Patent ID: 7524988

Claim:
A method for reducing an aldehyde impurity from acetic acid stream, said method comprising: (a) reacting methanol and carbon monoxide in the presence of a carbonylation catalyst, a catalyst stabilizer, methyl iodide, water and methyl acetate to produce an acetic acid stream comprising the catalyst, the catalyst stabilizer, methyl iodide, methyl acetate, water, acetic acid, and an aldehyde impurity; (b) flashing at least a portion of the acetic acid stream to a vapor stream comprising acetic acid, water, methyl acetate, methyl iodide and the aldehyde impurity, and a liquid stream comprising the catalyst and the catalyst stabilizer; (c) recycling the liquid stream to the reaction of step (a); (d) separating the vapor stream by distillation into an acetic acid product stream comprising acetic acid and water, and an overhead stream comprising methyl iodide, water, methyl acetate, acetic acid, and the aldehyde impurity; (e) condensing the overhead stream to produce a light, aqueous phase comprising water, acetic acid, and methyl acetate, and a heavy, organic phase comprising methyl iodide and the aldehyde impurity; (f) reacting at least a portion of the heavy, organic phase with a hydroxyl compound selected from the group consisting of C 4-10 alcohols, glycols, and glycerin to convert the aldehyde impurity to an acetal having a higher boiling point than acetic acid; (g) recycling the treated heavy phase of step (f) to the distillation of step (d), wherein the acetal goes with the acetic acid product stream as a heavy impurity; and (h) separating the acetal from the acetic acid product stream of step (g) by distillation.