Method for recycling polyamide compositions

Abstract

A method for recycling a polyamide composition includes pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition. The method can also include exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising a polyamide oligomer and / or monomer having a lower molecular weight than the polyamide oligomer in the polyamide oligomer composition.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 452,774, filed March 17, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION The present disclosure relates to a method for recycling thermoplastic polymers, which includes a pretreatment step to obtain low molecular weight oligomeric intermediate products from a nylon-containing feed. [Background technology]

[0003] It is becoming increasingly important to reduce the amount of scrap material generated from post-consumer and / or post-industrial plastics that ultimately ends up in landfills. In most cases, consumer items made from plastic components are disposed of in landfills or incinerators for disposal after their useful life ends. Efforts have been made to develop several technologies to break down materials into their constituent components for reuse / recycling. In-kind recycling and take-back programs are beginning to emerge. However, circularity currently does not exist. The thermoplastics industry has significant gaps in achieving circularity, and a consistent approach is needed. There remains a need in the plastics recycling industry to devise viable methods for recycling polyamides such as nylon 6, nylon 66, nylon 56, nylon 46, nylon 610, or nylon 612. Summary of the Invention

[0004] Various aspects of the present invention provide methods for recycling a polyamide composition. The methods include pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition. The methods also include exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising a polyamide oligomer and / or monomer having a lower molecular weight than the polyamide oligomer in the polyamide oligomer composition.

[0005] Various aspects of the present invention provide methods for recycling a polyamide composition. The methods include pretreating a polyamide composition containing a polyamide to produce a polyamide oligomer composition containing a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, the pretreatment including an enzyme treatment, a subcritical water treatment, a microwave treatment, or a combination thereof. The methods also include exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition containing a polyamide oligomer and / or monomer having a lower molecular weight than the polyamide oligomer in the polyamide oligomer composition.

[0006] Various aspects of the present invention provide methods for recycling polyamide compositions. The method includes separating a mixed plastics stream having more than 5% by weight of non-polyamide components to form a polyamide starting composition having 5% or less by weight of non-polyamide components. The method includes mechanically processing the polyamide starting composition to produce a polyamide composition, the polyamide composition having 5% or less by weight of non-polyamide components. The method also includes pretreating the polyamide composition to produce a polyamide oligomer composition containing polyamide oligomers having a lower molecular weight than the polyamides in the polyamide composition, the pretreatment including hydrothermal treatment, subcritical water treatment, supercritical water treatment, microwave treatment, enzyme treatment, solvent dissolution, acid hydrolysis, base hydrolysis, or a combination thereof. The method also includes exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition containing polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition.

[0007] Various aspects of the present invention provide polyamides formed from polyamide precursor compositions in methods for recycling polyamide compositions.

[0008] Various aspects of the present invention provide methods for recycling a polyamide composition, the methods including pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, the pretreatment including an enzymatic treatment.

[0009] Various aspects of the present invention provide methods for recycling polyamide compositions. The methods include separating a mixed plastics stream having more than 5 wt. % non-polyamide components to form a polyamide starting composition having 5 wt. % or less non-polyamide components. The methods include mechanically treating the polyamide starting composition to produce a polyamide composition, the polyamide composition having 5 wt. % or less non-polyamide components. The methods also include pretreating the polyamide composition to produce a polyamide oligomer composition comprising polyamide oligomers having a lower molecular weight than the polyamide in the polyamide composition, the pretreatment including an enzymatic treatment.

[0010] Various aspects of the present invention provide polyamides formed from the polyamide oligomer compositions of the methods for recycling polyamide compositions.

[0011] Various aspects of the disclosed methods can have advantages over other methods of recycling polyamide compositions. For example, in various aspects, the disclosed methods generate lower concentrations of tarry or high molecular weight side products and are more selective for generating low molecular weight oligomeric intermediates than other methods of recycling polyamide compositions, resulting in easier processing and higher yields. In various aspects, the disclosed pretreatment steps may be more selective for producing low molecular weight oligomeric intermediates than other methods for recycling polyamide compositions. In various aspects, the disclosed methods solve the problem of pyrolysis product formation (e.g., tar and high molecular weight by-products) during polyamide recycling via ammonolysis by incorporating the disclosed pretreatment steps that pre-crack the polyamide into a polyamide oligomer composition prior to ammonolysis, thereby providing easier processing and increased yields. In various aspects, the methods of the present disclosure involve gentler ammonolysis (e.g., having lower temperatures, lower pressures, less corrosive conditions, or a combination thereof) than other methods of recycling polyamide compositions, resulting in reduced production of undesirable by-products.

[0012] In various aspects, the disclosed enzymatic processes may be more specific (selective) for the formation of polyamide oligomers than currently available chemical or thermal decomposition processes. For example, the disclosed enzymatic processes may produce a crude product with lower concentrations of tar or high molecular weight by-products than other polyamide composition recycling methods, e.g., compared to chemical or thermal decomposition processes operating at higher temperatures or pressures.

[0013] The drawings illustrate generally, by way of example, but not by way of limitation, various aspects of the present invention. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a simplified block flow diagram illustrating aspects of the disclosed method. [Figure 2]FIG. 1 is a simplified block flow diagram illustrating aspects of the disclosed method. [Figure 3] FIG. 1 is a simplified block flow diagram illustrating aspects of the disclosed method. [Figure 4] FIG. 1 is a simplified block flow diagram illustrating aspects of the disclosed method. DETAILED DESCRIPTION OF THE INVENTION

[0015] Reference will now be made in detail to certain aspects of the disclosed subject matter. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that no attempt is made to limit the claims to the disclosed subject matter.

[0016] Throughout this document, values ​​expressed in range format should be understood to be interpreted in an open manner, not only to include the numerical values ​​explicitly recited as the limits of the range, but also to include all individual numerical values ​​or subranges subsumed within that range, as if each numerical value and subrange were explicitly recited. For example, a range of "about 0.1% to about 5%" or "about 0.1% to 5%" should be interpreted to include not only about 0.1% to about 5%, but also individual values ​​(e.g., 1%, 2%, 3%, and 4%) and subranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the stated range. A statement of "about X to Y" has the same meaning as "about X to about Y" unless otherwise indicated. Similarly, a statement of "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z" unless otherwise indicated.

[0017] In this document, the terms "a," "an," or "the" are used to include one or more unless the context clearly dictates otherwise. The term "or" is used to refer to a non-exclusive "or" unless otherwise indicated. The statements "at least one of A and B" or "at least one of A or B" have the same meaning as "A, B, or A and B." Additionally, phraseology or terminology used herein and not otherwise defined should be understood to be for descriptive purposes only and not limiting. Any use of section headings is intended to aid in the reading of the document and should not be construed as limiting. Information associated with a section heading may occur within or outside that particular section.

[0018] In the methods described herein, the acts may be performed in the particular order recited herein. Alternatively, in any aspect disclosed herein, specific acts may be performed in any order without departing from the principles of the invention, unless a temporal or operational order is explicitly recited. Furthermore, specified acts may be performed simultaneously unless the separate performance is expressly recited in the claim language or the literal meaning of the claim requires it. For example, a claimed act of performing X and a claimed act of performing Y may be performed simultaneously in a single operation, with the resulting process falling within the literal scope of the claimed process.

[0019] As used herein, the term "about" can allow for a degree of variation in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or the limits of a stated range, and includes the exact stated value or range.

[0020] As used herein, the term "substantially" refers to a majority or majority, such as at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%. As used herein, the term "substantially free" can mean having an absent or insignificant amount of material such that the amount of material present does not affect the material properties of a composition that includes the material, such that from about 0% to about 5% by weight of the composition is the material, or from about 0% to about 1% by weight, or less than, equal to, or greater than about 4.5%, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or less than or equal to about 0.001%, or about 0% by weight.

[0021] As used herein, the term "polymer" refers to a molecule having at least one repeating unit and can include copolymers.

[0022] As used herein, the terms "polyamide" and "nylon" are used interchangeably to define a type of thermoplastic polymer. Examples of polyamides or nylons include polyamide 46, polyamide 56, polyamide 66, polyamide 7, polyamide 610, polyamide 12, polyamide 612, polyamide 1212, and the like. A method for recycling a polyamide composition.

[0023] Various aspects of the present invention provide methods for recycling a polyamide composition. The methods include pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition. The methods also include exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising a polyamide oligomer and / or monomer having a lower molecular weight than the polyamide oligomer in the polyamide oligomer composition.

[0024] The polyamide composition can be a homogeneous composition. The homogeneous composition can include a uniformly sized solid, a semi-solid slurry, a slurry solution, a homogenized liquid solution of dissolved polymer, or a combination thereof. The polyamide composition can be a particulate composition. The particles can have any suitable shape, such as round particles, irregular particles, strips, or a combination thereof. The particles can have a diameter of less than 100 mm, less than 50 mm, less than 5 mm, or less than 1 mm. 50 The polyamide starting composition can have a particle size. The method can include mechanically treating the polyamide starting composition to form a polyamide composition. The polyamide starting composition can have the same composition as the polyamide composition. The mechanical treatment can include size reduction, cutting, grinding, shredding, particle formation, or a combination thereof. For example, the mechanical treatment can produce a uniform composition and / or a particulate composition.

[0025] The method can include separating a mixed plastic stream having more than 5% by weight of non-polyamide components to form a polyamide composition having 5% or less by weight of non-polyamide components. Separation can include melting point separation, dye test separation, electrostatic separation, flotation separation, melt phase separation, hot-hydraulic techniques, hot-melt techniques, cold-melt techniques, selective melting techniques, or combinations thereof. In some embodiments, separation includes flotation separation in water. Separation of the mixed plastic stream can remove thermoset polymers, polyesters, polyolefins, polycarbonates, or combinations thereof from the polyamides in the mixed plastic stream. For example, separation of the mixed plastic stream can remove PET, LDPE, LLDPE, PP, PVC, ABS rubber, polyacrylate, or combinations thereof from the polyamides in the mixed plastic stream.

[0026] The polyamide may be reinforced (e.g., glass fiber reinforced polyamide) or may be substantially free of reinforcement. The polyamide is a condensation polyamide. One example of a suitable condensation polyamide is the condensation product of adipic acid and hexamethylenediamine, commonly known as nylon 66 or poly-(hexamethylene adipamide). Another example of a suitable condensation polyamide is the condensation product of caprolactam, commonly known as nylon 6 or poly-(caprolactam). Yet another example of a suitable condensation polyamide is the condensation product of adipic acid and pentamethylenediamine, commonly known as nylon 56 or poly-(pentamethylene adipamide). The condensation product of sebacic acid and hexamethylenediamine, commonly known as nylon 610 or poly-(hexamethylene sebacamide), is another example of a suitable condensation polyamide. Other condensation polyamides can be produced by varying the chain length and composition of the organic diacids and diamines to produce different condensation polyamides with properties tailored for different end uses.

