JP2004331560A - Method for producing pyromellitic anhydride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing pyromellitic anhydride by purifying durene and subjecting purified durene to a catalytic vapor-phase oxidation reaction. <P>SOLUTION: In the method for producing pyromellitic anhydride by the catalytic vapor-phase oxidation reaction of durene, the durene is treated by a process for separating a low-boiling substance and/or a process for separating a high-boiling substance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing pyromellitic anhydride by a catalytic gas phase oxidation reaction of durene. More specifically, the present invention relates to a method for producing pyromellitic anhydride using purified durene.
[0002]
[Prior art]
Pyromellitic anhydride is widely used as a heat-resistant resin, a plasticizer, a curing agent for an epoxy resin, and the like, and is increasingly important as an industrial raw material.
[0003]
As a production method of pyromellitic anhydride, a production method by catalytic gas phase oxidation reaction of durene (1,2,4,5-tetramethylbenzene) is known. The use of zeolite-based catalysts has opened the possibility of obtaining large amounts of inexpensive raw material durene, and the possibility of obtaining it inexpensively has opened the way for the production of pyromellitic anhydride using catalytic gas-phase oxidation of durene. (For example, see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-7-171393 [0005]
[Problems to be solved by the invention]
However, the purity of the provided durene is not always stable, and the yield of pyromellitic dianhydride obtained by the catalytic gas-phase oxidation reaction of durene is fluctuated accordingly.
[0006]
Accordingly, an object of the present invention is to provide a method for producing pyromellitic anhydride by purifying durene and performing a catalytic gas phase oxidation reaction.
[0007]
[Means for Solving the Problems]
The present invention provides a method for producing pyromellitic anhydride by a catalytic vapor-phase oxidation reaction of durene, wherein the durene is treated in a low-boiling matter separation step and / or a high-boiling matter separation step. Manufacturing method.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for producing pyromellitic anhydride according to the present invention is a method for producing pyromellitic anhydride (hereinafter, "pyromellitic anhydride" may be referred to as "PMDA") by a catalytic gas phase oxidation reaction of durene. In a low-boiling matter separation step and / or a high-boiling matter separation step.
[0009]
The method for producing PMDA of the present invention will be described with reference to the drawings. FIG. 1 is a process chart showing an example of the PMDA manufacturing method of the present invention. In FIG. 1, the production process of PMDA includes (A) a purification process of durene, (B) a catalytic gas phase oxidation reaction of durene, (C) a collection process of PMDA, (D) an exhaust gas treatment process, and (E) a commercialization process. It can be divided into steps. In addition, a well-known method can be employ | adopted for a process (B)-(D). Hereinafter, each step will be sequentially described.
[0010]
(A) Purine Purification Step The impurities contained in durene include iso-durene, water, 1,2,4-trimethylbenzene, and 2,4,6-trimethylbenzaldehyde.
[0011]
In the low-boiling matter separation step, an oil-water separator is used to separate and extract water and water-soluble impurities contained in the crude durene as an aqueous phase, or the boiling point of durene is lower than 196.8 ° C. A step of heating at a temperature of, for example, 78 ° C. to 150 ° C. to remove light boilers contained in the crude durene is included. The heating / separating apparatus is not particularly limited as long as it can heat durene. Examples of the heating / separating apparatus include heat separation using an evaporator and a distillation column, heat separation using a shell-and-tube or a spiral heat exchanger, and separation using a flash tank. When such a step is performed, either a batch type or a continuous type may be performed, and the step may be performed under reduced pressure in order to promote evaporation. As described above, by reducing the amount of water and light boilers contained in the crude durene, the PMDA yield obtained in the catalytic gas phase oxidation reaction of durene is improved, and the obtained PMDA is prevented from being colored. Is obtained. Further, the life of the used catalyst can be improved.
