JPH08311059A - Purification of epsilon-caprolactone - Google Patents

Abstract

PURPOSE: To obtain ε-caprolactone in high yield by successively concentrating a bottom product with reboilers in >=2 stages in a step for removing high-boiling substances in a method for purifying the ε-caprolactone by distilling a reactional mixture prepared by oxidizing cyclohexanone and separating the ε-caprolactone from impurities. CONSTITUTION: (A) Low-boiling substances in a reactional mixture prepared by oxidizing cyclohexanone are distilled away in the first distillation step and (B) the second distillation step for distilling away the product ε-caprolactone from the first bottom product and separating the ε-caprolactone from high- boiling impurities is carried out by installing reboilers in >=2 stages (preferably 2 stages) to successively concentrate the bottom product in distilling the reactional mixture, separating the ε-caprolactone from the impurities, purifying the ε-caprolactone and providing the ε-caprolactone. Furthermore, the lactone concentration in the bottom product of the first reboiler in the second distillation step is preferably at least >=20wt.%, more preferably >=40wt.%.

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 distillation step (second distillation step) in which a product ε-caprolactone is distilled out 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]

The inventors of the present invention have found that a high ε-caprolactone yield can be obtained by sequentially concentrating bottom liquor using two or more stages of reboiler in the deboiling step. Heading, completed the present invention.

That is, according to the present invention, the reaction mixture obtained by oxidizing cyclohexanone is distilled to separate ε-
In the method for purifying caprolactone, the low-boiling substances contained in the reaction mixture are distilled off by the first distillation step (hereinafter referred to as “de-low boiling distillation step”), and then the first bottom liquid (de-low boiling distillation In the second distillation step of distilling the product ε-caprolactone from the liquid) to separate it from high-boiling impurities (hereinafter referred to as “dehigh-boiling distillation step”), two stages of reboiler are used in the deboiling distillation step, The present invention provides a method for purifying ε-caprolactone, which is characterized in that it is installed further and the bottoms are concentrated successively. Further, it is characterized in that the lactone concentration in the bottom liquor of the first reboiler in the high boiling distillation step is at a low concentration so that the lactone concentration is at least 20% by weight or more, and further concentration is carried out after the second reboiler. The present invention provides a method for purifying the ε-caprolactone. 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 distillation step, and as a result, has found that the amount of adipic acid and the like present in the distillation column of the deboiling column is high. It was found that a compound formed by ring opening of a lactone with hydrofluoric acid, adipic acid, or the like serves as a polymerization initiator, and the polymerization of ε-caprolactone proceeds in the main body of the distillation column or the reboiler. In the case of using the single-pass type thin film evaporator as in the above-mentioned JP-A-57-42684, the residence time in the reboiler was reduced, so that the polymerization loss of ε-caprolactone in the reboiler could be prevented. Guessed. Further, regarding the polymerization in the distillation column body of the deboiling column,
It is considered that, along with the concentration of the deboiling substance in the reboiler, adipic acid and the like that are deboiling substances along with ε-caprolactone are distilled out to the distillation column main body, and the above-described polymerization mechanism is caused. Therefore, it is presumed that even if the high boiling substance was highly concentrated by the reboiler, the yield of ε-caprolactone was not improved. Incidentally, the reboiler of the distillation column is conventionally used in a single stage because the purpose is to control equipment costs and operating costs by reducing the number of equipment used. Exceptionally, two or more stages of reboilers may be installed in parallel, but since the evaporative gas outlet is common,
It is considered to be functionally equivalent to the one concentrated using only one reboiler.

In the present invention, the reboiler is installed in two stages or more in the deboiling tower, and the bottoms are sequentially concentrated to reduce the high boiling acid distilled from the reboiler to the distillation tower.
It prevents polymerization loss in the tower. The term “two or more stages” in the present invention means that a plurality of reboilers having a liquid charging port, an evaporative gas outlet, and a bottom outlet are arranged in series. If the amount of product distilled from the reboiler installed in the distillation column and the amount of reflux liquid are large,
The high-boiling acid to be separated is also distilled along with the distillation of ε-caprolactone. However, when two or more reboilers are installed, first, the concentration of ε-caprolactone in the bottom liquid of the first-stage reboiler (hereinafter referred to as “first reboiler”) is maintained at a high concentration. As a result, the distillation of high boiling acid can be suppressed. Next, the second reboiler (hereinafter referred to as the "second reboiler") is used to re-concentrate the bottom product of the first reboiler, and the ε-caprolactone is distilled from the bottom product charged in the reboiler. Because the amount is small,
The amount of entrained high-boiling acid is small. Therefore, the amount of high-boiling acid distilled from the reboiler to the distillation column can be greatly reduced, as compared with the case of concentrating the high-boiling acid with a single-stage reboiler. As a result, it becomes possible to significantly prevent the polymerization loss in the distillation column. In carrying out the present invention, it is desirable to use the single-pass thin film evaporator described in JP-A-57-42684 for each reboiler in the deboiling step for distilling ε-caprolactone.

