DK151961B - Heterogeneous silver catalysts for use in the production of ethylene oxide as well as for the production of ethylene oxide by the use of the catalysts - Google Patents

Description

in

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The present invention relates to heterogeneous silver catalysts for use in the production of ethylene oxide by gas phase oxidation of ethylene by oxygen or an oxygen-containing gas mixture. The invention further relates to a process for producing ethylene oxide using the catalysts.

In general, the production of ethylene oxide in gaseous phase in solid-layered tubular reactors is carried out by reacting oxygen to ethylene on silver-based catalyst phases deposited together with any activating compounds on inert and refractory carriers formed essentially from alumina, silica / alumina, magnesium oxide, pumice, zircon, clay, ceramics, natural or artificial graphite, asbestos, natural or artificial zeolites or silicon carbide. In the prior art, solids having a low specific surface area are generally preferred, less than

ISLAND

10 m / g, and with high pore volume, which can go up to 20 to 60% by volume. The specific surfaces are determined in most of the cases by the nitrogen adsorption method, referred to as the BET method, and described by BRUNAUER, EMMET and TELLER in "The Journal of the American Chemical Society", Vol. 60, page 25 309, 1938, while measuring The porosity is performed by the method called the mercury porosimeter method recommended by EW WASHBURN in "Proceedings of the National Academy of Sciences of the United States", Volume 7, pages 115, 1927, and described by LC DRAKE in "Industrial 30 and Engineering Chemistry ", Volume 41, pages 780, 1949, and in" Industrial and Engineering Chemistry - Analytical Edition, Volume 17, page 782, 1945.

The choice of a carrier with appropriate texture and in accordance with the characteristics described above is not sufficient in itself for

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the activity of the lysates, selectivity with respect to ethylene oxide and shelf life also depends on the nature of the starting material for the active phase used and on the method used to precipitate it on the carriers.

It is known that the silver catalysts used in epoxy oxidation of ethylene can be prepared from metal compounds by two different methods: a) Coating the carrier with the metal compound 10 in suspension in a liquid.

b) Impregnating the carrier with the metal compound in solution in a suitably selected solvent.

In either case, the silver compounds should be readily degradable and able to readily release the silver onto the carrier. The nature of the composition of the metal compound and the solvent used is very important, it can significantly affect the activity and selectivity of the catalyst in connection with the texture of the carrier and the treatment leading to the metal separator. To obtain silver basins or agglomerates of silver basins of a shape and size favorable to the activity and selectivity with respect to ethylene oxide, the carriers are impregnated with solutions of organometallic silver compounds wherein the organic substrate (s) used contains a reactive group of acid character capable of forming a silver salt, as well as one or more nitrogen atoms or oxygen atoms suitable for forming a coordination bond with the metal atom.

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The first type of such compounds used consists of intramolecular silver complexes in which the acid group and the reactive groups capable of complexing metal form part of the same molecule. One can cite examples of impregnation of carriers with an aqueous solution of silver lactate mentioned in French Patent Specification No. 1,295,395 of 23 March 1961. The process described herein is complicated and delicate, and the resulting catalysts have only 10 poor productivity. Or impregnation with a pyridine solution of silver derivatives of anthranilic acid, picolinic acid or salicylic acid, which is disclosed in the specification of Danish patent application no. 4989/78 (French patent application no. 77.33 866 of 10/11/1977 in the applicant's name) . By this method, catalysts which are only slightly sensitive to CC 2 are obtained, but the yields of using these catalysts are only medium good and are inferior to yields obtained by using catalysts containing promoters. The process disclosed in French Patent No. 2 023 986 20 of 21/11/1969 is different therefrom, but it can be presumed to consist of impregnating the carriers in an aqueous environment with silver derivatives of tartaric acid, citric acid, malic acid or isobelic acid. Promoters are included here, but the yields of ethylene oxide are still low.

