Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Patent
1998-12-09
1999-09-14
Shah, Mukund J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
C07D20116, C07D22310
Patent
active
059524936
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to a process for purifying .epsilon.-caprolactam.
.epsilon.-Caprolactam is an important starting material for the production of polyamides (nylon 6). There are various ways of producing it industrially. The most popular option is by Beckmann rearrangement of cyclohexanone oxime (K. Weissermel, H. J. Arpe, Industrielle Organische Chemie, 4th edition, pp. 272). Alternatively, cyclohexanecarboxylic acid is produced from toluene via benzoic acid and rearranged with nitrosylsulfuric acid to the .epsilon.-caprolactam. Other processes are based on the cyclization of .omega.-aminocaproic acid derivatives, for example 6-aminocaproic esters (EP-A 376 123) or 6-aminocapronitrile (EP 659 741), in the presence of suitable, typically acidic, catalysts to form .epsilon.-caprolactam.
All .epsilon.-caprolactam processes give rise to by-products, the nature and quantity of which depend on the principle of the process, on the quality of the starting materials and also on the process parameters. On the other hand, the .epsilon.-caprolactam has to meet high purity requirements, especially in fibermaking. For this reason, each manufacturing process requires its own optimized purification process. The various purification processes are cited for example in Process Economics Program Report No. 41 B, Caprolactam and Nylon 6, March 1988, pp. 69.
These purification processes are generally combinations of extraction, distillation and/or crystallization processes. Highly contaminated caprolactam fractions, for example caprolactam purification residues, are frequently subjected to a catalytic hydrogenation. Removal of the catalyst is generally followed by a distillative workup or the return into the purification cycle. In the case of a catalytic suspension hydrogenation of the crude .epsilon.-caprolactam using Raney nickel (EP-A-138 241, JP-A-60-21145) the removal of the catalyst presents problems. In the case of a hydrogenation of the crude .epsilon.-caprolactam over fixed-bed catalysts (DE-A-1004616, DD-A-75083), decreasing activity or poisoning of the catalysts is likely over time.
It is an object of the present invention to provide a low-cost universally deployable purification process for .epsilon.-caprolactam.
We have found that this object is achieved, surprisingly, by using a complex hydride of aluminum or of boron.
The present invention accordingly provides a process for purifying .epsilon.-caprolactam, which comprises reacting crude .epsilon.-caprolactam with a complex hydride of aluminum or of boron.
Suitable complex hydrides of aluminum or of boron for the process of this invention are in particular sodium borohydride, lithium borohydride, potassium borohydride, calcium borohydride, sodium cyanoborohydride, sodium methoxyethoxyaluminum hydride, lithium tri-t-butoxyaluminum hydride.
The amount of hydride hydrogen used naturally depends on the concentration of the impurities in the .epsilon.-caprolactam. It is chosen so that an excess of hydride hydrogen is present, based on the impurities to be reduced. Preference is given to an excess of from 1.5 to five times, based on the stoichiometrically required hydride quantity.
It has been found that, to obtain an adequate reaction rate in the .epsilon.-caprolactam purification process of this invention, from 10 to 50% by weight of water, based on crude .epsilon.-caprolactam, has to be added to the reaction mixture when a borohydride is used.
In a preferred embodiment, the reaction is carried out in the presence of from 0.5 to 5 mol %, in particular from 1 to 4 mol % of NaBH.sub.4 and of from 10 to 50% by weight of water, based on crude .epsilon.-caprolactam. The sodium borohydride can be used in solid form or in the form of a commercially available aqueous solution.
The reaction is preferably carried out within the range from 10 to 150.degree. C., in particular within the range from 20 to 100 .degree. C. The reaction time is within the range from 0.5 h to 200 h, preferably within the range from 1 h to 100 h.
After the reaction has ended, w
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Weissermel et al., Ind. Org. Chem, 4th ed, p.272.
BASF - Aktiengesellschaft
Kifle Bruck
Shah Mukund J.
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