JPH08311058A - Purification of epsilon-caprolactone - Google Patents

Abstract

PURPOSE: To provide a method for purifying ε-caprolactone by which a high yield of the ε-caprolactone is obtained from a reactional mixture prepared by oxidizing cyclohexanone by distillation. CONSTITUTION: Low-boiling substances contained in a reactional mixture prepared by oxidizing cyclohexanone are distilled away by the first distillation step and high-boiling fraction impurities are then taken out in a low concentrated state as a bottom product in the second distillation step for distilling away the product ε-caprolactone from the first bottom product and separating the ε-caprolactone from high-boiling substances so as to provide at least >=20wt.% lactone concentration in the second bottom product. The ε- caprolactone contained in the second bottom product is subsequently evaporated with an evaporator and recovered in a method for purifying the ε-caprolactone by distilling the reactional mixture and separating the ε-caprolactone from the impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying ε-caprolactone, which is used in a high boiling point distillation step (second distillation step) in which a product ε-caprolactone is distilled to separate and remove high-boiling impurities. , An improved method for purifying ε-caprolactone which prevents a decrease in the yield of ε-caprolactone due to the polymerization of ε-caprolactone.

[0002]

2. Description of the Related Art Epsilon-caprolactone has applications such as polyester polyol for polyurethane synthesis and a raw material for polymers of other molding materials, and as a production method, a method obtained by oxidizing cyclohexanone is known as a typical one. ing. The oxidation of cyclohexanone includes a co-oxidation method with acetaldehyde and an oxidation method using an organic peracid such as peracetic acid as an oxidizing agent. Further, a distillation method is used to separate the target product from the reaction mixture obtained by the oxidation of cyclohexanone.

[0003]

However, in the conventional distillation method, there are problems such as a large amount of polymerization loss of ε-caprolactone in the distillation step, the yield is lowered, and the device is clogged. Therefore, in order to solve such a problem, the cause of the loss of ε-caprolactone is attributed to the high boiling Hartz component contained in the reaction mixture, and the high boiling Hartz is removed prior to the distillation of unreacted cyclohexanone. A method for purifying caprolactone is disclosed in Japanese Examined Patent Publication No. 60-16436. According to this method, ε from the reaction mixture obtained by the co-oxidation method of cyclohexanone and acetaldehyde
-In the purification of caprolactone, the loss of ε-caprolactone corresponding to about 15% in the cyclohexanone separation column is significantly reduced. However, due to the nature of the co-oxidation method used, 3 to 10 times the weight of cyclohexanone relative to ε-caprolactone remains in the reaction solution.

On the other hand, when ε-caprolactone is synthesized by an oxidation method with an organic peracid, the content of cyclohexanone in the reaction solution is 0.1 weight times or less that of ε-caprolactone. It is disclosed in the publication. Then, in the method, in the distillation step of distilling out ε-caprolactone and separating and removing the high-boiling-point impurities, it is proposed to distill with an apparatus equipped with a single-pass thin film evaporator to prevent polymerization loss of ε-caprolactone. ing. On the other hand, when the present inventors conducted distillation using a 20-plate tray under the pressure and temperature conditions described in the Examples of the publication, the loss rate due to the polymerization of ε-caprolactone was 2 It is about 3%, but the concentration of ε-caprolactone contained in the bottom liquid in this step is as high as 40% or more,
It was found that the ε-caprolactone yield was as low as 92%. Therefore, if the heating conditions of the evaporator are strengthened in order to reduce the concentration of ε-caprolactone contained in the bottom liquid,
The polymerization of ε-caprolactone was significantly promoted, and as a result, the yield of ε-caprolactone was not improved. In the industrial production process of ε-caprolactone, the above-mentioned practically low yield in the distillation step is a serious problem. Therefore, in the production of ε-caprolactone, it is eagerly desired to develop a method capable of achieving a high concentration of bottoms while suppressing the polymerization loss in the deboiling step and improving the yield of ε-caprolactone.

