JPH04330039A - Production of naphthalenecarboxylic acid - Google Patents

Abstract

PURPOSE:To eliminate the need of operation to recover a catalyst and a solvent and simplify waste liquor treatment by suppressing formation of by-products, obtaining high-purity naphthalenecarboxylic acid excellent in filterability in good yield and simultaneously enabling repeated use of a reaction filtrate. CONSTITUTION:A substituted naphthalene having one or more substituent groups selected from alkyl groups, acyl groups or their oxidation intermediates is oxidized with molecular oxygen in the presence of an oxidation catalyst containing a heavy metal in a solvent containing a lower aliphatic monocarboxylic acid to produce naphthalenecarboxylic acid such as naphthoic acid useful as a raw material for photographic chemicals, dyes, etc. In the process, the oxidative reaction is carried out in two stages and the oxidative reaction in the second stage is simultaneously conducted under conditions in which at least either of temperature and pressure is lower than that of the oxidative reaction in the first stage. Thereby, the objective high-purity compound, having high quality and excellent in hue is efficiently obtained. Furthermore, a catalyst is preferably added after the oxidative reaction in the first stage and the obtained reaction mixture is directly subjected to the oxidative reaction in the second stage, or the objective compound is recovered from the resultant reaction mixture. The residual solution is then subjected to the oxidative reaction in the second stage.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention involves the production of naphthalene carboxylic acid by oxidizing a substituted naphthalene compound with molecular oxygen in a solvent containing a lower aliphatic monocarboxylic acid in the presence of an oxidation catalyst containing a heavy metal compound. Regarding the method. In particular, the present invention relates to an efficient method for producing naphthalenecarboxylic acid that allows for the recycling of a reaction solution while obtaining a high-quality product.

0002

[Prior Art] Among naphthalenecarboxylic acids (hereinafter referred to as NCA) having at least one carboxyl group directly bonded to a naphthalene ring, naphthoic acid, which is a monocarboxylic acid, is useful as a raw material for photographic agents, dyes, etc. . In addition, naphthalene dicarboxylic acid (hereinafter referred to as NDCA), especially 2,6-isomer, is used in various products including polyethylene naphthalate because it provides films and textile products with excellent heat resistance, mechanical strength, and dimensional stability. Demand is increasing as a raw material for polyester, polyamide, etc. Furthermore, naphthalenetricarboxylic acids and naphthalenetetracarboxylic acids are seen as promising raw materials for highly functional resins and the like.

Such NCAs can be prepared by oxidizing the substituents of the corresponding alkyl- and/or acyl-substituted naphthalenes to carboxyl groups. The most common industrial method for producing NCA by oxidizing substituted naphthalene is a one-step liquid phase oxidation process using molecular oxygen in a solvent containing a lower fatty acid in the presence of a catalyst containing a heavy metal. be.

[0004] Regarding the method for producing NCA by liquid phase oxidation, various changes have been made so far, such as catalyst composition, addition of co-catalysts such as bromine and alkali metals, raw material-to-catalyst ratio, raw material-to-solvent ratio, and reaction temperature. Many proposals have been made regarding the reaction conditions (for example, Japanese Patent Publication No. 34-2666, Japanese Patent Publication No. 48-43893, Japanese Patent Publication No. 48-34153,
60-89445, 60-89446, 61-246144, and Japanese Unexamined Patent Publication No. 1-160943).

However, in either method, when liquid phase oxidation is performed in one step, it is difficult to carry out the reaction completely, and a considerable proportion of oxidized intermediates and unreacted raw materials are contained in the reaction product. cannot be avoided. Therefore,
The product cannot be put to practical use as it is, and must be subjected to further purification treatment, leading to higher costs and complicating the manufacturing process.

[0006] The liquid phase oxidation was performed in two stages with the expectation that the reaction would be more complete and a higher quality NCA product with fewer oxidized intermediates and unreacted materials would be obtained if the oxidation was performed in two stages. This has already been proposed. Special Public Service 1986-1349
No. 5 describes a method for producing 2,6-NDCA by two-stage oxidation. Specifically, the first stage is 10
The oxidation reaction is carried out at a reaction temperature of 0 to 150°C to an extent that no product is precipitated, and then the temperature is raised to 150 to 250°C to carry out the second stage oxidation reaction.

