JPH0448498B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a heteropolyacid catalyst for synthesizing methacrylic acid by catalytic gas phase oxidation or oxidative dehydrogenation of methacrolein, isobutyric acid, or isobutyraldehyde. Specifically, the present invention provides a catalyst that has strong physical strength and high selectivity for methacrylic acid and is used when producing methacrylic acid by catalytic gas phase oxidation or oxidative dehydrogenation of methacrolein, isobutyric acid, or isobutyraldehyde. Long-life phosphorus, molybdenum,
The present invention relates to a method for producing a catalyst whose main component is a heteropolyacid consisting of vanadium, an alkali metal salt thereof, and/or a partially substituted compound thereof. Methacrolein, isobutyric acid, or isobutyraldehyde is reacted with molecular oxygen at high temperature in the presence of a catalyst mainly composed of a heteropolyacid consisting of phosphorus, molybdenum, and vanadium or its alkali metal salt and/or a partially stationary compound thereof. Many catalysts have been proposed for producing methacrylic acid. For example, Special Publication No. 54-14089,
JP-A No. 53-31615 has PMoV system, JP-A-Sho 50-
No. 82013, JP-A-51-113818, JP-A-56-37050
PMoV in JP-A-57-297, JP-A-50-123619, JP-A-52-62220, and JP-A-55-2619.
(Alkali metal or Tl) based catalysts have been proposed. Although some of these exhibit relatively high conversion rates and selectivities, many of them are far from being industrial catalysts. This is because the catalyst strength, which is an essential condition for an industrial catalyst, is insufficient, and many of them only disclose small-scale laboratory reaction results. Industrial catalysts are required to have strength, such as crushing strength and abrasion resistance, to withstand collapse and powdering of the catalyst when it is transported or packed into a reactor. However, heteropolyacid catalysts were said to have weak physical strength. JP-A-56-37050 discloses that in order to give strength to these heteropolyacid catalysts, the carrier has an apparent porosity of 35 to 60%, an absorption rate of 20 to 50%, and an average pore diameter.
A supported catalyst using a heat-resistant inorganic material having a particle size of 40 microns or more, a specific surface area of 2 m ² /g or less, and a bulk specific gravity of 1.5 to 2.0 and a particle size of 3 to 10 mm is proposed. However, this supported catalyst has low catalytic activity. That is, the reaction temperature becomes as high as 350° C. when the contact time is 6 to 7.5 seconds, which poses a problem in terms of lifespan considering that heteropolyacids are thermally unstable. In addition, some of the inventors of the present invention previously discovered that not only catalytic performance but also mechanical strength could be improved by preparing a heteropolyacid catalyst in the presence of a nitrogen-containing heterocyclic compound, and filed a patent application (Japanese Patent Application Laid-Open No. No. 57-12830,
(No. 171443, No. 171444, No. 177347). However, it has been found that stronger catalysts are desirable as industrial catalysts. The present inventors conducted extensive research on catalysts containing phosphorus, molybdenum, and vanadium-containing heteropolyacids or their alkali metal salts and/or partially substituted compounds thereof as catalysts for methacrylic acid synthesis. The present invention was completed after discovering that a catalyst extruded with a specific amount of graphite added thereto has significantly increased physical strength, increased selectivity for methacrylic acid production, and extended catalyst life. did. The present invention relates to phosphorus-, molybdenum-, and vanadium-containing heteropolyacids or their alkali metal salts, which are used to synthesize methacrylic acid by reacting methacrolein, isobutyric acid, or isobutyraldehyde with molecular oxygen at high temperatures in the presence of a catalyst. When producing a catalyst for producing methacrylic acid whose main component is a partially substituted compound of The present invention relates to a method for producing a catalyst for producing methacrylic acid, which has strong physical strength and improved selectivity, and is characterized by extrusion molding the catalyst containing 50μ scale-like graphite. The method of adding graphite as a molding aid to molding a molded catalyst is a conventionally well-known method, and heteropolyacid catalysts have already been described in several publications. For example, Tokkosho
No. 56-38261 includes an example of adding talc and graphite to PMoCuAs (NH ₄ ), Japanese Patent Publication No. 58-26329.
