JP2018135275A - Method of purifying methacrylic acid and methacrylic acid crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high-purity methacrylic acid crystal with a low content of acrylic acid.SOLUTION: A method of purifying methacrylic acid includes a step of cooling a raw material containing methacrylic acid and acrylic acid in a crystallization tank to obtain a methacrylic acid crystal, wherein the step is a bath-type crystallization operation, characterized by cooling the raw material at a rate of 0.4-6.0°C/hr.SELECTED DRAWING: None

Description

  The present invention relates to a method for purifying methacrylic acid and methacrylic acid crystals.

  Methacrylic acid is obtained by catalytic gas phase oxidation of isobutylene, tertiary butyl alcohol, methacrolein or isobutyraldehyde with molecular oxygen in a one-stage or two-stage reaction. In this product, in addition to the target methacrylic acid (boiling point 161 ° C./760 mmHg, melting point 15 ° C.), for example, formic acid, acetic acid, propionic acid, maleic acid, citraconic acid, benzoic acid, toluic acid, terephthalic acid , Carboxylic acids such as acrylic acid, aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, methacrolein, benzaldehyde, tolualdehyde, furfural, phenol and the like are included as by-products. These impurities can be separated and purified to some extent by ordinary purification means such as extraction and distillation, but further reduction of the impurity concentration is desired.

  As a method for obtaining high-purity methacrylic acid, for example, Patent Documents 1 to 3 disclose a method for purifying methacrylic acid by a crystallization operation.

JP 2013-91653 A JP 2012-140471 A International Publication No. 2013/103112

  In the methods described in Patent Documents 1 to 3, the purity of methacrylic acid can be improved, but from the viewpoint of further improving the purity of methacrylic acid, the content of acrylic acid contained at a relatively high concentration, particularly among impurities. Therefore, there is a demand for a method capable of producing a methacrylic acid crystal having a higher purity and a higher purity.

  An object of the present invention is to provide a higher purity methacrylic acid crystal having a low acrylic acid content.

  The present invention includes the following [1] to [5].

[1] A method for purifying methacrylic acid comprising a step of cooling a raw material containing methacrylic acid and acrylic acid in a crystallization tank to obtain methacrylic acid crystals,
The process is a batch crystallization operation,
A method for purifying methacrylic acid, wherein the raw material is cooled at a rate of 0.4 to 6.0 ° C./hr.

  [2] The method for purifying methacrylic acid according to [1], wherein a distribution coefficient of the acrylic acid in the raw material to the methacrylic acid crystal represented by the following formula is 0.01 or less.

    Partition coefficient = (acrylic acid concentration in methacrylic acid crystal) / (acrylic acid concentration in raw material).

  [3] The method for purifying methacrylic acid according to [1] or [2], wherein the temperature of the raw material at the start of cooling and at the end of cooling is in the range of 4 to 8 ° C.

  [4] The method for purifying methacrylic acid according to any one of [1] to [3], wherein the raw material is cooled while stirring.

  [5] A methacrylic acid crystal having an acrylic acid concentration of less than 10 ppm by mass.

  According to the present invention, it is possible to provide a methacrylic acid crystal of higher purity having a low acrylic acid content.

[Method for purifying methacrylic acid]
The method for purifying methacrylic acid according to the present invention includes a step of cooling a raw material containing methacrylic acid and acrylic acid in a crystallization tank to obtain methacrylic acid crystals. Here, the process is a batch crystallization operation. In the step, the raw material is cooled at a rate of 0.4 to 6.0 ° C./hr. When cooling the raw material containing methacrylic acid and acrylic acid, the present inventors cooled the raw material at a rate of 0.4 to 6.0 ° C./hr, so that the acrylic acid content was less than that of the higher purity. It was found that methacrylic acid crystals were obtained. Hereinafter, details of the method according to the present invention will be described.

  The raw materials to be purified in the present invention are not particularly limited as long as methacrylic acid and acrylic acid are included, but for example, crude methacrylic acid produced by a direct oxidation method, an ACH method or the like can be used. In the direct oxidation method, for example, at least one compound selected from the group consisting of isobutylene, tertiary butyl alcohol, methacrolein and isobutyraldehyde is subjected to catalytic gas phase oxidation by molecular oxygen in a one-stage or two-stage reaction. Condensate obtained by condensing the obtained reaction gas, or adding methacrylic acid from an aqueous methacrylic acid solution obtained by adding water to the condensate of the reaction gas or absorbing the reaction gas in water, using an organic solvent. Extract. By distilling the extract, the organic solvent and non-volatile components can be removed to obtain crude methacrylic acid. In the ACH method, for example, crude methacrylic acid can be obtained by separating by-product methacrylic acid by extraction or distillation.

