Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G69/00—Macromolecular compounds obtained by reactions forming a carboxylic amide link in the main chain of the macromolecule
  • C08G69/48—Polymers modified by chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G69/00—Macromolecular compounds obtained by reactions forming a carboxylic amide link in the main chain of the macromolecule
  • C08G69/02—Polyamides derived from amino-carboxylic acids or from polyamines and polycarboxylic acids
  • C08G69/04—Preparatory processes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G69/00—Macromolecular compounds obtained by reactions forming a carboxylic amide link in the main chain of the macromolecule
  • C08G69/02—Polyamides derived from amino-carboxylic acids or from polyamines and polycarboxylic acids
  • C08G69/08—Polyamides derived from amino-carboxylic acids or from polyamines and polycarboxylic acids derived from amino-carboxylic acids
  • C08G69/14—Lactams
  • C08G69/16—Preparatory processes

Definitions

• the present invention relates to a process for removing low molecular weight constituents from polyamide 6 or from copolyamides based on caprolactam by extraction.
• the present invention relates to a device for removing low molecular weight constituents from polyamide 6 and from copolyamides based on caprolactam by extraction.
• the present invention relates to a process for the production of polyamide 6 or copolyamides based on caprolactam and an apparatus for carrying out this process.
• Polyamides their production and their use as engineering plastics are known. They are described, for example, in "Kunststoff-Handbuch", edited by G. W. Becker and D. Braun, published by Hanser-Verlag in Kunststoff and Vienna in 1998, volume 3 "Technical thermoplastics", volume 4 "Polyamides".
• the present invention relates to polyamide 6 and copolyamides based on
• Caprolactam Polyamide 6 is the homopolymer of caprolactam.
• Copolyamides based on caprolactam for the purposes of the present invention are copolyamides which contain at least 50% by weight of monomer units derived from caprolactam.
• these copolyamides based on caprolactam contain other repeating units connected by amide groups.
• these can be repeat units that are derived from adipic acid and hexamethylenediamine, that is to say polyamide 6,6 units.
• it can be repeating units derived from aminocarboxylic acids, for example the repeating units of polyamide 11 or
• Polyamide 6 or copolyamides based on caprolactam can be produced by various processes. The production can be carried out, for example, by the hydrolytic polymerization of caprolactam. This is the most technically significant process. It is also the method that is preferred according to the present invention. The preparation can also be carried out by alkaline lactam polymerization. The processes for the production of polyamide 6 or copolyamides based on caprolactam are described, for example, in the abovementioned plastics handbook, volume 3 “Technical thermoplastics”, sub-volume 4 “polyamides” on pages 22 to 75.
• Polyamide 6 or copolyamides based on caprolactam are usually produced by hydrolytic polymerization of caprolactam. If copolyamides based on caprolactam are to be produced, the necessary comonomers are added.
• the comonomers are preferably either mixtures of dicarboxylic acids and diamines or aminocarboxylic acids or lactams.
• volume 3 "Technical thermoplastics", sub-volume 4 "polyamides"
• polymerization is generally carried out as polymerization under normal pressure by adding usually 1 to 5% by weight of water at temperatures of usually 240 to 270 ° C. with the exclusion of atmospheric oxygen. It can be started with water-releasing compounds such as aminocarboxylic acid or AH salt (salt from adipic acid and hexamethylene diamine). It is usually started by water.
• the molar mass of the polyamide is predetermined by the water content, but in practice is expediently stabilized by regulators, for example by carboxylic acids or amines.
• the usual procedure is as follows: The water-containing caprolactam (if appropriate together with the comonomers and if appropriate together with further auxiliaries such as, for example, molecular weight regulators) is filled into the VK tube at the top. Excess water is distilled off here in order to achieve sufficiently high molar masses. The melt then flows through the tube in usually 15 to 30 hours at atmospheric pressure, being kept at a temperature between usually 240 and 270 ° C. At the end of the VK tube, the polyamide melt is pressed, for example with a gear pump, through round-hole nozzles as bristles into a water bath, cooled and then granulated.
• low-molecular compounds are formed. These are in particular oligomeric compounds which arise from caprolactam and, if appropriate, also from the comonomers. These low molecular weight
• the low molecular weight fractions result in products such as Injection molded bodies or foils and the like, which are produced from the polyamides, are adversely affected by the fact that the low molecular weight components diffuse to the surface and form a greasy film there.
