JP7665192B2 - Method for producing 2,5-dihydroxyterephthalic acid - Google Patents

Description

The present invention relates to a method for producing 2,5-dihydroxyterephthalic acid.

2,5-Dihydroxyterephthalic acid (hereinafter sometimes referred to as DHTA) is an aromatic dicarboxylic acid with two hydroxyl groups. It is used, for example, as a monomer for synthetic resins such as polyester, polyamide, and aramid, as well as a raw material for fluorescent agents and pharmaceutical intermediates, and demand for it is increasing year by year.

The Kolbe-Schmitt reaction has been known as a method for introducing a carboxyl group into a compound having a phenolic hydroxyl group. An example of the Kolbe-Schmitt reaction is a chemical reaction in which an alkali metal phenoxide (alkali metal salt of phenol) is brought into contact with carbon dioxide at high temperature and pressure to carboxylate the ortho position, and then salicylic acid is obtained after neutralization with an acid.

Regarding the production of DHTA, methods of production using this Kolbe-Schmitt reaction have also been proposed. For example, a method of contacting a dihydric phenol with carbon dioxide in the presence of an alkali metal carbonate and reacting in the presence of an alkali metal formate at a temperature higher than the melting point of the formate (Patent Document 1) and a method of reacting a hydroquinone dialkali metal salt with carbon dioxide in the presence of an alkali metal salt of phenol or naphthol (Patent Document 2) are known to improve the production rate mainly by adding an organometallic salt catalyst.

However, the crude DHTA produced by the Kolbe-Schmitt reaction contains residual alkali metals such as sodium and potassium, so purification steps to remove these metals are necessary for applications requiring higher purity.

As a method for purifying DHTA, a method has been proposed in which crude DHTA produced by the Kolbe-Schmitt reaction is acetylated, then recrystallized and hydrolyzed to obtain DHTA again (Patent Document 3). However, the recovery rate is less than half, so this method cannot be said to be industrially advantageous.

Special Publication No. 11-515031 JP 2013-245214 A Japanese Unexamined Patent Publication No. 49-11841

The object of the present invention is to provide a manufacturing method that can produce high-purity 2,5-dihydroxyterephthalic acid with a low alkali metal content.

In view of the above problems, the inventors conducted intensive research and discovered that high-purity 2,5-dihydroxyterephthalic acid with low alkali metal content can be prepared by washing 2,5-dihydroxyterephthalic acid crystals in a suspended state in the presence of an aqueous medium under high-temperature conditions, thus completing the present invention.

That is, the present invention includes the following preferred embodiments.
[1] A method for producing high-purity 2,5-dihydroxyterephthalic acid, comprising a step of washing crude 2,5-dihydroxyterephthalic acid in a suspended state at a temperature of 90 to 200° C. in the presence of an aqueous medium, wherein the content of alkali metals contained in the crude 2,5-dihydroxyterephthalic acid is 15 ppm or more, and the content of alkali metals contained in the high-purity 2,5-dihydroxyterephthalic acid is less than 15 ppm.
[2] The method according to [1], wherein the crude 2,5-dihydroxyterephthalic acid is obtained by reacting an alkali metal salt of hydroquinone with carbon dioxide and precipitating the resulting alkali metal salt of 2,5-dihydroxyterephthalic acid with an acid.
[3] The method according to [1] or [2], wherein the aqueous medium is an aqueous solution of a water-soluble organic solvent having a concentration of up to 90% by mass.
[4] The method according to [3], wherein the water-soluble organic solvent is one or more selected from the group consisting of methanol, ethanol, isopropanol, 2-methoxyethanol, 2-ethoxyethanol, ethylene glycol, glycerin, polyethylene glycol, acetone, tetrahydrofuran, N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide, hexamethylphosphoramide, and N-methyl-2-pyrrolidone.
[5] The method according to any one of [1] to [4], wherein the washing is carried out in the presence of 200 to 2,000 parts by mass of an aqueous medium relative to 100 parts by mass of crude 2,5-dihydroxyterephthalic acid.
[6] The method according to any one of [1] to [5], wherein the alkali metal is sodium and/or potassium.
[7] High-purity 2,5-dihydroxyterephthalic acid having an alkali metal content of less than 15 ppm.
[8] The high-purity 2,5-dihydroxyterephthalic acid according to [7], wherein the alkali metal is sodium and/or potassium.

According to the present invention, it is possible to obtain high-purity 2,5-dihydroxyterephthalic acid with a low alkali metal content.

In the present invention, the term "alkali metal salt" refers to a monoalkali metal salt and/or a dialkali metal salt.

