WATER PRESSURIZED MECHANICAL SEAL

TECHNICAL FIELD The present disclosure relates to agitated autoclave vessels and related methods which utilize agitator mechanical seals for maintaining low interfering mineral content in the vessels during polymerization processes occurring therein.

BACKGROUND

Polyamide polymers, such as nylon 6,6, can be synthesized using complex chemical engineering processes on a relatively large scale. These chemical engineering processes can include steps such as a salt strike step where polyamide (e.g., nylon 6,6) salt solutions are prepared, an evaporation step where some of the water from the salt solution is evaporated off and optionally certain additives can be included, an autoclave polymerization step where the salt solution is placed under heat and pressure for polymerization, and extrusion/cutting steps where the essentially final polymeric raw materials are formed. Other steps can also be included as understood generally by those skilled in the art.

With specific respect to the autoclave polymerization step in batch processes, it is noted that there are a number of autoclaves that can be used with acceptable results. One type of autoclave is the agitated autoclave, which typically includes a revolving auger within the autoclave vessel that is controlled from the outside of the autoclave vessel. In order to retain pressure within the vessel, a mechanical seal can be used where the agitator enters the autoclave vessel. However, because the chemistry of preparing polyamide polymers can be very sensitive, specific design parameters for the mechanical seal can be implemented to retain the integrity of the polymerization process.

SUMMARY

The disclosure herein relates to an agitated autoclave with a pressurized mechanical seal, a method of sealing an agitated autoclave, and a method of preparing polyamide polymer in an agitated autoclave. The agitated autoclave can comprise an autoclave vessel, an agitator, and a mechanical seal. The autoclave vessel can be adapted to receive and polymerize a polyamide salt composition to form a polyamide polymer. The agitator can include a shaft, an auger portion (e.g. inside of the vessel), and a drive portion (outside of the vessel). The mechanical seal can form a pressure boundary about the shaft at or adjacent to a wall of the autoclave vessel. The mechanical seal includes a pressurized water chamber pressurized with seal water that is also in contact with the shaft. The seal pressure can be greater than the vessel pressure within the autoclave vessel. The seal water in the pressurized water chamber can have a calcium content of less than 3 ppm and an iron content of less than 0.3 ppm. In one example, an automated agitated autoclave can include the agitated autoclave described above and a process controller. The process controller can include a pressure module for controlling pressure within the autoclave vessel, an agitation module for controlling the agitator, and a seal module for controlling seal water pressure within the pressurized water chamber.

In another example, a method of sealing an agitated autoclave about an agitator shaft can comprised assembling an autoclave vessel with an agitator positioned through a vessel wall of the autoclave vessel, attaching a mechanical seal to the shaft between the auger portion and the drive portion, and

pressurizing a water chamber with seal water. The agitator can include a shaft, an auger portion positioned within the autoclave vessel, and a drive portion positioned outside of the autoclave vessel for engaging with a drive mechanism. The mechanical seal can be adapted to form a pressure boundary about the shaft at or adjacent to the vessel wall. The seal water can be in contact with the shaft (where the shaft transitions from outside of the autoclave vessel to inside of the autoclave vessel) and can be held at a seal pressure greater a vessel pressure within the autoclave vessel. The seal water can have a calcium content of less than 3 ppm and an iron content of less than 0.3 ppm. In one example, the mechanical seal can further comprise a cooling water chamber operable to form a cooling jacket about the shaft, but unlike the seal water, the cooling water is typically not in contact with the shaft. In this example, the method can further comprise the step of flowing cooling water into or through the cooling water chamber.

In another example, a method of preparing a polyamide polymer in an agitated autoclave can comprise charging an agitated autoclave with a polyamide salt composition suitable for preparing a polyamide polymer, and pressurizing the agitated autoclave using various pressures suitable for forming the polyamide polymer. Additional steps can include agitating the polyamide salt composition while preparing the polyamide polymer. The agitator can include a shaft, an auger portion positioned within the autoclave vessel, and a drive portion positioned outside of the autoclave vessel for engaging with a drive mechanism. At a location adjacent to where the shaft transitions from outside of the autoclave vessel to inside of the autoclave vessel through a vessel wall, a mechanical seal is present that is pressure sealed with seal water. Furthermore, the seal water can be held at a pressure about the shaft (where the shaft enters the autoclave vessel through the vessel wall) that is greater than a pressure within the agitated autoclave, thus, preventing pressure within the autoclave vessel to be lost through the mechanical seal. Additionally, the seal water can have a calcium content less than 3 ppm and an iron content less than 0.3 ppm.

