阅读说明：本技术 通过ssp加水而脱除残余己内酰胺的方法 (Process for removing residual caprolactam by adding water to SSP ) 是由 M·K·古丁 C·E·施维尔 J·J·小特里亚 于 2019-06-27 设计创作，主要内容包括：本公开涉及由己内酰胺生产高分子量聚酰胺的方法。特别地,本公开涉及在固态聚合(SSP)的过程中加入水以脱除残余己内酰胺以形成具有低残余己内酰胺单体含量的高分子量聚酰胺,例如尼龙6和尼龙6,6共聚物的方法。加水步骤控制SSP过程特定时间以产生具有所需分子量和低残余己内酰胺单体含量的聚酰胺。(The present disclosure relates to a process for producing high molecular weight polyamides from caprolactam. In particular, the disclosure relates to a process for adding water during Solid State Polymerization (SSP) to remove residual caprolactam to form high molecular weight polyamides, such as nylon 6 and nylon 6,6 copolymers, having low residual caprolactam monomer content. The water addition step controls the SSP process for a specified time to produce a polyamide having a desired molecular weight and low residual caprolactam monomer content.)

1. A process for producing a polyamide having a low residual caprolactam content comprising:

(a) supplying a polyamide feedstock comprising caprolactam monomer to a solid state polymerization reactor;

(b) initiating polymerization of a polyamide feedstock in a solid state polymerization reactor; and

(c) water is added to the solid state polymerization reactor during polymerization to produce a high molecular weight polyamide solution comprising less than 0.6 wt.% residual caprolactam.

2. The process according to claim 1, wherein step (c) comprises adding a steam sweep gas to the solid state polymerization reactor.

3. The process of claim 2, wherein the steam sweep gas is added to the solid state polymerization reactor under vacuum.

4. A process according to any one of claims 2 or 3 wherein the steam sweep gas is added in combination with an inert sweep gas.

5. Process according to any one of claims 1-4, wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity of 60 to 300.

6. Process according to any one of claims 1 to 5, in which the high molecular weight polyamide solution comprises a polyamide having a relative viscosity equal to or less than 130.

7. Process according to any one of claims 1 to 6, wherein the polyamide starting material is solid state polymerized for less than 12 hours.

8. Process according to any one of claims 1-7, wherein the polyamide starting material is polymerized in the solid state polymerization reactor for less than 12 hours, wherein the high molecular weight polyamide solution comprises less than 0.6 wt.% residual caprolactam, and wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity of 60 to 300.

9. The process according to any one of claims 1-8, wherein step (c) comprises adding a steam purge gas to the solid state polymerization reactor, wherein the high molecular weight polyamide solution comprises less than 0.2 wt.% residual caprolactam, and wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity equal to or less than 130.

10. The process according to any one of claims 1 to 9, wherein the polyamide starting material comprises water-containing polymer pellets.

11. The method according to claim 10, wherein the polymer pellets comprise less than 25 wt% water.

12. The process according to claim 10 or 11, wherein step (c) comprises releasing steam from the polymer pellets during polymerization in the solid state polymerization reactor.

13. A process for producing a polyamide having a low residual caprolactam content comprising:

(a) supplying a polyamide feedstock comprising caprolactam monomer to a solid state polymerization reactor;

(b) polymerizing a polyamide feedstock in a solid state polymerization reactor; and

(c) a steam purge gas is added to the solid state polymerization reactor during polymerization to produce a high molecular weight polyamide solution comprising less than 0.6 wt.% residual caprolactam.

14. The method of claim 13, wherein the ratio of steam flow in grams per hour to the weight of the polymer pellets in grams is from 0.08:1 to 20: 1.

15. The process according to any one of claims 13 or 14, wherein the polyamide feedstock is polymerized in the solid state polymerization reactor for less than 12 hours, wherein the high molecular weight polyamide solution comprises less than 0.6 wt.% residual caprolactam, and wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity of 60 to 300.

16. The process according to any one of claims 13 to 15, wherein a steam purge gas is added to the polymerization reactor under vacuum during polymerization.

17. A process for producing a polyamide having a low residual caprolactam content comprising:

(a) supplying a polyamide feedstock comprising caprolactam monomer to a solid state polymerization reactor, wherein the polyamide feedstock comprises polymer pellets comprising water;

(b) polymerizing a polyamide feedstock in a solid state polymerization reactor; and

(c) releasing steam from the polymer pellets during polymerization in the solid state polymerization reactor to produce a high molecular weight polyamide solution comprising less than 0.6 wt.% residual caprolactam.

18. The method according to claim 17, wherein the polymer pellets comprise less than 25 wt% water.

19. The method according to any one of claims 17 or 18, wherein the polymer pellets comprise sub-capsules to release water into the solid state polymerization reactor at different temperatures.

20. The method according to any one of claims 17-19, wherein the polymer pellets release water into the solid state polymerization reactor at a controlled rate.

FIELD

The present disclosure generally relates to a process for producing high molecular weight polyamides comprising caprolactam monomer. In particular, the disclosure relates to a process for removing residual caprolactam by adding water during Solid State Polymerization (SSP) to form high molecular weight polyamides having low residual caprolactam content.

Background

Due to their advantageous properties, polyamides formed using caprolactam, e.g., epsilon-caprolactam ("caprolactam"), are used in a variety of applications, such as film forming, extrusion, molding, and food packaging films. For example, these polyamides have low crystallinity and lower melting points, as well as high drawability and clarity, which makes them particularly suitable for various film and extrusion applications.

However, in some cases, the caprolactam monomer used in the polymerization reaction may not be fully polymerized into the high molecular weight polyamide, and the resulting crude polymer product may contain residual low molecular weight caprolactam-containing components, such as caprolactam monomer and oligomers. In conventional processes, these low molecular components are usually removed by extraction with hot water. The monomeric caprolactam in the extraction water may be purified and purified to recapture the caprolactam and then recycled to the polymerization reactor. It is also possible to react the oligomers obtained in the extraction water back to caprolactam monomer by adding a resolving agent, which is then separated and washed to obtain monomers, which can then be reused.

