JPH0689002B2 - Method for producing pyromellitic dianhydride and catalyst used therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention is directed to pyromellitic dianhydride by vapor-phase catalytic oxidation of 1,2,4,5-tetramethylbenzene (durene) with a gas containing molecular oxygen. The present invention relates to a manufacturing method and a catalyst used for the method.

<Prior Art> Pyromellitic dianhydride (PMDA) has been widely used as a heat-resistant resin, a plasticizer, and a curing agent for epoxy resins. In the future, durene will be produced at a lower cost with an alkylation catalyst such as zeolite. The importance of PMDA as an industrial raw material is increasing more and more due to the increased possibility of being processed.

There are liquid-phase oxidation methods (nitric acid oxidation method, liquid-phase oxidation with cobalt acetate-sodium bromide system) and gas-phase catalytic oxidation method using a catalyst in the production method of PMDA. Although the method is suitable and the liquid phase method is the mainstream at present, it is expected that the gas phase catalytic oxidation method, which can be mass-produced, will become a commercial production method in the future in view of the demand for PMDA.

When producing PMDA from durene as a raw material by the vapor phase catalytic oxidation method, the catalyst component whose main component is vanadium pentoxide is supported on a carrier having a surface area of 1 m ² / g or less such as fused alumina (α-alumina) or silicon carbide. , As a catalyst. Even when only vanadium pentoxide is supported on the carrier as a catalyst component,
Although PMDA can be produced, there are problems such as a low PMDA yield because the conversion rate is low and many byproducts are present. For this reason, it has been attempted to use vanadium pentoxide as a main catalyst component, and to add several kinds of oxides (mainly metal oxides) as a catalyst component on a carrier for use. Regarding this catalyst, for example, Japanese Patent Publication No. 42-1008 and Japanese Patent Publication No. 42-15925.
No. 4, Japanese Patent Publication No. 43-26497, Japanese Patent Publication No. 45-4978, Japanese Patent Publication No. 45
−15018, Japanese Patent Publication No. 45-15252, Japanese Patent Publication No. 46-14332,
Although disclosed in JP-B-49-31972 and JP-B-49-31973, the reaction is sensitive to temperature when used in a fixed bed reactor which is an ordinary industrial catalytic reactor. There are problems such as those described below.

When industrially producing PMDA, a reaction tube with a diameter of about 1 inch is usually filled with about 0.5 to 2 liters of catalyst, and this reaction tube is immersed in a molten salt bath, and the durene is molecularly added from the upper part of the reaction tube. It is sent with an oxygen-containing gas (mainly air). In the catalyst layer, molecular oxygen and durene react due to the catalytic action.
Get PMDA. At this time, a part of the reaction proceeds excessively, and a gas in which durene is completely oxidized such as carbon dioxide and carbon monoxide is also generated.

When the catalysts disclosed by the above patents are used, they have high reactivity and even if PMDA can be produced with high selectivity, the gasification rate to carbon dioxide and carbon monoxide is high, and the gasification rate is 35% or less. Not a rate. Furthermore, these catalyst systems have a strong temperature dependence, and the gasification rate rapidly increases above the optimum reaction temperature, and the optimum reaction temperature range is narrow at 20 to 30 ° C.

When the reaction tube is filled with a catalyst, the height of the catalyst layer is
From 60 cm to 200 cm, it is natural that the temperature can be distributed by the heat of reaction, but the reaction heat of this reaction is 560 kcal / mol, which is considerably larger than the reaction for producing phthalic anhydride from orthoxylene or naphthalene, and theoretically This is 1.8 times more than when producing phthalic anhydride from orthoxylene.
Further, when the durene is completely gasified into carbon dioxide and carbon monoxide, the calorific value becomes extremely large, exceeding 1100 kcal / mol.

Therefore, in this reaction, which originally has a larger reaction heat than other partial oxidation reactions, the temperature distribution in the catalyst layer tends to become larger, and when a known catalyst is used, the gasification rate is 35% or more,
There is a problem that the temperature distribution in the catalyst layer becomes larger and larger, and as a result, the temperature deviates from the optimum temperature range of the catalyst, the gasification rate increases, and the PMDA yield decreases.

