JPS61140563A - Production of purified indole - Google Patents

Abstract

PURPOSE:To produce a high-purity indole from an indole-containing mixture in high recovery ratio, by treating the indole-containing mixture in combination of solvent extraction, distillation, and crystallization. CONSTITUTION:An indole-containing mixture is extracted with an extraxting solvent (e.g., monoethanolamine, sulfonate, etc.), the extracting solvent is separated from the prepared extracting solvent phase, to give an extraction mixture comprrising an indole as a main component. Then, the extraction mixture is distilled in such a way that the concentration of indole is >=80wt% and that of methylindole is <=5wt%, to give a crude indole. It is crystallized with a crystallizing solvent (preferably the same solvent used as the extracting solvent), to give a purified indole.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing indole, and particularly to a method for producing highly purified indole from a mixture containing indoles.

[Conventional technology]

Methods for producing highly purified indole from a mixture containing indoles include a method in which indole is separated into its alkali salt form using alkali hydroxide and then hydrolyzed, and monoethanolamine, dimethyl sulfoxide, pyrrolidone, etc. There is a known method for purifying indole by extracting it with a polar solvent, washing this extract with an alkane or cycloalkane that has a boiling point different from that of the hydrocarbons in the raw material to remove the accompanying hydrocarbons, and then distilling it. (JP 58-1358625 and JP 59-62)
565 Publication).

[Problem that the invention seeks to solve]

However, in the former method, there are problems such as equipment corrosion due to the use of highly concentrated alkali hydroxide at high temperatures, and in the latter method, a large amount of indole is used to increase the recovery rate and selectivity of indole. However, in addition to requiring a large amount of energy to recover the polar solvent, both methods are insufficient in the recovery rate of indole and the purity of the obtained indole. There was a problem that.

[Means and effects for solving the problems] The present invention has been devised in view of this point of view, and it combines the methods of solvent extraction, distillation, and crystallization to obtain a high recovery rate and high purity from an indole-containing mixture. This is a method for producing indole.

That is, in producing highly purified purified indole from a mixture containing indoles, the present invention extracts the mixture containing indoles with an extraction solvent, and separates the extraction solvent from the obtained extraction solvent phase to produce indole. An extraction mixture mainly composed of
A method for producing purified indole, which comprises distilling the methyl indole at a concentration of 0% by weight or more to a concentration of 5% by weight or less, and crystallizing the obtained crude indole in the presence of a crystallization solvent to produce purified indole. .

In J3 of the present invention, the indole-containing mixture used as the raw material C is a mixture containing indoles and hydrocarbons as main components, and the indole content M may be 1% by weight or more. The boiling point range is preferably 200 to 300°C at normal pressure.

An example of a raw material that satisfies these conditions is an indole-containing fraction obtained by distilling coal tar, and this indole-containing fraction contains alkyl indoles such as indole, methylindole, dimethylindole, etc. In addition to containing one or more types of indole, hydrocarbons such as naphthalene, biphenyl, methylnaphthalenes such as go-methylnaphthalene and 2-methylnaphthalene, 1,5-dimethylnaphthalene and 2,6- One or more types of dimethylnaphthalenes such as dimethylnaphthalene are contained.

Regarding this indole-containing fraction, preferably, the fraction with a boiling point of 220 to 270°C is subjected to deacidification and/or debasing treatment in an acid aqueous solution or an alkaline aqueous solution, thereby removing the indoles contained in the raw materials. Products from which acidic and/or basic components such as phenols, pyridines, and quinolines have been removed, or indole-containing fractions obtained by distillation of coal tar, or those obtained by deacidification and/or debasing treatment. Crude indoles are obtained by reacting the obtained treated product with an alkali metal hydroxide such as potassium hydroxide under heating conditions to hydrolyze the indole alkali produced.

In addition, when using this crude indole as a raw material, it is preferable to separate and remove water, pitch, sludge, etc. in advance. By deacidifying and/or debasing the raw material, it is possible to prevent the above acidic or basic components from being entrained with the indoles during extraction with an extraction solvent, thereby facilitating the subsequent purification process. can. In addition, by performing sludge removal treatment, etc., it is possible to prevent problems such as unclear interfaces and line blockages from occurring.

