JPS6021145B2 - Recovery method of ε-caprolactam - Google Patents

Description

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

In order to recover caprolactam from the Beckmann rearrangement reaction product solution, the reaction product solution is neutralized with an alkali such as ammonia, sulfuric acid is converted to ammonium sulfate, and the bonding force between caprolactam and sulfuric acid is reduced. The method used was to reduce the size of the caprolactam and then extract it with 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 caprolactam is extracted with an acidic organic solvent mainly containing phenols. . The method has the advantage that cabrolactam can be recovered at a high extraction rate, and that by concentrating the raffinate, sulfuric acid that can be recycled as a Beckmann rearrangement agent can be obtained.

However, recovery of go-caprolactam from a solution of go-caprolactam and an acidic organic solvent containing phenols after extraction is difficult with normal distillation operations, so it has not yet been carried out industrially. It is.

The present inventors have discovered a method for recovering caprolactam by combining re-extraction and distillation operations from a solution of caprolactam in the acidic organic solvent, and have arrived at the present invention. That is, the present invention provides a reaction product solution obtained by Beckman rearrangement of cyclohexanone oxime in the presence of sulfuric acid, using a phenol alone solvent or a mixed solvent of phenols and hydrocarbons, halogenated hydrocarbons, or alkyl ethers. The caprolactam extracted solution is distilled to remove the solvent to obtain a phenol-caprolactam solution with a phenol content of 3% or less, and then the solution is diluted with a mixed solvent of alkyl ethers and water. The present invention relates to a method for recovering caprolactam, which is characterized by obtaining caprolactam by extracting it and distilling the aqueous layer.

When carrying out the method of the present invention, the reaction product liquid obtained by Beckmann rearrangement of cyclohexanone oxime in the presence of sulfuric acid is diluted with water, and phenols alone or phenols and hydrocarbons, halogenated carbonized Caprolactam is extracted into the acidic organic solvent layer by contacting with a mixed solvent containing hydrogen or alkyl cables.

The acidic organic solvent may be a phenol solvent alone or a mixed solvent containing phenols.

When a mixed solvent is used, do-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, and the amount of solvent transferred to the sulfuric acid layer is reduced. It has the advantage that the amount of migration is small. In addition to phenol, cresol, and xylenol, examples of phenols include phenols having substituents such as alkyl groups, halogen atoms, and nitro groups, cresols,
Examples include xylenol.

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; examples of alkyl ethers include Examples include dipropyl 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, the ratio is 10 to 3 t% of caprolactam and 70 to 9 t% of acidic organic solvent.

When the extraction solution is distilled under reduced pressure, some of the phenols are extracted when a single solvent is used, but when a mixed solvent is used, the total amount of hydrocarbons, halogenated hydrocarbons, and alkyl ethers is extracted. is extracted from the crab, and then some of the phenols are distilled out. However, when the phenol content is less than 3%, especially less than 2x%, the phenols and caprolactam form adducts and cannot be easily separated by simple distillation. It disappears. Therefore, even if a phenol solvent alone or a mixed solvent containing phenols is used, a phenol-caprolactam solution with a phenol content of 3% or less can be obtained by distillation. It should be noted that the phenols, hydrocarbons, halogenated hydrocarbons, and alkyl alcohols distilled out by this distillation operation can be recycled and used again in the step of extracting caprolactam from the Beckmann rearrangement reaction product liquid. Next, the phenol-caprolactam solution with a phenol content of 3x% or less is extracted with a mixed solvent of alkyl ethers and water, and the aqueous layer contains caprolactam and caprolactam.
Each phenol is transferred to the organic layer.

The amount of alkyl ethers to be used is preferably 2 to 2 digits, particularly 5 to 1 digits, of the amount of phenols contained in the solution, and the amount of water to be used is 0.0 to 1 digit of the amount of caprolactam contained in the solution. 5 to 2 times, particularly 0.5 to 1 time is preferred.

