JPH1025481A - Method for recovering tar acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering tar acids from a phenolate, which is less problematic in waste disposal and can be practiced by using a compact apparatus. SOLUTION: In recovering tar acids contained in an aromatic oil, an aqueous phenolate solution 5 extracted from an aromatic oil 1 with an aqueous alkali solution is electrolyzed with an ion exchange membrane electrodialyzer 6 fitted with a bipolar membrane. The formed tar acids 7 together with a phenolate are withdrawn from the phenolate chamber of the electrodializer, and the phenolate 9 separated from the tar acids is recirculated into the chamber. According to this method, the concentration of the tar acids in the phenolate chamber can be regulated at a specified value or below, and therefore long continuous operation is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for separating and recovering tar acids contained in aromatic oils.
The present invention relates to a method of recovering tallic acids from phenolate, which is an alkali salt of tallic acid, by ion exchange membrane electrodialysis.

[0002]

2. Description of the Related Art Aromatic oils obtained from coke oven gas, coal dry distillation tar, coal liquefied oil, and the like contain tar acids such as phenol, cresol, and xylenol.
These are recovered industrially. Conventional techniques for recovering tar acids from aromatic oils include, for example,
No. 22788, KIRK-OTHMER edited by Encyclopedia of
chemical technology Third Edition vol.22 Wiley Int
As described in the tarand pitch section of ernational ('78),
First, an aromatic oil and an aqueous alkali solution are mixed and reacted to convert tar acid into an alkali salt form, that is, phenolate, and extract it into an aqueous layer. Then, the extracted alkali salt is decomposed with carbon dioxide gas and tar acid is again formed. The method of separation and recovery is generally used. In this method, an aqueous caustic soda solution is usually used as the aqueous alkali solution, but this alkali becomes a carbonate when phenolate is decomposed with carbon dioxide gas.
Therefore, in order to reuse this sodium carbonate, quick lime is added to regenerate and reuse the alkali. However, in this method, a large amount of calcium carbonate is produced as a by-product, and disposal thereof is a problem in terms of environmental conservation. In addition, the alkali recovery rate is not always high, and alkali needs to be replenished. Furthermore, a gas containing carbon dioxide such as blast furnace gas is used as a decomposition gas source, and a large amount of gas is used. When blast furnace gas is used, there are restrictions on the installation location.

[0003] In addition, acid /
The method of recovering the alkali itself is a known technique as shown in Japanese Patent Publication No. 32-3962, but it does not
Both the generated acid and the alkali are limited to water-soluble ones.
Although tallic acids are water-soluble, they have been considered to be difficult to apply because they have a relatively low solubility in water and a strong property of dissolving or swelling the resin.

[0004]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for recovering tallic acids from phenolate which can be operated with a compact apparatus and has less problems of waste disposal. is there.

[0005]

Means for Solving the Problems As a result of intensive studies on a recovery method free of by-products, the present inventors have found that if an ion exchange membrane electrodialysis apparatus equipped with a bipolar membrane is used, the alkali salt of tar acids can be used. It has been found that a certain phenolate can be decomposed under extremely mild conditions of normal temperature and normal pressure. It has also been found that if the concentration of the generated tallic acids is kept below a certain level, film contamination and deterioration can be prevented, and long-term operation is possible.

That is, according to the present invention, in the recovery of tar acid contained in aromatic oil, an aqueous phenolate solution extracted from an aromatic oil with an aqueous alkali solution is treated by an ion exchange membrane electrodialysis apparatus equipped with a bipolar membrane. This is a method for recovering tar acids, which is characterized by electrolysis.

The aromatic oil supplied as a raw material includes:
There is no particular limitation as long as it contains tallic acids, but preferably coal dry distillation tar or coal liquefied oil. More preferably, it is a fraction containing tallic acids obtained by distilling them at a relatively high concentration. The term "tar acids" as used in the present invention refers to compounds having an OH group directly bonded to an aromatic ring such as phenol and alkylphenol, and includes at least one or more of these, and may include some carboxylic acids. is there. The phenolate refers to such an alkali salt of tar acids, and may contain some salts of carboxylic acids.