The boiling point obtained by distillation of the above coal tar is 235~
An example of the composition (% by weight) of the indole-containing fraction (A) at 268° C. or lower and the crude indole (B) obtained by hydrolyzing the indole alkali is shown below.

Ingredient (A) (
8) 2-Methylnaphthalene 43.4 2.11-Methylnaphthalene 14.8 1.2 Dimethylnaphthalenes 18.6 1.4 Indole 3
．． 8 81.0 Methylindoles 0.711.
3 Others 18.7 3.0 In addition to the indole-containing fraction obtained by the above-mentioned distillation of coal tar, the indole-containing mixture as a raw material to which the method of the present invention is applied includes, for example, synthetic indoles, waste Any substance containing indole such as indole may be used, but in this case as well, except for those that can be separated and removed by distillation, the substance to be extracted with the extraction solvent should be prepared in advance as much as possible. It is desirable to separate and remove it.

In addition, the extraction solvent used in the method of the present invention may be any solvent that exhibits excellent selective solubility for the indoles in the raw materials, and the extraction method may include a method in which a polar solvent is used alone. There is a method of using a polar solvent and a non-polar solvent in combination.

Examples of the polar solvent used as an extraction solvent in the method of the present invention include monoethanolamine, jetanolamine, dimethyl sulfoxide, 2-pyrrolidone, N-methyl-2-pyrrolidone, sulfolane, glycerin diacetate, ethylene glycol, diethylene glycol, Triethylene glycol, tetraethylene glycol, etc. can be mentioned, and these polar solvents may be used alone or in a mixture of two or more thereof.

Many of these polar solvents dissolve water, but within the range of solubility, water may be added to serve as an extraction solvent. By adding water to a polar solvent, the solubility for indoles is slightly lowered, but the solubility for hydrocarbons is significantly lowered, and the selectivity for extraction of indoles is improved.

Therefore, if a water-containing extraction solvent is used by increasing the amount of extraction solvent used to compensate for the decrease in solubility, it is possible to obtain high purity indoles at a high recovery rate even with a small number of extraction stages. In addition, even in cases where it is difficult to form a minute layer with hydrocarbons using only polar solvents, it is possible to separate into two phases and extract indoles by using a water-containing extraction solvent. become.

In addition, in the method of using a polar solvent and a non-polar solvent as extraction solvents, the above-mentioned polar solvent is used as the first extraction solvent for extracting indoles, and the non-polar solvent is used as the second extraction solvent for extracting hydrocarbons.
In this method, indoles are extracted using a combination of these two types of extraction solvents. In this method, a non-polar solvent exhibits high dissolving power for hydrocarbons, especially aromatic hydrocarbons, which are extracted in small amounts into the polar solvent phase when indoles are extracted with a polar solvent. In addition to removing substances from the polar solvent phase, it also facilitates phase separation from the polar solvent phase during extraction.

Such nonpolar solvents include one or more types of alkanes and cycloalkanes having 5 to 10 carbon atoms selected from a group of nonpolar solvents consisting of alkanes having 5 to 10 carbon atoms and cycloalkanes. Specifically, as a class,
n-pentane, 1so-pentane, n-hexane, n-
Mention may be made of hebutane, n-octane, 1so-octane, cyclopentane, cyclohexane, methylcyclohexane, petroleum ether, petroleum benzine or mixtures thereof. Since the boiling point of such a nonpolar solvent is significantly different from the boiling point of the hydrocarbons in the raw material, it is easy to recover and reuse it.

Various types of extraction means can be used in carrying out the extraction method of the present invention, but in order to extract indole with the least amount of hydrocarbons at a high recovery rate, preferably It is a multi-stage extraction device that performs extraction in multiple stages, and specifically includes basic type extraction devices such as packed towers, perforated plate towers, baffle towers, stirring type extraction towers, and pulsating type extraction towers, as well as mixer-settler type extraction devices. Seed mold extraction equipment, etc.

