JPS6234419B2 - - 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 of reaction accelerators,
Many efforts have been made to improve carriers, silver compounds, etc. Among them, reports regarding reaction accelerators include, for example, JP-A-49-30286, JP-A-50-50307, JP-A-50-74589, JP-A-50-90591, and JP-A-52-
Numerous issues such as issue 25703 have been published. 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, and selectivity is still insufficient and should be considered in conjunction with activity. I have to go. Taking these matters into consideration, the inventors of the present invention have conducted intensive studies and have found that a larger amount of specified thallium can be produced by using a carrier with a larger specific surface area than the carriers that have been used on an industrial scale in this field. The present invention has been completed by discovering a catalyst that achieves unprecedentedly high activity, high selectivity, and improved durability by adding it in the form of a complex compound with other metals. In the present invention, an α-alumina main component carrier having a sodium content of 0.07% by weight or less and a specific surface area of 1 to 5 m ² /g is added to a decomposable silver solution with a silver loading rate of 5 to 25% by weight relative to the finished catalyst. , characterized in that it is produced by impregnating with an impregnating solution containing a complex compound of thallium and boron or a complex compound of thallium and titanium in an amount of 0.0005 to 0.03 gram equivalent per kilogram of the finished catalyst, followed by heating and reduction or thermal decomposition. This is a silver catalyst for producing ethylene oxide. Next, the present invention will be described in detail. It goes without saying that the catalyst used to produce ethylene oxide by gas-phase oxidation of ethylene is a silver catalyst, and 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, there are a wide range of differences in specific surface area, pore distribution, etc.
It varies greatly depending on specific pore volume, particle size, and shape, and these physical properties have a large influence on the performance of the catalyst. Therefore, it is a big problem for those skilled in the art to select a carrier with physical properties. Among them, the specific surface area of the carrier is related to the pore diameter and has a large influence on the catalyst performance, and must be carefully considered. 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. I need to choose something. This necessarily means the formation of small pore sizes. This is disadvantageous from the viewpoint of gas diffusion, retention, removal of reaction heat, and increase in the exposed area of the carrier, leading to a decrease in selectivity. Therefore, it cannot necessarily be said that the larger the specific surface area of the carrier, the better, and there are limitations. The specific surface area of most of the carriers employed on an industrial scale to date is 1 m ² /g or less, and even 0.5 m 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 of 1 m ² /g or less. The present inventors investigated to eliminate these drawbacks, and as a result, they were able to further improve the selectivity without causing a decrease in selectivity even when using a carrier with a large specific surface area of 1 m ² /g or more, and maintain and promote high activity and durability. We have found a catalyst that makes this possible. The present invention was achieved by using a carrier with improved constituent materials and a complex compound of thallium and boron or a complex compound of thallium and titanium as a reaction accelerator. In other words, the above-mentioned disadvantages due to the use of a carrier with a relatively large specific surface area can be eliminated by lowering the sodium content of the carrier, and in order to further improve selectivity and durability, complex compounds of thallium and boron or thallium can be used. It was found that the addition of a complex compound of titanium and titanium is effective. To be more specific, as mentioned above, the disadvantages of increasing the specific surface area of the carrier include negative effects on gas diffusion, retention, reaction heat removal, etc. due to miniaturization of the pore size, and an increase in the exposed surface of the carrier. It is surprising that sodium-resistance of the carrier results in the elimination of such disadvantages. A carrier with a specific surface area of 10 m ² /g or less usually contains more than 0.07% by weight of sodium (mainly Na ₂ O) due to its manufacturing method. Most of the carriers that have been used in catalysts for producing ethylene oxide have been such carriers, and not much consideration has been given to the carrier components since they are mainly α-alumina. Furthermore, no consideration is given to the sodium content present as an impurity in the carrier. However, according to our research, the sodium content in the carrier has a subtle effect on catalyst performance, and this effect is particularly pronounced in the case of carriers with a specific surface area of 0.5 m ² /g or less, which are commonly used in this field. Although the specific surface area of the carrier is small, it becomes larger when the specific surface area is 0.5 m ² /g or more, and it has been found that when the specific surface area is 1 m ² /g or more, the effect becomes significant. However, according to the present invention, carriers with a specific surface area of 1 m ² /g or more, which have not been used hitherto due to their low selectivity, can not only be used, but also become advantageous. These are the same as shown in the example below.
