JP7659310B2 - 5-Sulfoisophthalic acid tetrahydrate and its manufacturing method - Google Patents

Description

The present invention relates to 5-sulfoisophthalic acid tetrahydrate and its production method.

5-Sulfoisophthalic acid is generally obtained by, for example, reacting isophthalic acid with fuming sulfuric acid or the like to sulfonate the isophthalic acid (for example, Patent Documents 1 to 3). For this reason, 5-sulfoisophthalic acid contains sulfuric acid as an impurity (for example, Non-Patent Document 1, Patent Documents 2 and 3).

For example, Non-Patent Document 1 describes that 5-sulfoisophthalic acid contains 3% by weight of sulfuric acid. Patent Document 2 describes that as a result of a method for producing 5-sulfoisophthalic acid having a product precipitation step using a 30% to 40% sulfuric acid solution, the sulfate level in the monolithium 5-sulfoisophthalic acid salt obtained from the 5-sulfoisophthalic acid is 1000 ppm to 3000 ppm. It also describes that in order to reduce the sulfate level, acetic acid, water, a lithium cation generating compound, and 5-sulfoisophthalic acid are mixed and heated. Patent Document 3 describes that it has been difficult to remove sulfuric acid, which is an impurity, from 5-sulfoisophthalic acid, and that the sulfuric acid content can be reduced by mixing and stirring crude 5-sulfoisophthalic acid with an organic solvent containing an aliphatic ketone and/or alicyclic ketone, and then isolating 5-sulfoisophthalic acid from the organic solvent by solid-liquid separation.

JP 2004-331527 A Special Publication No. 2013-508377 German Patent Application Publication DE2804330A1

Zhurnal Strukturnoi Khimii 1989, 30(3), 174.

However, the above-mentioned conventional techniques use acetic acid and lithium salts or organic solvents to reduce the sulfuric acid content, which causes the problem that these remain as impurities.

One aspect of the present invention aims to provide 5-sulfoisophthalic acid and a method for producing the same, which has a reduced sulfuric acid content as an impurity and does not have the problem of substances used to reduce the sulfuric acid content remaining as impurities.

As a result of intensive research conducted by the present inventors to solve the above problems, they discovered that when crude 5-sulfoisophthalic acid was purified by a specific method using water, it was surprisingly possible to reduce the sulfuric acid content without using acetic acid or an organic solvent. Furthermore, they discovered through X-ray crystal structure analysis that the resulting 5-sulfoisophthalic acid was a previously unknown novel 5-sulfoisophthalic acid tetrahydrate, which led to the completion of the present invention. That is, the present invention includes the following aspects.

[1] 5-Sulfoisophthalic acid tetrahydrate.

[2] A crystal of 5-sulfoisophthalic acid tetrahydrate according to [1].

[3] A crystal of 5-sulfoisophthalic acid tetrahydrate according to [2], in which the crystal space group is P-1 (where "-" indicates an overline of 1), the unit cell has lattice constants a = 7.139(2) Å, b = 9.490(3) Å, c = 10.535(3) Å, α = 70.999(7)°, β = 77.158(7)°, and γ = 85.530(8)°.

[4] A crystal of 5-sulfoisophthalic acid tetrahydrate according to [2] or [3], having a sulfuric acid content of 2.0% by mass or less.

[5] A method for producing crystals of 5-sulfoisophthalic acid tetrahydrate, comprising a step of suspending or crystallizing a crude product containing 5-sulfoisophthalic acid monohydrate in water.

[6] A method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to [5], comprising a step of suspending a crude product containing 5-sulfoisophthalic acid monohydrate in water and incubating the resulting suspension at 34°C or lower for 5 minutes or more.

[7] A method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to [5], comprising the steps of dissolving a crude product containing 5-sulfoisophthalic acid monohydrate in water at a temperature of 34°C to 104°C, cooling the aqueous solution obtained in the above step, and, when the aqueous solution is at 38°C or lower and in a supersaturated state or in a state in which crystals have precipitated, adding seed crystals of 5-sulfoisophthalic acid tetrahydrate to cause crystallization, thereby obtaining crystals of 5-sulfoisophthalic acid tetrahydrate.

According to one aspect of the present invention, it is possible to provide 5-sulfoisophthalic acid, crystals of 5-sulfoisophthalic acid, and a method for producing the same, in which the content of sulfuric acid as an impurity is reduced and there is no problem that substances used to reduce the content of sulfuric acid remain as impurities.

