Method for producing organic acid

Abstract

This method for producing an organic acid comprises: preparing an electrodialysis tank having an anode, a cathode, and one or more electrodialysis units, wherein the electrodialysis unit has a bipolar membrane, a first cation exchange membrane, and a second cation exchange membrane, and wherein a desalination compartment is formed between the first cation exchange membrane and the second cation exchange membrane; and circulating an aqueous organic acid salt solution in a circulation path that includes the desalination compartment, while applying a voltage between the anode and cathode, thereby precipitating in the desalination compartment a solid that contains the free organic acid.

Description

Method for producing organic acids

[0001] The present disclosure relates to a method for producing or recovering free organic acids as solids by electrodialysis, and a method for recycling polyesters using the same.

[0002] Electrodialysis using a bipolar membrane is known as a method for recovering an acid component from an aqueous solution containing an inorganic or organic acid salt.

[0003] For example, Patent Document 1 discloses a method for recovering terephthalic acid and alkali components from alkaline processing wastewater from polyester fibers, which uses an ion exchange membrane electrodialysis cell partitioned by a bipolar membrane, an anion exchange membrane, and a cation exchange membrane, and having an anode chamber, an acid component concentrating chamber, a deionization chamber, an alkali component concentrating chamber, and a cathode chamber, and performs electrodialysis by feeding and circulating the treated alkaline processing wastewater through the deionization chamber, recovering the terephthalic acid component in the acid component concentrating chamber, and recovering the alkali component in the alkali concentrating chamber and the cathode chamber. Non-Patent Document 1 also discloses a method for recovering oily naphthenic acid by electrodialysis using an apparatus including a combination of a bipolar membrane and two cation exchange membranes.

[0004] Japanese Patent Application Publication No. 05-271150

[0005] Separation and Purification Technology, 212 (2019), 929-940

[0006] When recovering solids containing free organic acids by the conventional method disclosed in Patent Document 1, the organic acid anions must pass through an anion exchange membrane. However, the free organic acids may precipitate inside the anion exchange membrane, causing it to become clogged. To prevent this, it is necessary to constantly and precisely control the pH of the acid component concentration compartment and the deionization compartment.

[0007] The present disclosure relates to a method for more efficiently recovering a solid containing an organic acid in a free form from an aqueous solution containing an organic acid salt, or a method for producing a solid containing an organic acid in a free form.

[0008] The present disclosure includes the following [1] to

[13] , [1'] to [11'], and [1"] to [10"]. [1] A method for producing an organic acid, comprising: preparing an electrodialysis cell having an anode, a cathode, and one or more electrodialysis units disposed therebetween, the electrodialysis units having, in order from the anode side to the cathode side, a bipolar membrane, a first cation exchange membrane, and a second cation exchange membrane, an acid component chamber formed between the bipolar membrane and the first cation exchange membrane, a deionization compartment formed between the first cation exchange membrane and the second cation exchange membrane, and an alkaline component chamber formed on the cathode side of the second cation exchange membrane; and circulating an acid aqueous solution through a circulation path including the acid component chamber, an alkaline aqueous solution through a circulation path including the alkaline component chamber, and an organic acid salt solution containing an organic acid salt through a circulation path including the deionization compartment, while applying a voltage between the anode and the cathode, thereby precipitating a solid containing the organic acid in a free state generated from the organic acid salt in the deionization compartment. [2] The method according to [1], wherein the solid comprises crystals of the organic acid in a free state. [3] The method according to [2], wherein the crystals are needle-shaped crystals. [4] The method according to any one of [1] to [3], wherein the organic acid salt aqueous solution further contains an inorganic salt. [5] The method according to [4], wherein the inorganic salt contains one or more selected from sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, and sodium dihydrogen phosphate. [6] The method according to [4] or [5], wherein the concentration of the inorganic salt in the organic acid salt aqueous solution at 25°C before a voltage is applied between the anode and the cathode is 0.001 M or more and 1.0 M or less. [7] The method according to any one of [1] to [6], wherein the acid aqueous solution contains an acid, and the concentration of the acid in the acid aqueous solution at 25°C before a voltage is applied between the anode and the cathode is 0.001 M or more and 2.0 M or less. [8] The method according to any one of [1] to [7], wherein the organic acid salt is one or more selected from the group consisting of carboxylates, sulfonates, sulfinates, organic phosphates, and organic phosphites. [9] The method according to any one of [1] to [8], wherein the organic acid salt is a carboxylate.

[10] The method according to any one of [1] to [8], wherein the organic acid salt is a salt of a dicarboxylic acid.

[11] The method according to any one of [1] to [8], wherein the organic acid salt is a salt of terephthalic acid.

[12] The method according to any one of [1] to

[11] , further comprising recovering the alkaline component from the alkaline component chamber.

[13] A method for producing an organic acid or a method for recovering an organic acid, comprising: preparing an electrodialysis cell comprising an anode, a cathode, and one or more electrodialysis units disposed therebetween, the electrodialysis units having a bipolar membrane, a first cation exchange membrane, and a second cation exchange membrane arranged in this order from the anode side to the cathode side, wherein an acid component chamber is formed between the bipolar membrane and the first cation exchange membrane, a deionization chamber is formed between the first cation exchange membrane and the second cation exchange membrane, and an alkaline component chamber is formed on the cathode side of the second cation exchange membrane; and circulating an acid aqueous solution through a circulation path including the acid component chamber, an alkaline aqueous solution through a circulation path including the alkaline component chamber, and an organic acid salt solution containing an organic acid salt through a circulation path including the deionization chamber, while applying a voltage between the anode and the cathode, thereby precipitating a solid containing the free organic acid generated from the organic acid salt in the deionization chamber, wherein the voltage is 1 V or more and 300 V or less.

[0009] [1'] A method for recovering organic acids, comprising: preparing an electrodialysis cell having an anode, a cathode, and one or more electrodialysis units disposed therebetween, the electrodialysis units having, in order from the anode side to the cathode side, a bipolar membrane, a first cation exchange membrane, and a second cation exchange membrane, an acid component chamber formed between the bipolar membrane and the first cation exchange membrane, a deionization compartment formed between the first cation exchange membrane and the second cation exchange membrane, and an alkaline component chamber formed on the cathode side of the second cation exchange membrane; and circulating an acid aqueous solution through a circulation path including the acid component chamber, an alkaline aqueous solution through a circulation path including the alkaline component chamber, and an organic acid salt solution containing an organic acid salt through a circulation path including the deionization compartment, while applying a voltage between the anode and the cathode, thereby precipitating a solid containing the organic acid in a free state generated from the organic acid salt in the deionization compartment. [2'] The method according to [1'], wherein the solid contains crystals of the organic acid in a free state. [3'] The method according to [2'], wherein the crystals are needle-shaped crystals. [4'] The method according to any one of [1'] to [3'], wherein the organic acid salt aqueous solution further contains an inorganic salt. [5'] The method according to [4'], wherein the inorganic salt contains one or more selected from sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, and sodium dihydrogen phosphate. [6'] The method according to [4'] or [5'], wherein the concentration of the inorganic salt in the organic acid salt aqueous solution at 25°C before a voltage is applied between the anode and the cathode is 0.001 M or more and 1.0 M or less. [7'] The method according to any one of [1'] to [6'], wherein the acid aqueous solution contains an acid, and the concentration of the acid in the acid aqueous solution at 25°C before a voltage is applied between the anode and the cathode is 0.001 M or more and 2.0 M or less. [8'] The method according to any one of [1'] to [7'], wherein the organic acid salt is one or more selected from the group consisting of carboxylates, sulfonates, sulfinates, organic phosphates, and organic phosphites. [9'] The method according to any one of [1'] to [8'], wherein the organic acid salt is a carboxylate.[10'] The method according to any one of [1'] to [9'], wherein the organic acid salt is a salt of a dicarboxylic acid. [11'] The method according to any one of [1'] to [10'], further comprising recovering the alkaline component from the alkaline component chamber.

[0010] [1"] A method for recovering carboxylic acid, comprising: preparing an electrodialysis cell comprising an anode, a cathode, and one or more electrodialysis units disposed therebetween, the electrodialysis units having a bipolar membrane, a first cation exchange membrane, and a second cation exchange membrane arranged in this order from the anode side toward the cathode side, an acid component chamber being formed between the bipolar membrane and the first cation exchange membrane, a deionization chamber being formed between the first cation exchange membrane and the second cation exchange membrane, and an alkaline component chamber being formed on the cathode side of the second cation exchange membrane; and circulating an acid aqueous solution through a circulation path including the acid component chamber, an alkaline aqueous solution through a circulation path including the alkaline component chamber, and an aqueous carboxylate salt solution containing a carboxylate salt through a circulation path including the deionization chamber, while applying a voltage between the anode and the cathode, thereby precipitating a solid containing carboxylic acid in a free state generated from the carboxylate salt in the deionization chamber. [2"] The method according to [1"], wherein the solid comprises crystals of the carboxylic acid in a free state. [3"] The method according to [2"], wherein the crystals are needle-shaped crystals. [4"] The method according to any one of [1"] to [3"], wherein the aqueous carboxylate solution further contains an inorganic salt. [5"] The method according to [4"], wherein the inorganic salt contains one or more selected from sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, and sodium dihydrogen phosphate. [6"] The method according to [4"] or [5"], wherein the concentration of the inorganic salt in the aqueous carboxylate solution at 25°C before a voltage is applied between the anode and the cathode is 0.001 M or more and 1.0 M or less. [7"] The method according to any one of [1"] to [6"], wherein the carboxylate is an alkali metal salt or alkaline earth metal salt of one or more dicarboxylic acids. [8"] The method according to any one of [1"] to [7"], further comprising recovering the alkali component from the alkali component chamber. [9"] A method for recycling polyester, comprising: forming an aqueous carboxylate solution containing an alkali metal salt of a dicarboxylic acid by depolymerizing a polyester; and recovering the dicarboxylic acid from the aqueous carboxylate solution by the method according to any one of [1"] to [8"].[10"] The method according to any one of [1"] to [8"], wherein the acid aqueous solution contains an acid, and the concentration of the acid in the acid aqueous solution at 25°C before a voltage is applied between the anode and the cathode is 0.001 M or more and 2.0 M or less.

