Method to depolymerize nylon 66 using water and either an acid or a base

Abstract

In one aspect, the disclosure relates to methods for the depolymerization of a nylon, such as nylon 66. In one aspect, the method comprises contacting a solid feedstock comprising a nylon (e.g., nylon 66) with water, thereby forming a liquid mixture; reducing a temperature of the liquid mixture, thereby forming a cooled liquid mixture; and contacting the cooled liquid mixture with a reactant comprising an acid or a base, thereby forming a product. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present disclosure.

Description

ATTORNEY DOCKET NO.222204-2820METHOD TO DEPOLYMERIZE NYLON 66 USING WATER AND EITHER AN ACID OR A BASE CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims the benefit of and priority to U.S. Provisional Application No.63 / 745,519, filed on January 15, 2025 which is incorporated herein by reference in its entirety.BACKGROUND

[0002] Nylon 66 is an important thermoplastic that finds applications in the automotive, electrical, and textile industries. The global annual production of nylon 66 is approximately 3.2 million tons per year, making it one of the most widely produced specialty polymers and is the second highest produced polyamide behind the chemically similar nylon 6 polymer. There is growing concern about the accumulation of plastic waste, to which nylon 66 contributes, motivating the collection and recycling of plastic waste. Despite advances in plastic recycling, there is still a scarcity of methods that for cost effective and / or efficient depolymerization of nylons, such as nylon 66. These needs and other needs are satisfied by the present disclosure.SUMMARY

[0003] In accordance with the purpose(s) of the disclosure, as embodied and broadly described herein, the disclosure, in one aspect, relates to a method, comprising: contacting a solid feedstock comprising nylon with water, thereby forming a liquid mixture; reducing a temperature of the liquid mixture, thereby forming a cooled liquid mixture; and contacting the cooled liquid mixture with a reactant comprising an acid or a base, thereby forming a product comprising at least one monomer or a salt thereof, wherein the at least one monomer comprises a carboxyl group, an amine, ora combination thereof

[0004] In another aspect, the disclosure relates to a method, comprising: contacting a solid feedstock comprising nylon 66 with water, thereby forming a liquid mixture; reducing a temperature of the liquid mixture, thereby forming a cooled liquid mixture; and contacting the cooled liquid mixture with a reactant comprising an acid or a base, thereby forming a product comprising hexamethylene diamine, adipic acid, a salt thereof, a derivative thereof, or any combination thereof.

[0005] Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described aspects are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described aspects are combinable andATTORNEY DOCKET NO. 222204-2820interchangeable with one another.BRIEF DESCRIPTION OF THE FIGURES

[0006] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0007] FIG. 1 shows a representative schematic diagram for a method for depolymerization of nylon 66 where a proton accepting base is used in the depolymerization reaction.

[0008] FIG. 2 shows a representative schematic diagram for a method for depolymerization of nylon 66 where a proton donating acid is used in the depolymerization reaction.

[0009] FIG. 3 shows a representative schematic diagram of a system configured to implement a method as disclosed herein with various configurations for mixing water and nylon 66.

[0010] FIG. 4A and 4B show representative schematic diagrams of two different reactor configurations in a system configured to implement a method as disclosed herein.

[0011] FIG. 5A shows a representative reversible condensation reaction between nylon 66 monomers hexamethylene diamine (HMDA) and adipic acid (AA), forming a nylon 66 dimer and water.

[0012] FIG. 5B shows a representative general condensation reaction between end groups of nylon 66 oligomers, forming an amide linkage and water.

[0013] FIG. 5C shows a representative salt complex between nylon 66 monomers dissolved in water under neutral conditions and cyclic monomer of nylon 66 known to form at low concentrations during polymerization.

[0014] FIG. 6 shows a representative relationship between nylon 66 reaction profile and phase equilibrium boundaries assuming system is saturated with water, reproduced from Ref.16. Melting point and freeze point refer to nylon 66 polymer.

[0015] FIG. 7 shows a representative reaction profile (reproduced from Ref. 18) for nylon 66 polymerization with four primary operating steps: 1. preheating, 2. heating step, 3. depressurization, 4. finishing. Diagram shown to directionality of operating conditions and reactor composition as a function of the reaction time.

[0016] FIG.8 shows a representative summary of reactions associated with the ammonolysis process.

[0017] FIG. 9 shows representative stable end group (SE) and cyclopentanone (CP) forming reactions believed to be responsible for nylon 66 end group degradation behavior.

