WO2014135626A1 - Production of polyamides by hydrolytic polymerization and multiple extraction - Google Patents

Abstract

The invention relates to a method for producing polyamides, comprising a hydrolytic polymerization and at least two extraction steps, which do not occur in direct succession.

Description

 Production of polyamides by hydrolytic polymerization and multiple extraction

BACKGROUND OF THE INVENTION

The present invention relates to a process for the preparation of polyamides, comprising a hydrolytic polymerization and at least two extraction steps, which do not take place immediately after one another. STATE OF THE ART

Polyamides are among the world's most widely produced polymers and serve in addition to the main applications of fibers, materials and films a variety of other uses. Among polyamides, polyamide 6 is the most widely produced polymer at about 57%. The classical method for the production of polyamide 6 (polycaprolactam) is the hydrolytic polymerization of ε-caprolactam, which is still of great industrial importance. Conventional hydrolytic manufacturing processes are z. In Ullmann's Ecyclopedia of Industrial Chemistry, Online Edition 15.03.2003, Vol. 28, pp. 552-553 and Kunststoffhandbuch,% Thermoplastics: Polyamides, Carl Hanser Verlag, 1998, Munich, pp. 42-47 and 65 -70 described.

In the first step of the hydrolytic polymerization, a portion of the lactam used reacts by the action of water with ring opening to the corresponding ω-aminocarboxylic acid. This then reacts with further lactam in polyaddition and - condensation reactions to the corresponding polyamide. In a preferred variant ε-caprolactam reacts by the action of water with ring opening to amino caproic acid and then on to polyamide 6. The hydrolytic polymerization can be carried out in one or more stages. In general, the polycondensation takes place and - addition in a vertical tubular reactor (VK tube). The abbreviation "VK" stands for "simplified continuously". Optionally, a plant with pre-polymerization at elevated pressure can be used. The use of such a prereactor reduces the residence time required for the ring-opening reaction of the ε-caprolactam. At the end of the upright tube reactor (VK tube), a polyamide melt having a near-chemical composition is obtained from polyamide, lactam monomer, oligomers and water. The content of oligomers and monomers may, for. B. 8 to 15 wt .-% and the viscosity number of the crude polyamide, which is directly related to the molar mass and thus the processing properties, is usually between 1 10 to 160 ml / g. For many uses, eg. For example, for the production of films for packaging materials, a low residual monomer content in the polyamide is required, so that the crude polyamide is generally subjected before its further processing at least a partial removal of monomers and oligomers.

To reduce the content of low molecular weight components of the product of the hydrolytic polymerization is usually first granules of crude polyamide particles produced and then extracted with an extractant to remove residual monomers and oligomers. This is often done by continuous or discontinuous extraction with hot water, as z. Example, in EP 0 1 17 495 A2, DE 25 01 348 A and DE 27 32 328 A is described. For the purification of crude polyamide 6, the extraction with caprolactam-containing water (WO 99/26996 A2) or the treatment in the superheated steam stream (EP 0 284 986 A1) is also known. For reasons of environmental protection and economy, the extracted components, in particular in the case of polyamide 6, the caprolactam and the cyclic oligomers are recycled to the process. The extraction is usually followed by drying of the extracted polyamide. For many applications, higher molecular weight polyamides are needed which are not achieved by hydrolytic polymerization alone. To increase the molecular weight or the viscosity of the polyamide, subsequent condensation is then carried out after the extraction, wherein the polyamide is preferably present in the solid phase. For this purpose, the granules can be tempered at temperatures below the melting point of the polyamide, wherein especially the polycondensation tion progresses. This leads to the structure of the molecular weight and thus to increase the viscosity number of the polyamide. As a rule, the viscosity number of the polyamide 6 after extraction and post-polymerization is 180 to 260 ml / g. Postcondensation and drying are often carried out in one step (WO 2009/153340 A1, DE 199 57 664 A1).

DD 2090899 describes processes for Vakuumschmelzentmonomerisierung in which a polyamide extraction is preceded, in which the polyamide melt is brought into contact with liquid caprolactam caprolactam.

DD 227140 describes a process for the preparation of polyamide having a degree of polymerization DP> 200. The process is characterized by at least 5 successive stages. At the beginning of each drying stage, the surface of the molten polyamide to> 4 cm ² / g polyamide and the maximum diffusion path of the water in the melt set to <3 mm.

WO 03/040212 discloses a method for producing polyamide 6 by hydrolytic polymerization of ε-caprolactam under the action of water. Dewatering is achieved by increasing the surface area of the melt.

WO 2009/153340 A1 describes a continuous process for multi-stage drying and postcondensation of polyamide granules in solid phase, wherein:

1) the predrying is carried out in a continuous drying apparatus which is operated with inert gas, steam or a mixture thereof at a granule temperature in the range of 70 to 200 ° C and

2) the subsequent continuous postcondensation in a separate shaft with moving bed at a granule temperature in the range of 120 to 210 ° C is performed, wherein the shaft with inert gas, water vapor or a

Mixture thereof is operated and the inert gas is supplied at least two points along the shaft.

