Vinyl Acetate Production from Acetic Acid and Ethylene

The process under analysis comprises three major sections: (1) Reaction; (2) Separation; and (3) Purification.

Reaction. Make-up and recycled acetic acid streams pass through a vaporizer, along with fresh and recycled ethylene. The resulting feed stream, containing excess ethylene over acetic acid, is mixed with oxygen, preheated, and fed to multi-tube reactors. An oxidation reaction occurs over a palladium and gold catalyst. Heat is removed by evaporative cooling on the shell of the reactors. In the end, 8-10 wt% of ethylene and 15-35 wt% of acetic acid are converted to Vinyl Acetate. Water, CO2, and small quantities of ethyl acetate, ethylidene diacetate, and glycol acetates are the main by-products.

Separation. The reactor effluent is cooled and fed to the predehydration column, where a crude VAM stream is withdrawn from the bottom and stored. The overhead stream is separated into an organic phase, recycled to the column, and an aqueous phase, directed to a decanter downstream. The uncondensed gas is washed by acetic acid and the solution formed is routed to the crude VAM tank, while the gas from the scrubber is recycled to the reaction. Part of this gas is washed with water to remove residual acetic acid and directed to the crude VAM Tank. After water washing, the gas is directed to an absorption column, for CO2 removal by a potassium carbonate solution.

Purification. In the azeotropic column, the VAM-water mixture from the crude VAM tank and the aqueous phase separated in the predehydration column are distilled and fed to a decanter. At this point, the organic phase containing VAM is separated and directed to the light-ends column. The aqueous phase is routed to the wastewater column, which separates residual VAM from wastewater. Ethyl acetate is withdrawn and discharged, and acetic acid is recycled to the caporizer. The light-ends column strips off acetaldehyde and other volatiles from the crude Vinyl Acetate. Finally, residual acetic acid and heavy ends are removed in the pure VAM column, yielding Vinyl Acetate with 99.9 wt% purity.