The aqueous alkali solution is typically an aqueous solution of a hydroxide of an alkali metal such as sodium hydroxide or potassium hydroxide, but an aqueous sodium hydroxide solution is preferred. In the case of an aqueous sodium hydroxide solution, its concentration is about several% to 20%, preferably about 5 to 15%. Extraction with an aqueous alkali solution is performed by bringing an aromatic oil into contact with an aqueous alkali solution. Although there is no particular limitation on the contact method, a stirring mixer or the like is generally used. The amount of the aqueous alkali solution used is preferably a theoretical amount sufficient to neutralize the tar acids in the aromatic oil or a slight excess thereof in order to recover as much as possible. However, using a large excess reduces the current efficiency during electrolysis. By this extraction operation, the tar acids are converted into phenolates and transferred into the aqueous solution. The separation between the aqueous solution layer and the oil layer can be performed by standing separation or the like.

Next, the aqueous phenolate solution is electrolyzed by an ion exchange membrane electrodialyzer equipped with a bipolar membrane (hereinafter abbreviated as electrodialyzer). As this electrodialysis device, a known device can be used, but one having at least two chambers (cells) partitioned by at least two bipolar membranes and at least one ion exchange membrane interposed therebetween. It is necessary to be. Here, the ion exchange membrane may be any one or both of an anion exchange membrane and a cation exchange membrane, but is preferably a cation exchange membrane. In addition, a commercially available resin membrane can be used for the bipolar membrane and the ion exchange membrane.

When an aqueous phenolate solution is charged into a chamber (cell) defined by a bipolar membrane and an ion exchange membrane of this electrodialysis apparatus and a direct current is applied, electrolysis occurs, and a typical phenolate is used. In the case of sodium phenolate, phenoxy ions are likely to collect on the positive electrode side and sodium ions are likely to collect on the negative electrode side, but are separated by an ion exchange membrane and a bipolar membrane, so that any one of the at least two chambers (cells) is used. And reacts with hydrogen ions or hydroxide ions to produce tar acids and sodium hydroxide. In this manner, the separated or concentrated tar acids and the aqueous alkali solution are withdrawn from the electrodialysis device, and the tar acids and the aqueous alkali solution are separated or recovered.The tar acids are further purified by distillation or the like as necessary. Circulate in

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flow sheet showing an example of recovering tar acids from an aromatic oil. An aromatic oil 1 and an aqueous alkaline solution 2 are brought into contact in an extraction step 3, and the tar acids are extracted into the aqueous solution as phenolates. . Extraction process 3
In this case, a stirring mixer or the like is used, and the operation is preferably performed so that the total amount of tar acids in the aromatic oil 1 is extracted as much as possible. This extraction step is preferably performed at room temperature or at a temperature near the room temperature. As the aromatic oil 1, a fraction having a boiling point range of components such as phenol, cresol, and xylenol is preferable.

The deoxidized aromatic oil 4 is extracted from the extraction step 3 and sent to a separation / purification step, if necessary, to recover naphthalene and the like. On the other hand, phenolate aqueous solution 5
Is sent to the electrodialysis device 6, where it is electrolyzed.
In order to prevent the membrane from being contaminated in the electrodialysis device 6, it is preferable to install a filter or the like before the electrodialysis device 6 to purify the aqueous phenolate solution 5. Further, the concentration of the tar acids in the aqueous phenolate solution 5 needs to be controlled to be lower than its solubility, and its pH is preferably maintained at 8 or more in order to prevent damage to the film due to free tar acids.

The electrodialysis apparatus 6 will be described with reference to FIG. The electrodialysis device 6 includes two bipolar membranes 2
The chambers 1 and 22 and the cation exchange membrane 23 are divided into four chambers (cells). In the chambers (cells) at both ends, a positive electrode 24 and a negative electrode 25 are arranged so as to be connected to a DC power supply 26. Further, a chamber (cell) 27 partitioned by the bipolar membrane 21 and the cation exchange membrane 23 is referred to as a phenolate chamber 27 because phenolate mainly exists, and is partitioned by the bipolar membrane 22 and the cation exchange membrane 23. Room (cell)
28 is referred to as an alkali chamber 28 because alkali is mainly present.

