JPH09151160A - Purification of monocyclic aromatic carboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an improvement in both purity and yield at a stroke by converting CHO in 4-carboxybenzaldehyde which is a representative impurity in crude terephthalic acid into COOH when purifying the crude terephthalic acid. SOLUTION: Crude terephthalic acid is reacted with molecular oxygen in a molar amount within the range of at least 0.5, preferably >=1 to 30 times based on the amount of oxygen required to oxidize a substituent group in an incompletely oxidized stage in the crude substance into carboxyl group in the presence of a noble metallic catalyst such as platinum in an aqueous reactional medium at a high temperature. The monocyclic aromatic carboxylic acid undergoing the oxidizing treatment is then reacted with hydrogen in the presence of the noble metallic catalyst in the aqueous reactional medium. The monocyclic carboxylic acid is crystallized from the reactional product solution after the hydrogenating treatment and recovered to afford the purified product.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a crude monocyclic aromatic carboxylic acid obtained by oxidizing a substituent of a monocyclic aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent. On how to do.

[0002]

2. Description of the Related Art Monocyclic aromatic carboxylic acids are important chemical products and are widely used as raw materials for polymers, especially synthetic resins. For example, terephthalic acid, which is a typical monocyclic aromatic carboxylic acid, is a raw material for polyester resins, and trimellitic acid and pyromellitic acid are important raw materials for polyimide resins.

Terephthalic acid is produced by liquid phase oxidation of p-alkylbenzene (for example, JP-A-60-).
184043). In the crude terephthalic acid obtained,
4-Carboxybenzaldehyde (hereinafter "4-CBA")
Abbreviated)) and other impurities are included.
Even if a small amount of these impurities, the polyester produced by polycondensation of terephthalic acid and glycols is colored and the degree of polymerization is lowered, resulting in a quality defect.

Therefore, the purification of terephthalic acid containing impurities as described above is an important problem, and many solutions have been proposed so far. One of them is a method in which crude terephthalic acid is suspended in water or a mixed solvent of water / acetic acid and treated by oxidation or reduction (hydrogenation) (JP-B-41-20820, 43-23447, and JP-A-43-23447). 43-23448). In carrying out the oxidation or reduction treatment, there are many proposals that it is more efficient to carry out the treatment in a state where crude terephthalic acid is dissolved in water or a mixed solvent of water / acetic acid, rather than being suspended. 42-2
1819, the same 41-16860, the same 52-46122,
53-10051, 56-32319, 56-3
5174, ibid. 56-35653, ibid. 57-51373,
57-51374, 57-51818, and Japanese Patent Laid-Open No. 56-51818.
-79635, ibid. 56-103136).

In addition, a method of treating an aqueous solution of terephthalic acid with palladium or zinc as a catalyst (Japanese Patent Publication No. 41-2).
9131, 47-37607, 47-42213, 49-13780, 49-33189) and a method of treating an alkaline aqueous solution of terephthalic acid with oxygen (Japanese Patent Laid-Open No. Sho 5).
6-113738).

The known terephthalic acid refining techniques have some effects when the content of impurities is relatively small, but are not always satisfactory when the amount of impurities is large. Further, although the amount of 4-CBA, which is a main impurity, can be reduced, the hue of purified terephthalic acid is often not improved. In the conventional method, most of 4-CBA, which is an impurity, is converted into something other than terephthalic acid and discarded, so that the yield of terephthalic acid is low and a large amount of waste is generated from the refining process.

[0007] For example, the above-mentioned Japanese Patent Publication No. 52-462.
The method described in 12 is a method of treating a high temperature aqueous solution of crude terephthalic acid with a mixed gas containing a low concentration of oxygen in the presence of a noble metal catalyst. Even when the concentration of 4-CBA reaches several thousands ppm, this method is used. It can be removed. However, the mechanism is a decarbonylation reaction of an aldehyde with a noble metal catalyst and a small amount of oxygen, so even if the objective of purification can be achieved,
The higher the content of 4-CBA, the higher the amount of waste. The hue of the obtained purified terephthalic acid is also not sufficiently satisfactory.

As a method of improving these points, a method of oxidizing crude terephthalic acid as a high temperature aqueous solution and then treating with hydrogen was proposed (Japanese Patent Publication No. 7-8823). According to this, even if the target is crude terephthalic acid containing a relatively large amount of impurities such as 4-CBA, the impurity content can be reduced and the yield of terephthalic acid can be improved. The hue of purified terephthalic acid is also good. However, in this method, 4-CBA is not selectively converted to terephthalic acid, so that the terephthalic acid yield cannot be sufficiently improved. The remaining 4-CBA is reduced in the subsequent hydrorefining step and is lost as a large amount, and the amount of hydrogen required for hydrorefining becomes relatively large.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to improve the yield of carboxylic acid in a method for purifying a monocyclic aromatic carboxylic acid represented by terephthalic acid without the above-mentioned drawbacks of the prior art. Therefore, it is an object of the present invention to provide a purification method in which the amount of waste produced is small and the hue of the purified carboxylic acid is good.

[0010]

The method for purifying a monocyclic aromatic carboxylic acid according to the present invention oxidizes a substituent of a monocyclic aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent. In the method for purifying the crude monocyclic aromatic carboxylic acid thus obtained, (1) the crude monocyclic aromatic carboxylic acid is added to the crude monocyclic aromatic carboxylic acid in the presence of a Group VIII noble metal catalyst in a high temperature aqueous reaction medium. Oxidized by 0.5 to 30 moles of molecular oxygen per mole of oxygen molecule required to oxidize the substituents in the incomplete oxidation stage in the ring aromatic carboxylic acid to the carboxyl group, and further (2) Group VIII Hydrogen is applied in the presence of a noble metal catalyst for reduction, and (3) the produced monocyclic aromatic carboxylic acid is dissolved in the aqueous reaction medium at a high temperature, and solid-liquid separated from the noble metal catalyst, and then (4) ) Cool the reaction product Precipitating a monocyclic aromatic carboxylic acid with, and recovering.

