CS201007B2 - Method of making the ethylenoxyde - Google Patents

Description

The present invention relates to a process for producing ethylene oxide by contacting ethylene in vapor phase with an oxygen-containing gas in the presence of a silver catalyst.

Catalysts containing 1 to 35% by weight of silver on a porous refractory support are known to be suitable for producing ethylene oxide by controlled incomplete oxidation of ethylene by molecular oxygen. Many different modifications have been proposed to improve the activity and selectivity of silver catalysts. Such modifications include, for example, the support used, the method of manufacture, the physical form of the silver on the support, and the addition of certain additives to the catalyst.

It has been found that the selectivity of the catalysts may vary during the initial period of use in the production of ethylene oxide. During this time, the selectivity of some catalysts increases and then remains constant for a long period of time, while the selectivity of other catalysts gradually decreases and then remains constant or nearly constant. The author found that this initial activity is largely due to the stabilization of the silver particles present in the catalyst, which occurs at the onset of catalyst usage.

It is known from British Patent No. 1,413,251 that the addition of 0.0005-5 to 0.0030 grams equivalent weight per kilogram (based on the total catalyst) of at least one alkali metal ion selected from the group consisting of potassium, rubidium and cesium and simultaneously deposited with silver on the catalyst support results in an improvement in the selectivity of the catalyst thus obtained.

According to this British patent, alkali metal and silver are deposited simultaneously on the catalyst support because the catalysts obtained in this way have an optimum selectivity (75-81%). From Example VII of British Patent Specification No. 1,413,251 it is clear that when potassium deposited on the support after the silver is deposited, there is an increase in selectivity mengi than that obtained with the simultaneous deposit of silver and alkali metal.

The silver catalyst used in this example is obtained by impregnating the support with a solution of silver talc complex and then heating to reduce the silver salt to metallic silver. This silver catalyst has a selectivity of 69%.

After treatment with an aqueous potassium-containing solution, the selectivity increases to 73-74%, which is clearly less than the optimum above.

The effect on ethylene oxide selectivity was investigated by the inventor by the deposition of alkali metals on silver catalysts produced by other methods, for example by impregnating the support with a solution of silver nitrate and then reducing with hydrogen.

Such a catalyst typically exhibits a rapid initial improvement in activity and selectivity over a period of about 1 day and then a slow continuous continuous improvement for up to about 1 month.

A stabilized catalyst is obtained which has a selectivity of approximately 69 to 70% with an oxygen conversion of 40%. This improvement is usually maintained for many years. When cesium is deposited on a freshly produced catalyst of this type, only 1 to 2% higher selectivity than the stabilized unmodified catalyst is achieved after stabilization.

It has now been discovered that when freshly manufactured catalysts of this type are stabilized by heat treatment when used to produce ethylene oxide for a time sufficient to keep the selectivity constant (usually 1 to 4 weeks) or subjected to heat treatment, potassium deposition, rubidium or cesium allows for much greater improvement in selectivity (up to 6% or more).

It has been found that the particle size of the silver present in the catalyst usually varies during the initial period of use of the catalyst in ethylene oxide production. Larger silver particles with a diameter of, for example, 4 µm will disintegrate into smaller particles that are more stable under the reaction conditions used, while small silver particles, with a diameter of, for example, 0.1 µm, sinter to form more stable larger particles.

The stability of the individual particles is forced by surface tension under the reaction conditions used during ethylene oxide production. The diameter of the stable silver particles is usually distributed between 0.2 and 4 µm, in particular between 0.4 and 2.5 µm, but depends on the reaction conditions used. It has been discovered that a change in the size of the silver particles during the initial period of use of the catalyst significantly contributes to the change in catalyst activity and selectivity usually observed during that period.

The heat treatment of the catalyst used in the present invention may consist of using a silver catalyst for the oxidation of ethylene by molecular oxygen until a major proportion of the silver particles present in the catalyst reaches a size distribution close to that stable under the reaction conditions used in ethylene oxide production.