[0018] FIG. 10 shows a representative secondary-amine-forming reaction resulting in BHMTA byproduct.ATTORNEY DOCKET NO. 222204-2820

[0019] FIG. 11 shows a representative, simplified process diagram of nylon 66 alkaline hydrolysis process.

[0020] FIG. 12 shows representative potential configurations for the nylon 66 alkaline hydrolysis reactor design.

[0021] FIGS. 13A and 13B show a representative temperature profile of the case study reaction (FIG. 13A) and a representative graph of number average molecular weight vs. reaction temperature (FIG. 13B), where water concentration is 66 wt%.

[0022] FIGS. 14A-14C show representative comparisons of impurity yields and amide conversion for isothermal reaction at 270°C at different water concentrations (FIG. 14A), for reaction ramping linearly from 270°C to 200°C after 1.5 hours with a water concentration of 66.6 wt% (FIG. 14B), and for reaction ramping linearly from 270°C to 200°C after 1.5 hours and linearly from 200°C to 180°C with a water concentration 66.6 wt% (FIG. 14C).

[0023] FIG. 15 shows a representative process diagram of a reaction and a distillation section of a system configured to perform a method as disclosed herein.

[0024] FIGS. 16A-16C show representative comparisons of HMDA concentration in recycled water from mechanical vapor recompression to the fraction of water separate (FIG. 16A), utility demand (FIG. 16B), and HMDA yield (FIG. 16C). The water rate is 2 kg per kg nylon 66. Nonheat integrated design utility demands are labeled as “*”. Utilities duty is reported for the reaction and distillation section only.

[0025] FIG. 17A shows representative process design configurations.

[0026] FIGS. 17B and 17C show representative mechanical vapor recompression and nonheat integrated design utilities duty (FIG. 17B) and reaction time and HMDA yield (FIG. 17C). Mechanical vapor recompression design controls HMDA content in recycle water to 2,000 ppmw.

[0027] FIG. 18 shows a representative diagram of multi-effect + mechanical vapor recompression (MVR) configuration and summary of utility comparison to MVR design. The water rate is 2 kg / kg nylon and both designs control HMDA content in recycle water to 2,000 ppmw.

[0028] FIG. 19 shows a representative process diagram of an organic solvent extraction section of a system configured to perform a method as disclosed herein.

[0029] FIGS. 20A and 20B show representative comparisons of toluene rate on utility demand considering different fractions of toluene on solid after solid-liquid separation (FIG.20A) and comparison between mechanical vapor recompression and conventional design for toluene recovery (FIG. 20B).

[0030] FIG. 21 shows a representative process diagram of an a crystallization section of a system configured to perform a method as disclosed herein.

[0031] FIGS. 22A and 22B show representative impact of water concentration in firstATTORNEY DOCKET NO.222204-2820dissolution (S-500) on utility duty and solid product purity (FIG. 22A) and impact of NaCI crystallizer (CR-610) solvent purge rate expressed as AA fraction in solvent on utilities and solid product purity (FIG. 22B).

[0032] FIGS. 23A and 23B show representative impact of water concentration in the second dissolution (S-520) on utility duty and solute concentration in the first dissolution (S-500) (FIG.23A) and the impact of water concentration on solid product purity FIG. 23B).

[0033] FIGS. 24A-24C show representative effects of crystallization and wash parameters, the fraction of solvent on solids (FIG. 24A), wash separation efficiency (FIG. 24B), and wash ratio (FIG. 24C) on utility demand and solid product purity.

[0034] FIG. 25 shows a representative schematic diagram and details of MVR design and comparison of utility demand to conventional design.

[0035] FIGS. 26A and 26B show representative impact of the stoichiometric rate of NaOH in the alkaline hydrolysis reactor on utility demand (FIG. 26A) and feed and byproduct rates related to the NaOH addition (FIG. 26B).

[0036] FIG. 27 shows representative degradation reactions modeled and discussed herein.

[0037] FIGS 28A and 28B show representative impact of water concentration in melt on the condensation equilibrium constant (FIG. 28A) and the apparent heat of reaction (FIG. 28B).

[0038] Additional advantages of the disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the disclosure. The advantages of the disclosure will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed.DETAILED DESCRIPTION

[0039] Many modifications and other aspects disclosed herein will come to mind to one skilled in the art to which the disclosed compositions and methods pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosures are not to be limited to the specific aspects disclosed and that modifications and other aspects are intended to be included within the scope of the appended claims. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.

