FR2827294A1 - Batch production of polyamide, e.g. polyamide 6,6, from diacid and diamine involves polycondensation after adjusting the stoichiometry of the reaction mixture by adding diamine at a rate determined by end-group analysis - Google Patents

Abstract

A process for the production of polyamide from diacid and diamine involves adjusting the stoichiometry of the liquid mixture by adding diamine until the difference between carboxyl and amino end groups ( DELTA GT) reaches a required value, the rate of addition of diamine being determined by analysis of the mixture to determine the change in DELTA GT with time. A discontinuous process for the production of polyamides from diacids and diamines involves: (a) making a liquid mixture of diacid and diamine with a diacid/diamine mol ratio of more than 1; (b) adjusting the stoichiometry by adding diamine until the difference ( DELTA GT = GTC - GTA) between the amounts of carboxyl end groups (GTC) and amino end groups (GTA) (expressed in meq or mmols/kg polymer) reaches a given predetermined value, the rate of addition of diamine being dependent (at least at the end of addition) on the result of analysis of the diacid/diamine mixture to determine the change of DELTA GT with time; and (c) polymerisation to the required degree with elimination of water, with the proviso that, in stages (a) and (b), the diacid/diamine mixture (unpolymerized or at least partly polymerized) is kept at a temperature (\=H) sufficient to keep the mixture in the liquid state with no solidification. An Independent claim is also included for an apparatus for carrying out this process, comprising at least one reactor for stoichiometric adjustment, with a circulating loop for the mixture to be adjusted.

Description

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DISCONTINUOUS METHOD OF MANUFACTURING A POLYAMIDE
The field of the invention is that of the preparation of polyamide, in the liquid phase and in the absence of organic solvents or large amounts of water.

 More precisely, the invention relates to a batch process for producing a polyamide by direct amidification, and from at least one diacid and at least one diamine.

 Polyamides are polymers of considerable industrial and commercial interest. Thermoplastic polyamides are obtained by condensation of two different types of monomers or a single type of monomer. It is conceivable to have several different monomers in the same type.

 The invention applies to polyamides derived from two different types of monomers, for example poly (hexamethylene adipamide).

 Conventionally, the polyamides are prepared from at least one "diacid" monomer and at least one diamine monomer, dissolved in an organic solvent or in a mixture of organic solvents, in water, or in a mixed system solvent / water.

The "diacid" may be a dicarboxylic acid, a diester or a halide (eg, an acid chloride). The most common diacid monomer is adipic acid.

As for the diamine monomer, it is traditionally hexamethylenediamine.

 In addition to adipic acid (AA) and hexamethylene diamine (HMDA), the polyamides may be derived from other diamine or diacid monomers or even amino acid monomers or lactams (up to 25 mol%).

The most common industrial process for producing polyamide from two different monomers, a diacid and a diamine, is to form an acidic salt of amine: hexamethylene diamine adipate, better known as "salt N". ". The solution of this "salt N", which contains at least 50% by weight of "salt N", is optionally concentrated by evaporation of water. The polyamide is obtained by heating, at high temperature and pressure, this "salt N" solution, to evaporate the water and to maintain the medium in the liquid state.

 This removal of water by evaporation requires a lot of energy and, moreover, does not fully control the stoichiometry, since amine can be evaporated or entrained by water. This loss of amine is very difficult to control by changing the operating conditions of the process. In addition, it requires the implementation of a complex recovery process, but necessary on the

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 economic. Moreover, it is easy to understand that handling large volumes of water imposes constraints in terms of size and cost of the industrial equipment required.

 Many technical proposals have emerged to try to solve this problem of water in the preparation of polyamide. But these technical proposals were in vain because they did not make it possible to overcome the following difficulty: if one of the starting products is solid (adipic acid), the control of the quantity to be used for this solid compound is very delicate.

 Another alternative is to use starting monomers in the form of molten liquid, but in this case, the high temperatures required are likely to cause thermal degradation.

