Vessel having an induction heating element and method and apparatus including an induction heating element for preparing polyamide polymers - Patents.com

Abstract

A chemical vessel utilizing induction heating elements and useful for preparing polyamides such as nylon. The vessel may utilize an array of induction heating elements located within a process chamber. Also described are vessels, heat exchangers, processes, and apparatus useful for preparing polyamides.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This patent application claims the benefit of priority to U.S. Patent Application No. 63 / 114,220, filed November 16, 2020, which is incorporated by reference in its entirety.

[0002] FIELD OF THEINVENTION The present disclosure relates to the production of polyamides. The present disclosure also relates to the deployment of induction heating within the steps and processes of polyamide production. [Background technology]

[0003] Polyamides are versatile polymers that are easily processed into fibers, pellets, and films, and are useful across virtually all industries. Industrially important polyamides include polyamides prepared from the condensation of diacids and diamines (e.g., nylon-6,6) and polyamides prepared from lactams (e.g., nylon-6). Industrial-scale production of polyamides involves large amounts of heat transfer, which can limit the productivity of the production system.

[0004] Heat transfer fluids, which can be vapors and liquids, are one way of transferring heat to the vessel. However, heat transfer fluids can present various problems. For example, the fluids can involve large piping systems sized to allow good flow and heat distribution, which takes up valuable space within the vessel, thereby reducing the productivity of the vessel itself. The heat transfer fluid can reduce its temperature as it flows through the distribution system, which reduces the rate of heat transfer. Vapor heat transfer systems can generate condensate that overwhelms the piping system during peak heat fluxes and reduces the effective heat transfer area. Heat transfer fluids can also involve high temperature fluids that can be dangerous. Furthermore, managing such heat transfer fluids and systems can require frequent inspections, shutdowns, and ultimately high operating and maintenance costs. Steam systems pose particular hazards in terms of the need for containment to avoid explosive conditions. The chemicals themselves and their decomposition products can present environmental issues. Heat transfer fluids can be expensive, and their use on an industrial scale can require large volumes and expensive distribution systems. These factors can account for a significant portion of the construction and operating costs of a nylon production facility.

[0005] Electric heaters can also be used for chemical processing. However, electric heaters have had the general problem of poor control of surface temperature and, as a result, poor compatibility with sensitive reaction mixtures or viscous materials. Achieving high productivity with such heaters is limited by the difficulty of maintaining heat uniformity and consistency. Polymer degradation can be observed in areas of the vessel where the temperature deviates by surprisingly small amounts from the desired set point. Thus, although electric heaters can avoid complex piping systems that take up valuable vessel space, electric heaters are undesirable on an industrial scale for reaction mixtures involving viscous liquids or sensitive materials. Induction heating, one type of heating method, allows for the use of an electrical energy source to heat a susceptor via electromagnetic radiation, thus enabling the development of new heating systems. However, induction heating is not effective in all applications. There have been relatively few successful applications of induction heating for large-scale chemical processing. Most examples are limited to gas-phase processes and microreactors, which do not address the challenges of large-scale liquid-phase reactions.

[0006] Electrical power induction commercially offers induction heating systems for the exterior of large chemical reactors. These systems apply an electromagnetic field to the exterior of the vessel, which is itself the induction heating element. As the vessel walls heat up, they conduct heat from the vessel walls to the reactor contents. The total heat flux remains limited by the rate of conductive heat transfer from the reactor walls to the reactor contents.

[0007] The preparation of polyamides can involve sensitive and viscous reactants. There is a need for methods, vessels, and systems for producing polyamides with greater efficiency, lower energy costs, and reduced environmental impact. Summary of the Invention

[0008] The disclosure herein provides vessels, heat exchangers, methods, and systems useful for preparing polyamides. For example, the disclosure provides a chamber having an internal cavity and an outer wall, and a plurality of induction heating elements within the internal cavity of the chamber. Each induction heating element can include a susceptor and an induction coil connected to a power source. The heating elements can be positioned in an array that provides a channel between two or more heating elements in a circumferential direction about the axis of the chamber. The heating elements can also provide an axial channel between two or more of the heating elements.

[0009] The present disclosure also provides a process for preparing a polyamide polymer, the process including mixing a solution of polyamide precursors in a vessel including one, two, or more induction heating elements, e.g., a plurality of heating elements, and heating the polyamide precursors via electromagnetic induction to provide a polyamide polymer. The induction heating elements can each include a susceptor and an induction coil connected to a power source. The heating elements can be positioned in an array providing channels between the heating elements in a circumferential direction about the axis of the chamber. The heating elements can also provide axial channels between two or more of the heating elements. The process can also involve mixing an unreacted portion of the polyamide precursor with a prepolymer and heating the mixture to provide a polyamide polymer product, circulating the unreacted portion of the polyamide precursor through the vessel to remove water vapor, mixing the unreacted portion of the polyamide precursor with a prepolymer and heating the mixture to provide a polyamide polymer product.

[0010] The present disclosure further provides a system for preparing polyamide polymer. The system can include a chemical vessel with at least one addition inlet for adding liquid polyamide precursor, one or more chambers containing multiple induction heating elements, an agitator, a recirculator, or both configured to circulate reaction components through the one or more chambers of the vessel, at least one outlet for removing water vapor, and at least one outlet for removing polyamide polymer. The induction heating elements can each include a susceptor and an induction coil connected to a power source. The heating elements can be positioned in an array that provides a channel between two or more heating elements in a circumferential direction about the axis of the chamber. The heating elements can also provide an axial channel between two or more of the heating elements.

[0011] The present disclosure also generally provides for the use of internal induction heating, external induction heating, or both, to prepare polyamides. Such uses can include, for example, the use of the vessels, heat exchangers, methods, and systems described herein.

[0012] Advantages, some of which are unexpected, are achieved by various aspects of the present disclosure. For example, the present disclosure provides a chemical vessel with an internal induction heating element that provides higher productivity and faster, more efficient heating of the liquid reaction mixture. Polyamide production can include both low and high viscosity components that change over time, resulting in the viscosity of the reaction mixture increasing by several orders of magnitude over the course of the reaction. Moreover, polyamide production can involve a mixture of liquid organic and aqueous phases, vapor phases, salt precursors, and organic products and by-products. Additionally, the polymer product can suffer degradation if the vessel temperature deviates from the desired temperature set point. The presence of heating elements inside the vessel can adversely affect mixing, material flow, heat distribution, and product removal in complex ways. For example, poor mixing, material flow, or heat distribution can result in reduced product yields, polymer degradation, and longer processing times. As another example, internal heating elements can impede product removal. Moreover, the heating rate of a heating element is not necessarily predictive of overall process productivity in itself. For example, the surface heat, heating rate, or electrical efficiency of a given heating element does not necessarily confer a productivity gain due to the interplay of material flow, heat distribution, and product retention. Due to these various factors, the effect of various internal elements on such complex mixtures cannot be easily predicted. In various aspects, the present disclosure surprisingly and advantageously provides a vessel having internal heating elements oriented in a manner that achieves improved productivity without suffering from the productivity problems associated with poor mixing, poor heat distribution, or product retention.

[0013] In the drawings, which are not necessarily drawn to scale, like numerals may describe like components in different figures. Like numerals with different numeral suffixes may represent different instances of the like component. The drawings illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present specification. [Brief description of the drawings]

[0014] [Figure 1A]1A illustrates an arrangement of induction heating elements useful in a chemical vessel for preparing polyamides. FIG 1A shows a chemical vessel in which plate-type induction heating elements are located within the chamber and arranged in a stacked array. [Figure 1B] 1A illustrates an arrangement of induction heating elements useful in a chemical vessel for preparing polyamides. FIG. 1B shows a cross-sectional view of the array, where each plate represents a truncated cone, angled so that the open center of the truncated cone is lower and the outer edge of the truncated cone is higher, and the plates are spaced apart to provide radial and circumferential flow channels. [Figure 1C] 1A illustrates an arrangement of induction heating elements useful in a chemical vessel for preparing polyamides. FIG. 1C shows a cross-sectional view of a single induction heating element with multiple conductive tubes welded or sealed into a metal plate that is a susceptor. The tubes are electrically insulated from the susceptor plate. The tubes are spaced apart and can be insulated from each other. Under suitable process conditions and system load requirements, an insulated cable can be used in place of piping. The piping or cable provides the induction coil. [Figure 1D] Illustrate an arrangement of induction heating elements useful in a chemical vessel for preparing polyamides. FIG. 1D shows a top view of the array, the center of which provides an axial channel. An agitator can optionally be included in the vessel by utilizing the axial channel or by placing it in the space between or around the plate array. [Figure 2A]2A illustrates an arrangement of induction heating elements useful in a chemical vessel for preparing polyamides. FIG. 2A illustrates a chemical vessel with internal rod-type induction heating elements distributed and arranged concentrically across a circular mount. FIG. 2B shows a front view of the array, with the rods spaced to provide flow channels. FIG. 2C provides a cross-sectional top view showing multiple tubes welded to a support ring, the tubes containing an insulated induction coil. The coils can be formed by helical winding within each tube. The induction coils can be either conductive tubing or cable. An axial channel exists in the center of the array between the rods of the innermost ring, additional axial and circumferential channels exist between the concentric support rings, and radial flow channels exist between the rods. Agitators can be optionally included in the vessel by utilizing spaces of appropriate dimensions either between or around the heating elements. [Figure 2B] 2A illustrates an arrangement of induction heating elements useful in a chemical vessel for preparing polyamides. FIG. 2A illustrates a chemical vessel with internal rod-type induction heating elements distributed and arranged concentrically across a circular mount. FIG. 2B shows a front view of the array, with the rods spaced to provide flow channels. FIG. 2C provides a cross-sectional top view showing multiple tubes welded to a support ring, the tubes containing an insulated induction coil. The coils can be formed by helical winding within each tube. The induction coils can be either conductive tubing or cable. An axial channel exists in the center of the array between the rods of the innermost ring, additional axial and circumferential channels exist between the concentric support rings, and radial flow channels exist between the rods. Agitators can be optionally included in the vessel by utilizing spaces of appropriate dimensions either between or around the heating elements. [Figure 2C]2A illustrates an arrangement of induction heating elements useful in a chemical vessel for preparing polyamides. FIG. 2A illustrates a chemical vessel with internal rod-type induction heating elements distributed and arranged concentrically across a circular mount. FIG. 2B shows a front view of the array, with the rods spaced to provide flow channels. FIG. 2C provides a cross-sectional top view showing multiple tubes welded to a support ring, the tubes containing an insulated induction coil. The coils can be formed by helical winding within each tube. The induction coils can be either conductive tubing or cable. An axial channel exists in the center of the array between the rods of the innermost ring, additional axial and circumferential channels exist between the concentric support rings, and radial flow channels exist between the rods. Agitators can be optionally included in the vessel by utilizing spaces of appropriate dimensions either between or around the heating elements. [Figure 3A] Illustrate induction heating element arrangements useful in heat exchangers for preparing polyamides. FIG. 3A shows a cross-sectional side view of a horizontal heat exchanger including an array of rod-type induction heating elements arranged in the direction of flow. FIG. 3B shows a cross-sectional end view showing the tube arrangement. The heating elements are axially oriented in the direction of flow, but are not necessarily arranged in a symmetrical pattern, providing channels that do not necessarily lie on the axis of the vessel. The induction coil of the heating element can be formed from a helical winding of a conductive tube or cable within the heating element tube, or the induction coil can be external to the heat exchanger shell, or both. [Figure 3B]Illustrate induction heating element arrangements useful in heat exchangers for preparing polyamides. FIG. 3A shows a cross-sectional side view of a horizontal heat exchanger including an array of rod-type induction heating elements arranged in the direction of flow. FIG. 3B shows a cross-sectional end view showing the tube arrangement. The heating elements are axially oriented in the direction of flow, but are not necessarily arranged in a symmetrical pattern, providing channels that do not necessarily lie on the axis of the vessel. The induction coil of the heating element can be formed from a helical winding of a conductive tube or cable within the heating element tube, or the induction coil can be external to the heat exchanger shell, or both. [Figure 4A] 4 illustrates an arrangement of induction heating elements useful in a heat exchanger for preparing polyamides. The heat exchanger has internal cylindrical induction heating elements arranged in a concentric fashion. FIG. 4A shows a cross-sectional side view of a heat exchanger including an array of heating elements in the form of concentric open cylinders. FIG. 4B shows a cross-sectional top view of the heat exchanger, showing that the vessel includes concentric cylinders, each functioning as a heating element and providing an axial circumferential channel between the cylinder walls through which a liquid medium can flow. Each cylindrical shell can include windings of conductive tubing or cable forming an induction coil for that shell. [Figure 4B] 4 illustrates an arrangement of induction heating elements useful in a heat exchanger for preparing polyamides. The heat exchanger has internal cylindrical induction heating elements arranged in a concentric fashion. FIG. 4A shows a cross-sectional side view of a heat exchanger including an array of heating elements in the form of concentric open cylinders. FIG. 4B shows a cross-sectional top view of the heat exchanger, showing that the vessel includes concentric cylinders, each functioning as a heating element and providing an axial circumferential channel between the cylinder walls through which a liquid medium can flow. Each cylindrical shell can include windings of conductive tubing or cable forming an induction coil for that shell. [Figure 5A]Illustrate an arrangement of induction heating elements useful in a vessel stage for preparing polyamide. FIG. 5A shows a cross-sectional view of a stage with a tray, downcomer, and an array of induction heating elements. FIG. 5B shows a cross-sectional top view of the stage, showing a central downcomer and heating elements arranged in a butterfly configuration. Each element can have an outer shell that is a susceptor formed to seal the treatment liquid from the internal induction coil. The induction coil can be made from one or more windings of conductive tubing or insulated cable. [Figure 5B] Illustrate an arrangement of induction heating elements useful in a vessel stage for preparing polyamide. FIG. 5A shows a cross-sectional view of a stage with a tray, downcomer, and an array of induction heating elements. FIG. 5B shows a cross-sectional top view of the stage, showing a central downcomer and heating elements arranged in a butterfly configuration. Each element can have an outer shell that is a susceptor formed to seal the treatment liquid from the internal induction coil. The induction coil can be made from one or more windings of conductive tubing or insulated cable. [Figure 6A] 6A illustrates the use of an internal inductive heating array in a precursor mixing vessel and a distillation-polymerization column. [Figure 6B] Illustrating the use of internal induction heating arrays in a precursor mixing vessel and distillation-polymerization column, Figure 6B shows a top view of the stage tray and downcomer. [Figure 7] 1 illustrates the use of an internal induction heating array in a calandria recirculator heat exchanger. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Reference will now be made in detail to certain aspects of the disclosed subject matter. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the illustrated subject matter is not intended to limit the claims to the disclosed subject matter.

