JPS6366837B2 - - 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. To date, various studies have been conducted to improve the performance of these requirements, including reaction accelerators,
Many efforts have been made to improve carriers, silver compounds, etc. Among them, the report on reaction accelerators was published in 1973.
-4605, JP-A-49-30285, JP-A-50-74889
Many proposals have been made, such as No. 1, which aim to improve performance by adding alkali metals within a limited range. However, although the selectivity of most of these has certainly been improved to some extent, there are still many points to be considered regarding activity and durability. In particular, various efforts seem to have been made to address the durability problem of alkali metal-added catalysts with respect to a decrease in activity and selectivity during their use, but no solution has yet been reached. Although several reports have been published regarding carriers, there are still many unclear points and many points that need to be improved. For example, physical properties such as specific surface area, pore diameter, pore distribution, specific pore volume, and porosity of the carrier;
This includes elucidating and optimizing the effects of the chemical properties of carrier materials such as α-alumina, silicon carbide, silica, and zirconia on catalyst performance. In particular, the specific surface area of the carrier is also related to the pore diameter, and its influence on catalyst performance must be taken into consideration. In this respect, one progress is that the specific surface area of carriers that have recently been used on an industrial scale has increased compared to before. However, this results from the small increase in catalyst effective surface area relative to the ratio of increase in carrier specific surface area. Separation and atomization of silver particles and susceptibility to poisoning have emerged as new problems that need to be solved. As a result of intensive study on these matters, the present inventors have found that the deterioration of the alkali metal-added catalyst during its use can be minimized, the performance deterioration due to initial poisoning of the catalyst can be eliminated, and the activity can be maintained stably over a long period of time. We have discovered a catalyst that exhibits high selectivity. This will be explained in detail below. As mentioned above, conventional alkali metal-added catalysts suffer from significant deterioration in performance, particularly selectivity, during the period of use, necessitating a shortening of the period of use. Various efforts have been made to improve this, and for example, a method for regenerating a deteriorated catalyst by impregnating it with alkali metal again is disclosed in Japanese Patent Laid-Open No. 52-35193. Looking at this, it may be that the alkali metal added to the catalyst is scattered little by little during the period of use, or that it moves into the silver or carrier, weakening its function. There may also be an effect due to sintering of silver particles, but there is no proof of either. As a result of careful consideration of these points, the present inventors have determined that in the process of preparing a catalyst to which an alkali metal compound has been added, the catalyst after final activation is treated with carbon dioxide to reduce the poisoning effect. They discovered that a long-term stable, highly active, and highly selective catalyst could be obtained, and completed the present invention. That is, metallic silver particles are supported on a support with a specific surface area of 0.1 to 5 m ² /g so that the silver content is 5 to 25% by weight with respect to the finished catalyst. per kilogram of finished catalyst simultaneously with silver or before loading silver
The silver catalyst for producing ethylene oxide of the present invention is obtained by supporting 0.001 to 0.03 gram equivalent, then activating it at a temperature of 240 to 400°C with an air flow, and then fixing it at a temperature of 50 to 350°C with a carbon dioxide gas flow. It is. It is surprising that the effect of adding an alkali metal compound can be sustained for a longer time by treating the alkali metal-added catalyst with carbon dioxide gas after activation with air. This effect is particularly remarkable for catalysts with a low silver content. The inventors do not know what this is based on. However, it is also surprising that it is compatible with the following: That is, the alkali metal compound is fixed in the catalyst by carbon dioxide treatment. This is due to the difference in the amount of alkali metal compound extracted with alcohol depending on whether or not the alkali metal compound-added catalyst is treated with carbon dioxide gas. That is, as shown in Table 1 of Examples below, the amount of extraction clearly differs depending on whether or not carbon dioxide treatment is performed. This cannot be explained simply from solubility. Also, although it is not clear whether this is related to catalyst performance, the fact that they correspond does not seem to be a mere coincidence. It should also be noted that gases other than carbon dioxide have no effect. Mixing other gases with carbon dioxide gas is effective, but the effect is smaller and the processing time becomes longer, so other gases are only useful for diluting the carbon dioxide gas. Furthermore, although the higher the treatment temperature, the greater the effect, it is rather undesirable to raise the treatment temperature to such a high temperature that the shape of the catalyst substance changes. However, at low temperatures it takes longer. Therefore, although it is effective at 50 to 400℃, it is preferably 15 to 35 hours at a temperature of 150 to 300℃ around the activation temperature.
It is better to process for 30 hours. In addition to the durability of the catalyst, the carbon dioxide treatment has an additional effect on the shelf life of the catalyst. This applies when the catalyst containing an alkali metal compound is stored for a long time after activation, or when the catalyst is not used for a long time after production, such as when sending it to a remote location.
Deterioration may occur during use, and this tendency is particularly common with alkali metal compound-added catalysts that use a carrier with a high surface area and have a low silver content. However, catalysts treated with carbon dioxide gas do not exhibit this phenomenon and can be stored indefinitely. The reason for this is not known, but it may be related to the poisoning of the catalyst material. It is noteworthy that this can be suppressed by carbon dioxide treatment, and as seen in the examples, the effect is not small. The carbon dioxide treatment referred to herein is exactly the same as the method described above, and both effects can be obtained with a single treatment. 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, α-alumina is the main component as a porous refractory carrier. 0.1 to 5 m ² /g, preferably 1 to 3 m ^{2 /g}
Specific surface area in g, apparent porosity of 30-60% by volume, 0.2
Using a granular carrier with physical properties such as a specific pore volume of ~0.5 cc/g and a particle size of 3 to 20 mm, the decomposability of silver salts of organic acids, ammoniacal silver salts, etc. can be improved by impregnation. Impregnated with a solution of silver salt, silver is precipitated in the form of fine particles on the surface of the carrier and on the inner surface of the pores of the carrier by reduction or thermal decomposition, etc., in an amount of 5 to 25% by weight, preferably 5 to 20% by weight, based on the catalyst. The metal compound is preferably a water-soluble or alcohol-soluble salt of potassium, rubidium, cesium, preferably in an amount of 0.001 to 0.03 gram equivalent per kilogram of finished catalyst.
Either 0.008 to 0.03 gram equivalent is added to a silver solution and precipitated simultaneously with silver, or it is impregnated into a carrier prior to supporting silver, concentrated and dried, and precipitated on the surface of the carrier. The alkali metal compound-containing silver catalyst is then activated with a stream of air at 240-400°C for 24-100 hours, and then activated with a stream of carbon dioxide gas at 50-400°C, preferably 150-400°C.
Fixation is preferably carried out by heat treatment at a temperature of 300° C. for 5 to 35 hours, preferably 15 to 35 hours. 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 in this field so far. , 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 0.1 to 10 ppm of halogen compounds such as ethylene dichloride and diphenyl chloride as reaction inhibitors, reaction temperature 150 to 300°C, space velocity 3000 to
Conditions such as 10000 hr ^-1 (STP) and a pressure of 2 to 40 Kg/cm ² G can be suitably employed. The present invention will be described in detail below with reference to Examples and Comparative Examples to make it more specific, but the present invention is not limited to these Examples unless it goes against the spirit 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 430 g of silver into a slurry with 150 ml of water, add 400 ml of ethanolamine and stir well to dissolve it, then add 600 ml of water and stir well, then add 10 ml of 13.9 wt% cesium nitrate solution and stir to make an impregnating solution. was prepared. This solution has an apparent porosity of 57%, a BET specific surface area of 0.3 m ² /g, and a specific pore volume.
It was impregnated into 4000 ml of a preheated α-alumina carrier with a particle size of 5 mm and a particle size of 0.30 cc/g. 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 was covered with a heat medium.
Air was passed through the catalyst layer while gradually increasing the temperature from 100°C to 240°C, and the catalyst was activated by air flow at 240°C for 24 hours. Next, the flow of air was stopped while the temperature remained the same, and carbon dioxide gas was passed instead, and the activated catalyst was treated with carbon dioxide gas for 24 hours. The heating medium temperature was lowered to 180℃, and instead of carbon dioxide gas, 20% by volume of ethylene, 8% by volume of oxygen, 7% by volume of carbon dioxide, and the remainder consisted of inert gases such as nitrogen, methane, ethane, and argon, and A raw material mixed gas containing 1 ppm of ethylene chloride was introduced, and the reaction was carried out at a reaction pressure of 24 Kg/cm ² G, a space velocity of 5500 hr ^-1 (STP), and a heating medium temperature of 227°C. The results are shown in Table-1. Example 2 700g of silver nitrate and 1000g of monoethylene glycol
280 g of formamide was added to this solution and mixed well. Further, 40 ml of a 10% by weight aqueous cesium hydroxide solution was added to this liquid and mixed well. This solution was heated in advance to give an apparent porosity of 56%.
(BET) Specific surface area 1.54m ² /g, specific pore volume 0.34
cc/g, particle size 5mm α-alumina main component carrier 4000
ml was impregnated. The mixture was then heated at a temperature of 145 to 150° C. for 2 hours with gentle stirring. This catalyst was packed into a stainless steel reaction tube with an inner diameter of 25.0 mm and a tube length of 11000 mm, and the following activation and carbon dioxide treatment were carried out in exactly the same manner as in Example 1. Further, the reaction was carried out in the same manner as in Example 1 except that the heating medium temperature was finally set to 229°C. The results are in Table-1
Shown below. Comparative Example 1 A catalyst was prepared and a reaction was carried out in exactly the same manner as in Example 1, except that the carbon dioxide treatment was not performed. The results are shown in Table-1.