The method for obtaining the crude DHTA used in the present invention is not particularly limited, but it can be obtained, for example, by reacting an alkali metal salt of hydroquinone with carbon dioxide in a reaction medium, the so-called Kolbe-Schmitt reaction, and then subjecting the resulting alkali metal salt of 2,5-dihydroxyterephthalic acid to acid precipitation.

In the present invention, crude DHTA means DHTA having an alkali metal content of 15 ppm or more, and high-purity DHTA means DHTA having an alkali metal content of less than 15 ppm.

The reactor used in the Kolbe-Schmitt reaction may be any reactor used in a typical Kolbe-Schmitt reaction, and for example, an autoclave equipped with a stirrer and capable of handling high-pressure reactions is suitable. Furthermore, it is more preferable to use one that has a temperature control function and is equipped with an inlet tube for carbon dioxide or an inert gas, a thermometer support tube, a pressure gauge, and an exhaust tube.

Examples of the alkali metal salt of hydroquinone used in the Kolbe-Schmitt reaction include the lithium salt of hydroquinone, the sodium salt of hydroquinone, the potassium salt of hydroquinone, the rubidium salt of hydroquinone, and the cesium salt of hydroquinone. From the viewpoints of availability, cost, and reactivity, the sodium salt of hydroquinone and the potassium salt of hydroquinone are preferred, and from the viewpoint of superior reactivity, the potassium salt of hydroquinone is even more preferred.

The alkali metal salt of hydroquinone can be obtained by converting hydroquinone into an alkali metal salt using an alkali metal hydroxide or an alkali metal alkoxide such as an alkali metal t-butoxide, an alkali metal methoxide, an alkali metal ethoxide, or an alkali metal i-propoxide. In particular, from the viewpoint of economy, it is preferable to convert hydroquinone into an alkali metal salt using an alkali metal hydroxide.

When reacting an alkali metal salt of hydroquinone with carbon dioxide, the reaction may be carried out in the presence of an organic alkali metal salt.

As the organic alkali metal salt, an alkali metal salt of one or more organic compounds selected from the group consisting of phenol, naphthol, formic acid, acetic acid, propionic acid, isobutyric acid, palmitic acid, and stearic acid can be preferably used, and potassium acetate is particularly preferably used because of its excellent yield.

The reaction medium used in the reaction of the alkali metal salt of hydroquinone with carbon dioxide is liquid at the reaction temperature and pressure, and is inert to the reaction between the alkali metal salt of hydroquinone and carbon dioxide. Preferably, the reaction medium has a boiling point of 220°C or higher at atmospheric pressure.

As the reaction medium, aliphatic, alicyclic or aromatic hydrocarbons or ether compounds having residues of these are preferably used, examples of which include light oil, kerosene, gasoline, lubricating oil, white oil, alkylbenzene, alkylnaphthalene, hydrogenated triphenyl, diphenyl ether, alkylphenyl ether, alkyldiphenyl ether, high-boiling higher alcohols such as iso-octyl alcohol, and mixtures of these.

The amount of reaction medium used is at least 0.5 times, preferably 1 to 15 times, and more preferably 3 to 12 times the weight of the alkali metal salt of hydroquinone.

The reaction temperature between the alkali metal salt of hydroquinone and carbon dioxide is 150 to 320°C, preferably 200 to 300°C, and more preferably 230 to 290°C. At temperatures below 150°C, the reaction does not proceed, and at temperatures above 320°C, the reaction plateaus, resulting in energy loss and the risk of side reactions.

The pressure during the reaction between the alkali metal salt of hydroquinone and carbon dioxide is usually 0 to 10 MPa, preferably 0 to 5 MPa, and more preferably 0 to 1 MPa of carbon dioxide pressure. If the pressure during the reaction exceeds 10 MPa, equipment that can withstand high pressure is required, and this is not industrially advantageous.

The reaction time can be appropriately selected from a few minutes to 15 hours, preferably 10 minutes to 10 hours, more preferably 20 minutes to 10 hours, and particularly preferably 1 to 5 hours.

The alkali metal salt of DHTA obtained by this reaction can be subjected to a conventional method of conversion to an acid, such as acid precipitation, to obtain the crude DHTA used in the present invention.

The acid used for the acid precipitation is not particularly limited, but a mineral acid is preferably used. Examples of mineral acids include binary acids such as hydrochloric acid and hydrofluoric acid, and oxo acids such as sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. Organic acids such as acetic acid and propionic acid can also be used. Of these, sulfuric acid is particularly preferred.

The acids used for these acid precipitations are preferably in the form of an aqueous solution, since it is easier to control the reaction temperature, etc. For example, an aqueous solution of 70% by weight sulfuric acid is preferably used.