U.S. patent No.4,053,457 discloses a process for making polyamides from epsilon-caprolactam and/or other polyamide-forming starting compounds by polymerization and subsequent extraction of the polymer. The extract containing solvent, monomers and oligomers is concentrated in the absence of atmospheric oxygen. The surfaces in contact with the extract are made of a material that is inert under the conditions of the concentration process. The concentrate obtained is polymerized without further purification or isolation, alone or together with other polyamide-forming starting compounds.

In addition, it is desirable that the caprolactam-containing polyamide has a high molecular weight, for example to facilitate efficient processing and/or to achieve the above-mentioned properties. Generally, to form high molecular weight polyamides, a subsequent Solid State Polymerization (SSP) step can be used after the first polymerization and washing of the polymer. For example, U.S. patent No.6,069,228 discloses a process for preparing polyamide polymers by prepolymer formation in a reactor system comprising a reactor, flasher (flasher) and separator, crystallization of the prepolymer under controlled temperature conditions, and subsequent conversion of these crystallized prepolymers to high molecular weight polymers via SSP.

In the above process, polymers with high residual caprolactam levels are produced. In these cases, it is economical to recover residual monomer and recycle the recovered monomer back to the polymerization reactor. For polymers with low residual caprolactam levels, it is prohibitively expensive to install the large amount of (extensional) equipment required to recover such low levels of caprolactam monomer for recycle to the polymerization process.

In view of these references, there is a need for better control and removal of residual caprolactam in a solid state polymerization process while achieving desired molecular weight levels in the resulting polyamide. In addition, there is a need for improved processes for preparing high molecular weight polymers having lower levels of residual caprolactam.

SUMMARY

In some embodiments, the present disclosure relates to a process for producing a polyamide having a low residual caprolactam content, comprising: (a) supplying a polyamide feedstock comprising caprolactam monomer to a solid state polymerization reactor; (b) initiating polymerization of a polyamide feedstock in a solid state polymerization reactor; and (c) adding water to the solid state polymerization reactor during polymerization to produce a high molecular weight polyamide solution comprising less than 0.6 wt% residual caprolactam. In some aspects, step (c) comprises adding a steam purge gas to the solid state polymerization reactor. A steam purge gas may be added to the polymerization reactor under vacuum. In some aspects, the steam purge gas is added in combination with an inert purge gas. In some aspects, the high molecular weight polyamide solution comprises a polyamide having a relative viscosity of 60 to 300. In some aspects, the high molecular weight polyamide solution comprises a polyamide having a relative viscosity equal to or less than 130. In some aspects, the polyamide feedstock is polymerized in the solid state polymerization reactor for less than 12 hours, wherein the high molecular weight polyamide solution comprises less than 0.6 weight percent residual caprolactam, and wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity of 60 to 300. In some aspects, step (c) comprises adding a steam purge gas to the solid state polymerization reactor, wherein the high molecular weight polyamide solution comprises less than 0.2 wt% residual caprolactam, and wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity equal to or less than 130. In some aspects, the polyamide feedstock comprises aqueous polymer pellets. The polymer pellets may comprise less than 25 wt% water. In some aspects, step (c) comprises releasing steam from the polymer pellets during polymerization in the solid state polymerization reactor.

In some embodiments, the present disclosure relates to a process for producing a polyamide having a low residual caprolactam content, comprising: (a) supplying a polyamide feedstock comprising caprolactam monomer to a solid state polymerization reactor; (b) polymerizing a polyamide feedstock in a solid state polymerization reactor; and (c) adding a steam purge gas to the solid state polymerization reactor during polymerization to produce a high molecular weight polyamide solution comprising less than 0.6 wt% residual caprolactam. In some aspects, the ratio of steam flow in grams/hour to polymer pellet weight in grams is from 0.08:1 to 20: 1. In some aspects, the polyamide feedstock is polymerized in the solid state polymerization reactor for less than 12 hours, wherein the high molecular weight polyamide solution comprises less than 0.6 weight percent residual caprolactam, and wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity of 60 to 300. In some aspects, a steam purge gas is added to the polymerization reactor under vacuum while initiating polymerization.

In some embodiments, the present disclosure relates to a process for producing a polyamide having a low residual caprolactam content, comprising: (a) supplying a polyamide feedstock comprising caprolactam monomer to a solid state polymerization reactor, wherein the polyamide feedstock comprises polymer pellets comprising water; polymerizing a polyamide feedstock in a solid state polymerization reactor; and (c) releasing water from the polymer pellets during polymerization in the solid state polymerization reactor to produce a high molecular weight polyamide solution comprising less than 0.6 wt% residual caprolactam. In some aspects, the polymer pellets comprise less than 25 wt% water. In some aspects, the polymer pellets are preconditioned with water (preconditioned). In some aspects, the polymer pellets release water into the solid state polymerization reactor at a controlled rate.

Brief Description of Drawings

FIG. 1 shows a graph of the amount of residual caprolactam in a polyamide solution over time during SSP in accordance with an embodiment of the present disclosure.

Figure 2 shows a plot of relative viscosity of polyamides formed over time during an SSP process in accordance with embodiments of the present disclosure.

Detailed description of the invention

The present disclosure relates to a process for removing residual caprolactam monomer in a Solid State Polymerization (SSP) process to form high molecular weight polyamides, such as copolyamides, having a low (residual) caprolactam content. In some aspects, the present process simultaneously removes residual caprolactam, e.g., monomers and/or oligomers, and achieves high molecular weight polyamides. The method advantageously eliminates the water washing step, thereby improving process efficiency, reducing costs, and preventing polymer degradation. By eliminating the water wash step, the SSP process can also be controlled, for example for a specified time, to produce a polymer having a desired molecular weight. The resulting caprolactam-containing polyamides are useful in a variety of applications such as films, extrusions and fibers.

