PROCESS FOR RECOVERING CAPROLACTAM FROM A NEUTRALIZED REARRANGEMENT MIXTURE

Abstract: The invention relates to a process for recovering caprolactam from a neutralized rearrangement mixture, which rearrangement mixture comprises a solution of caprolactam in water and a solution of ammonium sulphate in water, by extraction with an organic solvent in a mixer, after which the resulting organic phase is separated from the aqueous phase in a separator and caprolactam is recovered from the organic phase, the organic solvent being dispersed in the neutralized rearrangement mixture in the mixer.

Description: PROCESS FOR RECOVERING CAPROLACTAM FROM A NEUTRALIZED REARRANGEMENT MIXTURE The invention relates to a process for recovering caprolactam from a neutralized rearrangement mixture, which rearrangement mixture comprises a solution of caprolactam in water and a solution of ammonium sulphate in water, by extraction with an organic solvent in a mixer, after which the resulting organic phase is separated from the aqueous phase in a separator and caprolactam is recovered from the organic phase. Such a process is already known from DE-A- 1031308, which describes how caprolactam is obtained from a mixture obtained after Beckmann rearrangement of cyclohexanone oxime in the presence of sulphuric acid, This rearrangement mixture is subsequently neutralized by means of, for instance, ammonia. This results in the formation of a mixture of 2 aqueous phases, one phase being a solution of caprolactam in water and the other phase being a solution of ammonium sulphate in water. This neutralized rearrangement mixture is then mixed with an organic solvent, in this case benzene, to extract the caprolactam. As a result an aqueous phase and an organic phase are formed. A drawback of this process is that when both phases are randomly mixed, the ammonium sulphate content of the organic solvent is relatively high. This has an adverse effect during upgrading and purification of caprolactam. The aim of the invention is to provide a process that will lower the ammonium sulphate content in the organic solvent . This is achieved in that the organic solvent is dispersed in the neutralized rearrangement mixture in the mixer. In the process carried out according to DE-A- 1031308 the ammonium sulphate contents of the organic phase are at least 350 ppm, while with the process according to the invention sulphate contents of at most 60 ppm can be achieved. Moreover in DE-A-1031308 also an extraction column is needed for extraction of the caprolactam from the water, which involves substantial investment costs. As mixer and separator commercially available mixer/separators can be used. These are items of equipment with a mixing section and a settling section. In the mixing section the liquids are combined and energy is imparted to the liquid mixture, for instance by means of a stirrer. As a result a dispersion is formed. The residence time of the dispersion in the settling section is long enough for the dispersed phase to coalesce, preferably with laminar flow taking place. Suitable mixers/separators are the box type, the IMI, the General Mills or the Kemira mixer/settler, as described in "Liquid-Liquid Extraction Equipment" by Godfrey J.C. and Slater M.J., Ed. Wiley, COP (1994), Ch. I, pp. 294-297. Although acceptable mixer configurations include stirred vessels, static mixers and pumps, stirred vessels are preferred. The neutralized rearrangement mixture comprises a solution of caprolactam in water and a solution of ammonium sulphate in water with the caprolactam content generally between 60 and 80 wt.% and the ammonium sulphate content generally between 30 and 50 wt . % . The organic solvent used that is used for extraction of caprolactam can be, for instance, benzene, toluene, a chlorinated hydrocarbon, for instance chloroform, trichloroethane, trichloroethene, an aliphatic or cycloaliphatic alcohol with 4-10 C atoms, or a mixture thereof. After the neutralized rearrangement mixture and the organic solvent have been mixed so as to extract the majority of the caprolactam in the organic solvent, with the organic solvent being dispersed in the neutralized rearrangement mixture according to the invention, an aqueous phase and an organic phase are formed. The aqueous phase contains ammonium sulphate and generally 1 wt.% or less caprolactam. The organic phase contains caprolactam and at most 60 ppm ammonium sulphate. The caprolactam concentration in the organic phase usually lies between 15 and 30 wt.