Title of Invention	"PROCESS FOR SEARCHING LACTAMS"
Abstract	Process for separating a lactam from the reaction flow resulting from the vapour-phase cyclizing hydrolysis of an aminonitrile having the general formula: in which R represents a linear or branched alkylene radical having from 3 to 12 carbon atoms, characterized in that said process comprises: cooling the reaction flow for not more than 1 hour, to a temperature of 50°C to 150°C and then distilling it, or cooling the reaction flow over a period of not more than 10 minutes and to a temperature of not more than 50 C before storing for a period of longer than or equal to 1 hour and then distilling it.

Title of Invention

"PROCESS FOR SEARCHING LACTAMS"

Abstract

Process for separating a lactam from the reaction flow resulting from the vapour-phase cyclizing hydrolysis of an aminonitrile having the general formula: in which R represents a linear or branched alkylene radical having from 3 to 12 carbon atoms, characterized in that said process comprises: cooling the reaction flow for not more than 1 hour, to a temperature of 50°C to 150°C and then distilling it, or cooling the reaction flow over a period of not more than 10 minutes and to a temperature of not more than 50 C before storing for a period of longer than or equal to 1 hour and then distilling it.

Full Text	PROCESS FOR TREATING LACTAMS 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°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°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°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. Accordingly, there is provided a process for separating a lactam from the reaction flow resulting from the vapour-phase cyclizing hydrolysis of an aminonitrile having the general formula: N»C-R-NH2 in which R represents a linear or branched alkylene radical having from 3 to 12 carbon atoms, characterized in that said process comprises: cooling the reaction flow for not more than 1 hour, to a temperature of 50"C to 150°C and then distilling it, or cooling the reaction flow over a period of not more than 10 minutes and to a temperature of not more than 50 C before storing for a period of longer than or equal to 1 hour and then distilling it. According to the invention there is provided a process for separating a lactam from the reaction flow resulting from the vapour-phase cyclizing hydrolysis of an aminonitrile which comprises cooling the reaction flow for not more than 1 hour, to a temperature of not more than 150°C and then distilling it. 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, cooling may involve 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, so as to reduce the temperature of the mixture to below 150°C, preferably below 100°C. As used herein, the term "cooling" covers the various modes indicated above, or equivalent modes. When the reaction flow is fractionated or distilled immediately, that is to say without storage, it is preferable, for the economy of the process, to cool the said flow over the shortest possible period, preferably less than or equal to 10 minutes, typically to a temperature of from 50°C to 150°C and preferably from 70°C to 120°C. It is also recommended to limit the duration of feeding of the distillation column, that is to say the time which elapses between the reaction flow leaving the hydrolysis reactor and the actual distillation, to a maximum of one hour, preferably 30 minutes. The distillation itself should be carried out such that the average residence time of the lactam in the distillation apparatus is less than or equal to 1 hour. When the reaction flow is not treated immediately and is stored for a period of longer than 1 hour, the cooling is desirably carried out over a period of less than or equal to 10 minutes and preferably to a temperature below or equal to 50°C. The lactam used in the present process is more particularly chosen from those which are obtained by vapour-phase cyclizing hydrolysis of an aliphatic aminonitrile of general formula (I): N=C-R-NH2 in which R represents a linear or branched alkylene radical having from 3 to 12 carbon atoms. Among the lactams, mention may be made more particularly of those which serve as starting material for the preparation of polyamides 4, 5, 6 and 11 and which are obtained from the aminonitriles of formula (I), in which the symbol R represents a linear alkylene radical having 3, 4, 5 or 10 carbon atoms. As indicated above, caprolactam whose polymerization gives polyamide 6, which is prepared from 6-aminocapronitrile (or epsilon-capronitrile), is the lactam preferentially used in the process of the invention. Typical processes for the preparation of lactams, by vapour-phase cyclizing hydrolysis of aminonitriles of formula (I), are disclosed in, for example, EP-A-0,659,741 and WO-A-96/22974. The lactam to be purified is generally in the form of an aqueous or alcoholic solution. Since the cyclizing hydrolysis is carried out in the vapour phase, the said lactam obtained is, more often than not, in aqueous solution. The lactam concentration of such a solution is generally from 20% to 80% on a weight for weight basis. The aminonitrile usually represents up to 15% of the weight of the lactam, and most frequently from 0% to 10% of this weight. The process of the invention generally makes it possible to limit the formation of oligomers to an amount such that the