JPH046235B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for accelerating the oxidation rate when impurities such as sulfur compounds contained in coal tar-based tar acids are oxidized with oxygen. Carboxylic oil obtained by distilling coal tar,
After extracting naphthalene oil with an alkaline aqueous solution such as caustic soda to form a tar salt, decomposing it with an acidic substance such as carbon dioxide or sulfuric acid to liberate crude tar acid, which is then distilled to produce phenol, orthocresol, and meth.・Tar acids such as para-cresol and xylenol are obtained, but since carbon oil and naphthalene oil contain a large number of compounds, even when separating tar acid, it is necessary to impurities other than tar acid are mixed into the In particular, sulfur compounds have similar chemical properties to phenols, so they are easily mixed in as impurities, which not only lowers purity but also adversely affects hue and the like. As a method for removing impurities such as sulfur compounds mixed in the tar acid, tar salt obtained by alkali extraction of tar oil is decomposed with an acidic substance to obtain crude tar acid, which is then distilled. In the method of obtaining tar acids such as phenols, cresols, xylenols, etc., tar salts or crude tar acids are brought into contact with an oxygen-containing gas at a temperature of 40 to 100°C, and the distillation is carried out at a temperature where the maximum temperature in the column is A method for producing tar acids characterized by vacuum distillation in a distillation column that does not exceed 200°C (Japanese Patent Application Laid-Open No. 115731/1983)
etc. have been proposed. However, when a sulfur compound such as thiophenol mixed in tar acid such as phenol is simply brought into contact with an oxygen-containing gas, the oxidation rate is slow and it takes a very long time. This invention was made in view of the above circumstances, and provides a method for accelerating the oxidation rate when oxidizing a sulfur compound mixed in tar acid such as phenol by contacting it with an oxygen-containing gas. That is, the present invention involves contacting tar acids such as phenol, ortho-cresol, meta-para-cresol, xylenol, etc. or mixtures thereof obtained by distilling coal tar-based crude tar acids with an oxygen-containing gas to remove the sulfur compounds contained therein. In a method for purifying tar acid by oxidizing it and then distilling it under reduced pressure, tar acids or a mixture thereof are mixed with an alkali metal salt,
After adding one or more of alkali metal hydroxides and alkali metal alkoxides,
This is a method for purifying tar acid, which is characterized by bringing it into contact with an oxygen-containing gas. Examples of alkali metals such as alkali metal salts, alkali metal hydroxides, and alkali metal alkoxides added as catalysts include lithium, sodium, and potassium; examples of these salts include carbonates, hydrogen carbonates, and tar acids. salt can be used. Further, when adding an alkali metal salt or an alkali metal hydroxide, it may be added as is or dissolved in water and/or alcohol. If the above-mentioned alkali metal salts, alkali metal hydroxides, and alkali metal alkoxides are added to tar acids or mixtures thereof, the oxidation rate of sulfur compounds such as thiophenol contained as impurities will be significantly improved, and oxygen-containing The contact time with gas can be greatly shortened. The amount of alkali metal salts, alkali metal hydroxides, and alkali metal alkoxides added in terms of alkali metal
It is preferably 0.01 to 2% by weight; less than 0.01% by weight has no effect, and more than 2% by weight produces pitch and makes distillation difficult. The temperature when contacting with oxygen-containing gas is 40~
100°C, preferably 60-90°C; lower temperatures slow down the reaction rate. Example 1 Approximately 150S of thiophenols obtained by distilling coal tar crude tar acid in a constant temperature water bath maintained at 50℃
Dissolve 0.5g of caustic soda in 500g of tar acid (35% phenol, 55% cresols, other xylenol, etc.) containing mg/Kg, without adding any additives, and charge the sample into a 500ml glass absorption bottle. Aeration is carried out by supplying air at a rate of 0.2/min to the bottom.
The aeration time and the reduction rate of thiophenol were measured. The results are shown in FIG. Note that thiophenol was analyzed using a potentiometric titration device and titrated with an iodine solution in an alcohol solvent. As shown in Figure 1, in the case of no addition of caustic soda (A), the rate of decrease in thiophenol was extremely slow, with approximately 140 Smg/Kg of thiophenol remaining even after 20 hours, but with the addition of 0.5 g of caustic soda.
In case (B), the amount decreased significantly to about 35 Smg/Kg after 20 hours, and the oxidation rate was significantly accelerated. Example 2 Purity 99 obtained by purifying and distilling tar-based crude tar acid
1.5 g of caustic soda was added to 500 g of phenol with a concentration of 1.5 g and aerated with air under the same conditions as in Example 1, and the aeration time and rate of decrease in thiophenol were measured. The results are shown in FIG. As shown in FIG. 2, the thiophenols in the phenol were almost completely oxidized by the 10-hour aeration treatment, which clearly demonstrates the effectiveness of the present invention. Example 3 After dissolving 1.5 g of various catalysts shown in Table 1 in 2 g of water, approximately
After adding it to 500 g of tar acid containing 150 Smg/Kg, air aeration was performed under the same conditions as in Example 1, and the oxidation rate of thiophenols was measured. Note that sodium methoxide alone was added without being dissolved in water.
Further, the oxidation rate was determined by regarding the value 3 hours after aeration as a straight line.

【table】

[Table] As shown in Table 1, sodium, potassium,
It is clear that carbonate and bicarbonate alkoxides of lithium also have catalytic activity, greatly increasing the oxidation rate. Example 4 Thiophenols used in Example 1 approximately 150S
1.5 g of caustic soda dissolved in 2 g of water was added to 500 g of tar acid containing mg/Kg, and the treatment temperature was 50℃ and 70℃.
C. and 80.degree. C. in the same manner as in Example 1, and the relationship between the treatment temperature and the oxidation rate of thiophenol was determined. The results are shown in Table 2. Note that the oxidation rate was determined in the same manner as in Example 3.

[Table] As shown in Table 2, the oxidation rate increases significantly as the treatment temperature increases, and it is clear that the treatment time can be significantly shortened by increasing the treatment temperature.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between aeration time and thiophenol reduction rate in Example 1 of the present invention, and FIG. 2 is a diagram showing the relationship between aeration time and thiophenol reduction rate in Example 2. It is a diagram.

Claims (1)

[Scope of Claims] 1 Tar acids such as phenol-ortho-cresol, meta-para-cresol, xylenol, etc. obtained by distilling coal tar-based crude tar acids, or mixtures thereof, are brought into contact with an oxygen-containing gas to oxidize the sulfur compounds contained therein. In a method for purifying tar acid, which is then distilled under reduced pressure, one or more of alkali metal salts, alkali metal hydroxides, and alkali metal alkoxides are added to tar acids or these compounds, and then an oxygen-containing gas is added. A method for purifying tar acid, which comprises bringing it into contact. 2 Alkali metal salts, alkali metal hydroxides,
2. The method according to claim 1, wherein the amount of the alkali metal alkoxide added is 0.01 to 2% by weight in terms of alkali metal.