According to the teaching of WO 2009/153340, the process measures for molecular weight build-up and for (partial) extraction are combined and, in particular, carried out in the after-condensation as solid / gas extraction. Since the second extraction is carried out simultaneously with the postcondensation at temperatures of greater than 120 ° C, it is imperative to emulate monomers (remonomerization) by cleavage of the polyamide. Thus, despite simultaneous treatment with steam and / or inert gas, the residual monomer content can not be satisfactorily reduced. The lowest values for the residual monomer content are calculated according to the

WO 2009/153340 in Examples 2 and 3 reaches and amounts to 1200 ppm. By comparison, by the method according to the invention by multiple extraction significantly lower values can be achieved, which increase only insignificantly in the case of a subsequent drying.

An alternative, industrially not yet heavily used route for the production of polyamides is the polycondensation of aminonitriles, eg. For example, the preparation of polyamide 6 from 6-aminocapronitrile (ACN). In a conventional procedure, this process involves nitrile hydrolysis followed by aminamidation, which are usually carried out in separate reaction steps in the presence of a heterogeneous catalyst, such as T1O2. A multi-step procedure has proved to be practicable since both reaction steps have different requirements with respect to water content and completeness of the reaction. Also in this synthesis it is many times advantageous to subject the resulting polymer to a purification to remove monomers / oligomers.

WO 00/47651 A1 describes a continuous process for the preparation of polyamides by reacting at least one aminocarbonitrile with water.

The known processes for the preparation of polyamides by hydrolytic polymerization are still in need of improvement. Thus, the content of residual monomer, especially ε-caprolactam, at the beginning of the postpolymerization below the melting point of the polyamide is well below the equilibrium value. Thus, during the final polymerization a re-reaction of the polyaddition (remonomerization) take place, so that the residual monomer content of the polyamide increases again in the last step of the production process. The present invention is therefore based on the object to provide an improved hydrolytic process for the preparation of polyamides, in which the aforementioned disadvantages are avoided. In particular, it should be possible by this method to provide a product with very low residual monomer content.

Surprisingly, it has now been found that this object is achieved by subjecting the reaction mixture obtained in the hydrolytic polymerization, the polyamide, water, unreacted monomers and oligomers subjected to granulation, then subjected to a first extraction, wherein unreacted monomers and oligomers be removed at least partially, the polyamide obtained after the first extraction is then subjected to postpolymerization in the solid phase and the product of the postpolymerization is then subjected to a further extraction. Subsequently, further workup steps, for. B. a drying done. By the process according to the invention, polyamides can be obtained with lower residual monomer content compared to conventional processes.

In particular, it is possible to provide polyamides which at the same time have a low residual content of monomeric lactam and of cyclic dimer.

SUMMARY OF THE INVENTION

The invention therefore provides a process for the preparation of polyamides, in which a) providing a monomer composition containing at least one lactam or at least one aminocarbonitrile and / or oligomers of these monomers, b) reacting the monomer composition provided in step a) in a hydrolytic polymerization at elevated temperature in the presence of water to obtain a reaction product, the polyamide C) reacting the reaction product obtained in step b) to obtain polyamide particles, d) treating the polyamide particles obtained in step c) with at least one first extractant, e) which in step d) f) the polyamide obtained in step e) is treated with at least one second extractant.

In a specific embodiment, the loaded extractant obtained in step f) is subsequently used for the extraction in step d). In particular, the extracted polyamide obtained in step f) of the process according to the invention is additionally subjected to drying (step g)).

Another object of the invention are polyamides, which are obtainable by the method described above and below. These polyamides are characterized by a very low residual monomer content, as can not be achieved with methods known from the prior art.

Another object of the invention is the use of polyamides, which are obtainable by the method described above and below, in particular for the production of granules, films, fibers or moldings.

DETAILED DESCRIPTION OF THE INVENTION In the context of the present invention, monomer is understood as meaning a low molecular weight compound as used in the preparation of the polyamide by hydrolytic polymerization for introducing a single repeating unit. These include the lactams and aminocarboxylic acid nitriles used. These include, for the preparation of the polyamides optionally used comonomers such as ω-aminocarboxylic acids, co-aminocarboxamides, co-Aminocarbonsäuresalze, ω-aminocarboxylic acid esters, diamines and dicarboxylic acids, dicarboxylic acid / diamine salts, dinitriles and mixtures thereof. In the context of the present invention, an oligomer is understood as meaning a compound as formed in the preparation of the polyamides by reaction of at least two of the compounds forming the individual repeat units. In this case, the oligomers have a lower molecular weight than the polyamides prepared according to the invention. The oligomers include cyclic and linear oligomers, especially cyclic dimer, linear dimer, trimer, tetramer, pentamer, hexamer and heptamer. Common methods for the determination of the oligomeric components of polyamides generally detect the components up to the heptamer.

