JPS60209259A - Catalyst for oxidation and its preparation - Google Patents

Abstract

PURPOSE:To obtain the titled catalyst having excellent selectivity coefficient to methacrylic acid, yield, and activity and the strength of the catalyst by using molybdovanadolinic acid having a cubic crystal structure, and prepared in the presence of quinolines and/or derivatives of quinolines. CONSTITUTION:Molybdovanadolinic acid prepared in the presence of quinolines and/or the derivatives of quinolines, and having a cubic crystal structure with about 11.85Angstrom lattice constant is used as a catalyst. The catalyst is used for the gaseous phase catalytic oxidation of aliphatic aldehydes or fatty acids having 4C such as methacrolein, isobutylaldehyde, and butyric acid, and is also used as a hetropolyacid compd. catalyst for manufacturing methacrylic acid. The selectivity coefficient to methacrylic acid, yield, and activity are excellent, and the strength of the catalyst is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxidation catalyst and a method for preparing the same. Specifically, the present invention provides a heteropolyacid compound catalyst for producing methacrylic acid by catalytic gas phase oxidation of C4 aliphatic aldehydes or fatty acids such as methacrolein, imbutyraldehyde, and isobutyric acid, and a method for preparing the same. Regarding.

Hetetetrapolyacids are strongly acidic and can easily oxidize other substances such as oxidizing agents, and although they themselves are reduced, they are easily reoxidized in the presence of an appropriate oxygen source, so they can be oxidized in the gas phase. It has been highly evaluated for its ability as a commercial catalyst, and in recent years research and development has been particularly active on molypdovanadophosphoric acid among heteropolyacid compounds.

Specifically, molybdovanadophosphoric acid, a type of heteropolyacid compound, is used as a catalyst in the general process of producing methacrylic acid by gas-phase oxidation using either methacrolein, isobutyraldehyde, or inbutyric acid as a raw material. Many uses have been proposed. Molybdovanadophosphoric acid is characterized by having strong oxidizing activity in gas phase oxidation, but on the other hand, because of its strong oxidizing power, sequential reactions that further oxidize the target product tend to occur. It has the disadvantage that it is difficult to obtain with good selectivity and yield. Furthermore, from the point of view of producing practical catalysts, molybdovanadophosphoric acid has very poor catalyst formability and mechanical strength, and when various manufacturing methods are used to increase the strength, changes in the physical properties of the catalyst result in poor catalyst formability and mechanical strength. However, it has been difficult to obtain a catalyst that is strong enough to withstand industrial use and has a sufficiently satisfactory yield.

A composition consisting of molypdovanadophosphoric acid or phosphorus-molybdenum as a product and other elements added thereto is used as a catalyst, and one selected from methacrolein, isobutyraldehyde, and isobutyric acid is used as a raw material in a gas phase. As an example of producing oxidized methacrylic acid, there is
158'17, JP 49-126616, JP 52-105113, JP 53-82715, JP 55-400324, JP 56-15238, JP 50-23013 It is reported in various publications. However, these methods have a low yield of methacrylic acid, which is the target product, and are not satisfactory for industrial use.

Furthermore, JP-A No. 57-12830 discloses a method for preparing a catalyst composition from molybdovanadophosphoric acid in the presence of a nitrogen-containing heterocyclic compound having a 5-membered ring and/or a 6-membered ring. Although the yield of methacrylic acid is quite high when catalysts made by these methods are used, the space velocity of the raw material gas during the reaction is low, so the space-time yield of methacrylic acid is low and the performance of the catalyst for industrial use remains unsatisfactory. is.

The present inventors have conducted intensive research on the structure of molybdovanadratic acid, its activity for producing methacrylic acid, its selectivity, and its catalytic strength. For example, when catalytic gas phase oxidation of methacrolein was carried out using molybdovanadophosphoric acid, which has a cubic crystal structure and consists of phosphorus-molybdenum-vanadium and oxygen, the selectivity to methacrylic acid, yield, and They found that the activity was very good and the strength of the catalyst was greatly improved, and they have now completed a catalyst that is advantageous for gas phase oxidation and a method for preparing the same.

Specifically, the present invention is specified as follows.

(1) An oxidation catalyst comprising free molypdovanadophosphoric acid, characterized by having a lattice constant of about 1t and a cubic crystal structure of ssi.

