JP3439510B2 - Method for producing high-purity 1,3-cyclohexadiene - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing high-purity 1,3-cyclohexadiene. More specifically, cyclohexene, 2-cyclohexene-1-ol, cyclohexene oxide, 2-cyclohexene-1
The present invention relates to a method for producing high-purity 1,3-cyclohexadiene from a mixture containing benzene.

1,3-Cyclohexadiene is a compound useful as a raw material for high heat resistance and high rigidity polymers and various organic intermediates.

[0003]

2. Description of the Prior Art As a method for producing 1,3-cyclohexadiene, 3-halogenocyclohexene and 1,
Dehydrohalogenation of 2-dihalogenocyclohexane, 3
A method is known in which acetoxycyclohexene is deacetic acid and 1,4-cyclohexanediol is dehydrated. However, these methods have extremely low selectivity and cannot be industrially manufactured.

On the other hand, as a method for synthesizing 1,3-cyclohexadiene from an oxygen-containing compound having a cyclohexane ring or a cyclohexene ring, 2-cyclohexen-1-ol is dehydrated in a gas phase using an alumina catalyst. Method (Vestsi Akad.Navuk Bel
orussk. SSR, Ser. Khim. Navu
k, (2) 20-4 (1965)) and the same dehydration reaction method using an alumina-boria catalyst (Dok).
l. Akad. Nauk. Belorussk. SSR
14 (8), 734-7 (1970)) and the like. By these methods, 1,3-cyclohexadiene is obtained with an extremely high selectivity of 99% or more.
In addition, a method of contacting cyclohexene oxide with a metal oxide catalyst such as alumina, titania, zirconia by a gas phase pulse reaction method at 150 ° C. (Bull. Chem. So.
c. Jpn. , 49 (2), 563-564 (197).
6)) has been reported. According to this method, the selectivity of 1,3-cyclohexadiene is as low as 56%, and there is no description of the purity of 1,3-cyclohexadiene after removing the high boiling substances.

Similarly, as a method using cyclohexene oxide as a raw material, a method of dehydration reaction using a silica / titania or silica / titania / magnesia catalyst in a liquid phase (JP-A-57-26628) has been reported. ing. With this method, only a low selectivity of around 50%
3-Cyclohexadiene has not been obtained. Furthermore, US
SR SU1,133,253 (1985) includes cyclohexene obtained by oxidizing cyclohexene with an organic peroxide, 2-cyclohexene-1-ol, cyclohexene oxide, 2-cyclohexene-1-one,
A method is described in which a mixture of cyclohexenyl hydroperoxides is passed as it is in a gas phase over clinoptilolite, which is a natural zeolite, at 270 to 300 ° C. to obtain a mixture containing 1,3-cyclohexadiene. However, the purity of cyclohexadiene obtained by this method is extremely low at around 30%, and in order to increase the purity, after dimerizing 1,3-cyclohexadiene from the obtained product and separating it from other products, Decompose the dimer,
A complicated purification method of returning to 3-cyclohexadiene is used.

[0006]

The method by the vapor phase dehydration reaction from 2-cyclohexen-1-ol is an excellent method in that highly pure 1,3-cyclohexadiene can be obtained. The industrial production method of 2-cyclohexene-1-ol as a raw material is, as described above, a method in which cyclohexene is oxidized with an organic peroxide to obtain a mixture of various oxygen-containing compounds, and cyclohexene is air-oxidized to obtain cyclohexenyl hydroperoxide. , A method of reacting this with cyclohexene to obtain a mixture of 2-cyclohexene-1-ol and cyclohexene oxide (Japanese Patent Publication No. 45-4).
No. 0045), cyclohexenyl peroxide is decomposed with an aqueous alkali solution to give 2-cyclohexene-1.
The method of obtaining all-ol ([Oxidation and reduction of organic compounds], published by Nankodo Co., Ltd., 1983, p. 51) is known. Among these, in the method via cyclohexenyl peroxide, 2-cyclohexen-1-one is produced as a by-product according to the study by the present inventors. Thus, all the methods for synthesizing 2-cyclohexen-1-ol can be obtained as a mixture of various oxygen-containing compounds, and it is necessary to suppress the conversion rate relatively in order to increase the selectivity of the oxidation reaction.
Usually also unreacted cyclohexene is included. Therefore, when the above-mentioned gas phase dehydration reaction is used, 2
It is necessary to separate the cyclohexene-1-ol, but when using a distillation method which is a separation method which is usually used industrially, it is difficult to separate it because the boiling points of various oxygen-containing compounds are relatively close. Therefore, a simple production method from the above mixture is industrially desired.

