JPS63107944A - Purification of naphthalene - Google Patents

Abstract

PURPOSE:To completely remove organic sulfur compounds which are hard to separate, by simple operation and to purify the titled compound useful as a raw material for drugs, etc., in high yield, by adding a hydroxyalkylamine derivative to crude naphthalene, melting under heating, cooling and separating precipitated crystal. CONSTITUTION:Crude naphthalene is blended with a hydroxyalkylamine derivative, preferably monoethanolamine, diethanolamine, triethanolamine, propanolamine, etc. Then the naphthalene is melted under heating preferably about 80 deg.C and cooled (to preferably 10-20 deg.C) to precipitate crystal. The crystal is separated to give purified naphthalene. The amount of the hydroxylamine derivative used in the reaction is 2-6 times, preferably 2-4 times as much as that of the crude naphthalene. A solvent for removing monoethanolamine attached to the separated naphthalene is hexane, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a method for refining crude naphthalene, commonly referred to as 95% naphthalene, to high quality and purity.

[Prior Art] Naphthalene is an important substance as a raw material for medicines, dyes, and other organic synthesis.
Sufficient purification is necessary.

On the other hand, even if the product is for insect repellent, which does not require high purity, if it is colored or smelled, the product value will be low.
From this point of view, it is necessary to refine it.

For this reason, many purification methods have been proposed in the past.
JP-A-54-144349), crystallization method from methanol (JP-A-47-47020), impurity removal method by adding aluminum chloride (JP-A-47-4702)
Publication No. 1), combined method of fractional crystallization and white clay treatment (Special Publication No. 470
No. 23), acetic anhydride addition method (Japanese Patent Publication No. 60-3051)
Publication No. V&), oxalic acid addition method (JP-A-53-14455
7), a metal or metal oxide catalyst addition method (JP-A-54-81247, JP-A-53-147048), and the like are known.

Among the conventional methods mentioned above, in the hydrogenation method, which is carried out on an industrial scale, it is necessary to add a step to remove tetralin, which is produced by hydrogenating a part of naphthalene, and ethylbenzene, which is a decomposition product of impurity thionaphthene. The product yield is about 60-80%. Similarly, in the fractional crystallization method, the removal of the sulfur compound thionaphthene is insufficient, so a desulfurization step must be added, and naphthalene is lost along with the fractionated mother liquor, resulting in a maximum product yield of about 80%. ing.

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

[Problems to be Solved] Unlike the above-mentioned conventional technology, the present invention can easily remove sulfur compounds in crude naphthalene that inhibit the synthesis reaction of naphthalene derivatives and product quality, and can also produce crude naphthalene with a high product yield. The present invention provides a method for purifying.

[As a result of intensive research into a method for purifying crude naphthalene, the person explaining the invention in detail added monoethanolamine, a polar solvent, to crude naphthalene, heated it to dissolve the naphthalene, and then purified the naphthalene and monoethanolamine. It has been discovered that highly purified naphthalene containing almost no thionaphthene can be obtained in high yield by cooling a homogeneous solution and separating the precipitated crystals, thereby achieving the present invention.

That is, this invention is a method for purifying naphthalene, which is characterized by adding a hydroxyalkylamine derivative to crude naphthalene, heating and dissolving the naphthalene, and then cooling and separating the precipitated crystals.

Hydroxyalkylamine derivatives such as monoethanolamine added to crude naphthalene have the property of selectively extracting thionaphthene, a sulfur compound, more than naphthalene, and when cooled and crystallized in this solution, hydroxyalkylamine This is thought to be because naphthalene, which is difficult to extract into derivatives, precipitates preferentially, and thionaphthene remains in the solution and is removed.

If the precipitated crystals are separated by filtration, highly purified naphthalene containing almost no sulfur compounds can be obtained, but since hydroxyalkylamine derivatives are attached, it is advisable to remove them. Various methods can be considered for its removal, but it is advantageous to extract naphthalene using a solvent that does not dissolve the hydroxyalkylamine derivative, and then recrystallize it in that solvent to separate and recover the naphthalene. In particular, if a solvent with a boiling point of 100° C. or lower is used, purified naphthalene of high purity can be efficiently obtained by vacuum drying the recrystallized product after naphthalene extraction.

