JPS6234418B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a silver catalyst used in the production of ethylene oxide by catalytic gas phase oxidation of ethylene with molecular oxygen. Catalysts used industrially to produce ethylene oxide by catalytic gas phase oxidation of ethylene with molecular oxygen are required to have high activity, high selectivity, and durability. In response to these demands, various studies have been made to date to improve the performance, and much effort has been made to improve reaction accelerators, carriers, silver compounds, etc. Among them, reports on reaction accelerators include, for example, JP-A-49-30286, JP-A-50-50307, and JP-A-Sho 50.
-No. 74589, Japanese Patent Application Publication No. 1973-90591, Japanese Patent Application Publication No. 1973-
Numerous issues such as issue 25703 have been published. However, there are still many unknown points regarding the carrier, and there are still many problems that need to be improved. For example, specific surface area, pore diameter, pore distribution,
Physical properties of the carrier such as specific pore volume and porosity,
There are also improvements to optimize the chemical properties of carrier materials such as α-alumina, silicon carbide, silica, and zirconia. The present inventors have also conducted research on suitable supports for use in silver catalysts for the production of ethylene oxide over many years, and have found that α- When an alumina support is used, it is possible to effectively use a support with a relatively high specific surface area, which is not generally used on an industrial scale in this field due to its low selectivity when used as a catalyst. The present invention was completed by discovering that when a silver catalyst containing thallium metal or a thallium compound as a promoter is used, a catalyst with unprecedentedly high activity, high selectivity, and durability can be produced. The present invention relates to ^a silver catalyst for producing ethylene oxide containing silver and thallium metal or a thallium compound in the carrier. 5-25% by weight of supported metallic silver particles and 0.0005% per kilogram of finished catalyst
This is a silver catalyst for producing ethylene oxide, characterized in that it contains thallium metal or thallium compound supported in an amount of ~0.03 gram equivalent. The present invention will be explained in more detail below. The catalyst used to produce ethylene oxide by catalytic gas phase oxidation of ethylene with molecular oxygen is a silver catalyst, and it goes without saying that most of them are silver-supported catalysts using a carrier. It is also well known that the carrier used is a porous refractory carrier based on alumina. However, even though it is simply a porous refractory carrier mainly composed of alumina, the specific surface area of the carrier and
Physical properties such as pore distribution, pore volume, particle size, shape, etc., and materials constituting the carrier, such as α-alumina, silica,
These physical and chemical properties, such as the chemical properties of silicon carbide, binder, etc., have a great influence on the performance of the catalyst. Therefore, it is a big problem for those skilled in the art how to select a carrier having properties. Among the physical properties of the carrier, the specific surface area is also related to the pore diameter, and has a large influence on the catalyst performance, so great care must be taken. In other words, from the standpoint of activity and durability, it is desirable that the specific surface area of the catalyst be large, and for that purpose, the specific surface area of the carrier should be large, but in order to increase the specific surface area of the carrier, the alumina particles of the carrier material should be small. You need to choose. That necessarily means the formation of small pore sizes. This is disadvantageous from the viewpoint of gas diffusion and retention and removal of reaction heat. It is also disadvantageous because the exposed area of the carrier surface increases. All of these things lead to a decrease in selectivity. Therefore, it cannot necessarily be said that the larger the specific surface area, the better, and limitations naturally arise. The specific surface area of most carriers that have been used on an industrial scale so far is 1 m ² /g or less, and
It is 0.5m ² /g or less. Although there are exceptional cases in which a carrier of 1 m ² /g or more is used, the selectivity is lower than that of a carrier with a low surface area. The present inventors investigated how to eliminate these drawbacks, and as a result, even if a carrier with a large specific surface area of 0.5 m ² /g or more is used, the selectivity does not decrease, and the selectivity is further improved and high activity and durability are achieved. We have discovered a catalyst that maintains and promotes this. That is, this is achieved by lowering the sodium content in the α-alumina of the constituent material of the carrier, and by reducing the sodium content of the carrier. It is surprising that such disadvantages due to physical properties can be improved by changing the chemical properties of the carrier, especially the sodium content in the carrier. α-Alumina, which is used as a carrier with a specific surface area of 10 m ² /g or less, is usually used for reasons related to its manufacturing method.
It usually contains 0.1% by weight (as Na ₂ O) or more of a sodium component (mainly Na ₂ O), and the resulting carrier contains 0.1% by weight (as Na ₂ O).
It is also common for the above sodium components to be included. Most of the carriers that have been used for silver catalysts for ethylene oxide production so far are of this kind, and the carrier component is mainly α-alumina, so it is preferable to have a high α-alumina content, so 90% by weight or more is preferred. Although the content of the carrier has been focused on and has become fairly fixed, other components have not been considered, much less the sodium component present as an impurity in the carrier. According to our research, the sodium component in the carrier has a subtle effect on the catalyst performance, and with carriers with a specific surface area of 0.5 m ² /g or less, which are commonly used in this field, this effect becomes smaller. Although quite small,
When it exceeds 0.5m ² /g, it gradually becomes larger and becomes 1
It was found that the effect becomes significant at m ² /g or more. However, according to the present invention, it is not only possible to use carriers of 1 m ² /g or more, which have not been used until now because of their low selectivity, but they are even superior in terms of activity and selectivity. As will be seen in the examples below, this is the same
Even if the carrier has a specific surface area of about 1.5 m ² /g, there is a difference in other physical properties between an α-alumina carrier with a low sodium content of 0.07% by weight or less and a carrier without it, but thallium metal or thallium compounds are added. It is surprising that when used as a catalyst, the selectivity differs by more than 6%. The reason for this effect is that it is better to have as little sodium as possible in the carrier, which is sometimes actively added as a reaction accelerator, and that it is better to use as little sodium as possible in the carrier, and that it is better to use the carrier without adding thallium metal or thallium compounds. A comparison of a silver catalyst using a carrier with a surface area of 1.54 m ² /g and a sodium content of 0.05% by weight or less and a silver catalyst using a carrier with a specific surface area of 1.51m ² /g and a sodium content of 0.40% by weight. The difference in selectivity was approximately 3.6%, and the literature also states that the adsorption of metal ions on alumina and silica
