Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
1999-08-18
2001-02-27
Kifle, Bruck (Department: 1611)
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
C540S539000
Reexamination Certificate
active
06194572
ABSTRACT:
The invention relates to a process to prepare &egr;-caprolactam by treating 6-aminocaproic acid, 6-aminocaproate ester or 6-aminocaproamide or mixtures comprising at least two of these compounds in the presence of superheated steam in which a gaseous mixture comprising &egr;-caprolactam and steam is obtained.
Such a process is described in U.S. Pat. No. 3,658,810. This patent publication describes a process to prepare &egr;-caprolactam by treating 6-aminocaproic acid, 6-aminocaproamide or mixtures of the two with superheated steam at a temperature from 200-350° C. and a pressure of between 0.05 and 0.5 MPa. The best results are obtained when a non-volatile phosphoric acid-catalyst is also present. The pressure is preferably according to the description between 0.1 and 0.3 MPa. It was presented as an advantage of this process that it could be performed at atmospheric pressure. All the examples illustrating the non-catalyzed process variant were performed at atmospheric pressure.
A disadvantage of this known process is that high yields are only obtainable when the non-volatile phosphoric acid is used. When the process is performed in the absence of a catalyst the highest yield illustrated in the examples of U.S. Pat. No. 3,658,810 is about 74%. The use of non-volatile phosphoric acids is not advantageous because special measures, such as the use of non corrosive reactor material, is needed. Furthermore when 6-aminocaproamide is used as substrate the catalyst will be consumed because ammonium phosphate will be formed.
The object of the present invention is a simple process to prepare &egr;-caprolactam in a high yield starting from 6-aminocaproic acid, 6-aminocaproate ester and/or 6-aminocaproamide.
This object is achieved in that the process is carried out in the absence of a catalyst at a temperature between 250 and 400° C. and at a pressure of between 0.5 and 2 MPa.
It has been found that with the process according to the invention high yields to &egr;-caprolactam can be achieved even though no additional catalyst is present. Another advantage is that the activity of the reaction is higher when compared to the activity at atmospheric pressure. Because of the higher activity smaller process equipment can be used.
U.S. Pat. No. 4,599,199 describes a process to prepare &egr;-caprolactam by treating 6-aminocaproic acid with superheated steam in a fluidized alumina bed at atmospheric pressure. This patent publication teaches a catalyzed process.
Processes to prepare &egr;-caprolactam starting from 6-aminocaproic acid are for example described in U.S. Pat. No. 4,730,040. In this patent publication a process is described in which 6-aminocaproic acid is converted to &egr;-caprolactam in the liquid phase in the absence of an additional catalyst at a temperature of 300° C. In such a process a liquid reaction mixture containing &egr;-caprolactam, unconverted 6-arminocaproic acid and oligomers is obtained. The present invention is different because &egr;-caprolactam is obtained in the gaseous phase, which phase does not contain substantial amounts of unconverted starting compounds and/or oligomers. This is advantageous because the purification of &egr;-caprolactam is easier compared to this prior art process.
The process according to the invention is carried out in the absence of a catalyst. By catalyst it is meant homogeneous and heterogeneous catalyst which are present in order to catalyze the reaction as for example illustrated in the earlier mentioned U.S. Pat. No. 3,658,810, which illustrates a homogeneous catalyst and in U.S. Pat. No. 4,599,199, which illustrates a heterogeneous alumina catalyst. It should be clear that a process, in which a negligible amount of a catalyst-like compound is present which compound does not affect the reaction noticably, is a process carried out in the absence of a catalyst according to this invention.
The starting mixtures comprising 6-aminocaproic acid, 6-aminocaproate ester and/or 6-aminocaproamide can be obtained by various processes. For example in U.S. Pat. No. 4,730,040 a process is described in which an aqueous mixture is obtained containing 6-aminocaproic acid and some &egr;-caprolactam starting from 5-formylvalerate ester. Further in EP-A-729943 a process is described in which an aqueous mixture is obtained containing 6-aminocaproic acid, 6-aminocaproamide and &egr;-caprolactam also starting from a 5-formylvalerate ester. U.S. Pat. No. 5,068,398 describes a process in which an aqueous mixture is obtained containing 6-aminocaproate ester and some &egr;-caprolactam starting from a 5-formylvalerate ester.
The starting compounds are preferably 6-aminocaproic acid and/or 6-aminocaproic amide because high yields to &egr;-caprolactam are possible when starting from this compound. Next to the 6-aminocaproic acid and/or 6-aminocaproamide some &egr;-caprolactam and/or oligomers of &egr;-caprolactam, 6-aminocaproic acid and/or 6-aminocaproamide can be present. A typical mixture which can be used as starting mixture for the present invention comprises between 5 and 50 wt % 6-aminocaproic acid, 10 and 50 wt % 6-aminocaproamide, 0 and 40 wt % &egr;-caprolactam and between 0 and 35 wt % of the ear mentioned oligomers in which the total of these fractions is 100 wt. %.
The 6-aminocaproate ester compound can be represented by the following general formula:
where R 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 is an alkyl group. Examples of R groups include methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, isobutyl, cyclohexyl, benzyl and phenyl. By preference R is methyl or ethyl.
Starting mixtures can also be obtained by the method as described below. Processes starting from 6-aminocapronitrile can also yield mixtures comprising 6-aminocaproic acid. Such mixtures can be advantageously used in the process according to the invention. Processes to prepare &egr;-caprolactam starting from 6-aminocapronitrile are for example described in U.S. Pat. No. 5,495,016. This patent publication describes a process to prepare &egr;-caprolactam by contacting 6-aminocapronitrile in a cyclization zone with water in the liquid phase at a temperature of about 300° C. at super atmospheric pressure resulting in an aqueous mixture containing ammonia, &egr;-caprolactam and &egr;-caprolactam precursors, for example 6-aminocaproic acid, 6-aminocaproic amide and oligomers. The weight ratio oligomers to &egr;-caprolactam is about 1:3 according to the examples. &egr;-caprolactam is isolated by distillation. The oligomers can be further converted, according to this patent publication, to &egr;-caprolactam by either recycling them to the cyclization zone or treating them in a further reactor in a similar fashion as performed in the cyclization zone.
A disadvantage of this process is that high concentration of oligomers are present in the reboilers of the various distillation steps. This can result in fouling due to solidification of the oligomers in pipes and other process equipment. Furthermore &egr;-caprolactam will polymerize to oligomers under these conditions (2 wt. % of the &egr;-caprolactam may polymerize according to Example I of U.S. Pat. No. 5,495,016) resulting in a loss of yield per pass.
By (1) contacting 6-aminocapronitrile with water under hydrolysis conditions, (2) separating water and ammonia, which is formed in the hydrolysis reaction, and (3) contacting the resulting mixture with superheated steam according to the process according to this invention, these problems are overcome.
It has been found that with the above described process &egr;-caprolactam can be obtained starting from 6-aminocapronitrile without the need to recycle or further process the oligomers formed in the process.
The contacting under hydrolysis conditions can be performed in any manner known to one skilled in the art. Under these hydrolysis conditions the nitrile group will react with water to an amide group or a carboxylic acid group and ammonia. Hydrolysi
Agterberg Frank P. W.
Buijs Wim
Guit Rudolf P. M.
Wolters Henricus F. W.
DSM N.V.
Kifle Bruck
Pillsbury & Winthrop LLP
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