[0040] Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0041] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual aspects described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other severalATTORNEY DOCKET NO.222204-2820aspects without departing from the scope or spirit of the present disclosure.

[0042] Any recited method can be carried out in the order of events recited or in any other order that is logically possible. That is, unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.

[0043] All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present disclosure is not entitled to antedate such publication by virtue of prior disclosure. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation.

[0044] While aspects of the present disclosure can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only and one of skill in the art will understand that each aspect of the present disclosure can be described and claimed in any statutory class.

[0045] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed compositions and methods belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0046] Prior to describing the various aspects of the present disclosure, the following definitions are provided and should be used unless otherwise indicated. Additional terms may be defined elsewhere in the present disclosure.A. DEFINITIONS

[0047] As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of,”ATTORNEY DOCKET NO. 222204-2820“including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of’ and “consisting of.” Similarly, the term “consisting essentially of’ is intended to include examples encompassed by the term “consisting of.

[0048] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

[0049] As used herein, nomenclature for compounds, including organic compounds, can be given using common names, IUPAC, IUBMB, or CAS recommendations for nomenclature. When one or more stereochemical features are present, Cahn-lngold-Prelog rules for stereochemistry can be employed to designate stereochemical priority, E / Z specification, and the like. One of skill in the art can readily ascertain the structure of a compound if given a name, either by systemic reduction of the compound structure using naming conventions, or by commercially available software, such as CHEMDRAW™ (Cambridgesoft Corporation, U.S.A.).

[0050] Reference to "a" chemical compound refers to one or more molecules of the chemical compound rather than being limited to a single molecule of the chemical compound. Furthermore, the one or more molecules may or may not be identical, so long as they fall under the category of the chemical compound. Thus, for example, "a" chemical compound is interpreted to include one or more molecules of the chemical, where the molecules may or may not be identical (e.g., different isotopic ratios, enantiomers, and the like).

[0051] As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a monomer,” “an acid,” or “a base,” includes, but is not limited to, two or more such monomers, acids, or bases, respectively.

[0052] As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, Reference to "a / an" chemical compound (e.g., nylon 66 or a carboxylic acid compound) refers to one or more molecules of the chemical compound rather than being limited to a single molecule of the chemical compound. Furthermore, the one or more molecules may or may not be identical, so long as they fall under the category of the chemical compound, protein, and antibody.

[0053] It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of theATTORNEY DOCKET NO. 222204-2820other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms a further aspect. For example, if the value “about 10” is disclosed, then “10” is also disclosed.

[0054] When a range is expressed, the range includes from the one particular value and / or to the other particular value. For example, where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure, e.g. the phrase “xto y” includes the range from ‘x’ to ‘y’ as well as the range greater than x’ and less than ‘y.’ The range can also be expressed as an upper limit, e.g., ‘about x, y, z, or less’ and should be interpreted to include the specific ranges of ‘about x,’ ‘about y,’ and ‘about z’ as well as the ranges of ‘less than x,’ less than y,’ and ‘less than z.’ Likewise, the phrase ‘about x, y, z, or greater’ should be interpreted to include the specific ranges of ‘about x,’ ‘about y,’ and ‘about z’ as well as the ranges of ‘greater than x,’ greater than y,’ and ‘greater than z.’ In addition, the phrase “about ‘x’ to ‘y’,” where ‘x’ and ‘y’ are numerical values, includes “about x’ to about ‘y’.”

[0055] It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “about 0.1% to 5%” should be interpreted to include not only the explicitly recited values of about 0.1% to about 5%, but also include individual values (e.g., about 1%, about 2%, about 3%, and about 4%) and the sub-ranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and other possible sub-ranges) within the indicated range.

[0056] As used herein, the terms “about,” “approximate,” “at or about,” and “substantially” mean that the amount or value in question can be the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art such that equivalent results or effects are obtained. In some circumstances, the value that provides equivalent results or effects cannot be reasonably determined. In such cases, it is generally understood, as used herein, that “about” and “at or about” mean the nominal value indicated ±10% variation unless otherwise indicated orATTORNEY DOCKET NO. 222204-2820inferred. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about,” “approximate,” or “at or about” whether or not expressly stated to be such. It is understood that where “about,” “approximate,” or “at or about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0057] The term “contacting” as used herein refers to bringing a disclosed analyte, compound, chemical, or material in proximity to another disclosed analyte, compound, chemical, or material as indicated by the context. In some instances, contacting can comprise both physical and chemical interactions between the indicated components. It is to be understood that chemical interactions can comprise a combination of covalent and non-covalent interactions, including one or more of ionic, dipolar, van der Waals interactions, and the like.