The number includes MoP - one or more alkaline earth metals - one or more alkali metals Tl - one or more V, W, Ni,
JP-A-51-11710 describes MoPCs - one or more of V, Nb, Ta - one or more of Tl, Ni, W, Pd,
No. 51-47590 has PMo-X (X: A group, one or more of A group), and JP-A-51-113818 has
PMoVKCs is also published in Japanese Patent Application Laid-open No. 58-65240.
Examples are described in which graphite is added and molded to a PMoCu (Kcs)-based catalyst composition.
However, in all of the methods of these Examples, graphite was added as a lubricant during tableting. Although the addition of graphite in the tableting method is effective in improving the moldability (slippage of the catalyst material), it has no effect on improving the catalyst strength, and on the contrary, it may impair the activity and selectivity of the catalyst. many. This is because the tablet-forming method simply mixes dried or calcined catalyst powder with graphite and molds it using only a compression operation, so the adhesion between the powders is weak and mechanical strength, especially abrasion resistance, becomes weak. It is thought that this is because of this. In addition, because it is a dry molding process, the amount of substances that are scattered during subsequent calcinations is small, or the pores are crushed due to strong compression, which reduces the pore volume and reduces the activity and selectivity of the catalyst. It is unavoidable to do so. On the other hand, in the extrusion molding method of the present invention, the catalyst material is not only simply mixed with graphite, but also kneaded through a medium such as water, so the adhesion becomes very dense and the material is further compressed and extruded. The target strength is improved. In addition, it has been found that since a large amount of substances are scattered during subsequent drying and calcination, the effective pore volume is large, and the catalytic activity and selectivity are increased. That is, in the present invention, when graphite is mixed into the catalyst material and a molded catalyst is produced by extrusion molding, substances that can be dispersed at high temperatures, such as water, alcohol, starch, wax, polyvinyl alcohol, and stearin, are added. It was discovered that the desired porosity can be imparted by coexisting organic acids such as acid, linoleic acid, ammonium nitrate, ammonium carbonate, carboxymethyl cellulose, and the like. According to the present invention, when producing a phosphorus, molybdenum, and vanadium-based heteropolyacid catalyst, the following characteristics can be pointed out by adding graphite to the catalyst material and molding it. (1) Physical strength (compressive strength, abrasion resistance, etc.), which is an essential condition as an industrial catalyst, increases dramatically.
For example, a catalyst made of PMoVCs is 5 mmφ x 5.5
When extruded into mmL pellets, the degree of pulverization of the catalyst molded without adding graphite (100 g of catalyst was
When placed in a x100mmL cylinder and rotated at 100rpm for 30 minutes, the weight loss (weight%) is 50% and the crushing strength (according to the Kiya hardness tester) is 0.4Kg/pellet (Comparative Example 1) Graphite A catalyst molded by adding 2% by weight of the powder showed a degree of pulverization of 3% and a crushing strength of 3.0 kg/pellet (Example 1). The effect of adding graphite is particularly remarkable in improving wear resistance. The reason for the remarkable improvement in catalyst strength is not clear, but differential thermal analysis and thermogravimetric analysis show that the added graphite does not burn and scatter at temperatures below 500°C, so it remains in the catalyst and combines with catalyst components in some way to improve catalyst strength. It is thought that this contributes to (2) When this catalyst is used in the methacrolein oxidation reaction, the maximum temperature of the catalyst layer due to the exothermic reaction is lowered, and the selectivity of methacrylic acid production is improved. This is thought to be because the graphite remaining in the catalyst has high thermal conductivity, which can increase the reaction heat removal rate and prevent the generated methacrylic acid from being further oxidized to carbon oxides. It will be done. (3) Since the maximum temperature of the catalyst layer is kept low and local high temperatures do not occur, the life of the catalyst is extended. (4) Since the catalyst strength increases, it becomes possible to mold it into a ring-shaped catalyst, and the advantages of a ring-shaped catalyst (improved selectivity, reduced pressure loss, improved catalyst life, etc.) can also be enjoyed. The ring-shaped catalyst has an outer diameter of 3 to 10 mm and a length of 0.5 to 2.0 mm of the outer diameter.
