JPH0649660B2 - Cyclohexane purification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying cyclohexane, and more specifically, in collecting high-purity cyclohexane required for industrial use of cyclohexane, methylcyclopentenes are particularly preferably used. The present invention relates to a method for purifying contained crude cyclohexane.

(Prior Art) Cyclohexane is an important industrial intermediate raw material and is produced by hydrogenation of benzene. The purity required for the product cyclohexane is extremely high, and in the hydrogenation of benzene, the amount of unreacted ene is reduced and other side reaction products such as cyclic methyl compounds are kept low. Is normal. Such a method for producing cyclohexane by simple hydrogenation of benzene has high industrial perfection, and since the process and reaction are simple,
Olefins are rarely mixed or left in the product cyclohexane. The technique intended by the present invention is a new technique applied to the following cases, for example, unlike the one related to the conventional simple method for producing cyclohexane.

Most of the industrial uses of cyclohexane are for obtaining a cyclohexanone / cyclohexanol mixture (hereinafter abbreviated as “olone”) by an oxidation reaction. However, recently, a method for obtaining cyclohexanol of pure water instead of olone is disclosed in, for example, JP-A-63-15673.
No. 6, Japanese Patent Publication No. 1-33453, etc. These methods involve partial hydrogenation of benzene to obtain a mixture of cyclohexene and cyclohexane, of which cyclohexene is hydrated in the presence of an acid catalyst to obtain cyclohexanol. Is technically completely different from and has high industrial value. However, on the other hand, it is known that in the hydration reaction of cyclohexene with an acid catalyst, methylcyclopentene, which is an isomer of cyclohexene, is produced as a by-product in addition to cyclohexanol (for example, Japanese Patent Publication No. 1-33453). Gazette). It was revealed in another study by the present inventors that it is optimal for the cyclohexanol production process to finally take out this methylcyclopentene together with cyclohexane which is another product of the partial hydrogenation reaction. ing. Here, crude cyclohexane containing methylcyclopentene, which is not available in the past, can be obtained, but as described above, the industrially required purity of cyclohexane is high, and a new technique for purifying the crude cyclohexane is required. .

Although an example of crude cyclohexane containing methylcyclopentenes has been shown above, the range to which the method of the present invention can be applied is naturally not limited to this example.

(Problems to be Solved by the Invention) Conventionally, crude cyclohexane containing, for example, several thousand ppm or more of methylcyclopentene is completely different from that obtained by the conventional hydrogenation reaction of benzene, and therefore its purification method is also known. Has not been done. For example, when it is attempted to separate methylcyclopentenes from the crude cyclohexane by a simple distillation operation, the relative volatility of cyclohexane and methylcyclopentenes is extremely close to 1, which is practically impossible. Separation by extractive distillation is also conceivable, but the specific volatility is still low, and a new component called an extraction solvent is required, so it cannot be said to be an industrially valuable method.

That is, a more simple and effective method for purifying the crude cyclohexane is strongly desired.

(Means for Solving the Problem) The inventors of the present invention have earnestly studied a method for simply and reliably purifying crude cyclohexane containing such methylcyclopentenes, and as a result, hydrogenated methylcyclopentenes to obtain methylcyclopentenes. It was concluded that the method of making pentane and then purifying by distillation is the most suitable means, and completed the present invention.

That is, the present invention, when collecting high-purity cyclohexane from crude cyclohexane containing methylcyclopentenes, the crude cyclohexane is hydrotreated in the presence of a catalyst to give methylcyclopentenes as methylcyclopentane, and then A method for purifying cyclohexane, characterized in that methylcyclopentane is separated and removed from the top of the column by distillation.

Hereinafter, specific embodiments of the present invention will be described.

The crude cyclohexane to be purified by the method of the present invention mainly contains methylcyclopentenes as impurities. Here, the methylcyclopentenes are
It refers to 1-methylcyclopentene, 3-methylcyclopentene and 4-methylcyclopentene, especially 1-methylcyclopentene and 3-methylcyclopentene.
The content of methylcyclopentenes is 0.01 to several tens% as a weight fraction in the crude cyclohexane. In addition to the methylcyclopentenes, other impurities such as benzene and cyclohexene, and hydrocarbons having 1 to 6 carbon atoms may be contained in the crude cyclohexane. This is because benzene and cyclohexene can be converted to cyclohexane by the hydrogenation treatment described later, while hydrocarbons having 1 to 6 carbon atoms can be easily removed from the top of the column by the distillation operation in the method of the present invention.