[0012]
After the low-boiling matter separation step, or when the low-boiling matter is not contained, the high-boiling matter is treated in the high-boiling matter separation step as it is. The high-boiling matter separation step refers to a step of heating at a temperature higher than the boiling point of durene, for example, 196.8 ° C. (boiling point of durene) to 250 ° C. to leave high-boiling substances as a residue and evaporate durene. . The heating device is not particularly limited as long as it is a device capable of heating and evaporating durene, and examples thereof include an evaporator. The concentration ratio in the evaporator is generally 10 to 1000 times, preferably 200 to 1000 times. The concentration ratio is expressed as 100 times when the amount of the raw material is 100 parts by mass and the residue is 1 part by mass. In the separation step of low-boiling and high-boiling substances, the oxygen concentration of the atmosphere of the apparatus in contact with durene is usually 10% by volume or less, preferably 5% by volume or less, and most preferably an inert gas atmosphere such as nitrogen gas. It is desirable that The evaporated durene can be used as a raw material for a catalytic gas phase oxidation reaction, if necessary, after its concentration is adjusted with air, oxygen, oxygen-enriched air, etc., and sufficiently mixed. By performing the concentration of durene under a low oxygen concentration, the formation of high-boiling impurities can be significantly prevented, so that the high-boiling impurities of duren can be concentrated to a high concentration, and the residue treatment cost can be reduced. . In addition, since the formation of high-boiling substances is extremely small, the boiling point rise is small even at a high concentration ratio, and it is not necessary to use an evaporator or a vacuum evaporator having a large transmission surface. Productivity can be improved.
[0013]
Through such a purification step, it is desirable that the purity of durene be 95% or more, preferably 98% or more, and more preferably 99% or more. By using such a raw material, the selectivity of PMDA in the catalytic vapor phase oxidation reaction of durene can be increased, and the color of the obtained crystal can be kept white. Furthermore, after long-term reaction, the reduction in PMDA yield can be reduced. By adopting such a method for purifying durene, it becomes possible to continuously purify durene, in particular, a high-boiling matter separation step and a catalytic gas phase oxidation reaction.
[0014]
In FIG. 1, duren is received in a container 9 such as a container. The temperature of the container is raised to melt the coarse duren, and the container is moved to the oil-water separator 13. For the movement, it is preferable to use the head difference by arranging the oil / water separator at a position lower than the container, but if necessary, the head is moved with pressurized nitrogen gas. After the water phase 11 is extracted in the oil / water separator 13, the remaining oil phase is sent to the flash tank 17. In the flash tank 17, light boilers 15 are removed from the heated oil phase by evaporation. The crude duren excluding light boilers is sent to the tank 19. The inside of the tank 19 is sealed in advance with nitrogen gas. Further, the crude durene from which light boilers have been removed is sent to an evaporator 22 via a pump 21. In the evaporator 22, durene is evaporated to obtain a raw material, and a high-boiling substance is extracted as a residue 23. The evaporator 22 is previously sealed with nitrogen gas. In the step of purifying durene, the atmosphere at the place where it comes into contact with durene in the apparatus or container used is usually set to an oxygen concentration of 10% by volume or less at the time of the treatment. Extrusion from the container 9, the concentration of oxygen in the container used in the flash tank 17 and the evaporator 22 is maintained in advance and at the time of processing to prevent the formation of high-boiling substances.
[0015]
(B) Catalytic gas phase oxidation reaction of durene As a method for producing PMDA by catalytic gas phase oxidation reaction of durene, a conventionally known method can be employed, and the following reaction conditions can be exemplified.
[0016]
Catalyst: Pellet catalyst containing vanadium pentoxide and titanium dioxide as main components. Durene concentration: 5 to 50 g / N (normal) m ³ , preferably 15 to 35 g / Nm ³
Space velocity: 1000-15000 hr ^-1
Reaction temperature: 340 ° C to 460 ° C
In FIG. 1, air 1 warmed by a blower 3 and a heat exchanger 5 and durene purified in a purification step are mixed and introduced into a reactor 25, and a catalytic vapor phase oxidation reaction of durene is performed to contain PMDA. Get the gas. The obtained PMDA-containing gas is cooled by a cooler 27 to a predetermined temperature.
[0017]
(C) PMDA collection step This is a collection method using reverse sublimation in which a vertical multitubular heat exchanger is used to flow a refrigerant outside the pipe, cool the PMDA-containing gas flowing in the pipe, and precipitate crystals. Thus, the following conditions can be exemplified.
