KR20150129791A - Production of polyamides by hydrolytic polymerization and multiple extraction - Google Patents

Abstract

The invention relates to a process for the preparation of polyamides comprising hydrolysis polymerization and two or more extraction steps which are not directly contiguous.

Description

Production of polyamides by hydrolysis polymerization and multiple extraction [0002] PRODUCTION OF POLYAMIDES BY HYDROLYTIC POLYMERIZATION AND MULTIPLE EXTRACTION [0003]

The invention relates to a process for the preparation of polyamides comprising hydrolysis polymerization and two or more extraction steps which are not directly contiguous.

Polyamides are one of the polymers that are produced on a large scale worldwide and are used in a number of additional end uses besides their primary use in fibers, materials and films. Of the polyamides, polyamide-6, which accounts for about 58%, is the most commonly produced polymer. The conventional process for producing polyamide-6 (polycaprolactam) is still hydrolysis polymerization of ε-caprolactam which is industrially very important. Conventional hydrolysis production processes are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, Online Edition 03.15.2003, vol. 28, pp. 552-553 and Kunststoffhandbuch, 3/4 Technische Thermoplaste: Polyamide [Plastics Handbook, 3/4 Industrial Thermoplastics : Polyamides], Carl Hanser Verlag, 1998, Munich, p. 42-47 and 65-70.

In the first step of the hydrolysis polymerization, a part of the lactam used is subjected to ring-opening reaction by the action of water to produce the corresponding? -Amino-carboxylic acid. The latter is then subjected to further addition and polycondensation with additional lactam to produce the corresponding polyamides. In a preferred variant, epsilon -caprolactam undergoes a ring opening reaction under the action of water to produce aminocaproic acid and then additionally polyamide-6. The hydrolysis polymerization can be carried out in one or more stages. Generally, polycondensation and heavy addition are carried out in a vertical tubular reactor (VK tube). The German abbreviation "VK" stands for "vereinfacht kontinuierlich" ["simplified continuous"]. Optionally, the plant can be used in the prepolymerization step at elevated temperatures. The use of this primary reactor reduces the residence time required for the ring opening reaction of epsilon -caprolactam. At the end of the vertical tubular reactor (VK tube), a polyamide melt having a composition close to chemical equilibrium and consisting of polyamide, lactam monomer, oligomer and water is obtained. The oligomer and monomer content can be, for example, 8-15 wt%, and the viscosity of the crude polyamide, which is directly related to molar mass and processing characteristics, is generally 110-160 ml / g.

For example, many of the end uses for the production of films for packaging materials require low residual monomer content in the polyamides, so that the crude polyamides typically undergo at least partial removal of the monomers and oligomers prior to further processing.

To reduce the content of low molecular weight components, generally pellets of crude polyamide particles are first obtained from the product of hydrolysis polymerization and then extracted with an extractant to remove residual monomers and oligomers. This is frequently done, for example, by continuous or batch extraction with hot water as disclosed in EP 0 117 495 A2, DE 25 01 348 A and DE 27 32 328 A, for example. For purification of crude polyamide-6, extraction with water containing caprolactam (WO 99/26996 A2) or treatment in a superheated steam stream (EP 0 284 986 A1) is also known. For reasons of environmental protection and economical feasibility, the extracted components, more specifically caprolactam and cyclic oligomers for polyamide-6, are recycled to the process. Extraction is generally followed by drying of the extracted polyamide.

Many applications require relatively high molecular weight polyamides that are not achieved with only hydrolysis polymerization. In order to increase the molecular weight or viscosity of the polyamide, post-condensation is carried out after extraction, and the polyamide is preferably in a solid phase. For this purpose, the pellets may be heat treated at a temperature below the melting point of the polyamide, during which the polycondensation is in particular continued. This increases the molecular weight of the polyamide and thus increases the viscosity of the polyamide. In general, the viscosity of polyamide-6 after extraction and post-polymerization is 180 to 260 ml / g.

Post-condensation and drying are frequently carried out in one step (WO 2009/153340 Al, DE 199 57 664 A1).

DD 2090899 discloses a vacuum melt demonomerization process in which upstream polyamide extraction involves contact of a polyamide melt with a caprolactam liquid.

DD 227140 discloses a process for preparing a polyamide having a degree of polymerization DP of more than 200. This process is characterized by five or more consecutive stages. At the start of each drying stage, the surface of the molten polyamide is adjusted to a polyamide of > 4 cm ² / g and the maximum diffusion distance of water in the melt is adjusted to <3 mm.

WO 03/040212 discloses a process for preparing polyamide-6 by hydrolysis polymerization of? -Caprolactam under the action of water. Dewatering is achieved by increasing the surface area of the melt.

WO 2009/153340 A1 discloses a continuous process for the multistage drying and post condensation of solid phase polyamide pellets, wherein

1) A preliminary drying process is carried out in a continuous drying apparatus operated with an inert gas or a vapor or a mixture of an inert gas and a vapor using a pellet temperature in the range of 70 to 200 ° C,

2) Subsequent post-condensation is carried out in a separate vertical conduit by means of a mobile phase at a pellet temperature in the range of 120 to 210 DEG C, the conduit is operated with a mixture of inert gas or vapor or inert gas and vapor, 2 or more.

