JPH0745486B2 - Recovery method of trimellitic anhydride - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for recovering trimellitic anhydride, and more specifically, for example, raw materials for electrodeposition paints, plasticizers,
In the process of producing trimellitic acid, which is useful as a raw material for the synthesis of alternating polyamideimides used for heat-resistant polymers, etc., it evaporates with the solvent in the process of melting trimellitic acid-containing wet cake to produce trimellitic acid. The present invention relates to a method for recovering trimellitic anhydride, which enables recovery of trimellitic anhydride without condensation.

[Prior Art and its Problems] Trimellitic acid is, for example, a raw material for electrodeposition paint, a plasticizer,
A method for producing trimellitic acid of high purity, which is useful as a raw material for synthesizing alternating polyamideimides used for heat-resistant polymers and the like, has been desired.

As a method for producing this trimellitic acid, for example, pseudomen [1,2,4-trimethylbenzene] is oxidized with air in the presence of a catalyst obtained from a heavy metal compound and a bromine compound and an acetic acid solvent to give trimellitic acid. A method of using an acid is known (Japanese Patent Publication No. 45-23732, Japanese Patent Laid-Open No. 46-7).
See JP 173, JP 47-6297, JP 562932, JP 57-16792, JP 58-5898, and the like. ).

By the way, in general, trimellitic acid is shipped after being purified by washing with a solvent as necessary and then converted into trimellitic anhydride by an intramolecular dehydration reaction by heating. In the method, in the step of heating the trimellitic acid-containing cake to convert it into trimellitic anhydride, a part of trimellitic anhydride is,
Since it is included in the steam of water or acetic acid that evaporates from the trimellitic acid-containing cake, it is necessary to recover trimellitic anhydride contained in this steam in order to achieve a production efficiency factory.

Conventionally, as a method of recovering this trimellitic anhydride, for example, a method of cooling and condensing trimellitic anhydride has been adopted (see JP-B-47-6297).

However, in this method, since the condensate becomes a slurry of trimellitic acid and trimellitic anhydride, this slurry adheres to the condenser and causes the trouble of the intramolecular dehydration reaction device by blocking the pipe. There is a problem that becomes.

An object of the present invention is to eliminate the above-mentioned problems, to prevent slurry from adhering to a condenser or clogging pipes, and thus not to cause troubles in a reaction device and an excellent anhydrous trimellitium. It is to provide a method of recovering an acid.

[Means for Solving the Problems] In order to solve the problems, as a result of extensive studies by the present inventor, trimellitic anhydride that evaporates with a solvent was introduced into a crystallization tank, If trimellitic acid is generated by reacting with water in the deposition tank, trimellitic anhydride can be recovered without condensation as in the conventional recovery method. Therefore, the slurry adheres to the condenser. Or to prevent the occurrence of troubles of the reactor without blocking the pipe, and found that it is possible to provide a highly efficient trimellitic anhydride recovery method, to the present invention Arrived

That is, the constitution of the present invention is such that, in the presence of acetic acid as a solvent, a reaction solution obtained by oxidizing pseudocumene with air is introduced into a crystallization tank, and then the trihydrate in the reaction solution in the crystallization tank is introduced. After filtering the trimellitic acid-containing slurry obtained by precipitating mellitic acid, the resulting trimellitic acid cake was introduced into the melting tank, and subsequently the trimellitic anhydride-containing vapor generated in this melting tank Is introduced into the crystallization tank, and trimellitic acid is produced by reacting trimellitic anhydride in the trimellitic anhydride-containing vapor with water in the crystallization tank to produce trimellitic acid. Is the method of collection.

The pseudomen [1,2,4-trimethylbenzene] to be used is used as a raw material in the method of the present invention, and commercially available ones can be used as they are. The one obtained by distillation of the fraction may be used, or the one obtained by methylation or disproportionation of benzene or xylene may be used.

The acetic acid to be used is used as a solvent in the method of the present invention, and the amount thereof is 2 times or more, preferably 4 to 10 times the amount of pseudomen used, for example, 0 It is preferably used as an aqueous acetic acid solvent containing about 60% by weight of water. When the concentration of acetic acid is high, the cost of recovering acetic acid may increase.

The air to be used is used as an oxidant in the method of the present invention, and if it is a gas containing molecular oxygen, pure oxygen, industrial exhaust gas or the like can be used in addition to air. However, air is industrially preferable.

