Method for producing 2,5-dihydroxyterephthalic acid

Abstract

To provide a production method that can produce high-purity 2,5-dihydroxy terephthalic acid with a low content of alkali metal.SOLUTION: A method for producing high-purity 2,5-dihydroxy terephthalic acid includes the step of cleaning, in the presence of an aqueous medium, crude 2,5-dihydroxy terephthalic acid at 90-200°C in a suspended state. The content of alkali metal contained in the crude 2,5-dihydroxy terephthalic acid is 15 ppm or more, and the content of alkali metal contained in the high-purity 2,5-dihydroxy terephthalic acid is less than 15 ppm.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing 2,5-dihydroxyterephthalic acid. [Background technology]

[0002] 2,5-Dihydroxyterephthalic acid (hereinafter sometimes referred to as DHTA) is an aromatic dicarboxylic acid with two hydroxy 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 the demand for it is increasing year by year.

[0003] Conventionally, the Kolbe-Schmitt reaction has been known as a method for introducing a carboxyl group into a compound having a phenolic hydroxyl group. For example, 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.

[0004] Regarding the production of DHTA, methods of production using this Kolbe-Schmitt reaction have also been proposed. For example, there is a method in which a dihydric phenol is contacted with carbon dioxide in the presence of an alkali metal carbonate, and reacted in the presence of an alkali metal formate at a temperature higher than the melting point of the formate (Patent Document 1), and there is a method in which a hydroquinone dialkali metal salt is reacted with carbon dioxide in the presence of an alkali metal salt of phenol or naphthol (Patent Document 2). It is known that the production rate can be improved mainly by adding an organometallic salt catalyst.

[0005] However, since the crude DHTA produced by the Kolbe-Schmitt reaction contains residual alkali metals such as sodium and potassium, a purification step to remove these metals is necessary for applications requiring higher purity.

[0006] 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, and this method cannot be said to be industrially advantageous. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 11-515031 [Patent Document 2] JP 2013-245214 A [Patent Document 3] Japanese Unexamined Patent Publication No. 49-11841 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a process for producing high-purity 2,5-dihydroxyterephthalic acid with a low alkali metal content. [Means for solving the problem]

[0009] In view of the above problems, the present inventors have conducted intensive research and have found that high-purity 2,5-dihydroxyterephthalic acid with a small amount of alkali metal can be prepared by washing crystals of 2,5-dihydroxyterephthalic acid in a suspended state in the presence of an aqueous medium under high temperature conditions, thereby completing the present invention.

[0010] 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. Effect of the Invention

[0011] According to the present invention, it is possible to obtain high-purity 2,5-dihydroxyterephthalic acid with a low alkali metal content. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In the present invention, the term "alkali metal salt" refers simply to a monoalkali metal salt and / or a dialkali metal salt.

[0013] The method for obtaining crude DHTA used in the present invention is not particularly limited. For example, crude DHTA can be obtained 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.

[0014] 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.

[0015] The reaction apparatus used in the Kolbe-Schmitt reaction may be any reaction apparatus used in a typical Kolbe-Schmitt reaction, and may be, for example, an autoclave equipped with a stirrer and capable of handling high-pressure reactions. More preferably, the reaction apparatus 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, an exhaust tube, and the like.

[0016] Examples of the alkali metal salt of hydroquinone used in the Kolbe-Schmitt reaction include lithium salt of hydroquinone, sodium salt of hydroquinone, potassium salt of hydroquinone, rubidium salt of hydroquinone, and cesium salt of hydroquinone. From the viewpoints of availability, cost, and reactivity, sodium salt of hydroquinone and potassium salt of hydroquinone are preferred, and potassium salt of hydroquinone is more preferred from the viewpoint of superior reactivity.

[0017] 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, an alkali metal i-propoxide, etc. In particular, from the viewpoint of economy, it is preferable to convert hydroquinone into an alkali metal salt using an alkali metal hydroxide.

[0018] The reaction between the alkali metal salt of hydroquinone and carbon dioxide may be carried out in the presence of an organic alkali metal salt.

[0019] 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 can be more preferably used because of its excellent yield.

[0020] 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 of the alkali metal salt of hydroquinone with carbon dioxide. Preferably, the reaction medium has a boiling point of 220° C. or higher at atmospheric pressure.

[0021] As the reaction medium, an aliphatic, alicyclic or aromatic hydrocarbon or an ether compound having a residue thereof is suitably used, and examples thereof include light oil, kerosene, gasoline, lubricating oil, white oil, alkylbenzene, alkylnaphthalene, hydrogenated triphenyl, diphenyl ether, alkyl phenyl ether, alkyl diphenyl ether, high-boiling higher alcohols such as iso-octyl alcohol, and mixtures thereof.

[0022] The amount of the reaction medium used is at least 0.5 times, preferably 1 to 15 times, and more preferably 3 to 12 times, the amount of the alkali metal salt of hydroquinone.

[0023] 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 lower than 150° C., the reaction does not proceed, whereas at temperatures higher than 320° C., the reaction plateaus, resulting in energy loss and the risk of side reactions.

[0024] The pressure during the reaction of the alkali metal salt of hydroquinone with 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, an apparatus capable of withstanding high pressure is required, which is not industrially advantageous.

[0025] The reaction time can be appropriately selected from the range of several minutes to 15 hours, preferably 10 minutes to 10 hours, more preferably 20 minutes to 10 hours, and particularly preferably 1 to 5 hours.

[0026] The alkali metal salt of DHTA obtained by such a reaction can be subjected to a conventional means for converting it to an acid, such as acid precipitation, to obtain the crude DHTA used in the present invention.