• the low-molecular-weight components diffused to the surface impair the surface appearance of the products made from the polyamides. The gloss is reduced, the color impression is impaired.
• Polyamides that are to be processed into films require a particularly low content of low molecular weight compounds.
• Polyamide 6 and copolyamides based on caprolactam immediately after the polymerization typically contain more than 5% by weight of low molecular weight compounds (caprolactam and its oligomers and optionally oligomers of the comonomers).
• Polyamides that are to be processed into injection molded articles should usually have a content of low molecular weight compounds of less than 1% by weight.
• Polyamides that are to be processed into films are usually subject to even higher requirements. They typically should not exceed a low molecular weight content of 0.1% by weight, better 0.05%.
• the low molecular weight compounds can be removed, for example, by extraction.
• the extraction is usually carried out by water or by liquids which predominantly contain water.
• Polyamide 6 or the copolyamide based on caprolactam are usually dried. This happens, for example, at temperatures between 90 and 130 ° C in an inert gas stream. For example, nitrogen can be used. By increasing the drying temperature to, for example, 180 to 190 ° C., the molecular weight of the polyamide can be increased further for special applications by means of a so-called post-condensation.
• the extraction of polyamide 6 or of copolyamides based on caprolactam is carried out discontinuously or continuously with water at temperatures which are below the boiling point of water at atmospheric pressure (ie below 100 ° C.).
• the processes known from the prior art for producing polyamide 6 and copolyamides based on caprolactam, which comprise extraction of polyamide 6 or copolyamides based on caprolactam have disadvantages.
• a disadvantage of the known methods is in particular that in order to fall below a certain content of low molecular weight components in the extracted polyamide, a high residence time of the polyamide in the extraction devices is required. This means that the space-time yield of the extraction processes is low.
• the result of the extraction according to the known technical processes is often not sufficiently good.
• the proportion of low molecular weight substances remaining in the polyamide is too high.
• the proportion of cyclic dimers of caprolactam remaining in the polyamide is too high.
• the countercurrent extraction is expediently carried out in such a way that the polyamide is moved downwards by gravity, the liquid which is used for the extraction (usually water) counteracting the gravity in countercurrent is led up to the polyamide.
• space-time yield means the throughput of the polyamide through a device for extracting the polyamide per unit of time and per unit volume of the device.
• the present invention has for its object to provide an improved process for the extraction of polyamide 6 or copolyamides based on caprolactam, which overcomes the disadvantages of the prior art and which allows the extraction with high space-time yield perform and to obtain a low content of low molecular weight substances, in particular caprolactam and oligomers, in the polyamide after the extraction.
• This object is achieved by a process for extracting polyamide 6 or copolyamides based on caprolactam, the polyamide 6 or the
• Copolyamide based on caprolactam is extracted with a liquid consisting of at least 80% by weight water at a temperature which is above the boiling point of this liquid at normal pressure.
• the present invention comprises an apparatus for the extraction of
• Polyamide or of copoyamides based on caprolactam comprising one Pre-extractor (1) and a pressure extractor (2) and an injector (5), which is connected downstream of the pre-extractor and with which the polyamide to be extracted can be conveyed from the pre-extractor into the pressure extractor.
• the present invention furthermore relates to a device for
• the method according to the invention has numerous advantages.
• the extraction according to the invention proceeds with a high space-time yield.
• the extraction according to the invention requires only small amounts of water per unit of polyamide.
• the proportion of the cyclic dimer of caprolactam in the extracted polyamide 6 or the extracted copolyamide based on caprolactam is very low. Due to the low space-time yield, the
• the extraction process according to the invention is more economical and cost-effective than the processes known from the prior art.
• the process according to the invention also has the advantage that the polyamide 6 or the copolyamides based on caprolactam are usually used in the extraction
• Form of granules are supplied, do not stick together during extraction or clump together, as usually occurs when polyamide 6 or the copolyamides based on caprolactam are brought together with aqueous liquids at high temperatures for a long time.
• the method according to the invention achieves the last-mentioned advantage in that the temperature is deliberately limited, so that the sticking or clumping does not occur.
• the extraction method according to the invention in the case in which it is carried out in countercurrent, has the advantage that it is not impaired by disadvantageous backmixing due to density differences in the extraction liquid.
• the reduction in water consumption during the extraction is also advantageous because the water has to be reprocessed after the extraction. This is usually done by evaporating the water.