FIG. 1 is a diagram showing a powder X-ray diffraction pattern of the crystals of 5-sulfoisophthalic acid tetrahydrate obtained in Example 1. FIG. 2 is a diagram showing a powder X-ray diffraction pattern of the crystals of 5-sulfoisophthalic acid tetrahydrate obtained in Example 2. FIG. 3 is an ORTEP diagram obtained by single crystal X-ray structure analysis of the crystal of 5-sulfoisophthalic acid tetrahydrate obtained in Example 2. FIG. 4 is a molecular packing diagram obtained by single crystal X-ray structure analysis of the crystal of 5-sulfoisophthalic acid tetrahydrate obtained in Example 2. FIG. 5 is a diagram showing the results of thermogravimetry of the crystals of 5-sulfoisophthalic acid tetrahydrate obtained in Example 2. FIG. 6 is a diagram showing an example of a method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention. FIG. 7 is a diagram showing an example of a method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention. FIG. 8 is a diagram showing a powder X-ray diffraction pattern of the crystals of 5-sulfoisophthalic acid monohydrate obtained in Comparative Example 1. FIG. 9 is an ORTEP diagram obtained by single crystal X-ray structure analysis of the crystal of 5-sulfoisophthalic acid monohydrate obtained in Comparative Example 1. FIG. 10 is a molecular packing diagram obtained by single crystal X-ray structure analysis of the crystal of 5-sulfoisophthalic acid monohydrate obtained in Comparative Example 1. FIG. 11 is a diagram showing the results of thermogravimetry of the crystals of 5-sulfoisophthalic acid monohydrate obtained in Comparative Example 1.

[1] 5-sulfoisophthalic acid tetrahydrate The present inventors have found that when crude 5-sulfoisophthalic acid is purified by a specific method of suspending or crystallizing it in water, crystals with a reduced sulfuric acid content are obtained. Furthermore, by X-ray crystal structure analysis of the crystals, it has been found that the obtained 5-sulfoisophthalic acid is a novel 5-sulfoisophthalic acid tetrahydrate that has not been known before. That is, one aspect of the present invention is 5-sulfoisophthalic acid tetrahydrate. Another embodiment of the present invention is a crystal of 5-sulfoisophthalic acid tetrahydrate.

The 5-sulfoisophthalic acid purity in the 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention is preferably 62% by mass to 78% by mass, more preferably 67% by mass to 78% by mass, and even more preferably 73% by mass to 77% by mass. Note that the "5-sulfoisophthalic acid purity" here refers to the purity of 5-sulfoisophthalic acid (excluding water of crystallization) contained in the crystals, and is a value measured by the method described in the Examples.

The sulfuric acid content in the 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention is preferably 2.0% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less. In the past, sulfuric acid contained as an impurity has been a problem in applications such as polymer additives of metal salts of 5-sulfoisophthalic acid and 5-sulfoisophthalic acid esters produced from 5-sulfoisophthalic acid as a raw material. By reducing the sulfuric acid content in the crystals of 5-sulfoisophthalic acid tetrahydrate, the problem of sulfuric acid contained in metal salts of 5-sulfoisophthalic acid and 5-sulfoisophthalic acid esters can be solved. Note that the "sulfuric acid content" here is a value measured by the method described in the examples.

The Hazen color unit number of an aqueous solution of 50% by mass of 5-sulfoisophthalic acid obtained by dissolving 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention in water is preferably 200 or less, more preferably 180 or less, and even more preferably 160 or less. The lower limit of the Hazen color unit number is 10. By having the Hazen color unit number of 200 or less, it is possible to reduce the coloring of the crystals. Therefore, it is possible to reduce impurities that cause coloring of 5-sulfoisophthalic acid and industrial products made from it. Note that the "Hazen color unit number" here is a value measured by the method described in the examples.

The average particle size of the crystals of 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention is preferably 50 μm to 2500 μm, more preferably 100 μm to 2000 μm, and even more preferably 150 μm to 1600 μm. By having the average particle size within the above range, filterability is improved. In addition, the effect of improving the quality of 5-sulfoisophthalic acid is achieved by reducing adhesion of the mother liquor to the crystals. Note that the "average particle size" of the crystals here is a value measured by the method described in the Examples.

The crystal of 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention may have a space group of P-1 (where "-" indicates an overline of 1), and the lattice constants of the unit cell may be a = 7.139(2) Å, b = 9.490(3) Å, c = 10.535(3) Å, and α = 70.999(7)°, β = 77.158(7)°, and γ = 85.530(8)°. Here, the values in parentheses indicate standard deviations.

The crystals of 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention have characteristic peaks in the powder X-ray diffraction spectrum at the following 2θ angles: 18.2±0.2°, 20.3±0.2°, 24.7±0.2°, 27.4±0.2°, 30.5±0.2°, and 32.0±0.2°.

The crystal shape of the 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention may be columnar.

