JPS637537B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention involves producing pyromellitic acid or its anhydride by catalytic gas phase oxidation of 1,2,4,5-tetramethylbenzene (hereinafter referred to as diurene) with a molecular oxygen-containing gas in the presence of a vanadium-containing catalyst. It is about the method. Specifically, in the present invention, a raw material gas containing 10 to 50 g/Nm ³ of raw material Diurene, 3 to 30% by volume of water vapor, and the remainder consisting of a molecular oxygen-containing gas, in the presence of a vanadium-containing catalyst, The present invention provides a method for obtaining pyromellitic acid or its anhydride in high yield and industrially by catalytic gas phase oxidation, and in particular, oxidizes the high temperature product gas containing the obtained pyromellitic anhydride with water or an aqueous medium. After collecting pyromellitic anhydride through a collection device consisting of a wall tower and a cleaning tower, a process is adopted in which a portion of the water vapor-containing exhaust gas discharged from the collection device is recycled and reused as part of the raw material gas. The present invention relates to an industrial method for producing pyromellitic acid or its anhydride with high productivity and high yield. Pyromellitic anhydride is used in heat-resistant resins, plasticizers,
It has been widely used as an epoxy resin curing agent, and its importance as an industrial raw material has been increasing in recent years. In addition to the catalytic gas phase oxidation method of diurene, liquid phase oxidation method of diurene and other synthesis methods from starting materials other than diurene have also been proposed. In general, the oxidation reaction of diurene is a reaction accompanied by extremely large heat, and in order to industrially efficiently produce pyromellitic anhydride by catalytic gas-phase oxidation of diurene, it is necessary to use a highly selective catalyst and the most economical method. A catalytic gas phase oxidation reaction process must be devised. As a method for producing pyromellitic anhydride by catalytic gas phase oxidation of diurene, there are many patent documents (for example, Belgian Patent No. 655686, Japanese Patent Publication No. 45
−4978, Special Publication No. 15018, Special Publication No. 15252
Special Publication No. 49-31972, Special Publication No. 49-31973, Special Publication No. 52-3931, etc. ) has been published. However, in these prior art examples, the concentration of diurene in the raw material gas composition is 20g/
The concentration is as low as Nm ³ or less, and the desired pyromellitic acid or its anhydride cannot be obtained in good yield, so it is not necessarily industrially satisfactory. The reaction heat of the catalytic gas phase reaction of diurene is extremely large compared to the phthalic anhydride synthesis reaction by oxidation of ortho-xylene, and the efficient removal of this reaction heat is the key to the catalyst used. In addition to performance, this is considered to be an important issue in obtaining pyromellitic anhydride in high yield. In other words, the general method is to pass a raw material gas with a low diurene concentration through a catalyst layer at a high temperature and high space velocity, thereby storing reaction heat to produce 4,5-dimethylphthalic anhydride, 4,6-dimethylisophthalic acid, and trimellitic acid. However, it is still unsatisfactory as an industrial production method in terms of productivity and yield. In view of the current situation, in order to further increase productivity, the present inventors produced pyromellitic acid or its anhydride in high yield even when the reaction was carried out at high temperature and high space velocity using a raw material gas with a high diurene concentration. As a result of continuing research on the process that can be used to improve the catalyst and various reaction conditions such as reaction temperature, space velocity, raw material diurene concentration, and raw material gas diluent, we decided to add a specific concentration of water vapor to the raw material gas. They found that the yield of pyromellitic anhydride or its anhydride was improved by 5 to 8% by weight compared to the case without additives, and they also improved the product collection method. We have now established an industrial method for producing the anhydride with high productivity and yield. That is, the present invention is specified as follows. (1) 1,2,4,5-tetramethylbenzene is 10
~50 g/Nm ³ - A pyromellit characterized by catalytic gas phase oxidation of a raw material gas containing 3 to 30% by volume of water vapor and the remainder being molecular oxygen-containing gas in the presence of a vanadium-containing catalyst. A method for producing an acid or its anhydride. (2) The vanadium-containing catalyst is at least one selected from the group consisting of oxides of vanadium, titanium, phosphorus, niobium, and antimony, and optionally alkali metals, alkaline earth metals, rare earth elements, zinc, and thallium. (1) above, characterized in that it is a catalyst comprising an oxide of an element supported on an inert carrier;