The viscosity number (Staudinger function, denoted by VZ, VN or J) is defined as VZ = 1 / cx (η - n _s ) / n _s . The viscosity number is directly related to the average molar mass of the polyamide and provides information about the processability of a plastic. The determination of the viscosity number can be carried out according to EN ISO 307 with an Ubbelohde viscometer. The process according to the invention has the following advantages:

The final extraction in step f) is the last step or to the extraction step joins no process step, which is associated with a higher thermal stress of the polymer, as z. B. occurs in the postpolymerization. Thus, the re-formation of monomers and / or oligomers, as occurs at higher temperatures than equilibrium reaction, avoided. Thus, very low residual monomer contents are made possible. During the first extraction in step d), a subsequent crystallization of the product of the hydrolytic polymerization can already take place. The proportion of crystalline product has an influence on the rate of postpolymerization in step e). This can be done faster than when you extract it would perform. The inventive method is thus characterized by a short residence time in the postpolymerization.

Step a)

In step a) of the process according to the invention, a monomer mixture which comprises at least one lactam or at least one aminocarbonitrile and / or oligomers of these monomers and optionally further components is reacted under polyamide-forming reaction conditions, a polyamide being formed.

According to the invention, polyamides are understood as meaning homopolyamides, copolyamides and polymers which comprise at least one lactam or nitrile and at least one further monomer and which have a content of at least 60% by weight of polyamide base units, based on the total weight of the monomer base units of the polyamide.

Homopolyamides are derived from an aminocarboxylic acid or a lactam and can be described by a single repeating unit. Polyamide 6 basic building blocks may for example be composed of caprolactam, aminocapronitrile, aminocaproic acid or mixtures thereof. Examples of homopolyamides are nylon 6 (PA 6, polycaprolactam), nylon 7 (PA 7, polyeneantholactam or polyhep tanamide), nylon 10 (PA 10, polydecanamide), nylon 1 1 (PA 11, polyundecanlactam) and Nylon 12 (PA 12, polydodecan lactam). Copolyamides are derived from several different monomers, the

Monomers are each interconnected by an amide bond. Possible Copolyamidbausteine can be derived, for example, from lactams, aminocarboxylic acids, dicarboxylic acids and diamines. Preferred copolyamides are polyamides of caprolactam, hexamethylenediamine and adipic acid (PA 6/66). Copolyamides may contain the polyamide components in various ratios.

Polyamide copolymers contain, in addition to the polyamide basic building blocks, further basic building blocks which are not connected to one another by amide bonds. The proportion of comonomers in polyamide copolymers is preferably at most 40% by weight, more preferably at most 20% by weight, in particular at most 10% by weight, based on the total weight of the basic building blocks of the polyamide copolymer.

The polyamides prepared by the process according to the invention are preferably selected from polyamide-6, polyamide-1 1, polyamide-12, and their copolyamides. and polymer blends thereof. Particularly preferred are polyamide-6 and polyamide-12, more preferably polyamide-6.

The monomer mixture provided in step a) preferably comprises at least one C5 to C12 lactam and / or an oligomer thereof. The lactams are in particular selected from ε-caprolactam, 2-piperidone (δ-valerolatam), 2-pyrrolidone (γ-butyrolactam), capryllactam, enanthlactam, laurolactam, mixtures thereof and oligomers thereof. Particularly preferably, in step a) a monomer mixture is provided which contains ε-caprolactam, 6-aminocapronitrile and / or an oligomer thereof. In particular, in step a) a monomer mixture is provided which contains exclusively ε-caprolactam or exclusively 6-aminocapronitrile as the monomer component.

Furthermore, it is also possible that in step a) a monomer mixture is provided which contains in addition to at least one lactam or aminocarbonitrile and / or oligomer thereof at least one monomer (M) copolymerizable therewith.

Suitable monomers (M) are dicarboxylic acids, for example aliphatic C4-10-alpha, omega-dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and dodecanedioic acid. Aromatic C8-2o-dicarboxylic acids such as terephthalic acid and isophthalic acid can also be used.

Diamines suitable as monomers (M) are α, ω-diamines having four to ten carbon atoms, such as tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine and decamethylenediamine. Particularly preferred is hexamethylenediamine.

Among the salts of said dicarboxylic acids and diamines which are suitable as monomers (M), preference is given in particular to the salt of adipic acid and hexamethylenediamine, so-called AH salt.

Suitable monomers (M) are also lactones. Preferred lactones are, for example, ε-caprolactone and / or γ-butyrolactone.

One or more chain regulators can be used in the preparation of the polyamides, for example aliphatic amines or diamines such as triacetonediamine or mono- or dicarboxylic acid such as propionic acid and acetic acid or aromatic carboxylic acids such as benzoic acid or terephthalic acid. Step b)

The reaction of the monomer mixture provided in step a) in a hydrolytic polymerization in step b) can be carried out by customary methods known to the person skilled in the art. Such a method is z. As in Kunststoff Handbuch,% engineering thermoplastics: polyamides, Carl Hanser Verlag, 1998, Munich, pp. 42-47 and 65-70 described. This disclosure is hereby incorporated by reference. Preferably, in step b) for hydrolytic polymerization, a lactam is subjected to ring opening under the action of water. This z. B. the lactam cleaved at least partially to the corresponding aminocarboxylic acid, which then further polymerized in the subsequent step by polyaddition and polycondensation. If, in a preferred embodiment, a monomer mixture containing caprolactam is provided in step a), it is at least partially opened to the corresponding aminocaproic acid under the action of water and then reacts under polycondensation and polyaddition to form polyamide 6. In an alternative embodiment, in step b ) an aminocarbonitrile, especially 6-aminocapronitrile, a polymerization under the action of water and optionally in the presence of a catalyst.

