JPS5852235A - Purification of 2,6-dimethylphenol - Google Patents

Abstract

PURPOSE:To obtain high-purity titled compound, in high purification yield, by dispersing molten crude 2,6-dimethylphenol in a small amount of an aqueous medium insufficient for the complete dissolution of the crude raw material, and cooling the dispersion followed by the separation of the produced crystals. CONSTITUTION:Crude 2,6-dimethylphenol is mixed with an aqueous medium. The amount of the medium is insufficient to dissolve the compound completely, preferably 1-5pts.wt. per 1pt.wt. of the crude raw material. The mixture is heated preferably at >=35 deg.C, and the molten crude material is dispersed in the aqueous solvent under stirring. The dispersion is cooled preferably to 5-30 deg.C, and the produced crystals of the objective compound is separated from the aqueous solvent to obtain the titled compound economically, in high purity. The resultant compound is useful as a raw material of polyphenylene oxide, and as synthetic intermediates, etc. in various organic chemical industries.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying 2,6-dimethylphenol.

2.6-dimethylphenol is a substance useful as a raw material for polyphenylene oxide, a synthetic intermediate in various organic chemical industries, and the like. 2.6-dimethylphenol can be obtained by methylation of phenol, but all of them contain impurities, mainly other phenols. Several methods are known for purifying this 2,6-dimethylphenol, but since crude 2,6-dimethylphenol contains phenolic impurities that are difficult to separate, it is necessary to purify it to a high purity. It is difficult to put on clothes. For example, only a small amount of ortho-cresol can be separated by distillation, and metaphresy and vala-cresol cannot be separated and removed. Furthermore, no improvement in purity was observed even with the sublimation method, and method C, in which 2,6-dimethylphenol was steam-distilled in an alkaline aqueous solution;
However, not only is the purification process extremely cumbersome, but oxidation occurs in the aqueous alkali solution, resulting in coloration in many cases.

In addition, among the crystallization methods, crystallization from a melt is difficult to obtain high-quality crystals, and the high viscosity of the mother liquor makes it difficult to cut the mother liquor during solid-liquid separation, resulting in insufficient purification effects. Also, in the method of recrystallizing from a solution, 2.6-
Since dimethylanisole is poorly soluble in water, it not only requires a special recrystallization solvent, but also has the problem of low purification yield.

The inventors of the present invention have conducted intensive research on a method for obtaining highly pure 2,6-dimethylanisole that is suitable as a raw material for polymerization reactions. , 6-dimethylphenol is mixed with an insufficient amount of aqueous solvent to completely dissolve 2,6-dimethylanisole, and heated to form the crude 2.
．． The molten 6-dimethylphenol is stirred and dispersed in the aqueous solvent, and the dispersion is then cooled.2.
We have discovered that 2,6-dimethylanisole can be obtained with high purity and high purification yield by a method of crystallizing 6-dimethylanisole and then separating the formed crystals from an aqueous solvent. completed.

Crude 2,6-dimethylphenol can be obtained, for example, directly from the synthesis step in which phenol or 0-cresol and methanol are reacted in the gas phase in the presence of a catalyst, or by pretreatment such as distillation as necessary. . This crude 6-dimetherphenol contains e, m-, or p-cresol! ! , isomers such as 5-12.4-12.6-1 or 1.4-dimethylanisole, various methyl-substituted phenols such as polymethylphenols having 8 or more methyl groups, and these methyl-substituted phenols. Generated by dehydration condensation of raw material phenols with methanol, such as anisole, o-, m+, p-methylanisole,
1.8-1! , 4-1, 6-23.4-dimethylanisole, polymethylanisole having three or more methyl groups, and the like are contained as impurities. The composition of crude 2,6-dimethylphenol obtained directly from such a synthesis process varies greatly depending on the reaction conditions. For example, when the molar ratio of methanol and phenol is 2 or more, the composition .6-dimethylanisole is 90 or more and contains several -cresol, and a small amount of snow, 4.6-) dimethylanisole, O-methylanisole, p-cresol, m
- Cresol and other substances containing dimethylphenol isomers are obtained. Furthermore, if the molar ratio of methanol and phenol is reduced to 2 or less, or if the reaction is carried out under relatively mild conditions, a product containing 60 or more o-cresol can be obtained.

Crude 2,6-dimeterphenol, which is the raw material of the present invention, is
The reaction product obtained as described above or a product obtained by distilling the reaction product to concentrate 2,6-dimethylanisole, or a 2,6-dimethylanisole fraction obtained by separating from coal tar fraction oil, etc. It is. Coarse 2,6-
Since the concentration of dimeterphenol is high, it can be easily purified to a high purity product, but even impurities of about 50% can be purified using the method C of the present invention; 6-dimethylphenol can be obtained.

Preferably, the raw material has a content of 2,6-dimethylanisole of 0- or more, more preferably 9b- or more.
, 6-dimeterphenol.