As described above, the crude monocyclic aromatic carboxylic acid to which the purification method of the present invention can be applied oxidizes the substituent of the monocyclic aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent. The alkyl substituent is typically a lower alkyl group having 1 to 3 carbon atoms such as methyl, ethyl, propyl and isopropyl. Examples of the partially oxidized alkyl substituent include oxygen-containing hydrocarbon groups other than the carboxyl group such as an aldehyde group and a hydroxyalkyl group.
The present invention is particularly effective in the case of purifying polycarboxylic acids such as dicarboxylic acids and tricarboxylic acids.

Such crude monocyclic aromatic carboxylic acids include o-xylene, m-xylene, p-xylene and p-xylene.
Toluic acid, trimethylbenzene, durene, or the like may be used as a starting material and may be obtained by oxidizing the starting material in a gas phase or a liquid phase. A preferable one is a crude product of a monocyclic aromatic carboxylic acid obtained by liquid phase oxidation with molecular oxygen using a catalyst such as cobalt, manganese, or bromine using a lower aliphatic carboxylic acid as a reaction medium. Examples of such a crude product include crude terephthalic acid produced by the production method described in JP-A-60-184043 and crude trimellitic acid produced by the production method described in JP-A-2-184652. In the method for producing terephthalic acid of JP-A-60-184043, paraxylene or metaxylene is used as a salt of cobalt or manganese (0.1 to 1% by mass as a metal atom) and a bromine compound (0.3 to 10% by mass as a bromine atom). %) In the presence of a catalyst with 1) for all metal atoms
It is a method of oxidizing by using a molecular oxygen-containing gas in an aqueous solution containing a 10-fold molar amount of an aromatic carboxylic acid, characterized by using calcium bromide and tetrabromobutane as bromine compounds.

In the purification method of the present invention, the crude monocyclic aromatic carboxylic acid is first subjected to an oxidation treatment in the form of a solution in an aqueous reaction medium at a high temperature under predetermined conditions.

The reaction medium used in the present invention is aqueous as described above, and is water or a medium containing water as a main component. An example of the latter is aqueous acetic acid. However, it is generally sufficient to use water such as distilled water or ion-exchanged water. The amount of reaction medium used is such that at the reaction temperature the crude monocyclic aromatic carboxylic acid is at least partially, preferably completely dissolved. Usually, 2 to 20 times the mass of the crude product is used. Particularly, the amount of 3 to 10 times is preferable. Needless to say, if the amount of the reaction medium is too small, the amount of the crude monocyclic aromatic carboxylic acid dissolved is small, and the purification by the oxidation reaction cannot be sufficiently performed. If it is too much, it does not interfere with the progress of the reaction,
It is economically disadvantageous in that it requires a large reactor and consumes more energy to recover the monocyclic aromatic carboxylic acid.

The reaction temperature is the temperature at which the crude monocyclic aromatic carboxylic acid is sufficiently dissolved in the reaction medium. At low temperatures the solubility is low and large amounts of solvent are required. If the temperature is too high, undesired decomposition reactions such as cleavage of aromatic rings and elimination of carboxyl groups occur. A preferable temperature is 200 to 330 ° C., and a particularly preferable temperature is 250.
~ 310 ° C.

As oxygen for oxidizing impurities, molecular oxygen contained in air, a mixed gas of oxygen and an inert gas (such as nitrogen) may be used, but air is sufficient.
The amount of oxygen supplied is an impurity present in the crude monocyclic aromatic carboxylic acid, which is oxidized to the carboxyl group based on the substituent in the incomplete oxidation stage which is the object of the oxidation treatment in the present invention. Therefore, when the number of oxygen molecules required is 1 mol, it is at least 0.5 mol, preferably 1 mol or more, particularly preferably 5 mol or more. When the supply amount of oxygen is insufficient, the oxidation reaction of impurities does not proceed and the decarbonylation reaction proceeds. On the other hand, an excessive amount of oxygen should be avoided because it causes undesirable side reactions such as generation of colored impurities and cleavage of aromatic rings, and the pressure resistance of the reactor must be increased.
It is preferably within a molar range. More preferably within 20 moles,
Particularly preferred is within 15 mol. The partial pressure of oxygen gas in the oxygen-containing gas is suitably 0.01 to 6 MPa, preferably 0.5 to 2 MPa.

The pressure of the entire reaction system is such that at least a part of the reaction medium can exist as a liquid. It is preferable that 50 mass% or more is present in the liquid phase portion, and it is particularly preferable that it is present in an amount of about 75 mass%. Pressure is the temperature of the system,
Since it is influenced by the oxygen partial pressure and the type and amount of the reaction medium, it cannot be generally stated, but it is usually 3 to 13 MPa, and the preferable range is 5 to 10 MPa.

