JPH0454149A - Production of high-purity isophthalic acid - Google Patents

Abstract

PURPOSE:To simply obtain high-purity isophthalic acid without providing expen sive purifying steps by oxidizing m-xylene with O2 in steps divided into the main oxidation and post-oxidation using specific hydrous acetic acid solvent and a catalyst. CONSTITUTION:m-Xylene is oxidized with O2 in the presence of a Co, Mn and Br-based catalyst in hydrous acetic acid solvent to provide isophthalic acid. In the process, the solvent and the catalyst are fed to an oxidation reactor so as to afford 10-35wt.% amount of the isophthalic acid and an intermediate, 300-1500ppm total amount of Co and Mn at 0.5-5 ratio of (Mn/Co) and 0.5-1.5 ratio [(Co + Mn)/Br] and the oxidation is carried out at 180-210 deg.C by keeping the O2 concentration of waste gases at 2-8vol.%. The main oxidation is performed at 500-10000ppm concentration of the 3-carboxybenzaldehyde in a crude product and the oxidation is further carried out to provide 100-800ppm concentration of the aforementioned aldehyde. The crude phthalic acid is then separated and crystals are purified simply by washing thereof with acetic acid. Thereby, the objective high-purity isophthalic acid is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing isophthalic acid by liquid phase oxidation of meta-xylene.

High-purity isophthalic acid is useful as an intermediate raw material for polymers such as unsaturated polyester resins, alkyd resins, modified polyester fibers, and heat-resistant polyamides.

[Prior art] As a method for producing aromatic carboxylic acids, aromatic hydrocarbons having aliphatic substituents are treated with molecular oxygen in the presence of a catalyst consisting of heavy metals and bromine in an aliphatic carboxylic acid solvent such as acetic acid. A method of liquid phase oxidation is known (Special Publication No. 34-2
No. 666, etc.), this method can also be applied to the production of isophthalic acid.

Japanese Patent Publication No. 60-48497 describes a specific method of oxidizing meta-xylene with air in the presence of cobalt, manganese and bromine in an acetic acid solvent, and this method is widely practiced industrially. The isophthalic acid obtained by this method contains 3-carboxybenzaldehyde (3CB
A) contains a large amount of impurities, and even if it is made into a polymer as it is, the hue will not be excellent and it will not be suitable for high-performance applications.

In particular, with the progress of industrial technology in recent years, quality requirements for polyester products as highly functional materials have become increasingly strict, and isophthalic acid with high purity and excellent whiteness is desired as a raw material for polyester.

In order to highly purify the crude isophthalic acid obtained by oxidation, Japanese Patent Publication No. 51-38698 and Japanese Patent Publication No. 51-32618
A method of hydrogenating and refining an aqueous solution of crude isophthalic acid at high temperature in the presence of a palladium catalyst is generally used, as shown in No.

On the other hand, terephthalic acid is produced by oxidizing paraxylene in the same manner as isophthalic acid, but a method of directly producing high-purity terephthalic acid is used. Specifically, Japanese Patent Publication No. 36732/1983 describes the production of terephthalic acid for direct polymerization by oxidizing paraxylene in a cobalt-manganese-bromine catalyst containing 1 to 20% by weight of manganese based on cobalt. The method was described. However, since this method uses a large amount of expensive cobalt, many methods for producing high-purity terephthalic acid have been proposed in which the oxidation conditions and oxidation method have been improved to reduce the amount of catalyst and acetic acid burned (Japanese Patent Publication No. 57-42053 No., JP 53-9736, JP 60-50775, JP 56-21015, JP 53-30700
JP-A-5379836, JP-A-54-70235, JP-A-56-14101, JP-A-56-5377, JP-A-47-31947, JP-A-4571-864).

[Problems to be solved by the invention] The conventional method for purifying crude isophthalic acid by hydrogenating in the presence of a palladium catalyst requires a separate hydrogenation reactor, crystallizer, etc., and requires a large amount of equipment for the purification equipment. This requires investment and labor, leading to an increase in manufacturing costs.

The inventors attempted to apply the above-mentioned method for producing high-purity terephthalic acid by oxidizing para-xylene to the production of isophthalic acid by oxidizing meta-xylene, but found the following problems. It was found that it cannot be applied to the production of isophthalic acid.

