JPS6021146B2 - Separation method of ε-caprolactam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating go-caprolactam from a reaction product solution obtained by Beckman rearrangement of cyclohexanone oxime in the presence of sulfuric acid.

Conventionally, in order to separate go-caprolactam from the Beckmann rearrangement reaction product solution, the reaction product solution was neutralized with an alkali such as ammonia, sulfuric acid was converted to ammonium sulfate, and the binding force between go-caprolactam and sulfuric acid was reduced. After that, caprolactam was extracted using an organic solvent such as benzene.

However, in this method, sulfuric acid is constantly consumed and ammonium sulfate is produced, but it is industrially difficult to regenerate and recover sulfuric acid from ammonium sulfate, and ammonium sulfate has extremely low market value.
This cannot be said to be an industrially advantageous method. So in recent years,
In order to improve these drawbacks, a method has been proposed in which the Beckmann rearrangement reaction product solution is diluted with water without being neutralized, and then go-caprolactam is extracted with an acidic organic solvent mainly containing phenol.

The method has the advantage that z-caprolactam can be recovered at a high extraction rate, and that by concentrating the raffinate, sulfuric acid that can be recycled as a Beckman rearrangement agent can be obtained.

However, it is difficult to further separate go-caprolactam from a solution of go-caprolactam and an acidic organic solvent containing phenol after extraction using normal distillation operations, so it has not yet been carried out industrially. be.

The present inventors have discovered a method for separating do-caprolactam by hydrogenating a solution of do-caprolactam in the acidic organic solvent, and have arrived at the present invention.

That is, the present invention extracts caprolactam from a reaction product obtained by rearranging cyclohexanone oxime in the presence of sulfuric acid using phenol alone or a mixed solvent of phenol and a hydrocarbon, a halogenated hydrocarbon, or an alkyl ether. The solution is distilled, the solvent is distilled off to obtain a phenol-go-caprolactam solution with a phenol content of 3 t% or less, and then only phenol is hydrogenated from the solution in the presence of a hydrogenation catalyst. This article relates to the characteristic separation method of docaprolactam.

When carrying out the method of the present invention, the reaction product liquid obtained by the Beckmann rearrangement of cyclohexanone oxime in the presence of sulfuric acid is diluted with water, and phenol is used as a sole solvent, or phenol and a hydrocarbon, halogenated hydrocarbon, or alkyl ether are used. and extract the caprolactam into the acidic organic solvent layer.

When the above-mentioned mixed solvent is used, caprolactam can be extracted in an extremely short time compared to when a single solvent is used, and the amount of sulfuric acid transferred to the solvent layer is small. It has the advantage that the amount of migration is small.

Examples of hydrocarbons include benzene, toluene, xylene, cyclohexane, methylcyclohexane, and ethylbenzene; examples of halogenated hydrocarbons include chloroform, carbon tetrachloride, ethylene chloride, ethane trichloride, and ethylidene chloride; and examples of alkyl ethers include dichloroethylidene. Examples include propyl ether and dibutyl ether.
The composition of the solution obtained when the caprolactam contained in the Beckmann rearrangement reaction product solution is sufficiently extracted is usually 10 to 30% by weight of caprolactam and 70 to 9% by weight of the acidic organic solvent. . When the extraction solution is distilled under reduced pressure, part of the phenol is distilled out when a single solvent is used, but when a mixed solvent is used, all of the hydrocarbons, halogenated hydrocarbons, and alkyl ethers are distilled out. Next, some of the phenol is expelled. However, when the phenol content is less than 3%, especially less than 2.9%, phenol and caprolactam form an adduct, and it is not possible to easily separate the two by simple distillation. become unable. Therefore, even if a phenol sole solvent or a mixed solvent containing phenol is used, a phenol-caprolactam solution with a phenol content of 3% or less can be finally obtained by distillation. The phenol, hydrocarbon, halogenated hydrocarbon, and alkyl ether extracted by this distillation operation can be recycled and used again in the step of extracting docaprolactam from the Beckmann rearrangement reaction product liquid. Next, in the phenol-caprolactam solution having a phenol content of 3 t% or less, only phenol is hydrogenated in the presence of a hydrogenation catalyst to obtain a cyclohexanol-caprolactam solution, which is distilled. Go-caprolactam is separated and obtained by known means such as crystallization.

