JPH09169669A - Separation of cyclohexene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject compound of high purity at a low cost by subjecting a mixture containing cyclohexene and at least one kind of cyclohexane and benzene to extractive distillation by using a solvent mixture of N- methyl pyrrolidone and water as an extracting agent. SOLUTION: This separation method comprises subjecting a mixture of (A) cyclohexene and (B) at least one of (i) cyclohexane and (ii) benzene to extractive distillation by using a mixture of (C) N-methyl-2-pyrrolidone with water as an extracting agent to separate the cyclohexene. For example, a mixture of the component (A) with the component (i) is subjected to extractive distillation using the mixture of the component (C), the component (i) is distilled off from the top of the distillation tower, the component (A) and N-methyl-2-pyrrolidone are drawn out of the tower bottom, and the component A alone is separated from the drawn liquor.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating cyclohexene from a mixture containing cyclohexene and at least one of cyclohexane or benzene.

[0002]

2. Description of the Related Art In recent years, attention has been paid to a method for producing cyclohexanol by hydrating cyclohexene obtained by a partial hydrogenation reaction of benzene. The partial hydrogenation reaction of benzene is usually carried out in the presence of a ruthenium catalyst and water, and usually a reaction mixture containing cyclohexene, unreacted benzene and by-produced cyclohexane is obtained (Patent Publication 3-
5370, Japanese Patent Publication No. 2-19098, Japanese Patent Application Laid-Open No. 4-0741
41 etc.). In order to obtain cyclohexene having a higher purity than the above-mentioned partial hydrogenation reaction mixture of benzene, a method of separating cyclohexene from the mixture becomes a problem. However, since the boiling points of the three components of cyclohexene, benzene and cyclohexane are very close to each other, it is difficult to separate them by ordinary distillation.

Therefore, the extractive distillation method is generally employed as a method for separating these mixtures. In this extractive distillation, a method using various extractants such as N-methylpyrrolidone, N, N-dimethylacetamide, adiponitrile, sulfolane, dimethyl malonate and dimethyl succinate has been proposed (JP-A-52-5733, JP-A-52-5733). JP 58-1
645724, JP-A-58-1645725, JP-A-5
8-172323, JP-A-62-295311, JP-A-4-41441, etc.). Further, the so-called γ ₀ approach is effective in selecting the extraction solvent in the extractive distillation. This γ ₀ approach is described in “Latest Distillation Engineering” (edited by Mitsuho Hirata, published by Nikkan Kogyo Shimbun, January 30, 1972).

[0004]

In the conventional extractive distillation using various extractants, the separation efficiency is not always sufficient, or when an expensive extractant is used, it is economically disadvantageous. Further, as described in JP-A-4-41441, the decomposed product of the extractant may cause corrosion of the distillation apparatus or may become a catalyst poison in various reactions as an impurity in cyclohexene.

[0005]

Means for Solving the Problems As a result of intensive investigations by the present inventors on a method for separating cyclohexene, the extractive distillation method using a mixed solvent of N-methyl-2-pyrrolidone and water as an extractant has The present invention has been achieved by finding that the problems can be solved at once. That is, the gist of the present invention is to separate cyclohexene from a mixture containing cyclohexene and at least one of cyclohexane or benzene by distillation to obtain a cyclohexene-rich component, wherein N-methyl-2-pyrrolidone is used as an extractant for extractive distillation. A method for separating cyclohexene is characterized by using a mixed solution of water and water.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, the mixture to be subjected to extractive distillation is at least one of cyclohexene and cyclohexane or benzene.
It includes seeds. Examples of the mixture that can be used in the present invention include a reaction mixture obtained by a partial hydrogenation reaction of benzene. In order to perform extractive distillation using a mixed liquid of N-methyl-2-pyrrolidone and water, usually,
A mixed solvent of N-methyl-2-pyrrolidone and water may be prepared in advance and this may be supplied to the distillation column.
Although 2-pyrrolidone and water may be separately supplied to the distillation column, the amount of water present relative to N-methyl-2-pyrrolidone is usually 0.1% by weight to the limit of dissolution, preferably 0.3 to 10% by weight, particularly preferably 0.5-5% by weight
It is. The main modes for separating cyclohexene by extractive distillation of a mixture containing cyclohexene and at least one of cyclohexane or benzene are as follows:
Can be considered.

