Silver catalyst and method of its production

The invention relates to a silver catalyst consisting of silver and a promoter and a porous refractory support material. It also relates to a process for the production of this catalyst, which is used for the production of ethylene oxide by oxidation of ethylene with oxygen.

Ethylene oxide is produced in large scale by direct oxidation of ethylene with oxygen in the presence of a silver catalyst. A general description of this method is in Kirk-Othmer: Encyclopecia of Chemical Technology, Vol. 9, pp. 432-471, John Wiley, London-NY, 1980.

The gas, containing ethylene and oxygen, is introduced at the top of the reactor. The reactor consists of a bundle of several thousand tubes with a length of 6 to 10 m. ethylene.

In addition to the formation of ethylene oxide, much of the ethylene, namely about 25%, is oxidized to carbon dioxide and water (total oxidation), as is evident. - from the following equations:

Formation of ethylene oxide 2 C2H₄ o 0₂ ---------> 2 C2H4O

Total oxidation₂H₄ o 3 0₂ ------- 3- 2 CO - C 2 H₂0

To control the temperature and dissipate heat, there is a 'heat transfer' environment around the tubes that dissipates the heat released from the reactor. The reaction gas, containing ethylene oxide and carbon dioxide, leaves the reactor and is fed to a processing unit where ethylene oxide and carbon dioxide are separated. The gas, devoid of ethylene oxide and carbon dioxide, is re-enriched with ethylene and oxygen and re-introduced into the doreactor. It is a continuous circulation with heterogeneous catalysis.

The supported catalyst is a silver catalyst. The quality of such a catalyst is basically characterized by its selectivity, its activity and its life.

Selectivity refers to the molar percentage of ethylene converted to ethylene oxide.

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The activity or activity is characterized by the concentration of ethylene oxide at the exit of the reactor under otherwise the same conditions (such as temperature, pressure, gas amount, catalyst amount).

The higher the ethylene oxide condensation, the higher the activity. Or, in other words, the lower the temperature to reach a certain ethylene oxide concentration, the higher the catalyst activity.

In addition to activity and selectivity, an important characteristic of catalyst quality is its service life. The efficiency of the catalyst deteriorates over time, i.e. the activity and selectivity continue to decrease, so that depending on the aging rate, the catalyst must be replaced sooner or later.

Such catalyst replacement is difficult, expensive, and associated with material loss. The old catalyst must be removed from several thousand tubes, tube by tube, and the tubes must then be filled with a new catalyst.

Such replacement takes place for several weeks and results in corresponding production losses. The old catalyst must then be reprocessed for silver recovery. Inevitably, there is a loss of silver. The carrier material cannot be reused.

Also in the production of a new silver catalyst there is a loss of silver. Large quantities of silver must be transported, silver must be secured, taxed and possibly cleared. A good silver catalyst for the production of ethylene oxide by direct oxidation of ethylene, with oxygen, should therefore, as far as possible, have a high activity and selectivity as well as a long service life.

The production of a supported silver catalyst has long been known. The supported silver catalysts are preferably produced in the following manner:

The support material is impregnated with a silver salt solution. The impregnated support material is dried to precipitate a silver salt on the support material.

The silver salt impregnated support material is subjected to the conditions under which the silver salt decomposes to form elemental silver which is finely dispersed on the support. This process may be purely thermal by heating to 170 to 400 ° C or may be carried out using reducing agents such as formaldehyde.

It has long been known that the efficiency of silver catalysts can be improved by so-called promoters. Promoters are those chemical elements which contribute to increasing the efficiency of the catalyst in amounts of 10 to 1000 mg / kg, based on the amount of silver. Potassium, rubidium and cesium have proven to be particularly effective promoters. When used, a selectivity of approximately 80% can be achieved with good activity.

More recently, it has been found that in the production of silver catalysts on a high efficiency support, not only the promoter itself, but also the type and method of its deposition on the support material, namely the moment of its application with respect to silver deposition, are important. Here, it seems to be of some importance when the deposited silver compound is reduced to metallic silver.

According to German Published Application No. 24 48 449, it should be advantageous to exclude the entire amount of the promoter and then the entire amount of silver on the support, followed by reduction of the deposited silver compound to metallic silver. In contrast, German Patent Publication Nos. 27 33 688 and 30 11 717 and British Patent Specification No. 20 02 252 recommend that, in the manufacture of a silver catalyst on a carrier with improved efficiency, all silver be deposited at the first impregnation and the second impregnation in the subsequent impregnation. all of the promoter, wherein the reduction of the deposited silver compound is carried out after the first impregnation under some special conditions.

In addition to these two previously known methods, a method for simultaneously depositing silver and a promoter on a support material is also known. This process for the production of a new silver catalyst with improved efficiency is described in German Published Application No. 23 00 512, 27 34 912, 29 51 969 and 29 51 970.

