JPS5936623B2 - Recovery method for indoles - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for recovering indoles.

Specifically, the present invention relates to a method for recovering indoles by separating and recovering indoles from a mixture containing nonpolar and/or slightly polar compounds present in coal tar. Alkylindoles such as indole and methyl indole are used as raw materials for perfumes, dyes, medicines, etc., and in recent years have also been used as raw materials for essential amino acids.

As a method for obtaining indole, in addition to synthesis, a method of separating and recovering indole present in coal tar is generally adopted. As a method for separating indole from coal tar, a fraction with a boiling point range of 220 to 270°C obtained by distilling coal tar is heated to 100 to 125°C with sodium or sodium amide, or heated to 220°C with potassium hydroxide. A common method is to heat to separate indole into an alkali salt, and then hydrolyze the separated alkali salt to obtain indole. However, this method uses expensive sodium and sodium amide, is dangerous, requires consideration of container material issues, and requires complicated operations, so it is not an efficient method. I can not say. Also,
KoksKhimii (4), 18 (1977) and Zh.
urnalPrikladnoiKhimii51,2
389 (1978) describes an example in which indole is separated from an indole fraction of coal tar by chromatography, but this is unsuitable and not advisable for processing a large amount of raw material. Furthermore KoksKhimii
(9) 29 (1977) using pyridine or quinoline and a 35% aqueous sulfuric acid solution, and Soviet Patent No. 59
No. 8889 describes a method for extracting indole from the indole fraction of coal tar using pentane and polar solvents (ethylene glycols, N-methylpyrrolidone, sulfolane, ethanolamine, dimethyl sulfate, etc.). In this method, there are problems in that it is not easy to separate and recover the solvent, and that separation and recovery requires a large amount of energy. As described above, conventional methods for separating indole from coal tar have drawbacks and problems, and no efficient method has yet been found. An object of the present invention is to provide an efficient method for separating and recovering indoles without such drawbacks and problems.

In order to achieve this objective, the present inventors developed an idea different from the conventional method of directly extracting the desired indole from raw materials by converting the above-mentioned indole into an alkali salt, or by solvent extraction, etc. Based on this, as a result of extensive research, we have found that indoles can be easily and efficiently obtained by extracting and removing non-target substances from raw materials using hydrocarbons and recovering indoles from the raffinate phase. This discovery led to the present invention.

That is, the present invention involves contacting a mixture containing indoles and a nonpolar and/or slightly polar compound present in coal tar with a solvent consisting of one or a mixture of two or more selected from alkanes and naphthenes. This is a method for recovering indoles, which is characterized by separating into an extraction phase rich in substances other than indoles and a raffinate phase rich in indoles, and removing a solvent from the raffinate phase to obtain indoles. .

The raw material in the present invention is a mixture containing indoles and nonpolar and/or slightly polar compounds present in coal tar.

The indoles may be one type of indole or alkylindoles such as methyl indole and dimethyl indole, or may be in the form of a mixture of two or more types. A compound present in coal tar that is nonpolar and/or
Examples of slightly polar compounds include naphthalene, biphenyl, 1-methylnaphthalene, 2-methylnaphthalene, 1,5-dimethylnaphthalene, 1,7-dimethylnaphthalene, 2,6-dimethylnaphthalene, ethylnaphthalene, acenaphthene, and fluorene. , dibenzofuran, etc., and the raw material may contain one or more of these. Specific examples of mixtures include fractions with a boiling point range of 200 to 300°C obtained by distilling coal tar, but are not limited to this, as long as they contain indoles and the above substances. Applicable. The content of indoles in the mixture can be applied in almost any range and is 3% by weight or more, preferably 40% by weight or more. The hydrocarbon solvent used in the present invention may be any alkanes or naphthenes, but from the viewpoint of extraction operations, they are in a liquid state at room temperature and normal pressure. Examples of alkanes include pentane, hexane, heptane, These include octane, nonane, decane, undecane, dodecane, etc., and naphthenes include cyclopentane, cyclohexane, methylcyclohexane, etc. As described above, alkanes and naphthenes having 5 or more carbon atoms, preferably 5 to 12 carbon atoms in one molecule are preferred. However, normally gaseous substances such as ethane, propane, butane, etc. can also be used by appropriately selecting operating conditions. Moreover, the hydrocarbon solvent to be used is not limited to one type, and a combination of multiple types may be used. The amount of solvent used is appropriately determined depending on the content of indoles in the raw material, etc., but when treating the above-mentioned fraction obtained by distilling coal tar, the amount of solvent used is 0% based on the weight of the raw material. .1 to 10 times the amount is sufficient.
In the present invention, by bringing the above-mentioned hydrocarbon solvent into contact with the above-mentioned mixture containing indoles, non-polar substances such as methylnaphthalenes, dimethylnaphthalenes, naphthalene, and biphenyl, which are non-target substances present in the raw materials, can be removed. The polar and/or slightly polar compounds are extracted, and most of the indoles are present in the raffinate phase.