The reaction in step b) is preferably carried out continuously.

Preferably, the hydrolytic polymerization in step b) in the presence of 0.1 to 25 wt .-% of added water, more preferably from 0.5 to 20 wt .-% of added water, based on the total amount of the monomers and oligomers used. Additional water formed in the condensation reaction is not included in this quantity. The hydrolytic polymerization in step b) can be carried out in one or more stages (for example in two stages). When the hydrolytic polymerization in step b) is carried out in one stage, the initial concentration of the water is preferably 0.1 to 4 wt .-% based on the total amount of the monomers and oligomers used. If the hydrolytic polymerization in step b) is carried out in two stages, then the VK tube is preferably a pre-press, for. B. a Druckvorreaktor, upstream. In the prepress stage, the initial concentration of water is preferably from 2 to 25% by weight, more preferably from 3 to 20% by weight, based on the total amount of the monomers and oligomers used. In a specific embodiment, the monomer mixture prepared in step a) consists of at least one lactam and the hydrolytic polymerization in step b) is carried out in the presence of from 0.1 to 4% by weight of water, based on the total amount of lactam used. Specifically, the lactam is ε-caprolactam.

The hydrolytic polymerization in step b) can be carried out in the presence of at least one regulator, such as propionic acid. If a regulator is used in step b) and the hydrolytic polymerization is carried out in two stages using a pressure precursor, the regulator can be used in the prepress and / or in the second polymerization stage. In a specific embodiment, the hydrolytic polymerization in step b) does not take place in the presence of a regulator.

The polyamides prepared in the process according to the invention may additionally contain conventional additives such as matting agents, for. As titanium dioxide, nucleating agents, z. As magnesium silicate, stabilizers, z. As copper (L) halides and alkali halides, antioxidants, reinforcing agents, etc., contained in conventional amounts. The additives are usually added before, during or after the hydrolytic polymerization (step b). The additives are preferably added before the hydrolytic polymerization in step b).

The reaction in step b) can take place in one or more stages (for example in two stages). In a first embodiment, the reaction in step b) is carried out in one stage. In this case, preferably the lactam or aminocarbonitrile and optionally oligomers thereof are reacted with water and optionally additives in a reactor.

Suitable reactors are the customary for the preparation of polyamides, known in the art reactors. The hydrolytic polymerization in step b) preferably takes place in a polymerization tube or a bundle of polymerization tubes. Specifically, at least one so-called VK tube is used for the hydrolytic polymerization in step b). The abbreviation "VK" stands for "simplified continuously". In a multi-stage embodiment of the reaction in step b) is preferably carried out at least one of the stages in a VK tube. In a two-stage embodiment of the reaction in step b), the second stage preferably takes place in a VK tube. In a two-stage embodiment of the reaction in step b), the first stage can take place in a pressure pre-reactor. When using an aminocarbonitrile, the reaction in step b) is generally carried out in several stages, the first stage preferably taking place in a pressure pre-reactor. In a suitable embodiment, polyamide 6 is prepared in a multi-stage process, especially a two-stage process. Caprolactam, water and optionally at least one additive, such as a chain regulator, are fed to the first stage and converted to a polymer composition. This polymer composition can be transferred under pressure or through a melt discharge pump to the second stage. This is preferably done via a melt distributor. The hydrolytic polymerization in step b) is preferably carried out at a temperature in the range of 240 to 280 ° C. In a multi-stage embodiment of the hydrolytic polymerization in step b), the individual stages can be carried out at the same or at different temperatures and pressures. When carrying out a polymerization step in a tube reactor, especially a VK tube, the reactor can have substantially the same temperature over the entire length. Also possible is a temperature gradient in the region of at least part of the tubular reactor. It is also possible to carry out the hydrolytic polymerization in a tubular reactor having two or more than two reaction zones, which are operated at different temperatures and / or at different pressures. The skilled person can the optimal conditions as needed, for. B. taking into account the equilibrium conditions.

If the hydrolytic polymerization in step b) takes place in one stage, the absolute pressure in the polymerization reactor is preferably in a range of about 1 to 10 bar, more preferably from 1, 01 bar to 2 bar. Particularly preferably, the single-stage polymerization is carried out at ambient pressure.

In a preferred embodiment, the hydrolytic polymerization in step b) is carried out in two stages. By pre-switching a so-called pressure stage, a process acceleration can be achieved by the rate-limiting cleavage of the lactam, especially of caprolactam, under elevated pressure under otherwise similar conditions as in the second reaction stage is performed. The second stage is then preferably in a VK tube, as previously described. Preferably, the absolute pressure in the first stage is in a range of about 1.5 to 70 bar, more preferably in a range of 2 to 30 bar. Preferably, the absolute pressure in the second stage is in a range of about 0.1 to 10 bar, more preferably from 0.5 bar to 5 bar. In particular, the pressure in the second stage is at ambient pressure. At the exit of the VK tube, the polyamide melt is then subjected to shaping to obtain polyamide particles.