A mixture of cyclohexene and cyclohexane is subjected to extractive distillation in the presence of N-methyl-2-pyrrolidone and water. Cyclohexane and water are distilled off from the top of the tower. It is preferable that the distillate is condensed and then separated into oil and water, all of the water is totally refluxed and returned from the top of the column into the column, and cyclohexane is returned at a predetermined reflux ratio and withdrawn. In this case, water is extracted from the column bottom together with cyclohexene and N-methyl-2-pyrrolidone. The extracted liquid is usually subjected to distillation, cyclohexene and water are distilled from the top of the column, the distillate is condensed, oil-water separation is performed, and the entire amount of water is returned to the top of the column. It is returned in a ratio and extracted and separated. And
N-methyl-2-pyrrolidone and water are discharged from the bottom of the column. The water after the oil-water separation of the withdrawal liquid may be returned from the top of the column to the inside of the column as described above, but may not be returned to the inside of the column, in which case N-methyl-2-pyrrolidone is withdrawn from the bottom of the column. The water after the oil-water separation can be reused as an extractant.

The mixture of cyclohexene and benzene is subjected to extractive distillation in the presence of N-methyl-2-pyrrolidone and water. Cyclohexene and water are distilled off from the top of the tower. A method is preferred in which the distillate is condensed and then oil-water separation is carried out, all of the water is completely refluxed and returned to the inside of the tower from the top of the tower, and cyclohexene is returned at a predetermined reflux ratio and withdrawn. In this case, water is extracted from the bottom of the column together with benzene and N-methyl-2-pyrrolidone. Further, the extracted liquid is usually subjected to distillation, benzene and water are distilled from the top of the column, the distillate is condensed, and then oil-water separation is carried out.
The water after oil-water separation may be returned to the inside of the tower, or may be reused as a solvent without returning it.

A first extractive distillation is carried out on a mixture of cyclohexene, cyclohexane and benzene in the presence of N-methyl-2-pyrrolidone and water. Cyclohexene, cyclohexane and water are distilled off from the top of the column. It is preferable that the distillate is condensed and then separated into oil and water, and then all of the water is completely refluxed and returned to the inside of the tower from the top of the tower, and cyclohexene and cyclohexane are returned at a predetermined reflux ratio and withdrawn. In this case, benzene and N-methyl-
Water is extracted with 2-pyrrolidone. The cyclohexane and cyclohexene extracted from the top of the column were subjected to a second extractive distillation in the presence of N-methyl-2-pyrrolidone and water, the cyclohexane and water were distilled off from the top of the column, and the distillate was condensed. After that, oil-water separation is performed, all the water is returned from the top of the tower to the inside of the tower, and cyclohexane is returned at a predetermined reflux ratio and withdrawn. In this case, water is extracted from the bottom of the column together with cyclohexene and N-methyl-2-pyrrolidone. The extracted liquid is usually subjected to distillation,
Cyclohexene and water are distilled from the top of the column, the distillate is condensed, and then oil-water separation is performed, and all the water is returned from the top to the inside of the column, and cyclohexene is returned at a predetermined reflux ratio and withdrawn and separated. . And from the bottom of the tower, N-methyl-
Withdraw 2-pyrrolidone and water. The water after the oil-water separation of the extracted liquid may be returned from the top of the tower to the inside of the tower as described above, but may not be returned to the inside of the tower.
-Withdraw methyl-2-pyrrolidone. The water after the oil-water separation can be reused as an extractant.

A mixture of cyclohexene, cyclohexane and benzene is subjected to a first extractive distillation in the presence of N-methyl-2-pyrrolidone and water. Cyclohexane and water are distilled off from the top of the column. After condensing the distillate,
A method is preferred in which oil-water separation is carried out, all of the water is completely refluxed and returned into the tower from the top of the tower, and cyclohexane is returned at a predetermined reflux ratio and withdrawn. In this case, water is extracted together with cyclohexene, benzene and N-methyl-2-pyrrolidone from the bottom of the column. The extracted liquid is distilled (second extractive distillation) to distill cyclohexene and water from the top of the column, the distillate is condensed, oil-water separation is performed, and the entire amount of water is returned to the top of the column to remove cyclohexene. It is advisable to return at a predetermined reflux ratio and withdraw and separate. In this case, water is extracted together with benzene and N-methyl-2-pyrrolidone from the bottom of the column. Further, the extracted liquid is usually subjected to distillation, benzene and water are distilled from the top of the column, the distillate is condensed, and then oil-water separation is carried out.The water after the oil-water separation may be returned to the inside of the tower or returned. Instead, it may be reused as an extractant.

