WO2014135627A1

WO2014135627A1 - Production of polyamides by hydrolytic polymerization and subsequent degassing

Info

Publication number: WO2014135627A1
Application number: PCT/EP2014/054326
Authority: WO
Inventors: Silke Biedasek; Achim Stammer
Original assignee: Basf Se
Priority date: 2013-03-07
Filing date: 2014-03-06
Publication date: 2014-09-12

Abstract

The present invention relates to a method for producing polyamides by hydrolytic polymerization, in which the polyamide is treated in a degassing device after the hydrolytic polymerization.

Description

Production of polyamides by hydrolytic polymerization and subsequent degassing

BACKGROUND OF THE INVENTION

The present invention relates to a process for the preparation of polyamides by hydrolytic polymerization, in which the polyamide is treated after the hydrolytic polymerization in a degassing device. 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 the polyamides, the polyamide 6 (polycaprolactam) is the most widely produced polymer with a share of about 57%. The classical method for the production of polyamide 6 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 lower residual monomer content in the polyamide is required, so that the crude polyamide before its further processing is generally subjected to at least partial removal of monomers and / or 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. B. in 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, polyamides with higher molecular weights are needed, which are not achieved by the hydrolytic polymerization alone. To increase the molecular weight or the viscosity of the polyamide can be carried out subsequent to the extraction and drying a post-condensation, wherein the polyamide is preferably present in the solid phase (solid phase condensation). For this purpose, the granules can be tempered at temperatures below the melting point of the polyamide, in particular, the polycondensation 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 polyamide 6 after extraction and postpolymerization is about 180 to 260 ml / g.

Postcondensation and drying are often carried out in one step, as described in WO 2009/153340 A1 and DE 199 57 664 A1.

DD 2090899 describes a process for removing low molecular weight constituents from a polyamide melt by subjecting them to extraction with monomeric caprolactam and then removing the monomer in vacuo.

DD 227140 describes a process for the production of polyamide having a degree of polymerization DP> 200. The process is characterized by at least 5 post-polymerization nander outgoing steps. At the beginning of each drying step, the surface of the molten polyamide is adjusted to> 4 cm ² / g of polyamide and the maximum diffusion path of the water in the melt 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.

EP 0 141 314 A2 describes a process for the preparation of dry polyamine caprolactam granules with a content of caprolactam and its oligomers of 8 to 13% by weight, wherein a caprolactam melt is poured into strands, the strands are cooled to 100 to 150 ° C. and at this temperature, until the Polyca- prolactam is largely crystallized, immediately granulated and leaves the granules in an inert gas stream with the exclusion of molecular oxygen for a period of 1 to 4 hours at a temperature of 100 to 150 ° C leaves and then cool. Degassing of the strand-shaped product at high temperatures in the melt state is not described.

EP 0 621 304 A1 describes flame-retardant thermoplastic molding compositions which are prepared by mixing in

A) 20 to 70 wt .-% of a magnesium hydroxide and

B) 0 to 70 wt .-% of conventional additives and processing aids in one

Melt of

C) 10 to 80 wt .-% of a polyamide prepolymer having a viscosity number of 40 to 100 ml / g

and subsequent post-condensation in solid phase, are available. In Examples 1 and 2, a polyamide prepolymer with magnesium hydroxide and chopped glass fibers is fed into an extruder, melted, mixed and formulated. The product thus obtained is extracted with water and dried in vacuo at 80 ° C (i.e., well below the melting temperature) for 12 hours. Only then is the dried product subjected to a strand granulation.

