DE2209392A1 - Process for activating silver catalysts - Google Patents

Description

SHELL INTIiIRIiATIOHALE RESEARCH MAATSCHAPPIJ N.V., The Hague, Netherlands

"Process for activating silver catalysts" (Addition to patent (patent application - P 2.1 59 346.4)

Priority: 1. Harz 1971, V.St.A. - No. 119 829

The present application relates to an improvement of the method for the production of silver catalysts according to patent,. (Patent application P 21 59 346.4).

The subject of the earlier law is, among other things, a Vg! 'Drive for the production of silver catalysts, which are made up of a porous support material and over the outer surface of the support material and composing the inner surface of the pores of the support material dispersed silver, a method of manufacture of silver deposits on the surface of solids, in particular suitable for the production of silver catalysts, and processes in which such a silver catalyst is used becomes, especially the direct oxidation of ethylene with molecular oxygen to ethylene oxide.

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The present application relates to a method for improving the effect of silver catalysts, which are composed of porous carrier material and silver distributed over the outer surface of the carrier material and the inner surface of the pores of the carrier material and in which the silver is in the form of discrete, almost hemispherical particles with a Is less than 1 micron in diameter, evenly distributed over the outside of the substrate and the inside surfaces of the pores and firmly adhered. The silver is on the surface of the outside of the substrate and on the inside surface of the pores in an amount of 2 up to
15 percent by weight of the total catalyst and especially in an amount of 3 up to 14 percent by weight of the total catalyst.

The hemispherical silver particles preferably have a diameter in the range from 1000 to 10,000 Å with a
average diameter from 1500 up to 7500 A. In particular, the silverteilcheri have a diameter in the range from 1500 up to 5000 δ and an average diameter of about 3000 ft.

In addition to the particle size, it is of crucial importance that the silver is applied in the form of discrete particles and essentially uniformly to both the inner and outer surfaces of the carrier material used. It
It is also important that the silver particles are firmly adhered to the deceptive material. If this is not the case, repeated use of the catalysts leads to gradual use

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Loss of silver from the support material, resulting in a loss of catalytic action and that of the catalyst itself Investment.

The support material to which the discrete silver particles are applied can be selected from a large number of conventional, porous, refractory catalyst support materials or from support material that is inert to the ethylene oxidation feed, the reaction product, and the reaction conditions. Such a conventional carrier material can be of natural or synthetic origin and preferably has a macroporous structure, that is to say a structure with a specific surface area of less than 10 ra ~ / g and preferably of less than 2 m / g. These support materials typically have a measurable porosity greater than 20 percent. Very suitable carrier materials are those made from compositions containing silicon oxide and / or aluminum oxide. Specific examples of suitable carrier materials are the aluminum oxides, including the material sold under the trade name "Alundum", charcoal, pumice stone, magnesium and zirconium oxides, diatomite, fuller's earth, silicon carbide, porous agglomerates consisting of silicon and / or silicon carbide, certain clays, artificial and natural Zeolites, gel-like materials made from oxides of heavy metals, such as molybdenum and tungsten, and ceramic materials.

Heat-resistant support materials particularly suitable for the production of catalysts according to the invention comprise substances based on aluminum oxide, in particular those made from α-aluminum oxide.

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In the case of support materials containing α-aluminum oxide, preference is given to those with a specific surface area of

2 2 ■ ■

0.03 mVg up to 1.0 in / g and a specific pore volume from 0.2 to 0.3 ml / g, in particular from 0.22 to 0.28 ml / g, is used. The specific surface area is determined according to the B.E.T. process determined, i.e., according to the details described by S. Brunauer, P.H. Emmet and E. Teller in J. Am. Chem. Soc. 60, 309-316 (1938) .Process described. The specific pore volume is made by a conventional mercury or water absorption process measured.

