EP1383822A1

EP1383822A1 - Method of producing polyamides

Info

Publication number: EP1383822A1
Application number: EP02735165A
Authority: EP
Inventors: Helmut Winterling; Gerd Blinne; Gunter Vogel
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2001-03-23
Filing date: 2002-03-20
Publication date: 2004-01-28
Also published as: KR20030094292A; AR042587A1; TW593430B; CN1208370C; CN1498238A; WO2002085968A1; US20040097692A1; DE10114690A1; CA2440856A1; BR0207858A; MXPA03007639A; JP2004526847A

Abstract

The invention relates to a method of producing polyamides in an aqueous reaction mixture that contains a nitrile, selected from 6-aminocapronitrile and adipodinitrile. The inventive method is characterized by using a nitrile through which, in its liquid state, a gas that is inert with respect to the nitrile, was led.

Description

Process for the production of polyamides

description

The present invention relates to a process for the preparation of polyamides in a water-containing reaction mixture which contains a nitrile selected from 6-aminocapronitrile and adiponitrile, characterized in that a nitrile which has been flowed through in the liquid state with a gas which is inert to the nitrile, and polyamides obtainable by such a process.

Processes for the preparation of polyamides in a water-containing reaction mixture which contains a nitrile selected from 6-aminocapronitrile and adiponitrile are generally known.

For example, US 2,245,129 describes the production of polyamides from an amino nitrile. According to Example 1, polycaprolactam (polyamide 6, nylon 6) is obtained by reacting 6-aminocapronitrile. According to Example 2, polyhexamethylene adipamide (polyamide 66, nylon 66) is obtained by reacting adiponitrile and hexamethylene diamine.

On page 3, lines 44-50, it is recommended to carry out the second or last polymerization step, which follows the first step to form precursors, under inert gas to avoid discoloration of the polyamide.

No. 4,436,898 describes (column 4, lines 4-8) that 2-cyanocyclopentylimine, which leads to gel formation and discoloration, can form intramolecularly in the production of polyamide from adiponitrile, hexamethylenediamine and water from the adiponitrile. In the same way, in the production of polyamide from 6-aminocapronitrile intramolecularly after a Thorpe reaction, as described for example in Jerry March, Advanced Organic Chemistry, 3rd Edition, John Wiley & Sons, New York, 1985, page 854, Imino functions arise from which, through intramolecular reaction with an amino group, cycles or through hydrolysis, keto groups are formed, which also lead to discoloration.

According to US 4,568,736, thermally stable polyamides can be obtained from 6-aminocapronitrile and water by using certain catalysts in the polymerization. In the production of polyamides from water-containing reaction mixtures which contain 6-aminocapronitrile or adiponitrile, cyclic compounds can thus arise intramolecularly from 6-aminocapronitrile or adipodinitrile, which lead to an undesirable discoloration of the polyamide.

From WO 00/24808 it is known (page 15, lines 19-21) that polyamides which have been prepared using 6-aminocapronitrile contain extractable constituents, such as caprolactam or low molecular weight oligomers. According to Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Edition, Vol. 19, John Wiley & Sons, New York, 1996, pages 493-495, this monomer and oligomer content deteriorates the polyamide quality and must therefore be reduced , This reduction is usually carried out industrially by extraction with hot water under pressure.

This extraction of polyamides, which were produced using 6-aminocapronitrile, can lead to an increase in the discoloration during this extraction.

The present invention was based on the object of providing a process for the preparation of polyamides from water-containing reaction mixtures which contain a nitrile selected from 6-aminocapronitrile and adiponitrile, which in a technically simple and economical manner converts to a less discolored polyamide the polymerization and, in addition, in the case of water-containing reaction mixtures which contain 6-aminocapronitrile, leads to a polyamide which shows no increase in discoloration during the extraction, and to polyamides obtainable by such a process.

Accordingly, the process defined at the outset was found.

According to the invention, a nitrile selected from 6-aminocapronitrile and adiponitrile is used.

6-aminocapronitrile and adiponitrile and processes for their preparation are known per se, for example from the prior art recognized at the outset.

In an advantageous embodiment, the molten nitrile can be used in pure form.

In this case, the lower temperature is determined by the melting point of the nitrile (melting point 6-aminocapronitrile: -34 ° C; melting point adiponitrile: + 1 ° C). Preferably comes one Temperature of at least 5, especially at least 20 ° C above the melting point into consideration.

