JPS636533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying and recovering 2,6-dimethylphenol. Specifically, 2,6-dimethylphenol containing phenolic impurities, for example, crude 2,6-dimethylphenol obtained by the reaction of phenols and methanol, containing water below the saturation concentration. The present invention relates to a method for obtaining purified 2,6-dimethylphenol by crystallizing 2,6-dimethylphenol and performing solid-liquid separation.

2,6-dimethylphenol is useful as a raw material for synthetic resins and polyphenylene oxide, and as a synthetic intermediate in various organic chemical industries. Among these, highly pure 2,6-dimethylphenol is required especially when used as a raw material for synthetic resins, and various purification methods have been proposed.

In the method of the present invention, crude 2,6-dimethylphenol containing phenolic impurities is O
-, m-, or P-cresol, 2,3-,
Isomers of 2,6-dimethylphenol such as 2,4-, 2,5- or 3,4-dimethylphenol, polymethylphenols having three or more methyl groups, or the hydroxyl groups of the various methyl nucleus-substituted phenols mentioned above. Ethers produced by dehydration condensation with alcohols such as methanol, such as anisole, O
-, m-, P-anisole, 2・3-, 2・4
-, 2,5-, 2,6-, 3,4-dimethylanisole, or polymethylanisole with three or more methyl groups, and other phenols and nuclei in which one or more methyl groups are substituted. 2,6- containing one or more types of anisole in which the hydroxyl group of a phenol is etherified, regardless of the presence or absence of substitution.
It is dimethylphenol. For example, crude 2,6-dimethylphenol is obtained by subjecting phenols and methanol to a gas phase reaction in the presence of a catalyst. The crude dimethylphenol obtained directly from such a synthesis process is
Although it varies greatly depending on the catalyst used in the synthesis and the reaction conditions, for example, a tubular reactor is filled with a catalyst mainly composed of chromium oxide, and raw materials with a molar ratio of methanol and phenol of 5/1 are reacted at a reaction temperature of 395°C. When reacted, phenol 0.1%, O-cresol 5.6%, 2,6-dimethylphenol 91%,
2,4,6-trimethylphenol 1.8%, O-
Methyl anisole 0.2%, other high boiling point compounds 1.3
%, and when the gas phase reaction is carried out at a reaction temperature of 410°C using the above-mentioned raw material equipment using a catalyst mainly composed of manganese oxide, phenol
0.2%, O-cresol 7.3%, 2,6-dimethylphenol 87%, 2,4,6-trimethylphenol 4.1%, O-methylanisole 0.3%, and other high-boiling compounds 1.1%. The method of the invention uses crude 2,6-dimethylphenol of this type. Crude 2. used in the method of the present invention.
The higher the concentration of pure 2,6-dimethylphenol in 6-dimethylphenol, the easier it is to obtain a high-purity product, but it can be used industrially even from impurities of 50% or less, for example 45%. High purity 2.6-
Dimethylphenol is obtained. Moreover, these crude 2,6-dimethylphenols are used directly from the synthesis process, or if necessary, after being pretreated by rough distillation or the like.

In the method of the present invention, the amount of water contained in crude 2,6-dimethylphenol is sufficient to be below the saturation concentration in the system, and usually
It ranges from 0.1% to 10% by weight relative to dimethylphenol. In addition, if it is difficult to supply a certain amount of water due to the actual water addition operation, or if the composition of the crude 2,6-dimethylphenol itself changes over time, add a certain amount of water. In cases where the effects of the present invention vary, the effects of the present invention may be exhibited by adding water at a saturation concentration or higher to the system, removing the aqueous phase that has separated into two phases, and then crystallizing the system.

Furthermore, 2.6% of phenols and methanol
-It is also possible to use the water produced during the synthesis of dimethylphenol in the crystallization step without completely removing it, but still containing an appropriate amount of water, that is, an amount below the saturation concentration.

In the method of the present invention, the method for crystallizing water-containing crude 2,6-dimethylphenol is usually cooling crystallization, in which a liquid heated to below the melting point of the system is left to stand or gradually cooled while stirring. Precipitate crystals. In this case, if the crude 2,6-dimethylphenol contains a substance that can serve as a solvent for the system, such as an alcohol component such as methanol, a concentration crystallization method can also be used. The conditions for crystallization may be atmospheric pressure, increased pressure, or reduced pressure, and the temperature is preferably 50°C or lower and -20°C or higher.

Various known methods can be used to separate the solid and liquid after crystallizing crude 2,6-dimethylphenol. For example, a pressure filter, a vacuum filter, a centrifugal filter, etc. can be used. Alternatively, depending on the slurry concentration during crystallization, a centrifugal sedimentation machine, a decanter, etc. can also be used. Further, the crystallization method may be either a batch method or a continuous method, and a cascade method may be used in which crystallization and crystal separation are performed a plurality of times.

