Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Patent
1999-07-27
2000-05-30
Shah, Mukund J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
C07D20108
Patent
active
060692464
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the treatment of lactams obtained directly from their synthesis process, avoiding the formation of oligomers as far as possible.
Lactams, and more particularly caprolactam which is the starting material for polyamide 6, are generally distilled in order to be separated from the compounds from which they have been prepared and from the by-products also formed during their synthesis.
Caprolactam is prepared industrially in a conventional manner by a Beckmann rearrangement reaction of cyclohexanone oxime with sulphuric acid or oleum, followed by neutralization of the medium with ammonia and then separation and purification of the caprolactam.
Lactams may also be obtained by cyclizing hydrolysis of aminonitriles. They must then be separated from the ammonia formed, the unreacted water, any solvent used, light organic compounds (that is to say those having a boiling point below that of the lactam), any unconverted aminonitrile, as well as heavier organic compounds (with a boiling point higher than that of the lactam).
Purification of the lactam, mainly by distillation, and more particularly its separation from water, is not always carried out immediately on leaving the cyclizing hydrolysis reactor.
It has been observed that lactam oligomers are formed when the reaction flow leaving the hydrolysis reactor is maintained at a temperature above about 50.degree. C. for a relatively long period of time. This is because maintaining the reaction mixture in the liquid condensed phase leads to the formation of oligomers.
Similarly, it has been observed that if the average residence time of the lactam in the distillation apparatus exceeds about one hour at a temperature above 100.degree. C., oligomers are also formed.
In addition, when the lactam is not distilled immediately after it has been prepared, the said lactam is sometimes stored for a period which may be relatively long, that is to say, as a guide, equal to several hours.
It has been observed that storage of the crude lactam for a period of a few hours, especially in solution, at a temperature equal to or above 50.degree. C. leads to the formation of oligomers of the said lactam.
Depending on the apparatus used, the presence of these oligomers formed during the various phases of the treatment of the flow obtained from the cyclizing hydrolysis reaction is liable to cause blockages, especially in the pipes between the reactor and the distillation column or the storage tank. In addition, the formation of oligomers reduces the overall yield of lactam and creates additional problems of purification and recycling.
The present invention overcomes these drawbacks by limiting the formation of lactam oligomers as far as possible.
The invention consists, more precisely, of a process for treating a lactam using the reaction flow obtained from a vapour-phase cyclizing hydrolysis of an aminonitrile, characterized in that the reaction flow leaving the hydrolysis reactor is cooled, over a period of less than or equal to 1 hour, to a temperature below or equal to 150.degree. C. before it is fractionated.
The cooling may be carried out in industrial processes by a heat exchanger with circulation of water, of air or, where appropriate, of vapour or heat-exchange fluid.
In practice, an implementation variant of the cooling will consist in recovering the calories from the reaction mixture obtained from the hydrolysis reaction.
These calories may be used directly to preheat a heat-exchange fluid which may then serve to preheat the reactants of the cyclizing hydrolysis, that is to say, essentially, the aminonitrile and the water.
They may also serve to preheat the steam used to heat the hydrolysis reactor.
They may also serve to generate steam which will be used in one or other phase of the process for the preparation of lactams.
This recovery of the calories from the mixture obtained from the cyclizing hydrolysis reaction may be supplemented by cooling with water or air, when the temperature of the said mixture reaches a value below 150.degree. C. or pr
Chiarelli Henri
Leconte Philippe
Kifle Bruck
Rhodia Fiber & Resin Intermediates
Shah Mukund J.
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