[0016] This disclosure describes, among other things, vessels, heat exchangers, methods, and systems useful for preparing polyamides. Polyamide production can require a large amount of heat input, and production rates can be limited by the maximum achievable heat flux of the system. However, polyamide production can involve a mixture of both low and high viscosities, and both liquid, gas, and solid phase elements. Some process vessels for nylon production, such as batch reactors, present challenges due to the nature of the polymerization. The feed to the vessel can contain low molecular weight reactants, including precursor salts, other additives or co-reactants, and generally a large proportion of water. This results in a low viscosity solution. The low viscosity of the solution can be easier to pump through the system than the product, which can be a higher viscosity solution. Higher heat transfer rates can be achieved by increasing the surface area of ​​the heater. However, as the reaction proceeds, the viscosity increases by several orders of magnitude to the point that removing the product from the high surface area heater can be problematic. Thus, the surface is designed to drain well to avoid material buildup and decomposition. Additionally, water vapor is generated during polyamide condensation and can be removed from the reaction environment to facilitate the reaction, and other vapor phase components, such as those provided by precursor decomposition, can be present as well.

[0017] In another example, nylon salts are converted to nylon polymers in either batch reactors or multi-stage continuous processes. In these cases, productivity is defined in part by the rate of heat transfer to the bulk mixture. In general, the rate of convective heat transfer to the bulk fluid is slower than the rate of conductive heat transfer through the metal vessel walls. Heat transfer to the vessel contents can be a limiting factor to overall productivity, but increasing heat transfer inside the vessel cannot be done at the expense of poor mixing or convective heat transfer in the bulk fluid, or at the expense of problematic product retention.

[0018] Furthermore, producing polyamides on a large scale presents additional challenges. Many polyamides require processing temperatures of 250°C or more, which, when combined with high pressure and industrial scale, precludes the use of polymeric materials for vessel body construction. Additionally, at scale, the heating medium closer to the vessel wall provides a shielding effect for the internal material. The vessels, heat exchangers, methods, and systems described herein may be useful for large-scale industrial production of polyamides. For example, various embodiments may involve vessels or chambers having diameters of at least or about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 meters. For example, various embodiments may involve the production of polyamides in batches of at least or about 1, 100, 1000, 2000, 3000, 4000, or at least or about 5000 kg. By applying the design principles described herein, a wide range of vessel ratios or batch sizes can be accommodated using suitable placement of heating elements. In various aspects herein, the disclosure describes the use of various arrays of induction heating elements to provide improved heat transfer, suitable for large-scale and industrial-scale production of polyamide polymer processes, with no adverse effects on convective heat transfer, mixing, and product retention, to provide improved overall productivity. 2 ~about 500m 2 , about 5m 2 ~ approx. 100m 2 , about 5m 2 ~ approx. 50m 2 , about 5m 2 ~about 30m 2 , about 10m 2 ~about 500m 2 , about 10m 2 ~ approx. 100m 2 , about 10m 2 ~About 50m 2 , or about 10m 2 ~about 30m 2 The ratio of heat transfer area to liquid volume is about 0.5 m 2 / m 3 ~ approx. 100m 2 / m 3 , about 1m 2 / m 3 ~ approx. 100m2 / m 3 , about 1m 2 / m 3 ~About 50m 2 / m 3 , about 1m 2 / m 3 ~about 25m 2 / m 3 , about 5m 2 / m 3 ~ approx. 100m 2 / m 3 , about 5m 2 / m 3 ~About 50m 2 / m 3 , about 5m 2 / m 3 ~about 30m 2 / m 3 , about 10m 2 / m 3 ~ approx. 100m 2 / m 3 , about 10m 2 / m 3 ~About 50m 2 / m 3 , or about 10m 2 / m 3 ~about 30m 2 / m 3 It could be.

[0019] The present disclosure provides a chemical vessel using internal induction heating useful for large scale polyamide preparation. The vessel can include an array of multiple induction heating elements within a chamber of the vessel. The induction heating elements include a susceptor and an induction heating coil. As used herein, "multiple" means two or more. For example, the multiple can include at least or about 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 27, 30, 35, 40, 45, or at least or about 50. In other examples, the multiple can include about 5 to about 15, about 5 to about 50, about 10 to about 30, about 20 to about 40, or about 2 to about 10.

[0020] The shape of the heating element typically corresponds to the shape of the susceptor, which may be relatively flat, such as a curved plate or fin, or may have a long aspect ratio, such as a rod or tube. The susceptor may be rod-like, plate-like, cylindrical, or variations thereof. For example, a plate-like susceptor may be substantially flat, a curved plate, a frustum-shaped, or a bowl-shaped. The susceptor may have a smooth outer surface or may optionally include ridges or fins to increase the interfacial area of ​​the side that contacts the process fluid. The susceptor may be solid, or may include an internal chamber, such as a hollow or internal piping. For example, the susceptor may be a hollow cylindrical rod, a hollow rectangular rod, a hollow shell of a cylinder, a hollow shell of a frustum. For example, the susceptor may be a rod, a plate, a cylinder, a prism, a rectangular solid, a fin, a frustum, a cone, or curved variations and segments thereof. The susceptor may be constructed of any suitable material. For example, the susceptor may be constructed of a stainless steel alloy, or a steel inner layer with an outer stainless steel cladding, or other suitable metallurgy appropriate for the particular role. Stainless steel construction may be sufficient for the temperature range required for various polyamide processes. Utilizing a core inner layer or pipe of magnetic alloy may improve the overall efficiency of the heater at steady state. For example, a dual layer susceptor may be fabricated by bonding an inner layer of magnetic steel to an outer layer of corrosion resistant, such as stainless steel or other metallurgy. The thickness of each layer may be specified separately to optimize the overall heating rate. In various aspects, the heating element is metal tubing that is bent and curved into the desired shape, which may be a high surface area shape or butterfly arrangement that allows an induction coil to be threaded through the tubing and the resulting supply and return connections to be located together.

[0021] The induction heating coil includes an electrical cable connected to a power source. In various embodiments, the induction heating coil can further include one or more of a shielding layer, an insulating layer, and a channel for liquid cooling. The internal induction coil can be constructed of any suitable conductive material. For example, the induction coil can be copper wiring. The wiring can be multi-twist wiring, which can improve heating efficiency in various embodiments. When tubing is utilized for long aspect ratio heating elements, etc., copper tubing can be sufficient, although other conductive materials can be utilized. At various lower temperatures that may be associated with polyamide processing, water cooling is not required, but for various high energy flux applications, water cooling can improve overall efficiency and performance. In various examples, it is advantageous to have tubing of sufficient diameter to improve water flow. In various further embodiments, square piping has been found to provide better overall temperature uniformity and efficiency than round piping. Temperature uniformity, system efficiency, and overall performance of various examples can be improved by incorporating a magnetic flux concentrator, such as the FLUXTROL 50 from Fluxtrol Inc. (Auburn Hills, MI).

[0022] As illustrated in the figure, there is an interaction between the shape and size of the susceptor, the proportions of the vessel, and the process unit fluid dynamics that affect heat transfer to the process fluid, which may also affect the efficiency of induction coil heating. The induction coil that heats the susceptor can take many suitable shapes and forms to achieve efficient heating of the susceptor while increasing the overall interfacial surface area with the process fluid. The induction heating coil can be single or multiple turns. The coils can be left-handed, right-handed, or alternate across the assembly. The coils can take forms such as rod or ear shapes and can be hairpin or parallel arrangements. The shape of the susceptor and the form of the induction coil can include any one or more of these forms in any combination to accommodate the demands of the process unit operation and achieve the overall desired process characteristics and good heat transfer. For example, the induction heating coil can form a helix. Some helical induction coils can correspond to commercially available helical coils, for example, as provided by "Complete Guide to Induction Coil Design" by Ambrell® Induction Heating Solutions, an electronic copy of which is available on the World Wide Web at sg-induction.com / wp-content / uploads / 2021 / 03 / Coil-Design-Induttore.pdf. Suitable helical shapes can be modified, for example, with straight sections or other modifications, as appropriate to tailor the heat transfer and flow characteristics of the susceptor in a particular reactor. For example, the induction coil can accommodate a susceptor that includes an extended surface area, such as fins.