In the extractive distillation, water is distilled from the top of the column to form an azeotrope with the top component, and this can be withdrawn. However, in order to eliminate the need for new water for N-methyl-2-pyrrolidone extracted from the bottom of the column and to prevent water from being mixed into the components at the top of the column, the distillation from the top of the column is performed as described above. It is preferable to condense the water to be discharged and the tower top component, separate the condensate into oil and water, and totally reflux the water to extractive distillation, thereby extracting water from the tower bottom together with N-methyl-2-pyrrolidone and the like. N
-When separating methyl-2-pyrrolidone from water and cyclohexene or benzene, the water after oil-water separation may be returned to the inside of the tower from the top of the tower, or may be reused as an extractant without returning to the inside of the tower. Good.

When carrying out the extractive distillation in the above-mentioned (1) to (3), a distillation column having a theoretical plate number of usually 15 or more, preferably 20 or more is used. Usually, a mixed solvent of N-methyl-2-pyrrolidone as a solvent and water is supplied to the upper side of the distillation column, and the mixture is supplied to the lower side of the middle stage of the distillation column. In all cases, the amount of extractant used is usually equal to or more than the amount of the mixture, and the column top pressure is usually 0.02 to 0.3 MPa.
It is. Furthermore, the reflux ratio is not particularly limited, but for example, in the case of a mixture of cyclohexane and cyclohexene, the reflux ratio is usually 2 to 10, preferably about 3 to 6. In the second extractive distillation, the mixed solution of N-methyl-2-pyrrolidone, which is the extractant, and water is already contained in the mixed solution used in the distillation step, but the composition of the separated components is Depending on the amount and amount, a mixed solvent of N-methyl-2-pyrrolidone and water may be additionally added for distillation.

In any process for obtaining cyclohexene, water may distill overhead, but it is necessary to eliminate the need for new additions of water and the outflow of water-soluble components. From the above, the water distilled from the top of the tower is totally refluxed after separating it from other components in oily water,
It is preferably withdrawn from the bottom of the column together with N-methyl-2-pyrrolidone. Next, a more specific embodiment of the present invention will be described with reference to the drawings, particularly regarding a method for separating and obtaining cyclohexene from a mixture containing three kinds of cyclohexene, cyclohexene, and benzene.

FIG. 1 shows the above-described method of first separating benzene and then cyclohexane and cyclocyclohexane from a mixture of cyclohexene, benzene and cyclohexane. In FIG. 1, a mixture containing three kinds of cyclohexene, cyclohexane and benzene is sent from a line 1 to a distillation column D1 and N-methyl-
A mixed solvent of 2-pyrrolidone and water is sent from line 2 to distillation column D1. In the distillation column D1, extractive distillation is performed, and cyclohexene, cyclohexane and water are extracted from the top of the column through line 3, condensed in a condenser, and then separated into a mixture of cyclohexene and cyclohexane in an oil-water separator and water, The total amount of this internal water is returned to the distillation column D1. A part of the mixture of cyclohexene and cyclohexane is returned to the distillation column D1 at a predetermined reflux ratio, and the rest is sent from the line 12 to the distillation column D3. A mixture of benzene, N-methyl-2-pyrrolidone and water is extracted from the bottom of the distillation column D1 through a line 4 and sent to the distillation column D2.

