Title of Invention	“A METHOD FOR THE PRODUCTION OF PELLETS OF POLYAMINED 6 OR COPOLYAMIDES”
Abstract	The invention relates to a method for the production of pellets of polyamide 6 or copolyamides, by - production of a melt of polyamide 6 or copolyamides by means of polymerization; - production of pellets from the melt by means of underwater pelletization into a process  fluid; - removal of the pellets from the site of underwater pelletization in the process fluid; and - supply of the pellets in the process fluid to an extraction stage; - extraction of low-molecular components as extract; - drying of the pellets after extraction; wherein the underwater pelletization stage and the extraction stage take place using the same process fluid. The invention further relates to a device for implementation of such a method.

Title of Invention

“A METHOD FOR THE PRODUCTION OF PELLETS OF POLYAMINED 6 OR COPOLYAMIDES”

Abstract

The invention relates to a method for the production of pellets of polyamide 6 or copolyamides, by - production of a melt of polyamide 6 or copolyamides by means of polymerization; - production of pellets from the melt by means of underwater pelletization into a process  fluid; - removal of the pellets from the site of underwater pelletization in the process fluid; and - supply of the pellets in the process fluid to an extraction stage; - extraction of low-molecular components as extract; - drying of the pellets after extraction; wherein the underwater pelletization stage and the extraction stage take place using the same process fluid. The invention further relates to a device for implementation of such a method.

