DE1770745A1 - Process for the production of pure caprolactam - Google Patents

Description

Process for the production of pure caprolactam.

The invention relates to a process for the production of pure caprolactam from the reaction mixture of the Beckmann rearrangement of cyclohexanone oxime with sulfuric acid. Caprolactam, which is produced by the Beckmann rearrangement, falls behind the neutralization of the rearrangement mixture with dilute sodium hydroxide solution or aqueous solution Ammonia solution generally as a two-phase mixture. The organic phase, also called lactam oil, can either be used together with the inorganic phase or also separately be subjected to cleaning. This is to be achieved that as large a part of the inorganic and organic by-products as possible and impurities are removed from the caprolactam.

Purification processes for caprolactam have become known in large numbers. It has been proposed to use oxidizing agents, adsorbents, such as, for example To use activated carbon and ion exchangers or to use the caprolactam by recrystallization, To free distillation or extraction of unwanted by-products. All Measures are aimed at the most important quality features of the pure lactam to increase, however, they are characterized by a greater or lesser effort the end. In some cases, additional, cost-generating auxiliary materials are also required. Farther The quality improvements achieved for the pure lactam can be found in most balls no longer meet today's requirements.

The extraction process is special because of its high effectiveness Meaning. The importance for this, the later iiactam quality decisive The influencing cleaning step was recognized at an early stage and through modifications improved. For example, from the GDR patent specification 13 123, a method is known in which this occurs in the neutralizate Lactan oil separated and one Is subjected to treatment with inert gases, air or water vapor with the aim of remove volatile impurities.

This is followed by extraction and distillation in a known manner. The known process which resulted in a permanganate number of 940 seconds is However, associated with the following disadvantages: Due to the separate processing of the Lactam oil and the aqueous phase also complicate the qualitatively and quantitatively different impurities the work-up process #. Furthermore, the treatment with inert gases is unspecific, the treatment with air for the product harmful as it promotes the formation of new impurities, and the Treatment with water vapor is incomplete as it only contains volatile impurities in this eliminated. After all, the inevitable ammonium sulfate is not required Dimensions removed.

It has also been suggested that the cleaning measures should be implemented first to be carried out on the extract obtained.

For example, it is named in DAS 1 031 308, the lactam from the two-phase, completely neutralized rearrangement mixture according to Beckmann Extract zil by an organic solvent and the organic lactam solution subsequently by washing with Water in amounts between 0.1 and 10%, based on the organic solution, to be extracted. The water should preferably be weakly angry. The washed organic caprolactam solution is then used subjected to distillation. This known method has the disadvantage that the acidic impurities, which decompose during the later distillation, cannot be removed from the extract and that the ammonium sulphate is also insufficient Measures is eliminated, as a result of which disturbances in the distillation stage set can.

Furthermore, there is a procedure through German Satentsenrift 953 168 for the purification of caprolactam became known, with aem the caprolactam from his Solution in a water-immiscible organic solvent using water is extracted, and the now aqueous caprolactam solution in turn a treatment with a water-immiscible organic solvent. This exhaustive re-extraction of the caprolactam from the organic phase with water Although it brings improvements in the ena quality of the pure lactam, From an energetic point of view, however, it is extremely expensive.

The above cleaning and extraction processes are only possible of a reaction mixture from that through complete neutralization of the product was obtained from the Beckmann rearrangement. The invention lies the object is based on the disadvantages inherent in the method described above to eliminate and to create a procedure in which through the simplest process management a caprolactam of the highest purity is obtained. This is done according to the invention in that the product of Beckmann's rearrangement is not completely, but rather only up to a pH value between 1.2 and 4.0, preferably between 1.8 and 3.0, neutralized, the caprolactam formed from the resulting two-phase mixture extracted with an organic solvent and the extract subsequently with a Solution from 6 to 50%, preferably from 12 to 30%, alkali treated in water, whereupon the aqueous phase is separated off and the organic phase is distilled subject.

It has been found, surprisingly, that very pure caprolactam is obtained obtained in a technically simple and advantageous manner if the product of the Beckmann rearrangement only partially and not completely neutralized.

