Process for the production of acetic acid

Claim 1

A process for the production of acetic acid which process comprises: (a) feeding methanol and carbon monoxide to a carbonylation zone in which there is maintained during the course of the process a liquid reaction composition comprising: (i) a rhodium carbonylation catalyst; (ii) methyl iodide; (iii) a carbonylation catalyst stabiliser comprising an iodide salt which is soluble in the reaction composition; (iv) a finite amount of water at a concentration of up to about 10% by weight; (v) methyl acetate at a concentration of at least 2% by weight; and (vi) acetic acid, (b) withdrawing liquid reaction composition from the reactor and introducing it, with or without the addition of heat, to a flash zone to form a vapour fraction comprising water up to about 8% by weight, acetic acid product, propionic acid by-product and the majority of the methyl acetate and methyl iodide from the flash zone feed, and a liquid fraction comprising involatile rhodium catalyst, involatile catalyst stabiliser, acetic acid, water and the remainder of the methyl acetate, methyl iodide and propionic acid by-product from the flash zone feed, (c) recycling the liquid fraction from the flash zone to the reaction zone, and recovering acetic acid product from the flash zone vapour fraction by use of a single distillation zone by: (d) introducing the vapour fraction from the flash zone into the distillation zone, as a vapour and/or liquid. (e) removing from the head of the distillation zone a light ends recycle stream comprising water, methyl acetate, methyl iodide and acetic acid, and (f) removing from the distillation zone at a point below the introduction point of the flash zone vapour fraction, an acid product stream having a water concentration of less than 1500 ppm and a propionic acid concentration of less than 500 ppm.