EP 0 1 17 495 describes the continuous production of polylactams in which a water-containing lactam composition is heated in a prepolymerization zone under a pressure of 1 to 10 bar with simultaneous evaporation of the water to a temperature of 220 to 280 ° C, prepolymer and steam continuously separated , which passes prepolymer in a polymerization zone and further polymerized under elevated pressure at a temperature of 240 to 290 ° C. Although this document teaches that the prepolymer is molten from the prepolymerization zone carry out and a degassing to remove water can undergo. However, it is not described that the prepolymer is present in a stranded form. Thus, it is specifically taught on page 3, lines 22-26 of this document that the prepolymer is first treated in a degassing extruder and only then poured the melt freed of water in strands and granulated. According to the specific embodiment of the single example, the prepolymer is separated in a separator in steam and melt, only then discharged in the form of strands and solidified in a water bath. The discharge in the form of strands is used according to the teaching of EP 0 1 17 495 cooling and solidifying for the following Granulations- step and not the degassing / dehydration. In summary, this document thus does not teach to form a polyamide prepolymer from a hydrolytic polymerization in the molten state into strands and to degas the stranded product at high temperatures in the melt state. 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 ΤΊΟ2. 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. In this synthesis route, too, it is often 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 ε-caprolactam at the beginning of the postpolymerization of the crude polyamide in the solid phase is well below the equilibrium value. Thus, a back reaction of the polyaddition (remonomerization) take place during the final postpolymerization, so that the residual monomer content of the polyamide increases again in the last step of the preparation process. In addition, the conventional processes are characterized by a comparatively long residence time in the postpolymerization, which is necessary in order to obtain a polyamide with a correspondingly high molecular weight or viscosity number. This leads to increased production costs. The present invention is therefore based on the object to provide an improved process for the preparation of polyamides by hydrolytic polymerization, 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 if the reaction mixture obtained in the hydrolytic polymerization, the polyamide, water, unreacted monomers and oligomers, instead of subjecting it to extraction, feeds directly strand into a degassing device, wherein the contained Water is at least partially removed, and then subjecting the mixture to a post-polymerization in the melt in a reaction zone. At this particular form of melt polymerization may be especially a further work-up, for. B. by granulation, extraction and / or drying, connect, but in particular no further postpolymerization in the solid phase, d. H. below the melting point of the polymer. According to the process of the invention, polyamides having a high molecular weight and low residual monomer content can be obtained with a reduced total process time compared to conventional processes.

SUMMARY OF THE INVENTION

The invention therefore provides a process for the preparation of polyamides, comprising: a) providing a monomer composition comprising 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 reacting at elevated temperature in the presence of water to obtain a reaction product containing polyamide, water, unreacted monomers and oligomers, c) forming the reaction product obtained in step b) into one or more strands, d) the strand-shaped product obtained in step c) Feed reaction product in a degassing and under reduced pressure and / or by contact treated with an inert gas, wherein the water contained is at least partially removed, and e) feeds the degassed reaction product obtained in step d) for post-polymerization in a reaction zone.

A specific embodiment relates to 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) see the provided in step a) monomer composition in a hydrolyti- see Polymerization at elevated temperature in the presence of water under

C) reacting the reaction product obtained in step b) in a melted state into one or more strands, d) the extruded reaction product obtained in step c), without prior to comminuting it to polyamide particles and without subjecting it to extraction beforehand, melt-feeding it into a deaerator and melt-treating it under reduced pressure and / or by contacting it with an inert gas, at least partially removing the water contained therein, and e ) feeds the degassed reaction product obtained in step d) in a melt-like manner into a reaction zone and subjects it to post-polymerization in the melt.

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 by 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, ω-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 ) / r \ 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.

In the context of the invention, a flowable reaction product is understood as meaning a mixture which is capable of flowing out of a hollow body (for example, a reaction tube arranged substantially vertically). Preferably, the reaction product is formed into strands and fed as a flowable strand-shaped reaction product in the degassing. Preferably, the reaction product obtained in step b) in a flowable state has a zero viscosity of 10 to 5 ^* 10 ³ Pa-s at 250 ° C.

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 these monomers and optionally further components is reacted under polyamide-forming reaction conditions, wherein a polyamide is 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, with a content of at least 60% by weight of polyamide base units, based on the total weight of the monomer building blocks of the polyamide. Homopolyamides are derived from an aminocarboxylic acid or a lactam or a diamine and a dicarboxylic acid and can be described by a single repeating unit. Polyamide 6 basic building blocks may be composed, for example, of caprolactam, aminocapronitrile, aminocaproic acid or mixtures thereof. Examples of homopolyamides are nylon 6 (PA 6, polycaprolactam), nylon 7 (PA 7, polyene antholactam or polyheptanamide), 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, wherein the monomers are 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 units 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, particularly preferred is 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. of it. 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, in addition to at least one lactam or aminocarbonitrile and / or oligomer thereof, contains 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. In the Plastics Handbook,% Technique see thermoplastics: polyamides, Carl Hanser Verlag, 1998, Munich, pp. 42-47 and 65-70. This disclosure is hereby incorporated by reference.

Preferably, in step b) for hydrolytic polymerization, a lactam is subjected to a 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 condensation 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 .-% 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 is carried out in two stages in step b), then the VK tube is preferably a pre-press, for. B. a Druckvorreak- gate 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) comprises 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 um

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) takes place in one stage. In this case, the lactam or aminocarbonitrile and optionally oligomers thereof are preferably reacted with water and, if appropriate, additives in a reactor for the reaction.

