Patent ID: 8017802

Claim:
A method of controlling impurities in a rhodium-catalyzed methanol carbonylation process for the manufacture of a glacial acetic acid product, comprising: a) reacting methanol, methyl acetate, dimethyl ether or mixtures thereof with carbon monoxide in the presence of a rhodium catalyst in a reaction vessel; b) maintaining in said reaction vessel a water concentration of 0.5 to 14 weight percent; such that the formic acid content in the resulting final glacial acetic acid product is controlled to an amount ranging from 15 ppm to 160 ppm; and c) contacting the acetic acid obtained from step b) with a silver exchanged cation exchange resin so that the total sulfur in the resulting final glacial acetic acid is in an amount less than 1 ppm, wherein the concentration of the formic acid in the final glacial acetic acid product is controlled by controlling the reaction vessel water concentration according to a mathematical correlation between the reactor water concentration and the formic acid concentration, the mathematical correlation being empirically determined by curve fitting data obtained by varying the reactor water concentration in the reaction vessel and measuring the formic acid concentration in the final glacial acetic acid product produced at a particular reactor water concentration.