Even if a carrier has a specific surface area of 1.5 m ² /g, a carrier with a low sodium content of 0.07% by weight or less and a carrier with a sodium content of more than 0.07% by weight will cause a complex between thallium and boron, even if other physical properties are somewhat related. It is surprising that when a catalyst is added with a compound or a complex compound of thallium and titanium, the selectivity differs by more than 6%. Although it is not possible to clarify the cause of such improved performance, 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. Furthermore, considering the fact that the adsorption of metal ions on alumina and silica strongly depends on pH, it is stated in the literature that the sodium component in the carrier is
It is thought that it is related to the PH distribution within the carrier and has a strong influence on the precipitation distribution of silver or even more so the complex compound of thallium and boron or the complex compound of thallium and titanium, and that this is related to the catalyst performance. I can think of it. In this sense, it is thought that the potassium component (mainly K ₂ O) in the carrier is also 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, just like sodium. Therefore, by using a carrier with a specific surface area of 1 m ² /g or more, it is possible to improve the activity and durability as seen in the examples below. It is noteworthy that the silver catalyst obtained by impregnation treatment with a decomposable silver solution containing the compound is also a catalyst with unprecedented performance of high activity, high selectivity, and durability. Until now, catalysts to which a reaction accelerator has been added, particularly catalysts to which an alkali metal compound has been added, have suffered from significant deterioration in performance, particularly selectivity, during their period of use, and many efforts have been made to counter this problem. In this respect, thallium-containing catalysts are catalysts that undergo relatively little deterioration, but are not an exception at all. Taking this point into consideration, the present inventors conducted various studies and found that further improvement can be achieved by adding a thallium compound in the form of a complex salt with another metal compound. That is, by adding a complex compound consisting of thallium and boron or titanium, such as thallium borate or thallium titanate, the deterioration in selectivity is slowed down compared to when conventional thallium compounds are added, and a slight improvement in selectivity is observed. It was done. The addition range of these complex compounds may be within the conventional addition range of thallium compounds based on thallium, but as the present inventors have already clarified in JP-A No. 52-25703, the addition amount should be determined in proportion to the carrier. Since there is a proportional relationship to the surface area to some extent, it is natural that when using a carrier with a larger specific surface area than before, the optimal addition range will be beyond the conventional range, and the lower limit of the conventional range will be substantially larger. . Also, the amount of metals other than thallium added that form the complex compound is determined by the structure of the complex compound and the amount of thallium added, but the structure of the complex compound should be selected so that the amount is 0.5 to 2 times that of thallium. be. Therefore, the addition range of the thallium complex compound is 0.0005 to 0.03 gram equivalent per kilogram of finished catalyst, preferably 0.001 to 0.02 gram equivalent, optimally 0.002 gram equivalent.
~0.01 gram equivalent. Any conventionally known method can be used to prepare the catalyst, but generally 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 an aqueous silver lactate solution is used. , etc. are impregnated into the carrier as described above. The complex compound of thallium and boron or the complex compound of thallium and titanium may be precipitated on the carrier before the silver, but since this increases the number of steps by one, it is better to impregnate the complex compound at the same time as the silver solution. Next, the impregnated carrier may be heated to decompose 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, the sodium content as a porous refractory carrier is 0.07.