Since this raffinate phase contains a small amount of solvent, this is removed by distillation or evaporation to recover the indoles. On the other hand, the extract phase is separated into a solvent and an extract by distillation or evaporation. The solvent separated from the extraction phase and the raffinate phase is cooled, liquefied under pressure if necessary, and reused as an extraction solvent. When the raw materials also contain alkylindoles such as indole and methylindole, the resulting indoles include methylindoles and dimethylindoles, which have boiling points and melting points considerably different from those of indole.
If it is necessary to separate this to obtain highly pure indole, it is possible to easily obtain 99% by weight or more of indole by further crystallizing or distilling this. In addition, if the raw material contains pitchi, it is difficult to extract it and it will be included as an impurity in the indoles, so it is preferable to remove it before the extraction operation.
It may be removed in the distillation step of the raffinate phase or in the subsequent purification step of indoles. Next, a series of steps will be described in accordance with the flow sheet shown in FIG. 1, from removing pitch from the raw materials in advance and then performing an extraction operation to purifying the obtained indoles. The raw material is introduced into the first distillation column A through tube 1, and the raw material from which high-boiling components and pitch have been removed is taken out through tube 2 and introduced into the upper part of extraction column B. In the extraction column B, it is brought into countercurrent contact with a solvent consisting of hydrocarbons introduced from the bottom via pipe 3. The extraction phase consisting of the solvent and non-target substances is taken out from the top of the extraction column B and sent to the solvent recovery column C through a pipe 4. The solvent recovered from the top of the solvent recovery column C is sent to a solvent storage tank F for reuse. The indole-rich raffinate phase removed from the bottom of extraction column B is sent via pipe 5 to solvent separation column D.
The solvent is taken out from the top of the solvent separation column D, a part of which is refluxed to the solvent separation column D, and the remainder sent to a solvent storage tank F through a pipe 6 to be reused as an extraction solvent. Indoles are obtained from the bottom of the solvent separation column D. In order to obtain even higher purity indole, the obtained indole is introduced into rectification column E through tube 7, and purified indole is taken out from the top. Note that a part of the indole distilled from the top is refluxed to the rectification column E. As for the extraction method, normal countercurrent extraction is preferred, but it can also be carried out using a combination of multiple mixers and settlers.

The equipment for countercurrent extraction is plate column type, packed column type,
It can be used in either the rotating disk tower format or the Souvre single tower format. Further, the extraction conditions are preferably room temperature and normal pressure, but if the raw material oil and/or raffinate oil solidify, it is necessary to perform extraction at a temperature higher than the melting point of these liquids.
Furthermore, since the solvent may evaporate at that time, in such a case, operation under pressure is required to prevent evaporation of the solvent. As described above, the present invention extracts and removes nonpolar and/or slightly polar compounds present in coal tar from a mixture containing indoles using alkanes and naphthenes as a solvent, and thereby extracts the nonpolar and/or slightly polar compounds present in coal tar. Indoles can be easily recovered from the indoles, and in particular substances such as methylnaphthalenes and dimethylnaphthalenes, which are extremely difficult to separate from the indoles by distillation, can be completely removed.