Therefore, various efforts have been made to remove the heat of reaction in the catalyst layer, but there are limits in terms of reaction engineering, and the raw material concentration to be supplied can be lowered, the height of the catalyst layer can be lowered, and the reaction tube The system had to be narrowed to lower the productivity and the reaction had to be carried out.

In order to basically solve this problem, it is important to develop a catalyst with a high selectivity to PMDA, a low gasification rate, and a wide optimum reaction temperature range. If this is the case, the temperature control in the catalyst layer becomes easy, and the production efficiency can be improved.

<Problems to be Solved by the Invention> Therefore, the object of the present invention is to obtain a high PMDA yield, carbon dioxide,
(EN) An industrially advantageous method for producing pyromellitic dianhydride, which has a low generation rate (gasification rate) of carbon monoxide, a low reaction heat, and a wide optimum temperature range of the reaction, and a catalyst used therefor. It is a thing.

<Means for Solving the Problems> That is, the present invention provides a first component comprising vanadium oxide, sodium oxide and molybdenum oxide, and a second component comprising at least one selected from chromium oxide, manganese oxide and niobium oxide. And an atomic ratio of metal elements of the supported oxide are Na / V = 0.1 / 10 to 1.0 / 10, Mo / V = 0.3 / 10 to 3.0 / 1.
0 and the atomic ratio of at least one element selected from the second component chromium oxide, manganese oxide and niobium oxide is Cr / V = 0.2 / 10 to 2.0 / 10, Mn / V = 0.1 / 10 to 1.5
The present invention provides a catalyst for producing pyromellitic dianhydride in the range of / 10, Nb / V = 0.5 / 10 to 3.0 / 10, and a method for producing pyromellitic dianhydride by catalytic gas phase oxidation of durene using the catalyst.

<Operation> First, the method for producing pyromellitic dianhydride of the present invention will be described.

In the production method of the present invention, 1,2,4,5-tetramethylbenzene (durene) is subjected to catalytic gas phase oxidation with a molecular oxygen-containing gas using a catalyst described below, preferably in a fixed bed reaction system. Pyromellitic dianhydride is obtained.

When using the fixed bed system, the reaction tube filled with the catalyst is
The inner diameter is about 1 inch, and in industrial scale production, the reaction tube is filled with 0.5 to 2.0 liters of catalyst, but the reaction is performed using the computer program developed by the inventors. Speed, mass transfer speed, heat transfer speed and each fluid,
It is possible to obtain the optimum value of the reaction conditions on an industrial scale by calculating using the physical property values of the solid and the like.

The reaction conditions of this reaction are 8,000 to 15,000 hr ^{-1 in} space velocity.
It is possible to carry out the reaction at a high level of
It is possible to carry out the reaction for 15,000 hr ⁻¹ or more, but it is not so advantageous because the pressure loss in the catalyst layer becomes large. Further, if the space velocity decreases, the gasification rate increases even when the present catalyst is used, and the raw material supply amount per hour also decreases, which is not advantageous in terms of production. Therefore, the space velocity is optimal in the range of 10,000 to 14000 hr ^-1 .

The concentration of durene in the source gas is durene (mol)
/ When air (mol) exceeds 0.25%, heat generation due to the catalytic oxidation reaction becomes remarkable, so that special means for suppressing the temperature rise of the catalyst layer is required. On the other hand, in the above space velocity range of the raw material gas, if productivity is taken into consideration, less than 0.1% is not efficient. Therefore, the concentration of durene in the raw material gas is preferably in the range of 0.1 to 0.25%.

The optimum temperature of the catalyst layer varies depending on the composition and composition ratio of the catalyst, and because the feed material concentration also varies, the heat generation amount in the catalyst layer and the rate of mass transfer and heat transfer due to the difference in space velocity are different. However, in terms of the composition of the catalyst, the catalyst with niobium oxide added is 390 to 460 ° C at the set temperature of the heating medium for heating the catalyst layer and 435 at the maximum temperature of the catalyst layer.
A relatively high temperature range of ℃ to 510 ℃ is good. The catalyst added with chromium oxide is 400 to 440 ° C at the set temperature, the catalyst layer maximum temperature is 426 to 488 ° C, and the catalyst added with manganese oxide is
The temperature range of 390 ℃ to 440 ℃ at the set temperature and 425 ℃ to 490 ℃ at the maximum temperature of the catalyst layer is good. Therefore, when the catalyst of the present invention is used, the set temperature of the heating medium for heating the catalyst layer is 390 ° C.
It is possible to carry out the reaction in a temperature range of 460 ° C to 460 ° C and a maximum catalyst layer temperature of 425 ° C to 510 ° C. If the temperature falls below this temperature range, the reaction activity of the catalyst decreases and the PMDA yield decreases. Further, if it is used in this temperature range or higher, the gasification rate becomes appropriate or higher, and the PMDA yield also decreases, which is not good.

