JP2500977B2 - Method for producing cyclohexanone - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a process for treating an oxidation reaction mixture containing cyclohexanol and cyclohexanone obtained by oxidation of cyclohexane.

[0002]

It is known to prepare cyclohexane with molecular oxygen in the presence of a boric acid compound or a cobalt catalyst and the like containing a mixture containing cyclohexanol and cyclohexanone. In this method, many by-products are produced in addition to the desired product. The by-products include carboxylic acids, alcohols, aldehydes, ketones, ethers, esters and hydrocarbons.
Of these, water-soluble carboxylic acids and lower alcohols can be removed by water extraction, and carboxylic acids and esters can also be saponified and removed in an alkaline aqueous solution. And most of the remaining by-products can be removed by the distillation process.

Further, cyclohexanone (boiling point: 156.5 ° C.) and cyclohexanol (boiling point: 161.0 ° C.), which are difficult to separate even in the above steps, and components very close to the boiling point, such as butylcyclohexyl ether, n-pentylcyclohexane. It is possible to remove most of cyclohexyl acetate, hexahydrobenzaldehyde and the like by adopting a specific distillation step (Japanese Patent Application No. 2-91639).

[0004]

However, it is difficult to completely remove impurities having a boiling point close to that of cyclohexanone or cyclohexanol even by the method of Japanese Patent Application No. 2-91639 described above, and a trace amount in cyclohexanone products is present. The inclusion of impurities was unavoidable.

[0005]

Cyclohexanone is industrially general as a raw material for producing caprolactam. That is, after reacting cyclohexanone with hydroxylamine to convert into cyclohexanone oxime,
Caprolactam is produced through the Beckmann rearrangement reaction.

The present inventors have conducted many years of research on the production process from cyclohexane to caprolactam, but hexahydrobenzaldehyde, which is one of the trace impurities in cyclohexanone, remains in the subsequent reaction step, It has been found that hexahydrobenzamide is formed during the Beckmann rearrangement, and the compound is one of the factors that deteriorate the quality of the product caprolactam. Specifically, the amount of volatile base in the product caprolactam (VB
It has been confirmed that the amount) increases due to the remaining hexahydrobenzamide, and affects the appearance, strength, etc. of the fiber product made from caprolactam. Therefore, as a result of extensive studies on means for sufficiently removing hexahydrobenzaldehyde in cyclohexanone, it was found that hexahydrobenzaldehyde in a reaction mixture containing cyclohexanol and cyclohexane can be removed by a specific alkali treatment, and the present invention was reached. .

That is, according to the present invention, a step of mixing an oxidation reaction mixture containing cyclohexanol and cyclohexanone obtained by the oxidation of cyclohexanone with an aqueous alkali solution and subjecting the mixture to a primary alkali treatment, the mixture treated with the primary alkali to an oil phase And a water phase, a step of adding an alkali compound of 20 to 5000 ppm to the oil phase and subjecting the oil phase to a second alkali treatment at a temperature of 60 to 150 ° C., a second alkali treatment A process for producing cyclohexanone, which comprises treating each step of removing cyclohexane from the oil phase and distilling and separating cyclohexanone.

The present invention will be described in detail below. The oxidation reaction mixture containing cyclohexanol and cyclohexanone in the present invention is a mixture obtained by liquid phase oxidation of cyclohexane with molecular oxygen.
When the oxidation reaction is carried out in the presence of a boric acid compound,
It is a mixture obtained by hydrolyzing the mixture after completion of the oxidation reaction and then separating the aqueous phase containing the boric acid compound. The main components of this mixture are unreacted cyclohexane, the target products cyclohexanol and cyclohexanone, and by-products such as esters and carboxylic acids. The content ratio of these is usually 85 to 95% by weight of unreacted cyclohexane, 4 to 13% by weight of the target product, and 1 to 2% by weight of by-products.

