JPH11140075A - Purification of epsilon-caprolactone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying ε-caprolactone reduced in acid value and moisture content. SOLUTION: A low-boiling fraction contained in a reactional solution is distilled off in the first distillation column to provide the first bottom liquid, which is then fed to the second distillation column having a concentrating section of three or more stages to distill off a low-boiling fraction from the column top of the second distillation column. A high-boiling substance is then taken out of the column bottom of the second distillation column to take out ε- caprolactone from any stage within the range of 30-90% of the number of stages from the feed stage of the second distillation column to the topmost stage from the side of the column bottom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying ε-caprolactone, and more particularly, to a method for purifying ε-caprolactone with reduced acid value and water content.

[0002]

2. Description of the Related Art ε-Caprolactone is a useful compound which is used as a raw material of a polyester polyol for the synthesis of polyurethane or a polymer material of other molding materials. It is.
As the production method, a method obtained by oxidizing cyclohexanone is known as a typical method. For the oxidation of cyclohexanone, there are a co-oxidation method with acetaldehyde and an oxidation method using an organic peracid such as peracetic acid as an oxidizing agent. There is a law. Further, as a method for separating a target substance from a reaction solution obtained by oxidizing cyclohexanone, JP-A-60-16 discloses
436, JP-A-3-33718, JP-A-4-9378 and the like disclose a distillation method.

[0003]

On the other hand, when a polymerization reaction is carried out using ε-caprolactone obtained by the above method as a raw material, impurities contained in the ε-caprolactone product greatly affect the reaction rate during polymerization, Particularly, the polymerization reaction rate often differs due to the difference in the acid value and the water content of the ε-caprolactone product. In addition, the product itself is liable to deteriorate due to acidic substances and moisture contained in the ε-caprolactone product.

[0004] In order to reduce the acid value and the water content, conventionally, a low-boiling fraction such as a low-boiling acid or water contained in a reaction solution is distilled off in a first distillation column to form a first vessel. A effluent is obtained, the first bottom effluent is supplied to the second distillation column, then ε-caprolactone is distilled in the second distillation column, and a purification system for separating from high boiling substances such as high boiling acid is constructed. In the purification system, the amount of distillate has been increased while the reflux ratio of the first distillation column has been increased, or the amount of withdrawal of the second bottom has been increased.

[0005] However, the purification yield decreases due to an increase in the distillate of the first distillation column and an increase in the amount of withdrawal of the second bottoms, so that the purification yield and the quality of ε-caprolactone product are improved. It is extremely difficult to achieve both. From this situation, in the industrial production of ε-caprolactone,
Development of a method for purifying ε-caprolactone that can improve the quality without lowering the purification yield of ε-caprolactone and that does not require special equipment and the like has been eagerly desired.

[0006]

The inventor of the present invention has determined that low boiling acid and water present in the second distillation column are distilled together with ε-caprolactone to cause deterioration of the quality of ε-caprolactone products, and The inventors have found that removing ε-caprolactone from a specific position in the second distillation column does not deteriorate the purification yield and can reduce the acid value and the amount of water, thus completing the present invention.

That is, the present invention provides a method for purifying ε-caprolactone, in which a reaction solution obtained by oxidizing cyclohexanone is separated from impurities by distillation, wherein a low-boiling fraction contained in the reaction solution is distilled off in a first distillation column. Then, the first bottoms are supplied to a second distillation column having three or more stages of concentrating sections, and low-boiling fractions are distilled off from the top of the second distillation column to obtain high-boiling products. Is extracted from the bottom of the second distillation column, and ε-caprolactone is taken out from any of the stages in the range of 30 to 90% from the bottom of the number of stages from the supply stage to the top stage of the second distillation column. And a method for purifying ε-caprolactone. It is another object of the present invention to provide a method for purifying ε-caprolactone, comprising removing ε-caprolactone in liquid form. Further, the reaction solution obtained by oxidizing cyclohexanone is a reaction solution obtained by oxidizing cyclohexanone with an organic peracid or a reaction solution obtained by co-oxidation of cyclohexanone and an aldehyde. It is intended to provide a method for purifying the ε-caprolactone. Hereinafter, the present invention will be described in detail.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a method for purifying ε-caprolactone, in which a reaction solution obtained by oxidizing cyclohexanone is separated from impurities by distillation.

