JPH0236296B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heteropolyacid-based shaped catalyst composition containing whiskers. To be more specific, the present invention molds a heteropolyacid catalytic active component based on molybdophosphoric acid or molybdovanadophosphoric acid in the coexistence of whiskers, thereby achieving excellent mechanical strength (crushing strength, abrasion resistance) for industrial use. To provide a shaped catalyst composition which exhibits excellent catalytic performance when producing methacrylic acid by oxidizing or oxidatively dehydrogenating methacrolein, isobutyraldehyde or isobutyric acid in the gas phase. With the goal. It has been known to use inorganic fibers or whiskers themselves as catalyst carriers (Japanese Patent Publication No. 53-38264).
(See the specifications of publications such as JP-A-58-3642, JP-A-58-3643, and JP-A-53-50051). However, the purpose of the catalysts disclosed in these publications is to use glass fibers, asbestos, or whiskers as a means for highly dispersing a catalytically active substance, that is, as a carrier, and the purpose of the present invention is to use whiskers as a catalytically active substance. It is not used as a molding aid, that is, it is not used as a molding aid. Furthermore, a method of adding inorganic fibers and organic fibers to a catalyst material to obtain a shaped catalyst with high strength is also known (Japanese Patent Publication No. 51-7475, Japanese Patent Publication No. 51-20357, etc.). However, until now, there have been no examples in which whiskers have been specifically used as shaping aids for catalysts based on heteropolyacid compounds, and even more so, there have been no examples in which whiskers having a specific range of shapes as disclosed in the present invention have been used as shaping aids. unknown. On the other hand, phosphorus is generally used as a catalyst for producing methacrylic acid through a catalytic gas phase reaction of methacrolein, isobutyraldehyde, isobutyric acid, etc.
Catalysts based on molybdenum or phosphorus-molybdenum-vanadium are excellent, and many reports have been made on these catalysts. Chemically, these compositions such as phosphorus-molybdenum or phosphorus-molybdenum-vanadium have a heteropolyacid structure, molybdophosphoric acid or molybdovanadophosphoric acid, and catalyst compositions based on these heteropolyacids themselves It has the disadvantage of extremely poor moldability, and various studies have been conducted on the form of the catalyst, mechanical strength, etc. in order to make it a practical catalyst. Regarding the form of the catalyst, commonly used are supported catalysts in which catalyst components are adhered to a suitable carrier, pressure-molded catalysts by tablet molding or extrusion molding, and granulated catalysts by tumbling granulation. Which form to use is determined by comprehensively considering the properties of the catalytic material, catalytic performance, and mechanical strength. It is extremely difficult to make it into a catalyst, and various reports have been published on its improvement. For example, JP-A-56-37050 discloses a catalyst composition in which an alkali metal element is added to phosphorus-molybdenum-vanadium and is supported on a heat-resistant inorganic substance to improve mechanical strength. Generally, when a supported catalyst is used in a catalytic gas phase reaction, it has the advantage of suppressing heat generation in the catalyst layer and suppressing sequential reactions of the target products, but the reaction temperature must be raised to maintain sufficient catalytic activity. As a result, there is a drawback that the life of the catalyst is likely to be adversely affected. Furthermore, when the catalyst material is pressure-molded by tablet molding or extrusion molding, the surface area and pore volume of the catalyst change, resulting in an undesirable phenomenon in which the catalyst performance deteriorates.
Moreover, as mentioned earlier, substances based on heteropolyacid compounds have the disadvantage that they are difficult to mold, so if only the catalyst material itself is molded without using molding aids or binders, sufficient mechanical strength can be achieved. It will not be something with. Moreover, when a molded catalyst is molded to give it strength, the catalyst performance generally deteriorates. As an example of solving such problems with shaped catalysts, for example, Japanese Patent Application Laid-Open No. 56-24048 describes a catalyst composition in which phosphorus-molybdenum and other metal elements are added to a catalyst composition in which a volatile substance or a fine powder carrier is added. A method is disclosed in which the surface area and pore volume of a catalyst are defined within a preferable range by molding, thereby providing strength without deteriorating catalyst performance. Further, Japanese Patent Publication No. 51-20357 discloses a method of mixing a catalyst composition with heat-resistant fibers such as glass fibers and ceramic fibers and extrusion molding the mixture to obtain a molded catalyst with high mechanical strength.