It is recommended to have a through hole that is 0.1 to 0.7 times the outer diameter. The present invention is effective for catalysts for producing methacrylic acid whose main components are heteropolyacids containing phosphorus, molybdenum _, or vanadium or their alkali metal salts and/or partially substituted compounds thereof. In the formula, X is one or more types of KRbCs, and Y is
Indicates one or more selected from CuSbAsFeCoMnWCr, and subscripts a to d are when Mo=12, a=0.5 to 3, b
= 0.1 to 3, c = 0 to 3, d = 0 to 3. Further, e takes a value determined by the valence of each element. ) The effect is remarkable when used. The amount of graphite used is 0.5 to the catalyst material
The effect is remarkable when molding is performed by adding ~5% by weight, preferably 1 to 3% by weight. If the amount used is less than 0.5% by weight, the effect of its addition is not clear, and if it is added more than 5% by weight, the catalyst strength will not improve as expected and the catalyst activity will decrease, which is not preferable. Graphite can be added at any stage before molding as long as it can be mixed uniformly with the catalyst material, but it is convenient to add it to the powder after drying and pulverization or to the clay-like material just before molding. High-temperature scattering additive when used in combination with graphite,
For example, 0.1 to 2% by weight of water, alcohol, starch, polyvinyl alcohol, organic acids such as stearic acid, their esters, carboxymethyl cellulose, ammonium nitrate, ammonium carbonate, etc.
A range of additives are used. Of course, if these conventionally known additives are added alone, along with talc, stearate, etc., the effects disclosed by the present invention cannot be obtained. The catalyst material itself according to the invention is prepared by known methods. For example, it is obtained in powder or clay form by evaporation concentration method, oxide mixing method, co-precipitation method, etc., and is baked at 300 to 450℃ after molding. It is important to use a preparation method that allows for It is also possible to use a method in which the catalyst material is prepared in the presence of a nitrogen-containing heterocyclic compound, such as pyridine, and the pyridine is removed by heat treatment after molding. The extrusion molding machine used in the present invention does not require any special equipment, and commonly used extrusion molding machines such as screw type, ram type, roll type or other types can be used. Starting materials for molybdenum used in the preparation of the catalyst of the present invention include molybdenum trioxide, molybdic acid, ammonium paramolybdate, etc. Elemental sources of phosphorus include orthophosphoric acid, phosphorus pentoxide,
Vanadium pentoxide, ammonium metavanadate, etc. can be used as a vanadium source such as ammonium phosphate. As the element source of the alkali metal, nitrate, carbonate, hydroxide, or chloride can be used, and as the element source of the Y component, nitrate, oxide, chloride, or ammonium salt of each element can be used. Phosphomolybdic acid, phosphovanadomolybdic acid, or their ammonium salts or alkali metal salts can also be conveniently used. An example of the catalyst preparation method in the present invention is shown. First, predetermined amounts of molybdenum trioxide and vanadium pentoxide are suspended in water. Add orthophosphoric acid to this and heat to reflux while stirring. Add the Y component compound, then add an aqueous alkali metal nitrate solution,
Heat and concentrate. Graphite is added to the resulting clay-like substance and mixed. If necessary, the humidity is adjusted with water or ammonium nitrate solution, extrusion molded, and after drying, the catalyst is calcined at 300 to 450°C. In the catalytic gas phase oxidation or oxidative dehydrogenation reaction according to the present invention, the feed gas composition is 1.0 to 10% by volume of a raw material compound such as methacrolein, isobutyric acid or isobutyraldehyde, and 1% by volume relative to the raw material.