(2) It is prepared in the presence of quinolines and/or quinoline derivatives, and has a lattice constant of about 1.
A method for preparing an oxidation catalyst comprising free molybdovanadophosphoric acid having a 1.85X cubic crystal structure.

The present invention will be explained in more detail below. The quinolines and derivatives thereof used in the present invention include compounds that form water-insoluble salts with molybdopanadophosphoric acid and can be easily eliminated. Particularly preferred quinoline compounds are quinoline, isoquinoline, or methylquinoline, and as derivative compounds thereof, it is particularly preferred to use these compounds in the form of water-soluble inorganic salts such as nitrates, sulfates, and hydrochlorides.

Nitrogen-containing compounds other than those mentioned above, such as aliphatic amines such as methylamine and ethylamine, undergo a decomposition reaction with heteropolyacid during catalyst preparation, so the desired salt cannot be obtained, and pyridine, piperazine, When a nitrogen-containing heterocyclic compound such as pyrroline is used, similar insoluble molypdovanadophosphate is produced, but the resulting catalyst has insufficient pore volume and specific surface area, resulting in a space velocity It was difficult to obtain sufficient activity when the concentration was high.

In preparing the catalyst of the present invention, various raw materials can be used.

Examples of molybdenum compounds include molybdenum trioxide, molybdic acid, sodium molybdate, ammonium paramolybdate, and molybdophosphoric acid.

Examples of vanadium compounds include vanadium pentoxide, ammonium metavanadate, sodium metavanadate, vanadyl oxalate, vanadyl sulfate, and the like.

Examples of the phosphorus compound include orthophosphoric acid, disodium hydrogen phosphate, ammonium phosphate, and niummonium phosphate.

The action of quinolines in the preparation of molypdovanadric acid in the present invention, for example, when quinoline is used, is as follows.

Atomic ratio P:Mo:V=1 prepared by a known method:
Moripdovanadric acid having a composition of 11:1 is an extremely water-soluble compound, and its crystal structure changes greatly depending on the crystal water it contains.

That is, when the water content is high (29 to 30 molecules of water per molecule of molypdovanadophosphoric acid), the lattice constant is approximately 2 a, s.
When the diamond-shaped structure of
-Kα), the diffraction line has a 2θ of 7.9”,
8,96.9.2-126.8" and 27.1".

When molypdovanadric acid is dissolved in water, it becomes a reddish-brown solution, but when an aqueous solution of quinoline nitrate is added to this solution, an orange-yellow precipitate is formed, and the supernatant becomes colorless and transparent. The presence of quinolinium ions was confirmed from the infrared absorption spectrum of this precipitate, and since there was no absorption attributed to quinoline, the reaction to produce quinolinium salt of molypdovanadophosphate was stoichiometric, and the excess It is thought that there is no adsorption of quinoline. Although this precipitate is a salt with a monovalent base, X-ray diffraction measurements show that the structure at this stage does not have a cubic structure like that of alkali metal salts, ammonium salts, or pyridinium salts, and is extremely Although the catalyst is amorphous, it is thought that this difference in crystalline state contributes to the high activity of the obtained catalyst.

The resulting precipitate was further heated at 300 to 600°C in a nitrogen stream.
When treated at a high temperature of , the color changes to a dark blue reduced color, and when this is treated again in air at a temperature in the range of 200 to 400'C, a yellow-green substance is obtained. In the measurement results of the infrared absorption spectrum of this substance, there was no absorption attributed to quinoline or quinolinium ions, and only the characteristic absorption of molypdovanadric acid was observed.

The results of X-ray diffraction measurements show that it has a cubic crystal structure with a lattice constant of approximately 11.85X, indicating that it has a cubic crystal structure with a lattice constant of approximately 11.85X. The crystal structure was different from that of quinolinium salts of dovanadophosphate, but was similar to that of alkali metal salts of molybdovanadophosphate.

Furthermore, the line width in the X-ray diffraction diagram was large, indicating that this substance was composed of extremely fine crystals.

Furthermore, the observed substance was water-soluble, and after dissolving it in water, the aqueous solution was evaporated to dryness, and X-ray diffraction was measured. Diffraction lines appeared and the crystal structure was close to the triclinic structure of free molypdovanadophosphate. From this, it was found that quinoline has the effect of changing the crystal structure of molypdovanadric acid to the cubic structure seen in its alkali metal salts and making the crystals finer. Similar effects were also observed when quinoline compounds other than quinoline and their derivatives were used.