Method described. (3) 1,2,4,5-tetramethylbenzene is 10
~50g/ ^Nm3 - Pyromellitic anhydride obtained by catalytic gas phase oxidation of a raw material gas containing 3 to 30% by volume of water vapor and the remainder being molecular oxygen-containing gas in the presence of a vanadium-containing catalyst. A method for producing pyromellitic acid or its anhydride, which comprises introducing a high-temperature generated gas containing pyromellitic acid or anhydride to a collection device using water or an aqueous medium. (4) The vanadium-containing catalyst is at least one selected from the group consisting of oxides of vanadium, titanium, phosphorus, niobium, and antimony, and optionally alkali metals, alkaline earth metals, rare earth elements, zinc, and thallium. (3) above, characterized in that it is a catalyst comprising an oxide of an element supported on an inert carrier;
Method described. (5) The method according to (3) or (4) above, wherein the collection device using water or an aqueous medium comprises a wet wall tower and a washing tower formed of water or an aqueous medium. (6) Maintaining the outlet temperature of exhaust gas discharged from a collection device using water or an aqueous medium at 40 to 80°C,
(3) above, characterized in that 15 to 85% of the total amount of exhaust gas is recycled and reused as part of the raw material gas;
The method described in (4) or (5). Hereinafter, specific embodiments of the present invention will be described. First, in the present invention, in the presence of a vanadium-containing catalyst, a raw material gas containing 10 to 50 g/Nm ³ of diurene, 3 to 30 volume % of water vapor, and the remainder consisting of a molecular oxygen-containing gas is passed through a contact gas. Although it undergoes phase oxidation, there is only a statement in the specification of Japanese Patent Publication No. 15018/1973 that the oxidizing agent can be diluted with water vapor and used by adding water vapor to the raw material gas. However, there is no disclosure of the effects of allowing a specific concentration of water vapor to coexist in the raw material gas as disclosed in the present invention. That is, according to experiments conducted by the present inventors, the yield of pyromellitic acid or its anhydride when 3 to 30% by volume of water vapor is added to the raw material gas and when no water vapor is added is higher than that of pyromellitic acid or its anhydride under the same reaction conditions. A control experiment conducted revealed that the amount increased by 5 to 8% by weight compared to the case where no water vapor was added. This effect was unexpectedly remarkable even for the inventors.
The mechanism of action is unknown, but one factor is that the added water vapor has some useful effect in the process of desorption of the generated pyromellitic anhydride from the catalyst, and that it causes side effects such as secondary oxidation of the product that progresses sequentially. In order to suppress the production of living organisms, it is estimated that when a particularly high concentration of raw material Diurene is used, it contributes to an improvement in the yield of pyromellitic anhydride. If the water vapor concentration added to the raw material gas is less than 3% by volume, the effect of improving the yield of pyromellitic anhydride will be small, and even if the water vapor concentration is too high, exceeding 30% by volume, the desired product pyromellitic anhydride will not be produced. The production of by-products such as trimellitic anhydride, which deteriorates the quality of the acid, increases, and the effect of improving the yield of pyromellitic anhydride is reduced. Methods for entraining water vapor in the raw material gas include introducing low-pressure steam from the outside into the inlet of the reactor, or collecting the generated pyromellitic anhydride using a collection device using water or an aqueous medium. A method can be applied in which a part of the exhaust gas containing water vapor saturated with vapor pressure at the temperature of the exhaust gas discharged from the collection device is circulated into the raw material gas. From this point of view, the latter method is preferable. When part of the exhaust gas from the collection device is circulated to the raw material system, the exhaust gas outlet temperature is maintained in the range of 40 to 80°C, preferably 45 to 75°C. If the temperature is too low, it will not be possible to efficiently recover pyromellitic anhydride at a high concentration, and if the temperature is too high, energy loss due to water evaporation will increase. In addition, the amount of exhaust gas recycled to the raw material system is 15% of the total exhaust gas.
