Some of the processes for manufacturing acetic acid are give below
- Acetaldehyde can be oxidized by the oxygen in the air to produce acetic acid.
2CH3CHO + O2 → 2CH3COOH
2. Liquid phase oxidation of butane:
- Liquified butane is combusted by air in use of various inorganic ions such as those to manganese, cobalt and chromium, peroxides type and then break down to generate acetic acid.
2C4H10 + 5 O2 → 4 CH3COOH + 2 H2O
3. Methanol Carbonylation:
- In this process methanol CH3OH and carbon-monoxide CO, chemically react for the production of acetic acid according as per the equation.
CH3OH + CO → CH3COOH
Acetic acid manufacturing process description by carbonylation of methanol in the presences of catalyst rhodium:
The process is carried out in a continuous stirred tank reactor. In this process methanol and CO are reacted in presence of Rhodium complex catalyst to give acetic acid. The liquid feed to the reactor consists of mixture of methanol feed stream used to scrub the effluent gas from the reactor. A recycle stream containing mostly methyl acetate, methyl iodide and recycled catalyst are introduced at the top and CO is sparged from the bottom of the reactor. A small amount of methyl iodide and rhodium catalyst will be added to make-up any loss.
The reaction is exothermic and its heat of reaction is 138 KJ/mol. Pressure in the reactor is 3Mpa and temperature is around 1900 C are maintained. All the gaseous effluent from the reactor is cooled to about 100C in a water cooled exchanger and condensed in a condenser. The liquid stream from the condenser goes to a high pressure separator to separate the un-reacted CO, CO2 and H2. Bottom liquid stream from the high pressure separator goes to low pressure separator for separating the methyl iodide, methyl acetate and mixed with the gas effluent from the high pressure separator. These gases are scrubbed in a scrubber with methanol to recover the methyl iodide and methyl acetate before leaves the system. The liquid from the scrubber is sent to reactor surge tank from there it goes to reactor.
The liquid from the reactor is removed and the pressure is let down and introduced into the light ends distillation column. Here the low boiling compounds are separated from the acetic acid and other less volatile components such as catalyst. These low boiling components contain methyl acetate and methyl iodide and they are recycled to the reactor.
Acetic acid, other high boiling compounds and rhodium component mixture is sent to catalyst recovery column where catalyst is separated as bottom product and recycled to reactor. The top product contains acetic acid and water is sent to dehydration tower where water is separated from the acetic acid. The acetic acid from the dehydration unit consists small amount of propionic acid to remove it and improve the concentration it is sent to heavier ends distillation column all the propionic acid is removed as bottom product. The top product contains acetic acid with 99% purity.