According to the teachings of WO 2009/153340, process manipulations for molecular weight increase and (partial) extraction are integrated and are carried out as solid / gas extraction, especially in post-condensation. Since the second extraction is carried out concurrently with the post condensation at temperatures above 120 ° C, there is always a need to modify (re-monomerize) the monomers as a result of redisociation of the polyamides. Thus, despite simultaneous treatment with steam and / or an inert gas, the residual monomer content can not be satisfactorily reduced. The lowest value of the residual monomer content is achieved according to Examples 2 and 3 of WO 2009/153340 and is 1200 ppm. On the other hand, according to the method according to the present invention, a much lower value can be achieved through multiple extraction, and this value increases only slightly in the case of subsequent drying.

Another route for the production of polyamides, which is not widely used on an industrial scale, is the preparation of polyamide-6 from polycondensation of aminonitriles, such as 6-aminocapronitrile (ACN). According to conventional procedures, the process comprises the subsequent amine amidation is carried out in a separate reaction step in the presence of a heterogeneous catalyst, such as a nitrile hydrolysis and generally TiO _2. Since the two reaction steps differed in terms of water content and reaction completion, a multi-stage operation method was found to be practical. Even in the case of this synthetic route, in many cases it is advantageous for the resulting polymer to undergo purification for the removal of monomers / oligomers.

WO 00/47651 A1 discloses a continuous process for preparing polyamides by reacting at least one aminocarbonitrile with water.

The process for preparing polyamides by known hydrolysis polymerization still requires improvement. For example, the residual monomer content, particularly the content of? -Caprolactam, is less than the equilibrium value when post polymerization is initiated below the melting point of the polyamide. Thus, during the final polymerisation, a reversible central (re-monomerisation) reaction can take place and the residual monomer content of the polyamide increases again at the end of the manufacturing process.

Accordingly, it is an object of the present invention to provide an improved hydrolysis process for the production of polyamides without the above-mentioned problems. More specifically, this process must be able to provide a product with a very low residual monomer content.

It has now surprisingly been found that this task is achieved by pelletizing a reaction mixture obtained by hydrolysis polymerization and comprising a polyamide, water, unconverted monomer and oligomer, and then first extracting the pellets to yield an unconverted monomer and an oligomer at least partially , Followed by post-polymerization in the solid phase of the polyamide obtained after the first extraction and then further extraction of the post-polymerization product. Thereafter, an additional work-up step may be followed, for example a drying operation. The process according to the invention can achieve a polyamide with a lower residual monomer content than conventional processes. More particularly, it is possible to provide a polyamide having a low residual content of a monomer lactam and a cyclic dimer at the same time.

Therefore,

a) providing a monomer composition comprising at least one lactam or at least one aminocarbonitrile and / or an oligomer of these monomers,

b) converting the monomer composition provided in step a) to a hydrolysis polymerization at elevated temperature in the presence of water to obtain a reaction product comprising polyamide, water, unconverted monomer and oligomer,

c) molding 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 extracting agent,

e) feeding the extracted polyamide particles obtained in step d) to a reaction zone for post polymerization,

f) treating the polyamide obtained in step e) with at least one second extracting agent

And a method for producing the polyamide.

In certain embodiments, the loaded (laden) extractant obtained in step f) is used for subsequent extraction in step d).

More particularly, the extracted polyamide obtained in step f) of the process according to the invention is further dried (step g)).

The present invention also provides polyamides obtainable by the methods described above and below. These polyamides are characterized by a very low residual monomer content which can not be achieved by methods known from the prior art.

The present invention also provides the use of polyamides obtainable by the methods described below and below, in particular for the production of pellets, films, fibers or shaped articles.

1 is a schematic diagram of one embodiment for practicing the method according to the present invention;
Figure 2 is a schematic representation of another embodiment for the implementation of the process according to the invention, wherein the loaded extractant derived from extraction (5) is fed to (3) for extraction.

In the context of the present invention, "monomers" means low molecular weight compounds used in the preparation of polyamides by hydrolysis polymerization for the introduction of single repeat units. These include the lactam and aminocarbonitrile used. These may also be used as ω-aminocarboxylic acid, ω-aminocarboxamide, ω-aminocarboxylic acid salt, ω-aminocarboxylic acid ester, diamine and dicarboxylic acid, dicarboxylic acid / &Lt; / RTI &gt; and mixtures thereof.

In the context of the present invention, an oligomer means a compound as formed in the preparation of polyamides by reaction of two or more compounds forming individual repeating units. These oligomers have lower molecular weights than the polyamides prepared according to the invention. Oligomers include cyclic and linear oligomers, particularly cyclic dimers, linear dimers, trimer, tetramer, pentamers, hexamers, and heptamers. Standard methods for the determination of oligomer components of polyamides generally cover the components up to heptamers.