Adjusted to be in the range of ~85%. If this ratio is too small, there will be an inconvenience that the exit temperature of the exhaust gas from the collection device must be extremely raised in order to secure the desired amount of water vapor for the reaction, and if the circulation ratio of the exhaust gas is too high, there will be a lack of oxygen in the system. Problems such as a decrease in the yield of pyromellitic anhydride and accelerated deterioration of the catalyst occur. The catalyst used in the present invention is a vanadium-containing catalyst, and a conventionally known catalyst for oxidizing diurene can be used. For example, V ₂ O ₅ −
_TiO2 , WO3 _- based, _{V2O5 - P2O5 - TiO2} , _MoO3 ,
WO ₃ series, V ₂ O ₅ −TiO ₂ (anatase type) − MoO ₃ ,
P ₂ O ₅ series, V ₂ O ₅ −TiO ₂ −Na ₂ O, P ₂ O ₅ series, V ₂ O ₅ −
TiO ₂ −P ₂ O ₅ −Nb ₂ O ₅ −K ₂ O, Cs ₂ O, V ₂ O ₅ −
It is _{a B2O3 - SnO2} , _P2O5 , _TiO2 , _Na2O system. Particularly preferred are oxides of vanadium, titanium, phosphorus, niobium and antimony, and optionally alkali metals, alkaline earth metals, rare earth elements,
A catalyst can be used in which an inert carrier supports a catalytic material comprising an oxide of at least one element selected from the group consisting of zinc and thallium. The catalyst material of this catalyst system is 1 to 80 parts by weight of V ₂ O ₅ ,
The main component is 99 to 20 parts by weight of TiO ₂ , and based on the total of 100 parts of both components, 0.01 to 5 parts by weight of Nb ₂ O ₅ , 0.02 to 10 parts by weight of P ₂ O ₅ , and 0.1 parts by weight of Sb ₂ O ₃ ~30 parts by weight. In addition, in addition to the above composition ratio, Na ₂ O, K ₂ O,
A total of 0.01 to 5 parts by weight of one or more of Rb ₂ O, Cs ₂ O, CaO, SrO, BaO, or a total of 0.01 of one or more of rare earth element oxides, ZnO, Tl ₂ O
It may contain up to 3 parts by weight. The rare earth elements referred to here are elements with atomic numbers 39 and 57 to 71,
Particularly preferred are yttrium, lanthanum, cerium, neodymium, gadolinium, terbium, and erbium. In addition, the oxides of each element as the catalyst material used here, that is, V ₂ O ₅ ,
_Nb2O5 , _{P2O5 , Sb2O3 , Na2O , K2O} , _Rb2O ,
_Cs2O , CaO, SrO, BaO, rare earth oxides, ZnO,
Sources of Tl ₂ O include oxides of these elements,
It can be appropriately selected from ammonium salts, sulfates, nitrates, organic acid salts, carbonates, chlorides, hydroxides, free acids, and the like. Furthermore, the catalyst material components shown in the text are not necessarily limited to the oxide forms described in the text, but are merely used to indicate their compositions. Effective in the catalytic material in this catalytic system
There are various methods for producing TiO ₂ , such as high-purity TiO ₂ obtained by synthesizing titanium ammonium sulfate using titanium tetrachloride as a raw material and thermally decomposing it, or heat-treating titanium hydroxide produced by hydrolyzing titanyl sulfate. TiO ₂ etc. are preferred, but are generally commercially available for pigments.
TiO ₂ can also be used satisfactorily by performing appropriate treatment to control the removal of harmful impurities.