[0027] The polyamide in the polyamide composition can include any suitable polyamide or nylon. For example, the polyamide in the polyamide composition can include N4, N5, N6, N7, N10, N11, N12, N46, N56, N66, N610, N612, or a combination thereof. The polyamide in the polyamide composition can include N6, N66, N56, N610, or a combination thereof. The polyamide in the polyamide composition can include N66. In various embodiments, the polyamide in the polyamide composition can include N4, N5, N6, N7, N10, N11, N12, N46, N56, N66, N610, N612, or a combination thereof, and the polyamide composition is substantially free of other polyamides. The polyamide can be 80% to 100%, or 95% to 100%, or 98% to 100%, or 100% to 80% or less and less than, equal to, or greater than 82, 84, 86, 88, 90, 92, 94, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5, 99, 99.2, 99.4, 99.6, 99.8, or 99.9% by weight of the polyamide composition.

[0028] The method includes pretreating a polyamide composition containing a polyamide to produce a polyamide oligomer composition containing a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition. The pretreatment can depolymerize the nylon polymer into its corresponding oligomeric intermediate components. The depolymerization can be partial (e.g., mild) so that primarily oligomers are formed rather than monomers. The pretreatment can include hydrothermal treatment, subcritical water treatment, supercritical water treatment, microwave treatment, enzyme treatment, solvent dissolution, acid hydrolysis, base hydrolysis, or a combination thereof. The pretreatment can include solvent dissolution, acid hydrolysis, base hydrolysis, or a combination thereof. The pretreatment can include enzyme treatment, subcritical water treatment, microwave treatment, or a combination thereof. The pretreatment can be carried out for any suitable period of time. The pretreatment can be carried out for 15 hours or less, e.g., from 1 minute to 15 hours, or from 1 hour to 15 hours, or from 5 hours to 15 hours, or from 15 hours or less and 1 minute or more, and less than, equal to, or greater than 5 minutes, 10, 20, 30, 40, 50 minutes, 1 hour, 1.5, 2, 4, 6, 8, 10, 12, or 14 hours. In various aspects, the produced polyamide oligomer composition can be d of the polyamide composition fed to the pretreatment. 50 At least 10 times lower than d 50 In various aspects, the polyamide can be washed or otherwise purified of various impurities prior to pretreatment.

[0029] The pretreatment can include an enzyme treatment. In some embodiments, the enzyme treatment can be the enzyme treatment described in International Biodeterioration & Biodegradation, Vol. 60, pp. 144-151 (2007) by Sudhakar et al. (incorporated herein by reference in its entirety), in which degradation of nylon 6 and 66 was demonstrated in a mineral salt medium at 35°C and pH 7.5 under immersion concentration conditions with the polymer as the sole carbon source. Table 1 in Sudhakar et al. provides a literature summary of similar microbial degradation of nylon 66 and 6. Such process steps can be included in the pretreatment, as in the present disclosure.

[0030] The enzyme treatment can be carried out at a temperature of 15° C. to 45° C., or 20° C. to 30° C., or 45° C. or less and 15° C. or more, and less than, equal to, or greater than 16, 18, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 34, 36, 38, 40, 42, or 44° C. The enzyme treatment can be carried out at a pressure of 0.5 atm to 2 atm, or 1 atm to 1.5 atm, or 2 atm or less and 0.5 atm or more, and less than, equal to, or greater than 0.6 atm, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9 atm. The enzymatic treatment can be carried out at a pH of about 5 to about 9, e.g., less than or equal to 9 and greater than or equal to 5, and less than, equal to, or greater than 5.5, 6, 6.5, 7, 7.5, 8, 8.5, or 9. In one aspect, the enzymatic treatment can be operated in a vessel that does not require an ASTM pressure rating. The enzymatic treatment can produce a product having a low concentration of tar (e.g., high molecular weight by-products).

[0031] Pretreatment can include subcritical water treatment, which can include treatment with water having a temperature of 200°C to less than 373.9°C, or 200°C to 300°C, or less than 373.9°C but equal to or greater than 200°C, and less than, equal to, or greater than 210°C, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, or 370°C. Subcritical water treatment can include treatment with water having a pressure of 20 atm to 217.8 atm, or 40 atm to 100 atm, or 217.8 atm or less and 20 atm or more, and less than, equal to, or greater than 30 atm, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or 210 atm. In one embodiment, subcritical water conditions include a temperature of about 250 to 300°C and a pressure range of about 65 to 75 atm, and treatment for 0.5 to 6 hours.

[0032] Pretreatment can include microwave treatment, which can include exposure to microwave energy in a solvent at a temperature of 100°C to 500°C, or 150°C to 250°C, or up to 500°C and up to 100°C, and less than, equal to, or greater than 120°C, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 280, 300, 350, 400, or 450°C. Microwave treatment can be carried out at pressures ranging from 1 atm to 1,000 atm, or from 20 atm to 80 atm, or from 1,000 atm to 1 atm or greater, and less than, equal to, or greater than 10 atm, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 250, 300, 400, 500, 600, or 800 atm. The solvent can be any suitable solvent, such as an alcohol or glycol, such as methanol or ethylene glycol. In one embodiment, microwave treatment can involve a temperature of about 190-250°C, a pressure range of about 20-100 atm, and a treatment time of 0.1-3 hours.

[0033] In yet another embodiment, about 10 wt. % nylon 66 in water can be partially hydrolyzed at 270°C and 57 atm for about 1 hour to produce sufficient oligomers that are 80% soluble in boiling water. Partial nylon hydrolysis can also be carried out in the presence of a heterogeneous acid catalyst, such as the strong acid Amberlyst™ resin.

[0034] The polyamide oligomer composition includes a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition. The polyamide oligomer composition can include dimers, trimers, tetramers, higher oligomers, or combinations thereof. The polyamide oligomer composition can have a molecular weight of 200 g / mol to 3,000 g / mol, 200 g / mol to 3,000 g / mol, 300 g / mol to 2,800 g / mol, 400 g / mol to 2,500 g / mol, 500 g / mol to 2,000 g / mol, 500 g / mol to 1,800 g / mol, or 500 g / mol to 1,500 g / mol, or 3, The polyamide oligomer composition may have a number average molecular weight of the polyamide oligomers therein of less than or equal to 600 g / mol, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,500, 1,600, 1,700, 1,800, 2,000, 2,200, 2,400, 2,600, or 2,800 g / mol. The method may further comprise dehydrating the polyamide oligomer composition to remove water therefrom.

[0035] The method can also include exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition containing polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition. Ammonolysis can include contacting the polyamide oligomer composition with a nitrogen source. The nitrogen source can be any suitable nitrogen source for ammonolysis, such as gaseous ammonia, liquid ammonia, dissolved ammonia, an ammoniacal solution, and an ammonia-rich medium, or a combination thereof. The nitrogen source can include gaseous ammonia. Ammonolysis can include contacting the polyamide oligomer composition with the nitrogen source at a reaction temperature between 200°C and 350°C, or at a temperature up to 350°C and equal to or greater than 200°C, and less than, equal to, or greater than 210°C, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, or 340°C. The ammonolysis can include contacting the polyamide oligomer composition with a nitrogen source at a reaction pressure of 500 to 2,000 Psig (34 to 136 atm), or less than 140 atm and greater than or equal to 30 atm, and less than, equal to, or greater than 40 atm, 50, 60, 70, 80, 90, 100, 110, 120, or 130 atm. The method can further include recovering, purifying, and recycling the unreacted nitrogen source back for reuse in the ammonolysis.

[0036] Ammonolysis of nylon 66 polymer produces a mixture of two oligomers, one containing amide groups and the other containing amine groups. The amide groups undergo dehydration or nitrification to nitriles under reaction conditions. The ammonolysis reaction is equilibrium-limited and driven by high concentrations of ammonia (nitrogen source), removal of the volatile HMD eventually formed by stripping with excess ammonia, and conversion of the amide to nitrile. Nitrilation is also equilibrium-limited and driven by removal of water and ADN from the reaction mixture. Ammonolysis of nylon 6 primarily produces caprolactam (CPLM), aminocapronitrile (ACN or N112), and 6-aminocaproamide (ACAM). However, cyclic dimers can also form under reaction conditions, and the nitrile groups are also active in the formation of undesirable by-products.

[0037] During ammonolysis, thermal decomposition of the amide, acid, nitrile, and amine components present in the system can potentially generate tar, CO, and many other undesirable by-products. The generation of tar-like decomposition products is highly undesirable in any chemical reaction system. These materials not only reduce the yield of desired products but also present operational and processing challenges. The disclosed method solves this problem of thermal decomposition product formation during nylon recycling by ammonolysis. The disclosed ammonolysis of low-molecular-weight oligomer / monomer intermediates obtained from partial nylon depolymerization pretreatment can provide superior ammonolysis performance in terms of monomer yield and ease of processing. The generation of high-molecular-weight tar-like materials can be reduced, thereby improving overall product yield.

[0038] The polyamide precursor composition can include polyamide monomer, polyamide oligomer, or a combination thereof. The polyamide precursor composition can include polyamide monomer or can be substantially free of polyamide oligomer. The polyamide monomer can be 0% to 100% by weight, or 1% to 100% by weight, or 90% to 100% by weight, or less than 100% and greater than 80% by weight, and less than, equal to, or greater than 82%, 84, 86, 88, 90, 92, 94, 95, 96, 97, 98, 99, or 99.9% by weight of the total amount of polyamide monomer and polyamide oligomer in the polyamide precursor composition. The polyamide precursor composition can include any suitable polyamide monomer corresponding to the polyamide to be exposed to the present method, such as hexamethylene diamine (HMD), aminocapronitrile, 6-aminocaproamide, dimethyl adipate, adipic acid, methyl 6-aminocaproate, or a combination thereof.

[0039] The method may further include purifying, purifying, or separating one or more components of the polyamide precursor composition.

[0040] The method may further include polymerizing the polyamide precursor composition or one or more components thereof to form one or more polyamides.

