METHOD AND SYSTEM FOR WET-CUTTING AND DRYING POLYAMIDE PELLETS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Provisional Patent 5 Application Serial No. 61/818,100, filed May 1, 2013, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

10 [0002] Polyamide is commonly manufactured from subunits in a reaction where water is progressively removed to drive the polymerization reaction forward. The process generates long viscous polymers that are often extruded into strands to permit further processing. Upon hardening the strands can be cut into pellets, also called flakes or granules. Unlike strands or bars, pellets can readily flow, can be

15 easily packaged, and later can be melted to form useful articles. Hence, pellets are a convenient commercial form of polyamide.

[0003] To allow extrusion, the viscous polyamide is heated to maintain it in a molten state. Upon extrusion, the strands are quickly cooled to stabilize the strands and accelerate their hardening in preparation for cutting. Water is a useful medium

20 for cooling polyamide strands. Hence, polyamide strands are often submerged in water or sprayed with water just after extrusion. Similarly, a wet pelletizer is often used to cut the polyamide strands into pellets. However, polyamide is somewhat hygroscopic. Extended exposure to water, especially at high temperatures, can lead to partial degradation, fusion, and changes in the properties of polyamide. Excessive

25 exposure to heat can cause polyamide yellowing. Polyamide pellets therefore should be quickly separated from the wet strands and from the wet pelletizer for drying at appropriate temperature to generate a useful commercial product. However, while pellet drying ideally occurs rapidly, it should not be done under conditions that give rise to yellowing, nor should it be done so slowly that substantial degradation,

30 hydrolysis, and pellet fusion occur. SUMMARY

[0004] The problems of quickly removing polyamide pellets from water sources and drying the pellets under appropriate conditions are solved by the systems and processes described herein. The water introduced by strand cooling and wet cut pelletization is substantially surface water. The centers of pellets generally have acceptable water content unless the pellets are exposed to moisture from strand cooling or pelletization for substantial periods of time. Hence, transport of the pellets from sites where water can be introduced solves part of the problem. A pellet spin dryer can be used to remove the majority of surface water. However, use of a spin dryer alone may not be adequate. To dry pellets sufficiently, a long pellet residence time in a spin dryer can be needed, or the spin dryer may need to be operated at high temperatures. A long residence time slows production. Use of high temperatures can cause pellet yellowing. Long residence times and high

temperatures also require use of significant energy.

[0005] These problems are solved by use of two drying devices: a spin dryer to remove the majority of water, and a sub-transport fluid bed dryer to dry the pellets to specification.

[0006] One aspect of the present subject matter is a system for manufacturing polyamide pellets comprising:

a) a spin dryer that removes a majority of surface water from wet polyamide pellets to generate partially dried pellets; and

b) a fluid bed dryer that dries and transports the partially dried pellets from the spin dryer to produce dried polyamide pellets.

[0007] Another aspect of the present subject matter is a system for manufacturing polyamide pellets comprising:

a) a wet-cut pelletizer that is configured to cut polyamide strands in water to generate pellets with a water layer on the exterior of the pellets; b) a spin dryer that flashes off the water layer; and

c) a fluid bed dryer that dries and transports the pellets from the spin dryer. [0008] Another aspect of the present subject matter is a method comprising: a) spin drying wet polyamide pellets to remove a majority of surface water from the wet polyamide pellets and generate partially dried pellets; and

b) further drying the partially dried pellets in a fluid bed dryer that dries and transports the pellets from the spin dryer.

[0009] Another aspect of the present subject matter is a method comprising:

a) wet-cutting polyamide strands in the presence of water to generate pellets with a water layer on the exterior of the pellets;

b) a spin drying the pellets to flash the water layer and generate partially dried pellets; and

c) further drying the partially dried pellets in a fluid bed dryer that dries and transports the pellets from the spin dryer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is an schematic diagram illustrating features of the drying systems described herein for continuous polyamide manufacturing systems, in accordance with various embodiments. DETAILED DESCRIPTION

[0011] Systems and processes described herein efficiently reduce polyamide pellet exposure to and absorption of water by quickly removing the pellets from water used during strand formation and pelletizing and efficiently drying the pellets without large energy expenditure.

[0012] Polyamide pellets can be made by cutting extruded polyamide strands. This can be done using a pelletizer, which automatically cuts the polyamide strands at selected intervals. The polyamide is in a molten state when emerging from the strand die, and the strands harden as they cool. Strands can be submerged in water or sprayed with water to facilitate strand cooling. Water can also be present during strand cutting. Thus, a "wet-cut" pelletizer can be used that cuts polyamide strands in an aqueous environment (e.g., under water or with water spraying the cutting area). There are benefits to use of water including, for example, fast cooling of molten polyamide, dust reduction, and somewhat cleaner pelletization. However, polyamide pellets can absorb water and the polyamide pellets should be dry before storage or packaging. Ideally, pellet drying is performed quickly and efficiently.

[0013] Pellet drying problems arise from variable amounts of water present in the pellets and from unexpected introduction of water during the drying process. For example, additional water from strand cooling or pelletization can be introduced at unexpected intervals (e.g., by dripping or splashing onto pellets that are being dried). The intermittent addition of variable amounts of water results in a poorly dried product or an increased drying time. Additional energy can be needed to dry the pellets adequately. The architecture of the manufacturing system could be adapted to reduce the incidence of unexpected water introduction, but such adaptation can lead to undesirable increases in the size or footprint of the system, and reconfiguration of the system may still provide inadequate pellet drying when a single drying unit is employed.

[0014] The problems of polyamide pellet drying are solved by employing two pellet drying units. A first pellet spin drying unit removes the majority of the water, while a second fluid bed drying unit completes the drying process and also conveys the pellets away from sources of water (e.g., from cooling strands or a wet-cut pelletizer).

[0015] The wet polyamide pellets can be manufactured in a continuous polyamide manufacturing system that generates water cooled polyamide strands. The water cooled polyamide strands can be cut in a wet-cut pelletizer. The wet-cut pelletizer can be any suitable wet-cut pelletizer. For example, the wet-cut pelletizer can be a tempered water system pelletizer available from Gala (Eagle Rock, VA), such as a Gala SLC pelletizer, Gala MAP pelletizer, or a Gala EAC pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), or a Rieter Automatik USG polymer strand granulating machine available from Rieter

Automatik Gmbh, Grossostheim, Germany. The wet-cut pelletizer can have any suitable throughput, such as about 1 L/min to about 5000 L/min, about 5 L/min to about 1000 L/min, about 10 L/min to about 100 L/min, or about 1 L/min or less, or 2 L/min, 3, 4, 5, 10, 15, 20, 25, 50, 100, 150, 200, 250, 500, 750, 1000, 2000, 3000, 4000, or about 5000 L/min or more. The wet-cut pelletizer can generate any suitable quantity of pellets per time, such as about 1000 pellets/min to about 100,000,000 pellets/min, about 10,000 pellets/min to about 50,000,000 pellets/min, or about 1000 pellets/min or less, or about 2000, 5000, 10,000, 20,000, 50,000, 100,000, 250,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, or about 100,000,000 pellets per minute. The temperature of the pellets exiting the pelletizer can be any suitable temperature, such as about 20 °C to about 250 °C, or about 30 °C to about 150 °C, or about 35 °C to about 100 °C, or about 20 °C or less, or about 30 °C, 50, 75, 100, 125, 150, 175, 200, 225, or about 250 °C or more. The total water content of the pellets exiting the pelletizer can be any suitable water content, such as about 0.05 wt to about 90 wt , about 0.1 wt to about 50 wt , 1 wt to about 30 wt , or about 0.05 wt or less, 0.5 wt , 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, or about 90 wt or more. The pellets can have any suitable diameter, such as about 3 mm to about 9 mm, or about 4 to about 7 mm, or about 3 mm or less, or about 4 mm, 5, 6, 7, 8, or about 9 mm or more. The pellets can have any suitable length, such as about 0.05 cm to about 10 cm, about 0.5 cm to about 5 cm, or about 0.1 cm or less, or about 0.15 cm, 0.2, 0.25, 0.3, 0.35, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, or about 10 cm or more. The pelletizer can require sharpening or maintenance at any suitable interval, such as about 1 month to about 200 months, or about 2 months to about 100 months, or about 1 month or less, 2 months, 6, 12, 24, 30, 36, 42, 48, 54, 60, 70, 80, 90, 100, 125, 150, 175, or about 200 months or more.

[0016] While the center of polyamide strands and pellets remain largely unaffected, use of water during strand cooling and pelletization introduces water to the surface of the pellets. In general, the drying process removes surface water from the pellets.

[0017] The first pellet spin drying unit is configured to receive wet pellets and water from a wet-cut pelletizer. The pellets can fall, or be swept or conveyed into the first pellet spin drying unit. [0018] The first pellet spin drying unit generally operates by spinning the pellets to remove water by centrifugal force while retaining the pellets within a screened cage. The pores in the screen have a pore size that permits water to pass through but that retains the pellets in the drying unit. A central rotor with impeller blades can be used to rotate the pellets. The impeller blades can also move the pellets through the dryer and towards the second fluid bed drying unit. The pellets are rotated through a stream of dry gas (e.g., dry air, dry nitrogen, or a combination thereof).

[0019] While dry air can be used to dry polyamide pellets, use of a dry inert gas or a dry inert gas with reduced oxygen content (e.g., nitrogen or nitrogen enriched air) can reduce oxidation.

[0020] An agglomeration screen can be present at the entry of the first spin drying unit to screen out agglomerated pellets, gel and other undesired particulates. Such a screen can prevent entry of particulates with a length or width larger than about 4 cm, or larger than about 3.5 cm, or larger than about 3 cm, or larger than about 2.5 cm, or larger than about 2 cm, or larger than about 1.5 cm.

[0021] The atmospheric pressure of the spin dryer can be varied. For example, the spin dryer can be maintained at reduced or increased pressure. Reduced pressures can include reduction in atmospheric pressure by 6 KPa - 14 KPa or more. For example, instead of a normal atmospheric pressure of about 760 mm Hg (Torr), the pressure during drying of pellets in the spin dryer unit can be less than about 700 mm Hg, or less than about 600 mm Hg, or less than about 500 mm Hg, or less than about 400 mm Hg, or less than about 300 mm Hg, or less than about 200 mm Hg, or less than about 100 mm Hg. For example, the spin dryer can dry the pellets at a reduced pressure of about 300 - 400 mm Hg.

[0022] Temperatures in the spin dryer can range from about 35 °C to about 200 °C, or from about 40 °C to about 175 °C, or from about 45 °C to about 150 °C, or from about 50 °C to about 125 °C. Lower temperatures can reduce yellowing but can also increase drying times.

[0023] The pellets can be dried for a time sufficient to remove the majority of water. Such a time depends upon the drying temperature and other variables such as the volume of water and pellets to be dried. [0024] The time to remove sufficient water can vary. The spin dryer and the fluid bed dryer generally remove and dry surface water. Hence, the residence time of pellets in these units is less than if the pellets needed internal drying. The pellets can have any suitable residence time in the spin dryer, such as about 1 second to about 2 hours, or about 5 seconds to about 20 minutes, or about 1 second or less, or about 5 s, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 s, 1.5 min, 2, 3, 4, 5, 6, 7, 8, 9, 10, 30 min, 1 hour, or about 2 hours or more.

[0025] The spin dryer can be any suitable spin dryer, such as a spin drying available from Carter Day in Minneapolis, MN, such as a Carter Day Spinaway Dryer, or a Carter Day Pressurized Spinaway Dryer. The spin dryer can have any suitable throughput, such as about 1 L/min to about 5000 L/min, about 5 L/min to about 1000 L/min, about 10 L/min to about 100 L/min, or about 1 L/min or less, or 2 L/min, 3, 4, 5, 10, 15, 20, 25, 50, 100, 150, 200, 250, 500, 750, 1000, 2000, 3000, 4000, or about 5000 L/min or more. The spin dryer can dry any suitable quantity of pellets per time, such as about 1000 pellets/min to about 10,000,000 pellets/min, about 10,000 pellets/min to about 5,000,000 pellets/min, or about 1000 pellets/min or less, or about 2000, 5000, 10,000, 20,000, 50,000, 100,000, 250,000, 500,000, 1,000,000, 5,000,000, or about 10,000,000 pellets per minute. The spin dryer can spin the pellets at any suitable RPM, such as about 20 RPM to about 500,000 RPM, or about 1,000 RPM to about 200,000 RPM, or about 20 RPM or less, or about 50 RPM, 100, 150, 200, 250, 500, 750, 1,000, 2,000, 3,000, 4,000, 5,000, 7,500, 10,000, 15,000, 20,000, 25,000, 50,000, 100,000, 150,000, 200,000, or about 500,000 or more. The pellets can be exposed to blowing air or gas having any suitable velocity and at any suitable temperature within the spin dryer, such as about 20 °C to about 300 °C, or about 30 °C to about 200 °C, or about 20 °C or less, or about 30 °C, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, or about 300 °C or more. The total water content of the pellets exiting the spin dryer can be any suitable total water content, such as about 0.1 wt to about 10 wt , or about 1 wt to about 5 wt , or about 0.1 wt or less, or about 0.5 wt , 1, 2, 3, 4, 5, 6, 7, 8, 9, or about 10 wt or more. The standard deviation of the wt total water content of the pellets exiting the spin dryer can be any suitable standard deviation, such as about 0.001 wt% to about 1 wt%, or about 0.001 wt% to about 0.5 wt%, or about 0.001 wt% or less, or about 0.005 wt%, 0.01, 0.05, 0.1, 0.5, or about 1 wt% or more.

[0026] The spin dryer removes the majority of water from the pellets. Most if not all of the water removed is surface water. For example, the pellet spin drying unit can remove up to 80%, or up to 82%, or up to 83%, or up to 85%, or up to 86%, or up to 88%, or up to 90%, or up to 91%, or up to 92%, or up to 93%, or up to 94%, or up to 95% of water from the pellets. By the time the pellets leave the pellet spin drying unit the pellets have less than about 15 wt%, or less than about 12 wt%, or less than about 10 wt %, or less than about 8 wt%, or less than about 7 wt%, or less than about 6 wt %, or less than about 5 wt%, or less than about 4 wt%, or less than about 3 wt %, or less than about 2 wt%, or less than about 1 wt % water, or less than about 0.8 wt%, or less than about 0.5 wt % water. After removal of such amounts of water, the pellets are conveyed into the fluid bed drying unit.

[0027] The fluid bed drying unit is configured to receive pellets from the pellet spin drying unit. The fluid bed dryer unit receives the pellets and can moves them away from the receiving area via a conveyor or through the use of air to fluidize the pellets over a weir at the other end of the dryer. For example, the conveyor can be a perforated conveyor belt, where the perforations are large enough to allow passage of a gaseous stream but are smaller than the pellets. The conveyor can also vibrate the pellets. Such vibration can reduce agglomeration of pellets. In some examples, hot dry air from underneath a perforated plate can be used to fluidize the pellets until the height of the fluidized pellets allows the pellets to fall over a weir at the far end of the unit (opposite the inlet), which can help to avoid maintenance of the conveyor belt, such as maintenance to fix jams caused by wayward pellets.

[0028] The pellets are fluidized from below with the gaseous stream that lifts and separates the pellets. The gaseous stream can be air, nitrogen or a combination thereof. For example, the gaseous stream can be dry filtered air. As indicated above for the spin dryer, while dry air is commonly used to dry polyamide pellets, use of a dry inert gas or a dry inert gas with reduced oxygen content (e.g., nitrogen or nitrogen enriched air) can reduce oxidation. The fluid bed drying unit can also employ dry air, or an atmosphere of nitrogen or nitrogen enriched air. [0029] Examples of suitable fluid bed dryers include those manufactured by the Witte Company of Washington, NJ (see, website at witte.com/products/fbdryer.php). Vibrating fluid bed dryers can also be used, for example, of the type commonly used to dry coated tablets for pharmaceutical applications. Such fluid bed dryers are commercially available from a number of manufacturers including Nicomac srl, Via Curiel, 12, 20060 Liscate, Milano, Italy.

[0030] The gaseous stream can also be heated to facilitate drying of the pellets. For example, the pellets can be heated in a fluidized stream of air at temperatures of about 80 °C to about 150 °C. Alternatively, temperatures in the fluid bed drying unit can range from about 35 °C to about 200 °C, or from about 40 °C to about 175 °C, or from about 45 °C to about 150 °C, or from about 50 °C to about 125 °C. Lower temperatures can reduce yellowing but can also increase drying times.

[0031] The atmospheric pressure of the fluid bed drying unit can also be varied. For example, the fluid bed drying unit can be maintained at reduced or increased pressure. Reduced pressures can include reduction in atmospheric pressure by 50- 100 Torr or more. For example, instead of a normal atmospheric pressure of about 760 mm Hg (Torr), the pressure during drying of pellets in the fluid bed drying unit can be less than about 700 mm Hg, or less than about 600 mm Hg, or less than about 500 mm Hg, or less than about 400 mm Hg, or less than about 300 mm Hg, or less than about 200 mm Hg, or less than about 100 mm Hg. For example, the fluid bed drying unit can dry the pellets at a reduced pressure of about 300 - 400 mm Hg.

[0032] The time to dry the pellets in the fluid bed drying unit can vary. The fluid bed drying unit is also drying mostly the surface of the pellets, which can require less time than drying the interior of the pellets. The pellets can have any suitable residence time in the fluid bed dryer, such as about 1 second to about 4 hours, or about 5 seconds to about 20 minutes, or about 1 second or less, or about 5 s, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 s, 1.5 min, 2, 3, 4, 5, 6, 7, 8, 9, 10, 30 min, 1 hour, 2, 3, or about 4 hours or more.

[0033] The fluid bed drying unit can include a classifier unit. The classifier unit allows removal of any "fines" (e.g., fines passing through 20 mesh) with a variety of shapes including those statically held. For example, the classifier can remove ribbons, streamers, angel hairs, and other fine particulates.

[0034] The fluid bed dryer can have any suitable throughput, such as about 1 L/min to about 5000 L/min, about 5 L/min to about 1000 L/min, about 10 L/min to about 100 L/min, or about 1 L/min or less, or 2 L/min, 3, 4, 5, 10, 15, 20, 25, 50, 100, 150, 200, 250, 500, 750, 1000, 2000, 3000, 4000, or about 5000 L/min or more. The fluid bed dryer can dry any suitable quantity of pellets per time, such as about 1000 pellets/min to about 10,000,000 pellets/min, about 10,000 pellets/min to about 5,000,000 pellets/min, or about 1000 pellets/min or less, or about 2000, 5000, 10,000, 20,000, 50,000, 100,000, 250,000, 500,000, 1,000,000, 5,000,000, or about 10,000,000 pellets per minute. The pellets can be exposed to blowing air or gas having any suitable velocity within the fluid bed dryer, such that a fluidized bed is formed. The air or gas within the fluid bed dryer can have any suitable temperature, such as about 20 °C to about 300 °C, or about 30 °C to about 200 °C, or about 20 °C or less, or about 30 °C, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, or about 300 °C or more. The pellets exiting the fluid bed dryer can be finished pellets.

[0035] The finished pellets can be generally uniformly dry, with no substantial difference in internal versus surface water content. The dried polyamide pellets can, for example, have a water content of less than 0.5 wt %, less than 0.4 wt %, less than 0.3 wt %, less than 0.2 wt %, less than 0.1 wt %, less than 0.05 wt %, or less than 0.02 wt %. The dried polyamide pellet product can also have a volatiles content as lower than about 1.5%, or lower than about 1.0%, or lower than about 0.5%. The total water content of the pellets exiting the fluid bed dryer can be any suitable total water content, such as about 0.01 wt% to about 5 wt%, or about 0.01 wt% to about 2 wt%, or about 0.01 wt% or less, or about 0.05 wt%, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.5, 3, 3.5, 4, 4.5 wt%, or about 5 wt% or more. The standard deviation of the wt% total water content of the pellets exiting the fluid bed dryer can be any suitable standard deviation, such as about 0.000,1 wt% to about 0.5 wt%, or about 0.001 wt% to about 0.1 wt%, or about 0.000,1 wt% or less, or about 0.005 wt%, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4 wt%, or about 0.5 wt% or more. [0036] The total water content of the finished pellets can be any suitable total water content, such as about 0.01 wt to about 5 wt , or about 0.01 wt to about 2 wt%, or about 0.01 wt% or less, or about 0.05 wt%, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.5, 3, 3.5, 4, 4.5 wt%, or about 5 wt% or more. The standard deviation of the wt total water content of the finished pellets can be any suitable standard deviation, such as about 0.000,1 wt to about 0.5 wt , or about 0.001 wt% to about 0.1 wt%, or about 0.000,1 wt% or less, or about 0.005 wt%, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4 wt%, or about 0.5 wt% or more. The yellowness index of the finished pellets can be any suitable yellowness index, and can be measured by any suitable method, such as ASTM D1925 or ASTM E313, such about 0.001 to about 50, about 0.01 to about 20, about 0.1 to about 15, or about 0.001 or less, 0.01, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 13, 14, 15, 20, 25, 30, 40, or about 50 or more. The oxidative degradation index (ODI) of the finished pellets can be any suitable ODI, such as about 0.01 to about 0.9, or about 0.1 to about 0.5, or about 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, or about 0.9 or more. The thermal degradation index (TDI) of the finished pellets can be any suitable TDI, such as about 0.01 to about 0.9, or about 0.1 to about 0.5, or about 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, or about 0.9 or more.

Example polyamide drying system

[0037] FIG. 1 shows an example polyamide pellet drying system. The system can include a spin dryer unit 10, with a receiving chute for polyamide pellets 20. The pellets are rotated in a rotating stream 30 to produce centrifugally removed water 50. A pellet retention screen 60 keeps the pellets in the spin dryer unit 10 and sequesters the drying pellets from the water drainage system, which includes a water removal drain 70. The spin dryer has an axle 80 operably configured to rotate the pellet retention screen 60. The spin dryer unit 10 has an upward gaseous stream 40 that supports and facilitates upward movement of the pellets as they dry. Upon partial removal of the water 50 from the pellets, they are conveyed into a fluid bed drying unit receiving area 90 of a fluid bed drying unit 100. The fluid bed drying unit 100 transports the pellets away from the receiving area 9 ^N 0 via a conveyor 120 operably connected to a conveyor motor 130. A gaseous stream 110 flows upwardly through the conveyor 120. The conveyor 120 also vibrates the pellets, which can reduce agglomeration. The dried pellets are delivered to dried pellet bin 140.

[0038] The systems and processes described herein can be used to manufacture or dry nylon 6, nylon 7, nylon 11, nylon 12, nylon 6,6, nylon 6,9; nylon 6,10, nylon 6,12, or copolymers thereof. Test Methods

[0039] 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.

[0040] 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.

[0041] 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 one 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

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The drying units and a process of making polyamides using such units are illustrated by the following Examples, which are intended to be example embodiments and not limiting.

[0049] General method. Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min through a extruder including an extrusion chamber having multiple die plates to produce nylon strands which are subsequently pelletized. The extrusion chamber has 10 die plates, each having 30 capillaries, with each capillary corresponding to an extruded strand. The strands emerge from the capillaries (e.g., die holes) at a rate of about 6.83 M/min per capillary. The emerging strands have a 6 mm diameter, a temperature of 270 °C, and a total weight percent water of about 0.1%, which is primarily internal water.

Example 1: Dry pelletizer.

[0050] The general method is followed. The strands travel to a dry pelletizer that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute.

[0051] The pelletizer requires shut-down for cleaning and sharpening

approximately every 2 weeks. Approximately 0.000,1 wt% of the pellets are fused.

Example 2: Wet Pelletizing with Conveyor Belt Dryer.

[0052] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0053] The pellets then enter a conveyor belt dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the conveyor belt dryer, they have a total moisture content of about 10 wt% and a temperature of about 80 °C. The conveyor belt dryer has a vibrating belt that holds the pellets with 100 °C air being blown up through the pellets. However, no fluidized bed is formed. The pellets are retained in the dryer for about 5 minutes. The pellets exit the dryer at a rate of about 4.8 million pellets per minute. The finished pellets have a total moisture content of about 0.7 wt with a standard deviation of about 0.2 wt , and a temperature of about 90 °C.

[0054] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 4. The finished pellets have a thermal degradation index of 0.35, and an oxidative degradation index of 0.3.

Example 3a: Wet Pelletizing with Spin Dryer.

[0055] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0056] The pellets enter a Carter Day Spinaway spin dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the spin dryer, they have a total moisture content of about 10 wt and a temperature of about 80 °C. The spin dryer spins the pellets at about 500 RPM and exposes the pellets to blowing 100 °C air. The pellets are retained in the spin dryer for an average time of about 5 minutes. The finished pellets have a total moisture content of about 0.7 wt with a standard deviation of about 0.2 wt , and have a temperature of about 90 °C.

[0057] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 4. The finished pellets have a thermal degradation index of 0.35, and an oxidative degradation index of 0.3. Example 3b: Wet Pelletizing with Sub-Transport Fluid Bed Pellet Dryer.

[0058] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0059] The pellets then enter a fluid bed dryer manufactured by Witte Company of Washington, NJ at a rate of about 4.8 million pellets per minute. When the pellets enter the fluid bed dryer, they have a total moisture content of about 10 wt and a temperature of about 80 °C. The fluid bed dryer has a vibrating belt that holds the pellets with 100 °C air being blown up through the pellets, forming an air-fluidized bed of pellets. The pellets are retained in the fluid bed dryer for about 5 minutes. The pellets exit the fluid bed dryer at a rate of about 4.8 million pellets per minute. The finished pellets have a total moisture content of about 0.5 wt with a standard deviation of about 0.2 wt , and have a temperature of about 90 °C.

[0060] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 5. The finished pellets have a thermal degradation index of 0.4, and an oxidative degradation index of 0.5.

Example 4: Wet Pelletizing with Spin Drying and with Conveyor Belt Dryer.

[0061] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0062] The pellets enter a Carter Day Spinaway spin dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the spin dryer, they have a total moisture content of about 10 wt and a temperature of about 80 °C. The spin dryer spins the pellets at about 500 RPM and exposes the pellets to blowing 100 °C air.

The pellets are retained in the spin dryer for an average time of about 30 seconds.

[0063] The pellets then enter a conveyor belt dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the conveyor belt dryer, they have a total moisture content of about 0.4 wt and a temperature of about 90 °C. The conveyor belt dryer has a vibrating belt that holds the pellets with 100 °C air being blown up through the pellets. However, no fluidized bed is formed. The pellets are retained in the dryer for about 2 minutes. The pellets exit the dryer at a rate of about 4.8 million pellets per minute. The finished pellets have a total moisture content of about 0.35 wt with a standard deviation of about 0.2 wt , and have a temperature of about 90 °C.

[0064] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 5. The finished pellets have a thermal degradation index of 0.4, and an oxidative degradation index of 0.5.

Example 5: Wet Pelletizing with Spin Dryer and Sub-Transport Fluid Bed Pellet Dryer, using 210 °C in Spin Dryer.

[0065] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0066] The pellets enter a Carter Day Spinaway spin dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the spin dryer, they have a total moisture content of about 10 wt and a temperature of about 80 °C. The spin dryer spins the pellets at about 500 RPM and exposes the pellets to blowing 210 °C air. The pellets are retained in the spin dryer for an average time of about 20 seconds.

[0067] The pellets then enter a fluid bed dryer manufactured by Witte Company of Washington, NJ at a rate of about 4.8 million pellets per minute. When the pellets enter the fluid bed dryer, they have a total moisture content of about 0.4 wt and a temperature of about 150 °C. The fluid bed dryer has a vibrating belt that holds the pellets with 100 °C air being blown up through the pellets, forming an air-fluidized bed of pellets. The pellets are retained in the fluid bed dryer for about 30 seconds. The pellets exit the fluid bed dryer at a rate of about 4.8 million pellets per minute. The finished pellets have a total moisture content of about 0.05 wt with a standard deviation of about 0.02 wt , and have a temperature of about 90 °C.

[0068] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 20 The finished pellets have a thermal degradation index of 0.4, and an oxidative degradation index of 0.5. Due to the drying efficiency of the fluid bed dryer, the fluid bed dryer occupies approximately 30% less volume than the drying systems of Examples 2 and 4. Example 6: Wet Pelletizing with Spin Dryer and Sub-Transport Fluid Bed Pellet Dryer, using 150 °C in Spin Dryer.

[0069] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0070] The pellets enter a Carter Day Spinaway spin dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the spin dryer, they have a total moisture content of about 10 wt% and a temperature of about 80 °C. The spin dryer spins the pellets at about 500 RPM and exposes the pellets to blowing 150 °C air. The pellets are retained in the spin dryer for an average time of about 25 seconds.

[0071] The pellets then enter a fluid bed dryer manufactured by Witte Company of Washington, NJ at a rate of about 4.8 million pellets per minute. When the pellets enter the fluid bed dryer, they have a total moisture content of about 0.4 wt% and a temperature of about 125 °C. The fluid bed dryer has a vibrating belt that holds the pellets with 100 °C air being blown up through the pellets, forming an air-fluidized bed of pellets. The pellets are retained in the fluid bed dryer for about 30 seconds. The pellets exit the fluid bed dryer at a rate of about 4.8 million pellets per minute. The finished pellets have a total moisture content of about 0.15 wt% with a standard deviation of about 0.02 wt%, and have a temperature of about 90 °C.

[0072] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt% of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 4. The finished pellets have a thermal degradation index of 0.37, and an oxidative degradation index of 0.35. Due to the drying efficiency of the fluid bed dryer, the fluid bed dryer occupies approximately 30% less volume than the drying systems of Examples 2 and 4.

Example 7: Wet Pelletizing with Spin Dryer and Sub-Transport Fluid Bed Pellet Dryer, using 210 °C in Fluid Bed Dryer.

[0073] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0074] The pellets enter a Carter Day Spinaway spin dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the spin dryer, they have a total moisture content of about 10 wt% and a temperature of about 80 °C. The spin dryer spins the pellets at about 500 RPM and exposes the pellets to blowing 100 °C air. The pellets are retained in the spin dryer for an average time of about 30 seconds.

[0075] The pellets then enter a fluid bed dryer manufactured by Witte Company of Washington, NJ at a rate of about 4.8 million pellets per minute. When the pellets enter the fluid bed dryer, they have a total moisture content of about 0.4 wt% and a temperature of about 90 °C. The fluid bed dryer has a vibrating belt that holds the pellets with 210 °C air being blown up through the pellets, forming an air-fluidized bed of pellets. The pellets are retained in the fluid bed dryer for about 20 seconds. The pellets exit the fluid bed dryer at a rate of about 4.8 million pellets per minute. The finished pellets have a total moisture content of about 0.05 wt% with a standard deviation of about 0.02 wt%, and have a temperature of about 150 °C.

[0076] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt% of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 20. The finished pellets have a thermal degradation index of 0.4, and an oxidative degradation index of 0.5. Due to the drying efficiency of the fluid bed dryer, the fluid bed dryer occupies approximately 30% less volume than the drying systems of Examples 2 and 4.

Example 8: Wet Pelletizing with Spin Dryer and Sub-Transport Fluid Bed Pellet Dryer, using 150 °C in Fluid Bed Dryer.

[0077] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0078] The pellets enter a Carter Day Spinaway spin dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the spin dryer, they have a total moisture content of about 10 wt% and a temperature of about 80 °C. The spin dryer spins the pellets at about 500 RPM and exposes the pellets to blowing 100 °C air. The pellets are retained in the spin dryer for an average time of about 30 seconds.

[0079] The pellets then enter a fluid bed dryer manufactured by Witte Company of Washington, NJ at a rate of about 4.8 million pellets per minute. When the pellets enter the fluid bed dryer, they have a total moisture content of about 0.4 wt% and a temperature of about 90 °C. The fluid bed dryer has a vibrating belt that holds the pellets with 150 °C air being blown up through the pellets, forming an air-fluidized bed of pellets. The pellets are retained in the fluid bed dryer for about 25 seconds. The pellets exit the fluid bed dryer at a rate of about 4.8 million pellets per minute. The finished pellets have a total moisture content of about 0.15 wt% with a standard deviation of about 0.02 wt%, and have a temperature of about 125 °C.

[0080] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt% of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 4. The finished pellets have a thermal degradation index of 0.37, and an oxidative degradation index of 0.35. Due to the drying efficiency of the fluid bed dryer, the fluid bed dryer occupies approximately 30% less volume than the drying systems of Examples 2 and 4. Example 9: Wet Pelletizing with Spin Dryer and Sub-Transport Fluid Bed Pellet Dryer

[0081] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0082] The pellets enter a Carter Day Spinaway spin dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the spin dryer, they have a total moisture content of about 10 wt and a temperature of about 80 °C. The spin dryer spins the pellets at about 500 RPM and exposes the pellets to blowing 100 °C air. The pellets are retained in the spin dryer for an average time of about 30 seconds.

[0083] The pellets then enter a fluid bed dryer manufactured by Witte Company of Washington, NJ at a rate of about 4.8 million pellets per minute. When the pellets enter the fluid bed dryer, they have a total moisture content of about 0.4 wt and a temperature of about 90 °C. The fluid bed dryer has a vibrating belt that holds the pellets with 100 °C air being blown up through the pellets, forming an air-fluidized bed of pellets. The pellets are retained in the fluid bed dryer for about 30 seconds. The pellets exit the fluid bed dryer at a rate of about 4.8 million pellets per minute. The finished pellets have a total moisture content of about 0.15 wt with a standard deviation of about 0.02 wt , and have a temperature of about 90 °C.

[0084] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 1.5. The finished pellets have a thermal degradation index of 0.30, and an oxidative degradation index of 0.20. Due to the drying efficiency of the fluid bed dryer, the fluid bed dryer occupies approximately 30% less volume than the drying systems of Examples 2 and 4.

Example 10: Wet Pelletizing with Spin Dryer and Sub-Transport Fluid Bed Pellet Dryer using Oxygen-Depleted Drying Gas.

[0085] The general method is followed. The strands travel to a wet pelletizer, a WSD-series pelletizer from Bay Plastics Machine (Bay City, MI), that cuts the strands into 2.5 mm-long pellets at a rate of about 4.8 million pellets per minute. The pellets are coated with water.

[0086] The pellets enter a Carter Day Spinaway spin dryer at a rate of about 4.8 million pellets per minute. When the pellets enter the spin dryer, they have a total moisture content of about 10 wt% and a temperature of about 80 °C. The spin dryer spins the pellets at about 500 RPM and exposes the pellets to blowing 100 °C nitrogen-enriched air (50% nitrogen, 50% air). The pellets are retained in the spin dryer for an average time of about 30 seconds.

[0087] The pellets then enter a fluid bed dryer manufactured by Witte Company of Washington, NJ at a rate of about 4.8 million pellets per minute. When the pellets enter the fluid bed dryer, they have a total moisture content of about 0.4 wt% and a temperature of about 90 °C. The fluid bed dryer has a vibrating belt that holds the pellets with 100 °C nitrogen-enriched air (50% nitrogen, 50% air) being blown up through the pellets, forming an air-fluidized bed of pellets. The pellets are retained in the fluid bed dryer for about 30 seconds. The pellets exit the fluid bed dryer at a rate of about 4.8 million pellets per minute. The finished pellets have a total moisture content of about 0.15 wt% with a standard deviation of about 0.02 wt%, and have a temperature of about 90 °C.

[0088] The wet-cut pelletizer requires shut-down for cleaning and sharpening approximately every 2 months. Approximately 0.000,02 wt% of the pellets are fused. The finished pellets have a yellowness index measured in accordance with ASTM D1925 of about 1.4. The finished pellets have a thermal degradation index of 0.30, and an oxidative degradation index of 0.18. Due to the drying efficiency of the fluid bed dryer, the fluid bed dryer occupies approximately 30% less volume than the drying systems of Examples 2 and 4. [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 system for manufacturing polyamide pellets comprising:

a) a spin dryer that removes a majority of surface water from wet polyamide pellets to generate partially dried pellets; and

b) a fluid bed dryer that dries and transports the partially dried pellets from the spin dryer to produce dried polyamide pellets.

[0096] 2. The system of statement 1, further comprising a extruder configured to generate polyamide strands from which the wet polyamide pellets are made.

[0097] 3. The system of statement 1 or 2, further comprising an extruder configured to generate strands of polyamide having a weight percent water of about 0.01% to 0.5%, or of about 0.05% to 0.3%, or of about 0.1% to 0.25%.

[0098] 4. The system of any of statements 1-3, wherein strands of polyamide emerging from an extruder in the system have a temperature of about 200-300° C.

[0099] 5. The system of any of statements 1-4, further comprising a water cooling system to cool extruded polyamide strands from which the wet polyamide pellets are made. [00100] 6. The system of any of statements 1-5, further comprising a wet-cut pelletizer configured to cut strands of polyamide in water to generate the wet polyamide pellets.

[00101] 7. The system of any of statements 1-6, wherein the wet polyamide pellets have a water layer on their exterior or are in a slurry with water.

[00102] 8. The system of any of statements 1-7, where the wet polyamide pellets have a weight percent water of about 1 wt to 50 wt , or of about 1 wt to 40 wt%, or of about 2 wt% to 30 wt%, or of about 3 wt% to 20 wt%.

[00103] 9. The system of any of statements 1-8, where wet polyamide pellets have a temperature of about 20 °C to about 200 °C, or about 30 °C to about 150 °C, or about 35 °C to about 100 °C.

[00104] 10. The system of any of statements 1-9, wherein the wet polyamide pellets have an acceptable yellowness index.

[00105] 11. The system of any of statements 1-10, configured to deliver wet polyamide pellets from a pelletizer to the spin dryer.

[00106] 12. The system of any of statements 1-11, wherein the spin dryer centrifugally removes water from the pellets.

[00107] 13. The system of any of statements 1-12, wherein the spin dryer comprises a screen or basket to retain the pellets while water is removed.

[00108] 14. The system of any of statements 1-13, wherein the spin dryer comprises a central rotor with impeller blades.

[00109] 15. The system of any of statements 1-14, wherein the spin dryer comprises a gaseous stream that lifts the pellets.

[00110] 16. The system of any of statements 1-15, wherein the spin dryer further comprises a heater.

[00111] 17. The system of any of statements 1-16, wherein the spin dryer further comprises a heater that is configured to maintain pellets in the spin dryer at a temperature of about 25 °C to about 200 °C, or of about 30 °C to about 180 °C, or of about 30 °C to about 150 °C, or of about 30 °C to about 100 °C. [00112] 18. The system of any of statements 1-17, configured to generate partially dried pellets with a pellet temperature at less than the polyamide pellets melting temperature when they emerge of the spin dryer.

[00113] 19. The system of any of statements 1-18, wherein the fluid bed dryer is configured to receive the partially dried pellets from the spin dryer.

[00114] 20. The system of any of statements 1-19, wherein the partially dried pellets have a weight percent water of about 0.3% or more, or of about 0.5% or more, or of about 1.0% or more, or of about 2.0% or more, or of about 3.0% or more when they enter the fluid bed dryer.

[00115] 21. The system of any of statements 1-20, wherein the fluid bed dryer comprises a gaseous stream that supports or fluidizes the pellets.

[00116] 22. The system of any of statements 1-21, wherein the fluid bed dryer comprises a conveyor for moving pellets through the fluid bed dryer.

[00117] 23. The system of any of statements 1-22, wherein the fluid bed dryer comprises a perforated conveyor with a gaseous stream that moves through the perforations.

[00118] 24. The system of any of statements 1-23, wherein the fluid bed dryer comprises a conveyor that agitates the pellets.

[00119] 25. The system of any of statements 1-24, wherein the fluid bed dryer comprises a heater.

[00120] 26. The system of any of statements 1-25, wherein the fluid bed dryer comprises a heater that heats a gaseous stream.

[00121] 27. The system of any of statements 1-26, wherein the fluid bed dryer comprises a heater configured to heat a gaseous stream at a temperature of about 25 °C to about 200 °C, or of about 30 °C to about 180 °C, or of about 30 °C to about 150 °C, or of about 30 °C to about 100 °C.

[00122] 28. The system of any of statements 1-27, wherein the dried pellets have a weight percent water of about 0.5% or less, or of about 0.4% or less, or of about 0.3% or less, or of about 0.2% or less, or of about 0.1% or less when they emerge from the fluid bed dryer. [00123] 29. The system of any of statements 1-28, configured for continuous manufacture of polyamide pellets.

[00124] 30. The system of any of statements 1-29, configured to synthesize nylon 6, nylon 11, nylon 12, nylon 6,6; nylon 6,9; nylon 6,10; nylon 6,12; or copolymers thereof.

[00125] 31. A method comprising:

a) spin drying wet polyamide pellets to remove a majority of surface water from the wet polyamide pellets to generate partially dried pellets; and

b) further drying the partially dried pellets in a fluid bed dryer to generate dried polyamide pellets.

[00126] 32. The method of statement 31, further comprising generating polyamide strands from molten polyamide.

[00127] 33. The system of statement 31 or 32, further comprising extruding strands of polyamide that are spaced at a strand separation distance sufficient to substantially avoid strand fusion.

[00128] 34. The method of any of statements 31-33, further comprising suspending polyamide strands under conditions sufficient to harden the polyamide strands, thereby generating hardened strands.

[00129] 35. The method of any of statements 31-34, further comprising generating polyamide strands having an average diameter of about 5 to 6.5 mm.

[00130] 36. The method of any of statements 31-35, further comprising generating polyamide strands having a weight percent water of about 0.01% to 0.5%, or of about 0.05% to 0.3%, or of about 0.1% to 0.25%, or of about 0.05% to 0.25%.

[00131] 37. The method of any of statements 31-36, further comprising generating polyamide strands having a temperature of about 200-300° C.

[00132] 38. The method of any of statements 31-37, further comprising cooling polyamide strands with water.

[00133] 39. The method of any of statements 31-38, wherein the wet polyamide pellets are in a slurry with water. [00134] 40. The method of any of statements 31-39, wherein the wet polyamide pellets are coated with water.

[00135] 41. The method of any of statements 31-40, wherein the wet polyamide pellets have an internal water content of about 0.1 wt % water.

[00136] 42. The method of any of statements 31-41, where the wet polyamide pellets have a temperature of about 20 °C to about 200 °C, or about 30 °C to about 150 °C, or about 35 °C to about 100 °C.

[00137] 43. The method of any of statements 31-42, wherein the wet polyamide pellets have an acceptable yellowness index.

[00138] 44. The method of any of statements 31-43, wherein water is

centrifugally removed from the wet polyamide pellets during spin drying.

[00139] 45. The method of any of statements 31-44, wherein the wet polyamide pellets are retained in a screen or basket while water is removed during spin drying.

[00140] 46. The method of any of statements 31-45, wherein the wet polyamide pellets are dried in a gaseous stream in while spin drying.

[00141] 47. The method of any of statements 31-46, wherein the wet polyamide pellets are heated at a temperature of about 25 °C to about 200 °C, or of about 30 °C to about 180 °C, or of about 30 °C to about 150 °C, or of about 30 °C to about 100

°C during spin drying.

[00142] 48. The method of any of statements 31-47, wherein the partially dried pellets have a weight percent water of about 0.3% or more, or of about 0.5% or more, or of about 1.0% or more, or of about 2.0% or more, or of about 3.0% or more after spin- drying.

[00143] 49. The method of any of statements 31-48, wherein the partially dried pellets are supported or fluidized by a gaseous stream that supports or fluidizes the pellets in the fluid bed dryer.

[00144] 50. The method of any of statements 31-49, wherein the partially dried pellets are moved through the fluid bed dryer on a conveyor.

[00145] 51. The method of any of statements 31-50, wherein the partially dried pellets are moved through the fluid bed dryer on a perforated conveyor with a gaseous stream that moves through the perforations. [00146] 52. The method of any of statements 31-51, wherein the partially dried pellets are agitated as they move along a conveyor in the fluid bed dryer.

[00147] 53. The method of any of statements 31-52, wherein the partially dried pellets are heated in the fluid bed dryer.

[00148] 54. The method of any of statements 31-53, wherein the partially dried pellets are heated at a temperature of about 25 °C to about 200 °C, or of about 30 °C to about 180 °C, or of about 30 °C to about 150 °C, or of about 30 °C to about 100 °C in the fluid bed dryer.

[00149] 55. The method of any of statements 31-54, wherein the dried pellets have a weight percent water of about 0.1%, or of about 0.2%, or of about 0.3%, or of about 0.4%, or of about 0.5%.

[00150] 56. The method of any of statements 31-55, wherein the pellets are manufactured in a continuous polyamide manufacturing system.

[00151] 57. The method of any of statements 31-56, wherein the polyamide is nylon 6, nylon 11, nylon 12, nylon 6,6; nylon 6,9; nylon 6,10; nylon 6,12; or copolymers thereof.

[00152] The following claims summarize features of the systems and methods described herein.