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 applied under pressure or through a melt discharge pump in be transferred 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 zone, which are operated at different temperatures and / or at different pressures. If the hydrolytic polymerization in step b) takes place in one stage, the absolute pressure in the polymerization reactor is preferably in a range from about 2 to 10 bar, more preferably from 1, 01 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 outlet of the VK tube, the reaction product is discharged strand-shaped. Preferably, the reaction product obtained in step b) is formed into strands in a flowable state and fed into the degassing device as a flowable strand-like reaction product. In particular, the reaction product obtained in step b) is in the molten state during the discharge, the strand molding and the subsequent entry into the degassing device.

Step c) Before being fed into the degassing device, the reaction product obtained in step b) is 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 in a flowable state into strands and fed as a flowable strand-shaped reaction product in the degassing.

The hole diameter is preferably in a range of 0.5 mm to 20 cm, more preferably 0.5 mm to 5 cm, most preferably 1 mm to 10 mm.

Step d)

In step d) of the process according to the invention, the flowable polyamide obtained in step b) is fed into a degassing device. The flowable polyamide obtained in step b) is treated under reduced pressure and / or by contact with an inert gas, wherein the water contained is at least partially removed.

Preferably, the strand-like reaction product obtained in step c) without it beforehand a comminution to polyamide particles, for. B. by granulation to be fed into the degassing in step d).

The strand-like reaction product obtained in step c) is preferably fed to the degassing device in step d) without being subjected to extraction beforehand. In a specific embodiment, the reaction mixture fed into the degassing device is guided solely by gravity through the degassing device.

In a specific embodiment, the reaction mixture fed into the degassing device is passed through the degassing device without contact with the wall of the degassing device.

In a preferred variant, the degassing device is flowed through with hot inert gas. As an inert gas, for example, nitrogen, CO2, helium, neon and are Argon and mixtures thereof. Preferably, nitrogen is used. The temperature of the inert gas flowing through the degassing device is preferably in a range of 180 to 290 ° C, preferably 240 to 280 ° C. The degassing device can in principle be operated at atmospheric pressure, elevated pressure or reduced pressure. The pressure in the degassing device is then preferably 1 mbar to 1, 5 bar, preferably 10 mbar to 1 bar. In a preferred variant, the degassing device is operated at reduced pressure. The pressure in the degassing device is preferably in a range of 10 mbar to 1 bar, more preferably 100 mbar to 800 mbar.

In a preferred embodiment, the degassing device is operated at reduced pressure and at the same time flows through with inert gas. The pressure in the degassing device is preferably in a range from 10 mbar to 1 bar, more preferably 100 mbar to 800 mbar. The temperature of the inert gas flowing through the degassing device is preferably in a range of 180 to 290 ° C, preferably 240 to 280 ° C.

As a degassing Strangentgaser, degassing containers (flash container), thin film evaporator, spray dryer, degassing columns with internals z. As steering plates, degasser with miscible internals and other conventional degassing. Preference is given to using strand degasifier.

The term strand degasser usually refers to a substantially vertical container having an inlet opening for the flowable reaction mixture at the upper end and an outlet opening at the lower end. The term essentially perpendicular here means that the strand degasser does not have to be arranged exactly perpendicular to the surface of the earth, but may deviate therefrom by up to 30 °, preferably by up to 20 °.

The strand degasser is preferably equipped for operation under inert gas and / or reduced pressure. Further preferably, the strand degasser is heatable, for. B. by means of superheated steam, gas burner or double jacket with heat transfer. Preferably, the flowable reaction mixture from step b) enters the strand degasser through a nozzle plate or perforated plate from above. One or more partial strands of the flowable reaction mixture are formed. The reaction mixture is then preferably transported through the strand degasser solely by the action of gravity. In one possible embodiment, the degassing device, preferably the strand degasser, can be arranged below that of the device for hydrolytic polymerization. The conveying process can be done by gravity. If necessary, one or more melt pumps can be used to assist the delivery process.

The degassing devices can usually be upstream or downstream of devices for regulating the pressure, for. B. Pressure control valves.

The degassing in step d) can be carried out in one stage (in a single degassing device). You can also multi-level z. B. two stages, in several degassing steps, which are arranged one behind the other and / or arranged in parallel. Preferably, the degassing is carried out in one stage.