In the crystals of 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention, the results of thermogravimetry (TG) show that the peaks that begin to absorb heat at around 27°C and around 49°C show a mass loss of three equivalents of water molecules relative to 5-sulfoisophthalic acid, and the peaks that begin to absorb heat at around 142°C show a mass loss of one equivalent of water molecules relative to 5-sulfoisophthalic acid. In this specification, "around" means ±5°C.

[2] Method for Producing Crystals of 5-sulfoisophthalic Acid Tetrahydrate 5-sulfoisophthalic acid tetrahydrate or a crystal thereof according to one embodiment of the present invention can be produced by suspending or crystallizing a crude product containing 5-sulfoisophthalic acid monohydrate in water. Thus, the present invention also includes a method for producing crystals of 5-sulfoisophthalic acid tetrahydrate, which includes a step of suspending or crystallizing a crude product containing 5-sulfoisophthalic acid monohydrate in water.

According to the above-mentioned production method, which includes a step of suspending or crystallizing in water, it is possible to obtain crystals of 5-sulfoisophthalic acid tetrahydrate with a reduced sulfuric acid content without using acetic acid, lithium salts, organic solvents, etc. Therefore, there is no problem with acetic acid, lithium salts, organic solvents, etc. remaining as impurities. Furthermore, since no organic solvents are used, the burden on the environment can be reduced, which can contribute to the achievement of Sustainable Development Goals (SDGs) such as Goal 12 "Ensure sustainable consumption and production patterns."

[2.1] Production method including a step of suspending in water A production method for crystals of 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention may include a step of suspending a crude product containing 5-sulfoisophthalic acid monohydrate in water and maintaining the suspension at 34° C. or lower for 5 minutes or more.

A crude product containing 5-sulfoisophthalic acid monohydrate is a crude product obtained by synthesizing 5-sulfoisophthalic acid, and usually contains 5-sulfoisophthalic acid monohydrate. It is preferable to use the crude product that has been extracted as crystals (crude crystals).

Figure 6 shows an example of a method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to this embodiment. The crude product is suspended in water. The amount of water in which the crude product is suspended is not particularly limited as long as the crude product is suspended without being completely dissolved, but is preferably 0.19 to 0.60 times by mass, more preferably 0.28 to 0.55 times by mass, and even more preferably 0.35 to 0.50 times by mass relative to the amount of 5-sulfoisophthalic acid (excluding water of crystallization) in the crude product.

The temperature of the water in which the crude product is suspended is not particularly limited as long as the crude product is suspended without being completely dissolved, but is preferably -20°C to 34°C, more preferably 0°C to 30°C, and even more preferably 7°C to 25°C. If the temperature of the water in which the crude product is suspended is -20°C or higher, the solution in which the crude product is suspended will not freeze, which is preferable. In addition, if the temperature of the water in which the crude product is suspended is 34°C or lower, the time required for 5-sulfoisophthalic acid tetrahydrate to form is short, which is preferable.

The method of suspending the crude product in water is not particularly limited. For example, the crude product may be poured into water, or water may be added to the crude product. However, it is more preferable to pour the crude product into water. It is even more preferable to pour the crude product into water while stirring it.

The crude product is then suspended in water and the resulting suspension is kept at 34°C or lower for 5 minutes or more. By keeping the suspension at 34°C or lower, it is possible to obtain crystals of 5-sulfoisophthalic acid tetrahydrate with good filterability. The temperature at which the suspension is kept is not particularly limited as long as it is 34°C or lower, but is more preferably 30°C or lower, and even more preferably 25°C or lower. The lower limit of the temperature at which the suspension is kept is also not particularly limited as long as it is -20°C or higher, but is more preferably 0°C or higher, and even more preferably 7°C or higher.

By keeping the suspension at 34°C or less for 5 minutes or more, it is possible to obtain crystals of 5-sulfoisophthalic acid tetrahydrate with good filterability. The time for keeping the suspension at 34°C or less is more preferably 15 minutes or more, and even more preferably 30 minutes or more. The upper limit of the keeping time is not limited to this, but is preferably 12 hours or less from the viewpoint of production efficiency. From the viewpoint of obtaining crystals of 5-sulfoisophthalic acid tetrahydrate with good filterability, it is more preferable that the keeping temperature is constant throughout the entire keeping time, but the temperature may vary as long as it is within the above-mentioned temperature range.

The method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to this embodiment may further include a step of filtering the crystals of 5-sulfoisophthalic acid tetrahydrate obtained by the above step. The method for filtering the crystals of 5-sulfoisophthalic acid tetrahydrate is not particularly limited, but examples include filtration using a normal filter medium, filtration such as centrifugal filtration, pressure filtration, and reduced pressure filtration.