As the hydroxyalkylamine derivative to be used, monoethanolamine, jetanolamine, triethanolamine, propanolamine, butanolamine, etc. can be used, and monoethanolamine is suitable.

The amount of monoethanolamine added is 2 to 6 times the weight of crude naphthalene, preferably 2 to 4 times the weight, because the amount of monoethanolamine added gives better results, but the recovery rate of naphthalene decreases. If the amount added is less than 2 times by weight, the amount of monoethanolamine included in the naphthalene crystals precipitated during recrystallization will increase, making it difficult to separate the crystals.

Recrystallization of naphthalene after addition of monoethanolamine is
This can be carried out by a conventional method, that is, a heating melting-cooling crystallization method. The appropriate temperature for dissolving the crude naphthalene is about 80° C., which is higher than the freezing point of the raw material crude naphthalene. Dissolved crude naphthalene and monoethanol 7
The temperature at which a homogeneous solution of min is cooled to precipitate crystals is
10-20℃, which is above the freezing point of monoethanolamine
is appropriate.

Solvents used to remove monoethanolamine attached to separated naphthalene crystals include aliphatic hydrocarbons such as hexane and heptane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, and monocyclic aromatics such as benzene and toluene. Hydrocarbons are suitable. The amount of these solvents added may be about 0.2 to 0.5 times the weight of the naphthalene crystals, and the temperature for extracting naphthalene should be 60 to 8
0°C is sufficient.

When recovering purified naphthalene by cooling and crystallizing the solvent used to extract this naphthalene, the temperature at which the crystals are precipitated is 0 to 10°C.
, preferably around 5°C.

The addition of monoethanolamine to extract and remove impurities from crude naphthalene and the addition of a solvent to remove monoethanolamine attached to naphthalene crystals can be crystallized while being continuously supplied according to the conventional method of cooling crystallization. can.

[Effects of the Invention] This invention is a simple process in which monoethanolamine is added to crude naphthalene, heated and dissolved, cooled to separate the precipitated crystals, extracted naphthalene with a solvent, recrystallized and separated. By this simple operation, organic sulfur compounds such as thionaphthene in crude naphthalene, which were conventionally considered to be the most difficult to remove, can be almost completely removed, and the product yield is also greatly improved.

Example 400 g of monoethanolamine (2 times the weight) was added to 200 g of crude naphthalene having the composition shown in Table 1, and the mixture was heated at 80°C.
The mixture was heated to dissolve crude naphthalene, allowed to cool to room temperature, and then cooled to 15° C. to precipitate crystals, and 189.9 g of naphthalene crystals were obtained using a centrifugal filter.

In order to remove monoethanolamine attached to the naphthalene crystals, 56.9 g of heptane was added, heated to 80°C to extract naphthalene, and then cooled to 5°C.
After centrifugal filtration and vacuum drying, purified naphthalene 164.
4g was obtained.

Table 2 shows the physical properties and chemical composition of this purified naphthalene.

In addition, commercially available products purified by the conventional hydrogenation method and fractional crystallization method were purchased, and the results of analysis are also listed in Table 2 in comparison with the method of the present invention.

As shown in Table 2, compared to the purified naphthalene produced by conventional hydrogenation and fractional crystallization methods, the purified naphthalene of the present invention has a lower total sulfur content. The content of impurities was low, and the naphthalene recovery rate was as high as 85.5%.

Claims (1)

[Claims] 1. A method for purifying naphthalene, which comprises adding a hydroxyalkylamine derivative to crude naphthalene, heating and dissolving the naphthalene, and then cooling and separating precipitated crystals. 2. The method for purifying naphthalene according to claim 1, characterized in that monoethanolamine, diethanolamine, triethanolamine, propanolamine, butanolamine, etc. are used as the hydroxyalkylamine derivative.