As the hydrogenation catalyst, reduced nickel, nickel oxide, a nickel catalyst prepared by adding an oxide such as copper, manganese, chromium, or molybdenum to each of the above two, or a palladium catalyst is used.

The hydrogenation reaction is generally carried out at a temperature of 70 to 200°C under hydrogen pressure.

No specific solvent is required, but water and saturated hydrocarbons and alcohols such as methanol, cyclohexane, cyclohexanol, and the like can be used. Through this reaction, only phenol is selectively converted to cyclohexanol while the go-caprolactam is hardly affected, and a cyclohexanol-go-caprolactam solution is formed. From the above-mentioned cyclohexanol-caprolactam solution, caprolactam can be easily separated and obtained by normal operations, and one of the cyclohexanol-caprolactam solutions can be easily separated and obtained.

Hexanol can also be recovered as a raw material for caprolactam. For example, if a cyclohexanol-caprolactam solution is distilled under reduced pressure at 7,000 mph over 700 days, the cyclohexanol content will be 1.00 μl.
Caprolactam is obtained, which is further distilled to obtain caprolactam which does not contain any cyclohexanol. Furthermore, when the hydrogenation reaction is carried out in a solvent, do-caprolactam can be crystallized simply by cooling the reaction product liquid. As described above, by carrying out the method of the present invention, go-caprolactam can be separated from the reaction product liquid obtained by Beckman rearrangement of cyclohexanone oxime in the presence of sulfuric acid without producing ammonium sulfate as a by-product.

Example 1 100 ml of Beckmann rearrangement reaction product liquid (containing 42 ml of caprolactam and 57 ml of sulfuric acid) was collected, 57 ml of water was added, and then mixed with a benzene-phenol (weight ratio 20:80) mixed solvent of 150 ml. Extracted three times.

After washing the extract with water to remove most of the sulfuric acid, the remaining sulfuric acid was neutralized with ammonia. Add the extract to 300 ml, 50 ml
Distillation was carried out under reduced pressure at ~70 qo, and further distillation was performed under reduced pressure at 720 qo on a day after 1 day. Distillation was stopped when 350 qo of phenol was distilled out. The residual liquid at that time consisted of 8.5 parts of phenol and 40.5 parts of caprolactam (phenol content: 17 wt%). This residual liquid was dissolved in 200 g of cyclohexane, charged into an autoclave having an internal volume of 100 g, and 4 tons of Raney nickel catalyst was added thereto. After pressurizing to 5 atmospheres with hydrogen, the hydrogenation reaction was carried out by overflowing to 14,000 degrees over 3 hours. When the reaction product liquid was analyzed by gas chromatography, the presence of phenol was not observed, and it was confirmed that the entire amount was converted to cyclohexanol. The reaction product solution was distilled under normal pressure to remove cyclohexane, and then on the evening of the 15th, vacuum distillation was performed using a 7030 to extract cyclohexanol. Add 1.5 liters of caustic soda to the residue, distill under reduced pressure at 2.5 liters of water and 113 qo, cut off 1 t% of the front distillate and 1 t% of the after-distillate, respectively. I got some prolactam for 32 days. When we performed this quality analysis, the PZ value was 3600 or more, and the UV value was 9.
It was 8.0% high purity do-caprolactam. Example 2 Beckmann rearrangement reaction product liquid 1 was prepared in the same manner as in Example 1.
The solution was extracted with a benzene-phenol mixed solvent, washed with water, neutralized to remove sulfuric acid, and then benzene and phenol were distilled off to obtain a caprolactum solution containing 2% phenol.

Claims (1)

[Claims] 1 Distill a solution in which ε-caprolactam is extracted from the reaction product solution obtained by Beckmann rearrangement of cyclohexanone oxime in the presence of sulfuric acid using phenol alone or a mixed solvent of phenol and a hydrocarbon, a halogenated hydrocarbon, or an alkyl ether. ε-caprolactam, characterized in that the solvent is distilled off to obtain a phenol-ε-caprolactam solution having a phenol content of 30 wt% or less, and then only phenol is hydrogenated to the solution in the presence of a hydrogenation catalyst. separation method.