In the electrodialysis apparatus thus constructed, the aqueous phenolate solution 5 charged in the phenolate chamber 27 is electrolyzed when an electric current is applied, and the generated cations such as sodium ions are converted into cations. Exchange membrane 23
And moves to the alkaline chamber 28. On the other hand, since anions such as phenoxy ions cannot pass through the cation exchange membrane 23, they stay in the phenolate chamber 27. The anions and cations thus generated react with hydrogen ions and hydroxide ions to become tar acids and alkali hydroxides, respectively.

An electrodialysis apparatus 6 in which an anion exchange membrane is used in place of the cation exchange membrane 23;
An anion exchange membrane may be further provided between the cation exchange membrane 23 and the bipolar membrane 21 to further divide the phenolate chamber into two, but an anion such as phenoxy ion may damage the membrane. Therefore, it is advantageous to provide a device having a structure in which this anion does not pass through the ion exchange membrane. Further, in order to increase the current efficiency, multiple chambers (cells) defined by the bipolar membrane and the ion exchange membrane can be provided,
In this case, there are a plurality of phenolate chambers and an alkali chamber. The dialysis current density is not particularly limited,
It may be about 0.01 to 30 A / dm ² . Electrodialysis device 6
The operating temperature may be room temperature. If the operating temperature is increased, even if the solubility of tar acids is increased, the electrical resistance of the film is increased and the efficiency is reduced.

The alkali hydroxide generated in the electrodialysis device 6 is extracted from the alkali chamber 28 as an aqueous solution, and can be circulated as the alkaline aqueous solution 2 used in the extraction step 3. On the other hand, tar acids are extracted from the phenolate chamber 27, but the entire amount of phenolate present in the phenolate chamber 27 may be converted into tar acids at one time. Since the risk of damaging the membrane increases, it is better to control the solubility to less than or equal to 10%. The solubility of tar acids at room temperature in the case of phenol is about 15% in water and about 20% in aqueous phenolate solution.

As a preferable method, a phenolate aqueous solution 5 is charged into an electrodialyzer 6 to electrolyze a part of the phenolate, and the phenolate is continuously extracted as a liquid 7 containing tar acids. There is a method in which the tar acid 12 is separated into the apparatus 8 and the phenolate aqueous solution 9 is circulated again to the electrodialysis apparatus 6. If the circulation continues, the phenolate concentration decreases. When the concentration falls below a certain concentration, the circulation is stopped and a new aqueous solution 5 is charged into the electrodialysis apparatus 6. With this method,
Not only does the tar acid concentration not increase to such an extent that the membrane is damaged, but also the membrane is less likely to be contaminated because of the appropriate flow rate, so that long-term continuous operation is possible. The flow rate of the aqueous solution with respect to the membrane is preferably 0.5 cm / sec or more, and more preferably 2 cm / sec or more.
The number of circulations is preferably 5 or more.

If the film is contaminated and the efficiency is reduced, the contaminant is soluble in alkali. Therefore, if the film is periodically washed with an alkaline aqueous solution, the contaminant can be dissolved and removed. Known methods can be used for cleaning the membrane.

The tar acids 12 are recovered by the tar acids recovery device 8. When the tar acids are precipitated or partially dissolved in the aqueous phenolate solution, a layer separation method can be applied. If so, it is preferable to apply a solvent extraction method. As the extraction solvent in this case, a solvent having a boiling point lower than that of tar acids, for example, light oils such as benzene, toluene, and xylene is preferable. When extracted with a solvent,
The extract 10 is charged into a solvent recovery unit 11 where the tar acids 12 are recovered, and the extraction solvent 13 is circulated to the tar acids recovery unit 8. As the solvent recovery device 11, a distillation device is the simplest, but in some cases, a crystallization device or the like can also be used.