The method for purifying ε-caprolactone of the present invention will be described with reference to FIG. Note that FIG. 1 shows a case where the reboiler has two stages. Also, the numbers in the figure may represent both the device and the contents. First, a reaction liquid obtained by an organic peroxyacid oxidation method or a reaction liquid obtained by a co-oxidation method, or a crude liquid obtained by desolvating the reaction liquid is supplied to a deboiling (first distillation) column 1 through a line 2. To do. 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 step, high-boiling substances such as adipic acid are also distilled out together with ε-caprolactone, but in the present invention, ε-caprolactone and these high-boiling substances are separated in the deboiling step, so there is no problem.

The low boiling point fraction 3 is removed by the deboiling tower 1,
A low boiling column bottoms liquid 4 containing a high boiling point substance such as a high concentration of high boiling acid and ε-caprolactone is supplied to a deboiling column 5. Here, the bottoms liquid 4 supplied to the deboiling tower 5 is sequentially separated into ε-caprolactone and a high boiling material by the first reboiler 7 and the second reboiler 9 of the deboiling tower 5, and the high boiling material is removed. Ε-caprolactone containing a low concentration of is supplied to the distiller of the deboiling column 5 via the line 10. In such a case, the concentration of ε-caprolactone in the bottom liquid 8 of the first reboiler 7 is 20%.
It is preferable that the heating conditions for the first reboiler 7 are set to 40% or more. This is because if the concentration of ε-caprolactone is 20% or more, the amount of high-boiling substances distilled from the first reboiler together with ε-caprolactone can be reduced. As a result,
High boiling substances such as adipic acid, which causes polymerization loss in the deboiling tower 5, can be made to have a low concentration, and polymerization loss of ε-caprolactone in the deboiling tower 5 can be effectively prevented. Further, the high boiling acid of the low boiling column bottom liquid 4 thus supplied to the deboiling column 5 is efficiently removed by the reboiler, and the high boiling impurities are mixed in the product ε-caprolactone obtained from the line 12. Can be further reduced, which also contributes to quality improvement.

The distiller of the deboiling tower 5 includes caprolactone oligomers and polymers, oxycaproic acid, adipic acid,
And in order to separate high-boiling point impurities of unknown structure,
It is preferably 10 stages or more. 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 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, a solvent of peracid, for example, organic acid such as ethyl acetate or 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.

[0014]

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%."

Reference Example 1 Cyclohexanone 60 g / hr and 30% ethyl peracetate solution 170.5 g / hr (51.4 g / hr for pure peracetic acid) in a flow reactor having an internal reaction volume of 1.8 liters. (1.1 mol times with respect to cyclohexanone) was charged and the reaction was continuously performed 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) The reaction mixture obtained in the above reference example was purified using the purifying 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 bottom liquid 6 from this tower is guided to the first reboiler 7, and the bottom liquid is fed to the second reboiler 7.
Led to reboiler 9. The operating conditions of the distillation column of the deboiling column 1 and the deboiling column 5 were as shown in Table-1. At this time, the lactone concentration contained in the first reboiler bottom liquor was 72%, and the second reboiler bottom liquor contained 10% lactone. Table 2 shows the loss rates of ε-caprolactone. The yield of ε-caprolactone was 97.1%.
The acid value of ε-caprolactone of the obtained product is 0.
It was 15 (KOHmg / g).

(Operating conditions) Deboiling column 1 in this embodiment
Table 1 shows the operating conditions of the still and the high boiling column removing tower 5.

[0018]

[Table 1]

(Comparative Example) The same procedure as in Example was carried out except that the reboiler of the deboiling tower 5 was provided in one stage (only the reboiler 7 was used in the figure). 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. Table 2 shows the loss rates of ε-caprolactone. The product ε-caprolactone yield was 93.2%. The acid value of ε-caprolactone of the obtained product was 0.30.

[0020]

[Table 2]

[0021]

INDUSTRIAL APPLICABILITY In the method for purifying ε-caprolactone in which the reaction mixture obtained by oxidizing cyclohexanone is separated from impurities by distillation according to the method of the present invention, the purification is carried out by installing two or more reboilers in the deboiling column. It became possible to substantially prevent the polymerization loss due to the process and achieve a high product ε-caprolactone yield. The increase in equipment cost due to the installation of multiple reboilers was such a beneficial effect that it did not pose any problem.

[Brief description of drawings]

FIG. 1 is a process diagram showing a method for purifying ε-caprolactone of the present invention.

[Explanation of symbols]

 1 De-low boiling tower 3 Low boiling fraction 4 First bottom liquid (low boiling tower bottom liquid) 5 De-high boiling tower 6 De-high boiling tower bottom liquid 7 Reboiler (first reboiler) 8 Reboiler 7 bottom Liquid 9 Reboiler (second reboiler) 11 Canned liquid of reboiler 12 Product ε-caprolactone

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. In the second distillation step of distilling the product ε-caprolactone from one bottom liquor to separate it from high-boiling-point impurities, it is characterized in that two or more stages of reboilers are installed in the second distillation step to successively concentrate bottom liquor. Ε-
Purification method of caprolactone. 2. The second reboiler is further concentrated after the second reboiler so that the lactone concentration in the bottom liquid of the first reboiler in the second distillation step is at least 20% by weight or more, and the lactone is further concentrated after the second reboiler. The method for purifying ε-caprolactone according to claim 1. 3. The method for purifying ε-caprolactone according to claim 1, wherein the reboiler has two stages.