Additional features and advantages of the invention will be apparent from the detailed description that follows, which illustrates, by way of example, features of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an automated agitated autoclave with a mechanical seal that is usable in accordance with examples of the present disclosure;

FIG. 2 is an exemplary graph depicting relative plots of pressure and agitation during a batch cycle for preparing a polyamide polymer in accordance with examples of the present disclosure;

FIG. 3 is a cross-sectional view of a mechanical seal that is useable with the autoclave of FIG. 1 in accordance with examples of the present disclosure; and

FIG. 4 is a cross-sectional view of an alternative mechanical seal that is useable with the autoclave of FIG. 1 in accordance with examples of the present disclosure.

It should be noted that the figures are merely exemplary of certain embodiments of the present invention and no limitations on the scope of the present invention are intended thereby.

DETAILED DESCRIPTION

Although the following detailed description contains many specifics for the purpose of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the disclosed embodiments.

Accordingly, the following embodiments are set forth without any loss of generality to, and without imposing limitations upon any claimed invention. Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

As used in this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a polyamide" includes a plurality of polyamides.

The term "polymenzable solution" or "polymenzable composition" refers to the solution or composition that is added to an agitated autoclave in accordance with examples of the present disclosure, and that upon processing the composition within the autoclave under certain heat and pressure profiles, a polymer can be formed that may be extruded or otherwise harvested for further use. It is noted, however, that as the polymenzable solution or composition begins to polymerize within the autoclave, the composition will begin to thicken into a polymer. Thus, it is difficult to delineate at what point it ceases to be a polymerizable solution or composition compared to a thickening polymer. As a result, for convenience, the term "polymerizable solution" or "polymerizable composition" may be used herein to describe the composition in the autoclave regardless of its polymerization state. Additionally, the term "solution" is not intended to describe every component in the composition, as some materials or additives may actually be dispersed in the liquid, e.g., titanium dioxide. The term "solution" or "composition" is merely used for convenience as some materials will be in solution at the outset.

The term "polyamide salt" refers to the salt that is included in the polymerizable composition (optionally along with other additives) that provides the basic polymerizable material for forming the polyamide polymer. If the polyamide polymer is nylon 6,6, for example, then the salt can be prepared from a condensation reaction between adipic acid and hexamethylene diamine. Other additives can also be included in the polyamide composition, either introduced prior to the agitated autoclave, or introduced directly into the agitated autoclave. Titanium dioxide, for example, may optionally be introduced directly into the autoclave during a second pressure cycle, whereas other additives, such as catalysts, anti-foaming agents, or the like, may be better suited for inclusion with the polymerizable salt prior to introducing the polymerizable composition into the agitated autoclave or during other pressure cycles in the autoclave, though this sequence or even the presence of these or other additives is not required.

The term "cycle" refers to the stages of a batch polymerization process as defined primarily by the pressure profile within the agitated autoclave. A first cycle (Cycle 1 ) occurs at the beginning of the batch process while the pressure is being increased from a low press to a relative high pressure. A second cycle (Cycle 2) occurs as the relative high pressure is maintained for a period of time, usually by modulating heat and venting the pressure at the same time. A third cycle (Cycle 3) occurs as the relative high pressure is reduced back to a low pressure (which can optionally be an even lower pressure than the initial low pressure as per the use of a vacuum). A fourth cycle (Cycle 4) occurs as the (vacuum) low pressure is maintained for a period of time. A fifth cycle (Cycle 5) occurs as the prepared polymer in the autoclave is being extruded by increased pressure from the agitated autoclave vessel. The agitator as described herein is typically used during Cycles 1 -4, and can be used at various RPM rates or under different timing profiles during those cycles.

The terms "relative high pressure" refer to pressures within a batch process where the pressure is at essentially its highest level. Thus, the pressure is "high" relative to the other pressure levels during the batch cycle process. For example, an initial low pressure can be increased to a relative high pressure during Cycle 2. In considering a pressure profile of a 5 cycle batch, when the pressure is at or about the highest pressure of a batch process profile, the "relative high pressure" has been reached. In some of the examples shown herein, a relative high pressure of about 16 to 20 Bar is shown, though other pressure profiles may provide a relative high pressure outside of this range. Thus, the mechanical seal typically includes a pressurized water chamber with seal water that is capable of being pressurized to accommodate at least the relative high pressure within the autoclave vessel, e.g., be brought to a slightly higher pressure than even the relative high pressure of the autoclave.

The term "agitating" refers to the state of the agitator while it is functioning at a level sufficient to cause at least some polymerizable composition or resultant polymer mixing. In one example, the agitator can be an auger that is spinning within the agitated autoclave at up to 100 RPM, but can range from 5 RPM to 90 RPM, for example.