 US Pat. No. 4,131,712 opts for molten liquid starting products. More specifically, this patent discloses a process for the preparation of high molecular weight polyamides in which a diacid-rich diacid / diamine mixture and a diamine-rich diacid / diamine mixture are separately prepared in stoichiometric proportions other than 1: 1. The diacid-rich component and the diamine-rich component are then contacted in the liquid state at a temperature high enough to prevent solidification, and in such proportions that the total amounts of diacid and diamine are as much as can, as close as possible to 1: 1 stoichiometry. The major disadvantage of this process is that the diamine added to the melt mixture, to adjust the 1: 1 stoichiometry, is subject to substantial volatilization. This is highly detrimental to performance and makes stoichiometric balancing difficult.

As is apparent from Example 4 of US-A-4 131 712, the diamine adjustment in the diacid mixture (1 mole) 1 diamine (0.5 mole) is carried out in two incorporations of 0.25 moles of diamine with gradual increase of the temperature from 1820C to 2500C to finish at 285 C.

This method of operation is approximate and does not achieve a molar ratio of diacid / diamine sufficiently close to 1 to ensure proper polymerization.

 International patent application WO-96/16107 discloses a continuous process for the preparation of polyamide in which a multi-stage reactor is fed with a melt mixture of adipic acid (AA) and hexamethylenediamine (HMDA) according to a stoichiometry 81 In this multi-stage reactor, the diamine adjustment is carried out by injecting the additional diamine in liquid or vapor form, against the current, at any stage of the reactor, with the exception of the first one. located at the head.

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The formed polyamide stream is recovered at the base of the reactor. The temperature of the reaction mixture inside the reactor is high enough to prevent solidification. The control of the diacid / diamide equilibrium is carried out by continuous analysis according to a near infra-red spectroscopy technique, on the outgoing polyamide flux. The supply of diamine to adjust the stoichiometry to a value close to 1: 1 is slaved to the values measured by the near infra-red continuous analysis.

This process requires the use of a special reactor for its implementation. The operation of the latter may be difficult to control. In addition, stoichiometry is controlled by the addition of diamine or a diamine-rich diacid / diamine mixture, which addition can cause high amplitude variations of the diacid / diamine ratio and variations in the total flow rate. the reactor. In short, the control of stoichiometry is delicate.

 US-6,169,162 (WO-99/61511) discloses a continuous process for producing polyamide from a dicarboxylic acid monomer and a diamine monomer. To make polyamide without adding water, this process proposes to make a 1: 1 molar ratio AA: HMDA mixture from solid AA, which is subjected to an oxygen removal treatment. , and from liquid HMDA. The deoxygenated AA is melted at a temperature of 170 C, then is mixed with HMDA liquid heated to 70 C. Then come homogenization through a static mixer and then a prepolymerization at 260 C in an open reactor . The prepolymer produced is subjected to near-infrared spectrometry analysis to determine the AA / HMDA molar ratio and to control the supply of starting HMDA and AA in return. The polymerization can then be continued in a polymerization finishing reactor at a temperature of 260-280 ° C. and at atmospheric pressure. The water present in the starting HMDA and the water of condensation are removed in the prepolymerization and finishing reactors of evaporation polymerization.

 An essential objective of the invention is to provide a process for producing polyamide from diacid monomers and diamine monomers, involving reduced amounts of water, while simplifying the process as much as possible and limiting complex and expensive.

 Another essential objective of the invention is to propose a method of manufacturing high molecular weight polyamide without water or solvent, making it possible to control the

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stoechiométrie de manière précise., et ce en réduisant autant que faire ce peut les pertes d'effluents d'HMDA, dont la récupération est complexe.

stoichiometry in a precise way, and this by reducing as much as possible the losses of effluents of HMDA, whose recovery is complex.

Another essential object of the invention is to provide a method for the manufacture of polyamide, in batch mode, by precisely controlling the stoichiometry to values close to 1: 1, while remaining flexible and economically acceptable.

These objectives, among others, are achieved by the present invention which relates to a batch process for manufacturing a polyamide from at least one diacid and at least one diamine, characterized in that it comprises the steps following essential elements: (a) preparation of a liquid mixture of diacid and diamine with a molar ratio of diacid / diamine> 1; b) adjusting the stoichiometry by adding diamine in the liquid mixture of diacid and diamine, until the difference (AGT = GTC-GTA) between the amount of carboxylic end groups (GTC) and the amount of groups amine terminals (GTA), expressed in meq (or mmol) / kg of polymer, either at a predetermined set point value, the diamine addition stream being enslaved at least at the end of the addition to the result of a analysis of the mixture of diacid and diamine to determine the evolution of AGT over time, c) polymerization with removal of water to the desired degree of polymerization; with the proviso that the liquid mixture of diacid / diamine, uncured or at least partially polymerized, is maintained in steps a) and b) at a temperature sufficient to maintain the medium in the liquid state and to avoid any solidification.

