Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-04-14
2003-01-21
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S312000, C528S324000, C528S329100, C528S332000, C528S335000, C528S336000
Reexamination Certificate
active
06509439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing polyamides from dinitriles and diamines and to related polyamide products produced from the process.
2. Description of Related Art
Currently, polyamides are being produced commercially from dicarboxylic acids and diamines. For example, Nylon 6,6 is commercially produced from adipic acid and hexamethylenediamine. Alternate routes to these materials have been explored within the art. For example, the art has taught processes to produce Nylon 6,6 from adiponitrile and hexamethylenediamine. Greenewalt, U.S. Pat. No. 2,245,129, discloses a process to produce polyamides by reacting adiponitrile, hexamethylenediamine, and water at a high temperature and pressure. However, the Greenewalt patent requires a two-stage process in which, after initial heating, the process must be discontinued to allow the reaction to cool, and then be subsequently heated again prior to recovering the polyamide. A modified process to react adiponitrile with hexamethylenediamine and water was disclosed by Onsager in U.S. Pat. No. 3,847,876, but at extremely high pressures of up to about 2000 psig.
The production of polyamides was improved by the introduction of catalysts to promote or enhance the production of polyamides. Several catalytic methods are disclosed, for example, in U.S. Pat. Nos. 4,490,521, 4,542,205, 4,603,192, 4,725,666, 4,749,776, 4,436,898, and 4,528,362. In addition, cocatalysts were introduced to further promote and enhance the production of polyamide. For example, a process of forming polyamides from adiponitrile, hexamethylenediamine, adipic acid, and water was described in Greene et al., U.S. Pat. No. 4,501,881.
Each of the methods described above, however, have the significant shortcoming of producing polyamides from adiponitrile and hexamethylenediamine concurrently with the production of significant levels of the dimer of the aliphatic diamine. In the case of hexamethylenediamine, the dimer produced would be bishexamethylenetriamine (BHMT). The diamine dimerization is promoted by the high temperatures and pressures required by the processes described above. (See Shyu, U.S. Pat. No. 4,739,035, and Liehr et al., U.S. Pat. No. 5,627,257). These diamine dimers or triamine by-products serve as crosslinkers for the linear polyamide chain, which can lead to a significant product quality deterioration.
The problems associated with the production of triamine by-products was partially overcome by the processes disclosed by Shyu et al., U.S. Pat. No. 4,739,035, and Liehr et al., U.S. Pat. No. 5,627,257. Shyu et al. teach a two-step process, wherein the first step includes the hydrolysis of adiponitrile with water, catalysts, and from 0 to 10 weight percent of the total hexamethylene diamine needed for the reaction. The second step includes adding the remainder of the hexamethylenediamine followed by polymerization. This two-step process provided triamine levels in the 560 to 1300 ppm levels as compared to the 1420 to 1610 ppm levels found through the teachings of other background art.
Liehr et al. describe a two-step process. The first step includes the nearly full hydrolysis of the adiponitrile to adipic acid utilizing a catalyst and a cocatalyst. The cocatalyst was described as a saturated aliphatic or aromatic dicarboxylic acid. The second step includes the addition of at least an equimolar amount of diamine followed by polymerization. Through use of this process, they were able to achieve triamine levels between 500 and 600 ppm. However, this process is hindered by the substantial amounts of cocatalyst required. For example, the Liehr process requires a level of the dicarboxylic acid cocatalyst from about 1 to 13 weight percent based on the adiponitrile level. In one example, they teach the use of 73 grams adipic acid cocatalyst in the hydrolysis of 487 grams of adiponitrile.
Each of the two-step processes described by Shyu et al. and Liehr et al. are also hindered by the inherent difficulty with discontinuous processes and significantly greater process length (time) when compared to continuous processes of the background art. The present invention overcomes the shortcomings of the background art providing a simplified continuous production process for polyamides with low levels of triamine impurities without the need for substantial amounts of cocatalysts.
SUMMARY OF THE INVENTION
The present invention is directed to a process for producing a polyamide comprising:
reacting a dinitrile with a diamine, water, and optionally a catalyst to form a reaction mixture;
heating the reaction mixture to a first elevated temperature of between about 180 to about 240° C., preferably, about 200 to about 220° C.; maintaining said temperature for 0.10 to 20 hours, preferably 0.10 to 10 hours; and optionally controlling the pressure in this heating step by venting;
then, after maintaining the first elevated temperature, subsequently heating the reaction mixture to a second elevated temperature of between about 250 to about 350° C., preferably, about 270 to about 300° C.; adding water to the reaction mixture before or after the second elevated temperature is reached; maintaining the pressure in the second heating step above atmospheric pressure by venting at least some of the water; and maintaining the second elevated temperature for a period of about 0.10 to about 10 hours, preferably 0.10 to 4 hours; and
recovering the polyamide.
In another embodiment of the invention, in the reacting step, the diamine is added in an amount within 10 mole percent of equimolar based on the dinitrile and at least a stoichiometric amount of water is added relative to the dinitrile.
In another embodiment of the invention, the step of heating the reaction mixture to a second elevated temperature is obtained under a reaction pressure of above atmospheric pressure. After maintaining the second elevated temperature, the reaction mixture is then optionally maintained at a third temperature of about 250 to about 350° C. while the reaction pressure is reduced to atmospheric pressure or less. This additional embodiment often allows for the more complete polymerization of the amides thereby achieving a higher molecular weight polyamide product.
In yet another embodiment of the invention, the dinitrile is adiponitrile and the diamine is hexamethylenediamine. The final polyamide produced when adiponitrile and diamine are used in the process of the present invention is poly(hexamethylene adipamide)(Nylon 6,6).
The polyamide can be produced in a continuous process and without the need for high levels of cocatalysts used in the prior art processes. Moreover, the polyamide has been found to exhibit low levels of triamine impurities.
The invention also relates to polyamides produced using these processes.
Further objects, features, and advantages of the invention will become apparent from the detailed description that follows.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The present invention is directed to a process for producing a polyamide from dinitriles and diamines. The process includes the step of contacting a dinitrile with a diamine, water, and optionally a catalyst to form a reaction mixture; heating the reaction mixture to a first elevated temperature of between about 180 to about 240° C., and maintaining the first elevated temperature for 0.10 to 20 hours; heating the reaction mixture to a second elevated temperature of between about 250 to about 350° C., wherein before or after the second elevated temperature is reached, water is added to the reaction mixture, some of the water is then subsequently removed, and the second elevated temperature is maintained for a period of about 0.10 to about 10 hours, preferably 0.10 to 4 hours; and recovering the polyamide. Optionally, the reaction mixture may be maintained at a third temperature of about 250 to about 350° C., that may be the same or different from the second elevated temperature, prior to recovering the polyamide, wherein at the third temperature, the reac
Hayes Richard Allen
Marks David N
Sunkara Hari Babu
Van Eijndhoven Maria
E. I. du Pont de Nemours and Company
Hampton-Hightower P.
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