The terms "seal water" and "cooling water" both refer to water. However, as cooling water is not directly involved in the sealing of the agitator at a surface of the autoclave vessel (where leaking of the water may occur), sealing water can be any water that is suitable for cooling the mechanical seal that is available, e.g., tap water, recycled water, deionized water, etc. However, with respect to the "seal water," as this water may include water that by design can leak from within a mechanical seal into the autoclave vessel (where the polymer is being prepared), this water should be water that is low in ion content, particularly iron and calcium ion content. For example, the seal water can have a calcium content of less than 3 ppm and an iron content less than 0.3 ppm.

In this disclosure, "comprises," "comprising," "containing" and "having" and the like can have the meaning ascribed to them in U.S. Patent law and can mean "includes," "including," and the like, and are generally interpreted to be open ended terms. The term "consisting of" is a closed term, and includes only the devices, methods, compositions, components, structures, steps, or the like specifically listed, and that which is in accordance with U.S. Patent law.

"Consisting essentially of or "consists essentially" or the like, when applied to devices, methods, compositions, components, structures, steps, or the like encompassed by the present disclosure, refers to elements like those disclosed herein, but which may contain additional structural groups, composition components, method steps, etc. Such additional devices, methods, compositions, components, structures, steps, or the like, etc., however, do not materially affect the basic and novel characteristic(s) of the devices, compositions, methods, etc., compared to those of the corresponding devices, compositions, methods, etc., disclosed herein. In further detail, "consisting essentially of or "consists essentially" or the like, when applied to devices, methods, compositions, components, structures, steps, or the like encompassed by the present disclosure have the meaning ascribed in U.S. Patent law and the term is open- ended, allowing for the presence of more than that which is recited so long as basic or novel characteristics of that which is recited is not changed by the presence of more than that which is recited, but excludes prior art embodiments. When using an open ended term, like "comprising" or "including," it is understood that direct support should be afforded also to "consisting essentially of language as well as "consisting of language as if stated explicitly.

Phrases such as "suitable to provide," "sufficient to cause," or "sufficient to yield," or the like, in the context of methods of synthesis, refers to reaction conditions related to time, temperature, solvent, reactant concentrations, and the like, that are within ordinary skill for an experimenter to vary to provide a useful quantity or yield of a reaction product. It is not necessary that the desired reaction product be the only reaction product or that the starting materials be entirely consumed, provided the desired reaction product can be isolated or otherwise further used.

It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range includes "about 'x' to about 'y'". To illustrate, a concentration range of "about 0.1 % to about 5%" should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1 %, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1 %, 2.2%, 3.3%, and 4.4%) within the indicated range. In an

embodiment, the term "about" can include traditional rounding according to significant figures of the numerical value. In addition, the phrase "about 'x' to 'y " includes "about 'x' to about 'y'".

The term "about" as used herein, when referring to a numerical value or range, allows for a degree of variability in the value or range, for example, within 10%, or, in one aspect within 5%, of a stated value or of a stated limit of a range.

Where features or aspects of the disclosure are described in terms of a list or a Markush group, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. For example, if X is described as selected from the group consisting of bromine, chlorine, and iodine, claims for X being bromine and claims for X being bromine and chlorine are fully described as if listed individually. For example, where features or aspects of the disclosure are described in terms of such lists, those skilled in the art will recognize that the disclosure is also thereby described in terms of any combination of individual members or subgroups of members of list or Markush group. Thus, if X is described as selected from the group consisting of bromine, chlorine, and iodine, and Y is described as selected from the group consisting of methyl, ethyl, and propyl, claims for X being bromine and Y being methyl are fully described and supported.

As used herein, all percent compositions are given as weight-percentages, unless otherwise stated. When solutions of components are referred to, percentages refer to weight-percentages of the composition including solvent (e.g., water) unless otherwise indicated.

As used herein, all molecular weights (Mw) of polymers are weight- average molecular weights, unless otherwise specified.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features that may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

With this in mind, there are several different types of autoclaves that are used to prepare polymeric raw materials. One particular type of autoclave is an agitated autoclave that includes an agitation member, such as an auger, for assisting with the polymerization process. The agitator assists with the process by controlling foaming while in use, providing salt flow mixing as well as continuous mixing of contents within the autoclave (no layered effect), controlling heat transfer, reducing vortex, drawing polymer through the autoclave, achieving higher productivity of autoclave vessels, providing a viscometer to measure relative viscosity (RV), etc. In one example, agitated autoclaves include an agitator with an auger portion or working end that resides inside of the autoclave vessel, and a drive end that interfaces with an agitator drive device, such as a motor, on an outside of the autoclave vessel. Thus, at a location where the shaft of the agitator enters the autoclave, a seal can be used in order to maintain pressure within the autoclave vessel, while at the same time, allowing the agitator shaft to revolve. More specifically, the seal can be a mechanical seal that includes a water seal feature which utilizes a pressure differential to maintain pressure within the autoclave vessel. However, with this pressure differential, water will inevitably enter the autoclave vessel. Thus, calcium carbonate at concentrations typically found in water can be problematic as water leaks from the mechanical seal into the autoclave vessel, particularly with many polyamide polymerization processes. For example, as the calcium carbonate interacts with phosphate catalysts that are often used in polyamide polymer systems, this catalyst is rendered less effective. Furthermore, the amount of iron content in typical water can also be problematic if it leaks into the autoclave vessel, as the polyamide polymer can unduly crosslink in a manner that may not be desirable.