The second type of these compounds used consists of compounds between an inorganic or organic silver salt and a molecule which contains one or more complex-forming groups capable of forming a coordination bond with the metal. French Patent Nos. 2,117,183 and 2,271,869 of 30/11/71 and 16/5/1975 refer to impregnation by means of aqueous solutions, which may contain ammonium hydroxide, of silver oxalate or silver carbonate attached to compounds such as ethylenediamine and ethanolamine. An example of the preparation is described

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4 from the compound Ag 2 (Cl 2 NE 2 -Cl 2 N 1 2) 2 ^ 2®A * The use of these catalysts, despite the presence of promoters, does not result in very high yields and, for the former, high CC .

5 - French Patent No. 2,253,747 of 4/12-1978, which appears to prefer ammonia as a complexing agent for silver carboxylates, but which emphasizes the importance of the addition to the aqueous impregnating liquid of a reducing amine. Here, a fairly high selectivity is obtained, which, however, requires the catalyst to have a very finely divided form, as well as the presence of promoters, and the yield of ethylene oxide is not very high.

- French Patent No. 2,351,700 of 18/5/1977, which uses aqueous complex solutions of the type

Ag (amine) 0 0 ^, preferring for the amines the general formula: R-t; oh - NHO 2 /

BT

wherein R 1 and R 2 are aliphatic residues.

These catalysts require the use of multiple promoters.

20 "French Patent Specification No. 2 336 974 of 23/11/1976, which seeks to show that special amino-group-containing complexing agents which can also play the role of solvent can be used to prepare catalysts from silver carboxylates. These are aliphatic polyamines and special amino ethers such as diethylenetriamine or bis (2-aminoethyl) oxide. These cat- 5

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Lysators are referred to in several contexts as prior art that can be improved.

- French Patent No. 2,215,267 of 24/01/1974, which uses as a complexing agent and solvent for silver acetate 5, pyridine compounds. In manufacturing, there is a risk of formation of ketene-silver compounds and productivity is low.

The great importance of the characteristics of the catalyst thus produced, 10 small silver crystals and especially of their size, their shape and their distribution on the carrier has been clearly demonstrated in French Patent Specification No. 2 271 869 of 16/5-1975 , No. 2 148 028 of 26/7/72, No. 2,352,810 of 25/7-1977, and in Belgian Patent Specification No. 852,123 of 4/3-1977, in 15 articles published by Peter HARRIOTT and employees of " Journal of Catalysis "Vol. 39 (3), page 395 (1975), Vol. 21 (1), page 56 (1971), and in disputes by J. Wu (1973):" The effect of crystallite size on the activity and selectivity of silver catalysts "at Cornell Univer-20 sity (USA) and by MM JARJOUI (1976): "The study of oxidation partial of the 1'ethylene and catalyst support contact to base d'argent" at the University of Lyon (France).

The effect of the silver catalysts of the invention 25 depends solely on the silver, and selectivity is obtained without promoters as well as in the prior art.

At the same time, CO 2 sensitivity is avoided, which is of great importance in industrial designs involving air recirculation.

It has now been found that the thermal treatment in inert, reducing or oxidizing atmosphere of carriers impregnated with complexes of silver salts with cyclic imino ethers of type oxazole (I), 2-

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6 oxazoline (II) and 3-oxazoline (III):

R D

R R

N - N R-- "NN, - t \ t Λ.Λ, -k" A Αγ "(1) (II) (III) or with cyclic alkyloxyimines of the type isoxazole (1V) and 2-isoxazoline (V) :

R R R R

Yt t-t rx ^ ^ <r

R

(IV) (V) led to very active catalysts whose high selectivity in ethylene oxide was only slightly influenced by the content of CO2 in the reaction components and the increase in productivity. In the general formulas for such compounds (i - Y), R is hydrogen, an alkyl group having from 1-10 carbon atoms 10 or a phenyl group. Scanning electron microscope observations of the catalysts of the present invention have demonstrated a homogeneous and regular distribution of the silver grains, which appear to be hemispherical and having an equivalent diameter of between 0.1 15 and 1 µm.

The present invention thus relates to heterogeneous silver catalysts of the kind mentioned in the preamble of claim 1, and these catalysts are characterized by the characterizing part of claim 1.

The invention further relates to a process for producing ethylene oxide of the kind mentioned in the preamble of claim 15, and the process is characterized by the characterizing part of claim 15 *.