[Table] Shows the ratio to the amount that was used.
Example 3 Apparent porosity 51%, BET specific surface area 1.54 m ² /
g, specific pore volume 0.34cc/g, particle size 5mm α-alumina carrier 4000ml was added to 18.5% by weight potassium nitrate solution.
10ml and 36.0% by weight cesium nitrate aqueous solution 10ml and water
After immersing in 1400 ml of aqueous solution, evaporating water at 90 to 100°C and drying, 570 g of silver nitrate and 200 ml of water were mixed into a slurry, 560 ml of ethanolamine was added to this, and 500 ml of water was added to the alkali metal compound support.
ml and stirred well to impregnate the silver solution. Then, while stirring gently, heat the mixture at a temperature of 80 to 120℃.
heated for an hour. 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 following activation and carbon dioxide treatment were carried out in exactly the same manner as in Example 1. Further, the reaction was carried out in the same manner as in Example 1 except that the heating medium temperature was finally set to 235°C. As a result, the reaction test results after 10 days showed a change rate of 8% and a selectivity of 82.2%. In addition, the reaction test results after one year showed that the heating medium temperature was 241℃.
The change rate was 8% and the selection rate was 81.2%. The amount of alkali added is 8.35× the total amount of potassium and cesium.
It was 10 ^-3 g equivalent/Kg catalyst. Examples 4 to 7 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. The results are shown in Table-2. Comparative Examples 2 to 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 in Table-2
Shown below.