In accordance with this, the disclosure herein relates to an agitated autoclave with a pressurized mechanical seal, a method of sealing an agitated autoclave, and a method of preparing polyamide polymer in an agitated autoclave. The agitated autoclave can comprise an autoclave vessel, an agitator, and a mechanical seal. The autoclave vessel can be adapted to receive and polymerize a polyamide salt composition to form a polyamide polymer. The agitator can include a shaft, an auger portion (e.g. inside of the vessel), and a drive portion (outside of the vessel). The mechanical seal can form a pressure boundary about the shaft at or adjacent to a wall of the autoclave vessel. The mechanical seal includes a pressurized water chamber pressurized with seal water that is also in contact with the shaft. The seal pressure can be greater than the vessel pressure within the autoclave vessel. The seal water in the

pressurized water chamber can have a calcium content of less than 3 ppm and an iron content of less than 0.3 ppm. In one example, an automated agitated autoclave can include the agitated autoclave described above and a process controller. The process controller can include a pressure module for controlling pressure within the autoclave vessel, an agitation module for controlling the agitator, and a seal module for controlling seal water pressure within the pressurized water chamber. In another example, a method of sealing an agitated autoclave about an agitator shaft can comprised assembling an autoclave vessel with an agitator positioned through a vessel wall of the autoclave vessel, attaching a mechanical seal to the shaft between the auger portion and the drive portion, and

pressurizing a water chamber with seal water. The agitator can include a shaft, an auger portion positioned within the autoclave vessel, and a drive portion positioned outside of the autoclave vessel for engaging with a drive mechanism. The mechanical seal can be adapted to form a pressure boundary about the shaft at or adjacent to the vessel wall. The seal water can be in contact with the shaft and can be held at a seal pressure greater a vessel pressure within the autoclave vessel. The seal water can have a calcium content of less than 3 ppm and an iron content of less than 0.3 ppm. In one example, the mechanical seal can further comprise a cooling water chamber operable to form a cooling jacket about the shaft, but unlike the seal water, the cooling water is typically not in contact with the shaft. In this example, the method can further comprise the step of flowing cooling water into or through the cooling water chamber.

In another example, a method of preparing a polyamide polymer in an agitated autoclave can comprise charging an agitated autoclave with a polyamide salt composition suitable for preparing a polyamide polymer, and pressurizing the agitated autoclave using various pressures suitable for forming the polyamide polymer. Additional steps can include agitating the polyamide salt composition while preparing the polyamide polymer. The agitator can include a shaft, an auger portion positioned within the autoclave vessel, and a drive portion positioned outside of the autoclave vessel for engaging with a drive mechanism. At a location adjacent to where the shaft transitions from outside of the autoclave vessel to inside of the autoclave vessel through a vessel wall, a mechanical seal is present that is pressure sealed with seal water. Furthermore, the seal water can be held at a pressure about the shaft (where the shaft enters the autoclave vessel through the vessel wall) that is greater than a pressure within the agitated autoclave, thus, preventing pressure within the autoclave vessel to be lost through the mechanical seal. Additionally, the seal water can have a calcium content less than 3 ppm and an iron content less than 0.3 ppm. With these general examples set forth above, it is noted in the present disclosure that when describing the automated agitated autoclaves or methods, individual or separate descriptions are considered applicable to one another, whether or not explicitly discussed in the context of a particular example or embodiment. For example, in discussing a particular agitator per se as they related to the device, the method embodiments are also inherently included in such discussions, and wee versa.