[0041] Various aspects of the present invention provide methods for recycling polyamide compositions that can be performed without ammonolysis. The methods can include pretreating a polyamide composition containing polyamide to produce a polyamide oligomer composition containing polyamide oligomers having a lower molecular weight than the polyamides in the polyamide composition, the pretreatment including enzymatic treatment. The polyamides in the polyamide composition can include N4, N5, N6, N7, N10, N11, N12, N46, N56, N66, N610, N612, or combinations thereof. The polyamides can represent 95% to 100% by weight of the polyamide composition, or 98% to 100% by weight, or up to 100% and greater than or equal to 80% by weight, and less than, equal to, or greater than 82%, 84, 86, 88, 90, 92, 94, 95, 96, 97, 98, 99, or 99.9% by weight. The enzyme treatment can be carried out at a temperature of 15°C to 45°C, 20°C to 30°C, or 45°C or less and 15°C or more, and less than, equal to, or greater than 16, 18, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 34, 36, 38, 40, 42, or 44°C, and at a pressure of 0.5 atm to 2 atm, or 1 atm to 1.5 atm, or 2 atm or less and 0.5 atm or more, and less than, equal to, or greater than 0.6 atm, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9 atm. The enzyme treatment can be carried out at a pH of about 5 to 9, e.g., less than or equal to 9 and greater than or equal to 5, and less than, equal to, or greater than 5.5, 6, 6.5, 7, 7.5, 8, or 8.5. The enzyme treatment can be carried out for 15 hours or less, e.g., from 1 minute to 15 hours, or from 1 hour to 15 hours, or from 5 hours to 15 hours, or from 15 hours or less and greater than or equal to 1 minute, and less than, equal to, or greater than 5 minutes, 10, 20, 30, 40, 50 minutes, 1 hour, 1.5, 2, 4, 6, 8, 10, 12, or 14 hours. The polyamide oligomer composition can include dimers, trimers, tetramers, higher oligomers, or combinations thereof.The polyamide oligomer composition can have a number average molecular weight of polyamide oligomers therein of 200 g / mol to 3,000 g / mol, or 500 g / mol to 1,500 g / mol, or 3,000 g / mol to 500 g / mol, and less than, equal to, or greater than 600 g / mol, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,500, 1,600, 1,700, 1,800, 2,000, 2,200, 2,400, 2,600, or 2,800 g / mol. The method can further include dehydrating the polyamide oligomer composition. The method can further include polymerizing the polyamide oligomer composition to form one or more polyamides therefrom.

[0042] The method can further include mechanically treating the polyamide starting composition to form a polyamide composition, e.g., to form a homogeneous composition and / or a particulate composition. The method can further include separating a mixed plastic stream having more than 5 wt% non-polyamide components to form a polyamide composition having 5 wt% or less non-polyamide components.

[0043] In various aspects, the method for recycling a polyamide composition that includes an enzyme treatment may not include ammonolysis. In other aspects, the method includes exposing a polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition that includes polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition. The ammonolysis may include contacting the polyamide oligomer composition with a nitrogen source. The nitrogen source may include gaseous ammonia, liquid ammonia, dissolved ammonia, an ammoniacal solution, and an ammonia-rich medium, or a combination thereof. The nitrogen source may be gaseous ammonia. Ammonolysis can include contacting the polyamide oligomer composition with a nitrogen source at a reaction temperature of 200° C. to 350° C., or up to 350° C. and up to 200° C., and less than, equal to, or greater than 210° C., 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, or 340° C., and a reaction pressure of 500 to 2,000 Psig (34 to 136 atm), or up to 140 atm and greater than or equal to 30 atm, and less than, equal to, or greater than 40 atm, 50, 60, 70, 80, 90, 100, 110, 120, or 130 atm. The method can further include recovering, purifying, and recycling the unreacted nitrogen source back for reuse in ammonolysis. The method can further include polymerizing the polyamide precursor composition to form one or more polyamides therefrom.

[0044] The disclosed method offers a practical solution for recycling nylon polymers. The disclosed method may be effective in depolymerizing various nylon components present in mixed plastic streams into their corresponding monomeric components. Further recovery and purification of these monomers yields a high-purity product suitable for reuse by recycling back to nylon production facilities. For example, nylon 66 can be processed in the disclosed method to produce purified hexamethylenediamine and adipic acid. Nylon 6 can be processed in the disclosed method to produce caprolactam. In one example, nylon 56 can be processed in the disclosed method to produce purified pentamethylenediamine and adipic acid. These monomers can be reused in the process to manufacture these nylons. Thus, the disclosed method is beneficial for reducing landfill volume while simultaneously providing circularity and carbon footprint optimization to the nylon industry. polyamide.

[0045] Various aspects of the present invention provide polyamides formed from polyamide precursor compositions or polyamide oligomer compositions formed by the disclosed methods of recycling polyamide compositions.

[0046] In various aspects, the polyamide can be formed from a polyamide precursor composition formed by a process comprising pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition. The process can also include exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising a polyamide oligomer and / or monomer having a lower molecular weight than the polyamide oligomer in the polyamide oligomer composition.

[0047] In various aspects, a polyamide can be formed from a polyamide oligomer composition formed by a process that includes pretreating a polyamide composition that includes a polyamide to produce a polyamide oligomer composition that includes a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, where the pretreatment includes an enzymatic treatment.

[0048] In various aspects, polyamides can be formed from a polyamide precursor composition that includes pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamides in the polyamide composition, the pretreatment comprising an enzymatic treatment. The method also includes exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising a polyamide oligomer and / or monomer having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition. [Example]

[0049] Various aspects of the present invention may be better understood with reference to the following examples, which are provided by way of illustration and not by way of limitation. The present invention is not limited to the examples described herein.

[0050] Abbreviations: adipic acid (AA); aminocapronitrile (ACN); aminocaproamide (ACAM); adiponitrile (ADN); bis-hexamethylene triamine (BHMT); caprolactam dimer (CLDIM); caprolactam (CPLM); cyanovaleramide (CVAM); dimer of aminocapronitrile and aminocaproamide (DNAC); hexamethylenediamine (HMD); hexamethyleneimine (HMI); polycaprolactam, polyamide 6, or nylon 6 (N6 or PA6); poly(hexamethylene adipamide), polyamide 6, 6, or nylon 6 (N6,6, N66, or PA66).

[0051] Materials Used in the Examples. The nylon 6,6 or "N6,6" specimens used in the examples were obtained from the INVISTA nylon 6,6 production facility. The reported number average molecular weight (Mn) of this material was determined (via NMR) to be approximately 14,000 g / mole, and the relative viscosity (RV) was approximately 36.5 (determined at an 8.4% concentration in 90% formic acid according to ASTM D789). The nylon 6,6 material used herein represents a commercially available polymer used in a variety of applications, including airbags and textile fibers. Commercially available materials, namely, formic acid, aqueous ammonium hydroxide, methanol, and ethylene glycol, were used in the examples. The nylon 6 or "N6" specimens used in the examples were commercially available materials. Nylon 6 and nylon 6,6 polymer specimens were mechanically ground in a blender using dry ice. The powdered polymer specimens could be easily filled into 25 mL test containers.

[0052] Test methods used in the examples: Analytical techniques used: GC was used for monomeric components and GC-MS was used for speciation of unknowns. NMR was used for chain end analysis and molecular weight (Mn) determination. LC-MS was used for speciation of oligomeric components. FT-IR was used for oligomer identification. DSC was used for melting point characterization. TGA was used for determination of volatile components.

[0053] Analytical samples for NMR were prepared by dissolving approximately 0.02 g of solid in approximately 0.050 g of trifluoroacetic acid (TFA), and then deuterated methylene chloride (CD2Cl2) was added to the polymer sample dissolved in approximately 1 g of TFA.

[0054] An analytical sample for LC-MS was prepared as follows: Approximately 0.01–0.02 g of the recovered solid was dissolved in hexafluoroisopropyl alcohol (HFIP). The low molecular weight oligomeric intermediate was solubilized in HFIP. The solution was filtered and analyzed by LC-MS. Example 1. Degradation of polyamides via solvent dissolution, acid / base treatment, or enzymatic treatment.

[0055] In embodiment 100 shown in Figure 1, mixed plastic stream 41 contains thermoplastic and thermoset materials. The materials contain a variety of used / end-of-life parts and articles, either in their used and / or partially shredded form. Thermoplastic components include reinforced and unreinforced nylon (polyamide), polyester (primarily PET), polyolefin (LDPE, LLDPE, polypropylene, or PP), or polycarbonate. Thermoset components include PVC, ABS rubber, and polyacrylate.

[0056] The mixed plastic stream 41 undergoes several steps of sorting / separation 102 to separate the thermoplastic materials from the thermoset materials. At 102, once the thermoplastics are separated, the stream undergoes further segregation to separate polyamides, such as N6 N66, from other non-polyamides, such as PP and PET, and to separate polyamides from each other. Separation may include melting point separation, dye test separation, electrostatic separation, flotation separation, melt phase separation, hot-hydraulic techniques, hot melt techniques, cold melt techniques, selective melt techniques, or combinations thereof, as described below.

[0057] Melting point separation can be performed based on the melting points of PP (156°C), N6 (220°C), N66, and PET (above 256°C). N66 and PET can be further separated by a dye test, where N66 is acid-dyeable, but PET is not.

[0058] Clothing and carpet fibers produced by methods such as shearing or shredding can be further classified by electrostatic separation: Nylon fibers are more susceptible to static charge than PP.

[0059] For example, in flotation separation, the material can be suspended in a liquid (e.g., water) with a density between PP (0.93 g / cc) and Nylon 6 (1.12 g / cc) / Nylon 66 (1.13 g / cc). The floating PP portion can be skimmed / filtered from the top.

[0060] The plastic material may be melted and allowed to phase separate. The molten PP, which floats to the top, can be skimmed / decanted, while the nylon melt can be collected at the bottom. The nylon melt viscosity can be reduced by adding a small amount of adipic acid or hexamethylenediamine to end-capping and then neutralizing.

[0061] Hot water pressure techniques (150-300 Psig; 170-200°C) may be used to separate non-nylon materials, primarily polyester, jute, and PP, from nylon components. Nylon 66 tends to melt at about 170°C in the presence of high-pressure water, while nylon 6 and PP melt at about 150°C and 175°C, respectively. Polyester and jute remain unaffected by these conditions.

[0062] In the hot melt technique, the material is contacted with a high-boiling solvent (with low vapor pressure) at high temperature (above 150°C). Under these conditions, the nylon dissolves while the PP melts. The PP floats to the top and can be skimmed / decanted if the solvent density is higher than that of the PP. Other materials, heavier than the solvent density, may settle to the bottom and can be filtered off. The hot melt nylon solution may undergo chemical treatment to depolymerize into valuable monomer precursors or oligomers. Alternatively, the polymer can be precipitated by cooling the solution, followed by filtration. Suitable solvents include those that boil above 100°C at atmospheric pressure, for example, those that boil above 150°C at atmospheric pressure.

