SU509206A3 - Catalyst for the oxidation of ethylene and ethylene oxide - Google Patents

Description

Sium can be used in quantities of 26 to 252, preferably 28 to 238, preferably 30 to 226 weight. ppm ppm. Such amounts of potassium, rubidium and / or cesium do not necessarily have to be total amounts of these metals in the catalyst. The amount of alkali metals is on the surface of the catalyst and it is specifically added to the catalysts along with the introduction of silver. Depending on the method of preparation of the carrier, a significant amount is contained in the pores of the carrier, often up to 10,000 weight. hours per million alkali metals (in most cases of potassium). It is assumed that the activity and selectivity of the catalysts do not depend on the total amount of alkali metal that is present in the pores of the support, in contrast to the influence of the alkali metal present on the surface along with silver. The proposed catalysts contain preferably 3-15 weight. % silver in the form of metallic silver, in terms of total catalyst, preferably 4-13 weight. % The use of even larger quantities of silver is not excluded, but from an economic point of view it is usually not used. Silver is deposited on the inner and outer surfaces of the carrier and should be uniformly dispersed over the entire surface of both surfaces. The physical form of the silver deposited on the carrier may be different, but this is not the case. Good results are achieved in the case of a controlled alkali metal content on the catalyst surface proposed by the present invention, provided that the silver is in the form of uniformly distributed in the form of a continuous layer, adherent, almost hemispherical discrete particles having the same size, which are less in diameter 1 micron (10,000 A). The best results are obtained when using a catalyst of this type, provided that the diameter of the silver particles is in the range of 1,000 to 10,000 A, and their average diameter is from 1,500 to 7,500. The carrier used for preparing the catalysts according to the invention can be selected from a large number of conventional porous refractory carriers, which are practically inert with respect to the initial components of the ethylene oxidation reaction, the reaction products under these reaction conditions. Such conventional materials may be of natural origin or synthesized, they should preferably have a macroporous structure, in which the sample is the surface area is less than 10, preferably less than 2. The apparent porosity of these materials of the carrier usually exceeds 20%. Fully acceptable carriers are materials based on siliceous compounds or alum, such as; aluminum oxides, charcoal; pumice; Mg oxide; zirconium dioxide, diatomaceous earth; Fuller's land; silicon carbide; porous agglomerates containing silicon and / / or silicon carbide, some types of clay, artificial and natural zeolites; gel materials based on metal oxides containing heavy metal oxides, in particular molybdenum and tungsten; ceramics, etc. Refractory carriers, which are particularly suitable for the preparation of the proposed catalysts, are clay-earth materials containing a -, preferably with a specific surface according to B. E. T. 0.03 - 1.0, and apparent porosity , measured in accordance with the usual method for the absorption of mercury or water, is in the range of 25 - 40 vol. The% advantage of adding certain alkali metals, in accordance with the present invention, is especially evident in the case of using a certain tin of a-AO3-based carriers. These carriers have almost equal pore sizes and can be characterized by the following parameters: the specific surface is in the range from 0.1 to 0.8, preferably from 0.15 to 0.6, and the apparent porosity is in the range from 42 to 56%, preferably from 46 to 52%. Regardless of the type of carrier used, it is preferable to pre-mold it into particles, pieces, lumps, cylindrical tablets, rings, spherical granules, and the like, which are suitable for use in fixed bed processes. Conventional fixed bed reactors for the oxidation of ethylene are, in most cases, made in the form of a large number of parallel long tubes (in a suitable casing) with a diameter of approximately 2.5 to 5.1 cm and a length of 7 to 14 m filled with a catalyst. In such reactors, it is desirable to use a carrier in the form of round granules, such as balls, rings, the diameter of which is from 2.5 to 20.3 mm. Thus, the proposed catalyst includes 1.5 to 20 wt. % (of the total catalyst weight) of silver and 0.00035 - 0.0030 g-eq / kg of potassium, rubidium and / or cesium, uniformly dispersed together with silver on the surface of a porous carrier with a specific surface in the range from 0.03 to 2. A more preferred catalyst contains 3-15 weight. % silver and 0.00040 - 0.00270 g-eq / kg of alkali metal catalyst - potassium, rubidium and / or cesium. The most preferred catalyst contains 4 to 13 weight. % silver in the form of strongly adherent hemispherical discrete particles having the same diameter, less than 1 micron, these particles are accordingly precipitated together with 0.00040 - 0.0019 g-eq / kg of potassium, rubidium and / or cesium, distributed in a uniform and the outer surface of a is AljOs, whose specific surface is in the range of from 0.1 to 0.8.

The catalyst must be prepared in such a way that co-precipitation of silver and the desired alkali metal (alkali metals) on the surfaces of the catalytic substrate is ensured, since simultaneous deposition with silver has a great importance on the efficiency achieved by the addition of alkali metals.