TiO ₂ exists in two types of crystal forms: anatase type and rutile type, and the anatase type is useful for the catalyst of the present invention. Furthermore, in the case of high-purity TiO ₂ made from titanium tetrachloride, it is also possible to use a mixture of rutile-type TiO 2 , but commercially available rutile-type TiO ₂ for pigments is TiO ₂ that has already been specially _treated . Therefore, excellent effects cannot be expected even if used in the present invention. The above-mentioned catalyst substance can be used as a shaped catalyst by itself or in combination with a shaping aid, but is preferably used by supporting it on an inert carrier. As the inert carrier, commonly known carriers such as silica, alumina, silicate, silicon carbide, anti-flintstone, and pumice are used. Preferred carriers include, for example, aluminum containing 10% or less as Al ₂ O ₃ and silicon carbide content of 10% or less. Silicon carbide-based carriers with a porosity of 50% or more and an apparent porosity of 10% or more give good results. Note that the shape of the carrier is not particularly limited, and any shape such as an unstable shape, a spherical shape, a cylindrical shape, a ring shape, a cylindrical shape, etc. can be adopted. To prepare the catalyst, TiO ₂ powder is dispersed in an aqueous solution containing vanadium, niobium, phosphorus, antimony, and other component elements, a nitric acid aqueous solution, an oxalic acid aqueous solution, or a hydrochloric acid aqueous solution to form a slurry.
This catalyst slurry was sprayed onto a preheated carrier using a sprayer, and then
A method of firing at ~650°C, preferably 400~550°C for several hours under a stream of air, under an air blanket, or under a stream of an inert gas such as nitrogen is preferred. In this case, the loading rate of the catalyst substance on the carrier varies depending on the specific gravity, shape, particle size, etc. of the carrier used, but for example, 3 to 10
When using a spherical silicon carbide carrier with a diameter of mm, 3 to 15 g of catalyst material is supported per 100 c.c. of the carrier. When the supported catalyst obtained as described above is used in the production method of the present invention, it is particularly useful that the catalyst material has the following physical properties. That is,
The total volume of pores with an average pore diameter in the range of 0.05 to 0.45μ is 50% relative to the total volume of pores with a pore diameter of 10μ or less.
The pores are distributed at a ratio that is greater than %. In general, the average pore diameter and pore volume distribution are influenced by catalyst preparation conditions such as catalyst composition and calcination conditions, but the catalyst of the present invention is particularly composed of TiO ₂ powder and other materials in the catalyst slurry. It is affected by the degree of dispersion with the catalyst material and the slurry concentration. That is, when the slurry has a high degree of dispersion and a high concentration, the average pore diameter and pore volume also tend to increase.
Taking these points into consideration, the catalyst material having the above-mentioned pore distribution is prepared by appropriately determining the catalyst composition, the degree of dispersion and concentration of the catalyst slurry, and the firing conditions. The reaction conditions for catalytic gas phase oxidation of diurene using the catalyst obtained as described above include a reaction temperature of 300 to 450°C, preferably 320 to 430°C, and a space velocity of 3000 to 15000 hr ^-1 (STP), preferably is 4000～
10000hr ^-1 (STP), raw material concentration 10-50g/
Nm ³ -source gas, preferably 20 to 40 g/Nm ³ -source gas, and the water vapor concentration in the source gas is 3 to 30% by volume. Although a molecular oxygen-containing gas is used as the oxidizing agent, air is preferably used, and it is also possible to use molecular oxygen diluted with an inert gas such as carbon dioxide or nitrogen. Thus, pyromellitic anhydride or its anhydride can be obtained in a high yield of 115-125% by weight. Subsequently, pyromellitic anhydride is separated and collected from the high temperature generated gas containing pyromellitic anhydride that has exited the reaction zone. As a collection method, it is usually considered to adopt an indirect cooling method in which crystals are crystallized on the wall surface of the cooler by allowing cooling or forced cooling. However, the collection method using indirect cooling method is
In order to remove the crystals that have crystallized, it is important to stop the equipment and scrape off the crystals that have formed on the wall of the cooler.