In addition, the method of operation of these extraction devices is preferably such that fresh extraction solvent of opposite polarity to the liquid being withdrawn from the extraction line is charged at a position close to the extraction line so that they are in countercurrent contact. By doing this, the transfer of hydrocarbons and non-polar solvents in the raw materials to the extraction solvent consisting of polar solvents is suppressed to a minimum, and the indole in the raw materials is effectively extracted. Indole can be extracted with good recovery and selectivity.

Next, the extraction solvent is separated from the extraction solvent phase obtained in the above extraction step to obtain an extraction mixture containing indoles as a main component. The method for separating this extraction solvent is not particularly limited, but when the extraction solvent is a polar solvent, it is usually carried out by distillation or extraction. For non-polar solvents, if used, this is usually done by distillation. The polar and/or non-polar solvent of the extraction solvent separated from the extraction solvent phase in this way is preferably recycled again to the extraction process and used as extraction solvent.

In addition, for an extraction mixture containing indoles as the main component obtained by separating the extraction solvent from the extraction solvent phase, next, the indole concentration is 80% or more and the methyl indole concentration is 5%.
The crude indole is obtained by distillation to obtain a type ω% or less, preferably an indole concentration of 85% by weight or more and a methyl indole concentration of 2% by weight or less. The indole concentration of the crude indole converted by distillation of this extraction mixture is 80f.
If the fi amount is lower than 5% by weight or the methyl indole concentration is higher than 5% by weight, it will be difficult to increase the purity of purified indole obtained by purification in the next crystallization step, and if you try to increase the purity, the recovery rate of indole will decrease. decreases.

The crude indole obtained by the above distillation is crystallized in the presence of a crystallization solvent, and the crystallization mother liquor is separated to obtain purified indole in a crystalline state.

The crystallization solvent used in this crystallization step is preferably one that is poorly soluble in indole and exhibits excellent solubility for impurities in the crude indole. Like polar solvents, carbon number is 5 or more
One type or a mixture of two or more types selected from a group of solvents consisting of 10 alkanes and cycloalkanes,
More preferably, the same non-polar solvent used as the extraction solvent is used.

The crystallization method may be any conventionally known method such as a normal recrystallization method, but from the viewpoint of recovery rate, it is preferable to completely dissolve the crude indole at its melting point. An insufficient amount of crystallization solvent and crude indole are mixed, heated and stirred, the crude indole is melted and dispersed in the crystallization solvent, and then cooled to precipitate crystals, which are then separated. This is the method to do it. In addition, if the non-polar solvent used in the above indole extraction step and the crystallization solvent used in this crystallization step are the same, all or part of the crystallization mother liquor recovered in this crystallization step may be mixed with an alkaline aqueous solution. After washing to remove most of the acidic components in the mother liquor, it can be recycled to the indole extraction process and reused.

〔Example〕

Hereinafter, the method of the present invention will be explained in detail according to a flow sheet according to an example of implementation.

Boiling point 220-270℃ obtained by distilling coal tar
The indole-containing mixture (1) obtained by washing the fraction with a 10% NaOH aqueous solution and a 30% H2SO4 aqueous solution to remove most of the acidic components and basic components was used as a raw material. The indole-containing mixture (1) is passed through a distillation tower (
2), and after removing the heavy pitch portion (3), it was charged into the middle part of an extraction column (4) having 5 theoretical plates.

Monoethanolamine (6) was charged into the extraction column (4) from the top of the column, and n-hexane (5) was charged from the bottom of the column, and the solvent ratio (raw material: monoethanolamine: Countercurrent extraction was performed under the conditions of 1:0.25:0.41 (n-hexane).

The monoethanolamine phase (7) extracted from the bottom of the extraction column (4) is charged into a distillation column (8) having 30 theoretical plates, and monoethanolamine (6) is recovered from the top of the column. , is circulated to the extraction column (4) together with a portion of newly charged monoethanolamine, and the bottom oil (9) containing a large amount of indoles is extracted from the bottom of the column and distilled using 30 theoretical plates. The mixture was charged into a column (10), subjected to precision distillation, and crude indole (11) was extracted from the top of the column, and a high-boiling component (12) containing methyl indoles as a main component was extracted from the bottom of the column.

