CS219313B2 - Method of making the silver catalysers - Google Patents

Abstract

1489335 Ethylene oxide preparation SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ BV 24 Oct 1974 [26 Oct 1973] 49962/73 Heading C2C [Also in Division B1] Ethylene oxide is made by the vapour phase oxidation of ethylene with O 2 in the presence of a silver catalyst which has been prepared by (a) impregnating a porous refractory support of surface area 0À03-10 m.<SP>2</SP>/g. with a solution of a compound of K, Rb or Cs in such a concentration, having regard to any leachable alkali metal in the support prior to impregnation, as to produce-optionally after extraction with a solvent after either step (b) or step (c)-in the final catalyst a content of 0À25-16 mg. e.w. of alkali metal per kilogram total catalyst for each square metre of surface area per gram of support, (b) at least partly drying the impregnated support, (c) contacting the at least partly dried product with a liquid phase containing a dissolved compound of Ag or a slurry of particles of Ag or Ag compound in an amount sufficient to deposit 1-25 wt. per cent Ag, based on the total catalyst, on the support surface, and (d) thermally treating the product of (c), optionally in the presence of a reducing agent, to convert the Ag compound to Ag metal. Preferably the oxidation is performed at 210-285‹ C. in the presence of a fixed bed of catalyst, an inert diluent gas and a chlorine-containing moderator.

Description

The invention relates to a process for the production of silver catalysts for the production of ethylene oxide.

Materials consisting of supported silver are known as suitable catalysts for the production of ethylene oxide by controlled incomplete oxidation of ethylene by molecular oxygen. A number of variations have been proposed to improve the efficiency and selectivity of these catalysts. These variations relate, for example, to the supports used, the production method, the physical form of the silver on the support and the addition of catalyst additives.

The alkali metals and their salts have been redesigned as additives to various silver catalysts for the production of ethylene oxide. U.S. Patent 2,125,333, one of the first publications relating to these catalysts, discloses "small amounts" of alkali metals, including both sodium and potassium, in silver catalysts.

In later patents this discovery has been further elaborated, but in part with contradictory recommendations. Thus, for example, U.S. Pat. No. 2,246,474 discloses that while the addition of 1000 wt. % of sodium hydroxide will improve silver catalysts, this amount of potassium hydroxide or cesium hydroxide has a detrimental effect on the efficiency of the catalyst. U.S. Pat. No. 2,615,900 discloses a large number of promoters suitable over a wide mass range, but without distinguishing the efficacy of the individual promoters. The use of a large number of alkali metal sulphates is disclosed in the patent. No. 2,671,764. In addition, U.S. Patent 2,765,238 discloses that the addition of 1 to 2000 ppm by weight of an inorganic compound, chlorine such as sodium chloride, to a catalyst carrier prior to the addition of silver improves the performance of the resulting catalyst.

However, U.S. Pat. No. 2,799,687 states that when 20 wt.%, Ppm to 1.6 wt. %. The inorganic halide (sodium chloride or preferably potassium chloride) in the form of discrete solid particles to the fluidized bed of the silver catalyst on the support, adversely affects the halide by inhibiting the activity of the catalyst. U.S. Pat. No. 3,144,416 discloses a number of promoters, but without any critical evaluation of their concentration. The use of alkali and alkaline earth metals as promoters is generally described in U.S. Pat. No. 3,563,913, which mentions in particular lithium, but without mentioning cesium, rubidium or potassium. These promoters are preferably added to the catalyst support before the support is impregnated with a solution containing the silver compound.

The use of lithium oxide supports having a pore volume in the range of 0.15 to 0.30 mVg and a surface area below 10 m ² / g is disclosed in U.S. Pat. No. 3,575,888. Use of some organic amides as solubilizing agents reducing agents to obtain uniformly spaced, well adhering, hemispherical, metallic silver deposits on catalyst supports are disclosed in U.S. Patent No. 3,702,259. According to Dutch Patent Application 7,300,162, catalysts containing at least one of alkali metal may be used. metals, potassium, rubidium and / or cesium. in an amount of 0.35 to 3.0 milligrams of alkali metal (mgat) per kg of catalyst, which metals are deposited simultaneously with silver on the catalyst support. The addition of potassium, rubidium and / or cesium in an amount exceeding this range is not preferred, and the addition of alkali prior to the addition of silver provides no or little advantage.

It is apparent from the prior art that the addition of alkali metal compounds alters, better or worse, the nature of the silver catalysts for ethylene oxide production.

It has now been found that by deposition of potassium, rubidium or cesium in critical amounts proportional to the surface area of the support which is carried out before the silver deposition, better catalysts for ethylene oxide production are obtained.