Step c)

In step c) of the process according to the invention, the polyamide obtained in step b) is subjected to shaping to obtain polyamide particles.

Preferably, the polyamide obtained in step b) is first formed into one or more strands. For this purpose, devices known to the person skilled in the art can be used. Suitable devices are for. As perforated plates, nozzles or nozzle plates. Preferably, the reaction product obtained in step b) is formed into strands in a flowable state and subjected to comminution as a flowable strand-like reaction product to form polyamide particles. The hole diameter is preferably in a range of 0.5 mm to 20 mm, more preferably 1 mm to 5 mm, most preferably 1, 5 to 3 mm.

The shaping in step c) preferably comprises a granulation. For granulation, the polyamide obtained in step b), formed into one or more strands, can be solidified and subsequently granulated. In z. B. Kunststoffhandbuch,% engineering thermoplastics: polyamides, Carl Hanser Verlag, 1998, Munich, pp. 68-69 suitable measures are described. A special method of shaping is underwater granulation, which is also known in principle to a person skilled in the art. Step d)

In step d), the polyamide particles obtained in step c) are subjected to a first extraction. Suitable methods and devices for extracting polyamide particles are known in principle to the person skilled in the art.

Extraction means that the content of monomers and optionally dimers and other oligomers in the polyamide is reduced by treatment with an extractant. Technically, this can be done for example by continuous or discontinuous extraction with hot water (DE 2501348 A, DE 2732328 A) or in the superheated steam stream (EP 0284968 W1). For extracting in step d), preference is given to using a first extractant which contains water or consists of water. In a preferred embodiment, the first extractant consists only of water. In a further preferred embodiment, the first extraction agent contains water and a lactam and / or its oligomers used to prepare the polyamide. In the case of polyamide 6, it is thus also possible to use caprolactam-containing water for the extraction, as described in WO 99/26996 A2. For the extraction in step d), the loaded extractant obtained in step f) is preferably used. Thus, the amount of processing wastewater can be minimized.

The temperature of the extractant is preferably in a range of 75 to 130 ° C, more preferably 85 to 120 ° C.

The extraction can be continuous or discontinuous. Preferred is a continuous extraction.

During extraction, the polyamide particles and the first extractant may be passed in cocurrent or countercurrent. Preferably, the extraction is in countercurrent.

In a first preferred embodiment, the polyamide particles are continuously extracted in countercurrent with water at a temperature <100 ° C and ambient pressure. Preferably, the temperature is then in a range of 85 to 99.9 ° C. In a further preferred embodiment, the polyamide particles are extracted continuously in countercurrent with water at a temperature> 100 ° C and a pressure in the range of 1 to 2 bar absolute. Preferably, the temperature is then in a range of 101 to 120 ° C. For extraction, it is possible to use customary devices known to the person skilled in the art. In a specific embodiment, at least one pulsed extraction column is used for the extraction.

The components contained in the loaded first extractant obtained in step d), selected from monomers and optionally dimers and / or oligomers, can be isolated and recycled to step a) or b).

It is possible to subject the extracted polyamide obtained in step d) to drying. The drying of polyamides is known in principle to the person skilled in the art. examples For example, the extracted granules may be dried by contact with dry air or a dry inert gas or a mixture thereof. Preference is given to an inert gas, for. As nitrogen, used for drying. The extracted granules may also be dried by contacting with superheated steam or a mixture thereof with a gas other than that, preferably an inert gas. For drying conventional dryer, z. B. countercurrent, crossflow, plate, tumble, paddle, trickle, cone, shaft dryer, fluidized beds, etc. are used. A suitable embodiment is the discontinuous drying in the tumble dryer or conical dryer under vacuum. Another suitable embodiment is the continuous drying in so-called drying tubes, through which a gas which is inert under the drying conditions is passed through. In a special embodiment, at least one shaft dryer is used for drying. Preferably, the shaft dryer is flowed through by a hot, inert under the Nachpolymerisationsbedingungen gas. A preferred inert gas is nitrogen.

Steps)

In step e), the extracted polyamide obtained in step d) is fed into a reaction zone for postpolymerization.

Preferably, the polyamide particles obtained in step d) are subjected to solid state polymerization for postpolymerization in step e). The polyamide is polymerized in the solid phase. The polyamide undergoes a heat treatment, the temperature being below the melting point of the polyamide.

Suitable as a reaction zone in which the postpolymerization takes place, are in principle devices, as they can also be used for drying z. B. Countercurrent, crossflow, plate, tumble, paddle, trickle, cone, shaft dryer, fluidized beds, etc. Preferably, at least one reactor is used as the reaction zone in which the postpolymerization takes place, more preferably at least one tubular reactor. In a special embodiment, at least one shaft dryer is used for postpolymerization. Preferably, the shaft dryer is flowed through by a hot, inert under the Nachpolymerisationsbedingungen gas. A preferred inert gas is nitrogen.

Suitable processes for postpolymerization of hydrolytically produced polyamides are known in principle to the person skilled in the art. The postpolymerization may, for. B. as in

WO 2009153340, EP 1235671 or EP 0732351. The postpolymerization in step d) can be carried out in one stage (in a single reaction zone). You can also multi-level z. B. two stages, take place in several reaction zones, which can be arranged one behind the other and / or in parallel. The postpolymerization is preferably carried out in one stage.