These acids are added dropwise until the pH of the aqueous medium solution is preferably 1.0 to 3.0, more preferably 1.2 to 2.5, and even more preferably 1.5 to 2.1.

The acid precipitation time varies depending on factors such as the scale of the reactor, but is preferably 10 to 150 minutes, and more preferably 30 to 120 minutes.

Acid precipitation is preferably carried out under an inert gas atmosphere such as nitrogen or helium.

The crystals precipitated by acid precipitation are separated into solid and liquid by conventional means such as filtration, and the target product, crude DHTA, is recovered. During solid-liquid separation, it is preferable to wash the crystals by pouring in an appropriate solvent. Water is the preferred solvent for use in solid-liquid separation.

The crude DHTA obtained in this way is subjected to the purification process.

In the production method of the present invention, the purification step is carried out by washing the crude DHTA in a suspended state in the presence of an aqueous medium at a temperature of 90 to 200°C.

If the temperature in the refining process is below 90°C, the effect of removing alkali metals will decrease. If the temperature in the refining process is above 200°C, the pressure inside the device will become very high, which may cause the device to break or burst.

The purification process is preferably carried out in a closed system. The closed system used in the purification process is preferably a heat-resistant and pressure-resistant purification device such as an autoclave, and preferably has an internal stirring device.

The pressure inside the refining device during the refining process is preferably 1.5 MPa or less, and more preferably 1.0 MPa or less. If the pressure inside the refining device exceeds 1.5 MPa, there is a risk of the device being damaged or bursting.

In the purification process, the aqueous solvent used for washing is preferably an aqueous solution of a water-soluble organic solvent with a concentration of up to 90% by mass.

The water-soluble organic solvent used in the present invention may be one or more selected from the group consisting of methanol, ethanol, isopropanol, 2-methoxyethanol, 2-ethoxyethanol, ethylene glycol, glycerin, polyethylene glycol, acetone, tetrahydrofuran (THF), N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide, hexamethylphosphoramide, and N-methyl-2-pyrrolidone. In terms of excellent impurity removal effect, one or more selected from the group consisting of methanol, isopropanol, acetone, and tetrahydrofuran are preferred. Two or more of these water-soluble organic solvents may be used in combination.

The amount of aqueous medium used is preferably 200 to 2,000 parts by mass per 100 parts by mass of crude DHTA. If the amount of aqueous medium used is less than 200 parts by mass per 100 parts by mass of DHTA, the effect of removing alkali metals may decrease. Furthermore, if the amount of aqueous medium used is more than 2,000 parts by mass per 100 parts by mass of DHTA, excess aqueous medium may be wasted, which may result in a decrease in production efficiency.

The washing time in the purification step is preferably 10 to 500 minutes, more preferably 30 to 360 minutes. If the washing time is less than 10 minutes, the effect of removing alkali metals from the DHTA crystals may decrease. If the washing time exceeds 500 minutes, the purification efficiency will reach a plateau, resulting in a loss of energy and the risk of by-products being generated.

The DHTA slurry (suspension) obtained in the purification process is separated and recovered from the slurry by conventional means such as centrifugation or filtration using a filter press. The recovered DHTA crystals are washed with cold water, hot water, etc., as necessary, and then dried.

The high-purity DHTA obtained in this way is suitable for use as a raw material for preparing various chemical products.

The content of alkali metals in the high-purity DHTA obtained by the method of the present invention is less than 15 ppm. Such alkali metals may be present as salts of DHTA, such as hydrochloride, sulfate, nitrate, phosphate, etc.

Thus, the present invention provides DHTA having an alkali metal content of less than 15 ppm.

The present invention will be described in detail below with reference to examples, but these are not intended to limit the scope of the present invention. The target substance, 2,5-dihydroxyterephthalic acid, was analyzed by the following method.

[High Performance Liquid Chromatography (HPLC)]
Equipment: Waters Alliance 2690/2996
Column model number: L-Column
Liquid volume: 1.0 mL/min Solvent ratio: _H2O (pH 2.3)/ _CH3CN = 95/5 (10 min) → 80/20 (3.5 min) → 5/95 (23.5 min), gradient analysis Wavelength: 229 nm
Column temperature: 40°C

Reference Example 1 (Preparation of crude DHTA)
78.2g (0.7mol) of hydroquinone and 92.4g (1.4mol) of acetic acid were charged into a 1L four-neck flask equipped with a stirrer and a temperature sensor and stirred. While cooling and stirring the mixture in a water bath under nitrogen flow, 332.2g (2.8mol) of 48% by mass aqueous potassium hydroxide solution was added dropwise over 2 hours, and the mixture was then kept at 50°C for 1 hour to prepare an aqueous solution of hydroquinone dipotassium salt/potassium acetate salt.

