Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2000-07-20
2003-06-17
Killos, Paul J. (Department: 1623)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S303000, C502S304000, C502S326000, C502S330000
Reexamination Certificate
active
06579824
ABSTRACT:
This application is a 371 of PCT/EP98/027816 filed Dec. 2, 1998.
The present invention relates to a catalyst which comprises palladium and/or its compounds, gold and/or its compounds, alkali metal compounds and at least one lanthanoid metal and/or its compounds, and to its use for preparing vinyl acetate from acetic acid, ethylene and oxygen or oxygen-containing gases.
It is known that ethylene can be converted in the gas phase with acetic acid and oxygen or oxygen-containing gases on palladium/gold/alkali metal-containing fixed bed catalysts into vinyl acetate.
The palladium/gold/alkali metal-containing catalysts have a particular noble metal distribution, with the noble metals being present in a shell on the carrier particles, while the core of the particles is substantially free of noble metals. Catalysts with this noble metal distribution are distinguished by an increased specific productivity (g of vinyl acetate/g of noble metal). The noble metal compound in shell form is achieved by impregnation and subsequent precipitation of the noble metals using alkaline compounds.
The process disclosed in U.S. Pat. No. 4,048,096 for preparing palladium, potassium and gold-containing catalysts entails initial impregnation of the carrier material with an aqueous solution which comprises a mixture of palladium and gold salts. The metal salts are then converted by treatment with alkalis into water-insoluble compounds and are fixed on the carrier material in this way. Subsequent treatment with a reducing agent reduces the palladium and gold compounds to the corresponding metals. Finally, the carrier material loaded with palladium and gold is treated with an alkali metal acetate solution and dried. The impregnation step with the aqueous solution containing palladium and gold salts is characterized by the volume of the impregnation solution corresponding to the pore volume of the carrier material. The resulting catalyst has a shell structure in which palladium and gels are dispersed in a shell thickness of about 0.5 millimeter over the surface of the carrier material.
U.S. Pat. No. 3,775,342 also discloses a process for preparing palladium, potassium and gold-containing catalysts by impregnation with a solution of palladium and gold salts, by subsequent treatment with an alkali solution, which results in water-insoluble palladium and gold compounds precipitating on the carrier, and by subsequent reduction of the metal compounds to the corresponding noble metals. Treatment of the carrier material with an alkali metal acetate solution can take place before or after the reduction step.
U.S. Pat. No. 5,185,308 discloses a palladium, potassium and gold-containing shell catalyst in which the noble metals are dispersed in a shell thickness of 1 millimeter over the carrier material. The known catalyst has a ratio of gold to palladium in the range from 0.6 to 1.25 by weight.
It is further known to prepare a palladium, potassium and gold-containing shell catalyst by washing a carrier material, which has been provided with a binder, for example an alkali metal or alkaline earth metal carboxylate, before the impregnation with an acid, and treating with a base after the impregnation (EP-A-0 519 435).
In the process disclosed in U.S. Pat. No. 5,332,710 for preparing a palladium, gold and potassium-containing shell catalyst, the carrier impregnated with an aqueous palladium and gold salt solution is immersed in an aqueous fixing solution containing sodium hydroxide or potassium hydroxide and agitated therein for at least 0.5 h.
It has now been found, surprisingly, that catalysts of this type can be distinctly improved by adding at least one lanthanoid metal and/or a lanthanoid metal compound, i.e. provide a higher space-time yield with identical or higher selectivity for vinyl acetate.
The invention accordingly relates firstly to a process for preparing vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases on a catalyst which comprises 0.5-2.0% by weight of palladium and/or its compounds, 0.2-1.3% by weight of gold and/or its compounds, and 0.3-10% by weight of alkali metal compounds on a carrier, wherein the catalyst additionally comprises 0.01-1% by weight of at least one lanthanoid metal and/or its compounds, the percentages relating to the metal contents, based on the total mass of the catalyst.
The invention secondly relates to a catalyst which comprises 0.5-2.0% by weight of palladium and/or its compounds, 0.2-1.3% by weight of gold and/or its compounds, and 0.3-10% by weight of alkali metal compounds on a carrier, wherein the catalyst additionally comprises 0.01-1% by weight of at least one lanthanoid metal and/or its compounds, the percentages relating to the metal contents, based on the total mass of the catalyst.
The procedure for preparing the catalysts according to the invention is preferably as follows (U.S. Pat. Nos. 3,775,342, 4,048,096, 5,332,710):
(1) First the carrier particles are impregnated one or more times by being intimately mixed with at least one solution of at least one salt of the elements palladium and gold, and of at least one salt of at least one lanthanoid metal.
(2) The pretreated carrier is treated with a fixing solution with an alkaline reaction, which results in the noble metals and the lanthanoid metals being precipitated in the form of water-insoluble compounds on the surface of the carrier particles, and thus being fixed.
(3) The noble metal compounds deposited on the carrier particles are reduced to the corresponding metals by treatment with a reducing agent. A noble metal shell doped with at least one lanthanoid metal is produced in this way on the surface of the carrier particles.
(4) Interfering anions are removed by washing the treated catalyst.
(5) The treated catalyst is dried at not above 150° C.
(6) The dried carrier is treated with a solution which contains at least one alkali metal compound.
(7) Finally, the treated carrier is dried at not above 150° C.
The procedure in step (1) can also be to apply the salt solutions containing catalytically active substances to the carrier by single or multiple spraying on, vapor deposition or immersion.
The term “lanthanoid metals” means the 14 rare earth elements cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, and the elements scandium, yttrium and lanthanum because their chemical behavior resembles that of the rare earth elements.
Suitable carriers are the known inert carrier materials such as silica, alumina, aluminosilicates, silicates, titanium oxide, zirconium oxide, titanates, silicon carbide and carbon. Particularly suitable carriers of this type are those with a specific surface area of 40 to 350 m
2
/g (measured by the BET method) and an average pore radius of 50 to 2000 Å (Angstrom) (measured by mercury porosimetry), especially silica (SiO
2
) and SiO
2
/Al
2
O
3
mixtures. These carriers can be used in any form such as, for example, in the form of beads, tablets, rings, stars or particles of other shapes, with a diameter or length and thickness generally of 3 to 9 mm.
Carriers of these types can be prepared, for example, from aerogenic SiO
2
or an aerogenic SiO
2
/Al
2
O
3
mixture which can be prepared, for example, by flash hydrolysis of silicon tetrachloride or a silicon tetrachloride/-aluminum trichloride mixture in an oxyhydrogen flame (U.S. Pat. No. 3,939,199).
Suitable solvents for the palladium, gold, alkali metal and lanthanoid metal salts are all compounds in which the selected salts are soluble and which can easily be removed again after the impregnation by drying. Suitable for the acetates are, in particular, unsubstituted carboxylic acids having 2 to 10 carbon atoms such as acetic acid, propionic acid, n- and iso-butyric acid and the various valeric acids. Among the carboxylic acids, acetic acid is preferred because of its physical properties and also for economic reasons. Water is particularly suitable for the chlorides and chloro and acetato com
Herzog Bernhard
Nicolau Toan
Wang Tao
Bierman, Muserlian and Lucas
Celanese Chemicals Europe GmbH
Killos Paul J.
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