The present invention relates to a process for the production of silver catalysts for the production of ethylene oxide, wherein at least one alkali metal compound is deposited on an atomic number 19 to 55 on a porous refractory carrier having a surface area of 0.03 m ² / g up to 10 m ² / g, characterized in that at least one of said alkali metal compound is applied to said carrier by impregnating it with a solution in an amount of 0.25 to 16 milligrams of alkali metal per kilogram of total catalyst support per each square meter of the specific surface area of the support relative to gram of catalyst support, the impregnated support is dried, the dried support is deposited with 1 to 25 wt% silver, based on the total amount of catalyst, by impregnating the support with a silver-containing compound and the carrier for converting the silver compound to metallic silver heats to heat between 100 ^° C and 375 ° C.

Preferably, the support is impregnated with at least one of said alkali metal compound in an amount of 0.25 to 14 or 0.50 to 14 milligrams of alkali metal per kilogram of total catalyst per square meter of specific support based on gram of catalyst support. The heating of the impregnated carrier is preferably carried out in the presence of a reducing agent.

Preferably. 4 to 16 weight percent silver based on the total catalyst is applied to the dried support. Preferably, the support impregnated with at least one alkali metal compound is dried by heating to a temperature in the range of from 100 ° C to 200 ° C in a stream of nitrogen.

The dried carrier may be impregnated with an aqueous solution containing a silver carboxylic acid salt and an organic amine alkaline solubilizing reducing agent. The solubilizing reducing agent may. be 1,2-diaminoethane.

It should be noted that the deposited amounts of potassium, rubidium and / or cesium are not necessarily the total amounts of these metals present in the catalysts. These are the amounts of alkali metals that are present on the surface of the catalyst and that are intentionally added to the catalyst prior to the addition of silver. It is not unusual that quite substantial amounts, often up to 1% by weight, are present in the porous carrier. % of the higher alkali metals (usually potassium) due to the use of carrier materials containing naturally occurring alkali metals or unintentionally added alkali metals during processing of the carrier. These amounts of higher alkali metals, present in the non-leachable carrier medium, do not contribute to increased catalyst performance and are neglected in determining alkali metal concentrations. However, the amounts of the higher alkali metals present in the leachable form in the carrier must be taken into account when determining the amount of the higher alkali metals deposited on the carrier. Indeed, an alternative method to provide all or part of the required amount of the higher alkali metal is to introduce the higher alkali metal of the carrier in leachable form during processing of the carrier.

The catalysts contain 1 to 25 wt. %, based on the total catalyst, of silver in the form of metallic silver. They preferably contain from 2 to 20 and in particular from 4 to 16 wt. % silver. Use of larger amounts of silver than 26 wt. % is not excluded, but is usually economically disadvantageous. The silver is deposited on the inner and outer p-surfaces of the catalyst support and is to be uniformly distributed on these surfaces.

The exact physical form of silver on the catalyst can vary and is not critical to the invention. However, very good results are obtained with surface-controlled alkali metal catalysts when the silver is present in the form of uniformly spaced, discontinuous, adherent, discrete particles having a uniform diameter below 1000 nm. Best results with this catalyst are obtained when the silver particles have diameters from 100 to 1000 nm and only the more preferred catalysts have silver particles having a mean diameter in the range of 150 to 750 nm.

The support used in the catalysts is selected from a large number of conventional porous refractory catalyst supports or support materials which are practically inert in the presence of the raw material, the resulting products and the reaction conditions in the oxidation of ethylene. Such conventional materials may be of synthetic origin or .přírodního as' preferably have a macroporous structure, i.e. a structure having a surface area from 10 m ² / g and preferably below 7 m ² / g. These carrier materials generally have an apparent mastery of greater than 20%. Very suitable carriers are those containing silicon and / or aluminum compounds.

Specific examples of suitable carriers are aluminum oxides (including materials bearing the trade name "Alundum"), activated carbon, pumice, magnesium oxide, zirconia, diatomaceous earth, selected clays, artificial and natural zeolites, and ceramics. Refractory carriers, particularly suitable for. the preparation of the catalysts of the invention include alumina-containing materials, in particular α-alumina. Of the carriers containing α-alumina, those having a specific surface area, as determined by Β, are preferred. Ε. T., in the range of 0.1 to 1.5. 7 m &lt; 2 &gt; / g and an apparent porosity, as determined by conventional mercury or water uptake procedures, in the range of 10 volume% to 50 volume%. Method Β. Ε. T. to determine the specific surface area is described in detail by Brunauer, Emmett and Teller in J. Am. Chem. Soc., 60, pp. 309-319 (1938).

Make the character used. The carrier of any carrier, the carrier preferably has the shape of particles, lumps, lumps, pellets, rings, beads and the like of a size suitable for use in the solid layer. Commonly used in the art, reactors for the oxidation of ethylene using a catalyst in a solid layer have the typical shape of a plurality of parallel elongated tubes (in a suitable jacket) approximately 2.5 to 5 cm in diameter and 7 to 14 m in length filled with catalyst . In such reactors, carriers shaped into round shapes such as balls, pellets, rings, tablets and the like having a diameter of 2.5 to 20 mm are preferably used.