In the case of pure nitrile, the upper temperature is determined by the decomposition of the nitrile and the vapor pressure at the respective temperature, with larger amounts of the nitrile being taken along with the gas flowing through as the temperature increases. A temperature of at most 50, in particular at most 30 ° C. is advantageous.

In another advantageous embodiment, the nitrile can be used together with a liquid diluent.

Suitable liquid diluents are inorganic compounds, such as water, or organic compounds, such as -C ₄ -alkanols, for example methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, such as ether, for example dioxane, such as aromatics, for example toluene, o-xylene, m-xylene, p-xylene, or mixtures thereof, such as water-C 1 -C 4 -alkanol mixtures, for example water-ethanol mixtures, preferably water.

In this case the lower temperature ^{■ is} determined by the melting point of the mixture. A temperature of at least 10, in particular at least 20 ° C. above the melting point of the mixture is preferred.

In the case of the mixture, the upper temperature is determined by the decomposition of the mixture and the vapor pressure at the respective temperature, with larger quantities of the mixture being carried along with the gas flowing through as the temperature increases. A temperature of at most 50, in particular at most 30 ° C. is advantageous.

The lower pressure should be at least the vapor pressure of the pure

Correspond to nitrile or the mixture at the selected temperature.

If you work at a lower pressure, nitrile or mixture with the gas flowing through is taken along to a large extent. The pressure should advantageously be 0.1 kPa, in particular 1 kPa, above the vapor pressure at the selected temperature.

In principle, there are no limits to the pressure. However, it has been shown that above a pressure of 300 kPa, in particular 200 kPa, with increasing pressure there are no further advantages with regard to the method according to the invention are, while the technical effort to control the pressure increases significantly.

According to the invention, a nitric gas flows through the nitrile.

For the purposes of the present invention, inert gases are considered which do not cause any chemical changes in the nitrile to be flowed through as a result of a reaction between nitrile and gas.

For technical reasons, such gases can contain impurities that are not inert to the nitrile. It goes without saying that the lower the content of such impurities in the inert gas, the better the advantageous effect of the process according to the invention.

Nitrogen, argon, helium, neon or mixtures thereof, preferably nitrogen, helium, argon or mixtures thereof, in particular nitrogen, argon or mixtures thereof, can advantageously be used as the inert gas.

In an advantageous embodiment, the inert gas can flow through the nitrile in the range from 0.01 to 100, preferably from 0.1 to 40, in particular from 1 to 15 m ³ gas / hour / m ³ nitrile.

If one chooses less than the amounts according to an advantageous embodiment, it has generally been observed to date that an increase in the amount can increase the advantageous effect of the method according to the invention.

If the amounts in accordance with an advantageous embodiment were exceeded, no significant increases in the advantage which can be achieved with the method according to the invention have so far been observed. In addition, if the quantities are too large, the technical outlay for separating the nitrile from the inert gas increases after flowing through.

In an advantageous embodiment, the inert gas can flow through the nitrile in the range from 1 to 200, preferably from 5 to 150, in particular from 10 to 80 minutes.

If one works with interruptions in the flow, the areas mentioned are understood as the sum of the times of the intervals. A longer time is not critical in itself. Thus, the nitrile can be stored for weeks using the method according to the invention without the advantage according to the invention being lost.

Shorter periods of time than those according to the advantageous embodiment can also be selected. According to previous observations, a further advantageous effect can be achieved in such a case by further application of the method according to the invention.

The flow through of the nitrile with the inert gas can be carried out in reactors known per se for the reaction of gases with liquids, for example tanks, stirred tanks, loop reactors, tubular reactors, bubble columns, reaction columns, thin-film reactors, gas-liquid bioreactors, with those for such Reactors known to supply gases in liquids, simple dipping, that is to say inlet pipes, or filter candles, are also carried out, for example from: Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol B4, VCH Verlagsgesellschaft mbH, Weinheim , 1992, pp. 167-337 and pp. 381-433, or Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol B2, VCH Verlagsgesellschaft mbH, Weinheim, 1988, pp. 25-31.

