Acrylonitrile Production from Propylene (Fluidized Bed Ammoxidation)

The process under analysis comprises four major sections: (1) Ammoxidation; (2) Separation; (3) Acetonitrile recovery; and (4) Purifcation.

Ammoxidation. CG propylene, ammonia and air are fed to a reactor, where an ammoxidation reaction occurs in the vapor phase, over fluidized catalysts. The reaction effluent comprises Acrylonitrile, hydrogen cyanide, acetonitrile, carbon oxides, as well as unconverted propylene and ammonia.

Separation. The reactor effluent is sent to a quench column, where unreacted ammonia is neutralized with sulfuric acid. The quenched gas is transferred to the nitrile absorber, where Acrylonitrile is absorbed and transferred to the recovery column. In the recovery column, acetonitrile and water are separated from Acrylonitrile and hydrogen cyanide.

Acetonitrile recovery. A liquid side stream from the recovery column, containing a mixture of acetonitrile and water, is sent to the acetonitrile stripper, where the it is distilled under vacuum to separate water and heavy organics. The acetonitrile-water azeotrope obtained is then distilled at high pressure into three streams: a bottom product comprising heavy impurities; an aqueous stream containing also some acetonitrile as column overhead, which is recycled to the acetronitrile stripper; and a side stream containing high-purity acetonitrile.

Purifcation. The organic phase from the recovery column is fed into the HCN column for the separation of HCN from Acrylonitrile. The Acrylonitrile-rich stream is transferred into the Acrylonitrile purification column, where column overhead gaseous stream flows into a condenser. The condensate is then sent to a decanter, in which the denser phase (mainly water) is withdrawn from decantation drum and recycled to the recovery column. The less dense phase is transferred to the acrylonitrile purifcation column, where fiber-grade Acrylonitrile product is withdrawn as a sidestream.