When certain types of α-alumina-containing carriers be used; the advantages of the special shape of the discrete silver particles are particularly emphasized. These alpha alumina supports are relatively uniform Pore diameter and are characterized in more detail by the following three parameters:

(1) They have B.E.T.-specific surface areas of 0.1 ra / g up to 0.8 m / g, preferably from 0.15 m / g up to 0.6 m / g;

(2) they have measurable porosities from k2 up to 56 (preferably from 46 up to 52) volume percent; and

(3) They have an average pore diameter of 1 up to

12 microns, preferably from 1.5 up to 10 microns, by mercury porosimetry measured, with a considerable .Teil of their pores, preferably at least 70 percent, a diameter in Range from 1.5 to 15 microns on v / ei st. Specific examples of these, particularly suitable carrier substances are those of the Norton Company under the name "Alundum" in the qualities LA-956, LA-5556, and LA-4118 traded carriers.

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In the earlier patent application mentioned above

(P 21 59 3 ^ 6.4) is also a method of making Silver catalysts of the type in question are disclosed and claimed. After that, a heat-resistant carrier substance is first mixed with a silver salt of a carboxylic acid and an organic Amine-containing solution impregnated and then heated, whereby the silver salts are broken down and a deposit of metallic silver is formed with the properties described above.

A preferred embodiment of this manufacturing process consists of the following stages:

a) The impregnation of the carrier material with an aqueous solution of a silver carboxylic acid salt and a silver dissolving agent organic amine with from 1 to 5 carbon atoms, which can also serve as a reducing agent, and

b) heating the impregnated carrier material to 100 to 375 ^° C. for 2 to 8 hours

The catalysts according to the earlier patent application are therefore excellent because they have a high degree of efficiency and high selectivity. Their initial effect can, however be less than desired. Accordingly, it would be advantageous to have a method for improving the initial effect of this Provide catalysts.

The inventive method for activating silver cables, which consists of a porous carrier material and over the outer surface of the carrier material and the inner surfaces of the Pores of the support material composed of distributed silver and

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in which the silver is in the form of discrete, almost hemispherical particles with a diameter of less than 1 micron , which are evenly distributed over the outside of the substrate and the inside surface of the pores and

are firmly adhered, according to patent (patent application

P 21 59 346.4) is characterized in that one

A. heating the catalyst 4 to 24 hours at a in the range between 175 ⁰ C and 3OO ° C lying temperature;

B. the catalyst contacted with one or more anhydrous alkanols having 1 or 2 carbon atoms in the molecule;

C. separating the activated catalyst.

The heating in stage A) can be carried out in air or in a non- oxidizing atmosphere, such as, for example, in nitrogen, argon, ethylene or methane. A suitable temperature range for heating is from 175 ° C to 30O ⁰ C and preferably from 200 to 275 ° C. In particular, temperatures of 220 ^° C. up to 250 ^° C. are used for the heating. The heating time required is generally from 4 to 24 hours, preferably from 8 to 16 hours. It is understood that the time used and the temperature used in general depend mutually from each other, with higher temperatures have a shorter heating time and lower temperatures a longer heating time is required.

The exact mode of action and the exact purpose of the heating are not fully known. It was observed, however, that when using the catalysts prepared by the above-described process, certain incompletely identical

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fixed derivatives of those involved in the manufacturing process organic amines volatilize from the surface of the catalyst during heating. The volatilized material appears to contain adducts of carbon dioxide and amines. In As a rule, it has been found that heating at 250 ° C. for 8 hours or heating at 220 ° C. for 16 hours is effective Achieving the desired activation of the catalyst is sufficient;

The heating can be carried out by any method. The treatment of the catalyst can be carried out in batches, e.g. with baskets in an oven, or continuously, e.g. on a continuous belt dryer.

After heating, the catalyst will be with one or more Brought alcohols with 1 to 2 carbon atoms in contact, that is, with methanol and / or ethanol. It can be smaller Amounts, e.g. up to 5 percent by volume of other materials, e.g. B. can in the ethanol denaturation amounts of benzene used must be present. Virtually anhydrous alkenols are preferably used. Definitely have to Avoid large amounts of water.