% relative to the total organic phase. The dispersion of the organic solvent and the neutralized rearrangement mixture is then fed into a separator where the aqueous and organic phases are separated. The residence time of the various phases in the separator will generally be less than 10 minutes and would more typically be between 10 seconds and 5 minutes . Preferably, the aqueous phase is subsequently transferred to a second mixer, to which solvent is again added. The solvent added in the second mixer is preferably the same solvent as in the first mixer. Here preferably also the organic phase is dispersed in the aqueous phase, in a second separator the aqueous phase is then separated from the organic phase . By mixing the organic phase in the aqueous phase, the present invention advantageously lowers the concentration of caprolactam and organic solvent remaining in the aqueous phase to minimize caprolactam and organic solvent losses. In addition, the present invention also improves the quality of the ammonium sulphate recovered from the aqueous phase . The aqueous phase separated from the second separator has a high content of ammonium sulphate, which can be crystallized out according to known methods . The temperature at which the extraction takes place usually lies between 30 and 60 °C. In instances where more than one mixer is utilized, it is anticipated that each of the mixers would be operated within this temperature range. In a preferred embodiment of the process according to the invention the organic solvent separated in the second separator is subsequently recycled to the first mixer. This has the advantage that the organic solvent is used in the most efficient way possible, which is most desirable from an economic and an environmental point of view. The organic phase that is separated from the first separator is preferably washed with water or with an alkaline aqueous solution. The alkali concentration of this aqueous solution generally lies between 0.01 and 5 wt . % relative to the amount of water. Preferably, the alkali concentration lies between 0.1 and 2 wt.%. Washing preferably takes place with water or with an alkaline solution having a very low alkali content. In the framework of the invention alkaline (earth) hydroxides and/or carbonates are used as alkali. Preferably, use is made of sodium hydroxide or potassium hydroxide. One skilled in the art can determine the amount of water with which the organic phase from the first separator can be washed. As a general rule, this amount will be between 0.1 and 5 wt . % relative to the amount of organic phase. Preferably, this amount will be between 0.5 and 2 wt.% relative to the amount of organic phase. After the organic phase has been washed, it is usually evaporated with addition of water. As a result, a caprolactam/water mixture is formed. The caprolactam content of this mixture is between 85 and 99.9 wt.% relative to the entire stream. The amount of water here is therefore 0.1-15 wt.%. For further purification of the caprolactam/water mixture formed various techniques can be employed, for instance ion exchangers, adsorbents or hydrogenation. Preferably, the caprolactam/water mixture is hydrogenated for further purification. Hydrogenation can take place using a state of the art method. A very suitable hydrogenation is described in EP-A-635487. To obtain the caprolactam in pure form without water, the caprolactam is distilled off from the water. Comparative Experiment A At 40 °C, 344 g of aqueous caprolactam solution, which contained 73.1 wt.% caprolactam, was introduced into a stirred glass reactor (CSTR) . Then, 863 g of ammonium sulphate solution (42.4 wt.% ammonium sulphate) was added and 852 g of benzene as organic solvent. The ammonium sulphate solution and the caprolactam solution had been obtained after neutralization of a rearrangement mixture obtained after a Beckmann rearrangement of cyclohexanone oxime in oleum. The phases were stirred so that the aqueous phase was dispersed in the benzene. After 5 minutes' stirring the aqueous and organic (benzenic) phases that had formed were separated from one another after the stirrer had stopped. After 20 seconds complete phase separation had been achieved. It was observed that the benzenic phase was turbid and the aqueous phase, which contained the ammonium sulphate, was clear. The benzenic, caprolactam-containing phase contained 350 mg/kg ammonium sulphate. Example I Comparative Experiment A was repeated. This time, however, the benzene was dispersed in the neutralized rearrangement mixture. After 3 minutes' stirring at 40 °C the benzenic phase and the aqueous phase that had formed were separated. Separation was achieved after 60 seconds. It was remarkable to note that the benzenic phase was clear and the aqueous phase turbid. The benzenic phase contained only 55 mg/kg of ammonium sulphate. Example II 780 g of aqueous phase with 39.5 wt.% ammonium sulphate, obtained from the first mixer, was introduced into a stirred reactor as in Comparative Experiment A. This ammonium sulphate solution was mixed with 709 g of benzene at 40 °C. After this, stirring took place so that the benzene was dispersed in the aqueous phase. After 5 minutes' stirring the aqueous - 1 - phase and the organic phase that had formed were separated. Phase separation was achieved after 55 seconds. Both phases were clear. Example III Example II was repeated. This time the aqueous phase was dispersed in the benzene. After 5 minutes' stirring the organic phase and the aqueous phase were separated; after 40 seconds phase separation had been achieved. It was observed that the organic phase was clear and the aqueous phase turbid due to benzene entrainment . This meant that loss of benzene, and thus of caprolactam, had occurred, which had not been the case in Example II.

