JPH09263566A - Purification of crude benzenedicarboxylic acid, catalyst used for purification and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purify a benezenedicarboxylic acid at a low cost in high purity by treating the benzenedicarboxylic acid with a hydrogen gas using a catalyst which has an improved life, is usable for a long period of time and is obtained by supporting an active component on activated carbon having specific properties. SOLUTION: In purifying a crude benzenedicarboxylic acid, obtained by oxidizing a dialkylbenzene, with a hydrogen gas, a catalyst obtained by using activated carbon having >=500m<2> /g total surface area and >=0.4ml/g pore volume of macropore as a carrier and supporting a noble metal of the group VIII to the depth of 50-1,000μm from the surface of the carrier is used as a catalyst. When the carrier is immersed in an aqueous solution of a salt of the noble metal of the group VIII, the aqueous solution of the salt in an acidic state of pH<=3 is impregnated into the carrier and the salt of the noble metal is reduced to give the objective catalyst. Platinum, palladium, rhodium, ruthenium, etc., are preferable as the noble metal.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an improvement in a method for purifying a crude benzenedicarboxylic acid obtained by oxidizing dialkylbenzene as an aqueous solution by catalytic hydrogenation.

[0002]

Benzene dicarboxylic acid, that is, phthalic acid, terephthalic acid and isophthalic acid are important chemical products, and are widely used as raw materials for various polymers, especially synthetic resins. Typical terephthalic acid is a raw material for polyester resin, and phthalic acid and isophthalic acid are useful as modifiers for polyester resin. Phthalic acid also occupies an important position as a raw material for thermosetting resins.

A typical method for producing terephthalic acid is p-
Liquid-phase oxidation of dialkylbenzenes (for example, JP-A-60-
184043). Impurities such as 4-carboxybenzaldehyde (hereinafter abbreviated as "4-CBA"), which is an incomplete oxide, are contained in the obtained crude terephthalic acid. Even if a small amount of these impurities, the polyester produced by the polycondensation of terephthalic acid and glycols is colored, or the degree of polymerization is reduced, which causes quality problems.

Therefore, it is necessary to purify terephthalic acid containing impurities such as 4-CBA, and how to carry out the purification efficiently and with high yield is an important issue.
A number of purification methods have been proposed so far, among them, a method of treating terephthalic acid in the form of an aqueous solution with hydrogen in the presence of a Group VIII noble metal catalyst (see US Pat. No. 3,584,039). ) Is evaluated as an excellent refining method to obtain fiber-grade high-purity terephthalic acid. According to this method, 4-CBA and other impurities causing coloration contained in the crude terephthalic acid are converted into compounds that are easy to remove and removed.
As the catalyst, usually, a group VIII noble metal supported on activated carbon is used.

However, since a catalyst in which palladium is supported on conventional activated carbon has a large rate of progress of catalytic reaction at the active sites on the surface of the carrier, by supporting palladium only on the outer surface of the carrier, a small amount of palladium is supported. It is intended to exhibit catalytic performance with metals. However, in the actual use of the catalyst, the catalyst is inevitably deteriorated because the surface is abraded by the collision of the catalysts in the use process and the supported palladium is peeled off.
In addition, catalyst performance deteriorates due to poisoning due to accumulation (masking) of metals such as cobalt and manganese contained as impurities in crude terephthalic acid, and also heavy metals such as copper and chromium generated by corrosion of equipment. There is a drawback that.

[0006]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art in a purification method of treating benzenedicarboxylic acid represented by terephthalic acid by hydrogenation in the presence of a Group VIII noble metal catalyst. That is, it is possible to prevent the physical separation of the noble metal catalyst supported on the activated carbon, the clogging of the pores, and the masking with the metal, thereby prolonging the life of the catalyst and advantageously carrying out the purification method. To provide.

It is also within the object of the present invention to provide a catalyst suitable for carrying out the above purification method and a method for its preparation.