[0011] A solid containing a free organic acid (such as a carboxylic acid) can be produced or recovered more efficiently from an aqueous solution containing an organic acid salt (such as a carboxylate).

[0012] 1 is a schematic diagram showing an example of an apparatus for recovering a solid containing an organic acid. FIG. 2 is a schematic diagram showing an example of the action of electrodialysis in an electrodialysis unit. FIG. 3 is a scanning electron microscope image of an anion exchange membrane after electrodialysis in Comparative Example 1. FIG. 4 is a scanning electron microscope image of an anion exchange membrane after electrodialysis in Comparative Example 1. FIG. 5 is a scanning electron microscope image of an anion exchange membrane after electrodialysis in Comparative Example 1. FIG. 6 is an infrared absorption spectrum of the anion exchange membrane, free terephthalic acid, and disodium terephthalate after electrodialysis in Comparative Example 1, and a differential infrared absorption spectrum between the liquid-contacting portion and the non-liquid-contacting portion. FIG. 7 is a scanning electron microscope image of a first cation exchange membrane (non-liquid-contacting portion) after electrodialysis in Example 2. FIG. 8 is a scanning electron microscope image of a first cation exchange membrane (liquid-contacting portion) after electrodialysis in Example 2. FIG. 9 is an infrared absorption spectrum of the first cation exchange membrane, free terephthalic acid, and disodium terephthalate after electrodialysis in Example 2, and a differential infrared absorption spectrum between the liquid-contacting portion and the non-liquid-contacting portion. FIG. 10 is a graph showing the relationship between the pH and conductivity in a desalting compartment and the current-flow time in the electrodialysis test of Example 1. 1 is a graph showing the relationship between the pH and conductivity in the deionizing compartment and the current-flow time in the electrodialysis test of Example 2. FIG. 2 is a graph showing the relationship between the residual rate of disodium terephthalate and the current-flow time in the electrodialysis tests of Examples 1 and 2. FIG. 3 is a graph showing the relationship between the current flowing through the electrodialysis device and the current-flow time in the electrodialysis tests of Examples 1 and 2. FIG. 4 is a scanning electron microscope image of crystals of terephthalic acid recovered in the electrodialysis test of Example 2. FIG. 5 is a graph showing the relationship between the pH in the deionizing compartment and the current-flow time in the electrodialysis test of Example 3. FIG. 6 is a graph showing the relationship between the conductivity of the deionizing compartment and the current-flow time in the electrodialysis test of Example 3. FIG. 7 is a graph showing the relationship between the residual rate of disodium terephthalate and the current-flow time in the electrodialysis test of Example 3. FIG. 8 is a graph showing the relationship between the current flowing through the electrodialysis device and the current-flow time in the electrodialysis test of Example 3. FIG. 9 is a graph showing the relationship between the pH in the deionizing compartment and the current-flow time in the electrodialysis test of Example 4. FIG. 10 is a graph showing the relationship between the conductivity of the deionizing compartment and the current-flow time in the electrodialysis test of Example 4. 1 is a graph showing the relationship between the residual rate of disodium terephthalate and the energization time in the electrodialysis test of Example 4. 2 is a graph showing the relationship between the current flowing through the electrodialysis device and the energization time in the electrodialysis test of Example 4. 3 is a schematic diagram showing an example of a recovery device for the electrodialysis test of Comparative Example 1.1 is a graph showing the relationship between the pH in the desalting compartment and the current application time in the electrodialysis tests of Examples 9 to 11. It is a graph showing the relationship between the conductivity of the desalting compartment and the current application time in the electrodialysis tests of Examples 9 to 11. It is a graph showing the relationship between the residual rate of disodium terephthalate and the current application time in the electrodialysis tests of Examples 9 to 11. It is a graph showing the relationship between the value of current flowing through the electrodialysis device and the current application time in the electrodialysis tests of Examples 9 to 11. It is a graph showing the relationship between the pH in the desalting compartment and the current application time in the electrodialysis tests of Examples 12 to 14. It is a graph showing the relationship between the conductivity of the desalting compartment and the current application time in the electrodialysis tests of Examples 12 to 14. It is a graph showing the relationship between the residual rate of disodium terephthalate and the current application time in the electrodialysis tests of Examples 12 to 14. It is a graph showing the relationship between the value of current flowing through the electrodialysis device and the current application time in the electrodialysis tests of Examples 12 to 14. It is a graph showing the relationship between the pH in the desalting compartment and the current application time in the electrodialysis tests of Examples 15 to 17. 1 is a graph showing the relationship between the conductivity of the desalting compartment and the current-flow time in the electrodialysis tests of Examples 15 to 17. 2 is a graph showing the relationship between the residual rate of disodium terephthalate and the current-flow time in the electrodialysis tests of Examples 15 to 17. 3 is a graph showing the relationship between the current value flowing through the electrodialysis device and the current-flow time in the electrodialysis tests of Examples 15 to 17. 4 is a graph showing the relationship between the pH of the desalting compartment and the current-flow time in the electrodialysis tests of Examples 16, 18, and 19. 5 is a graph showing the relationship between the conductivity of the desalting compartment and the current-flow time in the electrodialysis tests of Examples 16, 18, and 19. 6 is a graph showing the relationship between the residual rate of disodium terephthalate and the current-flow time in the electrodialysis tests of Examples 16, 18, and 19. 7 is a graph showing the relationship between the current value flowing through the electrodialysis device and the current-flow time in the electrodialysis tests of Examples 16, 18, and 19. 8 is a graph showing the relationship between the pH of the desalting compartment and the current-flow time in the electrodialysis tests of Examples 16, 20, and 21. 1 is a graph showing the relationship between the conductivity of the deionization compartment and the current-flow time in the electrodialysis tests of Examples 16, 20, and 21. 2 is a graph showing the relationship between the residual rate of disodium terephthalate and the current-flow time in the electrodialysis tests of Examples 16, 20, and 21. 3 is a graph showing the relationship between the current value flowing through the electrodialysis device and the current-flow time in the electrodialysis tests of Examples 16, 20, and 21.22 is a graph showing the relationship between the pH of the desalting compartment and the energization time in the electrodialysis test of Example 22. FIG. 23 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time in the electrodialysis test of Example 22. FIG. 24 is a graph showing the relationship between the residual rate of disodium terephthalate and the energization time in the electrodialysis test of Example 22. FIG. 25 is a graph showing the relationship between the value of current flowing through the electrodialysis device and the energization time in the electrodialysis test of Example 22. FIG. 26 is a graph showing the relationship between the pH of the desalting compartment and the energization time in the electrodialysis test of Example 23. FIG. 27 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time in the electrodialysis test of Example 23. FIG. 28 is a graph showing the relationship between the residual rate of disodium terephthalate and the energization time in the electrodialysis test of Example 23. FIG. 29 is a graph showing the relationship between the value of current flowing through the electrodialysis device and the energization time in the electrodialysis test of Example 23. FIG. 29 is a graph showing the relationship between the pH of the desalting compartment and the energization time in the electrodialysis test of Example 24. FIG. 29 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time in the electrodialysis test of Example 24. 2 is a graph showing the relationship between the residual rate of disodium terephthalate and the current application time in the electrodialysis test of Example 24. FIG. 3 is a graph showing the relationship between the current value flowing through the electrodialysis device and the current application time in the electrodialysis test of Example 24.

[0013] The present invention is not limited to the following examples.