The metal catalyst used as the oxidation catalyst is one or more of the noble metals of Group VIII of the Periodic Table, that is, ruthenium, rhodium, palladium, osmium, iridium and platinum, as described above. This catalyst
The compound having a substituent in the incomplete oxidation step, which is contaminated as an impurity in the crude monocyclic aromatic carboxylic acid, is further oxidized and selectively converted to the desired monocyclic aromatic carboxylic acid. . Highly active are platinum, palladium, rhodium and ruthenium. The catalyst may be used in the form of powder or granules, or may be used by supporting it on a carrier. As the carrier, activated carbon, graphite, alumina,
Zeolite, silica and the like can be used, but activated carbon is particularly preferable. The supported amount is preferably 0.1 to 5 mass% in terms of metal amount with respect to the total catalyst amount. The amount of the catalyst used depends on the reaction temperature, the concentration of impurities in the crude monocyclic aromatic carboxylic acid,
Although it depends on the conditions such as the residence time in the reactor,
Generally, the crude monocyclic aromatic carboxylic acid to noble metal component in the oxidation catalyst is about 200: 1 to about 30,000 by weight.
0: 1, preferably about 2,000: 1 to about 20,000.
It may be selected and used so that it becomes 0: 1. When the amount of the noble metal catalyst is small, the rate of oxidation reaction of impurities remains at a low value, while the presence of an excessive amount of the catalyst causes the decarbonylation reaction to proceed, which is not preferable.

The reaction time depends on the ratio of the crude monocyclic aromatic carboxylic acid to the oxidation catalyst, the oxygen concentration and the reaction temperature. As a measure of actual operation, the residence time during which the reaction mixture is in contact with the oxidation catalyst, or the feed weight rate (WHS
V), about 200 to 200,000 g (reaction solution) / g (noble metal component in the oxidation catalyst) · hr, preferably,
It is 1,000 to 100,000 g / g · hr.

Subsequently, in the present invention, oxygen is removed from the high temperature aqueous solution of the crude monocyclic aromatic carboxylic acid which has been subjected to the above-mentioned oxidation treatment by a known method such as a degassing tank or an oxygen absorption tower, and then predetermined. Hydrotreating is performed under the conditions of. For this hydrogenation treatment, a method that is generally adopted for hydrorefining terephthalic acid or benzene polycarboxylic acid can be used.

In the present invention, hydrogenation is carried out using hydrogen gas and a hydrogenation catalyst. The amount of hydrogen supplied is the amount of the compound 1 having a substituent in the incomplete oxidation stage present in the crude monocyclic aromatic carboxylic acid before the above-mentioned oxidation treatment.
At least 0.02 mol is required per mol, preferably 0.5 mol or more, particularly preferably 1 mol or more. If the amount of hydrogen supplied is insufficient, the decarbonylation reaction of the monocyclic aromatic carboxylic acid proceeds. On the other hand, if the amount of hydrogen is increased, the nuclear hydrogenation reaction of the aromatic ring proceeds, so a maximum of 20 mol, 10 mol or less for purification purposes is sufficient. Usually, 2 to 7 mol is optimum. The hydrogen partial pressure is suitably 0.01 to 3 MPa, preferably 0.1 to 2 MPa.

The reaction temperature is preferably 200 to 330 ° C.,
A particularly preferred temperature is 250 to 310 ° C. When the reaction temperature is low, the solubility of the crude monocyclic aromatic carboxylic acid in water becomes extremely low, and a large amount of solvent is required. On the other hand, if the temperature is too high, a nuclear hydrogenation and cleavage of an aromatic ring and a decomposition reaction such as elimination of a carboxyl group occur.

The overall pressure in the reaction system is such that at least part of the reaction medium can be in liquid form. 50 mass%
The above is preferably present in the liquid phase part, particularly preferably about 75% by mass. The pressure cannot be generally specified because it is affected by the temperature of the system, the hydrogen partial pressure, and the type and amount of the reaction medium, but it is usually 3 to 13 MPa, and the preferable range is 5 to 10 MPa.

The metal catalyst used as the hydrogenation catalyst is, as described above, a noble metal of Group VIII of the periodic table, that is, palladium, rhodium, ruthenium, osmium, iridium,
And one or more of platinum. This catalyst converts the coloring component in the monocyclic aromatic carboxylic acid after being subjected to the above-mentioned oxidation treatment into a colorless compound, and has a very small amount of the monocyclic aromatic ring having a substituent in the incomplete oxidation stage. Impurities such as carboxylic acids are hydrogenated and converted into compounds that can be easily separated from the target compound, a monocyclic aromatic carboxylic acid. Highly efficient catalysts are platinum, palladium, rhodium and ruthenium. The catalyst may be used in the form of powder or granules, or may be used by supporting it on a carrier.
As the carrier, activated carbon, graphite, alumina, zeolite, silica or the like can be used, but activated carbon is particularly preferable. The supported amount is suitably 0.1 to 5 mass% based on the total amount of catalyst. The amount of the catalyst used is determined by conditions such as the reaction temperature, the concentration of impurities in the crude monocyclic aromatic carboxylic acid, the residence time in the reactor, etc. The aromatic carboxylic acid may be selected and used in a weight ratio of about 200: 1 to about 30,000: 1, preferably about 2,000: 1 to about 20,000: 1. When the amount of noble metal catalyst is small, the effect of removing coloring components and the hydrogenation reaction rate of impurities remain low. On the other hand, the presence of an excessive amount of catalyst causes the decarbonylation reaction of monocyclic aromatic carboxylic acid and the nucleus of aromatic ring. It is not preferable because the hydrogenation reaction proceeds.

The reaction may be carried out continuously or in a batch operation.

The reaction time depends on the amount ratio of the crude monocyclic aromatic carboxylic acid to the hydrogenation catalyst, the hydrogen concentration and the reaction temperature. As a measure of actual operation, the residence time during which the reaction mixture is in contact with the hydrogenation catalyst or the feed weight rate (WH
SV), it is about 200 to 200,000 g (reaction solution) / g (noble metal component in the hydrogenation catalyst) · hr, preferably 1,000 to 100,000 g / g · hr.