[0018]
Inner diameter of collection tube: 50 to 500 mm, preferably 150 to 400 mm, more preferably 150 to 300 mm
Collection pipe inlet gas temperature: 150 ° C to 300 ° C
Average gas velocity in cooling pipe: 0.05-1 Nm / sec, preferably 0.05-0.5 Nm / sec
Temperature of cooling water or cooling medium for cooling the collection tube: 100 ° C to 250 ° C
In FIG. 1, a PMDA-containing gas cooled to a predetermined temperature by a cooler 27 is fed to a collector 29. The feed gas flows from the lower part of the collector to the upper part for easy collection. Further, it is preferable that the collector 29 is provided with a striking device for promoting the fall of the PMDA attached to the collection tube.
[0019]
(D) Exhaust gas treatment step In FIG. 1, the gas discharged from the upper part of the collector 29 is preheated by the exhaust gas heat exchanger 31, the exhaust gas is purified by the catalytic exhaust gas combustion device 33, and then discharged as the exhaust gas 35. As the catalyst used here, a known catalyst in which a noble metal such as platinum or palladium is supported on a carrier such as alumina, titania or silica can be used.
[0020]
(E) Production process In FIG. 1, the collected PMDA is discharged from the lower part of the collector 29 and held by the intermediate hopper 37. Thereafter, if necessary, the mixture is cooled by a cooler 39, crushed by a crusher 41 to a target particle diameter, and held by a product hopper 43. Then, it is collected as a product 45.
[0021]
By such a method, it is possible to produce PMDA in large quantities by the catalytic gas phase oxidation reaction of durene.
[0022]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples. This example is intended to illustrate the invention and is not intended to limit the invention.
[0023]
(Example 1)
PMDA was manufactured according to the flow sheet shown in FIG.
[0024]
After the temperature of the duren container 9 is raised to melt the coarse duren (durene purity: 93%), the coarse duren is extruded from the container 9 using the pressurized nitrogen gas 7, and the aqueous phase 11 is separated using the oil-water separator 13. I took it out. Further, durene in the oil phase was heated in a flash tank 17 (oxygen concentration in the atmosphere: 0.1% by volume), light boilers 15 were evaporated, and the residue was sent to a tank 19. The inside of the tank 19 was sealed with nitrogen gas 7. Subsequently, the liquid was sent from the tank 19 to the evaporator 22 via the pump 21. In the evaporator 22, durene was evaporated and separated from the high-boiling substance 23. The evaporator 22 was preliminarily sealed with nitrogen (oxygen concentration in the atmosphere: 0.1% by volume), and concentrated in a nitrogen atmosphere. As a result, the concentration could be increased up to 500 times (boiling point: 240 ° C.), and the amount of the residue was 0.2% by mass relative to the amount of feed to the evaporator. At that time, the purity of durene was 99.9%.
[0025]
The evaporated durene gas was supplied to the reactor 25 after mixing with the air 1. The reactor 25 is provided with a stainless steel reaction tube having an inner diameter of 25.4 mm and filled with a pellet catalyst having a diameter of 5 mm and a length of 5 mm and containing vanadium pentoxide and titanium dioxide as main components, and a durene concentration of 30 g / Nm. ^3. Space velocity: 5000 hr ^-1 : Catalytic gas phase oxidation was performed under the condition of a reaction temperature of 385 ° C. to generate a PMDA-containing gas.
[0026]
The generated PMDA-containing gas is once cooled to 250 ° C. in a heat exchanger 27 and then sent to a vertical multi-tube collector 29, which is flowed up-flow, and is collected on the inner wall of the collection tube filled in the collector 29. Precipitated as crystals.
[0027]
The precipitated crystals were taken out to an intermediate hopper 37, cooled in a cooler 39, pulverized by a pulverizer 41, and collected through a product hopper 43 as a product 45. The appearance of the obtained crystals was white. At this time, the conversion of durene was 99.8 mol%, and the selectivity to PMDA was 65 mol%. After 1000 hours, the selectivity decreased by 1.2 mol%. The appearance of the obtained PMDA crystal was white.