[0005]

[Means for Solving the Problems] The inventors of the present invention set the lactone concentration of the bottom liquid in the deboiling step to a low concentration condition of at least 20% or more, and then from the bottom liquid to an evaporator, preferably rectification. Reconcentrate using an evaporator without parts,
It was found that a high yield of ε-caprolactone can be obtained by recovering ε-caprolactone in the bottom liquid, and the present invention has been completed.

That is, in a method for purifying ε-caprolactone in which a reaction mixture obtained by oxidizing cyclohexanone is distilled to separate from impurities, a low boiling substance contained in the reaction mixture is distilled off in the first distillation step, In the second distillation step in which the product ε-caprolactone is distilled from one bottom liquor to separate it from high-boiling impurities, the high-boiling fraction impurities such that the lactone concentration in the second bottom liquor is at least 20% by weight or more. The present invention provides a method for purifying ε-caprolactone, which comprises recovering ε-caprolactone in a low-concentration state, and then evaporating and collecting ε-caprolactone contained in the second bottom effluent using an evaporator. . Further, the present invention provides the above-mentioned method for purifying ε-caprolactone, which comprises recycling the ε-caprolactone recovered by evaporation from the evaporator to the first or second distillation step or the oxidation reaction step. Further, the present invention provides a method for purifying ε-caprolactone, which comprises using an evaporator without a rectification section. Hereinafter, the present invention will be described in detail.

The present inventor has studied in detail the mechanism of polymerization in the distillation column of the deboiling column in the deboiling column (second distillation step), and as a result, the distillation column of the deboiling column It was found that a high boiling acid such as adipic acid present therein or a compound formed by ring opening of a lactone by adipic acid or the like serves as a polymerization initiator and the polymerization proceeds in the distillation column main body or its reboiler. Of these, JP-A-57-4
When a single-pass type thin film evaporator is used as in Japanese Patent No. 2684, it is presumed that the polymerization loss in the reboiler could be prevented because the residence time in the reboiler was reduced. On the other hand, regarding the increase in polymerization loss due to the increase in the concentration of bottom liquid (second bottom liquid) from the de-high boiling column, the increase in the concentration of the second bottom liquid in the reboiler It is considered that high boiling acids such as adipic acid are distilled out to the rectification section of the boiling column, and the above-mentioned mechanism of polymerization occurs here. Therefore, it is presumed that the yield of ε-caprolactone was not improved even if the second bottom liquid was highly concentrated. On the other hand, when the concentration of the second bottom liquor is carried out in the distillation step, there is a large amount of polymerization loss, whereas in the case of using only an evaporator, particularly an evaporator not equipped with a rectification column, almost no polymerization loss is observed. I found out. Therefore, in the present invention, the degree of condensation in the deboiling column is reduced to reduce the polymerization loss in the rectification section, and the bottoms thereof are re-concentrated using an evaporator, preferably an evaporator not equipped with a rectification column. did. Thus, it was possible to highly concentrate the bottom liquid while significantly reducing the polymerization loss as compared with the conventional method. In carrying out the present invention, not only the reboiler in the second distillation step for distilling ε-caprolactone but also the present evaporator is disclosed in JP-A-57-426.
It is desirable to use the single-pass thin film evaporator described in Japanese Patent Publication No. 84.

The method for purifying ε-caprolactone of the present invention will be described with reference to FIG. The numbers in the figure may represent both the device and the contents. First, the reaction solution obtained by the organic peroxyacid oxidation method or the reaction solution obtained by the co-oxidation method,
Alternatively, a crude liquid obtained by removing the solvent from the reaction liquid is supplied to the low boiling point (first distillation) column 1 through a line 2. When the crude liquid is used, it is the same as the method described in JP-B-60-16436, in which the high boiling point Harz is removed by the evaporation step after the deboiling treatment. Good. In this evaporation process, high-boiling substances such as adipic acid also have ε-
This is because it is distilled out together with caprolactone, but in the present invention, there is no problem because ε-caprolactone is separated from these high-boiling substances in the deboiling step.