In some embodiments, the present disclosure relates to a method of removing residual caprolactam monomer in an SSP process to form a high molecular weight polyamide solution. The process may include introducing water, such as steam, to the SSP process to reduce the caprolactam monomer content while maintaining the SSP process for a sufficient time to achieve a desired molecular weight to form a high molecular weight polyamide. The high molecular weight polyamides formed by this process have a low residual caprolactam content and the desired molecular weight (as measured by relative viscosity). In some aspects, the high molecular weight polyamide has a Relative Viscosity (RV) of about 60 to about 300 and a residual caprolactam concentration of less than 0.6 weight percent. The process produces a customizable, uniform polyamide having minimal to substantially no residual caprolactam monomer content.

As used herein, "polyamide" refers to a linear condensation polymer comprising amide groups (-NHCO-) that repeat in the polymer backbone, and "copolyamide" refers to a composition comprising a combination of multiple polyamide-forming monomers. Exemplary polyamides and polyamide compositions are described in Kirk-Othmer, Encyclopedia of Chemical Technology, Vol.18, pp.328-371 (Wiley 1982), the disclosure of which is incorporated herein by reference.

In short, polyamides are products which contain recurring amide groups as part of the main polymer chain. Linear polyamides are of particular interest and can be formed by condensation of difunctional monomers as is well known in the art. Polyamides are often referred to as nylons. Specific polymers and copolymers and their preparation can be found in the following patents: U.S. Pat. No.4,760,129 to Haering et al entitled "Process for Preparing high viscosity gases polymeric; U.S. Pat. No.5,504,185 to Toki et al entitled "Process for Production of Polyamides, Polyamides Produced by Said Process and polyamine Film or Sheet"; U.S. Pat. No.5,543,495 to Anolick et al entitled "Process for introducing the Molecular Weight of Polyamides and Other Condensation Polymers"; U.S. Pat. No.5,698,658 to Dujari et al entitled "Linear virtual High Molecular Weight Polyamides and Process for Producing the same"; U.S. Pat. No.6,011,134 to Marks et al entitled "Method for Manufacturing Poly (Hexamethylene Adipamide) from monomer and Hexamethylene Adipamide"; U.S. Pat. No.6,136,947 to Wiltzer et al, entitled "Process and Device for the Standardized connection of Polyamides"; U.S. patent No.6,169,162 to Bush et al entitled "Continuous polymerization Process"; "polyamine Chain Extension Process and Related polyamine Product" to Zahr; U.S. Pat. No.7,138,482 to Tanaka et al, entitled "Production Method of polyamine"; U.S. Pat. No.7,381,788 to Tsujii et al, entitled "Method for Continuous Production of polyamine"; and U.S. Pat. No.8,759,475 to Thierry et al entitled "Continuous products of Polyamides".

Unless otherwise indicated, percentages, parts per million (ppm), and the like refer to weight percentages or parts by weight based on the weight of the composition.

Unless otherwise indicated, the process temperature refers to the SSP set point.

As noted above, in conventional processes, polymers made by polymerization of caprolactam monomer typically include undesirable low molecular weight components. These low molecular weight compounds are formed as by-products of the polymerization reaction or as unreacted monomers, which have a detrimental effect on the properties of the polyamide and are therefore usually removed. For example, low molecular weight compounds may adversely affect products, such as injection molded products, by diffusing on their surface, thus forming a greasy film. These diffused low molecular weight compounds may also impair the surface appearance of the product, for example reduced gloss and impaired colour impression. Still further, residual caprolactam can deleteriously lead to: (1) build-up/plate-out on process equipment surfaces to cause downtime or reduced production throughput; (2) non-food contact eligible products according to regulatory specifications, such as FDA food contact specifications; and (3) interfere with adhesion between the film layers.

To avoid these problems, low molecular weight compounds are usually removed, for example by extraction. Extraction is usually carried out with hot water or with a liquid which contains mainly water. The residual caprolactam can be recaptured from these extraction waters, purified and, in some cases, reintroduced as a recycle stream into the polymerization process. However, these separate steps increase equipment and operating costs and may increase the color of the resin.

An alternative to water extraction is to remove residual caprolactam as part of the SSP process. In this process, caprolactam is volatilized at the SSP temperature and removed from the reactor. Caprolactam is, however, less volatile and requires more time to SSP using an SSP process step. If a longer time is required to remove caprolactam during the SSP process, the resulting molecular weight of the polymer product, e.g., nylon, may be outside the desired range, e.g., higher than desired. Conversely, if the SSP process is set for a time to achieve the desired molecular weight, the time may not be sufficient to adequately remove caprolactam and the residual caprolactam monomer and/or oligomer content is high.

The present inventors have now found that the addition of water during SSP can advantageously produce polyamides having the desired molecular weight and low residual caprolactam content. It was found that the addition of water during SSP (at some time during the polymerization of the polyamide feedstock) helps to remove residual caprolactam and form high molecular weight polyamides, such as nylon 6 and nylon 6,6 copolymers, having a low residual caprolactam monomer content and a desired relative viscosity (e.g., relative viscosity as a measure of molecular weight). Without being bound by theory, it is believed that the addition of water slows the molecular weight build of the polyamide and provides sufficient time for the removal of residual caprolactam. The water addition step controls the SSP process for a specific time (e.g., less time) to produce a polymer having a desired molecular weight and low residual caprolactam monomer content.

In some cases, the addition of water can be used to inhibit the forward polymerization process and limit molecular weight build to the desired RV. It has been found that residual caprolactam monomer is volatile at the temperatures of the SSP process. Thus, residual caprolactam can be volatilized and removed during the SSP process. By introducing water into the SSP reactor, the present inventors have advantageously slowed the molecular weight build process to enable efficient removal of caprolactam monomer. Without being bound by theory, it is believed that due to the high water solubility of caprolactam, the volatilized caprolactam preferentially leaves with water rather than a dry vapor stream, such as a nitrogen purge gas or vacuum.