(1) For the oxidation of meta-xylene, JP-A No. 47-31947
If post-oxidation is carried out after the main oxidation reaction as described in the issue, the intermediate metatoluic acid and 3CBA can be almost eliminated, but if the amount of 3CBA is reduced too much, the whiteness will be poor. Isophthalic acid is not obtained, and on the contrary, coloring impurities increase and the quality deteriorates.

(2) Since acetic acid cannot be recovered by the method shown in the terephthalic acid production method, the amount of acetic acid loss increases. This is because the solubility of isophthalic acid in acetic acid near the boiling point is about 10 times higher than that of terephthalic acid, and more isophthalic acid dissolves in the mother liquor obtained by separating the crystals.
This is because a thin film evaporator cannot be used because the fluidity of the boiling material remaining in the pot decreases.

An object of the present invention is to provide an industrially advantageous production method that can obtain high-purity isophthalic acid with excellent whiteness at a high yield through only an oxidation step and simple washing without providing an expensive purification step. That's true.

[Means for Solving the Problems] The present inventors focused on the oxidation characteristics of meta-xylene, and as a result of further intensive research into the applicability of the above-mentioned method for producing high-purity terephthalic acid, If oxidation is carried out to a certain limit by dividing it into main oxidation and post-oxidation using a certain amount of aqueous acetic acid solvent and catalyst, it becomes possible to recover acetic acid by purifying the mother liquor from which the crystals have been separated using a thin film evaporator, and also to recover acetic acid. The present invention was completed by discovering that it is possible to reduce the amount of acetic acid burned in the vessel, and that by washing the obtained crystals with fresh acetic acid, high purity isophthalic acid with excellent whiteness can be obtained.

That is, the present invention provides a method for producing isophthalic acid by oxidizing meta-xylene with an oxygen-containing gas in the presence of a cobalt-manganese-bromine catalyst in a hydrous acetic acid solvent. and its intermediates from 10 to 35% by weight, the total amount of cobalt and manganese from 300 to 1500 ppm, the atomic ratio of manganese to cobalt from 0.5 to 5 times, the atomic ratio of bromine to the total amount of cobalt and manganese. is 0.5
The solvent and catalyst are supplied so that the concentration is ~1.5 times, and the oxygen concentration of the exhaust gas is adjusted to 2 to 8 volumes χ at a temperature of 180 to 210°C.
(b) a first step in which the oxidation reaction is carried out while maintaining the temperature of The oxidation reaction product mixture obtained in the step is further oxidized so that the concentration of 3-henzaldehyde in the crude isophthalic acid is 100 to 800 ppm, and after separating the crude isophthalic acid, the mother liquor is diluted to a dilute r11i! A second step of purifying and recovering acetic acid using an evaporator, and (c) mixing the isophthalic acid crystals obtained in the second step with fresh acetic acid and stirring at a temperature of 100°C or higher, and then producing purified isophthalic acid. This is a method for producing high-purity isophthalic acid, characterized by having a third step of separating acid.

The present invention will be explained in detail below.

In the method of the present invention, in the first step, meta-xylene is oxidized in a hydrous acetic acid solvent with an oxygen-containing gas in the presence of a catalyst consisting of a cobalt compound, a manganese compound, and a bromine compound.

Meta-xylene is usually used as the oxidation raw material, but the substituents are not limited to methyl groups, but include ethyl, propyl, j-
It may be a propyl group, or one that can be oxidized to a carboxyl group such as an aldehyde or acetyl group. Further, one of the substituents may be a carboxyl group.

Meta-xylene is continuously fed to the oxidation reactor. The feed rate is 0.05 per hour per liter of solvent volume in the reactor.
~0.2 kg, and the reaction time is in the range of 10 to 120 minutes, preferably 20 to 90 minutes.

Hydrous acetic acid is used as a reaction solvent. The water concentration in acetic acid in the oxidation reactor is 3 to 15% by weight, preferably 5 to 1% by weight.
It is in the range of 2% by weight. If the water concentration is too low, the color quality of isophthalic acid tends to deteriorate and the amount of acetic acid burned increases. Furthermore, if the water concentration is too high, the oxidation activity will decrease.