[0063] In the low-temperature dissolution technique, the material is contacted with a solvent capable of dissolving nylon at low temperatures (below 150°C, preferably ambient temperature). Once the nylon components are dissolved, the insoluble non-nylon components can be filtered from the solution. The nylon resin can be recovered by stripping the solvent (using steam or vacuum) or by non-solvent dilution. Suitable solvents include those that boil at ≦150°C at atmospheric pressure.

[0064] A selective dissolution technique can be used, in which the plastic material is contacted with a solvent selective for nylon 6 (or 66) at a controlled temperature. The nylon 6-containing solution is separated by filtration and cooled (or diluted with a non-solvent) to precipitate the nylon 6. The remaining nylon 66 material can be treated with the same (or a different) solvent at a higher temperature to dissolve the nylon 66 from PP and other materials. As an example, a methanol / water mixture selectively dissolves nylon 6 from nylon 66 at 120-150°C, but also dissolves nylon 66 above 150°C. In either case, the dissolved polymer precipitates as a powder upon cooling to room temperature. Other solvents include benzyl alcohol, tetramethylene sulfone, and butane-1,4-diol.

[0065] Any or all of the above steps in combination will isolate the nylon components from the non-nylon components.

[0066] The segregated nylon component stream 43 obtained from collection / separation step 102 is then fed to chemical solution step 108. A separate mechanical pretreatment step 104 can receive a mixed nylon-containing feed stream 47 and pretreat this stream to produce a feed stream 51 suitable for step 108. Stream 51 can contain shredded or reduced-size carpet / apparel fibers, automotive parts, engineering polymer articles, etc.

[0067] Step 108 utilizes compatible solvent dissolution along with acid / base hydrolysis chemistry to chemically break down the nylon long chains into smaller chunks, thereby producing nylon oligomer (or short chain nylon constituents) stream 55. There may be other by-product stream 63 generated during this process, which can be recovered for sale or used as fuel.

[0068] Alternatively, the separated nylon component stream 53 from collection / separation 102, as well as stream 51 from mechanical pretreatment 104, may be subjected to an enzymatic biodegradation process 110, as described in Sudhakar et al., International Biodeterioration & Biodegradation, Vol. 60, pp. 144-151 (2007), resulting in a stream 57 of short-chain, low-molecular-weight nylon monomer or oligomer components (e.g., dimers, trimers, tetramers, etc.). Although not shown, stream 59 from process 108 can also be fed to enzymatic biodegradation process 110. These short-chain nylon oligomer materials can be readily repolymerized in a subsequent process 112, either in stream 57 or stream 59. A repolymerized material stream 61 can be recovered from repolymerization process 112 either in a ground state, pellets, fibers, or other usable form. Nylon polymer stream 61 has a recycled nylon content derived from mixed plastics stream 41 and / or mixed nylon-containing feed stream 47. Example 2. Degradation of polyamide via pretreatment and ammonolysis.

[0069] This example illustrates a method for recycling nylon-containing feed 71 to obtain purified diamine product 95 that is available for nylon polymerization. As shown in Figure 2, in embodiment 200, a pretreatment step 206 for nylon oligomer intermediates can be used prior to ammonolysis step 208. Depending on the quality of feed stream 77 and process economic considerations, step 206 can be an enzymatic biotreatment, a subcritical water treatment, a microwave digestion treatment, or a combination thereof.

[0070] It may be possible to feed nylon material stream 79 obtained from collection / separation step 202 and mechanical pretreatment step 204 (as described in Example 1) to ammonolysis step 208. However, such mixed feedstocks may contain high levels of contaminants that could adversely affect the ammonolysis process. Pretreatment step 206 may be effective in producing a consistent low molecular weight nylon oligomer stream 81, which is advantageous for ammonolysis step 208. The ammonolysis step may operate with an excess ammonia inlet stream 99. Ammonia recovery step 216 may collect and purify ammonia-rich gaseous effluent 96 to form ammonia recycle stream 97. A supplemental ammonia stream 98 maintains ammonia balance throughout the ammonolysis step, and streams 97 and 98 combine to form stream 99, which is fed to step 208. Heavies and tarry materials are recovered from step 208 and purged as stream 121, which can be used for fuel value.

[0071] Ammonolysis process effluent 83 can contain primary nylon monomers such as diamines, adipic acid precursors (e.g., cyano-amides or dinitriles), along with various other precursors (e.g., aminonitriles, mono- and dinitriles, lactams, etc.). Purification step 210 can treat ammonolysis effluent stream 83 to recover such components in high purity, such as lactam stream 85 or aminonitrile stream 87. The remaining effluent stream 89 can undergo one or more chemical conversions (e.g., reductive amination or hydrogenation) using hydrogen source 91 in step 212 to generate a consistent diamine-enriched stream 93. Diamine-enriched stream 93 can be further purified in step 214 to obtain purified diamine stream 95 having a purity suitable for end-use applications. Diamine-poor by-product 123 can also have utility in the nylon field. Example 3. Degradation of polyamide via solvent dissolution and / or acid / base treatment followed by pretreatment.

[0072] 3, the effluent 329 from chemical solution process 306 (which may include solvent dissolution, acid / base hydrolysis, or a combination thereof) can be fed to pretreatment process 308 instead of being fed directly to repolymerization process 310 (as shown by dotted line 335). Pretreatment process 308 can include enzymatic biotreatment, subcritical water treatment, microwave degradation treatment, or a combination thereof. Pretreatment process 308 can produce a consistent stream 331 of short-chain, low-molecular-weight nylon oligomers that can be advantageous for repolymerization process 310. The resulting nylon polymer stream 333 from process 310 has a recycled nylon content derived from mixed nylon stream 323 and mixed plastics stream 321 that was initially separated in collection / separation process 302 as non-nylon plastics stream 325. Step 202 is a collection / separation step to produce stream 323, and step 304 represents a mechanical pre-treatment step to produce a homogenous mixed nylon feedstock 327 from mixed nylon stream 323, which may contain post-industrial recycled (PIR) and / or post-consumer recycled (PCR) textile / garment fibers, auto parts, airbag fabric, etc. Example 4. Subcritical water pretreatment for nylon oligomer intermediate.

[0073] Approximately 1.2 grams of nylon polymer mixed with approximately 22.5 cc of deionized water was held in a 25 mL stainless steel sealed container at a temperature of approximately 275°C and a pressure of up to 68 atm (1000 Psig) for 1 hour and 6 hours. These temperature and pressure conditions result in subcritical water test conditions. Subcritical water conditions are known as conditions below the critical point of water (i.e., 373.95°C and 217.75 atm (3200.1 Psia)).

[0074] The nylon polymer specimens tested were nylon 6, labeled "N6," and nylon 66, labeled "N6,6." The resulting product was separated into liquid and solid phases by filtration. The liquid phase was analyzed by GC-MS, NMR, and LC-MS for speciation and quantification. The recovered solid phase was dissolved in a suitable solvent, and the homogenized solution was analyzed by LC-MS and NMR. The "as is" solid was used for FT-IR, DSC, and TGA analysis.

[0075] Test conditions included three media: i) neutral media (water), ii) acidic 0.01 M formic acid media, and iii) basic 0.01 M ammonium hydroxide media. For each test condition, a blank sample was run along with the polymer sample in water. Table 1 shows the speciation determined from GC-MS and LC-MS analysis. Table 2 shows the measured weight yields observed. Table 3 shows the reduction in number average molecular weight (Mn) from the tests performed.

[0076] [Table 1] ( a ) values ​​represent the integrated area from the GC-FID detector response. ( * ) Only the monomers (HMD and adipic acid or AA) are considered, not including oligomers. All weight percentages are based on total sample weight (1.2 g polymer + 22.5 cc deionized water, approximately 23.7 g total).

[0077] [Table 2]

[0078] [Table 3]

[0079] The neutral medium test was observed to result in good HMD yields from N6,6 depolymerization. In all tests at subcritical conditions, the formation of HMD, adipic acid, and oligomers was observed from N6,6 depolymerization. A comparison of Example 4b with Examples 4g-4h showed higher monomer and oligomer product yields as the run time increased from 1 hour to 6 hours, all else remaining constant. The 6-hour run also showed an increase in by-products, such as HMI and BHMT, compared to the 1-hour run results. Examples 4i and 4j of the N6 depolymerization tests yielded mostly caprolactam.

[0080] Molecular Weight (Mn) Determination. In each case in Table 3, the solids at the end of the run (1 hour run time) were filtered from the test medium. The recovered solids were 1 The polymers were analyzed by H-NMR to determine the terminal and intrachain HMD segments, and the terminal and intrachain adipic acid segments. From these measurements, the % HMD and % adipic acid at the chain ends were determined. The chain end values ​​of % HMD were used to estimate the molecular weight (Mn) values.

[0081] These examples demonstrate promising results that nylon polymers can be effectively depolymerized into their respective monomers and oligomers at subcritical conditions, where a greater than 10-fold molecular weight reduction was observed from the starting nylon polymer feed to its monomer and oligomer constituent components.

[0082] The resulting monomers, e.g., HMD and adipic acid in the case of N6,6, and caprolactam in the case of N6, can be recovered from the product and available for recycling. The oligomers, with molecular weights reduced by at least 10 times, can be suitably subjected to further reactions to depolymerize into additional monomer products. Examples 5a-5j. Microwave pretreatment of nylon oligomer intermediates.

[0083] A laboratory-scale single-reaction chamber microwave decomposition system (Model: UltraWAVE; Manufacturer: Milestone Inc.) was used in these examples. The apparatus was equipped with a microwave reaction monitoring panel and multiple test setups for running parallel reactions at once. All nylon depolymerization tests were conducted at a temperature of approximately 210°C and a maximum pressure of approximately 50 atmospheres for 1 hour.

[0084] In this example, three depolymerization test media were used: i) neutral, ii) acidic (0.01 M formic acid), and iii) basic (0.01 M ammonium hydroxide). Two solvents were also tested: methanol and ethylene glycol. Microwave depolymerization tests were performed by mixing approximately 0.1 grams of polymer with approximately 3 cc of any one of the selected test media or solvents. The polymers tested contained N6 and N6,6. At the end of each run, a representative liquid sample of the product was analyzed using GC and GC-MS methods. Table 4 shows the speciation determined from the GC-MS and LC-MS analyses.

[0085] [Table 4]

[0086] This example demonstrates promising results that nylon polymers can be rationally depolymerized into their respective monomers and oligomers by microwave technology. The monomers, e.g., HMD in the case of N6,6 and caprolactam in the case of N6, can be recovered from the product and are available for recycling. The reduced molecular weight oligomers can suitably undergo further reactions to depolymerize into additional monomer products. Example 6. Degradation of polyamide via pretreatment and ammonolysis.