The process according to the invention consists essentially of a direct amidification in batch mode. The principle is: on the one hand, to produce a diacid / liquid diamine mixture, without adding any water other than that possibly contained in the diamine, so as to have a molten liquid starting medium at temperatures low enough to prevent any damage;

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 and on the other hand, to implement a procedure for adjusting the desired stoichiometry, during which a regulation based on AGT analysis as a function of time is carried out.

 The use of a diacid / diamine liquid mixture with a low melting point makes it possible to work at low temperature (for example around 120 ° C.) and at around atmospheric pressure (for example approximately 1.05 bar).

de fusion Of du mélange diacide/diamine, telle que : Of : : ; 150oC, de préférence er 130 C. For the purposes of the invention, the expression "low melting point" means a temperature

Of melting of the diacid / diamine mixture, such as: Of:; 150 ° C, preferably 130 ° C.

 To avoid solidification or crystallization of the more or less polymerized monomer mixture, it must be maintained at a temperature above its melting point, under given pressure conditions. Thus, as the diamine is added during the adjustment step b), the heating temperature of the liquid diacid / diamine mixture must follow the increase in the melting temperature until the moment when the AGT reaches the predetermined set value, corresponding to a molar ratio of diacid 1 diamine Rb of the order of 1.

 There is thus a method of manufacturing polyamides without water or solvent, operating in batch mode ("batch") which is flexible, easy to implement and which allows to obtain quality polymers.

10AGT100 méq/kg avec une précision de +/-10 méq/kg.

According to a preferred embodiment of the invention, in the stoichiometric adjustment step b), the predetermined set value of the AGT is defined as follows:

10AGT100 meq / kg with an accuracy of +/- 10 meq / kg.

20 AGT 60 méq/kg avec une précision de +/-5 méq/kg.

L'une des caractéristiques essentielles du procédé discontinu selon l'invention dans son mode préféré de mise en oeuvre, tient à la réalisation de l'ajustement b) de la stoechiométrie sous pression autogène, de préférence dans une enceinte fermée. According to a preferred embodiment of the invention, in the stoichiometric adjustment step b), the predetermined set value of the AGT is defined as follows:

20 AGT 60 meq / kg with an accuracy of +/- 5 meq / kg.

One of the essential features of the batch process according to the invention in its preferred embodiment is the realization of the adjustment b) of the stoichiometry under autogenous pressure, preferably in a closed chamber.

 This advantageous method of operation makes it possible to avoid the evaporation of water (brought by the diamine and / or the polycondensation) and, in doing so, eliminates any loss.

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 to diamine (e.g., HMDA). This goes in the direction of improving the profitability of the process. In addition, this makes it possible to limit the evolution of the degree of polycondensation during step b) of adjustment and thus to improve the accuracy of the measurement of TFA.

 With regard to step a) of preparing the low melting point diacid / diamine liquid mixture, the diacid / diamine Ra molar ratio is preferably set between 75: 25 and 80:20.

 In practice, and according to an advantageous embodiment of the invention, this step a) is carried out in a container comprising a diacid / diamine liquid mixture foot (e.g.

AA / HMDA) with a low melting point and a Ra molar ratio, then diacid (for example adipic acid AA) in the form of solid and, more precisely, pulverulent form, and diamine (for example HMDA) which is incorporated in this foot are incorporated. is in liquid form, pure or diluted, for example at 90%, and which is maintained at a temperature between 50 and 100 C, preferably of the order of 70 C.

 The mixture of step a) is stirred.

 Step a) of preparing the low melting liquid diacid / diamine mixture (e.g., AA / HMDA) is essentially conducted at atmospheric pressure.

 The diacid and the diamine are introduced into the container of step a) simultaneously or one after the other.

 The use of a low melting point diacid / diamine liquid base (e.g., AA / HMDA) facilitates the dissolution of the diacid powder (eg adipic acid).

 It is preferable, in accordance with the invention, to remove, as far as possible, any trace of oxygen in the circuit and the stoichiometric adjustment container prior to the implementation of step b).