Determination of the exact concentrations of the higher alkali metal compounds and silver compounds contained in the impregnating solution usually requires several experiments, since the amount of higher alkali metal compounds and silver compounds deposited will depend in part on the porosity and surface area of the catalyst support. However, procedures by which the amount of higher alkali metal and silver applied can be varied as well as the analytical determination of the actual amount present. a variety of materials.

The impregnating liquid preferably contains a higher compound. alkaline. % of the metal in such a concentration that a higher alkali metal content of 0.25 to 14, in particular 0.50 to 14, mg milligram equivalents per kg of total catalyst, based on 1 square meter of catalyst surface area, is achieved.

In another variation, more alkali metal salts than required are deposited, and the catalyst particles obtained are contacted with a suitable solvent, for example anhydrous C 1 -C 2 alkanol, methyl or ethyl acetate, or tetrahydrofuran. The higher alkali metals are soluble in these solvents to a sufficient extent so that one or more washes with these. solvents to selectively remove the excess of the higher alkali metal, so that the amount remaining intact on the surface of the carrier will be within the concentration range characteristic of the process of the invention.

Thus, this method provides a suitable means of reducing the concentration of higher alkaline. of metal of values greater than 16 (mg / kg / kg) / (m2 / g), whether intentionally or accidentally, to specific concentrations ranging from 0.25 to 16 (mg / kg / kg) / m ² / g) which method is readily applicable when working on a scale.

A very good method for adding the desired higher alkali metals is to dissolve their compound in the aqueous phase in an amount to achieve the desired. adding an alkali metal to the finished catalyst when the carrier contacts the solution. Suitable higher-alkali metal compounds are usually all of them which are soluble in the aqueous phase. In this. There is no particular anion in the alkali metal compounds with any particular activity. For example, hydroxides, nitrates, nitrites, chlorides, iodides, bromides, acid carbonates, oxalates, acetates, tartrates, lactates or isopropoxides may be used. After impregnation with a higher alkali metal, the carrier can be dried by any suitable method, preferably at an elevated temperature of 100 to 200 ° C, for example for 0.5 to 8, especially 0.5 to 4 hours, where a variety of temperatures are suitable; when drying over. the heated carrier conducts inert gas. Suitable inert gases are nitrogen, air, hydrogen, rare gases, carbon dioxide, methane and mixtures thereof. The drying may be carried out at atmospheric pressure or at a pressure lower or higher than atmospheric. It is also possible. apply vacuum appropriately, or. freeze drying.

A number of methods for adding silver to carriers are known. In a typical procedure, the support is impregnated with an aqueous solution of silver nitrate, then dried and the silver is deduced with hydrogen or hydrazine as described in U.S. Pat. No. 3,575,888. In another method, the support is impregnated with an ammoniacal silver oxalate or carbonate solution and metallic silver. is obtained by thermal decomposition of this. salts. Silver. can also be added as described in U.S. Pat. No. 3,702,259, wherein the carrier is impregnated with special aqueous solutions of silver salts and a combination of ammonia, vicinal alkanolamines and / or vicinal alkyldiamides, and then heat treated. Other possible methods for adding silver include impregnating the support with a silver salt solution containing ethanolamine followed by reduction as described in Japanese Patent 19,606/1971, or adding a suspension of fine silver carbonate particles to the support followed by thermal decomposition as described. in U.S. Pat. No. 3,043,054, or finally, the addition of silver in the form of &quot; agglomerates &quot; of silver as described in U.S. Pat. No. 3,781,317. In each of these processes, silver is added to the carrier by contacting the carrier with a liquid phase containing either a silver solution or a suspension of silver particles or a silver compound.

A particularly preferred method of depositing silver is to add silver to the support from a basic solution, in particular from a basic solution containing a nitrogenous base. Examples of such nitrogen bases are ammonia, alkylaimines and alkanolaimines.

In a particularly preferred variation, the addition of silver to the catalyst support is carried out by processes such as those described in U.S. Pat. No. 3,702,259. This preferred method involves impregnating the support of aluminum oxide with aqueous solutions of certain silver salts and subsequently heat reducing the silver salt. . The silver impregnation solution consists essentially of

A. silver salts of carboxylic acid,

B. an alkaline solubilizing / reducing agent comprising an organic amine, and

C. other aqueous solvent needed to achieve the desired silver concentration.

Silver salts of suitable carboxylic acids include silver carbonate and silver salts of monohydric and polybasic carboxylic and hydroxycarboxylic acids having up to 16 carbon atoms per molecule. Silver carbonate and silver oxalate are particularly suitable silver salts, with silver oxalate being most preferred.