The temperature at which the catalysts are brought into contact with the alkenol (s) is not decisive. In general, however, the best results were achieved by heating the alcohol (s) to a temperature between 40 ° C and the boiling point (methanol G ^[ ;> C, ethanol 78 C)! (become) even though higher or lower temperatures are effective.

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The amount of alcohol used can vary. When treating the batches, it is generally advisable to use at least enough alcohol to completely submerge the catalyst. Better results are obtained from batch treatment when the catalyst is immersed a few times in fresh alcohol. Preferably the Catalyst from 2 to 4 times, most conveniently 3 times, immersed in fresh alcohol. Every contact treatment takes time preferably from 5 to 30 minutes, although time is not particularly critical. It can be seen that the described, Here marriage performed in batches without any additional information can be adapted to a continuous process.

As with heating, the exact mode of action is the alcohol contact treatment not known. It is perfectly possible, however, that the alcohol washing serves to remove any To remove most of the nitrates present in the catalyst, e.g. potassium nitrate. In general it may be sufficient to remove most of the nitrates present by a sufficient washing treatment with the alkanol, to obtain an effective catalyst. But it has also been observed that by washing with water, which also removes nitrates does not provide an effective catalyst.

If the catalyst is used for the direct oxidation of ethylene, a modification of the process which is preferably used is to carry out the activation process in the ethylene oxide reactors. It is well known that there are a large number of commercially used reactors of this type

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parallel, more vertical, filled with solid silver catalyst beds Tubes included. These tubes are a convenient place to perform the activation. Both the heating «stage Λ) how the alkanol contact treatment stage B) can, as well as the isolation stage C) easily in such a reactor carried out v / earth. This last step consists essentially in separating the catalyst from the alkanol. this can e.g. be carried out by sieving, straining, but also by a drying process that involves heating and the Passing large volumes of drying gas such as air, nitrogen, methane and ethylene over the catalyst. This Drying process should be continued until the alkanol (s) has been completely removed, as alkanol residues represent a possible contamination of the ethylene oxide product.

It is customary in industrial practice to carry out the direct oxidation of ethylene under circulatory conditions, very pure ethylene and very pure oxygen being fed into the circulation system, if desired together with a relatively small proportion of a powerful reactant, such as helium or methane that maintain a relatively high concentration of said non-reactant in the diluent gas can be, with the addition of ethylene and oxygen to compensate Substances added to the system have a relatively small decrement ig.strom nbgozogon is so that the prevailing in the circulatory system Conditions during continuous operation are kept essentially constant at all points and at least a part of the carbon dioxide by washing out of the,

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after the recovery of the ethylene oxide product by absorption and removal of the branch stream, the remaining gaseous circulation mixture is removed. In the use according to the invention activated silver catalysts, the conventional reaction temperatures are suitable, ie, reaction temperatures in the range of 190 ⁰ C up to 240 ° C and preferably from 205 ⁰ C to 22 ^ ⁰ C.

The activation method of the present invention is carried out by the following Examples explained in more detail. As usual, the comparative tests were carried out with a simplified system (single-through-flow method) instead of the circulation process carried out in the industrial scale production of ethylene oxide is used without exception.

example 1

A. A supported silver catalyst was prepared. A certain amount of spectroscopically pure silver nitrate was dissolved in water, thereby preparing a solution containing 67 percent by weight of silver nitrate. This solution was added at a temperature of 54 ° C. with a 5 percent molar excess to a concentrated potassium oxalate solution which was obtained by neutralizing a technically pure potassium hydroxide solution with technically pure oxalic acid. The silver oxalate precipitated, was separated off and washed repeatedly with water in an attempt to remove as large a part of the remaining nitrate ions as possible. The silver oxalate was then dissolved in ethylenediamine at 25 to 50 ° C. Then monoethanolamine was added and the solution was diluted with water, whereby an impregnation solution with

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21 weight percent silver, 1.1 mol ethylene diamine and 0.6 mol Ethanolamine received per mole of silver. A porous, heat-resistant one Carrier material (aluminum oxide from Norton Company with the trade name "Alundum") v / an intestine in a vacuum with this solution impregnated. The excess liquid was removed by shaking and the catalyst was then removed for 30 to 40 minutes heated at 150 ° C for a long time, whereby the silver oxalate disintegrated and a metallic silver deposit was obtained. The finished one The catalyst contained 8 weight percent silver.