The amount of solvent used is such that the total amount of isophthalic acid and its intermediates (methatoluic acid and 3CBA) is 10% in the oxidation reactor.
The amount is 35% by weight. Usually, the amount of solvent supplied in this case is 1 to 15 times by weight, preferably 3 to 12 times by weight, based on meta-xylene. If the total concentration of isophthalic acid and its intermediates is lower than 10χ, the amount of solvent will be relatively large, requiring a large crystal separator, and the amount of solvent to be treated in the solvent recovery process will be large. Not economical. Moreover, if this concentration is higher than 35χ, clogging is likely to occur in the pipes and crystallizers leading from the post-oxidation reactor to the crude isophthalic acid crystallizer.

The cobalt compounds, manganese compounds and bromine compounds of the catalysts are compounds that generate cobalt ions, manganese ions and bromide ions, respectively, and are well-known compounds used in liquid phase oxidation, such as carbonates and acetates of cobalt and manganese4. Hydrates, bromides, etc. are used. The bromine compound is preferably an inorganic compound that easily dissociates into ions when dissolved in a solvent, and particularly hydrobromic acid, cobalt bromide, manganese bromide, etc. are used.

The metal concentration of the catalyst is between 300 and 1500 pp per weight of solvent in the total amount of cobalt and manganese depending on the above compounds.
m is preferably in the range of 400 to 1200 ppm, and the ratio of manganese to cobalt is 0.
It is 5 to 5 times, preferably 0.8 to 4 times. The atomic ratio of bromine to the total amount of cobalt and manganese is 0.
It is used at a concentration of 5 to 1.5 times, preferably 0.6 to 1.2 times. By setting the concentration of each metal component within the above range, the 3CBA concentration can be maintained appropriately through the main oxidation and post-oxidation, isophthalic acid with excellent hue can be obtained, and the amount of acetic acid burned can be extremely low.

The reaction temperature in the first step is 180-210°C. The pressure is sufficient to maintain the liquid phase of the solvent, usually 10
The reaction is carried out in the range of ~25 kg/c+n''.

Air is usually used as the oxygen-containing gas.

Air is supplied into the reaction solution so that the oxygen concentration in the exhaust gas from the oxidation reaction is maintained at 2 to 8 volumes 1χ, preferably 3 to 6 volumes χ.

In the main oxidation reaction of the first step, operating factors such as residence time and reaction temperature are controlled so that the 3CBA of crude isophthalic acid obtained by oxidation under the conditions described above is in the range of 500 to 110,000 pp. do.

If 3CBA is too low at this stage, the degree of oxidation will be excessive,
As a result, the amount of coloring impurities is increased, and post-oxidation is not effective and the color quality is not improved. Furthermore, the amount of acetic acid burned increases, which is extremely disadvantageous economically. If the amount of 3CBA exceeds this range, 3CBA will not be sufficiently oxidized even after post-oxidation, and high purity isophthalic acid will not be obtained.

The above 3CBA of crude isophthalic acid was measured on crude isophthalic acid crystals obtained by solid-liquid separation of the oxidation reaction mixture extracted from the reactor of the first step.

In the second step, the oxidation reaction product mixture of the first step is first post-oxidized with an oxygen-containing gas. Generally, in the case of a continuous system, this post-oxidation is carried out by transferring the reactor from the main oxidation reactor in the first step to a crystallization tank, but it can also be carried out in the cooling process following the main reaction in the first step. The temperature of the post-oxidation is between the oxidation reaction temperature of the first step and a temperature 30° C. lower than the oxidation reaction temperature of the first step. Setting the oxidation reaction temperature in the second step higher than the temperature in the first step is not only industrially disadvantageous because heating is required, but also tends to cause deterioration in color quality. Furthermore, if the temperature is too low, post-oxidation will be insufficient and high purity isophthalic acid will not be obtained.

Air can be used as the oxygen-containing gas for post-oxidation, but the oxidation exhaust gas from the first step can also be used. The oxygen concentration in the exhaust gas in the second step is maintained at 2 to 7 volumes χ.

The treatment time for the post-oxidation should be sufficient time for the desired oxidation to substantially proceed, and is 1 to 300 minutes, preferably 2 minutes.
~120 minutes.

