JPH05997A - Method for separating para-hydroxybenzoic acid - Google Patents

Abstract

(57) [Summary] [Purpose] From the reaction mixture of the Kolbe-Schmidt reaction,
Development of efficient method for separating para-hydroxybenzoic acid. [Structure] The reaction mixture of the Kolbe-Schmidt reaction is extracted and separated using water and an organic solvent insoluble or sparingly soluble in water, and an alkaline earth metal hydroxide is added to the aqueous layer and stirred to generate. After separating and removing the insoluble matter, the filtrate was acidified with mineral acid and heated to dissolve para-hydroxybenzoic acid, and at the same time, phenol, substituted phenols and / or organic impurities were distilled off, and the residual solid was heated. A method for separating para-hydroxybenzoic acid, which comprises filtering and filtering the filtrate to precipitate para-hydroxybenzoic acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and obtaining parahydroxybenzoic acid from a reaction mixture obtained by reacting a phenol alkali or a mixture containing a phenol alkali and a substituted phenol alkali with carbon dioxide.

[0002]

2. Description of the Related Art Parahydroxybenzoic acid has a wide range of uses as a raw material for polymer materials, and recently, it has attracted attention as a raw material for liquid crystal polyesters having high strength and high heat resistance. Also, most of the alkyl esters are
It is also a useful substance as a fungicide for cosmetics and industry.

In the industrial production of parahydroxybenzoic acid, a solid-gas phase reaction by the so-called Kolbe-Schmidt method in which powdered potassium phenol and carbon dioxide are reacted under high temperature and pressure, and a reaction medium in which this reaction is inactive The method carried out in is used (for example, Japanese Patent Publication No. 50-51).
82, Japanese Patent Publication No. 43-26612, etc.). In addition, recently, a method of reacting a mixture of a phenol alkali and a substituted phenol alkali with carbon dioxide to synthesize parahydroxybenzoic acid with high yield and high selectivity (JP-A-02-124847) has been proposed by the present inventors. It has been reported, and as a suitable example thereof, a method using a potassium salt such as tar acid, which is a mixture of phenol obtained from coal tar and substituted phenols, as a raw material has been proposed.

Since the parahydroxybenzoic acid obtained by these reactions is actually an alkali metal salt, industrially, the following separation operation is mainly carried out.

For example, in Japanese Examined Patent Publication No. 55-19207,
Water and an organic solvent insoluble in water (which may also be used as a reaction medium) are added to the reaction mixture, the by-produced phenol and / or the reaction medium is extracted into an organic solvent layer, and the layers are separated to separate parahydroxybenzoic acid. An aqueous solution containing a potassium salt is obtained, then
A mineral acid is added to the aqueous solution for neutralization, unreacted phenol potassium is converted to a free acid, and an organic solvent insoluble in water is added again to extract and remove the released phenol, and the separated aqueous layer is separated. A method of crystallization of potassium mineral acid, para-hydroxybenzoic acid, and salicylic acid in stages after treatment with activated carbon and adjusting the acidity with mineral acid in two stages is disclosed.

[0006] However, the above reaction (Kolbe-Schmidt reaction) is carried out at 200 times in order to suppress the by-product of salicylic acid.
It is often done under high temperature of ℃ or more, and for that reason,
Although there is a small amount, by-products such as tar-like and resin-like colored substances of unknown structure cannot be avoided. Therefore, an operation for removing these impurities will be incorporated in the actual separation and acquisition step, and various methods have been reported.