An oxidation catalyst may be used in the oxidation. As the oxidation catalyst, a catalyst composed of a heavy metal compound and a bromine compound, which has been conventionally used in the method for producing trimellitic acid, can be preferably used.

Examples of the heavy metal compound include cobalt compounds and manganese compounds. The cobalt compound and the manganese compound are not particularly limited as long as they are soluble in acetic acid, but preferable are inductive acid salts such as acetate, propionate, naphthenate and octenoate; acetylacetonate. Induced complexes such as complexes, carbonyl complexes, ammine complexes and oxo complexes; halides such as chlorides and bromides, inorganic acid salts such as hydroxides, borates, nitrates and carbonates. Among these, particularly preferable are acetates, bromides, hydroxides, and carbonates.

Examples of the bromide include alkali metal bromides such as bromine, hydrogen bromide, ammonium bromide, sodium bromide, lithium bromide, potassium bromide, and cesium bromide; cobalt bromide, manganese bromide, cerium bromide, etc. Inorganic bromine compounds; organic bromine compounds such as tetrabromoethane, bromoacetic acid and benzyl bromide. Among these,
Sodium bromide, cobalt bromide, manganese bromide, ammonium bromide and the like are preferable, and sodium bromide is particularly preferable.

The above heavy metal compounds and bromides may be used alone or in combination of two or more.

When the heavy metal compound is used, the amount used is usually 0.01 to 1.0% by weight based on the acetic acid solvent. If the amount used is less than 0.01% by weight, the reaction rate may decrease, the production efficiency may deteriorate, and sufficient catalytic activity may not be obtained. On the other hand, if it exceeds 1.0% by weight, the formation of a salt between the metal catalyst and trimellitic acid cannot be ignored, and the product yield may decrease. When the cobalt compound and the manganese compound are used in an atomic ratio of cobalt metal and manganese metal (Co: Mn) of 5: 1 to 1:10, preferably 4: 1 to 1: 4. , And is particularly preferable in terms of activity and catalyst recovery operation.

The amount of the bromine compound used is 0/01 to 2.0% by weight in terms of the amount of bromine atom used relative to the acetic acid solvent, and the atomic ratio (Br / Co is based on the total amount of cobalt and manganese used.
+ Mn) is 2.51 to 2.99, preferably 2.6 to 2.9. If this ratio is less than 2.51, sufficient activity may not be obtained. On the other hand, when it exceeds 2.99, the activity is increased, but the incorporation of the bromine component into trimellitic acid cannot be ignored, and the purification cost and the catalyst cost may increase.

The pseudomen, acetic acid, air, and the above-mentioned oxidation catalyst used as needed are supplied into, for example, a batch reactor, and the oxidation reaction of the pseudomen proceeds in the reactor under the following conditions.

That is, the reaction temperature is usually 110 ~ 250 ℃, preferably
It is 130 to 230 ° C. If this reaction temperature is lower than 110 ° C., the reaction time required for the purification of trimellitic acid becomes remarkably long and the production efficiency may be lowered. On the other hand, 250
If the temperature is higher than 0 ° C, it may lead to an increase in the undesirable complete oxidation reaction or thermal decomposition reaction in the production of trimellitic acid, or an increase in the by-product of coloring impurities.

The reaction pressure is usually 4 to 50 kg / cm ³ · G, preferably 4 to
It is 30 kg / cm ³ · G. If the reaction pressure is below this range,
The acetic acid may not be able to maintain the liquid phase under the above reaction temperature. The oxygen partial pressure of the reaction system is preferably controlled by controlling the amount of the introduced air so that the oxygen concentration in the exhaust gas from the reactor is in the range of 1 to 8% by volume.

The reaction time cannot be unconditionally determined because it varies depending on the charged amount of raw materials and the like, the reaction temperature and the reaction pressure, but usually about 3 to 10 hours is sufficient.

The air oxidation reaction of pseudomen is preferably performed in a plurality of batch reaction tanks. For example, a plurality of batch reaction tanks are used, and the reaction in each batch reaction tank is staggered for a fixed time to carry out the oxidation reaction. When a plurality of batch reaction tanks are used in this manner and the air oxidation reaction is sequentially performed in each reaction tank, it is not necessary to install, for example, the same number of air compressors and exhaust gas treatment devices as the reaction tanks. It can be simplified.

