JPS63145249A - Production of methacrylic acid and/or methacrolein - Google Patents

Abstract

PURPOSE:To obtain the titled compound in excellent selectivity, productivity and catalyst life, by oxidizing isobutane in one step using a Mo-containing heteropolyacid having P or As as center atom or a salt of said polyacid as a catalyst in a state of high degree of reduction. CONSTITUTION:Methacrylic acid and/or methacrolein can be produced by oxidizing a gas containing isobutane in the presence or absence of oxygen at 250-450 deg.C using a catalyst comprising a Mo-containing heteropolyacid having P or As as center atom or its salt (e.g. phosphomolybdic acid, arsenomolybdic acid, etc.) at a reduction degree corresponding to 1-6 electrons, especially 2-4 electrons per one molecule of the heteropolyacid. Especially methacrylic acid can be produced from isobutane in high selectivity. The combined selectivity of methacrylic acid and methacrolein exceeds 50%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel method for producing methacrylic acid and/or methacrolein. Specifically, a method is described in which isobutane is oxidized in the gas phase in the presence of a catalyst to synthesize methacrylic acid and/or methacrolein in one step.

[Prior Art] Saturated hydrocarbons such as isobutane are conventionally considered to be inert gases, and it has been described that they are used as diluents for reaction gases during the oxidation of olefins and aldehydes. (For example, JP-A No. 55-2619) Since isobutane has extremely low reactivity, it is dehydrogenated using a dehydrogenation catalyst or an oxidative dehydrogenation catalyst to produce isobutylene, and then oxidized. A method using methacrolein or methacrylic acid is used.

In British Patent No. 1340891 SA, in the gas phase,
It has been shown that methacrolein can be obtained directly from unreactive isobutane in the coexistence of oxygen using antimony and molybdenum oxides as catalysts, although the yield is extremely low. However, the yield is low and this method is not industrially satisfactory.

Further, JP-A-55-62041 discloses a method for producing methacrylic acid by oxidizing isobutane in the coexistence of molecular oxygen using a catalyst consisting of antimony, molybdenum, phosphorus, and oxygen.

According to this method, it has been shown that when a raw material gas with an isobutane concentration of 10% is supplied, 10% of the isobutane in the raw material gas can be converted and methacrylic acid can be produced with a selectivity of 50%.

However, with this method, the catalyst life is not sufficient and the methacrylic acid production activity quickly decreases.

In addition, productivity is low due to the low space velocity of the raw material gas.
As an industrial manufacturing method, a satisfactory method has not yet been achieved.

[Problems to be Solved by the Invention] Accordingly, the object of the present invention is to provide methacrylic acid with excellent selectivity to the target product, productivity, and catalyst life that can be industrially implemented by a one-step oxidation method of isobutane. and/or to provide a method for producing methacrolein.

[Means for Solving the Problem] As a result of extensive research in order to solve the problem, the present inventors found that when oxidizing isobutane, a heteropolyacid or a salt thereof containing P or As as the central element and Mo is used. We discovered that when used as a catalyst in a highly reduced state, the selectivity of methacrylic acid improves and the productivity of methacrylic acid and methacrolein together also increases, and that this high productivity can be sustained for a long time. Completed the invention.

That is, when oxidizing isobutane-containing gas, the present invention oxidizes a heteropolyacid or its salt containing P or As as a central element and Mo at a temperature range of 250 to 450°C in the presence or absence of oxygen. This is a novel method for producing methacrylic acid and/or methacrolein, which is characterized by using a catalyst that has been reduced by one to six electrons per acid molecule.

The present invention provides a method for using a catalyst containing a specific heteropolyacid or a salt thereof in the presence or absence of oxygen.
The present invention relates to a method for producing methacrylic acid and/or methacrolein based on a novel concept characterized by carrying out an oxidation reaction while maintaining a highly reduced state.

According to the method of the present invention, methacrylic acid can be obtained from isobutane with particularly good selectivity, and the combined selectivity for methacrylic acid and methacrolein exceeds 60%. In addition, despite the method of using a catalyst in a reduced state in the oxidation reaction, which is considered to lead to a decrease in oxidation activity from the usual concept, the productivity of methacrylic acid and/or methacrolein did not decrease, and the productivity of methacrylic acid and/or methacrolein did not decrease. On the contrary, productivity will improve.

