Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2002-07-18
2003-04-15
Shah, Mukund J. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
Reexamination Certificate
active
06548697
ABSTRACT:
The present invention relates to a process for the oxidation of a C
2
to C
4
alkane to produce the corresponding alkene and carboxylic acid and to integrated processes in which the alkene and carboxylic acid are further used as reactants.
BACKGROUND OF THE INVENTION
Carboxylic acids are useful feedstocks for the production of alkenyl carboxylates. Thus, for example, acetic acid is used to manufacture vinyl acetate which is generally prepared commercially by contacting ethylene and acetic acid 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 may be produced by the catalytic oxidation of ethylene and/or ethane.
Integrated processes for producing acetic acid and/or vinyl acetate are known in the art. EP-A-0 877 727 discloses an integrated process for the production of acetic acid and/or vinyl acetate in any pre-determined and variable proportions from a gaseous feedstock comprising ethylene and/or ethane. The integrated process comprises a first step wherein ethylene and/or ethane is catalytically oxidised in a first reaction zone to produce a first product stream comprising acetic acid, water and ethylene and optionally ethane, carbon monoxide, carbon dioxide and/or nitrogen. The acetic acid and ethylene produced in this first reaction zone are then contacted in a second reaction zone with a molecular oxygen-containing gas in the presence of a catalyst to produce a second product stream comprising vinyl acetate, water, acetic acid and optionally ethylene. No mention is made of any control of the production ratio of ethylene to acetic acid from the catalytic oxidation of ethane and/or ethylene.
Research Disclosure 2244 of 1992(June) No. 338 describes a process for the oxidation of ethane and/or ethylene to produce acetic acid in which the by-product carbon monoxide is oxidised to carbon dioxide. According to this document, the acetic acid, unreacted ethane (if present) and ethylene is passed with or without carbon dioxide and water removal, to a reactor having a suitable catalyst for the production of ethyl acetate or, with the addition of oxygen, for the production of vinyl acetate. This document is silent on the control of the ratio of ethylene to acetic acid produced in the oxidation step.
In the manufacture of vinyl acetate from ethylene and acetic acid, the molar ratio of the fresh feed ethylene to acetic acid is desirably unity or approximately unity. Thus, in an integrated process in which ethane is oxidised in an oxidation reaction zone to produce ethylene and acetic acid for use in a second reaction zone for the production of vinyl acetate, to maximise overall integrated process efficiency and also vinyl acetate output, the molar ratio of ethylene to acetic acid produced in the oxidation reaction zone, is desirably unity or approximately unity depending upon the selectivity/yield in the second reaction zone.
Thus, there remains a need for a process for the oxidation of a C
2
to C
4
alkane to produce the corresponding alkene and carboxylic acid in which the molar ratio of alkene to carboxylic acid produced is adjusted or maintained at a pre-determined value.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for the oxidation of a C
2
to C
4
alkane to produce the corresponding alkene and carboxylic acid which process comprises contacting in an oxidation reaction zone, said alkane, a molecular oxygen-containing gas and optionally, at least one of the corresponding alkene and water, in the presence of at least two catalysts each active, with different selectivities, for the oxidation of the alkane to the corresponding alkene and carboxylic acid, to produce a product stream comprising alkene, carboxylic acid and water, and in which process the molar ratio of alkene to carboxylic acid produced in said oxidation reaction zone is adjusted or maintained at a pre-determined value by controlling the relative proportions of the at least two catalysts in said oxidation reaction zone.
Each of the alkane, molecular oxygen-containing gas, alkene and water may be introduced into the oxidation reaction zone as fresh feed and/or recycle component.
The selectivity of a catalyst for alkene or carboxylic acid is defined as the proportion of reactant which is converted to alkene or carboxylic acid by that catalyst.
If one or more of the catalysts in the oxidation reaction zone de-activate in use and it is necessary to replace catalyst during the process, the molar ratio of alkene to carboxylic acid produced may be maintained at a constant, pre-determined value by controlling the relative proportions of the catalysts in the oxidation reaction zone. Thus, if the activity and/or selectivity of the catalysts in the oxidation reaction zone change independently during the process, this may involve replacing at least part of the catalysts in the oxidation reaction zone by introducing catalysts into the oxidation reaction zone in different proportions to the proportions of catalysts already in the oxidation reaction zone, in order to maintain the molar ratio of alkene to carboxylic acid produced. Conversely, if the catalysts in the reactor deactivate such that their individual selectivities do not change, it may be possible to maintain the molar ratio of alkene to carboxylic acid produced by using for the replacement of catalysts in the oxidation reaction zone, catalysts in the same proportions as in the oxidation reaction zone.
The present invention also provides a method of adjusting the molar ratio of alkene to carboxylic acid produced, for example in response to changes in demand or requirement in down-stream processes by controlling the relative proportions of the at least two catalyst in the oxidation reaction zone.
The process of the present invention is particularly useful when the alkene and/or carboxylic acid products are used at least in part in integrated downstream processes, for example (a) for the production of ester by reacting the carboxylic acid with the alkene or an alcohol or (b) for the production of alkenyl carboxylate by the reaction of a molecular oxygen-containing gas with the carboxylic acid and alkene. Alkene and/or carboxylic acid may be recovered from the product of the oxidation reaction zone and/or additional alkene and/or carboxylic acid may be used in the down-stream process.
In a further embodiment of the present invention, the alkene and carboxylic acid may be produced in a molar ratio suitable for use in an integrated down-stream process, for example (a) for the production of ester by reacting the carboxylic acid with the alkene or (b) for the production of alkenyl carboxylate by the reaction of a molecular oxygen-containing gas with the carboxylic acid and alkene. If alkene and/or carboxylic acid is neither separately recovered from reaction product nor separately added to the downstream process, the molar ratio of alkene to carboxylic acid produced in the oxidation reaction zone is suitably approximately 1:1, for example, 0.8:1 to 1.4:1. A different ratio may be produced if alkene and/or carboxylic acid is separately recovered from the oxidation reaction product or separately added to the down-stream process. The molar ratio of alkene to carboxylic acid may then be adjusted by controlling the relative proportions of the at least two catalysts in the oxidation reaction zone, for example to meet changes in market demand or feedstock availability. Suitably, the molar ratio of alkene to carboxylic acid produced in the oxidation reaction zone is in the range 1:10 to 10:1.
Accordingly, the present invention provides an integrated process for the production of an alkyl carboxylate which process comprises the steps:
(a) contacting in an oxidation reaction zone a C
2
to C
4
alkane, a molecular oxygen-containing gas and optionally, at least one of the corresponding alkene and water in the presence of at least two cataly
Ellis Brian
Roberts Mark Stephen
BP Chemicals Limited
Nixon & Vanderhye
Shah Mukund J.
Tucker Zachary C.
LandOfFree
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