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The catalysts of the present invention are preferably prepared by a two-step process: a) impregnating the carrier with a solution of the selected silver compound. This impregnation 5 can be carried out either by immersing the carrier in the solution followed by dripping or distilling off the solvent, or by continuously sprinkling the carrier under such pressure and temperature conditions as to allow immediate disposal of the solvent.

b) heat treating the product thus produced so as to release the silver from the compound deposited on the carrier.

The silver salts that can be used are numerous: nitrate, sulfate, carbonate, formate, lactate, citrate, salicylate, maleate, malate, malonate, phthalate, tartrate, picolinate, anthranilate, salicylaldehyde complex, but clear silver carboxylates containing 1 are preferred. to 10 carbon atoms and 1 to 2 acid groups per molecule such as acetate, propionate, benzoate, oxalate or pivalate.

These salts may be replaced by the addition to the oxide-silver impregnation solution as well as an amount of acid equal to or preferably slightly greater than the theoretical amount corresponding to the metal salt formation. Generally, a molar excess of 5 to 25% of the acid is used relative to the stoichiometric amount.

As the solvent, the complexing agents mentioned in pages 5-6 of general formulas (I) -30 (V) are advantageously used, but these heterocyclic compounds have also been found to be excellent solubilizers for the silver compounds in a large number of solvents or 8

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mixtures of solvents. Thus, since the smallest amounts of cyclic imino ethers or cyclic alkyloxyimines that can be used are 2 moles of heterocyclic compound per ml. silver atom, impregnation can be carried out with solutions of high silver concentration, which can reach 300 to 400 g per minute. per liter, which is made with not very expensive ordinary solvents such as water, which may have been rendered ammonia-based, nitriles, e.g. acetonitrile, acrylonitrile, propionitrile, ketones such as acetone and methyl ethyl ketone, light alcohols, ethylene glycol and diethylene glycol and amines.

All methods which allow decomposition of the organosol compounds can be applied to the impregnated carriers. A particularly suitable treatment consists of a thermal decomposition under the following conditions: - heating from 20 to 280 ° C at a rate of 20 ° / h followed by a stay of 10 to 50 hours at 280-300 ° C. The treatment is carried out under rinsing with nitrogen and by any addition during the treatment of oxidizing or reducing compounds such as e.g. air, oxygen, hydrogen, formaldehyde.

The catalysts contain from 5 to 25 wt% silver, preferably from 8 to 20 wt%.

The nature and texture of the carrier used are of great importance. Refractory carriers such as alumina, silica / alumina, silicon carbide or zircon are mainly used. These carriers should have a fairly large grain size suitable for use in industrial reactors such as solid layers. They are available in the form of rings, lozenges, trunks, balls or extruded shapes in dimensions between 3.2 and 13 mm (1/8 and 1/2 inch) and with satisfactory mechanical properties.

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9 creates, which in no case leads to the formation of dust during the preparation of the catalyst, during its handling or use. The specific surfaces of these products are less than p 5 10 m / g, but even smaller surfaces, p 1 less than 2 m / g, and especially those between 0.1 and 1 m / g are preferred.

The apparent porosities made up of pores with radii greater than 0.25 µm should be at least from 40 to 100% by volume.

For the experiments carried out, a silica / alumina support, which is marketed by the company NORTON in the form of spheres with a grain size of 6.5 to 4.9 mm (1/4 or 3/16 inch), has been used, with specific p * 2 15 surface 0.30 m / g and with total pore volume of 0.34 cnr / g.

It has also been demonstrated in accordance with the prior art: a) that certain compounds such as halogenated hydrocarbon derivatives increase the selectivity of these 20 catalysts when added in small amounts to the reaction components. 1,2-dichloroethane at a maximum concentration of 1 ppm in the total gas volume presents a particularly interesting application.

b) it is possible to add these catalysts to the usual contents of 0 to 2% by weight of all classical silver activators such as: K, Ca, Cs, Ba, Pt, Ni, Sn, Cd, Sr, Li, Mg, Na, Rb,

Au, Cu, Zn, La, Ce, Rh, Be, Sb, Bi, Ti, Pd, Ir, Os,

Ru, Fe, Al.