Moreover, it is characterized by being able to maintain high productivity over long periods of time. As described above, the product selectivity, productivity, and catalyst life, which were insufficient when conventionally using isobutane as a raw material, were improved by the method of the present invention, and an industrially advantageous production method could be provided. .

Although there are many unknowns as to why a catalyst in a reduced state exhibits such excellent effects, the following effects are considered.

First, it is known that phosphomolybdic acid and arsenic molybdic acid undergo isomerization from α-type to β-type depending on the degree of reduction and reducing conditions [M.T.
“Heteropoly and isopolyoxometalates”,
Sbringer Verlag (M, T, Pope, “He
tetropoly and isopolyOxom
etalates”, Spring3er-Verlag
) (1983), it is inferred that the catalyst species and its composition are different from the oxidation state. Although the details of the influence of isomerization on the isobutane oxidation reaction are unknown, it is thought that the electronic state of the reduced catalyst species, which is different from the oxidation state, is working advantageously for the isobutane oxidation.

It is known that phosphomolybdic acid has various crystal structures; for example, 12-molybdophosphoric acid changes into cubic, triclinic, and tetragonal structures as the coordinated water decreases. On the other hand, 12-molybdophosphoric acid in a highly reduced state, such as a four-electron reduced product, is usually heated at 350°C, where a decrease in coordinated water is observed.
The crystal structure does not change even under high-temperature reaction conditions, maintaining a cubic crystal structure, and it has extremely high thermal stability. The fact that phosphomolybdic acid and the like in such a highly reduced state have a thermally stable crystal structure is considered to be the second reason why it exhibits excellent catalytic performance and catalyst life as an isobutane oxidation catalyst.

Third, the acidity of the heteropolyacid is weakened by reduction,
Strong adsorption of intermediate products due to isobutane oxidation is suppressed,
It is believed that the reduction in complete oxidation property is also a reason for the improvement in the selectivity of the target oxidation product.

The catalyst used in the present invention is composed of a heteropolyacid containing P or As as a central element and contains Mo, and it is important to use it in a state in which one to six electrons are reduced per molecule of the heteropolyacid.

As a heteropolyacid, P or As is the central element, and M
Those containing o as a poly atom include phosphomolybdic acid and arsenic molybdic acid. These are known to have various structures (chemistry area, Vol. 129. No.
12. ,,P2S5. Sasaki, Matsumoto).

A typical example is the Keggin structure represented by 12-molybdophosphoric acid. Furthermore, structures in which Mo constituting these phosphomolybdic acids and arsenic molybdic acids are partially substituted with vanadium, tungsten, etc. are also effective as catalysts of the present invention.

Furthermore, these salts can be used as catalysts.

Useful salts include ammonium salts, salts with amines such as pyridine and quinoline. This may be one that partially forms a salt with ammonium ions, or it may be one in which ammonium ions are partially or completely removed from an ammonium salt by calcination.

Also, Tl, Bi, Te, Pb, TI, Fe.

Salts of transition metals such as As, Ag+ Cr, Ni, Cu, Mn, and Co, alkali metals, alkaline earth metals, rare earth metals, and other metals, as well as mixtures containing these metals, are also effective as catalysts. Mixtures with ammonium salts can also be used.

Further, a carrier may be used for these catalysts.

As a carrier, silica, alumina, silicon carbide,
Examples include titania, zirconia, and diatomaceous earth.

These heteropolyacids can be prepared by known methods [e.g.
Ni Tusidinos, Industrial and Engineering Chemistry, Products Research
and Development (G, A, Tsigdino
s, lnd, Eng, chem, Prod, Re
s, Dev.

) Vol, 13. P2S5, 1974 and G.N. Tsigdinos, Inorganic Chemistry (G, A, Tsigdinos, Inor8
anic chemistry) Vol, 7°No3
．． (1968).

Ammonium salts can be synthesized from heteropolyacids. In this case, water-soluble ammonium salts such as aqueous ammonia, ammonium chloride, and ammonium nitrate can be used as the ammonium ion source. In addition, organic amines can also be used and are useful. Other metal salts or complexes can be used in catalysts by mixing heteropolyacids with salts such as metal carbonates, nitrates, chlorides, etc.