After completion of the hydroreduction treatment, the hydrogenation catalyst which is present as a solid in the aqueous reaction medium and the monocyclic aromatic carboxylic acid which is dissolved in the medium are separated. If the reaction is carried out by a continuous method in which the catalyst is used as a fixed bed and the reaction solution is passed therethrough, solid-liquid separation of the catalyst and the reaction solution can be naturally performed.

Generally, a monocyclic aromatic carboxylic acid is hardly soluble or almost insoluble in water under normal temperature and normal pressure, but its solubility in a reaction medium increases under high temperature and high pressure, so that it may be filtered or centrifuged in a dissolved state. It can be taken out by solid-liquid separation of the oxidation catalyst and the reaction product liquid by means.
The conditions of high temperature and high pressure at which a monocyclic aromatic carboxylic acid is easily dissolved in an aqueous medium are a temperature of 200 ° C. or higher and a pressure of 3 MPa or higher. Under these conditions, the solubility of the monocyclic aromatic carboxylic acid in water is It is at least about 10% by mass.
The practical limits are a temperature of 330 ° C. and a pressure of 10 MPa.
The preferred range is a temperature of 250 to 310 ° C and a pressure of 7 to 10MP.
a. The catalyst can be reused after being subjected to normal regeneration treatment such as reduction treatment.

Subsequent to solid-liquid separation, the obtained reaction liquid is cooled to crystallize a monocyclic aromatic carboxylic acid. The crystallization temperature is between 200 ° C and 30 ° C. 100-35 degreeC is preferable. At this time, the cooling rate is preferably 25 ° C / min or less, more preferably 10 ° C.
/ min or less. If the cooling rate is too fast, the precipitated monocyclic aromatic carboxylic acid particles become extremely fine, and separation from the mother liquor becomes difficult. The precipitated purified monocyclic aromatic carboxylic acid is recovered by means such as filtration and centrifugation.

Substituents in the incomplete oxidation stage, typically the formyl group --CHO, are reacted in an aqueous reaction medium at elevated temperature and pressure,
When a suitable amount of molecular oxygen is applied in the presence of a noble metal catalyst, it is oxidized to a carboxyl group. As a result, for example, a typical impurity contained in crude terephthalic acid is 4-
CBA becomes terephthalic acid, and the improvement of the purity and the improvement of the yield are realized all at once. Further hydrogenation treatment can significantly improve the hue by reducing other impurities, especially coloring components. The substituent in the incomplete oxidation stage here is a substituent such as aldehyde, hydroxyalkyl and alkyl.

[0031]

EXAMPLES In the following examples, the purity was measured by high performance liquid chromatography (HPLC), analytical column: Asahipak ODP-50 (Shodex), solvent: 10 mM.
-NaH was performed using ₂ PO ₄ + _5mM- tetrabutylammonium bromide (pH 7.5) aqueous solution / acetonitrile. Further, each monocyclic aromatic carboxylic acid was subjected to methyl esterification with diazomethane and then subjected to gas chromatography (GC) using an analytical column OV-17. Regarding the hue, the L value (brightness) and the a value [red (+) of a powder sample prepared and packed in a cylindrical glass cell were used.
.About.green (-)] and b value [yellow (+) to blue (-)] were determined.
The closer the L value is to 100 and the closer the a value and the b value are to 0, the closer it is to white.

Example 1 Paraxylene was oxidized according to the method described in JP-A-60-184043 to obtain crude terephthalic acid. The obtained crude terephthalic acid had a purity of 99% by mass and contained 4-CBA as an impurity of 10,000.
It contains ppm and the hue is [L 92, a-4, b8].

The crude terephthalic acid was purified using the experimental apparatus shown in FIG. This device is provided with a heater and a heat insulating material (not shown), and the temperature is accurately controlled by a temperature controller.

First, in a titanium reaction tank (1) having a condenser (11) and a gas injection pipe (12) on the upper part and equipped with a stirrer (13), the crude terephthalic acid 1
23 g, 25.9 g of 0.5% palladium on activated carbon catalyst and 600 g of water were charged. The valve (3) was opened and 5.16 Nl of air was injected through the gas blowing pipe (12). The injected oxygen corresponds to 5.9 moles per mole of oxygen molecules required to oxidize the substituents in the incomplete oxidation stage to carboxyl groups. While stirring with the stirrer (13), the reaction tank was heated with the heater (2) to raise the temperature. After the temperature in the reactor reaches 300 ° C and the pressure reaches 9.0 MPa,
The oxidation treatment was continued for 30 minutes.

After completion of the reaction, the heating in the heater (2) was stopped while stirring with the stirrer (13), and the temperature in the reaction tank was adjusted to 30
Cooled to ° C. Then, the air remaining in the reaction tank was removed by a vacuum pump through the exhaust gas line above the condenser (11), and the pressure in the system inside the reaction tank was set to 100 mmHg. The valve (3) was opened, and 0.18 Nl of hydrogen was injected through the gas blowing pipe (12). The injected hydrogen corresponds to 1 time mol of the compound having a substituent in the incomplete oxidation step before the oxidation treatment. While stirring by the stirrer (13), the reaction tank was heated by the heater (2) to raise the temperature. After the temperature in the reaction tank reached 800 ° C. and the pressure reached 9.0 MPa, hydrogenation treatment was performed for 30 minutes.

After the reaction was completed, the valve (5) was opened while maintaining the temperature, and the reaction mixture was mixed with the sintered metal filter (4).
Through a solid-liquid separation into a catalyst and a reaction product liquid, and the liquid was transferred to a cooling tank (6) provided with a condenser (61) through an introduction pipe (62).