On the other hand, a method of directly subjecting a product obtained by oxidizing cyclohexene with an organic peroxide to a gas phase dehydration reaction is simple as a production method, but the obtained 1,3-cyclohexadiene is benzene, cyclohexene or methylcyclopentene. Since it is obtained as a mixture of, separation is required. However, the boiling points of these compounds are very close to each other, and it is virtually impossible to separate them by distillation. Therefore, there is a problem that a complicated separation method is required as described above.

As described above, a simple method for producing high-purity 1,3-cyclohexadiene from an oxidation product derived from cyclohexene has not been known.

[0009]

Means for Solving the Problems As a result of intensive studies and studies to solve the above problems, the present inventors have found that cyclohexene and 2-cyclohexene-1 derived from cyclohexene can be obtained.
-Ol, cyclohexene oxide, 2-cyclohexene-1-one obtained by separating and removing cyclohexene from the mixture containing 2-cyclohexene-1-ol, cyclohexene oxide, 2-cyclohexene-1-one in a gas phase, It was found that high-purity 1,3-cyclohexadiene can be obtained by a simple method of subjecting to dehydration reaction, and the present invention has been completed.

That is, according to the present invention, when 1,3-cyclohexadiene is produced from a mixture containing cyclohexene, 2-cyclohexene-1-ol, cyclohexene oxide and 2-cyclohexene-1-one, cyclohexene is separated and removed from the mixture. A mixture containing 2-cyclohexene-1-ol, cyclohexene oxide and 2-cyclohexene-1-one is obtained, which is subjected to a dehydration reaction in a gas phase.
This is a method for producing 3-cyclohexadiene.

According to the method of the present invention, the purity of 1,3-cyclohexadiene after distilling and separating the high-boiling substance from the product is 90% or more, preferably 95% or more. You can also get things, and you don't need any complicated separation. The reason why high-purity 1,3-cyclohexadiene can be obtained simply by separating and removing cyclohexene from the raw material mixture is that 1,3-cyclohexene and the like are contained in the product, and thus 1,3
These compounds, which have a boiling point very close to that of cyclohexadiene, are mixed with 1,3-cyclohexadiene during the distillation to reduce the purity, but the removal of cyclohexene reduces the cyclohexene in the product and reduces the content of benzene and methylcyclopentene. It is thought to be due to the decrease in

Next, the present invention will be described in more detail. The raw material mixture of the present invention is a mixture containing cyclohexene, 2-cyclohexene-1-ol, cyclohexene oxide, and 2-cyclohexene-1-one. In these raw material mixtures, 1,3-cyclohexadiene is produced from 2-cyclohexene-1-ol and cyclohexene oxide, but 2-cyclohexene-1-one is, according to our detailed study, reaction conditions. Then high boiling 1,3
-It is believed that it does not give cyclohexadiene. Again 2
-When the amount of cyclohexen-1-one is too large, it adversely affects the deterioration of the catalyst. Therefore, the amount of 2-cyclohexen-1-one in the raw material mixture is in the range of 0.1 to 10% by weight,
Preferably 0.1 to 5% by weight, more preferably 0.1.
It is desirable to keep it within the range of 1 to 2% by weight.

The fact that the 2-cyclohexen-1-one has a high boiling point means a decrease in the yield of 1,3-cyclohexadiene, but it is a process advantage. This is because 2-cyclohexene-1-ol and 2-cyclohexene-1-one in the raw materials have very close boiling points and are difficult to separate by distillation, but 2-cyclohexene-1-ol becomes 1,3-cyclohexene by subjecting to reaction. This is because 2-cyclohexene-1-one becomes a high-boiling substance in hexadiene and can be separated by distillation.

The amounts of 2-cyclohexen-1-ol and cyclohexene oxide in the raw material are not particularly limited because they depend on the synthesis method in the first stage. The weight ratio of 2-cyclohexene-1-ol / cyclohexene oxide is in the range of 0.05 to 50, preferably 0.
In the range 1 to 10, more preferably 0.5 to 1.5
It is desirable that the range is.

