JPS6231983B2 - - 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 No. 49-30286, JP-A No. 49-87609, and JP-A No. 50-Sho.
50307, JP-A-50-74589, and JP-A-50-90591, many of them improve performance by adding alkali metals within a limited range. 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,
The physical properties of the carrier, such as pore volume and porosity, as well as α-alumina, silicon carbide, silica, etc.
Improvements have been made to optimize the chemical properties of support materials such as zirconia. The present inventors have also conducted research on suitable supports for use in silver catalysts for producing ethylene oxide over many years. As a result, we 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 used in a catalyst containing an alkali metal and/or an alkali metal compound as a promoter, a catalyst with unprecedentedly high activity, high selectivity, and durability could be produced. This will be discussed in 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 these catalysts are supported catalysts using a carrier. It is also well known that the carrier used is a porous granular carrier based on alumina. However, even though it is simply a porous granular carrier mainly composed of alumina, the physical properties such as the specific surface area, pore distribution, pore volume, particle size, shape, etc. of the carrier and the material constituting the carrier, such as α-alumina, vary widely. , silica, silicon carbide, clay, etc. These physical and chemical properties have a large 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 better to have a larger specific surface area of the catalyst, and for that reason, it is desirable that the specific surface area of the carrier is larger, 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. Considering this, 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 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. I found a way to maintain and promote it. This is simply achieved by lowering the sodium content of the carrier. This is particularly effective for supports with a high surface area of 1 m ² /g or more, and is also effective for catalysts containing increased amounts of alkali metal compounds. It is surprising that such disadvantages due to physical properties can be improved by changing the chemical properties of the carrier, particularly the sodium content of 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 supports that have been used for silver catalysts for ethylene oxide production so far are of this type, 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 carriers has become widely accepted, little consideration has been given to other components, and even less consideration has been given to the sodium component present as an impurity in the carrier. However, according to the present invention, the sodium component in the carrier has a subtle influence on the catalyst performance, and the negative influence is particularly severe in the case of carriers with a specific surface area of 0.5 m ² /g or less, which are conventionally used in this field. The smaller it gets, the smaller it becomes, but when it becomes 0.5 m ² /g or more, it gradually becomes larger, and when it becomes 1 m ² /g or more, the effect becomes noticeable. It is noteworthy that carriers of 1 m ² /g or more, which were previously unused due to low selectivity, can not only be used by lowering the sodium content, but also become superior in activity and selectivity. worth it. As you can see in the example below, this is the same thing.
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 the α-alumina carrier with a low sodium content of 0.07% by weight or less and the carrier with a non-sodium content. It is surprising that there is a difference of more than 7% in the selectivity. The inventors do not know what effect this has, and do not intend to make any particular argument.
However, it is important to note 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 the difference in selectivity between catalysts without alkali metals is approximately 4%. Furthermore, it has been stated in the literature that the adsorption of metal ions on alumina and silica is strongly dependent on pH, and when we take these into account, the sodium component in the carrier is When a carrier is impregnated with a containing solution, it is thought that it is related to the PH distribution within the carrier and has a stronger influence on the precipitation distribution of alkali metal than silver or more. I think this has something to do with 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, potassium components are also present in the carrier as K ₂ O.
It contains 0.1% by weight or more, and like sodium, it is thought that the effect will be further improved by reducing potassium to 0.07% by weight or less. Therefore, in order to use the low-sodium component carrier with a specific surface area of 0.5 m ² /g or more more effectively, an alkali metal compound must be added as a reaction accelerator. Any of potassium, rubidium, and cesium compounds are effective as the alkali metal compound to be added, but cesium compounds are particularly effective. It is also effective to use a mixture of two or more kinds, and in particular, the mixed use of potassium and cesium may be superior in activity to cesium alone, even though the selectivity is the same. Regarding the amount of the alkali metal compound added, it is also effective to exceed the amount found in known literature, and especially in the case of carriers with a large specific surface area, it is often necessary to discuss points beyond the conventional addition range. . The suitable range of the addition amount of the alkali metal and/or alkali metal compound of the present invention is as follows:
A range of 0.001 to 0.05 gram equivalent per kilogram, preferably 0.001 to 0.03 gram equivalent, particularly more than 0.008 gram equivalent and 0.03 gram equivalent or less is suitable. This range should be maintained whether one type or two or more types are added. 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 in cc/g and containing α-alumina as a main component, preferably 90% by weight or more, can be used. Further, 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. Silver content is 5-25% by weight based on the finished catalyst
Although 10 to 20% by weight is preferably selected, carrying more than 25% by weight is meaningless and uneconomical. Any conventionally known method can be used to prepare the catalyst, but generally the aqueous solution of the decomposable silver salt is an organic solvent solution, such as an aqueous silver nitrate solution, an ammonia solution of an inorganic or organic acid silver, or an organic amine solution. A carrier as described above is impregnated with an aqueous silver lactate solution or the like. The alkali metal compound may be precipitated onto 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 decomposition product 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 vapor phase catalytic oxidation of ethylene with molecular oxygen, sodium content is
0.5 to 5 m ² /g, preferably 1 to 5 m 2 /g, not more than 0.07% by weight
A carrier with physical properties such as 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 organic acid silver is added to this carrier. 100-300℃ after impregnation with degradable silver solution such as 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 alkali metal or alkali metal compound is one or more metals or compounds selected from potassium, rubidium, and cesium in the form of an aqueous or alcoholic solution in an amount of 0.001 to 0.05 gram equivalent per kilogram of the finished catalyst, preferably 0.001.
~0.03 gram equivalent, particularly more than 0.008 gram equivalent and less than 0.03 gram equivalent, can be added to the silver solution and precipitated simultaneously with silver, or can be precipitated on a carrier before or after silver precipitation. The alkali metal-containing silver catalyst is finally activated by an air stream at 100 to 400°C for 24 to 100 hours to complete the catalyst. The conditions that can be adopted in the method of producing ethylene oxide by oxidizing ethylene with molecular oxygen using the silver catalyst prepared by this method include all the conditions known so far in this field. , typical conditions at the production scale, i.e., raw gas composition: ethylene 0.5-40% by volume, oxygen 3
-10% by volume, carbon dioxide 5-30% by volume, the balance being nitrogen, inert gas such as argon, water vapor, lower hydrocarbons such as methane, ethane, etc. Also, ethylene dichloride, diphenyl chloride, etc. as reaction inhibitors. Halides, space velocity 1000~100000hr ^-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 the raw material gas x 100 Selectivity (%) = Number of moles of ethylene converted to ethylene oxide/Number of moles of ethylene reacted x 10
0 Example 1 Make 570 g of silver carbonate into a slurry with 200 ml of water, add 560 ml of ethanolamine, stir well to dissolve, then add 500 ml of water, stir well, and add to this.
10 ml of 18.5% by weight potassium nitrate solution and 10ml of 36.0% by weight cesium nitrate aqueous solution were added and stirred to prepare an impregnating solution. This solution has an apparent porosity of 51% BET
Specific surface area 1.54m ² /g, pore volume 0.34cc/g, particle size 5mm pre-heated sodium content 0.05% by weight
The following α-alumina support (as Na ₂ O) was impregnated with 4000 ml. Then, while stirring gently, heat the mixture to 80~
Heated at 120°C for 2 hours. 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.
Air was passed through the catalyst layer while gradually increasing the temperature from 0.degree. C. to 240.degree. C., and the catalyst was activated with air at 240.degree. C. for 24 hours. Next, the heating medium temperature is 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 is 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 heating medium temperature to 233°C at a space velocity of 5500hr ^-1 (STP). The results are shown in Table-1. 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 pore volume.
0.31cc/g, particle size 5mm, sodium content 0.40
The catalyst was prepared in the same manner as in Example 1, except that % by weight (as Na ₂ O) of α-alumina support was used, and the reaction was carried out in the same manner, except that the reaction temperature (thermal medium temperature) was 240 °C. I let it happen. The results are shown in Table-1.