Stable particle size distribution can be determined using an electron photomicrograph. When the production of ethylene oxide is carried out, for example, according to the invention, the diameter of the stable silver particles is usually distributed between 0.2 and 4 µm, in particular between 0.4 and 2.5 µm. When a stable particle size distribution is achieved, the selectivity to ethylene oxide is usually constant or nearly constant.

The time required for the heat treatment to stabilize the catalyst can be highly dependent on the particular catalyst and reaction conditions. Catalyst 3 is used as required

The 20,007 tor can also be used for longer than the time required to achieve stability. Although silver catalysts may be used in the production of ethylene oxide for many years, it may be advantageous for the catalysts to stabilize.

The selectivity of the silver catalysts used is improved by applying 0.00004 to 0.008 grams equivalent weight per kilogram (based on total catalyst) of at least one of the alkali metals selected from the group consisting of potassium, rubidium and cesium on such catalysts.

The heat treatment may also consist in subjecting a freshly prepared catalyst or a catalyst that has not yet been fully stabilized to a heat treatment other than simply using the catalyst. This treatment comprises heating the silver catalyst to an elevated temperature, suitably to 50 to 900 ° C and preferably to 200 to 800 ° C. Heating should be carried out continuously until the major part of the silver particles present in the catalyst reaches a size range which is close to that stable under the reaction conditions used in the production of ethylene oxide. As mentioned above, the diameter of the stable silver particles is usually distributed between 0.2 and 4 µm, especially between 0.4 and 2.5 µm.

The heat treatment for stabilization is achieved in a shorter period of time when carried out at higher temperatures. For example, good results are obtained by heating the catalyst for 5 to 20 hours at 400 to 750 ° C. The heating may be carried out in the presence of an inert gas such as nitrogen or an oxygen-containing gas such as air.

This gas can be continuously passed over the catalyst. In some cases, it may be advantageous to heat in the presence of an ethylene-containing atmosphere and / or one or more compounds which are commonly used as moderators in the production of ethylene oxide, for example compounds such as 1,2-dichloroethane, vinyl chloride or chlorinated polyphenyls.

The support used for silver catalysts may be selected from a large number of conventional porous refractory catalyst supports or support materials that are substantially inert in the presence of materials used in the oxidation of ethylene, products and reaction conditions.

Such conventional materials may be of natural or synthetic origin and preferably p

they have a macroporous structure, that is, the structure has a surface area below 10 m / g and preferably below 2 m / g. These carrier materials typically have an apparent porosity of greater than 20%. Highly preferred carriers include silica and / or aluminum mixtures.

Particular examples of suitable carriers are: aluminum oxides (including materials commercially available under the trade name Alundum), activated carbon, pumice, magnesia, natural zirconium oxide, diatomaceous earth, fuller's earth, silicon carbide, porous agglomerates containing silicon and / or silicon carbide, oxide silica, magnesium oxide, selected clays, artificial and natural zeolites and ceramic materials.

Particularly suitable non-flammable carriers include alumina-based materials, especially containing alpha-alumina. In this case the carrier containing the alpha-alumina may have a specific surface area measured by the BET method, for example 0.03 to 2.0 ru ^ / g _and an apparent porosity as measured by conventional absorption technique using a mercury or water, for example 25-65% · Method The BET for determining a specific surface area is described in detail by S. Brunauer ',

R. H. Emmet and E. Teller in J. Am. Chem. Soc., 60, 309-316 (938).

Particular examples of suitable carriers are those designated by Norton Company as Alundum LA-956, SA-5556, LA-4.18 and SA-101, or equivalents thereof.

Regardless of the nature of the carrier used, they are preferably formed into particles, blocks, pieces, pellets, rings or beads of a suitable size for use in a fixed bed. Conventional commercially available fixed bed ethylene oxidation reactors are typically in the form of multiple parallel tubing (in a suitable sheet) approximately 2.0 to 5 µm in diameter and up to 14 meters in length that are filled or partially filled with catalyst. In such reactors, it is desirable to use a carrier shaped into a round shape such as, for example, spheres, pellets, rings or tablets having a diameter of about 0.25 to 2.0 cm.