Next, the catalyst preparation method according to the present invention will be described using, for example, a case where the catalyst is prepared using quinoline.

Moripdovanadric acid obtained by a known method is dissolved in water, and an aqueous solution of an inorganic salt of quinoline (for example, quinoline sulfate) is added thereto to obtain a water-insoluble precipitate. Alternatively, water-soluble compounds of molypide/vanadium and phosphorus are dissolved in water, an aqueous solution of an inorganic salt of quinoline is added, and the solution is made acidic to obtain a water-insoluble precipitate. These precipitates were recognized as quinolinium salts of molybdovanadophosphoric acid based on the measurement results of X-ray diffraction and infrared absorption spectra.
Furthermore, since the particles are large, this precipitate can be easily filtered, which is very advantageous in the preparation of the catalyst, as compared to the alkali metal salt or ammonium salt of molypdovanadophosphoric acid, which is difficult to filter out in the known methods. The insoluble substance thus obtained is used as a starting material and molded to obtain a catalyst precursor. Next, this precursor is dried at high temperature to remove volatile components contained in it. The temperature varies depending on the type and physical properties of volatile components, but is in the range of 100°C to 300°C. Further, during drying, it is preferable that the oxygen concentration in the atmosphere be 5 liters (volume concentration) or less in order to suppress the decomposition of volatile components. Next, this dried product is further heated in an atmosphere of an inert gas (e.g., nitrogen, helium, argon, carbon dioxide, etc.) or a reducing gas (e.g., carbon oxide, methane, ethane, propane, etc.) at a temperature of 400°C in the range of 300 to 600°C. It is activated as a catalyst in the temperature range of ℃.

Alternatively, the above dried product is heated to a temperature in the range of 350 to 400°C from room temperature in an atmosphere in which air is diluted with an inert gas and the oxygen concentration is 5% (volume concentration) or less, and quinoline is desorbed and activated. may be used as a catalyst by simultaneously carrying out the reaction.

When these catalysts of the present invention are used in the production of methacrylic acid by gas phase oxidation, their selectivity and catalytic activity are extremely superior compared to catalysts that are not treated with quinoline, and this catalyst has excellent performance. However, by using quinolines and/or quinolines derivatives, the specific surface area is 10 to 14 m''/t, which is 2 to 6 times larger than that when quinolines are not used, and the pore volume is also increased. 0.35 to 0.45 rnl/l, which is 1.5 to 3 times higher than when quinolines are not used, and as a result, the finished catalyst becomes more porous and the bulk specific gravity of the catalyst becomes smaller. It was confirmed that moldability, mechanical strength, and even reproducibility during preparation were significantly improved.

If quinoline or its derivatives are not used in the preparation of the catalyst according to the present invention, precipitation filtration and molding during preparation are difficult; for example, even when molding is performed with the addition of a molding aid, the catalyst strength and degree of pulverization are slightly improved. However, on the other hand, the performance deteriorates so much that it cannot be used as a practical catalyst. Furthermore, when pyridine or the like is used in place of quinolines or their derivatives, although the catalyst performance and strength are improved, the space-time yield is still low and is unsatisfactory from an economic standpoint.

This fact also shows how effective the use of quinolines and their derivatives are in the present invention.

These effects of the present invention are considered to be due to the fact that the quinolines and their derivatives do not cause changes in the crystal structure of molypdovanadric acid, as well as in the surface and pore structure of the catalyst. As a result, the advantages of high activity and dramatically increased yield upon release were derived.

These catalysts not only have good performance, but also have good moldability and strong mechanical strength, so they can be used without a support, but if you consider the heat removal effect in the catalyst layer when used in an oxidation reaction, a support is required. It is also possible to use The carrier is generally an inert carrier such as silica, alumina,
Celite, silicon carbide, etc. are preferred, but are not limited to these.

In the preparation of the present invention, the quinolines and their derivatives may be added at the time mentioned above, or at the stage where all catalyst raw materials are mixed in an aqueous solution. The amount of quinolines and their derivatives used can be up to 10 times the mole of molypdovanadric acid, but preferably 0.5
It is in the range of ~6 times the mole. It is also possible to use quinolines and their derivatives in combination with other nitrogen-containing heterocyclic compounds such as pyridine.