Next, the catalyst of the present invention will be described.

The catalyst of the present invention supports a first component composed of vanadium oxide, sodium oxide and molybdenum oxide, and a second component composed of at least one selected from chromium oxide, manganese oxide and niobium oxide on an inert carrier. The atomic ratio of the metal elements of the supported oxide is Na / V = 0.1 / 10 to 1.0 / 10, Mo / V = 0.3 / 10 to 3.0 / 10.
The atomic ratio of at least one element selected from the second component chromium oxide, manganese oxide and niobium oxide is Cr / V = 0.2 / 10 to 2.0 / 10, Mn / V = 0.1 / 10. ~ 1.5 / 1
0, Nb / V = 0.5 / 10 to 3.0 / 10.

Such a catalyst is a novel catalyst for producing pyromellitic dianhydride obtained by the following studies by the present inventors.

Generally, the activity and reactivity of the catalyst for producing pyromellitic dianhydride are low with vanadium pentoxide alone, so various cocatalyst components (metal oxides) are added, but the type and amount of cocatalyst component added at this time Due to this, the activity and reactivity of the catalyst are greatly affected.

V ₂ O ₅ / CrO ₃ / Na ₂ O as a catalyst component, α-alumina, silicon carbide, etc. supported on a carrier with a specific surface area of 1 m ² / g or less and a particle size of 3 to 6 mmφ are vanadium atoms. Atomic ratio shows high activity in the range of Cr / V = 0.2 / 10 to 2.0 / 10, Na / V = 0.1 / 10 to 1.0 / 10, high yield (100 ^wt % in weight yield)
Thus, it is possible to produce pyromellitic dianhydride.

However, if the atomic ratios of both chromium and sodium deviate from the proper ranges, defects such as a decrease in the yield of pyromellitic dianhydride appear. Furthermore, even within the proper range, 35% or more of the supplied durene will be gasified and detected as carbon dioxide and carbon monoxide. If this gasification is large, it will be produced on an industrial scale using a large amount of catalyst. If you do
The amount of heat generated by the reaction increases, making it difficult to control heat removal. Therefore, it is better to reduce the gasification by complete combustion with large heat generation as much as possible.

As a catalyst for industrially producing PMDA, the inventors of the present invention have a gasification rate (%) (produced carbon dioxide, carbon monoxide vs. raw material%) even if the reactivity and selectivity to PMDA are the same.
In view of the fact that it is advantageous to suppress the reaction temperature from the viewpoint of controlling the reaction temperature and the life of the catalyst, as a result of earnest efforts, V ₂ O ₅
By adding MoO ₃ (molybdenum oxide) to the catalyst composition of / CrO ₃ / Na ₂ O, PMDA can be produced in high yield, and the gasification rate to carbon dioxide and carbon monoxide accompanying the reaction is at a low level. Therefore, the present invention has been accomplished by developing a catalyst having a wide reaction optimum temperature range.

The proper amount of molybdenum to be added is Mo / V = 0.3 / 10 to 3.0 / 10 in terms of atomic ratio with respect to vanadium atoms. If the molybdenum content is less than 0.3 / 10 in terms of Mo / V atomic ratio, the effect of adding molybdenum is not seen and the PMDA yield is 98% by weight.
With highly active catalysts exceeding (60 mol%), more than 35% (gasification rate 35%) of the raw material is still gasified. Conversely, Mo
When the content of molybdenum exceeds 3.0 / 10 in terms of the atomic ratio of / V, the gasification rate will certainly be 30% or less, but the catalytic activity itself will decrease, and therefore the PMDA yield will also decrease.