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These elements may be present in the finished catalysts in metal form or in the form of an oxide or a compound.

Examples 1 to 12 below illustrate the preparation and use of catalysts of the invention. The results obtained in these examples are expressed by total degree of conversion of ethylene and by the selectivity. Gas compositions are in vol% and the tests are carried out at atmospheric pressure unless otherwise indicated.

10 - Degree of total conversion of ethylene (TTG): mm «_ Number of moles of ethylene converted Number of moles of ethylene added x ± uu - Selectivity of conversion to ethylene oxide (SOE): ς nf - Number of moles of ethylene oxide formed" Number of moles of ethylene converted x χυυ # EXAMPLE_1 15 Into a flask designed for solids mounted on a rotary evaporator, 42.6 g of the NORTON SA 5239 (trade mark) grain size 6.5 mm (4/16 inch) is raised to raise the evaporator oil bath temperature. to 130 ° C and allowing the carrier to be degassed for 20 hours in vacuo, then adding dropwise to the stirred solution a solution of 16.5 g of silver acetate in 108 g of 2-methyl-2-oxazoline. After adding the total amount of solution, the carrier, which is impregnated and dried, is transferred to a tubular reactor to undergo a heat treatment for decomposition of the acetate and to release of metallic silver. This treatment is performed under a stream of nitrogen

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11 with a temperature rise of 20 ° / hour up to 270 ° C, at which temperature one stays for 18 hours. The silver content of the catalyst determined by analysis is 17% by weight. As a result, a scanning electron microscope study in conjunction with an X-ray microanalysis device results in a regular distribution on the carrier of silver crystal units of hemispherical appearance with an equivalent diameter of between 0.2 and 0.4 µm.

30 ml of this catalyst is placed in a reactor consisting of a stainless steel tube 600 mm long and 16 mm internal diameter. The reaction components fed into the bottom of the tube are preheated through a layer of porcelain rings of 200 mm height which also supports the catalyst layer. The heating of the entire equipment is ensured by circulating oil in a heating jacket.

The gases added to the reactor and flowing from the reactor are analyzed on-line by means of a dual-detector chromatograph: a flame ionization detector for ethylene oxide, methane, formaldehyde, propylene, propane, methanol and acetaldehyde, and a thermal heat conduction detector for oxygen, nitrogen, carbon dioxide, ethylene and water. Two columns with a diameter of 3.2 mm (1/8 inch) and a length of 2.5 m mounted in 25 series are filled, one with the filling material Chromosorb 101 (trademark), the other with Porapak Q (trademark).

Through the catalyst layer placed in the reaction vessel, a mixture of air-ethylene is fed 50% - 50% at atmospheric pressure for 47 hours between 177 ° C and 185 ° C. Then, through the reaction vessel, a gas flow of 9000 l in the normal state per minute is passed through. per hour and per hour. liter of catalyst, lysator consisting of a mixture of 13% ethylene, 5% oxygen, 82% nitrogen and 35 ppb 1,2-dichloroethane.

At 206 ° C and at a total conversion rate of ethylene

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12 at 5%, the selectivity to ethylene oxide is 78.5%.

EKSEMPEL_2

For 42.6 g of the carrier NORTON SA 5239 (trade mark) of 5 grain size 6.5 mm (4/16 casings), which is placed in a flask designed for solids and mounted on a rotary evaporator and previously degassed at 100 ° C for 1 hour under vacuum, a solution of 16.5 g of silver acetate in 108 g of oxazole is added dropwise, since the temperature of the oil bath in the evaporator is 100 ° C, the oxazole is distilled off as it is added. The impregnated carrier is then thermally treated by analogy to the procedure described in Example 1. Analysis shows a silver content of the catalyst of 16.5% by weight A scanning electron microscope study in connection with an X-ray microanalysis device shows a regular distribution of the silver crystal carrier. with hemispherical appearance and equivalent diameter of between 0.3 and 0.5 µm.