Alternatively, it is necessary to stop the product, heat it, melt it, and take it out.Therefore, if you want to collect it continuously, you have to alternately switch between at least two cooling devices to cool and take it out. In addition, the scraping method is economically disadvantageous as it requires a great deal of labor and equipment.
If done manually, hygiene problems arise. On the other hand, in the heating melting method, pyromellitic anhydride has a high melting point of 285-287°C and requires heating and melting with a high-temperature heat medium, resulting in a large energy loss.
In addition, it is difficult to apply because it easily deteriorates. For the reasons mentioned above, it is preferable to collect pyromellitic anhydride by directing the high-temperature generated gas to a collection device using water or an aqueous medium and recovering it as a slurry or aqueous solution. Conventionally known collection devices that use water or an aqueous medium can be used. For example, a method in which water or an aqueous medium is sprayed down in the form of raindrops or a film into a high-temperature generated gas, or a wall surface that is kept below the precipitation temperature of pyromellitic anhydride and water or an aqueous medium is flowed down so as to thinly cover the wall surface. There is a collection method in which the pyromellitic anhydride is introduced into a condenser having a pyromellitic anhydride and deposited on the wall of the condenser. However, in this method, the high-temperature produced gas is rapidly cooled, and the pyromellitic anhydride becomes extremely fine particles and becomes atomized, or crystals of pyromellitic anhydride crystallize at the contact point between the produced gas and the aqueous medium, forming lumps. This may cause problems such as growth and deterioration of the quality of pyromellitic anhydride, and it may be difficult to collect pyromellitic anhydride stably and efficiently. As the collecting device for pyromellitic anhydride in the production method of the present invention, it is preferable to use a device consisting of a wet wall tower and a washing tower formed of water or an aqueous medium, which eliminates the above-mentioned drawbacks. can. That is, the high-temperature product gas containing pyromellitic anhydride that has exited the reaction zone is introduced into a wetted wall tower formed of water or an aqueous medium, and heat exchange is performed between the high-temperature product gas and water or an aqueous medium. The temperature of the hot product gas is lowered below the dew point, the product gas is introduced into a washing tower and contacted with water or an aqueous medium to collect pyromellitic anhydride, and the pyromellitic anhydride is collected from the bottom of the wall tower and the washing tower. A method for collecting pyromellitic anhydride is adopted in which pyromellitic anhydride and pyromellitic acid are recovered as a slurry or an aqueous solution. That is, a hot product gas stream containing pyromellitic anhydride is introduced into a wet wall tower formed of water or an aqueous medium, and after heat exchange between the hot product gas and water or an aqueous medium, water or an aqueous medium is introduced. The medium collects pyromellitic anhydride. Since the pyromellitic anhydride collected in this way uses water or an aqueous medium, part or all of the anhydride becomes dihydrate and becomes pyromellitic acid as a slurry or aqueous solution of a mixture of the remaining pyromellitic anhydride and pyromellitic acid. be captured. The advantages of wet wall towers in this collection method are:
When high-temperature product gas is heat exchanged with water or an aqueous medium, the temperature of the high-temperature product gas gradually decreases, resulting in the growth of crystallized crystals, and there is almost no atomization of pyromellitic anhydride, making it difficult to collect. This is something that can be done easily. In other words, when water or an aqueous medium is sprayed onto a high-temperature product gas in the form of raindrops or a film, the high-temperature product gas comes into direct contact with the low-temperature water or aqueous medium in a short period of time, so the temperature of the product gas drops rapidly. However, the crystallized crystals remain fine and become atomized, making collection difficult; however, according to this method, collectable crystals of pyromellitic anhydride can be obtained. The second advantage is that since the inside of the wet wall column is covered with fluid water or an aqueous medium, crystals such as pyromellitic anhydride do not precipitate or settle on the wall surface of the vessel. Alternatively, since it is continuously carried out of the wet wall tower together with the aqueous medium, it can be operated continuously. A third advantage is that a considerable distance and space can be provided between the hot product gas inlet and the cold water or aqueous medium. Crystals do not precipitate at the supply port and make operations difficult. The fourth advantage is that