The reaction liquid obtained by performing the air oxidation reaction in the reaction tank is continuously introduced into the crystallization tank.

In the crystallization tank, the reaction proceeds under the following conditions to deposit a slurry containing trimellitic acid in an amount of 30 to 35% by weight.

The residence time of the reaction solution in the crystallization tank is usually
1 to 5 hours. If the reaction time is less than 1 hour, the precipitation of trimellitic acid may be insufficient. On the other hand, even if it is longer than 5 hours, the effect equivalent to that may not be exhibited.

In the method of the present invention, the trimellitic acid-containing slurry obtained in the crystallization tank is filtered, and the trimellitic acid-containing cake obtained by this filtration is introduced into the melting tank.

The filtration can be performed using, for example, a vacuum filter, a centrifugal filter, a filter press or the like.

In the method of the present invention, the trimellitic acid-containing cake obtained by performing the filtration may be washed if necessary.

As the cleaning liquid used for the above cleaning, for example, a 95% acetic acid aqueous solution can be preferably used. When performing the washing, the amount of the washing liquid used is about twice the amount of the liquid contained in the wet cake obtained during solid-liquid separation.

The trimellitic acid-containing cake is conveyed to the melting tank after or without washing. A belt conveyor, for example, can be suitably used for this transportation.

In the melting tank, an intramolecular dehydration reaction of trimellitic acid proceeds under the following conditions to produce trimellitic anhydride.

That is, the reaction temperature in the melting tank is 210 ° C or higher, preferably 220 to 240 ° C. If this temperature is less than 210 ° C, the intramolecular dehydration reaction of trimellitic acid may not proceed sufficiently.

The reaction pressure in the melting tank is usually 1 atm.

The amount of trimellitic anhydride produced under such conditions is about 80% of the content of trimellitic acid in the trimellitic acid-containing cake, acetic acid and water in the trimellitic acid-containing cake melt Evaporate in the tank. Here, the acetic acid in the trimellitic acid-containing cake was derived from the solvent and / or the cleaning liquid, and the water in the trimellitic acid-containing cake was contained in the solvent and / or the cleaning liquid. While coming from things,
It is derived from a by-product when a methyl group is converted into a carboxy group by the oxidation of pseudomen [1,2,4-trimethylbenzene]. The steam generated at this time contains a part of trimellitic anhydride together with the acetic acid and water.

One of the important points in the method of the present invention is that the trimellitic anhydride-containing vapor is introduced into the crystallization tank to react with water in the crystallization tank to produce trimellitic acid. It is to recover trimellitic anhydride in the steam containing trimellitic anhydride.

The reaction conditions in the crystallization tank are the same as the reaction conditions in the formation of the trimellitic acid-containing slurry described above.

That is, in the method of the present invention, in the crystallization tank, the formation of the trimellitic acid-containing slurry and the recovery of trimellitic acid proceeded simultaneously under the same conditions, and the trimellitic acid-containing cake was evaporated. The trimellitic anhydride in the steam containing trimellitic anhydride is finally recovered as a trimellitic acid-containing slurry containing 35 to 40% by weight of trimellitic acid.

Next, an example of a reaction apparatus that can be preferably used for the method of the present invention is shown in FIG. 1, and the method of the present invention will be described in the order of reaction steps.

That is, the pseudomen and acetic acid and, if necessary, the catalyst are supplied to the batch reactor 1 at the above-mentioned ratio and the air is introduced to perform the oxidation reaction of the pseudomen.

The reaction conditions in the batch reactor 1 are set as follows, for example.

That is, the reaction temperature is 110 ~ 250 ℃, preferably 130 ~ 230
℃.

The reaction pressure is 4 to 50 kg / cm ² , preferably 4 to 30 kg / cm ² .

The residence time cannot be unconditionally determined because it varies depending on the charged amount of raw materials, the reaction temperature and the reaction pressure.
For example, reaction temperature 140 ℃ -200 ℃, reaction pressure 4-20kg / c
In the case of m ² , 5 to 6 hours is sufficient.

In the reaction apparatus shown in FIG. 1, a batch reactor 2 similar to the batch reactor 1 is provided.

The reaction conditions in the batch reactor 2 are the same as those in the batch reactor 1 described above.
The reaction conditions are the same.