The oxidation of cyclohexanone includes an oxidation method using an organic peracid as an oxidizing agent and a co-oxidation method with an aldehyde. A reaction solution obtained by any of the oxidation methods can be preferably used in the present invention.

Examples of the organic peracid which can be used in the oxidation method include peracetic acid, perpropionic acid, formic acid and perisobutyric acid, and among these, peracetic acid and perpropionic acid are preferred. Further, a solvent for dilution may be used for the oxidation, and preferred examples of the solvent include esters such as ethyl acetate and methyl acetate. In the oxidation reaction of cyclohexanone, the organic peracid oxidizes cyclohexanone (bp 155 ° C.) to form ε-caprolactone (bp 98 to 99 ° C./2 mm
Hg), which itself is reduced, and acetic acid (bp 118.2 ° C.), propionic acid (bp 141.35 ° C.), formic acid (bp 100.5 ° C.) corresponding to the organic peracid used,
Organic acids such as isobutyric acid (bp 154.3 ° C.). Therefore, the reaction solution obtained by oxidizing cyclohexanone contains ε
-Includes caprolactone, organic acids such as acetic acid generated by reduction, and diluting solvents, and further includes by-products adipic acid (bp 265 ° C / 100 mmHg), oxycaproic acid, oligomers and polymers of caprolactone, and the like. . Here, an organic acid such as acetic acid generated by reduction has a lower boiling point than ε-caprolactone, and adipic acid, oxycaproic acid, oligomers and polymers of caprolactone have a higher boiling point than ε-caprolactone.

Aldehydes that can be used in the co-oxidation method include aliphatic aldehydes such as acetaldehyde and propionaldehyde and aromatic aldehydes such as benzaldehyde, methylbenzaldehyde and dimethylbenzaldehyde. In the co-oxidation, air or oxygen gas or the like is supplied to a solvent containing cyclohexanone and an aldehyde to oxidize the solvent, and a catalyst such as cobalt naphthenate may be added to the reaction solution. As a reaction solution of a typical aldehyde co-oxidation process supplied to the first distillation column, it is obtained by co-oxidation of cyclohexanone and acetaldehyde,
A reaction solution obtained by separating a catalyst from a reaction solution containing acetic acid, ε-caprolactone, acetaldehyde, cyclohexanone and a catalyst can be exemplified. Further, a reaction solution obtained by co-oxidation of cyclohexanone and dimethylbenzaldehyde and separating a catalyst and dimethylbenzoic acid from a reaction solution containing dimethylbenzoic acid, ε-caprolactone, dimethylbenzaldehyde, cyclohexanone and a catalyst can be exemplified.

Hereinafter, the method for purifying ε-caprolactone of the present invention will be described with reference to FIG. In FIG. 1, equipment attached to the distillation column is omitted.

The purification of ε-caprolactone is carried out by subjecting the reaction solution to low-boiling distillation and high-boiling distillation. First, a reaction solution obtained by oxidizing cyclohexanone is supplied to the first distillation column 1 from the line 2. In the first distillation column 1, low-boiling distillation is performed.
When the reaction solution is an oxidation method using an organic peracid as an oxidizing agent and peracetic acid is used as the organic peracid, acetic acid generated from peracetic acid (hereinafter, the organic acid is referred to as “acetic acid” for convenience) ), And distilling off low-boiling fraction 3 such as a diluting solvent such as ethyl acetate, and distilling off unreacted raw material cyclohexanone.

The first distillation column of the present invention may be either a tray column or a packed column. The distillation conditions of the first distillation column are as follows:
Although it can be appropriately selected depending on the supply rate of the reaction solution, the type of the distillation column, and the like, generally, the tower top temperature is 20 to 60 ° C, particularly 30 to 40 ° C, and the bottom temperature is 100 to 200 ° C.
The temperature is preferably 20 to 180 ° C., the top pressure is 200 mmHg or less, and the reflux ratio is 0.1 to 10, particularly preferably 0.5 to 5. Under these distillation conditions, the solvent and acetic acid can be efficiently distilled off as the low-boiling fraction 3 and the first bottoms 4 containing ε-caprolactone can be recovered from the bottom of the column. In addition, a part of ε-caprolactone is also distilled off as a low-boiling fraction 3. Distillation rate of ε-caprolactone is 0.5 to
3.0%.