The known silver catalyst of German Offenlegungsschrift No. 23 OO 512 consists of 1.5 to 20% by weight of silver and 0.001 to 0.05% by weight of potassium, rubidium and / or cesium as a promoter on a refractory, porous support material. the weight percent is based on the weight of the catalyst (total weight of the catalyst) and wherein the silver and the promoter are deposited on the support simultaneously. The application is carried out by impregnating the support material with an appropriate impregnating solution. The silver compound on the support is thermally converted (reduced) to metallic silver.

This silver catalyst has relatively good selectivity based on the potassium, rubidium and cesium promoters used. However, further attempts have been made to further increase selectivity and to improve other important properties, such as activity and durability, in a method for simultaneously secreting these silver promoters on a support material.

For this purpose, according to German Published Application No. 27 34 912 a

51 969 uses a special impregnation method, and according to German Published Application No. 29 51 970, the impregnated and activated catalyst is treated in a mill to remove 1 to 10% by weight of its surface, thereby also achieving a long service life.

Finally, a number of publications are known, for example German Published Patent Applications Nos. 24 54 972, 26 40 540, 27 23 918, 28 19 595 and 28 20 170, which disclose that new silver catalysts with high efficiency support are obtained, if, in addition to silver, a plurality of special promoter metals are deposited on the support, it is irrelevant what sequence the silver and the promoter are deposited on the support.

The prior art relating to the method of depositing a silver and a promoter on a support material and reducing the deposited silver compound to metallic silver shows that numerous methods are known which should lead to efficient silver supported catalysts.

However, there is still a need to develop new silver catalysts on a carrier having good properties, especially silver catalysts having high activity, selectivity and durability, since known manufacturing processes require in part special impregnation processes, special reduction methods and / or post-treatment of the finished catalyst.

It has now surprisingly been found that silver catalysts can be obtained on a support having high activity, selectivity and durability if simultaneous application of the silver and the promoter in the required amounts to the support material is not carried out simultaneously but in two stages, it applies quite a certain amount of silver and promoter.

It was not to be expected that this variant of the simultaneous deposition of silver and promoter would achieve such a high efficiency, whereas, according to German Published Application No. 29 51 970, repeated impregnation of the support using the corresponding impregnating solutions to simultaneously deposit the required amount of silver and the promoter is of no significance and allegedly the catalyst efficiency improvement can only be achieved by the post-treatment of the catalyst described therein layers.

It has further been found that silver catalysts with high activity, selectivity and durability can also be obtained when the deposition of silver, potassium, rubidium and / or cesium promoters on the support material is carried out by first depositing all of the silver and only a portion of the total amount of promoter and then the residual amount (of the total amount of promoter) is loaded.

The silver catalyst according to the invention consists of 3 to 20% by weight of silver and 0.003 to 0.05% by weight of potassium, rubidium and / or cesium as promoter on a refractory porous support, the weight percentages always referring to catalyst weight / finished catalyst weight or total catalyst weight wherein the silver and the promoter are deposited on the carrier material using an impregnating solution and the deposited silver compound is reduced to metallic silver and is characterized by: that silver deposition and reduction are carried out in one of the following ways:

a) 55 to 85% by weight of the total amount of silver and 15 to 45% by weight of the total amount of promoter in the first impregnation step are applied simultaneously b) drying the product obtained according to the composition; (b) in a second impregnation step and (d) heating the product obtained according to (c) to reduce the deposited silver compound to metallic silver; or (a) simultaneously or subsequently depositing the total amount of silver; and 15 to 45% by weight of the total amount of promoter in one or two impregnation steps, b '/ heats the sc product obtained according to paragraph a7 to reduce the deposited silver compound to metallic silver, c 7 (in a further impregnation step and d7 the product obtained according to paragraph c ') is dried.

The process of the invention for producing a silver catalyst, wherein the silver and the promoter are deposited on the support material using an impregnating solution and the deposited silver compound is reduced to metallic silver is characterized in that it is progressed. , in one of the following ways:

a) at the same time 55 to 85% by weight of the total amount of silver and 15 to 45% by weight of the total amount of promoter in the first impregnation step are applied, b / the product obtained under a) is dried; the promoter for the product obtained under b), d) heating the product obtained under c) to reduce the deposited silver compound to metallic silver, or a '/ simultaneously or sequentially depositing a total amount of silver and 15 to 45% by weight of the total amount of promoter in one or optionally two impregnation steps, b' / heating the product obtained according to a ') to reduce the deposited silver compound to metal silver, c '(the remainder of the total amount of promoter is applied to the product obtained according to b') in the next impregnation step, d '(the product obtained according to c') is dried.

