JP4928092B2 - Method for purifying aromatic dihydroxy compounds - Google Patents

Description

  The present invention relates to a method for purifying an aromatic dihydroxy compound. More specifically, the present invention is characterized by dissolving an aromatic dihydroxy compound in supercritical water or subcritical water and then releasing the supercritical state to cause crystallization. The present invention relates to a completely new method for purifying aromatic dihydroxy compounds.

  Aromatic dihydroxy compounds are widely used as raw materials for polycarbonate resins, epoxy resins, polyester resins, or phenol resins. Among them, 2,2-bis (4-hydroxyphenyl) propane, that is, bisphenol A (hereinafter referred to as BPA) is a chemical product useful as a raw material for polycarbonate resins and epoxy resins, and usually contains phenol and acetone. It is produced by reacting in the presence of an acidic catalyst. However, the BPA crystals obtained by this method contain phenol and BPA isomers, as well as impurities generated during the reaction, etc., and this influence tends to color the crystals. When the coloration degree of the BPA crystal is large, the quality of the polycarbonate resin or epoxy resin produced using this as a raw material is lowered. Therefore, it is desirable that the coloration degree of the BPA crystal is as low as possible and the purity is as high as possible.

  In recent years, methods for recovering aromatic dihydroxy compounds by chemical recycling of polycarbonate resins and epoxy resins have been widely studied, but even in this case, it is important to remove the impurities and inorganic substances contained in the resins. It is a difficult issue.

  Thus, various purification methods have been studied for the aromatic dihydroxy compounds. As a method for purifying BPA, for example, a method of supplying molten BPA to a flash distillation apparatus and evaporating and removing light-boiling substances containing phenol is known (Patent Document 1: Japanese Patent Application Laid-Open No. 2004-67617). However, the above method requires a thin film evaporator and a gas-liquid separator in addition to the flash evaporator, and the process is very complicated. On the other hand, a BPA purification method including a step of forming an adduct of BPA and phenol (Patent Document 2: Japanese Patent Application Laid-Open No. 59-233103), and BPA is dissolved in an organic solvent, and a poor solvent is added to perform re-treatment. A method of crystallizing is widely known (Patent Document 3: Japanese Patent Laid-Open No. 2-229126). However, since any of the above methods uses an organic solvent, there is a concern about an adverse effect on the environment, and there is a problem in economical efficiency. Further, the above purification method is not intended to remove inorganic salts which are hated particularly in electronic materials.

  As described above, firstly, there has been a strong demand for a method for purifying an aromatic dihydroxy compound that is simple in process and low in cost, and that can efficiently remove organic impurities and inorganic impurities without burdening the environment.

Japanese Patent Application Laid-Open No. 2004-67617, page 2 JP-A-59-233103, pages 1-2 JP-A-2-229126, page 1

  In view of the above problems, an object of the present invention is to provide a method for purifying an aromatic dihydroxy compound in a short time and with a simple process without using an organic solvent.

  As a result of intensive studies to solve the above problems, the present inventors have paid attention to the fact that aromatic dihydroxy compounds are dissolved in supercritical water or subcritical water under specific conditions. To achieve an effective and economical purification of aromatic dihydroxy compounds.

（ここで、Ｒ¹、Ｒ²、Ｒ³およびＲ⁴は互いに独立に水素原子、炭素数１〜１０のアルキル基、炭素数６〜１０のアリール基または炭素数７〜１０のアラルキル基またはハロゲン原子であり、そしてＷは単結合、炭素数１〜１０のアルキレン基、炭素数２〜１０のアルキリデン基、炭素数６〜１０のシクロアルキレン基、炭素数６〜１０のシクロアルキリデン基、炭素数８〜１５のアルキレン−アリーレン−アルキレン基、酸素原子、硫黄原子、スルホキシド基またはスルホン基である。）
で表される芳香族ジヒドロキシ化合物である請求項１または２に記載の芳香族ジヒドロキシ化合物の精製方法。
４．前記芳香族ジヒドロキシ化合物が２，２−ビス（４−ヒドロキシフェニル）プロパンである芳香族ジヒドロキシ化合物の精製方法。
５．前記超臨界水または亜臨界水への芳香族ジヒドロキシ化合物の溶解を３７４℃以上５００℃以下の温度範囲および１８ＭＰａ以上４０ＭＰａ以下の圧力範囲内で行なう芳香族ジヒドロキシ化合物の精製方法。 That is, the present invention is as follows.
1. Aromatic dihydroxy compound is dissolved in supercritical water or subcritical water in a range where the dielectric constant of the supercritical water or subcritical water is 5 or less, and then the supercritical or subcritical state is released and crystallized. A method for purifying an aromatic dihydroxy compound characterized by the following.
2. A method for purifying an aromatic dihydroxy compound, comprising using an aqueous solution of an aromatic dihydroxy compound in which an aromatic dihydroxy compound is dissolved in supercritical water or subcritical water as a filtering means.
3. The aromatic dihydroxy compound is represented by the following formula (1):