To remove the last traces of oxygen from the medium, it is advantageous to subject the latter to a steam treatment treatment, in particular water vapor ("stripping"). The diacid / diamine liquid mixture (eg AA / HMDA) with a low melting point obtained in step a) is optionally subjected to steam distillation and is then transferred to a chamber intended for adjusting the stoichiometry. in diacid and diamide.

It should be noted that during this transfer, the container for preparing the low melting liquid diacid / diamine mixture (e.g., AA / HMDA) is not supplied with diacid or diamine.

 Advantageously, a filtration of the mixture of step b) is carried out during or after the addition of the diamine.

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 According to an even more preferred embodiment of the invention, step b) of adjusting the stoichiometry is broken down as follows: b. 1) coarse adjustment of the stoichiometry by adding diamine in the low melting diacid / diamine liquid mixture (eg AA / HMDA), until the molar Rb diacid / diamine ratio is 1.1, preferably :; 1.04; b. 2) Fine adjustment of the stoichiometry by continuing the addition of the diamine in the mixture of step b. 1), until 10 AGT 100 meq / kg, with an accuracy of +/- 10 meq / kg, preferably AGT 60 meq / kg, with an accuracy of +/- 5 meq / kg; the diamine addition flux being enslaved to the result of an analysis of the mixture of diacid and diamine to determine the evolution of AGT over time.

 This procedure for adjusting the stoichiometry in two sequences is particularly advantageous industrially, particularly because of the time saving it provides.

 Thus, the first sequence consists of massively and rapidly adding the diamine, so as to perform most of the necessary adjustment, while in the second sequence, the addition of the diamine (eg HMDA) adjustment will be done slowly and according to a controlled incorporation rate.

 The regulation ensured during the step of fine adjustment of stoichiometry [step b. 1)] makes it possible to control precisely this operating phase.

 According to a preferred characteristic of the invention, provision is made, at least for the implementation of step b. 2) fine adjustment (preferably both), that the liquid mixture of diacid and diamine circulates in a loop.

 In practice, it is therefore circulated closed circuit, the load whose stoichiometry must be adjusted, first in a rough way, and more finely afterwards. This closed circuit or loop includes the stoichiometric adjustment container and is designed to allow the injection of diamine (e.g., HMDA).

 In the first gross adjustment sequence of the chromatometry [step b. 1)], the incorporation of diamine is carried out according to a given, predetermined quantity, at least equal to 50%, preferably 95%, of the mass of diamine to be added to reach Rb = 1.

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To prevent any risk of solidification, the temperature of the mixture is maintained during step b. 1) at a temperature above the melting temperature (for example at about 210 ° C.) in the loop circulation circuit.

For the second adjustment sequence [step b. 2)], the rest of the diamine is added precisely by controlling the evolution of! stoichiometry, using at least one probe and regularly measuring the ratio between the acid and amine functions present.

 Preferably, the AGT analysis of the mixture of diacid and diamine is carried out by a spectrometric analysis method in the Near Infra-Red (PIR), this method preferably involves a calibration.

consiste, en résumé, à mesurer l'absorbance d'un échantillon dans une gamme de longueurs d'ondes donnée et à réaliser une courbe d'étalonnage (calibration), par détermination de l'absorbance de différents échantillons, dont on a déterminé par une autre méthode les paramètres que l'on cherche à mesurer. This technique of spectrometric analysis PIR, is described in particular in US-5, 155,184, 5,532, 487 and 5,707, 870 and the application WO 96/11399. This technique

consists, in summary, to measure the absorbance of a sample in a given wavelength range and to perform a calibration curve (calibration), by determining the absorbance of different samples, which has been determined by another method the parameters we are trying to measure.

More generally, the AGT = f (time) analysis could be performed by any appropriate chemical and / or potentiometric methods. The spectrometric analysis by PIR simply corresponds to a preferred mode of analysis, already used in the application WO 96/16107 mentioned above.

 Preferably, the analysis of the AGT of the diacid and diamine mixture is carried out on the mixture circulating in a loop in the stoichiometric adjustment circuit, e. g. by a spectrometric analysis method in the Near Infra-Red.

 According to a remarkable characteristic of the invention, the addition of diamine in the diacid / diamine liquid mixture, during the fine-adjustment step b. 2), is performed upstream of the point (s) of analysis.