[0023] Maintaining a good operable temperature of the induction coil can be accomplished by transferring heat to the surrounding process fluid via a susceptor, or alternatively, the coil can be fabricated with piping to allow for the use of an internal cooling fluid. As a further example, a helical induction heating coil can have one or more helical turns wound with spaces between the turns for cross flow of fluid across the coil geometry, or one or more turns tightly wound to form a wall with no spaces between the turns. Another variation can be achieved with a combination of the two arranged in alternating sections depending on the flow regime within the vessel.

[0024] The electrical components of the coil may desirably be kept as cool as possible. For example, a steel alloy susceptor may suitably operate at temperatures in excess of 300°C, while an induction coil may be kept at 20-30°C. The use of thermal breaks or insulation may reduce or minimize the conductive heat flow through the thermal body and the effects of overheating of the components. Such insulation may be based on ceramic or glass or mineral fibers, including aluminosilicate or mullite polycrystalline fibers, or non-fibrous materials such as calcium silicate. For example, Microtherm® panels made by Promat are rigid microporous insulating boards that may be fabricated to conform to custom shapes with a suitably thin profile that allows them to be clamped around piping. Other forms and examples of thermal breaks may suitably be utilized, and those skilled in the art may identify additional such insulating materials and techniques.

[0025] Induction can be accomplished, for example, by exposing the susceptor to an alternating magnetic field provided by an induction coil at a frequency ranging from about 50 Hz to about 30 MHz. The frequency and susceptor can be selected to provide the desired target temperature for, for example, precursor melting or polyamide condensation polymerization. The present disclosure is not intended to be limited to any particular induction frequency or pulse pattern. For example, the frequency may be about 50Hz to about 5kHz, 50Hz to about 50kHz, 50Hz to about 100kHz, about 1kHz to about 80kHz, about 1kHz to about 60kHz, about 1kHz to about 50kHz, about 1kHz to about 40kHz, about 1kHz to about 30kHz, about 10kHz to about 100kHz, about 10kHz to about 80kHz, about 100kHz to about 1MHz, about 100kHz to about 500kHz, about 500kHz to about 30MHz, about 1MHz to about 30MHz, about 50Hz to about 30MHz, about 50Hz to about 300kHz, or about 50Hz to about 3kHz. Suitable frequencies can be ascertained by those skilled in the art. Appropriate induction coil frequencies can be ascertained by those skilled in the art.

[0026] In various embodiments, the target reaction temperature is about 50°C to about 500°C, about 50°C to about 400°C, about 50°C to about 380°C, about 50°C to about 360°C, about 50°C to about 350°C, about 50°C to about 340°C, about 50°C to about 320°C, about 50°C to about 300°C, about 50°C to about 280°C, about 50°C to about 260°C, about 50°C to about 250°C; about 100°C to about 500°C, about 100°C to about 400°C, about 100°C to about 380°C, about 100°C to about 360°C, about 100°C to about 350°C, about 100°C to about It may be about 340°C, about 100°C to about 320°C, about 100°C to about 300°C, about 100°C to about 280°C, about 100°C to about 260°C, about 100°C to about 250°C; about 150°C to about 500°C, about 150°C to about 400°C, about 150°C to about 380°C, about 150°C to about 360°C, about 150°C to about 350°C, about 150°C to about 340°C, about 150°C to about 320°C, about 150°C to about 300°C, about 150°C to about 280°C, about 150°C to about 260°C, about 150°C to about 250°C. For example, some polyamides require treatment at a temperature of 250°C or higher, and the target reaction temperature may be 250°C or higher.

[0027] The induction heating coil can be located within the susceptor. For example, the induction heating coil can be placed within a hollow portion of the susceptor, or the susceptor can be formed around the induction heating coil. For example, two pieces of metal can be welded together to form a layered structure that includes the induction coil and associated components to provide the desired susceptor shape with a sealed interior space that includes the induction heating coil. In another example, metal can be cast or molded around the induction heating coil.

[0028] The induction heating element can be made in any suitable manner. For example, the induction coil can be made of insulated cable or insulated multi-strand cable. It can be made of tubing appropriately sized to allow sufficient cooling water flow to avoid overheating the coil. An insulation layer between the coil and the heating surface can be included. Shielding can also be included to improve overall heater efficiency. The heating element can also include a magnetic flux concentrator to improve efficiency and provide a more uniform heat distribution in the heated portion. These elements can be connected to a power source designed to deliver the required power and frequency using well-known methodologies.

[0029] In various aspects, the induction heating element is axially oriented parallel to the axis of the vessel.

[0030] In various embodiments, the induction heating elements are rod-shaped and extend vertically at least a portion, most, or substantially the entire vertical working length of the chamber. In various embodiments, the induction heating elements are plate-shaped and extend at least a portion, most, or substantially the entire radial working width of the chamber. In various embodiments, the induction heating elements are circular and are stacked axially at least a portion, most, or substantially the entire working vertical length of the chamber. In various embodiments, the induction heating elements are circular and are concentrically arranged in an array that extends at least a portion, most, or substantially the entire working vertical length of the chamber. For example, for a chamber with a diameter of 1 meter, the heating elements can be in the shape of a frustum of a cone having an outer diameter that is at least or about 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.96, 0.97, 0.98, or about or at least 0.99 meters wide. In various further examples, the heating element may be in the shape of a truncated cone with an opening at the inner diameter, which may be about or 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, or about or at least 0.05 meters wide. The inner diameter may provide one or more spaces for a connecting cable or may provide a working space that allows axial flow. In various examples, the vessel does not have a stirrer. In various other examples, a stirrer may be optionally included in the inner diameter space, the space between the plate and the outer vessel wall, or the space formed between the plates, etc. The stirrer may be optional. Such a stirrer may be mechanical.

[0031] In various embodiments, the induction heating elements are arranged in an array to provide channels between the heating elements sized to allow the reaction medium to flow therethrough. For example, the channels can provide a distance between adjacent heating elements of about 1 cm to about 300 cm, about 1 cm to about 100 cm, about 1 cm to about 50 cm, about 1 cm to about 25 cm, about 1 cm to about 20 cm, about 5 cm to about 300 cm, about 5 cm to about 100 cm, about 5 cm to about 50 cm, about 5 cm to about 25 cm, about 5 cm to about 20 cm, 10 cm to about 300 cm, about 10 cm to about 100 cm, about 10 cm to about 50 cm, about 10 cm to about 25 cm, about 10 cm to about 20 cm, 20 cm to about 300 cm, about 20 cm to about 100 cm, or about 20 cm to about 50 cm. For example, the channel can be at least or about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, or 20 cm.

[0032] For example, the array of heating elements can provide one or more channels between two or more heating elements in a circumferential direction about the axis of the chamber. The heating elements can provide one or more axial channels between two or more of the heating elements. For example, the array can provide at least or about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 40, 50, or 100 channels, which can be axial, radial, circumferential, or a combination thereof. The array of heating elements can include a stack of two or more heating elements distributed axially to provide circumferential and radial channels between adjacent heating elements in the stack. The circumferential radial channels can be planar or helical. The array of heating elements can include heating elements distributed radially within concentric rings to provide one or more circumferential and axial channels between adjacent concentric rings. The heating elements can be distributed circumferentially to provide one or more radial channels between adjacent heating elements. Some examples can have a single heating element, which is shaped to provide one or more channels between and through the heating element. The vessel or chamber can have a vertical axis, or an axis corresponding to the main direction of flow within the vessel or chamber. For example, the flow within the vessel or chamber can be primarily vertical or horizontal. The flow can flow within the vessel, whether the flow is mechanically driven or can result from boiling action, such as in continuous or semi-continuous operation, or recirculation flow in batch operation. As used herein, "circumferential" space refers to the space surrounding a reference axis. In various examples, the circumferential direction can be completely circumferential or partially circumferential.

[0033] In various embodiments, the induction heating elements are positioned in an array parallel to the vertical axis or axis of the predominant product flow, or at a non-perpendicular angle. For example, in a batch reactor vessel, the heating elements are angled at a sufficient pitch to allow for a downward flow of product, or in a continuous reactor vessel, the heating elements are angled at a sufficient pitch to allow for a flow of product in the direction of product removal. For example, the induction heating elements can be in the form of plates oriented with a major axis parallel to the axis of the chamber, or at an angle other than perpendicular to the axis of the chamber. The heating elements can be in the shape of a truncated cone with an open inner diameter, and have an inclination angle of about 1° to about 80°. For example, the tilt angle can be at least or about 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 30°, 40°, 45°, 50°, 60°, 70°, or at least or about 80°. The heating element can be shaped or oriented so as not to provide a major surface perpendicular to the axis. In various examples, the heating element can have a major surface oriented parallel to the axis of the container or at an angle other than 90° to the axis.

[0034] The vessel may be a batch reactor vessel, a continuous reactor vessel, or a semi-continuous reactor vessel. For example, the vessel may be an autoclave. The vessel may include multiple stages, each of which may represent a chamber. For example, the vessel may be a distillation-polymerization column. The vessel may have multiple stages with staging trays and downcomers. The vessel may be a conductive material. In various aspects, the vessel may be mild steel, clad mild steel, solid stainless steel, or other non-ferrous metal vessels, or may be fabricated from layers of different materials. The vessel may have a wall thickness of at least or about 0.5 cm, 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, or at least or about 10 cm. In various examples, the vessel does not have an agitator. In various other examples, an agitator may be optionally included in the inner diameter space, the space between the plate and the outer vessel wall, or the space formed between the plates, etc. An agitator may be optional. Such an agitator may be mechanical. The agitator may be shaft driven or may be produced via a jet eductor. In various examples, the vessel does not include sparging or bubbling. In various other examples, the vessel includes sparging or bubbling.

[0035] The various vessels, heat exchangers, processes, and systems described herein can involve using a heating element to heat a polyamide precursor, a polyamide prepolymer, or a mixture containing one or more of a polyamide precursor, a polyamide polymer, or a polyamide product.

[0036] "Polyamide" can refer to a polymer having repeating units linked by amide bonds. Polyamides can result from monomers containing aliphatic, semi-aromatic, or aromatic groups. Polyamides can refer to polyamides including nylons, such as nylon-6,6 or nylon-6, resulting from a single monomer, two different monomers, or three or more different monomers. Thus, the term polyamide includes dimonomer polyamides. Polyamides can be nylons having dicarboxylic acid and diamine monomer units as monomer units. For example, if the dicarboxylic acid monomer unit is adipic acid and the diamine is hexamethylenediamine, the resulting polyamide can be nylon-6,6. Nylon-6 is a polyamide with caprolactam monomers. Polyamides can be copolymers that can be prepared from aqueous solutions or blends of aqueous solutions containing more than two monomers. In various aspects, polyamides can be produced by polymerization of dicarboxylic acid and diamine monomers. In some cases, polyamides can also be produced via polymerization of amino carboxylic acids, amino nitriles, or lactams. Suitable polyamides include, but are not limited to, those polymerized from the monomer units described herein. The term "polyamide" includes nylon-4,6, nylon-4,10, nylon-5,6, nylon-5,6 / 5T, nylon-5I / 5T, nylon-5,10, nylon-5,12, nylon-6, nylon-6,6, nylon-12, nylon-6,10, nylon-6,12, nylon-6T / DT, nylon-6I / 6T, and nylon-66 / 6T. In various embodiments, the polyamide is nylon-6,6. Polyamide prepolymers can refer to dimeric or oligomeric polymers that are intermediates in the target polyamide polymer product.

[0037] A polyamide "precursor" can refer to a mixture containing reagents that condense or polymerize, alone or together with other precursors, to form a polyamide. For example, the precursor can contain a diacid, a diamine, or both. The diacid can be a diacid salt. The diamine can be a diamine salt. For example, the diacid can be oxalic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, hexane-1,6-dioic acid (adipic acid), octane-1,8-dioic acid (suberic acid), azelaic acid, decane-1,10-dioic acid (sebacic acid), undecane-1,12-dioic acid, dodecane-1,12-dioic acid, maleic acid, glutaconic acid, traumatic acid, muconic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,2 - or 1,3-phenylene diacetic acid, 1,2- or 1,3-cyclohexane diacetic acid, benzene-1,2-dicarboxylic acid (phthalic acid), benzene-1,3-dicarboxylic acid (isophthalic acid), benzene-1,4-dicarboxylic acid (terephthalic acid), 4,4'-oxybis(benzoic acid), 4,4-benzophenone dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, pt-butylisophthalic acid, and 2,5-furandicarboxylic acid, and mixtures thereof. The dicarboxylic acid monomer unit may be adipic acid.The diamines are ethylenediamine, trimethylenediamine, tetramethylenediamine (putrescine), pentamethylenediamine (cadaverine), hexamethylenediamine, 2-methylpentamethylenediamine, heptamethylenediamine, 2-methylhexamethylenediamine, 3-methylhexamethylenediamine, 2,2-dimethylpentamethylenediamine, octamethylenediamine, 2,5-dimethylhexamethylenediamine, nonamethylenediamine, 2,2,4- and 2,4,4-trimethylhexamethylenediamine, decamethylendiamine, tetramethyldi ... The precursor may be camethylenediamine, 5-methylnonanediamine, isophoronediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,7,7-tetramethyloctamethylenediamine, bis(p-aminocyclohexyl)methane, bis(aminomethyl)norbornane, C2-C16 aliphatic diamines optionally substituted with one or more C1-C4 alkyl groups, aliphatic polyether diamines, and furandiamines such as 2,5-bis(aminomethyl)furan, xylylenediamine, and mixtures thereof. The diamine may be hexamethylenediamine. The precursor may be a di-salt or mono-salt. The precursor may be an aqueous salt mixture. As another example, the precursor may contain a lactam, for example, caprolactam.

[0038] 1A-1D, one embodiment of a vessel 100 is illustrated using a stacked array of induction heating elements 110 located therein. The vessel has a chamber interior cavity 101 defined by chamber walls 102. The vessel may be suitable for use as a polyamide autoclave, such as for the production of nylon-6,6. The vessel may be autoclaves of various sizes, for example, one meter in diameter. The chamber walls 102 may be a conductive material or a multi-layer structure including one or more conductive layers. In various examples, the chamber walls 102 may be optionally surrounded by an external induction coil 103, or alternatively, a hot oil or steam jacket may be used, or a combination of both. The interior cavity 101 may optionally include a stirrer having a stirrer shaft 104 and a stirrer post 105. A shroud baffle may be included around the stirrer to increase vertical flow. The vessel may have an outlet drain 106 for product removal, and the top flange of the vessel has one or more inlets 107 for adding precursor materials and one or more outlets 108 for removing vapor or releasing pressure. In this example, the agitator shaft 104, agitator posts 105, outlet drain 106, and the array of heating elements 110 can be described as being centrally located along the vertical axis of the vessel and chamber. A stacked array of internally located induction heating elements 110 distributes along the axis of the vessel and provides a radial circumferential flow channel 111 through which reactant materials can flow. The central opening of each of the vertically arranged heating elements 110 provides an axial flow channel 112, which is also the working space for the agitator shaft 104 and agitator posts 105. The agitator may also optionally include a mixing element operating in the annular space between the heating elements 110 and the vessel wall 102. The axial and radial flow channels are in fluid communication with each other. In various examples, at the periphery of the chamber, the heating elements terminate in front of the chamber wall to provide an axial circumferential flow channel 113 that is in fluid communication with the radial circumferential flow channel and the central axial flow channel.

[0039] The heating elements 110 are sized and shaped to be conveniently deployed in the polyamide vessel while maximizing the heat transfer surface area. Each heating element 110 represents a separate induction heating element and is shaped as a conical frustum. The conical frustum is assembled to stack size and mounted vertically to the bottom flange of the vessel. The inner diameter of the frustum is sized to allow working space for the stirrer shaft 104 and the support column 105. Each heating element 110 in the stack comprises two plates 114 welded or sealed together that enclose an induction coil 115 that includes electrically insulated metal tubing. An electrically insulated multi-twisted cable can be used in place of tubing. The electrically insulated metal tubing or cable of the induction coil can be arranged with some space apart from each other and insulated. The outer plate 114 is the susceptor for this internal coil design. Supply and return tubing or cables, not shown for clarity, run down a vertical pipe from each heating element through the base mount. The supply and return piping or cables may be interconnected or supported together or bundled through a single supply and return pipe. A water recirculation loop may be connected to the piping to keep the coil at a temperature below 40° C. This may reduce the cooling load and may be optionally configured to provide a thermal break between the coil and the susceptor plate. Thin insulation may also be sandwiched between the coil and the susceptor plate. The angle of the plate may allow for fluid circulation during heating and product discharge at the end of the batch cycle. FIG. 1A shows a batch reactor vessel using an exemplary stacked array of partially cut heating elements 110. FIG. 1B shows a cross-sectional view of an exemplary stacked array of heating elements 110. FIG. 1C shows a cross-sectional view of an exemplary individual heating element 110. FIG. 1D shows a top view of the exemplary array, where a central axial flow channel 112 is visible, surrounded by heating elements 110 having a substantially circular shape.

[0040] 2A-2C, one embodiment of a vessel 100 is illustrated using a concentric array of induction heating elements 120 located therein. The vessel has an interior chamber cavity 101 surrounded by chamber walls 102. The vessel may be suitable for use as a polyamide autoclave, such as for the production of nylon-6,6. The vessel may be autoclaves of various sizes, for example, 1 meter diameter. The chamber walls may be of a conductive material or multi-layer construction including one or more conductive layers, and may optionally be surrounded by an external induction coil 103, or alternatively a hot oil or steam jacket may be used, or a combination of both types of heating may be used. The interior cavity of the chamber may optionally include a stirrer having a stirrer shaft 104 and a stirrer post 105. A shroud baffle may be included around the stirrer to increase vertical flow. The vessel may have an outlet drain 106 for product removal, and the top flange of the vessel has one or more inlets 107 for adding precursor materials and one or more outlets 108 for removing vapor or releasing pressure. In this example, the agitator shaft 104, agitator post 105, outlet drain 106, and the array of heating elements 120 may be described as being centrally located along the vertical axis of the vessel and chamber. The concentric array includes internally located induction heating elements 120 that are rod shaped and distributed radially and concentrically from the axis of the vessel. The rods are attached to a circular support ring 121 at each concentric circle. Between the concentric rings, the array provides circumferential axial flow channels 122 through which the reactants can flow. Radial flow channels 123 are provided between adjacent rods on each support ring. The axial flow channels and the circumferential axial flow channels are in fluid communication via the radial flow channels between the rods. The array also provides a central axial flow channel 124, which is also the working space for the agitator shaft 104 and agitator posts 105. In various examples, there is an axial circumferential flow channel 125 around the periphery of the chamber between the chamber wall and the outermost ring of heating elements.The agitator may also optionally include a mixing element operating within the annular flow channel 125 .

[0041] Heating element 120 is a vertically oriented rod-shaped induction heating element that can be installed through the top or bottom flange of the vessel.

[0042] Each heating element 120 in the array represents a separate induction heating element. Each of these elements comprises a pipe with a coil of metal tubing inside, optionally including an insulating layer and a magnetic flux concentrator. The coils may be optionally made from an insulated multi-twisted cable. The coils may be formed by helical winding inside each tube. The induction coils may be either conductive tubing or cable. The interior of the pipes may be sealed from the process fluids through welding and the use of suitable process pipe fittings. The pipes representing the susceptors and providing the rod shape of the heating unit are connected at the top and bottom to flat metal support rings 121 that serve to fix the array. The connections may be welded, brazed or otherwise fixed to the supports. The supports are made of a suitable metal such as stainless steel, and these support rings are attached vertically to the top or bottom of the vessel. Although not shown for illustrative purposes, the supply and return lines for the power and liquid cooling of the induction coils run from each heating element through vertical pipes or tubes through the top or bottom of the vessel. The use of a thermal break between the piping coils and the susceptor pipes can reduce the heat load on the liquid cooling. The supply and return lines can be joined together or bundled through a single supply and return pipe. When the supply and return are combined, it is sized to ensure proper distribution across the multiple legs of the array. The rods are positioned vertically to allow for fluid circulation during heating and product discharge at the end of the batch cycle. FIG. 2A shows a batch reactor vessel using an exemplary concentric array of heating elements 110. FIG. 2B shows a cross-sectional view of an exemplary concentric array of heating elements 120. FIG. 2C shows a top view of an exemplary concentric array of heating elements 120.

[0043] 3A-3B, one embodiment of a flow-through heat exchanger 200 is illustrated using an array of inductive heating elements 220 located therein. The heat exchanger is suitable for heating reaction precursors and reaction mixtures. The heat exchanger has a chamber that can be considered a chamber having an internal cavity 201 surrounded by chamber walls 202. The heat exchanger is suitable for polyamidation processes such as for heating precursor materials during the diacid dissolution step and during salt preparation, including when placed in a recirculation loop around the vessel. The heat exchanger can be of various diameters and lengths. The chamber walls can be of a conductive material and can be optionally surrounded by an external inductive coil 203, although in some configurations of the heat exchanger an external coil can be used without any internal coil. In various examples, the inductive coil of the heating element can be formed from a helical winding of conductive tubing or cable within the heating element tube, or the inductive coil can be external to the heat exchanger shell, or both. The interior cavity of the chamber can include a baffle 204, which can take the form of inductively heated fins, baffles, plates or tubes, or any such combination, to both act as a heating surface and agitate the flow channel. The heat exchanger can have an end cap 205, which can serve to mount the heating elements and provide space for electrical and cooling fluid supply connections and lines. The vessel can have an inlet 206 and an outlet 207. In various examples, the inlet receives the addition of polyamide precursors, such as diacids or diamines, or a reaction medium from a polyamide process.

[0044] The heating elements 220 are rod-shaped and oriented axially relative to the main flow axis in the heat exchanger. However, as is clear from the illustration, the array need not have an axis of symmetry, nor be centered about the flow axis of the heat exchanger. The heating elements are spaced to provide flow channels between them, allowing for radial, axial, and circumferential flow. The baffles 204 can increase turbulence and radial flow through the unit. The baffles 204 may be heated or unheated. In various aspects, the baffles may be oriented radially from the flow axis, e.g., perpendicular to the flow axis, or angled radially from the flow axis but not perpendicular. The rods are attached to end caps 205. The heat exchanger may be part of a recirculator.

[0045] The induction coil is deployed within the heating element 220, and connections to the coil are made outside the process fluid in the end cap 205, allowing the interior of the rod to remain sealed from the process fluid. Supply and return lines for power and liquid cooling of the induction coil can pass through one or both end caps 205. The coil can optionally be made from insulated multi-twisted cable. The heating elements are positioned to allow fluid circulation during heating and product exhaust and flow. Figure 3A shows a cross-sectional view of the heat exchanger 200. Figure 3B shows an end view of the heat exchanger illustrating the placement of the induction heating elements.

[0046] 4A-4B, one embodiment of a flow-through heat exchanger 200 is illustrated using an array of concentrically arranged induction heating elements 230. The heat exchanger is suitable for heating reaction precursors and reaction mixtures. The heat exchanger has a chamber that can be considered as a chamber having an internal cavity 201 surrounded by chamber walls 202. The heat exchanger is suitable for polyamidation processes such as for heating precursor materials during the diacid dissolution step and during salt preparation, including when placed in a recirculation loop around a stirred vessel. For example, the heat exchanger can provide high flow rates and be suitable for use as a heat exchanger in a thermosiphon reboiler. The heat exchanger can be of various diameters and lengths. The chamber walls can be of a conductive material and can be optionally surrounded by an external induction coil. For example, the outermost cylinder can be the chamber wall 202 or can be the heating element 230. The heating element 230 provides multiple concentric flow channels 231. The heat exchanger may have multiple inlets 206 or a single inlet 206 that is then split into multiple flow channels. The heat exchanger may have multiple outlets 207 or a single outlet 207 summed from multiple flow channels. In various examples, the inlets receive the addition of polyamide precursors, such as diacids or diamines, or reaction media from the polyamide process. The heat exchanger may be part of a recirculator. For example, U.S. Pat. No. 3,900,450, incorporated herein by reference in its entirety, describes a thermosiphon reboiler where vertical flow and high energy flux are important. While variations of the aforementioned embodiment may be suitable for use as a reboiler heat exchanger or recirculator, including thermosiphon reboilers, the example illustrated in FIG. 4 is particularly suitable for reboilers and vertically oriented heat exchangers.

[0047] The heating elements 230 are concentric cylinders oriented axially relative to the axis of the main current in the heat exchanger. Flow channels allow for flow along the axis and circumferential flow around the axis. Each heating element has inner and outer walls that are sealed together to enclose an induction coil. The coils can be fabricated from insulated multi-twisted cable or electrically insulated conductive tubing connected to the coolant circuit. A thermal break can be provided between the coils and the susceptor to reduce the heat load on the cooling circuit. The walls of the cylindrical heating elements act as the susceptor. The innermost wall of each pair is typically the primary heating surface since it receives the higher magnetic flux. Channels allow for vertical fluid flow between each heating element 230. In a one meter diameter reboiler, 27 cylindrical heating elements 230 can be arranged concentrically. Supply connections can be made to one or both ends of each cylindrical heating element 230. An internal induction coil can be arranged spirally within each respective heating element 230. A return connection can be made to the opposite end of the array. Connections to the coils can be made outside the fluid flow path, for example, by using end caps on which the heating elements 230 are attached. The heating elements are axially positioned to allow for high vertical flow and high energy flux. Figure 4A shows a cross-sectional view of the heat exchanger 200. Figure 4B shows an end view of the heat exchanger illustrating the concentric arrangement of the heating elements and flow channels.

[0048] With reference to Figures 5A-5B, one embodiment of an inductively heated chamber 300 using an array of inductive heating elements 310 is illustrated. The depicted chamber represents one of several stages in a multistage vessel, such as a multistage sequential distillation-polymerization column. Examples of multistage polyamidation reaction vessels are described in U.S. Patent Nos. 3,900,450 and 5,674,974, each of which is incorporated herein by reference in their entirety. Multistage vessels require excellent temperature control at each staging, and require heater surface temperatures to be maintained within well-controlled limits to avoid product decomposition. In a vertical distillation-polymerization column, the rising vapors in the vessel create a predominantly vertical flow, but it may be advantageous for there to be mass transfer and radial mixing at each stage in the vertical sequence. Various examples described herein provide channeling in the reaction stages, which allows for vertical flow through the staging and an overall high energy flux, but does not suffer from problems associated with uneven heating, product loss, or poor mixing at the stage level.

[0049] The chamber 300 includes an interior cavity 301 that can correspond to a staging chamber and is at least partially surrounded by a chamber wall 302. The vessel can be suitable for use as a polyamide reactor vessel, such as for the production of nylon-6,6. The chamber can be of various sizes. The chamber includes a stage plate 303, which can be a distillation tray, and a downcomer 304. The stage plate can be perforated with a number of openings 305 to allow gas phase reactant material to pass from a lower stage to a higher stage. The downcomer can allow the flow of liquid reactant material from an upper stage to a lower stage. FIG. 5 depicts a stage liquid level 306 to illustrate how liquid reactant material accumulates within the staging chamber. The chamber 300 further includes an induction heating element 310. In various examples, the heating element can be plate-type, rod-type, or cylindrical. FIG. 5 depicts a heating element formed from piping bent into a butterfly configuration, thus having aspects of both a cylindrical and a plate-type heating element. For example, the butterfly heating element may correspond to a portion of a cylinder or toroidal shape, with the supply and return tubing pinched off where attached to the mounting support. The coil may be constructed of an insulated multi-twisted cable or electrically insulated conductive tubing connected to the coolant circuit. Providing a thermal break between the coil and the susceptor reduces the heating load on the cooling circuit. The chamber walls may be of a conductive material and may optionally be surrounded by an external induction coil 307 in one or more stages, or may optionally or alternatively include the use of another type of external heating system.

[0050] In various examples, the induction heating element 310 is located below the downcomer in the region of liquid accumulation for the stage. For example, the heating element 310 can be placed directly below the downcomer at the location of the liquid downflow so as to contact the downflow, or the heating element 310 can be placed below the downcomer but surrounding the region of the liquid downflow.

[0051] The heating elements can be arranged in vertical stacks. In this example, the downcomer can be described as being centrally located along the vertical axis of the chamber. A stacked array of internally located induction heating elements 310 are distributed along the axis of the chamber to provide radial circumferential flow channels 311 between the vertical stacks. As clearly illustrated in FIG. 5A, a central opening in each of the vertically arranged. The heating elements 310 provide axial flow channels 312, which also provide a space downcomer. The axial and radial flow channels are in fluid communication. In various examples, at the periphery of the chamber, the heating elements terminate in front of the chamber wall to provide axial circumferential flow channels 313 in fluid communication with the radial circumferential flow channels and the central axial flow channel.

[0052] The heating elements may also be arranged in a concentric fashion, as more clearly illustrated in FIG. 5B. Between the concentric rings, the array provides additional circumferential axial flow channels 314 through which reactant materials may flow between the heating elements. Between adjacent butterfly heating elements in each ring, partial radial flow channels 315 are provided that allow fluid communication between the concentric circumferential flow channels 314 and the other flow channels. The concentric array also allows for a central axial flow channel 312.

[0053] 6A-6B, one embodiment of an induction heating vessel 600 includes a heated precursor mixing vessel 100 and a multi-stage continuous reactor vessel 601 that is a distillation-polymerization column. The heated precursor mixing vessel 100 is illustrated using a stacked array of induction heating elements 110 located therein. The vessel can be used to achieve dissolution of polyamide precursor salts, such as adipate salts and hexamethylenediamine salts. The vessel has an interior chamber cavity 101 surrounded by chamber walls 102. The chamber walls can be a conductive material. In various examples, the chamber walls can be optionally surrounded by an external induction coil 103. The interior chamber cavity can include an agitator having an agitator shaft 104 and an agitator post 105. The vessel may have an outlet drain 106 for removing and transporting dissolved precursors to the multi-stage continuous reactor vessel 601, and the top flange of the vessel has one or more inlets 107 for adding precursor materials and one or more outlets 108 for removing vapors or releasing pressure. A stacked array of inductive heating elements 110 located inside distributes along the axis of the heated precursor mixing vessel, providing radial circumferential flow channels 111 through which reactant materials can flow. The central opening of each of the vertically arranged heating elements 110 provides an axial flow channel 112, which is also the working space for the stirrer shaft 104 and the stirrer post 105. The axial and radial flow channels are in fluid communication. In various examples, at the periphery of the chamber, the heating elements terminate in front of the chamber wall to provide an axial circumferential flow channel 113 in fluid communication with the radial circumferential flow channel and the central axial flow channel. The inner diameter of the frustum 110 can define an axial flow channel 112 sized to allow working space for the agitator shaft 104 and the support post 105 .

[0054] The multi-stage continuous reactor vessel 601 includes an interior cavity 611 that can correspond to a staging chamber and is at least partially surrounded by a chamber wall 612. The vessel includes a stage plate 613 and a downcomer 614. The vessel further includes induction heating elements 620 at the various stagings. In various examples, the heating elements can be plate type, rod type, or cylindrical. FIG. 6 depicts a heating element formed from tubing bent into a butterfly configuration, thus having both cylindrical and plate type heating element sides. The multi-stage continuous reactor vessel 601 includes an inlet 618 for dissolved precursor salt. An additional inlet 619 can be included, for example, for precursor material in vapor form. The vessel also includes an outlet 617 for gas by-product removal and an outlet 616 for removal of polyamide polymer product or removal of prepolymer product for further processing. The vessel can also include an agitator 630, for which the lower heating element provides a working space.

[0055] Referring to FIG. 7, an embodiment of an inductively heated thermosiphon reboiler 700 having a distillation-polymerization column and an inductively heated high vertical flow-through heat exchanger. The vessel can have an interior cavity 711 at least partially surrounded by chamber walls 712. The vessel can include multiple distillation stages, which can have distillation trays 713 and downcomers 714. The vessel has an outlet 717 for gas by-product removal and an outlet 716 for removal of polyamide polymer product or removal of prepolymer product for further processing. The vessel also has an inlet 718 through which precursors and reactants are supplied. An outlet 719 is provided for recirculation of liquid reaction medium, which is removed from the interior cavity 711 and transferred via a thermosiphon to the high vertical flow-through heat exchanger 200. The flow-through heat exchanger 200 can be an interior cavity 201 containing an array of concentrically arranged inductive heating elements 230, surrounded by chamber walls 202. The chamber walls may be of a conductive material and may optionally be surrounded by an external induction coil. The heating element 230 provides a plurality of concentric, axially aligned flow channels 231. The heat exchanger may have an inlet 206 coupled to an outlet 207 which is then split into a plurality of flow channels and then routed to the interior cavity 711 of the distillation-polymerization column through a transfer line and an inlet 718. The heat exchanger may create a thermosiphon so that a pump between the column interior cavity 711 and the heat exchanger 200 may be omitted.

[0056] The heating elements can be arranged in a variety of ways. For example, an internal coil fitted into the tube provides many options for arranging the heater throughout the fluid volume, such as a butterfly arrangement. Additionally, in other embodiments, the staging chamber can suitably utilize plate-type and rod-type heating elements. For example, it is possible to utilize a relatively large horizontal pancake-type heating element with a coil sealed inside two plates, with the plate heater located directly below the downcomer. This arrangement has been found to promote liquid distribution and not interfere with stage function. Smaller fins or plates can be fabricated based on the pancake design, allowing more than one heating element or array of heating elements to fit into the stage without interfering with mixing. Butterfly-type heating elements can provide the ability to obtain a larger surface area with the fewest number of connections. For example, the arrangement depicted in FIG. 5 can share support, mounting, and connecting cables between adjacent heating elements.

[0057] The connection to the coil can be made directly through the outer vessel wall from below or above the working liquid level, or through channels fabricated in the mountings of the heating elements from below or above the liquid. For example, the mounting and coil connections can run along the downcomer or along the stage tray. Many other variations are possible without departing from the use of the invention.

[0058] In each of these examples, variations in spacing and deviations from orientation, e.g., deviations from perpendicularity, can be used without departing from the use of the invention. For example, in various aspects, the vessel and heat exchanger need not include a single concentric array, but can include any number of separate heating elements, and the heating elements need not be concentric or even centered within the vessel. Inductively heated fins or plates can be optionally deployed. The vessel and heat exchanger can be fabricated with a rectangular cross section. The vertical walls can be dimpled or textured to promote turbulent flow. Many such variations can be utilized without departing from the spirit and scope of the invention as defined in the claims.

[0059] It should be understood that throughout this document, values ​​expressed in range format should be interpreted in a flexible manner to include not only the numerical values ​​expressly recited as the limits of the range, but also all individual numerical values ​​or subranges subsumed within the range, as if each numerical value and subrange were expressly recited. For example, a range of "about 0.1% to about 5%" or "about 0.1% to 5%" should be interpreted to include not only about 0.1% to about 5%, but also individual values ​​(e.g., 1%, 2%, 3%, and 4%) and subranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the recited range. A statement of "about X to Y" has the same meaning as "about X to about Y" unless otherwise indicated. Similarly, a statement of "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z" unless otherwise indicated.

[0060] In this document, the terms "a," "an," or "the" are used to include one or more unless the context clearly dictates otherwise. The term "or" is used to refer to a non-exclusive "or" unless otherwise indicated. The statements "at least one of A and B" or "at least one of A or B" have the same meaning as A, B, or A and B. In addition, phrases or terms used herein and not otherwise defined are for descriptive purposes only and should not be understood as limiting. Any use of section headings is intended to aid in the reading of the document and should not be construed as limiting. Information associated with a section heading may occur within or outside that particular section.

[0061] The term "system" may be used to describe an apparatus. The term "apparatus" may refer to a single device or to an interconnected assembly of individual devices.

[0062] In the methods described herein, unless a temporal or operational order is explicitly recited, acts may be performed in any order without departing from the principles of the invention. Moreover, specified acts may be performed simultaneously unless express claim language dictates that they be performed separately. For example, a claimed act of doing X and a claimed act of doing Y may be performed simultaneously in a single operation, with the resulting process falling within the literal scope of the claimed process.

[0063] The term "about" as used herein allows for a degree of variation in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or the limits of a stated range, and includes the exact stated value or range.

[0064] As used herein, the term "substantially" refers to a majority or majority, such as 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, or 100%. The term "substantially free" as used herein can mean having none or an insignificant amount of the material present such that the amount of the material present does not affect the material properties of the composition including the material, and the composition is from about 0% to about 5%, or from about 0% to about 1%, or less than about 5%, or less than, equal to, or greater than about 4.5%, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or less than about 0.001% by weight of the material. The term "substantially free" can mean that the composition contains only small amounts, such as from about 0% to about 5%, or from about 0% to about 1%, or less than about 5%, or less than, equal to or greater than about 4.5%, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or less than about 0.001%, or about 0% by weight of the material.

[0065] All publications, including non-patent literature (e.g., scientific journal articles), published patent applications, and patents, mentioned in this specification are incorporated by reference as if each was specifically and individually indicated to be incorporated by reference.

[0066] This specification includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. Such examples may include elements in addition to those shown or described. However, the inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the inventors also contemplate embodiments and aspects that use any combination or permutation of the elements shown or described with respect to a particular embodiment, or with respect to other examples shown or described herein. EXAMPLES

[0067] Comparative Example 1 The nylon autoclave reactor vessel is equipped with an external heating fluid jacket, an internal heating fluid coil, and an agitator configured to function within the internal coil. Heated Dowtherm A heat transfer fluid, available from Dow Chemical (Midland, MI), is distributed through the external jacket around the vessel and through the internal coil. The total heat transfer area is 11.84 m. 2 The ratio of heat transfer area to liquid volume is 12.38 m 2 / m 3 It is found that with an input heat transfer fluid temperature of 325°C, it takes 8.1 minutes to reach 275°C.

[0068] In subsequent batches following this initial nylon batch production, the residual polymer left over from the previous batch acts as an insulator, limiting heat transfer in the initial batch cycle. This resulting insulating resistance to Dowtherm A heating further increases batch cycle times in the early stages of the polymerization process. Comparative Example 2

[0069] The nylon autoclave reactor vessel is equipped with an external induction heating coil and agitator. The agitator is used at the same rotation speed as in Comparative Example 1. The total heat transfer area of ​​this arrangement is 6.16 m 2 The ratio of heat transfer area to liquid volume is 6.44 m 2 / m 3The induction heater allows the surface temperature to be increased by an additional 25° C. over the entire area. Despite the higher surface temperature, it is found that it takes 29.0 minutes to reach 275° C. Comparative Example 3

[0070] In the nylon autoclave reactor vessel described in Comparative Example 1, the vessel wall is about 23 mm carbon steel with an internal 3-4 mm SS316 cladding. The Dowtherm A heating raises the outer thick wall temperature to about 325-330°C. A strong temperature gradient exists across the vessel wall while attempting to maintain the desired temperature up to about 275°C. Once the polymerization step is complete, the heating is turned off. However, the Dowtherm A heating system has thermal inertia, even after the heating is stopped. This phenomenon continues to heat the vessel contents to temperatures up to about 10°C above the desired set point. The vessel system is equipped with a pressure relief device and care must be taken to ensure that this overheating does not lead to a pressure event. In addition, such slow thermal effects caused by the Dowtherm A system result in an increased gelling effect in the polymer production. Comparative Example 4

[0071] In the nylon autoclave reactor vessel described in Comparative Example 3, batch production of nylon 66 / 6T requires an internal surface temperature (temperature of the metal facing the reactive process fluid) of approximately 330-335°C to be able to obtain a good quality molten polymer lace upon completion. The Dowtherm A heating system becomes inefficient due to its upper operating temperature limit. Dowtherm A is a standard heat transfer fluid used in industry due to its stability at high temperatures, but operating the system near their upper temperature limit suffers from high decomposition rates. Batches require long cycle times due to this limit on Dowtherm A temperature, as well as the very small temperature driving force available for heating. Example 1

[0072] The nylon autoclave reactor vessel is equipped with an external induction heating coil, an agitator, and a high surface area internal heater utilizing an induction heating coil. The agitator is used at the same rotation speed as in the previous example. The total heat transfer area is 25.3 m. 2 The ratio of heat transfer area to liquid volume is 26.4 m 2 / m 3 Using the same higher surface temperature as in Comparative Example 2, the endpoint temperature is found to be reached in 2.6 minutes.

[0073] In subsequent batches following this first nylon batch, residual polymer from the previous batch acts as insulation. However, unlike Comparative Example 1, induction heating remains more or less unaffected by this added thermal resistance to heating. Example 2

[0074] In the nylon autoclave reactor vessel described in Example 1, induction heating is now applied to heat the vessel contents. Also, when induction heating is stopped, no overheating of the contents due to thermal inertia is observed. It is also observed that gelation is reduced when the Dowtherm A heating system is replaced with induction heating. Example 3

[0075] For the nylon 66 / 6T batch production described in Comparative Example 4, induction heating replaces the Dowtherm A heating system. Heating becomes more efficient due to a higher temperature driving force than that present in the Dowtherm A system. Overall batch cycle time improves. Good quality molten polymer lace is produced at the end of production. Example 4

[0076] A nylon autoclave reactor vessel as described in Example 1 above is used, except that the internal stirring is replaced with an external circulation loop. The circulated fluid stream is introduced back into the vessel through a nozzle. The external circulation loop can optionally be integrated with a heat exchange device for additional heating and / or to compensate for heat loss to the surroundings. A 25.3 m 2 nylon autoclave reactor vessel as in Example 1 is used.2 For a heat transfer area of ​​0.1 mm, similar performance is achieved for heat up cycle time. Exemplary Aspects

[0077] The following exemplary aspects are provided, the numbering of which should not be construed as designating an order of importance.

[0078] Aspect 1 is a chemical vessel comprising: a chamber having an outer wall and an interior cavity; one, two or more heating elements within an internal cavity of the chamber, each heating element comprising a susceptor and an induction coil, optionally connected to a power source; A chemical vessel is provided in which the heating elements are positioned in an array with circumferential and axial channels between one, two, or more of the heating elements, centered on the axis of the chamber, which axis is the vertical axis or axis corresponding to the primary direction of flow through the vessel.

[0079] Example 2 provides the chemical vessel of Example 1, wherein the array comprises a stack of two or more axially distributed heating elements with circumferential radial channels between adjacent heating elements in the stack.

[0080] Example 3 provides the chemical vessel of example 1 or 2, wherein the array comprises heating elements radially distributed within the concentric rings to provide one or more circumferential and axial channels between adjacent concentric rings.

[0081] Example 4 provides a chemical vessel of any one of Examples 1-3, wherein the array comprises a concentric arrangement of heating elements radially distributed within the concentric rings, and comprises one or more circumferential and axial channels between adjacent concentric rings.

[0082] Example 5 provides a chemical container according to any one of Examples 1 to 4, wherein the array comprises heating elements distributed circumferentially and comprises one or more radial channels between adjacent heating elements.

[0083] Example 6 provides the chemical vessel of any one of Examples 1 to 5, wherein the induction coil comprises an insulated cable, a conduit for a cooling fluid, or both.

[0084] Example 7 provides the chemical container of any one of Examples 1-6, wherein the induction coil comprises an insulated cable.

[0085] Example 8 provides the chemical vessel of any one of Examples 1-7, wherein the induction coil comprises a conductive tube that serves as a conduit for a cooling fluid.

[0086] Example 9 provides the chemical container of any one of Examples 1 to 8, wherein the induction coil comprises a helical winding of a conductive tubing or cable.

[0087] Example 10 provides the chemical container of any one of Examples 1-9, wherein the heating element further comprises a magnetic flux concentrator, optionally connected to a power source.

[0088] Example 11 provides the chemical vessel of any one of Examples 1-10, wherein the susceptor is a top plate and a bottom plate welded together to enclose an induction coil.

[0089] Example 12 provides the chemical vessel of any one of Examples 1-11, wherein the heating element comprises a rod, a curved plate, an open cylinder, an open truncated cone, or a combination thereof.

[0090] Example 13 provides the chemical vessel of any one of Examples 1 to 12, wherein the heating element is in the shape of a rod, a plate, a spiral, a truncated cone with an open inner diameter, an open cylinder, or a tube in a butterfly configuration.

[0091] Example 14 provides the chemical vessel of any one of Examples 1-13, wherein the heating element is a rod.

[0092] Example 15 provides the chemical container of any one of Examples 1-14, wherein the heating element is a plate.

[0093] Example 16 provides the chemical container of any one of Examples 1-15, wherein the plates are oriented with their major axes parallel to the axis of the chamber or at an angle other than perpendicular to the axis of the chamber.

[0094] Example 17 provides the chemical vessel of any one of Examples 1-16, wherein the heating element is in the shape of a frustum of a cone having an open inner diameter.

[0095] Example 18 provides the chemical vessel of any one of Examples 1-17, wherein the open inner diameter of the heating element is sized to provide a working space for the agitator.

[0096] Example 19 provides the chemical vessel of any one of Examples 1 to 18, wherein the heating element is in the shape of a truncated cone having an inclination angle of about 1° to about 80°.

[0097] Example 20 provides the chemical vessel of any one of Examples 1-19, wherein the heating element is an open cylinder.

[0098] Example 21 provides the chemical container of any one of Examples 1-20, wherein the heating element is shaped or oriented so as not to present a major surface perpendicular to the axis.

[0099] Example 22 provides the chemical vessel of any one of Examples 1-21, wherein the heating element has a major surface oriented parallel to an axis of the vessel or at an angle other than 90° to the axis.

[0100] Example 23 provides the chemical vessel of any one of Examples 1 to 22, wherein the chamber comprises a staging tray and a downcomer positioned parallel to an axis of the chamber.

[0101] Example 24 provides the chemical vessel of any one of Examples 1 to 23, wherein the chamber comprises a mechanical agitator comprising a post and shaft positioned along an axis of the chamber, a mechanical agitator comprising a nozzle or jet inductor, a sparging inlet or a bubbling inlet, or any combination thereof.

[0102] Example 25 provides the chemical vessel of any one of Examples 1 to 24, wherein the chamber comprises a mechanical agitator comprising a post and a shaft positioned along an axis of the chamber.

[0103] Example 26 provides the chemical vessel of any one of Examples 1 to 25, wherein the chamber does not include a mechanical agitator and does not include a sparging inlet or a bubbling inlet.

[0104] Example 27 provides the chemical container of any one of Examples 1 to 26, wherein the interior cavity of the chamber comprises a circular or annular shaped cavity.

[0105] Example 28 provides the chemical vessel of any one of Examples 1 to 27, further comprising an external induction coil along an outer wall of the vessel, the vessel wall being a susceptor.

[0106] Example 29 provides the chemical vessel of any one of Examples 1 to 28, wherein an exterior wall of the vessel is heated with a liquid or vapor heat transfer fluid.

[0107] Example 30 provides the chemical vessel of any one of Examples 1 to 29, wherein the vessel comprises an external circulation loop.

[0108] Example 31 provides the chemical vessel of example 30, wherein the external circulation loop comprises an external heat exchanger selected from the group consisting of induction heating, thermal fluid heating, electrical resistance heating, gas-fired heating, phase change media heating, heat pipes, steam heating, and combinations thereof.

[0109] Example 32 provides the chemical vessel of example 30 or 31, wherein the external circulation loop is configured for heating by a heat transfer fluid adapted to flow through an external jacket, by heating by an internal coil, by heating by an external induction coil along an outer wall of the external circulation loop acting as a susceptor, or a combination thereof, and the external circulation loop optionally includes an internal induction heating element.

[0110] Example 33 provides the chemical vessel of any one of Examples 30-32, wherein the external circulation loop comprises geometric elements along the internal cavity, the interior walls, or both, to increase heat transfer area.

[0111] Example 34 provides the chemical vessel of any one of Examples 30-33, wherein the external circulation loop does not include an internal induction heating element.

[0112] Example 35 provides the chemical vessel of any one of Examples 1 to 34, wherein the power source is external to the vessel and connected to the induction coil via axially oriented tubing passing through a top or bottom of the vessel.

[0113] Example 36 provides the chemical vessel of any one of Examples 1-35, wherein the interior cavity of the chamber has a radial diameter of 1 meter or greater.

[0114] Example 37 provides the chemical container of any one of Examples 1-36, further comprising an external inductive coil along an exterior of the chamber wall, the chamber wall being conductive.

[0115] Example 38 provides a process for preparing a polyamide polymer comprising mixing a solution of polyamide precursors in a chemical vessel according to any one of examples 1-37.

[0116] Example 39 is a process for preparing a polyamide polymer, comprising: mixing a solution of polyamide precursors in one, two or more containers, each comprising a susceptor and an induction coil, optionally connected to a power source; and heating the polyamide precursor via electromagnetic induction to provide a polyamide product.

[0117] Example 40 provides the process of example 39, wherein the heating elements are positioned in an array to provide one or more channels between the heating elements through which the mixture can flow.

[0118] Example 41 provides the process of example 39 or 40, wherein the channels comprise at least one channel that is circumferential about an axis of the vessel and at least one channel that is parallel to the axis of the vessel, the axis of the vessel being a vertical axis or an axis corresponding to a primary direction of liquid flow through the vessel.

[0119] Aspect 42 is heating the polyamide precursor to provide a prepolymer and water vapor from a portion of the polyamide precursor; circulating the unreacted portion of the polyamide precursor through the vessel; Removing water vapor; and mixing the unreacted portion of the polyamide precursor with a prepolymer; 42. The process of any one of aspects 39-41, further comprising heating to provide a polyamide product.

[0120] Example 43 is a process for preparing a polyamide polymer, comprising: mixing a solution of polyamide precursors in a chamber of a vessel, the chamber including a plurality of induction heating elements, each induction heating element comprising a susceptor and an induction coil, optionally connected to an external power source; heating the polyamide precursor to provide a prepolymer from a portion of the polyamide precursor; circulating the unreacted portion of the polyamide precursor through the chamber to remove water vapor from the chamber; mixing the unreacted portion of the polyamide precursor with a prepolymer and heating the mixture to provide a polyamide polymer product; the heating elements are positioned in an array providing one or more channels between the heating elements through which the mixture can flow; the one or more channels comprising at least one channel circumferential about an axis of the chamber and at least one channel parallel to the axis of the chamber; The process provides a process in which the axis of the chamber is a vertical axis, or an axis corresponding to the main direction of liquid flow in the continuous flow reactor vessel.

[0121] Example 44 provides the process of any one of Examples 39 to 43, wherein the polyamide precursor comprises a diacid, a diamine, or both.

[0122] Example 45 provides the process of any one of Examples 39 to 44, wherein the polyamide precursor comprises a diacid salt, a diamine salt, or both.

[0123] Example 46 provides the process of any one of Examples 39 to 45, wherein the polyamide precursor is heated to a dissolution temperature.

[0124] Example 47 provides the process of any one of examples 39 to 46, wherein the polyamide precursor is heated to a temperature to induce amide condensation.

[0125] Example 48 provides the process of any one of Examples 39 to 47, wherein the polyamide precursor comprises a diacid and a diamine.

[0126] Example 49 provides the process of any one of Examples 37 to 48, wherein the polyamide product is nylon-6,6.

[0127] Embodiment 50 is an apparatus for preparing a polyamide polymer, comprising: at least one inlet for adding a liquid polyamide precursor; a vessel comprising one or more chambers containing a plurality of heating elements, each heating element comprising a susceptor and an induction coil, optionally connected to a power source; an agitator, a recirculator, or both, configured to circulate reaction components through one or more chambers of the vessel; an outlet for removing water vapor; and an outlet for removing the polyamide polymer; the heating elements are positioned in an array providing one or more channels between the heating elements through which a liquid can flow; The device includes one or more channels, at least one channel that is circumferential about an axis of the vessel and at least one channel that is parallel to the axis of the vessel, the axis of the vessel being a vertical axis or an axis corresponding to a primary direction of liquid flow through the vessel.

[0128] Embodiment 51 is an apparatus for preparing a polyamide polymer, comprising: A vessel comprising a chamber containing one, two or more heating elements, each heating element comprising a susceptor and an induction coil, optionally connected to a power source; an inlet for adding liquid polyamide precursor to the vessel; an outlet for removing water vapor from the vessel; an outlet for removing the polyamide polymer from the container; the heating elements are positioned in an array that provides one or more channels between one, two or more heating elements through which a liquid can flow; The device includes one or more channels, at least one channel that is circumferential about an axis of the chamber and at least one channel that is parallel to the axis of the chamber, the axis of the chamber being a vertical axis or an axis corresponding to a primary direction of liquid flow through the container.

[0129] Example 52 provides the apparatus of example 50 or 51, wherein the array comprises a stack of two or more heating elements distributed axially with a circumferential radial channel between adjacent heating elements in the stack.

[0130] Example 53 provides an apparatus as described in any one of Examples 50 to 52, wherein the array comprises a concentric arrangement of heating elements radially distributed in the concentric rings and comprises one or more circumferential and axial channels between adjacent concentric rings.

[0131] Example 54 provides an apparatus described in any one of examples 50 to 53, wherein the array comprises heating elements distributed circumferentially about the axis of the chamber so as to provide one or more radial channels between adjacent heating elements.

[0132] Example 55 provides the apparatus of any one of Examples 50-54, wherein the induction coil comprises an insulated cable, a conduit for a cooling fluid, or both.

[0133] Example 56 provides the apparatus of any one of Examples 50-55, wherein the induction coil comprises a conductive tube that serves as a conduit for the cooling fluid.

[0134] Example 57 provides the apparatus of any one of Examples 50-56, wherein the induction coil comprises a helical winding of a conductive tubing or cable.

[0135] Example 58 provides the apparatus of any one of Examples 50-57, wherein the heating element is in the shape of a rod, a plate, a spiral shape, a truncated cone with an open inner diameter, an open cylinder, or a tube in a butterfly configuration.

[0136] Example 59 provides the apparatus of any one of Examples 50 to 58, wherein the chamber comprises a staging tray and a downcomer positioned parallel to an axis of the chamber.

[0137] Example 60 provides the apparatus of any one of Examples 50 to 59, wherein the chamber comprises a mechanical agitator comprising a post and shaft positioned along an axis of the chamber, a mechanical agitator comprising a nozzle or jet inductor, a sparging inlet or a bubbling inlet, or any combination thereof.

[0138] Example 61 provides the apparatus of any one of Examples 50-60, wherein the chamber does not include a mechanical agitator.

[0139] Example 62 provides the apparatus of any one of Examples 50-61, wherein the chamber does not include a sparging inlet or a bubbling inlet.

[0140] Example 63 provides the apparatus of any one of Examples 50 to 62, wherein the interior cavity of the chamber comprises a circular or annular shaped cavity.

[0141] Example 64 provides the apparatus of any one of Examples 50-63, further comprising an external induction coil along an outer wall of the vessel, the vessel wall being a susceptor.

[0142] Example 65 provides the apparatus of any one of Examples 50-64, wherein an outer wall of the vessel is heated with a liquid or vapor heat transfer fluid.

[0143] Example 66 provides the apparatus of any one of Examples 50 to 65, wherein the vessel comprises an external circulation loop.

[0144] Example 67 provides the apparatus of example 66, wherein the external circulation loop comprises an external heat exchanger selected from the group consisting of induction heating, thermal fluid heating, electrical resistance heating, gas combustion heating, phase change media heating, heat pipes, steam heating, and combinations thereof.

[0145] Example 68 provides an apparatus as described in example 66 or 67, wherein the external circulation loop is configured for heating by a heat transfer fluid adapted to flow through an outer jacket, by an internal coil, by heating by an external induction coil along an outer wall of the external circulation loop acting as a susceptor, or a combination thereof, and the external circulation loop optionally includes an internal induction heating element.

[0146] Example 69 provides the apparatus of any one of Examples 66-68, wherein the external circulation loop comprises geometric elements along the internal cavity, the internal walls, or both, to increase heat transfer area.

[0147] Example 70 provides the chemical vessel of any one of Examples 66-69, wherein the external circulation loop does not include an internal induction heating element.

[0148] Example 71 provides the apparatus of any one of Examples 50-70, wherein the heating element is located in a heat exchanger of a recirculator, a staging chamber of a multi-stage continuous reactor vessel, or an autoclave chamber of a batch reactor vessel.

[0149] Example 72 provides the apparatus of any one of Examples 50-71, wherein the vessel comprises a plurality of chambers oriented as successive stages within a distillation-polymerization column.

[0150] Example 73 provides the apparatus of any one of Examples 50-72, wherein the chamber is a heat exchanger in a recirculator of a thermosiphon reboiler.

[0151] Example 74 provides the apparatus of any one of Examples 35 to 73, wherein the vessel is a batch reactor vessel.

[0152] Example 75 provides the apparatus of any one of Examples 35 to 74, wherein the vessel is a continuous reactor vessel.

[0153] Example 76 is the chemical container of any one of Examples 1 to 38, wherein the polyamide is nylon-6,6.

[0154] The present invention provides a process according to any one of aspects 39 to 49, or an apparatus according to any one of aspects 50 to 75.

[0155] Example 77 provides a chemical vessel, process, or apparatus of any one or any combination of Examples 1-76, optionally configured according to the drawings.

[0156] Example 78 provides a chemical vessel, process, or apparatus of any one or any combination of Examples 1-77, configured such that each optionally described element or option is available for use or selection.

Claims

1. 1. A chemical vessel comprising: a chamber having an outer wall and an interior cavity; two or more heating elements within the internal cavity of the chamber, each comprising a susceptor and an induction coil, optionally connected to a power source; the heating elements are positioned in an array with circumferential and axial channels between two or more of the heating elements about an axis of the chamber, the axis being a vertical axis or an axis corresponding to a primary direction of flow through the vessel; A chemical vessel, wherein the induction coil comprises an insulated cable, a conduit for a cooling fluid, or both.

2. 1. A chemical vessel comprising: a chamber having an outer wall and an interior cavity; two or more heating elements within the internal cavity of the chamber, each comprising a susceptor and an induction coil, optionally connected to a power source; the heating elements are positioned in an array with circumferential and axial channels between two or more of the heating elements about an axis of the chamber, the axis being a vertical axis or an axis corresponding to a primary direction of flow through the vessel; The chemical vessel, wherein the induction coil comprises an insulated cable.

3. 1. A chemical vessel comprising: a chamber having an outer wall and an interior cavity; two or more heating elements within the internal cavity of the chamber, each comprising a susceptor and an induction coil, optionally connected to a power source; the heating elements are positioned in an array with circumferential and axial channels between two or more of the heating elements about an axis of the chamber, the axis being a vertical axis or an axis corresponding to a primary direction of flow through the vessel; A chemical vessel wherein the induction coil comprises a conductive tube that serves as a conduit for a cooling fluid.

4. 1. A chemical vessel comprising: a chamber having an outer wall and an interior cavity; two or more heating elements within the internal cavity of the chamber, each comprising a susceptor and an induction coil, optionally connected to a power source; the heating elements are positioned in an array with circumferential and axial channels between two or more of the heating elements about an axis of the chamber, the axis being a vertical axis or an axis corresponding to a primary direction of flow through the vessel; The chemical vessel, wherein the induction coil comprises a helical winding of conductive tubing or cable.

5. 5. The chemical container of claim 1, wherein the array comprises a stack of two or more heating elements distributed axially with circumferential radial channels between adjacent heating elements in the stack.

6. 5. The chemical vessel of claim 1, wherein the array comprises a concentric arrangement of the heating elements radially distributed in concentric rings and comprises one or more circumferential and axial channels between adjacent concentric rings.

7. 5. The chemical container of claim 1, wherein the array comprises heating elements distributed circumferentially and comprises one or more radial channels between adjacent heating elements.

8. 5. The chemical vessel of claim 1, wherein the heating element is in the shape of a rod, a plate, a spiral, a truncated cone with an open inner diameter, an open cylinder, or a tube in a butterfly configuration.

9. 5. The chemical vessel of claim 1, wherein the chamber comprises a staging tray and a downcomer positioned parallel to the axis of the chamber.

10. 5. The chemical vessel of claim 1, wherein the chamber comprises a mechanical agitator comprising a post and shaft positioned along the axis of the chamber, a mechanical agitator comprising a nozzle or jet inductor, a sparging inlet or a bubbling inlet, or any combination thereof.

11. 5. The chemical vessel of claim 1, wherein the chamber does not include a mechanical agitator and does not include a sparging or bubbling inlet.

12. The chemical vessel of claim 1 , wherein the interior cavity of the chamber comprises a circular or annular shaped cavity.

13. 5. The chemical vessel of claim 1, further comprising an external induction coil along an outer wall of the chamber, the outer wall of the chamber being a susceptor.

14. The chemical vessel of claim 1 , wherein the exterior wall of the vessel is heated with a liquid or vapor heat transfer fluid.

15. The chemical vessel of claim 1 , wherein the vessel comprises an external circulation loop.

16. 16. The chemical vessel of claim 15, wherein the external circulation loop comprises an external heat exchanger selected from the group consisting of induction heating, thermal fluid heating, electrical resistance heating, gas combustion heating, phase change media heating, heat pipes, steam heating, and combinations thereof.

17. 17. The chemical vessel of claim 16, wherein the external circulation loop is configured for heating by a heat transfer fluid adapted to flow through an outer jacket, by heating by an internal coil, by heating by an external induction coil along an outer wall of the external circulation loop acting as a susceptor, or a combination thereof, the external circulation loop optionally including an internal induction heating element.

18. 1. A chemical vessel comprising: a chamber having an outer wall and an interior cavity; two or more heating elements within the internal cavity of the chamber, each comprising a susceptor and an induction coil, optionally connected to a power source; the heating elements are positioned in an array with circumferential and axial channels between two or more of the heating elements about an axis of the chamber, the axis being a vertical axis or an axis corresponding to a primary direction of flow through the chemical vessel; the chemical vessel comprises an external circulation loop; A chemical vessel, wherein the external circulation loop includes geometric elements along the interior cavity, interior walls, or both, to increase heat transfer area.

19. 20. The chemical vessel of claim 18, wherein the external circulation loop does not include an internal induction heating element.

20. 1. A process for preparing a polyamide polymer comprising: mixing a solution of polyamide precursor in a vessel comprising one, two or more heating elements, each comprising a susceptor and an induction coil, optionally connected to a power source; and heating the polyamide precursor via electromagnetic induction to provide a polyamide product. the induction coil comprises an insulated cable, a conduit for a cooling fluid, or both; the heating elements are positioned in an array to provide one or more channels between the heating elements through which the mixture can flow; A process wherein the channels comprise at least one channel that is circumferential about an axis of the vessel and at least one channel that is parallel to the axis of the vessel, the axis of the vessel being a vertical axis or an axis corresponding to a primary direction of liquid flow through the vessel.

21. 1. A process for preparing a polyamide polymer comprising: mixing a solution of polyamide precursor in a vessel comprising one, two or more heating elements, each comprising a susceptor and an induction coil, optionally connected to a power source; and heating the polyamide precursor via electromagnetic induction to provide a polyamide product. the induction coil comprising a helical winding of a conductive tube or cable; the heating elements are positioned in an array to provide one or more channels between the heating elements through which the mixture can flow; A process wherein the channels comprise at least one channel that is circumferential about an axis of the vessel and at least one channel that is parallel to the axis of the vessel, the axis of the vessel being a vertical axis or an axis corresponding to a primary direction of liquid flow through the vessel.

22. heating the polyamide precursor to provide a prepolymer and water vapor from a portion of the polyamide precursor; circulating an unreacted portion of the polyamide precursor through the vessel; Removing water vapor; and mixing the unreacted portion of the polyamide precursor with the prepolymer; 22. The process of claim 20 or 21, further comprising heating to provide the polyamide product.

23. 22. The process of claim 20 or 21, wherein the polyamide precursor comprises a diacid and a diamine.

24. 22. The process of claim 20 or 21, wherein the polyamide product is nylon-6,6.

25. 1. An apparatus for preparing a polyamide polymer comprising: a vessel comprising a chamber containing two or more heating elements, each of said heating elements comprising a susceptor and an induction coil, optionally connected to a power source; an inlet for adding liquid polyamide precursor to said vessel; an outlet for removing water vapor from the vessel; an outlet for removing the polyamide polymer from the container; the heating elements are positioned in an array providing one or more channels between the two or more heating elements through which a liquid can flow; the one or more channels comprising at least one channel circumferential about an axis of the chamber and at least one channel parallel to the axis of the chamber, the axis of the chamber being a vertical axis or an axis corresponding to a primary direction of liquid flow through the vessel; An apparatus wherein the induction coil comprises an insulated cable, a conduit for a cooling fluid, or both.

26. 1. An apparatus for preparing a polyamide polymer comprising: a vessel comprising a chamber containing two or more heating elements, each of said heating elements comprising a susceptor and an induction coil, optionally connected to a power source; an inlet for adding liquid polyamide precursor to said vessel; an outlet for removing water vapor from the vessel; an outlet for removing the polyamide polymer from the container; the heating elements are positioned in an array providing one or more channels between the two or more heating elements through which a liquid can flow; the one or more channels comprising at least one channel circumferential about an axis of the chamber and at least one channel parallel to the axis of the chamber, the axis of the chamber being a vertical axis or an axis corresponding to a primary direction of liquid flow through the vessel; The apparatus, wherein the induction coil comprises a helical winding of a conductive tube or cable.

27. 27. The apparatus of claim 25 or 26, wherein the heating element is located in a heat exchanger of a recirculator, a staging chamber of a multi-stage continuous reactor vessel, or an autoclave chamber of a batch reactor vessel.

28. 27. The apparatus of claim 25 or 26, wherein the vessel comprises two or more chambers oriented as successive stages in a distillation-polymerization column.

29. 27. Apparatus according to claim 25 or 26, wherein the chamber is a heat exchanger in a recirculator of a thermosiphon reboiler.

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