Next, the first bottoms 4 (crude ε-caprolactone) containing ε-caprolactone is withdrawn from the bottom of the first distillation column 1 and supplied to the second distillation column 5. The second distillation column may be either a tray column or a packed column, but is characterized by having three or more plates, more preferably 3 to 45 plates, and particularly 10 to 35 plates. Specifically, the total number of stages is preferably 5 to 50, more preferably 15 to 4
There are 0 stages. This is because, within this range, distillation of the low-boiling fraction and separation of the high-boiling fraction can be performed efficiently. At this time, as long as the enrichment section has the number of stages in the above range, the supply to the second distillation column may be performed to the bottom of the second distillation column or to the intermediate portion of the second distillation column. In the present invention, the middle part of the second distillation column means any stage between them except for the bottom and top of the second distillation column.

In the second distillation column 5, re-elimination low-boiling distillation and de-high boiling distillation are performed. The distillation conditions of the second distillation column can be appropriately selected depending on the supply speed of the first bottoms 4, the type of the distillation column, and the like. In order to reduce the loss due to the polymerization of ε-caprolactone, the top temperature is set at 100 ° C. ~ 140 ° C, preferably 1
The temperature is 10 to 130 ° C, the bottom temperature is 120 to 200 ° C, preferably 130 to 160 ° C, the top pressure is 50 mmHg or less, and the reflux ratio is 0.1 to 10, preferably 0.3 to 5. Thereby, low-boiling fractions 6 such as low-boiling acid and water generated in the column are efficiently distilled off from the top of the column, and high-boiling substances such as caprolactone oligomers and adipic acid are removed from the second bottoms 7.
Because it can be separated from ε-caprolactone.

The present invention is characterized in that the purified ε-caprolactone (ε-caprolactone product) is taken out from any of the stages above the feed stage of the second distillation column 5 and below the uppermost stage. More preferably, 30 to 90%, particularly 50 to 80%, of the number of stages from the feed stage to the top stage from the column bottom side
From one of the stages in the range.
Within this range, high-boiling components and low-boiling fractions are excellently separated, and ε-
This is because it is particularly excellent in reducing the acid value and the water content of the caprolactone product. Here, the method of calculating the position of the extraction stage in the intermediate portion of the second distillation column is, for example, in the case where the supply stage is the bottom and the extraction stage is the fifth stage in the second distillation column having 20 stages,
(5/20) × 100 = 25%, (10/20) × 100 = when the feed stage is the bottom and the take-out stage is the tenth stage
It becomes 50%. Furthermore, in the case of supplying to the second stage of the second distillation column and taking out the sixth stage, ((6-2) /
(20-2)) × 100 = 22%.

In the removal of the ε-caprolactone product from the intermediate portion of the second distillation column, it is preferable to remove the ε-caprolactone product in a liquid state. When taken out in a gaseous state, low-boiling fractions, which are largely distributed on the gas phase side in the second distillation column, are also taken out together with the product, so that the concentration of the low-boiling fraction in the product increases. In order to take out the ε-caprolactone product in a liquid state, the liquid phase at the take-out stage may be taken out.

According to the purification method of the present invention, the ε-caprolactone product usually has an acid value of 0.07 to 0.10 mg KOH
/ G, and the water content is 70 to 120 ppm. Therefore,
When a polymerization reaction is carried out using the ε-caprolactone product of the present invention, the reaction rate can be improved, and deterioration of the ε-caprolactone product can be prevented.

[0020]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. “% And ppm” indicate “% by weight and ppm by weight” except where otherwise indicated.

(Measurement items) (1) Acid value: 1/1 per g of ε-caprolactone product
It was calculated from the titer required for neutralization with a 0N KOH solution. (2) Moisture: Analyzed with a Karl Fischer moisture analyzer.