The method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to this embodiment may further include a synthesis step of synthesizing 5-sulfoisophthalic acid to obtain a crude product containing 5-sulfoisophthalic acid monohydrate. The synthesis step is also not particularly limited, but an example of the synthesis step is a method of reacting isophthalic acid with fuming sulfuric acid or the like to sulfonate isophthalic acid, as shown in the following formula:

For example, after the sulfonation, the reaction product is dropped into water and the precipitated crystals are filtered to obtain hydrated crystals of 5-sulfoisophthalic acid monohydrate. The hydrated crystals can be used as a crude product containing 5-sulfoisophthalic acid monohydrate.

[2.2] Production method including a step of crystallization with water The production method of crystals of 5-sulfoisophthalic acid tetrahydrate according to one embodiment of the present invention may include the steps of: (a) dissolving a crude product containing 5-sulfoisophthalic acid monohydrate in water at a temperature of 34°C to 104°C; (b) cooling the aqueous solution obtained in the step (a); and (c) adding seed crystals of 5-sulfoisophthalic acid tetrahydrate to crystallize the solution when the aqueous solution is at 38°C or lower and in a state of being supersaturated or crystals being precipitated, thereby obtaining crystals of 5-sulfoisophthalic acid tetrahydrate. Although precipitation may occur without adding seed crystals, it is preferable to add them from an industrial perspective. FIG. 7 shows an example of the production method of crystals of 5-sulfoisophthalic acid tetrahydrate according to this embodiment.

<Step (a)>
The crude product containing 5-sulfoisophthalic acid monohydrate is as explained in the production method including the step of suspending in water described above, and therefore, explanation thereof will be omitted here.

In the process of dissolving the crude product containing 5-sulfoisophthalic acid monohydrate in water at a temperature of 34°C to 104°C, it is preferable that the 5-sulfoisophthalic acid monohydrate is completely dissolved, but it is not necessary that some of it is not dissolved.

Note that "dissolving in water at a temperature of 34°C to 104°C" means bringing the crude product into a dissolved state at 34°C to 104°C, and also includes the case where the aqueous solution in which the crude product is dissolved in water at a temperature below 34°C is heated to bring the aqueous solution into a dissolved state at 34°C to 104°C.

For example, as shown in FIG. 7, a suitable method is to suspend the crude product in water and heat the resulting suspension to 34°C to 104°C to dissolve 5-sulfoisophthalic acid monohydrate. Alternatively, the crude product may be added to water heated to 34°C to 104°C to dissolve it.

The amount of water in which the crude product is dissolved is not particularly limited, but is preferably 0.19 to 0.60 times by mass, more preferably 0.28 to 0.55 times by mass, and even more preferably 0.35 to 0.50 times by mass, relative to the amount of 5-sulfoisophthalic acid (excluding water of crystallization) in the crude product.

The temperature at which 5-sulfoisophthalic acid monohydrate is dissolved in water may be 34°C to 104°C, more preferably 45°C to 95°C, and even more preferably 60°C to 80°C. If the temperature at which 5-sulfoisophthalic acid monohydrate is dissolved in water is 34°C or higher, the particle size of the resulting 5-sulfoisophthalic acid tetrahydrate will be large, which is preferable. If the temperature at which 5-sulfoisophthalic acid monohydrate is dissolved in water is 104°C or lower, the temperature can be raised under normal pressure, which is preferable.

In order to dissolve 5-sulfoisophthalic acid monohydrate in water at a temperature of 34°C to 104°C, the crude product may be suspended in water and the resulting suspension may be heated to 34°C to 104°C, or the crude product may be poured into water at 34°C to 104°C, and the resulting solution may be kept at that temperature.

<Step (b)>
The cooling method in step (b) for cooling the aqueous solution at 34° C. to 104° C. obtained in step (a) is also not particularly limited, and examples of the cooling method include natural cooling, cooling using a water bath, and cooling using brine.

The cooling rate is not particularly limited, but is preferably 20°C/hour or less, more preferably 10°C/hour or less, and even more preferably 5°C/hour or less. If the cooling rate is within the above range, it is preferable because it is possible to obtain crystals of 5-sulfoisophthalic acid tetrahydrate with a large particle size.

<Step (c)>
When the aqueous solution cooled in step (b) is at 38° C. or lower and is in a supersaturated state or crystals are precipitated, seed crystals of 5-sulfoisophthalic acid tetrahydrate are added to the aqueous solution to cause crystallization, thereby obtaining crystals of 5-sulfoisophthalic acid tetrahydrate.

As seed crystals of 5-sulfoisophthalic acid tetrahydrate, crystals of 5-sulfoisophthalic acid tetrahydrate obtained by the manufacturing method including the above-mentioned step of suspending in water can be used.