The catalyst of the present invention is used in a gas phase oxidation reaction of a reaction gas containing methacrolein and/or isobutyraldehyde and/or isobutyric acid. Air is industrially advantageous as an oxygen source. As the diluent, for example, nitrogen, carbon dioxide, helium, an inert gas such as argon, -carbon oxide, water vapor, etc. can be used, but the use of water vapor is preferable in order to improve the yield.

The raw material concentration targeted in the oxidation reaction is 0.5 to 10
A range of capacitance is preferred. Further, the volume ratio of oxygen to the raw material is in the range of 0.5 to 10, preferably in the range of 1 to 5. The space velocity of the raw material gas is 50 (1-10,000 h
r'' (8TP), preferably from 1,000 to
A range of 5,000 hr' (STP) is appropriate. In addition, the reaction temperature depends on the type of raw materials used, but it is 220 to 35
It is in the range of 0°C.

When using the catalyst according to the present invention, the reactor is generally of a fixed bed type, but either a fluidized bed or a moving bed type can be used.

A method for preparing a catalyst using this product and a reaction example using the same will be explained below in detail, and the conversion rate, selectivity, and single flow yield in Examples and Comparative Examples shall comply with the following definitions.

Example 1 Molybdenum trioxide 144. Of, vanadium pentoxide8.
27? and 10.5 t of phosphoric acid (85% by weight) to 1 t of water.
1 and heated under reflux for 5 hours. The resulting dark red solution was filtered to remove a trace amount of insoluble solids, and then concentrated to dryness to give reddish brown crystals.

From the results of X-ray diffraction, fluorescent X-ray analysis, and infrared absorption spectroscopy, this crystal has an atomic ratio of P: excluding oxygen.
Mo: V = 1.09: 12: 1.0
It was confirmed that it was molypdovanadric acid with a triclinic structure of composition 9. The obtained crystals were dried, 81.71 F of them were dissolved in 10 omaA' of warm water, and 21.5 F of quinoline was added to 83.3 F of an aqueous solution of nitric acid with a concentration of 2N.
An insoluble precipitate formed upon addition of the solution in ml. This precipitate is filtered, washed with water, formed into a cylindrical shape with a diameter of 5111% and a height of 51HIL, and fired.
Atomic ratio excluding oxygen: P:Mo:V=1:11
: A catalyst oxide with a composition of 1 was obtained. This catalyst had good moldability, a compressive fracture strength of 3.0 kg/pellet or more, and sufficient mechanical strength.

In addition, the BET specific surface area, pore volume, and packing density of this catalyst are 12.8 rrt/y, o, and 39 m1, respectively.
/l and 0.78 t/crl. In the infrared absorption spectrum of this catalyst, no characteristic absorption of quinoline or quinolinium ions was observed, and only absorption characteristic of molypdovanadophosphoric acid was observed. This catalyst was water-soluble and exhibited properties typical of free molypdovanadric acid. However, in X-ray diffraction measurements, the main diffraction line (Cu-
α) is 2θ is 26.0°, 10.5″″, 18.3
°, 21.2@, 35.5', etc., and it was found to have a cubic structure with a lattice constant of about 11.85A, and the triclinic structure normally seen in free molypdovanadophosphate. The crystal structure was completely different from that of the alkali metal salt of molypdovanadophosphate. 50 ml of this catalyst was packed into a stainless steel O-tube with an inner diameter of 251 m and immersed in a molten salt bath at 310°C, and the volume ratio of methacrolein: oxygen: nitrogen: water vapor = 1: 3: 3 was placed inside the tube.
6:10 raw material mixed gas at a space velocity of 2000 hr'
The results shown in Table 1 were obtained.

Comparative Example 1 In Example 1, the temperature was increased to 350°C before adding quinoline.
It was calcined for 3 hours and used as a catalyst. Furthermore, this catalyst has poor moldability and compressive fracture strength of lkl? The catalyst was weak, less than /Bellet, had a specific surface area and pore volume smaller than the catalyst of Example 1, and had an extremely large bulk specific gravity. In X-ray diffraction measurement, 2θ is 8.9@ and 26.8'
At this time, a major diffraction line appeared, and its crystal structure was close to that of triclinic molybdovanadophosphate.