• the water distilling off can be used as fresh water for extraction.
• the highly concentrated mixture of water and caprolactam and its oligomers and other low molecular weight compounds remaining in the distillation bottoms can either be fed to the production of polyamides or must be disposed of.
• the extraction device according to the invention has numerous advantages.
• a continuous extraction process is made possible without problems with backmixing due to density differences.
• the extraction device enables a high space-time yield, low residual content of low molecular weight compounds after the extraction and prevents the polyamide from sticking or clumping during the extraction.
• the process according to the invention is preferably carried out continuously. It is preferred if the polyamide 6 or the copolyamide based on caprolactam and the liquid are conducted in countercurrent.
• polyamide 6 or the copolyamide based on caprolactam are moved downwards under the force of gravity and the liquid is directed upwards counter to the force of gravity.
• the difference in density is kept low by the extraction being carried out in two stages, with part of the extractable constituents being separated off in the first stage, which can also be operated below the boiling point of the liquid, so that in In the second stage, which is operated at a temperature above the boiling point of the liquid, the density difference remains small even with a low liquor ratio of water to polyamide.
• Liquid per 1 kg of polyamide 6 to be extracted or copolyamide based on caprolactam is 1 to 3 kg, preferably 2 to 3 kg.
• the liquid consists essentially of water.
• the extraction be carried out at a temperature of 100 to 130 ° C.
• Particularly preferred methods are those in which the extraction is carried out at a temperature of from 120 ° C. to 125 ° C. and preferably with a liquor ratio from polyamide to liquid from 1 kg to 2 kg to 1 kg to 3 kg and is preferably carried out over 10 to 14 hours.
• the pressure extractor is followed by a second injector (9) with which the delivery from the pressure extractor can take place.
• a device which comprises a line (4) for transporting the liquid from the upper end of the pressure extractor (2) to the pre-extractor (1).
• Another object of the present invention is a process for the production of polyamide 6 or copolyamides based on caprolactam, comprising an extraction according to one of the processes according to the invention.
• Polyamides preferred according to the invention are selected from the group consisting of polyamide 6 and copolyamides based on caprolactam, which contain at least 90% by weight of monomer units based on caprolactam. The remaining 10% by weight are preferably derived from the repeating units of the
• polyamide 6 is particularly preferred.
• the extraction is carried out with a liquid which consists of at least 80% by weight of water. It is preferred to carry out the extraction with water. Demineralized water is particularly preferred.
• injectors are preferably used to promote the suspensions of polyamide granules in water which are preferably present in the process according to the invention.
• Injectors are sucking propellant compressors, also called ejectors. They belong to the group of water jet solid fuel pumps. They are operated with water as a subsidy. The water transports the polyamide granulate to be conveyed. The polyamide granules leave the injector as a suspension in water. Delivery by injectors has the advantage that delivery from an area under atmospheric pressure to an area under excess pressure is possible without any problems.
• the use of other devices for conveying such as cellular wheel sluices fails to convey the suspension of polyamide granules in water from areas of low pressure to areas of high pressure.
• the delivery rate for delivery by injectors can be regulated by the water flow or by the back pressure after the injector. In the present
• injectors can be used to convey a suspension of plastic granules, preferably polyamide granules, in water (with water as the conveying medium). In addition, it is not known that this is also possible from areas of low pressure to areas of higher pressure. In addition, it is not known that the delivery rate can be regulated both with the flow of the conveying means (i.e. with the amount of water that is supplied as a delivery stream per unit of time) and with the pressure on the side of the injector on which the suspension is discharged.
• the plastic granulate to be conveyed can be either anhydrous, i.e. dry, or mixed with a small amount of water before being conveyed.
• So another aspect of the present invention is: A method for conveying a suspension of a plastic granulate, preferably a polyamide granulate, in water using an injector with water as the conveying medium.
• the difference in pressures is preferably 0.5 to 5, particularly preferably 1 to 1.5, bar.
• the delivery rate is controlled by the flow of water.
• the delivery rate is regulated by the pressure on the side of the injector on which the suspension is discharged. This can be done, for example, by means of a pressure-maintaining valve, so that the regulation of the delivery can take place independently of the pressure difference between the area from which the delivery is made and the area into which delivery is made.
• FIG. 1 shows a device according to the invention for the extraction of polyamide 6 or copolyamides based on caprolactam.