phenomenon has virtually no adverse effect. Such a content is generally less than or equal to 2% by weight of oligomers per unit weight of lactam and preferably less than or equal to 1% on a weight for weight basis. Preferably, in the process of the invention, the lactam is stored at a temperature below or equal to 40°C before being distilled if the storage period is longer than or equal to 1 hour, and/or the distillation is carried out such that the average residence time of the lactam in the distillation apparatus is less than or equal to 30 minutes. The Examples which follow further illustrate the present invention. Example 1 The cyclizing hydrolysis of 6-aminocapronitrile is carried out by passing 91 g/h of this compound and 85 g/h of water over 53 ml (22.7 g) of alumina at 300°C. At the reactor outlet, the gases are cooled rapidly (less than 5 minutes) to room temperature (about 20°C). A clear aqueous ammoniacal solution is obtained containing (chromatographic assay) 47.5% by weight of caprolactam and 2.9% by weight of aminocapronitrile. This corresponds to a degree of conversion (DC) of the aminocapronitrile of 94% and to a yield of caprolactam relative to the aminocapronitrile loaded (RY) of 93% (i.e. a selectivity towards caprolactam relative to the aminocapronitrile converted, or CY, of 99%). This solution is stored for 3 months at a temperature of about 20°C and is then reassayed by chromatography. No presence of precipitate is observed. 48% by weight of caprolactam and 2.7% by weight of aminocapronitrile are then found, which, bearing in mind the precision of the assays, means that these crude solutions of caprolactam are stable under these conditions. Comparative test 1 An aqueous solution containing 50% by weight of an equimolar mixture of caprolactam and ammonia is maintained at 150°C for 6 hours. By assaying, it is observed that 10% of the caprolactam has been converted, while a red-brown precipitate has been formed. Example 2 The cyclizing hydrolysis of 6-aminocapronitrile is carried out by passing 100 g/h of this compound and 64 g/h of water over 200 ml (135 g) of alumina at 300°C. At the reactor outlet, the gases are cooled rapidly (less than 5 minutes) to room temperature (about 20°C). A clear aqueous ammoniacal solution is obtained containing (chromatographic assay) caprolactam and aminocapronitrile in amounts corresponding to a degree of conversion of the aminocapronitrile of 95.5% and to a yield of caprolactam relative to the aminocapronitrile loaded of 95.5% (i.e. a selectivity towards caprolactam relative to the aminocapronitrile converted of 100%). Comparative test 2 The cyclizing hydrolysis of 6-aminocapronitrile is carried out by passing 100 g/h of this compound and 64 g/h of water over 200 ml (135 g) of the alumina used in Example 2 at 300°C. At the reactor outlet, the reaction flow is cooled and maintained at about 150°C for two hours (in total), before being cooled over 10 seconds to room temperature (about 20°C). During this period of maintenance at 150°C, the flow then includes a gaseous phase and a liquid condensed phase. An aqueous ammoniacal solution is obtained containing (chromatographic assay) caprolactam and aminocapronitrile in amounts corresponding to a degree of conversion of the aminocapronitrile of 98.5% and a yield of caprolactam relative to the aminocapronitrile loaded of 94% (i.e. a selectivity towards caprolactam relative to the aminocapronitrile converted of only 95%). This solution contains a precipitate of caprolactam oligomers. We claim: 1. Process for separating a lactam from the reaction flow resulting from the vapour-phase cyclizing hydrolysis of an aminonitrile having the general formula: N=C-R-NH2 in which R represents a linear or branched alkylene radical having from 3 to 12 carbon atoms, characterized in that said process comprises: cooling the reaction flow for not more than 1 hour, to a temperature of 50°C to 150oC and then distilling it, or cooling the reaction flow over a period of not more than 10 minutes and to a temperature of not more than 50°C before storing for a period of longer than or equal to 1 hour and then distilling it. 2. Process as claimed in claim 2 in which the reaction flow is cooled to 70°C to 120°C. 3. Process as claimed in any one of claims 2 to 4 in which the time which elapses between the reaction flow leaving the hydrolysis reactor and the actual distillation, is at most one hour. 4. Process as claimed in claim 5 in which said time is at most 30 minutes. 5. Process as claimed in any one of claims 2 to 6 in which the distillation is carried out such that the average residence time of the lactam in the distillation apparatus is not more than 1 hour. 6. Process as claimed in claim 7 in which the distillation is carried out such that the average residence time of the lactam in the distillation apparatus is not more than 30 minutes. 7. Process as claimed in claim 1 in which the lactam is cooled at a temperature of not more than 40°C before being stored for a period of longer than or equal to 1 hour. 8. Process as claimed in any one of the preceding claims in which R represents a linear alkylene radical having 3, 4, 5 or 10 carbon atoms. 9. Process as claimed in any one of claims 1 to 10 in which the lactam is caprolactam. 10. Process for separating a lactam substantially as herein described with reference to the foregoing examples.