Up to 40 ° C., the purified terephthalic acid was crystallized by cooling at a cooling rate of 20 ° C./min. After lowering the internal pressure of the cooling tank (6) to normal pressure, the valve (7) was opened to collect a slurry containing purified terephthalic acid.

The slurry was filtered under reduced pressure to separate the solid from the mother liquor. When the purity was measured after drying the solid, it was 99.99 mass% or more (4-CBA content 100
ppm or less), and the hue is [L 96, a -1.7, b
0.6], resulting in a brighter white color.
The recovery rate of terephthalic acid was 99% by mass or more.

Example 2 Using the same apparatus as in Example 1, the crude terephthalic acid produced in the same manner as in Example 1 was purified.

The operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 123 g 0.5% Ruthenium activated carbon catalyst 25.9 g Water 600 g Air 5.19 Nl = oxygen amount 5.9 times mol (reaction Conditions) Temperature 300 ° C., pressure 9.0 MPa, time 30 minutes Hydrotreatment (charge) Crude terephthalic acid 123 g 0.5% Ruthenium activated carbon catalyst 25.9 g Water 600 g Hydrogen 0.18 Nl (1 time mole) (reaction conditions) ) Temperature 300 ° C, pressure 9.0 MPa, time 30 minutes (crystallization condition) Cooling down to 40 ° C at a cooling rate of 20 ° C / min Result (refined product) Terephthalic acid purity 99.99% by mass or more 4-CBA included Quantity 100 ppm or less Hue [L 95.9, a -1.6, b 0.9] Terephthalic acid recovery rate 99 mass% or more.

Example 3 Using the same apparatus as in Example 1, crude terephthalic acid produced in the same manner as in Example 1 was purified.

The operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 123 g 0.5% Palladium activated carbon catalyst 25.9 g Water 600 g Air 0.87 Nl = 1 mole of oxygen (reaction conditions) Temperature 300 ° C, Pressure 9.3MPa, Time 30 minutes Hydrogenation (charge) Crude terephthalic acid 123g 0.5% Palladium activated carbon catalyst 25.9g Water 600g Hydrogen 0.18Nl (1 time mole) (reaction condition) Temperature 300 ℃, pressure 9.0MPa, time 30 minutes (crystallization condition) Cool down to 40 ℃ at a cooling rate of 20 ℃ / min Result (refined product) Terephthalic acid purity 99.99% by mass or more 4-CBA content 100ppm Hue [L 96, a -1.8, b 0.5] Terephthalic acid recovery rate 99 mass% or more.

Example 4 Using the same equipment as in Example 1, the crude terephthalic acid produced in the same manner as in Example 1 was purified. A water / acetic acid mixture was used as the reaction medium.
Other operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 123g 0.5% Palladium activated carbon catalyst 25.9g 50 mass% acetic acid aqueous solution 600g Air 5.19Nl = oxygen amount 5.9 times. Molar (reaction conditions) Temperature 300 ° C., pressure 9.0 MPa, time 30 minutes Hydrogenation treatment (charge) Crude terephthalic acid 123 g 0.5% Palladium activated carbon catalyst 25.9 g 50 mass% acetic acid aqueous solution 600 g Hydrogen 0.18 Nl ( (1 mol) (reaction condition) temperature 300 ° C, pressure 9.0 MPa, time 30 minutes (crystallization condition) cooling to 40 ° C at a cooling rate of 20 ° C / min Result (refined product) Terephthalic acid purity 99.99 Mass% or more 4-CBA content 100 ppm or less Hue [L 96.1, a-1.6, b 0.4] Terephthalic acid recovery rate 99 mass% or more.

Example 5 Using the same equipment as in Example 1, the crude terephthalic acid produced in the same manner as in Example 1 was purified. The operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 12.3 g 0.5% Palladium activated carbon catalyst 2.59 g Water 600 g Air 0.52 Nl = oxygen amount 5.9 times mol (reaction conditions ) Temperature 250 ° C., pressure 4.0 MPa, time 30 minutes Hydrotreatment (charge) Crude terephthalic acid 12.3 g 0.5% palladium on activated carbon catalyst 2.59 g water 600 g hydrogen 0.02 Nl (1 mole) (reaction) Conditions) Temperature 250 ° C, pressure 4.0 MPa, time 30 minutes (crystallization conditions) Cooling down to 40 ° C at a cooling rate of 20 ° C / min Result (refined product) Terephthalic acid purity 99.98% by mass or more 4-CBA Content 100 ppm or less Hue [L 95.8, a -1.6, b 0.9] Terephthalic acid recovery rate 99 mass% or more.

Example 6 Using the same apparatus as in Example 1, the crude terephthalic acid produced in the same manner as in Example 1 was purified. The operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 123 g 0.5% Palladium activated carbon catalyst 25.9 g Water 600 g Air 13.2 Nl = 15 times mole oxygen (reaction condition) Temperature 300 ° C , Pressure 9.5MPa, time 30 minutes hydrotreatment (charge) crude terephthalic acid 123g 0.5% palladium on activated carbon catalyst 25.9g water 600g hydrogen 0.18Nl (1 mol) (reaction condition) temperature 300 ° C, Pressure 9.0 MPa, time 30 minutes (crystallization condition) Cooling up to 40 ° C at a cooling rate of 20 ° C / min Result (refined product) Terephthalic acid purity 99.99% by mass or more 4-CBA content 100 ppm or less Hue [ L 95.9, a -1.6, b 0.7] Terephthalic acid recovery rate 99 mass% or more.