For example, JP-A-48-28445 discloses that
It is described that impurities in the aqueous solution containing the reaction mixture are filtered off as necessary to remove the reaction medium and the resinous substance. Further, adsorption decolorization with activated carbon is cited as a commonly used method. Japanese Patent Publication No. 46-43
As disclosed in No. 532, an aqueous solution of an alkali metal salt of oxybenzoic acids excluding parahydroxybenzoic acid is treated with chlorides, oxides, hydroxides, etc. of calcium, barium, magnesium to remove insoluble matter. There is also a way to remove it. JP-B-45-36497 describes a reductive decolorizing and refining method using powdered zinc.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Although the Schmitt reaction is carried out at a high temperature of 200 ° C. or higher, the amount of the Schmitt reaction may vary depending on the raw material and the like, but impurities such as tar-like or resin-like colored substances whose structure is unknown cannot be avoided. In particular, when a potassium salt of taric acid is used as a raw material as in JP-A-2-124847, impurities specific to coal tar are also mixed, so that the impurities increase.

However, among the conventional methods for removing impurities, the reductive decolorization method using zinc is not limited to phosphoric acid,
It is also uneconomical because treatment with a surfactant or the like is required, expensive metal is used, and waste liquid treatment is complicated. Further, with respect to other methods, there is a problem that the color removal effect is not certain when the amount of impurities is large, or if this is surely performed, a decrease in the yield of parahydroxybenzoic acid cannot be avoided. is there.

The present invention solves the above problems and provides a technique for efficiently separating parahydroxybenzoic acid from a reaction mixture by-products such as salicylic acids and phenols, a reaction medium, colored impurities and the like. With the goal.

[0011]

To achieve the above object, in a first embodiment of the present invention, a reaction mixture obtained by reacting a phenol alkali or a mixture containing a phenol alkali and a substituted phenol alkali with carbon dioxide is used. In the method for extracting para-hydroxybenzoic acid,
A first step in which the reaction mixture is extracted and separated using water and an organic solvent insoluble or hardly soluble in water, and a hydroxide of an alkaline earth metal is added to the aqueous layer obtained in the first step and stirred. Then, the second step of separating and removing the generated insoluble matter, the third step of acidifying the aqueous solution obtained in the second step with mineral acid, and heating the acidic water obtained in the third step Dissolving hydroxybenzoic acid and distilling and removing phenol, substituted phenols and / or organic impurities
Step, a fifth step of separating residual insoluble impurities in the heated acidic water obtained in the fourth step under heating, and the heated acidic aqueous solution obtained in the fifth step is cooled to precipitate parahydroxybenzoic acid. After that, a method for separating para-hydroxybenzoic acid is provided, which includes the respective step sequences of the sixth step of separating and obtaining the same from the acidic aqueous solution.

Here, after carrying out the above first to sixth steps, the parahydroxybenzoic acid is further dissolved in a solvent which dissolves the parahydroxybenzoic acid and does not substantially dissolve the alkali mineral acid, and the extract is separated. It is preferable to carry out the step of obtaining parahydroxybenzoic acid from the extract.

The phenol alkali and the substituted phenol alkalis are preferably phenol potassium and substituted phenol potassium. The mixture containing the phenol alkali and the substituted phenol alkalis is preferably a mixture containing potassium tarrate and / or potassium cresolate. The mineral acid is preferably sulfuric acid.

The present invention will be described in more detail below.
The mixture containing parahydroxybenzoic acid used in the present invention may be a so-called Kolbe-Schmidt reaction mixture in which a phenol alkali or a mixture containing a phenol alkali and a substituted phenol alkali is reacted with carbon dioxide. The alkali metal salt usually used is potassium salt.

When the reaction raw material is an alkali metal salt of tar acid obtained from coal tar, the tar-specific impurities are often contained in the reaction mixture.
Separation of parahydroxybenzoic acid from the reaction mixture has been difficult by conventional separation and purification methods, but the method of the present invention can be effectively used for treating such complicated reaction mixture. .

In the first aspect of the present invention, first, in the first step, the reaction mixture is extracted and separated using water and an organic solvent insoluble or hardly soluble in water.

The organic solvent used in the first step preferably has a high ability to dissolve the by-produced phenol and substituted phenols and / or the reaction medium. Further, any organic solvent inert to the reaction can also be used as the reaction medium. When used also as a reaction medium, a solvent having a higher boiling point is preferably used because the reaction pressure can be easily controlled.

