JPS6059238B2 - Purification method of ε-caprolactone - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for purifying caprolactone.

In particular, the present invention relates to a method for obtaining highly purified E-caprolactone with low water content by a simple distillation method. E-caprolactone is a compound used as a polyester polyol for polyurethane and as a polymer raw material for molding materials, etc., and a typical method for producing it is known to be obtained by oxidizing cyclohexanone.

These applications particularly require high purity E-caprolactone with low moisture content.

That is, the presence of moisture increases the oxidation of the polyester obtained by the reaction of E-caprolactone and an active hydrogen compound such as a polyol, causing problems in polyurethane applications. Furthermore, polycaprolactone having a molecular weight of tens of thousands or more is used as a molding material, but in order to obtain such a high molecular weight polyester, the water content must be 0.0% or less. In separating the target product from the reaction product by distillation, a commonly used method is to first distill off the low-boiling substances and then separate the target product from the high-boiling substances in a second distillation column.

However, in the case of E-caprolactone, this method is problematic in two ways. One of them is the large polymerization loss during distillation.

As a countermeasure, there is a method to first remove most of the high-boiling components by flash evaporation (Japanese Patent Application Laid-Open No. 81-34789), but there is also a method using single-pass thin film evaporation to remove high boiling points in the peracid method. I found out that it can be solved. It has been found that the second problem occurs when the latter method is adopted, or when a simple distillation method for eliminating low boiling points or eliminating high boiling points is adopted, even though some polymerization loss is tolerated. That is, when an attempt was made to separate the low-boiling reaction liquid from high-boiling components in a second distillation column and distilling high-purity E-caprolactone, water unexpectedly mixed into the distillate. It was found that the desired low moisture product could not be obtained.

Of course, water not only has a lower boiling point than E-caprolactone, but also has a lower boiling point than cyclohexanone, which belongs to the low boiling component in this purification process. It is surprising that this substance appears in the product tower distillate after the removal of low boiling, but with the goal of producing high quality E-caprolactone,
After conducting a strict moisture check, it was discovered that this problem actually existed. Although the details of the reason for the generation of such moisture are unknown, it is a side reaction in which by-products such as E-oxycaproic acid produced in the oxidation reaction of cyclohexanone cause an esterification reaction at the high temperature at the bottom of the product column. It is thought that water may be generated. The present inventor was the first to recognize the problem of water contamination, which is a problem when high-purity ξ-caprolactone is the goal, and introduced an inert gas into the condenser of the product column to prevent water condensation. I solved this.

That is, the present invention provides a method for purifying ε-caprolactone in which low-boiling components are removed by distillation from a reaction mixture obtained by oxidizing cyclohexanone, and then lactone is distilled out in a second distillation column. This method of purifying ε-caprolactone is characterized by condensing highly pure ε-caprolactone by introducing an inert gas into a vessel to prevent condensation of water. The reaction mixture to which this method is applied is obtained by oxidation of cyclohexanone. This includes co-oxidation of cyclohexanone and acetaldehyde, etc.
This includes oxidation of cyclohexanone with organic peracids (peracetic acid, perpropionic acid, perisobutyric acid, etc.) and hydrogen peroxide oxidation, but in the case of co-oxidation, a method to remove high-boiling components through preliminary flashing is recommended to prevent polymerization. Therefore, as in the present invention, the organic peracid oxidation method is often used to distill in the order of low boiling point and high boiling point. This will be explained using an example. The reaction mixture containing E-caprolactone obtained by the method of oxidizing cyclohexanone with peracetic acid consists of E-caprolactone, unreacted cyclohexanone, unreacted peracetic acid, ethyl acetate (solvent of peracetic acid), acetic acid, caprolactone oligomer, ．． Contains impurity components such as prolactone polymer, oxycaproic acid, adipic acid, and other byproducts of unknown structure.

Generally, separation by distillation is used as a means of purification, but in order to reduce polymerization loss, distillation is usually carried out under reduced pressure.