[0008]

The method for purifying crude benzenedicarboxylic acid according to the present invention is a method for purifying a crude benzenedicarboxylic acid obtained by oxidizing a dialkylbenzene.
In a purification method in which hydrogen gas is allowed to act in the presence of a catalyst containing a group noble metal as an active ingredient, the catalyst has a total surface area of 500 m ² / g or more and a macropore pore volume of 0.4 ml / g. It is characterized in that the activated carbon as described above is used as a carrier and a noble metal of Group VIII is supported from the surface of the carrier to a depth of 50 to 1000 μm.

The catalyst of the present invention, which is suitable for carrying out the above-mentioned purification method, has a total surface area of 500 m ² / g as a carrier.
The activated carbon having a macropore volume of 0.4 ml / g or more is used, and the depth from the surface of the carrier is 50 to 100.
It is a catalyst supporting a Group VIII noble metal up to 0 μm.

In this method for producing a catalyst, the carrier is immersed in an aqueous solution of a salt of a Group VIII noble metal to impregnate the carrier with the salt of the noble metal, and the aqueous solution of the salt is impregnated into the carrier in an acidic state of pH 3 or less. And then reducing the salt of the noble metal.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the catalyst of the present invention, the activated carbon used as a carrier has a total surface area (N ₂ adsorption-BET method) of 500 m ² / g or more, preferably 900 m ² / g or more. If the total surface area is small, the surface area of the supported metal, which is the active ingredient, is also small, and the catalytic activity that is useful for the purification method of the present invention cannot be obtained. There is no upper limit in use because the larger the total surface area, the more preferable. However, the total surface area that can be reached by activated carbon is theoretically about 2600 m ² / g. The pore volume of the macropores (measured by mercury porosimetry) is 0.4 ml / g or more, preferably 0.5 ml / g or more. If the pore volume of the macropores is too small, the supporting area of the noble metal, which is the active component, cannot be sufficiently obtained, and the catalytic activity becomes low. The upper limit of the pore volume of the macropores is not particularly specified, but if it is too large, the strength required for the carrier cannot be obtained sufficiently.

The activated carbon preferable for the production of the catalyst of the present invention is specifically granulated activated carbon sent by pulverizing raw materials such as charcoal, coconut shell charcoal, coal and coke and adding a binder thereto. And having the desired total surface area and macropore pore volume described above.

The noble metal of Group VIII of the periodic table supported on the above-mentioned activated carbon in the catalyst used in the purification method of the present invention is one or more of palladium, rhodium, ruthenium, osmium, iridium and platinum. is there. Preferred metals are platinum, palladium, rhodium, and ruthenium. Excellent results are obtained especially when palladium is used. The supported amount is suitably 0.1 to 5% by mass, especially 0.1 to 1% by mass, based on the total amount of the catalyst. The noble metal has a depth of 1000 μm from a depth of 50 μm or more, preferably 100 μm or more from the surface of the carrier.
It is important that the particles are supported up to m or less, preferably 500 μm or less. If the supported position is shallow, the catalyst deteriorates early. On the other hand, if it is too deep, the diffusion of the substrate is rate-determining, and the reaction rate is slow, which is not practical.

To prepare the catalyst of the present invention, a compound containing a salt of a noble metal of Group VIII of the periodic table prepared by adjusting the pH of the activated carbon having the desired total surface area and the pore volume of macropores described above to pH 3 or less with an acid. Noble metal of Group VIII is supported at a depth of 50 μm at the shallowest, preferably 100 μm at the shallowest, and 1000 μm at the deepest, preferably 500 μm from the surface of the carrier. Suitable Group VIII noble metals for the purposes of the present invention are palladium, rhodium, ruthenium and platinum, the salts of which are their chlorides, bromides, nitrates, amine salts, ammonium salts and the like. The pH of the aqueous solution of the Group VIII noble metal salt is adjusted to 3 or less by adding an acid such as hydrochloric acid, nitric acid or hydrofluoric acid. The pH is preferably 2 or less. When the pH is higher than 3, the metal supporting position becomes shallower than the intended depth.