The deboiling tower 1 removes the low boiling fraction 3 and
The first bottoms liquid 4 composed of ε-caprolactone and a high-boiling point substance such as high-boiling acid is supplied to the distillation unit of the deboiling column 5. The composition of the second bottoms liquid 7 in the deboiling tower 5 is such that the concentration of ε-caprolactone is 20% or more, preferably 40% or more.
It is preferable to set the heating conditions of the deboiling tower 5. In addition, it is preferable that the distiller of the deboiling column 5 has 10 or more stages in order to separate caprolactone oligomers and polymers, oxycaproic acid, adipic acid, and high-boiling-point impurity components of unknown structure. However, if too many stages are installed, the column bottom temperature may rise due to the pressure loss and the polymerization loss may be accelerated. Therefore, the range of 15 to 30 stages is more preferable.

The second bottom liquid 7 is supplied to the evaporator 8. Vapor condensate 10 containing ε-caprolactone from evaporator 8
Can be reused as the feed liquid for the deboiling column 5 via the line 4 or the line 2 as shown in FIG. Further, this vapor condensate 10 can be recycled to a previous step, for example, an oxidation reaction step. Here, since the evaporator 8 has an extremely small ratio of the amount of distillate to the charged liquid,
The amount of high-boiling acid such as adipic acid contained in the vapor condensate is small, and accumulation of high-boiling acid in the system due to reuse of the vapor condensate 10 is hardly seen. In this way, since the impurities can be efficiently separated by the evaporator 8, for example, the concentration of the high boiling acid in ε-caprolactone circulated and supplied to the deboiling column 5 becomes lower than that in the normal charging line 4. can do. Therefore, the product ε- obtained from the line 6 is combined with the fact that the de-high boiling column 5 is under a low concentration condition.
This will further reduce the inclusion of high boiling impurities in caprolactone and contribute to quality improvement.

The organic peracid used in the method for producing ε-caprolactone to which the present invention is applied is an organic acid having a --CO--OOH group such as peracetic acid, perpropionic acid, and perisobutyric acid, and is usually It is used in the form of a solution of acetone, ethyl acetate, acetic acid, etc. These organic peracids oxidize cyclohexanone into ε-caprolactone, which itself
Converts to organic acids such as acetic acid, propionic acid, and isobutyric acid, which have lower boiling points than caprolactone. When the co-oxidation method is used, cyclohexanone and acetaldehyde are used as raw materials to obtain ε-caprolactone and acetic acid by air oxidation.

The reaction mixture containing ε-caprolactone obtained by the organic peracid oxidation method includes ε-caprolactone, unreacted cyclohexanone, unreacted peracid, solvents for peracids such as organic acids such as ethyl acetate and acetic acid, It contains impurities such as caprolactone oligomer, caprolactone polymer, oxycaproic acid, adipic acid and other by-products of unknown structure. In the case of distilling and purifying a reaction mixture which is multi-component and unstable with heat, it is carried out under reduced pressure in order to reduce polymerization loss. For example, 100 mmHg or less in the deboiling tower 1 and 50 mm in the deboiling tower 5.
It is desirable to carry out at Hg or less. In addition, it is desirable that the evaporator 8 is also operated under reduced pressure as much as possible, as in the deboiling tower 5.
Further, it is preferable that the evaporator 8 does not have a rectification section in order to obtain a high product yield. However, it is also possible to attach a rectification section to improve the quality of the distillate to be reused. Of course, if it is not a problem that the quality is inferior, it can be directly recovered as ε-caprolactone without recycling.

[0013]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited thereto. In addition, all "%" in an Example represent "weight%."

(Operating conditions) Deboiling column 1 in the present embodiment
Table 1 shows the operating conditions of the distillation apparatus of No. 3, the distillation apparatus of the deboiling column 5, and the evaporator 8.

[0015]

[Table 1]

Reference Example 1 In a flow reactor having an internal reaction volume of 1.8 liters, 60 g / hr of cyclohexanone and 170.5 g / hr of a 30% ethyl peracetate solution (51.4 g / hr as pure peracetic acid, (1.1 mol times relative to cyclohexanone) was charged, and the reaction was continued at a reaction temperature of 50 ° C. When the obtained reaction mixture was analyzed, ε-caprolactone (CL-M) 28.78%; unreacted cyclohexanone 0.52%; unreacted peracetic acid 1.31%; byproduct adipic acid 0.59%; Caprolactone polymer (PCL) 0.30
%; Acetic acid 21.16%; solvent ethyl acetate 47.34%.