This method is thought to be effective to some extent when substituted naphthalene having a substituent with a relatively slow oxidation reaction is used as a raw material, such as the methyl-substituted naphthalene shown in the examples in this publication. It will be done. However, when substituted naphthalene, which has a fast oxidation rate such as isopropyl group and is therefore preferable from the viewpoint of reaction efficiency, is used as a raw material, the oxidation temperature in the first stage is not high enough, resulting in a polymer that is thought to be polyperoxide. It was found that it was produced in large quantities. Since the polymer once produced does not easily decompose, even if the second stage of oxidation is performed, the quality of the 2,6-NDCA obtained tends to deteriorate and the hue tends to be unsatisfactory.

[0008] As described above, it has been difficult to directly obtain NCA products of satisfactory quality using conventional methods.
Furthermore, it has conventionally been very difficult to efficiently separate the precipitated product from the reaction mixture extracted from the reactor after oxidation. This is mainly due to the fact that the particles of NCA and oxidized intermediates produced are very small and easily clog the filter cloth. This is a problem specific to NCA production that is not present in terephthalic acid production, where relatively large particles are produced. It is clear that this poor filterability is an impediment to smooth implementation, especially when industrializing the production of NCA by liquid phase oxidation in a continuous manner.

[0009] Generally, in the production of carboxylic acids by liquid phase oxidation of aromatic hydrocarbons, relatively expensive aliphatic carboxylic acid solvents and heavy metal catalysts are used. The remaining reaction filtrate after recovering the reaction product from the reaction mixture can be recycled and used.
It is necessary for industrialization.

In the case of the oxidation of substituted benzenes, such as the production of terephthalic acid by the oxidation of p-xylene, there is little production of by-products or polymers that inactivate the catalyst, and there is no problem in recycling the reaction filtrate. few.

However, in the case of oxidation of substituted naphthalene, by-products such as polymers and trimellitic acid that inactivate the catalyst are produced, and when the substituent is an isopropyl group, oxidation of by-products such as naphthol is produced. Reaction inhibitors are also produced. Therefore, if the reaction filtrate is recycled as it is, these by-products will accumulate in the reaction solution, and the yield of NCA will drop to an unacceptable level when the number of cycles is small.
It can only be used repeatedly a few times at most. Therefore,
Most of the reaction filtrate is extracted, the catalyst in the filtrate is recovered,
This requires a complicated operation of regenerating, removing by-products, and returning the reaction filtrate again, which is economically disadvantageous.

0012

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved process for the industrial production of NCAs by liquid phase oxidation of substituted naphthalenes with molecular oxygen, which overcomes the problems of the prior art. That's true. in particular,
(1) A high-quality NCA product with high purity and excellent hue can be obtained, (2) the reaction mixture has good filterability [filtration specific resistance value (described later) is 109 m/kg or less], (3) )
It is an object of the present invention to provide a method for producing NCA in which the yield does not significantly decrease even when the reaction filtrate is repeatedly recycled as it is (that is, the reaction filtrate has excellent recyclability).

[0013]

[Means for Solving the Problems] As a result of studies, the present inventors have found that when liquid phase oxidation is performed in two stages, the temperature and/or pressure of the first stage oxidation reaction is different from the conventional knowledge. It was discovered that the above object could be achieved by making the height higher than the eye level, and the present invention was completed. Here, the present invention provides "a substituted naphthalene having at least one substituent selected from an alkyl group, an acyl group, and an oxidized intermediate thereof,"
In a method for producing NCA by oxidation with molecular oxygen in a solvent containing a lower aliphatic monocarboxylic acid in the presence of an oxidation catalyst containing a heavy metal, the oxidation reaction is carried out in two stages, and the second stage oxidation reaction is Ni
The gist is ``Method for manufacturing CA''.

The second-stage oxidation reaction may be carried out using the reaction mixture from the first-stage oxidation reaction as it is, or may be carried out using the remaining reaction solution from which the NCA product has been recovered. The present invention will be explained in detail below.