A solubilizing / reducing agent comprising an organic amine is included in the impregnation solution used in the process. Suitable silver solubilizing / reducing agents including an organic amine are lower alkylenediamines of 1 to 5 carbon atoms per molecule, mixtures of lower alkanolamine of 1 to 5 carbon atoms with lower alkylenediamine of 1 to 5 carbon atoms, and mixtures of ammonia with lower alkanolamines or lower alkylenediamines having 1 to 5 carbon atoms. Four groups of solubilizing / reducing agents, including organic amines, are very preferred. These groups are:

A. Vicinal C 2 -C 4 alkylenediamines,

B. mixtures (1j of C 2 -C 4 vicinal alkanolamines with (2) C 2 -C 4 vicinal alkylenediamines,

C. mixtures of 2 to 4 carbon atoms of vicinal alkylenediamines with ammonia; and

D. mixtures of C 2 -C 4 vicinal alkanolamines with ammonia.

These preferred solubilizing / reducing agents are usually added in an amount of 0.1 to 10 moles per 1 mol of silver present.

Very preferred as solubilizing / reducing agents are

A. ethylenediamine,

B. ethylenediamine in combination with ethanol * amine.

C. ethylenediamine in combination with ammonia,

D. ethanolamine in combination with ammonia.

Most preferred is ethylenediamine, either alone or in combination with ethanolamine.

When ethylenediamine alone is used as solubilizing / reducing agent, it must be added in an amount of 0.1 to 5.0 moles of ethylenediamine per mole of silver.

When ethylenediamine and ethanolamine are used together as solubilizing / reducing agent, it is suitable to use 0.1 to 3.0 moles of ethylenediamine per mole of silver and 0.1 to 2.0 moles of ethanolamine per mole of silver.

When ethylenediamine or ethanolamine with ammonia is used, it is generally preferred to add at least about 2 moles of ammonia per mole of silver, and it is very convenient to add about 2 to about 10 moles of ammonia per mole of silver. The amount of ethylenediamine or ethanolamine used is suitably in the range of 0.1 to 2.0 moles per 1 mol of silver.

As already mentioned, it is important that certain controlled amounts of the higher alkali metals of the invention are present, which amounts are a function of the surface area of the catalyst support. These amounts are achieved either by the controlled addition of the alkali metal to the support in the first impregnation stage, or by the controlled removal of excess alkali metal from the impregnated catalyst support either before or after impregnation with the silver solution.

The heat treatment can be carried out at a temperature of 100 ° C to 500 ° C, preferably up to 375 ° C and in particular at a temperature of 125 ° C to 325 ° C for usually 0.5 to 8 hours needed to decompose the silver salt and form a clinging agent. Of metallic silver particles depositing on the surface of the support. At lower temperatures, silver salts do not decompose to a sufficient extent, so lower temperatures should be avoided. It is possible to work at more than one temperature.

Silver catalysts with a higher alkali metal promoter have been shown to be particularly selective in the direct oxidation of ethylene by molecular oxygen to ethylene oxide. The conditions for carrying out such an oxidation reaction in the presence of the silver catalysts of the present invention are broadly consistent with those known in the art. This includes, for example, suitable temperatures, pressures, residence times, diluents such as nitrogen, carbon dioxide, water vapor, argon, methane or other saturated hydrocarbons, the presence or absence of catalyst control agents, such as 1,2-dichloroethane , vinyl chloride or chlorinated polyphenyl compounds, suitably working in recycled or sequential conversions in separate reactors to increase ethylene oxide yields, or any other special conditions that may be selected in the processes for preparing ethylene oxide. Typically, pressures ranging from about atmospheric pressure to about 35 bar can be used. However, the use of high pressures is also within the scope of the invention. The molecular oxygen used as the reactant is obtained from conventional sources. A suitable oxygen source may be practically or relatively pure oxygen, a concentrated oxygen stream containing oxygen in larger amounts, with smaller amounts of at least one diluent such as nitrogen, argon, etc., or another oxygen containing stream, such as air. The use of the novel silver catalysts of the invention for the oxidation of ethylene is not limited to the use of certain conditions of those known to be useful.

In the preferred use of the silver catalysts of the invention, ethylene oxide is produced by contacting a gas containing at least 95% oxygen with ethylene in the presence of the catalysts of the invention at a temperature in the range 210 ^° C to 285 ° C, preferably in the range 2.25 ° C to 270 ° C.

The ethylene oxide obtained is separated and isolated from the reaction mixture by conventional known methods. The use of the silver catalysts of the present invention in the production of ethylene oxide provides a higher overall selectivity of ethylene to ethylene oxide oxidation at a given ethylene conversion than that achieved with conventional catalysts.

Although the cause of the higher selectivity achieved by the catalysts of the present invention is not fully understood, it has been proven experimentally that conventional silver catalysts (not containing higher alkali metals) promote ethylene oxide combustion upon its formation, while using higher alkali metal catalysts according to the invention. of the invention, this combustion occurs only to a lesser extent.

The invention is illustrated by the following examples.

Example 1

A variety of catalysts are prepared using alumina supports of varying surface area. The physical properties of these carriers are shown in Table I.