However, when the present inventors conducted various studies on the above method, it was found that mechanical strength would not be sufficient even when applied to a catalyst based on a heteropolyacid compound. Thus, it has been found that in any of these methods, the catalyst is insufficient in both mechanical strength and performance from the viewpoint of industrial use. Moreover, when performing a catalytic gas phase reaction industrially, there are various restrictions imposed by the reactor. For example, in a fixed bed reactor, catalyst destruction and powdering occur inside the reactor when filling the reaction tube with the catalyst and during the reaction. This may lead to an increase in the pressure drop or an increase in the blower load, and also lead to serious problems during production, such as automation of reaction raw materials and products and sequential reaction enhancement due to the increase in reaction pressure drop. On the other hand, JP-A-57-12830, JP-A-57-171443
-4 and JP-A-57-177347-8, a catalyst based on a heteropolyacid compound is prepared in the presence of a nitrogen-containing heterocyclic organic compound (for example, pyridine, piperidine, piperazine, etc.), and mechanically It has been reported that a catalyst with high strength and catalytic performance suitable for industrial use was obtained. However, in this technique, the preparation method is sometimes complicated, and there remains dissatisfaction in terms of industrial implementation. The present inventors improved these known techniques, searched for a catalyst that could be industrially manufactured and used as a practical catalyst, and developed the present invention. The present invention relates to a catalyst composition based on molybdophosphoric acid or molybdovanadophosphoric acid containing whiskers, and the above-mentioned heteropolyacid in which the whiskers have an average diameter of 5 microns or less and an average length of 1000 microns or less. A catalyst composition based on the compound is provided. According to the findings of the present inventors, the catalyst of the present invention obtained by combining a catalyst composition based on a heteropolyacid compound and a whisker and molded by extrusion molding, for example, has excellent crush strength, abrasion resistance, and drop strength as compared with the heteropolyacid compound. However, this catalyst is so excellent that it is hard to imagine.
When it was used in the catalytic gas phase reaction of isobutyraldehyde or isobutyric acid, no decrease in activity or selectivity for methacrylic acid was observed, and on the contrary, it became clear that the activity was improved. Moreover, although it has been conventionally said that products formed into cylindrical shapes (rings) by extrusion molding are generally weak in mechanical strength, there is no problem in mechanical strength even if rings are molded according to the method of the present invention. Moreover, the selectivity for methacrylic acid was further improved, and a catalyst which was industrially very advantageous as a catalyst for producing methacrylic acid by catalytic gas phase reaction was completed. In the present invention, extrusion molding is preferably employed as the catalyst molding method. This is because it is judged to be preferable after comprehensively considering ease, yield, reproducibility, and performance during catalyst production, but the method is not necessarily limited to extrusion molding, and generally known tablet molding can be used. The present invention can be applied to any of the following methods: method, rolling granulation method, and marmerizer molding method. The present invention will be explained in more detail below. A whisker is generally considered to be a single crystal fiber with a diameter of 200 microns or less and a length to diameter (aspect ratio) of 10 or more, but recently it has been interpreted broadly to include polycrystalline fibers. In the present invention, the average diameter is 5 microns or less, and the average length is 5 microns or less.
Those with a diameter of 1000 microns or less are preferably used. The material of the whiskers used in this invention is not limited to metals, but may also be refractories; specifically, metals such as tungsten, iron, and nickel, silicon carbide, boron carbide, titanium carbide, silicon nitride, silica alumina, Whiskers made of alumina oxide, titanium oxide, beryllium oxide, potassium titanate, calcium phosphate, etc., produced by known methods and remaining as whiskers in the shaped catalyst targeted by the present invention, are those made of the above materials. Any of these can be suitably used. As a result of various studies on the shape of the whiskers used, we found that the diameter and length may have a subtle effect on the mechanical strength of the catalyst. It has been found that mechanical strength is dramatically improved when the diameter is 1000 microns or less, preferably 500 microns or less. The whisker content can be effective with a small amount relative to the catalyst, but it varies somewhat depending on the type of whisker, and can be contained in a range of 1 to 50% by weight relative to the catalyst. Although there are many unknown points regarding the cause of the effect when using this specified whisker, it is thought to be as follows. In other words, in a heteropolyacid-based catalyst, the size of the constituent particles depends on the preparation conditions, but observation results show that they are spherical or block-shaped, about 1 micron or less, and therefore, the smaller the whisker diameter and the shorter the length to some extent. It is thought that the dispersion is better as the amount increases, and even in a small amount, it mechanically matches well with the catalyst particles, resulting in a revolutionary improvement in physical strength. The composition of the catalyst constituent elements that can be applied to this invention is not particularly limited as long as it is mainly composed of heteropolyacid compounds such as molybdophosphoric acid, molybdovanadophosphoric acid, and metal salts thereof.