The substituted naphthalene used as a raw material in the method for producing NCA of the present invention is any isomeric compound in which at least one substituent selected from an alkyl group, an acyl group, and their oxidized intermediates is bonded to the naphthalene ring. It is the body. Examples of substituents include alkyl groups such as methyl, ethyl and isopropyl, and acyl groups such as acetyl and formyl. Examples of oxidized intermediate groups include the following.

[0016]

[Chemical formula 1]

Specific examples of substituted naphthalene compounds useful as raw materials include methylnaphthalene, ethylnaphthalene, isopropylnaphthalene, dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene, methylisopropylnaphthalene, ethylisopropylnaphthalene, acetylmethylnaphthalene, acetylisopropylnaphthalene, Further examples include trialkylnaphthalenes. The method of the present invention is effective regardless of the type of substituted naphthalene used as a raw material, but is particularly useful for oxidizing naphthalene compounds having a highly reactive diisopropyl group as a substituent.

Naphthoic acid is produced from mono-substituted naphthalene compounds, naphthalene dicarboxylic acid (NDCA) is produced from di-substituted naphthalene compounds, and naphthalenetricarboxylic acid is produced from tri-substituted naphthalene compounds.

As the reaction solvent for liquid phase oxidation, a solvent containing a lower aliphatic monocarboxylic acid such as acetic acid, propionic acid, butyric acid, etc. is used. Acetic acid is particularly preferred. As the solvent, the lower monocarboxylic acid can be used as it is, but it can also be a mixed solvent with water or a hydrocarbon solvent such as chlorobenzene or bromobenzene, which is stable against oxidation.

As molecular oxygen, in addition to pure oxygen, air or a mixed gas of oxygen and an inert gas can be used. It is economical to use air as it is.

The oxidation catalyst contains at least one heavy metal such as cobalt, manganese, cerium, nickel, copper, iron, zinc, and usually also uses a bromine compound as a catalyst component. The heavy metal compound used is one that dissolves in a lower monocarboxylic acid solvent, and lower fatty acid salts such as acetate are particularly preferred. As the bromine compound, potassium bromide, sodium bromide, ammonium bromide, etc. can be used. Furthermore, ketones such as methyl ethyl ketone or alkali metal compounds such as potassium acetate may be used in combination as co-catalysts. The amount of catalyst used may be the same as conventional.

[0022] Liquid phase oxidation can be carried out under conventionally commonly employed reaction conditions. The reaction temperature is 20~
The temperature is 250°C, preferably 100-200°C, and the reaction pressure is suitably within the range of 0.2-20kg/cm2, preferably 3-15kg/cm2 as oxygen partial pressure.

A feature of the present invention is that the reaction is carried out in two stages, and the second stage reaction is carried out such that at least one of the reaction temperature and pressure is lower than the conditions adopted in the first stage reaction. . This improves the filterability of the product, increases the recyclability of the reaction filtrate containing the solvent and the catalyst, and makes it possible to recycle the reaction filtrate with almost no reduction in yield.

The reason for this is not clear, but by further performing the second stage oxidation using molecular oxygen under more gentle conditions, a lower acetic acid combustion rate can be obtained than under conditions of high temperature and pressure. In addition, it is possible to convert oxidized intermediates that cause a decrease in filterability and quality into NCA, and to some extent, polymers that inhibit oxidation, acids such as trimellitic acid, naphthols, and formic acid are burned by oxidation. Therefore, it is inferred that the quality of the NCA product is improved and at the same time, the recyclability of the reaction filtrate is also improved.

For this purpose, the second stage oxidation reaction must be performed at a reaction temperature of 5 to 200°C and/or lower than the first stage reaction.
or reaction pressure (oxygen partial pressure) of 1 to 18 kg/cm
It is preferable to lower it by 2. Both reaction temperature and pressure may be reduced in the second stage.