As the organic solvent used in the first step, those which can be used also as the reaction medium include, for example, aromatic hydrocarbons, aromatic ethers, aromatic alkanes, aromatic alkenes, aromatic ketones, and hydrides thereof. Or an aliphatic petroleum hydrocarbon, an aprotic polar solvent, an aromatic alcohol, an aliphatic higher alcohol, etc. These may be used alone or in combination of two or more as a mixed medium.

More specifically, for example, biphenyl, terphenyl, naphthalene, anthracene, ditolylethane, dibenzyltoluene, methylnaphthalene, isopropylnaphthalene, GS250 (a mixture of aromatic compounds containing methylnaphthalene as a main component), NeoSK. -oil
(Made by Soken Kagaku Co., Ltd.), Dowtherm (mixture of biphenyl and diphenyl ether), ethyl biphenyl, diphenyl ether, hydrogenated terphenyl, benzyl phenyl ether, benzophenone, kerosene and / or light oil having a boiling point of 150 ° C or higher, having 5 to 15 carbon atoms. Examples include fatty acid higher alcohols, or a mixture thereof.

On the other hand, when the organic solvent used in this first step is not used also as the reaction medium, the separation surface is better when the recovery is easy and the difference in boiling point between the reaction medium and / or by-produced phenol or substituted phenol is large. Therefore, those having a very high boiling point are not preferred.

Examples of such an organic solvent which is not used also as a reaction medium include aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, cyclohexane and decalin, benzene, toluene, xylene, 1-
Aromatic hydrocarbons such as methylnaphthalene, isopropylnaphthalene, tetrahydronaphthalene, acetophenone,
Ketones such as methyl isobutyl ketone, alcohols such as butanol and amyl alcohol, phenols such as phenol, cresol and xylenol, methyl acetate,
Examples thereof include esters such as ethyl acetate and methyl propionate, ethers such as diethyl ether, and the like.
You may use 1 type or may use 2 or more types together.

The organic solvent used in the first step is
As long as it is in a liquid state when used, liquefied hydrocarbons (ethane, propane,
Butane), hydrocarbons such as 2-methylnaphthalene and naphthalene that become liquid by heating, and a dimethylnaphthalene mixture that is liquid in a mixed state can also be used.

These organic solvents serve to dissolve the reaction medium and the by-produced phenol and / or substituted phenols, and to lower the viscosity of the reaction mixture to facilitate extraction and separation.

The amount of the organic solvent used varies depending on the amount of the reaction medium used, the amount of impurities, the reaction rate and the like, but since the alkali metal salt of parahydroxybenzoic acid is usually the main component of the reaction mixture, the reaction mixture 1 With respect to parts by weight, 0.
It is 1 part by weight or more, preferably 1 to 100 parts by weight.
If it is less than 0.1 part by weight, the extraction effect of the organic solvent is not exhibited, while if it is more than 100 parts by weight, it is not economical.

The amount of water used in the first step is not particularly limited as long as it is at least an amount capable of dissolving the alkali metal salt of parahydroxybenzoic acid. It may be determined in consideration of the amount of water adjustment in the fourth step and / or the fifth step.

The extraction method for extraction and separation is, for example, shaking extraction, extraction using a static mixer, stirring extraction, etc., and the separation method is stationary separation, centrifugation, etc.

Needless to say, the present invention can also be applied to a reaction mixture prepared without using a reaction medium.

Next, in the second step, in which the aqueous layer obtained in the first step is separated, an alkaline earth metal hydroxide is added thereto and the mixture is stirred, and the resulting precipitate is separated by filtration. This is the process of

Since the alkali metal salt of parahydroxybenzoic acid is easily soluble in water, it is transferred from the reaction mixture to the aqueous layer in the first step. However, since coloring impurities and the like are also transferred to this aqueous layer, in the second step, the coloring impurities and the like are treated with a hydroxide of an alkaline earth metal to be filtered out as a precipitate. .

