PROCESS FOR THE PRODUCTION OF ACETIC ACID

A process for the production of acetic acid which process comprises the steps of. (a) introducing methanol and/or a reactive derivative thereof and carbon monoxide into a first reaction zone containing a liquid reaction composition comprising a carbonylation catalyst, optionally a carbonylation catalyst promoter, methyl iodide, methyl acetate, acetic acid and water; (b) withdrawing at least a portion of the liquid reaction composition from the first reaction zone; (c) passing at least a portion of the withdrawn liquid reaction composition to a second reaction zone, wherein a gas feed comprising carbon monoxide is added to the liquid reaction composition withdrawn from the first reaction zone at one or more points upstream of the second reaction zone, one or more points within the second reaction zone, or a combination of one or more points upstream of the second reaction zone and one or more points within the second reaction zone; and (d) passing at least a portion of the liquid reaction composition from the second reaction zone into a flash separation zone to form: a vapour fraction, which comprises acetic acid, methyl iodide, methyl acetate and low pressure off-gas; and, a liquid fraction, which comprises carbonylation catalyst and optional carbonylation catalyst promoter; wherein the flow rate in kg of gas feed comprising carbon monoxide which is added to the second reaction zone per tonne of liquid reaction composition being passed to the flash separation zone (kg/te), is in the range of from 0.5F G to 1.2FG, wherein FG is defined according to equation 1: (1) FG=(0.296086962xtr )+(0.369636xRR )+(0.295878701xGP 0,8134 )-23.3448 wherein, tr is the residence time (seconds) of the liquid reaction composition within the second reaction zone which is calculated using equation 2: (2) tr =V2/Ff wherein, V2 is the volume of the second reaction zone (m3) and F f is the volumetric flow rate of liquid reaction composition to the flash separation zone (m 3 /s), R R is the reaction rate of the liquid reaction composition passed to the second reaction zone at the temperature at which it is withdrawn from the first reaction zone (mol/litre/hour), and Gp is the purity of the gas feed comprising carbon monoxide which is added to the second reaction zone expressed as the mass fraction of carbon monoxide in the gas feed. L'invention porte sur un procédé de production d'acide acétique, lequel procédé comprend les étapes consistant à : (a) introduire du méthanol et/ou un dé