If the inert gas contains droplets of the nitrile after flowing through the nitrile, these droplets can be removed from the inert gas by means of devices known per se, for example by means of droplet separators, fiber filters, swirl layer filters, fixed bed filters, fluid bed filters, cyclones, electrical separation, scrubbers, such as they are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol B2, VCH Verlagsgesellschaft mbH, Weinheim, 1988, pp. 13-15 - 13-25, or, for example, by means of the conversion of gases with liquids, for example from Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol B, VCH Verlagsgesellschaft mbH, Weinheim, 1992, pp. 167-337 and pp. 381-433, or Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol B2 , VCH Verlagsgesellschaft mbH, Weinheim, 1988, pp. 25-21 - 2_5-31, known devices can be separated.

In an advantageous embodiment, the use of tanks as a reactor and the supply of the inert gas by means of an inlet pipe come into consideration.

The nitrile obtainable by the process according to the invention can be used in the form of a water-containing reaction mixture for the production of polyamides by processes known per se. which, wherein the nitrile used in the known processes is replaced by the nitrile obtained according to the present process. According to previous observations, the parameters known for such methods can be adopted unchanged. Any advantageous adaptation of such methods to the nitrile obtainable according to the present method can easily be determined by a person skilled in the art by means of a few simple preliminary tests.

Polyamides are understood to mean homopolymers, copolymers, mixtures and grafts of synthetic long-chain polyamides which, as an essential component, have recurring amide groups in the main polymer chain. Examples of such polyamides are nylon 6 (polycaprolactam), nylon 6,6 (polyhexamethylene adipamide), nylon 4,6 (polytetramethylene adipamide). These polyamides are known to have the generic name nylon.

Such polyamides can advantageously be obtained by methods known per se from monomers selected from 6-aminocapro-nitrile or a, preferably equimolar, mixture of adipodi- nitriol and hexamethylene diamine, or mixtures thereof.

In another advantageous embodiment, a monomer selected from 6-aminocapronitrile or a, preferably equimolar, mixture of adipodinitriol and hexamethylenediamine, or mixtures thereof, can be used together with other monomers capable of forming polyamides, such as lactams, omega-aminocarboxylic acids, omega Aminocarboxylic acid nitriles, omega-amino carboxylic acid amides, omega-amino carboxylic acid salts, omega-amino carboxylic acid esters, equimolar mixtures of diamines and dicarboxylic acids, dicarboxylic acid / diamine salts, dinitriles and diamines or mixtures of such monomers.

As such, other monomers capable of forming polyamides come

Monomers or oligomers of a C to C ₂ or preferably C to C ₈ arylaliphatic or preferably aliphatic lactam, such as enantholactam, undecanolactam, dodecanolactam or caprolactam,

Monomers or oligomers of C - to C ₀ -, preferably C ₃ - to G _IB - aminocarboxylic acids, such as 6-aminocaproic acid, 11-aminoundecanoic acid, and their dimers, trimers, tetramers, pentamers or hexamers, and their salts, such as alkali metal salts , for example lithium, sodium, potassium salts, C - to Co -; preferably C - to Ciβ - aminocarboxylic acid nitriles, such as 11-aminoundecanoic acid nitrile,

Monomers or oligomers of C - to C ₂ o - amino acid amides, such as 6-aminocaproic acid amide, 11-aminoundecanoic acid amide and their dimers, trimers, tetramers, pentamers or hexamers,

Esters, preferably C 1 -C ₄ alkyl esters, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl ester, from C ₂ to Co -, preferably C - to Cig - aminocarboxylic acids, such as 6-aminocaproic acid esters, for example methyl 6-aminocaproate, 11-aminoundecanoic acid esters, for example methyl 11-aminoundecanoate,

Monomers or oligomers of a C ₂ - to C ₂ o -, preferably C - to Cχ - alkyldiamine, such as tetramethylene diamine or preferably hexamethylene diamine,

with a C - to C ₂ o ~ * preferably C ₂ - to C ₁₄ - aliphatic dicarboxylic acid or its mono- or dinitriles, such as sebacic acid, dodecanedioic acid, adipic acid, sebacic acid dinitrile or decanoic acid dinitrile,

as well as their dimers, trimers, tetramers, pentamers or hexamers,

Monomers or oligomers of a C to C ₂ or preferably C to C ₁₂ alkyldiamine, such as tetramethylene diamine or preferably hexamethylene diamine,

with a Cs - to C ₂ o "~ * preferably Cs - to C ₁₂ - aromatic dicarboxylic acid or its derivatives, for example chlorides, such as 2,6-naphthalenedicarboxylic acid, preferably isophthalic acid or terephthalic acid,