That is, in the illustrated reactor, two reactors, that is, a batch reactor 1 and a batch reactor 2, are used together, and the starting point of supply of raw materials, solvent, catalyst, etc. to each reactor is shifted. Therefore, the reaction is carried out industrially efficiently.

The unreacted gas (off gas) in the batch reactor 1 and the batch reactor 2 is discharged to the off gas squeezing step 3.
The acetic acid used as the solvent is recovered in the recovery acetic acid tank 4 and further sent to the acetic acid distillation column 5 for reuse.

The reaction-completed liquid obtained from the batch reactors 1 and 2 is introduced into the first crystallization tank 7 through the control valve 6, and the trimellitic acid-containing slurry is produced.

After the first crystallization tank 7 holds the slurry, the amount of the slurry in the first crystallization tank 7 before the reaction completion liquid is introduced is such that the reaction completion liquid is the first crystallization tank 7 Make sure to hold the remaining amount by flashing at 1 atm operating pressure.

Here, the operating pressure of the first crystallization tank 7 is usually 1 atm, the operating temperature is usually 110 to 120 ° C., and the residence time is 1 to
5 hours.

The trimellitic acid-containing slurry produced in the first crystallization tank 7 contains 30 to 35% by weight of trimellitic acid and is continuously introduced into the second crystallization tank 9 through the control valve 8. .

The operating pressure of the second crystallization tank 9 is usually 30 to 200 torr, the operating temperature is usually 40 to 70 ° C., and the residence time is 1 to 5 hours.

The trimellitic acid-containing slurry produced in the second crystallization tank 9 contains 35 to 40% by weight of trimellitic acid, and the obtained trimellitic acid-containing slurry has an average crystal grain size of 40 to 50 μm. is there.

By using the first crystallization tank 7 and the second crystallization tank 9 to carry out crystallization in two stages, generation of fine particles is suppressed, and the above bromine in the product trimellitic acid when a catalyst is used. Mixing of compounds can be suppressed.

The trimellitic acid-containing slurry thus obtained is continuously sent to the vacuum filter 11 through the control valve 10, and is separated into the trimellitic acid-containing cake and the filtrate by the vacuum filter 11.

The trimellitic acid-containing cake is washed with, for example, a washing liquid composed of an aqueous solution of 95% acetic acid to obtain a washed cake having a trimellitic acid content of 75%.

The washed cake thus obtained is conveyed to the melting tank 13 by an appropriate transfer means such as the conveyor 12.

In the melting tank 13, the washed cake is heated to dehydrate trimellitic acid in the washed cake.

Here, the reaction temperature in the melting tank 13, usually 220 ~ 240 ℃,
The reaction pressure is usually 500 to 900 torr and the residence time is 1
~ 3 hours.

The trimellitic anhydride-containing vapor generated in the melting tank 13 is
The pressure is adjusted to 760 torr by the control valve 14 and introduced into the second crystallization tank 9.

That is, the trimellitic anhydride in the steam containing trimellitic anhydride reacts with water in the slurry containing trimellitic acid in the second crystallization tank 9 to become trimellitic acid, and enters the slurry containing trimellitic acid. Be recovered. Further, acetic acid and water in the trimellitic anhydride-containing vapor are liquefied and recovered by the condenser 15 connected to the top of the second crystallization tank 9.

EXAMPLES Next, examples of the present invention will be shown to more specifically describe the method of the present invention.

Oxidation reaction Two batch type reactors consisting of a first reactor and a second reactor were used. First, 4 kg of acetic acid, 1 kg of pseudomen, 11 g of cobalt bromide, 21 g of manganese bromide and 8 g of sodium bromide were added to the first reactor, and 1 hour later, the introduction of air was started to start the reaction.

The reaction temperature was 140 ° C., the temperature was raised 3 hours and 15 minutes after the start of the reaction, the temperature was raised to 200 ° C. in 78 minutes, and the pressure was increased from 4 kg / cm ² to 20 kg / cm ² .

The reaction was continued as it was, and after 5 hours and 10 minutes from the start of the reaction, the supply of air was stopped to terminate the reaction.

On the other hand, 4 hours after the start of the supply of the raw materials and the like, the raw materials and the like were similarly fed to the other one reactor, and the reaction was performed under the same conditions as the above.