Alkali-promoted silver catalysts exhibit particularly high selectivity in the process of direct oxidation of ethylene with molecular oxygen to ethylene oxide.

In accordance with a preferred embodiment, silver catalysts should be used to obtain ethylene oxide by contacting an oxygen-containing gas separated from air and containing at least 95% oxygen with ethylene in the presence of the proposed catalysts at a temperature in the range of 210-285, preferably 225-270 ° C .

As a result of using the proposed silver catalysts in the processes for producing ethylene oxide, selectivity is obtained for the oxidation of ethylene to ethylene oxide at a given degree of ethylene conversion, which exceeds the conversion that is possible with conventional catalysts.

Despite the fact that the reason for such a high selectivity, which the used catalysts exhibit is not completely awake, it has been established experimentally that the use of conventional silver catalysts (not containing alkali metals in amounts corresponding to the present invention) causes the decomposition of ethylene oxide after its formation, while the use of catalysts containing from 0.00035 to 0.0030 g-eq / kg of precipitated alkali metal or metals does not cause even a slight decomposition of ethylene oxide.

Example 1

Catalyst A, according to the invention, is prepared as follows.

As the carrier for the catalyst, HB03 in the form of rings with a diameter of 8 mm is used. This carrier contains 99.3 wt. % ss-AoZ, 0.4 weight. % silica and 0.3 weight. % of oxides of other metals; the specific surface area of the carrier is 0.24, and the apparent porosity is 48-49 vol. % The average pore diameter of the carrier is 4.4 mm; 80% of its pores have a diameter in the range from 1.5 to 15 nm.

The carrier is impregnated with an aqueous solution.

silver salts containing a given amount of potassium. This solution is prepared as follows.

The silver oxide is mixed with an aqueous solution of oxalic acid dissolved in ethylene diamine, resulting in the formation of approximately 2 M solution of Ag2 (EN) 20264, where (EN is ethylene diamine), after which 10 vol. % ethanolamine to bring the system into a reducing state. The resulting solution contains about 22 wt. % silver. Potassium nitrate is added to this solution in an amount necessary to achieve a potassium concentration of 190 wt. per ppm. The carrier is impregnated with a solution of silver containing potassium, and to achieve complete saturation, the impregnation is carried out under a discharge. The excess liquid is removed and the carrier is immediately placed in an oven with forced air blowing, in which the catalyst is dried at a temperature of 290 ° C and the silver salt is reduced to silver metal. The total heating time is about 3 hours. The silver content in the catalyst is 7.8 wt. % and the potassium content in the catalyst is 60 wt. hours per million (0,0015 g-eq / kg of catalyst). The precipitate of silver on the catalyst is studied using an electron microscope. According to these observations, the sediment consists of discrete particles of the same size, with a diameter in the range of 0.2 - 0.4 nm (from 2000 to 4000 A). These particles are evenly distributed inside and outside the carrier. Re-shaking showed that silver particles were firmly held on the surface of catalyst support A.

For comparison, the above catalyst preparation process is repeated with the difference that in this case potassium is not added to the impregnating solution. The analysis showed that potassium is present in the solution at most 5 wt. h / m The catalyst (catalyst Aj) contains 7.8 wt. % silver and has a physical microstructure identical to the microstructure of catalyst A.

Catalysts A and AI are subjected to comparative tests in the process of producing ethylene oxide. In this case, 8-millimeter rings of catalyst A are crushed, and 3.5 g of particles of crushed catalyst, ranging in size from 30 to 40, are loaded into a reaction tube with a diameter of 5 mm and a length of 125 mm. A mixture of air and ethylene is passed over the catalyst in the presence of a chlorine-containing retarder, under the following reaction conditions.