-10 molecular oxygen and an inert gas as a diluent, such as nitrogen, carbon dioxide, or steam (particularly steam) is advantageous in suppressing the formation of by-products and improving the yield of the desired product. ), etc., onto the catalyst prepared as described above, at a temperature range of 200 to 400°C and a pressure of normal pressure to 10 atm, at a space velocity of 100 to 5000 hr ^-1 (STP). carried out by. When selecting methacrolein as a raw material, methacrolein does not necessarily have to be pure, and methacrolein-containing gas obtained by catalytically reacting isobutylene or tertiary-butanol can also be used. Recommended. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The conversion rate herein,
Selectivity and single flow yield are each defined as follows. Conversion rate (%) = Number of moles of reacted raw material compound / Number of moles of supplied raw material compound × 100 Selectivity (%) = Number of moles of methacrylic acid produced / Number of moles of reacted raw material compound × 100 Single flow yield (%) = Number of moles of methacrylic acid produced/Number of moles of supplied raw material compound x 100 Example 1 1766 g of ammonium paramolybdate and 106 g of ammonium metavanadate in 8000 ml of heated water
was dissolved and stirred. To this solution, 125.0 g of orthophosphoric acid (85% by weight) was added, followed by 1100 g of nitric acid, and a solution of 162.4 g of cesium nitrate dissolved in 1000 ml of water, followed by heating and concentration with stirring. The obtained slurry material was dried at 250℃ for 15 hours, crushed, added with 34g of graphite, and conditioned with water. It was then molded into a diameter of 5.0 mm and length of 6.0 mm using a screw extruder. After drying, it was air-filled. It was fired in a flowing stream at 400°C for 3 hours. The elemental composition of this catalyst oxide was Mo ₁₂ P ₁ 〓 ₃₀ V ₁ 〓 ₀₉ Cs ₁ 〓 ₀ in atomic ratio (excluding oxygen, the same applies hereinafter). 1500ml of the catalyst thus obtained was filled into a steel reaction tube with a diameter of 25.4mmφ, and a mixed gas was obtained by catalytic gas phase oxidation of isobutylene in the presence of a multi-component catalyst based on molybdenum, cobalt, bismuth, tungsten, and iron oxides. was introduced, the reaction temperature was 290℃, and the space velocity was
The reaction was carried out at 1200 hr ⁻¹ . Table 1 shows the reaction results, crushing strength measured by a Kiya hardness tester, and powdering rate. The average composition of the mixed gas was as follows. Methacrolein 3.5% by volume Isobutylene 0.04 〃 Methacrylic acid + acetic acid 0.24 〃 Water vapor 20 〃 Oxygen 9.2 〃 Other 67.0 〃 In this case, the single-stream yield of methacrylic acid based on the supplied isobutylene is 64.6 mol% in terms of the total from the previous reaction It was hot. Comparative Example 1 Example 1 except that graphite was not added
A catalyst with the same composition was obtained in the same manner. A reaction was carried out under the same conditions as in Example 1 using this catalyst. The results are shown in Table 1. Comparative Examples 2 and 3 Catalysts were obtained in the same manner as in Example 1, except that 34 g each of stearic acid and talc were added in place of graphite. Using this catalyst, a reaction was carried out under the same conditions as in Example 1, and the results shown in Table 1 were obtained. Example 2 2000g of molybdenum trioxide, vanadium pentoxide
115 g of cobaltous oxide, 43 g of cobaltous oxide, and 169 g of antimony trioxide were dispersed in 20 g of water. To this was added 146 g of 85% phosphoric acid, and after stirring under heating for about 3 hours, 377 g of cesium carbonate was added and the mixture was further boiled and refluxed for about 3 hours.
This aqueous solution was evaporated and concentrated, and 55 g of graphite was added to the resulting clay-like material, mixed well, pressed out, and fired at 350° C. for 2 hours under air circulation.