[Table] Example 8 A catalyst was prepared in the same manner as in Example 1 except for the conditions shown in Table 3. After activation, it was treated with carbon dioxide gas, and after cooling, it was extracted from the reaction tube and stored in a nylon bag for about 12 months. Thereafter, the reaction tube was filled again and a reaction was performed with a gas having the same composition as in Example 1. As a result, the results shown in Table 3 were obtained at a reaction temperature (heating medium temperature) of 227°C. Comparative Example 6 The same procedure as in Example 7 was carried out except that the carbon dioxide gas treatment was not performed after activation, and the reaction was carried out in the same manner after being stored in a nylon bag for 12 months.
I got results like 3.

【table】

Claims (1)

[Claims] 1. When producing ethylene oxide by catalytic gas phase oxidation of ethylene with molecular oxygen, an α-alumina carrier having a specific surface area of 0.1 to 5 m ² /g is added in an amount of 5 to 25% by weight based on the finished catalyst. 0.001 per kilogram of finished catalyst in a degradable silver solution with a silver loading of
Impregnated with an impregnating solution containing ~0.03 gram equivalent of alkali metal compound, concentrated and dried, supported, activated with a stream of air at a temperature of 240-400°C, and then heat-treated with a stream of carbon dioxide at a temperature of 50-400°C. A method for producing ethylene oxide, characterized by using a catalyst produced by 2. When producing ethylene oxide by catalytic gas phase oxidation of ethylene with molecular oxygen, an α-alumina support with a specific surface area of 0.1 to 5 m ² /g and an alkali metal compound of 0.001 to 0.03 gram equivalent per kilogram of the finished catalyst are used. Impregnated with an impregnating solution containing
After the alkali metal compound is supported on the carrier by concentration and drying, it is impregnated with a decomposable silver solution such that the silver loading rate is 5 to 25% by weight based on the finished catalyst, and the support is concentrated and dried, and then the catalyst is supported by an air flow. A method for producing ethylene oxide, which comprises using a catalyst produced by activation at a temperature of 240 to 400°C and then heat treatment at a temperature of 50 to 400°C with a flow of carbon dioxide gas.