[0058] As used herein, the term “derivative” refers to a compound having a structure derived from the structure of a parent compound and whose structure is sufficiently similar to those disclosed herein and based upon that similarity, would be expected by one skilled in the art to exhibit the same or similar activities and utilities as the claimed compounds. Exemplary derivatives include salts, esters, amides, salts of esters or amides, and N-oxides of a parent compound.

[0059] The term “alkyl” as used herein is a branched or unbranched saturated hydrocarbon group of 1 to 24 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, f-butyl, n-pentyl, isopentyl, s-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, and the like. The alkyl group can be cyclic or acyclic. The alkyl group can be branched or unbranched. The alkyl group can also be substituted or unsubstituted. For example, the alkyl group can be substituted with one or more groups including, but not limited to, alkyl, cycloalkyl, alkoxy, amino, ether, halide, hydroxy, nitro, silyl, sulfo-oxo, or thiol, as described herein. A “lower alkyl” group is an alkyl group containing from one to six (e.g., from one to four) carbon atoms. The term alkyl group can also be a C1 alkyl, C1-C2 alkyl, C1-C3 alkyl, C1-C4 alkyl, C1-C5 alkyl, C1-C6 alkyl, C1-C7 alkyl, C1-C8 alkyl, C1-C9 alkyl, C1-C10 alkyl, and the like up to and including a C1-C24 alkyl.

[0060] The term “cycloalkyl” as used herein is a non-aromatic carbon-based ring composed of at least three carbon atoms. Examples of cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, norbornyl, and the like. The term “heterocycloalkyl” is a type of cycloalkyl group as defined above, and is included within the meaning of the term “cycloalkyl,” where at least one of the carbon atoms of the ring is replaced with a heteroatom such as, but not limited to, nitrogen, oxygen, sulfur, or phosphorus. The cycloalkyl group and heterocycloalkyl group can be substituted or unsubstituted. The cycloalkyl group and heterocycloalkyl group can be substituted with one or more groupsATTORNEY DOCKET NO. 222204-2820including, but not limited to, alkyl, cycloalkyl, alkoxy, amino, ether, halide, hydroxy, nitro, silyl, sulfo-oxo, or thiol as described herein.

[0061] The term “alkenyl” as used herein is a hydrocarbon group of from 2 to 24 carbon atoms with a structural formula containing at least one carbon-carbon double bond. Asymmetric structures such as (A1A2)C=C(A3A4) are intended to include both the E and Z isomers. This can be presumed in structural formulae herein wherein an asymmetric alkene is present, or it can be explicitly indicated by the bond symbol C=C. The alkenyl group can be substituted with one or more groups including, but not limited to, alkyl, cycloalkyl, alkoxy, alkenyl, cycloalkenyl, alkynyl, cycloalkynyl, aryl, heteroaryl, aldehyde, amino, carboxylic acid, ester, ether, halide, hydroxy, ketone, azide, nitro, silyl, sulfo-oxo, or thiol, as described herein.

[0062] The term “cycloalkenyl” as used herein is a non-aromatic carbon-based ring composed of at least three carbon atoms and containing at least one carbon-carbon double bound, i.e., C=C. Examples of cycloalkenyl groups include, but are not limited to, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, cyclohexadienyl, norbornenyl, and the like. The term “heterocycloalkenyl” is a type of cycloalkenyl group as defined above, and is included within the meaning of the term “cycloalkenyl,” where at least one of the carbon atoms of the ring is replaced with a heteroatom such as, but not limited to, nitrogen, oxygen, sulfur, or phosphorus. The cycloalkenyl group and heterocycloalkenyl group can be substituted or unsubstituted. The cycloalkenyl group and heterocycloalkenyl group can be substituted with one or more groups including, but not limited to, alkyl, cycloalkyl, alkoxy, alkenyl, cycloalkenyl, alkynyl, cycloalkynyl, aryl, heteroaryl, aldehyde, amino, carboxylic acid, ester, ether, halide, hydroxy, ketone, azide, nitro, silyl, sulfo-oxo, or thiol as described herein.

