JPH0145514B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for purifying tar acid produced as a by-product from coal carbonization or coal gasification processes. Tar acid is originally a general term for phenols, cresols, and xylenols, but tar acid also contains basic nitrogen compounds such as aniline, pyridine, picoline, lutidine, and quinoline, which are generally referred to as tar bases. Contains impurities. Tar acid is a wood preservative, insecticide, and
Although it is used as a disinfectant, when it is used as a raw material for synthetic resins and plasticizers, the above impurities must be removed as much as possible. Furthermore, due to resource considerations, the source of materials for synthetic resins and the like has recently been replaced by coal-based materials rather than petroleum-based ones, so the development of a tar acid purification method has become a major issue. [Prior art] Conventionally, in order to obtain tar acid from the coal carbonization process, the raw materials such as tar light oil, carbol oil, naphthalene oil or absorption oil are washed with a dilute aqueous solution of caustic soda, thereby removing the tar acid in the raw material. The sodium salt is converted into soda salt, which is then subjected to steaming or light oil washing to remove neutral oil and tar base, followed by neutralization and decomposition with sulfuric acid or carbon dioxide gas, and further as necessary. Therefore, methods such as distillation have been adopted. However, in the above method, relatively low boiling point bases such as pyridine and picoline are easily removed in the steaming process, but high boiling point bases such as aniline and toluidine are difficult to remove. It is also unfavorable from an economic point of view, as it requires a large amount of light oil. [Problems to be Solved by the Invention] In view of the above, the present invention provides a method for purifying tar acid that easily removes high-boiling heterocyclic compounds such as aromatic amines and lutidine. [Means for Solving the Problems] The present inventors have discovered that the above problems can be solved by adding complexone to tar acid and distilling the mixture at a bottom temperature of 200° C. or lower. The tar acid referred to in the present invention refers to crude tar acid after neutralization and decomposition of tar acid sodium salt with an acid as described in the section of the prior art, and purified tar acid obtained by dehydrating and/or depitching the crude tar acid. , phenol, o-cresol, m/p-cresol, xylenol, etc. obtained by distilling purified tar acid. In other words, it refers to tar acid containing a basic nitrogen compound. Further, the complexone added prior to distillation is a compound having a functional group described in (i) below, and alkali metal salts thereof also exhibit similar effects. Typical examples of such complexons include nitrilotriacetic acid, ethylenediaminetetraacetic acid, triethylenetetraminehexaacetic acid, and 1,2-cyclohexyldiaminetetraacetic acid. The amount added naturally varies depending on the amount of basic impurities contained in the tar acid. It is appropriate to add an amount that is stoichiometrically equimolar to the amount of basic impurities estimated based on previously measured analytical values or past actual measurements, or slightly more than that. Further, the distillation conditions may be normal pressure, increased pressure, or reduced pressure. Practically speaking, it would be appropriate to carry out distillation under normal pressure or reduced pressure with a bottom temperature of approximately 200°C or less. [Operation] Although the basic impurity removal mechanism according to the method of the present invention is not necessarily clear, it is expressed by the following formula (ii). Based on this, it is presumed that the amino group in the impurity reacts with the carboxylic acid in the complexone to form an imide bond, which is difficult to distill off under distillation conditions. Comparative example: 200g of crude tar acid having the composition listed in Table 1.
Pour into a 200ml flask and keep the bottom temperature at 180°C under normal pressure.
Dehydration was carried out using a distillation column with 15 theoretical plates. That is, first, 33.5 g of water and oil were distilled from the top of the column.

[Table] Oil is mainly composed of phenol, which is azeotropically distilled with water. Then, while maintaining the bottom temperature at 180°C, it was subjected to vacuum distillation to reach a final pressure of 30 mmHg.
There were 14 g of pit-shaped pot residue left in the flask, and 144
g of dehydrated and removed pittitutal acid was distilled out (loss
8.5g). Table 2 shows the analytical values for basic nitrogen in dehydrated and despicytal acid. Example Complexons in an equimolar amount to the basic nitrogen compound contained in the crude tar acid listed in Table 1 were added, and the same operation as in the above comparative example was performed to dehydrate and
De-pitcitaric acid was obtained. The material balance is virtually unchanged from the comparative example.

〔effect〕

As shown in Table 2, the method of the present invention is particularly effective in removing basic nitrogen compounds with amino groups (aniline, toluidine, etc.) by simply adding a small amount of complexone and distilling. It can be carried out in a number of ways.

Claims (1)

[Claims] 1. A method for purifying tar acid, which comprises adding complexone to tar acid and distilling the mixture at a bottom temperature of 200°C or lower. 2. The method according to claim 1, wherein the amount of complexone added is equivalent to or more than the tar base contained in tar acid.