In the range of Mo / V = 0.3 / 10 to 3.0 / 10, the PMDA yield is improved to the same level or slightly increased as when no molybdenum is added. Also, as the gasification rate decreases, the amount of intermediate oxides increases slightly, but since these have different physical properties such as vapor pressure from PMDA and can be easily separated, it is almost a problem. Don't

Therefore, the preferable composition ratio of the V ₂ O ₅ / CrO ₃ / Na ₂ O / MoO ₃ catalyst is Cr / V = 0.2 / 10 to 2. in terms of atomic ratio to vanadium atom.
0/10, Na / V = 0.1 / 10 to 1.0 / 10, Mo / V = 0.3 / 10 to 3.0 / 10. Furthermore, molybdenum oxide is V ₂ O ₅ / MnO ₂ / Na ₂ O, V ₂ O ₅
Even for the catalyst composition of / Nb ₂ O ₅ / Na ₂ O, V ₂ O ₅ / CrO ₃ / Na ₂
It was found that, as with the O-based catalyst, when MoO ₃ is added as the fourth component, there is almost no decrease in activity, the gasification rate is low, the heat generated by gasification is small, and the catalyst composition is industrially advantageous. It was

The preferable catalyst composition ratio of V ₂ O ₅ / MnO ₂ / Na ₂ O / MoO ₃ and V ₂ O ₅ / Nb ₂ O ₅ / Na ₂ O / MoO ₃ is V ₂ O ₅ / CrO ₃ / Na ₂ O, respectively. / MoO ₃
It exists in the same manner as the system catalyst, and the atomic ratio to vanadium atom is Mn / V = 0.1 / 10 to 1.5 / 10, Na / V = 0.1 / 10 to 1.0 / 10, respectively.
Mo / V = 0.3 / 10 to 3.0 / 10: Nb / V = 0.5 / 10 to 3.0 / 10, Na / V = 0.
1/10 to 1.0 / 10 and Mo / V = 0.3 / 10 to 3.0 / 10.

Fused alumina (α-alumina), silicon carbide, cordierite or the like is preferably used as the inert carrier carrying the above catalyst components.

The supported amount of the catalyst component is in the range of 3% to 15% of vanadium pentoxide (weight) / support (weight), which shows sufficient catalytic activity.

Thus, molybdenum oxide is suitable as a catalyst component, but the binary system of vanadium oxide-molybdenum oxide or the ternary system of vanadium oxide-molybdenum oxide-phosphorus oxide shows almost no catalytic activity or has a catalytic activity. In any case, it is effective only in the low productivity region where the space velocity is 5000 hr ^-1 or less.

The vanadium pentoxide-based composite oxide catalyst for producing PMDA of the present invention containing molybdenum is produced as follows.

First, vanadium pentoxide or ammonium metavanadate is used as a vanadium source. Since these are hardly soluble in water, an organic acid is added to change them to a water-soluble state. The amount of the organic acid is 0.5 to 2.0 times equivalent to V atom, and oxalic acid and tartaric acid are preferable as the organic acid.

A substance that serves as a co-catalyst component is added to this aqueous solution. These are metal oxides and metal salts (ammonium salts,
Carbonate, chloride, nitrate, oxalate), soluble in water and
If it becomes a metal oxide at 400 ℃ ~ 500 ℃, there is almost no problem due to its form.

The catalyst aqueous solution thus prepared is preferably a carrier having a specific surface area of 1 m ² / g or less such as fused alumina (α-alumina) or silicon carbide having a particle size of 2 to 5 mmφ, or fused alumina or cordierite. It is manufactured by supporting 100 or more honeycomb-shaped carriers with a through gas passage per square inch.

As the supporting method, there are an impregnation method in which a carrier is put in a catalyst solution and concentrated to dryness, and a method in which the carrier is preheated and sprayed. α
In the case of a carrier having a high porosity such as alumina, the impregnation method is rather advantageous, but in the case of silicon carbide having a low porosity, the spraying method is advantageous.

After supporting the catalyst component in this manner, under air circulation,
It was calcined at 500 ° C. for 3 to 8 hours and used for the reaction experiment.

The catalyst was evaluated as follows.