[0063] The term “alkynyl” as used herein is a hydrocarbon group of 2 to 24 carbon atoms with a structural formula containing at least one carbon-carbon triple bond. The alkynyl group can be unsubstituted or substituted with one or more groups including, but not limited to, alkyl, cycloalkyl, alkoxy, alkenyl, cycloalkenyl, alkynyl, cycloalkynyl, aryl, heteroaryl, aldehyde, amino, carboxylic acid, ester, ether, halide, hydroxy, ketone, azide, nitro, silyl, sulfo-oxo, or thiol, as described herein.

[0064] The term “cycloalkynyl” as used herein is a non-aromatic carbon-based ring composed of at least seven carbon atoms and containing at least one carbon-carbon triple bound. Examples of cycloalkynyl groups include, but are not limited to, cycloheptynyl, cyclooctynyl, cyclononynyl, and the like. The term “heterocycloalkynyl” is a type of cycloalkenyl group as defined above, and is included within the meaning of the term “cycloalkynyl,” where at least one of the carbon atoms of the ring is replaced with a heteroatom such as, but not limited to, nitrogen, oxygen, sulfur, or phosphorus. The cycloalkynyl group and heterocycloalkynyl group can be substituted or unsubstituted. The cycloalkynyl group and heterocycloalkynyl group can be substituted with one or more groups including, but not limitedATTORNEY DOCKET NO. 222204-2820to, alkyl, cycloalkyl, alkoxy, alkenyl, cycloalkenyl, alkynyl, cycloalkynyl, aryl, heteroaryl, aldehyde, amino, carboxylic acid, ester, ether, halide, hydroxy, ketone, azide, nitro, silyl, sulfooxo, or thiol as described herein.

[0065] The term “aromatic group” as used herein refers to a ring structure having cyclic clouds of delocalized TT electrons above and below the plane of the molecule, where the TT clouds contain (4n+2) IT electrons. A further discussion of aromaticity is found in Morrison and Boyd, Organic Chemistry, (5th Ed., 1987), Chapter 13, entitled “ Aromaticity,” pages 477-497, incorporated herein by reference. The term “aromatic group” is inclusive of both aryl and heteroaryl groups.

[0066] The term “aryl” as used herein is a group that contains any carbon-based aromatic group including, but not limited to, benzene, naphthalene, phenyl, biphenyl, anthracene, and the like. The aryl group can be substituted or unsubstituted. The aryl group can be substituted with one or more groups including, but not limited to, alkyl, cycloalkyl, alkoxy, alkenyl, cycloalkenyl, alkynyl, cycloalkynyl, aryl, heteroaryl, aldehyde, — NH2, carboxylic acid, ester, ether, halide, hydroxy, ketone, azide, nitro, silyl, sulfo-oxo, or thiol as described herein. The term “biaryl” is a specific type of aryl group and is included in the definition of “aryl.” In addition, the aryl group can be a single ring structure or comprise multiple ring structures that are either fused ring structures or attached via one or more bridging groups such as a carbon-carbon bond. For example, biaryl to two aryl groups that are bound together via a fused ring structure, as in naphthalene, or are attached via one or more carbon-carbon bonds, as in biphenyl.

[0067] As used herein, the terms “amine” or “amino” are represented by the formula — NA1A2, where A1and A2can be, independently, hydrogen or alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, cycloalkynyl, aryl, or a heteroaryl group as described herein. A specific example of amino is — NH2.

[0068] As used herein, the terms “carboxyl” or “carboxyl group” are represented by the formula — C(O)OA1, wherein A1and A2can be hydrogen or alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, cycloalkynyl, aryl, or a heteroaryl group as described herein. A specific example of a carboxyl group is — C(O)OH (also referred to herein as carboxylic acid).

[0069] As used herein, a “residue” of a chemical species refers to the moiety that is the resulting product of the chemical species in a particular reaction scheme or subsequent formulation or chemical product, regardless of whether the moiety is actually obtained from the chemical species. For example, an isoprene residue in an polymer refers to one or more -CH2CH=C(CH3)CH2- units in the polymer, regardless of whether isoprene was used to prepare the polymer.