[0014] Fig. 1 is a schematic diagram showing an example of a recovery apparatus used to recover solids containing organic acids by electrodialysis. The recovery apparatus 100 shown in Fig. 1 includes an electrodialysis cell 50, an electrolyte tank 15, an acid component tank 25, a deionization compartment tank 35, an alkaline component tank 45, and piping connecting the electrodialysis cell 50 to the electrolyte tank 15, the acid component tank 25, the deionization compartment tank 35, or the alkaline component tank 45. The electrodialysis cell 50 is composed of an anode chamber 12 including an anode 11, a cathode chamber 14 including a cathode 13, and a plurality of electrodialysis units 5 disposed between the anode 11 (anode chamber 12) and the cathode 13 (cathode chamber 14). The plurality of electrodialysis units 5 are arranged in series from the anode 11 side toward the cathode 13 side. Each electrodialysis unit 5 includes a bipolar membrane 2, a first cation exchange membrane 3a, and a second cation exchange membrane 3b, arranged in this order from the anode 11 side toward the cathode 13 side. The bipolar membrane 2, the first cation exchange membrane 3a, and the second cation exchange membrane 3b are spaced apart from one another. An acid component chamber 20 is formed between the bipolar membrane 2 and the first cation exchange membrane 3a, a deionization chamber 30 is formed between the first cation exchange membrane 3a and the second cation exchange membrane 3b, and an alkaline component chamber 40 is formed on the cathode 13 side of the second cation exchange membrane 3b. The alkaline component chamber 40 of each electrodialysis unit 5 is formed between the bipolar membrane 2 and the second cation exchange membrane 3b of the electrodialysis unit 5 adjacent to the cathode 13 side. An additional bipolar membrane 2a is provided between the alkaline component chamber 40 of the electrodialysis unit 5 closest to the cathode 13 and the cathode chamber 14.

[0015] One electrodialysis unit 5 is a combination of one bipolar membrane 2, one first cation exchange membrane 3a, and one second cation exchange membrane 3b, arranged with either the acid component compartment 20 or the deionization compartment 30 interposed therebetween. The number of electrodialysis units included in one recovery device can be determined so that the total area of ​​the bipolar membrane 2, first cation exchange membrane 3a, and second cation exchange membrane 3b included in the recovery device falls within a range set in consideration of the processing capacity of the recovery device, etc. The number of electrodialysis units 5 included in one electrodialysis cell 50 is not particularly limited, and may be, for example, 1 to 100, 1 to 10, or 10 to 100.

[0016] An electrolyte aqueous solution is stored in the electrolyte tank 15, an acid aqueous solution is stored in the acid component chamber tank 25, an organic salt solution is stored in the deionization chamber tank 35, and an alkaline aqueous solution is stored in the alkaline component chamber tank 45. The anode chamber 12, the cathode chamber 14, the electrolyte tank 15, and the piping connecting them form a circulation path C1 for circulating the electrolyte aqueous solution. The acid component chamber 20, the acid component chamber tank 25, and the piping connecting them form a circulation path C2 for circulating the acid aqueous solution. The deionization chamber 30, the deionization chamber tank 35, and the piping connecting them form a circulation path C3 for circulating an organic salt solution containing an organic salt. The alkaline component chamber 40, the alkaline component chamber tank 45, and the piping connecting them form a circulation path C4 for circulating the alkaline aqueous solution. A liquid delivery device such as a liquid delivery pump is usually provided on each circulation path.

[0017] The anode 11, cathode 13, bipolar membrane 2, first cation exchange membrane 3a, and second cation exchange membrane 3b may be those commonly used in electrodialysis. The first cation exchange membrane 3a and the second cation exchange membrane 3b may be the same as or different from each other. The additional bipolar membrane 2a may be the same as the bipolar membrane 2. The areas (effective areas) of the bipolar membrane 2, first cation exchange membrane 3a, and second cation exchange membrane 3b are not particularly limited, but may be, for example, 20 cm ２ 4m or more ２The area here means the area when each ion exchange membrane is viewed from the thickness direction. The volumes of the acid component chamber 20, the deionization chamber 30, and the alkaline component chamber 40 are not particularly limited, but may be, for example, 2 cm ３ Over 8m ３ The thicknesses of the bipolar membrane 2, the first cation exchange membrane 3a, and the second cation exchange membrane 3b are not particularly limited and may be, for example, 0.15 mm or more and 0.30 mm or less. The distance between the bipolar membrane 2 and the first cation exchange membrane 3a (the width of the acid component chamber 20) is not particularly limited and may be, for example, 1.0 mm or more and 30.0 mm or less. The distance between the first cation exchange membrane 3a and the second cation exchange membrane 3b (the width of the deionization chamber 30) is not particularly limited and may be, for example, 1.0 mm or more and 30.0 mm or less. The distance between the second cation exchange membrane 3b and the bipolar membrane 2 (the width of the alkaline component chamber) is not particularly limited and may be, for example, 1.0 mm or more and 30.0 mm or less. The widths of the anode chamber 12 and the cathode chamber 14 are not particularly limited and may be, for example, 1.0 mm or more and 30.0 mm or less.

[0018] By electrodialysis, in which an electrolyte aqueous solution is circulated through circulation path C1, an acid aqueous solution is circulated through circulation path C2, an alkaline aqueous solution is circulated through circulation path C4, and an organic acid salt aqueous solution is circulated through circulation path C3 while a voltage is applied between anode 11 and cathode 13, a solid containing free organic acids generated from the organic acid salts is precipitated in deionization chamber 30.

[0019] 2 is a schematic diagram showing an example of the action of electrodialysis in an electrodialysis unit. － Na ＋ This example shows an example of electrodialysis in which a solid containing a free organic acid XH is recovered from an aqueous solution of an organic acid salt containing XH. When a voltage is applied between the anode 11 and the cathode 13, protons H generated by ionization of water are released from the bipolar membrane 2. ＋ is supplied to the acid component chamber 20, and hydroxide ions OH generated by ionization of water are released from the bipolar membrane 2a. － is supplied to the alkaline component chamber 40. At the same time, protons H ＋ permeates the first cation exchange membrane 3a and moves to the deionization compartment 30, and the sodium cation Na＋ permeates the second cation exchange membrane 3b and moves to the alkaline component chamber 40. As a result, a solid containing the free organic acid XH at a concentration exceeding the saturation concentration is precipitated in the deionization chamber 30. The lower the solubility of the organic acid (free form) in water, the more efficiently the organic acid (free form) can be recovered or produced as a solid. － Since the organic acid in the free state does not substantially permeate the first cation exchange membrane 3a, clogging of the membrane due to precipitation of the organic acid in the free state within the membrane is suppressed. In addition, an alkaline component (e.g., sodium hydroxide (NaOH)) concentrated in the alkaline component chamber 40 can be produced or recovered. According to the method of the present disclosure, the alkaline component can also be produced or recovered efficiently.

[0020] The solid precipitated in the desalting compartment 30 can be a substance that is solid at 25°C. This solid may include crystals of a free organic acid. According to the method of the present disclosure, solid particles (or crystalline particles) containing organic acid crystals and having a relatively large particle size can be efficiently produced. A large particle size is advantageous in terms of easy disposal of waste liquid generated during the washing of recovered solids. A large particle size is also advantageous in terms of reducing production process costs, such as by shortening filtration and drying times during recovery and washing, thereby improving production efficiency. For example, the precipitated solid may include particles (particularly crystalline particles) having a long side length of 0.0001 mm or more. The upper limit of the long side length of the particles is not particularly limited, but may be approximately 1 mm. The long side length of the particles can be observed, for example, using an electron microscope (SEM). Here, the long side length refers to the maximum distance between two parallel lines sandwiching each particle in an electron microscope (SEM) image. Particles having a large length may be needle-shaped crystals. The needle-like crystals can be formed, for example, by terephthalic acid. The particle size can also be quantitatively measured using a laser diffraction particle size distribution analyzer or the like. D when expressed as a cumulative distribution of particles containing crystals of a free organic acid is ８０ The median diameter may be, for example, 10 μm or more and 1000 μm or less, or 100 μm or more and 1000 μm or less.

[0021] The organic acid salt contained in the organic acid salt aqueous solution supplied to the desalting compartment 30 is water-soluble. The organic acid salt may be a salt that forms a poorly water-soluble free organic acid. According to the findings of the present inventors, even if a poorly water-soluble free organic acid precipitates in the desalting compartment 30, highly efficient electrodialysis can be continued for a long period of time. The organic acid that constitutes the organic acid salt may be a compound that can form an ester compound or polyester by condensation or polycondensation with an alcohol compound (e.g., a diol). The organic acid is a compound having an acidic functional group, and there is no limit to the number or type of acidic functional groups contained in one molecule. The acidic functional group of the organic acid may be, for example, a carboxyl group, a phenol group, a sulfate group, a sulfo group, a sulfino group, a phosphate group, a phosphoryl group, or a phosphite group.

[0022] Examples of organic acids include, but are not limited to, carboxylic acids, sulfonic acids, sulfinic acids, organic phosphoric acids, and organic phosphorous acids. That is, the organic acid salt may be, for example, one or more selected from the group consisting of carboxylic acid salts, sulfonate salts, sulfinate salts, organic phosphate salts, and organic phosphites, or may be a carboxylic acid salt. The carboxylic acid constituting the carboxylic acid salt may be a monocarboxylic acid having one carboxy group, a dicarboxylic acid having two carboxy groups, or a tricarboxylic acid having three carboxy groups. In particular, the organic acid may be a dicarboxylic acid.

[0023] Examples of monocarboxylic acids constituting the carboxylate include, but are not limited to, benzoic acid, salicylic acid, ferulic acid, prostaglandin E1, and prostaglandin E2.