Full Text	FORM 2 THE PATENTS ACT 1970 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See section 10 and rule 13) 1. ' Method and device for the production of polyamide ' 2. 1. (A) AUTOMATIK PLASTICS MACHINERY GMBH (B) Germany (C) Ostring 19, D- 63762 Grossostheim, Germany. The following specification particularly describes the invention and the manner in which it is to be performed. The invention relates to a method for the production of polyamide 6 or copolyamides according to the preamble of claim 1 as well as to a device for the production of polyamide 6 or copolyamides according to the preamble of claim 9. Polyamides are today used in a multiplicity of areas, such as for textiles, carpets or tyre cords, in the production of injection mouldings, such as in the automotive area, or in the production of plastic films or blown containers for packaging. In this connection, the multiplicity of positive properties is of particular significance, including the high durability and high thermal resistance combined with the good elasticity of polyamides. An overview of various methods for the production of polyamides, including caprolactam-based polyamide 6 or copolyamides, is provided in Kunststoff-Handbuch [Plastics Manual], Volume 3 "Technische Thermoplaste" [Technical Thermoplastics], Subvolume 4 "Polyamide" [Polyamides], published by G. W. Becker and D. Braun, Hanser-Verlag Munich and Vienna, 1998, pages 22 to 75. An overview of spinning applications of polyamides can be found, for example, in "Synthetische Fasern" [Synthetic Fibres], Handbuch für Anlagenplanung [Manual of Plant Engineering], Franz Fourné, Hanser-Verlag Munich and Vienna, 1995, pages 36 to 56. Generally, in currently established methods and devices for the production of polyamides, especially for the production of polyamide 6 or copolyamides, a caprolactam-based melt is subjected to polymerization. A thus produced polyamide melt is then first of all pelletized, for example by means of underwater pelletization or, alternatively, for example by means of strand pelletization. Such a pelletized polyamide material, however, usually still contains around 10% of low-molecular species or components, such as caprolactam and cyclic oligomers. In order to prevent a disruption by such low-molecular components during the further treatment of such a pelletized polyamide material, such low-molecular components are reduced by extraction to the level required for the particular application, the residual concentration thereof being thus adjusted. Conventionally, for this purpose, the pellets, which are dried after pelletization, are subjected to aqueous extraction, in the course of which the pellets conventionally take up considerable quantities of water. Consequently, such an extraction stage is followed by a further drying stage. Conventionally, the prior art makes use, for example, of inert-gas dryers, which are arranged downstream of a countercurrent extraction device. The water at the outlet of the extraction stage conventionally has an extract concentration, i.e. a concentration of low-molecular components, of over 10% by weight. This extraction water is either returned directly to the polymerization process or is reprocessed after extraction, wherein the extracted low-molecular components are recovered and can then be returned to the polymerization process. With regard to the above-described pelletization process, it must generally be ensured that there is compliance with a composition of the pelletization water that is suitable for a reliable pelletization process, with the extract concentration in the pelletization water normally being around 4% by weight. If this is not the case, the pelletization water cannot be optimally treated, because there is a foaming of the pelletization water. The direct supply of pelletization water to the extraction stage would undesirably lower the therein contained extract concentration. The required degree of dryness of the polyamide pellets (commonly referred to as PA chips) at the inlet to the extraction stage is around 1% by weight. Figure 1 shows a schematic representation of a device according to the prior art. A polymerized melt of caprolactam-based polyamide 6 or copolyamides is produced in a polymerization reactor 16 (corresponding arrow to polymerization reactor 16). In an underwater pelletizer 11, the polymerized melt is pelletized into pellets in pelletization water. Next, the pellets are dried of the pelletization water in a dryer 13 and are then supplied to an extraction device 12, where the extraction process takes place by means of extraction water in a separate extraction water circuit with integrated treatment device 14 for recovery of the extract. The recovered extract can be returned to the polymerization reactor. Extraction is followed by further drying of the pellets in a dryer 15. The pelletization water is treated in a separate circuit and is returned to the underwater pelletizer 11. The streams of material and water are identified by the corresponding arrows in Fig. 1. Publication WO 02/094908 A1 describes a method and device for the extraction of polyamide wherein the pelletization of polyamide melt into pellets is followed by a separate extraction of the low-molecular (residual) components using a special extraction water under specific conditions, more particularly in a plurality of stages at increased temperature and pressure. The object of the present invention is to overcome the disadvantages of the prior art and, more particularly, to provide a method and device for the production of pellets of polyamide 6 or copolyamides, said method/device making it possible, in simple and cost-effective, yet reliable manner, to produce pellets of polyamide 6 or copolyamides, said pellets being able to be further processed in simple manner. The object of the invention is achieved by a method having the features according to claim 1 and by a device having the features according to claim 9. Advantageous embodiments of the invention are defined in the respective subclaims. The method according to the invention for the production of pellets of polyamide 6 or copolyamides comprises the following steps: - production of a melt of polyamide 6 or copolyamides by means of polymerization. Polymerization is caprolactam-based. - production of pellets from the melt by means of underwater pelletization, for example by means of an underwater pelletizer of the kind produced and marketed by the applicant under the product name SPHERO, wherein the pellets are pelletized into a process fluid. - removal of the pellets from the site of underwater pelletization in the process fluid, and - supply of the pellets in the process fluid to an extraction stage. - extraction of low-molecular components, more particularly of components that were not completely polymerized, as extract, wherein extraction is preferably fluid-based or waterbased. - drying of the pellets after extraction. The method according to the invention is further characterized in that underwater pelletization and extraction take place using the same process fluid. According to the invention, therefore, both the underwater pelletization stage and also the extraction stage take place using a process fluid, wherein said process fluid is the same for both stages of the method, i.e. the fluid that is used for the underwater pelletization stage is the same fluid that is used for the extraction stage. In short, therefore, the transport fluid for underwater pelletization is the same as or identical to the extraction fluid used for extraction. According to the invention, therefore, a single process fluid is used both for the pelletization stage and also for transport of the pellets and also for the extraction of low-molecular components from the pellets. The method according to the invention makes it possible, on the one hand, to obviate the need for the intermediate drying phase that is conventionally provided in the prior art and which is provided between the pelletization and extraction stages. On the other hand, it is possible for the melt energy of the pellets that have been pelletized into the process water of the invention to be co-used for the required heating of the process fluid, this allowing energy savings to be made. Furthermore, it is thus possible in simple and cost-effective manner, by obviating the need to make available two different fluids, to provide according to the invention an especially simple and cost-effective, yet reliable method for the production of pellets of polyamide 6 or copolyamides, it being possible according to the invention for pellets to be made available that can be further processed in simple and reliable manner. In the method according to the invention, the process fluid can preferably have a composition equivalent to a composition after the extraction stage, preferably equivalent to a normally conventional composition after the extraction stage, wherein the process fluid contains preferably more than 10% by weight of extract, i.e. of low-molecular components. Consequently, the process fluid used in the method according to the invention can have the composition of an extraction fluid, which can further improve the reliability of the method with regard to the production of pellets that can be further processed in simple and especially easy manner. In a preferred embodiment of the method according to the invention, the process fluid can be carried in a first circuit between underwater pelletization stage and extraction stage and can be carried in a second circuit between extraction stage and treatment stage for removal of extract from the process fluid, wherein there is a fluid connection for the process fluid between the first circuit and the second circuit, with the result that the first circuit and the second circuit partially overlap at least there, i.e. where there is said fluid connection. It is thus possible in technically simple and therefore cost-effective manner for a closed circuit or two interconnected closed circuits, more particularly two directly interconnected closed circuits, to be preferably realized according to the invention. In the method according to the invention, in order to further improve the reliability of pelletization, the removal and supply of the pellets in the process fluid and the return of the process fluid to the pelletization stage in the first circuit, preferably in a fluid return connection, it is possible for the process fluid to