Claims: C L A I S 1. Process for recovering caprolactam from a neutralized rearrangement mixture, which rearrangement mixture comprises a solution of caprolactam in water and a solution of ammonium sulphate in water, by extraction with an organic solvent in a mixer, after which the organic phase formed is separated from the aqueous phase in a separator and caprolactam is recovered from the organic phase, characterized in that the organic solvent is dispersed in the neutralized rearrangement mixture . 2. Process according to claim 1, characterized in that the neutralized rearrangement mixture has a content of the caprolactam in water of between 60 and 80 wt.% and a content of ammonium sulphate in water of between 30 and 50 wt.%. 3. Process according to claim 1 or 2, characterized in that an organic solvent is added to the separated aqueous phase in a second mixer, the organic solvent being dispersed in the aqueous phase, after which the aqueous phase is separated from the organic phase in a second separator. 4. Process according to claim 3, characterized in that the organic solvent separated in the second separator is returned to the first mixer. 5. Process according to claim 4, characterized in that the organic solvent in the first mixer is the same as that in the second mixer. 6. Process according to any one of claims 1-5, characterized in that the separated organic phase from the first separator is washed with water or an alkaline aqueous solution. 7. Process according to claim 6, characterized in that the alkali concentration is between 0.1 and 2 wt.% relative to the amount of water. 8. Process according to claims 6-7, characterized in that the amount of water or alkaline aqueous solution with which the organic phase is washed lies between 0.1 and 5 wt . % relative to the organic phase. 9. Process according to any one of claims 1-8, characterized in that the organic phase is evaporated with water being added until a caprolactam/water mixture having a caprolactam content between 85 - 99.9 wt.% is obtained. 10. Process according to any one of claims 1-9, characterized in that the evaporated caprolactam/water mixture is subsequently hydrogenated. 11. Process according to any one of claims 1-10, characterized in the caprolactam is distilled. 12. Process as described in the introduction to the specification and elucidated on the basis of the examples .

Inventors: GROOT ZEVERT LOUISE ANNEMARIE, LEMMENS JOANNES ALBERTUS WILHE, SIMONS ANTONIUS JACOBUS FRANCI, GROOT ZEVERT, LOUISE, ANNEMARIE, LEMMENS, JOANNES, ALBERTUS, WILHELMUS, SIMONS, ANTONIUS, JACOBUS, FRANCISCUS
Applicants: DSM NV, GROOT ZEVERT LOUISE ANNEMARIE, LEMMENS JOANNES ALBERTUS WILHE, SIMONS ANTONIUS JACOBUS FRANCI, DSM N.V., GROOT ZEVERT, LOUISE, ANNEMARIE, LEMMENS, JOANNES, ALBERTUS, WILHELMUS, SIMONS, ANTONIUS, JACOBUS, FRANCISCUS
Application year: 1998
Main classification: C07D201
IPC codes: C07D201