Fill a reaction tube with an inner diameter of 1 inch with about 60cc of catalyst, and
Put in a molten salt bath at ~ 500 ℃, space velocity (SV) 3000 ~ 15000
/ hr, molar ratio (molar ratio of durene / air) 0.1-0.4%, oxidation reaction is performed, and the obtained product is converted into methyl ester compound with methanol / boron trifluoride complex salt,
The product is analyzed by gas chromatography, and the reaction gas is extracted with a syringe.
It was analyzed by gas chromatography.

<Example> (Example 1) To 6.0 g of vanadium pentoxide and 16.6 g of oxalic acid, 200 cc of water was added and kept in a warm bath, 0.5 g of ammonium chromate and 174 mg of sodium carbonate, and molybdic acid (molybdic acid content 80 wt%). 593 mg was added to prepare an aqueous catalyst solution. To this aqueous solution was added 60 g of α-alumina (particle size: 3 mmφ), concentrated to dryness on a warm bath with careful stirring, and then at 500 ° C for 3 hours.
The mixture was calcined under flowing air for a period of time to obtain a catalyst.

The composition of the obtained catalyst is V / Cr / Na / Mo = 10 / 0.5 / 0.5 in atomic ratio.
It was /0.5. This catalyst is placed in a reaction tube with an inner diameter of 1 inch.
An experiment was conducted by cc filling and immersing the reaction tube in the molten salt.

The reaction was performed as follows.

A raw material gas in which the molar ratio of durene and air was mixed at a ratio of 0.2: 100 was passed from the upper part of the reaction tube at a space velocity of 12000 hr ^-1 , and the molten salt temperature was kept at 400 ° C. The maximum temperature of the catalyst layer at this time was 437 ° C.

When the reaction gas was extracted with a syringe during the reaction and analyzed by gas chromatography, 29% of the feed material was gasified.

As a result of the reaction experiment, pyromellitic dianhydride (PMDA) was obtained in a yield of 113% by weight. The obtained product was analyzed by the following method.

When the product is about 5 g, 40 cc of methanol / boron trifluoride complex salt-containing methanol is added to the product and then refluxed for 1 hour to convert pyromellitic dianhydride into a methyl ester compound, and then 30 cc of chloroform and 20 cc of water are added. In addition, a methyl esterified product was extracted from the chloroform layer, and the chloroform layer was analyzed by gas chromatography.

The PMDA yield was expressed as product weight / raw material weight.

(Example 2) A reaction experiment was conducted in the same manner as in Example 1 except that the temperature of the molten salt was changed to 430 ° C.

Example 3 An experiment was conducted in the same manner as in Example 1 except that the temperature of the molten salt was 440 ° C. and the raw material concentration (molar ratio of durene / air) was 0.22%.

The results of Example 1, Example 2 and Example 3 are shown in Table 1.

It can be seen from Table 1 that the present catalyst is an industrially excellent catalyst system with almost no significant change in PMDA yield even when the set temperature is changed.

(Comparative Example 1) A catalyst was prepared in exactly the same manner as in Example 1 except that molybdic acid was not added, and was used in a reaction experiment under the same conditions as in Example 1. At this time, the maximum temperature of the catalyst layer was 452 ° C.

During the reaction, the reaction gas was extracted with a syringe and analyzed by gas chromatography. As a result, 39% of the feedstock was gasified.

As a result of the reaction experiment, pyromellitic dianhydride was obtained in a yield of 95% by weight.

From the above results, by adding molybdenum, the reaction temperature in the catalyst layer was lowered by 15 ° C and the gasification rate was lowered by about 10% as compared with the case where molybdenum was not added.

(Examples 4, 5, 6, 7 and Comparative Example 2) A catalyst was prepared and a reaction experiment was conducted in the same manner as in Example 1 except that the addition amount of molybdic acid was changed. The experimental results are shown in Table 2 together with Example 1 and Comparative Example 1.

From these results, it was found that the addition of Mo can suppress the gasification of durene into carbon dioxide and carbon monoxide, and can suppress the heat generation in the catalyst layer, which is an industrial problem. Also, in this case, the addition of Mo is PM when Mo / V is in the range of 0.3 / 10 to 3.0 / 10.
It was found that it had little effect on the DA yield and had an effect on lowering the gasification rate.