[Table] Comparative Examples 2 and 3 Catalysts were prepared in the same manner as in Example 1 and Comparative Example 1 except that no alkali metal compound was added in Example 1 and Comparative Example 1, and the reaction temperature was shown in Table 2. The same procedure as in Example 1 and Comparative Example 1 was carried out except for the temperature. The results are shown in the table-
Shown in 2. (Comparative Example 2 is the same as Example 1, Comparative Example 3 is the same as Comparative Example 1.
Based on)

[Table] Examples 2 to 4 Catalysts were prepared using the same method as in Example 1 except for the conditions shown in Table-3. The reaction was also carried out under the same conditions as in Example 1. The results are shown in Table-3. Comparative Examples 4-5 Catalysts were prepared using the same method as in Example 1 except for the conditions shown in Table 2. The reaction was also carried out under the same conditions as in Example 1. The results are shown in Table-3.

[Table] Comparative Example 6 The carrier used in the example had an apparent porosity of 53%, a BET specific surface area of 0.3 m ² /g, and a pore volume of 0.3.
A catalyst was prepared in the same manner as in Example 1, except that an α-alumina support with a particle size of 5 mm and a sodium content of 0.05% by weight (as Na ₂ O) was used instead, and the reaction temperature was set at 240 °C. The reaction was the same except that The reaction results were as follows. Change rate 8% Selectivity 75.4% Comparative example 7 The carrier used in the example had an apparent porosity of 53%, a BET specific surface area of 1.54 m ² /g, and a pore volume.
A catalyst was prepared in the same manner as in Example 1, except that an α-alumina support of 0.3 cc/g, particle size of 5 mm, and sodium content of 0.1% by weight (as Na ₂ O) was used, and the reaction temperature was adjusted to 240 °C. The reaction was carried out in the same manner except that the temperature was changed to ℃. The reaction results were as follows. Change rate 8% Selectivity 75.1% Comparative example 8 The carrier used in the example had an apparent porosity of 53%, a BET specific surface area of 0.3 m ² /g, and a pore volume of 0.3.
A catalyst was prepared in the same manner as in Example 1, except that an α-alumina support with a particle size of 5 mm and a sodium content of 0.1% by weight (as Na ₂ O) was used instead, and the reaction temperature was changed to 240°C. The reaction was the same except that The reaction results were as follows. Change rate 8% Selection rate 74.7%

Claims (1)

[Scope of Claims] 1. A silver catalyst for producing ethylene oxide containing silver and at least one of an alkali metal or an alkali metal compound in a carrier, with a sodium component of 0.07% by weight or less and a specific surface area of 0.5 to 5 m ² /g. - Fine metallic silver particles supported on an alumina carrier in an amount of 5 to 25% by weight based on the finished catalyst, and in addition to the amount present in the carrier, 0.001 to 0.05% by weight per kilogram of the finished catalyst.
A silver catalyst for producing ethylene oxide, characterized in that it contains a gram equivalent of at least one alkali metal or alkali metal compound. 2. The silver catalyst according to claim 1, wherein the carrier has a specific surface area of 1 to 3 m ² /g. 3. The silver catalyst according to any one of claims 1 to 2, wherein the alkali metal is cesium.