The seed crystals are added when the aqueous solution is supersaturated or crystals have precipitated, and the temperature is 38°C or lower, more preferably 37°C or lower, and even more preferably 35°C or lower. By adding the seed crystals at this point, the morphology of the plate crystals that are partially precipitated in step (b) can be changed to columnar crystals, and 5-sulfoisophthalic acid tetrahydrate is produced. If seed crystals are not added, the slurry viscosity will increase, making stirring and filtration difficult.

The amount of the seed crystals to be added is not particularly limited, but is preferably 0.1 ppm to 10 mass% relative to the amount of 5-sulfoisophthalic acid (excluding water of crystallization) in the crude product, more preferably 1.0 ppm to 1.0 mass%, and even more preferably 10 ppm to 0.1 mass%. If the amount of seed crystals is 0.1 ppm or more, 5-sulfoisophthalic acid tetrahydrate precipitates in a short time, which is preferable. Also, if the amount of seed crystals is 10 mass% or less, the crystals of 5-sulfoisophthalic acid tetrahydrate grow large, which improves filterability, which is preferable.

After the seed crystals are added, it is preferable to continue cooling the aqueous solution. By continuing the cooling, 5-sulfoisophthalic acid tetrahydrate is produced in a short time. It is preferable to continue cooling until the aqueous solution reaches a temperature of preferably -20°C to 34°C, more preferably 0°C to 30°C, and even more preferably 7°C to 25°C.

The method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to this embodiment may further include a step of filtering the crystals of 5-sulfoisophthalic acid tetrahydrate obtained by the above step. The filtration method is the same as the above-mentioned production method including the step of suspending in water, so a description thereof will be omitted.

The method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to this embodiment may further include a synthesis step of synthesizing 5-sulfoisophthalic acid to obtain a crude product containing 5-sulfoisophthalic acid monohydrate. This step is similar to the production method including the step of suspending in water described above, so a description of this step is omitted.

The manufacturing method according to this embodiment makes it possible to obtain crystals of 5-sulfoisophthalic acid tetrahydrate having a particularly large average particle size. The average particle size of the crystals of 5-sulfoisophthalic acid tetrahydrate obtained by the manufacturing method according to this embodiment is preferably 200 μm to 2500 μm, more preferably 400 μm to 2000 μm, and even more preferably 500 μm to 1600 μm.

In addition, according to the manufacturing method of this embodiment, it is possible to obtain crystals of 5-sulfoisophthalic acid tetrahydrate with reduced coloration. The Hazen color unit number of an aqueous solution of 5-sulfoisophthalic acid having a concentration of 50% by mass obtained by dissolving 5-sulfoisophthalic acid tetrahydrate obtained by the manufacturing method of this embodiment in water is preferably 200 or less, more preferably 180 or less, and even more preferably 50 or less.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[Measurement method]
<5-Sulfoisophthalic Acid Purity and Sulfuric Acid Content>
The purity of 5-sulfoisophthalic acid and the content of sulfuric acid in a wet cake of 5-sulfoisophthalic acid (hydrated crystals obtained by centrifugal filtration) were measured by the following method. First, 1.5 g of the wet cake was precisely weighed and dissolved in 80 mL of N,N-dimethylformamide. The obtained solution was titrated with 1 mol/L aqueous sodium hydroxide solution using an automatic titrator (manufactured by HIRANUMA Corporation, model: COM-1750) (method: inflection point detection, detection sensitivity: 1000), and the purity of 5-sulfoisophthalic acid and the content of sulfuric acid were measured by detecting the inflection point.

The sulfuric acid content of the wet cake of 5-sulfoisophthalic acid with a sulfuric acid content of 1% by mass or less was measured using ion chromatography [conductivity detector (Hitachi High-Tech Science Corporation, L-2470), pump (Hitachi High-Tech Science Corporation, L-2130), analytical column (Hitachi High-Tech Fielding Corporation, product name #2740 (4.6 mm I.D. x 150 mm)), column oven (Hitachi High-Tech Science Corporation, L-2350)] under the following conditions: column temperature: 40°C, mobile phase: distilled water containing 2.5 mol/L tris(hydroxymethyl)aminomethane and 2.3 mol/L phthalic acid, flow rate: 1.5 mL/min.

<Hazen unit color number>
The Hazen color unit number of the wet cake of 5-sulfoisophthalic acid was measured using a Hazen measuring instrument (manufactured by Tintometer, model: Nessleriser 2150) by adding 50 mL of a 50% by mass aqueous solution of 5-sulfoisophthalic acid to a 50 mL Nessler tube and using water as a blank.

<Average particle size>
The average particle size of the wet cake of 5-sulfoisophthalic acid is an average measured value obtained by dispersing the filtrate obtained by filtering the wet cake in the case of 5-sulfoisophthalic acid monohydrate, or a saturated aqueous solution of 5-sulfoisophthalic acid tetrahydrate in the case of 5-sulfoisophthalic acid tetrahydrate by applying ultrasonic waves for 30 seconds using an ultrasonic cleaner (manufactured by SND Corporation, model: US-705), and measuring the Feret diameter of 1,000 or more crystals using a microscope (manufactured by Keyence Corporation, model: VHX-500F).