In order to produce methacrylic acid in high yield, the following general formula P _a Mo _b V _c X _d Y _{e Of} [where P is phosphorus, Mo is molybdenum, V is vanadium, and X is an alkali metal and/or One or more elements selected from alkaline earth metal elements; Y is one or more elements selected from copper, silver, arsenic, antimony, tellurium, cobalt, bismuth, tungsten, and zirconium; O represents oxygen; . The subscripts a, b, c, d, e, and f represent each atomic ratio. When b = 12, a = 0.1 to 3.0, preferably 0.5 to 1.5, c = 0 to 6.0, preferably 0.1 to 2.5, and d = 0.05 to 5.0. Preferably 0.1-2.0 e=0.01-5.0 Preferably 0.05-2.0 f is a numerical value determined by the valence and atomic ratio of each element. ] A composition represented by the following is preferable. Furthermore, various catalyst raw materials can be used. Examples of phosphorus compounds include orthophosphoric acid,
Examples of molybdenum compounds such as disodium hydrogen phosphate, monoammonium phosphate, and diammonium phosphate include molybdenum trioxide, molybdic acid, sodium molybdate, ammonium paramolybdate, and phosphomolybdate; examples of vanadium compounds include vanadium pentoxide. , ammonium metavanadate, sodium metavanadate, vanadyl oxalate, vanadyl sulfate, etc. In addition, the X and Y components are selected from hydroxides, nitrates, sulfates, carbonates, halides, ammonium salts, oxyacids, etc. of the respective elements. The catalyst is prepared using phosphorus-molybdenum or phosphorus-molybdenum.
It is applicable to all known catalyst preparation methods based on molybdenum-vanadium. For example, to a previously prepared aqueous solution of molybdophosphoric acid or molybdovanadophosphoric acid, an aqueous solution of the compound of the other element required is added to create a slurry-like material, an appropriate amount of whiskers is added thereto, and the mixture is evaporated to dryness and then ground. to produce a whisker-containing heteropolyacid compound-based powder. Alternatively, the raw materials of phosphorus, molybdenum, vanadium and other necessary additional metal elements are added to water to form a slurry-like material, an appropriate amount of whiskers is added thereto, evaporated and dried, and then ground to obtain whisker-containing powder. After adding a small amount of water to the powder obtained in this way and mixing it thoroughly, an extrusion molding machine is used to mold the powder into, for example, 5.5 mmφ.