[0024] Examples of dicarboxylic acids constituting the carboxylate salt include, but are not limited to, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, ethylmalonic acid, adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, decalindicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorene acid, and 2,5-furandicarboxylic acid.

[0025] Examples of tricarboxylic acids constituting the carboxylate include, but are not limited to, trimesic acid and agaric acid.

[0026] Examples of sulfonic acids constituting the sulfonate salt include, but are not limited to, benzenesulfonic acid.

[0027] Examples of sulfinic acids constituting the sulfinic acid salt include, but are not particularly limited to, benzenesulfinic acid.

[0028] Examples of the organic phosphoric acid constituting the organic phosphate salt include, but are not limited to, benzenephosphonic acid. Examples of the organic phosphorous acid constituting the organic phosphite salt include, but are not limited to, benzenephosphinic acid.

[0029] Organic acid salts such as carboxylates, sulfonates, sulfinates, organic phosphates, and organic phosphites may be alkali metal salts, alkaline earth metal salts, ammonium salts, or combinations thereof. The alkali metal salts may be one or more selected from lithium salts, sodium salts, potassium salts, rubidium salts, cesium salts, and francium salts. The alkaline earth metal salts may be one or more selected from beryllium salts, magnesium salts, calcium salts, strontium salts, barium salts, and radium salts. The organic acid salts (e.g., carboxylates) may be, in particular, sodium salts, potassium salts, ammonium salts, or combinations thereof.

[0030] Specific examples of the carboxylate salt include sodium benzoate, potassium benzoate, ammonium benzoate, magnesium benzoate, calcium benzoate, sodium salicylate, potassium salicylate, ammonium salicylate, magnesium salicylate, calcium salicylate, disodium terephthalate, sodium hydrogen terephthalate, dipotassium terephthalate, potassium hydrogen terephthalate, ammonium hydrogen terephthalate, diammonium terephthalate, magnesium terephthalate, calcium terephthalate, disodium 2,5-furandicarboxylic acid, sodium hydrogen 2,5-furandicarboxylic acid, dipotassium 2,5-furandicarboxylic acid, potassium hydrogen 2,5-furandicarboxylic acid, ammonium hydrogen 2,5-furandicarboxylic acid, diammonium 2,5-furandicarboxylic acid, magnesium salt of 2,5-furandicarboxylic acid, and calcium salt of 2,5-furandicarboxylic acid.

[0031] Specific examples of sulfonates include sodium benzenesulfonate, potassium benzenesulfonate, ammonium benzenesulfonate, magnesium benzenesulfonate, and calcium benzenesulfonate.

[0032] Specific examples of sulfinic acid salts include sodium benzenesulfinic acid salt, potassium benzenesulfinic acid salt, ammonium benzenesulfinic acid salt, magnesium benzenesulfinic acid salt, and calcium benzenesulfinic acid salt.

[0033] Specific examples of the organic phosphate include sodium benzenephosphonate, potassium benzenephosphonate, ammonium benzenephosphonate, magnesium benzenephosphonate, and calcium benzenephosphonate.

[0034] Specific examples of organic phosphorous acids include sodium benzenephosphinate, potassium benzenephosphinate, ammonium benzenephosphinate, magnesium benzenephosphinate, and calcium benzenephosphinate.

[0035] The concentration of the organic acid salt in the aqueous solution of the organic acid salt (e.g., carboxylate, sulfonate, sulfinate, organic phosphate, or organic phosphite) to be subjected to electrodialysis can be adjusted arbitrarily within a range not exceeding the saturated concentration. The molar concentration of the organic acid salt in the aqueous solution of the organic acid salt at 25°C before the start of electrodialysis may be, for example, 0.001 M or more, or may be 1.0 M or less, 0.90 M or less, 0.80 M or less, 0.70 M or less, 0.60 M or less, 0.50 M or less, 0.40 M or less, 0.30 M or less, 0.20 M or less, 0.10 M or less, 0.09 M or less, 0.08 M or less, 0.07 M or less, 0.06 M or less, 0.05 M or less, 0.04 M or less, or 0.03 M or less. 1 M is 1 x 10 ３ mol / m ３ The molar concentration of the organic acid salt in the aqueous organic acid salt solution at 25° C. before the start of electrodialysis may be 0.001 M or more and 1.0 M or less.

[0036] The aqueous solution of an organic acid salt may further contain other components in addition to water and the organic acid salt. Examples of other components that can be contained in the aqueous solution of an organic acid salt include an inorganic salt as an electrolyte, an alkaline component (e.g., sodium hydroxide), and an alcohol compound (e.g., methanol, ethanol, ethylene glycol).

[0037] The inorganic salt may be a compound that exhibits strong acidity in the presence of protons, and such a compound is sometimes referred to as a conductor. When the organic acid salt aqueous solution contains such an inorganic salt, the pH of the organic acid salt aqueous solution is accelerated to decrease during electrodialysis, thereby increasing the efficiency of conversion from the organic acid salt to the organic acid (free form). In other words, the conversion from the organic acid salt to the organic acid (free form) can be completed in a shorter time. The inorganic salt that can be added to the organic acid salt aqueous solution may be, for example, a chloride, a sulfate, a nitrate, a phosphate, or a combination thereof. In particular, the inorganic salt may be one or more selected from sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, and sodium dihydrogen phosphate. The concentration of the inorganic salt in the aqueous solution of organic acid salt at 25°C before the start of electrodialysis may be, for example, 0.0005 M or more, 0.005 M or more, 0.01 M or more, 0.02 M or more, 0.03 M or more, 0.04 M or more, 0.05 M or more, 0.06 M or more, 0.07 M or more, 0.08 M or more, or 0.09 M or more, or may be 1.0 M or less, 0.90 M or less, 0.80 M or less, 0.70 M or less, 0.60 M or less, 0.50 M or less, 0.40 M or less, 0.30 M or less, 0.20 M or less, or 0.10 M or less. The concentration of the inorganic salt in the aqueous solution of organic acid salt at 25°C before the start of electrodialysis may be 0.0005 M or more and 1.0 M or less.

[0038] The aqueous electrolyte solution circulating through the circulation path C1 including the anode chamber 12 and the cathode chamber 14 may be an aqueous solution containing water and an electrolyte. The electrolyte is not particularly limited and may be, for example, an inorganic alkaline component (e.g., sodium hydroxide, potassium hydroxide) or an inorganic salt.

[0039] The acid aqueous solution circulating through the circulation path C2 including the acid component chamber 20 can be an acidic aqueous solution containing water and an acid. The acid in the acid aqueous solution can be an inorganic acid (e.g., sulfuric acid), an organic acid (e.g., methanesulfonic acid), or a combination thereof. The acid concentration at 25°C in the acid aqueous solution before the start of electrodialysis can be, for example, 0.001 M or more and 10.0 M or less, or 0.001 M or more and 2.0 M or less. The acid concentration at 25°C in the acid aqueous solution before the start of electrodialysis can be 0.005 M or more, 0.05 M or more, or 0.07 M or more, or 1.4 M or less, or 1.2 M or less.

[0040] The alkaline aqueous solution circulating through the circulation path C4 including the alkaline component chamber 40 may be an aqueous solution containing water and an alkaline component (e.g., sodium hydroxide). The concentration of the alkaline component in the alkaline aqueous solution at 25°C before the start of electrodialysis may be, for example, 0.001 M or more and 10.0 M or less, or 0.001 M or more and 2.0 M or less.

[0041] During electrodialysis, the temperatures of the electrolyte aqueous solution, the acidic aqueous solution, the organic acid salt aqueous solution, and the alkaline component aqueous solution may be, for example, 0° C. or higher and 95° C. or lower, or 5° C. or higher and 70° C. or lower. The voltage applied between the anode 11 and the cathode 13 is not particularly limited, and may be, for example, 1 V or higher and 300 V or lower, 10 V or higher and 300 V or lower, 15 V or higher and 300 V or lower, or 30 V or higher and 300 V or lower.

[0042] The aqueous solution of organic acid salt treated by the above-exemplified method may be an aqueous solution formed by depolymerization of a polyester or the like. In this case, the polyester or the like can be efficiently recycled by a method including forming an aqueous solution of organic acid salt containing an organic acid salt (e.g., a dicarboxylate) by depolymerization of a polyester or the like, and producing or recovering an organic acid (e.g., a dicarboxylic acid) from the aqueous solution of organic acid salt by a method according to the present disclosure. Examples of polyesters to be recycled include polycarboxylate esters, polysulfate esters, and polyphosphate esters. The method according to the present disclosure may also be applied to the recycling of polyethylene terephthalate.

[0043] The present invention is not limited to the following examples.

[0044] 1. Equipment and materials The following electrodialysis equipment and ion exchange membrane (effective membrane area: 550 cm) ２ An electrodialysis device, ASILYZER EX3B (product name, manufactured by ASTOM Corporation), and a bipolar membrane, NEOSEPTA BPU (product name, effective membrane area 550 cm), were used. ２ , manufactured by Astom Corporation) Cation exchange membrane Neocepta CBM (product name, effective membrane area 550 cm ２ , manufactured by Astom Corporation) Anion exchange membrane Neosepta AHA (product name, effective membrane area 550 cm ２ , manufactured by Astom Co., Ltd.)

