JP3045195B2 - Method for separating ε-caprolactone and aromatic carboxylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for separating ε-caprolactone and aromatic carboxylic acid from a reaction mixture containing ε-caprolactone and aromatic carboxylic acid. ε
-Caprolactone is an industrially important substance as an organic synthetic intermediate or a resin raw material, and aromatic carboxylic acids are useful substances as a stabilizer for vinyl chloride.

[0002]

2. Description of the Related Art As a method for purifying ε-caprolactone,
JP-A-53-34789 discloses a method of removing high-boiling Hartz before distilling a reaction mixture containing ε-caprolactone obtained by oxidizing cyclohexanone . As a method for producing ε-caprolactone, Japanese Patent Publication No. 34-5633 describes a method of reacting cyclohexanone with peracetic acid. Japanese Patent Publication No. 55-36667 describes the use of a peracid in a method for producing a lactone by oxidizing cyclic ketones with molecular oxygen in the liquid phase in the coexistence of an aldehyde,
An example of producing ε-caprolactone and p-toluic acid from cyclohexanone and p-tolualdehyde is disclosed.

[0003]

SUMMARY OF THE INVENTION The present inventors have studied a co-oxidation method of a cyclic ketone and an aromatic aldehyde,
We found a method to obtain lactones and aromatic carboxylic acids with high yield and high selectivity, and filed a patent application. ε-caprolactone is easy to polymerize at high temperature, especially when an acidic substance is present, polymerization is promoted and loss of ε-caprolactone is inevitable,
In addition, deterioration is easily caused. According to the method of JP-A-53-34789, ε
-When a reaction mixture containing caprolactone and an aromatic carboxylic acid is distilled, a part of the aromatic carboxylic acid is distilled off together with ε-caprolactone, so that it is difficult to separate them, and high-purity ε-caprolactone and aromatic Aromatic carboxylic acids could not be obtained.

[0004]

Means for Solving the Problems The inventors of the present invention have intensively studied a method for separating ε-caprolactone and an aromatic carboxylic acid having such a problem, and as a result, have first prepared a reaction mixture containing ε-caprolactone and an aromatic carboxylic acid. After cooling to separate the crystalline aromatic carboxylic acid, the mother liquor containing the residual aromatic carboxylic acid is treated in a thin film evaporator equipped with a distillation column at the subsequent stage, and a part of the distillate from the distillation column is refluxed. By returning as a liquid, it was found that ε-caprolactone could be almost completely separated from the aromatic carboxylic acid without alteration,
The present invention has been reached.

That is, the present invention provides a method for separating a reaction mixture containing ε-caprolactone and an aromatic carboxylic acid,
After crystallizing a part of the aromatic carboxylic acid and separating the crystals,
Ε-caprolactone and aromatic carboxylic acid, characterized in that a mother liquor containing residual aromatic carboxylic acid is treated in a thin film evaporator equipped with a distillation column in the subsequent stage, and a part of the distillate from the distillation column is returned as a reflux liquid. This is an acid separation method.

The reaction mixture containing ε-caprolactone and aromatic carboxylic acid in the present invention can be obtained by a method of co-oxidizing cyclohexanone and an aromatic aldehyde with molecular oxygen or a method of oxidizing cyclohexanone with an aromatic peracid. Specific examples of the aromatic carboxylic acid include benzoic acid, toluic acid, dimethylbenzoic acid, ethylbenzoic acid,
And anisic acid.

In the present invention, first, a part of the aromatic carboxylic acid of the reaction mixture containing ε-caprolactone and the aromatic carboxylic acid is crystallized to separate crystals. The cooling temperature for crystallization is 0-50 ° C. It is desirable that the aromatic carboxylic acid be crystallized as much as possible and separated as crystals, and if necessary, the reaction mixture may be concentrated in advance. As a crystallization apparatus, a usual cooling type crystallizer or a vacuum evaporation type crystallizer is used.