Reference Example 1 In a flow-through reactor having an internal volume of 2 liters, cyclohexanone was added at 60 g / Hr and a 30% solution of peracetic acid in ethyl acetate was added at 170.5 g / Hr (pure peracetic acid was 51.4 g / Hr). (1.1 mol times with respect to Hr and cyclohexanone) and continuously reacted at a reaction temperature of 50 ° C. The composition of the obtained reaction solution was ε-caprolactone 2
8.78%, unreacted cyclohexanone 0.52%, unreacted peracetic acid 1.31%, by-product adipic acid 0.59%, caprolactone polymer 0.30%, acetic acid 21.16%, solvent ethyl acetate 47. 34%. Then, the obtained reaction solution was supplied to the first distillation column of a 15-plate dish distillation column, where the top temperature was 35 ° C, the bottom temperature was 160 ° C, and the top pressure was 60 Torr.
r, low-boiling distillation at a reflux ratio of 1.0, solvent removal and acetic acid removal,
A first bottoms containing ε-caprolactone was obtained.

REFERENCE EXAMPLE 2 450 g / Hr of cyclohexanone, 1160 g of ethyl acetate solvent and 0.08 g of cobalt naphthenate containing 6% Co as a catalyst were charged into a batch type reactor having an internal volume of 2 liters. 360 g of acetaldehyde was added dropwise thereto over 5 hours, and the reaction temperature was maintained at 40 ° C. 1 after the end of dropping from the start of acetaldehyde charge
2.2 liter / Hr of oxygen gas was supplied until the time. The composition of the obtained reaction solution was ε-caprolactone 10.4
%, Unreacted cyclohexanone 11.7%, acetic acid 13.8
%, Unreacted acetaldehyde 8.4%, by-product adipic acid 0.3%, caprolactone polymer 0.50%, and solvent ethyl acetate 55.0%. Next, the obtained reaction solution was supplied to the first distillation column of a 15-plate dish distillation column, and the top temperature was 20 ° C., the bottom temperature was 180 ° C., the top pressure was 170 Torr,
Low-boiling distillation at a reflux ratio of 1.0, solvent removal and acetic acid removal, ε-
A first bottoms containing caprolactone was obtained.

(Example 1) The first bottom liquid obtained in Reference Example 1 was prepared using a glass vacuum jacket having a diameter of 40 mm.
319 g / Hr was supplied to the bottom of the Oldershaw distillation column, and distillation was performed at a top temperature of 119 ° C., a bottom temperature of 144 ° C., a top pressure of 15 Torr, and a constant reflux ratio (R / D = 100). , A second bottom liquid is withdrawn at 80.35 g / Hr, a low boiling fraction is distilled off at 3.6 g / Hr from the top of the column, and ε
-The caprolactone product was taken out in liquid form (235.05 g / H, product yield in the second distillation column: 73.7%) from the 10th stage from the bottom, not including the bottom of the second distillation column. ε
As a result of analyzing the quality of the caprolactone product, the acid value was 0.078 mgKOH / g, and the water content was 70 ppm.

(Example 2) The first bottom product was fed to the bottom of the second distillation column at 325.4 g / Hr, and 80.76 g from the bottom of the column.
/ Hr, the low-boiling fraction was distilled off from the top of the column at 3.4 g / Hr, and ε-caprolactone was counted from the bottom of the second distillation column, excluding the bottom, at the 15th stage from the bottom. To liquid (2
41.24 g / H, product yield in the second distillation column
(1%). As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.070 KOHmg / g, and the water content was 80 pp.
m.

Example 3 First bottom product was fed to the bottom of the second distillation column at 322.7 g / Hr, and 78.94 g from the bottom of the second distillation column.
/ Hr, the low-boiling fraction was distilled off from the top of the column at 3.5 g / Hr, and ε-caprolactone was counted from the bottom of the second distillation column, excluding the bottom, at the 15th stage from the bottom. To gaseous state (240.26 g / H, product yield in second distillation column 7
(4.5%). As a result of analyzing the quality of ε-caprolactone product,
The acid value is 0.100 KOHmg / g and the water content is 120
ppm.