[0027] The acid used for the acid precipitation is not particularly limited, but a mineral acid is preferably used. Examples of the mineral acid 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. Among these, sulfuric acid is particularly preferred.

[0028] The acid used for the acid precipitation is preferably an aqueous solution from the viewpoint of easiness in controlling the reaction temperature, etc., and for example, a 70% by mass aqueous solution of sulfuric acid is preferably used.

[0029] These acids are added dropwise until the pH of the aqueous medium solution becomes preferably 1.0 to 3.0, more preferably 1.2 to 2.5, and even more preferably 1.5 to 2.1.

[0030] The acid precipitation time differs depending on the scale of the reaction apparatus, but is preferably 10 to 150 minutes, more preferably 30 to 120 minutes.

[0031] The acid precipitation is preferably carried out in an atmosphere of an inert gas such as nitrogen or helium.

[0032] The crystals precipitated by acid precipitation are separated into solid and liquid by a conventional method such as filtration, and the target crude DHTA is recovered. During solid-liquid separation, it is preferable to wash the crystals by pouring a suitable solvent. The solvent used during solid-liquid separation is preferably water.

[0033] The crude DHTA thus obtained is subjected to a purification step.

[0034] In the production method of the present invention, the purification step is carried out by washing crude DHTA in a suspended state at a temperature of 90 to 200° C. in the presence of an aqueous medium.

[0035] If the temperature in the refining process is less than 90°C, the effect of removing alkali metals will decrease. If the temperature in the refining process is more than 200°C, the pressure inside the device will become very high, which may cause the device to break or burst.

[0036] The purification step is preferably carried out in a closed system. The closed system used in the purification step is preferably a heat-resistant and pressure-resistant purification device such as an autoclave, and preferably has an internal stirring device.

[0037] The pressure inside the purification device in the purification step is preferably 1.5 MPa or less, more preferably 1.0 MPa or less. If the pressure inside the purification device exceeds 1.5 MPa, the device may be damaged or explode.

[0038] In the purification step, the aqueous solvent used for washing is preferably an aqueous solution of a water-soluble organic solvent having a concentration of up to 90% by mass.

[0039] 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. From the viewpoint 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.

[0040] The amount of the aqueous medium used is preferably 200 to 2000 parts by mass relative to 100 parts by mass of crude DHTA. If the amount of the aqueous medium used is less than 200 parts by mass relative to 100 parts by mass of DHTA, the effect of removing alkali metals may decrease. If the amount of the aqueous medium used is more than 2000 parts by mass relative to 100 parts by mass of DHTA, the excess aqueous medium may be wasted, which may cause a decrease in production efficiency.

[0041] 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 DHTA crystals may decrease. If the washing time is more than 500 minutes, the purification efficiency may reach a plateau, resulting in energy loss and the generation of by-products.

[0042] The slurry (suspension) of DHTA obtained in the purification step is separated and recovered from the slurry by conventional means such as centrifugation, filtration with a filter press, etc. The recovered DHTA crystals are washed with cold water, hot water, etc., as necessary, and then dried.

[0043] The high purity DHTA thus obtained is suitable for use as a raw material for preparing various chemical products.

[0044] The high purity DHTA obtained by the process of the present invention contains less than 15 ppm of alkali metals, which may be present as salts of DHTA, such as hydrochlorides, sulfates, nitrates, phosphates, etc.

[0045] Thus, the present invention provides DHTA having an alkali metal content of less than 15 ppm. EXAMPLES

[0046] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited thereto. The target product, 2,5-dihydroxyterephthalic acid, was analyzed by the following method.

[0047] [High performance liquid chromatography (HPLC)] Instrument: Waters Alliance 2690 / 2996 Column model number: L-Column Flow rate: 1.0mL / 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: 229nm Column temperature: 40℃

[0048] 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 a nitrogen stream, 332.2g (2.8mol) of 48% by mass potassium hydroxide aqueous 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.

[0049] 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, then 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.

[0050] 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 bottomed flask equipped with a stirrer and a temperature sensor, 1896.4g of water was added, and the mixture was stirred at 90°C under a nitrogen stream for 30 minutes, and the aqueous layer was removed. The aqueous layer was transferred to a 5L bottomed 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% by mass 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.

[0051] 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.

[0052] Example 1 100.0 g of the crude DHTA obtained in Reference Example 1 and 500.9 g of 50% by mass aqueous methanol were added to a 1 L autoclave, and the atmosphere was replaced with nitrogen. The mixture was heated to 100°C while stirring in a suspended state, and then held at the same temperature for 1 hour. The suspension was cooled to 30°C, and then separated into solid and liquid, and then washed with 301.2 g of water. The obtained DHTA was dried at 100°C for 12 hours, and quantitatively analyzed by high performance liquid chromatography (HPLC) and inductively coupled plasma (ICP) emission spectrometry. The results are shown in Table 1.

[0053] 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.

[0054] As shown in Table 1, in Examples 1 to 5 of the present invention, in which the crude DHTA is suspended and washed in an aqueous medium at a temperature of 90 to 200° C., the alkali metal content can be significantly reduced compared to Comparative Examples 1 to 3. [Table 1]

Claims

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 which is an aqueous solution of a water-soluble organic solvent having a concentration of 30 to 90% by mass, wherein the crude 2,5-dihydroxyterephthalic acid has an alkali metal content of 15 ppm or more, and the high-purity 2,5-dihydroxyterephthalic acid has an alkali metal content of less than 15 ppm.

2. 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.

3. 3. The method according to claim 1, wherein the water-soluble organic solvent is at least one 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.

4. 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 relative to 100 parts by mass of crude 2,5-dihydroxyterephthalic acid.

5. The method according to any one of claims 1 to 4, wherein the alkali metal is sodium and / or potassium.

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