Considering these facts, such as the fact that it has been described that the sodium component in the carrier is strongly dependent on the PH distribution in the carrier when impregnated with a solution containing silver and thallium compounds, It is thought that this has a stronger influence on the precipitation distribution of thallium metal or thallium compound than that of silver. This seems to be related to catalyst performance. In this sense, the potassium component (mainly K ₂ O) in the carrier is thought to be involved, but according to the experiments of the present inventors, sufficient effects can be obtained by reducing the sodium component even if the potassium content remains the same as before. is obtained. However, the carrier also contains a potassium component in the form of K ₂ O of 0.1% by weight or more, and it is conceivable that the effect will be further improved by reducing potassium to 0.07% by weight or less, similar to sodium. Therefore, in order to use the low-sodium component carrier having a specific surface area of 0.5 m ² /g or more more effectively, a thallium compound must be added as a reaction accelerator. As the thallium compound to be added, both organic salts and inorganic salts are effective, but water-soluble compounds are particularly effective. Regarding the amount of thallium metal or thallium compound added, it is also effective to add the amount beyond the amount found in known literature, and especially in the case of a support with a large specific surface area, it is necessary to discuss points beyond the conventional preferred range. There are many. The range of suitable amounts of thallium metal or thallium compound added according to the present invention is from 0.0005 to 0.03 gram equivalents per kilogram of finished catalyst, preferably from 0.001 to 0.001.
0.02 gram equivalent. Regarding the carrier used, any conditions known in the art can be applied, except for the use of an α-alumina carrier with a specific surface area of 0.5 m ² /g or more and a low sodium content of 0.07% by weight or less, but preferably is apparent porosity 25-60%, specific pore volume 0.2-0.5
An α-alumina carrier having a particle size of 3 to 20 mm and a main component of α-alumina, preferably 90% by weight or more can be used. Also, as for the specific surface area, it is preferable to have a specific surface area of 0.5 m ² /g or more, and even 1 m ² /g or more, but a material with a specific surface area of 5 m ² /g or more has not been practically obtained and is not practical. Furthermore, carrier components other than α-alumina and sodium components (mainly Na ₂ O) are preferably contained in carriers commonly used in the art. The silver content is selected to be 5 to 25% by weight, preferably 10 to 20% by weight, based on the finished catalyst, but loading more than 25% by weight is meaningless and uneconomical. Any conventionally known method can be used to prepare the catalyst, but in general, an aqueous solution or an organic solvent solution of a decomposable silver salt, such as an aqueous silver nitrate solution, an ammonia solution or an organic amine solution of inorganic organic acid silver, or a lactic acid solution. The carrier as described above is impregnated with an aqueous silver solution or the like. The thallium metal or thallium compound may be precipitated on the carrier or may be added to the silver solution. Next, the impregnated carrier may be heated to decompose or reduce the decomposed product to form a catalyst, or the impregnated carrier may be reductively decomposed in a reducing atmosphere to form a catalyst. To describe the above more specifically, in the silver catalyst used when producing ethylene oxide by gas-phase catalytic oxidation of ethylene with molecular oxygen, sodium content is
0.5 to 5 m ² /g, preferably 1% by weight or less
A carrier with physical properties of a specific surface area of ~5 m ² /g, an apparent porosity of 25 to 60%, a specific pore volume of 0.2 to 0.5 cc/g, and a particle size of 3 to 20 mm is used, and an organic acid is added to this support. 100-300℃ after impregnation with degradable silver solution such as silver amine solution
The substance is heated to reduce or thermally decompose it. Silver is deposited in the form of fine particles on the inner and outer surfaces of the carrier in an amount of 5 to 25% by weight, preferably 10 to 20% by weight, based on the catalyst. The thallium compound is a compound selected from organic salts and inorganic salts in the form of an aqueous solution or an alcoholic solution at a rate of 0.0005 to 1 kg per kilogram of the finished catalyst.
0.03 gram equivalents, preferably 0.001 to 0.02 gram equivalents, can be added to the silver solution and precipitated simultaneously with the silver, or can be deposited on the support before or after silver precipitation. The thallium-containing silver catalyst is finally
The catalyst is completed by activation at 100-400℃ for 24-100 hours. In this method, all conditions known in this field can be adopted in the method of producing ethylene oxide by oxidizing ethylene with molecular oxygen using the prepared silver catalyst. , the general conditions at the production scale, i.e., the raw gas composition is 0.5-40% by volume of ethylene, 3-10% by volume of oxygen, 5-30% by volume of carbon dioxide, the balance being nitrogen, inert gas such as argon, water vapor, etc., and methane. , lower hydrocarbons such as ethane, and halides such as ethylene dichloride and diphenyl chloride as reaction inhibitors, space velocity 0.1 to 10000 hr ^-1
(STP), a pressure of 2 to 40 Kg/cm ² or the like can be suitably employed. The present invention will be described in detail below using Examples and Comparative Examples to make it more specific, but the present invention is not limited to these Examples unless it goes against the gist thereof. Note that the rate of change and selectivity described in the main text, Examples, and Comparative Examples were calculated using the following formula. Rate of change (%) = Number of moles of ethylene reacted/Number of moles of ethylene in raw material gas x 100 Selectivity (%) = Number of moles of ethylene converted to ethylene oxide/Number of moles of ethylene reacted x 100 Example 1 Carbonic acid Make 570 g of silver into a slurry with 200 ml of water, add 560 ml of ethanolamine, stir well to dissolve, then add 500 ml of water and stir well, then add 10 ml of 41.5% by weight thallium sulfate aqueous solution and stir. , an impregnating solution was prepared. This solution has an apparent porosity of 51%, a BET specific surface area of 1.54 m ² /g, and a specific pore volume.
4000 ml of a preheated α-alumina carrier with a sodium content of 0.05% by weight (as Na ₂ O) of 0.34 cc/g and a particle size of 5 mm was impregnated. Then, the mixture was heated at 80 to 120°C for 2 hours while stirring gently. This catalyst was packed into a stainless steel reaction tube with an inner diameter of 25.0 mm and a tube length of 11,000 mm, and the outside of the tube was heated to 100 mm using a heat medium.
The catalyst was activated by air at 240°C for 24 hours by passing air through the catalyst layer while gradually increasing the temperature from 0°C to 240°C. Next, the heating medium temperature was lowered to 180℃, and instead of the air flow, 20% by volume of ethylene, 8% by volume of oxygen, 7% by volume of carbon dioxide, and the remainder was nitrogen, an inert gas such as methane, ethane, argon, etc., and ethylene dichloride. A raw material mixed gas consisting of 1 ppm was introduced, and the reaction pressure was 24 Kg/cm ² G.
The reaction was carried out by increasing the heat medium temperature to 203℃ at a space velocity of 3000hr ^-1 (STP). The reaction results after 10 days are shown in Table 1.
It was as shown in. Comparative Example 1 The carrier used in Example 1 had an apparent porosity of 53%, a BET specific surface area of 1.51 m ² /g, and a specific pore volume.
0.31cc/g, particle size 5mm, sodium content 0.40
A catalyst was prepared in the same manner as in Example 1, except that an α-alumina support of % by weight (as Na ₂ O) was used, and the reaction was carried out in the same manner, except that the reaction temperature (thermal medium temperature) was 216 °C. . The results were as shown in Table 1.

