JP2925789B2 - Method for separating parahydroxybenzoic acid - Google Patents

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 phenol alkali or a mixture containing phenol alkali and a substituted phenol alkali with carbon dioxide.

[0002]

2. Description of the Related Art Parahydroxybenzoic acid has a wide variety of uses as a raw material for polymer materials, and has recently attracted attention as a raw material for liquid crystal polyesters having high strength and high heat resistance. Many 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 phenol potassium is reacted with carbon dioxide under high temperature and pressure, or an inert reaction medium (For example, Japanese Patent Publication No. 50-51).
No. 82, Japanese Patent Publication No. 43-26612, etc.). Recently, a method of synthesizing parahydroxybenzoic acid with high yield and high selectivity by reacting a mixture of phenol alkali and substituted phenol alkali with carbon dioxide has been proposed by the present inventors (Japanese Patent Application Laid-Open No. 02-124847). As a preferred example, a method is proposed in which a potassium salt such as tar acid, which is a mixture of phenol obtained from coal tar and substituted phenols, is used as a raw material.

[0004] Since the parahydroxybenzoic acid obtained by these reactions is actually an alkali metal salt, the following separation operation is mainly performed industrially.

For example, Japanese Patent Publication No. 55-19207 discloses that
Water and an organic solvent insoluble in water (which may also be used as a reaction medium) are added to the reaction mixture, and the by-produced phenol and / or the reaction medium are extracted and separated into an organic solvent layer, followed by separation of parahydroxybenzoic acid. Obtain an aqueous solution containing the potassium salt, then
The aqueous solution was neutralized by adding a mineral acid to convert unreacted phenol potassium to a free acid, to which an organic solvent insoluble in water was added again to extract and remove the released phenol, and the separated aqueous layer was separated. A method is disclosed in which after treatment with activated carbon, the acidity is adjusted in two steps with a mineral acid to crystallize potassium mineral acid, parahydroxybenzoic acid, and salicylic acid stepwise.

[0006] However, the above reaction (Kolbe-Schmidt reaction) is required to suppress salicylic acid by-product.
Often performed at high temperatures above ℃,
Although the amount is small, by-products such as tar-like and resin-like coloring substances of unknown structure cannot be avoided. Therefore,
The operation of 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 if necessary, impurities in an aqueous solution containing a reaction mixture are removed by filtration to remove a reaction medium and a resinous substance. In addition, adsorption and decolorization with activated carbon and the like are cited as commonly used techniques. Tokiko 46-43
As disclosed in Japanese Patent No. 532, an aqueous solution of an alkali metal salt of oxybenzoic acids other than parahydroxybenzoic acid is treated with calcium, barium, magnesium chloride, oxide, hydroxide or the like to remove insolubles. There are also ways to remove it. JP-B-45-36497 describes a reductive decolorization purification method using powdered zinc.

[0008]

As described above, as described above, Kolbe
Since the Schmidt reaction is performed at a high temperature of 200 ° C. or more, although there is a slight amount depending on the raw material and the like, by-products such as tar-like or resin-like coloring substances of unknown structure cannot be avoided. In particular, when a potassium salt of tar acid is used as a raw material, as in JP-A-2-124847, impurities peculiar to coal tar are also mixed, so that these impurities increase.

Among the above-mentioned methods for separating parahydroxybenzoic acid from a reaction mixture containing such impurities, the method disclosed in JP-B-55-19207 discloses that water and water-insoluble organic compounds are added to the reaction mixture. Although there is a step of performing liquid-liquid separation by adding a solvent, the generation of an emulsion at the interface cannot be avoided. In particular, when many emulsions are generated, measures such as prolonging the standing time and using a multi-stage decanter are required.

[0010] Furthermore, it is said that the alkali metal salt of parahydroxybenzoic acid is decomposed when heated in water. In response, Japanese Patent Publication No. 49-24470 discloses that the reaction mixture is heated at a high temperature in water. It proposes a method of dissolving it while putting it in and quenching, but the possibility of decomposition cannot be wiped out yet.

[0011] In addition, the conventional method has a problem in that multiple steps of pH adjustment are required to separate phenol, salicylic acid, and parahydroxybenzoic acid from the basic aqueous solution.