TABLE I

Catalyst support AND  В C D E business designation 1 - Carborun- Norton Girdler Péchiney idum Company SRS 6 SAHT-96 LA-4102 surface area, m ² / g 0.19 , 0.51 1.07 1.32 6.55 particle shape rings marbles rollers rings marbles 8 mm Avg. 5 mm Avg. 5 mm Avg. Avg. 2 to 15 mm 5 mm sodium content, wt. % 0.02 0.13 0.24 0.40 0.52 zinc content, wt. % - - 0.24 0.23 - SiO2 content, wt. % 0.26 2.37 0.15 0.28 2.5 iron content, mass % 0.09 0.45 0.04 0.03 0.05 trace elements other than Na, Zn, Si and Fe, wt. % kys- ličníků 0.33 0.85 0.25 0.3 0.3 apparent porosity, *) ob j / o 24 50 25 25 (40 mean diameter of the spring, microns 3.9 2 0.8 0.6 0.25 i% of pores have a diameter in the range of between ...... and ...... microns 1,5 - 15 0,3 - 10 0.4 - 1.2 0.2 - 1.5 0.1 - 0.9 feather volume, **) ml / g 0.23 0.25 0.22 0.45

*) Determined by water adsorption * * j Determined by mercury pore ometer

Catalysts labeled A-1, A-2,,. B-1, etc., are obtained by the process of the invention, i.e. by sequential deposition of alkali metal and silver. ·

Catalysts, designated NA-0, NB-0,. , NI-0 etc. are not obtained by the process of the invention because they do not contain an alkali metal. Catalysts designated NA-1, NA-2, ..., NB-1 etc. are also not prepared by the process. according to the invention, since the alkali metal and silver are deposited therein simultaneously.

To illustrate the preparation of the catalysts of the invention, the preparation of supported catalysts C is described below. Other catalysts of the invention are prepared analogously.

g support C having a surface area of 1.07 m ² / g, was first impregnated under pressure obsolutního 0,04.10 ⁵ Pa in a rotary evaporator, 8.5 ml of an aqueous solution containing in 1 ml · 3 mg of cesium hydroxide. The impregnated carrier is dried by heating at 110 ° C for 30 minutes and then for 2 hours. at 150 ° C under a stream of nitrogen.

The carrier is then impregnated with an aqueous silver salt solution. This solution is prepared as follows: dissolve 6 g of anhydrous silver nitrate and 3,3 g of potassium oxalate (K2C2O0.1 H2O) separately in 100 ml of water. The solutions were combined and heated in a water bath. The silver oxalate precipitate is centrifuged and the supernatant is decanted. The precipitate is then washed five times with 100 ml of distilled water at 60-90 ° C. After each. The precipitate is washed by centrifugation and the water is decanted. The precipitate is then dissolved in 10 ml of a mixture consisting of 75% by volume of 1,2-diaminoethane and 25% by volume. % water, with ice cooling. 30 g of the cesium-containing support are then initially impregnated at an absolute pressure of 0.04 mm Hg in a rotary evaporator with 8.5 ml of the above silver-containing mixture, then heated to 60 ° C by indirect heat exchange and hot water, again at absolute pressure to 0.04 bar ( ⁵ Pa) to partially remove the solvent, then spill onto a large filter paper, shake gently to remove excess moisture, then heat in a stream of nitrogen for 2 hours to reach 300 ° C at which is left for a further 2 hours. Then, the catalyst is cooled to ambient temperature. The silver content of the catalyst was 7.8 wt. %. The cesium content is 3.35 migev. per kg of catalyst. Examination of the catalyst by electron microscopy reveals that silver is deposited on the support in the form of discrete particles of uniform diameter in the range of 50 to 300 nm. The silver particles are evenly distributed over the support surface.

In the preparation of the non-alkali metal NA-0, ..., NI-0 series catalysts, the first impregnation step with the cesium hydroxide solution as described above is omitted, the other steps being substantially identical to those described above.

For the preparation of the catalysts of the NA-1, NA-2, NB-5 series, which do not correspond to the invention, the first impregnation step with cesium hydroxide is also omitted. Subsequent steps are carried out in substantially the same manner, except that the cesium hydroxide is added to an aqueous solution containing silver and ethylenediamine in sufficient quantity to achieve the desired alkali metal content in the resulting catalyst.

The catalysts prepared as above were tested for ethylene oxide production, comparing their performance. The reactor for this reaction consists of a tube having an internal diameter of 5 mm; it is filled with a length of 12 cm for each experiment. catalyst particles having dimensions ranging from 0.4 to 0.8 millimeters. These catalyst particles are prepared by crushing the catalyst particles obtained as described above.