Example 7 Using the same apparatus as in Example 1, the crude terephthalic acid produced in the same manner as in Example 1 was purified. The operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 123 g 0.5% Palladium activated carbon catalyst 25.9 g Water 600 g Air 5.19 Nl = oxygen amount 5.9 times mol (reaction condition) Temperature 300 ° C, Pressure 9.0MPa, Time 30 minutes Hydrogenation (charge) Crude terephthalic acid 123g 0.5% Palladium activated carbon catalyst 25.9g Water 600g Hydrogen 0.01Nl (0.05 times mole) (reaction condition) Temperature 300 ℃, Pressure 9.0MPa, Time 30 minutes (Crystallization condition) Cool to 40 ℃ at a cooling rate of 20 ℃ / min Result (refined product) Terephthalic acid purity 99.99% by mass or more 4-CBA content 100 ppm or less Hue [L 95.9, a -1.4, b 0.7] Terephthalic acid recovery rate 99 mass% or more.

Comparative Example 1 Crude terephthalic acid produced in the same manner as in Example 1 was purified using the same apparatus as in Example 1. The treatment was only oxidation and no hydrogenation.
The operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 123 g 0.5% Palladium activated carbon catalyst 25.9 g Water 600 g Air pressure 5.19 Nl = oxygen amount 5.9 times mol (reaction condition) Temperature 300 ℃, pressure 9.0MPa, time 30 minutes (crystallization condition) Cool down to 40 ℃ at a cooling rate of 20 ℃ / min Result (refined product) Terephthalic acid purity 99.99% by mass or more 4-CBA content 100ppm or less Hue [L 95.9, a-1.7, b 2.1] Recovery rate of terephthalic acid: 99% by mass or more.

When hydrogenation is not performed, the b value is set to 1
It was confirmed that it could not be lowered below.

[Comparative Example 2] Crude terephthalic acid produced in the same manner as in Example 1 was purified using the same apparatus as in Example 1. For the oxidation treatment, mere activated carbon which does not carry a precious metal catalyst was used. The operating conditions and the results are as follows: Oxidation treatment (charge) Crude terephthalic acid 123 g Activated carbon 24.6 g Water 600 g Air 5.19 Nl = oxygen amount 5.9 times mol (reaction conditions) Temperature 300 ° C., pressure 9.0 MPa, Time 30 minutes Hydrogenation treatment (charge) Crude terephthalic acid 123 g Activated carbon 24.6 g Water 600 g Hydrogen 0.18 Nl (1 mol) (reaction conditions) Temperature 300 ° C, pressure 9.0 MPa, time 30 minutes (crystallization conditions) ) Cooling down to 40 ° C at a cooling rate of 20 ° C / min Result (refined product) Purity of terephthalic acid 99.4 mass% or more 4-CBA content 1000ppm or less p-toluic acid content 4700ppm Benzoic acid content 200ppm Hue [ L 95.1, a -1.8, b 0.9] Terephthalic acid recovery rate of 97 mass% or more When no precious metal catalyst is used for the oxidation treatment, terephthalic acid is used. For conversion to Le acid is not complete, it was confirmed that the recovery rate is low.

Comparative Example 3 Using the same apparatus as in Example 1, the same crude terephthalic acid as that purified in Example 1 was purified. First, 123 g of the crude 2,6-terephthalic acid and the copper oxide catalyst 26 were placed in a titanium reaction tank (1) having a condenser (11) and a gas blowing pipe (12) in the upper part and equipped with a stirrer (13). 0.6 g and 600 g of water were charged. Open the valve (3) to open the gas injection pipe (1
5.19 Nl of air was injected from 2). The injected oxygen corresponds to 5.9 moles of oxygen molecules required to oxidize a substituent in the incomplete oxidation stage to a carboxyl group. While stirring with the stirrer (13), the reaction tank was heated with the heater (2) to raise the temperature. After the temperature in the reaction tank reached 300 ° C. and the pressure reached 9.0 MPa, the reaction was continued for 30 minutes.

After completion of the reaction, the valve (5) was opened while maintaining the temperature, and the reaction mixture was mixed with the sintered metal filter (4).
Through a solid-liquid separation into a catalyst and a reaction product liquid, and the liquid was transferred to a cooling tank (6) provided with a condenser (61) through an introduction pipe (62).

Up to 40 ° C., the purified terephthalic acid was crystallized by cooling at a cooling rate of 20 ° C./min. After reducing the internal pressure of the cooling tank (6) to normal pressure, the valve (7) was opened and the slurry containing purified terephthalic acid was collected.

The slurry was filtered under reduced pressure to separate the solid from the mother liquor. Next, in the reactor used for the above-mentioned oxidation reaction, 2,6-terephthalic acid collected by solid-liquid separation and 0.5% ruthenium activated carbon catalyst 2 which is a catalyst for the oxidation reaction.
5.9 g was charged and 600 g of fresh water was added. The valve (3) was opened, and 0.18 Nl of hydrogen was injected through the gas blowing pipe (12). The injected hydrogen corresponds to a molar ratio of 1 time with respect to the compound having a substituent in the incomplete oxidation step before the oxidation treatment. While stirring by the stirrer (13), the reaction tank was heated by the heater (2) to raise the temperature. Temperature in the reaction tank is 300 ℃, pressure is 9.0MP
After reaching a, the reaction was continued for 30 minutes.

After completion of the reaction, the valve (5) was opened while maintaining the temperature, and the reaction mixture was mixed with the sintered metal filter (4).
Through a solid-liquid separation into a catalyst and a reaction product liquid, and the liquid was transferred to a cooling tank (6) provided with a condenser (61) through an introduction pipe (62).