30 ml of the catalyst are placed in the reactor described in Example 1. An air-ethylene gas stream is fed 50% - 50% for 30 hours between 138 ° C and 184 ° C. Then, under a pressure of 20 bar, a gaseous mixture of 9000 l is added in the normal state per day. per hour and per hour. liter of catalyst composed of 13% ethylene, 5% oxygen, 35 ppb 1,2-dichloroethane, and varying contents of 00 pounds and nitrogen.

The results obtained are listed in Table 1 below.

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TABLE 1.

Input gas composition in% _ Tempera- T.T.G. Selectivity Nitrogen Nitrogen C0H / (tet C2H4 ° 2 C02 gene (° C) SOEtø) 13 5 0 82 218 5 75 13 5 10 72 229 5 77.5 13 5 14 68 225 5 77 EXAMPLE_3 I a solid-state flask placed on a rotary evaporator is placed 36 g of the NORTON SA 5239 (trade mark) carrier of 4.9 mm (3/16 inch) grain size, which is allowed to gas for 1 hour at 120 ° C under vacuum. Concurrently, 5 g of acetic acid is mixed with 100 g of 2-methylethyl-2-oxazoline, and 8.5 g of silver oxide are dissolved therein. Then, this solution is added dropwise to the carrier. Analysis after a heat treatment performed analogously to the IO described in Example 1 shows a silver content of the 13.5% by weight catalyst. 30 ml of this is placed in the reaction vessel described in Example 1. After an activation pretreatment with a mixture of air and ethylene 50% - 50% for 48 hours between 182 ° C and 15 218 ° C carried out at atmospheric pressure, reaction is added. the components under a pressure of 20 bar in the following mutual conditions and conditions:

Ethylene 13%, oxygen 5%, nitrogen 82%, 1,2-dichloroethane 35 ppb, gas velocity 9000 liters in the normal state per liter.

2 hours per hour. liter of catalyst. At 218 ° C after 58 hours of operation, the ethylene oxide selectivity is 77% at a total ethylene conversion rate of 5%

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EXAMPLE_4

Into a flask designed for solids and mounted on a rotary evaporator 37.5 g of the carrier NORTON SA 5239 (trade mark) with a grain size of 4.9 mm 5 (3/16 inch) If you proceed analogously to Example 1, you make a catalyst by impregnating this carrier by means of a pre-prepared solution of 8.9 g of silver oxide in 10.3 g of benzoic acid and 120 g of 2-methyl-2-oxazoline Analysis analyzed after thermal treatment shows a silver content of the catalyst of 14.2% by weight .

30 ml of this catalyst are placed in the reactor described in Example 1. After a prior activation treatment with a mixture of air-ethylene 15 50% - 50% for 114 hours between 198 ° C and 213 ° C at atmospheric pressure, the reaction components are added under a pressure of 20 bar in the following proportions:

Ethylene 13% oxygen 5%, nitrogen 82%, 35 ppb 1,2-dichloroethane. The total gas velocity is 9000 1 2o in the normal state per day. per hour and per hour. liter of catalyst.

At 232 ° C, the selectivity to ethylene oxide is 76.5% at a total ethylene conversion rate of 5%.

EKSEMPEL_5

It is placed in a flask intended for solids and mounted on a rotary evaporator 36.5 g of the carrier NORTON SA 5239 (trade mark) with a grain size of 4.9 mm (3/16 inch). Proceeding analogously to Example 1, a catalyst is prepared by impregnating this carrier by means of a previously prepared 30 solution of 8.6 g of silver oxide, 8.33 g of pivalic acid and 104 g of 2-methyl-2-oxazoline. Analysis after thermal treatment shows that the silver content of the catalyst is 16.6% by weight. 30 ml of this is placed in it

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15 in Example 1. After an activation pretreatment performed at atmospheric pressure with a mixture of air-ethylene 50% - 50% for 48 hours between 184 ° C and 200 ° C, the gaseous reaction components are sent in the following proportions:

Ethylene 13%, oxygen 5%, nitrogen 82%, 1,2-dichloro-ethane 35 ppb, the total rate being 9000 l in the normal state per day. per hour and per hour. liter of catalyst.

Under these circumstances, the selectivity at 224 ° C of ethylene oxide is 77% at a total ethylene conversion rate of 3.4%.