In the postpolymerization, the temperature in the reaction zone is preferably in a range from 120 to 185 ° C., more preferably from 150 to 180 ° C.

In the postpolymerization, the pressure in the reaction zone is usually in a range from 1 mbar to 1.5 bar, more preferably from 500 mbar to 1.3 bar.

In the multi-stage postpolymerization, the polymerization devices may be the same or different in size and type. For example, two identical polymerization devices, or two differently dimensioned polymerization devices can be used. For example, two polymerization devices can be operated in series, each having a different residence time characteristic. For example, two polymerization devices can also be operated in succession, each of the polymerization devices having different pressure stages. For example, two polymerization devices can be operated in succession, wherein each of the polymerization devices is flowed through by different amounts of inert gas. For example, two polymerization devices can also be operated in succession, each of the polymerization devices having different pressure stages and flowing through different amounts of inert gas.

The temperature control of the polyamide in the postpolymerization is usually carried out via heat exchangers, such as double jacket, internal heat exchangers or other suitable devices. In a preferred embodiment, the postpolymerization in step e) takes place in the presence of at least one inert gas. Then, the tempering of the polyamide in the postpolymerization can be done at least partially by the use of a hot inert gas.

In a first preferred embodiment, the reaction zone is traversed by hot inert gas during the postpolymerization. Suitable inert gases include, for example, nitrogen, CO2, helium, neon and argon, and mixtures thereof. Preferably, nitrogen is used.

In a further preferred embodiment, the postpolymerization in step e) takes place without mass transfer with the environment. Under a postpolymerization without mass transfer with the environment ", it is understood that after the extracted polyamide particles extracted in step d) are not transferred to the postpolymerization zone, no gas exchange takes place between the postpolymerization zone and the environment Post-polymerization in step e) no entry and also no discharge of components, eg of water, from the interior of the container into the environment and vice versa.

The residence time in the reaction zone in step e) is preferably 15 hours to 100 hours, more preferably 25 hours to 55 hours.

According to a preferred embodiment, the residence time of the polymer in step e) is selected such that the relative viscosity of the polyamide is at least 10%, preferably at least 15%, more preferably at least 20%, based on the relative viscosity of the polyamide before step d), increased.

The relative viscosity of the polyamide is usually used as a measure of the molecular weight. The relative viscosity is determined according to the invention at 25 ° C as a solution in 96 weight percent H2SO4 with a concentration of 1, 0 g of polyamide in 100 ml of sulfuric acid. The determination of the relative viscosity follows DIN EN ISO 307.

Step f) In step f), the polyamide particles obtained in step e) are subjected to a further extraction.

The extraction of polyamide particles is known in principle to a person skilled in the art and is described in detail in step d).

For extraction in step f), a second extractant containing water or consisting of water is preferably used. In a preferred embodiment, the second extractant consists only of water. In a specific embodiment, it is then recovered extractant that may still contain small amounts of monomer and / or oligomer.

The temperature of the extractant in step f) is preferably in a range of 75 to 120 ° C. The temperature of the extractant during the treatment in step f) is more preferably in a range from 50 to less than 120 ° C, especially from 75 to 18 ° C, especially from 80 to 15 ° C, more particularly from 85 to 110 ° C. Preferably, the polyamide is in the solid state (and not in the melt) during the treatment in step f).

The extraction in step f) can be continuous or discontinuous. Preferred is a continuous extraction.

In the extraction in step f), the polyamide particles and the first extractant can be conducted in cocurrent or countercurrent. Preferably, the extraction is in countercurrent. In a first preferred embodiment, the polyamide particles are continuously extracted in countercurrent with water at a temperature <100 ° C and ambient pressure. Preferably, the temperature is then in a range of 85 to 99.9 ° C.

In a further preferred embodiment, the polyamide particles are continuously extracted in countercurrent with water at a temperature> 100 ° C and a pressure in the range of 1 to 2 bar absolute. Preferably, the temperature is then in a range of 101 to less than 120 ° C.

The components contained in the loaded second extractant obtained in step f), selected from monomers and optionally dimers and / or oligomers, can be isolated and recycled to step a) or b).

In a preferred embodiment of the process according to the invention, the loaded second extraction agent obtained in step f) is subsequently used as the first extraction agent in step d). According to this variant, the same extractant is first brought into contact with the polyamide particles from the post-polymerization which are loaded to a lesser extent with monomers and / or oligomers and then with the higher polyamide particles loaded with monomers and / or oligomers from the hydrolytic polymerization. Thus, the amount of extractant to be worked up can be significantly reduced.

