PURPOSE: To provide a method for removing a carbonyl impurity from a carbonylation process.
CONSTITUTION: The carbonyl impurity is removed by driving a methyl iodide recirulation flow to a carbonylation reactor for carbonylating methanol or methyl acetate to actinc acid, acetic anhydride or both into reaction with an amino compd. forming a water-soluble nitrogen-contg. deriv. by reaction with carbonyl, separating an org. methyl iodide phase from the aq. deriv. phase and making treatment so as to remove the heavy impurity by distillation of the methyl iodide phase. The treatment of the methyl iodide recirculation flow to the carbonylation reactor drastically decreases the carbonyl existing in the acetic acid or acetic anhydride of the product and lessens the tar formation in an acetic anhydride production unit or acetic acid-acetic anhydride simultaneous production unit. The nitrile formation from the nitrogen-contg. deriv. during distillation is minimized by washing the nitrogen-contg. deriv. from the methyl iodide overhead by adding water to a distillation column.
MAAKU OO SUKEITSU
RATSUSERU KEI GIBUSU JIYUNIAA
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