Preferred alkaline earth metal hydroxides used in this step are calcium hydroxide, magnesium hydroxide, barium hydroxide and the like.

By this operation, that is, the amount of parahydroxybenzoic acid lost with precipitation was extremely small, and was about 0.3% in the case of Example 1 described later using calcium hydroxide, for example.

In this step, the hydroxide of alkaline earth metal may be added until the color precipitate does not increase. It is uneconomical to add more. Further, this operation may be performed at room temperature or under heating.

Next, as a third step, mineral acid is added to the filtrate to liberate parahydroxybenzoic acid.

The acidity at this time is pH 5 or less, preferably pH 4 or less, but when para-hydroxybenzoic acid is separated from the reaction mixture obtained by using a potassium salt of taric acid as a reaction raw material, this step is performed. It is preferable to adjust the pH to 2 or less because it also prevents coloration.

As the mineral acid, sulfuric acid, nitric acid, hydrochloric acid and the like can be exemplified, but sulfuric acid is preferable from the viewpoint of price and corrosiveness.

Next, in a fourth step, the acidic water is heated to dissolve the precipitated parahydroxybenzoic acid and distill off organic impurities such as phenol, substituted phenols, salicylic acid and / or residual organic solvent. Remove.

The temperature at which the acidic water is heated in the fourth step varies depending on the pH, the amount of water, etc. and cannot be generally stated, but the boiling temperature is usually preferred. Excessive heating above this is not preferable because of phenomena such as bumping.

When parahydroxybenzoic acid is separated from a reaction mixture obtained by using a potassium salt of tarric acid as a raw material, impurities which are considered to be derived from tar are dispersed in crystals when the temperature of acidic water is low. However, when the temperature rises, the residual phenols, the residual reaction medium, the residual extraction organic solvent and the like are dissolved to exist as an oil layer. By heating this acidic water and the oil layer, the oil layer is azeotropically distilled and gradually disappears, and impurities and tar-like substances become powdery solids, so separation from these hot solutions (acidic water) is easy. Becomes

By the way, when the organic impurities and the like are removed by distillation in the fourth step, it is preferable to adjust the concentration by distilling water as well. At this time, if the amount of water is small, the required amount of heat can be reduced, but if it is too small, azeotropic distillation with organic impurities cannot be sufficiently performed. The amount of water distilled out varies depending on the content of parahydroxybenzoic acid or the amount of residual organic medium or phenol. The amount of water to be distilled off, in other words, the amount of remaining water is
It is important because it depends on the success or failure of the fifth step.

That is, in the fifth step, which will be described later, the amount of water used for hot separation of the heated acidic water and the solid insoluble therein may be at least an amount at which parahydroxybenzoic acid can be dissolved. This is because an excess amount that is close to the required amount of benzoic acid dissolved is most preferable. In such a case, depending on the yield of para-hydroxybenzoic acid and the amount of the alkali metal salt of by-product mineral acid, when the para-hydroxybenzoic acid is dissolved, part of the alkali metal salt of mineral acid precipitates. Rest as
It is convenient because it can be partially removed together with the solid insoluble in the heated acidic aqueous solution, and when the heated acidic aqueous solution is separated and then the solid is precipitated by cooling (sixth step), para-hydroxybenzoic acid is added to the solution. This is because there is an advantage that the loss due to the acid remaining can be reduced. On the other hand, if the amount of water is less than the amount capable of dissolving para-hydroxybenzoic acid, para-hydroxybenzoic acid precipitates and is separated together with solids such as impurities and tar-like substances to be separated, and the yield is reduced, which is preferable. Absent.

The end point of the operation for removing the organic impurities and the like in the fourth step is usually judged by, for example, the following method with the end of the distillation removal of the distillative components other than water as a guide.