In the distillation column D2, benzene and N-methyl-2 are used.
-Pyrrolidone and water are separated by distillation, benzene and water are extracted from the top of the column through line 5, condensed by a condenser, and then separated into benzene and water by an oil-water separator, and the internal water is totally distilled column. Returned to D2. A part of benzene is returned to the distillation column D2 at a predetermined reflux ratio, and the rest is extracted from the line 13. N-methyl-2-pyrrolidone and water are extracted from the bottom of the column through line 6. On the other hand, a mixture of cyclohexene and cyclohexane is supplied to the distillation column D3 through a line 12, and a mixed solvent of N-methyl-2-pyrrolidone and water is supplied through a line 7 to perform extractive distillation. Cyclohexane and water are extracted from the top of the column through line 8, condensed in a condenser, and then separated into cyclohexane and water by an oil / water separator, and the internal water is returned to the total distillation column D3. A part of cyclohexane is returned to the distillation column D3 at a predetermined reflux ratio, and the rest is withdrawn from the line 14. Cyclohexene, N-methyl-2-pyrrolidone and water are extracted from the bottom of the column and sent to the distillation column D4 through line 9.

In the distillation column D4, cyclohexene, N-methyl-2-pyrrolidone and water are separated by distillation, cyclohexene and water are extracted from the top of the column through line 10, condensed in a condenser, and then separated in an oil / water separator. It is separated into cyclohexene and water, and the total amount of this internal water is returned to the distillation column D4. Part of cyclohexene is returned to the distillation column D4 at a predetermined reflux ratio, and the rest is withdrawn from the line 15. N-methyl-2-pyrrolidone and water are withdrawn from the bottom of the column through line 11. FIG.
Show the above method of first removing cyclohexane and then separating cyclohexene and benzene from a mixture containing cyclohexene, benzene and cyclohexane. In FIG. 2, a mixture of cyclohexene, benzene and cyclohexane is sent to the distillation column D1 through the line 1, and a mixed solvent of N-methyl-2-pyrrolidone and water is sent to the distillation column D1 through the line 2.

In the distillation column D1, extractive distillation is performed, cyclohexane and water are extracted from the top of the column through line 3, condensed in a condenser, and then separated into cyclohexane and water in an oil / water separator. All water is distillation column D
Returned to 1. A part of cyclohexane is returned to the distillation column D1 at a predetermined reflux ratio, and the rest is supplied to the line 1
Extracted from zero. Benzene, cyclohexene, N-methyl-2-pyrrolidone and water are extracted from the bottom of the column through line 4, and the mixture is supplied to the distillation column D-2. A mixed solvent of N-methyl-2-pyrrolidone and water is also supplied from the line 5 to the distillation column D2. Extractive distillation is also performed in the distillation column D2, and cyclohexene and water are extracted from the top of the column through line 6, condensed in a condenser, and then separated into cyclohexene and water in an oil-water separator, of which water is the entire amount. It is returned to the distillation column D2. Part of cyclohexene is returned to the distillation column D2 at a predetermined reflux ratio, and the rest is withdrawn from the line 11. Benzene, N-methyl-2-pyrrolidone and water are extracted from the bottom of the column through line 7 and supplied to the distillation column D3.

In the distillation column D3, benzene and N-methyl-
2-Pyrrolidone and water are separated by distillation, benzene and water are extracted from the tower top through line 8, condensed in a condenser, and then separated into benzene and water in an oil-water separator, and the total amount of this internal water is distilled. Returned to Tower D3. A part of benzene is returned to the distillation column D3 at a predetermined reflux ratio, and the rest is withdrawn from the line 12. N-methyl-2-pyrrolidone and water are withdrawn through the line 9 from the bottom of the column.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the following, “parts” means “parts by weight”.

Examples 1 to 6 Static simulator software ASPE manufactured by ASPENTEC
A distillation simulation using N was performed. (Note that the simulation physical property model was calculated by three-phase distillation using a modified UNIFAC.) At the 14th stage from the top of the distillation column having 18 theoretical plates, cyclohexane 3000 parts / hr and cyclohexene 3000 parts / hr were heated to 80 ° C. It is introduced at 1 atm, and the mixed solvent of N-methyl-2-pyrrolidone and water is 30,000 parts / Hr (including water 500
Part) is introduced at 80 ° C. and 1 atm, the reflux ratio is changed as shown in Table 1, and the extractive distillation is performed at a column top pressure of 0.1 MPa. At this time, cyclohexane and water distilled from the top of the column are separated into oil and water, of which water is returned to the fourth stage from the total amount. As a result, cyclohexane having the purity shown in Table 1 was 3
000 parts / hr, and cyclohexene and N
A mixture of methyl-2-pyrrolidone and water is obtained.
Since cyclohexene can be easily separated from N-methyl-2-pyrrolidone and water, higher purity of cyclohexane means that higher purity of cyclohexene can be obtained.