That is, the reaction mixture is first removed from the top of the first distillation column to remove low-boiling substances such as the solvent used in the reaction, the acid generated from the organic peracid, unreacted cyclohexanone, and water, and then the liquid from the bottom of the column is distilled into the second distillation column. is charged into a distillation column, unavoidable high-boiling byproducts such as adipic acid 4 are removed from the bottom of the column, and purified t-caprolactone is obtained from the top of the column. At this time, as mentioned above, water is probably generated from high-boiling substances and is contained in the product ε-caprolactone, making it impossible to obtain a high-quality product. As a result of various studies to solve this problem, the present inventors have discovered that high-quality ε-caprolactone can be produced by introducing an inert gas into the distillation condenser of the high-boiling tower to prevent water condensation. I found out. An example of an apparatus specifically implementing the present invention is shown in FIG. 1, and an example of the purification method will be described below.

The reaction mixture obtained by oxidizing cyclohexanone with peracetic acid is supplied to the delow boiling tower 1 through a vibrator 2, and acetic acid,
Low-boiling substances such as ethyl acetate (solvent of peracetic acid) and unreacted cyclohexanone and peracetic acid are collected from the vibrator 3. The conditions for this low-boiling removal column 1 are usually a pressure of 40 to 10 Ck at the top of the column.
! NHyl preferably 40-6; Hyl temperature 28-32
CC. Next, the bottom component with a water content of 0.01% or less is fed to a high-boiling removal distillation column 4, by-products such as polycaprolactone and adipic acid are removed from the bottom 5, and the product ε-caprolactone is removed from the top 7. get.

This operation is performed at a tower top pressure of 5 to 20 kH and a reflux ratio of 0.3 to
Distillation is carried out at a temperature of 55 to 75° C., and nitrogen is introduced as an inert gas from a vibrator 6 at 5 rr 101% based on ε-caprolactone to remove water. As described above, high quality ε can be obtained without having to undergo low boiling again.
It became possible to obtain monocaprolactone. The key to effectively carrying out the present invention is to keep the condensation temperature from 55 to
Moisture does not condense at 75°C, but virtually all of E-caprolactone condenses (varies depending on the pressure).Moisture cannot be removed simply by selecting the optimum temperature (depending on the pressure) and by setting the condensation temperature appropriately. There are two points: introducing an inert gas such as nitrogen into the inlet of the condenser to remove moisture.

In the following examples, all percentages are by weight unless otherwise specified.
[Reference example] 60 fI/hour of cyclohexanone and 170.5 ml of 30% peracetic acid ethyl acetate solution were placed in a flow reactor with a reaction internal volume of 1.8 e.
f/hr [51.1 y/hr as pure peracetic acid; 1.1 mole times that of cyclohexanone], and the reaction temperature was 50 y/hr.
Analysis of the reaction mixture obtained by continuous reaction at °C revealed that 28.78% of ε-caprolactone; 0.52% of unreacted cyclohexanone; 1.31% of unreacted peracetic acid; and 0.59% of by-product adipic acid. : Caprolactone polymer 0.30%
; acetic acid 21.16%; solvent ethyl acetate 47.34%.

[Examples and comparative examples]

The reaction mixture obtained in the above reference example was purified using the purification apparatus shown in FIG.

First, the reaction mixture was supplied to the first distillation column from the vibrator 2 at a rate of 230.5 y/hour, and was deboiled at a top pressure of 40w0nHy (temperature 29°C) and a reflux ratio of 0.6.
(temperature: 146°C), a bottoms liquid with a moisture content of 0.01% or less was obtained. This crude E-caprolactone is charged into a second distillation column,
When distilled at a column top pressure of 10TnIILHy (steam temperature 94°C, distillation condensation temperature 30°C) and a reflux ratio of 0.4, the water content in the obtained E-caprolactone had increased to 0.10%. When the distillation condensation temperature is raised to 55℃, the water content is 0.05
%, but it was still insufficient. (Comparative example without inert gas blowing from the vibrator 6) Nitrogen (5 mol% relative to the product) was blown in as an inert gas from the vibrator 6, and distillation was carried out at a distillation condensation temperature of 55°C, resulting in a moisture content of 0.01
% of purified ε-caprolactone (64.6 V/hr) was obtained.

As described above, according to the present invention, ε-caprolactone purified to a low water content that cannot be obtained by ordinary distillation methods can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an example of a distillation apparatus used in carrying out the present invention.

Claims (1)

[Claims] 1 In an ε-caprolactone purification method in which low-boiling components are removed by distillation from the reaction mixture obtained by oxidizing cyclohexanone, and lactone is distilled out in a second distillation column, inert gas is introduced into the condenser of the second distillation column. A method for purifying ε-caprolactone, which comprises condensing highly pure ε-caprolactone by introducing water to prevent condensation.