(Example 8) To 200 g of vanadium pentoxide and 22.1 g of oxalic acid was added 200 cc of water, and the mixture was kept in a warm bath, 0.5 g of manganese carbonate and 232 mg of sodium carbonate, and molybdic acid (molybdic acid content of 80 wt.
%) 791 mg was added to prepare an aqueous catalyst solution. To this aqueous solution, 80 g of α-alumina (particle size: 3 mmφ) was added, concentrated and dried on a warm bath with careful stirring, and then calcined at 500 ° C. for 3 hours under air flow to obtain a catalyst.

The composition of the obtained catalyst is V / Mn / Na / Mo = 10 / 0.5 / 0.5 in atomic ratio.
It was /0.5.

This catalyst was filled in a reaction tube having an inner diameter of 1 inch in an amount of 60 cc, and the reaction tube was immersed in a molten salt for an experiment.

The reaction was performed as follows.

A raw material gas in which the molar ratio of durene and air was mixed at a ratio of 0.2: 100 was passed from the upper part of the reaction tube at a space velocity of 12000 hr ^-1 , and the molten salt temperature was kept at 390 ° C. The maximum temperature of the catalyst layer at this time was 425 ° C.

When the reaction gas was extracted with a syringe during the reaction and analyzed by gas chromatography, 27% of the feed material was gasified.

As a result of the reaction experiment, pyromellitic dianhydride was obtained in a yield of 109% by weight. The obtained product was analyzed in the same manner as in Example 1.

Example 9 An experiment was performed in the same manner as in Example 8 except that the temperature of the molten salt was 440 ° C., the concentration of the raw materials (molar ratio of durene / air) was 0.22%, and the space velocity was 10,000 hr ⁻¹ . .

(Comparative Example 3) A catalyst was prepared and used in a reaction experiment in exactly the same manner as in Example 8 except that molybdic acid was not added.

The results of Example 9 and Comparative Example 3 were combined with the results of Example 8 to obtain a third value.
Shown in the table.

Table 3 shows that the catalyst with Mo added has PMDA even if the set temperature is changed.
No significant change was observed in the yield, indicating that the catalyst system is industrially excellent. Further, it can be seen from Example 8 and Comparative Example 3 that by adding Mo, the reaction temperature in the catalyst layer is lowered by 10 ° C. and the gasification rate is lowered by about 10% as compared with the case where Mo is not added.

(Example 10) 200 g of water was added to 8.0 g of vanadium pentoxide and 18 g of oxalic acid,
Keep in a warm bath, niobium oxalate (1 gram equivalent 511)
4.49 g and sodium carbonate 139 mg were added, and molybdic acid (molybdic acid content 80 wt%) 1.58 mg was further added to prepare a catalyst aqueous solution. This aqueous solution was supported by spraying it on 100 g of silicon carbide having an average particle size of 2.5 mmφ that had been preheated to 200 ° C., and after supporting, firing at 500 ° C. for 3 hours under air flow,
A catalyst was obtained.

The composition of the obtained catalyst is V / Nb / Na / Mo = 10 / 1.0 /
It was 0.3 / 1.0.

The catalyst was filled in a reaction tube having an inner diameter of 1 inch in an amount of 60 cc, and the reaction tube was immersed in a molten salt for an experiment.

The reaction was performed as follows.

A raw material gas in which the molar ratio of durene and air was mixed at a ratio of 0.24: 100 was passed from the top of the reaction tube at a space velocity of 12000 hr ^-1 ,
The molten salt temperature was maintained at 390 ° C. The maximum temperature of the catalyst layer at this time was 435 ° C.

When the reaction gas was extracted with a syringe during the reaction and analyzed by gas chromatography, 29% of the feed material was gasified.

As a result of the reaction experiment, pyromellitic dianhydride was obtained in a yield of 111% by weight. The obtained product was analyzed in the same manner as in Example 1.

(Comparative Example 4) A catalyst was prepared in exactly the same manner as in Example 10 except that molybdic acid was not added, and was used in a reaction experiment. The maximum temperature of the catalyst layer at this time was 451 ° C. When the reaction gas was extracted with a syringe during the reaction and analyzed by gas chromatography, 37% of the feed material was gasified.

As a result of the reaction experiment, pyromellitic dianhydride was obtained in a yield of 95% by weight.

From the above results, it is understood that the addition of molybdenum lowers the reaction temperature in the catalyst layer by 16 ° C. and the gasification rate by 8% as compared with the case where molybdenum is not added.

