Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Utility Patent
1999-05-24
2001-01-02
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S322000, C528S323000, C528S324000, C528S332000, C528S335000, C528S336000, C528S339000, C528S340000, C528S347000, C528S349000
Utility Patent
active
06169162
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to processes for producing polyamides from dicarboxylic acid monomers and diamine monomers. More particularly, the invention relates to a process for producing polyamides that does not require the addition of water to the reactants.
Polyamides can be produced by a two-step process in which a dicarboxylic acid and a diamine are reacted in water to form a salt, and then the salt is heated to cause polymerization. For example, adipic acid and hexamethylenediamine can be used to form nylon
6
,
6
. The water liberated by the polymerization as well as the water added with the reactants must eventually be removed from the product, for example by evaporation. This requires major amount of energy as well as additional process equipment. Therefore, it would be useful to produce polyamides without adding water to the reactants, in order to reduce the expense of removing water from the product, and in order to eliminate the intermediate (salt) product, thereby simplifying the overall process.
However, attempts to produce polyamides directly from the monomers without adding water have encountered a number of problems. Regulating the amounts of the monomers fed to the reaction is critical, because an excess of one or the other will adversely affect the molecular weight and thus the physical properties of the product. It has proven to be quite difficult to provide the precise regulation of reactant amounts that is required. Other problems with such direct polymerization processes include degradation of the monomers and/or the polymer product as a result of (1) being kept at high temperatures for lengthy periods of time (e.g., several hours), (2) contact of the molten monomers with oxygen, and (3) exposure to trace metal impurities in the materials from which the process equipment is made.
There is a long-standing need for improved processes for making polyamides directly from monomers.
SUMMARY OF THE INVENTION
One aspect of the invention is a process for producing a polyamide from dicarboxylic acid monomer and diamine monomer. One embodiment of the process includes the steps of:
(a) mixing molten dicarboxylic acid monomer and molten diamine monomer in equimolar amounts, thereby producing a molten reaction mixture;
(b) flowing the reaction mixture through at least one unvented reaction vessel, the residence time of the reaction mixture in the at least one unvented reaction vessel being between about 0.01 minutes and about 30 minutes, thereby forming a first product stream that comprises polyamide and water of polymerization; and
(c) flowing the first product stream through at least one vented vessel, whereby water of polymerization is removed, thereby forming a second product stream that comprises polyamide.
In another embodiment, the process includes the steps of:
(a) mixing molten dicarboxylic acid monomer and molten diamine monomer in equimolar amounts, thereby producing a molten reaction mixture; and
(b) flowing the reaction mixture through at least one unvented reaction vessel at a pressure between 0-500 psig, the residence time of the reaction mixture in the at least one unvented reaction vessel being between about 0.01 minutes and about 30 minutes, thereby forming a first product stream that comprises polyamide.
In this embodiment of the process, a second vessel, located downstream of the at least one unvented reaction vessel, is not required, but may optionally be used, for removal of water of polymerization, for further reaction, or for both purposes.
This process of the present invention can operate continuously, and there is no need to add water to the dicarboxylic acid, to the diamine, or to the reaction mixture. No additional dicarboxylic acid monomer or diamine monomer needs to be added after the mixing.
The molten dicarboxylic acid can be produced by the steps of:
removing oxygen from dry dicarboxylic acid by alternately subjecting the dry dicarboxylic acid in an oxygen removal pressure vessel to a vacuum and to inert gas pressure, thereby producing solid dicarboxylic acid that has reduced molecular oxygen content; and
feeding the solid dicarboxylic acid having reduced molecular oxygen content to a melter vessel which contains a quantity of molten dicarboxylic acid, whereby the solid dicarboxylic acid melts and a continuous stream of molten dicarboxylic acid is produced.
The solid dicarboxylic acid can be moved from the oxygen removal pressure vessel to the melter vessel by gravity. Preferably it is moved from the oxygen removal pressure vessel to the melter vessel by a combination of gravity and inert gas pressure in the oxygen removal pressure vessel. This arrangement permits the residence time of the dicarboxylic acid monomer in the melter vessel to be less than three hours.
In preferred embodiments of the process, the temperature of the reaction mixture in the at least one unvented reaction vessel is between about 220 and about 300° C. Preferably the pressure in the at least one unvented reaction vessel is between about 0-500 psig, more preferably between about 50-250 psig, most preferably between about 120-180 psig. The residence time of the reaction mixture in the at least one unvented reaction vessel is preferably between about 0.01 minutes and about 30 minutes, more preferably between about 0.5-30 minutes, most preferably between about 1-5 minutes. The first product stream exiting the at least one unvented reaction vessel typically contains less than 40% by weight unpolymerized monomers, preferably less than 10% by weight unpolymerized monomers. The residence time of the reaction mixture in the at least one vented reaction vessel is preferably from about 1 minute to about 60 minutes.
In one embodiment of the invention, a reactive diamine recovery system can be used. The at least one vented reaction vessel generates an offgas stream that comprises water vapor and vaporized diamine monomer, and the offgas is contacted with molten dicarboxylic acid monomer in a recovery column, whereby at least a portion of the vaporized diamine monomer reacts with the dicarboxylic acid monomer to form polyamide. A liquid effluent stream is generated from the recovery column that comprises polyamide and unreacted molten dicarboxylic acid monomer, and the liquid effluent stream is subsequently mixed with molten diamine monomer.
One specific embodiment of the invention is a continuous process for making nylon
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,
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from adipic acid and hexamethylenediamine (HMD), comprising:
removing oxygen from dry adipic acid by alternately subjecting the dry acid in an oxygen removal pressure vessel to a vacuum and to inert gas pressure, thereby producing solid adipic acid that has reduced molecular oxygen content;
feeding the solid adipic acid having reduced molecular oxygen content to a melter vessel which contains a quantity of molten adipic acid, whereby the solid adipic acid melts and a continuous stream of molten adipic acid is produced;
melting HMD;
mixing molten adipic acid and molten HMD in equimolar amounts, thereby creating a reaction mixture;
flowing the reaction mixture through at least one unvented reaction vessel, the residence time of the reaction mixture in the at least one unvented reaction vessel being between about 0.01 to about 5 minutes, thereby forming a partially polymerized nylon
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,
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reaction mixture;
flowing the partially polymerized reaction mixture through at least one vented reaction vessel, whereby the partially polymerized reaction mixture is further polymerized, producing nylon
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,
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, and wherein water of polymerization is removed.
In this specific embodiment, the relative viscosity (RV) of the partially polymerized nylon
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,
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reaction mixture exiting the unvented reaction vessel is between about 0 and about 3, and the relative viscosity of the nylon
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,
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exiting the vented vessel is between about 3 and about 15. Relative viscosity as used herein is the ratio of viscosity (in centipoises) at 25° C. of 8.4% by weight solution of polyamide in 90% formic acid (90% by weight formic acid and 10%
Bush Gregory E.
Cook Steven W.
Lembcke Robert M.
Schwier Chris E.
Hampton-Hightower P.
Howery Simon Arnold & White LLP
Solutia Inc.
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