A specific embodiment of the method according to the invention comprises the following steps: Treatment of the polyamide obtained in step e) with at least one second extractant to give a second extractant laden with monomers and / or oligomers, use of the loaded extractant obtained in step f) for extraction in step d),

Separation of the loaded extractant obtained in step d) into a fraction enriched in monomers and / or oligomers and a fraction depleted in monomers and / or oligomers, at least partially feeding the fraction enriched in monomers and / or oligomers into the fraction obtained in step a) provided monomer composition or the reaction zones used for the hydrolytic polymerization in step b), at least partially using the monomer and / or oligomer-enriched fraction as a second extraction agent in step f). Step g)

Preferably, the extracted polyamide obtained in step f) is subjected to drying. Suitable apparatus and methods for drying are previously described in step d), to which reference is hereby made. For drying conventional dryer, z. B. countercurrent, crossflow, plate, tumble, paddle, trickle, cone, shaft dryer, fluidized beds, etc. are used. For example, the extracted granules may be dried by contact with dry air or a dry inert gas or a mixture thereof. Preferably, an inert gas is used for drying. A suitable design is the discontinuous drying in the tumble dryer or conical dryer under vacuum. Another suitable embodiment is the continuous drying in so-called drying tubes, which are flowed through with a gas inert under the drying conditions. In a special embodiment, at least one shaft dryer is used for drying. Preferably, the shaft dryer is flowed through by a hot, under the Nachpolymerisations- conditions inert gas. A preferred inert gas is nitrogen.

The process according to the invention can be carried out continuously or batchwise, preferably it is carried out continuously. The process according to the invention leads to polyamides having particularly advantageous properties. A suitable measure of the polymer properties achieved is the viscosity number. The viscosity number (Staudinger function, denoted by VZ, VN or J) is defined as VZ = 1 / cx (η - n _s ) / n _s . The viscosity number is directly related to the average molar mass of the polyamide and provides information about the processability of a plastic. The determination of the viscosity number can be carried out according to EN ISO 307 with an Ubbelohde viscometer. The viscosity number of the polyamide obtained by the process according to the invention is preferably from 185 to

260 ml / g.

Preferably, the polyamide obtained has a residual monomer content of less than 0.1, preferably less than 0.055 wt .-%, particularly preferably less than 0.03 wt .-% to. The content of cyclic dimer is preferably less than 0.1% by weight, more preferably less than 0.05% by weight, in particular less than 0.025% by weight, very particularly preferably less than 0.01% by weight.

The polyamide obtained preferably has a residual lactam content of at most 0.055% by weight and a residual cyclic dimer content of at most 0.025% by weight.

The process is explained in more detail below by FIG. 1 and the examples.

Figure 1 shows schematically an embodiment for carrying out the method according to the invention.

Figure 2 shows schematically a further embodiment for carrying out the method according to the invention, wherein loaded extractant from the extraction (5) for the extraction in (3) is fed. The following reference symbols are used in FIGS. 1 and 2:

1 pre-press reactor

 2 VK pipe

 3 extraction

4 solid phase polymerization

 5 extraction

 6 drying

 A1, A2 inlet, outlet of the first extractant

 B1, B2 inlet, outlet of the second extractant

B2A1 line for feeding loaded extractant from (5) into (3) EXAMPLES

FIG. 1: Inventive process for the production of polyamide 6

Example 1 :

 The starting material used was an industrial scale polyamide 6 granulate having a viscosity number of 218 ml / g and a monomer content of 0.23%. The production of the polyamide 6 granules took place via the process steps pre-reaction in the pressure reactor, melt polymerization in the VK tube, hot water extraction and heat treatment. 300 g of granules were introduced into a 2L reactor and extracted at 95 ° C with 1000 g of water with stirring over 24 h. The extracted granules were dried for 16 hours under nitrogen transfer in a vacuum oven. The monomer content thereafter was 0.04%.

Example 2:

 The starting material used was an industrial scale polyamide 6 granulate having a viscosity number of 251 ml / g and a monomer content of 0.24%. The production of the polyamide 6 granules took place via the process steps pre-reaction in the pressure reactor, melt polymerization in the VK tube, hot water extraction and heat treatment. 450 g of granules were introduced into a 2L reactor and extracted at 105 ° C with 1500 g of water with stirring over 24 h. The extracted granules were dried for 16 hours under nitrogen transfer in a vacuum oven. The monomer content thereafter was 0.03%.

Examples 3-5:

The starting material used was an industrial scale polyamide 6 granulate having a viscosity number of 218 ml / g and a monomer content of 0.23%. The production of the polyamide 6 granules took place via the process steps pre-reaction in the pressure reactor, melt polymerization in the VK tube, hot water extraction and heat treatment. 625 g of granules were introduced into a 2L reactor and extracted at 95 ° C while stirring with water for 30 h. The water was continuously exchanged at a flow rate of 2 l / h. From the extracted granules three 80 g fractions were taken, which were dried successively in a drying apparatus. The drying apparatus consisted of a glass tube with frit bottom, which was heated by a double jacket. 80 g of granules were introduced into the preheated glass tube and flowed through for a certain residence time with hot nitrogen. After the residence time, the granules were removed. Conditions drying:

 Examples 6-8:

 The feedstock used was an industrial-scale polyamide 6 granulate having a viscosity number of 250 ml / g, a monomer content of 0.23% and a dimer content of 220 ppm. The production of the polyamide 6 granules was carried out via the process steps pre-reaction in the pressure reactor, melt polymerization in the VK tube, hot water extraction and heat treatment. This granulate was subjected to further hot water extraction and then dried. The hot water extraction was carried out in a continuous pulsed countercurrent extractor. The extractor had a capacity for about 8 tons of polyamide granules. The extractant used was fresh, deionized water. By pulsation is meant that the extractant water is not continuously fed into the extractor at a constant flow rate, but that the water is fed in pulses with high flow velocity.