<Powder X-ray diffraction>
The crystalline phase of the wet cake of 5-sulfoisophthalic acid was confirmed by powder X-ray diffraction analysis using a fully automated multipurpose X-ray diffractometer (manufactured by Rigaku Corporation, model: SmartLab).

<Single crystal X-ray structure analysis>
The crystal structure of the wet cake of 5-sulfoisophthalic acid was determined by single crystal structure analysis using a curved imaging plate single crystal automatic X-ray structure analyzer (manufactured by Rigaku Corporation, model: R-AXIS RAPID IIα).

<Thermogravimetry (TG)>
Thermogravimetry (TG) of the wet cake of 5-sulfoisophthalic acid was carried out by the following method: First, 10 to 12 mg of the wet cake was precisely weighed into an alumina open-type sample container, and the temperature was raised from 20° C. to 180° C. at a rate of 2° C./min while feeding nitrogen at a flow rate of 200 mL/min using a simultaneous differential thermal and thermogravimetry analyzer (manufactured by Hitachi High-Tech Science Corporation, model: TG/DTA6200).

Example 1
Isophthalic acid (300 g) was added to 28% by mass fuming sulfuric acid (822 g) that was 2.74 times by mass relative to the isophthalic acid while stirring, and the mixture of isophthalic acid and fuming sulfuric acid was kept at 190 ° C. for 2 hours, and then cooled to 100 ° C. Next, the reaction mixture was dropped into water (558 g) that was 1.86 times by mass relative to the isophthalic acid while stirring, and after cooling to 30 ° C., the precipitate was centrifuged at a rotation speed of 5000 rpm for 15 minutes. The obtained columnar crystals were hydrated crystals of 5-sulfoisophthalic acid (489 g), and as a result of evaluation with an automatic titrator, the 5-sulfoisophthalic acid content in the hydrated crystals was 89% by mass and the sulfuric acid content was 3% by mass. The yield from isophthalic acid was 98%.

Next, the hydrated crystals of 5-sulfoisophthalic acid (163 g) obtained by the above operation were added to 20°C water (61 g) with 0.42 times the mass of the 5-sulfoisophthalic acid in the hydrated crystals while stirring, and the suspension was kept at 20°C for 3 hours. At this time, the crystals of 5-sulfoisophthalic acid changed into columnar crystals 18 minutes after the start of the incubation. After keeping at 20°C for 3 hours, the suspension was centrifuged at a rotation speed of 5000 rpm for 15 minutes. The obtained columnar crystals were hydrated crystals of 5-sulfoisophthalic acid (73 g), and had an average particle size of 314 μm. As a result of evaluation with an automatic titration device, the content of 5-sulfoisophthalic acid in the hydrated crystals was 77% by mass, and as a result of evaluation with ion chromatography, the content of sulfuric acid in the hydrated crystals was 0.1% by mass. The yield from isophthalic acid was 38%. The Hazen color unit number of the aqueous solution of 5-sulfoisophthalic acid with a concentration of 50% by mass obtained by dissolving these hydrated crystals in water was 140.

The powder X-ray diffraction spectrum of this hydrated crystal is shown in Figure 1. In the powder X-ray diffraction spectrum, this hydrated crystal had characteristic peaks at the following 2θ angles: 18.1±0.2°, 20.2±0.2°, 24.6±0.2°, 27.3±0.2°, 30.5±0.2°, and 31.9±0.2°.

Comparative Example 1
In the production process of Example 1, the reaction mixture was cooled to 30° C., and the precipitate was centrifuged to obtain hydrated crystals of 5-sulfoisophthalic acid containing 3% by mass of sulfuric acid. The average particle size of the hydrated crystals was measured and found to be 30 μm. The hydrated crystals were dissolved in water to obtain an aqueous solution of 5-sulfoisophthalic acid with a concentration of 50% by mass, and the Hazen color unit number was 240.

Furthermore, single crystal X-ray structure analysis of this hydrated crystal showed that, when measured at 173K, it had unit cell dimensions: a = 14.1445 (14) Å; b = 10.9611 (10) Å; c = 13.5039 (13) Å; β = 98.727 (7)°; unit cell volume: V = 2069.4 (3) Å; number of asymmetric units in the lattice: Z = 8; and space group: C2/c. The molecular structure of this hydrated crystal obtained by single crystal X-ray structure analysis is shown in the ORTEP diagram in Figure 9, and the molecular packing diagram in Figure 10. This hydrated crystal was 5-sulfoisophthalic acid monohydrate.