The amount of silver is preferably 7 to 14% by weight and the amount of promoter is preferably 0.008 to 0.035%, based on the weight of the catalyst. The promoter is preferably cesium.

In the first process according to the invention, preferably 60 to 75% by weight of the total amount of silver and 25 to 40% by weight of the total amount of promoter are applied in step a / and the remainder of the total amount of silver and the total amount of promoter are applied. In the second process according to the invention, in step a), preferably 20 to 35% by weight of the total amount of the promoter is applied.

Suitable support materials for the silver catalysts according to the invention are conventional, commercially available, refractory and porous materials. They are materials which are also inert in the presence of reaction conditions for the oxidation of ethylene and for chemical compounds in this oxidation reaction.

The support material for the production of the silver catalysts according to the invention is not critical, for example, suitable supports are coal, corundum, silicon carbide, silica, alumina and mixtures of alumina and silica.

Alpha alumina is preferred because it has a largely uniform pore diameter. Has spe2 2 cifický^psurface 0.1 to 1 m²/ g, preferably^dou 0,² up to 0,6 m /^G / m^ěřeno zn^andmy way^bem BET / ,. specific pore volume 0.1 to 1 cm³/ g, preferably 0.2 to 0.6 cm³(g) measured by known mercury or water adsorption method, apparent porosity by volume of 20 to 70%, preferably 40 to 60% by volume (measured by known mercury or water adsorption method), average pore diameter 0.3 to 15 microns, preferably T and a percentage of pores with a diameter of 0.03 to 10 micrometers of at least 50% by weight (pore diameter and pore diameter distributions are ascertained, as is known, from specific surface area and apparent porosity).

The carrier material is preferably used - in the form of granules, spheres, rings, pellets and similar shapes. Examples of preferred alpha alumina or alpha alumina-containing material include Norton Company products SA 555Д and SA 5552 or United Catalyst SAHM. '

The application of the silver and the promoter to the carrier material in the process according to the invention is carried out by conventional impregnation methods. The carrier material is contacted with solutions, preferably soaked, the solutions consisting of a solvent and a sufficient amount of a silver compound and / or a promoter compound to eliminate the silver and promoter, whereupon the support material is separated from the excess solution and dried.

According to the first method of the invention, the carrier material is used. first impregnating so that 55 to 85% by weight, preferably 60 to 75% by weight of the total amount of silver - and

240965 6%, preferably 25 to 40% of the total promoter potential. After this first, the rest of the total amount of silver and the promoter is applied to the dried support material during the second impregnation. The solutions for both impregnation steps according to the invention therefore consist essentially of a solvent and of sufficient silver compound and promoter compound.

According to the second method of the invention, the carrier material is impregnated in step a '/. The total amount of silver is applied, but only 15 to 45% by weight of the total amount of promoter is used, preferably 20 to 35% by weight of the total amount of promoter.

This can be achieved by impregnating the carrier oaterial with a solution of at least one silver compound and then with a solution of at least one promoter (variant 1) or with a solution containing at least one silver compound and at least one promoter compound. , variant 2 /.

Thus, the solutions for step a * / consist essentially of a solvent and always a sufficient quantity of silver compound and promoter compound. Of both variants of step a '/, it is advantageous to simultaneously deposit the silver compound and the promoter compound. Depending on the carrier material used, the usable concentrations of the silver compound and the promoter in the solutions can be determined by a preliminary test and by analytical determination of the spots. actually precipitated compounds »it's quick and easy.

* .

The impregnations can be carried out in a manner known per se. Preferably, they are carried out by soaking the carrier material (soaking or pouring) with an impregnating solution in the vessel, whereby the solution penetrates the pores of the carrier mottrial by absorption and / or capillary action and excludes the silver and promoter compounds.

The excess impregnating solution is then treated (for example, by casting, dripping, separating or centrifuging), after which the fully impregnated carrier oattrial is dried. The amount of impregnating solution is generally chosen such that there is a volume excess of impregnating solution with respect to the volume of impregnated carrier.

Generally, 0.5 to 3 times, preferably 1 to 2 times the volume of impregnating liquid, based on the volume of the carrier oateral, is used. The impregnation time, i.e. the time the carrier oaterial remains in contact with the impregnating liquid, is naturally selected so as to deposit the necessary amount to exclude the silver compound and the promoter compound onto the carrier.

This time is generally from 5 to 60 minutes and depends in particular on the - ending of the silver compound and the promoter compound - in the impregnation solution, the carrier material used and its absorbent siotrope.

The temperature used may vary within wide limits. Generally, the impregnation is carried out at the temperature of the miter. Higher temperatures can also be used to accelerate impregnation. Thus, the impregnation temperature is generally 15 to 80 ° C, preferably 20 to 50 ° C. The impregnation is generally carried out at atmospheric pressure.