That is, when the heating is sufficiently performed, the phenols, the organic solvent, and the salicylic acids are distilled off together with water or alone. At a certain point, it is determined whether or not the phenols and salicylic acids are distilled off. In order to judge, a ferric chloride color reaction test was conducted on the distillate,
When no color is observed, the removal of distillate is stopped.

Next, in a fifth step, the heated acidic water and the residual insoluble impurities are separated by filtration while hot, and in a sixth step, the filtrate is cooled to precipitate parahydroxybenzoic acid. Separated from acidic aqueous solution.

For separating the heated acidic aqueous solution and the insoluble impurities, for example, a method such as filtration, decantation or centrifugation is preferably used. It is also effective to combine activated carbon treatment.

Also in carrying out the sixth step, the amount (or concentration) of the acidic aqueous solution is still important. At this time, if the amount (concentration) is such that the alkali metal salt of the mineral acid can be dissolved even when it is cold, it is preferable because the subsequent separation operation of the parahydroxybenzoic acid and the alkali metal salt of the mineral acid can be simplified. After separation of the hot solution (the end of the fifth step), the amount of water in the aqueous solution may be reduced as much as possible by a means such as concentration to increase the yield of parahydroxybenzoic acid.

In the sixth step, when the parahydroxybenzoic acid is precipitated by cooling, as described above, it is preferable that the alkali metal salt of the mineral acid remains in the mother liquor at the time of cooling, but the concentration is higher than that (water If the amount is small), the alkali metal salt of mineral acid will also precipitate together with para-hydroxybenzoic acid. In such a case, the following operation may be further performed.

That is, a mixture of parahydroxybenzoic acid and an alkali metal salt of a mineral acid obtained by cooling the aqueous solution obtained in the fifth step is separated from the solution, and then parahydroxybenzoic acid is separated from the separated mixture. The acid is extracted with solvent.

The solvent used here may be any solvent as long as it does not substantially dissolve the alkali metal salt of mineral acid and dissolves parahydroxybenzoic acid, such as acetone, methyl ethyl ketone, methyl. Aliphatic ketones such as isobutyl ketone, aliphatic alcohols such as methanol, ethanol, n-propanol, isopropanol and n-butanol, aliphatic halogenated hydrocarbons such as dichloromethane, chloroform and carbon tetrachloride, benzene, toluene, etc. And aromatic ethers such as diethyl ether, and ethers such as tetrahydrofuran.

The extraction operation is usually carried out at room temperature and atmospheric pressure, but it may be carried out under heating and / or stirring.

In this way, para-hydroxybenzoic acid is dissolved in the solvent, and the alkali metal salt of mineral acid remains in the solid state. This solid-liquid phase separation may be carried out by a method such as filtration, decantation or centrifugation. Further, the subsequent separation of parahydroxybenzoic acid from the extract may be carried out by a known method such as solvent removal, reprecipitation, crystallization and the like.

By the above operation, highly pure parahydroxybenzoic acid can be separated and obtained. However, if it is desired to further raise the purity, it can be purified by a recrystallization method which is usually performed. It does not reach.

[0052]

EXAMPLES The present invention will be described in more detail below by exemplifying a case where a potassium salt of tarric acid containing a large amount of impurities of unknown structure is used as a starting material. Therefore, it is obvious that the present invention can be applied to the Kolbe-Schmidt reaction product obtained by using ordinary phenol potassium.
It should be added that the present invention is not limited to the following examples.