Turning now to FIG. 1 , a schematic cross-sectional view of an automated agitated autoclave is shown. This FIG. is not necessarily drawn to scale, and does not show each and every detail that is typically present in an agitated autoclave, opting instead to show schematic representations of features particularly relevant to the present disclosure. Thus, an automated agitated autoclave 10 can include an autoclave vessel 20 and an agitator 30. The vessel includes a vessel wall 22, which is typically a cladded vessel wall, and the vessel wall and/or other structures are adapted to support one or more type of heating components 24, 26. In this example, external jacket heating components are shown at 24 and internal heating components are shown at 26. It is noted that the internal heating components can be present in either or both locations shown. In one example, the internal heating components are positioned nearer the agitator (as shown in phantom lines), to provide appropriate heat near the agitator. In this example, there may also be room near the exterior vessel wall 22 for a pair of wall scrapers (not shown) which act to remove the polymer from close contact with the vessel wall as the polymer is moved through the vessel. The external jacket heating components can be used to raise the temperature of the polymerizable composition or polymer contained within the vessel, and the internal heating components in particular can be used to prevent polymer from becoming adhered to an interior surface of the vessel wall. It is noted that the interior heating components are shown schematically in cross-section, but it is understood that any shape or configuration of interior heating components could be used. It is also noted that the heating components can be configured or adapted to carry any fluid known in the art for providing heat to autoclaves, including gases and/or liquids. Furthermore, at the bottom end of the autoclave vessel is a valve opening 28. The valve is not shown, but this is the location where polymer prepared in the autoclave is extruded for further processing.

With respect to a specific agitation process described herein, in the configuration shown, the agitator 30, and more particularly the auger portion 34 of the agitator, will bring the polymerizable composition (or polymer as it forms) upward toward a central region of the autoclave vessel 20 and downward toward the vessel wall 22 in the flow pattern 32 shown in FIG. 1 . Thus, in one specific example, when the auger is spinning, the auger is moving at an RPM level sufficient to cause at least some polymerizable composition or polymer mixing in accordance with the pattern shown. For example, the auger portion of the agitator can be spinning within the agitated autoclave at up to 100 RPM, but is normally set to a speed of 5 RPM to 90 RPM, or from 70 RPM to 90 RPM, for example. RPM levels outside this range can also be used, as would be appreciated by one skilled in the art. In further detail regarding the agitator, in addition to the auger portion shown as it resides within the autoclave vessel, a drive portion 36 is shown that is outside of the autoclave vessel which interfaces with an agitator drive 38, thereby causing the agitator to rotate.

Typically, the pressure in the autoclave is provided by the heating component and the heating module, but can additionally be introduced into the vessel with an injection line or valve 44 used to bring the polymerizable composition or other additives from an evaporator (not shown) into the autoclave. Furthermore, to control pressure as it rises in response to temperature or fluid injection, an autoclave vent 46 can also be present for venting gases from the autoclave vessel to reduce the pressure. Other inlet ports or venting ports 48 can also be present, such as an inlet port for injecting additives that may be separate from inlet ports or injection lines for introducing the polymerization composition. The injection lines, vents, inlet ports, valves, etc., shown generally at 44, 46, and/or 48, are provided as depicted for exemplary purposes only in the arrangement provided, as any arrangement or suitable structure for these devices can be used as would be understood by one skilled in the art.

The autoclave vessel 20 and the agitator 30 are typically configured so that a mechanical seal 36 is present at an interface between the outside of the vessel and the inside of the vessel. Thus, the mechanical seal is typically at or just above and adjacent to the vessel wall 22 where the agitator shaft enters the autoclave vessel. As previously described briefly, during a second cycle of the polymerization process within the autoclave, the pressure is brought to a relative high pressure during Cycle 2 where a substantially constant pressure is maintained. For example, the pressure during the second cycle can be maintained at from 16 to 20 Bar during the entire second cycle, though pressure profiles outside of this range are also useable in some examples. As this is the highest pressure in the vessel during the cycling processes described herein, in one example, the pressure maintained at the mechanical seal can be maintained or temporarily brought to a level that is even higher than this pressure level to avoid fluids or gases from being ejected from the pressurized autoclave vessel and out through the seal. Alternatively, the pressure can be modulated in the mechanical seal to stay above the pressure level within the autoclave vessel, but in some examples, the pressure in the mechanical seal need not be maintained at its highest pressure level at all times (as long as it stays above the pressure within the vessel). That being understood, if the pressure differential between the seal water in the mechanical seal and the autoclave vessel is too great, a significant amount of seal water may enter the autoclave vessel. Thus, the pressure profile for the seal water in the mechanical seal can be brought to a level that is greater than the pressure in the autoclave vessel, but can be maintained at levels that do not allow too much seal water to enter the autoclave vessel.

In further detail regarding, the autoclave of FIG. 1 can be adapted for automated control using a process controller 50, which includes various modules 60, 79, 80, 90 for carrying out general functions or process steps. For example, the heating component(s) 24, 26, inlet lines or valves 44, and vents 46 can be can be controlled by a pressure control module 60. The agitator 30, such as agitator RPM and drive device 42, can be controlled by an agitation module 70. The mechanical seal 36, including seal water pressure, can be controlled by a seal module 80. Other modules 90 can also be present, such as an extrusion module or other module that may be useful in accordance with examples of the present disclosure. The modules can work together to cycle the system in a manner to cause predictable batch polymerization of the polymerizable solution or composition.