(Wherein R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, or a halogen atom) And W is a single bond, an alkylene group having 1 to 10 carbon atoms, an alkylidene group having 2 to 10 carbon atoms, a cycloalkylene group having 6 to 10 carbon atoms, a cycloalkylidene group having 6 to 10 carbon atoms, or a carbon number. 8-15 alkylene-arylene-alkylene group, oxygen atom, sulfur atom, sulfoxide group or sulfone group.)
The method for purifying an aromatic dihydroxy compound according to claim 1, wherein the aromatic dihydroxy compound is represented by the formula:
4). A method for purifying an aromatic dihydroxy compound, wherein the aromatic dihydroxy compound is 2,2-bis (4-hydroxyphenyl) propane.
5 . Purification method of the preceding Symbol supercritical water or sub aromatic dihydroxy compound dissolved aromatic dihydroxy compound performing within the following pressure range 374 ° C. or higher 500 ° C. or less of the temperature range and 18MPa or 40MPa of the critical water.

  As described above, according to the present invention, an aromatic dihydroxy compound can be purified by an environmentally friendly and simple process to obtain an aromatic dihydroxy compound having a high purity that is optimal as a resin raw material.

  The present invention relates to a completely novel method for purifying an aromatic dihydroxy compound having the characteristics as described above, and an embodiment thereof will be described below.

  The present invention can be applied to an aromatic dihydroxy compound obtained by any production method. Examples of the production method include a reaction of a hydroxy compound and acetone in the presence of an acidic catalyst. Further, the present invention can be widely applied to aromatic dihydroxy compounds obtained not by synthesis from raw materials but by decomposition of resins. The aromatic dihydroxy compound may contain any impurities. Examples of the impurities contained include hydroxy compounds mainly composed of phenol, acetone, various by-products including highly condensed condensates, inorganic salts, A metal etc. are mentioned. Furthermore, the form of the aromatic dihydroxy compound used in the present invention may be any of known forms such as prills, flakes, and powders.

・・・（１）
（ここで、Ｒ¹、Ｒ²、Ｒ³およびＲ⁴は互いに独立に水素原子、炭素数１〜１０のアルキル基、炭素数６〜１０のアリール基または炭素数７〜１０のアラルキル基またはハロゲン原子であり、そしてＷは単結合、炭素数１〜１０のアルキレン基、炭素数２〜１０のアルキリデン基、炭素数６〜１０のシクロアルキレン基、炭素数６〜１０のシクロアルキリデン基、炭素数８〜１５のアルキレン−アリーレン−アルキレン基、酸素原子、硫黄原子、スルホキシド基またはスルホン基である。）、
で表される繰り返し単位からなるものを好ましいものとして挙げることができる。 The aromatic dihydroxy compound used in the present invention is not particularly limited, but the following formula (1)

... (1)
(Wherein R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, or a halogen atom) And W is a single bond, an alkylene group having 1 to 10 carbon atoms, an alkylidene group having 2 to 10 carbon atoms, a cycloalkylene group having 6 to 10 carbon atoms, a cycloalkylidene group having 6 to 10 carbon atoms, or a carbon number. 8 to 15 alkylene-arylene-alkylene group, oxygen atom, sulfur atom, sulfoxide group or sulfone group).
What consists of a repeating unit represented by these can be mentioned as a preferable thing.

The alkyl group having 1 to 10 carbon atoms may be linear or branched. Examples thereof include methyl, ethyl, propyl, butyl, octyl, decyl and the like. Examples of the aryl group having 6 to 10 carbon atoms include phenyl, tolyl, cumyl, naphthyl and the like. Examples of the aralkyl group having 7 to 10 carbon atoms include benzyl, 2-phenethyl, 2-methyl, 2-phenylethyl and the like.
As R ¹ , R ² , R ³ and R ⁴ , independently of each other, a hydrogen atom, a methyl group and a t-butyl group are preferable, and a hydrogen atom is particularly preferable.

The definition of W is also as follows.
The alkylene group having 1 to 10 carbon atoms may be linear or branched. Examples thereof include methylene, 1,2-ethylene, 2,2-propylene, 2,2-butylene, 1,1-decylene and the like.
Examples of the alkylidene group having 2 to 10 carbon atoms include ethylidene, propylidene, butylidene, and hexylidene.
Examples of the cycloalkylene group having 6 to 10 carbon atoms include 1,4-cyclohexylene and 2-isopropyl-1,4-cyclohexylene.
Examples of the cycloalkylidene group having 6 to 10 carbon atoms include cyclohexylidene and isopropylcyclohexylidene.
Examples of the alkylene-arylene-alkylene group having 8 to 15 carbon atoms include m-diisopropylphenylene group.
W is preferably a cyclohexylidene group or a 2,2-propylidene group, and particularly preferably a 2,2-propylidene group.