The reaction mixture containing ε-caprolactone and aromatic carboxylic acid used in the present invention can be obtained by co-oxidation of cyclohexanone and aromatic aldehyde or oxidation with aromatic peracid as described above. Contains trace amounts of impurities from aldehydes and catalysts. The mother liquor obtained by separating the crystals of the aromatic carboxylic acid usually contains 0.1 to 0.1% of ε-caprolactone.
It contains 5 weight times cyclohexanone, 0.01-0.8 weight times aromatic carboxylic acid, 0.01-0.3 weight times aromatic aldehyde and other trace impurities.

[0009] The mother liquor obtained by separating the crystals of the aromatic carboxylic acid is then treated in a thin-film evaporator equipped with a distillation column at the subsequent stage. Since the residence time is short, the thin film evaporator is used to avoid the deterioration of ε-caprolactone, and a rising film type or a falling film type can be used, but a stirring type thin film evaporator is particularly preferable. The vapor containing the aromatic carboxylic acid evaporated in the thin film evaporator is rectified in the distillation column. By rectifying part of the distillate from the top of the distillation column as a reflux liquid, rectification is promoted, and ε-
Completely separated from aromatic carboxylic acids without loss of caprolactone.

As the distillation column, a usual plate column or packed column is used. The reflux ratio varies depending on the number of theoretical plates and operating conditions. When the number of theoretical plates is about 5, the reflux ratio is preferably in the range of 0.1 to 10. It is preferred that the thin film evaporator and distillation column be operated at the lowest possible temperature and pressure to avoid the degradation of ε-caprolactone. The boiling point at normal pressure is 155.6 ° C for cyclohexanone, 178 to 250 ° C for the aromatic aldehyde corresponding to the above-mentioned aromatic carboxylic acid, and ε-
Caprolactone has a temperature of 235.3 ° C, and the aforementioned aromatic carboxylic acid has a temperature of 250 ° C or higher. Further, in the thin film evaporator, it is necessary to carry out the reaction at a temperature higher than the melting point of the aromatic carboxylic acid.

Next, the present invention will be described with reference to the drawings. FIG.
FIG. 2 is an example of a flowchart showing the method of the present invention. The reaction mixture containing ε-caprolactone and the aromatic carboxylic acid first enters the crystallizer 2 from the channel 1 to crystallize the crystalline aromatic carboxylic acid. Next, it is sent from the channel 3 to the crystal separator 4 where the crystalline aromatic carboxylic acid is separated therefrom. The filtered mother liquor after the separation of the crystalline aromatic carboxylic acid enters the thin film evaporator 7 from the flow path 6, and mainly the remaining aromatic carboxylic acid in the filtered mother liquor is separated from the flow path 8. The vapor obtained from the thin film evaporator 7 is sent from the flow channel 9 to the distillation column 10. A condenser 11 is provided at the upper part of the distillation column 10, and a part of the distillate is
By performing distillation while refluxing from 12, a mixed liquid of ε-caprolactone containing almost no aromatic carboxylic acid and unreacted cyclohexanone and aromatic aldehyde is separated from the flow channel 13.

[0012]

Next, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited by the following Examples and Comparative Examples.

Example 1 (Production of a reaction mixture containing ε-caprolactone and aromatic carboxylic acid) In a SUS316 high-pressure reactor equipped with a 15-liter internal volume stirrer and a reflux condenser, 66 mg of CoBr ₂ (hexahydrate), cyclohexanone Charge 6kg, supply at 2,480-dimethylbenzaldehyde 480g / H, reaction temperature 35 ℃, pressure 25kg / c
After air oxidation at m ² G, the supply of 2,4-dimethylbenzaldehyde was stopped, and air introduction was continued for another 2.5 hours. Excessive cyclohexanone was removed from the reaction solution obtained by such a semi-continuous method using an evaporator under reduced pressure. The composition of the obtained reaction mixture was 33.0 wt% of ε-caprolactone.
%, 2,4-dimethylbenzoic acid 46.3wt%, cyclohexanone
16.5 wt%, 1.3 wt% of 2,4-dimethylbenzaldehyde, and 2.9 wt% of other components.

