JP4173572B2 - Method for purifying ε-caprolactone - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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]
[Prior art]
ε-Caprolactone is a useful compound that has applications such as a polyester polyol for polyurethane synthesis and a polymer raw material for other molding materials, and has recently been in demand as a raw material for biodegradable plastics. As a typical production method, a method obtained by oxidizing cyclohexanone is known, and this cyclohexanone is oxidized by a co-oxidation method with acetaldehyde and an oxidation using an organic peracid such as peracetic acid as an oxidizing agent. There is a law. Furthermore, as a method for separating a target product from a reaction solution obtained by oxidation of cyclohexanone, a distillation method is disclosed in JP-A-60-16436, JP-A-3-33718, JP-A-4-9378 and the like.
[0003]
[Problems to be solved by the invention]
On the other hand, when a polymerization reaction is performed 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 the polymerization. The polymerization reaction rate is often different due to the difference in water content. In addition, the product itself is likely 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, low-boiling fractions such as low-boiling acid and water contained in the reaction liquid are distilled off in the first distillation column, and the first bottom liquid is removed. The first bottoms are fed to the second distillation column, then ε-caprolactone is distilled in the second distillation column, and a purification system for separating from high boiling point substances such as high boiling acid is constructed. While increasing the reflux ratio of the first distillation column, the amount of the distillate was increased, or the amount of the second bottoms extracted was increased.
[0005]
However, since the purification yield decreases due to an increase in the first distillation column distillate and an increase in the extraction amount of the second bottoms, both the purification yield and the quality of the ε-caprolactone product are improved. It is extremely difficult.
Under such circumstances, in the industrial production of ε-caprolactone, development of a method for purifying ε-caprolactone, which can improve the quality without reducing the purification yield of ε-caprolactone and does not require special equipment, is eagerly desired. Yes.
[0006]
[Means for Solving the Problems]
The present inventor has found 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 the ε-caprolactone product, and from the specific position of the second distillation column, ε -It has been found that the removal of caprolactone does not deteriorate the purification yield and the acid value and water content can be reduced, and the present invention has been completed.
[0007]
That is, the present invention relates to a method for purifying ε-caprolactone in which a reaction solution obtained by oxidizing cyclohexanone is distilled and separated from impurities, and a low-boiling fraction contained in the reaction solution is distilled off in a first distillation column. A bottoms is obtained, and then the first bottoms are supplied to a second distillation column having three or more stages of concentrating parts to distill off the low-boiling fraction from the top of the second distillation column. Ε-caprolactone is extracted from any column within the range of 50 to 75 % from the bottom of the distillation column and from the column bottom side of the number of stages from the supply column to the uppermost column of the second distillation column. A method for purifying caprolactone is provided. Further, the present invention provides a method for purifying ε-caprolactone, wherein ε-caprolactone is taken out in liquid form. Further, the reaction liquid obtained by oxidizing cyclohexanone is a reaction liquid obtained by oxidizing cyclohexanone with an organic peracid, or a reaction liquid obtained by co-oxidation of cyclohexanone and aldehyde. A method for purifying the ε-caprolactone is provided. Hereinafter, the present invention will be described in detail.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a method for purifying ε-caprolactone, in which a reaction solution obtained by oxidizing cyclohexanone is distilled to separate it from impurities.
[0009]
The oxidation of cyclohexanone includes an oxidation method using an organic peracid as an oxidizing agent and a co-oxidation method with an aldehyde, and any reaction solution obtained by any oxidation can be preferably used in the present invention.
[0010]
Examples of organic peracids that can be used in the oxidation method include peracetic acid, perpropionic acid, performic acid, and perisobutyric acid. Among these, peracetic acid and perpropionic acid are preferred. In addition, a diluting solvent may be used for the oxidation, and preferable solvents include esters such as ethyl acetate and methyl acetate.
In the oxidation reaction of cyclohexanone, the organic peracid oxidizes cyclohexanone (bp 155 ° C.) to ε-caprolactone (bp 98 to 99 ° C./2 mmHg), and is reduced by itself to acetic acid (bp 118) corresponding to the organic peracid used. .2 ° C.), propionic acid (bp 141.35 ° C.), formic acid (bp 100.5 ° C.), and isobutyric acid (bp 154.3 ° C.). For this reason, the reaction liquid obtained by oxidizing cyclohexanone contains ε-caprolactone, an organic acid such as acetic acid produced by reduction, and a diluting solvent. Further, adipic acid (bp 265 ° C./bp 100 mmHg), oxycaproic acid, caprolactone oligomers and polymers, and the like. Here, organic acids such as acetic acid produced by reduction have a lower boiling point than ε-caprolactone, and oligomers and polymers of adipic acid, oxycaproic acid and caprolactone have a higher boiling point than ε-caprolactone.
