JPS62149633A - Purification of naphthalene - Google Patents

Abstract

PURPOSE:To obtain the titled compound which is a synthetic raw material for medicines, etc., in high purity and yield, by adding a specific compound having a higher boiling point than that of naphthalene to crude naphthalene, distilling the mixture and completely removing organosulfur compounds, e.g. benzothiophene, etc., by simple operation. CONSTITUTION:An alcoholamine, e.g. diethanolamine, triethanolamine, di butanolamine or dipropanolamine, having a higher boiling point than that of naphthalene is added to crude naphthalene and the mixture is subjected to extractive distillation to collect a distillate having the boiling point of the naph thalene and remove organosulfur compounds, e.g. benzothiophene, etc. Thereby the aimed compound is purified. The amount of the diethanolamine to be used on the basis of the naphthalene is preferably 8 times or more. There is no particular limitation on the distillation tower to be applied. The distilling temper ature in distillation is 218 deg.C which is the boiling point of the naphthalene at a maximum under ordinary pressure and it is below that under reduced pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a prior art method for purifying crude naphthalene, commonly known as 96% naphthalene.Naphthalene is an important substance as a raw material for medicines, dyes, and other organic synthesis. In order to use them for these purposes, it is necessary to sufficiently purify them.

On the other hand, even in the case of insect repellents that do not require such high purity, if the product is colored and odored, the commercial value is low, so it is necessary to purify it for that reason as well.

For this reason, many purification methods have been proposed so far. For example, hydrogenation method (JP-A-53-119856, JP-A-54-144349), crystallization method from methanol (JP-B No. 47-47020), impurity removal method by addition of aluminum chloride (JP-A-47-1999) 47021), combined method of fractional crystallization and white clay treatment (Special Publication No. 47-47023),
Acetic anhydride addition method (JP 60-3051), oxalic acid addition method (JP 53-144557), metal or metal oxide catalyst addition method (JP 54-81247, JP 53-147048) No.) etc. are known.

Among the conventional methods mentioned above, in the hydrogenation method that has been implemented as an industrial model, a portion of naphthalene is hydrogenated to remove tetralin and benzothiophene decomposition products, ethyl It is necessary to add a process, and the product yield also decreases. Furthermore, in the same fractional crystallization method, since the removal of benzothiophene, which is a sulfur compound, is insufficient, it is necessary to add a desulfurization step, and naphthalene is lost together with the fractionated mother liquor, resulting in a decrease in product yield.

Other conventional methods also have problems in equipment corrosion resistance, product yield, and sulfur compound removal rate, and are not fully satisfactory.

On the other hand, the naphthalene-pentthiophene system has a low specific volatility, so in order to separate pentthiophene by distillation, it is necessary to distill naphthalene containing 1% benzothiophene from crude naphthalene containing 5% benzothiophene. It is said that a reflux ratio of 20 is required using a distillation column with 182 theoretical plates, or a reflux ratio of 30 with a distillation column of 122 theoretical plates (K o k
s iKhimiya No. 11' No. 32~
35, 1981).

Figure 1 shows that crude naphthalene having the composition shown in Table 1 of the experiments described below was subjected to 4i dense distillation at a reflux ratio of 20:1 using the distillation apparatus used in the examples, and a fraction with a boiling point of 218 to 220°C was extracted. The results of fractionation and analysis are shown.

As shown in FIG. 1, although the naphthalene purity increased slightly to 97%, the concentration of benzothiophene increased to 2.0% or more, and impurities were not significantly removed.

The above demonstrates how difficult it is to separate high-purity naphthalene from crude naphthalene by mere precision distillation, and that this is not a practical separation method.

Problems to be Solved The present invention provides a simple method for purifying crude naphthalene 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.

Means for Solving the Problems The inventors of the present invention, from a different perspective that is not bound by conventional law,
As a result of extensive research on an efficient method for purifying crude naphthalene,
By adding jetanolamine to crude naphthalene and subjecting it to distillation and collecting the fraction at the boiling point of naphthalene, benzothiophene can be easily and almost completely removed, resulting in a high yield of white, highly pure naphthalene. I found out that it can be obtained at a reasonable rate.

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 treating coal tar-based crude naphthalene since impurities, especially sulfur compounds, can be removed.

In the method of the present invention, the appropriate amount of jetanolamine to be used is 8 times or more by weight of naphthalene.

There are no particular limitations on the applicable distillation column. Any of the tray type, packed column type, bubble bell type, etc. may be used, and either the hatch type or continuous type may be used.