[0012] Further, in the case of limiting only to the method of removing impurities,
The reductive decolorization method using zinc and the like also require treatment with phosphoric acid, a surfactant, and the like, and are expensive because they use expensive metals and wastewater treatment is complicated. For other methods, such as when the amount of impurities is large, if the color removal effect is not reliable, or if this is performed reliably,
There is a problem that the decrease in the yield of parahydroxybenzoic acid cannot be avoided. Therefore, the method of separating parahydroxybenzoic acid after removing impurities by such a method is not a good method.

[0013] The present invention solves the above-mentioned problems by removing parahydroxybenzoic acid from by-products such as salicylic acids and phenols, reaction medium, and colored impurities without performing a liquid-liquid separation operation from the reaction mixture. It is an object of the present invention to provide a technology that can efficiently separate the garbage.

[0014]

According to a first aspect of the present invention, there is provided a reaction mixture obtained by reacting phenol alkali or a mixture containing phenol alkali and substituted phenol alkalis with carbon dioxide. In a method for removing parahydroxybenzoic acid,
A first step of washing the reaction mixture with a liquid hydrocarbon having 15 or less carbon atoms and / or an oxygen-containing compound having 10 or less carbon atoms other than carboxylic acid, and separating the washed mixture obtained in the first step into water; A second step of dissolving and acidifying the resulting aqueous solution with a mineral acid, heating the acidic water obtained in the second step to dissolve parahydroxybenzoic acid, and phenol, substituted phenols and / or A third step of distilling and removing organic impurities, a fourth step of separating the remaining insoluble impurities in the heated acidic water obtained in the third step under heating, and cooling the heated acidic aqueous solution obtained in the fourth step And separating and obtaining the parahydroxybenzoic acid from the aqueous acidic solution, thereby providing a method for separating parahydroxybenzoic acid, comprising the steps of a fifth step.

According to a second aspect of the present invention, the second step in the method for separating parahydroxybenzoic acid according to the first aspect of the present invention comprises the steps of: dissolving the washing residue obtained in the first step in water; A method for separating parahydroxybenzoic acid is characterized in that it is a step of adding and stirring an earth metal hydroxide, separating and removing generated insolubles, and acidifying the obtained aqueous solution with a mineral acid. Provided.

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

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

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

When the reaction raw material is an alkali metal salt of tar acid obtained from coal tar, the reaction mixture often contains impurities peculiar to tar.
Separation of parahydroxybenzoic acid from the reaction mixture has been difficult with conventional separation and purification methods, but the method of the present invention can be effectively used for treating such complicated reaction mixtures. .

In the first embodiment of the present invention, first, as a first step, the reaction mixture is washed with a liquid hydrocarbon having 15 or less carbon atoms and / or an oxygen-containing compound having 10 or less carbon atoms other than carboxylic acid.

As the liquid hydrocarbon having 15 or less carbon atoms,
Aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, cyclohexane, and decalin;
Examples thereof include aromatic hydrocarbons such as benzene, toluene, xylene, 1-methylnaphthalene, isopropylnaphthalene, and tetrahydronaphthalene, and mixtures of these hydrocarbons. It is also possible to use liquefied hydrocarbons (ethane, propane, butane) that become liquid under pressure, hydrocarbons such as 2-methylnaphthalene and naphthalene that become liquid when heated, and dimethylnaphthalene mixture that is liquid in a mixed state. it can.

These hydrocarbons dissolve the reaction medium and free phenols, but do not dissolve the alkali metal salt of parahydroxybenzoic acid. Therefore, the hydrocarbon is filtered to remove the alkali metal salt of parahydroxybenzoic acid. Can be easily separated. Note that hydrocarbons having 16 or more carbon atoms have a low effect because the reaction medium and free phenols have low dissolving power and high viscosity.

The oxygen-containing compound having 10 or less carbon atoms is such a compound, and may be any compound other than carboxylic acid, such as ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, methanol, ethanol, isopropanol and butanol. And phenols such as phenol, cresol and xylenol, esters such as methyl acetate, ethyl acetate and methyl propionate, and ethers such as tetrahydrofuran and dioxane.

The inadequacy of the carboxylic acid depends on the acidity of the carboxylic acid, but the presence of the carboxylic acid converts the alkali metal salt of parahydroxybenzoic acid into parahydroxybenzoic acid, and the detergent (solvent). )). In addition, oxygen-containing compounds having 11 or more carbon atoms have low effects because the extraction power of the reaction medium and free phenols is low.