The drying of the products obtained by impregnation (impregnated carrier oaterial) is generally carried out at a temperature of 20 to 150 ° C, preferably at a temperature of 50 to 120 ° C. Removal of the solvent is possible, for example, in hazel driers, rotary tube driers, or by passing hot inert gases such as nitrogen and / or carbon dioxide. The temperature is naturally controlled by the boiling point of the solvent used and the impregnating liquid.

The reduction on the carrier mottrial of the precipitated silver compound to metallic silver is carried out by heating. A temperature reduction of 170 to 400 ° C, preferably 200 to 350 ° C is generally required for the thermal reduction of the silver compound to metallic silver.

Heating to this temperature is possible, for example, in a hazel drier, in a rotary oven, in an electrically heated oven or by conducting inert gases heated to an appropriate temperature, for example air, nitrogen, carbon dioxide or a mixture thereof. Conversion of the silver compound to metallic silver is also possible by superheated steam. At said temperature, the heating time is generally 0.2 to 5 hours, preferably 0.3 to 1 hour.

Decomposition of the silver compound forms a strongly adherent precipitate of metallic silver particles on the support material (the promoter compounds are not reduced to the corresponding metal, thus the alkali metals potassium, rubidium and cesium are essentially in the form of their cations and not in the form of free metals). The silver (silver particles) are generally in the form of firmly adhered, substantially uniformly distributed, unrelated discrete particles having a diameter of less than 1.5 microns. In general, these silver particles have a diameter of 0.1 to 1 micron and an average diameter of 0.2 to 0 , 7 micrometers.

Suitable silver compounds, silver complexing agents, promoter compounds and suitable solvents as well as suitable impregnating solutions are then mentioned.

Silver salts are preferably silver salts. Suitable inorganic salts are, for example, silver nitrate and carbonate. Suitable organic salts are, for example, salts of mono- or polybasic carboxylic acids and hydroxycarboxylic acids with up to 6 carbon atoms, such as silver acetate, lactate and oxalate. The silver compounds are water-soluble and thermally degradable to metallic silver.

It is preferred to use silver complexing agents to increase the solubility of the silver compounds. Such complexing agents are, as is known, ammonia, amino acids and / or amines, such as C 2 -C 4 alkylenediamines, for example ethylenediamine, C 2 -C 4 alkanolamines, for example ethanolamine, monoalkylamino / dialkylamines and C 1 -C 4 trialkylamines (in the alkyl moiety), for example methylamine, isopropylamine, isobutylamine and secondary butylamine and polyamines.

Of these complexing agents, alkylamines, especially C 1 -C 4 monoalkylamines, are preferred. The complexing agents are used in sufficient amounts to convert the silver compound quantitatively to the silver aminocomplex. . This usually requires a slight molar excess of amino groups. Since the silver cation binds two amino groups, it is necessary to use at least 2 amino groups per mole of silver cations.

Suitable promoter compounds are the salts, hydroxides and oxides of said metals, potassium, rubidium and cesium. Salts are preferred, wherein the salt anion is not critical.

Inorganic salts include nitrate, chloride, carbonate and phosphate. Organic salts include salts of mono- and polyhydric carboxylic and hydroxycarboxylic acids having 1 to 6 carbon atoms, for example formate, acetate, oxalate, citrate and lactate. Like the silver compounds, the promoter compounds are water-soluble.

Suitable solvents for the silver and promoter compounds are water, aliphatic alcohols having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms, such as methanol, ethanol, propanol and isopropanol. aliphatic ketones having from 3 to 5 carbon atoms, such as acetone, aliphatic and cyclic ethers such as diethyl ether, methyl ether, dipropyl ether and dioxane, esters such as methyl acetate and ethyl acetate, acid amides such as dimethylformamide and nitriles such as acetonitrile and their mixtures.

In the presence of compounds. The silver and silver compounds and the promoter are preferably water and, in the presence of the promoter compound alone, the preferred solvents are aliphatic alcohols having 1 to 3 carbon atoms (optionally with a small amount of water as the solubilizer). ,

For the process step (a) of the process according to the invention, the impregnating solution consists essentially of (1) of water-soluble and heat-degradable (silver salt) contained in an amount of 30 to 40% by weight (2) of at least one (water-soluble) compound. a promoter, preferably cesium salt, present in an amount by weight of 0.02 to 0.04%, (3) from 20 to 30% by weight of water and (4) from 1 to 4 carbon monoalkylamine as a complexing agent for the silver salt in an amount of from 30 to 40% by weight, based on the weight of the solution.