Comparative Examples 1 to 5 Static simulator software ASPE manufactured by ASPENTEC
A distillation simulation using N was performed. (The simulation physical property model was calculated as a homogeneous system by modified UNIFAC.) As an extractant, only N-methyl-2-pyrrolidone was used instead of the mixed solvent of N-methyl-2-pyrrolidone and water ( Extractive distillation is performed in the same manner as in Example 1 except that 30,000 parts / Hr) is used and only cyclohexane is taken out from the top of the column. Table 1 shows the results.

[0022]

[Table 1]

Examples 7 to 15 Extractive distillation is conducted in the same manner as in Example 1 except that the reflux ratio is 3 and the flow rate of water in the mixed solvent is the amount shown in Table 2. Table 2 shows the results.

[0024]

[Table 2]

[0025]

INDUSTRIAL APPLICABILITY According to the present invention, highly pure cyclohexene can be efficiently obtained from a mixture containing cyclohexene and at least one of cyclohexane and benzene. Since N-methyl-2-pyrrolidone and water used in the extractive distillation of the present invention are chemically stable compounds and are also relatively inexpensive, when industrially producing high-purity cyclohexene for a long period of time, The present invention can be expected as an extremely advantageous method.

[Brief description of the drawings]

FIG. 1 is a flow chart showing an example of an embodiment of the invention according to claim 4;

FIG. 2 is a flow chart showing an example of an embodiment of the invention according to claim 5;

Claims (8)

[Claims] 1. A method for separating cyclohexene from a mixture containing cyclohexene and at least one of cyclohexane or benzene to obtain a cyclohexene-rich component by distillation, wherein N-methyl- is used as a solvent for extractive distillation.
A method for separating cyclohexene, which comprises using a mixed solution of 2-pyrrolidone and water. 2. A mixture of cyclohexene and cyclohexane is subjected to extractive distillation using a mixed solution of N-methyl-2-pyrrolidone and water to distill cyclohexane from the top of the column and cyclohexene and N-methyl from the bottom of the column. The method for separating cyclohexene according to claim 1, wherein 2-pyrrolidone is extracted and cyclohexene is separated from the extracted liquid. 3. A mixture of cyclohexene and benzene is subjected to extractive distillation using a mixed solution of N-methyl-2-pyrrolidone and water, and cyclohexene is distilled from the top of the column.
The method for separating cyclohexene according to claim 1, wherein benzene and N-methyl-2-pyrrolidone are extracted from the bottom of the column. 4. A mixture of cyclohexene, cyclohexane and benzene is subjected to a first extractive distillation using a mixed liquid of N-methyl-2-pyrrolidone and water to remove benzene and N-methyl-2-pyrrolidone from the bottom of the column. Cyclohexene and cyclohexane were distilled out from the top of the column, and the distillate was subjected to a second extractive distillation using a mixed liquid of N-methyl-2-pyrrolidone and water to distill cyclohexane from the top of the column. , From the bottom of the column cyclohexene and N-methyl-
The method for separating cyclohexene according to claim 1, wherein 2-pyrrolidone is extracted and cyclohexene is separated from the extracted liquid. 5. A mixture of cyclohexene, cyclohexane and benzene is subjected to extractive distillation using a mixed solution of N-methyl-2-pyrrolidone and water, cyclohexane is distilled from the top of the column, and cyclohexene, benzene and Withdrawing N-methyl-2-pyrrolidone, distilling the withdrawn liquid to distill cyclohexene from the top of the column,
The method for separating cyclohexene according to claim 1, wherein benzene and N-methyl-2-pyrrolidone are extracted from the bottom of the column. 6. The method for separating cyclohexene according to claim 2, wherein water is extracted from the bottom of the column in the extractive distillation. 7. The method for separating cyclohexene according to claim 2, wherein water is distilled from the top of the column in the extractive distillation. 8. The method for separating cyclohexene according to claim 2, wherein in the extractive distillation, the distillate of water from the top of the column is totally refluxed and water is extracted from the bottom of the column.