(Referred to as the Staudinger function, VN or J) viscosity number is defined as VN = 1 / cx (η- η s) / η s. The viscosity number is directly related to the average molar mass of the polyamide and provides information on the processability of the polymer. The viscosity can be obtained according to EN ISO 307 using the Ubbelohde viscometer.

The method according to the invention has the following advantages:

- There is no subsequent follow-up of any further processing steps associated with any significant thermal stresses on the polymer, such that the final extraction in step f) is the last processing step or that occurs, for example, in post polymerization, after said extraction step. Thus, modification of monomers and / or oligomers as occurs at relatively high temperatures as an equilibrium reaction is avoided. Thus, a very low residual monomer content is possible.

- During the first extraction in step d), post-crystallization of the product of the hydrolysis polymerization may already be carried out. The rate of the crystalline product affects the rate of post polymerization in step e). This can be done more quickly than prior to extraction. Thus, the process according to the invention is also characterized by a short residence time in post polymerization.

Step a)

In step a) of the process according to the invention, a monomer mixture comprising at least one lactam or at least one aminocarbonitrile and / or an oligomer of these monomers and possibly further components is converted at the polyamide forming reaction conditions to form a polyamide .

According to the present invention, the polyamide comprises a homopolymer comprising at least one lactam or nitrile and at least one additional monomer and having a polyamide basic unit content of at least 60% by weight, based on the total weight of the monomeric base units in the polyamide, Co-polymers and polymers.

The homopolymer is derived from an aminocarboxylic acid or a lactam and may be described as a single repeating unit. The polyamide-6 basic units may be formed from, for example, caprolactam, aminocapronitrile, aminocaproic acid or mixtures thereof. Examples of the homopolymer include nylon-6 (PA 6, polycaprolactam), nylon-7 (PA 7, polyenantolactam or polyheptanamide), nylon-10 PA 11, polyundecanolactam) and nylon-12 (PA 12, polydodecanolactam).

The copolymer is derived from several different monomers, and the monomers are bonded to each other by amide bonds. Possible copolymer units may be derived, for example, from lactams, aminocarboxylic acids, dicarboxylic acids and diamines. Preferred copolyamides are polyamides formed in caprolactam, hexamethylenediamine and adipic acid (PA 6/66). The copolyamide may contain polyamide units in various ratios.

The polyamide copolymers include polyamide basic units as well as additional basic units that are not linked together by amide bonds. The proportion of the comonomer in the polyamide copolymer is preferably 40% by weight or less, more preferably 20% by weight or less, particularly 10% by weight or less, based on the total weight of the basic units of the polyamide copolymer.

The polyamides produced by the process according to the invention are preferably selected from polyamide-6, polyamide-11, polyamide-12, and copolyamides and polymer blends thereof. Polyamide-6 and polyamide-12 are particularly preferable, and polyamide-6 is particularly preferable.

The monomer mixture provided in step a) preferably comprises at least one C ₅ - to C ₁₂ -lactam and / or oligomers thereof. The lactam is in particular selected from the group consisting of? -Caprolactam, 2-piperidone (? -Valerolactam), 2-pyrrolidone (? -Butyrolactam), caprylactam, enantholactam, lauryllactam, Oligomers. In step a) it is particularly preferred to provide a monomer mixture comprising? -Caprolactam, 6-aminocapronitrile and / or oligomers thereof. More particularly, in step a), a monomer mixture comprising exclusively? -Caprolactam or exclusively 6-aminocapronitrile is provided as a monomer component.

It is also possible to provide, in step a), a monomer mixture comprising at least one monomer (M) copolymerizable therewith, in addition to at least one lactam or aminocarbonitrile and / or oligomers thereof.

Suitable monomers (M) include aliphatic C _4-10 -a, omega-olefins such as dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and dodecanedioic acid - dicarboxylic acid. It is also possible to use aromatic C _8-20 -dicarboxylic acids such as terephthalic acid and isophthalic acid.

Examples of suitable diamines as the monomer (M) include α, ω-naphthylenes having 4 to 10 carbon atoms such as tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine and decamethylenediamine, Diamines may be used. Hexamethylenediamine is particularly preferred.

Particularly preferred among these salts of dicarboxylic acid and diamine as monomer (M) are salts of adipic acid and hexamethylenediamine called AH salts.

Suitable monomers (M) are also lactones. For example,? -Caprolactone and / or? -Butyrolactone are preferred lactones.

In the production of polyamides, one or more chain transfer agents such as aliphatic amines such as triacetone diamines or diamine or mono- or dicarboxylic acids such as propionic acid and acetic acid or aromatic carboxylic acids such as benzoic acid or terephthalic acid may be used.

Step b)

The conversion of the monomer mixture provided in step a) can be carried out by standard processes known to the person skilled in the art by hydrolytic polymerization in step b). Such processes are described, for example, in Kunststoff Handbuch, 3/4 Technische Thermoplaste: Polyamide, Carl Hanser Verlag, 1998, Munich, pp. 42-47 and 65-70. This disclosure is incorporated herein by reference in its entirety.