An oxygen / ethylene-containing mixture is passed through the catalyst bed in the presence of a small amount of vinyl chloride as moderator under the following conditions:

pressure throughput of ethylene in feedstock oxygen in feedstock nitrogen in feedstock concentration of moderator,, parts of vinyl chloride per million parts of feedstock

14,, 5. 105 Pa

3300 hours, / - ¹ mol. %

8.5 mol. %

61.5 mol. % ppm

The reaction temperature was adjusted. so as to achieve an oxygen conversion of 52% and selectivity to ethylene oxide was determined. The selectivity to ethylene oxide, expressed in. percent, is defined as the number of moles of ethylene oxide formed from 100 moles of ethylene converted. The results of the experiments described above are shown in Tables II to VI. As can be seen from these tables, similar results to the simultaneous application are achieved with the smallest surface area used by the sequential deposition method of the invention. However, in the case of more desirable carriers with a higher surface area, the process according to the invention yields much more advantageous catalysts than catalysts produced by a process not corresponding to the process according to the invention.

Catalysts manufactured with supports having a surface area of 0.19 m ² / g

TABLE II

Catalyst silver content cesium content reactor temperature, 0 ° C, to achieve 52% O2 conversion selectivity, oxidation to ethylene oxide,% wt. mgekv./kg wt. ppm A-l *) 7.0 0.86 114 259 79.9 A-2 7.6 1.01 134 255 80.3 A-3 7.9 1.11 148 259 80.7 A-4 7.6 1.49 198 265 79.8 A-5 8.2 1.65 220 261 79.0 NA-0 7.8 0 0 251 69.5 NA-1 8.3 0.77 103 254 80.3 NA-2 8.3 1.08 143 258 80.6 NA-3 7.7 1,25 166 263 80.2 NA-4 7.8 1.64 218 264 79.7 NA-5 8.0 1.89 252 295 76.1 ) A-1, A-2, .. ., B-1 etc. are the method according to catalysts ON- 1, NA-2, .., NB-1, etc. are catalytic- ready invention. heaters, prepared in a non- NA-0, NB-0 etc. are catalysts, according to invention by applying al-

according to the invention, without the addition of an alkali metal with silver, an alkali metal.

TABLE III

Catalysts manufactured with supports having a surface area of 0.51 m ² / g

Catalyst silver content cesium content reactor temperature. ^C C, to achieve a 52% O2 confidence selectivity of oxidation to ethylene oxide,% wt. mgekv./kg wt. PPm B-l *) 7.7 0.89 118 254 74.5 B-2 7.9 1.53 204 252 77.8 B-3 7.7 2.79 371 258 78.2 B-4 7.5 3.77 502 259 76.5 B-5 7.9 5.50 732 > 300 70.4 NB-0 7.7 0 0 . 251 71.0 NB-1 7.1 2.64 351 261 77.6 NB-2 7.4 3.78 503 274 76.1 NB-3 8.0 5.47 728 > 300 64

*) See footnote II.

TABLE IV

Catalysts manufactured with supports having a surface area of 1,07 m ² / g

Catalyst silver content cesium content reactor temperature, ° C, to reach 52% O2 conversion oxidation selectivity to ethylene, ¹ wt. mgekv./kg wt. PPm C-1 *) 8.4 1.56 208 237 77.7 C-2 8.8 3.52 468 249 78.4 C-3 10.7 6.03 802 ' 255 79.5 C-4 8.7 6.59 877 256 77.5 C-5 10.6 7.95 1058 268 76.4 NC-0 8.0 0 0 260 71.9 NC-1 8.0 1.87 249 251 75.1 NC-2 8.0 3.11 430 260 75.9 NC-3 8.4 4.08 543 252 76.2 NC-4 9.2 4.80 639 257 74.7 NC-5 8.0 5.43 722 320 67.8

*) See footnote II.

TABLE V

Catalysts manufactured with supports having a surface area of 1,32 m ² / g

Catalyst silver content cesium content Reactor temperature, ° C, to achieve 52% O2 conversion selectivity of oxidation to ethylene oxide,% mgekv./kg wt. ppm D-1 * j 6.6 4.19 557 260 67.0 D-2 6.0 6.35 884 265 73.2 D-3 6.9 7.69 1024 264 75.4 D-4 7.2 9.56 1272 261 74.3 ND-0 5.4 0 0 257 66.0 ND-1 5.4 4.08 543 293 65.6 ND-2 5.4 4.69 624 289 63.2

*] See footnote II.

TABLE VI

Catalysts manufactured with supports with a surface area of 6.55 m ² / g

Catalyst silver content cesium mass ppm, reactor temperature, ° C, to reach

52% O2 conversion selectivity oxidation to ethylene oxide,%

Ё-1 *) 11.5 25.7 3420 207 73.3 E-2 11.0 35.3 4690 205 75.4 E-3 11.2 39.5 5250 205 75.1 NE-0 9.4 0 0 220 50.0 NE-1 11.9 42.3 5621 277 42.4

*) See footnote II.