 The extractor was divided into three zones (top, middle and bottom) by three internal heat exchangers, in each of which different temperatures could be set. The granules leaving the extractor were continuously driven via a centrifuge into a shaft dryer. The shaft dryer had a capacity for about 16 1 polyamide granules. The drying was carried out with the aid of hot nitrogen, which was fed from below into the shaft dryer. Conditions extraction:

 Example 6 Example 7 Example 8

Throughput granules [kg / h] 330 450 600

Residence time granules [kg / h] 24 18 13.5 Throughput extraction capacity [kg / h] 740 490 580

Temperature above [° C] 98 90 80

Temperature middle [° C] 98 98 95

Lower temperature [° C] 95 95 95

Monomer content after extraction [ppm] 130 320 670

Conditions drying:

^* measured at operating temperature = "temperature down" Example 9:

The feed used was an industrial-scale polyamide 6 granulate having a viscosity number of 216 ml / g, a monomer content of 0.28% and a dimer content of 210 ppm. The production of the polyamide 6 granules was carried out via the process steps melt polymerization in the VK tube, hot water extraction and heat treatment. This granulate was subjected to further hot water extraction and then dried. The hot water extraction was carried out in a continuous countercurrent extractor. The extractor had a capacity for about 44 tons of polyamide granules. The extraction medium used was water which had an organic carbon content ("TOC", "total organic carbon") of 500 ppm. The extractor had an extractant recycling in the upper third, ie that part of the extractant emerging at the top of the extractor is returned to the upper third of the extractor. The granules leaving the extractor were continuously driven via a centrifuge into a shaft dryer. The shaft dryer had a capacity for about 40 tons of polyamide granules. The drying was carried out with the aid of hot nitrogen, which was fed below the upper third of the shaft dryer.

Conditions drying:

^* measured at operating temperature = "temperature down"

Claims

 claims A process for the preparation of polyamides comprising: a) providing a monomer composition containing at least one lactam or at least one aminocarbonitrile and / or oligomers of these monomers; b) the monomer composition provided in step a) in a hydrolytic polymerization at elevated temperature in the presence of C) reacting the reaction product obtained in step b) to obtain polyamide particles, d) the polyamide particles obtained in step c) with at least one first extraction agent e) receives the extracted polyamide particles obtained in step d) for subsequent polymerization in a reaction zone, f) the polyamide obtained in step e) is treated with at least one second extractant. Process according to claim 1, wherein the second extractant used in step f) contains water or consists of water. Process according to claim 1 or 2, wherein the temperature of the extractant during the treatment in step f) is in a range from 50 to less than 120 ° C, preferably from 75 to 18 ° C, particularly preferably from 80 to 15 ° C, lies. Method according to one of the preceding claims, wherein the polyamide is in the solid state during the treatment in step f). 5. The method according to any one of the preceding claims, wherein the extracted polyamide obtained in step f) is additionally subjected to drying (step g)) - 6. The method according to any one of the preceding claims, wherein the provided in step a) monomer composition ε-caprolactam or 6-aminocapronitrile and / or oligomers of these monomers. 7. The method according to any one of the preceding claims, wherein the reaction in step b) takes place in one or more stages. 8. The method according to any one of the preceding claims, wherein the reaction in step b), takes place in two stages and at least in the second stage, a substantially vertical tubular reactor is used. 9. The method according to any one of the preceding claims, wherein the shaping in step c) comprises a granulation. 10. The method according to any one of the preceding claims, wherein the first extractant used in step d) contains water or consists of water. 1 1. Process according to one of the preceding claims, wherein the polyamide obtained in step d) is subjected to solid state polymerization for postpolymerization in step e). The method of claim 1 1, wherein the post-polymerization used in step e) reaction zone comprises a tubular reactor or consists of a tubular reactor, specifically comprises a shaft dryer or consists of a shaft dryer. 13. The method according to any one of claims 1 1 or 12, wherein the temperature during the post-polymerization in step e) in a range of 120 to 185 ° C. 14. The method according to any one of the preceding claims, wherein the postpolymerization in step e) takes place without mass transfer with the environment. 15. The method according to any one of claims 1 to 14, wherein in the obtained in step d) loaded first extractant and / or contained in the obtained in step f) loaded second extractant components selected from monomers and optionally dimers and oligomers , isolated and recycled in step a) and / or b). 16. The method according to any one of claims 1 to 14, wherein the obtained in step f) loaded second extractant is used as the first extractant in step d). 17. The method according to any one of the preceding claims, wherein the method is carried out continuously. A polyamide obtainable by a process as defined in any one of claims 1 to 17. 19. A polyamide according to claim 18, which has a residual content of lactam of at most 0.055 wt .-% and a residual content of cyclic dimer of at most 0.05 wt .-%. 20. Use of a polyamide according to claim 18 or 19 or obtainable by a process as defined in any one of claims 1 to 17, for the production of granules, films, fibers or moldings.