The powder X-ray diffraction spectrum of this hydrated crystal is shown in Figure 8. In the powder X-ray diffraction spectrum, this hydrated crystal had characteristic peaks at the following 2θ angles: 10.4±0.2°, 11.8±0.2°, 21.1±0.2°, 25.3±0.2°, 32.7±0.2°, and 42.1±0.2°.

The results of thermogravimetry (TG) are shown in Figure 11.

Example 2
In the production process of Example 1, the reaction mixture was cooled to 30°C, and the precipitate was centrifuged to obtain hydrated crystals of 5-sulfoisophthalic acid monohydrate (163 g). The hydrated crystals were added to water (58 g) with a mass of 0.40 times the mass of the 5-sulfoisophthalic acid in the hydrated crystals while stirring. The temperature was raised to 70°C, and the solution was kept at the same temperature for 1 hour to completely dissolve the crystals of 5-sulfoisophthalic acid monohydrate. When the resulting solution was cooled to 47°C, plate crystals were precipitated. The solution was further cooled, and when the solution reached 35°C, the hydrated crystals of 5-sulfoisophthalic acid (18 mg) obtained in Example 1 with a sulfuric acid content of 0.1% by mass were added. The cooling was continued, and the crystals changed to columnar crystals at 34°C. Cooling was continued further to 15°C, and centrifugal filtration was performed for 15 minutes at a rotation speed of 5000 rpm to obtain columnar crystals, which were hydrated crystals of 5-sulfoisophthalic acid (94 g) with an average particle size of 1222 µm. Evaluation with an automatic titrator revealed that the content of 5-sulfoisophthalic acid in the hydrated crystals was 76% by mass, and evaluation by ion chromatography revealed that the content of sulfuric acid in the hydrated crystals was 0.1% by mass. The yield from isophthalic acid was 49%.

The Hazen color unit number of the aqueous solution of 5-sulfoisophthalic acid with a concentration of 50% by mass obtained by dissolving these hydrated crystals in water was 15.

Furthermore, single crystal X-ray structure analysis of this hydrated crystal showed that, when measured at 173K, it had unit cell dimensions: a = 7.139 (2) Å; b = 9.490 (3) Å; c = 10.535 (3) Å; α = 70.999 (7) °; β = 77.158 (7) °; γ = 85.530 (8) °; unit cell volume: V = 658.0 (3) Å; number of asymmetric units in the lattice: Z = 2; and space group: P-1. The molecular structure of this hydrated crystal obtained by single crystal X-ray structure analysis is shown in the ORTEP diagram in Figure 3, and the molecular packing diagram in Figure 4. This hydrated crystal was confirmed to be 5-sulfoisophthalic acid tetrahydrate.

The powder X-ray diffraction spectrum of this hydrated crystal is shown in Figure 2. In the powder X-ray diffraction spectrum, this hydrated crystal had characteristic peaks at the following 2θ angles: 18.2±0.2°, 20.3±0.2°, 24.7±0.2°, 27.4±0.2°, 30.5±0.2°, and 32.0±0.2°.

The X-ray analysis results for Examples 1 and 2 showed that both hydrated crystals were 5-sulfoisophthalic acid tetrahydrate.

The results of thermogravimetry (TG) are shown in Figure 5.

Comparative Example 2
Using isophthalic acid (300 g), 28% by mass fuming sulfuric acid (822 g) that is 2.74 times by mass relative to the isophthalic acid, and water (521 g) that is 1.74 times by mass, 5-sulfoisophthalic acid monohydrate (497 g) was obtained as a hydrated crystal in the same manner as in Comparative Example 1. As a result of evaluation with an automatic titrator, the content in the hydrated crystal was 88% by mass of 5-sulfoisophthalic acid and 4% by mass of sulfuric acid, and the yield from isophthalic acid was 98%. In addition, the average particle size was measured and found to be 35 μm. The Hazen color unit number of an aqueous solution of 5-sulfoisophthalic acid having a concentration of 50% by mass obtained by dissolving the hydrated crystal in water was 250.

〔summary〕
The 5-sulfoisophthalic acid purity and sulfuric acid content, as well as the Hazen color number and average particle size of the 5-sulfoisophthalic acid hydrates obtained in the Examples and Comparative Examples, are shown in Table 1.

As shown in Table 1, it was confirmed that the 5-sulfoisophthalic acid hydrate obtained in Examples 1 and 2 was a tetrahydrate, and the 5-sulfoisophthalic acid hydrate obtained in Comparative Examples 1 and 2 was a monohydrate. The amount excluding the 5-sulfoisophthalic acid purity and sulfuric acid content in the crystals of 5-sulfoisophthalic acid monohydrate obtained in Comparative Examples 1 and 2 was 8% by mass, and the amount excluding the 5-sulfoisophthalic acid purity and sulfuric acid content in the crystals of 5-sulfoisophthalic acid tetrahydrate obtained in Examples 1 and 2 was approximately 23% to 24% by mass. It can be seen that the difference between 8% by mass and approximately 23% to 24% by mass is due to the difference in the content of water of crystallization.