[0045] 2. Electrodialysis Test Comparative Example 1 An electrodialysis apparatus having the configuration shown in Fig. 22 was prepared as an organic acid recovery apparatus. In the recovery apparatus 101 shown in Fig. 22, a total of ten sets of ion exchange membranes, each set consisting of a bipolar membrane 2, an anion exchange membrane 4, and a cation exchange membrane 3, were arranged in order from the anode 11 side toward the cathode 13 side between an anode chamber 12 provided with an anode 11 and a cathode chamber 14 provided with a cathode 13. A bipolar membrane 2 was also arranged between the cation exchange membrane 3 located closest to the cathode 13 and the cathode 13. An acid component chamber 20 was formed between the bipolar membrane 2 and the anion exchange membrane 4, a deionization chamber 30 was formed between the anion exchange membrane 4 and the cation exchange membrane 3, and an alkali component chamber 40 was formed between the cation exchange membrane 3 and the bipolar membrane 2 on the cathode 13 side. Ten electrodialysis units 5, each consisting of three compartments, an acid component compartment 20, a deionization compartment 30 and an alkaline component compartment 40, were arranged in series between the anode 11 and the cathode 13.

[0046] 1000 mL of a 0.5 M NaOH aqueous solution was circulated as an electrolyte aqueous solution through the circulation path C1 including the anode chamber 12 and the cathode chamber 14, and 1000 mL of a 0.1 M H O ... ２ SO ４500 mL of an aqueous solution was circulated, 500 mL of a 0.1 M NaOH aqueous solution was circulated through circulation path C4 including alkaline component chamber 40, and 500 mL of a 0.5 M disodium terephthalate aqueous solution (containing 10% by volume of methanol, 0.5 M ethylene glycol, and 0.1 M NaOH) was circulated through circulation path C3 including desalting chamber 30. In this state, a voltage of 35 V was applied between anode 11 and cathode 13.

[0047] Immediately after the voltage was applied, the current value dropped to about 0.1 A, and electrodialysis did not substantially proceed. The anion exchange membrane 4 removed from the recovery device 101 was observed with a scanning electron microscope. Figure 3(a) is a scanning electron microscope image of the removed anion exchange membrane (magnification (at the time of observation): 30x). The liquid-contacting portion is the portion that had been in contact with the aqueous disodium terephthalate solution, and the non-liquid-contacting portion is the portion that had not been in contact with the aqueous disodium terephthalate solution. Figure 3(b) is an enlarged view of the non-liquid-contacting portion of the anion exchange membrane (magnification (at the time of observation): 500x). Figure 4 is a scanning electron microscope image of the liquid-contacting portion of the anion exchange membrane, with (a) being an enlarged view at 500x (at the time of observation) and (b) being an enlarged view at 1500x (at the time of observation). It was observed that crystals containing terephthalic acid had precipitated on and within the liquid-contacting portion of the anion exchange membrane, resulting in clogging of the membrane. This was thought to be because terephthalic acid ions were converted to a free form while passing through the anion exchange membrane 4 and precipitated inside the membrane. Figure 5 shows the infrared absorption spectra of the liquid-contacting and non-liquid-contacting portions of the anion exchange membrane, the differential infrared absorption spectrum between the liquid-contacting and non-liquid-contacting portions, and the infrared absorption spectra of free terephthalic acid and disodium terephthalate. The differential infrared absorption spectrum of the liquid-contacting and non-liquid-contacting portions of the anion exchange membrane 4 closely matched the spectrum of free terephthalic acid. This also supported the clogging of the membrane due to the precipitation of free terephthalic acid. From the above, it was confirmed that it was difficult to perform electrodialysis operation according to conventional methods with the membrane configuration of Comparative Example 1.

[0048] Example 1 An electrodialysis apparatus having the configuration shown in Figure 1 was prepared. In the recovery device 100 shown in Figure 1, a bipolar membrane 2, a first cation exchange membrane 3a, and a second cation exchange membrane 3b were arranged as a set of electrodialysis units 5 between an anode chamber 12 equipped with an anode 11 and a cathode chamber 14 equipped with a cathode 13. A total of ten sets of ion exchange membranes (electrodialysis units) were arranged in order from the anode 11 side toward the cathode 13 side. An additional bipolar membrane 2a was arranged between the cathode 13 and the second cation exchange membrane 3b constituting the electrodialysis unit 5 located closest to the cathode 13. 1000 mL of a 0.5 M NaOH aqueous solution was circulated as an aqueous electrolyte solution through a circulation path C1 including the anode chamber 12 and the cathode chamber 14, and 0.01 M H O ... ２ SO ４ 500 mL of the aqueous solution was circulated, 500 mL of a 0.01 M NaOH aqueous solution was circulated through the circulation path C4 including the alkaline component chamber 40, and 500 mL of a 0.01 M disodium terephthalate (Na ２ 500 mL of an aqueous solution of terephthalic acid (TPA) (containing 0.01 M NaOH) was circulated. Under this condition, a voltage of 15 V was applied between the anode 11 and the cathode 13, and electrodialysis was performed. Even after 60 minutes of current application, no membrane blockage occurred, and crystals precipitated in the desalting compartment 30. This was thought to be due to the inability of terephthalic acid ions to penetrate the cation exchange membrane. Before and during electrodialysis, the pH and conductivity of the solution in the desalting compartment, the current flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalic acid ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis.

[0049] Example 2 A 0.01M aqueous solution of disodium terephthalate (containing 0.01M NaOH) was circulated through the circulation path C3 including the desalting chamber 30. ２ SO ４Electrodialysis was performed under the same conditions as in Example 1, except that sodium sulfate (sodium sulfate) was added to a concentration of 0.01 M. No membrane clogging occurred, and crystals precipitated in the desalting compartment 30. The first cation exchange membrane 3a removed from the recovery device 100 was observed with a scanning electron microscope. FIG. 6 shows scanning electron microscope images of the non-liquid-contacting portion of the first cation exchange membrane that was not in contact with the disodium terephthalate aqueous solution, with (a) being an enlarged view at 50x (at the time of observation) and (b) being an enlarged view at 1000x (at the time of observation). FIG. 7 shows scanning electron microscope images of the liquid-contacting portion of the first cation exchange membrane that was in contact with the disodium terephthalate aqueous solution, with (a) being an enlarged view at 50x (at the time of observation) and (b) being an enlarged view at 1000x (at the time of observation). No precipitation of terephthalic acid was observed in the membrane, even in the liquid-contacting portion. FIG. 8 shows infrared absorption spectra of the liquid-contacting and non-liquid-contacting portions of the first cation exchange membrane, the differential infrared absorption spectrum between the liquid-contacting and non-liquid-contacting portions, and the infrared absorption spectra of free terephthalic acid and disodium terephthalate. The differential infrared absorption spectrum of the liquid-contacting and non-liquid-contacting portions of the first cation exchange membrane 3a did not suggest the presence of either free terephthalic acid or disodium terephthalate. Before and during electrodialysis, the pH and conductivity of the liquid in the desalting compartment, the current flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis.

[0050] Results of Examples 1 and 2 Table 1 shows the electrodialysis conditions for Examples 1 and 2. FIG. 9 is a graph showing the relationship between the pH and conductivity of the desalting compartment and the energization time in Example 1, and FIG. 10 is a graph showing the relationship between the pH and conductivity of the desalting compartment and the energization time in Example 2. FIG. 11 is a graph showing the relationship between the proportion of remaining disodium terephthalate (residual rate) estimated from UV absorbance (240 nm) and the energization time. FIG. 12 is a graph showing the relationship between the current value flowing through the electrodialysis device and the energization time. In Example 1, the residual rate of disodium terephthalate decreased to 65% after 60 minutes of energization. In Example 2, the residual rate of disodium terephthalate decreased to almost 0% about 10 minutes after the start of electrodialysis, and substantially all of the terephthalate crystallized in the desalting compartment as free terephthalic acid. In the case of Example 1, as shown in Figure 9, after the start of electrodialysis, the pH stagnated at about 5 to 6 and the conductivity decreased, which is thought to have resulted in a relatively gradual decrease in the residual rate of disodium terephthalate. In the case of Example 2, the pH rapidly decreased to 3 or less about 10 minutes after the start of electrodialysis, and the conductivity decreased to 3 mS / cm, and then began to increase again. In this way, it was thought that the addition of a conductor promoted the decrease in pH and maintained high conductivity for a long period of time, thereby enabling highly efficient recovery of free terephthalic acid.

[0051]

[0052] Crystals were recovered by filtration from the liquid in the desalting chamber of Example 2. The recovered crystals were confirmed to be crystals of free terephthalic acid by infrared absorption spectroscopy. Figure 13 is a scanning electron microscope image of the crystals recovered in Example 2. It was revealed that large needle-shaped crystals with a maximum long side length (particle size) of 0.1 mm were obtained.