However, although it depends on the composition of the crude raw material, those with 9$LO or more contain impurities with similar physical and chemical properties such as boiling point, such as m- and p-cresol, so distillation, etc. Not only is it extremely difficult to use other methods, but it is not necessary because the method of the present invention can sufficiently increase the purity without increasing the purity in advance.

The amount of aqueous solvent used to disperse the crude 2,6-dimeterphenol is insufficient to completely dissolve the 2,6-dimethylanisole; If stirring is performed above the temperature, C2,! , 6-dimeterphenol is sufficient to disperse it in the aqueous solvent.

The amount of the aqueous solvent used is preferably 1 to 10 parts by weight, more preferably 2 to 5 parts by weight, per 1 part by weight of crude 2,6-dimetherphenol.

If a large amount of impurities is used (other than when purifying crude 2,6-dimethylphenol containing 2,6-dimethylanisole), it is undesirable because the purification yield of 2,6-dimethylanisole will decrease, and if the amount used is small, Under such conditions, not only is it impossible to obtain a dispersion of 2,6-dimethylphenol, but conversely, crystallization occurs from a state in which the aqueous solvent is dispersed in 2,6-dimethylphenol. n-manufacturing effect is insufficient.

If an attempt is made to enhance the purification effect in this state, it is necessary to keep the crystallization rate low, and the purification yield will drop considerably.

The mixture of crude 2,6-dimedelphenol and the aqueous solvent is heated and stirred to disperse the crude 2,6-dimethylphenol in a molten state. The temperature at this time is 2.6-dimef
The temperature may be at least the temperature at which luphenol melts, preferably 857-60°C. In addition.

The melting point of 2,6-dimethylphenol is about 46°C, but since it contains impurities and exists with a small amount of water dissolved in an aqueous solvent, its melting start temperature is around 85°C. Although increasing the temperature can shorten the dispersion time, it is not advantageous to increase the temperature too high because heat loss increases.

Crude 2.6-i)) To melt the methylphenol, the crude 2.6-dimethylphenol and the aqueous solvent may be mixed at room temperature and then heated, but either one or The method of heating both in advance so that the temperature reaches or exceeds the melting temperature when mixed is an advantageous method not only when the method of the present invention is continuously woven. Further, the dispersion operation by stirring, the melting operation by heating 62, and the mixing operation may be performed simultaneously as long as the stirring is performed in the presence of 2,6-dimethylphenol in which the aqueous solvent is melted. Either one may be performed first.

When heated to C2 above the melting temperature of crude 2,6-dimeterphenol, a small amount of the aqueous solvent was melted! , two phases are formed: a 6-dimethylphenol phase and an aqueous solvent phase in which a small amount of 2,6-dimethylphenol is melted. When this is stirred, the 2,6-dimethylphenol phase is converted to C in the aqueous solvent phase.
It becomes a two-dispersed state.

Stirring involves adding crude 2,6-dimedelphenol to an aqueous solvent.
It is best to disperse it finely. The dispersion in which crude 2,6-dimedelphenol was dispersed in this way was
．． In order to crystallize 6-dimethylphenol (= cooled. During this cooling, the cooling rate is slowed to prevent melting!, 6-dimethylphenol from being supercooled more than necessary) It is desirable, and it is also advantageous to add seed crystals.

In addition, by increasing the stirring at the temperature at which 2,6-dimethylphenol crystals begin to precipitate, for example around s5°C, impurities are prevented from precipitating at the same time as 2,6-dimethylphenol, giving priority to 2,6-dimethylphenol. can be crystallized. C: Under stirring, 2.61-dimethylphenol is homogenized by heating to C; By cooling the dispersed dispersion at a slow cooling rate, pure 2.6 is produced before impurities precipitate. It is believed that -dimethylphenol crystallizes and precipitates, thereby allowing highly purified 2,6-dimethylphenol to be efficiently recovered. Therefore, the cooling temperature should theoretically be lower than the temperature at which 2.6-dimethylphenol crystals begin to precipitate, and higher than the temperature at which impurity crystals begin to precipitate; The temperature is lower than the temperature at which dimethylphenol crystals precipitate, preferably 5 to 30°C.

As a solid-liquid separation method after cooling the dispersion and crystallizing 2,6-dimethylphenol, conventionally known separation methods such as a pressure filtration method, a vacuum filtration method, a centrifugal filtration method, etc. are applied. It is also possible to form a precipitate of crystals. Depending on the situation, a centrifugal sedimentation machine or a decanter may also be used. In addition, this cooling crystallization method may be either a batch method or a continuous method (crystallization and crystal separation may be performed multiple times in a cascade method).

The obtained crystals are preferably washed with an aqueous solvent, and the amount of washing liquid is 06 to 10
Double weight is appropriate. Although washing may be carried out by filtration or the like, it is more efficient to disperse the material in an aqueous medium and wash it once. Note that it is sufficient to carry out the washing one or several times.

