The key conversion of ethanol to ethyl acetate proceeds in a vapour-phase dehydrogenation reaction, followed by polishing and refining to yield high-purity product.
The primary feedstock is ethanol, which is obtainable from crop starch fermentation and will usually contain small amounts of water and C4 compounds. Petro-ethanol is also compatible with this process.
It is necessary to remove the water from the feed to optimise the downstream dehydrogenation process.
The ethanol/water feed exists as an azeotropic mixture, and drying proceeds in two steps.
Firstly, an azeotrope column takes the feed to the ethanol/water azeotrope which removes the bulk of the water from the ethanol.
The column overheads, composed mainly of ethanol with a small amount of water, then pass through an ethanol mole sieve drying package which further reduces the feed’s water content to required levels.
The dried, superheated ethanol vapour then enters the dehydrogenation reactor.
The vapour stream then flows downwards through several heterogeneous catalyst beds to form ethyl acetate in a two-stage reaction:
In addition, a number of side reactions occur to produce aldehyde and ketone by-products, and these will be removed in the subsequent polishing step.
Finally, a resulting hot process stream comprising ethyl acetate, unreacted ethanol, hydrogen and by-products exits the vessel’s base and passes through several cooling steps to yield a mixture of hydrogen gas and crude liquid product.
This gas/liquid is separated, and the freed hydrogen, following purification and compression, partially returns to the process with the remainder available for export.
The separated crude liquid proceeds to the polishing stage.
This step removes the by-products and other possible problem species that cannot be separated from ethyl acetate by distillation.
The crude liquid product stream, and hydrogen gas recycled from dehydrogenation, enter the polishing reactor and flow downwards co-currently over a heterogeneous catalyst.
Here, a hydrogenation reaction converts the aldehyde and ketone by-products to alcohols:
The liquid stream leaving the polishing reactor comprises mainly ethyl acetate product, unreacted ethanol and traces of water and by-products. This stream proceeds to distillation.
A patented multi-stage distillation system separates and refines the product ethyl acetate to specification.
Additionally, unreacted ethanol is separated and recycled to the synthesis stage, and trace lights and heavies are removed.