The above results are also shown in the accompanying graph, in which the cesium contents in catalysts in ppm are plotted on the horizontal axis and the selectivity to ethylene oxide in% is plotted on the vertical axis. The selectivities of the catalysts made of the five different alumina listed in Table I are illustrated in the graph by five different symbols. The five curves formed by joining the respective series of symbols illustrate selectivity as a function of the cesium content of the surface gloss given for each of the curves. Four curves for surface areas of 0.19, 0.51, 1.07 and 1.32 m ² / g are constructed based on vertical axis and lower horizontal axis data, while a curve for surface area of 6.55 m ² / g is constructed based on vertical axis and upper horizontal axis data. Vertical arrows pointing to each of the five curves indicate the optimal cesium content of each of the four catalysts. These optimum cesium contents are shown in Table VII.

TABLE VII

Surface area of alumina, m ² / g optimal content of cesium, mass, mgeq./g selectivity at optimal cesium content,% optimal content of cesium divided by surface area (mass, mgekv./kg)/(m ² / g) 0.19 1.12 80.7 5.9 0.51 2.26 78.4 4,5 1.07 6.02 79.5 5.6 1.32 8.13 75.5 6.1 6.55 35.7 75.4 5.4

Example 2

The catalysts of the present invention are prepared by the procedure and materials of Example 1 containing varying amounts of potassium as the higher alkali metal. Potassium in the form of potassium hydroxide is added to the first impregnation solution instead of cesium. The catalyst mixtures thus prepared were tested as ethylene oxidation catalysts using the apparatus and procedure of Example 1. The composition of these catalysts, together with the results, are shown in Table VIII.

Catalysts, prepared with supports with a surface area of 0.19 m ² / g selectivity of oxidation to ethylene oxide,%

TABLE VIII

Catalyst silver content potassium content wt. wt, mq / kg p _; pm reactor temperature, ° C, to achieve 52% conversion Ог

F-l *) 7.8 1.74 68 256 NF-0 7.8 0 0 251

79.8

69.5

*) See footnote II.

Example 3

The catalysts of the present invention are prepared by the procedure and materials of Example 1 containing varying amounts of rubidium as the higher alkali metal. Rubidium in the form of rubidium hydroxide is added to the first impregnation solution instead of cesium hydroxide. The catalyst mixtures thus prepared were tested as ethylene oxidation catalysts using the apparatus and procedure of Example 1. The composition of the catalysts and the results of these tests are shown in Table IX.

TABLE IX

Catalysts prepared with supports having a surface area of 0.19 m ² / g selectivity of oxidation to ethylene oxide,% Catalyst content of silver rubidium content reactor temperature, ° C, to achieve 52% O2 conversion wt. mgekv./kg wt. PPm G-1 * 7.8 1.06 90 252 76.7 NG-0 7.8 0 0 251 69.5 *) See footnote II.

Example 4

By the method described in Example 1, a number of catalysts were prepared from the supports V, C, D and E shown in Table I, but using cesium nitrate instead of cesium hydroxide. For comparison, cesium-free catalysts A, F, K and P are shown in Table X. The catalysts are characterized by the properties given in Table X. The catalysts obtained are tested for the production of fixed bed ethylene oxide and the results obtained are compared with each other. The reactor consists of a 5 mm internal diameter tube, which is filled with catalyst particles the largest dimensions of which were in the range of 0.4 to 0.8 mm in each test at 16 cm in length.

A mixture of oxygen and ethylene is passed through the catalyst bed in the presence of a small amount

1,2-dichloroethane as moderator under the following conditions:

pressure through the amount of ethylene in the feedstock the amount of oxygen in the feedstock the amount of nitrogen in the feedstock

14.5.10 ⁵ Pa

3000 hours' ¹ mol. %

7.8 mol. %

62.2 mol. % moderator concentration, mass, parts of chlorine per 1 million raw material 1.5 ppm

The reaction temperature is adjusted to achieve 40% oxygen conversion and the selectivity to ethylene oxide is determined. The T40 and S40 values thus obtained are shown in Table X together with the number of operating hours elapsed at the time of determination.

TABLE X

Test no. catalyst surface area АЬОз m ² / g silver content % cesium content, mgat / kg diameter of silver particles, microns S40,% T40 ° C hours of operation 1 AND 0.51 12.8 0 0.1 —0.4 76.3 214 100 ALIGN! 2 В 0.51 12.1 0.72 0,05—0,5 78.7 220 95 3 C*) 0.51 9.4 1.07 0.1 —0.6 79.0 235 120 4 D ‘) 0.51 n, o 1.24 0.1 —0.6 79.0 235 120 5 E 0.51 9.6 1.30 0,05—0,4 79.0 222 **] 65 6 F 1.07 9.7 0 0.1 —0.4 75.4 210 40 7 G 1.07 8.5 0.32 0,05—0,3 75.9 210 115 8 H 1.07 8.4 0.68 0.1 —0.3 76.3 209 117 9 AND 1.07 9.0 2.21 0.1 —0.4 80.6 209 75 80.5 220 103 79.7 2128 260 10 AND 1.07 7.8 3.35 0,05—0,3 79.3 211 **) 60 11 к 1.32 8.0 0 0,05—0,2 73.9 205 85 12 L 1.32 9.5 1.07 0,05—0,2 75.6 212 150 13 M 1.32 7.5 2.19 0,05—0,3 76.8 215 145 14 N 1.32 7.8 2.26 0,05—0,3 77.1 208 50 77.5 223 116 77.5 222 215 15 Dec O 1.32 7.3 2.49 0,05—0,3 77.5 2327 167 16 P 6.55 9.4 0 0,05—0,3 50 215 30 17 Q 6.55 8.5 15 Dec 0,05—0,3 74.8 200 90 18 R 6.55 8.7 21 0,05—0,2 77.6 191 30 ) This catalyst is prepared by a single ** ) In this case apply instead of 1.5