Although it is already known from the German patent specification 854 359, ae pH value of a neutralization mixture to place between 3 and 8, however, it is advisable to set it to 6 on average. The following should be the raw lactam can be purified by distillation while using the ammonium sulfate solution alone extracted with an organic solvent. In finding the known Process not found the realization that one for the purpose of a -good cleaning effect in the strongly acidic range below pH = 4, preferably even below pH = 3.0 have to work. The recommended pH value at the time was 6 for caprolactam even in the basic range. In addition, the known method led due to the Not remotely omitting the further process steps according to the invention to lactams of the required purity. The partial neutralization only has an effect Use of the further features of the invention in an advantageous manner.

PAS 1 201 352 also provides a method for obtaining Lactam from an acidic reaction mixture by blunting with a base to one pH of the lower layer, not known above 5.5, being the one containing lactam upper layer extracted with an organic xow solvent and before or during the extraction continues to dull, so that the pH of the water phase during the remains above 5.0 throughout the extraction.

As an example, a pH value of 4 and in is used in the lower phase the upper l-Hase mentioned an increase in the pH value up to 8 before the extraction takes place with an organic solvent.

However, these pH values describe two-phase mixtures in relation to gas Caprolactam and ammonium sulphate solution have an alkaline and not an acidic range. It is even claimed that it works at a pH of 3.5 in the water phase for putting the extraction device out of operation.

Deposition of tarry components leads.

The less predictable and surprising was the fact that that the caprolactam losses in the relatively acidic inorganic phase according to the Invention by no means increased. Rather, the residual lactam levels were in the inorganic phase, the so-called raffinate, only between 200 and 400 ppm.

Partial neutralization is expediently carried out with a dilute aqueous solution Ammonia solution or caustic soda.

The extraction of the two-phase mixture is preferably carried out in itself carried out in a known manner in a multistage countercurrent extraction process, where the organic solvent, for example, benzene, cyclohexane, trichlorethylene, Methylene chloride or chloroform can be used.

The concentration of the alkali lye should be such that at the time the phase separation of the organic caprolactam solution and the aqueous shase less than 3.0% by weight of caprolactam are soluble in the aqueous phase.

Thanks to the extremely effective cleaning in the first stage of the process In addition to the quality improvements of the pure lactam, there will also be a considerable increase in yield reached in the amount of 3 to 4 mol%. The lead lactam obtained during the distillation is so little due to the preceding steps of the method according to the invention contaminated that a partial to complete without further cleaning measures Return to the process without loss of quality of the pure lactam is possible. Of the Distillation residue drops from approx. 3.5 mol% in known processes to 0.8 to 2.0 mol-5 in the process according to the invention. This is due to a variety of additions, especially of alkaline solutions during distillation. As is well known, cause Alkali additives at elevated temperature easily cause hydrolysis of the caprolactam, a Polymerisatbilaun: a decomposition of caprolactam or # -aminocaproic acid to 1,11-diaminounaesanone-6 ir. undesirable extent.

The impurities accompanying Qas Caprolactam permit To simplify matters, they can be divided into those with a basic, neutral and acidic character. The basic impurities in particular are removed by the method according to the invention very early on. removed with high efficiency, so that the subsequent Process steps are relieved and thus more effective. Most of the impurities are oxidizable with potassium permanganate in an acidic medium, so that the potassium iump ermanganate consumption , expressed in mg KMnO4 / kg examined lactam-containing product, a good measure represents for the cleaning effect.

According to the further invention, one switches between the extraction of the caprolactam with an organic solvent and the alkali treatment of the Extract a wash of the caprolactam extract obtained with neutral water in an amount such that the caprolactam is essentially in the organic solvent remains. The water washing of the caprolactam extract is done with non-acidified or neutral water in a one-step or multi-step process.