as well as their dimers, trimers, tetramers, pentamers or hexamers,

Monomers or oligomers of a C ₂ - to C ₂ o - * preferably C ₂ - to C ₁₂ -alkyldiamine, such as tetramethylene diamine or preferably hexamethylene diamine,

with a C ₉ - to C ₀ -, preferably C ₉ - to Cia - arylaliphatic dicarboxylic acid or its derivatives, for example chlorides, such as o-, m- or p-phenylenediacetic acid,

as well as their dimers, trimers, tetramers, pentamers or hexamers, Monomers or oligomers of a C ₆ - to C ₂ o ~ / preferably C ₆ - to Cio - aromatic diamine, such as m- or p-phenylenediamine,

with a C ₂ - to C ₂ o -, preferably C - to C ₁₄ - aliphatic dicarboxylic acid or its mono- or dinitriles, such as sebacic acid, dodecanedioic acid, adipic acid, sebaconitrile or decanoic dinitrile,

as well as their dimers, trimers, tetramers, pentamers or hexamers,

Monomers or oligomers of a C ₆ - to C ₂ o ~ preferably C ₆ - to Cio - aromatic diamine, such as m- or p-phenylenediamine,

with a Ca - to C ₀ -, preferably Ca - to Cχ - aromatic dicarboxylic acid or its derivatives, for example chlorides, such as 2,6-naphthalenedicarboxylic acid, preferably isophthalic acid or terephthalic acid,

as well as their dimers, trimers, tetramers, pentamers or hexamers,

with a Cg - to C ₂ o ~, preferably Cg - to Cis - arylaliphatic dicarboxylic acid or its derivatives, for example chlorides, such as o-, m- or p-phenylenediacetic acid,

as well as their dimers, trimers, tetramers, pentamers or hexamers,

Monomers or oligomers of a C ₇ to C ₀ , preferably Ca to Cig arylaliphatic diamine, such as m- or p-xylylenediamine,

with a C ₂ - to C ₂ o - / preferably C ₂ - to Cχ ₄ - aliphatic dicarboxylic acid or its mono- or dinitriles, such as sebacic acid, dodecanedioic acid, adipic acid, sebaconitrile or decanoic acid dinitrile,

as well as their dimers, trimers, tetramers, pentamers or hexamers,

Monomers or oligomers of a C ₇ to C ₂ o ~ * preferably Ca to Cia arylaliphatic diamine, such as m- or p-xylylenediamine,

with a C ₆ - to C ₂ o -, preferably C ₆ - to Cio - aromatic dicarboxylic acid or its derivatives, for example chlorides, such as 2, 6-naphthalenedicarboxylic acid, preferably isophthalic acid or terephthalic acid, as well as their dimers, trimers, tetramers, pentamers or hexamers,

Monomers or oligomers of a C ₇ - to C ₂ o - # preferably C ₈ - to Ciβ - arylaliphatic diamine, such as m- or p-xylylenediamine,

with a Cg - to Co - preferably Cg - to -C ₈ - arylaliphatic dicarboxylic acid or its derivatives, for example chlorides, such as o-, m- or p-phenylenediacetic acid,

as well as their dimers, trimers, tetramers, pentamers or hexamers,

as well as homopolymers, copolymers, mixtures and grafts of such starting monomers or starting oligomers.

In a preferred embodiment, in addition to a monomer selected from 6-aminocapronitrile or a, preferably equimolar, mixture of adipodinitriol and hexamethylene diamine, or mixtures thereof as lactam caprolactam, as diamine tetramethylene diamine, hexamethylene diamine or their mixtures and as dicarboxylic acid adipic acid, sebecanedioic acid, sebacic acid, sebacic acid , Terephthalic acid, isophthalic acid or mixtures thereof, particularly preferably as lactam caprolactam, as diamine hexamethylene diamine and as dicarboxylic acid adipic acid or terephthalic acid or mixtures thereof.

Those starting monomers or starting oligomers which lead to the polyamides nylon 6, nylon 6,6, nylon 4,6, in particular nylon 6 or nylon 66, are particularly preferred.

In a preferred embodiment, one or more chain regulators can be used in the production of the polyamides. Suitable chain regulators are advantageously compounds which have one or more, such as two, amino groups reactive in the formation of polyamide or one or more, such as two, carboxyl groups reactive in the formation of polyamide.

