KR790001365B1 - Process for recovery -caprolactam - Google Patents

Abstract

High purity ε-caprolactam with alky, values in the range required for polymn. was recovered from Beckmann rearrangement reaction mixts. by extg. the partially neutralized H2SO4 soln. with a water-immiscible solvent, extg. this soln. with water, reextg. ε-caprolactam from the water ext. with a water-immiscible solvent, evapg., and vacuum distg. the residue. In a typical example, CHCl3 was used as a solvent.

Description

Recovery method of ε-caprolactam

1 is a schematic diagram of an apparatus used in the method of the present invention, in which A, B and C represent closed extraction towers and D ₁ and D ₂ represent distillation columns,

The solid line represents the alkalinity measured over 120 days of the lactam produced by the embodiment of the present invention and the dashed line represents the alkalinity of the lactam recovered from conduit 9.

The present invention relates to a method for recovering [epsilon] -caprolactam by the Beckman potential method, and in particular, the lactam obtained by this method is suitable for polymerization into nylon. [epsilon] -Caprolactam can be obtained from cyclohexane and sulfuric acid such as pyrogenic sulfuric acid by the so-called Beckman potential. In the known lactam recovery method, the solution obtained by the Beckman potential is partially neutralized with an ammonia solution to produce an ammonium hydrogensulfate-containing solution that also contains a small amount of free sulfuric acid or ammonium sulfate depending on the degree of neutralization of the Beckman potential mixture. . The product is distilled and further extracted with water to obtain an organic solvent free from the lactam, which in turn is used to extract the lactam from the highly acidic solution. The obtained lactam solution in water is treated to first evaporate water at atmospheric pressure until the concentration of lactam is about 90% by weight, and then the remaining water is evaporated under reduced pressure. For further purification, the lactam is usually distilled off under reduced pressure. Lactam recovered in this way satisfies the requirements of various properties necessary for polymerization into nylon, such as melting point, color, sharpness and permanganate, but the lactam obtained in this way does not satisfy the alkalinity requirement, in this case meq per kg lactam The alkalinity displayed will be 0.05 or less. Alkaline is measured by dissolving 40 g of lactam in distilled water and increasing the volume to 200 ml by titrating the solution with 0.01 N hydrochloric acid in the presence of a mixed indicator that changes to pH5-6.

Alkali degrees of about 0.1 are generally obtained starting from different samples of the Beckman potential mixture of lactam and sulfuric acid with a constant alkalinity of at least 0.05 in the lactam recovered by the above-described method.

The alkaline degree required by the present invention extracts an aqueous solution of ε-caprolactam with an organic solvent that is not mixed with water to form a lactam solution in the organic solvent, and then recovers the solvent by evaporating from the solution. Can be obtained by distilling the lactam under reduced pressure.

The present invention provides a method for recovering ε-caprolactam from the Beckman potential mixture neutralized by producing ammonium hydrogensulfate, in which case the lactam is extracted with an organic solvent for lactam that is not mixed with water, and then The solvent is extracted with water and liberated from the lactam to obtain a lactam aqueous solution. The aqueous lactam solution thus obtained is extracted with an organic solvent that is not mixed with water to form a lactam solution in the organic solvent. The solvent is evaporated from the solution to separate the lactam and distilled under reduced pressure for further purification.

The method of the present invention needs to remove all of the water from the lactam solution by evaporation, and the energy is consumed to remove the water. In this case, the use of a suitable organic solvent, such as chloroform (heating evaporation 59 kcal / kg), in which the heat of evaporation is much lower than that of water in the second organic solvent extraction step, significantly reduces the evaporation cost. For example, evaporation heat of 1,260 kcal per kg lactam is required to evaporate water and chloroform from a lactam aqueous solution containing 30% by weight of lactam and 2% by weight of chloroform. However, extraction with chloroform yields a solution containing 34% by weight lactam and 3.8% by weight water in chloroform. Collectively, the evaporation of chloroform and water described above requires 167 kcal per kg lactam.

The present invention will be described in detail with reference to the accompanying drawings and examples.