The hydrotreatment of crude cyclohexane can be carried out in the gas phase or the liquid phase in the presence of a catalyst. As a catalyst,
Ordinary olefin hydrogenation catalysts and aromatic hydrocarbon hydrogenation catalysts may be used. Specifically, Ni catalysts, Pt, Pd, Ru
Noble metal catalysts such as, and Ni catalysts are preferable from an economical point of view. The hydrogenation condition depends on the content of impurities, but is usually room temperature to 300 ° C., preferably 50.
To 200 ° C., 1 to 100 atm, preferably 5 to 50 atm hydrogen pressure range. The reaction system is not particularly limited, but a fixed bed type so-called trickle bed type reaction method can be preferably used. By such a hydrotreatment, almost all of the methylcyclopentenes in the crude cyclohexane can be converted into methylcyclopentane.

Cyclohexane containing methylcyclopentane is then purified to high purity cyclohexane by distillation. The distillation operation can be carried out under normal pressure, or under reduced pressure or under increased pressure, and may be appropriately selected. By this distillation, a distillate rich in methylcyclopentane can be removed from the top of the column, and cyclohexane of extremely high purity can be collected from the bottom of the column. Even if the crude cyclohexane contains hydrocarbons having 1 to 6 carbon atoms other than cyclohexane and methylcyclopentenes, it can be easily removed from the top of the column together with methylcyclopentane by this distillation operation.

The purity of cyclohexane obtained by the method of the present invention as described above is sufficiently higher than the industrially required purity, specifically, 99% or higher, or 99.5% or higher,
Furthermore, 99.9% or more of cyclohexane can be obtained.

(Effects of the Invention) Crude cyclohexane containing methylcyclopentenes can be purified by the method of the present invention to obtain cyclohexane of extremely high purity, and its industrial value is high.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example <Hydrogenation treatment of crude cyclohexane> 93.0% by weight of cyclohexane, 4.5% by weight of methylcyclopentenes, 2.0% by weight of cyclohexene as other impurities, 0.5% by weight of saturated hydrocarbon having 4 to 6 carbon atoms % Of crude cyclohexane was supplied to the hydrotreating apparatus at 1.0 kg / Hr, and the hydrotreatment of crude cyclohexane was continuously performed. The hydrotreating apparatus was filled with 500 g of a Ni catalyst (G-33 manufactured by Nissan Gardler Co., Ltd.) as a hydrogenation catalyst, and the hydrogenation was performed under a hydrogen pressure of 50 atm while controlling the inlet temperature to 120 ° C. After the treatment, the liquid was continuously taken out and the composition thereof was analyzed to find that it was 94.9% by weight of cyclohexane, 4.6% by weight of methylcyclopentane, and 0.5% by weight of a saturated hydrocarbon having 4 to 6 carbon atoms. Methylcyclopentenes and cyclohexene were 0.01% by weight or less and were hardly detected.

<Acquisition of High-Purity Cyclohexane by Distillation> The liquid that has undergone the above-mentioned hydrogenation treatment is concentrated in 20 stages and in a recovery unit
Continuously feeding 1.0 kg / Hr to a distillation column having 0 stages,
Cyclohexane was purified. The reflux ratio is 40,
The distillate was continuously withdrawn at about 0.09 kg / hr from the top of the column, and its composition was analyzed.
The content was 7% by weight, methylcyclopentane 49.9% by weight, and saturated hydrocarbon having 4 to 6 carbon atoms 5.4% by weight. At this time, the composition of the liquid continuously collected from the bottom of the column was 99.97% by weight of cyclohexane and 0.0% of methylcyclopentane.
It was 3% by weight, and cyclohexane having an extremely high purity could be obtained.

Comparative Example The same crude cyclohexane as in Example was subjected to distillation operation in the same manner as in Example without performing hydrogenation treatment. The purity of cyclohexane continuously collected from the bottom of the column is similar to that of crude cyclohexane. Although saturated hydrocarbons having 4 to 6 carbon atoms are removed at the top of the column, methylcyclopentenes are hardly reduced, and purification of crude cyclohexane is performed. I couldn't.

Claims (1)

[Claims] 1. When collecting high-purity cyclohexane from crude cyclohexane containing methylcyclopentenes, the crude cyclohexane is hydrotreated in the presence of a catalyst to convert methylcyclopentenes to methylcyclopentane, and then distilled. A method for purifying cyclohexane, characterized in that methylcyclopentane is separated and removed from the top of the column by.