[0087] Figure 4 is a schematic diagram of a method 400 for recycling nylon polymers. Method 400 includes step 402 of collecting and separating a mixed plastic stream 1 into a non-nylon plastic stream 3 and a mixed nylon stream 5. Mixed plastic stream 1 can originate from residential, community, or industrial recycling facilities, a post-consumer recycled (PCR) stream, a post-industrial recycled (PIR) stream, or the like. Mixed plastic stream 1 can contain polyolefin materials such as HDPE, LDPE, LLDPE, polypropylene, and polybutylene; polyester materials such as PET and PBT; polycarbonate materials; acrylic materials such as ABS and acrylates; polystyrene materials; polyamide materials such as nylon and aramid nylon; polyurethane materials; and other such thermoset materials such as natural rubber, synthetic rubber, EPDM, VITON, and PVC.

[0088] Step 402 can include physical washing and separation techniques such as water / solvent washing, flotation separation, gravity separation, electrostatic separation, melt phase separation, separation by high / low temperature dissolution, selective solvent dissolution, and combinations thereof. Example 1 describes some of these mixed plastics separation techniques. A combination of any or all of these techniques will separate the nylon components from the non-nylon components of Stream 1.

[0089] The non-nylon plastic stream 3 can include non-nylon plastic components such as polyethylene, polypropylene, polybutylene, polycarbonate, polyurethane, polyester, etc. The mixed nylon stream 5 can contain components such as nylon 6, nylon 66, nylon 6X, nylon X6, etc. The "X" designation used herein refers to the various dicarboxylic acids or diamines used in the preparation of nylon. In one example, an X value of 10 in nylon 6X refers to the C6 dicarboxylic acid polymerized with hexamethylenediamine (HMD or HMDA) to make nylon 610. 10As another example, the X value of 5 in Nylon X6 can represent the five-carbon diamine, pentamethylenediamine (PMD or PMDA), polymerized with adipic acid to make Nylon 56. As yet another example, the X value of 12 in Nylon 6X can represent the C diamine, pentamethylenediamine (PMD or PMDA), polymerized with hexamethylenediamine to make Nylon 612. 12 It can represent a dicarboxylic acid. Such abbreviations and nomenclature for nylons is commonly practiced in the thermoplastics industry.

[0090] The nylon source can also include post-industrial recycled (PIR) materials, post-consumer recycled (PCR) materials, virgin off-spec nylon material from production facilities, or combinations thereof. In one example, the mixed nylon stream 5 can include materials from end-of-life automotive, electrical and electronic equipment, textile articles / parts, or combinations thereof. Another mixed nylon source can be engineering polymer articles / parts that may contain reinforcements, such as glass fibers, natural and cellulosic fibers, basalt fibers, or combinations thereof.

[0091] An optional mechanical pretreatment step 404 can remove the partially mixed nylon stream 7 from step 402 to produce a nylon stream 9 containing uniformly sized nylon pieces for acceptance in a subsequent step. Many conventional size reduction techniques are known and practiced in the solids management industry. Step 404 can include such conventional methods as stripping, chopping, champing, crushing, breaking, cutting, grinding, milling, pelletizing, or combinations thereof, of the fiber / fabric. Some techniques are dry processes, while some are wet processes using water and / or other solvents.

[0092] Method 400 includes step 406 of pretreating nylon material to obtain low molecular weight oligomeric intermediates. Step 406 processes mixed nylon stream 5 (and / or stream 9) to convert individual nylon components into their respective smaller oligomeric components as oligomeric intermediate stream 11. Step 406 can include a nylon depolymerization pretreatment step according to that described in Examples 4 and 5.

[0093] In one example, step 406 can include subcritical water depolymerization conditions, as demonstrated in Examples 4b, 4d, 4f, and 4g-4j. The resulting product contains some monomers from the depolymerization performed in step 406 and a mixture of dimers, trimers, tetramers, or other oligomeric components. As demonstrated in Example 4, high molecular weight nylon 66 effectively decomposes into HMD and adipic acid monomers, along with a corresponding oligomeric mixture having a number average molecular weight (Mn) at least 10 times lower than that of the fed nylon 66. Similarly, high molecular weight nylon 6 effectively decomposes into its caprolactam monomer, along with a corresponding oligomeric mixture having a number average molecular weight (Mn) significantly lower than that of the fed nylon 6.

[0094] In another example, step 406 can include microwave-assisted depolymerization conditions, as demonstrated in Example 5. The resulting product contains some monomers from the depolymerization performed in step 406 and a mixture of dimers, trimers, tetramers, or other oligomeric components. As demonstrated in Example 5, high molecular weight nylon 66 effectively decomposes into HMD and adipic acid monomers, along with a corresponding oligomeric mixture having a number average molecular weight (Mn) much lower than that of the fed nylon 66. Similarly, high molecular weight nylon 6 effectively decomposes into its caprolactam monomer, along with a corresponding oligomeric mixture having a number average molecular weight (Mn) significantly lower than that of the fed nylon 6.

[0095] Step 406 pretreats high molecular weight nylon material to produce oligomeric intermediate stream 11 enriched in monomeric and low molecular weight oligomeric components from any nylons fed to step 406. In one embodiment, nylon 56, when fed to step 406, yields its respective monomeric and low molecular weight oligomeric components. In another embodiment, an excess water removal substep can be included at the end of step 406 to dehydrate oligomeric intermediate stream 11 before feeding it to the next step.

[0096] Thus, step 406 is useful in the disclosed method 400 to obtain a low molecular weight nylon depolymerized stream.

[0097] Process 400 includes step 408 for completely decomposing low molecular weight oligomeric intermediate stream 11 into monomer stream 15. Step 408 uses either a catalytic or non-catalytic ammonolysis process in the presence of ammonia. Nylon ammonolysis is described in this disclosure and in Examples 7 and 8 and will not be repeated here. Ammonia management in step 408 is via fresh ammonia feed stream 23 to ammonia recovery step 410. Non-condensable vapor stream 17 containing excess ammonia is collected from step 408. Ammonia recovery step 410 condenses and purifies the excess ammonia from stream 17 and returns it to ammonolysis step 408 as ammonia recycle stream 19. Fresh make-up ammonia stream 21 is adjusted to maintain a proper ammonia mass balance in process 400.

[0098] Ammonolysis depolymerization step 408 can produce small amounts of tarry, high molecular weight, and heavy components. Such heavy and high molecular weight by-products produced in step 408 can be concentrated via a combination of distillative separation, steam stripping, and extraction and purged from process 400 as heavies / high boilers purge stream 13. In one example, concentrated stream 13 can be a pyrolysis oil that can be used to upgrade hydrogen and syngas upon high-temperature cracking. In another example, stream 13 can be useful as a by-product fuel due to its heat content in boilers for steam generation.

[0099] The monomer stream 15 exiting the ammonolysis process 408 can contain various nylon monomers and precursors as described in Example 7. Some non-limiting examples of nylon monomers and precursors may include lactams (e.g., caprolactam from nylon 6 or laurolactam from nylon 12); dinitriles (e.g., butanedinitrile, pentanedinitrile, or hexanedinitrile); diamines (e.g., butanediamine, pentanediamine, hexanediamine, decanediamine, or dodecanediamine); amides (e.g., adipamide); amino-nitriles (e.g., amino-butanenitrile, amino-pentanenitrile, or amino-hexanenitrile); cyano-amides (e.g., cyanovaleramide or cyanocaproamide); small amounts of various dimers; or combinations thereof.

[0100] Method 400 includes an initial product separation step 412 to recover readily separable monomers and precursors from monomer stream 15 exiting step 408. Step 412 can include one or more sequential and / or parallel distillation, decantation, and extraction substeps to separate the monomer components based on their boiling points and extraction efficiencies. For example, semi-purified stream 29 can contain lactams, while stream 31 can contain one or several small molecule aminonitriles and diamines, recovered as individual components or produced as a mixture. These monomers and intermediates can find use as recycle streams in their respective polymer production. For example, the recovered caprolactam in stream 29 can be further purified and recycled to a nylon 6 production facility. In another example, the recovered butanediamine in stream 31 can be further purified and recycled to a nylon 46 production facility.

[0101] Hexanedinitrile, hexanediamine, and amino-hexanenitrile components can be separated and concentrated in hydrogenation feed stream 27 exiting initial product separation step 412. Process 400 includes hydrogenation step 416 for converting hydrogenation feed stream 27 to diamines. Hydrogen source step 414 provides hydrogen via stream 33, and ammonia feed stream 25 is supplied from fresh make-up ammonia stream 21. Hydrogenation step 416 can be catalytic or non-catalytic and can be a low-pressure, medium-pressure, or high-pressure process. Some hydrogenation methods can include, for example, fixed-bed catalyst systems, slurry catalyst systems, solvent-assisted catalyst systems, or combinations thereof. In one example, 1,6-hexanedinitrile can be hydrogenated in the presence of ammonia using a reduced iron-based catalyst system at a pressure of 4500-5000 Psig and a temperature of 100-200°C. In another example, amino-hexanenitrile can be hydrogenated in the presence of ammonia using a Raney® nickel or Raney® cobalt catalyst system at pressures of 500-1500 Psig and temperatures of 60-150°C.

[0102] The hydrogenated product stream 35 from step 416 is further purified in diamine recovery / purification step 418 of method 400. Step 418 can use various substeps, such as diamine distillation based on the relative volatility of the components, ion exchange techniques, extraction using a preferential solvent, melt crystallization, or a combination thereof. Step 418 produces a diamine product stream 37 that meets or exceeds purity specifications for downstream applications. For example, diamine product stream 37 can be a purified HMD product of greater than 99.9 wt. % purity. Such an HMD product is suitable for recycling back to any nylon 6X production facility to make, for example, nylon 66, nylon 69, nylon 610, nylon 612, or other 6X nylons.

[0103] The disclosed method 400 is effective for recycling nylon polymers by converting them into their corresponding monomeric constituents and making them available in sufficient purity for recycling back into nylon production. The disclosed method 400 offers environmental and sustainability benefits. Example 7. Degradation of polyamide by ammonolysis without pretreatment.

[0104] Method 400 for recycling nylon polymer is carried out as described in Example 6 and represented schematically in Figure 4, excluding pretreatment step 406 for oligomeric intermediates. The nylon-containing stream obtained from step 402 and / or step 404 is fed directly to ammonolysis step 408 for nylon depolymerization in the presence of excess ammonia.