Example 1 Tar acid, which is a mixture of phenol and substituted phenols obtained from coal tar, was treated with potassium hydroxide and dried to obtain powdery potassium tarrate. When this was analyzed, in addition to phenol potassium, cresol potassium, and xylenol potassium, 7.8 wt% of a substance of unknown structure was contained.
738 g of this dry powdery potassium tarrate was put into a pressure resistant reactor, carbon dioxide gas was introduced, and the reaction pressure was 3.0 kg / cm ²
Under (G), the mixture was reacted at 270 to 290 ° C for 40 minutes to obtain a dark brown reaction mixture. From this, 15 g was weighed and used as a sample for separation. On the other hand, when a part of this sample (reaction mixture) was acidified and analyzed, 15 g of this separation sample showed that
Para-hydroxybenzoic acid in terms of free acid: 4.86 g,
It was found that salicylic acid: 0.05 g, phenol: 0.95 g, cresols: 3.18 g, etc. were contained. 15 g of this sample, 100 ml of water and 100 ml of toluene were placed in a separatory funnel, shaken at 70 to 80 ° C., then kept at 70 to 80 ° C. and allowed to stand to separate them. Next, the aqueous layer was separated, cooled to room temperature, 1.8 g of calcium hydroxide was added, and the mixture was stirred to cause black precipitation from the dark brown aqueous solution to become a light brown to pale yellow transparent liquid. . After the black precipitate was removed by filtration, sulfuric acid was added to the aqueous solution to adjust the pH to 2, and a pale yellowish brown precipitate was formed. This was heated and boiled (about 100 ° C.) while being supplemented with warm water, and the generated steam was distilled off from the side tube while dissolving the parahydroxybenzoic acid. At this time, some of the residual phenol, cresol, toluene, and salicylic acid are removed by azeotropic distillation or distillation. This operation was carried out until a ferric chloride test was conducted on the distillate until no coloration of blue to magenta was observed. As a result, the residual water amount is about 80m
It was concentrated to l. At this time, impurity solids insoluble in acidic water were floating in the system. The acidic water was then filtered hot. At that time, the filtrate was passed through a 0.25 g layer of activated carbon charged in the leg of the funnel. Then, the obtained filtrate is cooled to 5 ° C., and a white solid crystallized is separated and obtained by filtration, and then washed with cold water to obtain a purity of 9%.
4.07 g (isolation yield 83.7%) of 9.4% para-hydroxybenzoic acid was obtained.

(Example 2) Using 15 g of the same sample as in Example 1, the same operation was carried out except that the amount of residual water in the system after the heating distillation operation was about 60 ml, and the filtrate of heated acidic water was heated to 5 ° C.
Cooled to 9.4 g of a white solid. However, about half of that is potassium sulfate, which is 47.7 wt% of the total solids.
The only was parahydroxybenzoic acid. Therefore, acetone was added to this solid to extract parahydroxybenzoic acid and the solvent was removed to obtain 4.36 g of parahydroxybenzoic acid having a purity of 99.1% (separation yield: 89.7%).