Using this catalyst, a reaction was carried out under the same conditions as in Example 1, and the results shown in Table 2 were obtained.

Comparative Example 2 The quinoline used in Example 1 was replaced with pyridine,
A catalyst was also obtained in the same manner as in Example 1 except that the amount was changed to 13.61F. The results of X-ray diffraction measurements of this catalyst showed that the crystal structure was a cubic system similar to that of Example 1, but the specific surface area and pore volume were considerably smaller than those of the catalyst of Example 1. Example 1 using this catalyst
The reaction was carried out under the same conditions as above and the results shown in Table 2 were obtained.

Example 2 A catalyst was prepared in the same manner as in Example 1, except that the quinoline used in Example 1 was changed to inquinoline.

It was found from the results of X-ray diffraction that this catalyst had a cubic crystal structure, similar to the catalyst of Example 1. The reaction was carried out under the same conditions as in Example 1 except that this catalyst was used and the reaction temperature was 315°C, and the results shown in Table 1 were obtained.

Example 3 A catalyst was prepared in the same manner as in Example 1 except that methylquinoline was used instead of quinoline and the amount used was 23.9 f. Using this catalyst, the reaction temperature was t-300°C.
The reaction was carried out under the same conditions as in Example 1 except that Table 1
I got the result.

Example 4 Ammonium paramolybdate 88.3 f and amsonium metavanadate 5.3 t in heated water 2001RI
was dissolved and stirred. Add phosphoric acid (85% by weight) to this solution.
Continue adding 5.24t and then add 21.5f of quinoline to 1
When a solution dissolved in 90 lL of 0N nitric acid aqueous solution was added, an orange-yellow precipitate was formed.

The resulting clay-like material was molded into a cylinder with a diameter of 51 RI and a height of 5 mm, dried at 200°C for 15 hours, fired at 430°C in a nitrogen stream for 3 hours, and then heated in an air stream for 35 hours.
After firing at 0°C for 3 hours, the atomic ratio excluding oxygen was P:Mo:
A catalyst having a composition of V=1:11:1 was obtained. As in Example 1, this catalyst was made of free molybdovanadophosphoric acid, and therefore it was revealed from the measurement results of X-ray diffraction and infrared absorption spectrum that it had a cubic crystal structure. Furthermore, this catalyst has good moldability and compressive fracture strength of 3.0.
It was more than kgI/pellet. The reaction was carried out under the same conditions as in Example 1 except that this catalyst was used and the reaction temperature was 320°C, and the results shown in Table 1 were obtained.

Comparative Example 3 A catalyst was obtained in the same manner as in Example 4, except that quinoline was not added. Using this catalyst, a reaction was carried out under the same conditions as in Example 4, and the results shown in Table 2 were obtained.

Comparative Example 4 A catalyst was obtained in the same manner as in Example 4, except that pyridine 13.69 was used instead of quinoline. Using this catalyst, a reaction was carried out under the same conditions as in Example 4, and the results shown in Table 2 were obtained.

Example 5 A reaction was carried out under the same conditions as in Example 1 except that the catalyst of Example 1 was used and the raw material methaklerein was replaced with inbutyraldehyde, and the results shown in Table 3 were obtained.

Comparative Example 5 When inbutyraldehyde was oxidized using the catalyst of Comparative Example 1 under the same conditions as the reaction of Example 5, the results shown in Table 3 were obtained.

Example 6 5 oynl of the catalyst of Example 1 was filled into a stainless steel O-shaped tube with an inner diameter of 25 mm, immersed in a 310°C molten salt bath, and the volume ratio of isobutyric acid: oxygen: nitrogen: water vapor = 1: 1:2
Isobutyric acid was oxidized by passing a 2:1 raw material gas at a space velocity of 3000 h1'', and the results shown in Table 3 were obtained.

Comparative Example 6 When the catalyst of Comparative Example 1 was used to oxidize isobutyric acid under the same conditions as in Example 6, the results shown in Table 3 were obtained.

Claims (2)

[Claims] (1) An oxidation catalyst consisting of free molybdovanadophosphoric acid, which is characterized by having a cubic crystal structure with a lattice constant of about 1 tssX. (2) Free molybdovanadophosphoric acid having a cubic crystal structure with a lattice constant of about 11.85X, which is prepared in the presence of quinolines and/or quinoline derivatives. A method for preparing an oxidation catalyst consisting of: