DURING POLYMERIZATION PROCESS

TECHNICAL FIELD The present disclosure relates to a method and automated device for reducing foaming in an agitated autoclave.

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, an autoclave process 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.

These chemical engineering processes can either be batch processes or continuous process, and with respect to the autoclave, there are a number of autoclaves that can be used with acceptable results. Regardless of the autoclave selected for use, foaming during various cycles in the autoclave process can be problematic. This can be especially true in larger batches and as commercial pressures to provide more polymer throughput begin to exist. Thus, it would be an advancement in the art to discover and utilize various techniques for reducing foam, even in very large batches with relatively quick batch cycles. SUMMARY

The disclosure herein relates to methods of reducing foaming in an agitated autoclave, and automated agitated autoclaves adapted to reduce foam while cycling the autoclave, particularly during polyamide polymerization processes, such as nylon 6,6 polymerization processes.

In accordance with this, a method of preparing polyamide polymer can comprise the step of introducing a polymerizable composition including a polyamide salt into an agitated autoclave for polymerization. The method also includes the step of increasing pressure within the agitated autoclave during a first cycle until a relative high pressure is achieved while agitating the

polymerizable composition with an agitator. Additional steps include maintaining the relative high pressure during a second cycle at least in part by venting the agitated autoclave, and stopping or significantly reducing movement (by at least about 75%) of the agitator during at least a portion of the second cycle until a foam level within the agitated autoclave is reduced.

In another example, an automated agitated autoclave can comprise a heating component controlled by a heating module, an autoclave vent controlled by a venting module, and an agitator controlled by an agitation module. The venting module can at least partially control a second cycle by venting pressure from the autoclave to maintain a relative high pressure within the autoclave as the heating module increases the heating component temperature. The agitation module can modify the agitator from an agitating setting to a non-agitating setting during at least a portion of the second cycle.

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 that is usable in accordance with examples of the present disclosure;

FIG. 2 is an exemplary graph depicting the relationship between agitated autoclave pressure and agitator RPM during a batch cycle in accordance with examples of the present disclosure;

FIG. 3 is an exemplary graph depicting the relationship between agitated autoclave pressure, heat, and venting in relation to example times for activating and deactivating an agitator during a batch cycle in accordance with examples of the present disclosure; and

FIG. 4 is an exemplary series of graphs depicting the effects of stopping or significantly reducing agitation during at least a portion of the second cycle 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 "polymerizable composition" or "polymerizable solution" refers to the solution that is added to an agitated autoclave in accordance with examples of the present disclosure, and that upon processing the polymerizable

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 polymerizable composition begins to polymerize within the autoclave, the solution or slurry will begin to thicken into a polymer. Thus, it is difficult to delineate at what point it ceases to be a

polymerizable composition compared to a thickening polymer. As a result, for convenience, the term "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" 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 solution, 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, 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, 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. 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 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.

The term "foam level" refers to the volume of foam within the

polymerizable composition or resulting polymer prepared therefrom. The foam bubbles can be present above the polymerizable composition, e.g., within the head space of the vessel, and can also be present throughout the body of the polymerizable composition itself. Thus, a reduction in foam can be determined by considering how much foam has been reduced.

The terms "stopping" or "non-agitating" refers to reducing the speed of the agitator device to 0 RPM or a functional equivalent where essentially no agitation is contributing to the mixing of the polymerizable composition within the autoclave. Typically, the agitator is an auger where rotation is discontinued or shut down temporarily so that it is at rest within the polymerizable composition. Alternatively, the auger can be set to a speed of less than 5 RPM in the ever- thickening polymerizable composition, as this very slow rotation profile may be slow enough to be considered functionally stopped or in a non-agitating state. Thus, terms related to "stop" or "non-agitate" include both complete stopping of the agitator as well as functional stopping where only minor rotation levels are present. In one example, however, stopping can mean completely stopping movement to 0 RPM.

The term "significantly reducing" movement includes reducing movement of an agitator by at least about 75%. For example, reducing movement of an agitator from 60 RPM to 15 RPM represents a reduction of movement of 75%.

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. In some cases, less than 5 RPM may be considered to be in a stopped or non-agitated state if the polymerizable composition or polymer is not being effectively mixed together.

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 or auger 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. However, with specific respect to foaming, though the auger or agitator is generally thought to be a good tool to control foaming, it has been discovered that by discontinuing use of the auger or agitator at specific points in time, particularly associated with relative high pressure and venting during Cycle 2, surprisingly, additional foaming reduction has been discovered to be achievable.

In accordance with this, the present disclosure relates to methods of reducing foaming in an agitated autoclave, as well as an automated agitated autoclave for controlling foaming, particularly during polyamide polymerization processes, such as nylon 6,6 polymerization processes. The method of preparing polyamide polymer with reduced foaming can comprise multiple steps, such as introducing a polymerizable composition including a polyamide salt into an agitated autoclave for polymerization, and increasing pressure within the agitated autoclave during a first cycle until a relative high pressure is achieved while agitating the polymerizable composition with an agitator. Additional steps can include maintaining the pressure at the relative high pressure during a second cycle at least in part by venting the agitated autoclave, and stopping or significantly reducing movement (by at least about 75%) of the agitator during at least a portion of the second cycle until a foam level within the agitated autoclave is reduced. The "stopping" step can be by completely stopping the agitator from any movement, or by functionally stopping the agitator so it does not provide its intended agitation profile, e.g., less than 5 RPM. Alternatively, the agitator can be significantly reduced in movement by about 75% and still get some meaningful foam reduction. The step of stopping or significantly reducing movement (by at least about 75%) of the agitator can be under a variety of timing processes, such as during the entire second cycle, during a beginning portion of the second cycle and not during an end portion of the second cycle, or during an end portion of the first cycle and a beginning portion of the second cycle, but not during a beginning portion of the first cycle and an end portion of the second cycle, for example. Typically, the step of stopping or significantly reducing movement (by at least about 75%) of the agitator occurs during venting of the agitated autoclave, though this is not required.

Likewise, an automated agitated autoclave can comprise a heating component controlled by a heating module, an autoclave vent controlled by a venting module, and an agitator controlled by an agitation module. The venting module can at least partially control a second cycle by venting pressure from the autoclave to maintain a relative high pressure within the autoclave as the heating module increases the heating component temperature. The agitation module can modify the agitator from an agitating setting to a non-agitating setting during at least a portion of the second cycle.

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 or auger per se, the method embodiments are also inherently included in such discussions, and vice 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 or auger 30 in this example. 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 there are two different positions of internal heating components shown, one near the exterior wall of the vessel, and another nearer the auger (shown in phantom line). Either positioning can be used. In one example, when the internal heating component is nearer the auger, scrapers (not shown) can be positioned near the autoclave wall to remove polymer from the wall and toward the center of 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 or auger 30 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 agitating, 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 or 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 some cases, less than 5 RPM may be considered to be in a stopped or non-agitated state if the polymerizable composition or polymer is not being effectively mixed together. For example, the auger set at less than 5 RPM in an ever-thickening polymerizable composition may be slow enough to be considered functionally stopped or in a non-agitating state if there is no more mixing benefit to the batch than would be found in a standard autoclave or non-agitated autoclave. However, in another more typical example, the auger is completely stopped, e.g., turned off, disengaged, etc., and thus, the auger is not just stopped functionally, but literally in a non-spinning state.

Problems associated with foam 34 or foaming throughout the

polymerizable composition or in the head space 36 of an agitated autoclave vessel 20 typically occur to a great degree while the pressure is high and while there is a significant amount of venting occurring from the autoclave vessel. Typically, the pressured 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. It is noted that irrespective of the description and shown location of these inlets, valves, vents, etc., these or other ports can be used differently than shown for any purpose designed by the user, as would be appreciated by one skilled in the art. As previously briefly described, during a second cycle of the polymerization process within the autoclave, the pressure is brought to a relative high pressure to maintain a substantially constant pressure. 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. Regarding timing, the second cycle can last from 10 to 45 minutes, and the step of stopping or significantly reducing movement (by at least about 75%) of the agitator can be for an amount of time from about 30 seconds to about 7 minutes in length in one specific embodiment. In other embodiments, the stopping or significantly reducing movement can be for a longer period of time, such as for the entire second cycle, or for a longer period of time that does not span the entire second cycle.

To exemplify the relationship between the pressure cycles and the use of the agitator or auger, FIG. 2 sets forth one embodiment where the auger is shut down or otherwise stopped to reduce foaming of the polymerizable composition. 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 1 10a to a relative high pressure 120. 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 1 10b 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 to a high RPM level 130 toward the beginning of the first cycle and is then completely stopped 140 (0 RPM) at about the beginning of the second cycle. In this example, the stopped configuration straddles slightly the end of the first cycle and the beginning of the second cycle, but could likewise be shifted slightly to the right so that it is at or near 0 RPM during only the second cycle, or even throughout the second cycle. The agitator profile shown seems to work well with respect to reducing foaming, but the agitator can be shut down or otherwise functionally stopped at any place where foam reduction may be desired. That being stated, it has been found that shutting down or otherwise stopping or significantly reducing movement of the agitator for a short period of time, e.g., just enough to reduce the foaming to a desired level, is particularly advantageous in order to maximize the use of the agitator.

Returning now to FIG. 1 , foam 34 reduction can be measured by based on the foam that is at the top surface in the head space of the vessel, or

alternatively, based on the foam that is present throughout the polymerizable composition that is being used to form the polymer. It is noted that as the foam rises from the body of the polymerizable composition into the head space, some defoaming can occur naturally at or near the vessel wall 22 within the head space 36 while the agitator is spinning at a high RPM level. However, by stopping or significantly reducing movement of the agitator for a short period of time during Cycle 2, additional defoaming can be effectuated. As an example, the foam level present in the agitated autoclave can be reduced by at least 20% by volume before the agitator is restarted after the stopping step. In another example, the foam level can be reduced by at least 50% by volume. In still another example, the foam level can be reduced by at least 90% by volume. Once the foam has been reduced to an acceptable level, the systems and methods described herein can also include restarting the agitator after reducing the foam level, but before a third cycle is begun.

In further detail regarding the automated control of the agitated autoclave, a controller 50, which includes various modules 60, 80, 90 can be used to automatically carry out the general functions or process steps of the automated agitated autoclave. For example, the heating component(s) 24, 26 can be controlled by a heating module 60. The autoclave vent 46 or vents can be controlled by a venting module 80. The agitator, which in this case is an auger 30, can be controlled by an agitation module 90. The modules can work together to cycle the system in a manner to cause predictable batch polymerization of the polymerizable composition. FIG. 3 illustrates an example where the heating module, venting module, and agitation module work together to achieve acceptable polymerization results with acceptable levels of foaming in

accordance with examples of the present disclosure.

Specifically, FIG. 3 depicts a five cycle process of a similar nature of that described in Example 2, but with further detail regarding temperature and venting profiles. In this example, in preparation for starting the reaction process, a salt solution is brought into the agitated autoclave from an evaporator at from 80 wt% to 84 wt% concentration levels. During a first cycle (Cycle 1 ), the pressure is increased using heat, injection lines/valves, etc., and can be controlled using venting and/or vacuum procedures. Pressure levels in this system can range from vacuum pressures to about 20 Bar. Typically, during much or all of Cycle 1 , there is little to no venting.

In a second cycle (Cycle 2), the pressure is held substantially constant at a relative high pressure, e.g., from 16 to 20 Bar. This is carried out by venting the system, such as at maximum venting in some examples. In this specific example, maximum venting is shown at 2000 kg/hr (venting range from 0 to 2000 kg/hr), but it is noted that maximum venting may be at levels ranging from 1500 to 2500 kg/hr, depending on the system in place, though venting levels outside of this range can also be used. It is the combination of high pressure and high venting that leads to much of the foaming that occurs during the second cycle. Thus, the agitation module in combination with the agitator or auger can provide a variety of agitation profiles for reducing foaming during at least a portion of the second cycle. For example, the agitator can be automatically or otherwise be configured to be completely stopped (or functionally stopped) at or around point A, B, or C, and can be configured to be restarted or otherwise put back in an agitating state at or around point B, C or D. Any combination of these stopping (or significantly reducing movement) and starting points can be used to reduce foaming, depending on the process parameters or polymer being prepared. However, in one example, the auger is started toward the begging of Cycle 1 and stopped at about point A and restarted at about point C. In another example, the auger is started toward the begging of Cycle 1 and stopped at about point B and restarted at about point C. Also notable, during Cycle 2, the temperature is increased relatively steadily from a lower temperature to a higher temperature, e.g., ranging from about 185 °C to 285 °C in this example though temperature ranges outside of this can also be used. Cycle 2 typically ends at a specified temperature or by some other parameter, e.g., time, venting reduced to a certain level, relative viscosity target achieved, water content target achieved, etc. As a specific example, one can consider a process of preparing nylon 6,6. With nylon 6,6, a relative viscosity of about 3 to 5 units and a water content of about 0.08 to 0.1 gr/gr may be desirable at the end of Cycle 2.

As also shown in FIG. 3, a third cycle (Cycle 3) is defined primarily by a pressure reduction. At the end of the third cycle, there can also be some foaming, referred to as "third cycle foaming." This is not as severe as the second cycle foaming, and as this foaming activity is further along in the polymerization process, at about the start of the fourth cycle, the agitator is typically slowed to certain levels and then ultimately stopped in due course. Thus, there is not as significant of a reason to perform a stop and start function at this point in the cycle. At the end of Cycle 3, with specific reference again to nylon 6,6, the relative viscosity can be about 16 to 20 units and the water concentration can be about 0.002 to 0.006 gr/gr, for example.

A fourth cycle (Cycle 4) is characterized by an even lower pressure than initially present at the beginning of the autoclave process, and can be achieved using vacuum pressure. Furthermore, during the fourth cycle, there can be a ramping down of the agitator RPM. Notably, as shown more specifically in FIG. 2, a medium RPM level 150 can be used for a short period of time to reduce motor power consumption and an even lower RPM level 160 (4 to 15 RPM) can be chosen so that the auger can be used as a viscometer. Returning again to FIG. 3, at the end of Cycle 4, again for nylon 6,6, the relative viscosity can be about 32 to 40 units and the water content can be about 0.001 to 0.004 gr/gr.

A fifth cycle (Cycle 5) can be characterized as the casting or extrusion cycle where the polymer that is formed is extruded and pelleted for further use. Additional steps after extrusion are typically carried out, as would be understood by one skilled in the art.

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 solution 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, even though the present disclosure relates to mechanical devices and methods for reducing foaming, 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.

EXAMPLE

Foaming inside an autoclave can be detected using a series of thermocouples positioned at different levels or heights. If foaming occurs, the liquid foam will come into contact with one or more of the thermocouples positioned from bottom to top, which will measure a sudden increase in temperature. If foaming is very heavy or violent, all of the thermocouples will sense the foam, and heavy foaming may even partially block the autoclave vent- valve, showing up as a pressure peak. If there is low foaming, only lower positioned (or no) thermocouples will sense a temperature increase. By reducing foaming using the methods of the present disclosure, problems associated with foaming as described herein can be reduced or eliminated.

To illustrate, the graphs of FIG. 4 shows three comparative autoclave trends for pressure, vent valve output (venting), and the foam detector readings (foaming) for batches where the agitator was i) set at a consistent 60 RPM (Graph A), ii) temporarily reduced from 60 to 15 RPM (Graph B), and iii) briefly stopped (Graph C). Multiple thermocouple readings are also shown which represent at least three different thermocouples residing in the autoclave vessel at various heights, as described above. It is noted that the autoclave could be equipped with fewer or more thermocouples as desired (or none if foaming does not need to be measured outside of the present experiment). Essentially, as shown in Graph A, the foaming results in a significant pressure peak followed by a spike of vent valve output. Graph B, all but one thermocouple (the uppermost thermocouple) shows a sudden increase in temperature (which indicates medium foaming). In Graph C, only a single thermocouple (the lowermost thermocouple) measures a sudden increase in temperature which indicates only minor foaming.

Thus, in the present example, reducing the agitator speed from 60 RPM to 15 RMP at the indicated time provided acceptable foaming with no significant pressure peak or vent valve output spike. Furthermore, reducing the agitator speed from 60 RPM to 0 RPM at a similar point in time provided even further foam reduction. 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.