To exemplify the relationship between the pressure cycles and the use of the agitator, FIG. 2 sets forth one embodiment where the agitator cycle is shown as it relates to the pressure profile during several typical pressure cycles. More specifically, in this FIG., five pressure cycles are shown. Specifically, a first cycle (Cycle 1 ) occurs at the beginning of the batch process while the pressure is being increased from a low pressure 92a to a relative high pressure 94. A second cycle (Cycle 2) occurs as the relative high pressure is maintained for a period of time. A third cycle (Cycle 3) occurs as the relative high pressure is reduced to an even lower pressure 92b than initially present, which can be in some examples, reduced using a vacuum. A fourth cycle (Cycle 4) occurs as the lower (vacuum) pressure is maintained for a period of time. A fifth cycle (Cycle 5) occurs as the pressure is increased again for the purpose of extruding the polymer from the agitated autoclave vessel. Regarding the agitator profile in FIG. 2, in the example shown, the agitator is turned on to a relative high RPM level 96 (e.g., 70 to 90 RMP) toward the beginning of the first cycle and is maintained until it is reduced again during Cycle 4 in a stepwise manner. The first stepwise reduction 98a can be carried out to save power, and the second stepwise reduction 98b can be carried out to use the auger to test the viscosity of the polymer being formed in the autoclave vessel. It is noted that this profile is not required, as it can be stopped and started as desired, and the RPM profile can likewise be adjusted as may be desired.

Illustrated in FIG. 3 is a mechanical seal 100 in accordance with an embodiment of the present disclosure. The mechanical seal can form a pressure boundary about an agitator shaft 101 at or near a wall of a vessel 102, which in this case is an upper wall. The shaft can extend through an opening 103 in the vessel wall and through the mechanical seal to mechanically couple an agitator drive mechanism that is external to the vessel with an agitator auger disposed inside the vessel. In one aspect, the drive mechanism can rotate the shaft about a longitudinal axis 104 of the shaft. The opening of the vessel can be sized to permit unrestricted movement of the shaft within the opening. The mechanical seal can be coupled to the vessel 102 with one or more fasteners 105a, 105b. A seal 106, such as an O-ring, can be disposed between the vessel wall and the mechanical seal to minimize or prevent leakage of gas and/or loss of pressure from within the vessel. Alternatively, the seal can be merely a hard material on hard material seal, e.g., metal on metal seal, provided the junction where the two hard materials come together is very flat within very tight tolerances (e.g., optically measured and/or verified flatness). Alternatively, double mechanical seals, or seals with lapped joints can also be used. Essentially, any seal that substantially prevents fluid loss can be used.

The mechanical seal 100 can include an inner collar 1 10 disposed about the shaft 101 , such that a gap 107 exists between the inner collar and the shaft. The mechanical seal can also include a sleeve 120 disposed about the shaft, and can be in direct contact with the shaft. In one aspect, the sleeve can be configured to facilitate relative movement between the shaft and the sleeve, such as sliding contact. In another aspect, the sleeve can be configured to rotate with the shaft, such as with an interference fit. Seals 130, 131 can be associated with the sleeve and disposed about the shaft to prevent or minimize the passage of gas or liquid between the sleeve and the shaft.

The sleeve 120 can be coupled to an outer collar 140 via a bearing 150, such that the sleeve can move relative to the outer collar, the inner collar 1 10, and the vessel 102. The bearing can comprise a ball bearing, a roller bearing, a bushing, or any other suitable type of bearing or rotatable fitting. In one aspect, the bearing can comprise a spherical bearing to accommodate a misalignment or variation of the shaft 101 as the shaft rotates about the axis 104. A seal 132 can be disposed between the sleeve and the outer collar to prevent or minimize the passage of gas or liquid between the sleeve and the outer collar while also permitting relative movement between the sleeve and the outer collar.

The mechanical seal 100 can include a pressurized water chamber 160 formed, at least in part, by the inner collar 1 10. The pressurized water chamber can be fluidly coupled to a water source 161 via an inlet 162. The water source can provide seal water to the pressurized water chamber such that the seal water is in contact with the shaft and is held at a seal pressure greater than a vessel pressure within the vessel 102. Thus, the pressurized seal water, in combination with one or more seals 130, 131 , 132 can minimize or prevent the escape of gases from the vessel and/or maintain a pressure within the vessel. The seals 130, 131 , 132 disclosed herein can comprise an O-ring or any other suitable seal, e.g., very flat surfaces that minimize leakage, double mechanical seals, lapped joints, etc. In one aspect, the seal water in the pressurized water chamber can also function to cool various components of the mechanical seal, such as the inner collar and the sleeve 120, as well as the shaft 101 .

