Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2002-08-08
2004-02-24
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S332000, C528S335000, C528S339000, C528S340000, C528S347000, C526S059000
Reexamination Certificate
active
06696544
ABSTRACT:
The present invention relates to a process for the manufacture of polyamide.
It relates more particularly to the manufacture of polyamides resulting from the reaction between a diacid and a diamine.
Polyamides are polymers of great industrial and commercial importance. Thermoplastic polyamides are obtained either by reaction between two different monomers or by polycondensation of a single monomer. The invention applies to polyamides resulting from two different monomers, the most important polyamide of which is poly(hexamethylene adipamide). Of course, these polyamides can be obtained from a mixture of diacids and diamines. Thus, in the case of poly(hexamethylene adipamide), the main monomers are hexamethylenediamine and adipic acid. However, these monomers can comprise up to 25 mol % of other diamine or diacid monomers or even of amino acid or lactam monomers.
This class of polyamides resulting from two different monomers is generally manufactured by using, as starting material, an amino acid salt obtained by mixing a diacid with a diamine in a stoichiometric amount and in a solvent such as water.
Thus, in the manufacture of poly(hexamethylene adipamide), adipic acid is mixed with hexamethylenediamine in water to produce a hexamethylenediamine adipate better known under the name of Nylon salt or “N Salt”.
The solution of N salt is optionally concentrated by evaporating the water.
The polyamide is obtained by heating such a solution of Nylon salt at high temperature and high pressure to evaporate the water, while avoiding any formation of solid phase in order to prevent the mixture from setting solid.
This operation consumes a great deal of energy and also does not make it possible to completely control the stoichiometry as amine can be evaporated or entrained by the water. Such an entrainment or evaporation requires supervision of the process in order to reestablish the stoichiometry and can be troublesome as the diamine entrained can contaminate the effluents discharged by the production plant.
In addition, the need to heat to a high temperature under a high pressure can lead to the formation of decomposition compounds which contaminate the manufactured polyamide, in particular with regard to its color.
To avoid the use of water, processes without water have been provided without real success. This is because it is very difficult to control the stoichiometry between the two reactants when at least one of them is in a solid form.
In addition, it is impossible to feed the reactants in a liquid form as, at the temperature required, decomposition of the monomers takes place.
However, certain processes for the preparation of a polyamide without water and without solvent have already been provided. Thus, U.S. Pat. No. 4,131,712 discloses a process which consists in mixing, in the liquid state, a diacid-rich diamine/diacid mixture with a second diamine-rich diamine/diacid mixture, so as to obtain a composition which is as close as possible to stoichiometry. The mixture is maintained at a temperature sufficient to prevent any solidification and to carry out the polycondensation. However, in this process, it is difficult to control and to obtain a stoichiometric mixture as the diamine partially evaporates during the introduction of the diamine-rich mixture.
To avoid this disadvantage, a process for the manufacture of polyamide without water or solvent is disclosed in patent application WO 96/16107.
This process consists in feeding, into a first stage of a multi-stage reactor or plate column, a diacid or a diacid-rich diacid/diamine mixture and then feeding, at an intermediate stage, diamine or a diamine-rich diacid/diamine mixture while controlling the amount of diamine added in order to obtain a stoichiometric mixture, the stoichiometry being measured continuously by an analysis means, for example analysis by Near InfraRed (NIR).
This process requires the use of a special reactor for its implementation, the operation of which may prove to be difficult to control. Furthermore, the control of the stoichiometry is provided by the addition of diamine or of a diamine-rich diacid/diamine mixture, which can result in large variations in the diacid/diamine ratio and in variations in the total flow rate into the reactor.
One of the aims of the present invention is to provide a process for the manufacture of high molecular weight polyamide without water or solvent which makes it possible to control the stoichiometry, it being possible for this process to be carried out in reactors of simple design. In addition, the process is easy to direct.
To this end, the invention provides a process for the manufacture of a polyamide resulting from the reaction of at least one diacid with at least one diamine comprising the following stages:
preparing a first mixture of diacid and of diamine with a diacid/diamine molar ratio of between 0.8 and 0.995, preferably of between 0.95 and 0.99,
preparing a second mixture of diacid and diamine with a diacid/diamine ratio of between 1.005 and 1.2, preferably between 1.01 and 1.05,
introducing, in the molten form, a first stream of the first mixture and a second stream of the second mixture into a stirred polymerization reactor,
withdrawing, preferably continuously, a stream of polyamide prepolymer from said reactor,
feeding said polyamide stream into a finishing stage in order to obtain the desired degree of polymerization.
The first and second mixtures are preferably anhydrous. The term “anhydrous mixture” should be understood as meaning mixtures which can comprise up to 10% by weight of water. The term “anhydrous” is used in the present description in contrast with the conventional process, which uses an aqueous solution of Nylon salt.
The process of the invention also comprises a means for the continuous analysis of the mixture of the streams of the first and second mixtures, preferably the two streams, in order to determine the balance between acid and amine functional groups. The term “acid and amine functional groups” is understood to mean the total acid and amine functional groups present, which have or have not reacted. This process consists in controlling, from the result of the preceding analysis, at least one of the first and second streams of mixtures, preferably both streams, in order to obtain a ratio of the acid functional groups to the amine functional groups equal to the value desired according to the type of polyamide manufactured (by way of indication, the acceptable margin of variation for this ratio with respect to the desired value is plus or minus 0.0005).
According to a preferred embodiment of the invention, the analytical means is a Near InfraRed (NIR) spectrometric analysis device.
The process of the invention thus makes it possible to obtain a balanced polyamide by controlling the stoichiometry of the mixture. Furthermore, as the adjustment or the control of this stoichiometry is carried out by the control of the streams of the first and second mixtures, the size of the variation in the acid/amine ratio will be low after the mixing of the two streams, making it possible to obtain more homogeneous production.
In addition, as indicated above, the polymerization reactor is a simple reactor comprising only conventional stirring and heating means.
The reactors in which the first and second mixtures are prepared, and the polymerization reactor, are can, for example, be reactors with mechanical stirring or reactors with external recirculation. In the latter case, the feeding with mixtures and/or the withdrawing of the product and/or heating can advantageously be carried out in the recirculation loop. The reactors can be heated using a jacket device and optionally an internal coil. In addition, the reactors can be open to gases.
According to a preferred characteristic of the invention, the first and second mixtures of diacid and diamine are prepared by mixing, in the solid state, a diacid with the diamine in the presence of a small amount of water and then heating at moderate temperature in order to obtain an amine salt.
In another embodiment,
Helft Matthieu
Thierry Jean-Francois
Burns Doane Swecker & Mathis L.L.P.
Hampton-Hightower P.
Rhodianyl
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