Chain regulators which can advantageously be monocarboxylic acids, such as alkane carboxylic acids, for example acetic acid, propionic acid, such as benzene or naphthalene monocarboxylic acid, for example benzoic acid, dicarboxylic acids, such as C ₄ -Cχoalkanedicarboxylic acid, for example adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, C ₅ -C _8- cycloalkanedicarboxylic acids, for example cyclohexane-1,4-dicarboxylic acid, benzene- or naphthalenedicarboxylic acid, for example terephthalic acid, isophthalic acid,

Naphthalene-2, 6-dicarboxylic acid, C ₂ - to C ₂ o - / preferably C ₂ - to Cι ₂ - alkylamines, such as cyclohexylamine, C ₆ - to C ₂ o - preferred as Cg - to Cio ~ aromatic monoamines, such as aniline, or C - to Co -, preferably Cs - to Ciβ - arylaliphatic monoamines, such as benzylamine, diamines, such as C ₄ -Cιo-alkanediamines, for example hexamethylenediamine.

A chain regulator can advantageously be used in amounts of at least 0.01 mol%, preferably at least 0.05 mol%, in particular at least 0.2 mol%, based on 1 mol of acid amide groups of the polyamide.

A chain regulator can advantageously be used in amounts of at most 1.0 mol%, preferably at most 0.6 mol%, in particular at most 0.5 mol%, based on 1 mol of acid amide groups of the polyamide.

In another preferred embodiment, the polymerization or polycondensation is carried out by the process according to the invention in the presence of at least one pigment. Preferred pigments are titanium dioxide, it being possible for titanium dioxide to be present in the anatase modification, rutile modification or anatase-rutile modification mixture, or coloring compounds of an inorganic or organic nature. The pigments are preferably added in an amount of 0 to 5 parts by weight, in particular 0.02 to 2 parts by weight, based in each case on 100 parts by weight of polyamide. The pigments can be fed to the reactor with the starting materials or separately therefrom.

Process for the preparation of polyamides in a water-containing reaction mixture which contains a nitrile selected from 6-aminocapronitrile and adiponitrile, and, if appropriate, conventional additives, such as inorganic or organic pigments, homogeneous or heterogeneous catalysts, such as phosphorous acid, hypophosphorous acid or phosphoric acid and their alkali metal, alkaline earth metal or ammonium salts, such as Na ₃ P0 ₄ , Na ₂ HPθ ₄ , NaH ₂ P0, Na ₂ HP0 ₃ , NaH ₂ P0 ₃ , K ₃ P0, K ₂ HP0, KH ₂ P0, K ₂ HP0 ₃ , KH ₂ P0 ₃ , alkyl or aryl-substituted phosphorus-oxygen compounds, such as alkyl or aryl-substituted phosphonic acids of the formula RPO (OH) ₂ with R as alkyl or aryl radical, are known per se and are described, for example, in US Pat. No. 2,245,129, US 4,436,898, US 4,568,736, WO 00/24808.

The extraction which is advantageous in the case of polyamides which have been prepared using 6-aminocapronitrile can be carried out by processes which are known per se, the polyamide used in the known processes being replaced by the polyamide obtained according to the present process. According to previous observations, those known for such methods can be used Parameters are adopted unchanged. Any advantageous adaptation of such processes to the polyamide obtainable according to the present process can easily be determined by a person skilled in the art by means of a few simple preliminary tests. 5

Methods for extracting polyamides made using 6-aminocapronitrile are described, for example, in Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Edition, Vol. 19, John Wiley & Sons, New York, 1996, page 10,493 -495.

The polyamides obtainable by the process according to the invention can be processed according to the processes customary for polyamides into geometric structures, such as threads, fibers, flat structures and moldings, the lower tendency to discoloration of the polyamides according to the invention also being effective here.

For the purposes of the present invention, the discoloration is defined by the APHA number. The APHA number is determined in the manner described in Examples 20 as the difference in the extinction of a polyamide solution in formic acid at 470 nm and 600 nm. The lower the APHA number, the less discoloration of the polyamide.

Polyamides obtainable by the process according to the invention, which are essentially based on adiponitrile and hexamethylenediamine, preferably have an APHA number of less than 15, in particular less than 5.

Polyamides obtainable by the process according to the invention, which are essentially based on 6-aminocapronitrile, preferably have an APHA number of less than 15, in particular less than 5.

35 examples

Determination of the APHA number

a) Determination of the calibration factor f:

40

0.249 g of potassium hexachloroplatinate (IV) and 0.2 g of cobalt (II) chloride hexahydrate are dissolved in 500 ml of distilled water in a 1000 ml volumetric flask, 20 ml of hydrochloric acid with a density of 1.18 g / cm ^{3 are} added and the mixture is brought up to the mark filled up with distilled water.