In a single-stage degassing, the pressure in the degassing device is usually from 1 mbar to 1, 5 bar, preferably 10 mbar to 1 bar and the temperature usually at 180 to 290 ° C, preferably at 240 to 280 ° C. In the multi-stage degassing the degassing devices can be the same or different in type and size. For example, two equal degassing devices, or two different sized degassing devices can be used. For example, two degassing devices can be operated in succession, each of the degassing device having different pressure levels. For example, two degassing devices can be operated in succession, each of the degassing device having different amounts of inert gas. For example, two degassing devices can be operated in succession, each of the degassing device having different pressure levels and different amounts of inert gas.

In a two-stage degassing, the pressure in the degassing usually at 1 mbar to 1, 5 bar, preferably 10 mbar to 1 bar and the temperature is generally at 180 to 290 ° C, preferably at 230 to 280 ° C. The temperature usually differs insignificantly from the temperature in a single-stage degasification.

The temperature control of the polyamide in the degassing is usually carried out via heat exchangers, double jacket, tempered static mixer, internal heat exchanger or other suitable devices. The setting of the degassing pressure ckes are also taken in a conventional manner, for. B. by means of pressure control valves.

A suitable parameter for characterizing the degassing performance is the degassing number E _z = m / (npDL), where m: mass flow of the melt, p: density of the melt, D: diffusion coefficient, L: strand length. The degassing number is preferably 0.1 to 20.

In a multi-stage degassing, these times each relate to a single stage.

By degassing in step c), the water contained in the reaction mixture obtained in the hydrolytic polymerization is at least partially removed. The degassed reaction mixture obtained in step c) preferably has a water content of from 0.03 to 0.15% by weight, based on the total weight.

Due to the depletion of the water, the reaction mixture is no longer in the equilibrium set after the hydrolytic polymerization, so that the polycondensation reaction can continue to progress. This can already be done under the conditions prevailing in the degassing.

It is possible that in the degassing in step d), in addition, monomers and / or oligomers are removed from the reaction product. The components contained in the gaseous discharge from the degassing device can be condensed and at least partially recycled into the polymerization (step b)).

The degassed reaction product obtained in step d) can be completely or partially re-degassed in step d). Thus, further water removal of the recycled polymer product can be achieved.

Upon exiting the degasser, the partial strands of the reaction product can be reunited.

After the degassed reaction product leaves the degassing apparatus in step d), the reaction product is fed into a reaction zone. Preferably, the reaction product is pumped in a flowable form into a reaction zone. To For example, suitable devices known to the person skilled in the art can be used. A suitable device is z. B. a melt pump.

Steps)

In step e) of the process according to the invention, the degassed reaction product obtained in step d) is fed into a reaction zone for postpolymerization.

The resulting degassed reaction product from step d) is preferably fed into a reaction zone without first undergoing comminution to form polyamide particles.

The postpolymerization in step e) can be carried out in one or more stages (for example in two stages). In the two-stage postpolymerization in step e), the polymer obtained or part of the polymer obtained can be recycled to the postpolymerization after step e). In a preferred embodiment, the postpolymerization in step e) is carried out in one stage.

The reaction zone in which the postpolymerization takes place is preferably a reactor, more preferably a tubular reactor and in particular a tubular reactor having "plug-flow" characteristics, i. H. Approximately one plug flow is realized. The tubular reactor is characterized in that the state of the reaction mixture in the reactor can vary in the direction of flow with regard to the material and physical properties (for example temperature, composition, etc.), whereas for each individual cross section perpendicular to the flow direction the state of the reaction mixture is the same. Ideally, all volume elements entering the tube will have the same residence time in the reactor. Figuratively speaking, the liquid flows through the tube as if it were a series of easily slipping through the tube. This means that a cross-mixing perpendicular to the flow direction, ie a mass and heat transport in the radial direction, but virtually no back mixing in the flow direction, so no significant material and heat transport in the axial direction take place. The flows are usually turbulent and the laminar edge effects negligible. This is done by a tubular reactor with static mixers.

In the postpolymerization in step e), the temperature in the reaction zone is preferably in a range from 200 to 270 ° C., more preferably from 220 to 260 ° C. The temperature control of the polyamide in the postpolymerization in step e) is carried out for example via heat exchangers, such as double jacket, internal heat exchangers or other suitable devices. The residence time in the reaction zone in step e) is preferably 30 minutes to 24 hours, more preferably 1 hour to 12 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) has 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% by weight H 2 SO 4 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.

In a specific embodiment of the process according to the invention, the strand-like reaction product obtained in step c) is subsequently subjected to no comminution into polyamide particles (granulation) until completion of the postpolymerization in step e).