(Examples 11, 12, 13) Using the catalyst prepared in Example 10, the reaction was performed under the same conditions as in Example 10 except that only the set temperature was changed.

(Comparative Examples 5, 6, 7) Using the catalyst prepared in Comparative Example 4, the reaction was performed under the same conditions as in Comparative Example 4 except that only the set temperature was changed.

The results of Example 11, Example 12, Example 13 and Comparative Example 5, Comparative Example 6, and Comparative Example 7 are shown in Table 4 together with the results of Example 10 and Comparative Example 4.

The results shown in Table 4 are shown in FIG.

From the results shown in Table 4 and FIG. 1, the catalyst of the present invention having V / Nb / Na and further containing molybdenum has a small effect even if the set temperature is changed, and a large change in PMDA yield is not observed. It can be said that the catalyst can be stably used in a wide temperature range and is industrially advantageous. However, the V / Nb / Na-based catalyst of the comparative example in which molybdenum is not added as a catalyst component shows a PMDA yield of about 100% by weight in a narrow temperature range, but when the temperature exceeds the appropriate temperature range, the yield is extremely high. Deteriorates and cannot be industrially adopted.

(Comparative Example 8) 200 g of water was added to 8.0 g of vanadium pentoxide and 18 g of oxalic acid,
Keep in a warm bath and add titanium tetrachloride (1 gram equivalent 190) to 8
35 mg and sodium carbonate 326 mg were added, and molybdic acid (molybdic acid content 80 wt%) 1.58 mg was further added to prepare an aqueous catalyst solution. This aqueous solution was supported by spraying it on 100 g of silicon carbide having an average particle diameter of 2.5 mmφ that had been preheated to 200 ° C., and after supporting, it was calcined at 500 ° C. for 3 hours under air flow to obtain a catalyst.

The composition of the obtained catalyst is V / Ti / Na / Mo = 10 / 0.5 /
It was 0.7 / 1.0.

The catalyst was filled in a reaction tube having an inner diameter of 1 inch in an amount of 60 cc, and the reaction tube was immersed in a molten salt for an experiment.

The reaction was performed as follows.

A raw material gas in which the molar ratio of durene and air was mixed at a ratio of 0.24: 100 was passed from the upper part of the reaction tube at a space velocity of 14000 hr ^-1 , and the molten salt temperature was kept at 370 ° C. The maximum temperature of the catalyst layer at this time was 415 ° C.

When the reaction gas was extracted with a syringe during the reaction and analyzed by gas chromatography, 27% of the feed material was gasified.

As a result of the reaction experiment, pyromellitic dianhydride was obtained in a yield of 116% by weight. The obtained product was analyzed in the same manner as in Example 1.

(Comparative Examples 9, 10, 11, 12) Using the catalyst prepared in Comparative Example 8, the reaction was carried out under the same conditions as in Comparative Example 8 except that only the set temperature was changed.

The results of Comparative Examples 8 to 12 are also shown in Table 5. FIG. 2 is a graph of Table 5.

(Example 14) to (Example 18) 200 g of water was added to 8.0 g of vanadium pentoxide and 22.1 g of oxalic acid, and the mixture was kept in a warm bath, and sodium carbonate, molybdic acid (80 wt% as MoO ₃ ), niobium oxalate ( 1 gram equivalent
511), titanium tetrachloride, manganese carbonate and ammonium chromate were added in the amounts shown in Table 6 to prepare a catalyst solution. To this aqueous solution, 80 g of α-alumina (particle size: 3 mmφ) was added, concentrated to dryness while carefully stirring in a hot water bath, and then calcined for 6 hours under air flow to obtain a catalyst. The obtained catalyst was filled in a reaction tube having an inner diameter of 1 inch in an amount of 60 cc, and the reaction tube was immersed in a molten salt for an experiment.

The experimental results are shown in Tables 7 and 8.

Even if the second component, niobium oxide, manganese oxide, or chromium oxide is mixed and used as a catalyst component, there is no phenomenon that the catalytic activity is lowered or the gasification rate is increased due to its composite action. , PMDA could be produced in a high yield as in the case of using the second component alone.