Full Text

PROCESS FOR TREATING LACTAMS
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°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°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°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.
Accordingly, there is provided a process for separating a lactam from the reaction flow resulting from the vapour-phase cyclizing hydrolysis of an aminonitrile having the general formula:
N»C-R-NH2
in which R represents a linear or branched alkylene radical having from 3 to 12 carbon atoms, characterized in that said process comprises: cooling the reaction flow for not more than 1 hour, to a temperature of 50"C to 150°C and then distilling it, or cooling the reaction flow over a period of not more than 10 minutes and to a temperature of not more than 50 C before storing for a period of longer than or equal to 1 hour and then distilling it.
According to the invention there is provided a process for separating a lactam from the reaction flow resulting from the vapour-phase cyclizing hydrolysis of an aminonitrile which comprises cooling the reaction flow for not more than 1 hour, to a temperature of not more than 150°C and then distilling it.
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, cooling may involve 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, so as to reduce the temperature of the mixture to below 150°C, preferably below 100°C.
As used herein, the term "cooling" covers the various modes indicated above, or equivalent modes.
When the reaction flow is fractionated or distilled immediately, that is to say without storage, it is preferable, for the economy of the process, to cool the said flow over the shortest possible period, preferably less than or equal to 10 minutes, typically to a temperature of from 50°C to 150°C and preferably from 70°C to 120°C. It is also recommended to limit the duration of feeding of the distillation column, that is to say the time which elapses between the reaction flow leaving the hydrolysis reactor and the actual distillation, to a maximum of one hour, preferably 30 minutes. The distillation itself should be carried out such that the average residence time of the lactam in the distillation apparatus is less than or equal to 1 hour.
When the reaction flow is not treated
immediately and is stored for a period of longer than 1 hour, the cooling is desirably carried out over a period of less than or equal to 10 minutes and preferably to a temperature below or equal to 50°C.
The lactam used in the present process is more particularly chosen from those which are obtained by vapour-phase cyclizing hydrolysis of an aliphatic
aminonitrile of general formula (I):
N=C-R-NH2
in which R represents a linear or branched alkylene radical having from 3 to 12 carbon atoms.
Among the lactams, mention may be made more particularly of those which serve as starting material for the preparation of polyamides 4, 5, 6 and 11 and which are obtained from the aminonitriles of formula (I), in which the symbol R represents a linear alkylene radical having 3, 4, 5 or 10 carbon atoms.
As indicated above, caprolactam whose polymerization gives polyamide 6, which is prepared from 6-aminocapronitrile (or epsilon-capronitrile), is the lactam preferentially used in the process of the invention.
Typical processes for the preparation of lactams, by vapour-phase cyclizing hydrolysis of aminonitriles of formula (I), are disclosed in, for example, EP-A-0,659,741 and WO-A-96/22974.
The lactam to be purified is generally in the form of an aqueous or alcoholic solution. Since the cyclizing hydrolysis is carried out in the vapour phase, the said lactam obtained is, more often than not, in aqueous solution. The lactam concentration of such a solution is generally from 20% to 80% on a weight for weight basis. The aminonitrile usually
represents up to 15% of the weight of the lactam, and most frequently from 0% to 10% of this weight.
The process of the invention generally makes it possible to limit the formation of oligomers to an amount such that the phenomenon has virtually no adverse effect. Such a content is generally less than or equal to 2% by weight of oligomers per unit weight of lactam and preferably less than or equal to 1% on a weight for weight basis.
Preferably, in the process of the invention, the lactam is stored at a temperature below or equal to 40°C before being distilled if the storage period is longer than or equal to 1 hour, and/or the distillation is carried out such that the average residence time of the lactam in the distillation apparatus is less than or equal to 30 minutes.
The Examples which follow further illustrate the present invention.
Example 1
The cyclizing hydrolysis of 6-aminocapronitrile is
carried out by passing 91 g/h of this compound and
85 g/h of water over 53 ml (22.7 g) of alumina at
300°C.
At the reactor outlet, the gases are cooled rapidly (less than 5 minutes) to room temperature (about 20°C).
A clear aqueous ammoniacal solution is
obtained containing (chromatographic assay) 47.5% by weight of caprolactam and 2.9% by weight of aminocapronitrile. This corresponds to a degree of conversion (DC) of the aminocapronitrile of 94% and to a yield of caprolactam relative to the aminocapronitrile loaded (RY) of 93% (i.e. a selectivity towards caprolactam relative to the aminocapronitrile converted, or CY, of 99%).
This solution is stored for 3 months at a temperature of about 20°C and is then reassayed by chromatography. No presence of precipitate is observed. 48% by weight of caprolactam and 2.7% by weight of aminocapronitrile are then found, which, bearing in mind the precision of the assays, means that these crude solutions of caprolactam are stable under these conditions.
Comparative test 1
An aqueous solution containing 50% by weight of an
equimolar mixture of caprolactam and ammonia is
maintained at 150°C for 6 hours. By assaying, it is
observed that 10% of the caprolactam has been
converted, while a red-brown precipitate has been
formed.
Example 2
The cyclizing hydrolysis of 6-aminocapronitrile is
carried out by passing 100 g/h of this compound and
64 g/h of water over 200 ml (135 g) of alumina at 300°C.
At the reactor outlet, the gases are cooled rapidly (less than 5 minutes) to room temperature (about 20°C).
A clear aqueous ammoniacal solution is
obtained containing (chromatographic assay) caprolactam and aminocapronitrile in amounts corresponding to a degree of conversion of the aminocapronitrile of 95.5% and to a yield of caprolactam relative to the aminocapronitrile loaded of 95.5% (i.e. a selectivity towards caprolactam relative to the aminocapronitrile converted of 100%).
Comparative test 2
The cyclizing hydrolysis of 6-aminocapronitrile is
carried out by passing 100 g/h of this compound and
64 g/h of water over 200 ml (135 g) of the alumina used
in Example 2 at 300°C.
At the reactor outlet, the reaction flow is cooled and maintained at about 150°C for two hours (in total), before being cooled over 10 seconds to room temperature (about 20°C). During this period of maintenance at 150°C, the flow then includes a gaseous phase and a liquid condensed phase.
An aqueous ammoniacal solution is obtained containing (chromatographic assay) caprolactam and aminocapronitrile in amounts corresponding to a degree
of conversion of the aminocapronitrile of 98.5% and a yield of caprolactam relative to the aminocapronitrile loaded of 94% (i.e. a selectivity towards caprolactam relative to the aminocapronitrile converted of only 95%). This solution contains a precipitate of caprolactam oligomers.