In a further specific embodiment of the process according to the invention, the reaction product in steps c), d) and e) is permanently in the melted state.

The postpolymerization in step e) can additionally improve the properties of the polymers. This is especially true for the adjustment of the desired viscosity of the polymers for further processing. The viscosity number of the polyamide obtained by the process according to the invention is preferably 185 to 260 ml / g.

In a specific embodiment of the process according to the invention, the polyamide obtained in step e) is subjected to shaping to obtain polyamide particles, especially a granulation.

Granulation is particularly useful if the polyamide is to be subsequently extracted. For granulation, the polyamide can be cast in strands, solidified and then granulated. Another method is underwater granulation, which is known in principle to a person skilled in the art.

In a specific embodiment of the process according to the invention, the polyamide obtained in step e), optionally after a granulation, is extracted and / or dried.

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 extraction, an extractant containing water or consisting of water is preferably used. In a preferred embodiment, the extractant consists only of water. In a further preferred embodiment, the extraction medium contains water and a lactam 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.

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 extractant may be passed in cocurrent or countercurrent. Preferably, the extraction is in countercurrent.

In a first preferred embodiment, the polyamide particles are continuously borrowed 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 in countercurrent with water at a temperature> 100 ° C and a pressure in Extracted range from 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.

For reasons of environmental protection and economy, the extracted monomers and optionally dimers and / or higher oligomers are preferably recovered from the extractant and recycled. The loaded extractants contained in the extraction extraction components selected from monomers and optionally dimers and / or oligomers can be isolated and recycled in step a) or b). A specific embodiment of the method according to the invention comprises the following steps:

Separation of the resulting loaded extractant 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 monomer composition provided in step a) or hydrolytic Polymerization in step b) used reaction zones, at least partially re-use of the depleted in monomers and / or oligomers fraction as extractant. Preferably, the extracted polyamide is subjected to drying. The drying of polyamides is known in principle to the person skilled in the art. 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 them with superheated steam or a mixture thereof with a different gas, 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, 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, inert under the Nachpolymerisationsbedingungen gas. A preferred inert gas is nitrogen.

It is also possible to dry the polyamide only without prior extratraction. The polyamide obtained after extraction and drying preferably has a content of residual monomers in the range of greater than 0 to 0.1 wt .-%. Preferably, the polyamide obtained after extraction and drying has a residual monomer content of less than 0.05, preferably less than 0.03 wt .-%, on. Preferably, the polyamide obtained after extraction and drying has a content of cyclic dimer of less than 0.1, preferably less than 0.08 wt .-%, particularly preferably less than 0.02 wt .-%, on.

The process according to the invention can be carried out continuously or batchwise, preferably it is carried out continuously.

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.

The following reference symbols are used in FIG. 1:

1 pre-press reactor

2 VK pipe

3 strand degassing

4 Polymerization in the plug-flow reactor

5 extraction

6 Drying EXAMPLES

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

Table 1: Summary of the results of Example 1 a to 1 d and the starting sample A melt of a technically available polyamide 6 intermediate, which was taken from the polyamide 6 production process after melt polymerization in a VK tube, was transferred by means of a nozzle with an exit opening of 4 mm diameter into a polymer strand which was at 270 ° C falls a drop distance of 800 mm in nitrogen countercurrent and is collected in a tempered at 250 ° C vessel. In this vessel, the melt lingered under nitrogen overlay for postpolymerization. After cooling, the resulting polyamide block was first ground in a hammer mill with dry ice cooling and then by means of ultracentrifugal mill with cooling with liquid nitrogen. The now present particles with diameters of 2 to 3 mm were 48 h with deionized water at 95 ° C extracted. For the extraction 625 g of granules were placed in a 2 L stirred tank and extracted with a water flow of 2 L / h. From the extracted material 80 g were dried at 120 ° C with a nitrogen transfer of 1 1 L / h.

Of the samples obtained, the viscosity number (VZ) was determined according to EN ISO 307: 2007 on solutions of the polyamide in 96% strength by weight sulfuric acid at a concentration of 1 g per 100 ml. The caprolactam content was determined by gas chromatography.

The experimental conditions and results are shown in Table 1.