EKSEMPEL_6

29.5 g of the carrier NORTON 5239 (trade mark) of grain size 6.5 mm (4/16 inch) is placed in a flask calculated for solids mounted on a rotary evaporator. By analogy to the procedure of Example 1, a catalyst is prepared by impregnating the carrier by a solution of 9 g of silver oxide in 5 g of acetic acid, 28.2 g of 2-methyl-2-oxazoline and 202 ml of acetonitrile. After thermal treatment, the analysis shows that the silver content of the catalyst is 19% by weight. 30 ml of this catalyst is placed in a reaction vessel consisting of a stainless steel tube 355 mm long and 16 mm internal diameter which is heated by a bath of molten nitrates. The reaction components added at the bottom of the reactor are preheated through a 42 mm height porcelain filling.

The analytical equipment is identical to that described in Example 1.

After an activation pretreatment with a mixture of air-ethylene 50% - 50% for 30 hours between 157 ° C and 175 ° C at atmospheric pressure, the reaction components are added under a pressure of 20 bar in the following proportions: 16

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Ethylene 13%, oxygen 5%, nitrogen 82%, 1,2-dichloroethane 35 pp "b. With a total rate of 9000 liters in the normal hour and per liter catalyst, a 195 ° C selectivity is achieved to 77% ethylene-5 oxide at 5% ethylene conversion · EXAMPLE_7 In a solid-state flask mounted on a rotary evaporator, put 36 g of carrier NORTON SA 5239 (trade mark) with grain size 0.48 mm (3/16 torrents.) One raises;

the temperature of the oil bath in the evaporator to 100 ° C, and I

the carrier is degassed for 1 hour and 30 minutes under vacuum. Simultaneously, an Er-lenmeyer flask containing 90 g of oxazole is poured into 5 g of pure acetic acid; 8.6 g of silver-oxide are added in small fractions. The mixture is stirred for 1 hour to facilitate the solution, then left to stand for half an hour.

This solution is then added dropwise to the stirred carrier so that evaporation of the solvent is immediate. After adding the total amount of solution, the carrier, which is impregnated and dried, is transferred to a tubular reactor therein to undergo a thermal treatment intended to release metallic silver.

This treatment is carried out under a stream of nitrogen at a temperature rise of 20 ° C / hour up to 270 ° C, at which temperature it is maintained for 18 hours. The silver content of the catalyst determined by analysis is 12% by weight.

30 ml of this catalyst is placed in a reactor 30 consisting of a stainless steel tube 600 mm long and 16 mm internal diameter. The reaction components supplied at the bottom of the tube are preheated through a layer of porcelain rings of 200 mm height, which is also 17

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supports the catalyst layer. The heating of the entire system is ensured by oil circulation in a heating jacket. The gases emitted to the reactor and from the reactor are analyzed on-line by means of a double detection system chromatograph: a flame ionization detector for ethylene oxide, methane, formaldehyde, propylene, propane, methanol and acetaldehyde and a heat conductivity detector for oxygen, nitrogen, carbon dioxide, ethylene. and water. Two columns with 1 ° diameter 0.32 mm (1/8 casing) and length 2.5 m mounted in series are filled, one with the chromos orb 101 (trademark) filler, the other with Porapak Q (trademark),

Through the catalyst layer placed in the reactor, the air-ethylene mixture is sent 50% - 50% at atmospheric pressure for 48 hours between 156 ° C and 178 ° C. A gas stream of 9000 l is then supplied to the reaction vessel in the normal state per day. per hour and per hour. liter of catalyst consisting of a mixture of 13% ethylene, 5% oxygen, 82% nitrogen and 35 ppm 1,2-dichloroethane. After 45 hours with reaction components at 217 ° C, the total ethylene conversion rate of 5% and ethylene oxide selectivity is 77.5%.

EKSEMPEL_8

36.5 g of the carrier NORTON SA 5251 25 (trade mark) with a grain size of 0.48 µm (3/16 inch) placed in a flask intended for solids and mounted on a rotary evaporator and pre-degassed at 100 ° C are added. for one hour under vacuum a filtered solution of 13.5 g of silver propionate in 87 g of oxazole. Keeping the temperature at the evaporator oil bath at 100 ° C distills the oxazole as it is added. The impregnated carrier is then thermally treated analogously to the procedure described in Example 7. Catalyst 18

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the silver content of the tor is 12.5% by weight.