The crude benzenedicarboxylic acid which is the object of the purification method of the present invention is obtained by oxidizing dialkylbenzene having a total of two alkyl substituents or partially oxidized alkyl substituents on the benzene ring. . Here, the “alkyl substituent” means a lower alkyl group having 1 to 3 carbon atoms such as methyl, ethyl, propyl and isopropyl. The “partially oxidized alkyl substituent” refers to an oxygen-containing hydrocarbon group other than a carboxyl group such as an aldehyde group or a hydroxyalkyl group.

More specifically, the crude benzenedicarboxylic acid to be purified according to the present invention is prepared by using o-xylene, m-xylene, p-xylene, p-toluic acid, etc. as a raw material, and by using this as a gas phase or a liquid phase. It was obtained by oxidation. A preferable one is a liquid phase using a lower aliphatic carboxylic acid as a reaction medium, and a crude product of benzenedicarboxylic acid obtained by oxidizing the above raw material with molecular oxygen using a catalyst such as cobalt, manganese, or bromine. is there. Examples of such a crude product include crude terephthalic acid and crude isophthalic acid produced by the production method described in JP-A-60-184043. In the method for producing terephthalic acid disclosed in JP-A-60-184043, p-xylene or m-xylene is used as a salt of cobalt or manganese (0.1 to 1 as a metal atom).
Wt%) and bromine compound (0.3 to 1 as bromine atom)
(0% by weight) in the presence of a catalyst added, in an aqueous solution containing 1 to 10 moles of aromatic carboxylic acid with respect to all metal atoms, using a molecular oxygen-containing gas for oxidation. It is characterized by using potassium bromide and tetrabromobutane as bromine compounds.

The reaction medium used in the purification method of the present invention is aqueous 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 distilled water, water for ion exchange, or the like. The amount of reaction medium used is such that the crude benzenedicarboxylic acid is at least partially, preferably completely, dissolved at the reaction temperature. Usually, 2 to 20 times the weight of the crude product is used. Especially 3 ~
A 10-fold amount is preferable. If the amount of reaction medium is too small,
Needless to say, the amount of crude benzenedicarboxylic acid dissolved is small, and purification by the hydrogeno-reduction reaction is not sufficiently performed.
If the amount is too large, there is no problem in the progress of the reaction, but it is economically disadvantageous because a large reactor is required and the energy consumption required for recovery of benzenedicarboxylic acid increases.

The reaction temperature is selected such that the amount of the crude benzenedicarboxylic acid dissolved in the reaction medium is sufficient.
At low temperatures the solubility is low and a correspondingly large amount of solvent is required. If the temperature is too high, undesirable decomposition reactions such as elimination of carboxyl groups will occur. A preferable temperature is 200 to 330 ° C, and a particularly preferable temperature is 250 to 310 ° C.

The amount of hydrogen supplied for purification is at least 1 mol, preferably 2 mol or more, relative to 1 mol of formylbenzoic acid represented by 4-CBA present in the crude benzenedicarboxylic acid. is there. If the amount of hydrogen supplied is insufficient, the decarbonylation reaction of benzenedicarboxylic acid proceeds. On the other hand, if the amount of hydrogen is excessively large, the nuclear hydrogenation reaction of the benzene ring proceeds, so the maximum amount is 20 mol. For purification purposes, 10 mol or less 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 pressure in the entire reaction system is such that at least a part of the reaction medium can exist as a liquid. 50 mass%
The above is preferably present in the liquid phase part, particularly preferably about 75% by mass. The appropriate pressure cannot be generally determined because it is influenced 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 hydrogenation-reduction catalyst used in the purification method of the present invention is characterized in that a specific activated carbon is used as a carrier and a noble metal of Group VIII of the Periodic Table is supported deep inside thereof.

Activated carbon generally has macropores (pore size> 50).
Mesopores (pore size 20 to 500Å) are distributed on the inner wall of 0Å), and micropores (pore size <20Å) are distributed on the inner wall of the mesopore. In the present invention, the activated carbon has macropores having a large pore size which are highly developed on the surface of the activated carbon.