In some embodiments, the residual caprolactam monomer is volatile at a temperature of the SSP process of from 140 ℃ to 240 ℃, e.g., from 150 ℃ to 230 ℃, from 160 ℃ to 220 ℃, from 165 ℃ to 215 ℃, from 170 ℃ to 210 ℃, from 175 ℃ to 205 ℃, from 180 ℃ to 200 ℃, or from 185 ℃ to 195 ℃. As an upper limit, the residual caprolactam monomer is volatile at an SSP temperature of less than 240 ℃, e.g., less than 230 ℃, less than 225 ℃, less than 220 ℃, less than 210 ℃, less than 200 ℃, or less than 190 ℃. As a lower limit, the residual caprolactam monomer is volatile at an SSP temperature of greater than 140 ℃, e.g., greater than 145 ℃, greater than 150 ℃, greater than 160 ℃, greater than 165 ℃, greater than 170 ℃, greater than 175 ℃, greater than 180 ℃, or greater than 185 ℃.

Advantageously, it has been found that the removal of residual caprolactam from polyamides delays the tendency of residual caprolactam monomer to plate out on metal surfaces. Precipitation typically occurs when residual caprolactam monomer volatilizes from the polymer melt at high processing temperatures and then condenses on the metal surfaces of the processing equipment. This precipitation creates unwanted flaws and defects in the film and/or other end products. The reduction or elimination of residual caprolactam in the polyamide advantageously results in the reduction or elimination of precipitation. The process also advantageously produces polyamides that meet FDA regulations (21CFR 177.1500(b) (4.1)) that require low residual caprolactam levels for food contact applications.

In addition, this method prevents residual caprolactam from blooming to the film surface, which can cause various problems such as reduced adhesion to other polymer film layers, e.g., maleated polyethylene, poly (ethylene vinyl alcohol), and haze to limit film clarity.

The manner in which water is added to the SSP process can vary widely so long as water is provided as described herein. In some aspects, water is added to the SSP reactor in a purge gas. The term "purge gas" may refer to a gas stream that passes through the reactor headspace during polymerization. The purge gas entrains reactor vapors, e.g., volatile reaction components such as residual caprolactam, from the reactor. As mentioned above, caprolactam volatilizes under SSP conditions. In operation, a steam purge gas is fed to the inlet of the SSP reactor, e.g., at the first end of the reactor under SSP conditions. The purge gas then continues through the reactor to purge the volatile components and exits via an outlet at the opposite end of the reactor. In some embodiments, a vacuum may be used in addition to the steam sweep gas to facilitate the removal of volatile components. The steam purge gas advantageously removes residual caprolactam and can inhibit the forward polymerization process (e.g., by lowering the temperature) and limit molecular weight build to the desired RV.

In some aspects, the SSP process can be operated at atmospheric pressure with a steam purge gas. In some aspects, the SSP process may be run under vacuum conditions to facilitate movement of the purge gas. In some aspects, the steam purge gas may be added to the SSP reactor under low or high vacuum. In some embodiments, the steam purge gas is operated in a co-current mode. In other embodiments, the steam sweep gas is operated in a convective manner. The method can be configured using any standard SSP run.

In some embodiments, when SSP is conducted under vacuum, a small amount of an inert gas, such as nitrogen, may be fed to the SSP reactor. Nitrogen is swept out of the reactor under vacuum and may carry other volatile species. In this case, the nitrogen gas may also be referred to as purge gas. The purge gas is typically added at a location in the SSP reactor that is as far as possible from the location where the vacuum is applied to the SSP reactor.

In some aspects, the steam purge gas may be introduced into the SSP reactor in combination with the inert purge gas. In some aspects, the steam purge gas may be added to the SSP reactor under vacuum or under combined operation, e.g., under vacuum with an inert purge gas.

In some embodiments, steam or water (e.g., from polymer pellets) may be added to the SSP reactor during the SSP process at the time the polymer begins to build molecular weight. In some embodiments, the polymer begins to grow molecular weight at a temperature greater than 120 ℃, e.g., greater than 125 ℃, greater than 130 ℃, greater than 135 ℃, greater than 140 ℃, or greater than 150 ℃. Steam or water may be added continuously throughout the SSP cycle or added initially to remove caprolactam and then stopped for the remainder of the SSP cycle when the final molecular weight is achieved.

In some aspects, the SSP process can introduce water into the process by using polymer pellets having a desired water content incorporated into the polymer pellets. At the SSP temperature, water evaporates from the polymer pellets and effectively adds water and/or steam, e.g., releases steam to the SSP reactor. In some embodiments, the polymer pellets may provide a controlled release of water into the reactor. For example, the polymer pellets may include sub-capsules (sub-capsules) to provide controlled release of a specific amount of water at different time intervals or at different temperatures. In some embodiments, at least half of the volume of water in the polymer pellets is released into the SSP reactor at 6 hours. In some embodiments, a portion of the water in the polymer pellets is released into the SSP reactor every 1 hour. In some embodiments, a portion of the water in the polymer pellets is released to the SSP reactor at spaced temperatures in the reactor.

In some aspects, the polymer pellets can be preconditioned with water prior to charging into a reactor, such as an SSP dryer. In some aspects, the polymer pellets may be charged to an SSP dryer and liquid water may be added to the vessel, thereby allowing the water to be absorbed by the pellets in the SSP reactor. Advantageously, this process is compact, simple and does not require a separate water washing step beyond the conventional SSP process, thereby improving the efficiency of the process. In some aspects, the water may be introduced into the SSP reactor (e.g., via a water stream) in liquid form (e.g., via a water stream) and may be boiled in the SSP reactor to provide steam.

In some embodiments, the polymer pellets may comprise 0.5 to 50 wt%, e.g., 1 to 45 wt%, 2 to 40 wt%, 4 to 35 wt%, 5 to 30 wt%, 8 to 25 wt%, 10 to 20 wt%, or 12 to 15 wt% water. For an upper limit, the polymer pellets may comprise less than 50 wt% water, such as less than 40 wt%, less than 30 wt%, less than 25 wt%, less than 20 wt%, or less than 15 wt%. With respect to the lower limit, the polymer pellets may comprise greater than 0.5 wt% water, such as greater than 1 wt%, greater than 2 wt%, greater than 4 wt%, greater than 5 wt%, greater than 6 wt%, or greater than 8 wt%.

In some embodiments, the high molecular weight polyamide solution produced after SSP has a (residual) caprolactam content of 0.01 wt.% to 0.6 wt.%, such as 0.02 wt.% to 0.5 wt.%, 0.05 wt.% to 0.4 wt.%, 0.1 wt.% to 0.3 wt.%, or 0.15 wt.% to 0.25 wt.%. As far as the upper limit is concerned, the high molecular weight polyamide solution has a (residual) caprolactam content of less than 0.6 wt.%, for example less than 0.55 wt.%, less than 0.5 wt.%, less than 0.4 wt.%, less than 0.3 wt.%, less than 0.25 wt.%, less than 0.2 wt.% or less than 0.15 wt.%. With respect to the lower limit, the high molecular weight polyamide solution has more than 0.01 wt. -%, such as more than 0.02 wt. -%, more than 0.04 wt. -%, more than 0.05 wt. -%, more than 0.06 wt. -%, more than 0.07 wt. -%, more than 0.08 wt. -% or more than 0.09 wt. -% of (residual) caprolactam. In some aspects, the high molecular weight polyamide solution is free of (residual) caprolactam.

In some aspects, the water addition step slows the SSP process to achieve a polyamide with a desired molecular weight. In some cases, the molecular weight of the polyamide in the high molecular weight polyamide solution can be correlated to the Relative Viscosity (RV). In some embodiments, the polyamide has an RV of 60 to 300, e.g., 65 to 250, 70 to 200, 75 to 150, 80 to 140, 85 to 135, 90 to 130, or 95 to 120. With respect to the lower limit, the polyamide has an RV of greater than 60, such as greater than 65, greater than 70, greater than 75, greater than 80, or greater than 85. With respect to the upper limit, the polyamide has an RV of less than 300, e.g., less than 250, less than 200, less than 180, less than 160, less than 150, less than 140, less than 130, or less than 120.

In some embodiments, the high molecular weight polyamide solution has a viscosity number VN of 100mL/g to 250mL/g, such as 120mL/g to 240mL/g, 140mL/g to 220mL/g, 150mL/g to 210mL/g, 160mL/g to 200mL/g, or 170mL/g to 190 mL/g. With respect to the lower limit, the high molecular weight polyamide solution has a VN of greater than 100mL/g, for example greater than 105mL/g, greater than 110mL/g, greater than 120mL/g, greater than 130mL/g or greater than 140 mL/g. With respect to the upper limit, the high molecular weight polyamide has a VN of less than 250mL/g, e.g., less than 240mL/g, less than 220mL/g, less than 200mL/g, less than 180mL/g, or less than 160 mL/g.

In some embodiments, water, e.g., steam, is added to the SSP process to achieve a low (residual) caprolactam content. In some embodiments, the ratio of steam flow (grams/hour) to polymer pellet weight (grams) is from 0.01:1 to 100:1, e.g., from 0.02:1 to 80:1, from 0.04:1 to 60:1, from 0.06:1 to 40:1, from 0.08:1 to 20:1, from 0.1:1 to 10:1, from 0.5:1 to 5:1, from 0.8:1 to 2:1, or from 1:1 to 1.5: 1. For the upper limit, the ratio of steam flow to polymer pellet weight is less than 100:1, such as less than 90:1, less than 80:1, less than 60:1, less than 50:1, less than 40:1, less than 20:1, or less than 10: 1. For the lower limit, the ratio of steam flow to polymer pellet weight is greater than 0.01:1, such as greater than 0.02:1, greater than 0.08:1, greater than 0.1:1, greater than 0.5:1, or greater than 1: 1.

In some aspects, the process achieves a beneficial combination of a desired RV, a desired residual caprolactam content, and/or a desired molecular weight. In some aspects, water is added to the SSP process to increase the polymerization time to enable sufficient removal of residual caprolactam. In some aspects, the high molecular weight polyamide solution has an RV within the ranges and limits recited above and/or a caprolactam content within the ranges and limits recited above. In some aspects, the process achieves a high molecular weight polyamide solution having a caprolactam content of less than 0.2 wt.% and an RV of 80 to 150.

In some aspects, the composition (formation) of the polyamide feedstock introduced into the SSP reactor can vary, so long as caprolactam is used as at least one monomer in the formation of the polyamide feedstock. For example, the polyamide starting material may comprise a caprolactam-containing copolyamide to obtain a polymer mixture of polyamide, caprolactam and caprolactam oligomer. In some aspects, caprolactam and higher lactams of up to 12 ring members, or mixtures thereof, are suitable. In some embodiments, the polyamide feedstock is introduced into the SSP reactor as polymer pellets.

In some embodiments, the polyamide feedstock may comprise PA-6, PA4,6, PA-6,9, PA-6,10, PA-6,12, PA11, PA12, PA9,10, PA9,12, PA9,13, PA9,14, PA9,15, PA-6,16, PA9,36, PA10,10, PA10,12, PA10,13, PA10,14, PA12,10, PA12,12, PA12,13, PA12,14, PA-6,13, PA-6,15, PA-6,16, PA-6,13, PAMXD,6, PA4T, PA5T, PA 6T, PA10T, PA12T, PA4, PA T, PA5T, PA T, terpolymers and mixtures thereof.

In some aspects, the polyamide starting material may comprise a polyamide made by ring opening polymerization or polycondensation, including copolymerization and/or copolycondensation, of a lactam. For example, these polyamides may include, for example, those made from propiolactam, butyrolactam, valerolactam, laurolactam, caprolactam, or combinations thereof. In some embodiments, the polyamide is a polymer derived from the polymerization of caprolactam. In addition, the polyamide composition may comprise a polyamide made by copolymerization of a lactam and a nylon, such as the copolymerization product of caprolactam and PA-6, 6.

In some embodiments, the polyamide starting material may be a condensation product of one or more dicarboxylic acids, one or more diamines, one or more aminocarboxylic acids, and/or a ring-opening polymerization product of one or more cyclic lactams, such as caprolactam and laurolactam. In some aspects, the polyamide feedstock can include aliphatic, aromatic, and/or semi-aromatic polyamides and can be a homopolymer, copolymer, terpolymer, or higher order polymer. In some aspects, the polyamide feedstock comprises a blend of two or more polyamides. In some embodiments, the polyamide feedstock comprises an aliphatic or aromatic polyamide or a blend of two or more polyamides.

In some aspects, the dicarboxylic acid may comprise one or more of adipic acid, azelaic acid, terephthalic acid, isophthalic acid, sebacic acid, and dodecanedioic acid. In some aspects, the dicarboxylic acid can comprise adipic acid, isophthalic acid, and terephthalic acid. In some aspects, the dicarboxylic acid may comprise an aminocarboxylic acid, such as 11-aminododecanoic acid.

In some aspects, the diamine can comprise one or more of butanediamine, hexanediamine, octanediamine, nonanediamine, 2-methylpentanediamine, 2-methyloctanediamine, trimethylhexanediamine, bis (p-aminocyclohexyl) methane, m-xylylenediamine, p-xylylenediamine, decanediamine, undecanediamine, dodecanediamine, tridecanediamine, butanediamine, pentanediamine, hexanediamine, and the like. Other examples of only exemplary aromatic diamine components include phenylenediamines, such as 1, 4-diaminobenzene, 1, 3-diaminobenzene, and 1, 2-diaminobenzene; diphenyl (thio) ether diamines such as 4,4 ' -diaminodiphenyl ether, 3 ' -diaminodiphenyl ether and 4,4 ' -diaminodiphenyl sulfide; benzophenone diamines such as 3,3 '-diaminobenzophenone and 4, 4' -diaminobenzophenone; diphenylphosphindiamines such as 3,3 '-diaminodiphenylphosphine and 4, 4' -diaminodiphenylphosphine; diphenylalkylenediamines such as 3,3 '-diaminodiphenylmethane, 4' -diaminodiphenylmethane, 3 '-diaminodiphenylpropane and 4, 4' -diaminodiphenylpropane; diphenylsulfide diamines such as 3,3 '-diaminodiphenylsulfide and 4, 4' -diaminodiphenylsulfide; diphenylsulfone diamines such as 3,3 '-diaminodiphenylsulfone and 4, 4' -diaminodiphenylsulfone; and benzidines such as benzidine and 3, 3' -dimethylbenzidine.

In some aspects, the polyamide feedstock comprises a physical blend of aliphatic, semi-aromatic, and/or aromatic polyamides to obtain properties that are intermediate or synergistic in the properties of the respective polyamides.

While much of the discussion above is directed to polyamide feedstocks, particularly copolyamides of PA-6,6 and PA-6, it is expected that the process described herein can be applied to all polyamides from aliphatic polyamides (traditionally PA-6,6 and PA-6 or other aliphatic nylons) to copolyamides with aromatic components (e.g., p-phenylenediamine and terephthalic acid) to copolymers, such as copolymers of adipic acid esters with 2-methylpentamethylenediamine and 3, 5-dicarboxybenzenesulfonic acid (or sulfoisophthalic acid in its sodium sulfonate form).

Experimental procedures

The following test methods can be used to measure the mechanical and chemical properties of the polymer and drawn filaments.

The Relative Viscosity (RV) of nylon refers to the ratio of solution or solvent viscosities as measured by ASTM D789 (this year) in a capillary viscometer at 25 ℃. The solvent was formic acid containing 10 wt% water and 90 wt% formic acid. The solution was 8.4 wt% polymer dissolved in solvent.

RV(η_r) Is the ratio of absolute viscosity of the polymer solution to formic acid:

η_r＝(η_p/η_f)＝(f_r x d_p x t_p)/η_f

wherein: d_pDensity of the formic acid-polymer solution at 25 c,

t_pthe mean flow-out time of the formic acid-polymer solution, s,

η_fabsolute viscosity of formic acid, kPa x s (E +6cP)

f_rViscometer tube factor, mm²/s(cSt)/s＝η_r/t₃

Typical calculations for a 50RV specimen are:

η_r＝(f_r x d_p x t_p)/η_f

wherein

f_rViscometer tube index, usually 0.485675cSt/s

d_pDensity of polymer-formic acid solution, typically 1.1900g/ml

t_pAverage run-off time of polymer-formic acid solution, typically 135.00s

η_fAbsolute viscosity of formic acid, typically 1.56cP

To obtain η_rRV of 50.0 ═ 0.485675cSt/s x 1.1900g/ml x 135.00s)/1.56 cP.

Term t₃Is the time to flow of the S-3 calibration oil required to determine the absolute viscosity of formic acid as in ASTM D789 (this year).

Table 1 below provides an exemplary conversion table for the RV test method. Table 1 compares ASTM D789 (this year) RV test method with other standard viscosity measurements.

The residual caprolactam was determined by dissolving 0.1 gram of nylon in 3 ml of a solution containing 90% formic acid. Nylon was precipitated from the solution by adding 7 ml of 10% aqueous methanol. The resulting solution was filtered through a 0.45 micron PTFE syringe filter into a High Pressure Liquid Chromatography (HPLC) vial. The HPLC conditions were as follows:

mobile phase A)10mM methanesulfonic acid; and B) acetonitrile;

gradient:

sample Loop size 10 μ L

Column Phenomenex Kinetex 5 μm EVO C18HPLC column

Column temperature 50 deg.C

Detector-Diode Array Detector (DAD) set at 210nm

These conditions gave the following HPLC chromatogram.

Calibration the instrument was calibrated using solutions containing 59ppm, 117ppm, 228ppm, 435ppm and 587ppm caprolactam in methanol solution. These standards produced the following caprolactam calibration curves.

Examples

The following examples demonstrate that the process according to the present disclosure produces polyamides having low residual caprolactam content and desired molecular weight (as measured by relative viscosity) as compared to polyamides formed by conventional processes.