45 The extinction E _{0 of} this solution is measured in 5 cm cuvettes at a wavelength of 470 nm against distilled water. The calibration factor f is then calculated as f = 100 / Eo-

b) Preparation of the polyamide solution

7 g of polyamide are dissolved in a 200 ml Erlenmeyer flask in 100 ml of formic acid at room temperature within 16 hours. The solution is then centrifuged at 35000 G.

c) measurement of the color number

The absorbance E of the polyamide solution is measured in a 5 cm cell at a wavelength of 470 nm (E ₄₇₀ ) and 600 nm (E _δ00 ) against formic acid.

The APHA number (in Pt-Co units) is then determined as follows:

APHA number = f * (E ₄₇₀ - E ₆₀₀ )

Production of the polyamides

The polyamides were prepared using a mixture of 6-aminocapronitrile (6-ACN) and deionized water. The 6-aminocapronitrile-water mixture was stored in a 2 1 batch tank provided with a lance suitable for introducing gas and fed via a piston pump to an apparatus according to FIG. 1 of DE-A-19804023.

The first process stage (1) with an empty volume of 1 liter and an inner length of 1000 mm was carried out with extruded titanium dioxide granules, which according to: Ertl, Knözinger, Weitkamp: "Handbook of heterogeneous catalysis", VCH Weinheim, 1997; Page 98ff. The strand granules consisted of 100% Ti0 ₂ , which was present in the so-called anatase modification, and had a strand length between 2 and 14 mm, a strand thickness of approx. 2 mm and a specific surface area of 110 m ² / g.

A 2 liter separating tank was used as the second stage (2).

The third stage (3) with an empty volume of 1 liter and an inner length of 1000 mm was filled with the titanium dioxide extrudate described in process stage (1). In this flow tube, the reaction mixture could still be mixed with water from a receiver (see FIG. 1 mentioned). The fourth stage (4) again consisted of a separating vessel (volume 5 liters), from which the polymer melt produced was drawn out in the form of a strand with the aid of a gear pump (A).

example 1

A 6-aminocapronitrile-water mixture with the composition according to Table 1 was stored under nitrogen for two hours in the batch kettle and nitrogen was passed through the mixture over the lance for two hours.

The throughput D given in Table 1 is the mass flow of the reaction mixture from the batch boiler through the first process stage. The water throughput WZ in the third process stage is based on the throughput of the reaction mixture in the first process stage and is given in percent. The pressures and temperatures in the four stages are summarized in Table 1.

The polyamide obtained from the fourth stage was dried in a vacuum drying cabinet at 3 kPa and 70 ° C. for 24 hours.

An APHA number of 3 was determined.

Example 2

The procedure was as in Example 1, with the exception that the polyamide was extracted by heating 100 parts by weight of polyamide in 400 parts by weight of deionized water at a temperature of 100 ° C. for 32 hours under reflux and with nitrogen blanketing Removal of the water was gently dried and dried in a vacuum drying cabinet at 3 kPa and 70 ° C for 24 hours.

An APHA number of 3 was determined.

Comparative Example 1

The procedure was as in Example 1, with the exception that nitrogen was not passed through the 6-aminocapronitrile-water mixture.

An APHA number of 21 was determined. Comparative Example 2

The procedure was as in Example 2, with the exception that nitrogen was not passed through the 6-aminocapronitrile-water mixture.

An APHA number of 37 was determined.

Table 1

Claims

claims

1. Process for the preparation of polyamides in a water-containing reaction mixture which is a nitrile selected from

Contains 6-aminocapronitrile and adiponitrile, characterized in that a nitrile is used which has a gas which is inert to the nitrile flowing through in the liquid state.

2. The method according to claim 1, wherein nitrogen, argon, helium, neon or mixtures thereof are used as the inert gas.

3. The method according to claim 1, wherein the inert gas used is nitrogen, argon or mixtures thereof.

4. The method according to any one of claims 1 to 3, wherein one flows through the nitrile in the range of 0.01 to 100 m ³ gas / hour / m ³ nitrile with the inert gas.

5. The method according to claims 1 to 4, wherein one flows through the nitrile in the range of 1 to 200 minutes with the inert gas.

6. polyamide, obtainable by a process according to claims 1 to 5.