Table 1

Example throughput residence time in the tempeviscosity number caprolactam

Schmelzestrang rierten vessel to VZ salary

[g / min] post-polymerization [h]

Sample after - - 134 9.92% VK tube

1a 2.0 6 201 0.02%

1 b 2.0 8 211 0.02%

Claims

Patent claims

1 . Process for the production of polyamides, in which a monomer composition is provided which contains at least one lactam or at least one aminocarboxylic acid nitrile and/or oligomers of these monomers, the monomer composition provided in step a) in a hydrolytic polymerization at elevated temperature in the presence of water to obtain a Reaction product, which contains polyamide, water, unreacted monomers and oligomers, forms the reaction product obtained in step b) into one or more strands, feeds the strand-shaped reaction product obtained in step c) into a degassing device and under reduced pressure and / or by in Bring into contact treated with an inert gas, the water contained being at least partially removed, and e) feeding the degassed reaction product obtained in step d) into a reaction zone for post-polymerization.

Method according to claim 1, wherein the monomer composition provided in step a) contains ε-caprolactam or 6-aminocaproonitrile and / or oligomers of these monomers.

3. 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.

Method according to one of the preceding claims, wherein the reaction product obtained in step b) is formed into strands in a flowable state and fed into the degassing device as a flowable strand-shaped reaction product.

Method according to one of the preceding claims, wherein the strand-shaped reaction product obtained in step c) is fed into the degassing device in step d) is fed in without first being crushed into polyamide particles and without first subjecting it to extraction.

6. The method according to any one of the preceding claims, wherein the temperature of the reaction mixture fed into the degassing device upon entry into the degassing device is 180 ° C to 290 ° C, preferably 240 ° C to 280 ° C.

7. The method according to any one of the preceding claims, wherein the degassing device used in step d) is a strand degasser.

8. The method according to any one of the preceding claims, wherein the treatment of the reaction mixture in the degassing device in step d) takes place at a temperature of 180 ° C to 290 ° C.

9. The method according to any one of the preceding claims, wherein the treatment of the reaction mixture in the degassing device in step d) takes place at a pressure of 1 mbar to 1.5 bar, preferably 10 mbar to 1 bar.

10. The method according to any one of the preceding claims, wherein the degassing device is flowed through with inert gas in step d).

1 1 . Method according to one of the preceding claims, wherein the degassing device in step d) is operated at reduced pressure and at the same time inert gas flows through it.

12. The method according to any one of the preceding claims, wherein a melt of the reaction product obtained in step d) is used for the post-polymerization in step e).

13. The method according to any one of the preceding claims, wherein the reaction zone used for post-polymerization in step e) comprises a tubular reactor or which consists of a tubular reactor, with preference being given to using a tubular reactor which has plug-flow characteristics.

14. The method according to any one of the preceding claims, wherein the residence time in the reaction zone in step e) is 30 minutes to 24 hours.

15. The method according to any one of the preceding claims, wherein the strand-shaped reaction product obtained in step c) is subsequently used until the end of the Post-polymerization in step e) is not subjected to comminution into polyamide particles (granulation).

16. The method according to any one of the preceding claims, wherein the reaction product in steps c), d) and e) is in the molten state.

17. A process for producing polyamides according to one of the preceding claims, in which a) a monomer composition is provided which contains at least one lactam or at least one aminocarboxylic acid nitrile and/or oligomers of these monomers, b) the monomer composition provided in step a) in a hydrolytic - table polymerization at elevated temperature in the presence of water to obtain a reaction product which contains polyamide, water, unreacted monomers and oligomers, c) the reaction product obtained in step b) is formed in the melted state into one or more strands, d) that The strand-shaped reaction product obtained in step c), without first being crushed into polyamide particles and without first being subjected to extraction, is fed in melt form into a degassing device and treated in the melt under reduced pressure and/or by bringing it into contact with an inert gas, whereby the water contained is at least partially removed, and e) the degassed reaction product obtained in step d) is fed in melt form into a reaction zone and subjected to post-polymerization in the melt.

18. The method according to any one of the preceding claims, wherein in an additional step f) the polyamide obtained from step e) is subjected to shaping to obtain polyamide particles, especially granulation.

19. The method according to any one of the preceding claims, wherein the polyamide obtained in step e) or step f) is subjected to a treatment with at least one extractant in an additional step g).

20. The method according to any one of the preceding claims, wherein in step d) monomers isolated from the polyamide and optionally oligomers are recycled in step a) or b).

21. Method according to one of the preceding claims, wherein the method is carried out continuously.

22. Polyamides obtainable by a process as defined in any one of claims 1 to 21.

23. Use of a polyamide, obtainable by a process as defined in one of claims 1 to 21, for the production of granules, films, fibers or shaped bodies.