EP1083989A1

EP1083989A1 - Catalyst based on palladium, cadmium, alkali and lanthanoids and a method for producing vinyl acetate

Info

Publication number: EP1083989A1
Application number: EP98965733A
Authority: EP
Inventors: Bernhard Herzog; Tao Wang; Ioan Nicolau
Original assignee: Celanese Chemicals Europe GmbH; Celanese International Corp
Current assignee: Celanese Sales Germany GmbH; Celanese International Corp
Priority date: 1997-12-11
Filing date: 1998-12-02
Publication date: 2001-03-21
Also published as: ID25474A; WO1999029419A1; DE19755022C2; CA2313644A1; US6346501B1; DE19755022A1; BR9813560A; KR20010032973A; CN1281385A; JP2001525245A

Abstract

The invention relates to a catalyst which contains palladium and/or compounds thereof, cadmium compounds, alkali metal compounds and at least one lanthanoid metal. The invention also relates to the utilization of the catalyst in order to produce vinyl acetate from acetic acid, ethylene and oxygen or gases containing oxygen.

Description

CATALYST BASED ON PALLADIUM, CADMIUM, ALKALI AND LANTHANOIDS AND METHOD FOR PRODUCING VINYL ACETATE

The present invention relates to a catalyst which contains palladium and / or its compounds, cadmium compounds, alkali metal compounds and at least one lanthanide metal compound, and its use for the production of vinyl acetate from gases containing acetic acid, ethylene and oxygen or oxygen.

It is known that in the gas phase, ethylene can be reacted with acetic acid and oxygen or oxygen-containing gases over fixed bed catalysts containing palladium / cadmium / alkali metal to give vinyl acetate. According to US-A-4 902 823, US-A-3 939 199, US-A-4 668 819, the catalytically active metal salts are applied to the catalyst support by impregnation, spraying, vapor deposition, dipping or precipitation. The production of a catalyst containing palladium, cadmium and potassium is also known, a support material provided with a binder, for example an alkali metal or alkaline earth metal carboxylate, being washed with an acid before impregnation and treated with a base after impregnation (EP-A- 0 519 435).

According to EP-A-0 634 209, catalysts containing palladium, cadmium and potassium are prepared by soaking the carrier particles with thorough mixing with a solution of palladium, cadmium and potassium salts and then drying them immediately, the dynamic viscosity of the Solution is at least 0.003 Pa • s and the solution volume during impregnation is 5 to 80% of the pore volume of the carrier particles. According to EP-A-0 634 208 one can use a solution volume when impregnating that is more than 80% of the pore volume of the carrier particles. However, in this mode of operation, the time until the start of drying must be so short that after the end of drying a shell of 5 to 80% of the pore volume contains the metal salts mentioned.

Catalysts containing palladium, cadmium and potassium can also be prepared by the process disclosed in EP-A-0 634 214 in such a way that the carrier particles are mixed thoroughly with a solution of palladium, cadmium and potassium salts in the form of Drops of an average diameter of at least 0.3 mm or sprayed in the form of liquid jets and then dried immediately, the dynamic viscosity of the solution being at least 0.003 Pa • s and the solution volume when sprayed being 5 to 80% of the pore volume of the carrier particles.

It is known from PCT application WO 96/37455 that such catalysts can be considerably improved by adding at least one rhenium and / or at least one zirconium compound. For example, a coated catalyst containing palladium, cadmium, and potassium shows a space-time yield (grams of vinyl acetate formed per liter of catalyst and hour) of 922 (g / l'h), while after addition of zirconium under otherwise identical conditions, an initial output of 950 g / l " h is observed.

Surprisingly, it has now been found that palladium, cadmium and potassium-containing catalysts are significantly improved by adding at least one lanthanide metal compound, ie they have a higher space-time yield with the same or higher selectivity for vinyl acetate. An object of the invention is accordingly a process for the production of vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases on a catalyst which contains palladium and / or its compounds, cadmium compounds and alkali metal compounds on a support, characterized in that the Catalyst additionally contains at least one lanthanoid metal compound.

Another object of the invention is a catalyst which contains palladium and / or its compounds, cadmium compounds and alkali metal compounds on a support, characterized in that the catalyst additionally contains at least one lanthanoid metal compound.

The term "lanthanide metals" includes the 14 rare earth elements cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, as well as the elements scandium, yttrium and lanthanum Understand rare earth elements similar chemical behavior.

The known inert carrier materials such as silica, aluminum oxide, aluminum silicates, silicates, titanium oxide, zirconium oxide, titanates, silicon carbide and carbon are suitable as carriers. Carriers of this type 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 (angstroms) (measured using mercury porosimetry), especially silica ( Si0 ₂ ) and Si0 ₂ -Al ₂ 0 ₃ mixtures. These carriers can be used in any form, such as in the form of spheres, tablets, rings, stars or other shaped particles, whose diameter or length and thickness is generally 3 to 9 mm.

Such carriers can be produced, for example, from aerogenic Si0 ₂ or an aerogenic Si0 ₂ -Al ₂ 0 ₃ mixture, which can be produced, for example, by flame hydrolysis of silicon tetrachloride or a silicon tetrachloride-aluminum trichloride mixture in a detonating gas flame (US-A -3 939 199).

Suitable solvents for the palladium, cadmium, alkali metal and lanthanide metal salts are all compounds in which the selected salts are soluble and which can be easily removed by drying after impregnation. If acetates are used, unsubstituted carboxylic acids with 2 to 10 carbon atoms, such as acetic acid, propionic acid, n- and isobutyric acid and the various valeric acids, are particularly suitable. Because of their physical properties and also for economic reasons, acetic acid is preferred among the carboxylic acids. Water is particularly suitable for the chlorides, chloro and acetate complexes. The additional use of a further solvent is expedient if the salts are not sufficiently soluble in acetic acid or in water. For example, Dissolve palladium chloride in an aqueous acetic acid much better than in glacial acetic acid. Possible additional solvents are those which are inert and miscible with acetic acid or water. Examples of additives for acetic acid are ketones such as acetone and acetylacetone, furthermore ethers such as tetrahydrofuran or dioxane, but also hydrocarbons such as benzene.

Several salts of palladium, cadmium, alkali metal and the respective lanthanoid metal can be applied, however in general, exactly one salt is applied from each of these elements.

Either so-called "impregnated" catalysts can be produced, in which the catalytically active metal compounds have penetrated to the core in the carrier particles, or so-called "shell catalysts", in which the metal salts have not penetrated to the core, but only in one more or less large outer part of the carrier particles, ie the so-called "shell" of the particles.

The elements to be applied in each case palladium, cadmium, alkali metal and lanthanide metal can be applied in the form of salt solutions individually or in any combination in any order, preferably a single solution is used which contains these elements to be applied in the form of salts. It is particularly preferred to use a single solution which contains exactly one salt from each of these elements to be applied. This solution can also contain a mixture of salts of at least two different lanthanoid metals, preferably this solution contains a salt of only one lanthanoid metal.

If one speaks in the following in general about “the solution of the salts”, the same applies mutatis mutandis in the event that several solutions are used in sequence, each containing only a part of the total salts to be applied, the individual parts add to the total amount of salts to be applied to the carrier.

The procedure for the preparation of impregnated catalysts is preferably as follows (US Pat. No. 4,902,823, US Pat. No. 3,393,199, US Pat. No. 4,668,819): The catalyst support is impregnated with the solution of the active components in such a way that the support material is covered with the solution and, if necessary, excess solution is then poured off or filtered. With regard to solution losses, it is advantageous to use only the amount of solution which corresponds to the integral pore volume of the catalyst support and to mix thoroughly so that the particles of the support material are uniformly wetted. It is expedient to carry out the impregnation process and the mixing at the same time, for example in a rotary drum or a tumble dryer, and drying can follow immediately. Furthermore, it is generally expedient to measure the composition of the solution used to impregnate the catalyst support in such a way that the desired amount of active substances is applied by one impregnation. However, this amount can also be applied by means of several impregnations, drying preferably after each impregnation.

To produce coated catalysts, the procedure is preferably one of the three following, always using a solution of at least one salt of at least one of the elements palladium, cadmium, alkali metal and lanthanoid metal with a dynamic viscosity of at least 0.003 Pa · s, preferably 0.005 to

0.009 Pa • s is used:

1. The carrier particles are sprayed one or more times with intimate mixing with the solution of the salts in the form of drops with an average diameter of at least 0.3 mm or in the form of liquid jets and dried immediately after each spraying. The "immediate" drying means that the drying of the sprayed particles must be started. It is generally sufficient if drying of the particles is started within 30 minutes after the end of spraying. The solution volume is 5 to 80% of the pore volume of the carrier particles with each spraying. This method is described in detail in EP-A-0 634 214, to which reference is hereby expressly made (incorporation by reference).

2. The carrier particles are soaked one or more times with thorough mixing with the solution and dried immediately after each soaking. The "immediate" drying means the same as in the first method, and the volume of solution with each impregnation is 5 to 80% of the pore volume of the carrier particles. This method is described in detail in EP-A-0 634 209, which is also expressly incorporated by reference.

3. The carrier particles are impregnated with the solution one or more times and dried after each impregnation, but in contrast to the second method, the volume of the solution is not limited. It is now more than 80% of the pore volume with each soak. Because of the larger volume of solution, intimate mixing is not absolutely necessary, although generally useful. Instead, the duration of each impregnation and the time to the start of the subsequent drying, ie the time from the start of each impregnation to the start of the subsequent drying, must now be so short that after the end of the last drying a bowl of 5 to 80% of the pore volume of the carrier particles contains the catalytically active elements. How short this time must be chosen for this purpose can be seen easily determined by preliminary tests. This method is described in detail in EP-A-0 634 208, to which express reference is hereby made.

The impregnated or sprayed catalyst support is preferably dried under reduced pressure (0.01 to 0.08 MPa) both in the case of fully impregnated catalysts and in the case of coated catalysts. The drying temperature should generally be 50 to 80 ° C, preferably 50 to 70 ° C. Furthermore, it is generally advisable to carry out drying in an inert gas stream, for example in a nitrogen or carbon dioxide stream. The residual solvent content after drying should preferably be less than 8% by weight, in particular less than 6% by weight.

The finished palladium, cadmium, alkali metal and catalysts containing at least one lanthanide metal have the following metal contents:

Palladium content generally 0.6-3.5% by weight, preferably 0.8-3.0% by weight; in particular 1.0-2.5% by weight

Cadmium content: generally 0.1-2.5% by weight, preferably 0.4-2.5% by weight; in particular 1.3-2% by weight

Alkali metal content: generally 0.3-10% by weight. Potassium is preferably used.

Potassium content in general 0.5-4.0% by weight, preferably 1.0-3.0% by weight; in particular 1.5-2.5% by weight Lanthanoid metal content: generally 0.01-1% by weight, preferably 0.05-0.5% by weight, in particular 0.2-0.5% by weight.

If more than one lanthanoid metal is used for doping the catalysts containing palladium, cadmium and alkali metal, the term “lanthanoid metal content” is understood to mean the total content of all lanthanoid metals contained in the finished catalyst. The percentages given always relate to the amounts of the elements palladium, cadmium, alkali metal and lanthanide metal present in the catalyst, based on the total mass of the catalyst (active elements plus anions plus support material).

Suitable salts are all salts of palladium, cadmium, an alkali metal and a lanthanoid element which are soluble; the acetates, the chlorides, the acetato and the chloro complexes are preferred. However, in the case of interfering anions, e.g. in the case of chlorides, it must be ensured that these anions are largely removed before the catalyst is used. This is done by washing out the doped carrier, e.g. with water after the metals have been converted into an insoluble form, for example by reduction and / or by reaction with alkaline compounds.

Particularly suitable as salts of palladium are the carboxylates, preferably the salts of aliphatic monocarboxylic acids with 2 to 5 carbon atoms, for example the acetate, propionate or butyrate. Also suitable are, for example, nitrate, nitrite, oxide hydrate, oxalate, acetylacetonate or acetoacetate. Because of its good solubility and availability, palladium acetate is the particularly preferred palladium salt. Acetate is particularly suitable as a cadmium compound.

The alkali metal compound used is preferably at least one sodium, potassium, rubidium or cesium compound, in particular at least one potassium compound. Carboxylates, in particular acetates and propionates, are particularly suitable as compounds. Also suitable are compounds which change into the alkali acetate under the reaction conditions, such as the hydroxide, the oxide or the carbonate.

The chlorides, nitrates, acetates and acetylacetonates are particularly suitable as the lanthanide metal compound.

If reduction of the palladium compounds is carried out, which is sometimes useful, a gaseous reducing agent can be used. Examples of suitable reducing agents are hydrogen, methanol, formaldehyde, ethylene, propylene, isobutylene, butylene or other olefins. The reduction temperature is generally between 40 and 260 ° C, preferably between 70 and 200 ° C. In general, it is expedient to use a reducing agent which is diluted with inert gas and contains 0.01 to 50% by volume, preferably 0.5 to 20% by volume, of reducing agent for the reduction. For example, nitrogen, carbon dioxide or an inert gas are suitable as inert gases. The reduction can also be carried out in the liquid phase at a temperature of from 0 ° C. to 90 ° C., preferably from 15 to 25 ° C. For example, aqueous solutions of hydrazine, formic acid or alkali borohydrides, in particular sodium borohydride, can be used as reducing agents. The amount of reducing agent depends on the amount of palladium; the reduction equivalent should be at least the simple oxidation equivalent, but larger amounts of reducing agent are harmful Not. The reduction is carried out after drying.

The vinyl acetate is generally prepared by passing gases containing acetic acid, ethylene and oxygen at from 100 to 220 ° C., preferably 120 to 200 ° C., and at pressures from 0.1 to 2.5 MPa, preferably 0.1 up to 2.0 MPa, over the finished catalyst, whereby unreacted components can be circulated. Dilution with inert gases such as nitrogen or carbon dioxide may also be advantageous. Carbon dioxide is particularly suitable for dilution, since it is formed in small quantities during the reaction.

