JPS606953B2 - Method for recovering ε-caprolactone precursor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering go-caprolactone precursor.

In particular, the present invention provides a heat treatment method for preparing a mixture containing caprolactone or/and a precursor of caprolactone and a lactone having 4 to 6 carbon atoms or/and a lactone precursor other than caprolactone and a precursor of caprolactone. The present invention relates to a method for separating go-caprolactone and other lactones by evaporation or diffusion and recovering a go-caprolactone precursor. In the method of the present invention, the go-caprolactone precursor is a polymer of go-caprolactone and an ester compound obtained from 6-hydroxycaproic acid and a monohydric or dihydric alcohol having 3 to 8 carbon atoms, and is a lactone precursor. is an ester compound obtained from hydroxycaproic acid having 4 to 6 carbon atoms and a monohydric or dihydric alcohol having 3 to 8 carbon atoms, and 4 carbon atoms.
It is a polymer obtained from the lactones of ~6.

Lactones other than caprolactone include butyrolactone, y-valerolactone, y-caprolactone, 6-valerolactone, 6-caprolactone, and the like. Go-caprolactone easily reacts with ammonia to become go-caprolactone, and is an important intermediate product as a raw material for producing nylon-6.

In addition, caprolactone easily becomes polyester by ring opening, and can be used as a plasticizer for synthetic resins and as an effective modifier for polyols, polyesters, urethane resins, etc. produced by reaction with polyhydric alcohols. Caprolactone is an extremely useful compound as an industrial raw material. However, there are various difficulties in using go-caprolactone in a state containing other lactones, that is, in an impure state, for these purposes. For example, highly purified do-caprolactone is required as a raw material for go-caprolactam, and if it is used as a plasticizer, it is difficult to achieve a modification effect if it contains other lactones, and it is a major cause of quality fluctuations. becomes. Therefore, in order to use it for the above-mentioned purposes, it is necessary to highly purify caprolactone. As a conventional method for separating lactones, for example, a separation method using distillation that takes advantage of the difference in relative volatility between lactones is known.

However, the 3 hmH of various lactones shown below
The specific volatility in saddle bs is 6-caprolactone and gokap. 1.27 between lactones, 1.42 between 6-valerolactone and go-caprolactone, 1.83 between 8-caprolactone and go-caprolactone, 3.00 y- between valerolactone and go-caprolactone. The ratio between butyrolactone and caprolactone is 3.45, and for example, separating 6-valerolactone and caprolactone by distillation requires a large reflux ratio and a large number of stages because the specific volatility is extremely low. On the other hand, lactones have poor thermal stability and rapidly polymerize when heated. It is necessary to avoid keeping the temperature above 150°C for a long time.

Furthermore, separation by distillation requires a reduced pressure and a large number of stages. Plate columns or packed columns are usually considered for this kind of distillation, but as the number of plates increases, the pressure difference between the top and bottom of the distillation column increases.
It is virtually impossible to avoid deterioration such as polymerization of lactones at the bottom of the column. In order to avoid this, it is necessary to reduce the pressure at the top of the column and perform a distillation operation under high vacuum, but this increases the size of the equipment and greatly reduces economic efficiency. As described above, the use of distillation to separate lactones, particularly to remove 6n valerolactone and/or 6-caprolactone from go-caprolactone, has various drawbacks and is disadvantageous for industrial use. . When cyclizing and esterifying hydroxyacids obtained by air oxidation of cyclohexane to obtain lactones, alcohols are added to make the amount of alcoholic hydroxyl groups in the reaction system exceed the carboxyl groups present in the system. The crude lactone obtained by applying the temperature and pressure at which it is extracted contains many impurities, and it is particularly difficult to separate it by distillation6.
-It often contains large amounts of valerolactone and 6-caprolactone.