Comparative examples a and B relate to polyamides formed using conventional techniques/processes, such as by polymerizing epsilon caprolactam and/or other polyamide forming starting compounds, extracting the polymer with hot water, concentrating an aqueous extract containing water, monomers and oligomers, and Solid State Polymerization (SSP) of the aqueous extract to form a polyamide solution. The polyamide solutions of comparative examples a-C were produced by a process similar to the commercial scale SSP process (no water was added, nor was there water before the water wash). These examples were carried out using a Thermogravimetric (TGA) instrument. TGA was used to heat 70 mg of polyamide starting material to 190 ℃ and then the starting material was held for 2, 4 and 6 hours. TGA was purged with 50sccm of helium to effectively purge volatiles from the instrument.

Comparative example a was produced under vacuum while comparative example B was produced at atmospheric pressure. Table 2 shows the Relative Viscosity (RV) and caprolactam concentration of the polyamide solutions of comparative examples a and B at various times during the SSP process.

As shown in table 2, the polyamide solution of comparative example a has reached an RV of greater than 100 before the amount of caprolactam is below 0.6% by weight. Comparative example a achieved either the desired RV or a low residual caprolactam content, but not both. For example, at 6.75 hours SSP time, the process achieved a target RV of 78, but the residual caprolactam level was still very high, 0.705 wt%. At 12 hours SSP time, the residual caprolactam content had dropped to 0.269 wt.%, but RV was extremely high, 242.7.

For comparative example B, it can still be seen that in a short time (2 hours SSP) the process achieved a polyamide solution with an RV of 81, but a residual caprolactam level of up to 0.59 wt.%. At longer SSP times, the polyamides achieve lower residual caprolactam contents, but very high RV.

Comparative example C:

the polyamide solution of comparative example C was produced under vacuum in an SSP process with a nitrogen purge gas. Table 3 shows the Relative Viscosity (RV) and wt% caprolactam of comparative example C at different times during SSP with nitrogen addition.

As shown in table 3, the addition of nitrogen purge during SSP reached an RV of 69 after 3 hours SSP, but the amount of caprolactam was greater than 0.6 wt%. At 6 hours, the residual caprolactam content of the polyamide solution had decreased to 0.3% by weight, but the RV was 133. Although the nitrogen purge performed well than comparative examples a and B, it still did not achieve low residual caprolactam content at an acceptable RV.

Examples 1 and 2

The polyamides of examples 1 and 2 were prepared by the SSP process with water (steam) added to the SSP reactor. In this process a small-scale laboratory-sized SSP reactor is used, which contains a gas chromatography oven (GC oven), copper tubing inside the GC oven, and a vacuum pump. The GC oven included a 150mL stainless steel cylinder containing the polyamide feedstock. Approximately 20 pounds of steam was fed into the GC oven via a needle valve that controlled the amount of steam entering the GC oven. The needle valve supplies steam to a copper tube connected to a gas cylinder in the oven. The gas cylinder is discharged into the cold trap through the copper pipe. Table 4 shows the RV and caprolactam contents of the polyamide solutions of examples 1 and 2 at various times during SSP with steam addition under vacuum conditions.

Vapor flow as condensate collected in cold trap

Table 4 shows that surprisingly both low residual caprolactam levels and the desired RV are achieved by adding water (steam) during the SSP process. For example, the polyamide solution had less than 0.2 wt.% residual caprolactam and an RV of 72 after a 6 hour SSP time for example 1 (high steam flow). In addition, the polyamide solution had 0.2% by weight of residual caprolactam and an RV of 94 after 6 hours SSP time for example 2 (low steam flow). Surprisingly, the addition of steam during the SSP process (regardless of the steam flow) achieves a low residual caprolactam and controls the RV of the polyamide solution within an acceptable range.

Examples 3 to 8

The polyamides of examples 3-8 were prepared using the method described above for examples 1 and 2, with steam sweep gas added during the SSP process. A steam purge gas is introduced through the inlet of the reactor and purged through the reactor to the outlet of the reactor to remove volatile components from the reactor. Steam purge gas was added at various flow rates and under low vacuum (87torr) or high vacuum (37 torr). Table 5 shows the RV, Viscosity Number (VN) and caprolactam concentration obtained at various times during SSP with the addition of steam sweep gas at different pressures and different steam flow rates.

Examples 3-6 show the effect of steam flow on caprolactam weight% and RV. Examples 3 to 6 each have a caprolactam content of less than 0.49% by weight after only 3 hours SSP, while the polyamide solution has an RV of from 52 to 55. Surprisingly, the addition of steam greatly reduced the caprolactam content while controlling the RV of the polyamide at various steam flow rates. The polyamide solution of example 3 had 0.31 wt.% caprolactam and 53 RV after 3.3 hours SSP at a steam flow of 0.4 mL/min. Even at low steam flow, example 4 exhibited a caprolactam reduction (compared to the initial caprolactam content) of greater than 75% while keeping the RV at 55.

Examples 7 and 8 show residual caprolactam levels and RV after 6 hours SSP at steam flow rates of 0.01mL/min and 0.1mL/min, respectively. Examples 7 and 8 achieve both low residual caprolactam levels and desirable RV by adding steam during the SSP process. It has been unexpectedly found that the addition of steam to the SSP process, regardless of the steam flow rate, removes caprolactam while controlling molecular weight build. After 6 hours SSP, examples 7 and 8 had residual caprolactam levels of less than 0.2 wt.% and RV of less than 115. It can be seen that the addition of steam to the SSP process slows the molecular weight build up, thereby providing sufficient time for the removal of residual caprolactam.

FIG. 1 shows the residual caprolactam content during 6 hours SSP for comparative example C and examples 3-8. Specifically, FIG. 1 shows a plot of the amount of residual caprolactam during 6 hours SSP for comparative example C (nitrogen purge under low vacuum), examples 3-6 (steam purge under low vacuum), and examples 7 and 8 (steam purge under high vacuum). It can be seen that the addition of steam purge reduced the residual caprolactam content to below 0.2 wt% after 6 hours SSP. Surprisingly, for a given SSP time, the addition of steam results in faster caprolactam removal than nitrogen.