Therefore, it is particularly suitable for use in mixtures mainly containing these substances and indoles. Furthermore, the solvent used for extraction in the present invention is inexpensive and harmless, easy to separate and recover and recycle, and requires less energy for recovery. Furthermore, since methylnaphthalenes and dimethylnaphthalenes can be completely removed by extraction, highly purified (99% by weight or more) indoles can be easily obtained with a high recovery rate by the subsequent distillation method. Furthermore, since the petathylnaphthalene on the extraction phase side is completely transferred, the oil from which the solvent has been removed from the extraction phase can be used as a raw material for purification of methylnaphthalene. The present invention will be explained in more detail below using Examples.

Examples 1-3 Boiling point range 240-2 obtained by distillation of coal tar
Put the 70°C fraction 50f7 into an extraction container and perform extraction at a solvent ratio (solvent:raw material weight ratio) of 1.The resulting raffinate phase is further extracted at the same solvent ratio, and in the same manner, a total of 6
Two extractions were performed at room temperature and pressure.

After the solvent contained in the final raffinate phase was removed by evaporation, the composition of the raffinate oil was investigated using gas chromatography. The results are shown in Table 1. The raw material composition at this time was as follows.

Example 4 Extraction operation was carried out under the same conditions as in Example 1 except that n-pentane was used as the solvent and the solvent ratio was 0.5 and 3.

The results are shown in FIG. 2, including the results of Example 1, as a relationship among the solvent ratio, raffinate oil composition, and indole recovery rate. In addition, in this figure, the composition is shown in weight % excluding pitch.
Examples 5 and 6 The same raw materials as in Example 1 were used at 2 kg/Hr and the solvent was used at 4 K.
The mixture was introduced into an extraction column at a ratio of g/Hr, and countercurrent extraction corresponding to 5 theoretical plates was performed at room temperature and pressure.

The results are shown in Table 2. Raffinate oil 1 obtained in Example 5
kg was distilled to obtain indole 580V with a purity of 99% by weight as shown below.

The indole recovery rate in distillation was 95% by weight, and the indole recovery rate based on the raw material of Example 5 was 89% by weight.
It was hot. Composition of obtained indole: Example 7 A raw material having the same composition as in Example 1 was introduced into the first distillation column A as shown in FIG. 51 to remove pitch from the raw material, and then transferred to the extraction column B. (the number of theoretical plates is 5) to perform countercurrent extraction, then the solvent is removed from the raffinate oil obtained in the solvent separation column D, and then the purified indole is introduced into the rectification column E. I got it.

Table 3 shows the compositional relationships at each stage of the process.

[Brief explanation of drawings]

FIG. 1 is a flow sheet of one embodiment of the present invention. In the figure, A is the first distillation column, Company B's extraction column, C is the solvent recovery column, D is the solvent separation column, and E is the rectification column. numbers 1, 2
, 3, 4, 5, 6, and 7 are conduits, and arrows indicate flows. FIG. 2 is a graph showing the relationship between the solvent ratio, raffinate oil composition, and indole recovery rate in Examples 1 and 4. In the figure, curves A and B indicate the weight percent of indole and methylnaphthalene in the raffinate oil, respectively, and C is the indole recovery curve.

Claims (1)

[Claims] 1. A mixture containing indoles and a nonpolar and/or slightly polar compound present in coal tar with a solvent consisting of one or a mixture of two or more selected from alkanes and naphthenes. A method for recovering indoles, which comprises contacting and separating into an extraction phase rich in substances other than indoles and a raffinate phase rich in indoles, and removing a solvent from the raffinate phase to obtain indals. 2 The nonpolar and/or slightly polar compound has a boiling point of 200 to
A method for recovering indoles according to item 1, which are substances in the range of 300°C. 3. The method for recovering indoles according to item 1, wherein the content of indoles in the mixture is 40% by weight or more. 4. The method for recovering indoles according to item 1, wherein the alkanes and nanthenes have 2 to 12 carbon atoms in the molecule. 5. The method for recovering indoles according to item 1, in which highly pure indoles are obtained by crystallizing or distilling the raffinate oil obtained by removing the solvent from the raffinate phase.