Acetic Acid Production from Methanol

The process under analysis comprises three major sections: (1) Catalyst Preparation; (2) Carbonylation; and (3) Purification.

Catalyst Preparation. Initially, recycled rhodium catalyst is treated to recover the rhodium. The treated catalyst is mixed with fresh catalyst, promoter (methyl iodide) and stabilizer (iodide salt) and dissolved in hot acetic acid under carbon monoxide pressure.

Carbonylation. The reactor is fed with methanol, recycle streams, the catalyst solution and carbon monoxide. The reaction occurs in the liquid phase, where dissolved carbon monoxide is combined with methanol yielding Acetic Acid. Gases vented from the reactor are cooled to recover methanol, methyl iodide and methyl acetate. Uncondensables are sent to the methanol scrubber, to prevent loss of low boiling components such as methyl iodide. Liquid product is drawn off from the carbonylation reactor at a rate sufficient to maintain a constant level, and fed to a flash vessel where the catalyst solution is withdrawn as a base stream. The product overhead of the flash vessel, a crude Acetic Acid stream containing methyl iodide, methyl acetate, and water (up to 6 wt%), is sent to purification columns.

Purification. The crude Acetic Acid stream is purified in distillation columns, yielding glacial Acetic Acid product. Methyl iodide, methyl acetate, and water recovered in the purification steps are returned to the process.