  Specific examples of such aromatic dihydroxy compounds include 2,2-bis (4-hydroxyphenyl) propane (ie BPA), bis (4-hydroxyphenyl) methane, 1,1-bis (4′-hydroxyphenyl) ethane. 1,2-bis (4′-hydroxyphenyl) ethane, bis (4-hydroxyphenyl) phenylmethane, 1,1-bis (4′-hydroxyphenyl) -1-phenylethane, 2- (4′-hydroxy) Phenyl) -2- (3′-hydroxyphenyl) propane, 2,2-bis (4′-hydroxyphenyl) butane, 1,1-bis (4′-hydroxyphenyl) isobutane, 4,4′-dihydroxydiphenyl, etc. Is mentioned.

  Next, the supercritical water or subcritical water used in the present invention will be described. The supercritical fluid indicates a substance in a state exceeding the critical temperature and the critical pressure, and the supercritical water indicates water having a critical temperature of 374 ° C. or higher and a critical pressure of 22 MPa or higher. In the present invention, subcritical water refers to water that is at a temperature of 350 ° C. or higher and a pressure of 18 MPa or higher and is not in a supercritical state. Supercritical or subcritical water is known to vary widely in physical properties such as density, ion product, ion concentration, dielectric constant, etc., depending on its temperature and pressure, and these are easily controlled. It is possible. As a result, the dissolving power of the substance of supercritical water or subcritical water changes within a very large range, and the solute molecules have an effect comparable to that of exchanging the solvent. Furthermore, supercritical water or subcritical water has a lower viscosity than liquid, so the diffusion of substances is faster, and the reaction in supercritical water or subcritical water is less likely to be diffusion-controlled than the reaction in normal liquid. There are also advantages. From a practical point of view, water is the cheapest, non-toxic, flame retardant, less burden on the environment, excellent in thermal stability, and is not ideally oxidized. .

  The dissolution of the aromatic dihydroxy compound in the supercritical water or subcritical water in the present invention is preferably performed within the range where the dielectric constant of the supercritical water or subcritical water is 10 or less, more preferably 5 or less. It is preferable. The dielectric constant is a coefficient indicating the relationship between the electric charge in the substance and the force applied thereby, and is an index of the polarity of the solvent. Since the dielectric constant of water at room temperature is as large as about 80, inorganic substances such as electrolytes dissolve well, but organic substances hardly dissolve. However, when the temperature is raised, the dielectric constant gradually decreases, and in the case of supercritical water or subcritical water at 374 ° C. or higher, the value is about 10 and the value of an organic solvent having a small polarity. As a result, a phenomenon opposite to that of normal water occurs in which organic matter dissolves well but inorganic matter hardly dissolves. In the present invention, the solubility of the aromatic dihydroxy compound in supercritical water can be improved by setting the dielectric constant to 10 or less. A dielectric constant of 10 or more is not preferable because the solubility of the aromatic dihydroxy compound decreases and thermal decomposition proceeds.

  Furthermore, the dissolution of the aromatic dihydroxy compound in supercritical water or subcritical water in the present invention is preferably performed at a temperature of supercritical water or subcritical water of 374 ° C. or higher and 500 ° C. or lower, which is the critical temperature. Is preferably 430 ° C. or lower. A temperature of 374 ° C. or lower is not preferable because the dielectric constant of supercritical water increases rapidly and the solubility of the aromatic dihydroxy compound decreases. Further, if the temperature is 500 ° C. or higher, the thermal decomposition reaction of the aromatic dihydroxy compound proceeds and the generation of the by-product hydroxy compound or its derivative is caused, which may cause a decrease in purity or coloring of the obtained aromatic dihydroxy compound. This is not preferable.

  The pressure condition is preferably 18 MPa or more and 40 MPa or less, more preferably 20 MPa or more and 30 MPa or less. When the pressure is 40 MPa or more, a large amount of energy cost is required in an industrial process, and a great load is imposed on safety and economy, which is not preferable. On the other hand, if it is 18 MPa or less, the physical properties peculiar to the above-mentioned subcritical water are difficult to be expressed.

  The reaction time in the present invention is not particularly limited, but the aromatic dihydroxy compound can be dissolved in a very short time of 5 minutes or less under the above conditions. Prolonging the dissolution time is not preferable because the decomposition of the dihydroxy compound proceeds to lower the purity, and the processing amount per unit time decreases or the volume of the container increases in an industrial process.