It is molded into a cylindrical shape of x6 mmL or a ring with a space of through hole inner diameter 2.0 mmφ in the outer shape of the cylinder, and after drying, it is calcined at 350 to 400°C in the presence of air to obtain a catalyst. Further, when the present invention is used in combination with the catalyst preparation method using the nitrogen-containing heterocyclic organic compound described above, a step of eliminating the organic compound is added before calcination. That is, heat treatment may be performed in an atmosphere of an inert gas (for example, nitrogen, helium, argon, carbon dioxide) or a reducing gas such as a hydrocarbon at a temperature in the range of 200 to 600°C. In addition to the timing mentioned above, whiskers may be added by any method in which the starting materials of the catalyst constituent elements are made into a slurry in the presence of water, and the slurry is mixed into the powder obtained by evaporation, drying, and pulverization. All of the catalysts obtained in this manner are in an extremely good molded state, and the results of mechanical strength measurements of these catalysts also show that they are extremely excellent. As described above, the whisker-added catalyst of the present invention not only makes it possible to mold heteropolyacid compound-based catalysts as desired and use them industrially, which has been considered difficult until now, but also improves the physical properties of the catalyst. This not only increases activity but also alleviates heat accumulation in the catalyst layer, resulting in the advantages of suppressing undesirable sequential reactions and improving reaction selectivity. It has been found. When the catalyst of the present invention is used in a catalytic gas phase reaction, methacrolein, isobutyraldehyde or isobutyric acid is used as a raw material, and molecular oxygen is mixed with any of these to carry out the reaction. Air is industrially advantageous as an oxygen source, and inert gases such as nitrogen, carbon dioxide, helium, argon, carbon monoxide, and water vapor can be used as diluents, but the use of water vapor is particularly This is also advantageous for the purpose of suppressing by-products. The raw material concentration targeted in the reaction is 0.5 to 10
A range of % by volume is preferred. The volume ratio of oxygen to raw material is in the range of 0.5 to 10. The space velocity of the supplied gas is suitably in the range of 100 to 5000 hr ^-1 (STP). When using a catalyst, the reactor is generally in a fixed bed format, but as mentioned above, the catalyst has excellent mechanical strength, so a fluidized bed,
Any type of moving bed can be used satisfactorily. The preparation method and test results of the catalyst according to the present invention will be explained below with reference to examples, and the mechanical strength of the catalyst was measured by the following method. Compressive strength: Using a Kiya type hardness tester, a load was applied in the vertical axis direction of the catalyst particles or in a direction perpendicular to the vertical axis, and the load at which cracks occurred was measured. (The pellets were measured only in the vertical axis direction.) Abrasion degree: The catalyst was placed in a cylinder made of 12-mesh stainless steel wire mesh with an inner diameter of 100 mmφ and a width of 100 mm.
After putting 50 g of catalyst into the cylinder and rotating the cylinder continuously for 30 minutes at a speed of 100 revolutions per minute, the weight of the catalyst remaining inside the cylinder was measured, and the wear rate was calculated using the following formula. Wear rate (%) = Catalyst weight (50 g) - Catalyst weight (g) remaining in the wire mesh after rotation / Catalyst weight (50 g) x 100 Drop strength: When the inner diameter is 25 mmφ and the length is
30g of catalyst was dropped from the top of a 5000mmL iron pipe and received by a 4-mesh sieve, the weight of the catalyst remaining on the sieve was measured, and the falling strength rate was measured using the following formula. Falling strength rate (%) = Weight of catalyst remaining on the sieve (g
)/catalyst weight (30g) x 100 In addition, the conversion rate, selectivity,
Single-stream yield shall comply with the following definition. Conversion rate (%) = Number of moles of aldehyde or acid consumed/Number of moles of aldehyde or acid supplied x 100 Selectivity (%) = Number of moles of methacrylic acid or methacrolein produced/Number of moles of aldehyde or acid consumed ×100 Single flow yield (%) = Number of moles of methacrylic acid produced/Number of moles of aldehyde or acid supplied ×100 Also, in the description of the shape of the catalyst, the pellet is a cylinder of 5.5 mmφ x 6 mmL, and the ring is 5.5 mm. mmφ
It means a cylindrical piece measuring 6mmL with a through hole of 2mmφ in inner diameter. Example 1 441.4 g of ammonium paramolybdate and 24.4 g of ammonium metavanadate in 1000 ml of heated water
g was dissolved and stirred. A solution of 31.2 g of phosphoric acid (84% by weight) dissolved in 100 ml of water was added to this solution and stirred to obtain a slurry based on a phosphorus-molybdenum-vanadium compound. Add cesium nitrate to this slurry.
40.6g dissolved in 200ml water and silicon carbide whiskers (fiber diameter 0.1~0.5μm, length 10~
100 μm) was added, evaporated and dried, and the resulting solid was pulverized to obtain powder as a molding raw material. After adding a small amount of water and mixing well, this powder was formed into pellets using an extrusion molding machine, dried at 250°C, and then calcined at 400°C for 4 hours under air circulation to obtain an atomic ratio of P _1.3 excluding oxygen.
Catalytic oxide with composition Mo ₁₂ V ₁ Cs ₁ (whiskers 2
(wt% content) was obtained. The results of measuring the mechanical strength of this catalyst are shown in Table 1. Reaction method: Fill a stainless steel U-shaped tube with an inner diameter of 25 mmφ with 50 ml of catalyst, immerse it in a molten salt bath at 280°C, and add methacrolein: oxygen: nitrogen: water = 1:5 by volume into the tube.