 According to an advantageous embodiment of the invention, the mixture, whose stoichiometry is to be adjusted, is filtered and / or homogenized during its circulation in a loop during step b. 1) and / or step b. 2).

 As for the filtration, it occurs during or after the incorporation of the diamine.

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 The homogenization is preferably carried out by means of at least one static mixer. The homogenization is intended to guarantee a reliable continuous analysis and to ensure the intimate mixing of the diamine incorporated with the mixture to be adjusted.

Even more preferably, at least one homogenization is provided before the analysis station provided on the loop and at least one homogenization upstream of the diamine injection point in the loop.

 According to one variant, it is possible to implement a regulation in the context of the coarse adjustment according to step b. 1). For this purpose: the mixture of diacid and diamine is analyzed to determine the evolution of AGT over time, and the diamine incorporation flux is enslaved to the result of the analysis so that Rb buzz 1, preferably Rb buzz 04.

 With regard to the temperature 8 of the liquid diacid / diamine mixture (e.g.

AA / HMDA) with a low melting point, it is above its melting point # f, preferably 0 8f + 20oC.

 It emerges from the preferred embodiment of the method according to the invention, as presented above, that step a) is carried out in a chamber different from that used for steps b. 1) and b. 2) adjustment.

 When the adjustment is complete, the entire adjusted charge is preferably transferred from the adjustment container to another reaction chamber in which the c) finishing step of the polymerization is carried out with the elimination of water.

 According to one variant, the polymerization could be carried out in the same reaction chamber as the adjustment of the stoichiometry.

 Step c) consists of a polycondensation carried out, preferably, in at least one "polymerizer" constituted by an autoclave, according to the usual conditions of the polycondensation cycle.

 In the preferred embodiment of the process according to the invention, two polymerizers are used alternately.

 Another remarkable characteristic of the process of the invention is that it comprises at least one of the following conventional steps:

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 a step d) of relaxing the polymerization finishing medium to remove the residual water by evaporation, a step e) of keeping the temperature under reduced or atmospheric pressure of the polymer, - a step f) shaping (preferably form of granules) of the polyamide obtained.

 According to step e), the polyamide can then be maintained for a predetermined time at a polymerization temperature under atmospheric pressure or reduced to obtain the desired degree of polymerization.

 These final finishing steps are those used in conventional industrial processes for producing polyamide from an aqueous solution of amine salt.

 Advantageously, the quantity of water to be removed, during the complete cycle of the polymerization, is less than or equal to at least 70%, preferably at least 80% by weight relative to the amount of water to be evaporated in known processes using concentrated N salt solutions.

 The process of the invention can be used for the manufacture of poly (hexamethylene adipamide) from adipic acid as the diacid monomer and hexamethylene diamine as the diamine monomer.

 The process of the invention also makes it possible to manufacture other polyamides from diacid monomer chosen from the group comprising glutaric, suberic, sebacic, dodecanedioic, isophthalic, terephthalic, azelaic, pimelic and naphthalene dicarboxylic acids, for example.

 As diamine monomers, in addition to hexamethylenediamine, mention may also be made of heptamethylene diamine, tetramethylene diamine, ocamethylenediamine, nonamethylene diamine, decamethylene diamine, 2-methylpentamethylenediamine and undecamethylenediamine. dodecamethylene diamine, xylylene diamine, isophoron diamine.

 When they are used as comonomers, they are added preferentially in admixture with M or HMDA. or added in the stoichiometric adjustment loop.

 It emerges from the general description above, that the process according to the invention makes it possible to manufacture a polyamide from diamide and diacid, without the use of massive amounts of water or solvent, in equipment of simple design and

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 easy to use. In addition, the technique according to the invention for adjusting the stoichiometry of a liquid mixture diacid / diamine (eg AA / HMDA) with a low melting point, with a regulation according to the evolution over time of the AGT measured on a loop (eg by PIR spectrometry), preferably in two sequences, respectively coarse and fine, makes it possible to optimize the adjustment time and obtain a diacid / diamine ratio in the vicinity of the desired Rb value close to 1.

 According to another of its aspects, the present invention relates to a device for implementing the method as described above.