In the present invention, it is necessary to separate and remove cyclohexene from the raw material mixture. The term "removal" used herein means to remove 90% or more, preferably 95% or more, and more preferably 99% or more of cyclohexene contained in the raw material mixture. As a method of separating and removing, generally used distillation methods and adsorption separation methods are effective.

In the present invention, a mixture containing 2-cyclohexene-1-ol, cyclohexene oxide and 2-cyclohexene-1-one after separating cyclohexene is subjected to a dehydration reaction in a gas phase. In this case, the mixture after separating cyclohexene may be subjected to a dehydration reaction in the gas phase as it is, or a part of cyclohexene oxide in the mixture and / or a component having a higher boiling point than the above three components may be separated and removed. The mixture may be dehydrated.

When a part of cyclohexene oxide is separated and removed, the removal rate can be arbitrarily selected according to the demand for 1,3-cyclohexadiene and cyclohexene oxide. However, in this case as well, the mixture to be subjected to the gas phase dehydration reaction always contains cyclohexene oxide, and the amount thereof is in the range of 0.1 to 50% by weight, preferably 0.5.
To 40% by weight, more preferably 1 to 30% by weight.

When a part of cyclohexene oxide is separated, it is also possible to separate a part of cyclohexene and a part of cyclohexene oxide at the same time. In the present invention,
2-Cyclohexene-1-ol, cyclohexene oxide and 2-cyclohexene-1 thus obtained
The mixture containing lon is subjected to a dehydration reaction in the gas phase.
A catalyst is used when performing this dehydration reaction.

The catalyst used in the present invention includes
Examples thereof include those generally called acid / base catalysts such as metal oxides and metal sulfates. Among them, metal oxide catalysts having excellent thermal stability are preferable, and metal phosphates, zeolites, and γ-alumina are more preferable. Particularly preferred are metal phosphates. The reaction temperature for the gas phase dehydration reaction is in the range of 200 to 400 ° C, preferably 250 to 400 ° C, more preferably 300 to 380 ° C.
Is the range. The reaction pressure is not particularly limited as long as the reaction conditions can be maintained in the gas phase, and may be normal pressure, increased pressure or reduced pressure.

The reaction system in the present invention may be a batch system or a flow system, but a flow system is preferred. The feed rate of the raw material mixture in the case of using the flow system is 0.05 to 20 hr ⁻¹ in LHSV (a value obtained by dividing the supply volume of the liquid raw material per hour by the volume of the catalyst layer), preferably 0.
1 to 10 hr ^-1 , more preferably 0.2 to 5 hr
It is in the range of ^-1 . The raw material mixture may be mixed with an inert gas such as nitrogen, helium, or argon at an arbitrary ratio and supplied to the catalyst layer.

The product of the gas phase dehydration reaction in the present invention is
The main product is 1,3-cyclohexadiene, and its selectivity reaches 60% or more, preferably 80% or more. The reaction product contains unreacted cyclohexene oxide, by-products formylcyclopentane, and cyclohexanone, but almost no 2-cyclohexene-1-ol or 2-cyclohexene-1-one.

The recovery of 1,3-cyclohexadiene from the product can be easily carried out by an ordinary distillation operation. In that case, the purity of 1,3-cyclohexadiene after removing the oxygen-containing compound and further removing the water by azeotropic distillation reaches 90% or more, preferably 95% or more. If necessary, cyclohexene oxide can be recovered from the separated oxygen-containing compound and reused.

[0023]

The present invention will be described in more detail with reference to the following examples.

[0024]

Example 1 1000 g of cyclohexene containing 2% by weight of cyclohexenyl hydroperoxide was charged into a titanium autoclave, pressurized to 50 atm with nitrogen containing 6% oxygen, and then kept under stirring at 70 ° C. for 1 hour. did. Then, the gas phase part was purged to atmospheric pressure, then pressurized again to 50 atm with nitrogen containing 6% oxygen, and stirred for 1 hour. The same operation was repeated 5 times in total (reaction time 5 hours), and then cooled to room temperature and the contents were analyzed. The analysis was performed by gas chromatography and iodometric titration.

The composition of the resulting mixture was as follows: Cyclohexene: 80.4% by weight Cyclohexenyl hydroperoxide: 18.6 〃 2-Cyclohexen-1-ol: 0.5 〃 2-Cyclohexen-1-one: 0.5 〃 1 g of molybdenum dioxyacetylacetonate was added to 1000 g of the above mixture. In addition, the epoxidation reaction was carried out under stirring conditions at 70 ° C. for 3 hours. The obtained mixture (hereinafter referred to as mixture I) was analyzed by gas chromatography, and it was found that it had the following composition.