In particular, when 6-hydroxycaproic acid is obtained by air oxidation of cyclohexane and this is used as a raw material to make do-caprolactone, or when 6-hydroxycaproic acid is produced as a by-product when cyclohexanone or cyclohexanol is made by oxidation of cyclohexane, do-caprolactone is produced. When producing lactone, it contains many lactones that are difficult to separate by distillation. The content of these lactones varies depending on the oxidation conditions of cyclohexane, but the 6-valerolactone concentration is 2 to 3% by weight, and the 8-caprolactone concentration is 0 to 5% by weight.
% by weight, a range of 30-8% by weight of caprolactone concentration is usual. For example, 6-valerolactone 2% by weight
, 8% by weight of crude caprolactone, a distillation system consisting of two distillation columns, a low-boiling separation column and a high-boiling separation column, is required. That is, 6-valerolactone, which has a boiling point lower than that of caprolactone, is separated from the top of the column in a low-boiling separation column, and then high-purity caprolactone is distilled from the top in a high-boiling separation column. As mentioned above, the relative volatility, which indicates the difficulty of distillation separation between 6-valerolactone and docaprolactone, is 1.42.
Therefore, the distillate composition is 6 - 90% by weight of valerolactone.
, the number of theoretical plates required to separate 3% by weight of caprolactone, 1% by weight of 6-valerolactone, and 9% by weight of caprolactone in the bottom liquid composition is about 5.
The actual number of plates should be around 10 bags considering Takeshi efficiency. Therefore, the pressure difference between the caprolactone top and the bottom of the column becomes large, which raises the temperature at the bottom of the column, and deterioration due to polymerization is unavoidable.This results in deterioration of quality and a decrease in the yield of caprolactone, making it disadvantageous to use it industrially. be. The present inventors have conducted various studies on methods for recovering caprolactone precursors from lactone compounds without the above-mentioned drawbacks.
It was found that when lactones are heated, there are differences in the rate of decrease of each lactone monomer and the residual rate of lactone monomers.

At the same time, it was found that when a lactone precursor is heated, the lactones produced from the lactone precursor differ in the production rate depending on the lactone. That is, it was discovered that 8-valerolactone and/or 6-caprolactone can be easily separated from docaprolactone by utilizing this property, and the present invention has been achieved. That is, the present invention provides do-caprolactone and/or go-caprolactone precursors, and lactones having 4 to 6 carbon atoms other than these go-caprolactone and z-caprolactone precursors, or/and do-caprolactone precursors.
and a method of recovering a caprolactone precursor by heating a mixture containing a lactone precursor, taking advantage of the fact that there is a difference in the proportion of monomers present as lactones between caprolactone and other lactones. It is.

-caprolactone and/or -caprolactone precursor used as a raw material mixture in the method of the present invention, and -caprolactone and other lactones having 4 to 6 carbon atoms or - and lactone precursors other than the -caprolactone precursor. A mixture obtained by any method can be used.

Further, the mixture may be only lactones containing z-caprolactone, a lactone oligomer containing a go-caprolactone precursor, or an ester of a lactone containing go-caprolactone and a monohydric or dihydric alcohol. good.

As raw materials for such a mixture, it is possible to use a go-caprolactone liquid obtained by oxidizing cyclohexane with peracetic acid and a go-caprolactone liquid obtained by cyclizing 6-hydroxycaproic acid obtained by air oxidation of cyclohexane. , especially glutaric acid obtained by air oxidation of cyclohexane followed by extraction with water, 6-hydroxycaproic acid containing 5-hydroxycaproic acid, etc.
A reaction mixture obtained by concentrating and crystallizing adipic acid from a reaction mixture containing adipic acid as a main component, separating it, dehydrating the resulting aqueous solution in the presence of alcohol, and then cyclizing the oxyacid with a lactone. It is most effective when used. The reaction mixture obtained by this method contains low-boiling substances with a boiling point lower than that of the lactones produced in the oxidation process of the alcohol and/or cyclohexane, and/or lactones produced in the process of lactone cyclization of oxyacids. It also contains low-boiling substances with low boiling points. In the method of the present invention, low-boiling substances and/or alcohols in a free state in the reaction mixture obtained by such a method are simultaneously separated. In the method of the present invention, the mixture containing at least go-caprolactone or/and go-caprolactone precursor and other lactones having 4 to 6 carbon atoms and/or lactone precursors is maintained at a predetermined temperature under a pressure. The lactones present as monomers and/or the alcohols present in the free state and/or the low-woven fabrics are then heated by single evaporation or diffusion to produce lactones such as 6-valerolactone and 6-caprolactone. Highly purified caprolactone can be obtained by separating and converting the obtained caprolactone precursor into a lactone moat.