The total operation time from the start of the supply of the raw materials and the like until the total amount of the reaction finished liquid was withdrawn was 8 hours, and the reaction time was repeated by two batch reactors in which the supply time of the raw materials and the like was shifted by 4 hours.

That is, in each of the first and second reactors, the time from the start of the supply of the raw material to the end of the withdrawal of the reaction completion liquid is 8 hours, and the raw material supply timing to the first reactor and the raw material supply timing to the second reactor are set. The air oxidation reaction was alternately performed in the first reactor and the second reactor while being staggered for 4 hours. And
After the lapse of 5 hours from the supply of the raw materials, the reaction-terminated liquid was withdrawn from the first reactor into the first crystallization tank under the conditions described in the next crystallization. On the other hand, in the second reaction tank, the raw material supply is started 4 hours after the start of the supply of the raw material to the first reaction tank, and after 7 hours after the start of the raw material supply, the reaction completion liquid is discharged. The transfer from the second reactor to the first crystallization tank was completed.

By alternately operating the first reactor and the second reactor in this manner, the reaction-terminated liquid was sequentially supplied to the first crystallization tank.

Crystallization The total amount of the 20 kg / cm ² · G, 200 ° C reaction-terminated liquid obtained in the above oxidation reaction was adjusted to 760 torr with a control valve, and once every 4 hours for 45 minutes, the first crystallization tank I pulled it out.

Here, the operating pressure of the first crystallization tank is 760 torr and the operating temperature is 1
It was set at 17 ° C.

The slurry produced in the first crystallization tank was continuously withdrawn at 1.2 kg / hour into the second crystallization tank through the control valve.

In the first crystallization tank, since the first reaction-completed liquid has been transferred from the first reaction tank, the liquid has been transferred at regular intervals, and a certain amount of slurry has been transferred into the first crystallization tank. The slurry was transferred from the first crystallization tank to the second crystallization tank, as described above, so that the above remained.

The operating pressure of the second crystallization tank was set to 50 torr and the operating temperature was set to 45 ° C.

The slurry produced with the residence time in the second crystallization tank being 3 hours was continuously withdrawn at 1.0 kg / hour.

Filtration and washing The slurry obtained by the above crystallization was introduced into a vacuum filter through a control valve at 1.0 kg / hour, and separated into a wet cake and a filtrate.

The resulting wet cake was washed with a 95% acetic acid aqueous solution 0.2k
It was washed at g / hour to obtain washed cake 0.45 kg / hour.

Anhydrous and recovery of trimellitic anhydride 0.4 kg of washed hair obtained above was conveyed to a melting tank using a conveyor, and a molten liquid was retained in the melting tank at a temperature of 240 ° C for a residence time of 1 hour. Pulled out.

At this time, the pressure of the generated steam is adjusted to 760 torr by the control valve.
And was introduced into the second crystallization tank.

When the content of trimellitic acid in the slurry obtained from the second crystallization tank before the introduction of the steam was compared with the content of trimellitic acid in the slurry after the introduction of the steam, The content of trimellitic acid in the slurry increased by 5% by weight, and it was confirmed that trimellitic anhydride in the steam was recovered in the slurry.

EFFECTS OF THE INVENTION According to the method of the present invention, (1) trimellitic anhydride is not recovered by condensation unlike the conventional method, but trimellitic anhydride is recovered in the slurry. The slurry does not adhere to the condenser and the pipe is not clogged. (2) Therefore, trouble does not occur in the reaction device. (3) Moreover, a new device is not required, so that the efficiency is improved. It is possible to provide a method for recovering trimellitic acid anhydride, which has various advantages such as excellent properties.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a reaction apparatus which can be used for carrying out the method of the present invention.

Claims (1)

[Claims] 1. A reaction solution obtained by oxidizing pseudocumene with air in the presence of acetic acid as a solvent is introduced into a crystallization tank, and then trimellitic acid in the reaction solution is removed in the crystallization tank. After filtering the trimellitic acid-containing slurry obtained by precipitation, the trimellitic acid cake obtained was introduced into a melting tank, and subsequently the trimellitic anhydride-containing vapor generated in the melting tank was crystallized as described above. A method for recovering trimellitic acid, which is characterized in that the trimellitic acid is introduced into a precipitation tank, and trimellitic acid in the vapor containing trimellitic anhydride is reacted with water in the crystallization tank to produce trimellitic acid. .