[0011]
Examples of the aldehyde 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. Co-oxidation may be carried out by supplying air or oxygen gas or the like in a solvent containing cyclohexanone and aldehyde, 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, a catalyst is obtained from a reaction solution obtained by co-oxidation of cyclohexanone and acetaldehyde and containing acetic acid, ε-caprolactone, acetaldehyde, cyclohexanone and a catalyst. The separated reaction liquid can be illustrated. Further, a reaction solution obtained by co-oxidation of cyclohexanone and dimethylbenzaldehyde and obtained by separating the catalyst and dimethylbenzoic acid from a reaction solution containing dimethylbenzoic acid, ε-caprolactone, dimethylbenzaldehyde, cyclohexanone and a catalyst can be exemplified.
[0012]
Hereinafter, the purification method of ε-caprolactone of the present invention will be described with reference to FIG. In FIG. 1, the equipment attached to the distillation column is omitted.
[0013]
Purification of ε-caprolactone is carried out by delow boiling distillation or dehigh boiling distillation of the reaction solution. First, a reaction liquid obtained by oxidizing cyclohexanone is supplied from the line 2 to the first distillation column 1. In the first distillation column 1, delow 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 the peracetic acid (hereinafter, the organic acid is described as “acetic acid” for convenience) And a low-boiling fraction 3 such as a diluting solvent such as ethyl acetate is distilled off and the unreacted raw material cyclohexanone is distilled off.
[0014]
The first distillation column of the present invention may be either a plate column or a packed column. The distillation conditions of the first distillation column can be appropriately selected depending on the reaction liquid supply rate, the type of the distillation column, and the like. Generally, the column top temperature is 20 to 60 ° C., particularly 30 to 40 ° C., and the column bottom temperature is 100. It is preferable to be -200 ° C, particularly 120-180 ° C, the top pressure is 200 mmHg or less, and the reflux ratio is 0.1-10, especially 0.5-5. This is because, under this distillation condition, 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. A part of ε-caprolactone is also distilled off as the low boiling fraction 3. The distillation rate of ε-caprolactone is 0.5 to 3.0%.
[0015]
Next, the first bottoms 4 (crude ε-caprolactone) containing ε-caprolactone is extracted 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 plate column or a packed column, but is characterized by having a concentrating part having three or more stages, more preferably 3 to 45 stages, particularly 10 to 35 stages. Specifically, the total number of stages is preferably 5 to 50, and more preferably 15 to 40. This is because within this range, the low-boiling fraction can be distilled off and the high-boiling fraction can be separated efficiently. At this time, if the concentration unit 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 middle 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.
[0016]
In the second distillation column 5, redelow low boiling distillation and dehigh boiling distillation are performed.
The distillation conditions of the second distillation column can be appropriately selected depending on the supply rate of the first bottoms 4, the type of the distillation column, etc., but in order to reduce the loss due to the polymerization of ε-caprolactone, the top temperature is 100. It is -140 degreeC, Preferably it is 110-130 degreeC, Tower bottom temperature 120-200 degreeC, Preferably it is 130-160 degreeC, Tower top pressure is 50 mmHg or less, Reflux ratio 0.1-10, Preferably it is 0.3-5. As a result, the low-boiling fraction 6 such as low-boiling acid and moisture generated in the column is efficiently distilled off from the top of the column, and high-boiling products such as caprolactone oligomer and adipic acid are removed from the second bottom 7 This is because it can be separated from ε-caprolactone.
[0017]
The present invention is characterized in that purified ε-caprolactone (ε-caprolactone product) is taken from any stage above the supply stage of the second distillation column 5 and below the uppermost stage. More preferably, it is characterized by taking out from any stage in the range of 30 to 90%, particularly 50 to 80% from the bottom side of the number of stages from the supply stage to the uppermost stage. This is because in this range, the high-boiling component and the low-boiling fraction are excellent in separation, and the acid value and water content of the ε-caprolactone product are particularly excellent.
Here, the calculation method of the position of the extraction stage in the middle part of the second distillation column is, for example, (5/20) when the supply stage is the bottom and the extraction stage is the fifth stage in the second distillation column with 20 stages. ) × 100 = 25%, (10/20) × 100 = 50% when the supply stage is at the bottom and the extraction stage is the 10th stage. Further, in the case where the second distillation column is supplied to the second stage and the take-out stage is the sixth stage, ((6-2) / (20-2)) × 100 = 22%.