Advantageously, this device comprises at least one stoichiometric adjustment chamber, comprising a loop for circulating the mixture whose stoichiometry is to be adjusted.

 According to a preferred embodiment of the device, the loop for circulating the mixture, the stoichiometry of which is to be adjusted, comprises: at least one analyzer of the amount of diacid / diamine, this analyzer preferably being a near infra-red spectrometer, - Diamine addition means in the liquid mixture whose stoichiometry is to be adjusted, which means being designed such that is provided at least one addition point disposed upstream of the analyzer.

 Advantageously, this loop for circulating the mixture whose stoichiometry is to be adjusted, comprises: homogenization means constituted by at least one static mixer and preferably a static mixer disposed upstream of the analyzer and another arranged just downstream of the diamine injection point in the circuit, and at least one filter.

 Other advantages, details of the invention will appear more clearly in view of the example which describes below, without limitation, the manufacture of polyamide by the method and the device according to the invention.

 The description of the protocol is made with reference to the single appended figure which shows a block diagram of the device according to the invention.

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EXAMPLE:
The AA, in powder form, is contained in a silo 1, saturated with inert gas, for example nitrogen.

 HMDA is contained in a flask 2 and is in pure or diluted form.

The balloon 2 is provided with an electric pin 15 making it possible to maintain the HMDA at a temperature, for example of the order of 70.degree.

 A low melting point mixture of diacid and diamine composed of 2785 g of pure AA and 726 g of 90% HMDA is transferred respectively from silo 1 and flask 2 into a preparation container 3. a mixture of low melting point of diacid and diamine, which is stirred, closed, and heated to 130 C.

 A pump 16 makes it possible to route the HMDA into the container 3 via a pipe 17. This pipe connecting the balloon 2 to the container 3 has a branch 18 which forms a loop bringing the HMDA back into the balloon 2 The pipe 17 is also provided with a mass meter 17a and a valve 17b.

 The container 3 comprises stirring means 25, means 26 for driving water vapor impurities such as oxygen, a water discharge 27, and pressure and temperature sensors not shown on the drawing.

 This container 3, heated and insulated as all pipes carrying hot fluids, operates with stirring with a base of low melting point AA / HMDA melting tank equivalent to at least one batch.

 The AA and the HMDA are introduced simultaneously or one after the other on the low melting base of the AA / HMDA molten mixture of the container 3. Care is taken not to withdraw AA / HMDA mixture. low melting point during feeding of AA and HMDA.

 Downstream of the low melting point AA / HMDA mixture preparation container 3, there is provided a pump 28 useful for transferring the low melting point ANHMDA mixture into a stoichiometric adjustment chamber 4 via a pipe 29 equipped with a filter 30 and a valve 31, and naturally, it too, heated and insulated.

 This stoichiometry adjustment chamber 4 comprises stirring means 32, a steam injection system 33 preventing the entry of oxygen into the system during emptying and a valve 34. It is comparable to a stirred autoclave, 7.5 liter closed, heated by a coolant and equipped with a loop 5 recirculation and adjustment of stochiometry.

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 From the base of this stoichiometric adjustment chamber 4, emanates a pipe 7 forming the loop 5 and opening into the upper part of the enclosure 4. This heated stoichiometry adjustment loop 5 comprises, from upstream to downstream, a valve 8, a pump 9, a filter 10, a first static mixer 11, analysis means 12 by stoichiometry in the near-infrared PIR of the difference between the concentrations in acid functions and amine, a heat exchanger (heating means) 13 and a second static mixer 14.

 The recirculation and stoichiometry adjustment loop 5 is supplied with HMDA via two lines 19 and 20, allowing it to be fed with HMDA. These ducts 19 and 20 comprise, respectively, a valve 21 and a valve 22 and also a mass counter 23, on the one hand, and a pump 24, on the other hand.

 The means 4 and 5 for adjusting the stoichiometry are heated and insulated so as to maintain the temperature of the AA / HMD mixture which progresses from the melting temperature of the mixture, approximately equal to 100 C, to the temperature final mixture of the prepolymerized and molten mixture which is about 210 C in 30 minutes.

 At the same time, 1735 g of 90% HMDA are gradually injected into the recirculation loop.

 According to the invention, this injection is carried out in two sequences: fine adjustment and coarse adjustment.