[0105] Tables 5A-5G below summarize the ammonolysis depolymerization for the nylon feeds tested. Approximately 15 grams of starting nylon polymer undergoes ammonolysis depolymerization in excess ammonia for each test run. Approximately 1.46 g / min of gaseous ammonia is continuously fed to the reaction for the total run time in each case. The ammonolysis reaction temperature is varied from 225°C to 350°C. The ammonolysis reaction time is monitored to achieve at least 50% conversion of the starting material at each temperature. The ammonolysis step is operated at a pressure of approximately 68 atm (1000 Psig). The ammonolysis step is operated in continuous-stirred tank reactor (CSTR) mode.

[0106] The vapor and liquid products obtained from the ammonolysis tests are summarized in the tables for each of the nylon-containing feeds: nylon 66 (Tables 5A-5B), nylon 6 (Tables 5C-5D), and a 50:50 (wt:wt) nylon 66:nylon 6 blend (Tables 5E-5G).

[0107] In Tables 5A-5G, the following definitions are used: Conversion (%) = (g of fed mass - g of unconverted mass) / (g of fed mass) × 100; Monomer yield (%) for nylon 66-containing feed: Yield (%) = (moles of ADN + HMD + CVAM) / (moles of fed polymer) × 100; Monomer yield (%) for nylon 6-containing feed: Yield (%) = (moles of CPLM + ACN + ACAM) / (moles of fed polymer) × 100. Total monomer yield (%) for mixed feeds containing nylon 6 and nylon 66 = (monomer yield (%) from nylon 66-containing feed) × weight % of nylon 66 fraction in the mixed feed + (monomer yield (%) from nylon 6-containing feed) × weight % of nylon 6 fraction in the mixed feed. The term "tar" refers to a collection of high-boiling, and potentially high-molecular-weight, components formed, for example, from the oligomerization of components with nitrile end groups.

[0108] [Table 5]

[0109] [Table 6] ( * ) Excess NH3 can be recovered and recycled back to the ammonolysis step via step 410 (as shown in Figure 4). (^) The term "other" includes adipamide and dimers of HMD with adipamide and CVAM. (&) NH3 and CO2 values ​​represent components likely to be present in dissolved state in the liquid phase. The liquid phase weight percent values ​​are based on the final remaining liquid mass excluding the unconverted polymer mass.

[0110] [Table 7]

[0111] [Table 8] (^) The term "other" includes low molecular weight species. ( * ) Excess NH3 can be recovered and recycled back to the ammonolysis step via step 410 (as shown in Figure 4). (&)NH3 values ​​represent components likely to be in solution in the liquid phase. The liquid phase weight percent values ​​are based on the final remaining liquid mass excluding the unconverted polymer mass.

[0112] [Table 9] (1) Nylon 66 monomer (including precursor yield) for HMD, ADN, and CVAM. (2) Nylon 6 monomer (including precursor yields) for CPLM, ACN, and ACAM.

[0113] [Table 10] (^) The term "other" includes low molecular weight species. ( * ) Excess NH3 can be recovered and recycled back to the ammonolysis step via step 410 [as shown in Figure 4). (&)NH3 values ​​represent components likely to be in solution in the liquid phase.

[0114] [Table 11] (^) The term "other" includes low molecular weight species. ( * ) Excess NH3 can be recovered and recycled back to the ammonolysis step via step 410 (as shown in Figure 4). (&) NH3 and CO2 values ​​represent components likely to be present in dissolved state in the liquid phase. The liquid phase weight percent values ​​are based on the final remaining liquid mass excluding the unconverted polymer mass.

[0115] The nylon 66-containing feed is observed to depolymerize into its primary monomer, hexamethylenediamine (HMD), and the monomer precursors, adiponitrile (ADN) and cyanovaleramide (CVAM). Cyanovaleramide is the precursor to adipic acid formed in the ammonolysis step. Adiponitrile is the precursor to HMD. Tar formation is believed to result from the thermal decomposition of other nylon 66 monomers, adipic acid, and other high molecular weight species formed.

[0116] The nylon 6-containing feed is observed to depolymerize into its monomer caprolactam (CPLM) and its precursors, aminocapronitrile (ACN) and aminocapramide (ACAM). The two caprolactam precursors, ACN and ACAM, can be chemically converted back to caprolactam and recovered. Tar formation is believed to be due to thermal decomposition of high molecular weight species. The liquid phase contains primarily the formed tar and dimers.

[0117] A 50:50 (wt:wt) mixed nylon 66:nylon 6 containing feed is observed to depolymerize to the nylon 6 monomer caprolactam (CPLM) and its precursors, i.e., aminocapronitrile (ACN) and aminocapramide (ACAM), and also the nylon 66 primary monomer, hexamethylenediamine (HMD), and monomer precursors, i.e., adiponitrile (ADN) and cyanovaleramide (CVAM).

[0118] In all of the above cases, significant tar formation was observed when the ammonolysis step was carried out at high temperatures. While the overall yield of nylon 6 monomer was not significantly affected by tar formation, the monomer yield for nylon 66 showed a decrease as tar formation increased. When mixed nylon feeds contained nylon 66 components, adipic acid was considered a likely precursor for tar formation.

[0119] Therefore, it would be desirable to have a process for nylon polymer recycling that can substantially reduce tar formation and improve yields of desirable monomer products. It would also be advantageous to have a process in which less tar formation is better from a processability and operating cost standpoint, such as less frequent equipment cleaning / shutdown. Example 8. Ammonolysis of a nylon oligomer intermediate.

[0120] A process 400 for recycling nylon polymer is carried out in the presence of a pretreatment step 406 for oligomeric intermediates, as described in Example 6 and represented schematically in Figure 4. The nylon-containing stream obtained from step 402 and / or step 404 is pretreated according to the steps described in Example 4. The dehydrated nylon oligomeric intermediate feed is then fed to an ammonolysis step 408 for complete depolymerization in the presence of excess ammonia.

[0121] Unlike Example 7 for the nylon 66-containing feed, it is unexpectedly observed that the nylon 66 oligomer intermediate feed from pretreatment step 406 can be depolymerized in ammonolysis step 408 at much lower temperatures and with reduced excess ammonia.

[0122] In one example, a typical product from the subcritical water pretreatment step 406 is a nylon 66 oligomer intermediate feed having a number average molecular weight in the range of 600-1500 g / mol, e.g., 1100 g / mol. This low molecular weight feed is depolymerized in the ammonolysis step 408 at a temperature 50° C. lower than that required for the nylon 66-containing feed shown in Example 7.

[0123] In another example, a typical product from microwave decomposition pretreatment step 406 is a nylon 66 oligomer intermediate feed having a lower molecular weight than the molecular weight of the nylon 66-containing feed. This low molecular weight feed is depolymerized in ammonolysis step 408 at a temperature 25° C. lower than that required for the nylon 66-containing feed shown in Example 7.

[0124] Similar results are observed for nylon 6 and mixed nylon 66:nylon 6 oligomer intermediate products obtained from either of the two pretreatment steps, i.e., subcritical water pretreatment (Example 4) and microwave digestion pretreatment (Example 5), when compared to nylon 6-containing feed.

[0125] The pretreatment step 406 allows the ammonolysis step 408 to operate at a lower temperature and reduced ammonia content. As disclosed, when a pretreatment step is performed before the ammonolysis step, tar formation is reduced. The yields of monomer and monomer precursor products are improved when the pretreatment step 406 is implemented. Example 9. Caprolactam recovery from nylon 6 feedstock.

[0126] A 500 cc resin kettle was used for the steam stripping process. The kettle contained a mechanical stirrer, N2 purge, distillation head, and condenser. During operation, condensate was collected as it exited the condenser. Steam generated from deoxygenated distilled water was introduced into the molten charge through a stainless steel tube. The kettle was heated with an electric heating mantle. The temperature within the kettle was controlled by adjusting the temperature at the mantle / kettle interface via a thermocouple.

[0127] A first set of experiments was conducted to demonstrate the acid-catalyzed steam stripping of caprolactam from nylon 6 feedstock. The nylon 6 feedstock was not pretreated to obtain low molecular weight oligomeric intermediates.

[0128] Approximately 500 g of nylon 6 material was charged to the kettle along with approximately 14.2 g of NaH2PO4·H2O and approximately 2.9 g of 85% phosphoric acid. Approximately 90 cc / h (water equivalent) of steam was fed to the kettle. At the end of each run up to 3 hours, an additional 25.4 g of nylon 6 feed was added to replenish the nylon 6 depolymerized in the kettle. The catalyst concentration as 85% H3PO4 ranged from 2.8 to 3.7 wt%. The temperature in the reactor ranged from 297°C to 301°C during the 4-hour run. The caprolactam concentration in the distillate ranged from 32 to 37.3 wt%.

[0129] A second set of experiments was conducted to demonstrate base-catalyzed steam stripping of caprolactam from nylon 6 feedstock. Approximately 100 g of nylon 6 feedstock, approximately 85.7 g of 6-aminocaproic acid, and approximately 26.1 g of NaOH (equivalent to approximately 100 g of sodium aminocaproate) were charged to a kettle. Approximately 180 cc / h (water equivalent) of steam was continuously fed. At the end of each run period up to 3 hours, an additional 100 g of nylon 6 feed was added to replenish the nylon 6 depolymerized in the kettle. The catalyst concentration as NaOH ranged from 7.5 to 23 wt%. The temperature in the reactor ranged from 318 to 333°C for the first 4 hours of run and from 280 to 318°C for the next 6 hours. The caprolactam concentration in the distillate ranged from 16 to 42.5 wt% for the first 4 hours of run and from 7 to 38 wt% for the next 6 hours.

[0130] The experiments were conducted similarly to the first set, except that no catalyst was used. The temperature in the reactor ranged from 255°C to 307°C during the 5-hour run. The caprolactam concentration in the distillate ranged from about 10 to 17.4 wt%.

[0131] In this example, the overall monomer (caprolactam) recovery was low if the nylon 6 was not partially depolymerized to obtain low molecular weight oligomeric intermediates. Example 10. Acid catalysis experiments with mixed nylon feedstock (nylon 6 and 66).

[0132] An acid-catalyzed steam stripping process was conducted on a mixed nylon feed containing 10:90 (wt:wt) nylon 66:nylon 6. This mixed nylon feedstock was not pretreated to obtain low molecular weight oligomeric intermediates. The same NaH2PO4·H2O and H3PO4 catalyst system as in Example 9 was used, but at an initial level of 16.25% based on 85% H3PO4. Additional feed containing 25.5:2.8 (g / g) nylon 6:nylon 66 was added every hour until one hour before the end of the run. A high rate of caprolactam stripping was observed. However, some nylon 66 degradation products were detected, primarily adiponitrile, cyclopentanone, hexylamine, 6-aminocapronitrile, and nylon 66 cyclic monomers. Neither HMD nor adipic acid was observed. During the first 5 hours of operation, the temperature ranged from 245 to 317°C, the catalyst composition as 85% H3PO4 ranged from 16 to 21 wt%, and the caprolactam concentration in the distillate ranged from about 17 to 40 wt%.

