionic metal iodide, and methyl iodide, acetic acid, methyl acetate, and water;
• (b) an evaporation step of separating a reaction mixture obtained in the reaction step with or without heating into a vapor stream and a liquid residuum stream;
• (c) a first distillation step of distilling at least a portion of the vapor stream in a first distillation column to form a first overhead stream and a side stream, wherein the first overhead stream comprises water, methyl iodide, and/or acetaldehyde, and the side stream comprises acetic acid;
• (d) a phase separation step of condensing the first overhead stream in one or more condensers, collecting condensates in a receiver, and separating the condensates into an upper phase and a lower phase;
• (e) a second distillation step of distilling at least a portion of the lower phase in a second distillation column to form a second mixture comprising acetaldehyde;
• (f) an acetaldehyde separation step of separating the second mixture into an acetaldehyde stream and a first return stream;
• and at least one step selected from the group consisting of (g) to (k):
• (g) a purifying step of purifying the side stream to obtain an acetic acid product stream;
• (h) an off-gas treatment step of absorbing one or more off-gas streams from the process with an absorption solvent and forming a carbon monoxide stream and a second return stream;
• (i) a high-boiler removal step of removing a higher boiling component from the acetic acid product stream;
• (j) an iodine removal step of contacting the acetic acid product stream with an ion-exchange resin and separating an iodine compound from the acetic acid product stream;
• and
• (k) an extraction step of extracting acetaldehyde from the acetaldehyde stream to form an extract and a raffinate, wherein the extract comprises acetaldehyde and the raffinate comprises methyl iodide;
• wherein the mass composition of 1,1-dimethoxyethane in a liquid stream of the process is controlled to be not more than 0.2 wt. % by maintaining the amount of unreacted methanol in the reaction mixture to less than 1 wt. % based on the total weight of the reaction mixture.