When used in the present invention, the various heteropolyacids described above are reduced by one to six electrons per molecule.

Here, the number of electrons for reduction is an average representation of the entire system, and does not necessarily mean that each ion is equal. Since phosphomolybdenum or arsenic molybdic acid is easily reduced, it can easily be reduced to a low reduction state of less than -electron. However, at such a low degree of reduction, in isobutane oxidation, the selectivity for methacrylic acid is low and the catalytic activity quickly decreases. On the other hand, it has been reported that the redox of molybdenum-based heteropolyacids is no longer reversible at a degree of reduction exceeding six electrons, making them undesirable as oxidation catalysts. Therefore, the degree of reduction is preferably in the range of - to six electrons. Particularly preferred is a reduction degree equivalent to two to four electrons. In this way, any known reduction method may be used to prepare a catalyst with a particularly high degree of reduction, and various methods are exemplified below.

A reduced heteropolyacid aqueous solution can be easily obtained by making a fully oxidized heteropolyacid into an aqueous solution up to saturated solubility and using a reducing agent such as hydrazine or ascorbic acid in an amount equivalent to the desired degree of reduction. Further, even if a base metal such as reduced iron is used, it can be easily reduced in an aqueous solution.

Alternatively, electrolytic reduction is also effective. A reduced heteropolyacid catalyst can be prepared by supporting these on a suitable carrier or directly drying them and then calcining them in an inert gas such as nitrogen or helium or in a reducing gas such as hydrogen.

When reducing in solution, for example, tetrahydrofuran,
It is also possible to perform reduction using the above reducing agent in a state in which an oxygen-containing organic substrate such as dioxane or polyethylene glycol is added.

Reduction in the gas phase is also possible. In this case, it is only necessary to contact the heteropolyacid in the oxidized state with a reducing gas. Hydrogen, carbon oxide, ammonia gas, etc. can be used as the reducing gas. Alternatively, a method of contacting with a reducing hydrocarbon such as isobutyne or propylene may be used. When reducing in the gas phase, a temperature range of 150 to 600°C is preferred.

More preferably, the reduction is carried out at 400° C. or lower, which is the decomposition temperature of the non-reduced substance.

In addition, ammonium salts or amine salts of heteropolyacids are heated at 350 to 600°C in an inert gas because reducing ammonia gas and the like are eliminated by heating at 350°C or higher.
The reduced product can be easily obtained by simply heating at 450°C, which is the decomposition temperature of the ammonium salt or amine salt, and it is possible to obtain a reduced form of the heteropolyacid with partial or complete acid form of the ammonium ion. A reduced product can be obtained. In this case, in preparing the ammonium salt or amine salt of the heteropolyacid, the amount of ammonium ion or amine added is preferably 3 moles or more per mole of phosphomolybdic acid or arsenic molybdic acid. If less than 3 moles of ammonium ions or amines are added, a non-uniform mixture may be formed in which some of the ammonium ions or amines forms a precipitable salt and the rest remains as a free acid. Even if left to dry, a heterogeneous mixture of ammonium salt and free acid is formed. When this is heat-treated, the amount of reducing ammonia produced is insufficient and a high degree of reduction may not be obtained, which is not preferable. Further, reduced heteropolyacids also result in a non-uniform mixture, which is not preferable. In order to compensate for the insufficient degree of reduction and achieve uniformity of the reduced heteropolyacid, it is preferable to heat in a reducing gas such as hydrogen, -carbon oxide, or hydrocarbon rather than in an inert gas, and the decomposition of the catalyst is less likely. There is an advantage.

The catalyst reduced by various reduction methods as mentioned above has a 150 to 6
It is preferable to use it in the reaction after activating it by firing in an inert gas or reducing gas atmosphere at a temperature range of 00°C, particularly preferably 300 to 450°C. This step is especially necessary when adjustment is made by liquid phase reduction.

From the viewpoint of suppressing the decomposition of the catalyst during adjustment, it is preferable to increase the stability of the catalyst by reducing it before firing, but after firing at a temperature below the decomposition temperature of the non-reduced
A method of reducing is also possible.

Therefore, it is also possible to gradually reduce the non-reduced substance with isobutane gas in an isobutane oxidation reaction system to form a catalyst with a degree of reduction of one to six electrons.

Among the reduced heteropolyacid catalysts obtained in this way, those in which the heteropolyacids are in a completely acid form are soluble in water, so they are titrated with an aqueous solution of potassium permanganate, and the solution turns from green to yellow. An accurate degree of reduction can be determined using this as the end point.

The raw material gas supplied to the reaction is an isobutane-containing gas, and the concentration of isobutane is 1 to 100 mol%, preferably 1 to 80 mol%. Other hydrocarbons may be mixed in as long as they do not affect the reaction. 5 steam
It is advantageous to supply about 40 mol % because the target product can be obtained with a higher selectivity. Further, it is possible to use the diluent gas as the raw material gas. Nitrogen, helium, argon, carbon dioxide, etc. can be used as the diluent gas.

Unreacted isobutane can be recovered and used again. At that time, carbon monoxide, carbon dioxide, and reaction products from the pond may be mixed in as long as they do not affect the reaction. Furthermore, methacrolein produced at the same time can be recovered and added to a portion of the raw material gas.

The reaction can be carried out either in the presence of oxygen or in the absence of oxygen. In either case, it is important to carry out the reaction while maintaining the degree of reduction of the catalyst from one electron to six electrons.

When the reaction is carried out in the presence of oxygen, molecular oxygen can be mixed into the raw material gas and supplied at the same time. It is preferable to use a molar ratio of oxygen and isobutane in the range of 0.1 to 2. If the concentration of molecular oxygen in the raw material gas is too high, the catalyst will be oxidized too much and the degree of reduction will be less than 1. So I don't like it. On the other hand, if the oxygen concentration is too low, the catalyst will be reduced by more than six electrons, causing deterioration of the catalyst.

The oxygen concentration is preferably 0.5 to 30 mol%, particularly preferably 1 to 15 mol%.

When the reaction is carried out in the absence of oxygen, a gas containing oxygen is used separately from an isobutane-containing gas that does not contain oxygen, and the gas is brought into contact with the catalyst alternately with the isobutane-containing gas. The catalyst, whose degree of reduction has increased due to the reaction in the absence of oxygen, is reoxidized to return the degree of reduction from one electron to six electrons, and the reaction is continued by repeating the reaction and regeneration. The oxygen concentration in the gas used in the operation of bringing the catalyst into contact with Vi element is not particularly limited, but a concentration of 0.1% or more is advantageous because it can shorten the time required for regeneration. Even if the concentration is too high, the effect of shortening the regeneration time will be weak. Preferably 0.5 to 30 mo1%
The concentration is Inert gases such as water vapor, nitrogen, helium, carbon dioxide, argon, etc. can be used to dilute to the desired concentration. The oxygen-containing gas may be recovered after being brought into contact with the catalyst and used again as an oxygen source.

In the method of alternately contacting isobutane and oxygen, it is possible to select optimal reaction conditions for the reduction process with isobutane and the oxidation process with oxygen, and the degree of reduction of the catalyst can be easily controlled.

As an oxygen source, oxygen is supplied simultaneously with isobutane.
Alternatively, in either case of alternate supply, pure oxygen gas or air may be used.

In particular, when supplying isobutane and oxygen alternately, it is supplied without mixing, so even if cheap air is used as the oxygen source, nitrogen and isobutane do not mix, so there is no need for a process to separate them. have

The reaction temperature is selected from the range of 250 to 450°C. At low temperatures, the reaction rate is low, and at high temperatures, catalyst decomposition and complete oxidation of reaction products tend to occur.

Further, when isobutane and oxygen are supplied alternately, the temperature during regeneration with oxygen gas is also selected from the range of 250 to 450°C.

The reaction pressure can be set over a wide range from reduced pressure to increased pressure, but normal pressure to 2 atmospheres is industrially advantageous.

The contact time between the reaction gas and the catalyst (the value obtained by dividing the catalyst capacity by the supply amount per part of the raw material gas at the reaction temperature) is 0.
A range of 0.05 to 50 seconds is suitable.

Usually it is in the range of 0.1 to 20 seconds.

The type of reactor can be freely selected, and fluidized beds, fixed beds, moving beds, etc. can be used.

The generated methacrylic acid and methacrolein are cooled, absorbed,
They can be separated and purified by a known appropriate method such as distillation to produce the respective products. Unreacted isobutane can be recovered and used again as a raw material. In addition, after recovering methacrylic acid from the reaction gas by a known method such as cooling condensation, absorption, adsorption, etc., part or all of the recovered gas containing methacrolein is again supplied to the reactor as part or all of the raw material. be able to.

[Example Example 1 Phosphormolybdic acid ()13PMot20ao'30H2
0: Nippon Inorganic Chemical) 100g was dissolved in 100ml of water, 2.123ml of hydrazine hydrate was added, and the mixture was heated to 80°C to perform 4-electron reduction.

This was evaporated to dryness, molded into pellets at a pressure of about 100 kg/cm2, and ground into pellets to select particles of 10 to 20 meshes. This was heated at 200°C in a nitrogen stream for 1
After that, it was baked at 420°C for 3 hours.

2.5g of this catalyst is Pyrex with an inner diameter of 6mm! ! It was filled into a U-shaped container and placed in a constant temperature bath. Set the temperature of the thermostat to 350
℃, a) a mixed gas of 62 mol% isobutane and 38 mol% water vapor was applied for 5 seconds at a contact time of 1.5 seconds, and b
) A mixed gas of 20 mol % oxygen, 42 mol % helium, and 38 mol % water vapor was passed through the mixture for 10 seconds at a contact time of 1.5 seconds in conjunction with a timer.

After 3 hours, the reaction gas was analyzed by gas chromatography, and it was found that 8% of isobutane had been converted, the selectivity for methacrylic acid was 48%, and the selectivity for methacrolein was 12%. Isobutine was not detected. At this time, the catalyst was in a state equivalent to 3.8 electron reduction (the degree of reduction was measured by dissolving the catalyst in water and titrating it with an aqueous potassium permanganate solution). After 100 hours of further reaction, the conversion rate of isobutane was 7%, the selectivity of methacrylic acid was 45%, and the selectivity of methacrolein was 14%, which were almost the same as after 3 hours. Isobutine was not detected.

Further, the degree of reduction of the catalyst at this time was equivalent to 3.1 electron reduction.

Comparative Example 1 A phosphomolybdic acid catalyst with a degree of reduction of 0 was prepared in the same manner as in Example 1, except that the reduction operation with hydrazine hydrate was not performed and the calcination temperature was lowered from 420°C to 350°C.

This catalyst was reacted under the same conditions as in Example 1.

When the reaction gas was analyzed after 3 hours, the conversion rate of isobutane was 3%, methacrylic acid was not detected, and the selectivity for methacrolein was 35%. The degree of reduction of the catalyst at this time was equivalent to 0.2 electron reduction.

Example 2 Sodium molybdate (Na2MoO4.2H2Q)
To a solution of 121 g dissolved in 200 ml of water, add 3
20g of 0% arsenic acid solution was added. Add sulfur @80m to this solution.
After adding 1, 300 ml of ethyl ether was added. The lower layer separated into three layers was taken out and air-dried to obtain arsenic molybdic acid. 100ml of this arsenic molybdic acid 1008
was dissolved in water and subjected to electric field reduction to obtain a 4-electron reductant. This was evaporated to dryness, molded into a pellet shape at a pressure of about 100 kg/cm2, and ground, and particles of 10 to 20 meshes were selected. This was fired in a nitrogen stream at 200°C for 1 hour and then at 420°C for 3 hours.

2.5 g of this was packed into the same reactor as in Example 1.

The temperature was maintained at 350°C, and 10 mol% of isobutane and 1 mol% of oxygen were added.
A mixed gas containing 0 mol% steam, 38 mol% helium, and 42 mol% helium was supplied for a contact time of 1.5 seconds. Analysis of the reaction gas after 3 hours revealed that the conversion rate of isobutane was 9.5%.
The selectivity for methacrylic acid was 42%, and the selectivity for methacrolein was 23%. The degree of reduction of the catalyst at this time is 3.2
It was equivalent to electron reduction.

Comparative example 2 2.5 g of the catalyst from Example 2 was charged into the same reactor.

The reaction temperature was maintained at 350°C, and 10 mol% of isobutane, 30 mol% of oxygen, 38 mol% of water vapor, and 22 mol% of helium were added.
A mixed gas of 100 ml was supplied with a contact time of 1.5 seconds. When the reaction gas was analyzed after 3 hours, the conversion rate of isobutane was 3.
The selectivity for methacrylic acid was 7% and the selectivity for methacrolein was 30%. At this time, the degree of reduction of the catalyst is 0
．． This corresponded to 6-electron reduction.

Example 3 Powdered ammonium phosphomolybdate (Japan Inorganic Chemistry Department) was molded into a pellet shape at a pressure of about 100 kg/cm 2 and pulverized to separate 20 mesh particles from 1O. This was subjected to reduction treatment at 300° C. in a hydrogen stream to prepare a catalyst equivalent to 4-electron reduction.

Using the same reactor as in Example 1, 2.58% of this catalyst was used, the reaction temperature was 370°C, and the contact time of the isobutane-containing gas was 1.5%.
The conditions were the same as in Example 1, except that the oxygen-containing gas was allowed to flow for 5 seconds at a contact time of 1.5 seconds.
The reaction was carried out. When the reaction gas was analyzed after 3 hours,
8% of the isobutane was converted and the selectivity for methacrylic acid was 5.
6%, and the selectivity for methacrolein was 10%. At this time, the catalyst was in a state equivalent to 3.9 electron reduction. After continuing the reaction for 100 hours, the conversion rate of isobutane was 7.
%, the selectivity of methacrylic acid was 54%, and the selectivity of methacrolein was 11%, and the results after 3 hours were almost maintained. Further, the degree of reduction of the catalyst at this time was equivalent to 3.5 electron reduction.

Example 4 23.6 g of phosphomolybdic acid was dissolved in lOml of water, 4.1 g of 65% nitric acid was added, and the mixture was thoroughly stirred, followed by the addition of 0.79 g of pyridine. This solution was stirred at 60° C. for 1 hour and then dried. This was molded into a pellet shape under a pressure of about 100 kg/am2, and the pellet was pulverized to select particles of 10 to 20 mesh sizes. This was heated in a hydrogen stream for 30
A catalyst equivalent to 4-electron reduction was prepared by reduction treatment at 0°C.

When 2.5 g of this catalyst was used in the same reactor as in Example 1 and the reaction gas was analyzed, 5% of the isobutane was converted, the selectivity for methacrylic acid was 43%, and the selectivity for methacrolein was 21%. there were. At this time, the catalyst was in a state equivalent to 1.5 electron reduction.

Example 5 Bismuth nitrate [B i (N 0s) 3.5H20 9.7
Add 2g of phosphomolybdic acid 4 and stir well.
Added 7g. This solution was stirred at 60° C. for 1 hour and then dried using a rotary evaporator.

After drying this at 150°C for 1 hour, it was
Reduction was performed at 300° C. for a time to obtain a catalyst equivalent to 3.2 electron reduction.

The reaction was carried out in the same reactor and under the same conditions as in Example 1. Analysis of the reaction gas after 100 hours showed that 9% of the isobutane had been converted, the selectivity for methacrylic acid was 55%, and the selectivity for methacrolein was 14%. At this time, the catalyst was in a state equivalent to 2.6 electron reduction.

Examples 6 to 19 In Example 6, various metal salts were used in place of bismuth nitrate to prepare catalysts and carry out reactions.

The results are shown in Table 1. Note that the degree of reduction of the catalyst after 100 hours remained in the range of 2.5 to 3.5.

Table 1 Example 20 Disodium hydrogen phosphate (Na2HPO4φ12) 12
0) 17.9g was dissolved in 100ml of water. This and 22.4 g of sodium metavanadate (NaVOa) dissolved in room ml of hot water were mixed, and after cooling, 5 ml of concentrated sulfuric acid was added. Separately, sodium molybdate (N
85 ml of concentrated sulfuric acid was added to a solution in which 121 g of a2MoO4.2H20) was dissolved in 200 ml of water. Next, 500 ml of ethyl ether was added and the mixture was stirred using a separating funnel, left to stand, and the intermediate phase was taken out and air-dried to obtain 10-molybdo-2-vanadophosphoric acid. Log this and add 4.0g of ammonium nitrate (NH4N03) to 100ml
of water was added to the solution. Furthermore, ethylene glycol 1. After adding Og, the mixture was dried at 60° C. using a rotary evaporator. After drying this at 100°C for 1 hour, it was treated at 300°C in a hydrogen stream to obtain a catalyst.