The amount of the catalyst used is determined by conditions such as the reaction temperature, the concentration of impurities in the crude benzenedicarboxylic acid, and the residence time in the reactor. Generally, the amount of the crude benzenedicarboxylic acid relative to the noble metal component in the catalyst is About 20 in mass ratio
0: 1 to about 30,000: 1, preferably about 2000: 1
˜about 20,000: 1 may be selected and used. When the amount of noble metal catalyst is small, the effect of removing coloring impurities and the hydrogenation reaction rate of impurities remain low, while the presence of an excessive amount of catalyst causes decarbonylation of benzenedicarboxylic acid and nuclear hydrogenation of the benzene ring. And proceed with undesired reactions such as.

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

The reaction time varies depending on the ratio of the crude benzenedicarboxylic acid to the hydrogenation reduction 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 hydroreduction catalyst or the feed weight rate (W
HSV), it is about 200 to 200,000 g (reaction solution) / g (noble metal component in the hydrogenation reduction catalyst) .hr, preferably 1000 to 100,000 g / g.hr.

After completion of the hydroreduction treatment, the catalyst present as a solid in the aqueous reaction medium and the benzenedicarboxylic acid 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 with the catalyst can be naturally performed.

Benzenedicarboxylic acid is generally sparingly soluble or almost insoluble in water under normal temperature and normal pressure, but its solubility increases under high temperature and high pressure. Therefore, when it is dissolved in water, filtration / centrifugation is carried out. The hydroreduction catalyst and the reaction product liquid can be taken out by solid-liquid separation. The high-temperature and high-pressure conditions under which benzenedicarboxylic 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 benzenedicarboxylic acid in water is at least about 10% by mass. There is.
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.

Following the solid-liquid separation, the reaction solution obtained is cooled to crystallize benzenedicarboxylic acid. The crystallization temperature is between 200 ° C. and 30 ° C. A preferable temperature range is 100 to 35 ° C. At this time, the cooling rate is preferably 25 ° C./min or less, and more preferably 10 ° C./min or less. If the cooling rate is too fast, the precipitated benzenedicarboxylic acid particles will be extremely fine, and separation from the mother liquor will be difficult. The purified benzenedicarboxylic acid that has precipitated is recovered by means such as filtration and centrifugation.

[0029]

EXAMPLES In the following examples, the purity was measured by high performance liquid chromatography (HPLC) using an analytical column: Bio-Sil C18 HL 90-5S (BI).
ORAD), solvent: acetonitrile / 3% aqueous acetic acid. Regarding the hue, the L value (brightness), a, of a powder sample prepared and packed in a cylindrical glass cell,
The value [red (+) to green (-)] and the 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.

[Catalyst Preparation Example 1 (Example)] When the properties of granulated activated carbon (manufactured by Wako Pure Chemical Industries, Ltd.) were analyzed, the total surface area was 1216 m ² / g and the pore volume of macropores was 0.4.
It was 97 ml / g.

The above activated carbon was converted into 0.1N hydrochloric acid (activated carbon 1 g
Per 1 ml of hydrochloric acid). Add palladium chloride to 0.
A solution (pH 2) having a concentration of 0.01 to 0.02 mol was dissolved in 1N hydrochloric acid, and this solution was added to an amount of activated carbon having a supported amount of 0.5% by mass, and the mixture was allowed to stand at room temperature for one day. It was filtered through a glass filter, washed thoroughly with distilled water, washed until the pH of the washing liquid reached about 5, and then dried in vacuum. This was reduced by heating in a hydrogen stream at 300 ° C. for 4 hours.

The catalyst prepared by the above method contained about 0.5% by weight of palladium, calculated as palladium metal, based on the dry catalyst composition. EPM
When the distribution of palladium inside the catalyst particles was examined by A (electron probe microanalysis), as shown in FIG.
Palladium was uniformly supported from the surface to a depth of about 300 μm.

[Catalyst preparation example 2 (comparative example)] When crushed activated carbon (manufactured by Kishida Chemical Co., Ltd.) was analyzed for its properties, the total surface area was 1209 m ² / g and the pore volume of macropores was 0.2.
It was 01 ml / g.