Up to 40 ° C., the purified terephthalic acid was crystallized by cooling at a cooling rate of 20 ° C./min. After lowering the internal pressure of the cooling tank (6) to normal pressure, the valve (7) was opened to collect a slurry containing purified terephthalic acid.

The slurry was filtered under reduced pressure to separate the solid from the mother liquor. When the purity was measured after drying the solid, it was 99.99% by mass or more, and the hue was [L 95.
5, a -1.6, b 0.8]. The 4-CBA content was 100 ppm or less.

However, it was confirmed that when a copper oxide catalyst was used, the decarbonylation reaction proceeded, and a large amount of benzoic acid was produced in the reaction mother liquor. Therefore, the recovery rate of terephthalic acid was a low value of 90% by mass.

[Comparative Example 4] Crude terephthalic acid produced in the same manner as in Example 1 was purified using the same apparatus as in Example 1. The operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 123 g 0.5% Palladium activated carbon catalyst 25.9 g Water 600 g Air 0.18 Nl = 0.2 times mole oxygen (reaction conditions) Temperature 300 ° C., pressure 9.0 MPa, time 30 minutes Hydrogenation (charge) Crude terephthalic acid 123 g 0.5% Palladium activated carbon catalyst 25.9 g Water 600 g Hydrogen 0.18 Nl (1 mol) (reaction condition) Temperature 300 ℃, pressure 9.0MPa, time 30 minutes (crystallization condition) Cool down to 40 ℃ at a cooling rate of 20 ℃ / min Result (refined product) Terephthalic acid purity 98 mass% or more 4-CBA content 100ppm or less p- Toluic acid content 6200ppm Benzoic acid content 5800ppm Hue [L 95.1, a-1.7, b 0.5] Terephthalic acid recovery rate 97 mass% Oxygen There is decarbonylation reaction because it was insufficient proceeds, was produced a large amount of impurities.

Example 8 Using the same apparatus as in Example 1, the following crude trimellitic acid produced by the method described in JP-A-2-196752 was purified: Purity: 99% by mass Impurity amount 1,2 -Dicarboxy-4-toluene 10,000 ppm Hue: [L90, a-4.4, b13].

The above-mentioned reaction vessel was charged with 117 g of the above-mentioned crude trimellitic acid, 25.9 g of 0.5% ruthenium activated carbon catalyst and 600 g of water. Subsequently, 13.2 Nl of air was injected. The injected oxygen corresponds to 15 moles of oxygen molecules required to oxidize a substituent in the incomplete oxidation stage to a carboxyl group. The reaction tank was heated with stirring to raise the temperature. The temperature in the reaction tank is 300
After reaching ℃ and pressure of 9.3 MPa, the reaction was continued for 90 minutes.

After completion of the reaction, the reaction mixture was subjected to solid-liquid separation into a catalyst and a reaction product solution while maintaining the temperature, and the solution was transferred to a cooling tank. Up to 40 ° C., it was cooled at a cooling rate of 20 ° C./min to crystallize trimellitic acid. After reducing the internal pressure of the cooling tank to normal pressure, a slurry containing trimellitic acid was collected.

The slurry was filtered under reduced pressure to separate the solid from the mother liquor. Then, the collected trimellitic acid and 25.9 g of 0.5% palladium activated carbon catalyst were charged into the reactor used for the above oxidation reaction, and 600 g of new water was added. Subsequently, 1.1 Nl of hydrogen was injected. The injected hydrogen corresponds to a molar ratio of 6 times that of the compound having a substituent in the incomplete oxidation stage before the oxidation treatment. The reaction tank was heated with stirring to raise the temperature. After the temperature in the reaction tank reached 300 ° C. and the pressure reached 9.0 MPa, the reaction was continued for 30 minutes.

After completion of the reaction, the reaction mixture was subjected to solid-liquid separation into a catalyst and a reaction product solution while maintaining the temperature, and the solution was transferred to a cooling tank. The purified trimellitic acid was crystallized by cooling at a cooling rate of 20 ° C / min up to 40 ° C. After reducing the internal pressure of the cooling tank to normal pressure, a slurry containing purified trimellitic acid was collected.

The slurry was filtered under reduced pressure to separate the solid from the mother liquor. When the purity was measured after drying the solid, it was 99.9 mass% or more, and the hue was [L 95.
2, a-2.0, b1.1]. One of the impurities
2-dicarboxy-4-toluene content is 100ppm
Below, the recovery rate of trimellitic acid is 99.5 mass%
That was all.

Example 9 Using the same apparatus as in Example 1, the following crude pyromellitic acid produced by the method described in JP-A-2-184652 was purified by the same operation as in Example 8: Purity : 97 mass% Impurity amount 1,2-dicarboxy-4,5-phthalide 12,000 ppm 2,4,5-tricarboxytoluene 12,000 ppm Hue: [L 90, a -4.4, b 13].

The operating conditions and results are as follows: Oxidation treatment (charge) Crude pyromellitic acid 70.5 g 0.5% Ruthenium activated carbon catalyst 21.6 g Water 600 g Air 22.9 Nl = 26 times oxygen amount Molar (reaction conditions) Temperature 300 ° C, pressure 10MPa, time 30 minutes Hydrogenation (charge) Crude pyromellitic acid 0.5% Palladium activated carbon catalyst 21.6g Water 600g Hydrogen 1.1Nl (6 times mole) (reaction) Conditions) Temperature 300 ° C, pressure 9.0 MPa, time 30 minutes (crystallization condition) Cooling up to 40 ° C at a cooling rate of 20 ° C / min Result (refined product) Pyromellitic acid purity 99.99% by mass or more 1, 2-dicarboxy-4,5-phthalide content 100 ppm or less 2,4,5-tricarboxytoluene content 100 ppm or less Hue [L 95, a -1.9, b 1.3] Pyromellitic acid recovery rate is 98% by mass or more.