With the aid of the catalysts according to the invention, it is possible to produce more vinyl acetate per reactor volume and time with the same reaction conditions and at the same time improved selectivity. This makes it easier to work up the crude vinyl acetate obtained, since the vinyl acetate content in the reactor starting gas is higher, which furthermore leads to energy savings in the work-up part. A suitable workup is e.g. in US-A-5 066 365.

If, on the other hand, you want to keep the space-time yield constant, you can lower the reaction temperature and thus carry out the reaction more selectively with the same overall performance, thereby saving educts. At the same time, the amount of carbon dioxide formed as a by-product and therefore to be discharged and the loss of entrained ethylene associated with this discharge are reduced. In addition, this driving style leads to an extension of the catalyst life. The following examples are intended to illustrate the invention, but do not limit it. The percentages of the elements palladium, cadmium, potassium and the lanthanoid metal are percentages by weight, based on the total mass of the catalyst.

Si0 _{2 was} used as the catalyst support material, from which tablets with a diameter and a height of 6 mm each were made according to DE-OS 3 912 504. These tablets were used as a catalyst support. The pore volume of 1 1 carrier was 392 ml.

Example] I

At 65 ° C, 25.3 g (0.11 mol) of palladium acetate, 25 g (0.09 mol) of cadmium acetate, 25.3 g (0.26 mol) of potassium acetate and 6.82 g (0.016 mol) of ceracetylacetonate were dissolved in 130 ml of glacial acetic acid dissolved (solution volume = 33% of the pore volume) and the highly viscous solution filled into a pre-heated to 65 ° C. 1 1 catalyst support were also heated to 65 ° C and placed in a flask. The entire impregnation solution was poured over the carrier particles and thoroughly mixed until the entire impregnation solution had been absorbed by the catalyst support. This process ended after 3 minutes. Drying was carried out in a nitrogen stream at 65 ° C. and 0.02 MPa to constant weight. The finished catalyst contained 2.0 wt% Pd, 1.7 wt% Cd, 1.7 wt% K and 0.38 wt. -% Ce. Comparative example] _____

The procedure was as in Example 1, but the addition of lanthanide metal salts in the impregnating solution containing palladium acetate, cadmium acetate and potassium acetate was dispensed with. The finished catalyst contained 2.0% by weight of Pd, 1.7% by weight of Cd and 1.7% by weight of K.

The catalyst according to the invention prepared according to Example 1 and the catalyst prepared according to Comparative Example la were tested by the following method. 225 ml of the respective catalyst were introduced into a reaction tube with an inner diameter of 20 mm and a length of 65 cm. The gas to be reacted was then passed over the catalyst over a period of 5 days at a pressure of 0.8 MPa (reactor inlet) and a catalyst temperature of 150 ° C. This gas consisted of 58 vol% ethylene, 25 vol% nitrogen, 12 vol% acetic acid and 5 vol% oxygen; the results are shown in the table.

Space-time yield in grams of vinyl acetate per liter of catalyst per hour.

C0 ₂ selectivity in%, based on the amount of ethylene converted. Surprisingly, it was found that even small additions of lanthanoid metal compounds to the known palladium, cadmium and potassium-containing catalysts significantly improve the CO ₂ selectivity and the performance (space-time yield) of these catalysts in the production of vinyl acetate.

Claims

claims

1.) Process for the production of vinyl acetate in the gas phase from ethylene, acetic acid and oxygen or oxygen-containing gases on a catalyst which contains palladium and / or its compounds, cadmium compounds and alkali metal compounds on a support, characterized in that the catalyst additionally contains at least one lanthanide metal compound.

2.) Process according to claim 1, characterized in that the catalyst contains at least one potassium compound.

3.) Process according to claim 1 or 2, characterized in that the catalyst contains 0.01 wt .-% to 1 wt .-% lanthanoid metal, based on the total mass of the catalyst.

4.) Process according to one of claims 1 to 3, characterized in that the catalyst contains 0.05 wt .-% to 0.5 wt .-% lanthanoid metal, based on the total mass of the catalyst.

5.) Catalyst containing palladium and / or its compounds, cadmium compounds and alkali metal compounds on a support, characterized in that the catalyst additionally contains at least one lanthanoid metal compound.

6.) Catalyst according to claim 5, characterized in that the catalyst contains at least one potassium compound.

7.) Catalyst according to claim 5 or 6, characterized in that the catalyst contains 0.01 wt .-% to 1 wt .-% lanthanoid metal, based on the total mass of the catalyst.

8.) Catalyst according to one of claims 5 to 7, characterized in that the catalyst contains 0.05% by weight to 0.5% by weight of lanthanide metal, based on the total mass of the catalyst.