30 ml of catalyst are placed in the reactor described in Example 7. A gaseous stream of air and ethylene 5 in the ratio of 50% -50% for 46 hours between 140 ° C and 16 ° C is sent through this at atmospheric pressure. Then, under a pressure of 20 bar, a gaseous mixture of 9000 liters is added in the normal state per day. per hour and per hour. liter of catalyst consisting of 13% ethylene, 5% oxygen, 82% nitrogen, to which is added 35 ppb 1,2-dichloromethane. At 185 ° C at a total ethylene conversion rate of 5%, the selectivity with respect to ethylene oxide is 80%. EXAMPLE_9 In a flask designed for solids and mounted on a rotary evaporator, 42.5 g of the carrier NORTON SA 5239 (trademark) is placed. with grain size 0.64 mm (1/4 inch). The temperature of the evaporator oil bath is raised to 120 ° C and the carrier degassed for 1 hour under vacuum. During this time, 16.5 g of silver acetate are dissolved in a mixture of 92 g of water and 18 g of oxazole under stirring. The solution is then added dropwise to the stirred carrier.

Thermal analysis analysis analogous to that described in Example 7 shows a silver content in the catalyst of 11.5% by weight. 30 ml of the catalyst is placed in the reactor described in Example 7.

After an activation pretreatment by means of a mixture of air-ethylene 50% - 50% for 48 hours between 162 ° C and 185 ° C carried out at atmospheric pressure, 3o is added under a pressure of 20 bar and a speed of 9000 liters in the normal state per day. per hour and per hour. per liter of catalyst the gaseous reaction components in the following proportions:

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19

Ethylene 13%, oxygen 5%, nitrogen 82% and 35 ppb 1,2-dichloroethane. At 228 ° C after 50 hours of operation, the ethylene oxide selectivity is 77.8% at a total ethylene conversion rate of 4.5% · EXAMPLE_10

Into a flask intended for solids mounted on a rotary evaporator 36 g of the carrier CARBO-RUNDON SAHT 96 (trade mark) with grain size 0/64 mm (1/4 inch). Proceeding analogously to Example 9, a lo catalyst is prepared by impregnating this carrier with a pre-filtered solution of 14 g silver acetate in 94 g oxazole. Analysis after thermal treatment shows a silver content in the catalyst of 16% by weight.

30 ml of this catalyst is placed in a laboratory reactor operating under 15 pressures, which consists of a 355 mm long stainless steel tube and 16 mm internal diameter heated by a bath of molten nitrates. The reaction components added at the bottom of the reactor are preheated in a 42 mm high porcelain filling. The gas mixture at the inlet and outlet of the reactor is analyzed by means of a device analogous to that described in Example 7.

A mixture of air-ethylene 50% - 50% at 25 atmospheric pressure for 48 hours between 137 ° C and 155 ° C is passed through the catalyst layer placed in the reactor. Then, under a pressure of 20 bar, 9000 liters are added in the normal state per day. per hour and per hour. 1 liter of catalyst of a gaseous mixture containing 13% ethylene, 5% oxygen, 82% nitrogen and 35 ppb 1,2-dichloroethane. At 30 ° C 191 ° C, the ethylene oxide selectivity is 77% at a total conversion rate of 5% ·

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EXAMPLE_11 Into a flask designed for solids placed on a rotary evaporator containing 36 g of the carrier NORTON SA 5239 (trade mark) of grain size 0.64 mm (1/4 inch) 5, add a pre-filtered solution of 14 g of silver acetate in 126 g of oxazole. The carrier immersed in the liquid is degassed at room temperature for 1 hour and 30 minutes under vacuum. The oil bath of the evaporator is heated to 80 ° C and the oxazole is distilled off under a pressure of 40 mm. After complete distillation of the oxazole, the impregnated carrier is dried and then allowed to undergo a thermal treatment analogous to that described in Example 7. Analysis shows a silver content of 15.8% by weight in the catalyst. 30 ml of this 15 are placed in the reactor described in Example 10 and after an activation treatment carried out at atmospheric pressure with a flow of air-ethylene 50% - 50% for 48 hours between 150 ° C and 168 ° C, is added under pressure of 20 bar and a speed of 9000 liters in the normal mode per day. hours per hour and per hour. a liter of catalyst a gaseous mixture containing 13% ethylene, 5% oxygen, 82% nitrogen and 35 ppb 1,2-dichloroethane. At 190 ° C, the ethylene oxide selectivity is 70% at a total ethylene conversion rate of 4%.