The prepared aqueous solution and 529.3 g of diesel were transferred to a 2 L autoclave purged with nitrogen and stirred. The mixture was then heated to 160°C while being stirred under a nitrogen stream. 218.9 g of diesel was added and the mixture was kept at 160°C for 2 hours, after which it was sealed and heated to 230°C. The nitrogen was replaced with carbon dioxide gas and the reaction was carried out at 0.3 MPa and 230-250°C for 3 hours while being stirred.

After the reaction was completed, the mixture was cooled to 100°C, 532.9g of water and 23.2g of 70% sulfuric acid were added, and the contents were transferred to a 5L bottomless flask equipped with a stirrer and a temperature sensor, 1896.4g of water was added, and the mixture was stirred at 90°C for 30 minutes under a nitrogen stream, and the aqueous layer was removed. The aqueous layer was transferred to a 5L bottomless flask equipped with a stirrer and a temperature sensor, 5.5g of activated carbon was added, and the mixture was stirred at 90°C for 30 minutes under a nitrogen stream, and then insoluble matter was removed by filter filtration. The filtrate was heated to 90°C under a nitrogen stream, and 70% sulfuric acid was added dropwise over 90 minutes while stirring at the same temperature until the pH reached 2.0, to precipitate crude DHTA. The resulting suspension was cooled to 70°C, and then solid-liquid separation was performed, followed by washing with 493.2g of water. The resulting crude crystals were dried at 100°C for 12 hours to obtain 108.5g of crude DHTA.

The obtained crude DHTA was quantitatively analyzed by high performance liquid chromatography (HPLC) and inductively coupled plasma (ICP) emission spectrometry. The results are shown in Table 1.

Example 1
100.0 g of crude DHTA obtained in Reference Example 1 and 500.9 g of 50% by weight methanol water were added to a 1 L autoclave, and then nitrogen replacement was performed, and the suspension was heated to 100 ° C. while stirring, and the temperature was maintained for 1 hour. The suspension was cooled to 30 ° C., and then solid-liquid separation was performed, followed by washing with 301.2 g of water. The obtained DHTA was dried at 100 ° C. for 12 hours, and quantitative analysis was performed by high performance liquid chromatography (HPLC) and inductively coupled plasma (ICP) emission spectrometry. The results are shown in Table 1.

Examples 2 to 5, Comparative Examples 1 to 3
DHTA was obtained in the same manner as in Example 1, except that the purification conditions were changed as shown in Table 1. The obtained DHTA was quantitatively analyzed by high performance liquid chromatography (HPLC) and inductively coupled plasma (ICP) emission spectrometry. The results are shown in Table 1.

As shown in Table 1, in the case of suspending and washing crude DHTA in an aqueous medium, Examples 1 to 5 of the present invention, which are carried out at temperatures of 90 to 200° C., can significantly reduce the alkali metal content compared to Comparative Examples 1 to 3.

Claims (5)

A method for producing high-purity 2,5-dihydroxyterephthalic acid, comprising a step of washing crude 2,5-dihydroxyterephthalic acid in a suspended state at a temperature of 90 to 200°C in the presence of an aqueous medium that is an aqueous solution of a water-soluble organic solvent having a concentration of 30 to 90% by mass, wherein the content of alkali metals contained in the crude 2,5-dihydroxyterephthalic acid is 15 ppm or more, and the content of alkali metals contained in the high-purity 2,5-dihydroxyterephthalic acid is less than 15 ppm. The method according to claim 1, wherein the crude 2,5-dihydroxyterephthalic acid is obtained by reacting an alkali metal salt of hydroquinone with carbon dioxide and precipitating the resulting alkali metal salt of 2,5-dihydroxyterephthalic acid with an acid. The method according to claim 1 or 2, wherein the water-soluble organic solvent is one or more selected from the group consisting of methanol, ethanol, isopropanol, 2-methoxyethanol, 2-ethoxyethanol, ethylene glycol, glycerin, polyethylene glycol, acetone, tetrahydrofuran, N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide, hexamethylphosphoramide, and N-methyl-2-pyrrolidone. The method according to any one of claims 1 to 3, wherein the washing is carried out in the presence of 200 to 2,000 parts by mass of an aqueous medium per 100 parts by mass of crude 2,5-dihydroxyterephthalic acid. The method according to any one of claims 1 to 4, wherein the alkali metal is sodium and/or potassium.