[Table] Comparative Example 2 A catalyst was prepared in the same manner as in Example 1, except that the thallium compound was not added in Example 1, and a catalyst was prepared in the same manner as in Example 1, except that the reaction temperature was set to the temperature shown in Table 2. Konatsuta. The results were as shown in Table 2. Comparative Example 3 In Comparative Example 1, a catalyst was prepared in the same manner as in Comparative Example 1, except that no thallium compound was added, and the reaction temperature was set to the temperature shown in Table 2.
I did the same thing. The results were as shown in Table-2.

[Table] Example 2 The same procedure as in Example 1 was carried out except that the carrier, the added amount of the thallium compound, and the reaction temperature were changed as shown in Table 3. The results were as shown in Table-3.

【table】

Claims (1)

[Scope of Claims] 1. In a silver catalyst for producing ethylene oxide containing silver and thallium metal or thallium compound in the carrier, an α-alumina carrier having a sodium component of 0.07% by weight or less and a specific surface area of 0.5 to 5 m ² /g,
Metallic silver fine particles supported at 5 to 25% by weight on the finished catalyst and 0.0005 to 1 kg per kilogram of the finished catalyst
A silver catalyst for producing ethylene oxide, characterized in that it contains 0.03 gram equivalent of supported thallium metal or thallium compound. 2. The catalyst according to claim 1, wherein 0.001 to 0.02 gram equivalent of thallium metal or thallium compound is supported per kilogram of the finished catalyst.