These oxygen-containing compounds can dissolve the reaction medium, phenol and / or substituted phenols by-produced in the reaction, and lower the viscosity of the reaction mixture to facilitate filtration and washing, as in the case of the above-mentioned carbon hydrogen. There is an effect to make it. Furthermore, since some of these oxygen-containing compounds have a dissolving ability also for alkali salicylate, which is a reaction by-product, they are also effective in removing salicylic acids.

The washing temperature may be at least the melting point of the used detergent (solvent). When processing at a temperature higher than the boiling point, it is necessary to use a heat exchanger such as a reflux pipe in order to condense the generated solvent vapor.However, since the viscosity decreases as the temperature increases, filtration and separation become easier, The temperature is preferably set to a high temperature because the power of extracting the detergent with respect to impurities, in particular, alkali metal salts of salicylic acids increases.

The amount of the cleaning agent used depends on the amount of the reaction medium used,
Although it depends on the amount of impurities, the reaction rate, and the like, usually, an alkali metal salt of parahydroxybenzoic acid is the main component of the reaction mixture. Therefore, 0.1 part by weight or more, preferably 1 to 1 part by weight of the reaction mixture. 100 parts by weight. 0.1
If the amount is less than the weight part, the effect of extracting the detergent is not exhibited,
On the other hand, if it is more than 100 parts by weight, it is not economical. It should be noted that, even if the solvent is used for cleaning, if the solvent still has a dissolving ability, it can be used repeatedly.

There is no particular limitation on the timing of adding the detergent. For example, the reaction mixture may be taken out of the reaction vessel and added after cooling it, or a cleaning agent may be introduced into the reactor after the reaction. Further, in order to remove most of the reaction medium, a filtration operation may be performed before the treatment with the detergent, and the detergent may be used thereafter.

After the treatment with the detergent, the washing residue is separated by filtration, but this filtration operation is not particularly limited. The filtering material may be determined according to the particle size of the solid residue after the washing treatment, and the filtration may be performed at the same or lower temperature as the treatment of the detergent.

It is needless to say that the present invention can be applied to a reaction mixture performed without using a reaction medium.

Next, as a second step, the washing residue is dissolved in water, and a mineral acid is added to the resulting aqueous solution to liberate parahydroxybenzoic acid.

The acidity at this time is pH 5 or less, preferably pH 4 or less. However, this step may be used when separating parahydroxybenzoic acid from a reaction mixture obtained by using a potassium salt of tar acid as a reaction raw material. It is preferable to adjust the pH to 2 or less because it also prevents coloring.

Examples of the mineral acid include sulfuric acid, nitric acid, hydrochloric acid and the like, but sulfuric acid is preferred from the viewpoint of cost and corrosiveness.

Next, as a third step, this acidic water is heated to dissolve the precipitated parahydroxybenzoic acid and to distill out 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 third step depends on the pH, the amount of water, and the like, and cannot be unconditionally determined, but the boiling temperature is usually preferred. Excessive heating is not preferable because there are phenomena such as bumping.

In the case of separating parahydroxybenzoic acid from a reaction mixture obtained by using a potassium salt of tar acid as a raw material, impurities considered to be derived from tar are dispersed in crystals when the temperature of acidic water is low. However, when the temperature is increased, it is dissolved in the residual phenols and the residual reaction medium, the residual washing organic solvent, and the like, and becomes present as an oil layer. By heating the 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 that they can be easily separated from the hot solution (acidic water). Becomes

In the third step, it is preferable to adjust the concentration by distilling out water when distilling out organic impurities and the like in the third step. The amount of water to be distilled depends on the content of parahydroxybenzoic acid or the amount of the remaining organic medium or phenol. The amount of the water to be distilled, in other words, the amount of the remaining water is important because it is related to the success or failure of the fourth step.

That is, in the fourth step to be described later, the amount of water used for hot separation of heated acidic water and insoluble solids may be not less than the amount in which parahydroxybenzoic acid can be dissolved. This is because an excess amount close to the required amount of dissolving benzoic acid is most preferable. In such a case, depending on the yield of parahydroxybenzoic acid and the amount of potassium by-produced mineral acid, when the parahydroxybenzoic acid is dissolved, part of the alkali metal salt of the mineral acid remains as a precipitate and is heated. This is advantageous because it can be partially removed together with the solids insoluble in the acidic aqueous solution, and when the heated acidic aqueous solution is separated and cooled to precipitate the solid (fifth step), parahydroxybenzoic acid is also contained in the solution. This is because there is an advantage that the loss due to remaining can be reduced. On the other hand, if the amount of water is less than the amount capable of dissolving parahydroxybenzoic acid, parahydroxybenzoic acid is precipitated, and is separated together with impurities to be separated and solids such as tar-like substances, thereby lowering the yield. Absent.