[0018]
The epsilon-caprolactone product is preferably taken out from the middle portion of the second distillation column in a liquid state. This is because, when taken out in a gaseous state, the low-boiling fraction distributed in the gas phase side in the second distillation column is also taken out together with the product, resulting in an increase in the concentration of the low-boiling fraction in the product.
In order to take out the ε-caprolactone product in liquid form, the liquid phase part in the take-out stage may be taken out.
[0019]
According to the purification method of the present invention, an ε-caprolactone product usually has an acid value of 0.07 to 0.10 mg KOH / g and a water content of 70 to 120 ppm. Therefore, when the polymerization reaction is carried out using the ε-caprolactone product of the present invention, the reaction rate can be improved and the deterioration of the ε-caprolactone product can be prevented.
[0020]
【Example】
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. “% And ppm” indicates “% by weight and ppm by weight” except where otherwise indicated.
[0021]
(Measurement item)
(1) Acid value: Calculated from titration required for neutralization with 1/10 N KOH solution per gram of ε-caprolactone product.
(2) Moisture: Analyzed with a Karl Fischer moisture analyzer.
[0022]
(Reference Example 1)
In a flow reactor with an internal volume of 2 liters, cyclohexanone at 60 g / Hr, 30% peracetic acid in ethyl acetate at 170.5 g / Hr (51.4 g / Hr as pure peracetic acid, 1. 1 mol times), and the reaction was continued at a reaction temperature of 50 ° C. The composition of the resulting reaction solution was 28.78% ε-caprolactone, 0.52% unreacted cyclohexanone, 1.31% unreacted peracetic acid, 0.59% byproduct adipic acid, and 0.30% caprolactone polymer. And acetic acid 21.16% and solvent ethyl acetate 47.34%.
Subsequently, the obtained reaction liquid is supplied to the first distillation column of a 15-stage plate-type distillation column, and is removed at a column top temperature of 35 ° C., a column bottom temperature of 160 ° C., a column top pressure of 60 Torr, and a reflux ratio of 1.0. The first bottomed liquid containing ε-caprolactone was obtained by boiling distillation, solvent removal, and acetic acid removal.
[0023]
(Reference Example 2)
A batch reactor having an internal volume of 2 liters was charged with 450 g / Hr of cyclohexanone, 1160 g of solvent ethyl acetate, and 0.08 g of cobalt naphthenate containing 6% Co as a catalyst. Acetaldehyde 360g was dripped at this over 5 hours, and reaction temperature was maintained at 40 degreeC. Oxygen gas 2.2 liter / Hr was supplied from the start of acetaldehyde charging to 1 hour after the completion of the dropping. The composition of the obtained reaction solution was 10.4% ε-caprolactone, 11.7% unreacted cyclohexanone, 13.8% acetic acid, 8.4% unreacted acetaldehyde, 0.3% byproduct adipic acid, caprolactone polymerization Product 0.50%, solvent ethyl acetate 55.0%.
Subsequently, the obtained reaction liquid is supplied to the first distillation column of a 15-stage plate-type distillation column, and is reduced at a column top temperature of 20 ° C., a column bottom temperature of 180 ° C., a column top pressure of 170 Torr, and a reflux ratio of 1.0. The first bottomed liquid containing ε-caprolactone was obtained by boiling distillation, solvent removal, and acetic acid removal.
[0024]
(Example 1)
The first bottom liquid obtained in Reference Example 1 is supplied to the bottom of a 20-stage Oldershaw distillation column having a glass vacuum jacket with a diameter of 40 mm at a rate of 319 g / Hr. The top temperature is 119 ° C. and the bottom temperature is 144. The second bottomed liquid was extracted from the bottom of the tower at 80.35 g / Hr, and the low-boiling fraction was 3.6 g / from the top of the tower. Distilled with Hr, and the ε-caprolactone product was counted from the 10th stage from the bottom including the bottom of the second distillation column (235.05 g / H, product yield in the second distillation column: 73.7%) I took it out. As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.078 mgKOH / g, and the water content was 70 ppm.
[0025]
(Example 2)
The first bottoms are supplied to the bottom of the second distillation column at 325.4 g / Hr, the second bottoms are withdrawn from the bottom at 80.76 g / Hr, and 3.4 g of a low-boiling fraction is discharged from the top of the tower. / Hr and ε-caprolactone was counted from the bottom, not including the bottom of the second distillation column, from the bottom 15th stage (241.24 g / H, product yield 74.1% in the second distillation column) The same operation as in Example 1 was carried out except that it was taken out in step 1. As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.070 KOH mg / g, and the water content was 80 ppm.