  The concentration of acrylic acid contained as an impurity in the raw material used in the method according to the present invention is preferably 1000 ppm to 7000 ppm by mass, more preferably 1200 ppm to 5000 ppm. Preferably, it is 1500 mass ppm or more and 3000 mass ppm or less. When the concentration is 1000 ppm by mass or more, it can be used as a raw material without excessive costs. Moreover, when this density | concentration is 7000 mass ppm or less, the influence on the quality of a methacrylic acid crystal can be reduced. In addition, the density | concentration of acrylic acid in a raw material uses the gas chromatography (Main body: GC-17A (a product name, Shimadzu Corp. make), analysis column: HP-FFAP (a brand name, Agilent Technologies make)). Can be measured.

  In addition to acrylic acid, the raw materials according to the present invention include formic acid, acetic acid, propionic acid, citraconic acid, benzoic acid, maleic acid, toluic acid, terephthalic acid, formaldehyde, acetaldehyde, propionaldehyde, methacrolein, benzaldehyde, tolualdehyde Impurities such as furfural and phenol may be contained. The concentration of impurities other than acrylic acid contained in the raw material is preferably 10000 mass ppm or less in total, and more preferably 6000 mass ppm or less. The total concentration of the impurities can be measured in the same manner as the concentration of acrylic acid.

  In addition, the raw material may be mixed with one or more polar organic substances as the second component, and the crystallization operation may be performed. It is preferable to mix a polar organic substance as the second component because crystallization operability is improved.

  As the polar organic substance that is the second component, any polar organic substance that does not form a solid solution with methacrylic acid during crystallization can be used without particular limitation. Examples of such polar organic substances include alcohols such as methanol, ethanol, propanol and butanol, diethyl ether, dioxane, tetrahydrofuran, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, methacryl Examples include methyl acid, ethyl methacrylate, methyl acrylate, and ethyl acrylate. Among these, as the polar organic substance, a compound selected from the group consisting of alcohol, methyl methacrylate and methyl acrylate is preferable, and methanol is more preferable. As the polar organic substance, these compounds can be used alone, or two or more kinds can be mixed and used.

  When the raw material contains the second component, the content of the second component in the raw material is preferably 1 to 35% by mass, more preferably 3 to 30% by mass, and 3 to 10% by mass. More preferably. By setting the content to 1% by mass or more, the temperature at which methacrylic acid crystals start to precipitate, that is, the temperature difference between the crystal precipitation temperature and the freezing point of methacrylic acid increases, and the crystallization operation becomes easy. In addition, when the content is 35% by mass or less, the crystal precipitation temperature is not significantly lowered, and a lot of energy and cost are not required for cooling.

  The crystallization apparatus used in the method according to the present invention is not particularly limited as long as it is a batch crystallization apparatus. For example, “Chemical Engineering Handbook Revised 6th Edition” issued by Maruzen Co., Ltd., 1999, 489-523. The apparatus described on page can be used. In addition, a BMC (Backmixing Column Crystallizer) type crystallizer (Nippon Steel Chemical Co., Ltd .: Japan), a CDC (Cooling Disk Crystallizer) crystallizer (Gouda Co., Netherlands), and an FFC (Falling Film Crystallizer) crystallizer (Sullerzer crystallizer) Switzerland) can also be used. In particular, a stirring tank and a cooler provided with a cooling jacket for bringing a cooling medium into contact with the peripheral surface of the stirring tank from the outside, and the inside of the stirring tank by heat exchange with the peripheral surface of the stirring tank as a heat transfer surface A suspension type jacket cooling type crystallization tank (stirring tank type crystallization apparatus) capable of cooling and holding the suspended crystal slurry in the stirring tank is preferred.

  In the method according to the present invention, for example, the raw material is charged into a crystallization tank of the crystallization apparatus and cooled to precipitate methacrylic acid crystals (crystallization operation). Thereby, a slurry in which methacrylic acid crystals are precipitated can be obtained. The crystallization operation is performed batchwise from the viewpoint of depositing and growing crystals over time. Further, it is preferable to cool the raw material while stirring at the time of cooling from the viewpoint of eliminating temperature distribution and concentration distribution unevenness in the crystallization tank.

  The cooling rate when cooling the raw material is 0.4 to 6.0 ° C./hr, preferably 0.5 to 4.0 ° C./hr, and 0.6 to 3.0 ° C./hr. More preferably, it is more preferably 0.7 to 2.0 ° C./hr. When the cooling rate is 0.4 ° C./hr or more, a methacrylic acid crystal having a small acrylic acid content can be obtained. Moreover, since the cooling rate is 6.0 ° C./hr or less, no equipment capable of high-speed cooling is required, so that the cost can be reduced. In addition, this cooling rate shows reducing the temperature of the raw material in a crystallization tank at this rate. For example, when the crystallization operation is performed using the suspension-type jacket cooling crystallization tank, the temperature of the raw material in the crystallization tank also decreases in conjunction with a decrease in the temperature of the cooling medium circulating in the jacket. . Therefore, the temperature of the raw material in the crystallization tank can be lowered at a speed within the above range by setting the cooling rate within the above range with an apparatus for controlling the temperature of the cooling medium. The cooling rate can be changed as long as it is within the above range, but linear cooling in which cooling is performed at a constant rate is preferable.