For step c), the impregnating solution consists essentially of (1) of a water-soluble and heat-dissolvable (salt). (2) of at least one (water-soluble) promoter salt, preferably cesium salt, in an amount of 0.045 to 0.07% by weight; (3) of 20 to 30% by weight; water and (4) from a C 1 -C 4 monoalkylamine as a complexing agent for the silver salt, contained in an amount of 30 to 40% by weight, based on the weight of the solution. (It goes without saying that the actual concentration of the silver salt and the promoter salt depends on the amount of silver and the promoter to be deposited on the support material.) It is not important to dry the product obtained under (c) before carrying out the process of (d). Evaporation of the solvent occurs by heating to a reducing temperature in step d).

The following impregnating solutions are expediently used for the step a) of the process according to the invention: The solution for depositing silver on the support material according to variant 1 consists essentially of (1) water-soluble and heat-degradable salts. (2) from 20 to 30% by weight of water; and (3) from monoalkylamine of 1 to 4 carbon atoms as a complexing agent for the silver salt, contained by weight of 30 to 40% by weight of silver; the application of the promoter according to variant 1 consists essentially of (1) at least one water-soluble and / or alcohol-soluble promoter salt, preferably cesium salt, present in an amount of from 0.01 to 0.03% by weight, (2) from 0 to 5% by weight of water and (3) from an aliphatic alcohol having from 1 to 3 carbon atoms in an amount supplementing the solution to 100% by weight; solution for the simultaneous deposition of the silver compound and the promoter according to variant 2 of the method according to paragraph a *) consists essentially of (1) of water-soluble and heat-degradable (silver salts) contained in an amount of 30-40% by weight (2) (water-soluble) salts of the promoter, preferably cesium salt, in an amount of from 0.01 to 0.03% by weight, (3) from 20 to 30% by weight of water and (4) from monoalkylamine of 1 to 4 carbon atoms as complexing agents for silver salt, in the amount of 30 to 40% by weight, based on the weight of the solution.

The ophthalmic impregnating solution for the process of paragraph c 'consists essentially of (1) at least one water and / or alcohol-soluble promoter salt, preferably cesium salt, present in an amount by weight of 0.04 to 0.08% by weight. (2) from 0 to 5% by weight of water and (3) from an aliphatic alcohol with 1 to 3 carbon atoms to make up the solution per 100 l, the percentages always refer to the weight of the solution. (It goes without saying that the actual concentration of silver salt and promoter salt in the impregnation solutions depends on the amount of silver and promoter to be deposited on the support material.).

In the first stage variant a), intermediate drying is expediently carried out, i.e. drying is carried out after impregnation with the silver compound solution and before impregnation with the promoter compound. It is not important to dry the product obtained according to paragraph a '(before processing according to paragraph b'). Indeed, the solvent evaporation from the support material can also be carried out. in step b '), in which heating to higher temperatures is also carried out.

In the second process of the invention, in many cases, it has proven advantageous to undergo a silver catalyst obtained according to steps a '(d) to undergo a wash in which the catalyst is contacted with a solvent in which a soluble promoter compound is deposited on a carrier.

The washing is carried out especially if the finished catalyst contains too much promoter. In fact, washing can simply remove excess promoter.

The washing can also be carried out in order to achieve a certain, optimal concentration of the alkali metal in the finished catalyst simply and quickly.

Water, C 1 -C 4 aliphatic alcohols or mixtures thereof are preferably used as washing liquids. A particularly preferred scrubbing liquid consists of methanol, ethanol, propanol and / or isopropanol and water in an amount of 0 to 20% by weight, based on the weight of the scrubbing liquid.

The washing can be carried out in a manner known per se, the catalyst being contacted with the washing liquid and then separated from the washing liquid and dried. Preferably, the washing is carried out by pouring the catalyst into a container containing the washing liquid and then separating it from it by centrifugation, filtration, suction suction or simple decanting.

The length of time the catalyst is left in contact with the wash liquid is not in itself critical. It depends primarily on the amount of promoter compound to be dissolved and is generally 0.2 to 20 minutes, preferably 0.5 to minutes.

Usually one wash is sufficient. However, it may be advantageous to carry out a sequential washing in which the catalyst is washed two to five times, suitably two to three times, preferably using always fresh / new, unused / washing liquids.

The amount of wash liquid (single wash or repeated wash) is controlled by the amount of catalyst and is naturally metered such that the catalyst is in contact with the liquid, optionally with stirring. Suitably this amount (by volume) is about one third of the amount of catalyst (volume by volume), preferably the washing liquid is used in an amount of 1 to 3 times with respect to the amount of catalyst.

Temperature and pressure are not critical when washing; the washing may be carried out without or under pressure. In general, the washing is carried out at a temperature of 15 to 80 ° C, preferably at a temperature of 20 to 50 ° C.