Preferably, in step b), the hydrolytic polymerization is carried out by ring opening the lactam under the action of water. This may, for example, at least partially cleave the lactam, producing the corresponding aminocarboxylic acid which is further polymerized by subsequent addition and polycondensation at a later stage. In a preferred embodiment, in step a), when a monomer mixture comprising caprolactam is provided, the caprolactam is at least partially opened under the action of water to produce the corresponding aminocaproic acid, which is then subjected to a polycondensation and a heavy addition reaction Polyamide-6. Alternatively, in step b), aminocarbonitrile, in particular 6-aminocapronitrile, is polymerized under the action of water and optionally in the presence of a catalyst.

The conversion in step b) is preferably continuous.

Preferably, the hydrolysis polymerization in step b) is carried out by adding 0.1 to 25% by weight, more preferably 0.5 to 20% by weight, of water, based on the total amount of monomers and oligomers used. The additional water formed in the condensation reaction is not included in this stated amount.

The hydrolysis polymerization in step b) may be carried out in one or more stages (e.g., two stages). If the hydrolysis polymerization in step b) is carried out in one stage, the starting concentration of water is preferably 0.1 to 4% by weight, based on the total amount of monomers and oligomers used. If the hydrolysis polymerization in step b) is carried out in two stages, it is preferred to connect the VK tube to a preliminary pressure stage, e.g. downstream of the preliminary pressure reactor. In the preliminary pressure stage, the starting 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 monomers and oligomers used.

In a particular version, the monomer mixture provided 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. The lactam is especially? -Caprolactam.

The hydrolysis polymerization in step b) may be carried out in the presence of one or more modifiers such as propionic acid. If the modifier is used in step b) and the hydrolysis polymerization is carried out in two stages using a preliminary pressure stage, the modifier may be used in the preliminary pressure stage and / or the second stage of polymerization. In a particular version, the hydrolysis polymerization in step b) is not carried out in the presence of a modifier.

The polyamides prepared by the process according to the present invention may further contain additives such as quenchers (e.g. titanium dioxide), nucleating agents (e.g. magnesium silicate), stabilizers (such as copper halide (I) and alkali metal halides) , Reinforcing agents, and the like, in conventional amounts. The additives are generally added before, during or after the hydrolysis polymerization (step b). It is preferred to add the additive before the hydrolysis polymerization in step b).

The conversion in step b) may be carried out in one or more stages (e.g., two stages). In the first embodiment, the conversion in step b) is carried out in one stage. In this case, it is preferred that the lactam or aminocarbonitrile and any oligomers thereof react with water and optionally additives in the reactor.

Suitable reactors are those known to those skilled in the art and are conventional in the production of polyamides. Preferably, the hydrolysis polymerization in step b) is carried out in a polymerisation tube or a polymerisation tube bundle. In particular, for the hydrolysis polymerization in step b), one or more VK tubes are used. The German abbreviation "VK" stands for "vereinfacht kontinuierlich" ["simplified continuous"]. In the multistage version of the conversion in step b), preferably one or more steps are carried out in the VK tube. In the two-step version of the conversion in step b), the second step is preferably carried out in the VK tube. In a two-step version of the conversion in step b), the first step may be carried out in a preliminary pressure reactor. If aminocarbonitrile is used, the conversion in step b) is generally carried out in two or more stages, preferably the first stage being carried out in a preliminary pressure reactor.

In a preferred embodiment, the polyamide-6 is prepared by a multistage process, in particular a two-stage process. Caprolactam, water and optionally at least one additive such as a chain transfer agent are fed to the first stage and are converted to a polymer composition. The polymer composition can be transferred to the second stage under pressure or by a melt discharge pump. This is preferably carried out by a melt dispenser.

The hydrolysis polymerization in step b) is preferably carried out at a temperature in the range from 240 to 280 占 폚. In the multistage version of the hydrolysis polymerization in step b), the individual steps may be carried out at the same or different temperatures and pressures. If a polymerization step is carried out in a tubular reactor, in particular a VK tube, the reactor can have substantially the same temperature over its entire length. Another possibility is the temperature gradient in at least a partial region of the tubular reactor. Another possibility is to carry out hydrolysis polymerization in a tubular reactor having two or more reaction zones operated at different temperatures and / or different pressures. Those skilled in the art will be able to select the necessary optimum conditions, for example, in consideration of equilibrium conditions.

When the hydrolysis polymerization in step b) is carried out in one stage, the absolute pressure in the polymerization reactor is preferably in the range of about 1 to 10 bar, more preferably 1.01 bar to 2 bar. It is particularly preferable to carry out the one-step polymerization at normal pressure.

