JPH0788323B2 - Purification method of naphthalene - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying crude naphthalene, which is commonly called 95% naphthalene, to high quality and high purity.

[Prior Art] Naphthalene is an important substance as a raw material for medicines, dyes, and other organic synthetic materials.
It needs to be sufficiently purified. On the other hand, even in the case of an insect repellent that does not require such a high degree of purity, it is necessary to purify in that sense as the product value is low if it is colored or odorized.

Therefore, various purification methods have been proposed in the past. For example, a hydrogenation method (JP-A-53-119856, JP-A-54-54)
144349), a crystallization method from methanol (JP-B 47-4).
7020), impurity removal method by adding aluminum chloride (Japanese Patent Publication No. 47-47021), combined use of fractional crystallization and clay treatment (Japanese Patent Publication No. 47023), acetic anhydride addition method (Japanese Patent Publication No. 60-
3051), oxalic acid addition method (JP-A-53-144557), metal or metal oxide catalyst addition method (JP-A-54-812).
47, JP-A-53-147048) and the like are known.

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

The other conventional methods also have problems in any of the corrosion resistance of the apparatus, the product yield, and the removal rate of sulfur compounds, and are not sufficiently satisfactory.

[Problems to be Solved] The present invention is different from the above-mentioned prior art, and can easily remove a sulfur compound in crude naphthalene that hinders the synthesis reaction of naphthalene derivatives and the product quality, and the crude naphthalene with a high product yield. The present invention provides a method for purifying the above.

[Details of the Invention] As a result of earnest research on a method for purifying crude naphthalene, the present inventors have added monoethanolamine, which is a polar solvent, to crude naphthalene, and heating the naphthalene to dissolve the naphthalene. The inventors have found that a highly purified purified naphthalene containing almost no thionaphthene can be obtained in a high yield by cooling a homogeneous solution of an amine and separating a precipitated crystal product, and arrived at the present invention.

That is, the present invention is a method for purifying naphthalene, which comprises adding a hydroxyalkylamine derivative to crude naphthalene, heating and dissolving the naphthalene, and then cooling to separate the precipitated crystalline substance.

Hydroxyalkylamine derivatives such as monoethanolamine added to crude naphthalene have the property of selectively extracting thionaphthene, which is a sulfur compound, over naphthalene, and if cooled and crystallized in this solution, hydroxyalkylamine It is considered that naphthalene, which is difficult to extract into the derivative, preferentially precipitates, and thionaphthene is residually removed in the solution.

If the precipitated crystal is filtered off, highly purified purified naphthalene containing almost no sulfur compound can be obtained, but it is advisable to remove it because the hydroxyalkylamine derivative is attached. As a method for removing it, various methods are conceivable, but it is advantageous to use a solvent that does not dissolve the hydroxyalkylamine derivative, extract naphthalene, and then recrystallize it in the solvent to separate and recover naphthalene. In particular, if a solvent having a boiling point of 100 ° C. or lower is used, a highly purified purified naphthalene can be efficiently obtained by vacuum-drying the recrystallized product after the naphthalene extraction.

As the hydroxyalkylamine derivative used, monoethanolamine, diethanolamine, triethanolamine, propanolamine, butanolamine and the like can be used, but monoethanolamine is suitable.
The larger the amount of monoethanolamine added, the better the result. However, since the recovery of naphthalene decreases, it is 2 to 6 times by weight, preferably 2 to 4 times by weight that of crude naphthalene. If the amount of addition is less than 2 times by weight, the amount of monoethanolamine contained in the naphthalene crystals precipitated during recrystallization increases, and there is a drawback that the operation of separating the crystals becomes difficult.

Recrystallization of naphthalene after addition of monoethanolamine
A usual method, that is, a method of heating dissolution-cooling crystallization can be performed. The temperature at which the crude naphthalene is dissolved is appropriately about 80 ° C. or higher, which is higher than the freezing point of the raw material naphthalene. The temperature at which the dissolved homogeneous solution of crude naphthalene and monoethanolamine is cooled to precipitate crystals is 10 to 20 ° C., which is higher than the freezing point of monoethanolamine.

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, or 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 crystal product, and the temperature for extracting the naphthalene may be 60 to 80 ° C.

When the purified naphthalene is recovered by cooling and crystallization of the solvent from which this naphthalene is extracted, the temperature at which crystals are precipitated is 0 to 10 ° C.
It is preferably around 5 ° C.

Monoethanolamine for extracting and removing impurities in crude naphthalene and addition of a solvent for removing monoethanolamine adhering to the naphthalene crystal can both be crystallized while being continuously supplied according to a conventional cooling crystallization method. it can.

[Effects of the Invention] The present invention is simple in that after adding monoethanolamine to crude naphthalene and heating and dissolving it, cooling is performed to separate the precipitated crystalline substance, and the naphthalene is extracted with a solvent and recrystallized for separation. It is possible to almost completely remove the organic sulfur compound such as thionaphthene in the crude naphthalene, which has been considered to be the most difficult to remove by a simple operation, and the product yield is significantly improved.

Example To 200 g of crude naphthalene having the composition shown in Table 1, 400 g (2 times by weight) of monoethanolamine was added, heated to 80 ° C. to dissolve the crude naphthalene, allowed to cool to a greenhouse, and then cooled to 15 ° C. Crystals were precipitated 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, and naphthalene was extracted by heating to 80 ° C, cooled to 5 ° C, centrifugally filtered and vacuum dried, and 164.4 g of purified naphthalene was added. Got

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

A commercially available product purified by the conventional hydrogenation method and fractional crystallization method was purchased, and the analysis results are shown in Table 2 in comparison with the method of the present invention.

As shown in Table 2, the purified naphthalene of the present invention has not only a low total sulfur content but also a low content of impurities such as tetralin, as compared with the conventional hydrogenated and fractionated crystallization purified naphthalene. Moreover, the naphthalene recovery rate was 85.5%, which was a high yield.

Claims (2)

[Claims] 1. A method for purifying naphthalene, which comprises adding a hydroxyalkylamine derivative to crude naphthalene, heating and dissolving the naphthalene, and then cooling to separate the precipitated crystal product. 2. The method for purifying naphthalene according to claim 1, wherein monoethanolamine, diethanolamine, triethanolamine, propanolamine, butanolamine or the like is used as the hydroxyalkylamine derivative.