The most important point in the second step is to adjust the concentration of 3CBA in the oxidation reaction solution obtained in the post-oxidation to 100 to 800 pp.
m. This is due to the following reason, and was obtained as a result of intensive study by the inventors.

(]) The oxidized reaction mixture is cooled to crystallize isophthalic acid, and the crystalline isophthalic acid is separated into solid and liquid.Isophthalic acid is purified in the next third step, but 3CBA in the oxidized reaction solution By setting the concentration within the above range, isophthalic acid with high purity and excellent whiteness can be obtained in the third step.

(2) The mother liquor obtained when isophthalic acid is separated into solid and liquid contains acetic acid, water, benzoic acid, metatoluic acid, 3CBA, isophthalic acid, and high boiling substances such as phthalic acid, trimellitic acid, and coloring substances. It will be done. As a result of detailed study by the inventors, the fluidity of high-boiling substances is higher than that of benzoic acid than that of isophthalic acid.
It was found that the acetic acid solution and other components could be separated using a thin film evaporator by setting 3 CBA within the above range, depending largely on the composition ratio of CBA, metatoluic acid, and trimellitic acid. Therefore, by setting the concentration of 3CBA within the above range, acetic acid can be recovered.

Note that if the concentration of 3CBA in the oxidation reaction solution obtained in the post-oxidation is higher than 800 ppm, highly pure isophthalic acid cannot be obtained even if purified in the third step. Furthermore, when the concentration of 3CBA is lowered to less than 1100 pp by post-oxidation, purified isophthalic acid is likely to be colored, and metatoluic acid etc. are also significantly reduced at the same time, resulting in a marked decrease in the fluidity of high-boiling substances obtained by distillation of the mother liquor. , separation of acetic acid using a thin film evaporator becomes impossible.

The oxidation reaction solution obtained by post-oxidation is usually transferred to a crystallizer and finally cooled to 110 to 80°C to precipitate isophthalic acid crystals. Next, the crystals are separated by a filtration operation and sent to the third step. Most of the mother liquor is returned to the oxidation reactor in the first step, but a portion is purified in a thin film evaporator and separated into melt-like high-boiling substances and acetic acid, and acetic acid is recovered. In order to reduce the load on the thin film evaporator, it is preferable to distill a portion of the mother liquor in advance and purify the bottom liquid using the thin film evaporator.

As mentioned above, this liquid contains acetic acid, isophthalic acid, benzoic acid,
Due to the moderate content of metatoluic acid, 3CBA and high boilers, acetic acid can be separated using a thin film evaporator. As the thin film evaporator used in the present invention, for example, a type manufactured by Luwa is suitable, and the flow rate of the heat medium is adjusted so that the temperature of the concentrated liquid is 130 to 230°C. Further, it is preferable that the aqueous acetic acid solution separated from the mother liquor distillation column and the acetic acid from the thin film evaporator be further rectified, and the produced water is separated by this rectification. The recovered acetic acid is
It is used as a solvent in the process and for cleaning in the third process.

In the third step, the isophthalic acid crystals separated from the reaction mixture of the second step are made into a suspension using fresh acetic acid, stirred at a temperature of 100° C. or higher, and then the isophthalic acid crystals are separated.

The acetic acid used for washing the isophthalic acid crystals is fresh acetic acid, which is not the mother liquor separated from the crude isophthalic acid crystals in the previous step. This acetic acid may be hydrous acetic acid, and the amount thereof is 1 to 5 times the weight of isophthalic acid. It is sufficient for the holding temperature in the stirring treatment to be 100°C or higher, and it is not necessarily necessary to raise the temperature to a temperature at which isophthalic acid is completely dissolved. Further, the holding time is in the range of 10 to 60 minutes.

After such washing treatment, purified isophthalic acid with extremely high whiteness can be obtained by drying.

The mother liquor after isophthalic acid crystals are separated in the third step can be used as a solvent for liquid phase oxidation in the first and second steps, whereby the isophthalic acid dissolved in the mother liquor is recovered in the oxidation step.

[Example] Next, the present invention will be explained in more detail with reference to Examples. However, the present invention is not limited to these Examples.