(Example 1) The reaction mixture obtained in the above reference example was purified using the purification apparatus shown in FIG. First, the reaction mixture was supplied at a rate of 230.5 g / hour through line 2, low-boiling substances were removed in the deboiling tower 1, and then the first bottoms liquid was fed to the deboiling tower 5 through line 4. The product ε-caprolactone is distilled out from the line 6. Further, the second bottoms liquid was led to the evaporator 8 through the line 7, the contained ε-caprolactone was distilled off, and the vapor condensate was recycled through the line 10 to the high boiling point column 5. The operating conditions of the distillation apparatus for the low boiling point column 1 for distillation, the distillation apparatus for the high boiling point column for desorption 5 and the evaporator 8 were in accordance with the conditions shown in Table 1. At this time, the lactone concentration in line 7 is 66.
%, And the lactone concentration in the high boiling point liquid discharged through the line 9 was 10%. The loss rate of ε-caprolactone is shown in Table 2, and the proportion of ε-caprolactone and its polymer in each device are shown in Table 3. The yield of ε-caprolactone was 97.1%. The acid value of the obtained product ε-caprolactone was 0.15 (KOHmg / g).

(Comparative Example 1) The same procedure as in Example 1 was carried out except that the liquid feeding from the line 7 to the evaporator was stopped and the high boiling point liquid was directly discharged from here. However, the heating amount of the reboiler was adjusted so that the concentration of lactone was reduced to 10% in order to reduce the loss of lactone content accompanying the discharge of the high boiling point liquid. At this time, the high boiling column 5
The bottom temperature of the column was 160 ° C. The loss rate of ε-caprolactone is shown in Table 2, and the proportion of ε-caprolactone and its polymer in each device are shown in Table 3. The product ε-caprolactone yield was 92.3%. The acid value of the obtained product ε-caprolactone is 0.30 (KOHmg /
g).

(Comparative Example 2) Comparative Example 1 except that the heating amount of the reboiler is adjusted so that the lactone concentration in the bottom liquid is 20% in order to suppress the polymerization loss in the deboiling tower 5.
I went the same way. At this time, the bottom temperature of the deboiling tower 5 is 15
It was 3 ° C. Table 2 shows the loss rate of ε-caprolactone.
Table 3 shows the proportions of ε-caprolactone and its polymer in each device. The product ε-caprolactone yield was 92.0%. The acid value of the obtained product ε-caprolactone was 0.30 (KOHmg / g).

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

INDUSTRIAL APPLICABILITY According to the method of the present invention, in the method for producing ε-caprolactone in which the reaction mixture obtained by oxidizing cyclohexanone is separated from impurities by distillation to obtain a lactone, polymerization loss due to the purification step is substantially prevented. It has become possible to achieve a high product ε-caprolactone yield.

[Brief description of drawings]

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

[Explanation of symbols]

 1 De-deboiling tower 3 Low boiling fraction 4 First bottom liquid 5 De-high boiling column 6 Product ε-caprolactone 7 Second bottom liquid 8 Evaporator 10 Vapor condensate

Claims (3)

[Claims] 1. A method for purifying ε-caprolactone in which a reaction mixture obtained by oxidizing cyclohexanone is distilled to separate impurities from the reaction mixture. Product from one can
In the second distillation step of distilling caprolactone to separate it from high-boiling-point impurities, the high-boiling-point distillate impurities are taken out in a low-concentration state so that the lactone concentration in the second bottoms liquid is at least 20% by weight or more. A method for purifying ε-caprolactone, which comprises evaporating and collecting ε-caprolactone contained in the second bottom liquid using an evaporator. 2. The method for purifying ε-caprolactone according to claim 1, wherein the ε-caprolactone recovered by evaporating from the evaporator is recycled to the first or second distillation step or the oxidation reaction step. 3. The method for purifying ε-caprolactone according to claim 1, wherein an evaporator without a rectification section is used.