Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Patent
1999-04-23
2000-08-08
Dentz, Bernard
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
540540, 540451, 546243, 548553, C07D20108, C07D20116
Patent
active
061003964
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the purification of lactams by liquid-liquid extraction and/or treatment with ion-exchange resin.
Among the most common lactams, caprolactam is a very important compound, since it is a starting material for polyamide 6 which is used in considerable amounts worldwide.
One process for obtaining caprolactam, and by analogy other lactams, is to carry out a cyclizing hydrolysis of the corresponding aminonitrile, 6-aminocapronitrile, to give caprolactam.
A simple distillation of the lactam thus obtained is not sufficient to give the said lactam a purity which is compatible with the quality required for the applications of the corresponding polyamide. This is the case most particularly as regards caprolactam for the textile applications of polyamide 6.
Amounts of unconverted aminonitrile which are still too large remain, as well as smaller, but nevertheless excessive, amounts of other by-products.
The lactam and the aminonitrile from which it is derived could theoretically be separated by distillation. However, it turns out in practice that during heating, a certain amount of an addition product of these two compounds is probably formed, this addition product subsequently retrograding and re-releasing the aminonitrile which it was desired to separate. Consequently, a simple distillation does not allow excellent separation of aminonitrile and lactam.
Patent WO-A-96/20923 recommends a process for purifying caprolactam which involves the following sequence of operations. Firstly, caprolactam is prepared by reacting 6-aminocapronitrile with water, the light compounds and the heavy compounds in the crude caprolactam are then removed, after which the caprolactam obtained from the above step is treated with hydrogen in the presence of a catalyst, at a temperature of 50-150.degree. C. and at a pressure of from 1.5 to 250 bar, to give a mixture A, which is either passed in the form of a solution in a solvent, on an ion-exchange resin containing acidic functions, or is distilled off in the presence of sulphuric acid, and finally the mixture B1 or B2 obtained in one of the above two steps is distilled in the presence of a base to give the pure caprolactam.
When that patent is analysed in greater detail, it is observed that the process is very intimately linked with the purification of the caprolactam prepared by liquid-phase hydrolysis. This emerges very clearly from the examples for carrying out the invention.
It is also observed that the purification process described is a complex process comprising multiple steps. It also appears to be very expensive and very energy-intensive, since the first step after the preparation of the caprolactam consists practically in distilling all of the products obtained from the reaction. Indeed, it is envisaged to distil the light products, i.e. the products with the lowest boiling points, and to separate out the heavy products, i.e. the products with the highest boiling points. This therefore necessarily involves the distillation of all of the caprolactam which, by definition, has a boiling point which is intermediate between those of the light products and the heavy products.
The Applicant has found, unexpectedly, relative to the teaching of patent WO-A-96/20923, that lactams prepared by cyclizing hydrolysis of aminonitriles in a vapour phase can be obtained in a purity of the same order as those of the lactams prepared in a liquid phase, by using a purification process which does not involve the prior distillation of all of the constituents of the reaction mixture obtained from the hydrolysis reaction.
The only operation prior to the present purification process is the removal of the ammonia formed, this removal usually consisting in distilling off the said ammonia.
The present invention consists of a process for purifying a lactam obtained from the cyclizing vapour-phase hydrolysis of an aliphatic aminonitrile, characterized in that, after most of the ammonia contained therein has been removed, the said lactam is subjected to a liquid-liquid extraction
REFERENCES:
patent: 2357484 (1944-09-01), Martin et al.
patent: 2405969 (1946-08-01), Martin
patent: 2828307 (1958-03-01), Soeterbroek et al.
patent: 3248388 (1966-04-01), Wintersberger et al.
patent: 5496941 (1996-03-01), Ritz
Chemical Abstracts, vol. 68, No. 2, Jan. 8, 1968, Columbus, Ohio, US; Abstract No. 6128, Temple, Diana M. "Liquid ion-exchange separation of some physiologically active amines", XP002027598 see abstract & Australas. J. Pharm. (1966), 47(559), S62-S64.
Gayet Hubert
Leconte Philippe
Perrona Philippe
Dentz Bernard
Rhodia Fiber and Resin Intermediates
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