Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
2000-08-09
2001-12-25
Kifle, Bruck (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
active
06333412
ABSTRACT:
The invention relates to a process to prepare &egr;-caprolactam from a starting mixture containing a 6-aminocaproate ester, in which in a first step (1) the 6-aminocaproate ester is converted into 6-aminocaproic acid and 6-aminocaproamide by reaction with water in the presence of ammonia at a temperature of between 50 and 250° C., with a separate or simultaneous removal of alcohol(s), and in a subsequent step (2) the 6-aminocaproic acid and 6-aminocaproamide are cyclizised at an elevated temperature.
Such a process is described in U.S. Pat. No. 4,731,445. This publication describes a process in which first methyl 5-formylvalerate is contacted with ammonia and hydrogen in the presence of methanol as solvent and a hydrogenation catalyst. In this step methyl 6-aminocaproate and a small amount of &egr;-caprolactam is obtained. In a second step, the excess ammonia and hydrogen are removed from the reaction mixture. In a third step, the methyl 6-aminocaproate is reacted with water in the presence of a small amount (0.1 to 2 wt. %) of ammonia at a temperature of 50 to 250 ° C. The released methanol is simultaneously removed. Example 1 of U.S. Pat. No. 4,731,445 discloses the reaction of methyl 6-aminocaproate with water in the presence of an almost negligible amount of ammonia at a temperature of about 100° C. The resulting aqueous mixture, which mixture contains 6-aminocaproic acid and small amounts of 6-minocaproamide and &egr;-caprolactam, is heated to a emperature of 330° C. In this step the 6-aminocaproic acid and 6-aminocaproamide reacts by cyclization to &egr;-caprolactam.
A disadvantage of the process described in U.S. Pat. No. 4,731,445 is that the rate of the reaction in the third step in which 6-aminocaproate ester is converted into 6-aminocaproic acid and 6-aminocaproamide is relatively small. Furthermore it would be advantageous if the reaction rate of 6-aminocaproate ester into 6-aminocaproic acid and 6-aminocaproamide could be improved in order to make this process more attractive for commercial use on a large scale.
The object of the invention is to provide a process according to which the 6-aminocaproate ester can be converted into 6-aminocaproic acid and 6-aminocaproamide with an improved reaction rate.
This object is achieved in that in step (1) the 6-aminocaproate ester is converted into 6-aminocaproic acid and 6-aminocaproamide in the presence of an amount higher than 2 wt. % and less than or equal to 25 wt. % NH
3
(relative to the total amount of the starting mixture).
It has been found that with the process of the invention the rate of the reaction of 6-aminocaproate ester into 6-aminocaproic acid and 6-aminocaproamide in step (1) is higher than the rate of the reaction disclosed in U.S. Pat. No. 4,731,445. An advantage of the process according to the invention is that a smaller volume of process equipment can be used in step (1) for obtaining comparable degrees of conversion of 6-aminocaproate ester to 6-aminocaproic acid and 6-aminocaproamide. From an economical/investment point of view smaller process equipment is desired.
In the first step (1) of the process according to the invention 6-aminocaproate ester is converted into 6-aminocaproic acid and 6-aminocaproamide by reaction with water in the presence of ammonia.
The starting mixture fed to the first step therefore should at least contain 6-amino caproate ester, water and ammonia. Other compounds may be present in the starting mixture, e.g. methanol.
The amount of 6-aminocaproate ester in the liquid mixture fed to the first step (1) (starting mixture) generally exceeds 0.5 wt. % calculated on the amount of organic compounds present in the starting mixture. Organic compounds are here defined as &egr;-caprolactam and &egr;-caprolactam precursors and side-reaction products, which may be present in small amounts. &egr;-Caprolactam precursors are defined as 6-aminocaproic acid, 6-aminocaproate ester, 6-aminocaproamide and oligomers of these compounds.
In the process according to the invention 6-aminocaproic acid and/or 6-aminocaproamide may also be present in the starting mixture. Next to the 6-aminocaproate ester and optionally the 6-aminocaproic acid and/or 6-aminocaproamide, also &egr;-caprolactam and/or oligomers of 6-aminocaproic acid and/or 6-aminocaproamide may be present. A typical composition of organic compounds which can be used in the starting mixture for the present invention comprises between 0.5 and 100 wt. % 6-aminocaproate ester, 0 and 30 wt. % 6-aminocaproic acid, 0 and 50 wt. % 6-aminocaproamide, 0 and 50 wt. % &egr;-caprolactam and between 0 and 30 wt. % of the earlier mentioned oligomers in which the total of these fractions is about 100 wt. % of the organic compounds.
Ammonia and/or water may be added to or removed from and/or may already be present in a reaction mixture which also contains 6-aminocaproate ester. Thus the ammonia and/or water concentration can be kept and/or adjusted to the desired value within the general and preferred ranges before feeding the starting mixture to the first step (1) of the process according to the invention. Removal of ammonia and/or water can be done by for example flashing or stripping.
The amount of ammonia present in the starting mixture is higher than 2 and less than or equal to 25 wt. %. The term “ammonia” means free NH
3
and does not include the amount of NH
3
present in the form of for example a terminal amide group of a compound optionally present in the starting mixture. An example of such a compound is 6-aminocaproamide. The ammonia concentration in step (1) is preferably lower than 20 wt. %, more preferably lower than 15 wt. %. The ammonia concentration in step (1) is preferably higher than 3 wt. % and more preferably higher than 5 wt. %.
The total concentration of organic compounds essentially consisting of 6-aminocaproate ester and—if present—6-aminocaproic acid, 6-aminocaproamide, &egr;-caprolactam and oligomers of 6-aminocaproic acid and 6-aminocaproamide in the starting mixture is preferably between about 0.2 and 50 wt. %. The sum of the amounts of organic compounds, ammonia, water and other compounds like methanol in the starting mixture 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.
The temperature in step (1) of the process according to the invention is between 50 and 250° C., preferably between 60 and 160° C. and most preferably between 90 and 140° C.
The pressure of the first step (1) is not critical. Depending on the pressure the reactor can be operated as a full liquid mixture or as a mixture where a liquid and a vapor phase coexist. Methanol and ammonia may be partly stripped from the mixture.
The starting mixture of the process according to the invention may be obtained with various known processes. For this invention it is not critical how the starting mixture is obtained.
The starting mixture may be, for example, obtained as the reaction product of the reduction of 5-cyanovalerate ester.
The starting mixture of the process according to the invention may also for example be obtained as the reaction product of the reductive amination of a 5-formylvalereate ester. Examples of possible processes are described in EP-A-729943, EP-A-729944, U.S. Pat. Nos. 4,766,237, 4,730,041, 4,731,445 and 5,068,398.
The reductive amination mixture may contain, next to the 6-aminocaproate ester and optionally 6-aminocaproic acid, 6-aminocaproamide, &egr;-caprolactam and/or oligomers, some alcohol. The alcohol generally is the corresponding alcohol of the ester group of the 6-aminocaproate ester. The alcohol can be separated from the reductive amination mixture by means of stripping or distillation before this mixture is fe
Guit Rudolf P. M.
Lane Samuel L.
DSM N.V.
Kifle Bruck
Pillsbury & Winthrop LLP
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