The washed catalyst can be dried, for example, by means of an inert gas such as nitrogen, carbon dioxide, air or a mixture thereof and / or by heating the catalyst, and pressurized to accelerate drying.

The temperature at which the drying is carried out is not critical. Suitably, the heat of the boiling liquid used is controlled. Suitably the drying temperature is 20 to 150 ° C, preferably the drying is carried out at a temperature of 50 to 120 ° C.

In the case of the silver catalyst of the invention, the silver is deposited on the inner and outer surfaces of the support material substantially evenly. In contrast, the alkali metal (alkali metal compound) is unevenly distributed.

There is a higher promoter concentration in the outer layers of the carrier body than in the inner layers. Thus, the promoter is in the form of a concentration gradient such that each carrier body externally has a higher promoter concentration than in the interior.

The silver catalyst of the invention has a high activity and selectivity and a long service life. Due to its long life, it has a high efficiency for a relatively long period of use. This is associated with the advantage that, when using the silver catalyst according to the invention, its replacement or regeneration is only necessary after a relatively long period of use.

The process for producing the silver catalyst according to the invention is simple and easy to carry out.

It does not involve any complicated or expensive operations, nor does it require any special impregnating solutions.

The conditions of use of the catalyst of the invention, such as temperature, pressure, residence time, diluents, braking agents to control catalytic oxidation of ethylene by oxygen, recycling, technical measures to increase ethylene oxide yield and the like are known per se.

Reaction te^plota is general^E 150 to 400 ° C preferably ²00 and 300 ° C, rea^točn^and tla^to 0^,15 Dec up to 3 MPa, preferably 1 to 2 MPa. The feed mixture used generally contains 5 to 30% by weight of ethylene, 3 to 15% oxygen and the remainder inert gases such as nitrogen, carbon dioxide, water vapor, methane, ethane, argon and the like gases, as well as vinyl chloride. 2-dichloroethane and similar substances as braking agents. The ethylene oxide is isolated from the reaction product in a manner known per se and the gas mixture is optionally purified and reprocessed as is known.

In a preferred use of the silver catalyst of the present invention, ethylene oxide is produced by oxidizing ethylene with a gas mixture containing about 8.5% oxygen by weight at 200 ° C.^of 270 ° C in the presence of new st^řbkata^lyzátoru.

The following examples illustrate the invention in more detail. Examples 1 to 4 relate to the first process and Examples 5 to 8 to the second process for producing the catalyst of the invention.

He did

For the preparation of the catalyst according to the invention, a solution is prepared which contains (percentages by weight):

13.03 g (37.9441 ») of silver nitrate

9.10 g (26.4997%) of distilled water

0.01 g (0.0291%) cesium nitrate

12.20 g (35.5271%) of isobutylamine.

Alpha alumina in the mold is completely immersed in this solution as the carrier material^E in^andlečků with speci^Fický povrc^hem ^0,3 m²/G, ^{for time} AND⁵ rnin^Tue p^ři t^{eplotě m}no^tnose^ti. After dripping excess impregnating solution through a sieve, the wet support material is dried for 30 minutes^nut ^při te^plot 105 ° C in atmos^féAir and dirt / grade a^/ ab /.

After cooling, the semi-finished catalyst is impregnated with a solution consisting of the following components (percentages by weight each) as described above:

13.03 g (36.6557%) of silver nitrate

10.00 g (28.1318%) of distilled water

Cesium nitrate 0.017 g (0.0478%)

12.50 g (35.1647%) of isobutylamine, and dried (step c).

The drying is followed by a half-hour reduction in a rotary tube furnace preheated to 300 ° C> ^pec^and se ve^de mixture of air and steam^tou (degree d). Gets^towith a silver tattoor, ^toIt contains 11.4% by weight of silver and 0.015% by weight of cesium.

The first impregnation applied 74% by weight of the total amount of silver and 33% by weight of the total amount of cesium, and the second impregnation always applied the remaining amount.

ml of the catalyst thus prepared is charged to a stainless steel pressure reactor; and ^dO ^thand^toov^éhabout the reactor ^extemperature ²10 ° C^toat ^pl^y1.3 MPa closes^{dí p}rovozní p^lyn, consisting by volume of 30% ethylene, 50% methane, 8.5% oxygen, 0.0003% vinyl chloride, the remainder being nitrogen. The spatial time velocity is 3000 N 1 gas per liter of catalyst per hour.

The reactor effluent contains 1 vol_;5 % ethylene oxide. of which the selectivity (i.e. moles of ethylene oxide formed per mole of ethylene reacted) was recalculated (82.1% at 6% ethylene conversion).

Under the above-mentioned conditions, the catalyst selectivity decreased by only 4 points after 4 months (i.e. to 81.8%).

