Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
2002-08-02
2003-12-09
Kifle, Bruck (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
C540S538000, C540S539000
Reexamination Certificate
active
06660857
ABSTRACT:
The invention relates to a process for the preparation of &egr;-caprolactam starting from 6-aminocaproic acid, 6-aminocaproamide, 6-aminocaproic ester, 6-aminocapronitrile, oligomers or polymers of these compounds or mixtures comprising at least two of these compounds.
Such a process is described in JP-A-51039684. This patent publication describes a process to prepare &egr;-caprolactam from nylon-6 polymer using an adduct of &egr;-caprolactam and terephthalic acid, isophthalic acid or adipic acid as depolymerisation catalyst.
A disadvantage is that the catalyst is a process-foreign compound resulting in &egr;-caprolactam containing undesired impurities. Such impurities would not be present when the process is performed in the substantial absence of such process-foreign compounds.
The object of the present invention is a process for the preparation of &egr;-caprolactam in which the above mentioned disadvantage is avoided or at least reduced.
This object is achieved in that the process is performed in the presence of N-(5-carboxypentyl)-&egr;-caprolactam and/or derivative thereof in an amount of less than 50 wt. % and more than 0.1 wt. % (based on the total reaction mixture).
It has been found that the rate of the reaction of the process according to the invention is significantly higher than the rate of reaction of a process for the preparation of &egr;-caprolactam starting from the above mentioned compounds performed in the substantial absence of N-(5-carboxypentyl)-&egr;-caprolactam and/or derivative thereof or performed in the presence of higher amounts of N-(5-carboxypentyl)-&egr;-caprolactam and/or derivative thereof. This is advantageous because smaller reactor equipment can be used and/or less residence time is needed resulting in less degradation reactions. Degradation reactions result in yield loss and/or in the formation of undesirable by-products making the purification of &egr;-caprolactam more difficult. Another advantage is that N-(5-carboxypentyl)-&egr;-caprolactam and/or derivative thereof is a process-own compound so that the process of the invention does not result in &egr;-caprolactam containing extra impurities due to the use of a process-foreign catalyst compound.
JP-A-45022946 describes a process for the preparation of &egr;-caprolactam by reacting N-(5-carbamoylpentyl)-&egr;-caprolactam with aqueous ammonia at a temperature of 350° C. The compound N-(5-carboxypentyl)-&egr;-caprolactam itself is known from JP-A-45022946. The use of N-(5-carboxypentyl)-&egr;-caprolactam or derivative thereof as reaction rate enhancing compound in a process for preparing &egr;-caprolactam from 6-aminocaproic acid, 6-aminocaproamide, 6-aminocaproic ester, 6-aminocapronitrile, oligomers or polymers of these compounds or mixtures comprising at least two of these compounds is however not disclosed. N-(5-carboxypentyl)-&egr;-caprolactam is said to be obtained by processing the distillation residue that is obtained in the distillation of crude &egr;-caprolactam obtained by the reaction of caprolactone and aqeous ammonia. The N-(5-carboxypentyl)-&egr;-caprolactam must subsequently be converted into N-(5-carbamoylpentyl)-&egr;-caprolactam before the latter compound is reacted with aqueous ammonia at a temperature of 350° C. to obtain &egr;-caprolactam.
With N-(5-carboxypentyl)-&egr;-caprolactam is meant a compound with the following structural formula:
With N-(5-carbamoylpentyl)-&egr;-caprolactam is meant a compound with the following structural formula:
In the present application, the term N-(5-carboxypentyl)-&egr;-caprolactam derivative include compounds with the following structural formula:
or with the following structural formula:
wherein R′ is NH
2
or OR
1
; n is at least 1; R″ is OH, NH
2
or OR
1
; R
1
is preferably an organic group with 1 to 20 carbon atoms and more preferably with 1 to 6 carbon atoms. The organic group is an alkyl, cycloalkyl, aryl or aralkyl group. More preferably R
1
is an alkyl group wit 1 to 6 carbon atoms. Examples of R
1
groups include methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, isobutyl, cyclohexyl, benzyl and phenyl. By preference R
1
is methyl or ethyl.