be at a temperature independent of the second circuit, preferably in an extraction fluid connection. In order to allow an especially reliable pelletization stage, it is preferably possible in the method according to the invention, during underwater pelletization and during removal and supply of the pellets, for the process fluid to be at an increased pressure with respect to ambient pressure, the pressure being preferably equal to or greater than 1 bar, more preferably equal to or greater than 3 bar, still more preferably equal to or greater than 4 bar. This also makes it possible reliably to prevent or at least to reduce any foaming of the process fluid. In such a method according to the invention, it is possible for the extraction stage to take place at a pressure lower than the increased pressure, preferably at ambient pressure, wherein, prior to extraction, the pressure of the process fluid can be reduced from the increased pressure to the lower pressure, preferably to ambient pressure. The extraction stage, therefore, takes place at a reduced pressure with respect to the pelletization stage. Alternatively, however, in the method according to the invention, the extraction stage can take place at the increased pressure, wherein, after extraction and prior to drying, the pressure is reduced from the increased pressure to a lower pressure, preferably to ambient pressure. Consequently, for example, it is preferably possible according to the invention for the pelletization and extraction stages to take place at increased pressure, preferably at the same increased pressure. This may possibly further increase the efficiency of the extraction stage, i.e. this can improve the effectiveness of the extraction of low-molecular components. In order, according to the invention, to be able to further improve a smooth process under, where possible, all process conditions and especially in the case of a high delivery rate, it is possible for a delivery rate of process fluid during underwater pelletization and during removal and supply of the pellets in the process fluid and a delivery rate of process fluid during extraction to be adjusted to a delivery rate ratio of at least 3:1. The device according to the invention for the production of pellets of polyamide 6 or copolyamides can be used for implementation of the method according to the invention. The device according to the invention has an underwater pelletizer, wherein, from a melt of polyamide 6 or copolyamides polymerized in a polymerization reactor, said underwater pelletizer pelletizes pellets into a process fluid, wherein there is a fluid removal connection between the underwater pelletizer and an extraction device, wherein the process fluid with the therein contained pellets is removed from the underwater pelletizer through said fluid removal connection and is supplied to the extraction device. Positioned downstream of the extraction device is a dryer for drying the pellets. According to the invention, no such dryer is required upstream of the extraction device and is therefore omitted according to the invention, especially as, according to the invention, a direct fluid connection is provided between underwater pelletizer and extraction device. In the device according to the invention, the underwater pelletizer and the extraction device are operated with the same process fluid, wherein, between the extraction device and the underwater pelletizer, there is, in addition to the fluid removal connection for process fluid and therein contained pellets from the underwater pelletizer to the extraction device, also a fluid return connection for the process fluid without pellets from the extraction device back to the underwater pelletizer. According to the invention, this allows a connection according to the invention between underwater pelletizer/underwater pelletization stage and extraction device/extraction of lowmolecular components through one and the same process fluid and it also allows the return of the process fluid from the extraction device to the underwater pelletizer according to the invention. This makes it possible, according to the invention, to provide a device which permits in especially simple and therefore cost-effective manner the still reliable production of pellets of polyamide 6 or copolyamides. In order to allow, in especially simple manner, an adjustability of the composition of the process fluid, it is possible in the device according to the invention for a treatment device to be provided for the process fluid, preferably in the region of an extraction fluid connection of the extraction device. In the device according to the invention, it is preferably possible for the process fluid to be carried in a first circuit between the underwater pelletizer and the extraction device through the underwater pelletizer, the fluid removal connection, at least one part of the extraction device, a common fluid connection and the fluid return connection and to be carried in a second circuit between the extraction device and a treatment device through the common fluid connection, the extraction fluid connection, the treatment device and at least one part of the extraction device, wherein there is the common fluid connection between the first circuit and the second circuit, with the result that the first circuit and the second circuit partially overlap at least there. Consequently, it is preferably possible according to the invention for there to be a closed system of the process fluid circuit, wherein the process fluid is used for both the pelletization stage and also the extraction stage and is able to circulate accordingly, wherein the entire device according to the invention and/or the entire system of underwater pelletizer and extraction device according to the invention employs one and the same process fluid. In the device according to the invention, to further improve the reliability of pelletization, removal and supply of the pellets in the process fluid and return of the process fluid to the pelletization stage in the first circuit, it is possible, preferably in the region of the fluid return connection, for the process fluid to be at a temperature independent of the second circuit. For this purpose, it is possible for temperature-measuring and temperature-regulating devices to be provided in the respective regions/parts. In the device according to the invention, it is possible, at least in the region of the underwater pelletizer, for the process fluid to be at an increased pressure with respect to ambient pressure and, at least in the extraction device, for it to be at a lower pressure than the increased pressure, preferably at ambient pressure, wherein there is at least one pressure reduction device, preferably in the fluid removal connection, between the underwater pelletizer and the extraction device. This allows an especially simple adjustment of different pressure levels in the device according to the invention. In the device according to the invention, it is possible, also in the region of the underwater pelletizer and in the extraction device, for the process fluid to be at an increased pressure with respect to ambient pressure, wherein there is a pressure reduction device between the extraction device and the dryer, said dryer being positioned downstream of said extraction device, i.e. it is possible for the extraction device to be a pressure extraction device. Consequently, it is preferably possible according to the invention for the extraction stage to take place at increased pressure in the extraction device, this making it possible to further improve the efficiency of the extraction stage through the higher temperatures that are then possible. The fluid removal connection of the device according to the invention can be provided with an air lock for the removal of pellets/agglomerates. This makes it possible, particularly during startup of the device, for start-up material to be removed in a simple manner. It should be noted that all the features and advantages of the invention that have been hereinabove described in connection with the method according to the invention apply also, mutatis mutandis, to the device according to the invention, and vice versa. The invention will now be explained in greater detail with reference to the appended sample schematic drawings, in which: Figure 1 shows a schematic representation of a prior-art device; Figure 2 shows a schematic representation of a device according to a preferred embodiment of the invention; and Figure 3 shows a schematic representation of a further preferred embodiment of a device according to the invention. Figure 1 was already described hereinabove in connection with the discussion of the prior art. Figure 2 shows a schematic representation of an example of a device for the production of pellets of polyamide 6 or copolyamides, said device being especially suitable for implementation of the method according to the invention, according to a first preferred embodiment of the invention. A polymerized melt of caprolactam-based polyamide 6 or copolyamides or of suitable cyclic dimers/oligomers is produced in a polymerization reactor 6. The production of such a melt is otherwise known and is therefore not described in any greater detail here. The device according to the invention provides for an underwater pelletizer 1 which pelletizes the polymerized melt from the polymerization reactor 6 in the form of pellets into a process fluid. The process fluid with the therein contained pellets is transported away from the underwater pelletizer 1 through a fluid removal connection 7 and is supplied to an extraction device 2. This is indicated by the corresponding arrows in Fig. 2. In the embodiment presented in Fig. 2, a pressure reduction device 8 is provided between the underwater pelletizer 1 and the extraction device 2 in the fluid removal connection 7. This makes it possible to reduce the increased pressure in the region of the underwater pelletizer 1 with respect to the lower pressure in the region of the extraction device 2. The fluid removal connection 7 is provided with an air lock 10 for the removal of pellets. Said airlock 10 can be used during start-up of the device for the simple removal of pellets/agglomeratesfrom a start-up material. The mixture of process fluid and therein contained pellets enters the extraction device 2, the pellets being moved in a downward direction (see the region below the horizontal line in the