As a first step, the above-mentioned oxidation reaction mixture containing cyclohexanol and cyclohexanone is mixed with an alkaline aqueous solution to carry out a primary alkaline treatment. By this step, impurities such as esters in the oxidation reaction mixture are saponified, and carboxylic acids and alkali salts are extracted and removed into an aqueous phase.

The alkali compound used in the alkaline aqueous solution is generally a caustic alkali such as caustic soda and caustic potash, but an alkali carbonate such as sodium carbonate and potassium carbonate may be used together. It is also possible to carry out a multi-step treatment in which the first step is a treatment with an alkali carbonate aqueous solution and the second step is a treatment with a caustic alkaline aqueous solution. The alkali concentration in the alkaline aqueous solution is usually 0.1 to 40% by weight,
It is preferably 1 to 30% by weight. The amount of the caustic aqueous solution used is usually 0.5 to 10 of the ester component in the oil phase.
It is selected in the range of double weight, preferably 1 to 5 weight. The conditions for the primary alkali treatment are usually 50 to 95 ° C., preferably 70 to 90 ° C. and usually 0.1.
~ 2 hours, preferably 0.2-0.5 hours. If the treatment temperature is low, the saponification reaction will be slow, and if the treatment temperature is high, a part of the target product, cyclohexanone, will be lost due to the condensation reaction.Therefore, the amount of by-products in the reaction mixture should be adjusted appropriately. It is desirable to select the conditions.

In the second step, the mixture subjected to the primary alkali treatment is separated into an oil phase and an aqueous phase. Since the alkaline component remains on the aqueous phase side and a little oil phase component is mixed in, the aqueous phase can be reused for the primary alkaline treatment in the first step. In addition, since some water-soluble impurities remain on the oil phase side, it is preferable to completely remove the water-soluble impurities by further mixing and washing the oil phase with pure water and separating the phases. When such water washing is carried out, the alkali concentration of the oil phase after liquid separation usually remains at several ppm or less.

In the third step, an alkali compound of 20 to 5000 ppm is added to the oil phase separated in the second step, and a secondary alkali treatment is carried out at a temperature of 60 to 150 ° C. By the secondary alkali treatment, hexahydrobenzaldehyde, which is a by-product that could not be sufficiently removed by the primary alkali treatment, is decomposed by a condensation reaction or the like, and as a result, hexahydrobenzaldehyde in cyclohexanone can be almost completely removed. .

As the method of the secondary alkali treatment, the same alkali compound as that used in the primary alkali treatment, as it is or in the form of a solution, is added to the oil phase and 20 times to the oil phase.
~ 5000 ppm, preferably 100-2000 ppm
At a concentration of 60 to 150 ° C., preferably 100 to
At 130 ° C, usually 0.2 to 4 hours, preferably 0.5 to
Heat treatment for 3 hours. If the temperature of the heat treatment or the alkali concentration is higher than the range, the yield decrease due to the condensation reaction of cyclohexanone becomes a problem, while if it is lower than the range, the progress of the decomposition of hexahydrobenzaldehyde is delayed, which is preferable. Absent.

The above-mentioned secondary alkali treatment may be carried out while distilling and separating unreacted cyclohexane contained in the oil phase. Specifically, the oil phase was introduced into the bottom of the distillation column, a predetermined amount of alkali compound was added, and the bottom temperature was adjusted to 60.
Set the condition in the range of ~ 150 ℃, cyclohexanone,
Cyclohexane having a lower boiling point and by-products having a lower boiling point may be distilled off from cyclohexanol. When such a method is adopted, the total amount of the alkali compounds to be added is an amount corresponding to 20 to 5000 ppm with respect to the oil phase before distillation. May be added in.

In the fourth step, distillation is carried out by a known method to remove cyclohexane and separate and collect cyclohexanone. As a distillation method, components such as unreacted cyclohexane having a lower boiling point than cyclohexanone are distilled off in the first distillation column, while the bottom liquid is supplied to the second distillation column for distillation. A general method is to distill out most of cyclohexanone in the second distillation column and separate and recover it. The bottom liquid of the second distillation column is supplied to the third distillation column and further distilled to distill cyclohexanol and the remaining cyclohexanone, and cyclohexanol in the distillate is dehydrogenated to give cyclohexanone. And can be circulated to the first distillation column.