The potassium, rubidium and / or cesium ions may be deposited on the stabilized catalyst by impregnating it with a solution of one or more compounds of these alkali metals in a suitable solvent or solvent mixture.

Examples of suitable compounds are hydroxides, nitrates, chlorides, iodides, bromides, acidic and potassium carbonates, rubidium or cesium or organic derivatives of these alkali metals, for example their alkoxides such as isopropoxide, or their salts with organic carboxylic acids such as formates, ootanes , šlavelany, blamed and lactates.

Suitable solvents are water and organic solvents, for example C 1 -C 6 alcohols such as methanol, ethanol and isopropyl alcohol, or C 1 -C 6 alkanones such as acetone and the like.

If desired, the solubility of the alkali metal compound (s) in the solvent may be increased by the use of complexing agents such as macrocyclic polyethers of the type described in British Patent Nos. 1,108,921 and 1,285,367.

The organic solvent may optionally contain water to increase the solubility of the alkali metal compound in the solvent. However, in some salt-solvent combinations, the presence of a higher concentration of water may be detrimental to the final embodiment, so that the amount of water present in the solvent is preferably below 20% by weight, and particularly preferred below 10% by weight. Preference is given to solvents having a boiling point below 100 ° C, in particular methanol, ethanol and acetone. The amount of the impregnation solution and the concentration of the alkali metal therein should be sufficient to contain 0.00004 to 0.008, preferably 0.0001 to 0.002 gram equivalents, per kilogram of total catalyst.

The impregnation is preferably carried out by contacting the catalyst stabilized by heat treatment with a solution of the compound or alkali metal compounds for a time allowing the concentration of the alkali metal or metals in the impregnation solution to be constant. This can be done, for example, by continuously mixing the catalyst with the impregnation solution or by recirculating the impregnation solution with a fixed catalyst bed.

The excess solution should be removed after the iupulum ij. In order to remove a further excess of impregnating eye, a clean solvent rinse may then optionally be performed. Catalyst? preferably not after quarry drying. The drying may be carried out at atmospheric, reduced, but at elevated pressure. The catalyst may be heated to a temperature above the boiling point of the solvent used. for example to a temperature of 60 to 200 ° C for a period of, for example, 0.5 to 24 hours. During the drying of the irvi catalyst, a gas such as nitrogen, air, hydrogen, noble gases, carbon dioxide, methane or mixtures thereof may be passed through the catalyst. Vacuum drying at room temperature can also be performed.

If desired, the ethylene oxide catalyst of the present invention can be prepared in a reactor used to produce ethylene oxide. For example, a solution of at least one potassium, rubidium and / or cesium compound can be passed through a reactor containing a silver catalyst that has been used previously in the production of ethylene oxide for a time sufficient to stabilize it, and then excess solvent can be removed by catalyst at a temperature above the boiling point of the solvent used in the impregnation solution.

Optionally, the fresh silver catalyst can be stabilized by heat treatment in the ethylene oxidation reactor under heat treatment other than by using the catalyst as described above, and then the alkali metal compound solution can be passed through the reactor and then the excess solution is removed and dried.

This not only improves the selectivity of the silver catalysts on which the alkali metal is deposited, but often also the activity. That is, at low reaction temperatures, modified catalysts provide higher conversion than untreated catalysts, or that given conversions can be achieved at lower reaction temperatures. The use of lower reaction temperatures is of interest in practice since at higher temperatures the formation of undesirable by-products such as carbon dioxide, formaldehyde and / or acetaldehyde increases.

SUMMARY OF THE INVENTION The present invention provides a process for producing ethylene oxide by contacting ethylene in vapor phase with a gas containing molecular oxygen at a temperature of 150 to 300 ° C in the presence of 1 to 35% silver by weight, based on total catalyst. a total catalyst of at least one alkali metal ion selected from the group consisting of potassium, rubidium and cesium on a porous refractory support, which is carried out using a silver catalyst obtained by heat treating a silver catalyst containing 1 to 35% by weight of silver based on the total catalyst, on a porous refractory support, at a temperature of 150 to 900 ° C, until most of the silver particles have a stable diameter of 0.2 to 4 microns, by depositing an alkali metal or alkali metals on the catalyst thus obtained, by applying a solution of at least one compound alkali metal and then removing the solvent.