extraction device 2 in Fig. 2). The process fluid is supplied through the common fluid connection 3 and the fluid return connection 3a back to the underwater pelletizer 1 and is also supplied through the extraction fluid connection 3b to a treatment device 4 and is supplied after the treatment device 4 through the extraction fluid connection 3b to the extraction device 2. There is a delivery rate ratio of 3:1 between a delivery rate of process fluid during underwater pelletization through the underwater pelletizer 1 and the removal and supply of the pellets contained in the process fluid through the fluid removal connection 7 as well as through the fluid return connection 3a and a delivery rate of process fluid during extraction by the extraction device. In the embodiment presented in Fig. 2, the process fluid then flows from bottom to top through at least one part of the extraction device 2. The pellets move in a downward direction. Both are indicated by the corresponding arrows in Fig. 2. The device presented in Fig. 2 forms a first circuit between the underwater pelletizer 1 and the extraction device 2 through the underwater pelletizer 1, the fluid removal connection 7, at least one part of the extraction device 2, the common fluid connection 3 and the fluid return connection 3a and a second circuit between the extraction device 2 and the treatment device 4 through the common fluid connection 3, the extraction fluid connection 3b, the treatment device 4 and the at least one part of the extraction device 2, wherein the common fluid connection 3 is common to the first circuit and to the second circuit, with the result that the first circuit and the second circuit partially overlap at least there. The fluid connection for the process fluid between the extraction device 2 and the underwater pelletizer 1 is through the fluid return connection 3a and the fluid connection for the process fluid with the therein contained pellets is through the fluid removal connection 7. The device presented in Figure 2 is, according to the invention, filled with a single process fluid and is operated therewith, i.e. the process fluid in the region of the underwater pelletizer 1 is the same as the process fluid in the region of the extraction device 2. Removal of the pellets downstream of the extraction device 2 can be accomplished, for example, by means of a rotary seal air lock (not shown in Fig. 2). Provided downstream thereof is a dryer 5 for drying the pellets, which pellets can then be suitably stored and further processed. The extract of low-molecular components obtained in the treatment device 4, which extract was in the process fluid, is recovered by the treatment device 4 and can be returned to the polymerization reactor 6 for polymerization. This is indicated by the broken line in Fig. 2. Furthermore, it can be seen in the region of the polymerization reactor 6 in Fig. 2 that the starting products for polymerization are otherwise supplied to the polymerization reactor 6 from an external source (indicated by a corresponding arrow in the region of the polymerization reactor 6 in Fig. 2). Generally, it should be noted that the device presented in Fig. 2 (and also the one presented in the following Fig. 3) is provided in suitable places, more particularly at branches, with suitable valves, pressure and temperature sensors, feed pumps, filters, heat exchangers and similar. For reasons of clarity of representation, however, such devices are not shown. Figure 3 shows a schematic representation of an example of a second preferred embodiment of the device according to the present invention. The embodiment presented in Fig. 3 differs from the embodiment presented in Fig. 2 merely in that, in this case, the pelletization and extraction stages take place at the same or at substantially the same increased pressure and in that pressure reduction does not take place until before the dryer 5 through provision of a pressure reduction device 9 between the extraction device 2 and the dryer 5. Otherwise the embodiment presented in Fig. 3 is identical to the embodiment described in connection with Fig. 2. With the device according to the invention as described hereinabove, it is possible to implement, in particular, the method according to the invention. This results, according to the invention, in a simple and cost-effective means of reliably producing pellets of polyamide 6 or copolyamides, said pellets being particularly suitable for further processing. We Claim:- 1. Method for the production of pellets of polyamide 6 or copolyamides, by - production of a melt of polyamide 6 or copolyamides by means of polymerization; - production of pellets from the melt by means of underwater pelletization into a process fluid; - removal of the pellets from the site of underwater pelletization in the process fluid; and - supply of the pellets in the process fluid to an extraction stage; - extraction of low-molecular components as extract; - drying of the pellets after extraction; characterized in that the underwater pelletization stage and the extraction stage take place using the same process fluid. 2. Method according to claim 1, characterized in that the process fluid has a composition equivalent to a composition after the extraction stage, wherein the process fluid contains preferably more than 10% by weight of extract. 3. Method according to claim 1 or 2, characterized in that the process fluid is carried in a first circuit between underwater pelletization stage and extraction stage and is carried in a second circuit between extraction stage and a treatment stage for removal of extract from the process fluid, wherein there is a fluid connection for the process fluid between the first circuit and the second circuit, with the result that the first circuit and the second circuit partially overlap at least there. 4. Method according to claim 3, characterized in that, in the first circuit, preferably in a fluid return connection, the process fluid is at a temperature independent of the second circuit, preferably in an extraction fluid connection. 5. Method according to any one of claims 1 to 4, characterized in that, during the underwater pelletization stage and during removal and supply of the pellets, the process fluid is at an increased pressure with respect to ambient pressure, the pressure being preferably equal to or greater than 1 bar, more preferably equal to or greater than 3 bar, still more preferably equal to or greater than 4 bar. 6. Method according to claim 5, characterized in that the extraction stage takes place at a pressure lower than the increased pressure, preferably at ambient pressure, wherein, prior to extraction, the pressure of the process fluid is reduced from the increased pressure to the lower pressure, preferably to ambient pressure. 7. Method according to claim 5, characterized in that the extraction stage takes place at the increased pressure, wherein, after extraction and prior to drying, the pressure is reduced from the increased pressure to a lower pressure, preferably ambient pressure. 8. Method according to any one of claims 1 to 7, characterized in that a delivery rate of process fluid during the underwater pelletization stage and during removal and supply of the pellets in the process fluid and a delivery rate of process fluid during the extraction stage is adjusted to a delivery rate ratio of at least 3:1. 9. Device for the production of pellets of polyamide 6 or copolyamides, with an underwater pelletizer (1), wherein, from a melt of polyamide 6 or copolyamides polymerized in a polymerization reactor (6), said underwater pelletizer (1) pelletizes pellets into a process fluid, wherein there is a fluid removal connection (7) between the underwater pelletizer (1) and an extraction device (2), wherein the process fluid with the therein contained pellets is removed from the underwater pelletizer (1) through said fluid removal connection (7) and is supplied to the extraction device (2); and with a dryer (5), positioned downstream of the extraction device (2), for drying the pellets, characterized in that the underwater pelletizer (1) and the extraction device (2) are operated with the same process fluid, wherein there is a fluid return connection (3a) for the process fluid between the extraction device (2) and the underwater pelletizer (1). 10. Device according to claim 9, characterized in that a treatment device (4) is provided for the process fluid, preferably in the region of an extraction fluid connection (3b) of the extraction device (2). 11. Device according to claim 9 or 10, characterized in that the process fluid is carried in a first circuit between the underwater pelletizer (1) and the extraction device (2) through the underwater pelletizer (1), the fluid removal connection (7), at least one part of the extraction device (2), a common fluid connection (3) and the fluid return connection (3a) and is carried in a second circuit between the extraction device (2) and a treatment device (4) through the common fluid connection (3), the extraction fluid connection (3b), the treatment device (4) and at least one part of the extraction device (2), wherein there is the common fluid connection (3) between the first circuit and the second circuit, with the result that the first circuit and the second circuit partially overlap at least there. 12. Device according to any one of claims 9 to 11, characterized in that, at least in the region of the underwater pelletizer (1), the process fluid is at an increased pressure with respect to ambient pressure and, at least in the extraction device (2), is at a lower pressure than the increased pressure, preferably at ambient pressure, wherein there is at least one pressure reduction device (8), preferably in the fluid removal connection (7), between the underwater pelletizer (1) and the extraction device (2). 13. Device according to any one of claims 9 to 12, characterized in that, in the region of the underwater pelletizer (1) and in the extraction device (2), the process fluid is at an increased pressure with respect to ambient pressure, wherein there is a pressure reduction device (9) between the extraction device (2) and the dryer (5), said dryer (5) being positioned downstream of said extraction device (2). 14. Device according to any one of claims 9 to 13, characterized in that the fluid removal connection (7) is provided with an air lock (10) for the removal of pellets/agglomerates. Dated this 4th day of May 2010.

Full Text

FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

1. ' Method and device for the production of polyamide '

2.

1. (A) AUTOMATIK PLASTICS MACHINERY GMBH
(B) Germany
(C) Ostring 19, D- 63762 Grossostheim, Germany.

The following specification particularly describes the invention and the manner in which it is to be performed.

The invention relates to a method for the production of polyamide 6 or copolyamides according to the preamble of claim 1 as well as to a device for the production of polyamide 6 or copolyamides according to the preamble of claim 9.

Polyamides are today used in a multiplicity of areas, such as for textiles, carpets or tyre cords, in the production of injection mouldings, such as in the automotive area, or in the production of plastic films or blown containers for packaging. In this connection, the multiplicity of positive properties is of particular significance, including the high durability and high thermal resistance combined with the good elasticity of polyamides.

An overview of various methods for the production of polyamides, including caprolactam-based polyamide 6 or copolyamides, is provided in Kunststoff-Handbuch [Plastics Manual], Volume 3 "Technische Thermoplaste" [Technical Thermoplastics], Subvolume 4 "Polyamide" [Polyamides], published by G. W. Becker and D. Braun, Hanser-Verlag Munich and Vienna, 1998, pages 22 to 75. An overview of spinning applications of polyamides can be found, for example, in "Synthetische Fasern" [Synthetic Fibres], Handbuch für Anlagenplanung [Manual of Plant Engineering], Franz
Fourné, Hanser-Verlag Munich and Vienna, 1995, pages 36 to 56.

Generally, in currently established methods and devices for the production of polyamides, especially for the production of polyamide 6 or copolyamides, a caprolactam-based melt is subjected to polymerization. A thus produced polyamide melt is then first of all pelletized, for example by means of underwater pelletization or, alternatively, for example by means of strand pelletization. Such a pelletized polyamide material, however, usually still contains around 10% of low-molecular species or components, such as caprolactam and cyclic oligomers. In order to prevent a disruption by such low-molecular components during the further treatment of such a pelletized polyamide material, such low-molecular components are reduced by extraction to the level required for the particular application, the residual concentration thereof being thus
adjusted. Conventionally, for this purpose, the pellets, which are dried after pelletization, are subjected to aqueous extraction, in the course of which the pellets conventionally take up considerable quantities of water. Consequently, such an extraction stage is followed by a further drying stage. Conventionally, the prior art makes use, for example, of inert-gas dryers, which are arranged downstream of a countercurrent extraction device.

The water at the outlet of the extraction stage conventionally has an extract concentration, i.e. a concentration of low-molecular components, of over 10% by weight. This extraction water is either returned directly to the polymerization process or is reprocessed after extraction, wherein the extracted low-molecular components are recovered and can then be returned to the polymerization process.

With regard to the above-described pelletization process, it must generally be ensured that there is compliance with a composition of the pelletization water that is suitable for a reliable pelletization process, with the extract concentration in the pelletization water normally being around 4% by weight. If this is not the case, the pelletization water cannot be optimally treated, because there is a foaming of the pelletization water.

The direct supply of pelletization water to the extraction stage would undesirably lower the therein contained extract concentration. The required degree of dryness of the polyamide pellets (commonly referred to as PA chips) at the inlet to the extraction stage is around 1% by weight.

Figure 1 shows a schematic representation of a device according to the prior art. A polymerized melt of caprolactam-based polyamide 6 or copolyamides is produced in a polymerization reactor 16 (corresponding arrow to polymerization reactor 16). In an underwater pelletizer 11, the polymerized melt is pelletized into pellets in pelletization water. Next, the pellets are dried of the pelletization water in a dryer 13 and are then supplied to an extraction device 12, where the extraction process takes place by means of extraction water in a separate extraction water circuit with integrated treatment device 14 for recovery of the extract. The recovered extract can be returned to the polymerization reactor. Extraction is followed by further drying of the pellets in a dryer 15. The pelletization water is treated in a separate circuit and is returned to the underwater pelletizer 11. The streams of material and water are identified by the corresponding arrows in Fig. 1.

Publication WO 02/094908 A1 describes a method and device for the extraction of polyamide wherein the pelletization of polyamide melt into pellets is followed by a separate extraction of the low-molecular (residual) components using a special extraction water under specific conditions, more particularly in a plurality of stages at increased temperature and pressure.

The object of the present invention is to overcome the disadvantages of the prior art and, more particularly, to provide a method and device for the production of pellets of polyamide 6 or copolyamides, said method/device making it possible, in simple and cost-effective, yet reliable manner, to produce pellets of polyamide 6 or copolyamides, said pellets being able to be further processed in simple manner.

The object of the invention is achieved by a method having the features according to claim 1 and by a device having the features according to claim 9.

Advantageous embodiments of the invention are defined in the respective subclaims.

The method according to the invention for the production of pellets of polyamide 6 or
copolyamides comprises the following steps:

- production of a melt of polyamide 6 or copolyamides by means of polymerization.
Polymerization is caprolactam-based.
- production of pellets from the melt by means of underwater pelletization, for example
by means of an underwater pelletizer of the kind produced and marketed by the
applicant under the product name SPHERO, wherein the pellets are pelletized into a
process fluid.
- removal of the pellets from the site of underwater pelletization in the process fluid, and
- supply of the pellets in the process fluid to an extraction stage.
- extraction of low-molecular components, more particularly of components that were
not completely polymerized, as extract, wherein extraction is preferably fluid-based or
waterbased.
- drying of the pellets after extraction.

The method according to the invention is further characterized in that underwater pelletization and extraction take place using the same process fluid. According to the invention, therefore, both the underwater pelletization stage and also the extraction stage take place using a process fluid, wherein said process fluid is the same for both stages of the method, i.e. the fluid that is used for the underwater pelletization stage is the same fluid that is used for the extraction stage. In short, therefore, the transport fluid for underwater pelletization is the same as or identical to the extraction fluid used for extraction. According to the invention, therefore, a single process fluid is used both for the pelletization stage and also for transport of the pellets and also for the extraction of low-molecular components from the pellets.

The method according to the invention makes it possible, on the one hand, to obviate the need for the intermediate drying phase that is conventionally provided in the prior art and which is provided between the pelletization and extraction stages. On the other hand, it is possible for the melt energy of the pellets that have been pelletized into the process water of the invention to be co-used for the required heating of the process fluid, this allowing energy savings to be made. Furthermore, it is thus possible in simple and cost-effective manner, by obviating the need to make available two different fluids, to provide according to the invention an especially simple and cost-effective, yet reliable method for the production of pellets of polyamide 6 or copolyamides, it being possible according to the invention for pellets to be made available that can be further processed in simple and reliable manner.

In the method according to the invention, the process fluid can preferably have a composition equivalent to a composition after the extraction stage, preferably equivalent to a normally conventional composition after the extraction stage, wherein the process fluid contains preferably more than 10% by weight of extract, i.e. of low-molecular components. Consequently, the process fluid used in the method according to the invention can have the composition of an extraction fluid, which can further improve the reliability of the method with regard to the production of pellets that can be further processed in simple and especially easy manner.

In a preferred embodiment of the method according to the invention, the process fluid can be carried in a first circuit between underwater pelletization stage and extraction stage and can be carried in a second circuit between extraction stage and treatment stage for removal of extract from the process fluid, wherein there is a fluid connection for the process fluid between the first circuit and the second circuit, with the result that the first circuit and the second circuit partially overlap at least there, i.e. where there is said fluid connection. It is thus possible in technically simple and therefore cost-effective manner for a closed circuit or two interconnected closed circuits, more particularly two directly interconnected closed circuits, to be preferably realized according to the invention.

In the method according to the invention, in order to further improve the reliability of pelletization, the removal and supply of the pellets in the process fluid and the return of the process fluid to the pelletization stage in the first circuit, preferably in a fluid return connection, it is possible for the process fluid to be at a temperature independent of the second circuit, preferably in an extraction fluid connection.

In order to allow an especially reliable pelletization stage, it is preferably possible in the method according to the invention, during underwater pelletization and during removal and supply of the pellets, for the process fluid to be at an increased pressure with respect to ambient pressure, the pressure being preferably equal to or greater than 1 bar, more preferably equal to or greater than 3 bar, still more preferably equal to or greater than 4 bar. This also makes it possible reliably to prevent or at least to reduce any foaming of the process fluid.

In such a method according to the invention, it is possible for the extraction stage to take place at a pressure lower than the increased pressure, preferably at ambient pressure, wherein, prior to extraction, the pressure of the process fluid can be reduced from the increased pressure to the lower pressure, preferably to ambient pressure. The extraction stage, therefore, takes place at a reduced pressure with respect to the pelletization stage.

Alternatively, however, in the method according to the invention, the extraction stage can take place at the increased pressure, wherein, after extraction and prior to drying, the pressure is reduced from the increased pressure to a lower pressure, preferably to ambient pressure. Consequently, for example, it is preferably possible according to the invention for the pelletization and extraction stages to take place at increased pressure, preferably at the same increased pressure. This may possibly further increase the efficiency of the extraction stage, i.e. this can improve the effectiveness of the extraction of low-molecular components.

In order, according to the invention, to be able to further improve a smooth process under, where possible, all process conditions and especially in the case of a high delivery rate, it is possible for a delivery rate of process fluid during underwater pelletization and during removal and supply of the pellets in the process fluid and a delivery rate of process fluid during extraction to be adjusted to a delivery rate ratio of at least 3:1.

The device according to the invention for the production of pellets of polyamide 6 or copolyamides can be used for implementation of the method according to the invention. The device according to the invention has an underwater pelletizer, wherein, from a melt of polyamide 6 or copolyamides polymerized in a polymerization reactor, said underwater pelletizer pelletizes pellets into a process fluid, wherein there is a fluid removal connection between the underwater pelletizer and an extraction device, wherein the process fluid with the therein contained pellets is removed from the underwater pelletizer through said fluid removal connection and is supplied to the extraction device. Positioned downstream of the extraction device is a dryer for drying the pellets. According to the invention, no such dryer is required upstream of the extraction device and is therefore omitted according to the invention, especially as, according to the invention, a direct fluid connection is provided between underwater pelletizer and extraction device. In the device according to the invention, the underwater pelletizer and the extraction device are operated with the same process fluid, wherein, between the extraction device and the underwater pelletizer, there is, in addition to the fluid removal connection for process fluid and therein contained pellets from the underwater pelletizer to the extraction device, also a fluid return connection for the process fluid without pellets from the extraction device back to the underwater pelletizer.

According to the invention, this allows a connection according to the invention between underwater pelletizer/underwater pelletization stage and extraction device/extraction of lowmolecular components through one and the same process fluid and it also allows the return of the process fluid from the extraction device to the underwater pelletizer according to the invention. This makes it possible, according to the invention, to provide a device which permits in especially simple and therefore cost-effective manner the still reliable production of pellets of polyamide 6 or copolyamides.

In order to allow, in especially simple manner, an adjustability of the composition of the process fluid, it is possible in the device according to the invention for a treatment device to be provided for the process fluid, preferably in the region of an extraction fluid connection of the extraction device.

In the device according to the invention, it is preferably possible for the process fluid to be carried in a first circuit between the underwater pelletizer and the extraction device through the underwater pelletizer, the fluid removal connection, at least one part of the extraction device, a common fluid connection and the fluid return connection and to be carried in a second circuit between the extraction device and a treatment device through the common fluid connection, the extraction fluid connection, the treatment device and at least one part of the extraction device, wherein there is the common fluid connection between the first circuit and the second circuit, with the result that the first circuit and the second circuit partially overlap at least there. Consequently, it is preferably possible according to the invention for there to be a closed system of the process fluid circuit, wherein the process fluid is used for both the pelletization stage and also the extraction stage and is able to circulate accordingly, wherein the entire device according to the invention and/or the entire system of underwater pelletizer and extraction device according to the invention employs one and the same process fluid.