The end point of the distilling removal operation of the organic impurities and the like in the third step is usually determined by, for example, the following method with reference to the end of distilling out the distillation components other than water.

That is, when heating is sufficiently performed, phenols, organic solvents, and salicylic acids are distilled off together with water or alone. At a certain point, it is determined whether phenol or salicylic acids have been distilled off. In order to judge, a distillate was subjected to a ferric chloride color reaction test,
When coloration is no longer observed, distilling is stopped.

Next, as a fourth step, the heated acidic water and the remaining insoluble impurities are separated by filtration while hot, and as a fifth step, the filtrate is cooled to precipitate parahydroxybenzoic acid. Separate and acquire from acidic aqueous solution.

For the separation of the heated acidic water from the insoluble impurities, for example, a method such as filtration, decantation, or centrifugation is suitably used. It is also effective to combine activated carbon treatment.

Also in performing the fifth step, the amount (or concentration) of the acidic aqueous solution is important. At this time, an excess amount (concentration) that dissolves the alkali metal salt of the mineral acid even at the time of cooling can simplify the subsequent separation operation of parahydroxybenzoic acid and the alkali metal salt of the mineral acid, but is preferable. After the separation of the hot solution (the end of the fourth step), the amount of water in the aqueous solution may be reduced as much as possible by means such as concentration to increase the yield of parahydroxybenzoic acid.

In the fifth step, when parahydroxybenzoic acid is precipitated by cooling, as described above, the concentration of the alkali metal salt of the mineral acid remaining in the mother liquor at the time of cooling is good, but it is higher (water ), The alkali metal salt of the mineral acid is precipitated together with the parahydroxybenzoic 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 fourth step is separated from the solution, and then the separated mixture is separated from parahydroxybenzoic acid. The acid is extracted with a solvent.

The solvent used herein may be any solvent which does not substantially dissolve the alkali metal salt of the mineral acid and dissolves parahydroxybenzoic acid, for example, 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 and the like And ethers such as diethyl ether and tetrahydrofuran.

The extraction operation is usually performed under normal temperature and normal pressure, but may be performed under heating and / or stirring.

Thus, the parahydroxybenzoic acid is dissolved in the solvent, and the alkali metal salt of the mineral acid remains in a solid state. This solid-liquid phase separation may be performed by a method such as filtration, decantation, or centrifugation. Further, the subsequent separation of parahydroxybenzoic acid from the extract may be performed by a known method such as solvent evaporation, reprecipitation, and crystallization.

By the above-mentioned operations, high-purity parahydroxybenzoic acid can be separated and obtained. However, if it is desired to further increase the purity, it can be said that the purification can be carried out by a usual recrystallization method or the like. Less than.

Also, the following method (second embodiment of the present invention)
It is useful for further increasing the purity of parahydroxybenzoic acid.

This is a method of adding another step between the first step and the second step in the method of the first aspect of the present invention. More specifically, after dissolving the washing residue obtained in the first step in water, and adding a mineral acid (the second step in the method of the first embodiment of the present invention), the aqueous solution is added to the alkaline earth. This is a method in which a step of adding a metal hydroxide, stirring, and separating a formed precipitate by filtration is added.

Preferred examples of the alkaline earth metal used as a hydroxide in this step include calcium hydroxide, magnesium hydroxide and barium hydroxide.

The amount of parahydroxybenzoic acid lost by this operation, ie, by precipitation, was extremely small, for example, about 0.33% in Example 3 described below using calcium hydroxide.

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

When this step is added, a mineral acid is added to the filtrate, and the third and subsequent steps may be performed in the same manner as described above.

When this step is added, the purity of parahydroxybenzoic acid finally obtained increases, but the yield tends to decrease slightly.