• the pre-extractor 1 operated under atmospheric pressure is fed with unextracted polyamide granules 3 from the polymerization.
• Water 4, which comes from the pressure extractor 2 serves as the extraction medium.
• the injector 5 which is operated with water 6 as the conveying medium, the polyamide granules, after the water has been separated off in the device 7, are fed to the pressure extractor 2, which is operated with water 8 in countercurrent to the polyamide granules.
• a second injector Via a second injector
• the extracted polyamide is discharged from the pressure extractor and the drying supplied.
• the delivery rate of the injectors can be regulated by the flow of the delivery medium or by the pressure in the line that serves to remove the suspension.
• pressure control valves are installed in these lines (not shown in the drawing).
• the device according to FIG. 1 has the advantage that by removing part of the low molecular weight compounds in the pre-extractor 1, the pressure extractor 2 does not have the disadvantage of backmixing due to density differences even with a low liquor ratio of water to polyamide.
• the polyamide was fed to the pressure extractor, which was operated at 100 to 120 ° C.
• the residence time in the pressure extractor was 6 hours.
• the liquor ratio water to polyamide was 1.3 to 1.
• the extract content after the pressure extractor was 0.3 to 0.6% by weight.
• the polyamide was fed to the pressure extractor, which at
• the residence time in the pressure extractor was 10 to 14 Hours.
• the liquor ratio water to polyamide was 2.5 to 1.
• the extract content after the pressure extractor was 0.25 to 0.4%.
• the dimer content dropped from 0.4 to 0.8% before the pre-extractor to 0.01 to 0.03% after the pressure extractor.
• Examples 1 and 2 show that a good extraction quality can be achieved with a small amount of water, which is sufficient for conventional applications in the injection molding field.
• the increase in the amount of water, temperature and dwell time in Example 2 results in an extraction quality which is suitable for applications in the packaging film area for foods, where particularly low levels of extract are required.
• the experiments relate to the determination of the extraction rate of the cyclic dimer of the caprolactam from vacuum-lactamized PA 6 compared to unextracted PA 6.
• Vacuum-lactamized means that a portion of the lactam was removed from the PA 6 in vacuo at elevated temperature by distillation.
• PA 6 which is largely free of monomeric caprolactam (vacuum- lactamized PA 6), is strongly temperature-dependent. In comparison to the extraction speed of the oligomers of caprolactam-containing (unextracted) PA 6, the following picture emerges: at an extraction temperature of 95 ° C, the dimer from vacuum-lactamized PA 6 is extracted much more slowly than from unextracted PA 6. However, at an extraction temperature of 125 ° C the extraction of the oligomers from both types of PA 6 is equally fast.
• Oligomer content should reduce to the required level.
• Such an extraction concept has the advantage that the backmixing problem (caused by the density gradient) that occurs in the single-stage aqueous extraction does not occur. As a result, smaller specific water consumption per mass unit of PA 6 to be extracted can be realized, which in the end results in the saving of
• Test series 3 Extraction of vacuum-lactamized polyamide 6 at 95 ° C
• Test series 5 Extraction of unextracted PA 6 at 95 ° C
• Test series 6 Extraction of unextracted PA 6 at 125 ° C
• test series 7 to 9 for extraction under increased pressure were carried out in the temperature range from 95 to 125 ° C. 125 ° C correspond to an overpressure of approx. 2.5 bar.
• test series 7 Extraction of unextracted PA 6 at 95 ° C
• Test series 8 Extraction of unextracted PA 6 at 110 ° C
• Test series 7 The results of the mono- and oligomer content determination are summarized in the following table. Table 6 Extraction of unextracted PA 6 at 110 ° C
• Test series 9 Extraction of unextracted PA 6 at 125 ° C
• test series 7 to 9 show that the extraction rate increases sharply during the transition from 95 to 110 to 125 ° C. At temperatures of 135 ° C, the granules stuck together. The extraction at 135 ° C could therefore not be carried out.

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• Polyamides (AREA)

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• 2001
  • 2001-05-21 DE DE10124579A patent/DE10124579A1/de not_active Withdrawn
• 2002
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  • 2002-05-08 EP EP02740573A patent/EP1401913A1/de not_active Withdrawn
  • 2002-05-08 JP JP2002592378A patent/JP2004528459A/ja active Pending
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  • 2002-05-08 WO PCT/EP2002/005043 patent/WO2002094908A1/de not_active Application Discontinuation
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