[0020]

EXAMPLES A liquefied oil obtained by partial hydrogenation of coal was subjected to atmospheric distillation to obtain an aromatic oil fraction having the composition and properties shown in Table 1. This aromatic oil fraction was extracted with a 10% by weight aqueous solution of sodium hydroxide to give a phenolate content of 0.15%.
A kg / liter aqueous phenolate solution was prepared.

The surface area is 1000 cm each.
² A bipolar membrane (20 cm wide × 50 cm high) (Neosceptor CMX manufactured by Tokuyama Corporation) and a cation exchange membrane are arranged so that the membrane interval is 0.7 to 0.8 cm. The ion exchange membrane electrodialysis apparatus shown in FIG. 2 having a chamber, an alkali chamber and a negative electrode chamber was assembled.

Into the phenolate chamber of the ion-exchange membrane electrodialysis apparatus, 1 liter of the above-mentioned phenolate aqueous solution was filtered through a sintered metal filter having an aperture of 10 μm, and then charged continuously from the bottom upward. Circulated at a rate of 270 liters / hr. At this time, the liquid moving speed at the film interface was 5 cm / s. The reaction liquid extracted from the phenolate chamber was extracted with xylene using a static mixer, and then circulated through the phenolate chamber.

An average voltage of 5 V is applied to the ion exchange membrane electrodialyzer.
When a direct current of 10 to 15 A was passed through the chamber and electrolysis was performed for 100 minutes, sodium hydroxide 47 g
Was recovered as an aqueous solution, and almost all of the phenolate was decomposed. Further, the xylene extract was distilled to recover 110 g of tar acids. The composition is shown in Table 2. Although some contamination was observed on the surface of the bipolar film, it was confirmed that the contamination was easily redissolved by washing with a 10% by weight aqueous sodium hydroxide solution.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

The phenolate decomposition method by electrodialysis according to the present invention has no by-products, is less compact, and has less restrictions on the installation place, as compared with the conventional carbon dioxide decomposition method.
In addition, by controlling the concentration of tar acid in the phenolate chamber to a certain level or less, a long-term continuous operation becomes possible.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention.

FIG. 2 is a configuration example of an ion exchange membrane electrodialysis apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Aromatic oil 2 Alkaline aqueous solution 3 Extraction process 5 Phenolate aqueous solution 6 Electrodialyzer 8 Tar acids recovery apparatus 9 Circulating phenolate aqueous solution 11 Solvent recovery apparatus 12 Tar acids 21, 22 Bipolar membrane 23 Cation exchange membrane 24 Positive electrode 25 Negative electrode 27 Pheno Rate room 28 Alkaline room

 ────────────────────────────────────────────────── ─── Continued from the front page (72) Inventor Kazuhiko Mizuuchi 1-11-1-13-116 Yokodai, Isogo-ku, Yokohama-shi, Kanagawa

Claims (4)

[Claims] 1. In recovering tar acids contained in an aromatic oil, an aqueous phenolate solution extracted from an aromatic oil with an alkaline aqueous solution is charged into an ion exchange membrane electrodialysis apparatus equipped with a bipolar membrane, A method for recovering tar acids, comprising electrolysis. 2. The method for recovering tar acids according to claim 1, wherein the aromatic oil is a coal carbonized tar or a coal liquefied oil. 3. An aqueous phenolate solution is added to two bi-ports.
A cation exchange membrane is provided between the membranes to form a phenolate chamber and an alkaline chamber.
The tallic acid is electrolyzed to produce tallic acids and alkali hydroxide, and the generated tallic acids are discharged from the phenolate chamber.
The alkali hydroxide is extracted from the alkali chamber, and the aqueous phenolate solution containing tallic acids extracted from the phenolate chamber is subjected to ion exchange after collecting the tallic acids by layer separation and / or solvent extraction. The method for recovering tar acids according to claim 1, which is circulated through a membrane electrodialysis apparatus. 4. A method for controlling the concentration of tallic acid in an aqueous phenolate solution containing tallic acids extracted from a phenolate chamber to a concentration at which substantially no undissolvable tallic acids are present. Item 4. The method for recovering tar acids according to Item 3.