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reaction zone; (c) passing at least a portion of the withdrawn liquid reaction composition to a second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carbon monoxide is added to the liquid reaction composition withdrawn from the first reaction zone at one or more points upstream of the second reaction zone, one or more points within the second reaction zone, or a combination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 0.5FG to 1.2FG, wherein FG is defined according to equation 1: (1) FG=(0.296086962×tr)+(0.369636×RR)+(0.295878701×GP0.8134)−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 Ff is the volumetric flow rate of liquid reaction composition to the flash separation zone (m3 / s), RR 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reaction rate of the liquid reaction composition passed to the second reaction zone at the temperature at which it is withdrawn from the first reaction zone (mol / litre / hour), and Gp is the purity of the gas feed comprising carbon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.