 At first, approximately 95% of HMDA required for adjustment is injected rapidly and massively via line 19 into loop 5. Naturally, this incorporation is correlated with a temperature increase of the mixture so as to avoid any risk of solidification. 95% of the necessary HMDA makes it possible to reach a molar ratio of diacid / diamide Rb = 1.04.

 Then, the remaining 5% is added precisely and slowly by controlling the evolution of the stoichiometry by means of the near-infrared stoichiometric probe PIR 40.

 The injection rate is adjusted so as to maintain the reaction mixture above the melting point of the dry mixture, so as to avoid any risk of solidification. The Near Infrared measurement 12 installed on the recirculation loop 5 is used to accurately control the stoichiometry of the mixture. The terminal group A obtained (GTC-GTA) is 30 meq / kg +/- 5 meq / kg.

 The prepolymerized stoichiometric mixture thus obtained is maintained in recirculation for 15 minutes at 210 ° C. under autogenous pressure and then transferred to a polymerizer 6, via a pipe 35.

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 The mixture is finally subjected to a standard polycondensation which makes it possible to obtain a PA 6.6 which can be used for injection and molding. The continuous and customary processes for the manufacture of PA 6.6 are described, for example, in the book "Polymerization processes" Schildknecht edition (Wiley interscience, 1977) pp. 424-467 (Chapter 12 "Preparation of 6, 6-nylon and related polyamides" by Donald B. JACOBS and Joseph ZIMMERMAN). The final PA 6.6 at a viscosity index of 136 ml / g measured in formic acid diluted according to the conditions and recommendations of international standard ISO 307-1984) and an AGT of 27 meq / kg.

Claims (28)

 1. - Batch process for the manufacture of a polyamide from at least one diacid and at least one diamine, characterized in that it comprises the following essential steps: a) preparation of a liquid mixture of diacid and diamine with a diacid / diamine molar ratio> 1; b) adjusting the stoichiometry by adding diamine in the liquid mixture of diacid and diamine, until the difference (AGT = GTC-GTA) between the amount of carboxylic end groups (GTC) and the amount of groups amine terminals (GTA), expressed in meq (or mmol) / kg of polymer, either at a predetermined set point value, the diamine addition stream being enslaved at least at the end of the addition to the result of a analysis of the mixture of diacid and diamine to determine the evolution of AGT over time, c) polymerization with removal of water to the desired degree of polymerization; with the proviso that the liquid mixture of diacid / diamine, uncured or at least partially polymerized, is maintained in steps a) and b) at a temperature sufficient to maintain the medium in the liquid state and to avoid any solidification.  2. - Method according to claim 1, characterized in that in step b) of stoichiometric adjustment, the predetermined set value of the AGT is defined as follows: AGT 100 meq / kg with a precision of + / - -10 meq / kg.  3. A process according to claim 2, characterized in that in the stoichiometric adjustment step b), the predetermined set value of the AGT is defined as follows: AGT 60 meq / kg with a precision of + / - -5 meq / kg. <Desc / Clms Page number 16>  4. - Process according to claim 1 to 3, characterized in that step b) of adjusting the stoichiometry is carried out under autogenous pressure.  5. - Method according to claim 4, characterized in that step b) of adjusting the stoichiometry is performed in a closed chamber.  6. - Process according to any one of claims 1 to 5, characterized in that it carries out a removal of oxygen, preferably by steam distillation.  7. - Process according to any one of claims 1 to 6, characterized in that a filtration of the mixture of step b), is carried out during or after the addition of the diamine.  8. - Process according to any one of claims 1 to 7, characterized in that the prepolymerized mixture obtained at the end of step b), is transferred into at least one polymerization reactor.  the temperature 0 of maintaining in the liquid state of the diacid / diamine mixture during steps a) and b), is greater than the melting temperature Of said mixture, preferably 0 ef + 20oC.