Examples of alkyl ethers include ethyl butyl ether,
Examples include ethylpropyl ether, ethyl amyl ether, dipropyl ether, dibutyl ether, and diamyl ether. In addition to alkyl ethers, hydrocarbons such as benzene, toluene, chloroform, or halogenated hydrocarbons may be used as solvents for extracting phenols with a dielectric constant of 2. Although organic solvents such as those mentioned above are conceivable, these solvents are not preferred because they extract caprolactam as well as phenols, and the concentration of caprolactam in the aqueous layer becomes extremely low. On the other hand, the dielectric constant of cyclohexane, methylcyclohexane, etc. is 2. Although lower hydrocarbons do not entrain prolactam, they are not preferred because they have a poor ability to extract and separate phenols from adducts of phenols and caprolactam. When a mixed solvent of alkyl ethers and water is used as the citrus agent, the content of phenols in the caprolactam aqueous solution can be suppressed to 0.1 wt % or less based on caprolactam. In addition, since the aqueous layer extracted in this way contains a certain amount of phenols, it may be necessary, for example, to undergo ion exchange resin treatment, oxidation treatment, or addition of carbonic soda and distillation. High purity docaprolactam can be recovered by On the other hand, after all the alkyl ethers were removed from the organic layer by distillation, the organic layer was recycled to the phenol solvent distillation separation step again to recover the docaprolactam contained in the organic layer, and the phenol content was reduced to 3. % or less of phenols and caprolactam, and extraction with a mixed solvent of alkyl ethers and water is repeatedly performed.

As described above, by carrying out the method of the present invention, high purity caprolactam can be recovered from the reaction product liquid obtained by rearranging cyclohexanone oxime in the presence of sulfuric acid without producing ammonium sulfate as a by-product. Example
1 100% reaction product solution obtained by Beckman rearrangement of cyclohexanone oxime in the presence of sulfuric acid (42% caprolactam)
After collecting 57% of sulfuric acid (containing 57% of sulfuric acid) and adding 57% of water,
Benzene-phenol (weight ratio 20:80) mixed solvent 1
Extraction was carried out 3 times in 50 days.

After washing the extract with water to remove most of the sulfuric acid, the remaining sulfuric acid was neutralized with ammonia. 300 ml of extract, 50 ml of extract
Distillation was carried out under reduced pressure at ~7,000 ml, and then distilled under reduced pressure at 7,000 ml. Distillation was stopped when 350 ml of phenol was distilled out. The residual liquid at that time consisted of 8.5 parts of phenol and 40.5 parts of do-caprolactam (phenol content: 17 wt%). Distill this residual liquid. After extracting three times with a mixed solvent consisting of 68 parts of lopyl ether and 41 parts of water to transfer f-caprolactam to the aqueous layer, the water was evaporated and 1.
5 was added and distilled under reduced pressure at 113° C. for 2.5 days, and 1% of the front distillate and 1% of the after distillate were cut off to obtain 23% of caprolactam. When this quality analysis was performed, it was found to be highly pure docaprolactam with a PZ value of 3600 or more and a UV value of 98%. Example 2 Using the same machine as Example 1, Beckman rearrangement reaction product liquid 100
Caprolactam was collected, diluted with water, extracted with a benzene-phenol solvent, washed with water and neutralized to remove sulfuric acid, and then benzene and phenol were removed to obtain 50% caprolactam (phenol content: 2%). Obtained.

Claims (1)

[Claims] 1 From the reaction product liquid obtained by Beckman rearrangement of cyclohexanone oxime in the presence of sulfuric acid, a phenol sole solvent,
Alternatively, ε-
The caprolactam extracted solution is distilled, the solvent is distilled off to obtain a phenol-ε-caprolactam solution with a phenol content of 30 wt% or less, and the solution is then extracted with a mixed solvent of alkyl ethers and water. and distilling the aqueous layer to obtain ε-caprolactam.