[0070] As used herein, the terms “optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.ATTORNEY DOCKET NO.222204-2820

[0071] Unless otherwise specified, temperatures referred to herein are based on atmospheric pressure (i.e. one atmosphere).B. INTRODUCTION

[0072] Disclosed herein are methods for depolymerizing a nylon. As used herein, nylon refers to a polymer or copolymer comprising repeat units formed from residues of one or more monomers that include at least one of a carboxyl group (e.g., carboxylic acid, — C(O)OH), an amine (e.g., a primary amine, — NH2), or a combination thereof. For example, nylon 66 (also known as nylon 6,6 or nylon 6 / 6) refers to a copolymer comprising repeat units formed from residues of hexamethylene diamine and adipic acid. Another term for nylon, as used herein, is polyamide. In one aspect, disclosed herein are methods for depolymerizing an aliphatic nylon (an aliphatic polyamide). In one aspect, nylon 66 can also be referred to as polyamide 66.

[0073] Nylon 66 is a common thermoplastic used in the automotive industry, electronics, and textiles and is produced from the monomers adipic acid and hexamethylenediamine. Chemical depolymerization of nylon 66 to produce monomers is a method that expands the scope of recoverable waste material and incentives collection of plastic waste. The chemical recycling of nylon 66 is complicated by formation of a salt complex between the monomers adipic acid and hexamethylenediamine. Chemical recycling of nylon 66 has been limited considering the difficulty isolating hexamethylenediamine from adipic acid. Methods have been considered where an acid or base is added to neutralized on monomer as a non-volatile, water soluble salt and drive hydrolysis equilibrium to monomers. The free monomer is separated, and the neutralized monomer is released, by addition of an acid or base producing a salt byproduct. This conventional method is limited by the low reaction temperature needed for a strong acid or base. Mass transport limits the reaction with nylon 66 in the solid phase requiring either excess reactant or excessive reaction time.

[0074] In one aspect, disclosed herein is a method providing a preliminary depolymerization step with water under neutral conditions to produce a homogeneous mixture of nylon 66 oligomer that reacts with an acid or base in a homogeneous system at lower temperatures. The disclosed methods allow for more cost and / or resource efficient depolymerization of nylon 66 compared to conventional methods, requiring relatively lower operating temperatures and reduced consumption of solvents, such as acids and bases, to accomplish depolymerization. The disclosed methods also reduce the rate of degradation of nylon 66 compared to conventional methods.C. METHODS FOR DEPOLYMERIZATION OF NYLON

[0075] In one aspect, disclosed herein is a method comprising contacting a solid feedstock comprising a nylon (a polyamide, e.g., an aliphatic polyamide) with water, thereby forming a liquid mixture; reducing a temperature of the liquid mixture, thereby forming a cooled liquidATTORNEY DOCKET NO. 222204-2820mixture; and contacting the cooled liquid mixture with a reactant comprising an acid or a base, thereby forming a product comprising at least one monomer or a salt thereof, wherein the at least one monomer comprises a carboxyl group (e.g., carboxylic acid), an amine (e.g., a primary amine), or a combination thereof. In one aspect, the monomer can be a carboxylic acid compound, a dicarboxylic acid compound, an amine compound, a diamine compound, a salt thereof, or any combination thereof. Examples of carboxylic acid and / or dicarboxylic acid compounds include, but are not limited to, adipic acid, dodecanedioic acid, 11-aminoundecanoic acid, and co-aminolauric acid. Examples of amine compounds and / or a diamine compounds include, but are not limited to, 1 ,4-diaminobutane, hexamethylene diamine, 11-aminoundecanoic acid, and co-aminolauric acid. In another aspect, the product can comprise at least two monomers or salts thereof, wherein at least one of the monomers comprises a carboxyl group and at least another one of the monomers comprises an amine.

[0076] In one aspect, the method can include introducing nylon under high pressure of about 25 MPa to about 100 MPa to water at a temperature of about 250 °C to about 300 °C. In one aspect, the nylon can be introduced to water using an extruder where, for example, the nylon is a nylon melt. The nylon can be dissolved in the water and combined and / or fed at a rate of about 0.1 kg of water to about 10 kg of water per kg of nylon. The nylon can be allowed to react with water in a reactor (e.g., a plug flow type reactor) for about 0.1 hours to about 15 hours. The homogenous mixture of water and nylon can be introduced to a plug flow type reactor that can be designed as a series of pipes or cylindrical vessel. Inserts such as static mixers or mechanical agitators can also used in the reactor to improve heat transfer.