(Separation of Aromatic Carboxylic Acid) The above reaction mixture was supplied to a jacketed crystallizer according to the flow shown in FIG. 1, and crystallization was performed by adjusting the flow rate of the refrigerant so that the internal temperature was 5 ° C. . The average residence time was 2 hours. The obtained slurry was filtered with a basket-type centrifuge. The composition of the mother liquor separated from the flow path 6 was as follows: ε-caprolactone 55.6 wt%, 2,4-dimethylbenzoic acid 9.5 wt%, cyclohexanone 27.8 wt%, 2,4-dimethylbenzaldehyde 2.2
wt% and other components were 4.9wt%. The separated mother liquor is continuously supplied at 540 g / h to a thin-film evaporator with a packed tower of 5 theoretical stages, an absolute pressure of 5 mmHg, a discharge temperature of the thin-film evaporator of 169 ° C,
Distillation was performed at a distillation column top temperature of 94 ° C. and a reflux ratio of 0.4. As a result, 465 g / h of a distillate from the flow path 13 was obtained, and its composition was 63.9 wt% of ε-caprolactone and 32.
It was 2 wt%, 2.55 wt% of 2,4-dimethylbenzaldehyde, and 50 ppm of 2,4-dimethylbenzoic acid. 75g from channel 8
At a rate of / h, a composition containing 3.9 wt% of ε-caprolactone, 68.4 wt% of 2,4-dimethylbenzoic acid, and 27.7 wt% of other high boiling components was separated. In this case, there was almost no alteration of ε-caprolactone, and about 99% of the charged amount was distilled off.
Almost all 2,4-dimethylbenzoic acid is recovered from the channel 8.

Comparative Example 1 The reaction mixture obtained in Example 1 was introduced into a thin film evaporator.
Distillation was performed without reflux. The temperature at the top of the distillation column was 96 ° C, and the heating source was adjusted so that the discharge temperature of the thin film evaporator was 169 ° C. As a result, the distillate from the channel 13 was 485 g / h
The composition was 61.5 wt% ε-caprolactone, 2,4-
Dimethylbenzoic acid 4.0wt%, cyclohexanone 30.9wt
% And 2,4-dimethylbenzaldehyde was 2.44 wt%.
From the channel 8, ε-caprolactone was added at a rate of 55 g / h.
A composition containing 3.0 wt%, 2,4-dimethylbenzoic acid 57.6 wt%, and other high-boiling components 39.4 wt% was isolated. In this case, there was almost no deterioration of ε-caprolactone, and about 9
9.4% is distilled, but the separation of 2,4-dimethylbenzoic acid is insufficient.

[0016]

According to the method of the present invention, the aromatic carboxylic acid is almost completely separated from the reaction mixture containing ε-caprolactone and the aromatic carboxylic acid, and the ε-caprolactone is almost completely degenerated and the entire amount is recovered. . The present invention is a very useful method for producing ε-caprolactone from cyclohexanone.

[0017]

[Brief description of the drawings]

 FIG. 1 is an example of a flowchart showing the method of the present invention. 2: Crystallizer 4: Crystal separator 7: Thin film evaporator 10: Distillation tower

Claims (1)

(57) [Claims] 1. A thin film evaporator provided with a distillation column in the latter stage after separating a reaction mixture containing ε-caprolactone and an aromatic carboxylic acid by crystallizing a part of the aromatic carboxylic acid to separate the crystals. Treating the mother liquor containing the residual aromatic carboxylic acid with, and returning a part of the distillate from the distillation column as a reflux liquid, wherein ε-caprolactone and aromatic carboxylic acid are separated.