The N-(5-carboxypentyl)-&egr;-caprolactam and N-(5-carbamoylpentyl)-&egr;-caprolactam can for example be prepared by the method as described in for example JP-A-45022946. The N-(5-carboxypentyl)-&egr;-caprolactam may be formed or can for example be prepared from di-(5-carboxypentyl)amine using the conditions as applied in the process of the invention according to the following reaction scheme:
The di-(5-carboxypentyl)amine may be formed or can for example be prepared from 6-aminocaproic acid using the conditions as applied in the process of the invention according to the following reaction scheme:
The di-(5-carboxypentyl)amine may be formed or can for example be prepared from 6-aminocaproic acid and a 5-formylvaleric acid ester using the conditions as described in for example WO-A-9835938 according to the following reaction scheme:
The compound with formula
in which R′ is as defined above, may be formed or can for example be prepared from 6-aminocaproic acid and 6-aminocaproamide (in case R′ is —NH
2
) or from 6-aminocaproic acid and 6-aminocaproate ester (in case R′ is —OR
1
) using the conditions as applied in the process of the invention.
In case the term N-(5-carboxypentyl)-&egr;-caprolactam is stated below, it should be read as N-(5-carboxypentyl)-&egr;-caprolactam and/or derivative thereof.
The N-(5-carboxypentyl)-&egr;-caprolactam may be added at the beginning of the process according to the present invention. The N-(5-carboxypentyl)-&egr;-caprolactam may also already be present in a reaction mixture obtained in a previous process step, which also contains at least one of 6-aminocaproic acid, 6-aminocaproamide, 6-aminocaproic ester, 6-aminocapronitrile, oligomers or polymers of these compounds.
Is has been found that the presence of N-(5-carboxypentyl)-&egr;-caprolactam in the reaction mixture in an amount of between 0.1 and 50 wt. % (based on the total reaction mixture) results in an increase of the reaction rate. With “the total reaction mixture” is meant the starting compound or mixture of starting compound (optionally containing water) which is fed to the process according to the invention. It has been found that the presence of N-(5-carboxypentyl)-&egr;-caprolactam in the reaction mixture in an amount higher than 50 wt. % results in a decrease of the reaction rate. The amount of N-(5-carboxypentyl)-&egr;-caprolactam in the reaction mixture is preferably between 0.1 wt. % and 10 wt. % (based on the total reaction mixture).
The amount of N-(5-carboxypentyl)-&egr;-caprolactam can also be kept at and/or brought to the desired value within the above general and preferred ranges by adding or by removing N-(5-carboxypentyl)-&egr;-caprolactam, for example by purging.
The process according to the invention may be performed in the gas phase by contacting the starting compound(s) (6-aminocaproic acid, 6-aminocaproamide, 6-aminocaproic ester, 6-aminocapronitrile, oligomers or polymers of these compounds or mixtures comprising at least two of these compounds) with superheated steam at a temperature of between 150 and 500° C. and a pressure of between 0.1 and 2 MPa.
An example of a possible gaseous phase process is described in WO-A-9837063. The process may also be performed in the liquid phase at elevated temperatures and super atmospheric pressures such as for example described in U.S. Pat. No. 4,730,040, EP-A-729944 and WO-A-9809944.
The process according to the invention is preferably performed in the gas phase. The gas phase processes are advantageous because &egr;-caprolactam is obtained in a gaseous steam phase in which no or partically no oligomers are present. This is advantageous because the purification of &egr;-caprolactam is easier. The gas phase is preferably performed as described in WO-A-9837063, the complete disclosure is incorporated herein as reference. The gas phase process is preferably performed at a temperature of between 2
Agterberg Frank P. W.
Guit Rudolf P. M.
Offermanns Matthias R. J.
DSM N.V.
Kifle Bruck
Pillsbury & Winthrop LLP
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