Weight% or less, 1 to 5 m ² /g, preferably 1 to 3 m ^{2 /} g
Specific surface area of g, apparent porosity of 25-60%, 0.2-0.5
A granular α-alumina support with a specific pore volume of ml/g and a particle size of 3 to 20 mm is used, and after impregnating it with a degradable silver solution such as an amine solution of organic acid silver,
Reduce or thermally decompose by heating to ~300℃. 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 complex of thallium is preferably in the form of an aqueous or alcoholic solution of boron and thallium, titanium and thallium, particularly and most preferably thallium borate or thallium titanate, at a concentration of 0.0005 g/kg 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 precipitated onto the support prior to the silver. The thallium complex compound-containing silver catalyst is finally activated by air flow at 100 to 400°C for 24 to 100 hours to complete the catalyst. In the method of producing ethylene oxide by oxidizing ethylene with molecular oxygen using the silver catalyst prepared by this method, all the conditions known in this field can be adopted. However, the typical conditions at the production scale, i.e. 0.5 to 40% ethylene by volume as the raw gas composition,
3 to 10% by volume of oxygen, 5 to 30% by volume of carbon dioxide, the balance being nitrogen, inert gas such as argon, water vapor, etc., lower hydrocarbons such as methane, ethane, etc. Ethylene dichloride, diphenyl chloride, etc. as reaction inhibitors. halogen compound 0.1~10ppm, reaction temperature 150~300℃, space velocity 3000~10000hr ^-1
(STP), a pressure of 2 to 40 Kg/cm ² G, etc. 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 Acetic acid A solution of 690 g of silver dissolved in 600 ml of hot water was added dropwise to 560 ml of ice-cooled ethanolamine, stirred well, and 100 ml of a 4.7% by weight thallium borate aqueous solution was added.
was added to prepare an impregnating solution. This solution had an apparent porosity of 56%, a BET specific surface area of 1.54 m ² /g, a specific pore volume of 0.34 ml/g, a particle size of 5 mm, and a preheated solution with a sodium content of 0.05% by weight or less (mainly as Na ₂ O). It was impregnated into 4000ml of α-alumina carrier. 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 circulated through the catalyst layer while gradually increasing the temperature from 100°C to 240°C, and the catalyst was activated by air at 240°C for 24 hours. Next, the temperature of the heating medium 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, the remainder being nitrogen, methane,
A raw material mixed gas consisting of an inert gas such as ethane, argon, etc. and 1 ppm of ethylene dichloride was introduced, and the reaction pressure was 24 Kg/cm ² G, the space velocity was 3000 hr ^-1 (STP), and the heating medium temperature was raised to 201°C. I went there. The reaction results after 10 days and after 1 year were as 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 specific pore volume.
A catalyst was prepared in the same manner as in Example 1 except that an α-alumina support with a particle size of 0.31 cc/g and a particle size of 5 mm and a sodium content of 0.40 wt% (mainly as N ₂ O) was used, and the reaction temperature (heating medium) was The reaction was carried out in the same manner except that the temperature (temperature) was 215°C. The results were as shown in Table 1.

[Table] Examples 2 to 3 The same procedure as in Example 1 was carried out except that the catalyst and reaction temperature shown in Table 2 were changed. The results were as shown in Table-2. Comparative Example 2 The same procedure as Comparative Example 1 was conducted except that thallium borate was not added and the reaction temperature was changed to the one shown in Table 2. The results are as shown in Table-2. Comparative Example 3 The same procedure as in Example 1 was conducted except that thallium borate was not added and the reaction temperature was changed to the one shown in Table 2. The results were as shown in Table-2. Comparative Examples 4 to 5 The same procedure as in Example 1 was carried out except that the catalyst and reaction temperature were changed to those shown in Table 2. The results were as shown in Table-2.

【table】

Claims (1)

[Scope of Claims] 1. An α-alumina main component carrier having a sodium content of 0.07% by weight or less and a specific surface area of 1 to 5 m ² /g is decomposed to a silver loading rate of 5 to 25% by weight relative to the finished catalyst. per kilogram of finished catalyst in silver solution
A silver catalyst for producing ethylene oxide, which is produced by impregnating with an impregnating liquid containing 0.0005 to 0.03 gram equivalent of a complex compound of thallium and boron or a complex compound of thallium and titanium, followed by heating and reduction or thermal decomposition. . 2. The silver catalyst according to claim 1, wherein the complex compound of thallium and boron is thallium borate. 3. The silver catalyst according to claim 1, wherein the complex compound of thallium and titanium is thallium titanate. 4. The amount of thallium and boron complex compound or thallium and titanium complex compound contained in the decomposable silver solution is 0.001 to 0.02 per kilogram of finished catalyst.
The silver catalyst according to any one of claims 1 to 3, which is in gram equivalent.