We claim:
1. Process for separating a lactam from the reaction flow resulting from the vapour-phase cyclizing hydrolysis of an aminonitrile having the general formula:
N=C-R-NH2
in which R represents a linear or branched alkylene radical having from 3 to 12 carbon atoms, characterized in that said process comprises:
cooling the reaction flow for not more than 1 hour, to a temperature of 50°C to 150oC and then distilling it, or cooling the reaction flow over a period of not more than 10 minutes and to a temperature of not more than 50°C before storing for a period of longer than or equal to 1 hour and then distilling it.
2. Process as claimed in claim 2 in which the reaction flow is
cooled to 70°C to 120°C.
3. Process as claimed in any one of claims 2 to 4 in which the
time which elapses between the reaction flow leaving the
hydrolysis reactor and the actual distillation, is at most one
hour.
4. Process as claimed in claim 5 in which said time is at most 30
minutes.
5. Process as claimed in any one of claims 2 to 6 in which the
distillation is carried out such that the average residence time
of the lactam in the distillation apparatus is not more than 1
hour.
6. Process as claimed in claim 7 in which the distillation is
carried out such that the average residence time of the lactam
in the distillation apparatus is not more than 30 minutes.
7. Process as claimed in claim 1 in which the lactam is cooled at
a temperature of not more than 40°C before being stored for a
period of longer than or equal to 1 hour.
8. Process as claimed in any one of the preceding claims in
which R represents a linear alkylene radical having 3, 4, 5 or
10 carbon atoms.
9. Process as claimed in any one of claims 1 to 10 in which the
lactam is caprolactam.
10. Process for separating a lactam substantially as herein
described with reference to the foregoing examples.

Documents:

2663-del-1997-abstract.pdf

2663-del-1997-claims.pdf

2663-del-1997-correspondence-others.pdf

2663-del-1997-correspondence-po.pdf

2663-del-1997-description (complete).pdf

2663-del-1997-form-1.pdf

2663-del-1997-form-13.pdf

2663-del-1997-form-19.pdf

2663-del-1997-form-2.pdf

2663-del-1997-form-3.pdf

2663-del-1997-form-4.pdf

2663-del-1997-form-6.pdf

2663-del-1997-gpa.pdf

2663-del-1997-petition-138.pdf

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Patent Number

214803

Indian Patent Application Number

2663/DEL/1997

PG Journal Number

09/2008

Publication Date

29-Feb-2008

Grant Date

15-Feb-2008

Date of Filing

19-Sep-1997

Name of Patentee

RHONE-POULENC FIBER AND RESIN INTERMEDIATES

Applicant Address

25 QUAI PAUL DOUMER, 92408 COURBEVOIE CEDEX, FRANCE

Inventors:

#	Inventor's Name	Inventor's Address
1	HENRI CHIARELLI	LOTISSEMENT VIALARZEU, RUE DU 30 MAI 1994, 69360 COMMUNAY, FRANCE
2	PHILIPPE LECONTE	43 RUE SAINTE-BEUVE, 69330 MEYZIEU, FRANCE

PCT International Classification Number

C07D 201/16

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	96 13203	1996-10-24	France