Example 2 (comparative example)

According to this comparative example, the total amount of cesium and silver is applied in only one impregnation.

The support material of Example 1 is impregnated with only one solution consisting of the following components (% by weight):

31.5 g (49.4910%) of silver nitrate

15.6 g (24.5098%) of distilled water

0.048 g (0.0754%) cesium nitrate

16.5 g (25.9238%) of ethylenediamine and dried and reduced as in Example 1. The finished catalyst contains 11.3% silver and 0.016% cesium by weight.

A long-term test with this catalyst over 4 months under the conditions of Example 1 revealed:

required temperature for 1.5% by volume ethylene oxide 218 ° C selectivity at 6% ethylene conversion 79.3% selectivity after 1 month 79/1%

He did

In this example, illustrating the catalyst according to the invention, a solution consisting of the following components (% by weight) is prepared:

12,000 g (37,4859%) of silver nitrate

9.000 g (28.1145%) of distilled water

Cesium acetate 0.012 g (0.0375%)

11,000 g (34.3621%) of secondary butylamine.

Alpha alumina in the form of spheres of 8 mm diameter and a specific surface area of ​​0.2 m / g for 10 minutes, as in Example 1, was immersed in this solution as a support material and dried.

After cooling, the semi-solid catalyst is again impregnated with a solution consisting of the following components (percentages by weight each) as described above:

12,000 g (37,4789%) of silver nitrate

9,000 g (28,1092%) of distilled water

Cesium acetate 0.018 g (0.0562%)

11,000 g (34.3557%) of the secondary butylamine and the catalyst was dried. The drying is followed by a 20 minute reduction in a glass tube preheated to 280 ° C as a furnace (40 liters of air and 20 liters of nitrogen per hour) flow through the furnace.

A silver catalyst containing 11.5% silver and 0.019% cesium is obtained. The first impregnation applied 68% total silver and 37% total cesium / percent. always the remaining amount of silver and cesium is applied in the second impregnation.

ml of the finished catalyst was used as in Example 1 for 4 months in a pressure apparatus with the following results:

<td>required temperature for 1,5% ethylene oxide by volume selectivity at 6% ethylene conversion selectivity after 4 months</td><td>222 [deg.] C 81.8% 81.5.%</td>

Example 4

In this example, cesium and rubidium salts are used as promoters. Otherwise, the procedure of Example 3 was followed.

The solution for the first impregnation has this composition (percentages are always by weight); 12,000 g (37,4906%) of silver nitrate.

9,000 g (28.1180%) of distilled water

Cesium carbonate 0.005 g (0.0156%)

0.003 g (0.0094%) of rubidium nitrate

11,000 g (34.3664%) of secondary butylamine.

The solution for the second impregnation has the following composition (percentages are always by weight):

12,000 g (36,8992%) of silver nitrate

9.500 g (29.2119%) of distilled water

0.012 g / 0.0369% cesium carbonate

0.009 g. (0.02 77%) rubidium nitrate

11,000 g (33,8243%) of secondary butylamine

The finished catalyst contains 11.2% silver, 0.013% cesium and 0.008% rubidium by weight. In the first impregnation stage. 71% by weight of the total amount of silver and 25% by weight of the total amount of promoter are deposited, with the remainder of the silver and promoter being applied at the second impregnation.

Test use over 2 months according to Example I shows the following results:

^pot^Řebn^and te^plot for volume 1^,5 % ethyleneox^andat 226 ° C selectivity at 6% ethylene conversion 81.7% selectivity at two months 81.5%

Example 5

For the production of the catalyst according to the invention, alpha alumina in the form of spheres with a diameter of 8 mm and a specific weight of 0.3 m @ 3 / kg is used as the support material. In glass. the flask evacuated with the carrier material is poured perfectly over a solution of silver and cesium, which has the following composition: (percentages are always by weight):

30,000 g (38.4556%) of silver nitrate

20,000 g / 25.6371% distilled water

28,000 g (35.8919%) of isobutylamine

Cesium nitrate 0.012 g (0.0154%)

After standing for 15 minutes, excess solution was decanted off. It is dried for 45 minutes in an oven, which is passed through nitrogen at 110 ° C / degree and / or

A mixture of air and nitrogen (40 liters of air and 20 liters of nitrogen per hour) is then passed through the dry sample in a glass tube for 30 minutes at 280 ° C. After the reduction of the silver salt, a catalyst containing 8.6% by weight of silver and 0.0038% of cesium (step b) was obtained.

The crude catalyst cooled to room temperature is now impregnated with the following cesium salt solution (step с):

<td>methanol cesium nitrate distilled water</td><td> 95,000 % 0,045 % 4,955 %</td>

(Percentages are always by weight.)