FIG. 2 shows RV of polyamide solutions during 6 hours SSP for comparative example C and examples 3-8. It can be seen that the addition of steam controls the SSP process to produce a polymer having the desired molecular weight and low residual caprolactam monomer content. Surprisingly, the addition of steam purge during SSP results in both faster caprolactam removal and lower RV, e.g., slower molecular weight build, for a given SSP time as compared to nitrogen purge.

Examples 9 to 11

Examples 9-11 used the SSP process described above. In each of examples 9-11, the polymer pellets were preconditioned with water prior to SSP. These examples were tested under vacuum with steam added to the SSP reactor. Table 6 shows the RV, Viscosity Number (VN) and caprolactam concentration obtained at various times during SSP for each example.

Preconditioning the polymer pellets with water prior to SSP effectively reduces caprolactam concentration and controls molecular weight build. At various steam flow rates, the moisture content in the polymer pellets used in examples 9-11 inhibited molecular weight build up and significantly reduced caprolactam content after 6 hours SSP. Surprisingly, preconditioning the polymer pellets with water and adding steam during SSP work in combination to remove caprolactam efficiently and slow down molecular weight build-up.

Detailed description of the preferred embodiments

The following embodiments are contemplated. All combinations of features and embodiments are contemplated.

Embodiment 1 a process for producing a polyamide having a low residual caprolactam content, the process comprising: (a) supplying a polyamide feedstock comprising caprolactam monomer to a solid state polymerization reactor; (b) initiating polymerization of a polyamide feedstock in a solid state polymerization reactor; and (c) adding water to the solid state polymerization reactor during polymerization to produce a high molecular weight polyamide solution comprising less than 0.6 wt% residual caprolactam.

Embodiment 2 the embodiment of embodiment 1 wherein step (c) comprises adding a steam sweep gas to the solid state polymerization reactor.

Embodiment 3 the embodiment of embodiment 2 wherein the steam sweep gas is added to the solid state polymerization reactor under vacuum.

Embodiment 4 an embodiment of any of embodiments 2 or 3 wherein the steam sweep gas is added in combination with an inert sweep gas.

Embodiment 5 the embodiment of any of embodiments 1-4 wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity of 60 to 300.

Embodiment 6 the embodiment of any one of embodiments 1 to 5 wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity equal to or less than 130.

Embodiment 7 the embodiment of any one of embodiments 1 to 6 wherein the polyamide starting material is solid state polymerized for less than 12 hours.

Embodiment 8 the embodiment of any one of embodiments 1-7 wherein the polyamide feedstock is polymerized in the solid state polymerization reactor for less than 12 hours, wherein the high molecular weight polyamide solution comprises less than 0.6 weight percent residual caprolactam, and wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity of 60 to 300.

Embodiment 9 the embodiment of any one of embodiments 1 to 8, wherein step (c) comprises adding a steam purge gas to the solid state polymerization reactor, wherein the high molecular weight polyamide solution comprises less than 0.2 wt% residual caprolactam, and wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity equal to or less than 130.

Embodiment 10 the embodiment of any one of embodiments 1 to 9 wherein the polyamide feedstock comprises aqueous polymer pellets.

Embodiment 11 the embodiment of embodiment 10 wherein the polymer pellets comprise less than 25 wt% water.

Embodiment 12 an embodiment of embodiment 10 or 11, wherein step (c) comprises releasing steam from the polymer pellets during polymerization in the solid state polymerization reactor.

Embodiment 13 a process for producing a polyamide having a low residual caprolactam content comprising: (a) supplying a polyamide feedstock comprising caprolactam monomer to a solid state polymerization reactor; (b) polymerizing a polyamide feedstock in a solid state polymerization reactor; and (c) adding a steam purge gas to the solid state polymerization reactor during polymerization to produce a high molecular weight polyamide solution comprising less than 0.6 wt% residual caprolactam.

Embodiment 14 embodiment 13 wherein the ratio of steam flow in grams/hour to the weight of the polymer pellets in grams is from 0.08:1 to 20: 1.

Embodiment 15 embodiment of any one of embodiments 13 or 14 wherein the polyamide feedstock is polymerized in the solid state polymerization reactor for less than 12 hours, wherein the high molecular weight polyamide solution comprises less than 0.6 weight percent residual caprolactam, and wherein the high molecular weight polyamide solution comprises a polyamide having a relative viscosity of 60 to 300.

Embodiment 16 the embodiment of any one of embodiments 13 to 15, wherein a steam sweep gas is added to the polymerization reactor under vacuum during polymerization.

Embodiment 17 a process for producing a polyamide having a low residual caprolactam content comprising: (a) supplying a polyamide feedstock comprising caprolactam monomer to a solid state polymerization reactor, wherein the polyamide feedstock comprises polymer pellets comprising water; (b) polymerizing a polyamide feedstock in a solid state polymerization reactor; and (c) releasing steam from the polymer pellets during polymerization in the solid state polymerization reactor to produce a high molecular weight polyamide solution comprising less than 0.6 wt.% residual caprolactam.

Embodiment 18 the embodiment of embodiment 17 wherein the polymer pellets comprise less than 25 wt% water.

Embodiment 19 embodiment of any one of embodiments 17 or 18 wherein the polymer pellets comprise sub-capsules to release water into the solid state polymerization reactor at different temperatures.

Embodiment 20 the embodiment of any one of embodiments 17 to 19, wherein the polymer pellets release water into the solid state polymerization reactor at a controlled rate.

Although the present invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those skilled in the art. Such modifications are also considered to be part of the present invention. Based on the above discussion, relevant knowledge in the art, and the references discussed above in connection with the detailed description of the related art descriptions and embodiments, the disclosures of which are all incorporated herein by reference, further description is deemed unnecessary. Further, it should be understood from the above discussion that aspects of the present invention and portions of the various embodiments may be combined or interchanged, in whole or in part. Furthermore, those of ordinary skill in the art will recognize that the foregoing description is by way of example only, and is not intended to limit the present invention.