The 1'orerung that the caprolactam is essentially an organic solvent remains, wira by amounts of water between 1 and 15 vol, based on the caprolactam extract, Fulfills. The fact that the water for the extract wash is not acidified, is important insofar as it succeeds not only to free the extract largely from ammonium sulfate or sulfate ions, but also save auxiliary materials (acid and alkali). Ammonium sulfate in the extract would have an unfavorable effect in the subsequent distillation. Through the extract wash In addition to the removal of the ammonium sulphate, a number of unspecified, Oxydable organic impurities extracted from aer organic solution, what manifests itself in a reduction in the consumption of potassium permanganate. Werner becomes one Weakening of the alkali solution used in the subsequent process stage the reaction of residual ammonium sulfate with alkali to alkali metal sulfate is avoided. Even an additional water wash of the caprolactam extract following the alkali treatment is advantageous.

It is also advantageous if the washing of the caprolactam extract with water, weakly lactam-containing aqueous phase in the circuit in the Returning the extraction apparatus. This results in further, albeit small, lactam losses prevented without the oxidizable impurities in the return of the aqueous Phase in the extraction apparatus and after reaching a steady state in the the same measure were returned to the organic phase.

According to the further invention, the alkali treatment is used organic caprolactam solution Mixtures of aqueous potassium or sodium hydroxide solution with their neutral salts, such as sulfates, chlorides, carbonates and nitrates, causing a reduction of the lactam solubility and thus the lactam losses are achieved.

The process according to the invention is explained in more detail below with the aid of examples: Example 1: Reaction product from the Beckmann rearrangement of cyclohexanone oxime with 20% oleum at 95 to 1000 ° C. was increasingly neutralized with 15% ammonia water with intensive cooling and stirring. Aliquots of this inhomogeneous mixture were kept at a pH of 2.0; 5.0 and 8.0 taken. From these samples, like the organic phase with the caprolactam and the inorganic phase with the ammonium sulfate isotiers and both phases were examined separately. The potassium permanganate consumption in sulfuric acid solution was determined for both phases, and the organic phase was also examined for the relative contents of oxime and aniline by gas chromatography. The test results were compiled in the following table 1: Table 1 pH value inorganic phase organ. Phase (lactam oil) of the new KmnO4 consumption KMnO4 consumption Relative contents tralisats mg / kg mg / kg 8 130 3410 1.6 3.5 5 160 3160 2.0 3.0 2 240 2780 1.0 1.0 The numerical values clearly show that the inorganic phase is capable of eliminating weakly basic by-products such as oxime and aniline and oxidizable products from the organic phase at a pH value of 2. This is shown by the fact that the potassium permanganate consumption of the organic phase has decreased to 2,780 mg / kg, while the potassium permanganate consumption of the inorganic phase has increased to 240 mg / kg.

Example 2: Reaction product from Beckmann rearrangement of cyclohexanone oxime with 20% oleum ei 9b to 1110 ° C surde with intensive cooling and stirring neutralized with 15% ammonia water to a pH value of 2.5. 4,460 kg / h this two-phase, partial neutralizate were with 1,940 kg / h of benzene in a multilevel Extraction process extracted in countercurrent. The benzene extract had key figures as shown in column 1 of Table 2 below. Then followed a treatment with 5% of a 10% aqueous sodium hydroxide solution, based on the volume of the extract. As column 2 of Table 2 shows, after separation of the sodium-alkaline Pnase in the benzene phase, which has now practically become colorless, a consumption of potassium permanganate of 139 mg / kg was measured, while an ammonium sulfate content was practically no longer detected could be.

Table 2 2 1 2 Lactam content% w / w 28.0 26.9 Ammonium sul- g / l 0.63 no longer fat content detectable KMnO4 consumption mg / kg 326 139 Example): The reaction product from the Beckmann rearrangement was neutralized analogously to Example 2 to a pH of 2.5. 4,460 kg / h of this two-pr, partial neutraliz-at was extracted with 1,940 kg / h benzene in a multistage extraction process in countercurrent.

The benzene extract had indicators like them in Column 1 of Table 3 below are shown. In contrast to example 2 the extract was additionally mixed with 5% neutral water, based on the volume of the extract, washed intensively, where the key figures according to column 2 of the table 3 set; the extract was pale yellow in color. This was followed by treatment with 3 ß of a 12% aqueous sodium hydroxide solution, based on the volume of the water washed extract. As column 3 of Table 3 shows, that was now practical colorless benzene extract after separation of the alkaline aqueous, brown outer water phase ammonium sulfate no longer detectable.