[0133] An acid-catalyzed steam stripping process was also conducted on a mixed nylon feed containing approximately 50:50 (wt:wt) nylon 66:nylon 6. The same NaH2PO4·H2O and H3PO4 catalyst system as in Example 9 was used, but at an initial level of 17.7% based on 85% H3PO4. Additional feed containing approximately 13:13 (g / g) nylon 6:nylon 66 was added every hour during the 5-hour run. The temperature ranged from 265 to 295°C, and the caprolactam concentration in the distillate ranged from approximately 8 to 11.5 wt%. The distillate was relatively clean, containing essentially only caprolactam but with small amounts of nylon 66 decomposition products, primarily cyclopentanone.

[0134] In this example, the overall monomer recovery was low when the mixed nylon feed was not partially depolymerized to obtain low molecular weight oligomeric intermediates. Example 11. Base catalysis experiments with mixed nylon feedstock (nylon 6 and 66).

[0135] A base-catalyzed steam stripping process was conducted on a mixed nylon feed containing approximately 50:50 (wt:wt) nylon 66:nylon 6. This mixed nylon feedstock was not pretreated to obtain a low molecular weight oligomeric intermediate. The starting composition contained 100 g each of nylon 6 and 66, approximately 85.7 g of 6-aminocaproic acid, and approximately 26.1 g of NaOH (equivalent to approximately 100 g of sodium aminocaproate). Approximately 90 cc / h (water equivalent) of steam was fed to the kettle. An additional 12.7 g of each nylon feed was added at the end of each run period up to 3 hours. The catalyst concentration as NaOH ranged from 7.7 to 9.1 wt%. The temperature in the reactor ranged from 261°C to 278°C during the 4-hour run. The caprolactam concentration in the distillate ranged from 3.5 to 3.8 wt%, while the HMD concentration ranged from 2.7 to 5.1 wt%.

[0136] In this example, the overall monomer recovery was low when the mixed nylon feed was not partially depolymerized to obtain low molecular weight oligomeric intermediates. Example 12. Base catalysis experiments with nylon 66.

[0137] A base-catalyzed steam stripping process was performed on a nylon 66 feed. The nylon feedstock was not pretreated to obtain a low-molecular-weight oligomeric intermediate. The starting composition was 200 g of nylon 66, approximately 85.7 g of 6-aminocaproic acid, and approximately 26.1 g of NaOH (equivalent to approximately 100 g of sodium aminocaproate). Approximately 90 cc / h (water equivalent) of steam was fed to the kettle. An additional 25.6 g of nylon 66 feed was added at the end of each run period throughout the 6-hour run. The catalyst concentration as NaOH ranged from 7.8 to 10.2 wt%. The temperature in the reactor ranged from 260 to 283°C. The HMD concentration in the distillate ranged from 3.5 to 22.1 wt%. A small amount of caprolactam (less than 5%) formed from the aminocaproic acid component was initially detected, which then decreased over time (to less than 1%) as it was consumed. In this example, the overall monomer recovery was low when the mixed nylon feed was not partially depolymerized to obtain low molecular weight oligomeric intermediates.

[0138] The terms and expressions which have been employed are used as terms of description, not of limitation, and there is no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the aspects of the invention. Thus, while the invention has been specifically disclosed by certain aspects and optional features, it will be understood that modifications and variations of the concepts disclosed herein may be reclassified by those skilled in the art, and that such modifications and variations are considered to be within the scope of the invention as defined by the scope of the aspects of the invention. Exemplary embodiments.

[0139] The following exemplary aspects are provided, the numbering of which should not be construed as designating an order of importance.

[0140] Aspect 1 is a method for recycling a polyamide composition, the method comprising: pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition; and exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition.

[0141] Aspect 2 provides the method of aspect 1, wherein the polyamide composition is a homogeneous composition.

[0142] Aspect 3 provides a method according to aspect 2, wherein the homogenous composition comprises a uniformly sized solid, a semi-solid slurry, a slurry solution, a homogenized liquid solution of dissolved polymer, or a combination thereof.

[0143] Aspect 4 provides the method of any one of Aspects 1-3, wherein the polyamide composition is a particulate composition.

[0144] Example 5 provides the method of any one of Examples 1-4, further comprising mechanically treating the polyamide starting composition to form the polyamide composition.

[0145] Example 6 provides the method of example 5, wherein the mechanical treatment comprises size reduction, cutting, grinding, shredding, particle formation, or a combination thereof.

[0146] Example 7 provides the method of any one of Examples 1-6, further comprising separating a mixed plastics stream having greater than 5 wt. % non-polyamide components to form a polyamide composition having 5 wt. % or less non-polyamide components.

[0147] Example 8 provides the method of Example 7, wherein the separation comprises melting point separation, dye test separation, electrostatic separation, flotation separation, melt phase separation, hot-hydraulic techniques, hot dissolution techniques, cold dissolution techniques, selective dissolution techniques, or a combination thereof.

[0148] Aspect 9 provides a method according to aspect 7 or 8, wherein the separation comprises flotation separation in water.

[0149] Example 10 provides the method of any one of Examples 7-9, wherein the separation of the mixed plastic stream removes thermoset polymers, polyesters, polyolefins, polycarbonates, or combinations thereof.

[0150] Example 11 provides the method of any one of Examples 7-10, wherein the separation of the mixed plastic stream removes PET, LDPE, LLDPE, PP, PVC, ABS rubber, polyacrylate, or a combination thereof.

[0151] Example 12 provides the method of any one of Examples 1 to 11, wherein the polyamide in the polyamide composition comprises N4, N5, N6, N7, N10, N11, N12, N46, N56, N66, N610, N612, or a combination thereof.

[0152] Example 13 provides the method of any one of Examples 1 to 12, wherein the polyamide in the polyamide composition comprises N6, N66, N56, N610, or a combination thereof.

[0153] Example 14 provides the method of any one of Examples 1 to 13, wherein the polyamide in the polyamide composition comprises N66.

[0154] Example 15 provides the method of any one of Examples 1 to 14, wherein the polyamide is 95% to 100% by weight of the polyamide composition.

[0155] Example 16 provides the method of any one of Examples 1 to 15, wherein the polyamide is 98% to 100% by weight of the polyamide composition.

[0156] Aspect 17 provides the method of any one of aspects 1 to 16, wherein the pretreatment comprises hydrothermal treatment, subcritical water treatment, supercritical water treatment, microwave treatment, enzyme treatment, solvent dissolution, acid hydrolysis, base hydrolysis, or a combination thereof.

[0157] Example 18 provides a method according to any one of Examples 1 to 17, wherein the pretreatment comprises solvent dissolution, acid hydrolysis, base hydrolysis, or a combination thereof.

[0158] Aspect 19 provides the method of any one of aspects 1 to 18, wherein the pretreatment comprises an enzyme treatment, a subcritical water treatment, a microwave treatment, or a combination thereof.

[0159] Aspect 20 provides the method of any one of aspects 1 to 19, wherein the pretreatment comprises an enzymatic treatment, and the enzymatic treatment is carried out at a temperature of 15°C to 45°C, a pH of 5 to 9, and a pressure of 0.5 atm to 2 atm.

[0160] Aspect 21 provides a method according to aspect 20, wherein the enzymatic treatment is carried out at a temperature of 20° C. to 30° C., a pH of 6 to 9, and a pressure of 1 atm to 1.5 atm.

[0161] Aspect 22 provides the method of any one of Aspects 1 to 21, wherein the pretreatment comprises subcritical water treatment, and the subcritical water treatment comprises treatment with water having a temperature of 200°C to less than 373.9°C and a pressure of 20 atm to 217.8 atm.

[0162] Aspect 23 provides the method of aspect 22, wherein the subcritical water treatment comprises treatment with water having a temperature of 200° C. to 300° C. and a pressure of 40 atm to 100 atm.

[0163] Example 24 provides the method of any one of Examples 1 to 23, wherein the pretreatment comprises microwave treatment, the microwave treatment comprising exposure to microwave energy in a solvent at a pressure between 1 atm and 1,000 atm and a temperature between 100°C and 500°C.

[0164] Example 25 provides a method according to example 24, wherein the microwave treatment comprises exposure to microwave energy in a solvent at a pressure between 20 atm and 80 atm and a temperature between 150°C and 250°C.

[0165] Example 26 provides a method according to any one of Examples 1 to 25, wherein the pretreatment is carried out for a period of 15 hours or less.

[0166] Example 27 provides the method of any one of Examples 1 to 26, wherein the polyamide oligomer composition has polyamide oligomers therein having a number average molecular weight of 200 g / mol or more and 3,000 g / mol or less.

[0167] Example 28 provides the method of any one of Examples 1 to 27, wherein the polyamide oligomer composition has polyamide oligomers therein having a number average molecular weight of 500 g / mol or more and 1,500 g / mol or less.

[0168] Example 29 provides the method of any one of Examples 1 to 28, wherein the polyamide oligomer composition comprises a dimer, trimer, tetramer, higher oligomer, or combinations thereof.

[0169] Example 30 provides the method of any one of Examples 1 to 29, further comprising dehydrating the polyamide oligomer composition.

[0170] Example 31 provides the method of any one of Examples 1 to 30, wherein the ammonolysis comprises contacting the polyamide oligomer composition with a nitrogen source.

[0171] Example 32 provides the method of example 31, wherein the nitrogen source comprises gaseous ammonia, liquid ammonia, dissolved ammonia, an ammoniacal solution, and an ammonia-rich medium, or a combination thereof.

[0172] Example 33 provides the method of example 31 or example 32, wherein the nitrogen source is gaseous ammonia.

[0173] Example 34 provides the method of any one of Examples 31 to 33, wherein the ammonolysis comprises contacting the polyamide oligomer composition with a nitrogen source at a reaction temperature of 200° C. to 350° C. and a reaction pressure of 30 atm to 140 atm.

[0174] Example 35 provides a method according to any one of Examples 31 to 34, further comprising recovering, purifying, and recycling the unreacted nitrogen source back for reuse in ammonolysis.

[0175] Example 36 provides the method of any one of Examples 1 to 35, wherein the polyamide precursor composition comprises a polyamide monomer.

[0176] Example 37 provides the method of any one of Examples 1 to 36, wherein the polyamide monomer is 0% to 100% by weight or 1% to 100% by weight of the total amount of polyamide monomer and polyamide oligomer in the polyamide precursor composition.