since it is a wet wall tower, it has good heat exchange efficiency and the apparatus can be made smaller compared to an air-cooled crystallizer. Although the shape of the wetted wall tower used in this method is not particularly limited, it is desirable that the water or aqueous medium forming the wetted wall not form raindrops or mist. In addition, the size of the wetted wall tower can be appropriately determined depending on the amount and characteristics of the high-temperature product gas introduced, as long as it can cool the high-temperature product gas to the temperature at which crystals are precipitated. . The temperature of such high-temperature product gas is introduced into the wet wall tower at a temperature higher than the dew point of the product gas, taking into account blockage of gas flow pipes, precipitation of crystals at the wet wall inlet, etc. Considering that the column is a crystallizer and the separation operation of the collected pyromellitic anhydride is performed, a temperature as close to the dew point as possible and up to 100°C higher than the dew point, preferably about 20°C higher than the dew point, is suitable. be. Water or aqueous media forming wet walls include:
In addition to water such as pure water, tap water, and industrial water, it may also be an aqueous slurry containing collected pyromellitic anhydride, or a separated liquid obtained by separating collected pyromellitic anhydride. The temperature of the water or aqueous medium is not particularly limited as long as it is in liquid form and flows through the container walls, but when using the water or aqueous medium in circulation, the calorific value of the high-temperature mixed gas and the evaporated water are released outside the system. Usually 40~
Operated at 80℃. The flow rate of water or aqueous medium is
The amount should cover the entire wall surface of the wetted wall tower, and is determined by the type of wetted wall tower and the amount of evaporation associated with heat exchange. The temperature of the hot product gas containing pyromellitic anhydride is lowered in the wet wall column, and the pyromellitic anhydride contained therein crystallizes. Although some of the crystallized solids are collected by the water or aqueous medium flowing down the wet wall column, the majority remains in the gas mixture and is brought into contact with the water or aqueous medium in the washing column. The pyromellitic anhydride-containing gas which has passed through the wetted wall column can be easily collected, since the pyromellitic anhydride no longer becomes atomized when it comes into contact with water or an aqueous medium in the form of rain drops or spray. After collecting pyromellitic anhydride as described above, the outlet temperature of the exhaust gas discharged from near the top of the cleaning tower is maintained at 40 to 80℃, and the total amount of exhaust gas is
15-85% is recycled and reused as part of the raw material gas. Next, one embodiment of the present invention will be described with reference to the drawings. Air for reaction passes through line 1 from blower 101, is heated in preheater 102, passes through line 2, mixes with the circulating gas coming from line 11, and then passes through line 3 (if necessary, steam for adjustment from line 12 to line 3). (can also be added to the
The reactor 103 (having the shape of a multi-tubular heat exchanger, with a catalyst filled in the tubes and a heat medium circulating outside the tubes) is entered from the line 5. The pyromellitic anhydride-containing gas generated by the reaction enters the wet wall tower 104 (water or an aqueous medium is supplied from the nozzle 21 to form a thin film on the wall of the tower) through line 6, where it is gradually cooled and then passed through line 7. The exhaust gas then enters the cleaning tower 105 (where the water or aqueous medium supplied from the shower nozzle 25 and the reaction gas are brought into contact in a countercurrent flow), and after the products are collected and separated, the exhaust gas is kept warm to prevent moisture in the gas from condensing. It passes through line 8 and is divided into line 9 and line 10. The remainder of the exhaust gas to be reused for the reaction is discharged outside the system from line 10 via line 9, and the exhaust gas from line 10 is pressurized by blower 107 and then passes through line 11 to line 2.
It is mixed with more air and circulated to the reactor. The products collected in the wet wall column 104 and the washing column 105 are transferred as an aqueous solution or slurry from the bottom of each column via lines 22 and 23 and then via line 24 to a purification step. The water or aqueous medium supplied to the wetting wall tower and the washing tower is replenished through lines 26 to 106, with the temperature adjusted so that the exhaust gas outlet temperature from the washing tower is at the set temperature. Although the present invention has been described above, it will be explained in more detail by showing examples below. Example 1 5700g of reagent grade TiCl ₄ was gradually dropped into water.