Example 1 (First step) A first reactor made of pressure-resistant titanium, which is equipped with a stirring device, a reflux cooling device, and a heating device, and has a raw material inlet, an air inlet, an exhaust gas outlet, and a reflux liquid reflux port. A second pressure-resistant titanium reactor and a crystallizer are equipped with a stirring device, a reflux cooling device, and a heating device, and have an air inlet, an exhaust gas outlet, a reflux liquid reflux port, and a reaction product inlet and outlet. A continuous oxidation reaction of meta-xylene was carried out.

In the first reactor, 100 parts by weight of meta-xylene, to which 0.561 parts of cobalt acetate tetrahydrate, 1.656 parts of manganese acetate tetrahydrate, and 1.117 parts of hydrobromic acid (47χ)
The catalyst concentration was 147 ppm of cobalt and 412 ppm of manganese per solvent weight.
Bromine (576 ppm) was oxidized while blowing air.

The air supply amount was adjusted so that the temperature was maintained at 200° C. and the pressure was 16.5 kg/cm 2 G, and the oxygen concentration of the oxidized exhaust gas was maintained at 5z. The metaxylene feed rate in this case is 0.17 kg/hour per 1i of solvent volume held in the reactor, the average residence time is about 30 minutes, and the total concentration of isophthalic acid and its intermediates in the oxidation reactor is 15 It was .6χ.

(Second step) The oxidation reaction mixture obtained in the first reactor is transferred to the second reactor, where the temperature is 195°C and the pressure is 12kg/c.
Post-oxidation was carried out with air under conditions of m2G and average residence time of 50 minutes. The oxygen concentration of the exhaust gas at this time was maintained at 3χ. The amount of (cO□+Co) produced in the exhaust gas in the oxidation step, which is an indicator of acetic acid combustion, was 0.41 mol per mol of raw material meta-xylene.

The oxidation reaction mixture that was post-oxidized in the second reactor was
"Isophthalic acid crystals were precipitated in a crystallizer of "C". Isophthalic acid was separated from the obtained slurry by filtration while washing with acetic acid. The separated mother liquor was concentrated by distillation, and the distillation column bottom liquid was When the concentrated liquid was continuously supplied to a thin film evaporator in which a heating medium kept at °C was circulated for 6 hours while adjusting the flow rate of the heating medium so that the temperature reached 200°C, high boiling substances were successfully separated. did it.

(Third step) A suspension obtained by adding 1.5 times the weight of fresh acetic acid (moisture 10χ) to the isophthalic acid crystals separated by filtration was transferred to a washing tank and maintained at a temperature of 150°C for 30 minutes with stirring. Washed P! Cool the suspension to 100°C,
The mixture was filtered and separated again, and then dried to obtain 155 parts by weight of purified isophthalic acid. As a result, the yield of isophthalic acid based on meta-xylene as a raw material was 93.0 mol χ, and purified isophthalic acid with high purity and excellent whiteness was obtained.

Example 2 In Example 1, the catalyst concentration in the first step was increased to 1.5 times,
The oxidation reaction was carried out at a temperature of 200''C. As a result, purified isophthalic acid with high purity and excellent whiteness was obtained, and the separation of high boiling substances in the thin film evaporator in the second step was also good.

In Example 2, the oxidation reaction was carried out at a temperature of 215°C in the first step. As a result, the low concentration of 3 CBA in the crude isophthalic acid crystals resulting from post-oxidation in the second step resulted in poor fluidity of high-boiling substances, making the thin film evaporator inoperable.

60 parts by weight of meta-xylene was added to the first main reactor, 0.561 parts of cobalt acetate tetrahydrate, and 1.0 parts of manganese acetate tetrahydrate.
656 parts of hydrobromic acid (47 χN, 551 parts) and 496.2 parts of acetic acid (moisture 10 χ) were fed continuously as a raw material solution.The catalyst concentration was 276 pprrl of cobalt, 773 ppm of manganese, and bromine per weight of solvent. 1
500 pI) m) and oxidized while blowing air. In this oxidation, the temperature was 190°C, the pressure was 16.5 kg/
The air supply amount was adjusted to maintain the condition of cm2G and the oxygen concentration of the oxidizing exhaust gas to 5χ. Meta-xylene supply rate is 1 volume of acetic acid solvent possessed by the reactor! 0.09kg per hour
The average residence time was about 55 minutes, and the total concentration of isophthalic acid and its intermediates in the oxidation reactor was 19.0x.