The average particle size of the crystals of 5-sulfoisophthalic acid tetrahydrate obtained in Examples 1 and 2 was larger than that of the crystals of 5-sulfoisophthalic acid monohydrate obtained in Comparative Examples 1 and 2. In Examples 1 and 2, 5-sulfoisophthalic acid tetrahydrate had improved filterability compared to 5-sulfoisophthalic acid monohydrate. This is believed to be due to the improved filterability resulting from the larger particle size. In addition, the crystals of 5-sulfoisophthalic acid tetrahydrate had a significantly reduced sulfuric acid content and reduced coloration compared to the crystals of 5-sulfoisophthalic acid monohydrate.

5-Sulfoisophthalic acid is extremely useful industrially as a raw material for metal salts of 5-sulfoisophthalic acid, which are used as additives in polymer production, and alkyl esters of 5-sulfoisophthalic acid, which are used as modifiers for polyesters. In addition, since sulfuric acid contained as an impurity in 5-sulfoisophthalic acid has an undesirable effect on these applications as additives and modifiers, the 5-sulfoisophthalic acid of the present application, which has a reduced sulfuric acid content, is extremely useful industrially.

Claims (6)

A crystal of 5-sulfoisophthalic acid tetrahydrate with a crystal space group of P-1 (where "-" indicates an overline of 1), unit cell lattice constants of a = 7.139(2) Å, b = 9.490(3) Å, c = 10.535(3) Å, α = 70.999(7)°, β = 77.158(7)°, and γ = 85.530(8)°. The crystals of 5-sulfoisophthalic acid tetrahydrate according to claim 1, having a sulfuric acid content of 2.0% by mass or less. A method for producing crystals of 5-sulfoisophthalic acid tetrahydrate, comprising the step of suspending a crude product containing crystals of 5-sulfoisophthalic acid monohydrate in water to obtain crystals of 5-sulfoisophthalic acid tetrahydrate,
The crystals of 5-sulfoisophthalic acid monohydrate have unit cell dimensions: a=14.1445(14) Å; b=10.9611(10) Å; c=13.5039(13) Å; β=98.727(7)°; unit cell volume: V=2069.4(3) Å; number of asymmetric units in the lattice: Z=8; and are in the space group C2/c; when measured at 173K,
The crystal of 5-sulfoisophthalic acid tetrahydrate has a crystal space group of P-1 (where "-" indicates an overline of 1), and the lattice constants of the unit cell are a = 7.139(2) Å, b = 9.490(3) Å, c = 10.535(3) Å, α = 70.999(7)°, β = 77.158(7)°, and γ = 85.530(8)°. The method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to claim 3, comprising a step of suspending a crude product containing crystals of 5-sulfoisophthalic acid monohydrate in water and incubating the suspension at 34° C. or lower for 5 minutes or longer. The method for producing crystals of 5-sulfoisophthalic acid tetrahydrate according to claim 3 or 4, wherein the amount of water in which the crude product is suspended is 0.19 to 0.60 times by mass relative to the amount of 5-sulfoisophthalic acid (excluding water of crystallization) in the crude product. A method for producing crystals of 5-sulfoisophthalic acid tetrahydrate, comprising a step of crystallizing a crude product containing crystals of 5-sulfoisophthalic acid monohydrate with water,
A step of dissolving a crude product containing crystals of 5-sulfoisophthalic acid monohydrate in water at a temperature of 34° C. to 104° C.;
cooling the aqueous solution obtained in the previous step;
and a step of adding seed crystals of 5-sulfoisophthalic acid tetrahydrate to the aqueous solution at a temperature of 38° C. or lower and in a state of being supersaturated or in which crystals have precipitated, thereby obtaining crystals of 5-sulfoisophthalic acid tetrahydrate,
The crystals of 5-sulfoisophthalic acid monohydrate have unit cell dimensions: a=14.1445(14) Å; b=10.9611(10) Å; c=13.5039(13) Å; β=98.727(7)°; unit cell volume: V=2069.4(3) Å; number of asymmetric units in the lattice: Z=8; and are in the space group C2/c; when measured at 173K,
The crystals and seed crystals of 5-sulfoisophthalic acid tetrahydrate have a crystal space group of P-1 (where "-" indicates an overline of 1), and the lattice constants of the unit cell are a = 7.139(2) Å, b = 9.490(3) Å, c = 10.535(3) Å, α = 70.999(7)°, β = 77.158(7)°, and γ = 85.530(8)°.

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