In some manufacturing processes, the pressure within the vessel 102 can vary throughout the course of a process. In one aspect, the water source 161 , which can include or be operable with a pump, can maintain a constant or other predetermined pressure difference between the seal pressure in the pressurized water chamber 160 and the vessel pressure as the pressure varies within the vessel. Thus, more pressure within the pressure seal may be needed during Cycle 2 of the polymerization cycle than would be needed during Cycle 4, for example. Thus, a lower pressure can be maintained in the pressurized water chamber during Cycle 4 than during Cycle 2. In one example, the pressure difference (in Bar) between the vessel pressure and the seal pressure can be at least 2%, at least 5%, at least 10%, at least 25%, or at least 50% with the pressure seal being greater than the vessel pressure. The slightly higher water pressure within the mechanical seal need not follow or be proportional to the upward and downward pressure changes within the autoclave vessel, but this is an optional aspect of the disclosure. That being described, in short, the pressure seal can be configured to provide a water pressure that functionally keeps the polyamide polymeric composition and associated gaseous pressure within the autoclave vessel, but at the same time, allows as minimal of a leakage from the pressure seal into the autoclave vessel as may be practical or desirable for a given batch run, e.g., from essentially no leakage into the autoclave vessel to only a very small of water leakage into the autoclave vessel is ideal. For example, the leakage from the pressurized water chamber of the mechanical seal into the pressurized autoclave vessel can be essentially none, or less than 1 %, less than 5%, less than 10%, less than 20%, or less than 50% by weight of the water used in the pressurized water chamber during a given batch run (e.g. Cycles 1 -4 where the agitator is used). As mentioned, during use, some of the seal water from the pressurized water chamber 160 can leak and enter the vessel 102, such as by passing between the inner collar 1 10 and the shaft 101 and running down the shaft into the vessel. In one aspect, the seal water provided by the water source 161 to the pressurized water chamber can have a calcium content of less than 3 ppm and/or an iron content of less than 0.3 ppm. In another example, the calcium content can be less than 1 ppm and/or the iron content can be less than 0.1 ppm.

Furthermore, the seal water can comprise demineralized water having a resistivity of at least 1 ΜΩ, at least 5 ΜΩ, at least 10 ΜΩ, at least 15 ΜΩ, or at least 18 ΜΩ. That being stated, as soon as the deionized water comes out of typical systems used to prepare the water and the water is exposed to the atmosphere, it can dramatically lose resistivity as it quickly becomes ionized again. Thus, though resistivity is often used to determine the degree of demineralization or deionization of water, it is notable that this is not the only consideration. For example, if 1 ΜΩ water is essentially deionized with respect to many ions, but has more than 0.3 ppm iron, this water may still be undesirable for use, as the presence of iron ions may be more problematic for the formation polyamide polymers than many other minerals or ions that may also be present in the water. Thus, of particular interest is the substantial removal of iron and calcium ions from the seal water used in the pressurized water chamber 160. In short, it is noted that ordinary water can present problems when introduced to the chemical processes described herein. However, very low calcium and/or iron content in the seal water as set forth herein can minimize or reduce such problems, even with relatively high leakage from the mechanical seal and into the autoclave.

That being stated, not all leakage is problematic. In one aspect, the gap 107 between the inner collar 1 10 and the shaft 101 can prevent or minimize contact between the inner collar and the shaft as the shaft rotates about the axis 104. However, due to imperfections or imbalances in the shaft, the shaft can contact or rub the inner collar as the shaft rotates. In this case, leaking seal water from the pressurized water chamber 160 can provide some lubrication for the rotating shaft against the inner collar. In one aspect, the agitator can be balanced to prevent or minimize vibrations of the rotating shaft that can lead to leakage, but the added benefit of lubrication and a small amount of leakage may be desirable in some circumstances, particularly if the water is substantially devoid of calcium and/or iron.

The mechanical seal 100 can also include cooling water chamber 170 operable to form a cooling jacket about the shaft 101 , but which is not in contact with the shaft. As shown in the figure, the cooling water chamber can be included in the outer collar 140 to cool the various components of the mechanical seal. The cooling water chamber can receive water from a cooling water source 171 into an inlet 172. Because the cooling water chamber is not in contact with the shaft, the water used in the cooling water chamber can be any suitable type of water and is not limited to the more purified water as set forth herein for the seal water. However, in one aspect, the cooling water source can be the same as the seal water source. In another aspect, the cooling water can be circulated through the cooling water chamber and discharged via an outlet 173. In a further aspect, the cooling water can be recirculated or recycled from the outlet to the inlet of the cooling water chamber. A heat exchanger 174 can be used to cool the water from the outlet prior to delivery of the recirculated water to the inlet.