The oxidation reaction mixture obtained in the first reactor was transferred to the second reactor and post-oxidized with air under the conditions of temperature 185° C., pressure 12 kg/cm 2 G, and average residence time 50 minutes.

The oxygen concentration of the exhaust gas was maintained at 3χ.

As a result of carrying out the same operations as in Example 1, purified isophthalic acid with high purity and excellent whiteness was obtained, and the separation of high boiling substances in the thin film evaporator in the second step was also good.

Comparative Example 2 The same procedure was used as in Example 3 except that 1.795 parts of cobal acetate and 0.442 parts of manganese acetate tetrahydrate were used (ratio of manganese to cobalt: 0.25).

As a result, since the concentration of 3CBA in the post-oxidized isophthalic acid crystals in the second step was low, the fluidity of high-boiling substances was poor, and the thin film evaporator was inoperable.

Comparative Example 3 The first step was the same as in Example 1, and the post-oxidation in the second step was 1
The test was carried out at 65°C and a pressure of kg/cm2G. As a result,
Although the thin film evaporator performed well, the purified isophthalic acid had a high concentration of 3CBA and was colored.

This 1■''± The first step and the second step were the same as in Example 1, and the cleaning temperature in the third step was 90°C. As a result, coloring was observed in the purified isophthalic acid.

Table 1 shows the main operating conditions of each Example and Comparative Example and the analysis results of crude isophthalic acid and purified isophthalic acid crystals.

The crude isophthalic acid in Table 1 was obtained by taking the oxidation reaction mixture directly from the first reactor and the second reactor into a pressure-resistant sample container, washing it with acetic acid at 100°C, and then subjecting it to solid-liquid separation.

The methods for measuring 3CBA and resin color are as follows.

(1) 3CBA: Quantitative value determined by polarography; 3CBA must be 50 ppm or less for high purity isophthalic acid.

(2) Resin color: Ratio of isophthalic acid: fumaric acid: neopentyl glycol: propylene glycol = 57:43:50:53 (
The resin color of the resulting styrene solution (resin 60 edition x) is shown in Hazen color number. The smaller the Hazen color number is, the better the resin color is, and as high purity isophthalic acid, it needs to be at least 30 or less.

〔Effect of the invention〕

According to the present invention, high-purity isophthalic acid with extremely excellent color quality can be obtained industrially and very easily as a raw material for polymers such as unsaturated polyester resins, alkyd resins, and heat-resistant polyamides for highly functional applications. Furthermore, the method of the present invention does not require an expensive purification process, so the construction cost is low, the amount of acetic acid used is small, and high purity isophthalic acid can be obtained in high yield.

Patent applicant: Mitsubishi Gas Chemical Co., Ltd. Agent: Patent Attorney Sadafumi Kohori

Claims (1)

[Claims] A method for producing isophthalic acid by oxidizing meta-xylene with an oxygen-containing gas in the presence of a cobalt-manganese-bromine catalyst in a hydrous acetic acid solvent, comprising: (a) isophthalic acid per weight of solvent in an oxidation reactor; The total amount of acids and their intermediates is 10 to 35% by weight, the total amount of cobalt and manganese is 300 to 1500 ppm, the atomic ratio of manganese to cobalt is 0.5 to 5 times, the bromine atoms to the total amount of cobalt and manganese. The ratio is 0.5
The oxidation reaction is carried out by supplying a solvent and a catalyst so as to increase the amount by ~1.5 times, maintaining a temperature of 180 to 210°C, and an oxygen concentration of exhaust gas of 2 to 8% by volume, and crude isophthalic acid obtained in this step. (b) The oxidation reaction product mixture obtained in the first step is further oxidized to reduce the concentration of 3-carboxybenzaldehyde in the crude isophthalic acid. A second step of adjusting the 3-benzaldehyde concentration to 100 to 800 ppm and separating crude isophthalic acid, and then purifying the mother liquor using a thin film evaporator to recover acetic acid, and (c) isophthalic acid obtained in the second step. A method for producing high-purity isophthalic acid, comprising a third step of mixing crystals with fresh acetic acid and stirring at a temperature of 100° C. or higher, and then separating purified isophthalic acid.