The reaction was carried out by passing a 34:10 raw material gas mixture at a space velocity of 1000 hr ^-1 . The reaction results are shown in Table-1. Comparative Example 1 Table 2 shows the strength measurement results of a catalyst prepared in the same manner as in Example 1 except that the amount of silicon carbide whiskers was zero, but the molding condition was also much worse than that of the catalyst of Example 1. From a practical standpoint, this was not entirely satisfactory. The same reaction as in Example 1 was carried out using this catalyst, and the results were as shown in Table 2. Example 2 The amount of whiskers used in Example 1 was 23.8g.
A catalyst was prepared in the same manner except for the following. Table 1 shows the strength measurement results and the results obtained when reacting under the same conditions as in Example 1. Example 3 A catalyst was prepared in the same manner as in Example 2 except that the catalyst was molded into a ring shape during extrusion molding. Table 1 shows the catalyst strength measurement results and the results obtained when the reaction was carried out under the same conditions as in Example 1. Comparative Examples 2 to 4 The same operation as in Example 1 except that the whiskers used in Example 1 were replaced with other fibers or fine powder shown in Table 2, and the amount used and catalyst were changed to those shown in Table 2. A catalyst was obtained, and the results shown in Table 2 were obtained. As a result of considering industrial use, the catalysts of these comparative examples all had unsatisfactory mechanical strength and could not be molded into a ring shape. Example 4 492.8 g of 12-molybdophosphoric acid was dissolved in 500 ml of water and stirred at room temperature. Add 48.7 cesium nitrate to this solution.
g, a solution of 5.0 g of copper nitrate dissolved in 200 ml of water and silicon nitride whiskers (0.2 to 0.5 μmφ x 50 to 300 μm
ml) was added, evaporated to dryness, and pulverized to obtain a powder as a molding raw material. This powder is thoroughly mixed with a small amount of water, molded into a ring using an extruder, and dried at 370°C.
By firing in an air stream for 4 hours to remove oxygen, the atomic ratio
A catalyst oxide having a composition of P ₁ Mo ₁₂ Cs _1.2 Cu _0.1 (containing 5% by weight of whiskers) was obtained. Table 3 shows the results of measuring the mechanical strength of this catalyst. Using this catalyst, a reaction was carried out in the same manner as in the reaction example of Example 1, except that the reaction temperature was changed to 320°C, and the results shown in Table 3 were obtained. Comparative Example 5 A catalyst was prepared in the same manner as in Example 4 except that the amount of silicon nitride used was zero, and the reaction was carried out under the same conditions as in Example 4 to obtain the results shown in Table 4. Example 5 441.4 g of ammonium paramolybdate and 18.3 g of ammonium metavanadate in 1000 ml of heated water
g was dissolved and stirred. 100g of pyridine in this solution
and 31.2 g of phosphoric acid (85% by weight) were added, followed by a solution of 200 ml of nitric acid (specific gravity 1.38), 21.4 g of rubidium hydroxide and 3.5 g of silver nitrate dissolved in 200 ml of water, and while stirring, potassium titanate whiskers (0.2 47.5 g of ~0.5 μmφ×10-100 μml) was added and concentrated by heating. After drying, the resulting clay-like material was crushed, mixed well with a small amount of water, and formed into a ring shape using an extruder. After drying at 250℃, it was heated at 450℃ in a nitrogen stream.
The mixture was calcined for 4 hours at 400°C in an air stream for 2 hours to obtain a catalyst oxide (containing 10% by weight of whiskers) having an atomic ratio of P _1.3 Mo ₁₂ V _0.75 Rb _1.0 Ag _0.1 excluding oxygen. The results of measuring the mechanical strength of this catalyst and the results of the reaction under the same reaction conditions as in Example 1 (however, only the reaction temperature was changed to 290°C) were as shown in Table 3. Example 6 The following changes were made in Example 5: the amount of ammonium metavanadate was changed to 24.4 g, the amount of rubidium hydroxide was changed to 48.7 g of cesium nitrate, and the amount of potassium titanate whisker was changed to 47.5 g as in Example 1. 33.3g of silicon carbide whiskers,
Furthermore, it was prepared in the same manner as in Example 5 except that the catalyst shape was changed to pellets, and the atomic ratio excluding oxygen was P _1.3.
