JPH032128B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for purifying crude naphthalene, commonly referred to as 95% naphthalene, obtained from naphthalene oil, a medium oil in coal tar fraction oil. Prior Art Naphthalene is an important substance as a raw material for medicines, dyes, and other organic synthesis, but in order to use it for these purposes, it must be sufficiently purified.
Even in the case of insect repellent products that do not require such high purity, if they are colored and odorized, their commercial value will be low, so refining is desirable for that reason as well. For this reason, many purification methods have been proposed so far. For example, hydrogenation method (JP-A-53-119856
(Japanese Patent Publication No. 54-144349), crystallization method from methanol (Japanese Patent Publication No. 47-47020), impurity removal method by adding aluminum chloride (Japanese Patent Publication No. 47-47021), combined method of fractional crystallization and white clay treatment (Japanese Patent Publication No. 47-47021) Special Publication No. 47-47023),
Acetic anhydride addition method (Japanese Patent Publication No. 60-3051), oxalic acid addition method (Japanese Patent Publication No. 53-144557), metal or metal oxide catalyst addition method (Japanese Patent Publication No. 54-81247,
53-147048) etc. are known. Among the conventional methods mentioned above, in the hydrogenation method implemented on an industrial scale, it is necessary to add a step to remove ethylbenzene, which is a decomposition product of tetralin and thionaphthene, which are produced by hydrogenating a portion of naphthalene. , product yield also decreases.
Furthermore, in the same fractional crystallization method, since removal of the sulfur compound thionaphthene is insufficient, a desulfurization step must be added, and naphthalene is lost together with the fractionated mother liquor, resulting in a decrease in product yield. Other conventional methods also improve equipment corrosion resistance, product yield,
It has a problem in one of the sulfur compound removal rates and is not fully satisfactory. Problems to be Solved by the Invention The present invention provides a simple naphthalene purification method that replaces the above-mentioned conventional techniques, can remove sulfur compounds that inhibit the naphthalene derivative synthesis reaction and product quality, and has a high product yield. It is something to do. Means to Solve the Problem The inventors of the present invention have searched for a wide range of efficient purification methods from a different perspective that is not constrained by conventional methods.
By adding monoethanolamine to crude naphthalene and subjecting it to distillation, and distilling off the fraction below the boiling point of the amine, naphthalene that is almost completely free of thionaphthene can be easily produced in high yield. I found out that it can be obtained with The naphthalene to which the method of the present invention is applied is not particularly different from conventional crude naphthalene. The method of the present invention is extremely effective for coal tar-based crude naphthalene because impurities, especially sulfur compounds, can be removed. In the method of the present invention, the appropriate amount of monoethanolamine to be used is 4 times mole or more (twice the amount by weight) relative to naphthalene. There are no particular limitations on the applicable distillation column. Either tray type, packed column type or bubble bell type is acceptable.
Moreover, either a batch process or a continuous process can be adopted. The maximum distillation temperature is approximately 171°C, which is the boiling point temperature of monoethanolamine under normal pressure. This temperature was determined experimentally along with the amount of monoethanolamine used. Effect The theory of the method of the present invention has not yet been completely elucidated. However, from the experimental facts, the method of the present invention can be regarded as a type of azeotropic distillation. This is because the boiling point of naphthalene is approximately 218℃, and that of thionaphthene, a typical impurity, is approximately 221℃.
However, by applying the method of the present invention, the target naphthalene is distilled out from the top of the column together with monoethanolamine at a temperature of 171°C or lower, which is far lower than its boiling point, and thionaphthene is distilled off as a so-called bottom residue. This is because it will be put away. In other words, monoethanolamine plays the role of greatly changing the specific volatility of the components to be distilled, that is, increasing the specific volatility of naphthalene and decreasing that of thionaphthene. It is thought that it plays the same role as the agent itself and selectively azeotropes naphthalene during the distillation process. The reason why it was mentioned above that continuous distillation is possible is that it is possible to distill azeotropic monoethanolamine while continuously feeding it to the top of the column according to the conventional method of azeotropic distillation. In addition, in place of monoethanolamine, diethanolamine and other alcohol amines which are homologous,
It is anticipated that it will be possible to use different types of polar substances. Example 155.3 g of the crude naphthalene shown in Table 1 was mixed with 291.9 g of monoethanolamine, and a fraction having a boiling point of 171° C. or less of the amine was distilled off under normal pressure. The distillation apparatus used was a 50-stage helipack type, and the reflux ratio was 20:1. The distilled fraction is a mixture of naphthalene and monoethanolamine, and its total amount is 411.0g.
It is. After cooling this to room temperature, it was centrifuged to obtain 136.4 g of crystalline material. Since monoethanolamine, which is an azeotropic agent, was still attached to this crystal, it was removed by washing with water at room temperature and dried to obtain 134.4 g of white naphthalene crystals. Its physical properties and chemical composition are as shown in the product column of the present invention in Table 3, and the yield is 90.3%.

[Table] Table 2 shows the material balance and analysis results for naphthalene.

[Table] Analytical values After centrifuging the fraction below 171℃ mentioned above,
The quality of the washed and dried product of the present invention was compared with that of the conventional hydrogenation method and fractional crystallization method, as shown in Table 3.

[Table] Effects of the Invention As mentioned above, the method of the present invention is a simple method of adding monoethanolamine, distilling it, separating the crystallized substance after cooling, and washing and drying it with water. The purification efficiency is extremely excellent, and as compared in Table 3, organic sulfur compounds such as thionaphthene, which were conventionally considered the most difficult to remove, have been completely removed, and the product yield has been greatly improved. . Therefore, it can be said that this is the most suitable method for purifying naphthalene to be used as a raw material for organic synthesis.

Claims (1)

[Scope of Claims] 1. Monoethanolamine is added to crude naphthalene and subjected to distillation, a fraction below the boiling point of the amine is distilled off, and this is cooled to separate precipitated naphthalene crystals. A method for purifying crude naphthalene, characterized by: 2. The purification method according to claim 1, wherein the distilled fraction has a boiling point of about 171°C under normal pressure.