In a preferred version, the hydrolysis polymerization in step b) is carried out in two stages. With the upstream connection of the pressure end, process acceleration by the implementation of the rate determining cleavage of lactam, in particular caprolactam, under elevated pressure can be achieved under conditions similar to those in the second reaction step. The second step is then preferably carried out in a VK tube as described above. The absolute pressure in the first step is preferably in the range of about 1.5 to 70 bar, more preferably in the range of 2 to 30 bar. The absolute pressure in the second stage is preferably in the range of about 0.1 to 10 bar, more preferably in the range of 0.5 to 5 bar. More specifically, the pressure in the second step is room temperature.

Subsequently, at the outlet of the VK tube, the polyamide melt is molded to obtain polyamide particles.

Step c)

In step c) of the process according to the invention, the polyamide obtained in step b) is molded 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 those skilled in the art can be used. Suitable devices are, for example, apertured plates, nozzles or die plates. Preferably, the reaction product obtained in step b) is formed into a strand of free-flowing state and is pulverized in the form of a strand of a free-flowing reaction product to obtain polyamide particles. The hole diameter is preferably in the range of 0.5 mm to 20 mm, more preferably in the range of 1 mm to 5 mm, and most preferably in the range of 1.5 to 3 mm.

Preferably, the molding in step c) comprises pelleting. For pelletization, the polyamide obtained in step b) which has been molded into one or more strands can be solidified and then pelletized. For example, Kunststoffhandbuch, 3/4 Technische Thermoplast: Polyamide, Carl Hanser Verlag, 1998, Munich, p. 68-69, discloses suitable methods. The specific molding process is also basically pelletized in water, which is known to the person skilled in the art.

Step d)

In step d), the polyamide particles obtained in step c) are first extracted.

Suitable processes and apparatus for the extraction of polyamide particles are basically known to those skilled in the art.

Extraction means treating the content of monomers and optional dimers and further oligomers in polyamides by treatment with an extracting agent. This can be done industrially, for example, in continuous or batch extraction (DE 2501348 A, DE 2732328 A) or in a superheated steam stream (EP 0284968 W1) using hot water.

It is preferred to extract in step d) using a first extracting agent comprising water or consisting of water. In a preferred version, the first extracting agent consists only of water. In a more preferred version, the first extractant comprises a lactam and / or oligomers thereof used in the preparation of water and polyamides. Thus, in the case of polyamide-6, it is also possible to extract using water containing caprolactam as disclosed in WO 99/26996 A2. It is preferred to extract in step d) using the loaded extractant obtained in step f). Thus, the amount of wastewater that requires treatment can be minimized.

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

Extraction can be carried out continuously or batchwise. Continuous extraction is preferred.

In extraction, the polyamide particles and the first extracting agent may be cocurrent or countercurrent. Countercurrent extraction is preferred.

In the first preferred embodiment, the polyamide particles are continuously extracted with water and counter current at a temperature of 100 DEG C or lower and at normal pressure. In this case, the temperature is preferably in the range of 85 to 99.9 ° C.

In a further preferred embodiment, the polyamide particles are continuously extracted with water and countercurrent at a temperature of 100 DEG C or less and a pressure of 1-2 bar (absolute). In this case, the temperature is preferably in the range of 101 to 120 占 폚.

For extraction, conventional devices known to those skilled in the art can be used. In a particular version, extraction is performed using one or more pulsed extraction columns.

The components present in the loaded first extractant obtained in step d), selected from monomers and optional dimers and / or oligomers, may be recycled to step a) or b) separately for this purpose.

The extracted polyamide obtained in step d) can be dried. The drying of the polyamides is basically known to those skilled in the art. For example, the extracted pellets may be dried by contact with dry air or dry inert gas or mixtures thereof. It is preferable to use an inert gas such as nitrogen for drying. The extracted pellets may also be dried by contacting them with superheated water vapor or a mixture thereof with another gas, preferably an inert gas. For drying, a conventional dryer such as a countercurrent dryer, an AC dryer, a fan dryer, a rotary dryer, a paddle dryer, a cross drier, a cone dryer, a tower drier, a fluidized bed and the like can be used. It is suitable to dry batchwise in a rotary dryer or cone dryer under reduced pressure. It is more preferable to perform continuous drying in a tubular drier through which gas inert in the drying condition flows. In a particular version, drying is carried out using at least one top drier. Preferably, a high temperature inert gas which is inert under post polymerization conditions flows through the top drier. The preferred inert gas is nitrogen.

Step e)

In step e), the extracted polyamide obtained in step d) is fed to the post-polymerization reaction zone.

Preferably, the polyamide particles obtained in step d) undergo a solid phase polymerization, for the post polymerization in step e). This entails polymerizing the polyamide in a solid phase. The polyamide is heat treated at a temperature below the melting point of the polyamide.

A suitable reaction zone where post polymerization occurs is basically a device that can be used for drying, such as a countercurrent dryer, an alternator drier, a fan drier, a rotary drier, a paddle drier, a cross drier, a cone drier, a tower drier, It is preferable to use at least one reactor, more preferably at least one tubular reactor, as a reaction zone where post polymerization occurs. In a particular version, post polymerization is carried out using one or more top driers. Preferably, a high temperature inert gas which is inert under post polymerization conditions flows through the top drier. The preferred inert gas is nitrogen.