A catalyst oxide having a composition of Mo ₁₂ V ₁ Cs _1.2 Ag _0.1 (containing 7% by weight of whiskers) was obtained. Table 3 shows the results of measuring the mechanical strength of this catalyst and performing the reaction under the same reaction conditions as in Example 1. Example 7 A catalyst was prepared in the same manner as in Example 6 except that the shape of the catalyst was changed to a ring. Table 3 shows the strength measurement results and the results of the reaction under the same conditions as the reaction example of Example 1. Comparative Example 6 The catalyst of Example 7 was prepared without silicon carbide whiskers. The table below shows various measurement results for this catalyst.
4. Comparative Example 7 In the catalyst of Example 7, silicon carbide whiskers were replaced with the same amount of fumed silica (Aerosil 10).
~40 μm). Various measurement results of this catalyst are shown in Table 4. Example 8 Everything was prepared in the same manner as in Example 6 except that the amount of ammonium metavanadate was 36.6 g, the amount of silver nitrate was 7.1 g, and the amount of silicon carbide whisker was 71.4 g, and the atomic ratio excluding oxygen was P _1.3.
A ring-shaped catalyst oxide (containing 15% by weight of whiskers) with the composition Mo ₁₂ V _1.5 Cs _1.2 Ag _0.2 was obtained. The mechanical measurement results of this catalyst are shown in Table 5. Further, using this catalyst, the reaction was carried out in the same manner as in the reaction example of Example 1 except that methacrolein was replaced with isobutyraldehyde, and the results were as shown in Table 5. Comparative Example 8 A catalyst was obtained in the same manner as in Example 8 except that the amount of silicon carbide whiskers was reduced to zero. Table 5 shows the results of measuring the mechanical strength of this catalyst and the results obtained when the same reaction as in Example 8 was carried out. Example 9 441.4 g of ammonium paramolybdate and 30.5 g of ammonium metavanadate in 1000 ml of heated water
g was dissolved and stirred. 100g of pyridine in this solution
and 36.0 g of phosphoric acid (85% by weight) were added, followed by 200 ml of nitric acid (specific gravity 1.38), a solution of 40.6 g of cesium nitrate, 8.8 g of strontium nitrate, 10.1 g of copper nitrate dissolved in 200 ml of water, and 15.2 g of antimony trioxide. The mixture was heated and concentrated while stirring. The obtained clay-like substance was dried and pulverized to obtain a powder. 71.4 g of the same silicon dioxide whisker used in Example 4 and a small amount of water were added and mixed thoroughly, and then molded into a ring shape using an extrusion molding machine. This was dried at 250°C, then fired at 450°C in a nitrogen stream for 4 hours, and then fired at 400°C in an air stream for 2 hours to give an atomic ratio of P _1.5 Mo ₁₂ V _1.25 Cs _1.0 excluding oxygen.
Catalytic oxide (whisker) with composition Sr _0.2 Cu _0.2 Sb _0.5
(containing 15% by weight). Table 5 shows the results of measuring the mechanical strength of this catalyst. Fill a stainless steel U-shaped tube with an inner diameter of 25 mmφ with 50 ml of this catalyst, immerse it in a molten salt bath at 270°C, and fill the tube with a volume ratio of isobutyric acid: oxygen: nitrogen: water = 2:
The reaction was carried out by passing a mixed gas of 3:90:5 at a space velocity of 2000 hr ^-1 . The reaction results are shown in Table-5. Comparative Example 9 A catalyst was prepared in the same manner as in Example 9 except that the amount of silicon dioxide whiskers used was zero. Table 5 shows the results of measuring the mechanical strength of this catalyst and the results of the oxidation reaction of isobutyric acid under the same conditions as in Example 9.

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Claims (1)

[Claims] 1. A shaped catalyst composition with excellent mechanical strength, comprising a heteropolyacid-based compound containing whiskers. 2. The catalyst composition according to claim 1, wherein the heteropolyacid is molybdophosphoric acid or molybdovanadophosphoric acid. 3. The catalyst composition according to claim 1, wherein the whiskers have an average diameter of 5 microns or less and an average length of 1000 microns or less.