[0026]
(Example 3)
The first bottom is fed to the bottom of the second distillation column at 322.7 g / Hr, the second bottom is withdrawn from the bottom at 78.94 g / Hr, and 3.5 g of low boiling fraction is taken from the top of the tower. / Hr, and epsilon-caprolactone was counted from the bottom, including the bottom of the second distillation column, from the 15th stage (240.26 g / H, product yield 74.5% in the second distillation column) The operation was performed in the same manner as in Example 1 except that it was taken out. As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.100 KOH mg / g, and the water content was 120 ppm.
[0027]
(Comparative Example 1)
The first bottom is fed to the bottom of the second distillation column at 323.5 g / Hr, the second bottom is withdrawn from the bottom at 85.3 g / Hr, and ε-caprolactone is distilled from the top. The same operation as in Example 1 was carried out except that it was taken out (238.2 g / H, product yield 73.6% in the second distillation column).
As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.131 KOH mg / g, and the water content was 180 ppm.
[0028]
(Comparative Example 2)
The first bottoms are supplied to the bottom of the second distillation column at 324.1 g / Hr, the second bottoms are withdrawn from the bottom at 77.21 g / Hr, and 3.3 g of low-boiling fraction is extracted from the top of the tower. / Hr, and ε-caprolactone was liquid from the 5th stage from the bottom including the bottom of the second distillation column (243.59 g / H, product yield 75.2% in the second distillation column) The same operation as in Example 1 was carried out except that it was taken out in step 1. As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.175 KOH mg / g and the water content was 60 ppm.
[0029]
Example 4
The first bottom liquid obtained in Reference Example 2 is supplied to the bottom of the second distillation column at 323.8 g / Hr, and the second bottom liquid is withdrawn from the bottom at 85.2 g / Hr. Distillate was distilled off at 3.3 g / Hr, and the ε-caprolactone product was counted from the 15th stage from the bottom including the bottom of the second distillation column (235.3 g / H, product in the second distillation column). The same operation as in Example 1 was conducted except that the product was taken out at a yield of 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.
[0030]
(Comparative Example 3)
The first bottoms obtained in Reference Example 2 is supplied to the bottom of the second distillation column at 325.3 g / Hr, the second bottoms is withdrawn from the bottom at 86.1 g / Hr, and ε- The same operation as in Example 1 was carried out except that caprolactone was distilled off (239.2 g / H, product yield 73.5% in the second distillation column).
As a result of analyzing the quality of the ε-caprolactone product, the acid value was 0.144 KOH mg / g, and the water content was 195 ppm.
[0031]
(result)
As a result of examining the acid value and the amount of water by changing the take-out stage of the ε-caprolactone product by changing the take-out stage of the ε-caprolactone product with the first take-out liquid supply amount, the supply stage, and the second take-out liquid withdrawal amount being almost constant. Compared with Comparative Example 1 and Comparative Example 3 in which the ε-caprolactone product was taken out from the top of the tower, both the acid value and the water content could be reduced.
[0032]
【The invention's effect】
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 moisture content than the product obtained by the conventional method without deteriorating the yield.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a method for purifying ε-caprolactone.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 First distillation column 2 Line 3 Low boiling fraction 4 First bottoms 5 Second distillation column 6 Low boiling fraction 7 Second bottoms 8 ε-Caprolactone product take-out section

Claims (5)

In the purification method of ε-caprolactone in which the reaction liquid obtained by oxidizing cyclohexanone is distilled and separated from impurities, the low boiling fraction contained in the reaction liquid is distilled off in the first distillation column to obtain the first bottom liquid. Then, the first bottoms are supplied to a second distillation column having three or more stages of concentrating portions, the low boiling point fraction is distilled off from the top of the second distillation column, and the high boiling point is removed from the bottom of the second distillation column. A method for purifying ε-caprolactone, which is extracted and ε-caprolactone is extracted from any of the stages in the range of 50 to 75 % from the bottom side of the number of stages from the supply stage to the uppermost stage of the second distillation column. Purification process according to claim 1 Symbol placement No ε- caprolactone to the ε- caprolactone, wherein the retrieving a liquid. The method for purifying ε-caprolactone according to claim 1 or 2 , wherein the reaction solution obtained by oxidizing cyclohexanone is a reaction solution obtained by oxidizing cyclohexanone with an organic peracid. The method for purifying ε-caprolactone according to claim 1 or 2 , wherein the reaction solution obtained by oxidizing cyclohexanone is a reaction solution obtained by co-oxidation of cyclohexanone and aldehyde. The method for purifying 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 aldehyde, and ε-caprolactone is taken out in a gaseous state. .

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