Suitable processes for the post polymerization of hydrolytically prepared polyamides are basically known to those skilled in the art. Post polymerization can be carried out, for example, as disclosed in WO 2009153340, EP 1235671 or EP 0732351.

Post polymerization in step d) can be carried out in one stage (in a single reaction zone). This may be carried out in more than one but, for example, two stages in a plurality of reaction zones which may be arranged in series and / or in parallel. It is preferable to perform post polymerization in one stage.

In post polymerization, the temperature in the reaction zone is preferably in the range of 120 to 185 占 폚, more preferably in the range of 150 to 180 占 폚.

In the post polymerization, the pressure in the reaction zone is generally in the range from 1 mbar to 1.5 bar, more preferably from 500 mbar to 1.3 bar.

In post-cascade polymerization, the polymerization apparatus may be the same or different in type and size. For example, two identical polymerization apparatuses or two polymerization apparatuses of different sizes may be used. For example, two successive polymerization devices each having different residence time characteristics can be operated. For example, each polymerization device may operate two successive polymerization devices having different pressure levels. For example, two successive polymerization apparatuses in which different inert gas flow rates flow through each polymerization apparatus may be operated. For example, two successive polymerization apparatuses may be operated in which each polymerization apparatus has different pressure levels and different inert gas flow rates flow through each polymerization apparatus.

In post polymerization, the temperature of the polyamide is generally controlled by an external jacket, a heat exchanger such as an internal heat exchanger, or other suitable device. In a preferred embodiment, the post polymerization in step e) is carried out in the presence of at least one inert gas. In this case, the temperature of the polyamide in post polymerization is at least partially controlled by using a high temperature inert gas.

In a first preferred embodiment, during post polymerization, a high temperature inert gas flows through the reaction zone. Suitable inert gases are, for example, nitrogen, CO ₂ , helium, neon and argon, and mixtures thereof. It is preferred to use nitrogen.

In a further preferred embodiment, the post polymerization in step e) is carried out without mass transfer with the environment. "Post polymerization without mass transfer to environment" means that no mass transfer occurs between the polymerization zone and the environment after the extracted polyamide particles obtained in step d) have been fed to the post-polymerization zone. More specifically, the gas stream does not pass through the post-polymerization zone during post polymerization. Thus, during the post polymerization in step e) there is neither the introduction nor the discharge of components, such as water, from the inner vessel to the environment and vice versa.

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

In a preferred embodiment, the residence time of the polymer in step e) is 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) Or more.

The relative viscosity of the polyamides is generally used as a measure of molecular weight. The relative viscosity is measured according to the invention as a solution in 96 wt% H ₂ SO ₄ with a concentration of 1.0 g polyamide in 100 ml sulfuric acid at 25 ° C. The measurement of the relative viscosity is in accordance with DIN EN ISO 307.

Step f)

In step f), the polyamide particles obtained in step e) are further extracted.

Extraction of the polyamide particles is basically known to those skilled in the art and is described in detail in step d).

It is preferred to extract in step f) using a second extracting agent comprising water or consisting of water. In a preferred version, the second extractant is made solely of water. In certain embodiments, in this case, it is still a recovered extractant which may contain small amounts of monomers and / or oligomers.

The extraction temperature in step f) is preferably in the range of 75 to 120 占 폚.

The extraction temperature during the treatment in step f) is more preferably in the range from 50 ° C to less than 120 ° C, in particular from 75 to 118 ° C, in particular from 80 to 115 ° C, more particularly from 85 to 110 ° C.

Preferably, the polyamide is in a solid state (not in a molten state) during the treatment in step f).

The extraction in step f) can be carried out continuously or batchwise. Continuous extraction is preferred.

In the extraction in step f), the polyamide particles and the first extracting agent can be guided in cocurrent or countercurrent. Countercurrent extraction is preferred.

In a first preferred embodiment, the polyamide particles are continuously countercurrently extracted using water at a temperature of 100 DEG C or less and at normal pressure. In this case, the temperature is preferably in the range of 85 to 99.9 ° C.

In a further preferred embodiment, the polyamide particles are continuously extracted in countercurrent at temperatures above 100 DEG C and pressures in the range of 1-2 bar (absolute). In this case, the temperature is preferably in the range from 101 ° C to less than 120 ° C.

The components present in the loaded second extractant obtained in step f), selected from monomers and optional dimers and / or oligomers, may be recycled to step a) or b) separately for this purpose.

In a preferred version of the process according to the invention, the loaded second extractant obtained in step f) is used as the first extractant in a later step d). In this variant, the same extracting agent is first contacted first for extraction with a relatively low loaded polyamide particle which is derived from the post polymerization and / or oligomer loading, and then the monomer and / or oligomer loading resulting from the hydrolysis polymerization is relatively And contacts the highly loaded polyamide particles. Therefore, the amount of the extracting agent to be subjected to the work-up treatment can be obviously reduced.