A 60% aqueous solution was prepared, and 2940 g of reagent grade sulfuric acid was added to this TiCl ₄ aqueous solution with stirring. On the other hand, prepare a saturated aqueous solution containing 3940 g of special grade ammonium sulfate heated to 100°C, and add this saturated aqueous solution to the TiCl ₄ −
Add to H ₂ SO ₄ aqueous solution with stirring and leave to stand.
Titanium ammonium sulfate [(NH ₄ ) ₂ SO ₄・
TiOSO ₄ H ₂ O] was precipitated. This was separated separately and then calcined at 750°C for 10 hours to obtain 2300g of TiO ₂ . Dissolve 514 g of oxalic acid in 6400 c.c. of deionized water to make an oxalic acid solution, and add 257 g of ammonium vanadate,
16.2g ammonium monophosphate and niobium chloride
Hydrochloric acid aqueous solution containing 12.2g and antimony trioxide 120
1800 g of the above TiO ₂ to the prepared solution obtained by adding
was added and stirred for 30 minutes to form a catalyst slurry. 2000 c.c. of SiC carrier (SiC content 98.5%) with an average particle size of 5 mm and an apparent porosity of 20% is placed in a stainless steel rotary furnace that can be heated from the outside and preheated to 200 to 250°C. While rotating the rotary furnace, the catalyst slurry was sprayed onto the carrier to support 180 g of the catalyst material.
It was then calcined for 8 hours at 530°C under a stream of air. The composition of the finished catalyst thus obtained is V ₂ O ₅ :
TiO ₂ :P ₂ O ₅ :Nb ₂ O ₅ :Sb ₂ O ₃ =10:90:0.5:
It was 0.3:6. The pore distribution of the catalyst prepared in this way was measured using a mercury intrusion porosimeter, and the pore diameter was
The pore volume occupied by pores of 0.05 to 0.45 μ was 89% of the total pore volume of 10 μ or less. The obtained catalyst was immersed in a molten salt bath maintained at 390°C (hereinafter molten salt temperature is abbreviated as NT (°C)) in a stainless steel reaction tube with a diameter of 25 mm until the height of the catalyst layer reached 1.5 m. Filled. 30g/N there
A raw material gas consisting of diurene at a concentration of m ³ , water vapor at 10% by volume, and the balance being air was passed through the reactor at a space velocity of 5000 hr ⁻¹ for reaction. The reaction gas was led to a crystallizer and a water-washed collector to collect the product. When the entire collected product was dissolved in hot water and analyzed, pyromellitic acid was obtained in a yield of 119.3% by weight in terms of pyromellitic anhydride. Comparative Example 1 Using the same catalyst as that prepared in Example 1, an oxidation reaction of diurene was carried out under the same reaction conditions as in Example 1 except that the raw material gas did not contain water vapor, and the product was analyzed. As a result, pyromellitic acid was obtained in a yield of only 113.5% by weight calculated as pyromellitic anhydride. Example 2 Ilmenite was mixed with 80% concentrated sulfuric acid, and after a sufficient reaction, the mixture was diluted with water to obtain a titanium sulfate aqueous solution. Iron pieces were added as a reducing agent to reduce the iron in the ilmenite to ferrous ions, which were then cooled and separated as ferrous sulfate.
The aqueous titanium sulfate solution thus obtained was heated to boiling and hydrolyzed to precipitate hydrous titanium oxide. After thoroughly washing this, it was fired at a temperature of 800° C. for 4 hours under air circulation. This was subjected to jet air flow pulverization treatment, with an average particle size of approximately 0.5 μ and a specific surface area of 22 m ² /
g of anatase-type TiO ₂ was obtained. Aqueous hydrochloric acid solution containing predetermined amounts of ammonium vanadate, primary ammonium phosphate, niobium chloride, antimony trioxide, cesium carbonate, and the above TiO ₂
Using the catalyst solution obtained by adding , it was supported on a SiC carrier in the same manner as in Example 1, and the composition of the finished catalyst obtained by firing was V ₂ O ₅ :TiO ₂ :P ₂ O ₅ : in weight ratio.