[0053] Example 3 A 0.01M aqueous solution of disodium terephthalate (containing 0.01M NaOH) was circulated through the circulation path C3 including the desalting chamber 30. ２ SO ４Electrodialysis was performed under the same conditions as in Example 1, except that terephthalate ion was added to a concentration of 0.001 M, 0.005 M, 0.01 M, 0.02 M, 0.05 M, or 0.1 M. Under all conditions, membrane clogging did not occur, and crystals precipitated in the desalting compartment 30. Before the start of electrodialysis and during electrodialysis, the pH and conductivity of the liquid in the desalting compartment, the current flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis.

[0054] Results of Example 3 Table 2 shows the electrodialysis conditions for Example 3. FIG. 14 is a graph showing the relationship between the pH of the desalting compartment and the energization time. FIG. 15 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time. FIG. 16 is a graph showing the relationship between the percentage of remaining disodium terephthalate (residual rate) estimated from UV absorbance (240 nm) and the energization time. FIG. 17 is a graph showing the relationship between the current value flowing through the electrodialysis device and the energization time. These graphs suggest that the higher the conductor concentration, the greater the effect of promoting the pH reduction in the desalting compartment, the higher the conductivity, and the higher the conversion efficiency of disodium terephthalate to free terephthalic acid. However, even with the lowest conductor concentration of 0.001 M, nearly 100% conversion of disodium terephthalate to terephthalic acid (free form) was achieved within 60 minutes of energization.

[0055]

[0056] Example 4 Electrodialysis was performed under the same conditions as in Example 1, except that NaCl (sodium chloride) was added as a conductor to a concentration of 0.01 M, 0.05 M, or 0.1 M to a 0.01 M disodium terephthalate aqueous solution (containing 0.01 M NaOH) circulated through circulation path C3, including deionization compartment 30. No membrane clogging occurred, and crystals precipitated in deionization compartment 30. Before and during electrodialysis, the pH and conductivity of the solution in the deionization compartment, the current flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis.

[0057] Results of Example 4 Table 3 shows the conditions for electrodialysis in Example 4. Fig. 18 is a graph showing the relationship between the pH of the deionization compartment and the energization time in Example 4. Fig. 19 is a graph showing the relationship between the conductivity of the deionization compartment and the energization time. Fig. 20 is a graph showing the relationship between the proportion of remaining disodium terephthalate (residual rate) estimated from UV absorbance (240 nm) and the energization time. Fig. 21 is a graph showing the relationship between the current value flowing through the electrodialysis device and the energization time. As can be seen from these graphs, even when NaCl was used as the conductor, Na ２ SO ４ It was confirmed that similar results were obtained when the conductor was used. The results of Examples 3 and 4 suggest that when the pH of the desalting compartment 30 is reduced to 4 or less by adding a conductor, the conversion efficiency from disodium terephthalate to terephthalic acid (free form) increases to nearly 100%.

[0058]

[0059] Example 5: The circulation path C3 including the desalting chamber 30 was charged with NaH ２ P.O. ４ (sodium dihydrogen phosphate) or NaNO ３ Electrodialysis was carried out under the same conditions as in Example 1, except that only sodium nitrate was circulated at the concentrations shown in Table 4.

[0060]

[0061] The pH of the deionization compartment after 60 minutes of current application is shown in Table 1. As shown in Table 1, under all conditions, the pH of the deionization compartment was reduced to 4 or less by adding conductor. ２ P.O. ４ or NaNO ３ It was also suggested that the cations of ...

[0062] Example 6 The concentration of disodium terephthalate in the aqueous solution of disodium terephthalate circulated through the circulation path C3 was changed to 0.03 M (containing 0.01 M NaOH), and Na was added as a conductor to the aqueous solution of disodium terephthalate. ２ SO ４ Electrodialysis was performed under the same conditions as in Example 1, except that HCl was added to a concentration of 0.02 M. Table 5 shows the electrodialysis conditions for Example 6. No membrane clogging occurred, and crystals precipitated in the desalting compartment 30. Before the start of electrodialysis and during electrodialysis, the pH and conductivity of the liquid in the desalting compartment, the current flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis.

[0063]

[0064]

[0065] The measurement results are shown in Table 6. After 30 minutes of application of the current, disodium terephthalate was converted to terephthalic acid (free form) at almost 100%, and crystallization occurred.

[0066] Example 7 H circulated through circulation path C2 ２ SO ４The concentration of the aqueous solution was changed to 0.1 M, the concentration of disodium terephthalate in the aqueous disodium terephthalate solution circulated through circulation path C3 was changed to 0.1 M, the amount of the aqueous disodium terephthalate solution was changed to 200 mL, NaOH was added to the aqueous disodium terephthalate solution to a concentration of 0.01 M, and NaOH was added to the aqueous disodium terephthalate solution. ２ SO ４ An electrodialysis test was performed under the same conditions as in Example 1, except that 0.02 M of conductor was added and the voltage applied between the anode 11 and the cathode 13 was changed stepwise as shown in Table 8. Table 7 shows the electrodialysis conditions for Example 7. No membrane blockage occurred, and crystals precipitated in the desalting compartment 30. Before the start of electrodialysis and during electrodialysis, the pH and conductivity of the solution in the desalting compartment, the current flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis.

[0067]

[0068]

[0069] The measurement results are shown in Table 8. When the voltage was increased to 35.1 V after 30 minutes of current application, and current application was continued, the pH decreased, and disodium terephthalate was converted to terephthalic acid (free form) at almost 100%, followed by crystallization.

[0070] Example 8 H circulated through circulation path C2 ２ SO ４ The concentration of the aqueous solution was changed to 1M, and H ２ SO ４ The amount of the aqueous solution was changed to 1000 mL, the concentration of disodium terephthalate in the aqueous disodium terephthalate solution circulated through the circulation path C3 was changed to 0.4 M, the amount of the aqueous disodium terephthalate solution was changed to 100 mL, NaOH was added to the aqueous disodium terephthalate solution so that the concentration became 0.01 M, and Na ２ SO ４An electrodialysis test was performed under the same conditions as in Example 1, except that 0.02 M of conductor was added and the voltage applied between the anode 11 and the cathode 13 was changed stepwise as shown in Table 10. Table 9 shows the electrodialysis conditions for Example 8. No membrane blockage occurred, and crystals precipitated in the desalting compartment 30. Before the start of electrodialysis and during electrodialysis, the pH and conductivity of the solution in the desalting compartment, the current flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis.

[0071]

[0072]

[0073] The measurement results are shown in Table 10. When the voltage was increased to 35.1 V after 30 minutes of current application, and current application was continued, the pH decreased, and disodium terephthalate was converted to terephthalic acid at almost 100%, followed by crystallization.

[0074] Example 9 The concentration of disodium terephthalate in the aqueous solution of disodium terephthalate circulated through the circulation path C3 was changed to 0.1 M, the amount of the aqueous solution of disodium terephthalate was changed to 200 mL, NaOH was added to the aqueous solution of disodium terephthalate to a concentration of 0.025 M, and NaOH was added to the aqueous solution of disodium terephthalate. ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 1, except that (conductor) was added to a concentration of 0.05 M and the voltage applied between the anode 11 and the cathode 13 was set to 35 V.

[0075] Example 10 H circulated through circulation path C2 ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 9, except that the concentration of the aqueous solution was changed to 0.1M.

[0076] Example 11 H circulated through circulation path C2 ２ SO ４The concentration of the aqueous solution was changed to 0.1M, and the Na in the disodium terephthalate aqueous solution was ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 9, except that the concentration of the conductor was changed to 0.1M.

[0077] Results of Examples 9 to 11 Table 11 shows the conditions for the electrodialysis tests of Examples 9 to 11. In the electrodialysis tests of Examples 9 to 11, no membrane clogging occurred, and crystals precipitated in the desalting compartment 30. Before the start of electrodialysis and during electrodialysis, the pH and conductivity of the liquid in the desalting compartment, the current value flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis. Figure 23 is a graph showing the relationship between the pH of the desalting compartment and the energization time. Figure 24 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time. Figure 25 is a graph showing the relationship between the percentage of remaining disodium terephthalate (residual rate) and the energization time. Figure 26 is a graph showing the relationship between the current value flowing through the electrodialysis device and the energization time. As shown in the graph of Figure 25, 100% conversion of disodium terephthalate to terephthalic acid (free form) was achieved in a short time under all conditions. ２ SO ４ It was confirmed that the higher the concentration of the aqueous solution, the higher the conversion efficiency from disodium terephthalate to free terephthalic acid. From a comparison of Examples 9 to 11, it was confirmed that the higher the concentration of the conductor in the desalting compartment 30, the more accelerated the decrease in pH in the desalting compartment. When the conversion efficiency from disodium terephthalate to free terephthalic acid is high, the crystallization of terephthalic acid can be completed in a shorter time.

[0078]

[0079] Example 12 H circulated through circulation path C2 ２ SO ４The concentration of the aqueous solution was changed to 1 M, the concentration of disodium terephthalate in the aqueous disodium terephthalate solution circulated through circulation path C3 was changed to 0.4 M, the amount of the aqueous disodium terephthalate solution was changed to 100 mL, NaOH was added to the aqueous disodium terephthalate solution so that the concentration became 0.1 M, and NaOH was added to the aqueous disodium terephthalate solution. ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 1, except that the concentration of was 0.02 M and the voltage applied between the anode 11 and the cathode 13 was set to 35 V.