 9. - Process according to any one of claims 1 to 8, characterized in that 10. - Process according to any one of claims 1 to 9 characterized in that, in step a), the molar ratio Ra diacid: diamine between 75: 25 and 80: 20.  11. - Method according to any one of claims 1 to 10, characterized in that step b) of adjusting the sthiometry is broken down as follows: b. 1) coarsely adjusting the stoichiometry by adding diamine to the liquid diacid / diamine mixture until the Rb diacid / diamine molar ratio is # 1.1, preferably # 1.04; b. 2) Fine adjustment of the stoichiometry by continuing the addition of the diamine in the mixture of step b. 1), until 10 # #GT # 100 meq / kg with an accuracy of +/- 10 meq / kg, preferably 20 # #GT # 60 meq / kg, with an accuracy of +/- 5 meq / kg; <Desc / Clms Page number 17>  the diamine addition flux being enslaved to the result of an analysis of the mixture of diacid and diamine to determine the evolution of AGT over time.  12. A process according to any one of claims 1 to 11, characterized in that, at least for the implementation of step b. 2) fine adjustment (preferably both), the liquid mixture of diacid and diamine circulates in a loop.  13. - Method according to any one of claims 1 to 12, characterized in that, in step b. 1), the incorporation of diamine is carried out according to a given predetermined amount of at least 50%, preferably 95%, of the mass of diamine to be added to reach Rb = 1.  14. - Process according to any one of claims 1 to 13, characterized in that, in step b1): - the mixture of diacid and diamine is analyzed to determine the evolution of AGT in time, - and the diamine incorporation flux is slaved to the result of the analysis so that Rb <1.1, preferably R '' 1.04.  15. - Process according to any one of claims 1 to 14, characterized in that the analysis of the mixture of diacid and diamine is carried out by a spectrometric analysis method in the Near Infra-Red.  16. - Process according to any one of claims 12 to 15, characterized in that, the analysis of the mixture of diacid and diamine to determine the evolution of AGT in time, is performed on the mixture circulating in the loop. .  17. The process as claimed in claim 16, characterized in that the addition of diamine in the diacid / diamine liquid mixture during the fine-adjustment step b. 2) is performed upstream of the point (s) of analysis. 18. A process according to any one of claims 12 to 17, characterized in that a filtration step is performed on the mixture circulating in the loop. <Desc / Clms Page number 18>  19. - Process according to any one of claims 12 to 18, characterized in that the mixture circulating in the loop is subjected to at least one homogenization, preferably by means of at least one static mixer.  20. - Method according to any one of claims 1 to 19, characterized in that step a) is performed in a different chamber than that used for steps b. 1) and / or b. 2) adjustment.  a step e) of maintaining the temperature under reduced or atmospheric pressure of the polymer, a step f) shaping (preferably in the form of granules) of the polyamide obtained.

 21. A process according to any one of claims 1 to 20, characterized in that it comprises at least one of the following steps: a step d) relaxation of the polymerization finishing medium to remove the residual water by evaporation,  22. - Process according to any one of claims 1 to 21, characterized in that the diacid monomers are chosen from the list comprising adipic acid, glutaric, suberic, sebacic, dodecanedioic, isophthalic, terephthalic, azeolic, pimetic.  the decamethylene diamine,! Methyl-2-pentamethylenediamine, undecamethyl; diamine, dodecamethylene diamine, xylylene diamine.

 23. - Process according to any one of claims 1 to 22, characterized in that the diamine monomers are chosen from the list comprising hexamethylene diamine, heptamethylene diamine, octamethylene diamine, nonamethylene diamine,  24. - Process according to any one of claims 1 to 23, characterized in that the diacid monomer comprises at least 80 mol% of adipic acid.  25. - Process according to any one of claims 1 to 24, characterized in that the diamine monomer comprises at least 80 mol% of hexamethylenediamine. 26.-Device for implementing the method according to any one of claims 1 to 18, characterized in that it comprises at least one enclosure <Desc / Clms Page number 19>  of adjustment of! stoichiometry, comprising a mixture circulation loop whose stoichiometry is to be adjusted.  27. - Device according to claim 26, characterized in that the circulation loop of the mixture whose stoichiometry is to be adjusted, comprises: at least one analyzer of the amount of diacid / diamine, this analyzer being preferably a near spectrometer infra-red, - diamine addition means in the liquid mixture whose stoichiometry is to be adjusted, which means being designed such that is provided at least one addition point disposed upstream of the analyzer.  28. - Device according to claim 26 or 27, characterized in that the circulation loop of the mixture whose stoichiometry is to be adjusted, comprises: - homogenization means consisting of at least one static mixer and preferably a mixer static disposed upstream of the analyzer and another disposed just downstream of the diamine injection point in the circuit, and - at least one filter.