FIG. 4 illustrates a mechanical seal 200 in accordance with another embodiment of the present disclosure. This embodiment is similar in many respects to the mechanical seal 100 of FIG. 3, with many of the same features. As some of these features are identical or similar to that described in FIG. 3, they are not redescribed here except to say that the discussion of FIG. 3 applies to the embodiment shown in FIG. 4 in many respects. In this embodiment, however, due to a lack of a bearing, a shaft 201 is configured to slide relative to an outer collar 240 as the shaft rotates about a longitudinal axis 204 of the shaft. A recess 208 formed in the outer collar can reduce the available contact surface area between the shaft and the outer collar, thereby reducing friction. This aspect of the recess can also facilitate assembly of the shaft and the outer collar. The recess can also reduce the costs of manufacturing of the outer collar by reducing the length over which a tight tolerance may be maintained.

With reference to nylon 6,6 in particular, a typical batch size in accordance with examples of the present disclosure can be from about 1000 Kg to about 1500 Kg, and can be cycled during the batch within the autoclave at from about 100 to 120 minutes. Batch sizes and timing outside of these ranges can also be used, depending on equipment and polymer choices, or other considerations within the knowledge of one skilled in the relevant arts.

As mentioned, the polyamide polymers prepared in accordance with examples of the present disclosure can be nylon-type polyamides, such as nylon 6,6 or nylon 6. A polymerizable composition used to form nylon 6,6 polymer, for example, can be prepared initially using a salt strike process where adipic acid and hexamethylene diamine reacted. Water present in this composition, either introduced as a solvent to carry the reactants or by the condensation reaction of the adipic acid and the hexamethylene diamine, can be removed when the salt solution is introduced into an evaporator to remove a portion of the water prior to introduction into the agitated autoclave as described herein. This solution, referred to herein as the polymerizable composition, can include the nylon 6,6 salt, as well as other additives, such as anti-foaming agents, catalysts, antioxidant stabilizers, antimicrobial additives, optical brighteners, acid-dyable polymer, acid dyes or other dyes, or the like, as is generally known in the art. If the objective is to whiten the product, titanium dioxide can also be included, but is usually added directly to the autoclave to avoid agglomeration. When prepared for polymerization in the autoclave, the polyamide salt, such as nylon 6,6 salt, can be present in the polymerizable composition in an amount ranging from about 50 wt% to 95 wt%, for example.

If a catalyst is added, the catalyst can be present in the polymerizable polyamide composition in an amount ranging from 10 ppm to 1 ,000 ppm by weight. In another aspect, the catalyst can be present in an amount ranging from 10 ppm to 100 ppm by weight. The catalyst can include, without limitation, phosphoric acid, phosphorous acid, hypophosphoric acid arylphosphonic acids, arylphosphinic acids, salts thereof, and mixtures thereof. In one embodiment, the catalyst can be sodium hypophosphite, manganese hypophosphite sodium phenylphosphinate, sodium phenylphosphonate, potassium phenylphosphinate, potassium phenylphosphonate, hexamethylenediammonium bis- phenylphosphinate, potassium tolylphosphinate, or mixtures thereof. In one aspect, the catalyst can be sodium hypophosphite. The polyamide compositions prepared in accordance with embodiments disclosed herein can be improved in whiteness appearance through the addition of an optical brightener, such as titanium dioxide. Such polyamides can exhibit a permanent whiteness improvement and can retain this whiteness improvement through operations such as heat setting. In one embodiment, the optical brightener can be present in the polymerizable polyamide in an amount ranging from 0.01 wt% to 1 wt%.

In addition, these polymerizable polyamides may contain an antioxidant stabilizer or an antimicrobial additive as is known in the art. Additionally, the polymerizable composition may contain an anti-foaming additive. In one embodiment, the anti-foaming additive can be present in the polymerizable composition in an amount ranging from 1 ppm to 500 ppm by weight.

The polymerizable compositions, in accordance with embodiments of the present disclosure, can be inherently acid dyeable, but may also be rendered into a basic dyeing form by modifying these polymers or copolymers with a cationic dye copolymerized in the polymer. This modification makes compositions particularly receptive to coloration with base dyes.

As a further note, some of the functional units described in this

specification have been labeled as "modules," in order to more particularly emphasize their implementation independence. For example, a "module" may be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like. Modules may also be implemented in software for execution by various types of processors. An identified module of executable code may, for instance, comprise one or more blocks of computer instructions, which may be organized as an object, procedure, or function.

Nevertheless, the executables of an identified module need not be physically located together, but may comprise disparate instructions stored in different locations which comprise the module and achieve the stated purpose for the module when joined logically together. Indeed, a module of executable code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within modules, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different storage devices. The modules may be passive or active, including agents operable to perform desired functions.

Although the subject matter has been described in language specific to structural features and/or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements can be devised without departing from the spirit and scope of the described technology.