B. A sample of the catalyst from Part A of this example was tested as a catalyst for the production of ethylene oxide. Pieces of the catalyst were crushed and 3.5 g of the particles ranging in size from 383 to 529 microns into one 127 mm long reaction tube with a diameter of 5.08 mm. An air-ethylene mixture was in the presence of a Chlorine-containing braking substance passed over the catalyst under the following reaction conditions:

Pressure, atmospheres abs. 15th

Space flow velocity. Hours 2360 ethylene feed, mole percent 30

Ethylene / oxygen ratio 3.75

Concentration of the chlorine contained in the braking substance _{p, TpM}

It was maintained at a temperature of 21O ⁰ C for 72 hours and the catalyst periodically listed · the efficiency by measuring the degree of conversion of oxygen. The oxygen conversion observed is listed in Table I.

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Table I. Op conversion Duration of operation "in percent S do n'Jen 12.1 1 12.1 1? 14.2 24 15.3 56 12.2 48 11.7 72

The temperature was then increased to determine the temperature at which 40 percent oxygen conversion occurs. A temperature of over 250 ^° C. was required. The selectivity of the conversion of ethylene into ethylene oxide was less than 20 percent.

C. Four samples of the catalyst prepared in Part A of this example were treated for activation. First, the samples were heated to ^ air in an oven for 2 hours at 23O ⁰ C. A sample (Sample A) was then washed three times at 50 ° C. with approximately the same volume of anhydrous ethanol.

Another sample (Sample B) was then washed three times at 50 ° C with approximately the same volume of anhydrous methanol.

The other samples (Samples C and D) were given the same treatment (Sample C) with isopropanol and (Sample D) with V / water.

The four catalyst samples were then separated from the wash solutions and completely dried.

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- 115 -

D. The four samples prepared in Part C of this example were tested as ethylene oxidation catalysts according to the procedure and in the system from Part B of this example. The results of these experiments showed that the catalysts treated according to the invention (samples Λ and B) showed a very extraordinarily improved behavior, while the other catalysts
(C and D) showed slight improvements at best.
The oxygen conversion was noted at 210 C and is in
Table II listed.

Table e II

Operational oxygen conversion at 21O ⁰ G in
duration, percent

Hours of catalyst of untreated ca-

AB C D catalyst

(from part B)

1 48.3 48.2 12, 8th 15th , 6 12.1 12th 43.2 45.2 13, 3 15th , 3 12.1 24 - 43.3 14, 5 - 14.2 36 47.5 45.3 - - 13.3 48 49.4 45.7 - 27 , 6 12.2 72 53.1 46.1 - 31 , 9 11.7

Two of the four catalysts treated were ultimately used to determine the amount required for 40 percent oxygen conversion Temperature checked. This temperature and the observed selectivity for ethylene oxide are given in the table III listed.

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Table III

Catalyst sample To achieve a 40 percent selectivity

oxygen conversion at 40 percent

e rf ο i'der 1 i chc ^ T omp era tujr- gor

Λ 204

B 204

74, 8th as 74, 6th smaller 20th

B e i s p i e 1 2,;

A silver catalyst was prepared by following the procedure in Example 1, Part A. Since the solution concentrations were somewhat different in this preparation, the finished catalyst contained 7.8 percent by weight silver. 14 kg of this material was placed in a single 10.1 m long reactor tube with a diameter of 4.4 cm. Initially, this catalyst was relatively ineffective and required a temperature of over 250 C for a 40 percent oxygen conversion with a selectivity for ethylene oxide of less than 20 percent. A summary of the conditions and results of this experiment are shown in Table IV. After heating in Ostündigem Äthylenoxydationsreaktor on etv / a 240 ⁰ C, the catalyst was washed twice in each case, washed with about two bed volumes of the ethanol catalyst. After drying in the reaction tube, the catalyst was again examined for its effectiveness with regard to ethylene oxidation and showed excellent behavior. The results of this test are shown in Table IV.