  The temperature of the raw material at the start of cooling and at the end of cooling is preferably in the range of 4 to 8 ° C, more preferably in the range of 5 to 7.5 ° C, and in the range of 6 to 7 ° C. More preferably it is. When the temperature is 4 ° C. or higher, the operation can be performed without the presence of excessive crystals in the crystallization tank. On the other hand, when the temperature is 8 ° C. or lower, it is possible to maintain the crystal productivity per batch operation at an acceptable value. In addition, it is preferable that the temperature of a raw material exists in the said temperature range from cooling start to completion | finish of cooling. The difference between the cooling start temperature and the cooling end temperature is not particularly limited, but is preferably 0.1 to 3 ° C, more preferably 0.2 to 2 ° C, and 0.3 to 1 ° C. Is more preferable.

  The time for cooling within the range of the cooling rate of the present invention is preferably 0.1 to 2 hours, more preferably 0.2 to 1.5 hours, and further preferably 0.3 to 1.2 hours. Since the cooling time is 0.1 hour or longer, no equipment capable of high-speed cooling is required, so that the cost can be reduced. On the other hand, when the cooling time is 2 hours or less, a methacrylic acid crystal having a low acrylic acid concentration can be obtained.

  From the viewpoint of further growing the methacrylic acid crystal, after cooling the raw material to precipitate the methacrylic acid crystal, the temperature of the raw material is once increased to reduce the number of crystals in the crystallization tank, and then the cooling of the present invention. It is preferable to perform cooling at a speed. For example, after cooling the raw material to 7 ° C or less and confirming the precipitation of methacrylic acid crystals, the raw material temperature is raised to a temperature exceeding 7 ° C and held, and the number of crystals in the crystallization tank is reduced to about half. Then, cooling can be performed at the cooling rate of the present invention. The number of crystals can be confirmed visually.

  The obtained slurry containing methacrylic acid crystals can be separated into methacrylic acid crystals and a mother liquor. Thereby, a methacrylic acid crystal can be obtained. On the other hand, the separated mother liquor contains concentrated impurities including acrylic acid, methacrylic acid, and the second component when the second component is added.

  The method for separating the methacrylic acid crystal and the mother liquor is not particularly limited as long as it is a method capable of separating the solid and the liquid. For example, a known solid-liquid separation device such as a filtration device or a centrifugal separation device, or a combination thereof can be used. Specific examples of the separation apparatus include, for example, Tadashi Shimizu: “Purification of organic compounds by Kureha continuous crystal purification apparatus”, Chemical Engineering, Vol. 27, No. 3 (1982), p. 49. KCP apparatus etc. which are mentioned. The type of separation operation may be either a batch type or a continuous type. Further, methacrylic acid and the second component can be recovered from the separated mother liquor and reused or repurified.

  The relationship between the acrylic acid concentration in the raw material and the acrylic acid concentration in the obtained methacrylic acid crystal is preferably such that the distribution coefficient of acrylic acid in the raw material to the methacrylic acid crystal is 0.01 or less. It is more preferably 008 or less, and further preferably 0.006 or less. Here, the distribution coefficient is a coefficient indicating how much acrylic acid in the raw material is distributed to methacrylic acid crystals, and is a value represented by the following formula.

Partition coefficient = (acrylic acid concentration in methacrylic acid crystal) / (acrylic acid concentration in raw material)
When the distribution coefficient is 0.01 or less, a methacrylic acid crystal having a lower acrylic acid content can be obtained. The distribution coefficient is preferably low, and the lower limit of the range of the distribution coefficient is not particularly limited.

  The acrylic acid concentration in the methacrylic acid crystal is measured by the following method. In order to remove methacrylic acid crystals in the crystallization tank and remove the mother liquor on the surface of the methacrylic acid crystals, the methacrylic acid crystals were placed on a Kimwipe (trade name, manufactured by Nippon Paper Crecia Co., Ltd.) Wipe off the mother liquor. This operation is repeated several times by changing the position of the crystal, and the obtained crystal is transferred to a vial, and the acrylic acid concentration in the methacrylic acid crystal is measured in the same manner as the acrylic acid concentration measurement in the raw material.

