Iridium-catalyzed carbonylation process for the production of acetic acid

摘要

A process as provided for producing an acetic acid process stream having less than 400 ppm propionic acid and less than 1500 ppm water. Methanol or a reactive derivative thereof and carbon monoxide is fed to a carbonylation reactor in which there is maintained during the course of the process a liquid reaction composition containing an iridium carbonylation catalyst, methyl iodide co-catalyst, a promoter, water at a concentration of less than about 8% by weight, methyl acetate, acetic acid, and propionic acid by-product and its precursors. Liquid reaction composition is withdrawn from the carbonylation reactor and introduced to a flash zone to form a vapor fraction comprising water, acetic acid product, propionic acid by-product, methyl acetate, methyl iodide and propionic acid precursors, and a liquid fraction comprising involatile iridium catalyst, involatile optional promoter or promoters, acetic acid and water. The liquid fraction is recycled from the flash zone to the carbonylation reactor and introduced into a first distillation zone where a light ends recycle stream is removed and recycled to the carbonylation reactor, A process stream is removed from the first distillation zone comprising acetic acid, propionic acid by-product and less than 1500 ppm water. If the process stream comprises greater than 400 ppm propionic acid, the process stream is introduced into a second distillation zone where propionic acid by-product is removed together with an acetic acid process stream containing less than 400 ppm propionic acid and less than 1500 ppm water.