[0077] After reacting or during reacting, the temperature of the reaction mixture can be gradually reduced by about 15% to about 60% or reduced to a temperature of about 125 °C to about 250 °C. The temperature can be reduced at a rate of about 0.1 °C per minute to about 15 °C per minute, about 5 °C per minute to about 15 °C per minute, or about 0.1 °C per minute to about 10 °C per minute. In the context of a continuous plug flow type reaction, the temperature gradient in the reactor can be related to the reaction fluids average residence time in the reactor. When the temperature in the reactor is controlled at a gradient, heat can be removed from the reactor by a coolant. In one aspect, the coolant can be vaporizing water. The coolant into the reactor can split between different compartments operating at different pressures allowing different temperatures of coolant in the reactor. In one aspect, vapor generated from the coolant is used as a heat source elsewhere in the process. The controlled lowering of the temperature can also be instantaneous by flashing of the liquid reaction. Here, the pressure of the reacting fluid in the reactor is lowered, vaporizing some water, which lowers the temperature of the reacting fluid. The pressure loss in the reactor can be supplied by friction loss, an orifice, or valve. Vapor generated by the reacting fluid can be vented at different points in the reactor or remain in the reactor.ATTORNEY DOCKET NO.222204-2820

[0078] The water reacts with nylon forming a low molecular weight mixture of oligomers in the liquid mixture. The solid-liquid equilibrium temperature of a nylon oligomer can decrease with decreasing molecular weight of the oligomer. The temperature of the reaction can be reduced at a rate such that the nylon oligomer remains in solution and does not precipitate. Without wishing to be bound by theory, it can be said that the depolymerization reaction of nylon with water is exothermic and equilibrium favors lower molecular weight oligomers at lower temperatures.

[0079] Following reducing the temperature or during the process of reducing the temperature, a reactant comprising a base or and acid can be added to the cooled reaction mixture. The amount of acid or base added can be a molar amount sufficient enough to react with the polymer. The acid or base can be added at a single point (e.g., a single feed point into a reactor) or at multiple points (e.g., at multiple points distributed in the reactor). When the acid or base is added at multiple points, the rate can be controlled so the concentration of the acid or base does not exceed about 1 wt% to about 20 wt%, about 1 wt% to about 10 wt%, or about 10 wt% to about 10 wt% of the reaction solution at any point. The reaction following the addition of acid or base, while conceptually described as a separate reaction section, can be a part of the already discussed reactor where the process utilizes a single reactor with acid or base introduced at one or more intermediate points in the reaction. The cooled reaction mixture and acid or base can be allowed to react for about 0.1 hours to about 10 hours, optionally at a temperature of about 100 °C to about 250 °C. The temperature can be maintained isothermally. In one aspect, the temperature of the reaction can be controlled either using a coolant or by flashing the reaction liquid. After reacting, in one aspect, the method can further comprise reducing the temperature of the mixture to a temperature of about 50 °C to about 175 °C.

[0080] The nylon and water can be combined, mixed, or otherwise allowed to interact. In one aspect, the nylon and water can be combined, mixed, or otherwise allowed to interact in an amount of about 0.1 kg of water to about 10 kg of water, about 0.1 kg of water to about 8 kg of water, about 0.1 kg of water to about 6 kg of water, about 0.1 kg of water to about 4 kg of water, about 0.1 kg ofwaterto about 2 kg of water, about 1 kg ofwaterto about 10 kg of water, about 2 kg ofwaterto about 10 kg of water, about 4 kg ofwaterto about 10 kg of water, about 6 kg ofwaterto about 10 kg of water, about 8 kg of waterto about 10 kg of water, about 0.5 kg ofwaterto about 10 kg of water, about 0.5 kg ofwaterto about 8 kg of water, about 0.5 kg of water to about 6 kg of water, about 0.5 kg of water to about 4 kg of water, or about 0.5 kg ofwaterto about 2 kg of water per kg of solid feedstock or nylon. In another aspect, the nylon and water can be combined, mixed, or otherwise allowed to interact at a pressure of about 25 MPa to about 100 MPa, about 25 MPa to about 75 MPa, about 25 MPa to about 50 MPa, about 50 MPa to about 100 MPa, about 75 MPa to about 100 MPa, or about 59 MPa to aboutATTORNEY DOCKET NO. 222204-282075 MPa. In another aspect, the nylon and water can be combined, mixed, or otherwise allowed to interact at a temperature of about 250 °C to about 300 °C, about 250 °C to about 290 °C, about 250 °C to about 280 °C, about 250 °C to about 279 °C, about 260 °C to about 300 °C, about 270 °C to about 300 °C, about 280 °C to about 300 °C, about 260 °C to about 290 °C, about 270 °C to about 290 °C, or about 260 °C to about 280 °C. In another aspect, the nylon and water can be combined, mixed, or otherwise allowed to interact for about 0.1 hours to about 15 hours, about 0.1 hours to about 12 hours, about 0.1 hours to about 10 hours, about 0.1 hours to about 8 hours, about 0.1 hours to about 6 hours, about 0.1 hours to about 4 hours, about 0.1 hours to about 2 hours, about 1 hour to about 15 hours, about 2 hours to about 15 hours, about 4 hours to about 15 hours, about 6 hours to about 15 hours, about 8 hours to about 15 hours, or about 10 hours to about 15 hours.

