Acetic Anhydride Plant

Manufacture of Acetic Anhydride (Ketene Route)

Manufacture of Acetic Anhydride via the Ketene Process

Chemical Reactions Involved:

2. Formation of Acetic Anhydride from Ketene and Acetic Acid:

Process Description: 1. Vaporization and Cracking:

- Acetic Acid Vaporization: Acetic acid is first vaporized and mixed with a catalyst, typically Triethyl Phosphate.
- Cracking Coils: The vaporized mixture is passed through cracking coils made of special alloy steel. These coils are housed within a furnace where temperatures of 1000ºC to 1100ºC are maintained using Light Diesel Oil (LDO) or natural gas as fuel.
- Ammonia Injection: A small quantity of ammonia is injected into the system to prevent the reverse reaction (reformation of acetic acid from ketene).

2. Cooling and Condensation:

- Cooling: The products of cracking (ketene and water) are cooled in a series of coolers, where unreacted acetic acid and water are removed.
- Absorption: The remaining ketene is then taken to a series of absorption towers, where it is absorbed in acetic acid to form crude acetic anhydride.

3. Purification:

- Washing Tail Gases: The tail gases are washed with chilled water to remove all traces of acetic acid and acetic anhydride before being released into the atmosphere via a vacuum pump.
- Distillation of Crude Acetic Anhydride: The crude acetic anhydride (75-85% purity) from the first absorption tower is taken to a distillation and purification system operating under vacuum.
- Recovery of Acetic Acid: Unreacted acetic acid, recovered from the top condenser, is returned to the absorption system.
- Final Purification: The bottoms of the distillation column are fed into a second column where pure acetic anhydride is obtained as a product from the top.

4. Recovery of Acetic Acid:

- Dilute Acetic Acid Treatment: The dilute acetic acid (30-45% strength) obtained during the process is concentrated back to glacial acetic acid using a solvent extraction plant, typically employing ethyl acetate as the solvent.
- Reuse: The recovered glacial acetic acid is reused in the production of acetic anhydride.

1. Acetic acid	1285 Kgs
2. Dry Saturated steam at 8 Kg/Cm²	5500 Kgs
3. Electric power (Battery limit)	180 KWH
4. Cooling Water	260 M³
5. Process Water	0.5 m³
6. Referigeration at 4° C	10TR
7. Referigeration at – 10°C	3TR
8. Light Diesel Oil	250 Ltrs.
9. Tri Ethyl Phosphate	2.5 Kgs
10. Ammonia	1 Kgs.
11. Solvent	25 Kgs.