After completion of the first stage oxidation reaction, the obtained reaction mixture may be directly subjected to the second stage oxidation reaction. In this case, the reaction may be continued by simply lowering one or both of the reaction temperature and/or pressure. Alternatively, the NCA produced from the reaction mixture obtained in the first stage oxidation,
For example, it is possible to collect the reaction solution by appropriate means such as filtration, and then subject the remaining reaction solution to the second stage oxidation reaction. In either case, a catalyst may be added before or during the start of the second stage oxidation reaction. Addition of catalyst is effective in further improving the yield.

The liquid phase oxidation of the present invention can be carried out in a continuous, semi-continuous or batch manner. Further, different reaction methods can be used, such as the first stage oxidation being carried out continuously or semi-continuously and the second stage oxidation being carried out batchwise.

In the semi-continuous reaction, generally, a solution in which a catalyst is dissolved in a reaction solvent is charged into an oxidation reactor, and a molecular oxygen-containing gas and substituted naphthalene as a raw material are continuously supplied to this reactor. The reaction is carried out by this. After the reaction is continued for a predetermined time without replenishing or withdrawing the solution, all the reaction solution is withdrawn and the reaction product is recovered from it. In the continuous reaction, the solution is continuously replenished and withdrawn so as to keep the liquid level approximately constant, and the reaction product is recovered from the withdrawn reaction liquid.

When carrying out the method of the present invention in a continuous manner, two oxidation reactors are prepared, and the reaction mixture leaving the first reactor is used as it is, or the remaining reaction liquid from which NCA has been recovered is fed to the second oxidation reactor. The second stage reaction may be carried out at low temperature and/or low pressure by charging it into a reactor. In the case of a batch type or continuous reaction type, one or two oxidation reactors may be used.

[0030] The distribution ratio of the first stage and second stage oxidation reactions is not particularly limited. For example, when carrying out the reaction in the semi-continuous manner described above, the step of supplying substituted naphthalene as a reaction raw material is the first stage oxidation reaction, and after the supply is finished, at least one of the temperature and pressure is lowered and the second stage oxidation reaction is carried out. can be performed batchwise.

After completion of the second stage oxidation reaction, NCA can be easily recovered from the reaction mixture by filtration. Therefore, the amount of reaction solvent used is preferably such that the catalyst is completely dissolved and most of the product is precipitated. As explained above, the method of the invention improves the filterability of the product so that it can be easily filtered without problems such as clogging of the filter cloth.

The product is of high quality because it has undergone a two-step oxidation reaction, but it may be subjected to further purification treatment if desired. The reaction filtrate from which the products were separated mainly consists of the catalyst, solvent and dissolved NCA products,
Contains some reaction by-products. This can be recycled as a catalyst-containing reaction solvent in the first stage oxidation reaction of the method of the present invention. That is, a catalyst component and, if necessary, a solvent are added to this reaction filtrate to prepare a reaction solution, and the raw materials substituted naphthalene and molecular oxygen can be supplied to the solution for further reaction.

As shown in the examples below, even if the reaction filtrate is repeatedly recycled in this manner, no significant decrease in yield occurs. In conventional reaction methods, the yield decreases when the reaction filtrate is recycled, so the catalyst has to be repeatedly used through a complicated operation of recovering the catalyst from the reaction filtrate and regenerating it. Furthermore, at this time, the solvent is also separated and recovered in a separate process, which increases the cost of recovery.

Therefore, the method of the present invention makes it possible to recycle the reaction filtrate as a catalyst and a solvent, which is extremely advantageous for industrialization.

[0035] The present invention will be illustrated by examples below.
The present invention is not limited to this. The filtration specific resistance value of the reaction mixture shown in Examples and Comparative Examples is calculated from the following basic formula of filtration resistance: θ/V=V/K+2v/K from filtration time θ (sec) and filtrate volume V (m2) Ruth's low-pressure filtration coefficient K (m/s) was obtained using the following equation.

K=2・ΔP・(1−m・s)・μ・s・α/ρ In the formula, α (m/kg): filtration specific resistance, v (m3/m
2): Volume of filtrate per unit area that produces a filter slag that provides resistance equal to the resistance of the filter media, ΔP (kg/m2): Differential pressure between operating pressure and atmospheric pressure, m (
-) : Dry and wet weight ratio of cake, s (-)
: Solid mass fraction in slurry, ρ (kg/m3
): Density of filtrate, μ (kg/m.sec): Viscosity of filtrate.