The same procedure as in Catalyst Preparation Example 1 was carried out except that the above activated carbon was not treated with 0.1N hydrochloric acid, and the same amount of palladium was carried. The catalyst thus prepared is
When calculated as palladium metal, it contained about 0.5% by weight of palladium, based on the dry catalyst composition. E
According to the PMA analysis, as shown in FIG. 3, palladium was supported from the surface of the catalyst particles to a depth of about 30 μm.

[Catalyst Usage Example] The catalyst life was measured for each of the catalysts prepared in Catalyst Preparation Examples 1 and 2. The evaluation was carried out using a 1.5-liter titanium autoclave having the configuration shown in FIG.

About 200 g of crude terephthalic acid (impurity 4-CBA content: 2,180 ppm) was added to the autoclave (1).
Water (about 670 ml) was added thereto, and the mixture was sealed and heated with a mantle heater (2) at a temperature of 285 ° C. to dissolve the crude terephthalic acid, and hydrogen was injected. About 2 g of the catalyst (5) pre-loaded in the catalyst holder (4) was immersed in the solution (6) in which the crude terephthalic acid was dissolved, and kept at the same temperature for reaction for about 5 hours. This operation was repeated with only the raw material terephthalic acid and water being replaced, and the catalyst being the same.

When the quality of purified terephthalic acid was examined for each batch, when the catalyst of Catalyst Preparation Example 2 (Comparative Example) was used, the impurity 4-CBA remained in the product in an amount of about 20 ppm in the fourth batch. Was recognized.

On the other hand, when the catalyst prepared in Catalyst Preparation Example 1 (Example) was used, the impurity 4-CBA did not remain in the 4th batch and about 50 ppm remained in the 6th batch.

[0039]

INDUSTRIAL APPLICABILITY In the purification of a crude product of benzenedicarboxylic acid typified by terephthalic acid produced by oxidation of dialkylbenzene by catalytic hydrogenation, a noble metal of Group VIII, which is a catalytically active component, is treated with activated carbon having a specific property. By using as a carrier and supporting the particles from the surface to a deep position, the life of the catalyst is improved and the catalyst can be used for a long time. Therefore, according to the present invention, purification of benzenedicarboxylic acid can be carried out at a lower cost than before,
We can provide high quality products.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the structure of an apparatus used for an experiment of an example of the present invention and a comparative example.

FIG. 2 is an EPMA photograph showing a state in which palladium is supported on activated carbon for the catalyst of the example of the present invention. (EP
MA condition is voltage 20KV, current 1 × 10 ^-7 A)

FIG. 3 is an EPMA photograph showing a situation in which palladium was supported on activated carbon for the catalyst of Comparative Example of the present invention. (EP
(MA conditions are the same as in Fig. 2)

[Explanation of symbols]

 1 Autoclave 2 Mantle heater 3 Agitator shaft 4 Catalyst holder 5 Catalyst 6 Crude terephthalic acid aqueous solution

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location // C07B 61/00 300 C07B 61/00 300 (72) Inventor Nobuaki Urasato Gongendo, Satte City, Saitama Prefecture 1134-2 Research & Development Center, Cosmo Research Institute, Ltd.

Claims (3)

[Claims] 1. A purification method in which hydrogen gas is allowed to act on a solution of crude benzenedicarboxylic acid obtained by oxidizing dialkylbenzene in the presence of a catalyst containing a Group VIII noble metal as an active component, Total surface area is 50
0m ² / g or more, macropore volume 0.4ml / g
The activated carbon described above is used as a carrier, and the depth from the surface of the carrier is 5
A method for purifying crude benzenedicarboxylic acid, which comprises using a Group VIII noble metal supported up to a position of 0 to 1000 μm. 2. As the carrier, activated carbon having a total surface area of 500 m ² / g or more and a macropore pore volume of 0.4 ml / g or more is used, and the depth from the carrier surface is 50 to 1000.
A catalyst supporting a Group VIII noble metal up to μm. 3. When the carrier is immersed in an aqueous solution of a salt of a Group VIII noble metal to impregnate the carrier with the salt of the noble metal, the aqueous solution of the salt is impregnated into the carrier in an acidic state of pH 3 or less, and then the noble metal Claim 2 consisting of reducing salt
The method for producing the catalyst according to the item.