When using the method of the present invention, that is, when crude 2,6-dimethylphenol containing water below the saturation concentration is purified by crystallization, compared to the case where no water is contained at all, if the yield is the same, the higher temperature side The crystallization and separation operations can be carried out in a vacuum, which not only reduces the use of energy due to unnecessary cooling, but also reduces the
The purity of dimethylphenol is also high. In addition, when purified 2,6-dimethylphenol of the same degree of purity is obtained, purified 2,6-dimethylphenol can be obtained with a higher yield, and it is effective in concentrating and removing impurities, and it is effective for post-treatment and recycling of these impurities. There is also the advantage that the burden of use is reduced. Furthermore, regardless of the presence or absence of crystals, the viscosity of a crude 2,6-dimethylphenol solution is considerably lower when the system contains water than when it does not contain any water, making it difficult to handle the crystallization mother liquor. This makes it easier to drain the liquid during separation operations such as crystal filtration, which not only reduces the loss of purity due to the adhesion of the purified 2,6-dimethylphenol filtrate, but also reduces operation time and allows the use of inexpensive equipment. There will also be benefits.

The effect of the presence of water in crude 2,6-dimethylphenol can be seen in the particle size of the precipitated particles; the presence of water avoids unnecessary supersaturation, reduces the generation of fine crystals, and maintains an appropriate crystal size. Spirit 2 and 6
- Obtaining dimethylphenol brings about effects such as improved product purity and ease of handling.

The present invention will be explained below with reference to Examples.

Example 1 2,6-dimethylphenol was added to a 500ml separable flask equipped with a stirrer, thermometer, and liquid feeder.
88%, phenol 0.2%, O-cresol 7.4%,
2,4,6-Trimethylphenol 400g of crude 2,6-dimethylphenol (4.4%) and 6g of water were added, and while stirring, the temperature was gradually cooled from 50°C to 35°C over about 2 hours, and 2,6-trimethylphenol was added. Dimethylphenol crystals were precipitated. When this was separated using a centrifuge, 72g of crystals were obtained, containing 99.6% or more of 2,6-dimethylphenol and 0.1% or less of O-
Analysis values showed cresol and 0.25% of 2,4,6-tolumethylphenol.

When the same experiment was conducted in a water-free system, the amount of crystals obtained was 43 g, and the concentration of 2,6-dimethylphenol in the crystals was 98.3%.

Example 2 Using the same apparatus as in Example 1, 63% of 2,6-dimethylphenol, 22.1% of O-cresol, 2.
400 g of crude 2,6-dimethylphenol solution containing 14.9% of 4,6-trimethylphenol and 100 ml of water.
was added to separate the two phases, and then the oil phase was cooled to 10°C to precipitate crystals. This was separated using a centrifuge to obtain 65 g of crystals. Gas chromatography analysis of crystals revealed that 2,6-dimethylphenol
96.3%, O-cresol 2.7%, and 2,4,6-trimethylphenol 1.0%.

When the same experiment was performed without using water,
The amount of crystals was 43 g, and the content of 2,6-dimethylphenol was 89%.

Example 3 A tablet-shaped catalyst with a diameter of 4.8 mmφ and a thickness of 4 mm containing 0.5% by weight of silicon oxide in manganese dioxide was packed into a stainless steel reaction tube with an inner diameter of 75 mm to a height of 75 cm, and the molar ratio of methanol to phenol was 5/1. raw materials were introduced at LHSV 0.57hr ^-1 , and the reaction temperature was 410~
The alkylation reaction of phenol was carried out at 450℃.

The reaction product was condensed using a heat exchanger kept warm with 80°C water. The resulting condensate contained 95% 2,6-dimethylphenol, 2.4% O-cresol,
2,4,6-trimethylphenol 1.7%, O-
Methyl anisole 0.3%, other high boiling point compounds 0.6
It contained %.

While heating this condensate to 60℃ and keeping it in a liquid state,
1.4 parts of water was added to 100 parts of the condensate, and the mixture was gradually cooled to 38°C with sufficient stirring to precipitate crystals.
The amount of crystals obtained was 33 parts per 100 parts of the condensate, and the purity of 2,6-dimethylphenol in the crystals was 99.4.
It was %.

Furthermore, the filtrate obtained in the above crystal separation was cooled to 34°C and crystals were precipitated again. The amount of crystals obtained was 32 parts per 100 parts of the initial condensate, and the purity of 2,6-dimethylphenol was 99.1. It was %.

Claims (1)

[Claims] 1 Crude 2.6- containing phenolic impurities
1. A method for purifying 2,6-dimethylphenol, which comprises crystallizing and separating 2,6-dimethylphenol in a state in which dimethylphenol contains water at a saturation concentration or less.