[Comparative Example 5] Crude terephthalic acid produced in the same manner as in Example 1 was purified using the same apparatus as in Example 1. The operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 12.3 g 0.5% Palladium activated carbon catalyst 2.59 g Water 600 g Air 5.19 Nl = 59 times mol oxygen (reaction condition) Temperature 300 ° C, pressure 9.0 MPa, time 30 minutes Hydrogenation (charge) Crude terephthalic acid 12.3 g 0.5% palladium activated carbon catalyst 2.59 g water 600 g hydrogen 0.054 Nl (3 times mole) (reaction conditions) Temperature 300 ℃, Pressure 9.0MPa, Time 30 minutes (Crystallization condition) Cool down to 40 ℃ at a cooling rate of 20 ℃ / min Result (refined product) Terephthalic acid purity 99.7 mass% or more 4-CBA content 400 ppm or less Benzoic acid content 1800 ppm Hue [L 94.8, a -1.5, b 0.8] Terephthalic acid recovery rate 96 mass% Side reaction due to excessive oxygen content Look, became the recovery rate of terephthalic acid is a low value.

[Comparative Example 6] Crude terephthalic acid produced in the same manner as in Example 1 was purified using the same apparatus as in Example 1. The operating conditions and results are as follows: Oxidation treatment (charge) Crude terephthalic acid 123 g 0.5% Palladium activated carbon catalyst 25.9 g Water 600 g Air 5.19 Nl = oxygen amount 5.9 times mol (reaction condition) Temperature 300 ° C., pressure 9.0 MPa, time 30 minutes Hydrogenation treatment (charge) Crude terephthalic acid 123 g 0.5% Palladium activated carbon catalyst 25.9 g Water 600 g Hydrogen 3.6 Nl (20 times mole) (reaction condition) Temperature 300 ℃, pressure 9.0MPa, time 30 minutes (crystallization condition) Cool down to 40 ℃ at a cooling rate of 20 ℃ / min Result (refined product) Terephthalic acid purity 99.4 mass% or more 4-CBA content 100ppm or less Benzoic acid content 100 ppm or less 1,4 Cyclohexanedicarboxylic acid content 200 ppm Hue [L 96, a -1.7, b 0.4] Terephthalic acid recovery rate 8 wt% or less hydrogen content proceeds nuclear hydrogenation of an aromatic ring because it was excessive, be generated 1,4-cyclohexanedicarboxylic acid was confirmed.

[0069]

INDUSTRIAL APPLICABILITY In accordance with the present invention, a suitable noble metal catalyst in an aqueous reaction medium is used to react an appropriate amount of oxygen with the crude monocyclic aromatic carboxylic acid to thereby convert the substituent in the incomplete oxidation stage into a carboxyl group. Impurities can be converted to the desired products by oxidation to. As a result, not only the purity of the monocyclic aromatic carboxylic acid but also the yield is improved. further,
By using a noble metal catalyst and allowing a slight amount of hydrogen to act thereon, the hue of the monocyclic aromatic carboxylic acid is significantly improved. Therefore, the use of the monocyclic aromatic carboxylic acid purified according to the present invention helps improve the hue of the polymer from which it is derived.

[Brief description of the drawings]

FIG. 1 is a conceptual vertical cross-sectional view showing the configuration of an experimental device used in an example of the present invention.

[Explanation of symbols]

1 Reaction Tank 11 Condenser 12 Gas Injection Tube 13
Stirrer 2 Heater 4 Sintered metal filter 6 Cooling tank 61 Condenser 62 Introducing pipe 3, 5, 7 Valve

Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C07C 51/265 2115-4H C07C 51/265 51/47 2115-4H 51/47 51/487 2115-4H 51 / 487 63/307 2115-4H 63/307 63/313 2115-4H 63/313 // C07B 61/00 300 C07B 61/00 300 (72) Inventor Nobuaki Urasato 1134-2 Gongendo, Satte City, Saitama Prefecture Sumo Research Institute R & D Center

Claims (4)

[Claims] 1. A method for purifying a crude monocyclic aromatic carboxylic acid obtained by oxidizing a substituent of a monocyclic aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent, wherein (1 ) Oxidizing the crude monocyclic aromatic carboxylic acid to the carboxyl group in the incomplete oxidation stage of the crude monocyclic aromatic carboxylic acid in the presence of a Group VIII noble metal catalyst in a high temperature aqueous reaction medium. Oxidation with 0.5 to 30 moles of molecular oxygen per mole of oxygen molecule required for the reaction, and further (2) reduction by the action of hydrogen in the presence of a Group VIII noble metal catalyst. The ring aromatic carboxylic acid is dissolved in the high temperature aqueous reaction medium and solid-liquid separated from the precious metal catalyst, and then (4) the reaction product liquid is cooled to precipitate and recover the monocyclic aromatic carboxylic acid. A monocyclic aromatic compound characterized by Purification method of family carboxylic acid. 2. The step (2) is carried out by reacting 0.02 to 10 mol of hydrogen with respect to 1 mol of the compound having a substituent in the incomplete oxidation stage present in the crude monocyclic aromatic carboxylic acid. The purification method according to claim 1, which is carried out. 3. The purification method according to claim 1, wherein the monocyclic aromatic carboxylic acid is a dicarboxylic acid. 4. The method according to claim 1 or 2, wherein the monocyclic aromatic carboxylic acid is a polycarboxylic acid which is a tricarboxylic acid or more.