Acetic acid produced from methanol in sophisticated continuous stirred tank reactor by carboxylation process. It is also produced by dehydrogenation and oxidation of ethanol which is famous for production plants. In addition to the above two methods, acetaldehyde can also be used as raw material for producing acetic acid in large scale by oxidation. Conversion of acetaldehyde to acetic acid takes place in the liquid phase at temperature 60-70 oC with the support of a catalyst. The process involves three stages
- Acetaldehyde oxidation
- Acetaldehyde absorption present in outlet gas after oxidation
- Separation of unreacted acetaldehyde present in acetic acid.
The chemical reaction in the presence of manganese acetate (Mn(CH3COO)2) catalyst:
- CH3CHO + O2 → CH3COOOH (peracetic acid unstable)
- CH3COOOH + CH3CHO → CH3CO.O.O.CHOH.CH3 → 2CH3COOH
Acetic acid manufacturing process description:
Acetaldehyde in liquid form is fed to the bottom of the reactor along with oxygen (air). The reaction initiated by the catalyst to form peracetic acid as an intermediate compound. Peracetic acid is so unstable and soon it reacts with other acetaldehyde molecules to form a compound of peroxide. Two molecules of acetic acid are obtained by the rigorous decomposition of peroxide compound of peracetic acid and acetaldehyde. The reactor is designed in a tray tower model so that the separation and conversion of peracetic acid are controlled well. Peracetic acid has a property of explosion at temperate higher than operating temperature. A cooling system is provided to the tower to maintain the temperature ranging from 60-75 oC. Separation of acetic acid and unreacted acetaldehyde is done within the reactor tray tower. All the vapours reach the top of the column and then passed to the condenser for acetic acid recovery. Unreacted acetaldehyde is sent back to the reaction column.
From the worldwide acetic acid production, 50% of acetic acid is consumed in producing vinyl acetate, 15% for cellulose acetate, 10% for butyl isopropyl acetate. Remaining quantity is used for acetic anhydride, acetanilide, acetyl chloride, acetamide, dimethyl ester, chloroacetic acids manufacturing units.
Alternative process methods:
Acetaldehyde can be produced via liquid phase from acetic acid. This process uses catalyst made from Platinum, Cerium oxide, zirconium oxide and Tin dioxide. Alumina (alpha) act as the support for the catalyst mixture. The raw materials acetic acid and water are fed to the batch reactor with the catalyst mixture. This process has the possibility of achieving 95% selectivity to acetic acid.