Cyclohexene: 67.1% by weight 2-Cyclohexene-1-ol: 16.5 〃 Cyclohexene oxide: 15.1 〃 Epoxycyclohexanol: 0.3 〃 2-Cyclohexene-1-one: 0.9 〃 Mixture I above Was subjected to vacuum distillation under a pressure of 50 mmHg to remove the molybdenum catalyst and epoxycyclohexanol to obtain a mixture having the following composition (hereinafter referred to as mixture II).

Cyclohexene: 67.6% by weight 2-Cyclohexene-1-ol: 16.3 〃 Cyclohexene oxide: 15.3 〃 2-Cyclohexene-1-one: 0.8 〃 The above mixture II is further added under normal pressure at about 80 ° C. By distillation, cyclohexene is separated and removed, and a mixture having the following composition (hereinafter,
Mixture III) was obtained.

2-Cyclohexen-1-ol: 50.5% by weight Cyclohexene oxide: 47.1 〃 2-Cyclohexen-1-one: 2.4 〃 Using the above mixture III as a raw material, a gas phase dehydration reaction was carried out under the following conditions. I went there. Catalyst: β-type calcium phosphate (Ca ₃ (PO ₄ ) ₂ ) 9-
20 mesh particle size Reaction temperature: 350 ° C. Reaction pressure: Normal pressure LHSV: 1 hr ⁻¹ Diluent: Diluted 5 times with nitrogen and supplied to the catalyst layer.

The results of 5 hours and 100 hours after the start of the reaction are shown in Table 1. The composition of the product liquid is the composition of organic substances excluding water, and the purity of 1,3-cyclohexadiene is the purity after removing water by azeotropic distillation.

[0030]

[Table 1]

As shown in Table 1, the purity of 1,3-cyclohexadiene after recovery by distillation was 98% or more, and an extremely high purity was obtained.

[0032]

Example 2 Mixture III from Example 1 is further added to 50 mmH
Part of the cyclohexene oxide was separated by subjecting to vacuum distillation at a pressure of g. The composition of the resulting mixture is as follows. 2-Cyclohexene-1-ol: 81.7
% By Weight Cyclohexene Oxide: 14.4 〃 2-Cyclohexene-1-one: 3.8 〃 Using this mixture as a raw material, a gas phase dehydration reaction was carried out under the following conditions.

Catalyst: the same calcium phosphate as in Example 1 Reaction temperature: 320 ° C. Reaction pressure: Normal pressure LHSV: 2 hr ⁻¹ Diluent: Diluted 3.5 times with nitrogen and supplied to the catalyst layer.

The results after 5 hours from the start of the reaction were as follows. Product liquid composition 1,3-cyclohexadiene: 87.6% by weight 1,4-cyclohexadiene: 0.1 〃 benzene: 0.4 〃 cyclohexene: 0.5 〃 formylcyclopentane: 3.9 〃 cyclohexanone: 7. 8 〃 Other high boiling point: 8.0 〃 The conversion was 100% with 2-cyclohexene-1-ol and cyclohexene oxide. The selectivity of 1,3-cyclohexadiene was 92.1%, and the purity of 1,3-cyclohexadiene after removing the oxygen-containing compound by distillation recovery was 98.9% by weight.

[0035]

Example 3 Except that γ-alumina was used as the catalyst,
The vapor phase dehydration reaction was carried out under exactly the same conditions as in Example 1. The reaction results for 5 hours after the start of the reaction were as follows. Product liquid composition 1,3-cyclohexadiene: 79.0% by weight 1,4-cyclohexadiene: 0.4 〃 benzene: 1.5 〃 cyclohexene: 1.4 〃 methylcyclopentenes: 0.1 〃 formylcyclopentane: 7.9 Cyclohexanone: 6.9 〃 Other high boiling point: 2.8 〃 The conversion was 100% with 2-cyclohexen-1-ol and cyclohexene oxide. The selectivity of 1,3-cyclohexadiene was 83.5%, and the purity of 1,3-cyclohexadiene after removing the oxygen-containing compound by distillation was 95.9% by weight.

[0036]

Example 4 A gas phase dehydration reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was 260 ° C. The reaction results 5 hours after the start of the reaction were as follows. Product liquid composition 1,3-cyclohexadiene: 68.9% by weight benzene: 0.1 〃 cyclohexene: 0.1 〃 formylcyclopentane ： 2.8 〃 cyclohexanone ： 2.8 〃 other high boiling point: 2.8 〃 cyclohexene Oxide: 22.5〃2-cyclohexen-1-ol conversion is 100%,
The conversion of cyclohexene oxide was 60%.
The selectivity of 1,3-cyclohexadiene is 93.5.
%, The purity of 1,3-cyclohexadiene after removing the oxygen-containing compound by distillation was 99.6%.

[0037]

Example 5 Mixture I of Example 1 was distilled at atmospheric pressure at about 80 ° C. to remove cyclohexene to obtain a mixture having the following composition containing a molybdenum catalyst. 2-Cyclohexen-1-ol: 50.2% by weight Cyclohexene oxide: 46.2 〃 Epoxycyclohexanol: 3.4 〃 2-Cyclohexene-1-one: 9.6 〃 Layer of quartz sand obtained by heating this mixture to 200 ° C After removing the molybdenum catalyst by passing it through the gas phase in the gas phase, a gas phase dehydration reaction was performed under the following conditions.

Catalyst: the same calcium phosphate catalyst as in Example 1 Reaction temperature: 330 ° C. Reaction pressure: Normal pressure LHSV: 0.8 hr ⁻¹ Diluent: Diluted 5 times with nitrogen and supplied to the catalyst layer.

The reaction results 5 hours after the start of the reaction were as follows. Product liquid composition 1,3-cyclohexadiene: 78.4% by weight 1,4-cyclohexadiene: 0.3 〃 benzene: 1.4 〃 cyclohexene: 1.4 〃 methylcyclopentenes: 0.2 〃 formylcyclopentane: 9.2 〃 Cyclohexanone: 5.8 〃 Other high boiling point: 9.6 〃 The conversion was 100% with 2-cyclohexene-1-ol and cyclohexene oxide. The selectivity of 1,3-cyclohexadiene was 83.5%, and the purity of 1,3-cyclohexadiene after removing the oxygen-containing compound by distillation was 96.0%.

[0040]

Example 6 1000 g of cyclohexene containing 0.4% by weight of cumene hydroperoxide was charged into a titanium autoclave, and nitrogen containing 6% oxygen was stirred at 90 ° C. under a pressure of 6 atm at 1.3 l / min. While supplying. After 7 hours, the mixture was cooled to room temperature and analyzed by gas chromatography and iodometric titration to obtain a mixture having the following composition.

2-Cyclohexene-1-ol: 30.0% by weight Cyclohexene oxide: 5.0 〃 2-Cyclohexene-1-one: 2.0 〃 Cyclohexenyl hydroperoxide: 3.0 〃 Cyclohexene: 60.0 〃 The mixture was distilled under a pressure of 100 mmHg at about 40 ° C. to remove cyclohexene to obtain a mixture having the following composition.

2-Cyclohexen-1-ol: 75.0% by weight Cyclohexene oxide: 12.5 〃 2-Cyclohexene-1-one: 5.0 〃 Cyclohexenyl hydroperoxide: 7.5 〃 Using this mixture as a raw material The vapor phase dehydration reaction was performed under the following conditions.

Catalyst: the same γ-alumina as in Example 3 Reaction temperature: 360 ° C. Reaction pressure: Normal pressure LHSV: 0.5 hr ⁻¹ Diluent: Diluted 4 times with nitrogen and supplied to the catalyst layer.

The reaction results for 6 hours after the start of the reaction were as follows. Product liquid composition 1,3-cyclohexadiene: 60.4% by weight 1,4-cyclohexadiene: 0.5 〃 benzene: 4.9 〃 cyclohexene: 1.1 〃 methylcyclopentenes: 0.1 〃 formylcyclopentane: 10.9 〃 cyclohexanone: 10.9 〃 Other high boiling point: 11.2 〃 The conversion rate is 10% for 2-cyclohexene-1-ol, cyclohexene oxide and cyclohexenyl peroxide.
It was 0%. The selectivity of 1,3-cyclohexadiene was 67.5%, and the purity of 1,3-cyclohexadiene after removing the oxygen-containing compound by distillation was 90.1% by weight.