Pressure, atm. abs.15

Volumetric speed, hour-3300

The ethylene content in the source gas, mol. %thirty

Ethylene to oxygen ratio 3.75 The moderator content, ppm, based on chlorine equivalent 10-15 The reaction temperature is controlled taking into account the need to achieve a degree of oxygen conversion of 52% and the selectivity of the catalyst with respect to ethylene oxide is determined. When using catalyst A, a temperature of 253 ° C is necessary to achieve the usual degree of oxygen conversion (52%). The selectivity to ethylene oxide was found to be 78%. In contrast, in the case of using a catalyst not covered by the present invention (catalyst AI), the selectivity for ethylene oxide is only 69%. EXAMPLE 2 Catalyst B was prepared in accordance with the method described in example 1 for preparing catalyst A. A carrier similar to that used in example 1 was impregnated with an aqueous solution of potassium and silver salts, which was prepared as follows. An aqueous solution of silver nitrate is mixed with an aqueous solution of oxalate K. Collect Ag oxalate precipitate, wash with deionized water until potassium content is 800 ppm. This Ag oxalate containing K is then dissolved in an aqueous solution of ethylenediamine and used for impregnation of the carrier by the method described in example 1. The resulting catalyst contains 7.8 wt. % silver and co-precipitated potassium 62 wt. ppm. For comparison, catalyst Bb is prepared by the same procedure. However, the amount of silver oxalate leaching is changed. The catalyst contains precipitated potassium 310 weight. ppm. When using catalyst B as a catalyst for the oxidation of ethylene, as described in example 1, the usual conversion rate for catalyst B was achieved at a temperature of 253 ° C, and the selectivity for ethylene oxide was 78.6%. It has been established that BI catalyst is inactive, as a catalyst for the process of producing ethylene oxide. Froze Using raw materials and, in accordance with the method described in Example 1, a series of silver catalysts with different potassium contents are prepared. The composition of such catalysts, each of which contains 7.8 ± 0.3 weight. % silver is given in table. 1. Table 1

Each of these catalysts is subjected to a test for a long period of time in a pilot reactor for the oxidation of ethylene, whose diameter is about 45 mm and its length is about 12 m. The experiments are carried out under the following conditions.

Pressure abs. atm.15,3

Temperature, ° С245-260

Volumetric speed, hour-3300

Ethylene content in the original

gas,% 30

Ethylene to

oxygen3.5

Conversion rate

oxygen%

52

The optimal content of the reaction retarder, weight. hours per million, in terms of chlorine equivalent of -14

The results of these experiments showing the selectivity of the catalyst with respect to the oxidation of ethylene to ethylene oxide are given in Table one.

PRI me R 4.

Catalysts containing various amounts of rubidium as an alkali metal additive are prepared using the feedstock and in accordance with the general preparation technology described in Example 1. In this case rubidium in the form of rubidium nitrate is introduced into the impregnating solution. Catalysts prepared in this way are subjected to tests in the preparation of ethylene oxide using the equipment 5.

Catalysts containing various amounts of cesium as an alkali metal additive are prepared using the feedstock and in accordance with the general preparation technology described in Example 1.

PRI me R 6 (comparative).

Two series of catalysts are prepared using the raw materials: materials and the general method of preparation, which are described in

The techniques and technologies described in Example 1. The compositions of such catalysts, together with the results of experiments for the preparation of ethylene oxide using these catalysts, are given in the following table. 2

table 2

In this case, instead of potassium, cesium is introduced into the impregnating solution in the form of cesium nitrate. The composition of such catalysts, together with the results of their tests in the course of the processes for producing ethylene oxide, are given in the table below. 3

Table 3

Example 1, except that different amounts of sodium are introduced into one set of catalysts, and different amounts of lithium are introduced into another set of catalysts.

AND

These catalysts contain 7.8 wt. % silver and 0.005 to 0.15 g-eq / kg of lithium or sodium catalyst.

Such catalysts were tested as catalysts for the oxidation of ethylene using equipment and technology described in Example 1. Within the limits of the usual experimental accuracy, the use of these catalysts showed no improvement in selectivity.

Example 7 (comparative).

A catalyst containing not more than 5 wt. ppm of co-precipitated potassium is prepared according to the method described in Example 1. It contains 7.8 wt. % silver. When tested as a catalyst for the oxidation of ethylene, the selectivity is 69%. Samples of this catalyst are treated with aqueous solutions of potassium in order to introduce various amounts of potassium into the catalyst. Even with the addition of amounts within the range of 0.00090 to 0.00220 g-eq / kg of catalyst, the maximum increase in selectivity is 4-5%.

Claims (3)

1. A catalyst for the oxidation of ethylene to ethylene oxide, consisting of silver with the addition of one or more alkali metals on a carrier, characterized in that, in order to increase the activity and selectivity of the catalyst, potassium, rubidium and / or cesium are used as alkali metals in the amount of 0.00035 - 0.0030 g-eq / kg of catalyst, mainly 0.00040 - 0.0019 g-eq / kg. 2. Catalyst on n. 1, that is, with the fact that it contains potassium in the amount of 0.00077 - 0.0023 g-eq / kg of catalyst, mainly 0.001-0.0021 g-eq / kg, rubidium - 0.0006 - 0.0030 g-eq / kg of catalyst, mostly 0.00075 - 0.0027 g-eq / kg, cesium - 0.00035 - 0.0019 g-eq / kg of catalyst, mainly 0.0004 - 0.0017 g-eq / kg. 3. Catalyst according to claim 1, characterized in that the carrier contains 0.03 - 2, preferably 0.1 - 0.8, with a specific surface.