[0177] Example 38 provides the method of any one of Examples 1 to 37, wherein the polyamide monomer is 90% to 100% by weight of the total amount of polyamide monomer and polyamide oligomer in the polyamide precursor composition.

[0178] Example 39 provides the method of any one of Examples 1 to 38, wherein the polyamide precursor composition comprises hexamethylenediamine (HMD), aminocapronitrile, 6-aminocaproamide, dimethyl adipate, adipic acid, methyl 6-aminocaproate, or a combination thereof.

[0179] Example 40 provides the method of any one of Examples 1 to 39, further comprising purifying, clarifying, or separating one or more components of the polyamide precursor composition.

[0180] Example 41 provides the method of any one of Examples 1 to 40, further comprising polymerizing the polyamide precursor composition or one or more components thereof to form one or more polyamides.

[0181] Aspect 42 is a method of recycling a polyamide composition, the method comprising: pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, wherein the pretreatment comprises an enzyme treatment, a subcritical water treatment, a microwave treatment, or a combination thereof; and exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition.

[0182] Aspect 43 is a method of recycling a polyamide composition, the method comprising: separating a mixed plastics stream having greater than 5 wt. % non-polyamide components to form a polyamide starting composition having 5 wt. % or less non-polyamide components; mechanically treating a polyamide starting composition to produce a polyamide composition, wherein the polyamide composition has 5 wt. % or less of non-polyamide components; pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, the pretreatment comprising a hot water treatment, a subcritical water treatment, a supercritical water treatment, a microwave treatment, an enzyme treatment, a solvent dissolution, an acid hydrolysis, a base hydrolysis, or a combination thereof; and exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition.

[0183] Example 44 provides a polyamide formed from the polyamide precursor composition of any one of Examples 1-43.

[0184] Example 45 is a method of recycling a polyamide composition, the method comprising: A method is provided, comprising pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, wherein the pretreatment comprises an enzymatic treatment.

[0185] Aspect 46 provides a method according to aspect 45, wherein the enzymatic treatment is carried out at a temperature of 15°C to 45°C, a pH of 5 to 9, and a pressure of 0.5 atm to 2 atm.

[0186] Aspect 47 provides a method according to aspect 45 or 46, wherein the enzymatic treatment is carried out at a temperature of 20° C. to 30° C., a pH of 6 to 9, and a pressure of 1 atm to 1.5 atm.

[0187] Aspect 48 provides a method according to any one of aspects 45 to 47, wherein the enzymatic treatment is carried out for a period of 15 hours or less.

[0188] Example 49 provides the method of any one of examples 45-48, further comprising mechanically treating the polyamide starting composition to form the polyamide composition.

[0189] Example 50 provides the method of any one of Examples 45-49, further comprising separating a mixed plastics stream having greater than 5 wt. % non-polyamide components to form a polyamide composition having 5 wt. % or less non-polyamide components.

[0190] Example 51 provides the method of any one of Examples 45 to 50, wherein the polyamide in the polyamide composition comprises N4, N5, N6, N7, N10, N11, N12, N46, N56, N66, N610, N612, or a combination thereof.

[0191] Example 52 provides the method of any one of Examples 45 to 51, wherein the polyamide oligomer composition has polyamide oligomers therein with a number average molecular weight of 200 g / mol or more and 3,000 g / mol or less.

[0192] Example 53 provides the method of any one of Examples 45 to 52, wherein the polyamide oligomer composition has polyamide oligomers therein having a number average molecular weight of 500 g / mol or more and 1,500 g / mol or less.

[0193] Example 54 provides the method of any one of Examples 45 to 53, wherein the polyamide oligomer composition comprises a dimer, trimer, tetramer, higher oligomer, or combinations thereof.

[0194] Example 55 provides the method of any one of Examples 45-54, further comprising exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition.

[0195] Example 56 provides the method of example 55, further comprising polymerizing the polyamide precursor composition to form one or more polyamides therefrom.

[0196] Example 57 provides the method of example 55 or 56, wherein the ammonolysis comprises contacting the polyamide oligomer composition with a nitrogen source.

[0197] Example 58 provides the method of example 57, wherein the nitrogen source comprises gaseous ammonia, liquid ammonia, dissolved ammonia, an ammoniacal solution, and an ammonia-rich medium, or a combination thereof.

[0198] Example 59 provides the method of example 57 or example 58, wherein the nitrogen source is gaseous ammonia.

[0199] Example 60 provides the method of any one of Examples 57 to 59, wherein the ammonolysis comprises contacting the polyamide oligomer composition with a nitrogen source at a reaction temperature of 200° C. to 350° C. and a reaction pressure of 30 atm to 140 atm.

[0200] Example 61 provides the method of any one of Examples 57-60, further comprising recovering, purifying, and recycling the unreacted nitrogen source back for reuse in ammonolysis.

[0201] Example 62 provides the method of any one of Examples 45 to 61, further comprising dehydrating the polyamide oligomer composition.

[0202] Example 63 provides the method of any one of Examples 45 to 62, further comprising polymerizing the polyamide oligomer composition to form one or more polyamides.

[0203] Embodiment 64 is a method of recycling a polyamide composition, the method comprising: separating a mixed plastics stream having greater than 5 wt. % non-polyamide components to form a polyamide starting composition having 5 wt. % or less non-polyamide components; mechanically treating a polyamide starting composition to produce a polyamide composition, wherein the polyamide composition has 5 wt. % or less of non-polyamide components; and pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, wherein the pretreatment comprises an enzymatic treatment.

[0204] Example 65 provides a polyamide formed from the polyamide oligomer composition of any one of Examples 45-64.

[0205] Example 66 provides the method or polyamide of any one or any combination of Examples 1-65, optionally configured such that all recited elements or options are available for use or selection.

Claims

1. 1. A method for recycling a polyamide composition, said method comprising: pre-treating the polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition; and exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition.

2. 10. The method of claim 1, wherein the polyamide composition comprises a particulate composition, a semi-solid slurry, a slurry solution, a homogenized liquid solution of dissolved polymer, or a combination thereof.

3. 10. The method of claim 1, further comprising mechanically treating a polyamide starting composition to form said polyamide composition, wherein said mechanical treatment comprises size reduction, cutting, grinding, shredding, particle formation, or a combination thereof.

4. 10. The method of claim 1, further comprising separating a mixed plastics stream having greater than 5 wt.% non-polyamide components to form the polyamide composition having 5 wt.% or less non-polyamide components, wherein the separating of the mixed plastics stream removes thermoset polymers, polyesters, polyolefins, polycarbonates, or combinations thereof.

5. 2. The method of claim 1, wherein the polyamide in the polyamide composition comprises N4, N5, N6, N7, N10, N11, N12, N46, N56, N66, N610, N612, or a combination thereof, and the polyamide is 95% to 100% by weight of the polyamide composition.

6. 10. The method of claim 1, wherein the polyamide in the polyamide composition comprises N66.

7. 10. The method of claim 1, wherein the pretreatment comprises hydrothermal treatment, subcritical water treatment, supercritical water treatment, microwave treatment, enzyme treatment, solvent dissolution, acid hydrolysis, base hydrolysis, or a combination thereof.

8. 2. The method of claim 1, wherein the polyamide oligomer composition has polyamide oligomers therein having a number average molecular weight of 200 g / mol or more and 3,000 g / mol or less.

9. 10. The method of claim 1, wherein the pretreatment comprises an enzymatic treatment, the enzymatic treatment being carried out at a temperature of 15°C to 45°C, a pH of 5 to 9, and a pressure of 0.5 atm to 2 atm.

10. 2. The method of claim 1, wherein the pretreatment comprises subcritical water treatment, the subcritical water treatment comprising treatment with water having a temperature of from 200° C. to less than 373.9° C. and a pressure of from 20 atm to 217.8 atm.

11. 10. The method of claim 1, wherein the pretreatment comprises microwave treatment, the microwave treatment comprising exposure to microwave energy in a solvent at a pressure of 1 atm to 1,000 atm and a temperature of 100°C to 500°C.

12. 10. The method of claim 1, wherein the ammonolysis comprises contacting the polyamide oligomer composition with a nitrogen source at a reaction temperature of from 200°C to 350°C and a reaction pressure of from 30 atm to 140 atm, wherein the nitrogen source comprises gaseous ammonia, liquid ammonia, dissolved ammonia, an ammoniacal solution, and an ammonia-rich medium, or a combination thereof.

13. 10. The method of claim 1, wherein the polyamide monomer is 90% to 100% by weight of the total amount of polyamide monomer and polyamide oligomer in the polyamide precursor composition.

14. 10. The method of claim 1, further comprising polymerizing the polyamide precursor composition or one or more components thereof to form one or more polyamides.

15. 1. A method for recycling a polyamide composition, said method comprising: separating a mixed plastics stream having greater than 5 wt. % non-polyamide components to form a polyamide starting composition having 5 wt. % or less non-polyamide components; mechanically treating the polyamide starting composition to produce the polyamide composition, wherein the polyamide composition has 5 wt. % or less of non-polyamide components; pretreating the polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, the pretreatment comprising subcritical water treatment, enzyme treatment, or a combination thereof; and exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition.

16. 1. A method for recycling a polyamide composition, said method comprising:

1. A method of producing a polyamide oligomer composition comprising: pretreating a polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, wherein the pretreatment comprises an enzymatic treatment, the enzymatic treatment being conducted at a temperature of 15° C. to 45° C., a pH of 5 to 9, and a pressure of 0.5 atm to 2 atm for a duration of 15 hours or less.

17. 17. The method of claim 16, further comprising exposing the polyamide oligomer composition to ammonolysis to produce a polyamide precursor composition comprising polyamide oligomers and / or monomers having a lower molecular weight than the polyamide oligomers in the polyamide oligomer composition.

18. 20. The method of claim 17, further comprising polymerizing the polyamide precursor composition to form one or more polyamides therefrom.

19. 17. The method of claim 16, further comprising polymerizing the polyamide oligomer composition to form one or more polyamides.

20. 1. A method for recycling a polyamide composition, said method comprising: separating a mixed plastics stream having greater than 5 wt. % non-polyamide components to form a polyamide starting composition having 5 wt. % or less non-polyamide components; mechanically treating the polyamide starting composition to produce the polyamide composition, wherein the polyamide composition has 5 wt. % or less of non-polyamide components; and pre-treating the polyamide composition comprising a polyamide to produce a polyamide oligomer composition comprising a polyamide oligomer having a lower molecular weight than the polyamide in the polyamide composition, wherein the pre-treatment comprises an enzymatic treatment.

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