Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-07-29
2001-05-01
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C562S545000, C562S546000, C560S261000
Reexamination Certificate
active
06225496
ABSTRACT:
The present invention relates to a process for the production of vinyl acetate from ethylene, acetic acid and an oxygen-containing gas in the presence of a catalyst.
BACKGROUND OF THE INVENTION
Fluid bed processes for the production of vinyl acetate from ethylene, acetic acid and an oxygen-containing gas in the presence of a fluid bed catalyst are known from, for example, EP-A-0685449, EP-A-0685451 and EP-A-0672453.
EP-A-0685449 discloses a process for manufacturing vinyl acetate in a fluid bed reactor comprising feeding ethylene and acetic acid into the fluid bed reactor through one or more inlets, feeding an oxygen-containing gas into the fluid bed reactor through at least one further inlet, co-joining the oxygen-containing gas, ethylene and acetic acid in the fluid bed reactor while in contact with a fluid bed catalyst material to enable the ethylene, acetic acid and oxygen to react to produce vinyl acetate and recovering the vinyl acetate from the fluid bed reactor.
The manufacture of vinyl acetate from ethylene, acetic acid and oxygen is an exothermic reaction and it is necessary to provide means to cool the fluidised bed reactor heat liberated. Failure to do so could lead to loss of temperature control of the reactor and eventually thermal runaway. In addition to the safety implication of thermal runaway there is the probability of catalyst damage/deactivation as a result of the high temperatures involved.
One means of cooling the system is to inject a liquid into the reaction wherein the liquid is introduced into the reactor for the purpose of removing heat therefrom by evaporation of the liquid.
Water may be used for this purpose, because water has a relatively high latent heat of evaporation. The introduction of water for this purpose, whilst effectively cooling the reaction, however, has surprisingly been found to adversely affect the selectivity to vinyl acetate product. Alternatively, the liquid acetic acid may be used to cool the system. EP-A-0847982 discloses the introduction of recycled acetic acid for this purpose. EP-A-0847982 further states that water may be present in the recycle stream as a by-product of the reaction. In practice, it is very difficult and practically inconvenient to remove all water from the acid recycle stream.
BRIEF DESCRIPTION OF THE INVENTION
We have now found that the selectivity of vinyl acetate product can be maintained at an acceptable level and the reaction system kept at the desired operating temperature by introducing recycled liquid acetic acid into the reactor wherein the recycle stream comprises a low, but effective, concentration of water.
Accordingly, the present invention provides a process for the production of vinyl acetate said process comprising:
(a) feeding ethylene, acetic acid and an oxygen-containing gas into a reactor, co-joining the ethylene, acetic acid and oxygen-containing gas at elevated temperature in the reactor in the presence of a catalyst material (i) to produce a product mixture comprising vinyl acetate, (ii) a liquid by-product comprising acetic acid and water and (iii) a gaseous by-product comprising carbon dioxide; (b) separating the liquid by-product from the product mixture; (c) treating the liquid by-product to reduce the water content therein; and (d) recycling the treated liquid by-product to the reactor in which the amount of water entering the reactor comprises less than 6 wt %, preferably less than 4 wt %, more preferably less than 3 wt % of the total of acetic acid and water entering the reactor.
The present invention solves the problem associated with the prior art by maintaining the temperature of reaction and obtaining high selectivity of vinyl acetate product by introducing water into the reactor, at relatively low levels, suitably admixed with acetic acid in the liquid by-product recycle. By the acetic acid entering the reactor is meant the total acetic acid, namely the fresh acetic acid and recycle acetic acid.
In the present invention, restricting the amount of water entering the reactor reduces the adverse effect water has been found to have on the reaction, whilst still achieving a cooling effect.
The present invention provides a process for the production of vinyl acetate from ethylene, an oxygen-containing gas and acetic acid. The ethylene may be substantially pure or may be admixed with one or more of nitrogen, methane, ethane, carbon dioxide, hydrogen and/or low levels of C
3
/C
4
alkenes or alkanes. The ethylene in the combined feed to the reactor may be at least 60 mol %.
The oxygen-containing gas may be air or a gas richer or poorer in molecular oxygen than air. Suitably, the gas may be oxygen diluted with a suitable diluent, for example, nitrogen, argon or carbon dioxide. Preferably, the oxygen containing gas is oxygen.
The catalyst suitable for use in the process of the present invention is a Group VIII metal based catalyst on a support. Preferably, the Group VIII metal is palladium. Suitable sources of palladium include palladium (II) chloride, sodium or potassium tetrachloropalladate (II) (Na
2
PdCl
4
, or K
2
PdCl
4
), palladium acetate, H
2
PdCl
4
, palladium (II) nitrate, and palladium (II) sulphate. Suitably, the palladium concentration is at least 0.2% by weight, preferably greater than 0.5% by weight, especially about 1% based upon the total weight of catalyst. The palladium concentration may be as high as 10% by weight.
In addition to palladium, the catalyst may suitably comprise a promoter. Suitable promoters include gold, copper and/or nickel. The preferred metal is gold. Suitable sources of gold include gold chloride, tetrachloroauric acid HAuCl
4
, NaAuCl
4
, KAuCl
4
, dimethyl gold acetate, barium acetoaurate or gold acetate. The preferred compound is HAuCl
4
. The metal may be present in an amount of from 0.1 to 10% by weight in the finished catalyst.
In addition to the palladium and the promoter, the catalyst may also suitably comprise a co-promoter which is a metal selected from Group I, Group II, lanthanide or transition metals, for example cadmium, barium, potassium, sodium, iron, manganese, nickel, antimony and/or lanthanum which are present in the finished catalyst as salts, typically acetates. Generally potassium will be present. The metal may be present in a concentration of from 0.1 to 15%, preferably 1 to 5% by weight of metal in the finished catalyst. Suitably, the catalyst may comprise up to 15% by weight co-promoter. Where the process is carried out in a fixed bed reactor, it is preferred to have a co-promoter concentration of 3 to 11% by weight. Where the process is carried out in a fluid bed reactor, and especially with liquid acetic acid, the preferred concentration of co-promoter is up to 6% by weight, especially 2.5 to 5.5% by weight where a liquid acetic acid feed is used. Where the acid is introduced in the vapour phase the co-promoter may be present in a concentration up to 11 wt %.
The catalyst is a supported catalyst. Suitable supports include porous silica, alumina, silica/alumina, silica/titania, titania, zirconia or carbon. Preferably, the support is silica. Suitably, the support may have a pore volume from 0.2 to 3.5 mL per gram of support, a surface area of 5 to 800 m
2
per gram of support and an apparent bulk density of 0.3 to 1.5 g/mL. For fluid bed operation, the support may typically have a particle size distribution such that at least 60% of the catalyst particles have a particular diameter of below 200 microns. Preferably, at least 50%, more preferably at least 80% and most preferably at least 90% of the catalyst particles have a particular diameter of less than 105 microns. Preferably no more than 40% of the catalyst particles have a diameter of less than 40 microns.
The catalyst may suitably be prepared according to the method described in detail in EP -A-0672453. Suitably, the first stage of the catalyst preparation process involves impregnation of the support material with a solution containing the required Group VIII metal and the promoter metal in the form of soluble salts. Examples of such salts are soluble halide de
Baker Michael James
Bristow Timothy Crispin
Clarke Robert William
Kitchen Simon James
Williams Bruce Leo
BP Chemicals Limited
Deemie Robert W.
Geist Gary
Nixon & Vanderhye
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