The above operating conditions of the distillation column are all such that the column top pressure is 20 to 500 Torr, preferably the first and the second.
The pressure is sequentially reduced in the second and third order. The column top temperature is usually controlled in the range of 50 to 150 ° C. according to the column top pressure.

[0017]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the description of the examples as long as the gist thereof is not exceeded. Example 1 Cyclohexane was subjected to liquid-phase oxidation with molecular oxygen in the presence of boric acid, and then hydrolyzed to separate an aqueous phase, and the following composition was obtained (determined by gas chromatography).

[0018]

[Table 1] 100 parts / hr of the oxidation reaction mixture of Example 1 was mixed with 20 parts / hr of a 1.5 wt% aqueous sodium hydroxide solution, and the mixture was stirred at 85 ° C.
A mixing treatment was continuously performed at the temperature of 20 ° C. for an average residence time of 20 minutes, and then the treated mixture was allowed to stand and separate to separate into an oil phase and an aqueous phase. When the oil phase components recovered here were analyzed, they had the following composition.

[0019]

[Table 2]

After adding 200 ppm of caustic soda to the oil phase, it was supplied to the first distillation column to distill off cyclohexane (first distillation column conditions: column bottom temperature 120 ° C., column top temperature 60.
C., tower top pressure 400 Torr). At this time, the amount of hexahydrobenzaldehyde in the bottom liquid after distillation was 1 ppm.
It was below (below the detection limit). Then, the bottom liquid is
It was supplied to a distillation column, and purified cyclohexanone was distilled off and recovered from the top of the column. (Second distillation column conditions: column bottom temperature 110 ° C.,
Tower top temperature 70 ° C., tower top pressure 50 Torr).

Comparative Example 1 Example 1 except that no caustic soda was added in Example 1.
It carried out similarly to. 90 ppm of hexahydrobenzaldehyde was contained in the recovered cyclohexanone.

Reference Example Cyclohexanone obtained from Example 1 and Comparative Example 1 was reacted with hydroxylamine sulfate by a conventional method to convert into cyclohexanone oxime, which was then catalytically reacted with sulfuric acid to produce caprolactam by Beckmann rearrangement reaction. . The amount of volatile base (VB amount) in the obtained caprolactam product was 5 ppm when the cyclohexanone of Example 1 was used, and 15 ppm when the cyclohexanone of Comparative Example 1 was used. The amount of VB was quantified by the titration method.

[0023]

According to the method of the present invention, high-quality cyclohexanone containing a small amount of hexahydrobenzaldehyde, which is one of the impurities, can be obtained. The cyclohexanone is suitable as a raw material for producing high-quality caprolactam.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location // C07B 61/00 300 C07B 61/00 300 C07C 27/12 310 C07C 27/12 310 (72) Inventor Yu Kanda, No. 1 Shiroishi Kurosaki, Yawatanishi-ku, Kitakyushu, Fukuoka Prefecture Mitsubishi Kasei Co., Ltd. Kurosaki Plant (56) References Japanese Patent Publication No. 41-14906 (JP, B1)

Claims (1)

(57) [Claims] 1. A step of mixing an oxidation reaction mixture containing cyclohexanol and cyclohexanone obtained by the oxidation of cyclohexane with an aqueous alkali solution and subjecting the mixture to a primary alkali treatment, and the mixture treated with the primary alkali into an oil phase and an aqueous phase. A step of separating the liquid phase into the oil phase, a step of adding 20 to 5000 ppm of an alkali compound to the oil phase, and a step of performing a secondary alkali treatment at a temperature of 60 to 150 ° C., a cyclohexane from the oil phase subjected to the secondary alkali treatment Excluding
A step of removing cyclohexanone by distillation, and treating in each step of.