A particular version of the method according to the invention comprises the following steps:

- Treating the polyamide obtained in step e) with at least one second extracting agent in step f) to obtain a monomer and / or oligomer-loaded second extracting agent,

- Using the loaded extractant obtained in step f) for extraction in step d)

- Separating the loaded extractant obtained in step d) into a monomer and / or oligomer-enriched fraction and a monomer and / or oligomer-free fraction,

- Feeding at least a portion of the monomer and / or oligomer sparged fraction into the monomer composition provided in step a) or the reaction zone used in the hydrolysis polymerization in step b)

- Using at least part of the monomer and / or oligomer-removed fraction as the second extractant in step f).

Step g)

Preferably, the extracted polyamide obtained in step f) is dried. Apparatus and processes suitable for drying are disclosed in step d) above and are hereby incorporated by reference. For drying, a conventional dryer such as a countercurrent dryer, an AC dryer, a fan dryer, a rotary dryer, a paddle dryer, a cross drier, a cone dryer, a tower drier, a fluidized bed and the like can be used. For example, the extracted pellets may be dried by contact with dry air or an inert gas or a mixture thereof. It is preferable to use an inert gas for drying. It is suitable to dry batchwise in a rotary dryer or cone dryer under reduced pressure. It is more suitable to continuously dry in a tubular drier through which inert gas flows under drying conditions. In a particular version, drying is carried out using at least one top drier. Preferably, a high temperature inert gas which is inert under post polymerization conditions flows through the top drier. The preferred inert gas is nitrogen.

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

The process according to the invention leads to polyamides having particularly advantageous properties. A suitable measure of the polyamide properties obtained is the viscosity number. (Referred to as the Staudinger function, VN or J) viscosity number is defined as VN = 1 / cx (η- η s) / η s. The viscosity number is directly related to the average molar mass of the polyamide and provides information on the processability of the polymer. The viscosity can be obtained according to EN ISO 307 using the Ubbelohde viscometer. The viscosity of the polyamides obtained by the process according to the invention is preferably 185 to 260 ml / g.

Preferably, the resulting polyamide has a residual monomer content of less than 0.1%, preferably less than 0.055% by weight, more preferably less than 0.03% by weight. The cyclic dimer content is preferably less than 0.1% by weight, more preferably less than 0.05% by weight, especially less than 0.025% by weight, most preferably less than 0.01% by weight.

Preferably, the resulting polyamide has a residual lactam content of 0.055 wt% or less and a residual cyclic dimer content of 0.025 wt% or less.

The method is detailed below in accordance with Figure 1 and the embodiment.

Example

Figure 1: Method according to the invention for the production of polyamide-6

Example 1:

The feedstock used was a polyamide-6 pellet prepared on an industrial scale with a viscosity of 218 ml / g and a monomer content of 0.23%. The polyamide-6 pellets were prepared through a process step of preliminary reaction in a pressure reactor, melt polymerization in a VK tube, hot water extraction and heat treatment. 300 g of pellets were introduced into a 2 l reactor and extracted with 1000 g of water at 95 DEG C with stirring over 24 hours. The extracted pellets were dried in a vacuum drying cabinet under a nitrogen blanket for 16 hours. The monomer content thereafter was 0.04%.

Example 2:

The feedstock used was a polyamide-6 pellet prepared on an industrial scale with a viscosity of 251 m // g and a monomer content of 0.24%. The polyamide-6 pellets were prepared through a process step of preliminary reaction in a pressure reactor, melt polymerization in a VK tube, hot water extraction and heat treatment. 450 g of pellets were introduced into a 2 l reactor and extracted with 1500 g of water at 105 DEG C with stirring over 24 hours. The extracted pellets were dried in a vacuum drying cabinet under a nitrogen blanket for 16 hours. The monomer content thereafter was 0.03%.

Example 3-5:

The feedstock used was a polyamide-6 pellet prepared on an industrial scale with a viscosity of 218 ml / g and a monomer content of 0.23%. The polyamide-6 pellets were prepared through a process step of preliminary reaction in a pressure reactor, melt polymerization in a VK tube, hot water extraction and heat treatment. 625 g of pellets were introduced into a 2 l reactor and extracted at 95 캜 with stirring over 30 hours. In this process, water was continuously exchanged at a flow rate of 2 l / h. Three 80 g fractions were taken from the extracted pellets and they were successively dried in a drying apparatus. The drying apparatus consisted of a glass tube having a frit base heated by an outer jacket. 80 g of pellets were introduced into the preheated glass tube and hot nitrogen was passed through it over a certain residence time. After the residence time, the pellets were removed.

Examples 6-8:

The feedstock used was a polyamide-6 pellet prepared on an industrial scale having a viscosity of 250 ml / g, a monomer content of 0.23% and a dimer content of 220 ppm. The polyamide-6 pellets were prepared through a process step of preliminary reaction in a pressure reactor, melt polymerization in a VK tube, hot water extraction and heat treatment. These pellets were further extracted with hot water and then dried. The hot water extraction was carried out in a continuous pulsating flow extractor. The extractor had a capacity for about 8 t of polyamide pellets. The extraction agent used was fresh deionized water. The pulsation means that the extraction water is not continuously conveyed to the reactor at a constant flow rate, but instead, the water is supplied in a pulsating manner at a high flow rate. The extractor was divided into three internal heat exchangers into three zones (top, middle and bottom), each of which could set a different temperature.