On the other hand, the n-hexane phase (13) extracted from the top of the extraction column (4) was extracted from the distillation column (
14), recovered n-hexane (5) from the top of the column, and circulated it to the extraction column (4) together with a portion of the newly charged n-hexane. A hydrocarbon oil (15) containing naphthalene and dimethylnaphthalene as main components and almost no indoles was recovered.

The above crude indole (11) was then charged into a stirring tank (17) with 3 times the amount of n-hexane (16) and heated and stirred at 50°C, and the molten crude indole was mixed with n-hexane ( 16) and cooled to 1.5°C to precipitate crystals, charged to a centrifuge (18) for solid-liquid separation, and then transferred to a stirring tank (19) and a centrifuge again for crystals. The same crystallization was repeated with (20) to obtain purified indole (21) in a crystalline state. Regarding the crystallization mother liquor (22) obtained in this second crystallization, the crystallization mother liquor obtained in the first crystallization was mixed with 10% Na in a stirring tank (23).
Indole-containing filtrate (1) combined with that washed with oI-1 aqueous solution and removing heavy pitch (3)
It was charged into the middle part of the extraction column (4) together with the extractor.

The recovery rate of indole with respect to the indole-containing mixture (1) is 66% by weight, and the indole concentration in the recovered mother liquor (24) recovered by washing the crystallization mother liquor of the first crystallization is 4% by weight. In addition, the compositions of the raw material indole-containing mixture (1), the bottom oil (9) of the distillation column (8), the crude indole (11), and the purified indole (21) were investigated. The results are shown in Table 1.

Table 1 [Effects of the Invention] According to the present invention, by combining the methods of solvent extraction, distillation, and crystallization, indole can be produced with high recovery rate and high purity from an indole-containing mixture.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow sheet of a manufacturing process showing an example of the method of the present invention.

Claims (8)

[Claims] (1) In producing high-purity purified indole from a mixture containing indoles, the mixture containing indoles is extracted with an extraction solvent, the extraction solvent is separated from the resulting extraction solvent phase, and indoles are the main component. Obtain an extraction mixture with an indole concentration of 80% by weight or more,
A method for producing purified indole, which comprises distilling the methyl indole to a concentration of 5% by weight or less, and crystallizing the obtained crude indole in the presence of a crystallization solvent to produce purified indole. (2) The method for producing purified indole according to claim 1, wherein the extraction solvent separated and recovered from the extraction solvent phase is recycled as an extraction solvent in the indole extraction step. (3) The method for producing purified indole according to claim 1 or 2, wherein a polar solvent and a non-polar solvent are used as extraction solvents. (4) Crystallization of crude indole is performed by mixing crude indole with an insufficient amount of crystallization solvent to completely dissolve the crude indole at the melting point of the crude indole, heating and stirring the mixture, and crystallizing the crude indole. The method for producing purified indole according to any one of claims 1 to 3, which comprises melting and dispersing it in a solvent, cooling it to precipitate crystals, and then separating the crystals. (5) Claims 1 to 4, wherein the crystallization solvent is one or a mixture of two or more selected from a group of solvents consisting of alkanes and cycloalkanes having 5 to 10 carbon atoms. Any method for producing purified indole. (6) Claim 5, wherein the crystallization solvent obtained by separating the crystallization solvent from the mother liquor recovered in the crystallization of crude indole is recycled as a non-polar solvent used in the indole extraction process. Method for producing purified indole. (7) Claims 1 to 6, wherein the indole-containing mixture is obtained by treating a fraction of coal tar with a boiling point of 200 to 300°C at normal pressure with an acid and alkali aqueous solution in advance. A method for producing purified indole. (8) A mixture containing indoles is obtained by reacting a fraction of coal tar with a boiling point of 200 to 300°C at normal pressure with an alkali metal hydroxide under dehydration conditions, and hydrolyzing and neutralizing the obtained alkali metal salt of indole. A method for producing purified indole according to any one of claims 1 to 6, which is obtained by: