COMPOUNDING SIDE STREAM FOR POLYAMIDE SYNTHESIS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application Serial No. 61/818,201, filed May 1, 2013, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND [0002] Additive addition to polyamide in a continuous polyamide manufacturing process is problematic. If the additive is mixed with the reactant mixture early in the polymerization process, the processing equipment can become fouled with additive and degradation products of the additive. If the additive is mixed with substantially polymerized polyamide, mixing to uniformity is difficult because the polyamide is so viscous. Moreover, the additive solvent can upset the polymerization reaction especially, for example, if the solvent is water. Water is a product of the

polymerization reaction. Substantial amounts of water can drive the polymerization reaction in the opposite direction or lead to side reactions.

[0003] Impurities can be introduced into the polyamide either from the additive mixture or as a result of reaction between the components of the polymerization mixture and the additive or its solvent. The polymerization reaction mixture is in molten form. When additive is introduced, the heat can promote side product formation. The polymerization mixture is often subjected to reduced pressure to help drive the polymerization reaction forward. The viscosity of the polymerization mixture often necessitates pumping or other forces to move the polymers through the manufacturing system. A pressure differential between the additive solution and the polymerization mixture can cause blow back into the additive inlet and fouling of the additive feed apparatus.

[0004] Additives can be premixed with a polymer carrier (also referred to as a diluent). This premixed additive and polymer is commonly referred to as a "master batch." While the use of a master batch can overcome some of the problems attendant to introducing the additive earlier in the process, injecting the carrier polymer itself may introduce problems if it is not identically the same as the reaction product of the polymerization reaction being carried out. If the carrier polymer is different from the reaction product, then the carrier polymer represents an impurity in the product. Even if the carrier polymer has a substantially similar chemical formula to that of the product, the carrier polymer may differ by degree of polymerization (as reflected by molecular weight). Thus it would be desirable to provide a process and apparatus for introducing additive in a way that takes full advantage of the mixing benefits of master batch operation without introducing unde sired impurities into the product stream.

SUMMARY

[0005] Systems and processes for mixing additive into a polyamide polymer stream are described herein that can solve the problems of inadequate mixing, contaminate introduction, side product formation, and equipment fouling.

[0006] One example of a system is a continuous polyamide manufacturing system that includes:

a side stream compounding unit with at least one upstream inlet, at least one mixing chamber and at least one downstream outlet;

wherein the side stream unit is positioned parallel to a main polyamide flow line of the continuous polyamide manufacturing system; wherein the at least one mixing chamber is configured to mix an additive with substantially polymerized polyamide diverted through at least one of the upstream inlets; and

wherein each of the downstream outlets is positioned upstream of a polyamide extruder or a polyamide strand forming unit.

[0007] The side stream compounding unit can also include at least one additive reservoir, at least one pump, at least one impeller, at least one mixer, at least one flow meter, one or more vents, or a combination thereof. [0008] The continuous polyamide manufacturing system can include a reactant reservoir, evaporator, polymerization reactor, batch reactor flasher, finisher, polyamide strand forming unit, extruder, and combinations thereof.

[0009] Also described herein are methods of using such a system with such a side stream compounding unit. For example, one method for mixing additives into a polyamide polymer stream involves:

(a) diverting substantially polymerized polyamide from an upstream line in a continuous polyamide manufacturing system to generate a polyamide side stream;

(b) mixing an additive into the polyamide side stream to generate a polyamide-additive side mixture; and

(c) returning the polyamide-additive side mixture to a downstream line in the system to generate a polyamide-additive main stream;

wherein, upon diversion, the substantially polymerized polyamide from the upstream line has a water content of about 0.1% - 3 wt%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic diagram illustrating exemplary features that can included in a side stream compounding unit described herein, which is part of a continuous polyamide manufacturing system.

DETAILED DESCRIPTION

[0011] As described herein, addition of additives to a polyamide polymerization mixture can be problematic because such addition can result in formation of contaminates and side products, as well as equipment fouling. When the polyamide polymerization mixture becomes viscous, uniform mixing of additive into the mixture is problematic. A desired uniformly mixed polyamide-additive product that is free of contaminates, side products, and gel (e.g., a disordered solid material that can include oxidative or thermal degradation products) can be obtained by use of the processes and the side stream compounding unit described herein. The polyamide can be any suitable polyamide, such as nylon 6, nylon 7, nylon 11, nylon 12, nylon 6,6, nylon 6,9; nylon 6,10, nylon 6,12, or copolymers thereof.

[0012] The side stream compounding unit described herein can be configured within a continuous polyamide manufacturing system at a position where the polyamide is substantially polymerized. For example, the substantially polymerized polyamide diverted into the side stream compounding unit can have a water content of less than 5 wt , or less than 2 wt , or less than 1.5 wt . Any suitable amount of the main stream can be diverted into the side steam compounding unit, such as about 0.01 wt to about 99.9 wt , about 1 wt to about 80 wt , about 1 wt to about 30 wt , about 0.01 wt or less, 0.1 wt , 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.9 wt%, or about 99.99 wt or more. The main stream from which the diverted stream is taken can have any suitable flow rate, such as about 1 L/min to about 1,000,000 L/min, or about 10 L/min to about 100,000 L/min, or about 1 L/min or less, 10 L/min, 20, 30, 40, 50, 60, 70, 80, 90, 100, 125, 150, 175, 200, 225, 250, 275, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1,000, 2,500, 5,000, 10,000, 50,000, 100,000, 500,000, or about 1,000,000 L/min or more.

[0013] Such positioning avoids fouling (e.g., with additive, contaminates, and additive-polymerization side products) of equipment employed during early stages of the polymerization process. Thus, equipment such as an evaporator used to reduce the water content of reactants, a reactor used to facilitate polymerization of reactants, and a flasher unit for increasing the molecular weight of polymers remain free of contaminates, additive, and side-product build-up that can be generated by early introduction of additives to the polymerization process. Contaminates, additive, and side products can accumulate on equipment, for example, on heated surfaces, in equipment surface irregularities, and in places where eddies occur in the flow of the polymerization mixture. Such accumulation can lead to formation and build-up of additional problematic materials such as gel.

[0014] The side stream compounding unit described herein is configured within a continuous polyamide manufacturing system at a position where the polyamide is substantially polymerized. However, the side stream compounding unit described herein is also configured within a continuous polyamide manufacturing system at a position prior to extrusion of the polymerized polyamide product. Addition of additive during extrusion can introduce solvents and other materials that can adversely affect the quality of the polyamide product. A side stream compounding unit configured within the manufacturing system at a position prior to extrusion of the polymerized polyamide product permits further processing, mixing and removal of additive solvent.

[0015] For example, the side stream compounding unit can be positioned just prior to a finisher unit or just after a finisher unit within a continuous polyamide manufacturing system.

[0016] At this point in the manufacturing system, the polymerization mixture is substantially polymerized. The water content of the mixture has been reduced significantly compared to polymerization mixtures in early phases of the system. For example, the water content of the substantially polymerized polyamide upon diversion into the side stream compounding unit can be about 2% by weight or less. The water content can be as low as about 1% by weight or even as low as about 0.1% by weight. For example, the water content of the substantially polymerized polyamide upon diversion into the side stream compounding unit can be less than 0.9%, less than 0.7%, less than 0.6%, less than 0.5%, less than 0.4%, less than 0.3%, or less than 0.2%.

[0017] The substantially polymerized polyamide, upon diversion into the side stream compounding unit, is viscous. For example, the substantially polymerized polyamide can have a relative viscosity of about 2.3 to 100, or 9-20, or 30-100, as measured by the methods described herein. The relative viscosity of the

substantially polymerized polyamide can be at least about 0.4 greater that the relative viscosity of the original mixture of subunits prior to polymerization.

[0018] In general, the side stream compounding unit is configured to receive substantially polymerized polyamide from an upstream line of a continuous polyamide manufacturing system to generate a polyamide side stream. The side stream compounding unit then mixes additive with the polyamide side stream to generate a polyamide-additive side mixture, and returns the polyamide-additive side mixture to a downstream line of the continuous polyamide manufacturing system to generate a polyamide-additive main stream. The polyamide-additive main stream can be mixed to generate a substantially homogeneous polyamide-additive product. Such mixing of the polyamide-additive main stream can occur within the

downstream line or in a separate chamber of the continuous polyamide

manufacturing system.

[0019] The additive can be any suitable additive. For example, the additive can be a polymerization catalyst, end-capping agent (e.g., to terminate polymerization), heat stabilizer (e.g., to help reduce or prevent heat-induced oxidation of the polymer), light stabilizer (e.g., to help reduce or prevent photo-oxidation of the polymer), lubricant (e.g., reduce stickiness, increase processability), anti- microbial agent, colorant, reinforcing agent (e.g., to add strength or rigidity to polymer), filler (e.g., to lower cost of polymer or to enhance properties of the polymer such as strength or rigidity), flame retardant agent, fluoropolymer (e.g., toughen, compatibilize, promote adhesion, or increase flexibility), antimony trioxide (e.g., flame retardant), polycapro lactone (e.g., increase processability or enhance impact resistance of product polymer), delusterant, titanium dioxide (e.g., anatase or rutile form, a delusterant at 0.0001 wt to about 0.05 wt or about 0.01 wt , a whitening colorant at about 0.05 wt to about 5 wt or about 0.1 wt to about 1 wt or about 0.1 wt to about 0.3 wt ), zinc sulfide (e.g., delusterant), or a combination thereof. The additive can be a dye, pigment, glass fiber, asbestos fiber, carbon fiber, aromatic polyamide fiber, gypsum fiber, calcium silicate, kaolin, calcined kaolin, wollastonite, talc, chalk, phosphate, phosphoric acid, phosphorous acid ester, phosphinic acid ester, phosphorous acid ester, organic phosphine oxide, sodium hypophosphite, acetic acid, propionic acid, benzoic acid, succinic acid, vinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene,

tetrafluoroethylene, perfluoroalkyl perfluorovinyl ether or a combination thereof. The additive can occur at any suitable concentration in the polymer, such as

0.000,001 g/L or less, 0.000,005 g/L, 0.000,01, 0.000,05, 0.000,1, 0.000,5, 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 30, 35, 40, 45, 50, 75, or about

100 g/L or more, or about 0.000,001 wt or less, or about 0.000,005 wt , 0.000,01, 0.000,05, 0.000,1, 0.000,5, 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 10, 15, or about 20 wt or more. The additive can be added to the main stream neat or diluted in a suitable carrier material, such as a solvent (e.g., water or an organic solvent) or such as a polymer carrier, such as a polymer carrier with substantially identical composition as the main polymer stream. The additive can be added to the main stream with 0.000,001 g additive/L carrier fluid or less, or 0.000,005 g/L, 0.000,01, 0.000,05, 0.000,1, 0.000,5, 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100, 150, 200, 250, 300, 350, 400, 450 g/L, or about 500 g/L or more, or about 0.001 -20 wt %, or about 0.01 -15 wt %, or about 0.01 -10 wt , or about 0.1 -10 wt , or about 0.1 - 9 wt , or about 0.01 - 8 wt , or about 0.01 - 7 wt %, or about 0.01 - 6 wt %, or about 0.01 -5 wt %, or about 0.1 - 3 wt %.

[0020] The side stream compounding unit can include a number of features or components. For example, side stream compounding unit can include at least one additive reservoir, at least one mixing chamber, one or more mixers, one or more heating units, one or more cooling units, one or more pumps, one or more valves, one or more detectors, one or more vents, and one or more connecting lines to facilitate movement of materials between at least one additive reservoir, at least one mixing chamber, and the continuous polyamide manufacturing system.

[0021] The side stream compounding unit can include one mixing chamber, or more than one mixing chamber. When more than one mixing chamber is present, the mixing chambers can be configured in series or in parallel. For example, mixing chambers configured in series can allow increasing amounts of substantially polymerized polyamide or additive to be sequentially introduced into a series of chambers containing different ratios of polyamide to additive. One chamber can accept or contain a selected ratio of molten polyamide to additive, and after the polyamide and additive are mixed, that mixture can be moved to a second chamber, where more substantially polymerized polyamide or additive is introduced. After mixing, the polyamide-additive mixture can be moved to a third chamber, where more substantially polymerized polyamide or additive is introduced, and so on. Such gradual addition can facilitate generation of a homogeneous polyamide- additive side mixture with optimal ratios of additive to polyamide, while avoiding side reactions, polymer degradation, gel formation, and inconsistencies in the physical and chemical properties not only of the polyamide-additive side mixture, but also in the final polyamide-additive product.

[0022] Thus, side stream compounding unit can include, and the processes described herein can involve, a number of mixing chambers maintained in series, for example, a series of 2-10 mixing chambers. One additive reservoir can be operably linked to the first mixing chamber in the series. Alternatively, each mixing chamber can independently be linked to a master additive reservoir or to a separate, individual additive reservoir. The structure of the side stream compounding unit can also be varied so that some mixing chambers are operably linked to one or more additive reservoirs, while other mixing chambers are not.

[0023] The side stream compounding unit can also include more than one mixing chamber, where the mixing chambers are configured in parallel. For example, different mixing chambers can separately be operably linked to different additive reservoirs. After addition and mixing of a different type of additive to each mixing chamber, the contents of the different mixing chambers can be emptied

independently into different downstream sites of a main polyamide flow line in the continuous polyamide manufacturing system. Alternatively, the contents of the different mixing chambers arranged in parallel can be emptied into a larger, master mixing chamber, which then is emptied into a downstream site of a main polyamide flow line in the continuous polyamide manufacturing system. Such a parallel arrangement of mixing chambers allows flexibility in merging different additives into different sites of a main stream of a polyamide polymerization reaction. For example, additives that could interact with each other in concentrated form can be handled separately and later merged in more dilute form into the main polyamide stream.

[0024] The side stream compounding unit can therefore include, and the processes described herein can involve, a number of mixing chambers maintained in parallel, for example, about 2-10 mixing chambers arranged in parallel. One or more of the mixing chambers configured in parallel can be operably linked to at least one additive reservoir. [0025] The one or more mixing chambers can each have at least one mixer. A variety of mixers can be employed such as a paddle mixer, a ribbon mixer, a helical mixer, a dual- shaft mixer, a planetary mixer, a double planetary mixer, a high speed disperser, a kneader, a double kneader, and the like.

[0026] The one or more mixing chambers can have vents to allow volatile components (e.g., water or additive solvent) to be removed. Such vents can also be present in one or more of the additive reservoirs.

[0027] The one or more mixing chambers can also be configured to maintain the mixture under reduced pressure.

[0028] The side stream compounding unit can be operably linked to a main polyamide flow line in the continuous polyamide manufacturing system to receive substantially polymerized polyamide from an upstream site in the system and return a polyamide-additive side mixture to a downstream site in the system.

[0029] The side stream compounding unit can be operably linked to a main polyamide flow line in the continuous polyamide manufacturing system via flow lines and valves. At least one inlet valve can be positioned at the upstream site in the main polyamide flow line to control the diversion of substantially polymerized polyamide into the side stream compounding unit. Such inlet valve(s) can be positioned close to the junction between a main flow line of the polyamide manufacturing system and a diversion flow line emptying into a mixing chamber of the side stream compounding unit. Such a configuration can reduce flow turbulence in the main flow line and avoid creation of a stagnant side pocket of polyamide (which may gel and clog the inlet valve or other parts of the unit or system).

[0030] In various embodiments, the side stream compounding unit can have a polished interior, to help prevent formation or adhering of gel therein. Any suitable portion of the interior of the side stream compounding unit and associated transfer lines and valves can be polished to any suitable degree, such that gel formation or adherence to the interior of one of more parts of the side stream compounding unit is reduced. The term "roughness average" (R _a ) is the measured average from the surface peaks and valleys of those irregularities and expressed in micrometers (μιη) and in micro-inches (μίη). Surface texture measurement is known to those of ordinary skill in the art and employs a surface profile instrument. A known surface profiler instrument is available from TAYLOR-HOBSON, a company of AMETEK, INC., 1100 Cassatt Road, P.O. Box 1764, Berwyn, Pennsylvania, 19312 USA. In some examples, the polished surface in the interior of the side stream compounding unit can any suitable average surface roughness, such as an average surface roughness of no greater than about 6.00 μιη, of between about 1.00 μιη and about 6.00 μιη, of between about 0.90 μιη and about 1.50 μιη, of between about 0.60 μιη and about 1.00 μιη, of no greater than about 0.5 μιη, of no greater than about 0.10 μιη, of between about 0.10 μιη and about 0.80 μιη, or of between about 0.90 μιη and about 1.50 μιη.

[0031] Additional inlet valves can be positioned at an entry to one or more mixing chambers of the side stream compounding unit to control or regulate the flow of substantially polymerized polyamide into the chamber(s).

[0032] One or more outlet valves can be positioned at the downstream site in the main polyamide flow line to control emptying of one or more mixing chambers and entry of the polyamide-additive side mixture into the main flow line of the polyamide manufacturing system. At least one outlet valve can be positioned close to the junction between the downstream site of a main flow line of the polyamide manufacturing system and a flow line that empties a mixing chamber of the side stream compounding unit. Such an outlet valve can be configured to reduce flow turbulence in the main flow line and avoid creation of a stagnant side pocket of polyamide (which may gel and clog parts of the downstream system).

[0033] The inlet and outlet valves can be operably linked to one or more detectors. For example, the inlet or outlet valves can be operably linked to a flow detector to allow monitoring of the volume or amount of material flowing through the valve. Thus, for example, a detector can be operably linked to an inlet valve so that the detector can monitor or regulate the volume of substantially polymerized polyamide flowing through the valve as it is diverted into the side stream

compounding unit. When the unit includes such a flow detector-inlet valve, the valve can be programmed to close when a selected volume of substantially polymerized polyamide is diverted into the side stream compounding unit. [0034] The inlet valve can alternatively or separately be operably linked to a detector in one or more of the mixing chambers. For example, such a mixing chamber detector can detect when a selected amount or volume of additive is present in a mixing chamber. When such a mixing chamber detector is operably linked to the inlet valve, the inlet valve can be actuated by the detector to open and divert substantially polymerized polyamide into a mixing chamber. Alternatively, a mixing chamber detector can detect when a selected amount or volume of substantially polymerized polyamide is present in a mixing chamber. When such mixing chamber detector is operably linked to the inlet valve, the mixing chamber detector can actuate the inlet valve to close so that the selected volume of substantially polymerized polyamide can be retained in a mixing chamber and mixed with additive. Combinations of detectors can therefore be used to control when one or more inlet valves open and close.

[0035] One or more outlet valves can be positioned at one or more exit lines leading from one or more mixing chambers of the side stream compounding unit to regulate the emptying of the mixing chamber(s). Similarly, an outlet valve can be positioned at the junction between the downstream site of a main flow line of the polyamide manufacturing system and a flow line that empties a mixing chamber of the side stream compounding unit.

[0036] The outlet valves can be operably linked to one or more detectors. For example, a detector can be positioned within a mixing chamber to monitor the temperature, pressure, or composition of the materials in a mixing chamber. In another example, a detector can be positioned in an exit line from a mixing chamber or at the junction of a flow line that empties the mixing chamber and the main flow line of the polyamide manufacturing system. A detector in the mixing chamber can, for example, detect when the additive and the substantially polymerized polyamide are mixed, or when the composition of materials in a mixing chamber has a selected composition, temperature or pressure. The mixing chamber detector can be operably linked to one or more outlet valves. One or more outlet valves can be opened when a selected composition, water content, composition homogeneity, temperature or pressure is detected by the detector in a mixing chamber. The mixing chamber detector can also be operably linked to one or more outlet valves to close the valves if the composition, temperature or pressure of the materials in a mixing chamber deviates from a selected composition, water content, composition homogeneity, temperature or pressure.

[0037] One or more flow-monitoring detectors can also be positioned in an exit line leading out of a mixing chamber, or to at the junction of a flow line that empties a mixing chamber and the main flow line of the polyamide manufacturing system. Such flow-monitoring detectors can be operably linked to one or more outlet valves to regulate the flow of the polyamide-additive side mixture into the downstream line of the polyamide manufacturing system. For example, such flow-monitoring detectors can actuate one or more outlet valves to reduce or increase the volume of polyamide-additive side mixture into the downstream line of the polyamide manufacturing system. Regulation of the outlet valves can therefore be mediated by detectors that detect the volume, composition, temperature or pressure of the polyamide-additive side mixture.

[0038] One or more additive valves can be positioned between the additive reservoir and a mixing chamber of the side stream compounding unit. Such additive valves can open and close to allow additive to flow into a selected mixing chamber. One or more detectors can be operably linked to the one or more additive valves. For example, detectors operably linked to one or more additive valves can detect the volume, composition, temperature or pressure of the additive and actuate opening or closing of the one or more additive valves. Thus, for example, when an appropriate additive volume has flowed into a mixing chamber, a flow-detector can actuate closing of one or more additive valves. When the temperature, composition or pressure of the additive is within a selected range or when a measured parameter crosses a threshold value, the additive valve can open to release additive into a mixing chamber. Similarly, when the temperature, composition or pressure of the additive is outside of a selected range, the additive valve can close or remain closed.

[0039] One or more additive valves can also be operably linked to one or more detectors in a mixing chamber. Detectors in a mixing chamber can detect the composition, temperature or pressure of the materials in the mixing chamber, as explained above. When the mixing chamber detectors detect a selected composition, temperature or pressure range, the mixing chamber detector can actuate one or more additive valves to open and release additive into the mixing chamber. The mixing chamber detector(s) can also be operably linked to one or more additive valves to close the valves if the composition, temperature or pressure of the materials in a mixing chamber deviates from a selected composition, temperature or pressure.

[0040] The side stream compounding unit can be configured to mix the materials in the mixing chamber for any suitable period of time, such that sufficient mixing has occurred to generate a substantially homogenous mixture that is ready to be returned to the main flow line. For example, the average time that substantially polymerized polyamide spends in the mixing chamber before being returned to the downstream line can be about 0.000,1 s to about 1 h, or about 0.001 s to about 30 min, or about 0.01 s to about 20 min, or about 0.000,1 s or less, or about 0.001 s, 0.01 s, 0.1 s, 0.5 s, 1 s, 2 s, 3 s, 4 s, 5 s, 10 s, 15 s, 20 s, 30 s, 40 s, 50 s, 1 min, 1.5 min, 2 min, 3 min, 4 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 40 min, 50 min, or about 1 h or more.

[0041] One or more heating units can be configured to maintain the temperature of materials within the side stream compounding unit. For example, the entire side stream compounding unit can be enclosed within a thermally regulated chamber. Alternatively, the temperatures of one or more additive reservoirs, one or more mixing chambers, one or more valves, and the various lines of the side stream compounding unit can be regulated separately by separate heating units.

[0042] Separate regulation of the temperature of different components of the side stream compounding unit has some advantages. For example, a mixing chamber can be heated above an additive reservoir to maintain substantially polymerized polyamide in the mixing chamber in a molten state while avoiding thermal decay of a thermally sensitive additive. If the additive is thermally sensitive, for example, it can be maintained at a lower temperature until just before entry into the mixing chamber. For example, the additive can be heated to a selected temperature by heating the additive in a line extending from the additive reservoir to the mixing chamber. A mixing chamber can also be heated above or below the temperature of an additive reservoir to facilitate mixing or reaction of materials in these

components of the unit.

[0043] Thus, the side stream compounding unit can include one or more flow line heating units, one or more mixing chamber heating units, one or more additive reservoir heating units, and one or more valve heating units.

[0044] The heating units can separately be operably coupled to a thermostat or other device that can actuate or terminate heat output to regulate the temperature of a component (e.g., flow line, mixing chamber, additive reservoir, or valve) in the side stream compounding unit.

[0045] One or more cooling units can also be operably linked to a component of the side stream compounding unit. Such cooling units can also be operably coupled to a thermostat to initiate or terminate cooling of a component of the side stream compounding unit. For example, a cooling unit can be configured to cool the additive reservoir, or facilitate regulation of the temperature in the additive reservoir. Although, the mixing chamber, valves and flow lines may only occasionally need cooling, cooling units can also be operably linked to these components as well, for example, so that the temperature of each component is maintained within specified limits.

[0046] One or mixers can be positioned with the mixing chambers or the additive reservoirs to mix materials therein. The mixers can facilitate mixing of the materials to homogeneity. The mixers can be regulated by one or more detectors to initiate mixing of the materials at selected speeds or within a selected time period. For example, if the additive water content is significantly different from the water content of the substantially polymerized polyamide, a detector the mixers can be actuated to initiate mixing of the more viscous substantially polymerized polyamide at an appropriate speed and the speed can be varied as more additive is introduced.

[0047] One or more pumps can be integrated into various flow lines and other components of the side stream compounding unit. For example, one or more pumps can be operably integrated into one or more flow lines leading from an upstream line in a continuous polyamide manufacturing system and into one or more mixing chambers. One or more pumps can be also operably integrated into one or more flow lines leading from an additive reservoir and into one or more mixing chambers. Similarly, one or more pumps can be operably integrated into one or more flow lines leading from one or more mixing chambers and into a downstream line in a continuous polyamide manufacturing system. One or more pumps can also be operably positioned between mixing chambers.

[0048] Accordingly, the side stream compounding unit can include a number of components including at least one additive reservoir, at least one mixing chamber, one or more mixers, one or more heating units, one or more cooling units, one or more pumps, one or more valves, one or more detectors, one or more vents, and one or more connecting lines to facilitate movement of materials between at least one additive reservoir, at least one mixing chamber and the continuous polyamide manufacturing system.

[0049] The downstream line in a continuous polyamide manufacturing system can also have one or more mixers such as one or more static mixers (in line), paddle mixers, ribbon mixers, kneaders, helical mixers, dual-shaft mixers, planetary mixers, double planetary mixers, high or low speed dispersers, double kneaders, and the like. See, e.g., Perry's Chemical Engineering Handbook, 5th Ed., at pages 19-22. The downstream line in a continuous polyamide manufacturing system can also have one or more separate mixing chambers to facilitate mixing of the additive- containing polymer mixture (the 'master batch') with the polymer in the

downstream line. Such downstream mixing chambers can also have a one or mixers, such as any of those described herein, or any mixer available to those of skill in the art.

[0050] The side stream compounding unit and methods of using such a unit provide uniform additive mixing, reduce contaminate introduction, avoid side product formation, and do not result in equipment fouling. Gel formation is avoided. Gel can form in stagnant pockets as well as irregularities or eddies in the flow of polymer through the system. The side stream compounding unit, and methods of using such a unit, facilitates flow and additive mixing into the polyamide. The side stream compounding unit also can reduce or avoid gel formation within the manufacturing system. Exemplary side stream compounding unit

[0051] FIG. 1 is a schematic diagram illustrating one example of a side stream compounding unit. The side stream compounding unit is operably linked to a continuous polyamide manufacturing system, for example, by a diversion flow line 20 and an outlet flow line 50 connected to a main polyamide flow line in the continuous polyamide manufacturing system. The side stream compounding unit can be downstream of a component 10 of the continuous polyamide manufacturing system. For example, the component 10 can be a flashing unit or a finishing unit of the continuous polyamide manufacturing system. Substantially polymerized polyamide without additive 60 can therefore be diverted into the side stream compounding unit and substantially polymerized polyamide with additive 70 can be removed or flow out of the side stream compounding unit. Valves such as valves 15, 25, 35, and 45 can regulate the flow of materials (e.g., additive or substantially polymerized polyamide) from one region or component of the side stream compounding unit to another. For example, substantially polymerized polyamide can be diverted by a diversion flow line 20 into a mixing chamber 30. Additive can also flow into the mixing chamber 30 from an additive reservoir 40, where mixing can occur. The side stream compounding unit can therefore produce substantially polymerized polyamide with additive 70. Polyamide manufacture

[0052] The term "polyamide" means a polymer containing a plurality of amide linkages. Polyamides, for example, aliphatic polyamides having at least 85 per cent aliphatic linkages between repeating amide units are also known as nylon. The term "linear" means that the polyamides are obtainable from bifunctional reactants where the structural units are linked end-to-end and in chain- like fashion. As such, this term is intended to exclude three-dimensional polymeric structures that might be present in polymers derived from triamines or from tribasic acids.

[0053] The aliphatic polyamides can be obtained from dibasic carboxylic acids and other amide-forming derivatives of dibasic carboxylic acids such as anhydrides, amides, acid halides, half esters, and diesters; when reacted with a primary or secondary amine. The formation of substantially all aliphatic polyamides polymers, from monomers consisting of dicarboxylic acids and diamines, can be accomplished by reaction of a primary or secondary diamine (diamines having at least one hydrogen attached to each nitrogen) and either a dicarboxylic acid or an amide- forming derivative of a dibasic carboxylic acid.

HOOC-R-COOH + H ₂ N-R'-NH ₂ → -[NH-R'-NH-CO-R-CO] _m - + nH ₂ 0 where R and R' represent divalent hydrocarbon radicals.

[0054] The product generated is composed of long chains built up from a series of identical units consisting of:

-NH-R'-NH-CO-R-CO- where water is the only co-product of polymer formation.

[0055] Carothers introduced a naming convention for diamine and diacid polyamides which was adopted into use. As a result, the "structural unit" of the polymer derived from one molecule each of diacid and diamine was named for the number of carbon atoms in the respective radicals, R and R'. Naming the polyamide from hexamethylene-l,6-diamine and adipic acid "nylon 6,6" (polyhexamethylene adipamide) was a consequence of this convention.

[0056] Commercial processes for preparing polyamides can include continuously passing an aqueous solution of a diamine-dibasic carboxylic acid salt at super- atmospheric pressure through a continuous reaction zone. See, e.g., U.S. Patent No 2,361,717 to Taylor; U.S. Patent No. 2,689, 839 to Heckert.

[0057] Polyamides can be prepared by heating substantially equimolecular amounts of diamine and dicarboxylic acid or an amide forming derivative of a dibasic carboxylic acid under condensation polymerization conditions. Such condensation polymerization conditions generally include temperatures of about 180°C to 300° C.

[0058] For example, in a nylon 6,6 process, the continuous polymerization reactor can be fed an aqueous solution of hexamethylene diammonium adipate (nylon 6,6 salt) having a concentration in a range of between 35 and 65% by weight. The concentration of hexamethylene diammonium adipate is adjustable in an optional evaporator upstream of the reactor. The effluent from the flasher stage (which is also referred to as the secondary reactor) includes polyamide pre-polymer, typically with a relative viscosity of about 9-20. This stream is fed into a finishing apparatus. Control variables in the finishing apparatus can include temperature, pressure and hold-up volume. These control variables are adjustable such that a final polymer of the desired relative viscosity, typically in the range of 30 to 100, is obtained. Temperature in the finishing apparatus is maintained in the range of 270° to 290° C. Pressure is maintained at 250 to 640 millibars. Hold-up volumes are approximately 20 to 40 minutes.

[0059] The product has fiber- forming properties when a sufficiently high molecular weight is achieved. For example, such fiber-forming occurs when polyamides have an intrinsic viscosity range of about 0.5 and 2.0; as measured in m- cresol solution.

[0060] Polymerization is complete when the desired degree of polymerization is achieved. The degree of polymerization is indirectly expressed in terms of polymer viscosity. The degree of polymerization, often measured as relative viscosity or RV, is a proxy measurement for viscosity and molecular weight in turn.

[0061] At elevated temperatures, the degree of polymerization is a function of and is limited by the amount of water present. A dynamic equilibrium exists between polymer and water on the one hand, and depolymerized polymer (or even the reactants) on the other. Polyamides having an RV considerably higher than that attainable through equilibration with steam at atmospheric pressure are often desirable.

[0062] The properties of a given polyamide can vary, especially with the molecular weight of the polyamide. The polyamide properties are also influenced by the nature of its terminal groups, which in turn is dependent upon which reactant is used in excess, the diamine or the diacid.

[0063] The average molecular weight of a polyamides can be difficult to determine, but precise knowledge of average molecular weights is generally not important for most purposes. Others have recognized that roughly two stages or degrees of polymerization exist: low polymers whose molecular weights probably lie in the neighborhood of 1000 to 4000, and fiber forming polyamides whose molecular weights probably lie above at least 7000. A distinction between low polymers and the high polymers or "superpolymers" is that the former when molten are relatively less viscous. The high polymers are quite viscous, even at

temperatures 25° C above their melting points.

[0064] In contrast to low polymers, the high polymers of polyamides are readily spun into strong, continuous, pliable, permanently oriented fibers. However, the low polymers, for example those having a smaller unit length than about 9, can be converted into high polymers by continuing the polymerization reaction.

[0065] Fiber- forming polyamides generally have high melting points and low solubility. Those derived from the simpler types of amines and acids are generally opaque solids that melt or become transparent at a fairly definite temperatures. Below their melting points the fiber-forming polyamides generally exhibit sharp X- ray crystalline powder diffraction patterns, which is evidence of their crystalline structure. The densities of these polyamides generally lie between 1.0 and 1.2. The density of nylon 6,6 is usually identified as 1.14 grams per cubic centimeter.

[0066] Polyamides can have individual units of similar structure. The average size of these individual units, the average molecular weight of the polymer, is subject to deliberate control within certain limits. The further the polymerization reaction has progressed, the higher the average molecular weight (and intrinsic viscosity) will be. If the reactants are used in exactly equimolecular amounts during polymerization, and heating is continued for a long time under conditions that permit the escape of the volatile products, polyamides of very high molecular weight are obtained. However, if either reactant is used in excess, the

polymerization can proceed to a certain point and then essentially stop. A point at which polymerization ceases is dependent upon the amount of diamine or dibasic acid (or derivative) used in excess.

[0067] A convenient method of preparing polyamides can include making a salt by mixing approximately chemically equivalent amounts of the diamine and the dicarboxylic acid in a liquid. The liquid can be a poor solvent for the resultant salt. The salt that separates from the liquid can then be purified, if desired, by crystallization from a suitable solvent. These diamine-dicarboxylic acid salts are crystalline and have definite melting points. They are soluble in water and can be crystallized from certain alcohols and alcohol- water mixtures.

[0068] The preparation of fiber- forming polyamides from the diamine- dicarboxylic acid salts can be carried out in a number of ways. The salt can be heated in the absence of a solvent or diluent to a reaction temperature (180° - 300° C) under conditions that permit the removal of the water formed in the reaction.

[0069] The polyamide polymerization reaction can be subjected to reduced pressure, for example, an absolute pressure equivalent to 50 to 300 mm of mercury (67 to 400 millibar) to facilitate substantially complete polymerization. For example, the reaction vessel in which the polyamide is prepared can be evacuated before allowing the polymer to solidify.

[0070] In general, no added catalysts are required in the above described processes of polyamide formation. However, certain phosphorus containing materials can exert a certain degree of catalytic function. The phosphorus containing materials can include metal phosphonates. The use of added catalysts can facilitate production of high molecular weight materials. Test Methods

[0071] Thermal degradation index (TDI) is a measurement that correlates with a polymer's thermal history. A lower TDI indicates less severe temperature history during manufacture. A TDI determination method available to the skilled person measures the optical absorbance of a 1% (by weight) solution of the polymer in 90% formic acid at a wavelength of 292 nm.

[0072] Oxidative degradation index (ODI) is a measurement that correlates with a polymer's exposure to oxidizing conditions during its high temperature manufacture. A lower ODI indicates less severe oxidative degradation during manufacture. It is determined by measuring the optical absorbance of a 1% (by weight) solution of the polymer in 90% formic acid at a wavelength of 260 nm.

[0073] Relative viscosity (RV) refers to the ratio of solution and solvent viscosities measured in a capillary viscometer at 25° C. RV by ASTM D789-06 is the basis for this test procedure and is the ratio of viscosity (in centipoises) at 25 °C. of 8.4% by weight solution of polyamide in 90% formic acid (90% by weight formic acid and 10% by weight water) to the viscosity (in centipoises) at 25°C of 90% formic acid alone.

Definitions

[0074] The term "about" as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

[0075] The term "substantially" as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

[0076] The term "solvent" as used herein refers to a liquid that can dissolve a solid, liquid, or gas. Nonlimiting examples of solvents are silicones, organic compounds, water, alcohols, ionic liquids, and supercritical fluids.

[0077] The term "air" as used herein refers to a mixture of gases with a composition approximately identical to the native composition of gases taken from the atmosphere, generally at ground level. In some examples, air is taken from the ambient surroundings. Air has a composition that includes approximately 78% nitrogen, 21% oxygen, 1% argon, and 0.04% carbon dioxide, as well as small amounts of other gases.

[0078] Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of "about 0.1% to about 5%" or "about 0.1% to 5%" should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement "about X to Y" has the same meaning as "about X to about Y," unless indicated otherwise. Likewise, the statement "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z," unless indicated otherwise.

[0079] In this document, the terms "a," "an," or "the" are used to include one or more than one unless the context clearly dictates otherwise. The term "or" is used to refer to a nonexclusive "or" unless otherwise indicated. In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

[0080] The polyamide side stream unit and a process of making polyamides using such a unit are illustrated by the following Examples, which are intended to be purely exemplary and not limiting of the invention.

EXAMPLES

[0081] Continuous polymerization process. The following process is performed in the Examples. In a continuous nylon 6,6 manufacturing process, adipic acid and hexamethylenediamine are combined in a salt strike in an approximately equimolar ratio in water to form an aqueous mixture containing nylon 6,6 salt having about 50 wt% water. The aqueous salt is transferred to an evaporator. The evaporator heats the aqueous salt to about 125-135 °C (130 °C) and removes water from the heated aqueous salt, bringing the water concentration to about 30 wt%. The evaporated salt mixture, having a relative viscosity of about of about 1.4-1.9 (1.6), is transferred to a reactor. The reactor brings the temperature of the evaporated salt mixture to about 218-250 °C (235 °C), allowing the reactor to further remove water from the heated evaporated salt mixture, bringing the water concentration to about 10 wt%, and causing the salt to further polymerize. The reacted mixture is transferred to a flasher. The flasher heats the reacted mixture to about 270-290 °C (280 °C), allowing the flasher to further remove water from the reacted mixture, bringing the water concentration to about 0.5 wt%, and causing the reacted mixture to further polymerize. The flashed mixture, having a relative viscosity of about 9 to 20 (13), is transferred to a finisher. The finisher subjects the polymeric mixture to a vacuum to further remove water, bringing the water concentration to about 0.1 wt%, such that the polyamide achieves a suitable final range of degree of polymerization before transferring the finished polymeric mixture to an extruder and a pelletizer.

Example la: Addition of Additives to Partially Polymerized Nylon

[0082] A 10% aqueous suspension of titanium dioxide anatase form additive preheated to 130° C is pumped into the partially- formed polyamide solution that exits the evaporator, the time interval from heating to injecting being not greater than 30 seconds. The polyamide stream exiting the evaporator has a flow rate of about 75 L/min, the 10% additive steam has a flow rate of about 1.7 L/min. These merging streams flow into the reactor. The polymer exiting the finisher at 59 L/min has an intrinsic viscosity of 0.9 and contains 0.3 wt% of the additive.

[0083] After operating for 12 weeks the system is shut down. Significant deposits of additive are observed in the flasher and other downstream parts. The titanium dioxide agent coats out on the heat transfer surfaces with an average thickness of about 0.2 mm, reducing the efficiency of heat transfer in the process. Example lb: Addition of Additives to Partially Polymerized Nylon in the

Extruder

[0084] A side stream additive unit is located downstream from the flasher. An inlet valve is opened to divert about 5 wt of the substantially polymerized nylon from a main stream of nylon into a mixing chamber of the side stream additive unit. The mixing chamber is uniformly heated to a temperature equivalent to the substantially polymerized nylon in the main stream (about 280 °C). The mixing chamber mixes titanium dioxide anatase form additive with the diverted

substantially polymerized nylon to form a homogeneous additive stream with a water content of about 0.1-0.2 wt and a temperature of about 280 °C. The polymer mixture flows through the mixing chamber at about 3 L/min, has an average total residence time in the mixing chamber of about 10 minutes, and attains a titanium dioxide concentration of about 6 wt . The homogeneous nylon- additive stream passes through an outlet valve to rejoin the main stream in a polyamide extruder, which extrudes the polyamide into strands. The pressure of the material entering the mixing chamber is affected by the pressure of the material leaving the flasher, and the pressure of the material exiting the mixing chamber is affected by the pressure of the material in the extruder. Small variations in pressure between the exiting material from the flasher and the material in the extruder cause pressure variations in the mixing chamber, making it difficult to consistently maintain forward flow of the additive from the additive chamber. Blowbacks of polymer mixture into the additive inlet occur, fouling the additive feed apparatus with polymer mixture, requiring the additive system to be taken offline for cleaning. The final product has an average concentration of the titanium dioxide of about 0.3 wt ; however, due to the proximity of additive addition to the extrusion process, mixing of the additive in the main stream is not thorough and consistent, giving pellets with varying additive concentration, and correspondingly lowering product quality.

Example lc: Addition of Additives to Partially Polymerized Nylon using a Pre-

Made Nylon 6,6 Carrier Fluid

[0085] A side stream additive unit is located downstream from the flasher. An additive unit mixes titanium dioxide anatase form additive with a pre-made nylon 6,6 polymer carrier fluid for addition to the main stream. The mixing chamber of the additive unit is uniformly heated to a temperature equivalent to the substantially polymerized nylon in the main stream (about 280 °C). The mixing chamber generates a homogeneous additive stream with a water content of about 0.1-0.2 wt and a temperature of about 280 °C. The polymer mixture in the mixing chamber has a titanium dioxide concentration of about 6 wt . The polymer mixture flows from the mixing chamber, out of the additive unit, and into the main stream upstream of the extruder at about 3 L/min. The polymer mixture has an average total residence time in the mixing chamber of about 10 minutes. The final product has a concentration of the titanium dioxide of about 0.3 wt . The degree of

polymerization of the nylon 6,6 carrier fluid is not a perfect match at all times to the degree of polymerization of the nylon 6,6 in the main stream. Adding the additive to the main stream in the pre-made nylon 6,6 carrier fluid causes variation in the degree of polymerization of the nylon 6,6 product, lowering product quality.

Example Id: Addition of Additives to Partially Polymerized Nylon using a

Nylon 6 Carrier Fluid

[0086] A side stream additive unit is located downstream from the flasher. An additive unit mixes titanium dioxide anatase form additive with a pre-made nylon 6 polymer carrier fluid for addition to the main stream. The mixing chamber of the additive unit is uniformly heated to a temperature equivalent to the substantially polymerized nylon in the main stream (about 280 °C). The mixing chamber generates a homogeneous additive stream with a water content of about 0.1-0.2 wt and a temperature of about 280 °C. The polymer mixture in the mixing chamber has an average total residence time in the mixing chamber of about 10 minutes and has a titanium dioxide concentration of about 6 wt . The polymer mixture flows from the mixing chamber, out of the additive unit, and into the main stream upstream of the extruder at about 3 L/min. The final product has a concentration of the titanium dioxide of about 0.3 wt . The nylon 6 carrier fluid is a different polymer than the nylon 6,6 main stream. Adding the additive to the main stream in the nylon 6 adds a nylon 6 impurity to the nylon 6,6 product, lowering product quality. Example 2: Improved Method for Additive Addition to Substantially

Polymerized Nylon

[0087] A side stream additive unit is located downstream from the flasher. An inlet valve is opened to divert about 5 wt of the substantially polymerized nylon from a main stream of nylon into a mixing chamber of the side stream additive unit. The mixing chamber is uniformly heated to a temperature equivalent to the substantially polymerized nylon in the main stream (about 280 °C). The mixing chamber includes a device for mixing the titanium dioxide with the substantially polymerized nylon to form a homogeneous nylon- additive stream with a water content of about 0.1-0.2 wt and a temperature of about 280 °C. The polymer mixture flows through the mixing chamber at about 3 L/min, has an average total residence time in the mixing chamber of about 10 minutes, and attains a titanium dioxide concentration of about 6 wt . The homogeneous nylon- additive stream passes through an outlet valve to rejoin the main stream upstream of the extruder. The final product has a concentration of the titanium dioxide of about 0.3 wt .

[0088] After operating for 12 weeks the system is shut down. No additive deposits are observed upstream of the extruder. The heat transfer surfaces are free of additive and less gel formation is observed at locations where additive had accumulated in the process described in Example la. Little pressure variation occurs between the inlet of the mixing chamber and the outlet of the mixing chamber, making forward flow of the additive into the mixing chamber easy to maintain, avoiding polymer blowbacks into the additive inlet, as contrasted with Example lb. Since the carrier fluid for the additive is taken from the main nylon 6,6 stream, the degree of polymerization is an exact match, causing no degradation in product quality, as contrasted with Examples lc and Id. [0089] All patents and publications referenced or mentioned herein are indicative of the levels of skill of those skilled in the art to which the present subject matter pertains, and each such referenced patent or publication is hereby specifically incorporated by reference to the same extent as if it had been incorporated by reference in its entirety individually or set forth herein in its entirety. Applicants reserve the right to physically incorporate into this specification any and all materials and information from any such cited patents or publications.

[0090] The specific methods, devices and compositions described herein are representative of preferred embodiments and are examples and not intended as limitations on the scope of the present subject matter. Other objects, aspects, and embodiments will occur to those skilled in the art upon consideration of this specification, and are encompassed by the present subject matter. It will be readily apparent to one skilled in the art that varying substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention.

[0091] The present subject matter illustratively described herein suitably may be practiced in the absence of any element or elements, or limitation or limitations, which is not specifically disclosed herein as essential. The methods and processes illustratively described herein suitably may be practiced in differing orders of steps, and the methods and processes are not necessarily restricted to the orders of steps indicated herein or in the claims.

[0092] Under no circumstances may the patent be interpreted to be limited to the specific examples or embodiments or methods specifically disclosed herein. Under no circumstances may the patent be interpreted to be limited by any statement made by any Examiner or any other official or employee of the Patent and Trademark

Office unless such statement is specifically and without qualification or reservation expressly adopted in a responsive writing by Applicants.

[0093] The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intent in the use of such terms and expressions to exclude any equivalent of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention as claimed. Thus, it will be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims and statements of the invention.

[0094] The invention has been described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

Statements:

[0095] 1. A method for mixing additives into a polyamide polymer stream comprising:

(a) diverting substantially polymerized polyamide from an upstream line in a continuous polyamide manufacturing system to generate a polyamide side stream;

(b) mixing an additive into the polyamide side stream to generate a polyamide-additive side mixture; and

(c) returning the polyamide-additive side mixture to a downstream line in the system to generate a polyamide-additive main stream;

wherein, upon diversion, the substantially polymerized polyamide from the upstream line has a water content of about 0.1% - 3 wt%.

[0096] 2. The method of statement 1, wherein upon diversion, the substantially polymerized polyamide in the upstream line has a water content of about 0.1 - 2 wt%. [0097] 3. The method of statement 1 or 2, wherein upon diversion, the substantially polymerized polyamide in the upstream line has a water content of about 0.1 - 1 wt%.

[0098] 4. The method of any of statements 1-3, wherein the additive contains a solvent, and the solvent is substantially removed from the polyamide-additive side mixture prior to return to the downstream line.

[0099] 5. The method of any of statements 1-4, wherein water is removed from the polyamide-additive side mixture prior to return to the downstream line.

[00100] 6. The method of any of statements 1-5, wherein the polyamide- additive side mixture is returned downstream when it has a water content that is 0.9 - 1.1 times the polyamide water content in the downstream line.

[00101] 7. The method of any of statements 1-6, wherein the weight percent additive in the polyamide-additive side mixture is about 0.001 -20 wt , or about 0.01 -15 wt %, or about 0.01 -10 wt %, or about 0.1 -10 wt %, or about 0.1 - 9 wt %, or about 0.01 - 8 wt %, or about 0.01 - 7 wt %, or about 0.01 - 6 wt %, or about 0.01 -5 wt %, or about 0.1 - 3 wt %.

[00102] 8. The method of any of statements 1-7, wherein the weight percent additive in the polyamide-additive main stream is about 1-5 wt .

[00103] 9. The method of any of statements 1-8, wherein the continuous polyamide manufacturing system comprises a reactant reservoir, evaporator, polymerization reactor, batch reactor flasher, finisher, polyamide strand forming unit, extruder, and combinations thereof.

[00104] 10. The method of any of statements 1-9, wherein the diverting from the upstream line is after a polyamide polymerization reaction mixture has passed through a flasher in the system.

[00105] 11. The method of any of statements 1-10, wherein the polyamide- additive side mixture is returned downstream after a flasher in the system.

[00106] 12. The method of any of statements 1-11, wherein the diverting from the upstream line is after a polyamide polymerization reaction mixture has passed through a finisher in the system. [00107] 13. The method of any of statements 1-12, wherein the polyamide- additive side mixture is returned downstream after a polyamide polymerization reaction has passed through a finisher.

[00108] 14. The method of any of statements 1-13, wherein the polyamide- additive side mixture is returned to the main polyamide flow line prior to a polyamide strand forming unit in the system.

[00109] 15. The method of any of statements 1-14, wherein the polyamide- additive side mixture is returned to the main polyamide flow line prior to extrusion of polyamide through an extruder.

[00110] 16. The method of any of statements 1-15, further comprising mixing the polyamide-additive main stream after returning the polyamide-additive side mixture to the downstream line.

[00111] 17. The method of any of statements 1-16, further comprising mixing the polyamide-additive main stream to homogeneity after returning the polyamide- additive side mixture to the downstream line.

[00112] 18. The method of any of statements 1-17, wherein after return of the polyamide-additive side mixture to the downstream line of the system, the polyamide-additive main stream is mixed in a mixing unit of the system.

[00113] 19. The method of any of statements 1-18, wherein the additive is a polymerization catalyst, end-capping agent, heat stabilizer, light stabilizer, lubricant, anti- microbial agent, colorant, reinforcing agent, filler, flame retardant agent, fluoropolymer, antimony trioxide, polycaprolactone, zinc sulfide, delusterant, titanium dioxide, or a combination thereof.

[00114] 20. The method of any of statements 1-19, wherein the additive is a dye, pigment, glass fiber, asbestos fiber, carbon fiber, aromatic polyamide fiber, gypsum fiber, calcium silicate, kaolin, calcined kaolin, wollastonite, talc, chalk, phosphate, phosphoric acid, phosphorous acid ester, phosphinic acid ester, phosphorous acid ester, organic phosphine oxide, sodium hypophosphite, acetic acid, propionic acid, benzoic acid, succinic acid, vinylidene fluoride, hexafluoropropylene,

chlorotrifluoroethylene, tetrafluoroethylene, perfluoroalkyl perfluorovinyl ether or a combination thereof. [00115] 21. The method of any of statements 1-20, wherein the additive is heated prior to mixing with the polyamide side stream.

[00116] 22. A continuous polyamide manufacturing system comprising

a side stream compounding unit with at least one upstream inlet, at least one mixing chamber, and at least one downstream outlet;

wherein the side stream compounding unit is positioned or configured parallel to a main polyamide flow line of the continuous polyamide manufacturing system;

wherein the at least one mixing chamber is configured to mix an additive with substantially polymerized polyamide diverted through at least one of the upstream inlets; and

wherein each of the downstream outlets is positioned upstream of a polyamide extruder or a polyamide strand forming unit.

[00117] 23. The system of statement 22, wherein each of the upstream inlets is configured to divert substantially polymerized polyamide from the main polyamide flow line at a position in the main polyamide flow line between a flasher unit and the polyamide extruder unit or the polyamide strand forming unit in the system.

[00118] 24. The system of statement 22 or 23, wherein each of the upstream inlets is configured to divert substantially polymerized polyamide from the main polyamide flow line at a position in the main polyamide flow line between a finisher unit and the polyamide extruder unit or the polyamide strand forming unit in the system.

[00119] 25. The system of any of statements 22-24, wherein at least one of the upstream inlets comprises a detector to detect an amount or volume of the substantially polymerized polyamide diverted into the mixing chamber of the side stream compounding unit.

[00120] 26. The system of any of statements 22-25, wherein at least one of the upstream inlets is operably linked to a detector that closes the operably linked upstream inlet when a selected amount or volume of the substantially polymerized polyamide is diverted into at least one mixing chamber of the side stream

compounding unit. [00121] 27. The system of any of statements 22-26, wherein at least one of the upstream inlets is operably linked to a detector that detects the substantially polymerized polyamide water content in the main polyamide flow line.

[00122] 28. The system of any of statements 22-27, wherein at least one of the upstream inlets is operably linked to a detector that detects the substantially polymerized polyamide water content in the main polyamide flow line, and wherein the detector opens at least one of the upstream inlets when a selected substantially polymerized polyamide water content is detected.

[00123] 29. The system of any of statements 22-28, wherein at least one of the mixing chambers comprises a mixer configured to mix the additive and the substantially polymerized polyamide to homogeneity.

[00124] 30. The system of any of statements 22-29, wherein at least one of the mixing chambers comprises a mixer operably linked to a detector configured to detect how uniformly the additive and the substantially polymerized polyamide are mixed.

[00125] 31. The system of any of statements 22-30, wherein the downstream outlet is operably linked to a detector configured to open the downstream outlet when the additive and the substantially polymerized polyamide are uniformly mixed.

[00126] 32. The system of any of statements 22-31, wherein the side stream compounding unit comprises a heater configured to uniformly heat at least one of the mixing chambers.

[00127] 33. The system of any of statements 22-32, wherein the side stream compounding unit comprises a heater configured to uniformly heat at least one of the mixing chambers and to maintain a mixture of additive and substantially polymerized polyamide in a molten state within the heated mixing chamber.

[00128] 34. The system of any of statements 22-33, wherein the side stream compounding unit comprises a heater configured to uniformly heat at least one of the mixing chambers and to promote further polymerization of substantially polymerized polyamide as it is mixed with the additive. [00129] 35. The system of any of statements 22-34, wherein the side stream compounding unit comprises at least one additive reservoir.

[00130] 36. The system of any of statements 22-35, wherein the side stream compounding unit comprises a heater configured to uniformly heat the additive before the additive is mixed with substantially polymerized polyamide.

[00131] 37. The system of any of statements 22-36, wherein the side stream compounding unit comprises a heater with a thermostat configured to regulate the temperature of materials in at least one of the mixing chambers or at least one additive reservoir.

[00132] 38. The system of any of statements 22-37, wherein the side stream compounding unit further comprises a detector to monitor the water content of a mixture comprising the substantially polymerized polyamide in a mixing chamber.

[00133] 39. The system of any of statements 22-38, wherein at least one of the downstream outlets is operably linked to a water content detector that activates release of a mixture of additive and substantially polymerized polyamide through the outlet and into a main polyamide flow line of the system when a selected water content of the mixture is detected.

[00134] 40. The system of any statements 22-39, wherein the side stream further comprises a pump, an impeller, a flow meter, one or more vents, or a combination thereof.

[00135] 41. The system of any statements 22-40, wherein at least one of the upstream inlets is operably linked to a detector that detects water content of the substantially polymerized polyamide.

[00136] 42. The system of any statements 22-41, wherein the substantially polymerized polyamide is diverted through at least one of the upstream inlets when the substantially polymerized polyamide has a water content of about 0.1% - 3 wt%.

[00137] 43. The system of any statements 22-42, wherein the substantially polymerized polyamide is diverted through at least one of the upstream inlets when the substantially polymerized polyamide has a water content of about 0.1 - 2 wt%. [00138] 44. The system of any statements 22-43, wherein the substantially polymerized polyamide is diverted through at least one of the upstream inlets when the substantially polymerized polyamide has a water content of about 0.1 - 1 wt .

[00139] 45. The system of any of statements 22-44, wherein at least one mixing chambers has a vent.

[00140] 46. The system of any of statements 22-45, wherein at least one of the mixing chambers has a vent through which additive solvent, water or a combination thereof can pass.

[00141] 47. The system of any statements 22-46, wherein at least one of the downstream outlets is operably linked to a detector that detects water content of a mixture in a mixing chamber.

[00142] 48. The system of any of statements 22-47, wherein the polyamide- additive side mixture is returned downstream when it has a water content that is 0.9 - 1.1 times the polyamide water content in the downstream line.

[00143] 49. The system of any of statements 22-48, wherein the continuous polyamide manufacturing system comprises a reactant reservoir, evaporator, polymerization reactor, batch reactor flasher, finisher, polyamide strand forming unit, extruder, or combinations thereof.

[00144] 50. The system of any of statements 22-49, wherein the main polyamide flow line comprises a mixer positioned in the main polyamide flow line after the downstream outlet.

[00145] 51. The system of any of statements 22-50, wherein the continuous polyamide manufacturing system further comprises a mixing unit positioned in the main polyamide flow line after the downstream outlet.

[00146] 52. The system of any of statements 22-51, wherein the additive is a polymerization catalyst, end-capping agent, heat stabilizer, light stabilizer, lubricant, anti- microbial agent, colorant, reinforcing agent, filler, flame retardant agent, fluoropolymer, antimony trioxide, polycaprolactone, zinc sulfide, delusterant, titanium dioxide, or a combination thereof.

[00147] 53. The system of any of statements 22-52, wherein the additive is a dye, pigment, glass fiber, asbestos fiber, carbon fiber, aromatic polyamide fiber, gypsum fiber, calcium silicate, kaolin, calcined kaolin, wollastonite, talc, chalk, phosphate, phosphoric acid, phosphorous acid ester, phosphinic acid ester, phosphorous acid ester, organic phosphine oxide, sodium hypophosphite, acetic acid, propionic acid, benzoic acid, succinic acid, vinylidene fluoride, hexafluoropropylene,

chlorotrifluoroethylene, tetrafluoroethylene, perfluoroalkyl perfluorovinyl ether or a combination thereof.

[00148] 54. The system of any of statements 22-53, wherein the weight percent additive in the polyamide-additive side mixture is about 0.001 -20 wt , or about 0.01 -15 wt %, or about 0.01 -10 wt %, or about 0.1 -10 wt %, or about 0.1 - 9 wt %, or about 0.01 - 8 wt %, or about 0.01 - 7 wt %, or about 0.01 - 6 wt %, or about 0.01 -5 wt %, or about 0.1 - 3 wt %.

[00149] The following claims summarize features of the systems and methods described herein.