In the process of the invention, the mother liquor obtained by solid-liquid separation usually contains impurities such as C: a small amount of 2,6-dimethylphenol. This mother liquor can be reused as an aqueous solvent by expelling the phenolic compounds by means such as steam stripping, and the phenolic compounds recovered by such steam stripping or solvent extraction can be reused. The chemical compounds can be used as they are, or after crude distillation, they can be converted into crude x, e-? ) to which the method of the present invention can be applied.

According to the method of the present invention, compared to the method of crystallizing without adding a medium or adding a small amount of medium, the purity of the obtained 2,6-dimethylphenol is not only high, but also the purification yield is extremely high. Compared to the recrystallization method in which solvent C is dissolved, the amount of solvent used is significantly smaller, making the purification operation easier and the purification yield higher.Also, In the method of the present invention,
Since an aqueous solvent is used, there is no need to use expensive organic solvents, and the mother liquor used for purification is also extremely easy to treat.C
In addition, when recovering and reusing the raw material components that have migrated to the mother liquor side, it does not require troublesome operations such as steam distillation to remove the solvent, making it extremely economical and of high practical value. It is.

The present invention will be specifically described below based on Examples.

Actual weaving example 1 Crude 2,6-dimeterphenol having the composition shown in Table 1 was used as a raw material, mixed with a predetermined amount of water, heated to about 60 to 60°C, and stirred to melt the raw material. and dispersed in water.

After continuing stirring and maintaining the dispersed state for about 5 to 2 hours, cooling was performed. Cooling is relatively rapid to about s5~40'C, and when the temperature reaches about 85°C, 2.6
- A very small amount of dimethylphenol crystals was added to prevent supercooling. After that, it is left to stand and gradually cooled to about 20℃, and when the crystals of snow and 6-dimethylphenol have sufficiently precipitated, the crystals are separated by vacuum filtration, and the same amount of snow as the amount of raw materials is prepared at 0℃. The mother liquor adhering to the crystals was washed off with water.

The yield, composition, and recovery rate of 2,6-dimethylphenol of the obtained crystals were as shown in Table 1. In addition, the composition is an analysis value by gas chromatography.

Next, Table 2 shows the results obtained for experiment numbers 8 and 91. Also, for experiment numbers 8 and 9, 15 parts by weight of the obtained crystals were mixed with 60 parts by weight of water, and this was heated to 60 to 60°C. The mixture was heated and stirred to melt the crystals.

In addition, the mother liquor was extracted with the same amount of toluene as the amount of raw materials, and the resulting oil content was analyzed.
For example, in the case of experiment number 1, 2.6-dimethylphenol is 6*1@weight-1O-cresol is &9090 parts by weight-
Cresol is L8080 parts by weight - cresol is 2'! 5
In the case of experiment number 2, 1,6-dimethylphenol was 8&87% by weight, 1O-cresol was 159% by weight, p-cresol was 10% by weight, and 2,5-dimethylphenol was 1194% by weight. Ta.

Table 3 Example 2 Table 4 Table 6: Using crude 2,6-dimethylphenol having the composition shown as a raw material, 200 parts by weight of the raw material C2 and 800 parts by weight of water were mixed, and C2 and C2 were mixed in the same manner as in Example 1. and then cooled. The crystal precipitation temperature is 20-30℃, and the
After cooling to ℃, the same liquid was separated using a centrifuge to obtain crystals (first 0 operation).

The composition of this crystal and the recovery rate of 2,6-dimethylphenol were as shown in Table 4. Next, 66 parts by weight of the obtained crystals were mixed with 260 parts by weight of water, dispersed in the same manner as in Example 1, and cooled. The crystal precipitation temperature [is approximately s2℃,
After cooling to b°C, the same liquid was separated using a centrifuge to obtain crystals (No. 4 operation). The composition of the crystals and the recovery rate of 2,6-dimethylphenol were as shown in Table 4.

Part 1 Table

Claims (1)

[Scope of Claims] (1) Crude λ6-dimethylphenol is mixed with an insufficient amount of an aqueous solvent to completely dissolve the 1,6-dimedelphenol and heated. The molten dimedelphenol is stirred and dispersed in an aqueous solvent,
This is a method for purifying 2,6-dimethylphenol, in which the dispersion system is then cooled to crystallize 6-dimethylphenol, and the resulting crystals are then separated from the aqueous solvent. (2) A method for purifying 2,6-dimethylphenol according to claim S, which uses 1 to 5 parts by weight of an aqueous solvent per 1 part by weight of crude 2,6-dimethylphenol. (The method for purifying 6-dimethylphenol according to claim 1 or the electrocution claim, wherein the temperature during dispersion is s5°C or higher, and the temperature during cooling is s to SO°C.