Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-12-14
2001-01-30
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S231000, C560S261000, C562S548000
Reexamination Certificate
active
06180821
ABSTRACT:
PROCESS
The present invention relates generally to an integrated process for the production of acetic acid and/or vinyl acetate and in particular to an integrated process for the production of either acetic acid or vinyl acetate or both acetic acid and vinyl acetate in any pre-determined and variable proportions from a gaseous feedstock comprising ethylene and/or ethane.
Acetic acid, useful as a feedstock for the production of vinyl acetate, may be prepared by several methods as commonly practiced in the industry, for example by the liquid phase carbonylation of methanol and/or a reactive derivative thereof in the presence of a Group VIII noble metal catalyst, an alkyl iodide promoter and a finite concentration of water; however this process does not readily lend itself to integration since small quantities of iodide in the acid are known to be poisons for palladium-based vinyl acetate catalysts. Alternatively, acetic acid may be produced by the catalytic oxidation of ethylene and/or ethane. However, this process though attractive from the point of view of integration, suffers from the disadvantage that large quantities of water are produced as a by-product of the process. Moreover, in a preferred method of operation water (steam) is added to the feedstock to improve selectivity. This, and the generated water, requires removal, necessitating expensive product separation.
Vinyl acetate is generally prepared commercially by contacting acetic acid and ethylene with molecular oxygen in the presence of a catalyst active for the production of vinyl acetate. Suitably, the catalyst may comprise palladium, an alkali metal acetate promoter and an optional co-promoter (for example, gold or cadmium) on a catalyst support. Acetic acid produced by carbonylation generally requires extensive purification to remove inter alia iodides arising from the catalyst system generally employed because iodides are recognised as potential vinyl acetate catalyst poisoners. The ethylene feedstock generally requires purification to remove inert hydrocarbons such as ethane present in cracker products. Alternatively, the process for the production of vinyl acetate requires a costly purge to remove the accumulated hydrocarbons.
Combinations of processes for producing vinyl acetate are known in the art.
Thus, GB-A-1,139,210 discloses a vapour phase process for the production of unsaturated organic esters from a feed mixture consisting of an alkene and an oxygen-containing gas which does not require the presence of an organic carboxylic acid in the initial reaction mixture and, more specifically, for the preparation of vinyl acetate from ethylene and oxygen in the absence of acetic acid in the initial feed mixture. The process comprises contacting a gaseous feed comprising an alkene and an oxygen-containing gas with a catalyst comprising a palladium—or platinum—group metal or metal compound supported on alumina to obtain a reaction product mixture containing the unsaturated organic ester, the catalysts preferably being in sequence. The disclosure does not mention the use of mixed hydrocarbon feedstocks, the production of water and its removal, the recovery of acetic acid, or indeed any details of the various items of plant employed or their inter-relationship.
Research Disclosure, June 1992, page 446, discloses a process for the production of an acetic acid-containing product from ethane and/or ethylene which comprises:
(i) reacting ethane and/or ethylene with oxygen in an oxidation stage to produce an acetic acid-containing reaction product mixture containing, in addition to the acetic acid, unreacted ethane and ethylene and/or unreacted ethylene and carbon monoxide, optionally together with carbon dioxide and water;
(ii) subjecting the reaction product mixture with or without separating the acetic acid to an oxidation in which the carbon monoxide is selectively oxidised to carbon dioxide in the presence of the unreacted ethane and ethylene, and/or unreacted ethylene;
(iii) removing the carbon dioxide from the mixture, and
(iv) recycling the unreacted ethane optionally together with the ethylene, and/or the unreacted ethylene to the ethane and/or ethylene oxidation stage.
In an embodiment of this invention reaction product from step (ii) comprising acetic acid, unreacted ethane (if present) and ethylene is passed with or without cartoon dioxide and water removal to a reactor having a suitable catalyst for the production of ethyl acetate or, with addition of oxygen, for the production of vinyl acetate. There is no mention in this disclosure of the recovery of both acetic acid and vinyl acetate, nor of the role of water.
GB-A-1209727 discloses a process for preparing vinyl acetate by the catalytic oxidation of ethylene in the presence of acetic acid, which avoids the accumulation of impurities in the recycled gases and at the same time supplies the necessary acetic acid for preparing the vinyl acetate, the process being essentially characterised by the steps of drawing a convenient fraction of the recycled gases from the reactor in which the vinyl acetate is formed, catalytically oxidising the ethylene contained in said fraction to acetic acid with the aid of gaseous oxygen and supplying the acetic acid formed to the reactor in which the vinyl acetate is formed, the conditions being such that the content of by-products in the recycled gases is kept below 20% by volume, and the amount of acetic acid formed is sufficient to replace the acetic acid consumed in the preparation of vinyl acetate. No mention is made of the use of mixed hydrocarbon feedstocks, nor of recovering both acetic acid and vinyl acetate as products, nor of co-produced water and its role in the process.
There is a need for an integrated process capable of producing at least one of the products acetic acid and vinyl acetate.
Accordingly the present invention provides an integrated process for the production of acetic acid and/or vinyl acetate which comprises the steps:
(a) contacting in a first reaction zone a gaseous feedstock comprising ethylene and/or ethane, and optionally steam, with a molecular oxygen-containing gas in the presence of a catalyst active for the oxidation of ethylene to acetic acid and/or ethane to acetic acid and ethylene to produce a first product stream comprising acetic acid, water and ethylene (either as unreacted ethylene and/or as co-produced ethylene), and optionally ethane, carbon monoxide, carbon dioxide and/or nitrogen,
(b) contacting in a second reaction zone in the presence or absence of additional ethylene and/or acetic acid at least a portion of the first gaseous product stream comprising at least acetic acid and ethylene and optionally also one or more of water, ethane, carbon monoxide, carbon dioxide and/or nitrogen with a molecular oxygen-containing gas in the presence of a catalyst active for the production of vinyl acetate to produce a second product stream comprising vinyl acetate, water, acetic acid and optionally ethylene;
(c) separating the product stream from step (b) by distillation into an overhead azeotrope fraction comprising vinyl acetate and water and a base fraction comprising acetic acid;
(d) either (i) recovering acetic acid from the base fraction separated in step (c) and optionally recycling the azeotrope fraction separated in step (c) after partial or complete separation of the water therefrom to step (c), or
(ii) recovering vinyl acetate from the azeotrope fraction separated in step (c) and optionally recycling the base fraction separated in step (c) to step (b), or
(iii) recovering acetic acid from the base fraction separated in step (c) and recovering vinyl acetate from the overhead azeotrope fraction recovered in step (c).
The process of the combination of steps (a) to (c) and (d)(i) may be considered as a process for the production of acetic acid by the oxidation of an ethylene and/or ethane feedstock in which the co-produced or added water is advantageously removed by distillation as a vinyl acetate/water azeotrope, leaving a substantially dried acetic acid product, the vinyl acetate
Jobson Simon
Watson Derrick John
BP Chemicals Limited
Deemie Robert W.
Nixon & Vanderhye
Wilson James O.
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