The reaction was carried out in the same reactor and under the same conditions as in Example 1. Analysis of the reaction gas after 100 hours showed that 8% of the isobutane had been converted and the selectivity for methacrylic acid was 62%.
The amount of methacrolein released was 10%. At this time, the catalyst was in a state equivalent to 3.8 electron reduction.

Example 21 Phosphormolybdic acid (Nippon Inorganic Chemical) 218 and 2.9 g of phosphotungstic acid (Nippon Inorganic Chemical) were dissolved in 100 ml of water and stirred at 60° C. for 2 hours. After that, 60℃
and dried on a rotary evaporator. The obtained crystals were mainly H3PMo1, 04o-nl120.

Using this sample No. 18, a catalyst was prepared in the same manner as in Example 20. The reaction was carried out under the same conditions as in Example 2. Analysis of the reaction gas after 3 hours showed that 7% of the isobutane had been converted, the selectivity for methacrylic acid was 58%, and the selectivity for methacrolein was 14%.

At this time, the catalyst was in a state equivalent to 3.2 electron reduction.

Example 22 2.5 g of the catalyst prepared in Example 21 was tested using the same reactor as in Example 1. However, the gas used is
l> A mixed gas of 10 mol% isobutane, 20 mol% water vapor, and 70 mol% helium, and 2) [I W 10 mol%
, a mixed gas of 20 mol % water vapor and 70 mol % helium. 1) gas for 5 seconds, then 2) gas 10 seconds.
were fed into the reactor in alternating seconds. Contact time was 1.28'. Analysis of the reaction gas after 100 hours showed that 10% of the isobutane had been converted and the selectivity for methacrylic acid was 5.
The selectivity for methacrolein was 13%. At this time, the catalyst was in a state equivalent to 3.6 electron reduction.

Example 23 A catalyst equivalent to 3.5 electron reduction was prepared according to the procedure of Example 3, except that ammonium phosphomolybdate was heat treated at 450°C in a nitrogen stream instead of heating in a hydrogen stream.

A reaction was carried out using this catalyst 2.58 under the same conditions as in Example 22, except that the reaction temperature was 320°C. Analysis of the reaction gas after 100 hours showed that 9% of the isobutane had been converted, the selectivity for methacrylic acid was 61%, and the selectivity for methacrolein was 9%. At this time, the catalyst was in a state equivalent to 3.4 electron reduction.

Example 24 4.85 g of bismuth nitrate (Bi(NO3)s) was added dropwise to a solution of 2.04 g of nitric acid added to water 25 (Inl). Next, 23.4 g of phosphomolybdic acid was added, followed by ascorbic acid 5. .28g was added and heated at 60°C for 1 hour.20.2g of fine powder silica (Nippon Aerosil TT600) was added and stirred for 1 hour.Then, it was dried with a rotary evaporator to obtain the The resulting solid was calcined at 350°C for 1 hour.

A reaction was carried out using this catalyst under the same reaction conditions as in Example 1. When the reaction gas was analyzed after 100 hours, the -isobutane conversion rate was 12%, the methacrylic acid selectivity was 48%, and the methacrolein selectivity was 21%.

At this time, the catalyst was in a state equivalent to 2.9 electron reduction.

Example 25 In Example 24, silicon carbide log and ammonia water (
25% by weight) was added, and the firing temperature was increased to 420°C.
The same operation as in Example 24 was performed except for changing to .

A reaction was carried out using this catalyst under the same reaction conditions as in Example 1. Analysis of the reaction gas after 100 hours revealed that the isobutane conversion rate was 10%, the methacrylic acid selectivity was 49%, and the methacrolein selectivity was 18%.

At this time, the catalyst was in a state equivalent to 3.2 electron reduction.

[Effects] According to the method of the present invention, high productivity of methacrylic acid and/or methacrolein can be maintained for a long period of time. Furthermore, the reductivity of methacrylic acid is improved, and the productivity of combining methacrylic acid and methacrolein is also improved.

Claims (1)

[Claims] When oxidizing isobutane-containing gas, P is
Alternatively, a method for producing methacrylic acid and/or methacrolein, characterized by using a catalyst in which a heteropolyacid or its salt containing As as a central element and containing Mo is reduced by one to six electrons per molecule of the heteropolyacid.