In a preferred process of the invention, ethylene oxide is produced by reacting an oxygen-containing gas, preferably containing at least 95% oxygen, with ethylene in the presence of a diluent gas and one of the aforementioned moderators, on a catalyst at a temperature between 190 and 285 ° C. 275 ° C.

The ethylene oxide produced is separated in the next stage of the production process. The recovery of ethylene oxide from the reaction products is carried out by conventional methods.

In the present invention, patent rights are not required for a process for the production of ethylene oxide using so-called depleted silver catalysts from earlier long-term production of ethylene oxide by impregnating them with a impregnating solution containing

1. 0,2 to 5% by weight of water,

2. 0.05 to 0.4% by weight of cesium or rubidium nitrate a

3. a C 1 -C 3 aliphatic alcohol and wherein the alcohol is then removed at a temperature of 70 to 120 ° C, preferably at 90 to 110 ° C, optionally with nitrogen purge.

The following Examples illustrate the invention.

He did

The silver catalyst used for 8.5 years in the production of ethylene oxide on an industrial scale was used as the starting material for the production of the A-0 catalysts described in this example. The silver catalyst contains 10.5% by weight of silver deposited on a carrier manufactured and sold by the Norton Company under the trade name Alundun SA-101 containing 90.4% by weight of alpha-alumina, 8.5% by weight of silica and 1.1% by weight The carrier is impregnated with an aqueous silver nitrate solution, then dried and reduced with hydrogen. The support is in the form of hollow cylinders having a diameter of approximately 8.0 mm and a length of approximately 8 mm. It has a specific surface area of 0.05 m / g, an apparent porosity of 43 to 47% by volume, and a mean pore diameter of 25 µm. The diameter of the silver particles present in the catalyst is in the range of 0.4 to 2 µm. The original freshly prepared catalyst contained silver in the form of particles having a diameter of 2 to 4 µm.

By measuring the water absorption, the pore volume of the silver catalyst is determined. It was found to be 0.144 ml / g. The cesium, rubidium and potassium impregnation solutions listed in Table 1 below contain the alkali metal compounds in a concentration such that upon impregnation of the silver catalyst with the solution, the desired amount of alkali metal compound is present in the pore retention solution after removal of excess solution.

An amount of 100 g of catalyst is impregnated with 100 ml of the impregnation solution for at least 10 minutes. After removal of excess solution, the catalyst is dried in an oven at 120 ° C for 17 hours or in a vacuum dryer at 27 Pa at room temperature (20 ° C).

The individual conditions used in the production of the catalysts are shown in Table I. The starting catalyst for the production of Catalyst X is a fresh silver catalyst similar to the catalyst used to produce the A-0 catalyst but not used in the production of ethylene oxide.

In the production of Catalyst Y, the same fresh silver catalyst was first used for 140 hours to produce ethylene oxide, and then the cesium compound was deposited thereon.

Table I

Catalyst Compound Concentration of ions Solvent used Concentration Conditions alkaline alkali metal during preparations alka- drying metal in the impregnation impregnating solution political solution vu v kata- in mg / 100 ml lysator in ppm

AND Cs-ac ^x 49.4 abs.ethanol 50 ^{17 h} 0 at 120 ° C (B) Cs-ac 49.4 acetone-3% HgO 50 3 h at 120 ° C C Cs-ac 49.4 abs. ethanol 50 ^{17 h} 0 at 20 ° C under vacuum D Cs-ac 49.4 ethanol-10% vol H ₂ 0 50 16 h at 120 ° C E CsNO ₃ 50 methanol-0.5 h ₂ o % vol. 50 16 h 0 at 120 ° C F CsNO-j 100 ALIGN! methanol-0.5 h ₂ o % vol. 100 ALIGN! ^{17 h} 0 at 120 ° C G CSjCO ^ 41.7 methanol-0.5 h ₂ o % vol. 50 16 h at 120 ° C H cšhco ₃ 50. methanol-0.5 H _g 0 % vol. 50 17 ^h oC at 120 ^ob AND CsHCO ₃ 50 acetone-3,5% vol H ₂ 0 50 ^{17 h} 0 at 120 ° C TO CsCI 43.2 abs. ethanol 50 ^{17 h} 0 at 120 ° C L Rb ₂ CO ₃ 29.5 abs. methanol 32 ^{17 h} 0 at 20 ° C M RbN0 ₃ 75.6 methanol-0.5 H 2 O % vol. 64 ^{17 h} 0 at 120 ° C

Catalyst Alkali metal compound

Concentration of ions Solvent used Concentration Conditions alkali metal during preparations alka- drying in the impregnation impregnating solution political flow vu v kata- in mg / 100 ml lysator in ppm

N Rb-ac 37.1 abs. methanol 32 17 h at 120 Noc: 2 ° C 0 K-ac 25.1 abs. methanol 15 Dec 17 h at 120 Noc: 2 ° C X CsNO ₃ 100 ALIGN! methanol-0,5% v / v h ₂ o 100 ALIGN! 17 h at 120 ° c Y Cs-ac 49.4 abs. ethanol 50 1.5 h at 120 ° c

and c = acetate

The modified catalysts listed in Table 1 and the untreated catalysts are used to produce ethylene oxide after loading into a reactor tube having an internal diameter of 2 cm and a bed length of 20 cm. A gaseous mixture containing 25% by weight of ethylene, 8% by weight of oxygen, 0.5 to 2 ppm of dichloroethane is passed over the catalyst, the remainder being nitrogen, at atmospheric pressure and an hourly space velocity of 250 h ¹ .

The selectivity to ethylene oxide achieved at 40% oxygen conversion by weight and the temperature required to achieve this oxygen conversion are shown in Table 2.

Table 2

Catalyst Selectivity to ethylene oxide Temperature% w / w ° C

untidy 69.3 268 AND 74.2 271 (B) 71.4 280 C 74.3 273 D 75.2 265 E 75.2 251 F 75.7 254 G 74.9 268 H 75.2 265 AND 72.8 272 TO 72.8 278 L 72.5 272 M 72.0 275 N 72.2 276 0 70.7 275 X 70.4 297 Y 72.4 268

Example

The following catalysts were used to produce ethylene oxide using the method described in Example 1, except that 7 ppm vinyl chloride was used as moderator instead of dichloroethane.

The catalysts U and W used are silver catalysts containing potassium of the type described in British Patent Specification No. 1,413,251.

Catalyst V is prepared by impregnating 100 g of catalyst U with 200 ml of a solution containing 36 mg of CsCl in acetone containing 25% water by volume. The impregnation is accomplished by recirculating the catalyst impregnating solution through the bed five times.

After removing the excess solution, the catalyst was dried in an oven at 120 ° C for 17 hours. The cesium content was 84 ppm.

Catalyst Z is prepared by impregnating 100 g of catalyst W with 200 ml of a solution containing 12 mg of CsCl in acetone containing 5% water. The impregnation and subsequent drying is carried out as indicated for catalyst V. The catalyst contains 66 ppm cesium.

The selectivity to ethylene oxide achieved at 40% oxygen conversion by weight and the temperature required to achieve this oxygen conversion are shown in Table 3.

Table 3

Catalyst Selectivity to ethylene oxide% by weight Temperature Noc: 2 ° C AT 72.2 260 IN 76.3 260 W 70.2 258 OF 75.8 256

Example 3

Catalyst Q is prepared as follows:

Alundum LA-5556, a product of the Norton Company, in the form of hollow cylinders having a diameter of about 8 mm and a length of about 8 mm is used as the catalyst support. This carrier contains 99.3% alpha-alumina, 0.4% silica and 0.3% other metals and has a surface area of 0.24 m ² / g and an apparent porosity of 48 to 49% by volume.

The carrier has a mean pore diameter of 4.4 mm as determined by mercury porosity and 81% of its pores have a diameter in the range of 1.5 to 15 µm.

A solution of 118.3 g of AgNO3 in 75 ml of water is stirred with a solution of 51.2 g of sodium squalate in 833 ml of carbon dioxide-free water at 80 DEG C. and water is added until the total volume of the mixture is 1167 ml. is maintained at 80 ° C for 30 minutes.

It is then cooled to 50 ° C, decanted and 167 ml of carbon dioxide-free water are added to the remaining suspension. The silver stavelan was filtered off and washed five times with 167 ml of carbon dioxide-free water while the effluent contained sodium. The filter cake is suspended in 167 ml of water and the suspension is cooled with ice and water. The impregnation solution is then prepared by mixing the suspension with 50 ml of ethylenediamine and 16.7 ml of monoethanolamine.

500 ml of the carrier is impregnated twice with the impregnating solution and then the solution is removed and the carrier is dried at 200 ° C for 5 hours. The dry carrier is then impregnated again with the impregnating solution and, after removing the excess solution onto the carrier, is dried at 200 ° C for 18 hours. The catalyst obtained contains 12.5% by weight of silver. The diameter of the silver particles present on catalyst Q was determined by electron microscopy and was found to be approximately 0.1 to 0.2 µm.

Catalyst E is prepared by impregnating catalyst Q with a solution containing 49.4 mg of cesium acetate in 100 mL of ethanol by the method described in Example 1. The catalyst is dried at 120 ° C for 17 hours. The cesium content is 50 ppm.

Catalyst S is prepared by heating Catalyst Q to 700 ° C for 6 hours. The silver particles present in the catalyst S were found to have a diameter of 0.5 to 2 µm.

Catalyst T is prepared by impregnating the catalyst with a solution containing 49.4 mg of cesium acetate in 100 ml of ethanol by the method described in Example 1. The catalyst is dried at 120 ° C for 5 hours. The cesium content is 50 ppm.

Catalysts Q, R, S and T are used to produce ethylene oxide in the same manner as the catalysts described in Example 1. The ethylene, oxygen and nitrogen mixture contains 1.7 ppm of dichloroethane.

The selectivity to ethylene oxide achieved at 40% oxygen conversion by weight and the temperature required to achieve this oxygen conversion are summarized in Table 4.

Table 4

Catalyst Selectivity to ethylene oxide% by weight Temperature ° C Q 79.5 230 R 79.2 234 WITH 69.8 271 T 78.5 247

The data given in the examples show that it is advantageous to use the silver catalyst produced in a manner not yet described for the production of the ethyl ester oxide according to the invention,

Claims (5)

A process for producing ethylene oxide by contacting ethylene in vapor phase with a molecular oxygen-containing gas at a temperature of 150 to 300 ° C in the presence of 1 to 35% by weight of silver, based on total catalyst, and 0.00004 to 0.008 grams equivalent per kilogram. a catalyst of at least one alkali metal ion selected from the group consisting of potassium, rubidium and cesium on a porous refractory support, characterized in that a silver catalyst obtained by heat treatment of silver is used, a catalyst containing 1 to 35% by weight of silver, based on the total catalyst; on a porous refractory support, at a temperature of 150 to 900 ° C, until most of the silver particles have a stable diameter of 0.2 to 4 microns, by depositing an alkali metal or alkali metals on the catalyst thus obtained, by applying a solution of at least one alkali metal compound and then removing the solvent. 2. The method of claim 1, wherein a silver catalyst is used, the heat treatment of which is used to oxidize ethylene to molecular oxygen at a temperature of at least 150 DEG C. until at least a major portion of the silver particle has a stable diameter of 0.2 to 4 microns. . 3. A process according to claim 1, wherein the catalyst is heat treated by heating for 5 to 20 hours at a temperature of 400 to 750 ° C. 4. Process according to any one of claims 1 to 3, characterized in that a catalyst is used to which the alkali metal compounds are applied in the presence of a solvent consisting of an alkanol or an alkanol having from 1 to 6 carbon atoms. Process according to any one of Claims 1 to 4, characterized in that a catalyst is used to which the compounds have been applied from a solution containing at most 20% and preferably at most 10% by weight of water.