[Methacrylic acid crystals]
In the methacrylic acid crystal according to the present invention, the concentration of acrylic acid is less than 10 ppm by mass. The methacrylic acid crystals can be obtained by the method for purifying methacrylic acid according to the present invention. The concentration of acrylic acid in the methacrylic acid crystal is preferably 8 ppm by mass or less, more preferably 6 ppm by mass or less, and still more preferably 5 ppm by mass or less.

  As a crystallizer, a glass suspension jacket cooled crystallization tank (125 ml) equipped with a stirring mechanism was used. The crystallization operation was carried out batchwise. As a cooling medium, Etabline EC-Z (trade name, manufactured by Tokyo Fine Chemical Co., Ltd.) was used. NTB-221 (trade name, manufactured by Tokyo Rika Co., Ltd.) was used for temperature control of the cooling medium.

  For measuring the concentration of acrylic acid in methacrylic acid crystals, gas chromatography (main body: GC-17A (product name, manufactured by Shimadzu Corporation), analysis column: HP-FFAP (trade name, manufactured by Agilent Technologies)) is used. Using. In addition, the detection limit of acrylic acid in the concentration measurement is 10 mass ppm.

Example 1
Raw material containing methanol, phenol and acrylic acid added to methacrylic acid (Mitsubishi Rayon Co., Ltd.), methanol at 5.6% by mass, phenol at 0.40% by mass, and acrylic acid at the concentrations shown in Table 1. Was prepared.

  80 ml of the raw material was placed in a glass suspension jacket cooling type crystallization tank, and a cooling medium having a set temperature of 6.5 ° C. was circulated through the jacket while stirring with a small stirrer. When the temperature of the raw material in the crystallization tank became around 6.9 ° C., crystallization was confirmed in the crystallization tank. Here, the set temperature of the cooling medium was changed to 7.3 ° C., the stirring was stopped, and the system was on standby until the number of crystals in the crystallization tank decreased. After confirming that the number of crystals in the crystallization tank has been reduced to about half, the set temperature of the cooling medium is changed to 7.0 ° C., and the set temperature is lowered to 6.5 ° C. over 0.7 hours. (Cooling rate: 0.714 ° C./hr), linear cooling was performed. In addition, the raw material temperature in a crystallization tank fell in connection with the fall of the preset temperature of a cooling medium.

  When the set temperature reached 6.5 ° C., the cooling was terminated, and methacrylic acid crystals in the crystallization tank were collected with tweezers. In order to remove the mother liquor on the surface of the collected methacrylic acid crystal, the methacrylic acid crystal was placed on Kimwipe (trade name, manufactured by Nippon Paper Crecia Co., Ltd.), and the mother liquor on the surface was wiped off in a folded manner. This operation was repeated several times while changing the position of the crystal, and the resulting crystal was transferred to a vial and the acrylic acid concentration was measured. The results are shown in Table 1.

(Example 2)
Crystallization was carried out in the same manner as in Example 1 except that the set temperature of the cooling medium was decreased from 7.0 ° C. to 6.5 ° C. over 1.2 hours (cooling rate: 0.417 ° C./hr). The operation was carried out to obtain methacrylic acid crystals, and the acrylic acid concentration was measured. The results are shown in Table 1.

(Comparative Example 1)
Crystallization was carried out in the same manner as in Example 1 except that the set temperature of the cooling medium was decreased from 7.0 ° C. to 6.5 ° C. over 2.2 hours (cooling rate: 0.227 ° C./hr). The operation was carried out to obtain methacrylic acid crystals, and the acrylic acid concentration was measured. The results are shown in Table 1.

(Comparative Example 2)
The crystallization operation was performed in the same manner as in Example 1 except that the set temperature of the cooling medium was decreased from 7.0 ° C. to 6.5 ° C. over 72 hours (cooling rate: 0.0069 ° C./hr). The methacrylic acid crystals were obtained and the acrylic acid concentration was measured. The results are shown in Table 1.

Claims (5)

A method for purifying methacrylic acid comprising a step of cooling a raw material containing methacrylic acid and acrylic acid in a crystallization tank to obtain methacrylic acid crystals,
The process is a batch crystallization operation,
A method for purifying methacrylic acid, wherein the raw material is cooled at a rate of 0.4 to 6.0 ° C./hr. The method for purifying methacrylic acid according to claim 1, wherein a distribution coefficient of the acrylic acid in the raw material to the methacrylic acid crystal represented by the following formula is 0.01 or less.
Partition coefficient = (acrylic acid concentration in methacrylic acid crystal) / (acrylic acid concentration in raw material)   The method for purifying methacrylic acid according to claim 1 or 2, wherein the temperature of the raw material at the start of cooling and at the end of cooling is in the range of 4 to 8 ° C.   The method for purifying methacrylic acid according to any one of claims 1 to 3, wherein the raw material is cooled while stirring.   A methacrylic acid crystal having an acrylic acid concentration of less than 10 ppm by mass.