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Pressure j atm abs.

Space route speed, Hours -1

Ethyleiir.uspej.aunf ;, mole percent

Contained in the braking substance Ch 1 ο 11 '. on ζ en t r & ti on, G c wi ch t s -TpM

To achieve a 52% S au ers tοffum \ 'and 1 \ mg required 1 i ch e temperature, in ^ C

Selectivity with regard to ethylene oxide, in percent

16

3300

30th

254

69.9

treat] t

16

3300

30th

230 76.1

Example 3

A silver catalyst was prepared according to Example 1, Part A. This catalyst contained 7.8 weight percent silver. When tested as an ethylene oxidation catalyst, this catalyst showed good initial effectiveness. A sample of this catalyst was then subjected to a treatment by heating them Z hours at 230 ⁰ C and then washed three times with ethanol and separated from the wash liquid v / urde. The treated material was then tested as an ethylene oxidation catalyst. Even with this active catalyst, the activation maneuvering was useful. The initial activity was increased as shown in Table V.

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- 16 Table V

Operating oxygen conversion at 210 ^° C., in percent

Hours "untreated catalyst treated catalyst

1 37.8 39.0

12 32.3 35.9

24 35.8 40.4

36 35.7 42.5

48 35.4 52.1

72 45.0 52.7

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Claims (9)

Paten t a ηs ρ r ü c h e 1. Process for the activation of silver catalysts, which consist of a porous support material and cover the outer surface of the carrier material and the inner surfaces of the pores of the carrier material composed of distributed silver and in which the Silver is present in the form of discrete, nearly hemispherical particles less than 1 micron in diameter, which are evenly distributed over the outside of the carrier material and the inside surface of the pores and firmly adhered according to patent (patent application P 21 59 346.4), characterized in that one A. heat the catalyst to a temperature ranging between 175 ° C and 300 ° C for 4 to 24 hours; B. the catalyst with one or more anhydrous alkanols contacted with 1 or 2 carbon atoms in the molecule; C. separating the activated catalyst. 2. The method according to claim 1, characterized in that the heating in stage A takes place in a temperature range between 200 ⁰ C and 275 ° C. 3. The method according to claim 1 and 2, characterized in that the contact treatment with the alkanol in stage B is repeated will. 4. The method according to claim 1 to 3, characterized in that the I! Ethanol is used as the only alkanol. 209848/1004 5. The method according to claim 1 to 4, characterized in that ethanol is used as the only alkanol. 6. The method according to claim 1 to 5, characterized in that in stage A heated ^{to temperatures of 220 0} C to 250 ^{0 C for 0 to 16 hours.} 7. Process for the direct oxidation of ethylene with molecular Oxygen to ethylene oxide, characterized in that silver catalysts according to Claims 1 to 6 are used. 8. The method according to claim 7, characterized in that the reaction temperature is in the range between 190 C and 240 ° C and preferably from 205 ° C to 225 ° C. 9. The method according to claim 7 or 8, characterized in that it is carried out as a circulation process, with ethylene and Oxygen of high purity can be fed into the circulation system, if desired together with such a. . ■ small amount of a non-reactant, such as helium or methane, that a relatively high concentration in the diluent gas can be maintained that a small bypass flow to compensate for the other than ethylene and oxygen introduced into the system Substances are removed that the conditions prevailing in the circulation system during operation at each point be kept constant that at least some of the carbon dioxide removed by visualization from the gaseous circulation mixture which remains after the separation of the ethylene oxide by absorption and the removal of the branch stream. 209848/1004