[0045]

Example 7 1000 g of cyclohexene containing 2% by weight of cyclohexenyl hydroperoxide was charged into a titanium autoclave, pressurized to 50 atm with nitrogen containing 6% oxygen and stirred at 90 ° C. in a gas phase every hour. Part purging and refilling were repeated 5 times (reaction time 5 hours).

The contents were cooled to room temperature and subjected to gas chromatography and iodometric titration analysis to obtain a mixture having the following composition. Cyclohexene: 63.4% by weight Cyclohexenyl hydroperoxide: 30.2 〃 2-Cyclohexen-1-ol: 2.3 〃 2-Cyclohexen-1-one: 4.1 〃 Molybdenum dioxyacetylacetonate was added to 1000 g of this mixture. 6 g was added and the epoxidation reaction was carried out at 80 ° C. for 3 hours.

The composition of the resulting mixture was as follows: 2-Cyclohexene-1-ol: 26.5% by weight Cyclohexene oxide: 22.1 〃 Epoxy cyclohexanol: 2.1 〃 2-Cyclohexene-1-one: 6.1 〃 Cyclohexene: 43.2 〃 This mixture is treated at a pressure of 100 mmHg. The mixture was distilled under reduced pressure to remove the molybdenum catalyst and epoxycyclohexanol to obtain a mixture having the following composition.

2-Cyclohexen-1-ol: 26.3% by weight Cyclohexene oxide: 22.8 〃 2-Cyclohexene-1-one: 6.3 〃 Cyclohexene: 44.6 〃 Furthermore, this mixture was heated at normal pressure at about 80 ° C. Distillation removed cyclohexene to obtain a mixture having the following composition.

2-Cyclohexene-1-ol: 47.5% by weight Cyclohexene oxide: 41.1 〃 2-Cyclohexene-1-one: 11.4 〃 Using this mixture as a raw material, the gas phase dehydration reaction is the same as in Example 1. I went under the conditions. Table 2 shows the reaction results 5 hours and 100 hours after the start of the reaction.

[0050]

[Table 2]

[0051]

Comparative Example 1 Using the mixture II of Example 1 as a raw material, a gas phase dehydration reaction was carried out under the following conditions without separating cyclohexene. The catalyst, reaction temperature, and reaction pressure were the same as in Example 1, and the amount of nitrogen in the diluent was adjusted so that the contact time was the same as in Example 1.

The reaction results 5 hours after the start of the reaction are shown below. Product liquid composition 1,3-cyclohexadiene: 19.9 wt% benzene: 2.9〃 cyclohexene: 65.0〃 methylcyclopentenes: 6.8〃 formylcyclopentane: 2.3〃 cyclohexanone: 2.3〃 other High boiling point: 0.8 〃 The conversion was 100% with 2-cyclohexene-1-ol and cyclohexene oxide. The selectivity of 1,3-cyclohexadiene was 73.1%, and the purity of 1,3-cyclohexadiene after removing the oxygen-containing compound by distillation was 21.0%.

Furthermore, 1,3-cyclohexadiene / (1,
The ratio of (3-cyclohexadiene + benzene) is 0.87 in this example, whereas it is 0.99 in Example 1, and it is understood that benzene is a large by-product when cyclohexene coexists.

[0054]

According to the method of the present invention, a simple method can be used.
High-purity 1,3-cyclohexadiene of 0% or more, preferably 95% or more can be obtained. This is extremely advantageous for industrial implementation.

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Claims (5)

(57) [Claims] 1. When producing 1,3-cyclohexadiene from a mixture containing cyclohexene, 2-cyclohexene-1-ol, cyclohexene oxide, and 2-cyclohexene-1-one, cyclohexene is separated and removed from the mixture to obtain 2-hexene. Cyclohexene-1-ol,
A process for producing high-purity 1,3-cyclohexadiene, which comprises obtaining a mixture containing cyclohexene oxide and 2-cyclohexene-1-one and subjecting the mixture to a dehydration reaction in a gas phase. 2. The method according to claim 1, wherein the amount of 2-cyclohexen-1-one in the raw material mixture is in the range of 0.1 to 10% by weight. 3. The weight ratio of 2-cyclohexen-1-ol / cyclohexene oxide in the raw material mixture is
2. The range of 0.5 to 1.5.
The method described. 4. The method according to claim 1, wherein a phosphate is used as a catalyst when the dehydration reaction is carried out in the gas phase. 5. The method according to claim 1, wherein the reaction temperature in the dehydration reaction in the gas phase is in the range of 200 to 400 ° C.