Plate 3 1 2 3 Lactam content% w / w 28.5 26.3 26.1 Ammonium sul- g / l 0.66 0.13 no quantity fat content 0.13 detectable KMnO4 consumption mg / kg 392 197 80 Example 4: A continuously operating extraction apparatus was fed in countercurrent with 1.8 m3 / h benzene and 4.8 m3 / h product of the Beckmann rearrangement of cyclohexanone oxime and an oleum, which was brought to a pH of 2 with 15% ammonia water , 3 had been neutralized. The benzene extract had characteristic numbers as given in column 1 of table 4. The separated aqueous phase with aeL ammonium sulfate had a lactam content of only 340 ppm. The extract was then washed in a mixer with 150 l / h of demineralized water. After the separation, the aqueous phase was returned to the extraction apparatus; the extract had key figures which can be seen in column 2 of table 4. 2.3 m3 / h of the washed extract were then intensively treated with 70 l / h of 25% sodium hydroxide solution. The benzene caprolactam solution had the key figures shown in column 3 of table 4. After the sodium hydroxide treatment, the benzene was distilled off, whereupon the raw lactam obtained was subjected to a multi-stage vacuum distillation in a manner known per se. The pure lactam produced here had key figures as they are listed in column 4 of table 4. The pure lactam also contained about 0.4 mg / kg a of volatile bases. The end product had a freezing point of 690 C; the UV transmission of a 50% caprolactam solution in water was 65% at a wavelength of 260 and 96% at 290 mμ.

Table 4 1 2 3 4 Lactam content wt% 25.1 23.2 23.2 # 100 Ammonium sul- g / l 0.56 0.12 not - fat content more verifiable KMnO4 consumption mg / kg 376 196 91 15 KMnO4 number sec. - - -> 3000 Example 5: For the purpose of comparison, the Beckmann rearrangement reaction mixture was neutralized to a pH between 5 and 8 in a known manner. The neutralizate was extracted with benzene as in Example 3, except that the extract was not washed with neutral water and with alkali lye.

Eventually, after the benzene was stripped off, a multi-stage one Distillation carried out, which resulted in an end product of flying metrics: Potassium permanganate number: 500 to 600 sec.

Potassium permanganate consumption: 30 to 80 mg / kg volatile bases: 0.6 meq / kg Freezing point: 68.8 ° C UV transmission in 50% aqueous caprolactam solution at a wavelength of 26G mµ 44% and at 290 mµ 60%. The end product of this known The method is the same as that of the method according to the invention far inferior.

In all trials, the potassium permanganate number was based on the following standard measured: 3 g Co Cl2 # 6 H2O + 2 g CuSO4 # 5 H2O were in 1000 ml of distilled water solved.

- 5 claims -

Claims (5)

Claims 1. Process for the production of pure CaDrolactam from the reaction mixture of the Beckmann rearrangement of cyclohexanone oxime with sulfuric acid, characterized in that the product of Beckmann rearrangement up to a pH value between 1.2 and 4.0, preferably between 1.8 and 3.0, neutralized, from the resulting two-phase mixture, the caprolactam formed with an organic one Solvent extracted, and the extract subsequently with a solution of 6 - 50 %, preferably 12-30% alkali treated in water, whereupon the aqueous Phase separated and the organic phase subjected to a distillation. 2. The method according to claim 1, characterized in that between the extraction of aes caprolactam with an organic solvent and the alkali treatment of the extract a wash of the extract with neutral water of such an amount carries out that the Caprolactau essentially. Remains in the organic solvent. 3. The method according to claim 1 and 2, characterized in that # one the lactam-containing, resulting from washing the caprolactam extract with water, recirculates the aqueous phase in the gene extraction apparatus. 4. The method according to claim 1, characterized in that one for Alkali treatment of the organic caprolactam solution Mixtures of aqueous potash resp. Caustic soda with its neutral rollers such as sulfates, chlorides, carbonates, Nitrates. 5. The method according to claim 1 to 4, characterized in that one to connect to the alkali treatment of the organic caprolactam solution and before Distillation an additional wash with neutral water and the hieroei resulting aqueous phase to the extraction apparatus for the first extraction with neutral Supplies water.