by impregnation and heated in ppm 1,2-dichloroethane 3 ppm 1,2-dichloro.

At 300 ° C ethane, the temperature is corrected to 1.5 ppm from ppm.

Experiments not in accordance with the process of the invention.

Council A:

Catalysts containing varying amounts of lithium as an alkaline coke not within the scope of the invention are prepared by the process and using the materials of Example 1.

Lithium in the form of lithium hydroxide is added to the first impregnation solution instead of cesium hydroxide. The catalyst mixtures thus prepared were tested as ethylene oxidation catalysts using the apparatus and procedure of Example 1. The composition of these catalysts, together with the test results, are shown in Table XI.

TABLE XI

Lithium-containing catalysts prepared with supports having a surface area of 0.19 m ² / g

Catalyst silver content lithium content reactor temperature, ° C, to achieve 52% O2 conversion selectivity of oxidation to ethylene oxide,% wt, mg / kg ppm NH-0 7.8 0 0 251 69.5 NH-1 6.9 28 200 250 73.5 NH-2 6.9 56 390 250 72.4 NH-3 6.9 72 500 252 72.8

*) See footnote II

Council B:

Catalysts containing varying amounts of sodium as the alkali metal not within the scope of the invention are prepared by the procedure and materials of Example 1. Sodium in the form of sodium hydroxide is added to the first impregnation solution instead of cesium hydroxide. The catalyst mixtures thus prepared were tested as ethylene oxidation catalysts using the apparatus and procedure of Example 1. The composition of these catalysts, together with the test results, are shown in Table XII.

Sodium-containing catalysts prepared with supports having a surface area of 0.19 m ² / g

TABLE XII

Catalyst content sodium content 'temperature of reactor ^C C selectivity of silver wt. wt. to achieve oxidation to mgekv./kg ppm 52% O2 conversion ethylene oxide,%

N1-0 7.8 0 0 251 69.5 N1-1 7.1 1,22 28 252 72.3 N1-2 7.1 2.17 50 251 74.1 N1-3 7.1 3.22 74 249 75.7 N1-4 7.1 3.57 82 254 75.5 N1-5 7.1 4.39 101 254 75.5

An object of the invention

Claims (8)

Method for producing silver catalysts for producing ethylene oxide, wherein silver and at least one alkali metal compound of atomic number 19 to 55 are deposited on a porous refractory support having a surface area of from 0.03 m ² / g to 10 m ² / g, characterized in that at least one of said alkali metal compound is applied to said carrier by impregnating with a solution in an amount of 0.25 to 16 milligrams of alkali shell per kg of total catalyst support per square meter of Specific Carrier Surface per gram of support of the catalyst, the impregnated support is dried, 1 to 25% by weight of silver, based on the total amount of catalyst, is deposited on the dried support, impregnating the support with a silver compound containing liquid and then heating the impregnated support to convert the silver compound to metallic silver to 100 ° C to 375 ° C. 2. The process of claim 1 wherein the carrier is impregnated with at least one of said alkali metal compound in an amount of 0.25 to 14 milligrams of alkali metal per kilogram of total catalyst per square meter of specific surface area of the support, per gram of catalyst support. 3. The process of claim 1, wherein the support is impregnated with at least one of said alkali metal compound in an amount of 0.50 to 14 milligrams of alkali metal per kilogram of total catalyst per square meter of specific support surface area per gram of catalyst support. 4. The method according to any one of items 1 to 3, characterized in that the heating of the impregnated carrier is carried out in the presence of a reducing agent. 5. The method according to any one of items 1 to 4, characterized in that from 4 to 16 wt. % silver, based on the total amount of catalyst. 6. The method according to any one of items 1 to 5, characterized in that the carrier impregnated with the at least one alkali metal compound is dried by heating to a temperature in the range of from 100 ° C to 200 ° C in a stream of nitrogen. 7. The method of any one of items 1 to 6, characterized in that the dried support is impregnated with an aqueous solution containing a silver carboxylic acid salt and an organic amine alkaline sodubilizing reducing agent. 8. The process of claim 7 wherein the solubilizing reducing agent is 1,2-d laminate ethane.