  The embodiment of the present invention may be any of a flow type, a semi-batch type, or a batch type reactor, but the use of the flow type is preferable because the throughput can be increased. In addition, since the solubility of inorganic salts in supercritical water or subcritical water is very low, an inorganic dihydroxy compound aqueous solution in which an aromatic hydroxy compound is dissolved in supercritical water or subcritical water is used as a filtration means. It is possible to remove impurities. Although the filtration method is not particularly limited, for example, a filter medium such as a membrane filter, a filter paper, and a sintered filter can be used. Moreover, foreign substances other than inorganic salts, such as a mineral insoluble in supercritical water, are removed by the filtration treatment.

  The aromatic dihydroxy compound dissolved in supercritical water or subcritical water can be easily crystallized and recovered by releasing the supercritical state after passing through the filtration means as necessary. The release of the supercritical state is performed by lowering the temperature and pressure to any temperature pressure below the critical point. For example, it can be lowered to room temperature and normal pressure, and it is a poorly used crystallization operation from a good solvent. No addition of solvent is necessary. In addition, a known crystallization operation such as cooling can be used in combination as required.

  The aromatic dihydroxy compound purified by the present invention has the features that the residual solvent amount is low, the purity is high, and the coloring degree is low compared with the aromatic dihydroxy compound purified by other methods. High-quality resins can be obtained by using as raw materials for epoxy resins, polycarbonate compound resins, and other resins.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

[Example 1]
In a tube-type reaction tube made of SUS316 having a total internal volume of 6 mL, 0.1 g of crude BPA obtained by hydrolysis of polycarbonate was charged, and 1.1 g of water was charged so that the pressure became 25 MPa, followed by sealing. After the inside of the reaction tube was replaced with argon to make an inert atmosphere, it was immersed in a sand bath preheated to 400 ° C. and held for 3 minutes. Here, the relative dielectric constant in the above condition = 2. Thereafter, the reaction tube was immersed in water and rapidly cooled to room temperature, and the contents were taken out into a glass bottle. As a result, colorless BPA needle crystals were observed under a temperature and pressure condition of 20 ° C. and 0.1 MPa.
The crystals were collected and dissolved in diethyl ether, and this solution was analyzed by gas chromatography (HP5890). As a result, it was confirmed that the purity of the BPA was 99%.

[Comparative Example 1]
The reaction tube was charged with 0.1 g of crude BPA obtained by hydrolysis of polycarbonate, charged with 4.8 g of water so that the pressure was 30 MPa, and sealed. After the inside of the reaction tube was replaced with argon to make an inert atmosphere, it was immersed in a sand bath preheated to 270 ° C. and held for 30 minutes. Here, the relative dielectric constant under the above conditions was 25. Then, when the reaction tube was immersed in water and rapidly cooled to room temperature, the content was taken out into a glass bottle, and the content was colored brown.
The contents were dissolved in diethyl ether in the same manner as in Example 1 and analyzed by gas chromatography. As a result, formation of phenol, isopropylphenol, and the like due to secondary decomposition of BPA was confirmed, which proved undesirable.

Claims (5)

Aromatic dihydroxy compound is dissolved in supercritical water or subcritical water in a range where the dielectric constant of the supercritical water or subcritical water is 5 or less, and then the supercritical or subcritical state is released and crystallized. A method for purifying an aromatic dihydroxy compound characterized by the following.   The method for purifying an aromatic dihydroxy compound according to claim 1, wherein an aqueous solution of the aromatic dihydroxy compound in which the aromatic dihydroxy compound is dissolved in supercritical water or subcritical water is provided to a filtration means. The aromatic dihydroxy compound is represented by the following formula (1):

(Wherein R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, or a halogen atom) And W is a single bond, an alkylene group having 1 to 10 carbon atoms, an alkylidene group having 2 to 10 carbon atoms, a cycloalkylene group having 6 to 10 carbon atoms, a cycloalkylidene group having 6 to 10 carbon atoms, or a carbon number. 8-15 alkylene-arylene-alkylene group, oxygen atom, sulfur atom, sulfoxide group or sulfone group.)
The method for purifying an aromatic dihydroxy compound according to claim 1, wherein the aromatic dihydroxy compound is represented by the formula:   The method for purifying an aromatic dihydroxy compound according to claim 3, wherein the aromatic dihydroxy compound is 2,2-bis (4-hydroxyphenyl) propane. The aromatic dihydroxy compound according to claim 1 or 2, wherein the aromatic dihydroxy compound is dissolved in the supercritical water or subcritical water within a temperature range of 374 ° C to 500 ° C and a pressure range of 18 MPa to 40 MPa. Purification method.