[0057]

The present invention will be described in more detail with reference to the case where a potassium salt of tar acid containing a large amount of impurities of unknown structure is used as a starting material. Therefore, it is clear that the present invention can be applied to a Kolbe-Schmidt reaction product using ordinary phenol potassium as a raw material.
It should be noted that the present invention is not restricted by the following examples.

Example 1 Tar acid, which is a mixture of phenol obtained from coal tar and substituted phenols, was treated with potassium hydroxide and dried to obtain powdered potassium tarate. As a result of analysis, it was found that in addition to phenol potassium, cresol potassium, and xylenol potassium, a substance of unknown structure was contained at 6.4 wt%.
36.2 g of this dry powdered potassium tarrate were put into 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 the reaction pressure was 3.2 kg / cm ² (G ) At 290 ° C for 40 minutes 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 contained 4.17 g of parahydroxybenzoic acid, 0.01 g of salicylic acid, and 0.01 g of phenol in terms of free acid. 0.53 g, cresols: 3.03 g, and high boiling gas oil: about 17.8 g. 80 g of acetone was added to 30 g of the sample, and filtered while stirring. The resulting residual solid mainly composed of potassium parahydroxybenzoate was dissolved in 100 ml of water, and sulfuric acid was added to this aqueous solution to adjust the pH to 2, whereby a dark brown precipitate was formed. Next, heat and boil it (about 100 ° C)
While dissolving parahydroxybenzoic acid, the generated steam was distilled off by attaching a side tube and concentrated. At this time, some of the remaining phenol, cresol, organic solvent (light oil), and salicylic acid were removed by azeotropic distillation or distillation, and impurity solids insoluble in acidic water floated in the system. The amount of distillate was about 30 ml. Next, the acidic water was filtered while hot. At that time, the filtrate was passed through a 0.2 g activated carbon layer charged to the funnel leg. Then, the obtained filtrate was cooled to 5 ° C., and the crystallized white solid was separated and obtained by filtration. The solid was washed with cold water to have a purity of 99.5%.
3.62 g of parahydroxybenzoic acid (separation yield 86.
7%).

Example 2 The same operation as in Example 1 was carried out except that the amount of water used for dissolution was changed to 50 ml, and the filtrate of the heated acidic water was cooled to 5 ° C. to obtain a white solid 8. 0.07 g was obtained. However, about half was potassium sulfate, and only 48.6 wt% of the total solids was parahydroxybenzoic acid. Then, acetone was added to this solid to extract parahydroxybenzoic acid, the solvent was removed, and parahydroxybenzoic acid 3.84 having a purity of 99.2% was obtained.
g (separation yield 91.1%).

Example 3 Tar acid, which is a mixture of phenol obtained from coal tar and substituted phenols, was treated with potassium hydroxide and dried to obtain powdered potassium tarate. As a result of analysis, it was found that, in addition to phenol potassium, cresol potassium, and xylenol potassium, 4.1 wt% of a substance of unknown structure was contained.
28 g of this dry powdered potassium tarate was put into a pressure-resistant reactor together with 50 g of a high-boiling fraction of light oil (150 to 230 ° C./10 mmHg), carbon dioxide gas was introduced, and the reaction pressure was 3 kg / c.
The reaction was carried out at 280 ° C. for 40 minutes under m ² (G) to obtain 81.76 g of a dark brown reaction mixture. Mix well, 30g
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 contained 4.11 g of parahydroxybenzoic acid, 0.007 g of salicylic acid, and 0.007 g of methylsalicylic acid in terms of free acid. : 0.21 g, phenol: 0.49 g, cresols: 2.96 g, and high-boiling light oil: 18.35
g was found to be contained. A sample (30 g) was placed on a glass filter, and filtered while adding toluene (36 g). Further, 35 g of acetone was added, and the mixture was filtered with stirring. The obtained residual solid mainly composed of the potassium salt of parahydroxybenzoic acid is dissolved in 100 ml of water, and 1.5 g of calcium hydroxide is added thereto. When the mixture is stirred, a black precipitate is formed from the dark brown aqueous solution, and the light brown to light yellow color is obtained. It became a clear liquid. After the black precipitate was removed by filtration, sulfuric acid was added to the aqueous solution to adjust the pH to 2, whereby a pale yellow-brown precipitate was formed. Next, this was heated and boiled (about 100 ° C.), and while dissolving parahydroxybenzoic acid, the generated steam was distilled off by attaching a side tube and concentrated. At this time, the remaining phenol,
Part of cresol, organic solvent (light oil) and salicylic acid were removed by azeotropic distillation or distillation, and impurity solids insoluble in acidic water floated in the system. The amount of distillate was about 30 ml. Next, the acidic water was filtered while hot. At that time, the filtrate was passed through a 0.2 g activated carbon layer charged to the funnel leg. Then, the obtained filtrate was cooled to 5 ° C., and the crystallized white solid was separated and obtained by filtration. The solid was washed with cold water, and 3.51 g of 99.8% pure parahydroxybenzoic acid (separated yield). 85.4%).