1 is a schematic view of the apparatus used in the present invention, in which A, B and C in the drawings indicate a sealed extraction tower, other extraction devices may be used instead of the closed extraction tower, and D ₁ and D ₂ are distillation towers. Is displayed. A partially neutralized Beckman potential mixture, composed of an aqueous solution of lactam and ammonia hydrogensulfate, is fed to extraction tower A through conduit 1 and an organic solvent such as chloroform is fed through conduit 2 and extracted in a countercurrent fashion. Ammonium hydrogensulfate liberated from lactam is discharged through conduit 3 on the upper side, and the lactam-rich solvent containing dissolved water and sulfuric acid is neutralized to sulfuric acid and then transferred to distillation column D ₁ through conduit 4. The solvent is concentrated in the distillation column D ₁ , and a part of the solvent is removed by condensation and distillation at the top of the tower by the coolant pipe, and the condensate is discharged through the conduit 5 to remove the water incorporated therein and then used again in the aforementioned extraction step. The lactam concentrate is introduced into the extraction tower 6 through conduit 6 and the lactam is extracted in a more countercurrent manner with the aid of water supplied through the pipe 7. In fact, the solvent liberated from the lactam is discharged through conduit 8 and used again as an extractant to remove the lactam from some of the neutralized Beckman-potential mixtures described above. The lactam solution obtained therefrom is introduced into the third extraction column C through the conduit 9 from the top of the extraction tower A, where the lactam is further extracted in a countercurrent manner with the aid of the organic solvent supplied through the conduit 10. The water liberated from the lactam is recycled through conduit 7, and the lactam-rich solvent containing a small amount of water is introduced into the second distillation column D ₂ through conduit 11 to distill off the solvent and then condense through conduit 12 from the tower. Drain as water. The distilled water is left in separator 13 and returned as reflux to extraction tower D ₂ through conduit 14.

The organic solvent liberated from the water is transferred to extraction column C through conduit 10. The lactam melt containing water is transferred via conduit 15 to a distillation plant (not shown) where water is removed under reduced pressure and the lactam is distilled off. Extraction water continues to circulate again through conduit 7, extraction tower B, conduit 9, extraction tower C and conduit 7 during the above-described treatment. Impurities washed in this circulation system accumulate. Thus, the circulation system is provided with a supply conduit 16 and a discharge conduit 17 for fresh water supply so that impure water can be replaced periodically or continuously. Extraction tower C may use an organic extractant different from that used in extraction tower A. As a method of simplifying the operational control, it is preferable to use the same organic solvent in the extraction column A and the extraction column C.

The solvent used in view of the acidic nature of the aqueous solution initiator containing lactam should be a very good dispersion efficiency of lactam in water. Furthermore, it is preferable that the boiling point is relatively low for the next step of removing the solvent by distillation.

In particular, suitable solvents are chlorinated hydrocarbons such as chloroform, methyl chloride and 1-2 dichloroethane.

An embodiment using the apparatus of FIG. 1 will now be described in detail. In a device capable of producing about 3 kg of lactam per hour, cyclohexa is continuously introduced through conduit 1 at a rate of 13 kg per hour at a rate of 13 kg per hour to neutralize the potential mixture with a Beckman potential. This solution contains 3.39 kg of lactam. Next, introducing 10 kg of chloroform per hour through conduit 2 yields 24.2 wt% of a lactam solution in chloroform at the bottom of extraction tower A. Concentrating the solution in distillation column D ₁ gives 5.7 kg of 60 wt% lactam solution in chloroform. Obtained. Extracting this solution with 8 kg of water from Extraction Column B yields 11.66 kg of an aqueous solution containing 29.6 wt% lactam and 2 wt% chloroform. Extracting the lactam of this aqueous solution with 8 kg of chloroform in the extraction column C yielded 11.9 kg of a solution containing 28.6 wt% lactam and 3 wt% water. The resulting solution can be further treated under reduced pressure by processing means (not shown).

The alkalinity measured over 120 days of the thus produced lactam is as indicated by the solid line in FIG. 2, and the alkalinity of the lactam recovered from the sample of the aqueous solution removed from conduit 9 is indicated by the dotted line in FIG. 2. same. The first 70 days of the continuous process need not be replaced.

The invention is subject to the scope of the claims, but also includes the following embodiments.

(1) The method of claim wherein the two organic extraction steps are carried out with an organic solvent of the same composition.

(2) The method of embodiment (1), wherein the organic solvent described above is chloroform, methylene chloride or 1,2-dichloroethane.

(3) A method for recovering ε-caprolactam substantially as described above and in the accompanying drawings and examples.

Claims (1)

As described above and shown in the drawings, ammonium hydrogensulfate is produced from the neutralized Beckman power source mixture, the lactam is extracted with an organic solvent that is not mixed with water, and then the above-mentioned organic solvent is extracted with water. The lactam solution was removed from the lactam to obtain an aqueous solution of lactam. The lactam aqueous solution was extracted with an organic solvent that was not mixed with water to form a lactam solution in the organic solvent. The solvent was then evaporated to separate the lactam from the above-described solution, Further distillation to purify, the method for recovering ε-caprolactam.

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