[0080] Example 13 Na in the aqueous disodium terephthalate solution circulated through circulation route C3 ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 12, except that the concentration of was changed to 0.05M.

[0081] Example 14 Na in the aqueous disodium terephthalate solution circulated through circulation route C3 ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 12, except that the concentration of was changed to 0.1M.

[0082] Results of Examples 12 to 14 Table 12 shows the conditions for the electrodialysis tests of Examples 12 to 14. In the electrodialysis tests of Examples 12 to 14, no membrane clogging occurred, and crystals precipitated in the desalting compartment 30. Before and during electrodialysis, the pH and conductivity of the solution in the desalting compartment, the current value flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis. Figure 27 is a graph showing the relationship between the pH of the desalting compartment and the energization time. Figure 28 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time. Figure 29 is a graph showing the relationship between the percentage of remaining disodium terephthalate (residual rate) and the energization time. Figure 30 is a graph showing the relationship between the current value flowing through the electrodialysis device and the energization time. These graphs confirm that the higher the conductor concentration, the more accelerated the decrease in pH in the desalting compartment and the higher the conversion efficiency from disodium terephthalate to free terephthalic acid. In other words, it was suggested that the crystallization of terephthalic acid was completed in a shorter time.

[0083]

[0084] Example 15 H circulated through circulation path C2 ２ SO ４ The concentration of the aqueous solution was changed to 0.1 M, the concentration of disodium terephthalate in the aqueous disodium terephthalate solution circulated through circulation path C3 was changed to 0.1 M, the amount of the aqueous disodium terephthalate solution was changed to 200 mL, NaOH was added to the aqueous disodium terephthalate solution to a concentration of 0.1 M, and NaOH was added to the aqueous disodium terephthalate solution. ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 1, except that the concentration of

[0085] Example 16 Na in the aqueous disodium terephthalate solution circulated through circulation route C3 ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 15, except that the concentration of was changed to 0.05M.

[0086] Example 17 Na in the aqueous disodium terephthalate solution circulated through circulation route C3 ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 15, except that the concentration of was changed to 0.1M.

[0087] Results of Examples 15-17 Table 13 shows the conditions for the electrodialysis tests of Examples 15-17. In the electrodialysis tests of Examples 15-17, no membrane clogging occurred, and crystals precipitated in the desalting compartment 30. Before and during electrodialysis, the pH and conductivity of the solution in the desalting compartment, the current value flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis. Figure 31 is a graph showing the relationship between the pH of the desalting compartment and the energization time. Figure 32 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time. Figure 33 is a graph showing the relationship between the percentage of remaining disodium terephthalate (residual rate) and the energization time. Figure 34 is a graph showing the relationship between the current value flowing through the electrodialysis device and the energization time. These graphs confirm that the higher the conductor concentration, the more accelerated the decrease in pH in the desalting compartment and the higher the conversion efficiency from disodium terephthalate to free terephthalic acid. In other words, it was suggested that the crystallization of terephthalic acid was completed in a shorter time.

[0088]

[0089] Example 18 H circulated through circulation path C2 ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 16, except that the concentration of the aqueous solution was changed to 0.01M.

[0090] Example 19 H circulated through circulation path C2 ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 16, except that the concentration of the aqueous solution was changed to 1M.

[0091] Results of Examples 16, 18, and 19 Table 14 shows the conditions for the electrodialysis tests of Examples 16, 18, and 19. The results of Example 16 are as described above under "Results of Examples 15 to 17." In the electrodialysis tests of Examples 18 and 19, no membrane clogging occurred, and crystals precipitated in the desalting compartment 30. Before and during electrodialysis, the pH and conductivity of the solution in the desalting compartment, the current flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis. Figure 35 is a graph showing the relationship between the pH of the desalting compartment and the energization time. Figure 36 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time. Fig. 37 is a graph showing the relationship between the proportion of remaining disodium terephthalate (residual rate) and the energization time. Fig. 38 is a graph showing the relationship between the value of the current flowing through the electrodialysis device and the energization time. From these graphs, it can be seen that the H ２ SO ４ It was confirmed that the higher the concentration of the aqueous solution, the more accelerated the decrease in pH in the desalting compartment and the higher the conversion efficiency from disodium terephthalate to free terephthalic acid. In other words, it was suggested that the crystallization of terephthalic acid was completed in a shorter time.

[0092]

[0093] Example 20 An electrodialysis test was carried out under the same conditions as in Example 16, except that the voltage applied between the anode 11 and the cathode 13 was set to 20V.

[0094] Example 21 An electrodialysis test was carried out under the same conditions as in Example 16, except that the voltage applied between the anode 11 and the cathode 13 was set to 28 V.

[0095] Results of Examples 16, 20, and 21 Table 15 shows the conditions for the electrodialysis tests of Examples 16, 20, and 21. The results of Example 16 are as described above under "Results of Examples 15 to 17." In the electrodialysis tests of Examples 20 and 21, no membrane blockage occurred, and crystals precipitated in the desalting compartment 30. Before and during electrodialysis, the pH and conductivity of the solution in the desalting compartment, the current flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis. Figure 39 is a graph showing the relationship between the pH of the desalting compartment and the energization time. Figure 40 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time. Fig. 41 is a graph showing the relationship between the proportion of remaining disodium terephthalate (residual rate) and current application time. Fig. 42 is a graph showing the relationship between the value of the current flowing through the electrodialysis device and current application time. These graphs confirm that when a constant voltage is applied between the anode 11 and the cathode 13, the higher the applied voltage, the more rapidly the pH in the desalting compartment decreases, and the higher the conversion efficiency from disodium terephthalate to free terephthalic acid. This suggests that crystallization of terephthalic acid is completed in a shorter time.

[0096]

[0097] In the electrodialysis of Example 20, the NaOH aqueous solution circulating through the circulation path C4 was found to contain hydroxide ions (OH － The concentration of hydroxide ions was calculated by acid-base titration. The amount of hydroxide ions increased by electrodialysis was calculated from the volume of the NaOH aqueous solution and the hydroxide ion concentration, and was found to be 81.4 mmol. The increase in hydroxide ions was due to the disodium terephthalate, NaOH, and Na contained in the disodium terephthalate aqueous solution before the application of current for electrodialysis. ２ SO ４ Sodium ions (Na ＋ ) moves to the alkaline component chamber 40 by electrodialysis, and hydroxide ions (OH －This is because NaOH was produced in the alkaline component chamber 40 due to the electrolysis. The aqueous solution of disodium terephthalate before the application of current for electrodialysis contained disodium terephthalate, NaOH, and Na ２ SO ４ Sodium ions (Na ＋ ), the sodium ions (Na ＋ ) moved to the alkaline component chamber 40 and was converted to NaOH. That is, it was confirmed that free terephthalic acid crystals were produced and recovered in the deionization chamber 30 by electrodialysis, and the sodium ions (Na ＋ ) showed that NaOH can be produced and recovered in the alkaline component chamber 40.

[0098] Example 22: Depolymerization of Polyethylene Terephthalate (PET) A granular PET sample was prepared by washing and flaking collected waste PET bottles and freeze-pulverizing them. 125 g of methanol was placed in a benchtop kneader (PNV-1, Irie Shokai Co., Ltd.). 114 g (2.85 mol) of sodium hydroxide and 250 g of the PET sample (amount of substance based on repeating units: 1.30 mol) were added to the methanol in the kneader at room temperature (27°C) to form a powdery mixture containing the PET sample, sodium hydroxide, and methanol. The resulting powdery mixture was kneaded at a rotation speed of 50 rpm for 9 minutes without heating. Kneading was stopped, and the disodium terephthalate and ethylene glycol produced by the depolymerization reaction were dissolved in 2.3 L of water. The aqueous solution containing the solids was filtered to recover the solids (unreacted PET sample) and the filtrate (depolymerized solution).

[0099] Depolymerization rate The solid matter recovered from the aqueous solution was dried by heating in an oven at 100°C for 12 hours or more. The mass W of the solid matter (unreacted PET sample) after drying was ｆｉｎ The amount (g) of the polymer was measured. The depolymerization rate was calculated using the following formula. The depolymerization rate was 99.4%. Depolymerization rate (%) = [(W ｉｎｔ -W ｆｉｎ ) / W ｉｎｔ]×100 In the above formula, W ｉｎｔ is the mass (g) of the PET sample subjected to depolymerization.