Example 4 Using 30 g of the same sample as in Example 3, the amount of water used for calcium hydroxide treatment was 5
The same operation was performed except that the amount was 0 ml, and the filtrate of the heated acidic water was cooled to 5 ° C. to obtain 7.9 g of a white solid. However, about half the amount is potassium sulfate, and 4
Only 8.4 wt% was parahydroxybenzoic acid.
Then, acetone was added to this solid to extract parahydroxybenzoic acid, and the solvent was removed, thereby obtaining 3.75 g of parahydroxybenzoic acid having a purity of 99.6% (separation yield: 91.2%).

[0062]

According to the present invention, as described above, according to the present invention, the liquid-liquid separation operation involving the generation of emulsion is not performed, and the acidification operation is performed in one step. Thus, parahydroxybenzoic acid can be efficiently separated from the reaction medium, by-products and colored impurities. The present invention, even when there are many colored impurities, such as a reaction mixture obtained when using tar acid as a raw material,
The effect can be certainly exhibited, and parahydroxybenzoic acid useful as an industrial raw material can be provided.

Continuation of the front page (72) Inventor Nobuyuki Sato 1 Kawasaki-cho, Chiba-shi, Chiba Prefecture Kawasaki Steel Corporation Research and Development Headquarters (72) Inventor Akira Matsuura No. 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. (56) References JP-A-3-227955 (JP, A) JP-A-3-200740 (JP, A) JP-A-3-109348 (JP, A) JP-A-2-160747 (JP, A) JP-A-51-43736 (JP, A) JP-B-49-48304 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C07C 51/42 C07C 65 / 03

Claims (6)

(57) [Claims] 1. A method for removing parahydroxybenzoic acid from a reaction mixture obtained by reacting phenol alkali or a mixture containing phenol alkali and substituted phenol alkalis with carbon dioxide, the reaction mixture comprising a liquid having 15 or less carbon atoms. A first step of washing and separating with an oxygen-containing compound having 10 or less carbon atoms other than hydrocarbons and / or carboxylic acids, the washing residue obtained in the first step is dissolved in water, and the resulting aqueous solution is converted into a mineral acid. A second step in which the acidic water obtained in the second step is heated to dissolve parahydroxybenzoic acid, and a third step of distilling and removing phenol, substituted phenols and / or organic impurities, A fourth step of separating the remaining insoluble impurities in the heated acidic water obtained in the third step by heating, the fourth step;
A step of cooling the heated acidic aqueous solution obtained in the step to precipitate parahydroxybenzoic acid, and separating and obtaining the parahydroxybenzoic acid from the acidic aqueous solution. Separation method. 2. In the second step of the method for separating parahydroxybenzoic acid according to claim 1, the washing residue obtained in the first step is dissolved in water, and then a hydroxide of an alkaline earth metal is added. A method of separating parahydroxybenzoic acid, which comprises a step of stirring and stirring to separate and remove generated insolubles, and acidifying the resulting aqueous solution with a mineral acid. 3. The method according to claim 1, further comprising dissolving parahydroxybenzoic acid and dissolving parahydroxybenzoic acid in a solvent that does not substantially dissolve the alkali mineral acid, followed by extraction. A method for separating parahydroxybenzoic acid, comprising the step of separating and obtaining parahydroxybenzoic acid from the extract. 4. The method for separating parahydroxybenzoic acid according to claim 1, wherein the phenol alkali and the substituted phenol alkali are phenol potassium and substituted phenol potassium. 5. The separation of parahydroxybenzoic acid according to claim 1, wherein the mixture containing the phenol alkali and the substituted phenol alkali is a mixture containing potassium tarrate and / or potassium cresylate. Method. 6. The method for separating parahydroxybenzoic acid according to claim 1, wherein the mineral acid is sulfuric acid.