Example 3 Tar acid, which is a mixture of phenol and substituted phenols obtained from coal tar, was treated with potassium hydroxide and dried to obtain powdery potassium tarrate. When this was analyzed, in addition to phenol potassium, cresol potassium, and xylenol potassium, 6.4 wt% of a substance of unknown structure was contained.
36.2 g of this dry powdery potassium tarrate was put in a pressure resistant reactor together with 60 g of a high boiling fraction of light oil (150 to 230 ° C / 10 mmHg), carbon dioxide gas was introduced, and a reaction pressure of 3.2 kg / cm ² (G The reaction was performed at 290 ° C. for 40 minutes under the conditions described above to obtain a dark brown reaction mixture. This was mixed well and 30 g was weighed to obtain a sample for separation. On the other hand, when a part of this sample (reaction mixture) was acidified and analyzed, 30 g of this separation sample was converted into free acid, parahydroxybenzoic acid: 4.17 g, salicylic acid: 0.01 g, phenol: 0 It was found that 0.53 g, cresols: 3.03 g and high boiling point diesel oil: about 17.8 g were contained. 30 g of this sample, 100 ml of water and 100 ml of toluene were placed in a separatory funnel, shaken at 70 to 80 ° C., and then kept at 70 to 80 ° C. and allowed to stand to separate them. Next, the aqueous layer was separated, cooled to room temperature, 1.5 g of calcium hydroxide was added, and the mixture was stirred, whereupon a black precipitate was produced from the dark brown aqueous solution to give a pale brown to pale yellow transparent liquid. . After the black precipitate was removed by filtration, sulfuric acid was added to the aqueous solution to adjust to pH 2, and a pale yellowish brown precipitate was formed. This was heated and boiled (about 100 ° C.) while being supplemented with warm water, and the generated steam was distilled off from the side tube while dissolving the parahydroxybenzoic acid. At this time, residual phenol, cresol, organic solvent (light oil and toluene), and part of salicylic acid are removed by azeotropic distillation or distillation. This operation was carried out until a ferric chloride test was conducted on the distillate until no coloration of blue to magenta was observed. As a result, it was finally concentrated until the residual water amount became about 70 ml.
At this time, impurity solids insoluble in acidic water were floating in the system. The acidic water was then filtered hot. At that time, the filtrate was passed through 0.2 g of the activated carbon layer charged in the leg of the funnel. Then, the obtained filtrate was cooled to 5 ° C., and the crystallized white solid was separated and obtained by filtration, and then washed with cold water to obtain 3.43 g of parahydroxybenzoic acid having a purity of 99.6% (separated yield). Rate 82.3%).

[0056]

EFFECTS OF THE INVENTION Since the present invention is constructed as described above, according to the present invention, the acidification operation is carried out in one stage,
The reaction medium, by-products and colored impurities can be efficiently separated from parahydroxybenzoic acid. The present invention provides a para-hydroxybenzoic acid useful as an industrial raw material, which can surely show its effect even when there are many colored impurities like a reaction mixture obtained when tarric acid is used as a raw material. You can

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuyuki Sato             1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.             Corporate Technology Research Division (72) Inventor Matsuura Akinori             1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.             Corporate Technology Research Division

Claims (5)

[Claims] 1. A method of removing para-hydroxybenzoic acid from a reaction mixture obtained by reacting a phenol alkali or a mixture containing a phenol alkali and a substituted phenol alkali with carbon dioxide, wherein the reaction mixture is insoluble in water or water or The first step of extracting and separating using a poorly soluble organic solvent, the hydroxide of alkaline earth metal is added to the aqueous layer obtained in the first step, and the mixture is stirred to separate and remove the resulting insoluble matter. 2 step, 3rd step of acidifying the aqueous solution obtained in the 2nd step with mineral acid, heating the acidic water obtained in the 3rd step to dissolve para-hydroxybenzoic acid, phenol Fourth step of distilling and removing phenols and / or organic impurities, the fourth step
Fifth step of separating residual insoluble impurities in the heated acidic water obtained in the step under heating, the heated acidic aqueous solution obtained in the fifth step is cooled to precipitate parahydroxybenzoic acid, The sixth step of separating and acquiring from the acidic aqueous solution,
A method for separating para-hydroxybenzoic acid, which comprises the following steps: 2. After carrying out the method according to claim 1, para-hydroxybenzoic acid is further dissolved in a solvent in which para-hydroxybenzoic acid is dissolved and alkali mineral acid is not substantially dissolved, and the extract is separated. A method for separating para-hydroxybenzoic acid, comprising the step of obtaining para-hydroxybenzoic acid from the extract. 3. The method for separating para-hydroxybenzoic acid according to claim 1, wherein the phenol alkali and the substituted phenol alkali are phenol potassium and substituted phenol potassium. 4. The method for separating parahydroxybenzoic acid according to claim 1 or 2, wherein the mixture containing the phenol alkali and the substituted phenol alkalis is a mixture containing potassium tarrate and / or potassium cresylate. 5. The method for separating parahydroxybenzoic acid according to claim 1, wherein the mineral acid is sulfuric acid.