JPH0354996B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for purifying tar acid obtained from a coal carbonization or coal gasification process. Prior Art In order to obtain tar acid from coal tar obtained in a coal carbonization process, various fractions of the coal tar, especially tar light oil, carbol oil, naphthalene oil or absorption oil, are usually washed with a dilute aqueous caustic soda solution. By converting the tar acid contained in the distillate into soda salt and then applying a steaming method or a light oil washing method to the aqueous soda salt solution, neutral oils such as naphthalene and pyridine are removed. A method is employed in which such low-boiling point tar bases are removed, and then neutralized with sulfuric acid or carbon dioxide gas, thereby separating and recovering the free acid. As can be seen from this recovery method, the main components of tar acid are phenol, cresol, xylenol, etc., but it inevitably contains basic nitrogen compounds called tar bases such as aniline, pyridine, picoline, lutidine, and quinoline as impurities. are doing. Such impurities do not need to be particularly purified and removed when tar acid is used as a wood preservative, insecticide, fungicide, etc.; If it is directed to raw materials, it needs to be removed as much as possible. In the steaming method described above, not only is it difficult to remove high-boiling point tar bases such as aniline and toluidine, but also the large amount of heat consumption is unfavorable from an economic point of view. The same applies to light oil cleaning. Problems to be Solved by the Invention The present invention provides a method for purifying tar acid that easily reduces aromatic amino compounds such as aniline or toluidine. Means for Solving the Problem The present inventors used an aliphatic polycarboxylic acid that can be converted into an acid anhydride through an intramolecular dehydration reaction, an anhydride of the acid, or a salt of the acid into the tar acid to be treated. It has been found that the above-mentioned problems can be easily solved by adding one or more of these to distillation. The tar acid to be treated to which the method of the present invention is applied is:
Crude tar acid, which is liberated by acid neutralization of the sodium tar acid salt mentioned in the prior art section, and a low level of purification obtained by dehydrating and/or depitching this crude tar acid. Tar acid obtained by distilling this lower tar acid (tentatively named lower tar acid), phenol, O-cresol, m.
p-cresol, xylenol, etc., all of which are basic nitrogen compounds that should be removed;
In particular tar acid, which contains some aromatic amino compounds. It is important that the aliphatic polycarboxylic acid () added to such tar acid can be converted into an acid anhydride through an intramolecular dehydration reaction. Such acids are equally used in free form ( ), in acid anhydride ( ) form or in salt form ( ). Typical examples of these are succinic acid, citraconic acid, and glutaric acid in the form of ().
In the form of these acids, they are sodium salts, potassium salts, ammonium salts, etc. These added polycarboxylic acids are (),
Regardless of whether it is in the form of ( ) or ( ), it is in the form of powder at room temperature, so after adding it to the tar acid to be treated and stirring well, distillation is started. At the distillation temperature, the added aliphatic polycarboxylic acid () and the aromatic amino compound in the tar acid to be treated react according to the following formula (a), resulting in a high boiling point imide compound (in the formula, *). Acid anhydrides () and salts () undergo similar reactions to become imide compounds while producing water or alcohol as by-products. In the case of salt (), it is better to first change it to the form (), so
At the same time as the addition, a strong acid such as sulfuric acid may be added and distillation may be carried out in its presence. The imide compound produced by the above reaction formula (a) is
Of course, it is a substance with a higher boiling point than any other tar acid, so when the tar acid to be treated is distilled, it remains at the bottom of the column as a residue, and the tar acid that is distilled out does not contain aromatic amino compounds that are impurities. It is. Since the method of the present invention is generally explained as above, the amount of acid to be added to the tar acid to be treated is controlled by the amount of aromatic amino compound contained in the tar acid to be treated. . In other words, (a)
Although the theoretical equivalent of the formula is sufficient, in reality, it is preferable to add 2 to 4 times the theoretical amount in consideration of the reaction rate, etc. On the other hand, when an aliphatic monocarboxylic acid is used instead of adding an aliphatic polycarboxylic acid in the method of the present invention, the monocarboxylic acid and an aromatic amino compound as an impurity react to form an amide bond (- A compound with CONH−) is produced. However, compared to the imide compound shown in reaction (a), it is less stable and easily decomposed. Therefore, the ability to fix aromatic amino compounds is insufficient and it is not practical. This is the reason for excluding the use of aliphatic monocarboxylic acids in the present invention. Examples 1 to 3, Comparative Example 200g of crude tar acid having the composition listed in Table 1 was
A 200 ml flask is charged, and glutaric acid (Example 1), glutaric anhydride (Example 2) or sodium glutarate (Example 3) is added in an amount twice the amount of the aromatic amino compound it contains; Or without addition (comparative example), under normal pressure, bottom temperature
First, dehydration was performed at 180°C using a distillation column with 15 theoretical plates.

[Table] The above dehydration is the distillation of water and oil from the top of the column. The oil component is phenol etc. that is distilled out by azeotropic distillation with water, and the amount thereof in both Examples and Comparative Examples is 33.5 g. Then, while maintaining the bottom temperature at 180°C, vacuum distillation was carried out to reach a final pressure of 30 mmHg.
In both the examples and comparative examples, 10 g of pot residue remained in the flask, and 150 g of dehydrated and depitched tar acid (corresponding to purified tar acid in the example) was distilled from the top of the column. The distillation loss was 6.5 g. The results of analysis of the type and content of aromatic amino compounds contained in the distilled tar acid and raw material crude tar acid are shown in Table 2.

[Table] Effects of the Invention As can be seen from Table 2, according to the method of the present invention, basic nitrogen compounds represented by aromatic amino compounds were selectively removed, and the quality of the obtained tar acid was significantly improved. It has become a thing. Such purification can be done using very common acids (),
It can be said that it is simpler and more effective than other conventional purification methods, since it is sufficient to add an acid anhydride () or a salt () and perform a distillation operation as usual.

Claims (1)

[Claims] 1. It is characterized by adding to tar acid an aliphatic polycarboxylic acid that can be converted into an acid anhydride through an intramolecular dehydration reaction, or the acid anhydride, or a salt of the acid, and then distilling the mixture. Method for purifying tar acid. 2. The purification method according to claim 1, wherein the aliphatic polycarboxylic acid is succinic acid, citraconic acid, or glutaric acid. 3. The purification method according to claim 1, wherein the amount added is approximately 2 to 4 times the equivalent of the aromatic amino compound in the tar acid to be treated.