For this purpose, the crude catalyst in the vessel was completely covered with the solutions and left at room temperature for minut10 minutes. After decanting and drying at 110 ° C in a nitrogen purged dryer (step d '), a catalyst with a content of 0.0125% cesium and 8.6% silver is obtained. (Thus, in the first impregnation, the total amount of silver and 30% by weight of the total amount of cesium was deposited and in the second impregnation the residual amount of cesium was applied.)

In the reactor, 25 ml of the catalyst thus obtained are tested at 200 DEG C. and under normal pressure using a gas mixture consisting of 30% by volume of ethylene, 50% by volume of methane, 8.5% by weight of oxygen, 0.0003% by weight of vinyl chloride. nitrogen.

The space and time rate is 400 N1 of gas per liter of catalyst per hour. The gas leaving the reactor contained 1% by volume of ethylene oxide. From this, the selectivity (i.e. moles of ethylene oxide formed per mole of ethylene reacted) was calculated to be &amp; gt; 81% at 5% ethylene conversion.

In the long-term test under the given conditions, the selectivity decreased by only 0.3 points to 81.2% within three months.

Example 6

In this example of the invention, alpha alumina in the form of spheres of 8 mm diameter with a specific surface area of ​​0.2 m / g is used as the support material. In a beaker it is poured perfectly over a solution consisting of the following components (% are always by weight):

30,000 g (39,4659%) silver nitrate

20,000 g (26.3106%) of distilled water

22,000 g (28.9417%) of secondary butylamine

4.000 g (5.2621%) ethylenediamine

Cesium nitrate (0.015 g / 0.0197%) and left for 15 minutes. After decanting off the excess impregnating solution, it is dried for 30 minutes in a dryer under a nitrogen atmosphere at 100 ° C (step a).

To reduce the silver nitrate on the carrier to metallic silver, heat in a dryer (80 liters of air and 60 liters of nitrogen per hour) for one hour to 250 ° C / degree b *^Ť/.

<img file="CS240965B2_D0001.tif" />

240965 ' 14

The crude catalyst obtained contains 8.6% by weight silver and 0.0045% cesium. Crude catalyst^sé'^napouŠ^{tí po} doto ¹⁵ m^andnut ^tím^tabout thawing^if cesium (degree c ') / percent is always by weight /:

methanol 95,00% distilled water 4,9% cesium acetate 0,05%

Po o^dde^toan^tov^andand dried^{í p}O ^dO^bu 30 m^andnut ^při. te^plot^E 100 ° C / stu^pEⁿ d '/ se z^andSilver catalyst containing 8.6% by weight silver and 0.0107% cesium, with 40% by weight of the total amount of cesium being deposited in the first impregnation step.

The catalyst is tested as described in Example 1, in a long-term test for 3 months, giving the following results:

after^clE^bn^and te^plota ^pro volumes^E 1^,3 % ethylⁿoxide 196^,0 ° C selectivity at 5% ethylene conversion 81.6% selectivity at 3 months' 81.3%

Example 7 (comparative)

In this comparative example, the total amount of silver and cesium is deposited in one impregnation step (one-stage simultaneous deposition of the total amount of silver and promoter). The carrier and the working method correspond to Example 1.

The impregnation solution has the following composition (percentages are always by weight):

30,000 g (38.4369%) of silver nitrate

20,000 g (25.6246%) of distilled water

28,000 g / 35.8744. % / secondary butylamine

Cesium nitrate 0.050 g (0.0641%)

The finished catalyst contains 8.5 wt% silver and 0.0130 wt% cesium.

The catalyst test for two months under the conditions of Example 1 yields the following results:

temperature required for 1,3% by volume ethylene oxide _r 1⁹³^ ° C selectivity at 5% ethylene conversion 80.2% selectivity at two months 80.1%

Example 8 (comparative example)

According to this comparative example, all the amount of cesium is deposited in the second impregnation step, with all the amount of silver being deposited in the first impregnation step. The support and the process follow Example 1.

The impregnating solution for the first impregnation has the following composition (percentages are always by weight):

30.0 g (38.46%) of silver nitrate

20.0 g (25.64%) of distilled water

28.0 g (35.90%) of secondary butylamine

After reduction of the deposited nitrate to the silver, the catalyst obtained contains 8.6% by weight of silver. The total amount of cesium is now applied in the next impregnation (percentages are always by weight):

<td>methanol distilled water cesium nitrate</td><td> 95,00 % 4,93 % 0,07 %</td>

The finished catalyst q contains 8.6% by weight silver and 0.0135% cesium.

à · 't $:

Testing of this catalyst for one month under the conditions of Example 1 showed these results;

* * ;

required temperature for 1,3% ethylene oxide by volume 194,0 ° C selectivity at 5% ethylene conversion 79,8% selectivity after 1 month 79,6%