In the device according to the invention, to further improve the reliability of pelletization,
removal and supply of the pellets in the process fluid and return of the process fluid to the
pelletization stage in the first circuit, it is possible, preferably in the region of the fluid return connection, for the process fluid to be at a temperature independent of the second circuit. For this purpose, it is possible for temperature-measuring and temperature-regulating devices to be provided in the respective regions/parts.

In the device according to the invention, it is possible, at least in the region of the underwater pelletizer, for the process fluid to be at an increased pressure with respect to ambient pressure and, at least in the extraction device, for it to be at a lower pressure than the increased pressure, preferably at ambient pressure, wherein there is at least one pressure reduction device, preferably in the fluid removal connection, between the underwater pelletizer and the extraction device. This allows an especially simple adjustment of different pressure levels in the device according to the invention.

In the device according to the invention, it is possible, also in the region of the underwater pelletizer and in the extraction device, for the process fluid to be at an increased pressure with respect to ambient pressure, wherein there is a pressure reduction device between the extraction device and the dryer, said dryer being positioned downstream of said extraction device, i.e. it is possible for the extraction device to be a pressure extraction device. Consequently, it is preferably possible according to the invention for the extraction stage to take place at increased pressure in the extraction device, this making it possible to further improve the efficiency of the extraction stage through the higher temperatures that are then possible.

The fluid removal connection of the device according to the invention can be provided with an air lock for the removal of pellets/agglomerates. This makes it possible, particularly during startup of the device, for start-up material to be removed in a simple manner.

It should be noted that all the features and advantages of the invention that have been hereinabove described in connection with the method according to the invention apply also, mutatis mutandis, to the device according to the invention, and vice versa.

The invention will now be explained in greater detail with reference to the appended sample schematic drawings, in which:

Figure 1 shows a schematic representation of a prior-art device;
Figure 2 shows a schematic representation of a device according to a preferred
embodiment of the invention; and
Figure 3 shows a schematic representation of a further preferred embodiment of a
device according to the invention.

Figure 1 was already described hereinabove in connection with the discussion of the prior art. Figure 2 shows a schematic representation of an example of a device for the production of pellets of polyamide 6 or copolyamides, said device being especially suitable for implementation of the method according to the invention, according to a first preferred embodiment of the invention.

A polymerized melt of caprolactam-based polyamide 6 or copolyamides or of suitable cyclic dimers/oligomers is produced in a polymerization reactor 6. The production of such a melt is otherwise known and is therefore not described in any greater detail here. The device according to the invention provides for an underwater pelletizer 1 which pelletizes the polymerized melt from the polymerization reactor 6 in the form of pellets into a process fluid. The process fluid with the therein contained pellets is transported away from the underwater pelletizer 1 through a fluid removal connection 7 and is supplied to an extraction device 2. This is indicated by the corresponding arrows in Fig. 2. In the embodiment presented in Fig. 2, a pressure reduction device 8 is provided between the underwater pelletizer 1 and the extraction device 2 in the fluid removal connection 7. This makes it possible to reduce the increased pressure in the region of the underwater pelletizer 1 with respect to the lower pressure in the region of the extraction
device 2.

The fluid removal connection 7 is provided with an air lock 10 for the removal of pellets. Said airlock 10 can be used during start-up of the device for the simple removal of pellets/agglomeratesfrom a start-up material.

The mixture of process fluid and therein contained pellets enters the extraction device 2, the pellets being moved in a downward direction (see the region below the horizontal line in the extraction device 2 in Fig. 2). The process fluid is supplied through the common fluid connection 3 and the fluid return connection 3a back to the underwater pelletizer 1 and is also supplied through the extraction fluid connection 3b to a treatment device 4 and is supplied after the treatment device 4 through the extraction fluid connection 3b to the extraction device 2. There is a delivery rate ratio of 3:1 between a delivery rate of process fluid during underwater pelletization through the underwater pelletizer 1 and the removal and supply of the pellets contained in the process fluid through the fluid removal connection 7 as well as through the fluid return connection 3a and a delivery rate of process fluid during extraction by the extraction device. In the embodiment presented in Fig. 2, the process fluid then flows from bottom to top through at least one part of the extraction device 2. The pellets move in a downward direction. Both are indicated by the corresponding arrows in Fig. 2.

The device presented in Fig. 2 forms a first circuit between the underwater pelletizer 1 and the extraction device 2 through the underwater pelletizer 1, the fluid removal connection 7, at least one part of the extraction device 2, the common fluid connection 3 and the fluid return connection 3a and a second circuit between the extraction device 2 and the treatment device 4 through the common fluid connection 3, the extraction fluid connection 3b, the treatment device 4 and the at least one part of the extraction device 2, wherein the common fluid connection 3 is common to the first circuit and to the second circuit, with the result that the first circuit and the second circuit partially overlap at least there. The fluid connection for the process fluid between the extraction device 2 and the underwater pelletizer 1 is through the fluid return connection 3a and the fluid connection for the process fluid with the therein contained pellets is through the fluid removal connection 7.

The device presented in Figure 2 is, according to the invention, filled with a single process fluid and is operated therewith, i.e. the process fluid in the region of the underwater pelletizer 1 is the same as the process fluid in the region of the extraction device 2.

Removal of the pellets downstream of the extraction device 2 can be accomplished, for example, by means of a rotary seal air lock (not shown in Fig. 2). Provided downstream thereof is a dryer 5 for drying the pellets, which pellets can then be suitably stored and further processed.

The extract of low-molecular components obtained in the treatment device 4, which extract was in the process fluid, is recovered by the treatment device 4 and can be returned to the polymerization reactor 6 for polymerization. This is indicated by the broken line in Fig. 2. Furthermore, it can be seen in the region of the polymerization reactor 6 in Fig. 2 that the starting products for polymerization are otherwise supplied to the polymerization reactor 6 from an external source (indicated by a corresponding arrow in the region of the polymerization reactor 6 in Fig. 2).

Generally, it should be noted that the device presented in Fig. 2 (and also the one presented in the following Fig. 3) is provided in suitable places, more particularly at branches, with suitable valves, pressure and temperature sensors, feed pumps, filters, heat exchangers and similar. For reasons of clarity of representation, however, such devices are not shown.

Figure 3 shows a schematic representation of an example of a second preferred embodiment of the device according to the present invention.