Example 1 5.54 g (0.022 mol) of cobalt acetate tetrahydrate
, manganese acetate tetrahydrate 5.45g (0.022mol)
, 7.46 g (0.022 mol) of cerium acetate monohydrate, 7.95 g (0.066 mol) of potassium bromide,
A catalyst solution was prepared by dissolving 6.85 g (0.066 mol) of potassium acetate and potassium acetate in 230 ml of acetic acid, and the catalyst solution was charged into a 500 ml titanium autoclave. Air inside the autoclave is 30kg/cm2・G
After pressurizing the catalyst to 200° C., the catalyst liquid was heated to 200° C. while supplying air at a flow rate of 120 l/hr. After this, 2
,6-diisopropylnaphthalene (2,6-DIPN)
70 g (0.33 mol) was fed into the autoclave over 4 hours to carry out the first oxidation reaction.

After the supply of 2,6-DIPN is finished, the temperature is lowered to 1
The temperature was lowered to 80 °C and the internal pressure was lowered to 15 kg/cm2 G (oxygen partial pressure 3 kg/cm2 G), and the second stage oxidation reaction was carried out for 1 hour while supplying only air without adding a catalyst. Ta. After the reaction is complete, stop the air supply,
The autoclave was cooled to room temperature, the reaction mixture was collected, and the solids were filtered off. The solid matter was washed with a dilute aqueous sulfuric acid solution and then dried to obtain 73.1 g (yield: 92.1 mol%) of 2,6-NDCA. The purity of this product is 99.
2%, and its by-product content was 0.8%. The filtration specific resistance value during solid matter filtration is 3.0×107 m
/kg, and the filterability was very good.

A catalyst solution having the same composition as above was prepared by adding the insufficient amount of catalyst and solvent to the remaining filtrate after filtering the solid matter from the reaction mixture, that is, the reaction filtrate.
It was charged into a 0 ml titanium autoclave, and two-stage oxidation of 2,6-DIPN was carried out in exactly the same manner as above. 2 of 2,6-DIPN by circulating the reaction filtrate.
The reaction operation of stage liquid phase oxidation was repeated 10 times in total. The yield of 2,6-NDCA in each reaction is shown in Table 1 below. The yields of NDCA in Table 1 are in mole percent.

[0040]

[Table 1]

Comparative Example 1 An oxidation reaction of 2,6-DIPN was carried out in the same manner as in Example 1 except that the second stage oxidation reaction was not carried out. after that,
The reaction mixture was treated as in Example 1 to give 2,6-N
72.8 g (91.5% yield) of DCA product was obtained. The purity of this product was 98.5% and its by-product content was 1.5%. The filtration specific resistance value during solid matter filtration was 8 x 109 m/kg, indicating poor filtration performance.

The remaining reaction filtrate after solid matter was filtered off from the reaction mixture was adjusted in composition in the same manner as in Example 1 and then recycled to repeat the liquid phase oxidation reaction of 2,6-DIPN. The reaction conditions for the second and subsequent reactions were the same as those for the first reaction in Comparative Example 1. When this reaction operation was repeated five times, the yield was less than 50%, so at that point, the repetition of the reaction by recycling the reaction filtrate was stopped. The reaction results for each round are shown in Table 2 below.

[0043]

[Table 2]

From Table 2, it can be seen that the yield decreased substantially in the second reaction, and after the third reaction, the yield decreased to an unacceptable level.

Example 2 Example 1 was repeated, but after the first stage oxidation reaction, which was carried out while supplying 2,6-DIPN, the reaction mixture was taken out of the autoclave and the remaining solids were filtered off. After returning the filtrate to the autoclave and adding the missing amount of catalyst and solvent to prepare a catalyst solution, the temperature was 180°C, the air pressure was 15 kg/cm2・G, and the air supply amount was 120 liters.
The second stage oxidation reaction was carried out for 1 hour under the same conditions as in Example 1. A solid substance was filtered from the obtained reaction mixture of the second stage oxidation, and this solid substance was washed with water together with the solid substance of the first stage and dried.