Nb ₂ O ₅ : Sb ₂ O ₃ : Cs ₂ O=20:80:1.0:0.5:8:
It was 0.2. Place the above catalyst in a stainless steel reaction tube with an inner diameter of 25 mm.
It was filled to a height of 1.5m. Diurene at a concentration of 30 g/Nm ³ , water vapor and oxygen-containing gas at a volume of about 8% were added thereto at an SV of 5000 hr ^-1.
NT was introduced into a reactor maintained at 380°C. The reaction product gas is introduced into a wet wall tower and a washing tower, and the product is collected and recovered as an aqueous solution or slurry. After that, the exhaust gas from the washing tower is washed without being dehumidified.
% was discharged outside the system, and the remaining exhaust gas was circulated into the raw material gas. The temperature of the water supplied to the wet wall tower and the washing tower or the liquid from which the product was separated from the recovered liquid was adjusted so that the top temperature of the washing tower was in the temperature range of 60 to 63°C. Analysis of the product obtained by repeating crystallization and separate steps from the liquid recovered from the wet wall tower and washing tower revealed that pyromellitic acid was obtained in a yield of 111.8% by weight as pyromellitic anhydride. The acid value of this pyromellitic acid was 882. Separate analysis of the reaction product gas revealed that the single-stream yield of pyromellitic anhydride was 120.2% by weight. Examples 3 to 6 Catalysts having the compositions shown in Table 1 were prepared in the same manner as in Example 1 and subjected to reactions. The results obtained are shown in Table 2.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention. 101...Blower, 102...Preheater, 10
3... Reactor, 104... Wet wall tower, 105...
Washing tower, 106... heat exchanger, 107... blower.

Claims (1)

[Claims] 1 1,2,4,5-tetramethylbenzene is 10
~50g/Nm ³ - Contains raw material gas and 3% water vapor
1. A method for producing pyromellitic acid or its anhydride, which comprises catalytically oxidizing a raw material gas consisting of ~30% by volume and a molecular oxygen-containing gas in the presence of a vanadium-containing catalyst. 2. The vanadium-containing catalyst contains oxides of vanadium, titanium, phosphorus, niobium, and antimony, and optionally at least one element selected from the group consisting of alkali metals, alkaline earth metals, rare earth elements, zinc, and thallium. 2. The method according to claim 1, wherein the catalyst is made by supporting an inert carrier on an inert carrier. 3 1,2,4,5-tetramethylbenzene is 10
~50g/Nm ³ - Contains raw material gas and 3% water vapor
Collection of high-temperature gas containing pyromellitic anhydride obtained by catalytic gas-phase oxidation of a raw material gas consisting of ~30% by volume and the remainder consisting of molecular oxygen-containing gas in the presence of a vanadium-containing catalyst using water or an aqueous medium. A method for producing pyromellitic acid or its anhydride, the method comprising introducing pyromellitic acid or anhydride into an apparatus. 4. The vanadium-containing catalyst contains oxides of vanadium, titanium, phosphorus, niobium, and antimony, and optionally at least one element selected from the group consisting of alkali metals, alkaline earth metals, rare earth elements, zinc, and thallium. 4. The method according to claim 3, wherein the catalyst comprises a catalytic material comprising an oxide of . 5. The method according to claim 3 or 4, characterized in that the collection device using water or an aqueous medium comprises a wet wall tower and a washing tower formed of water or an aqueous medium. 6 The outlet temperature of exhaust gas discharged from a collection device using water or an aqueous medium is maintained at 40 to 80°C, and 15 to 85% of the total amount of exhaust gas is recycled and reused as part of the raw material gas. The method according to claim 3, 4 or 5.