The heat treatment in the method of the present invention is performed at a temperature of 150 to 350°C;
Preferably it is 200 to 300°C, and a pressure that can maintain this temperature is used. At this time, if the heating temperature is lower than this range, it is not practical because the reaction of converting do-caprolactone into its precursor is slow, and if the heating temperature is higher than this range, caprolactone and its precursor will thermally decompose. It will not give you an advantage because you will have favoritism. The most preferable pressure range is generally 1 to 100 k9/g of crucian carp, particularly 20 to 50 k9/g of crucian carp.

In order to efficiently convert caprolactone into its precursor within the above temperature and pressure range and at the same time to prevent the generated precursor from thermal decomposition, the reaction time is 1 to 1.
About 8 minutes is good, and 1 to 18 minutes is particularly preferable. The reaction time is determined so that the lactones remaining as monomers can be sufficiently removed. Lactone monomers may be removed by a single evaporation method or by a diffusion method using a packed column, a bridge wall column, a bubble column, etc. Alternatively, a heated and pressurized lactone mixture may be supplied under reduced pressure. However, the lactone monomer may be removed.

The pressure for the lactone separation operation is 5 to 760 hmHga, preferably 20 to 10 hmH, and the temperature is 50 to 300qC, preferably 15
It is 0-25000.

Under the above pressure conditions, if the temperature is below this range, it is difficult to remove residual lactones and low-boiling substances sufficiently, and if the temperature is higher than this range, the lactones that need to be separated from caprolactone become lactones. This is not preferable because it tends to become a precursor. In this way, according to the method of the present invention, the distillate contains low-boiling substances, alcohols, and alcohols.
Lactones other than caprolactone are concentrated, while the bottoms contain low polymers of c-caprolactone and/or c-caprolactone.
Since the precursors of ester and ester are concentrated, highly pure caprolactone can be obtained by lactonization treatment.

These contents will be explained in more detail with reference to FIG.

Figure 1 shows the reduction rate of lactone monomer when a mixture of 3% by weight of 6-valerolactone and 7% by weight of do-caprolactone was sealed in a glass tube and heated at 260oC, and the reduction rate of lactone monomer prepared by heating in advance. wt% of 6-valerolactone precursor 3 and caprolactone precursor 7
This figure shows the relationship between the monomer production rate and time when a weight percent mixture of .

In other words, the reduction rate of docaprolactone monomer is 1.6
- The reduction rate of valerolactone monomer 1 is shown in 2.

The present invention utilizes the fact that when lactone monomers are heated, the rate of reduction from lactone precursor to lactone precursor differs to separate lactones and purify caprolactone. The production rate of the 6-valerolactone monomer from the 6-valerolactone precursor varies from 3 to 4. By removing the 6-valerolactone monomer present after the reaction, the concentration of the caprolactone precursor in the reaction solution increases. To explain in more detail, when caprolactone and 6-valerolactone monomers are heated under pressure, the residual ratio of each monomer shows a time change of 1 and 2. On the other hand, when the go-caprolactone precursor and the 6-valerolactone precursor are used as raw materials, monomers like 3 and 4 are produced over time. Therefore, if the lactone monomer is removed by single evaporation or dissipation using a packed column, compensation column, bubble column, etc., the concentration of caprolactone precursor in the remaining liquid will increase, making it difficult to separate by distillation.
- It is possible to separate valerolactone.

In carrying out the method of the present invention, low-boiling substances produced in the step of air oxidation of monohydric or dihydric alcohols having 3 to 8 carbon atoms and cyclohexane and/or low-boiling substances produced in the step of cyclization of lactones There is no problem even if it exists in the raw material.

When carrying out the method of the present invention, these alcohols change the monomer residual rate of lactones to some extent, but this does not make it difficult to carry out the method of the present invention.

Furthermore, the low boiling point substances hardly change the residual rate of lactone monomers and do not make it difficult to carry out the method of the present invention. These alcohols and/or low boilers can be removed at the same time as the lactone monomers are removed. If the concentration of the caprolactone precursor in the bottoms obtained in this way does not reach the target concentration, by repeating the heating and separation according to the method described in the present invention using the bottoms as a raw material, It is possible to adjust the concentration of lactones in the can liquid to a predetermined concentration.