The pellets discharged from the extractor were continuously transferred to a tower dryer through a centrifuge. The top drier had a capacity for about 16 t of polyamide pellets. And drying was performed by nitrogen at a high temperature supplied from the bottom to the tower drier.

Example 9:

The feedstock used was a polyamide-6 pellet prepared on an industrial scale having a viscosity of 216 ml / g, a monomer content of 0.28% and a dimer content of 210 ppm. The polyamide-6 pellets were prepared through a process step of melt polymerization, hot water extraction and heat treatment in a VK tube. These pellets were further extracted with hot water and then dried. Hot water extraction was performed in a continuous countercurrent extractor. The extractor had a capacity for about 44 t of polyamide pellets. The extraction agent used was water with an organic carbon content ("TOC", "total organic carbon") of 500 ppm. The extractor has an extractant recycle line at the upper thde, which means that a portion of the extractant that is discharged from the top of the extractor is recycled back to the upper thde of the extractor.

The pellets discharged from the extractor were continuously transferred to a tower dryer through a centrifuge. The top drier had a capacity for about 40 t of polyamide pellets. Drying was performed by high-temperature nitrogen supplied to the upper side of the top dryer.

In Figures 1 and 2, the following symbols are used:
1 preliminary pressure reactor
2 VK tube
3 extraction
4 Solid phase polymerization
5 extraction
6 Drying
A1, A2 inlet and outlet for first extraction
B1, B2 Entrance and exit for second extraction
A conduit for the supply of the extractant loaded from B2A1 (5) to (3)

Claims (20)

As a method for producing a polyamide,
a) providing a monomer composition comprising at least one lactam or at least one aminocarbonitrile and / or an oligomer of these monomers,
b) converting the monomer composition provided in step a) to a hydrolysis polymerization at elevated temperature in the presence of water to obtain a reaction product comprising polyamide, water, unconverted monomer and oligomer,
c) molding 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 extracting agent,
e) feeding the extracted polyamide particles obtained in step d) to a reaction zone for post polymerization,
f) treating the polyamide obtained in step e) with at least one second extracting agent
&Lt; / RTI &gt; The process according to claim 1, wherein the second extractant used in step f) comprises water or consists of water. Process according to claim 1 or 2, characterized in that the temperature of the extracting agent during the treatment in step f) is in the range from 50 ° C to less than 120 ° C, preferably from 75 to 118 ° C, more preferably from 80 to 115 ° C . 4. Process according to any one of claims 1 to 3, wherein the polyamide is in a solid state during the treatment in step f). Process according to any one of claims 1 to 4, wherein the extracted polyamide obtained in step f) is further subjected to a drying operation (step g). 6. Process according to any one of claims 1 to 5, wherein the monomer composition provided in step a) comprises? -Caprolactam or 6-aminocapronitrile and / or an oligomer of these monomers. 7. The method according to any one of claims 1 to 6, wherein the conversion in step b) is performed in one or more stages. 8. A process according to any one of claims 1 to 7, wherein the conversion in step b) is carried out in two stages and a substantially vertical tubular reactor is used in at least the second stage. 9. Process according to any one of the preceding claims, wherein the forming in step c) comprises pelleting. 10. A process according to any one of claims 1 to 9, wherein the first extractant used in step d) comprises water or comprises water. 11. Process according to any one of the preceding claims, wherein the polyamide obtained in step d) is subjected to solid phase polymerization for post polymerization in step e). The process according to claim 11, wherein the reaction zone used in the post polymerization in step e) comprises or consists of a tubular reactor, and in particular comprises a drying tower or consists of a drying tower. The process according to claim 11 or 12, wherein the temperature during the post polymerization in step e) is in the range of 120 to 185 占 폚. 14. The process according to any one of claims 1 to 13, wherein the post polymerization in step e) is carried out without mass transfer to the environment. 15. Process according to any one of the preceding claims, characterized in that the components present in the loaded laden first extractant obtained in step d) and / or in step f), selected from monomers and optional dimers and oligomers, ) Is separated and recycled to steps a) and / or b). 15. The process according to any one of claims 1 to 14, wherein the loaded second extractant obtained in step f) is used as the first extractant in step d). 17. The method according to any one of claims 1 to 16, which is carried out continuously. A polyamide obtainable by a process as defined in any one of claims 1 to 17. The polyamide according to claim 18, wherein the residual lactam content is 0.055 wt% or less and the remaining cyclic dimer content is 0.05 wt% or less. The use of a polyamide obtainable by a process as defined in any one of claims 1 to 17 or a polyamide according to claims 18 or 19 for the production of pellets, films, fibers or shaped articles.

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