The composition of this catalyst oxide excluding oxygen is
Mo ₁₂ P ₁ 〓 ₀₉ V ₁ 〓 ₀₉ Cs ₂ 〓 ₀ Co ₀ 〓 ₅ Sb ₁ 〓 ₀ . A reaction was carried out using the thus obtained catalyst in the same manner as in Example 1 except that the reaction temperature was 310°C. Table 1 shows the reaction results and catalyst strength. Example 3 The graphite used in Example 2 was 138
A catalyst was prepared in the same manner except that g was used, and the reaction was carried out under the same conditions as in Example 2 except that the reaction temperature was changed to 320°C. Table 1 shows the reaction results and catalyst strength. Comparative Example 4 A catalyst was prepared in the same manner as in Example 2 except that graphite was not added. Using this catalyst, a reaction was carried out under the same reaction conditions as in Example 2, and the results shown in Table 2 were obtained. Comparative Example 5 A viscous substance obtained in the same manner as in Example 2 was dried,
After pulverization, 55 g of graphite was added and mixed well, and then molded into a tablet with an outer diameter of 5 mm and a length of 5 mm using a tablet molding machine, and calcined in air at 350° C. for 2 hours to obtain a catalyst. Using this catalyst, a reaction was carried out in the same manner as in Example 2, and the results shown in Table 1 were obtained. Example 4 1766 g of ammonium molybdate and 97 g of ammonium metavanadate were dissolved in 8000 ml of water, and 406 g of pyridine was added. 144g of 85% orthophosphoric acid
diluted in 400ml of water, add 40g of copper nitrate and
118 g of a 60% orthoarsenic acid solution was dissolved and added to the above aqueous solution, and the solution was aged with stirring while heating. Finally, a solution of 47 g of potassium hydroxide dissolved in 400 ml of water was added, and graphite was added to the resulting clay-like substance.
After adding 26g and mixing well, the outer diameter is 5.0mm, the length is 6mm,
It was extruded into a ring shape with a through hole diameter of 1.5 mm.
After drying, this catalyst was calcined at 430℃ for 3 hours in a nitrogen stream, and then calcined for 3 hours at 400℃ in an air stream until the atomic ratio excluding oxygen was Mo ₁₂ P ₁ 〓 ₅ V ₁ Cu ₀ 〓 ₂ K ₁ 〓 ₀ We obtained a catalyst represented by As ₀ 〓 ₆ . Using this catalyst, the reaction temperature was set to 290°C, and the reaction was carried out under the same conditions as in Example 1. Table 1 shows the reaction results and catalyst strength. Example 5 The amount of graphite used in Example 3 was
A catalyst was prepared in the same manner except that the amount was increased to 52 g, and the reaction was carried out under the same conditions as in Example 3 to obtain the results shown in Table 1. Comparative Example 6 A catalyst was prepared in the same manner as in Example 4 except that graphite was not used, and the reaction was carried out under the same conditions as in Example 3 to obtain the results shown in Table 1.

【table】

[Table] Example 6 Using the catalyst of Example 4, a mixed gas with a volume ratio of isobutyric acid:acid:steam:=5.0:10.0:10.0:75.0 was introduced at a space velocity of 2000 hr ^-1 and the reaction was carried out at a reaction temperature of 280°C. The results shown in Table 2 were obtained. Comparative Example 7 The same reaction as in Example 6 was carried out using the catalyst of Comparative Example 6, and the results shown in Table 2 were obtained.

[Table] Example 7 Using the catalyst of Example 4, isobutyraldehyde:oxygen:steam:nitrogen=5.0:12.5:10.0:72.5
A mixed gas in a volumetric ratio was introduced at a space velocity of 800 hr ^-1 and the reaction was carried out at a reaction temperature of 280° C. The results shown in Table 3 were obtained. Comparative Example 8 The same reaction as in Example 7 was carried out using the catalyst of Comparative Example 6, and the results shown in Table 3 were obtained.

【table】

Claims (1)

[Claims] 1 Phosphorus-, molybdenum-, and vanadium-containing heteropolyacids or their alkali metal salts and/or one of them are used as catalysts for synthesizing methacrylic acid by catalytic gas phase oxidation or oxidative dehydrogenation of methacrolein, isobutyric acid, or isobutyraldehyde. When producing a methacrylic acid synthesis catalyst containing a partially substituted compound as a main component, it is characterized by containing 0.5 to 5% by weight of graphite to the catalyst material and extrusion molding, which has strong physical strength. A method for producing a catalyst for methacrylic acid synthesis with improved selectivity.