Therefore, in the present invention, the most preferable reaction temperature and pressure or reaction time and number of separations may be determined depending on the composition of the raw material mixture.

The bottom liquor thus obtained by the process of the invention primarily contains do-caprolactone precursors, i.e., do-caprolactone oligomers and/or esters with alcohols. Go-caprolactone can be easily obtained by heating the bottoms under reduced pressure. Although the z-caprolactone thus obtained contains a small amount of lactones, low-boiling compounds, and high-boiling compounds, it can be purified by conventionally known methods such as distillation. It can be fully used as a raw material for producing lactams, polyesters, polyols, etc. The specific method of the present invention will be described below with reference to Examples, but the present invention is not limited to the aspects of these Examples.

Example 1 -Caprolactone 33. 8-valerolactone 10.2% by weight, 1,6-hexanediol 16. 2 using a mixture containing 40.0% by weight of Tsuru and 40.0% by weight of low-boiling substances.
A continuous experiment was carried out in which the reaction tube was passed through a reaction tube at 8 pi0, 35 kg/G, and a reaction time of 36 minutes, and after passing through the reaction section, single evaporation was performed at 30 hmHga, and the removal rate of 6-valerolactone was 72. % by milk weight, and the caprolactone distillation rate is 0. weight%,
The distillation rate of 1,6-hexanediol was 38.7% by weight, and the low boiling point removal rate was 91. It was box weight%.

When a cyclization reaction is performed using the bottoms (Bots 1) under conditions of 270OO and 300mmH, the amount of caprolactone is 82. Kame weight %, 6-valerolactone 6.9 weight %
, 1.6-hexanediol 0.8% by weight, low purity 9.
A 7% by weight go-caprolactone solution was obtained. Example
2 Using the bottoms of the first separation (bottoms 1) conducted in Example 1, the nitrogen flow rate was 250 pm, 42.6 pm/Hr, L/G.
=1. Under the overall conditions, the inner diameter is 20 ribs, the length is 1.5 skin, and the diameter is 1.
Stripping of 6-valerolactone was carried out using a packed column filled with a porcelain Raschig ring on the side.

As a result, the removal rate of 6-valerolactone was 95.2% by weight, the prolactone distillation rate was 4.7% by weight, and the 1,6-hexanediol recovery rate was 22%. Box weight%, low boiling point removal rate unevenness. 2
The concentration of 6-valerolactone contained in the caprolactone obtained by the cyclization reaction of the bottoms is 0.4% by weight.
%Met. Example 3 A continuous experiment was conducted in which the bottoms 1 obtained in Example 1 was passed through a reaction tube under the same conditions as in Example 1, and after passing through the reaction tube, the bottom liquid 1 was passed through the reaction tube.
Flash distillation was performed using gas to remove low-boiling compounds such as 8-valerolactone.

The tank liquid after this flush is 27000, 3000 hmHga
Gokap obtained by cyclization under the conditions described above. The lactone contained only 2.5% by weight of 6-valerolactone.

[Brief explanation of the drawing]

Figure 1 shows a mixture of % by weight of go-caprolactone 7 and % by weight of 6-valerolactone 3, and a mixture of % by weight of go-caprolactone precursor 7 and % by weight of 6-valerolactone precursor 3 prepared by heating in advance. This figure shows the relationship between the abundance ratio (wt%) of the lactone monomer and time when each of the monomers is heated to 260 qo separately, where 1 is the reduction rate of the 6-cabrolactone monomer and 2 is the reduction rate of the 6-valerolactone monomer. 3 shows the monomer reduction rate, 3 shows the production rate of go-caprolactone monomer, and 4 shows the production rate of 6-valerolactone monomer. ※'figure

Claims (1)

[Claims] 1 A mixture containing ε-caprolactone or/and an ε-caprolactone precursor and a lactone having 4 to 6 carbon atoms or/and a lactone precursor other than ε-caprolactone and the ε-caprolactone precursor,
A method for recovering an ε-caprolactone precursor from the mixture, characterized in that after heat treatment at a temperature of 350°C, single evaporation or diffusion is performed.