[0028]
Further, the gas discharged from the upper part of the collector was once heated in the heat exchanger 31, then processed in the catalytic exhaust gas combustion treatment device 33 filled with a catalyst in which platinum was supported on an alumina carrier, and discharged as exhaust gas 35. .
[0029]
(Example 2)
Example 1 was carried out in the same manner as in Example 1 except that nitrogen for durene extrusion, a nitrogen sealing gas for a tank, and a nitrogen gas adjusted to an oxygen concentration of 10% by volume were used as a nitrogen sealing gas for an evaporator.
[0030]
As a result, the concentration in the concentrator could be increased up to 200 times (boiling point: 218 ° C.), and the amount of the residue was 0.5% by mass based on the amount of feed to the evaporator. The durene conversion in the reactor was 99.8 mol%, and the selectivity of PMDA was 65 mol%. After 1000 hours, the decrease in selectivity was 1.25 mol%. The appearance of the obtained PMDA crystal was white.
[0031]
(Comparative Example 1)
In Example 1, the water phase was not removed by the oil-water separator of Duren, the light boiler was not removed by the flash tank, the nitrogen for durene extrusion, the nitrogen sealing gas of the tank, and the nitrogen sealing gas of the evaporator were air. The procedure was performed in the same manner as in Example 1 except that
[0032]
As a result, the concentrator was able to concentrate only to a concentration magnification of 30 times (boiling point: 208 ° C.), and the amount of the residue was 3.3% by mass with respect to the amount of feed to the evaporator. The durene conversion in the reactor was 99.8 mol%, and the selectivity of PMDA was 61 mol%. After 1000 hours, the selectivity decreased by 1.5 mol%. The appearance of the obtained PMDA crystal was slightly brown.
[0033]
(Comparative Example 2)
In Example 1, the water phase was not removed by the Duren oil-water separator, the light boiler was not removed by the flash tank, the nitrogen seal gas in the tank and the nitrogen seal gas in the evaporator were changed to air, and the high pressure in the evaporator was changed. The procedure was performed in the same manner as in Example 1 except that the separation of the boilers was eliminated.
[0034]
As a result, the concentrator was able to concentrate only to a concentration magnification of 30 times (boiling point: 208 ° C.), and the amount of the residue was 3.3% by mass with respect to the amount of feed to the evaporator. The durene conversion in the reactor was 99.8 mol%, and the selectivity of PMDA was 58 mol%. After 1000 hours, the selectivity decreased by 2.5 mol%. The appearance of the obtained PMDA crystal was slightly brown.
[0035]
【The invention's effect】
According to the method of the present invention, the selectivity of PMDA in the catalytic vapor phase oxidation reaction of durene can be increased, and the color of the obtained crystal can be kept white. Furthermore, after long-term reaction, the reduction in PMDA yield can be reduced.
[Brief description of the drawings]
FIG. 1 is a drawing showing a flow sheet of an example of a PMDA manufacturing method of the present invention.
[Explanation of symbols]
1 ... air,
3. Blower,
5 ... heat exchanger,
7 ... Nitrogen gas,
9 ... container (container),
11 ... aqueous phase,
13. Oil / water separator,
15 ... light boiler,
17 ... Flash tank,
19 ... Tank,
21 ... pump,
22 ... Evaporator,
23 ... residue,
25 ... reactor,
27 ... cooler,
29… Collector,
31 ... exhaust gas heat exchanger,
33: catalytic exhaust gas combustion device
35 ... exhaust gas,
37 ... Intermediate hopper,
39 ... cooler,
41 ... crusher,
43… Product hopper,
45 Product.

Claims (2)

A method for producing pyromellitic anhydride by a catalytic vapor-phase oxidation reaction of durene, wherein the durene is treated in a low-boiling matter separation step and / or a high-boiling matter separation step. The method according to claim 1, wherein the low-boiling matter separation step and / or the high-boiling matter separation step is performed in a state where the oxygen concentration is 10% by volume or less.

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