(Comparative Example 1) The first bottom product was fed to the bottom of the second distillation column at 323.5 g / Hr, and 85.3 g / Hr from the bottom of the second distillation column.
Example 1 was repeated except that the second bottom liquid was withdrawn with Hr, and ε-caprolactone was distilled off from the top of the column (238.2 g / H, product yield in the second distillation column: 73.6%).
The same operation was performed. As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.131 KOHmg / g,
The water content was 180 ppm.

(Comparative Example 2) First bottom product was supplied to the bottom of the second distillation column at 324.1 g / Hr, and 77.21 g from the bottom of the column.
/ Hr, the low-boiling fraction was distilled off at 3.3 g / Hr from the top of the column, and ε-caprolactone was counted from the bottom of the second distillation column, excluding the bottom, at the fifth bottom stage. To liquid (24
3.59 g / H, product yield in the second distillation column 75.2
%), Except that it was removed in the same manner as in Example 1.
As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.175 KOHmg / g, and the water content was 60 ppm.

Example 4 The first bottom product obtained in Reference Example 2 was fed to the bottom of the second distillation column at a rate of 323.8 g / Hr, and the second bottom product from the bottom was 85.2 g / Hr. And the low-boiling fraction was distilled off at 3.3 g / Hr from the top of the column, and the ε-caprolactone product was counted from the bottom of the second distillation column, counting from the bottom not including the bottom.
The same operation as in Example 1 was performed, except that gas was taken out from the column (235.3 g / H, product yield in the second distillation column: 72.7%). As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.082 mgKOH / g, and the water content was 79 ppm.

(Comparative Example 3) The first bottom product obtained in Reference Example 2 was supplied to the bottom of the second distillation column at 325.3 g / Hr, and the second bottom product was supplied from the bottom at 86.1 g / Hr. And ε-caprolactone was distilled off from the top of the column and taken out (23).
9. . 2 g / H, product yield in the second distillation column 73.5
%), Except that the operation was the same as in Example 1. As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.144K.
OH mg / g and water was 195 ppm.

(Results) The acid value and the water content were examined by making the supply amount of the first bottom liquid, the supply stage, and the extraction amount of the second bottom liquid almost constant, and changing the extraction stage of the ε-caprolactone product. As a result, both the acid value and the water content could be reduced as compared with Comparative Examples 1 and 3 in which the ε-caprolactone product was taken out from the top of the second distillation column.

[0032]

According to the present invention, ε-caprolactone can be efficiently purified using conventional equipment. The ε-caprolactone product obtained by the purification method of the present invention has less acid value and water content than the product obtained by the conventional method without deteriorating the yield.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for purifying ε-caprolactone.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First distillation column 2 Line 3 Low boiling point fraction 4 First bottoms 5 Second distillation column 6 Low boiling point fraction 7 Second bottoms 8 Removal part of ε-caprolactone product

Claims (5)

[Claims] In a method for purifying ε-caprolactone, wherein a reaction solution obtained by oxidizing cyclohexanone is separated from impurities by distillation, a low-boiling fraction contained in the reaction solution is distilled off in a first distillation column. A bottom product is obtained, and then the first bottom product is supplied to a second distillation column having three or more concentrating units, and a low-boiling fraction is distilled off from the top of the second distillation column to remove a high-boiling product from the second distillation column. Ε-caprolactone is withdrawn from the bottom of the distillation column, and ε-caprolactone is taken out from any stage within a range of 30 to 90% from the bottom of the number of stages from the supply stage to the top stage of the second distillation column.
A method for purifying caprolactone. 2. The removal of ε-caprolactone from the second distillation column is carried out from any stage within a range from 50 to 80% from the bottom of the number of stages from the supply stage to the top stage of the second distillation column. The method for purifying ε-caprolactone according to claim 1, wherein 3. The method for purifying ε-caprolactone according to claim 1, wherein ε-caprolactone is taken out in a liquid state. 4. The ε-caprolactone according to claim 1, wherein the reaction solution obtained by oxidizing cyclohexanone is a reaction solution obtained by oxidizing cyclohexanone with an organic peracid. Purification method. 5. The ε-caprolactone according to claim 1, wherein the reaction solution obtained by oxidizing cyclohexanone is a reaction solution obtained by co-oxidation of cyclohexanone and an aldehyde. Purification method.