(Comparative Example 13) A catalyst was prepared under the same conditions as in Comparative Example 8 except that titanium tetrachloride, sodium carbonate, and molybdic acid were not added, and used for the reaction experiment.

(Comparative Example 14) A catalyst was prepared under the same conditions as in Comparative Example 8 except that titanium tetrachloride and sodium carbonate were not added, and was used in a reaction experiment.

(Comparative example 15) Comparative example except that 2 g of ammonium dihydrogen phosphate was added
A catalyst was prepared under the same conditions as 14 and used in the reaction experiment.

Table 9 shows the results of the reaction experiments of Comparative Example 13, Comparative Example 14, and Comparative Example 15. The reaction results of Comparative Example 13, Comparative Example 14, and Comparative Example 15 all had a problem that the PMDA yield was low.

<Effects of the Invention> As a raw material, inexpensive durene, which has been supplied in large quantities with the development of the petrochemical industry by the catalyst of the present invention,
It is possible to industrially advantageously produce pyromellitic dianhydride (PMDA) in a high yield in a wide range of optimum reaction temperature regions while suppressing heat generation in the catalyst layer, and the effect is significant.

[Brief description of drawings]

FIG. 1 and FIG. 2 are graphs showing the relationship between the set temperature of the heating medium for heating the catalyst layer, the gasification rate, and the PMDA yield, respectively.

Claims (10)

[Claims] 1. A first component comprising vanadium oxide, sodium oxide and molybdenum oxide, and chromium oxide,
A second component comprising at least one selected from manganese oxide and niobium oxide is supported on an inert carrier, and the atomic ratio of metal elements of the supported oxide is Na / V = 0.1 / 10-1.0 / 10, Mo / V = 0.3 / 10-3.0 / 10, and the atomic ratio of at least one element selected from the second component chromium oxide, manganese oxide and niobium oxide is Cr / V = 0.2 / 10 to 2.0 / 10, Mn / V = 0.1 / 10 to 1.5 / 10, Nb
A method for producing pyromellitic dianhydride, which comprises subjecting durene to catalytic gas phase oxidation with a gas containing molecular oxygen, using a catalyst having a ratio of /V=0.5/10 to 3.0 / 10. 2. The method for producing pyromellitic dianhydride according to claim 1, wherein the catalytic gas phase oxidation reaction is carried out in a fixed bed. 3. The production method according to claim 1, wherein the catalytic gas phase reaction has a space velocity of raw material gas = SV (1 / hr) of 1000.
A method for producing pyromellitic dianhydride, which is carried out at 0 to 14000 and a durene concentration of 0.1 to 0.25% durene (mol) / air (mol). 4. The method for producing pyromellitic dianhydride according to claim 1, wherein the heat medium temperature for heating the catalyst layer during the catalytic gas phase reaction is 390 to 460 ° C. 5. The method for producing pyromellitic dianhydride according to claim 1, wherein the second component is niobium oxide. 6. The production method according to claim 1, wherein the second component is niobium oxide, and the heating medium temperature for heating the catalyst layer during the catalytic gas phase reaction is 390 to 460 ° C. Manufacturing method. 7. A first component comprising vanadium oxide, sodium oxide and molybdenum oxide, and further chromium oxide,
A second component comprising at least one selected from manganese oxide and niobium oxide is supported on an inert carrier, and the atomic ratio of metal elements of the supported oxide is Na / V = 0.1 / 10-1.0 / 10, Mo / V = 0.3 / 10-3.0 / 10, and the atomic ratio of at least one element selected from the second component chromium oxide, manganese oxide and niobium oxide is Cr / V = 0.2 / 10 to 2.0 / 10, Mn / V = 0.1 / 10 to 1.5 / 10, Nb
A catalyst for producing pyromellitic dianhydride, which is used in the case of producing pyromellitic dianhydride by vapor-phase oxidation of durene having a range of /V=0.5/10 to 3.0 / 10. 8. The catalyst for producing pyromellitic dianhydride according to claim 7, wherein the inert carrier is α-alumina or silicon carbide. 9. The catalyst for producing pyromellitic dianhydride according to claim 7, wherein the amount of the catalyst component supported on the inert carrier is 3 to 15% of vanadium pentoxide (weight) / carrier (weight). 10. The catalyst for producing pyromellitic dianhydride according to claim 7, wherein the second component is niobium oxide.