The distillation temperature during distillation is approximately 218°C, which is the boiling point of naphthalene under maximum normal pressure, and of course is lower than that under vacuum. This temperature was determined experimentally along with the amount of jetanolamine used.

Function The theory of the method of the present invention has not yet been completely elucidated. However, in view of experimental facts, the method of the present invention can be regarded as a type of extractive distillation.

This is because jetanolamine selectively extracts benzothiophene from naphthalene during the distillation process, leaving it in the bottom of the still. On the other hand, naphthalene, which is difficult to extract, does not azeotrope with jetanolamine and is distilled out at the boiling point temperature of naphthalene.

The reason why it was mentioned above that continuous distillation is possible is that it is possible to carry out distillation while continuously feeding the extractant jetanolamine from the top of the distillation column according to the conventional method of extractive distillation.

It is expected that in place of jetanolamine, it is possible to use alcohol amines having a boiling point higher than the boiling point of naphthalene, such as triethanolamine, dipropanolamine, and jetanolamine, which are homologous.

Specific Examples Next, explanation will be given with reference to FIG. 2, which shows a process diagram suitable for carrying out the method of this invention.

Crude naphthalene (I〈) as a raw material is introduced into the middle stage of the distillation column (2) through the pipe (1), and jetanolamine is circulated through the pipe (9) and the distillation column (10) is fed into the middle stage of the distillation column (2). The jetanolamine (L) supplied to the distillation column (2) is introduced from the upper part of the distillation column (2) and subjected to distillation.

The ratio of raw material crude naphthalene and jetanolamine to be introduced is 8 parts by weight or more.

Purified naphthalene is distilled out from the pipe (3) at the top of the distillation column (2), and a part of it is recovered as purified naphthalene (N) via the pipe (5). The reflux is carried out through the pipe (4
) with a reflux ratio of 2:1 to 30:1, preferably 5
21 to 20:l. A mixture containing jetanolamine, extracted benzothiophene, and a small amount of undistilled suphthalene is extracted from the bottom of the distillation column (2) via a pipe (6) and sent to a solvent recovery column (7). Introduce. From the top of the solvent recovery column (7), benzothiophene concentrate and remaining naphthalene are distilled out through a pipe (8), and from the bottom of the column, jetanolamine, which does not contain benzothiophene, is distilled out through a pipe (9). Collected by pipe (IQ)
It is recycled to the distillation column (2) together with the jetanolamine (L) supplied from the distillation column (2).

Example 464.0 g of jetanolamine was mixed with 58.0 g of crude naphthalene having the composition shown in Table 1, and the mixture was heated to 100 mmHg.
Under vacuum, 49.2 g of a fraction below 144° C., which is the boiling point of naphthalene, was distilled off. The distillation apparatus used was a helipack packed type with 50 theoretical plates, and the reflux ratio was 20:1.

The material balance and analysis results for the distilled naphthalene are summarized in Table 2.

Furthermore, commercially available products purified by the conventional hydrogenation method and fractional crystallization method were purchased and analyzed, and the results are shown in Table 3 in comparison with the method of the present invention. As shown in Table 3, it is clear that the method of the present invention is superior in both product quality and product yield.

Table 1 Table 2 Table 13 Effects of the Invention As mentioned above, the method of the present invention is a simple operation of adding jetanolamine to crude naphthalene and distilling it.
Only high-purity naphthalene is obtained as a fraction, and organic sulfur compounds such as benzothiophene, which were difficult to remove in conventional products, are completely removed, and the product yield is also significantly improved.

[Brief explanation of drawings]

Figure 1 shows the precision distillation of crude naphthalene with the composition shown in Table 1 using a Helipak packed distillation apparatus with 50 theoretical plates to determine the naphthalene concentration and benzothiophene concentration for each 10% of the 218-220'C fraction. FIG. 2 is a graph showing the results of the analysis, and is a diagram of a specific implementation process of the present invention. (2)--1 distillation column, (7)--m-solvent recovery column (
1) (3) (4)' (5) (6) (8) (9) (10)
-m-pipeline, (I()-m-crude naphthalene (L
) - 11 jetanolamine (N) - 11 Harei Naphthalene

Claims (2)

[Claims] (1) A method for purifying naphthalene, which comprises adding an alcohol amine having a boiling point higher than the boiling point of naphthalene to crude naphthalene, subjecting it to extractive distillation, and distilling off a fraction having the boiling point of naphthalene. (2) Alcohol amines with a boiling point higher than that of naphthalene include diethanolamine, triethanolamine,
The method for purifying naphthalene according to claim 1, which comprises adding dibutanolamine or dipropanolamine.