The embodiment presented in Fig. 3 differs from the embodiment presented in Fig. 2 merely in that, in this case, the pelletization and extraction stages take place at the same or at substantially the same increased pressure and in that pressure reduction does not take place until before the dryer 5 through provision of a pressure reduction device 9 between the extraction device 2 and the dryer 5. Otherwise the embodiment presented in Fig. 3 is identical to the embodiment described in connection with Fig. 2.

With the device according to the invention as described hereinabove, it is possible to implement, in particular, the method according to the invention. This results, according to the invention, in a simple and cost-effective means of reliably producing pellets of polyamide 6 or copolyamides, said pellets being particularly suitable for further processing.

We Claim:-

1. Method for the production of pellets of polyamide 6 or copolyamides, by
- production of a melt of polyamide 6 or copolyamides by means of polymerization;
- production of pellets from the melt by means of underwater pelletization into a process
fluid;
- removal of the pellets from the site of underwater pelletization in the process fluid; and
- supply of the pellets in the process fluid to an extraction stage;
- extraction of low-molecular components as extract;
- drying of the pellets after extraction;
characterized in that
the underwater pelletization stage and the extraction stage take place using the same process fluid.

2. Method according to claim 1, characterized in that the process fluid has a composition
equivalent to a composition after the extraction stage, wherein the process fluid contains
preferably more than 10% by weight of extract.

3. Method according to claim 1 or 2, characterized in that the process fluid is carried in a first circuit between underwater pelletization stage and extraction stage and is carried in a second circuit between extraction stage and a treatment stage for removal of extract from the process fluid, wherein there is a fluid connection for the process fluid between the first circuit and the second circuit, with the result that the first circuit and the second circuit partially overlap at least there.

4. Method according to claim 3, characterized in that, in the first circuit, preferably in a fluid return connection, the process fluid is at a temperature independent of the second circuit, preferably in an extraction fluid connection.

5. Method according to any one of claims 1 to 4, characterized in that, during the underwater pelletization stage and during removal and supply of the pellets, the process fluid is at an increased pressure with respect to ambient pressure, the pressure being preferably equal to or greater than 1 bar, more preferably equal to or greater than 3 bar, still more preferably equal to or greater than 4 bar.

6. Method according to claim 5, characterized in that the extraction stage takes place at a
pressure lower than the increased pressure, preferably at ambient pressure, wherein, prior to extraction, the pressure of the process fluid is reduced from the increased pressure to the lower pressure, preferably to ambient pressure.

7. Method according to claim 5, characterized in that the extraction stage takes place at the increased pressure, wherein, after extraction and prior to drying, the pressure is reduced from the increased pressure to a lower pressure, preferably ambient pressure.

8. Method according to any one of claims 1 to 7, characterized in that a delivery rate of process fluid during the underwater pelletization stage and during removal and supply of the pellets in the process fluid and a delivery rate of process fluid during the extraction stage is adjusted to a delivery rate ratio of at least 3:1.

9. Device for the production of pellets of polyamide 6 or copolyamides, with an underwater pelletizer (1), wherein, from a melt of polyamide 6 or copolyamides polymerized in a polymerization reactor (6), said underwater pelletizer (1) pelletizes pellets into a process fluid, wherein there is a fluid removal connection (7) between the underwater pelletizer (1) and an extraction device (2), wherein the process fluid with the therein contained pellets is removed from the underwater pelletizer (1) through said fluid removal connection (7) and is supplied to the extraction device (2); and with a dryer (5), positioned downstream of the extraction device (2),
for drying the pellets,
characterized in that
the underwater pelletizer (1) and the extraction device (2) are operated with the same process fluid, wherein there is a fluid return connection (3a) for the process fluid between the extraction device (2) and the underwater pelletizer (1).
10. Device according to claim 9, characterized in that a treatment device (4) is provided for the process fluid, preferably in the region of an extraction fluid connection (3b) of the extraction device (2).

11. Device according to claim 9 or 10, characterized in that the process fluid is carried in a first circuit between the underwater pelletizer (1) and the extraction device (2) through the underwater pelletizer (1), the fluid removal connection (7), at least one part of the extraction device (2), a common fluid connection (3) and the fluid return connection (3a) and is carried in a second circuit between the extraction device (2) and a treatment device (4) through the common fluid connection (3), the extraction fluid connection (3b), the treatment device (4) and at least one part of the extraction device (2), wherein there is the common fluid connection (3) between the first circuit and the second circuit, with the result that the first circuit and the second circuit partially overlap at least there.

12. Device according to any one of claims 9 to 11, characterized in that, at least in the region of the underwater pelletizer (1), the process fluid is at an increased pressure with respect to ambient pressure and, at least in the extraction device (2), is at a lower pressure than the increased pressure, preferably at ambient pressure, wherein there is at least one pressure reduction device (8), preferably in the fluid removal connection (7), between the underwater pelletizer (1) and the extraction device (2).

13. Device according to any one of claims 9 to 12, characterized in that, in the region of the underwater pelletizer (1) and in the extraction device (2), the process fluid is at an increased pressure with respect to ambient pressure, wherein there is a pressure reduction device (9) between the extraction device (2) and the dryer (5), said dryer (5) being positioned downstream of said extraction device (2).

14. Device according to any one of claims 9 to 13, characterized in that the fluid removal
connection (7) is provided with an air lock (10) for the removal of pellets/agglomerates.

Dated this 4th day of May 2010.

Documents:

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Patent Number

270523

Indian Patent Application Number

916/MUMNP/2010

PG Journal Number

01/2016

Publication Date

01-Jan-2016

Grant Date

29-Dec-2015

Date of Filing

04-May-2010

Name of Patentee

MAAG AUTOMATIK GMBH

Applicant Address

Ostring 19, D- 63762 Grossostheim, Germany

Inventors:

#	Inventor's Name	Inventor's Address
1	Stefan DEISS	Rheinstrasse 7 D- 55896 Harxheim Germany.

PCT International Classification Number

C08G 69/16, B01D 11/02,B29B 9/06

PCT International Application Number

PCT/DE2008/001929

PCT International Filing date

2008-11-20

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10 2007 057 189.7	2007-11-28	Germany