EXAMPLE_12 In a flask intended for solids mounted on a rotary evaporator, place 42.5 g of the carrier NORTON SA 5239 (weather mark) with grain size 0.64 mm (1/4 inch). The carrier is degassed under the same conditions as described in Example 7. A pre-filtered solution of 16.5 g silver acetate in 112 g isoxazole and 27.1 g water is added dropwise to this carrier in such a way that The isoxazole and water distill off as these substances are added. After one has

Claims (16)

1. Heterogeneous silver catalysts for use in the production of ethylene oxide by gas phase oxidation of ethylene by oxygen or an oxygen-containing gas mixture, which catalysts are prepared from solutions of organosilver compounds which are impregnated on refractory carriers and then heat treated by the impregnated carrier has released silver in the form of silver grains on the carrier, characterized by the fact that silver salt complexes of organic or inorganic silver salts with oxazole or oxazoline compounds of the general formulas have been used: DK 151961B RR \ UR \ == N, -χΛ RR ° RR 0 R CD (II) (III) RRR> R ίπγ —t J. N ---. R 0 (IV) (V) wherein R represents a hydrogen atom, a C 1 -C 4 alkyl group or a phenyl group. Catalysts according to claim 1, characterized in that oxazole has been used for the formation of the silver salt complex 5. Catalysts according to claim 1, characterized in that 2-oxazoline or 3-oxazoline has been used for the formation of the silver salt complex. Catalysts according to claim 1, characterized in that isoxazole has been used for the formation of the silver salt complex. Catalysts according to claim 1, characterized in that 2-isoxazoline has been used for the formation of the silver salt complex. Catalysts according to any one of claims 1-5, characterized in that the complexing agents according to claims 1-5, which are substituted by one or more C 1 -C 20 alkyl groups, have been used for the formation of the silver salt complex. and / or with one or more phenyl groups. Catalysts according to any one of claims 1-6, characterized in that they are prepared from 5 from a solution of a silver compound in one of the mentioned complexing agents. Catalysts according to any one of claims 1-6, characterized in that they are prepared from a solution of one of the aforementioned organosulfur complexes 10 in solvents such as water, which may be made ammonia, nitriles, alcohols, ketones, light glycols. and amines. Catalysts according to claim 8, characterized in that a number of molecules of complexing agent having at least twice the number of silver atoms used have been added to the impregnating solution used. Catalysts according to any one of claims 7-9, characterized in that silver oxide and an amount of the acid corresponding to the compound of between 100% and 125% of the stoichiometric amount needed are added in place of the silver compound used. for the complete conversion of the silver oxide to compound. Catalysts according to claim 10, characterized in that a silver carboxylate containing 1 to 10 carbon atoms and 1 to 2 acid groups is used instead of silver oxide. molecule. Catalysts according to claim 11, characterized in that the silver carboxylate used is silver acetate. DK 151961B Catalysts according to any one of claims 1-12, characterized in that uniform grains of uniform shape and having an equivalent diameter of 0.1-1 µm are uniformly distributed over the surface of the carrier. Catalysts according to any one of claims 1-13, characterized in that they contain 5-25% by weight of silver. Catalysts according to any one of claims 1-14, characterized in that alumina and silica-alumina carriers having a specific surface area of less than 1 m2 / g and having an apparent porosity of at least 40% by volume are generally formed by pores with radius greater than 0.25 ^ urn. A process for producing ethylene oxide by gas phase oxidation of ethylene with oxygen or with an oxygen-containing gas mixture using a heterogeneous silver catalyst, characterized in that a catalyst according to any one of claims 1 to 15 is used.