Using the reaction filtrate obtained in the second stage filtration, the second and subsequent two-stage oxidation reactions were carried out in the same manner as above. A total of 10 reactions were repeated in this manner. The yield of 2,6-NDCA in each round, the purity of the product, and the filtration specific resistance value of the solid in the second oxidation were almost the same as in Example 1.

Example 3 This example shows an example of continuous oxidation. Cobalt acetate, manganese acetate, cerium acetate, potassium bromide and potassium acetate were dissolved in acetic acid to obtain Co: 0.42% in acetic acid.
, Mn: 0.39%, Ce: 0.98%, K: 1
．． 7%, and Br: 1.7% (all weight%
) was prepared. This catalyst liquid and
2,6-DIPN at a temperature of 200°C and an air pressure of 30k
The mixture was continuously charged into a continuous oxidation reactor having a first stage internal volume of 10 liters, which was adjusted to an air flow rate of 2.8 Nm3/hr and an air flow rate of 2.8 Nm3/hr, to carry out a first stage oxidation reaction. The residence time in the first stage reactor was approximately 5 hours.

The reaction mixture continuously extracted from the first stage reactor was heated at a temperature of 180° C. and an air pressure of 15 kg/kg.
cm2·G, and the air flow rate was adjusted to 0.2 Nm3/hr, which was continuously charged into a second-stage continuous oxidation reactor to perform a second-stage oxidation reaction. The residence time in the second stage reactor was approximately 1 hour. The two-stage continuous reaction described above was continued for 8 hours while the reaction mixture continuously extracted from the second-stage reactor was collected in a receiving tank. After completion of the reaction, solid matter is filtered from the collected reaction mixture, washed with water and dried,
-NDCA was obtained. The filtration specific resistance value at this time is 5.0×
It was 108 m/kg. The purity of the product obtained is 9
9.0%, and the content of by-products was 1.0%. The reaction yield was 90.1 mol%.

Comparative Example 2 Liquid phase oxidation of 2,6-DIPN was carried out continuously in the same manner as the first stage reaction of Example 3, except that the second stage oxidation reaction was not carried out. The reaction mixture extracted from the first-stage reactor was collected as it was in a receiving tank, and after the reaction was completed, the solid matter was filtered off. The filtration specific resistance value at this time is 2.0×1010 m/
It was kg. The purity of the product obtained was 98.2%, and its by-product content was 1.8%. The reaction yield was 88.7 mol%.

[0050]

[Effects of the Invention] The method for producing NCA by two-stage liquid phase oxidation of the present invention can produce a product with high purity and excellent color in good yield, and the product has excellent filterability. Therefore, it can be easily recovered by filtration. moreover,
Since the reaction filtrate can be used repeatedly, wastewater treatment becomes easy, and high-quality NCAs can be produced economically and efficiently, making it extremely useful for industrial production of NCAs. .

Claims (4)

[Claims] Claim 1: A substituted naphthalene having at least one substituent selected from an alkyl group, an acyl group, and an oxidation intermediate thereof is oxidized in a solvent containing a lower aliphatic monocarboxylic acid in the presence of an oxidation catalyst containing a heavy metal. Below, in the method of producing naphthalene carboxylic acid by oxidation with molecular oxygen, the oxidation reaction is carried out in two stages, and the second stage oxidation reaction is
1. A method for producing naphthalenecarboxylic acid, which is carried out under conditions where at least one of temperature and pressure is lower than in the first stage oxidation. 2. The method according to claim 1, wherein after the first stage oxidation reaction, the obtained reaction mixture is directly subjected to the second stage oxidation reaction. 3. The method according to claim 1, wherein after the first stage oxidation reaction, the residual liquid from which the naphthalene carboxylic acid product is recovered from the resulting reaction mixture is subjected to the second stage oxidation reaction. 4. The method according to claim 1, wherein after the first stage oxidation reaction, a catalyst is added and then the second stage oxidation reaction is performed.