[0100] Terephthalic Acid Conversion Rate A portion of the depolymerized solution, which was the filtrate obtained by removing solids from the aqueous solution after depolymerization, was diluted 250-fold with a diluent (1 N HCl aqueous solution: isopropanol = 1:9 (v / v)) to obtain a sample solution for analysis. The obtained sample solution was analyzed by HPLC under the following conditions to quantify the terephthalic acid in the depolymerized solution. Column: L-column 2 ODS 2.1 mm × 150 mm, particle size 2 μm (Chemicals Evaluation and Research Institute, Japan) Column temperature: 35°C Mobile phase A: 0.1% acetic acid containing water Mobile phase B: 0.1% acetic acid containing acetonitrile Flow rate: 0.2 mL / min Linear gradient: 15% B (0 min) → 80% B (26 min) Detector: photodiode array (wavelength 190-600 nm) Based on the HPLC quantitative results, the terephthalic acid conversion rate was calculated using the following formula. Terephthalic acid conversion rate (%) = [(W ｔｐａ / 166) / (W ｉｎｔ / 192)] × 100 In the above formula, W ｉｎｔ is the mass (g) of the PET sample subjected to depolymerization, and W ｔｐａ is the mass (g) of terephthalic acid produced by depolymerization in free form, calculated based on the quantitative results of HPLC. 166 is the molecular weight of terephthalic acid, and 192 is the repeating unit of PET (C １０ H ８ O ４ ) is the formula weight of the terephthalic acid. The terephthalic acid conversion rate was 101%. The concentration of disodium terephthalate in the depolymerization solution was 0.54 M. The solution contained 0.54 M of ethylene glycol (EG) produced by the depolymerization, 0.1 M of excess NaOH not consumed in the depolymerization reaction, and 1.62 M of methanol (MeOH).

[0101] Electrodialysis test The depolymerized solution, which is the filtrate obtained by removing solids from the aqueous solution after depolymerization, was diluted with water to prepare a depolymerized solution for electrodialysis with a disodium terephthalate concentration of 0.1 M. ２ SO ４was added to a concentration of 0.05 M. 200 mL of the depolymerization solution for electrodialysis was circulated through the circulation line C3, and H ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 1, except that the concentration of the aqueous solution was changed to 0.1M.

[0102] Example 23 The depolymerized solution obtained in Example 22 was diluted with water to prepare a depolymerized solution for electrodialysis, with the concentration of disodium terephthalate adjusted to 0.4 M. ２ SO ４ was added so that the concentration became 0.05 M. 100 mL of the depolymerization solution for electrodialysis was circulated through the circulation line C3, and H ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 1, except that the concentration of the aqueous solution was changed to 1 M and the voltage applied between the anode 11 and the cathode 13 was set to 35 V.

[0103] Example 24 The depolymerization solution obtained in Example 22 was added with Na ２ SO ４ was added to the circulation line C3 so as to have a concentration of 0.2 M, thereby preparing a depolymerization solution for electrodialysis. 100 mL of the depolymerization solution for electrodialysis was circulated through the circulation line C3, and H ２ SO ４ An electrodialysis test was carried out under the same conditions as in Example 1, except that the concentration of the aqueous solution was changed to 1 M and the voltage applied between the anode 11 and the cathode 13 was set to 35 V.

[0104] Results of Examples 22, 23, and 24 Table 16 shows the conditions for the electrodialysis tests of Examples 22, 23, and 24. In the electrodialysis tests of Examples 22, 23, and 24, no membrane clogging occurred, and crystals precipitated in the desalting compartment 30. Before the start of electrodialysis and during electrodialysis, the pH and conductivity of the solution in the desalting compartment, the current value flowing through the electrodialysis device, and the UV absorbance (240 nm) of the supernatant were measured. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of the UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis. Figure 43 is a graph showing the relationship between the pH of the desalting compartment and the energization time in Example 22. Figure 44 is a graph showing the relationship between the conductivity of the desalting compartment and the energization time in Example 22. FIG. 45 is a graph showing the relationship between the proportion of remaining disodium terephthalate (residual rate) and current flow time in Example 22. FIG. 46 is a graph showing the relationship between the value of current flowing through the electrodialysis device and current flow time in Example 22. FIG. 47 is a graph showing the relationship between the pH of the desalting compartment and current flow time in Example 23. FIG. 48 is a graph showing the relationship between the conductivity of the desalting compartment and current flow time in Example 23. FIG. 49 is a graph showing the relationship between the proportion of remaining disodium terephthalate (residual rate) and current flow time in Example 23. FIG. 50 is a graph showing the relationship between the value of current flowing through the electrodialysis device and current flow time in Example 23. FIG. 51 is a graph showing the relationship between the pH of the desalting compartment and current flow time in Example 24. FIG. 52 is a graph showing the relationship between the conductivity of the desalting compartment and current flow time in Example 24. FIG. 53 is a graph showing the relationship between the proportion of remaining disodium terephthalate (residual rate) and current flow time in Example 24. 54 is a graph showing the relationship between the current value flowing through the electrodialysis device and the current application time in Example 24. It was confirmed that disodium terephthalate contained in the depolymerization solution obtained by alkaline depolymerization of PET can be recovered as free terephthalic acid by crystallization. The obtained terephthalic acid (free form) can be used as a raw material for polyester.

[0105]

[0106] Example 25 H circulated through circulation path C2２ SO ４ An electrodialysis test was conducted under the same conditions as in Example 13, except that the amount of aqueous solution was changed to 1000 mL. No membrane clogging occurred, and crystals precipitated in the desalting compartment 30. The concentration of terephthalate ions remaining in the supernatant was calculated from the ratio of UV absorbance (240 nm) at each measurement time after the start of electrodialysis to the UV absorbance (240 nm) before the start of electrodialysis. After 90 minutes of current application, the terephthalate ions remaining in the supernatant decreased to approximately 10%, with 90% being converted to free terephthalic acid and precipitated as crystals. An aqueous solution containing terephthalic acid crystals was recovered from circulation path C3. The particle size distribution of the obtained terephthalic acid crystals was measured using a laser diffraction particle size distribution analyzer using a scattering method. From the obtained particle size distribution, the 20% particle size (D ２０ median diameter), 50% particle diameter (D ５０ median diameter) and 80% particle diameter (D ８０ The results are shown in Table 17.

[0107] Comparative Example 2: 10 mL of a 0.4 M aqueous solution of disodium terephthalate (containing 0.1 M NaOH) was diluted with 30 mL of water, and then 1 M H ２ SO ４ The aqueous solution was added dropwise to crystallize free terephthalic acid. When the pH was reduced to 2 or less, the particle size distribution of the resulting terephthalic acid crystals was measured in the same manner as in Example 25. The results are shown in Table 17.

[0108]

[0109] As shown in Table 17, it was confirmed that the crystals of terephthalic acid obtained by the method of the example had a significantly larger size than the crystals obtained by the general neutralization crystallization method.

[0110] 2, 2a...bipolar membrane, 3a...first cation exchange membrane, 3b...second cation exchange membrane, 4...anion exchange membrane, 5...electrodialysis unit, 11...anode, 13...cathode, 15...electrolyte tank, 20...acid component chamber, 25...tank for acid component chamber, 30...demineralization chamber, 35...tank for demineralization chamber, 40...alkaline component chamber, 45...tank for alkaline component chamber, 50...electrodialysis cell, 100, 101...recovery device, C1, C2, C3, C4...circulation path.

Claims

1. A method for producing an organic acid, comprising: preparing an electrodialysis cell having an anode, a cathode and one or more electrodialysis units disposed therebetween, the electrodialysis units having a bipolar membrane, a first cation exchange membrane and a second cation exchange membrane arranged in this order from the anode side to the cathode side, an acid component chamber being formed between the bipolar membrane and the first cation exchange membrane, a desalting chamber being formed between the first cation exchange membrane and the second cation exchange membrane, and an alkaline component chamber being formed on the cathode side of the second cation exchange membrane; and circulating an acid aqueous solution through a circulation path including the acid component chamber, an alkaline aqueous solution through a circulation path including the alkaline component chamber, and an organic acid salt aqueous solution including an organic acid salt through a circulation path including the desalting chamber, while applying a voltage between the anode and the cathode, thereby precipitating a solid including a free organic acid generated from the organic acid salt in the desalting chamber.

2. The method of claim 1, wherein the solid comprises crystals of the organic acid in a free form.

3. The method of claim 2, wherein the crystals are needle-shaped crystals.

4. The method of claim 1, wherein the aqueous organic acid salt solution further comprises an inorganic salt.

5. The method of claim 4, wherein the inorganic salt comprises one or more selected from sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, and sodium dihydrogen phosphate.

6. The method according to claim 4 or 5, wherein the concentration of the inorganic salt in the aqueous organic acid salt solution at 25° C. before a voltage is applied between the anode and the cathode is 0.001 M or more and 1.0 M or less.

7. The method according to claim 1, wherein the acid aqueous solution contains an acid, and the concentration of the acid in the acid aqueous solution at 25° C. before a voltage is applied between the anode and the cathode is 0.001 M or more and 2.0 M or less.

8. The method according to claim 1, wherein the organic acid salt is at least one selected from the group consisting of a carboxylate, a sulfonate, a sulfinate, an organic phosphate, and an organic phosphite.

9. The method of claim 1, wherein the organic acid salt is a carboxylate.

10. The method of claim 1, wherein the organic acid salt is a salt of a dicarboxylic acid.

11. The method of claim 1, wherein the organic acid salt is a salt of terephthalic acid.

12. The method of claim 1, further comprising recovering the alkaline component from the alkaline component chamber.