[0081] After reacting or during the reaction, the temperature of the nylon and water can be reduced by about 15% to about 60%, about 25% to about 60%, about 35% to about 60%, about 45% to about 60%, about 15% to about 50%, about 15% to about 40%, or about 15% to about 30%. In another aspect, the temperature of the nylon and water liquid mixture can be reduced to about 125 °C to about 250 °C, about 125 °C to about 225 °C, about 125 °C to about 200 °C, about 125 °C to about 175 °C, about 125 °C to about 150 °C, about 150 °C to about 250 °C, about 175 °C to about 250 °C, about 200 °C to about 250 °C, about 225 °C to about 250 °C, or about 150 °C to about 220 °C.

[0082] In one aspect, the reactant (including and acid or a base) and liquid mixture can be combined, mixed, or otherwise allowed to interact for about 0.1 hours to about 10 hours, about 0.1 hours to about 8 hours, about 0.1 hours to about 6 hours, about 0.1 hours to about 4 hours, about 0.1 hours to about 2 hours, about 1 hours to about 10 hours, about 2 hours to about 10 hours, about 4 hours to about 10 hours, about 6 hours to about 10 hours, about 8 hours to about 10 hours, or about 0.1 hours to about 5 hours. In another aspect, the reactant and liquid mixture can be combined, mixed, or otherwise allowed to interact at a temperature of about 100 °C to about 250 °C, about 100 °C to about 225 °C, about 100 °C to about 200 °C, about 100 °C to about 175 °C, about 100 °C to about 150 °C, about 125 °C to about 250 °C, about 150 °C to about 250 °C, about 175 °C to about 250 °C, about 200 °C to about 250 °C, or about 120 °C to about 220 °C. An acid selected can be a strong acid such as hydrochloric acid, sulfuric acid, nitric acid, the like, or a combination thereof. A base can be a strong base such as potassium hydroxide, ammonium hydroxide, the like or a combination thereof.

[0083] Following reacting the reactant and liquid mixture, the resulting product can be cooled to a temperature of about 50 °C to about 175 °C, about 50 °C to about 150 °C, about 50 °C to about 125 °C, about 50 °C to about 100 °C, about 50 °C to about 75 °C, about 75 °C to about 175 °C, about 100 °C to about 175 °C, about 125 °C to about 175 °C, about 150 °C to about 175 °C, or about 60 °C to about 150 °C. The product yield for the disclosed method (e.g., yieldATTORNEY DOCKET NO. 222204-2820of hexamethylene diamine, adipic acid, a salt thereof, a derivative thereof, or any combination thereof) can range from about 85% to about 100%, about 85% to about 99%, about 85% to about 95%, about 85% to about 90%, about 90% to about 100%, or about 95% to about 100%.

[0084] When the reactant comprises an acid, the product can comprise a carboxylic acid or dicarboxylic acid and an amine, a diamine, a salt thereof, or a derivative thereof (e.g., an amine salt or diamine salt). The method can further comprise separating the carboxylic acid or dicarboxylic acid (e.g., a non-volatile compound) from the amine, the diamine, a salt thereof, or a derivative thereof (e.g., a volatile compound). As used herein, a volatile compound refers to a compound that has a relatively high vapor pressure at room temperature. A non-volatile compound refers to a compound that has a relatively low or negligible vapor pressure at room temperature.

[0085] When the reactant comprises a base, the product can comprise an amine or diamine and a carboxylic acid, dicarboxylic acid, a salt thereof, or a derivative thereof (e.g., a salt of a carboxylic acid or a salt of a dicarboxylic acid). The method can further comprise separating the carboxylic acid, the dicarboxylic acid, a salt thereof, or a derivative thereof (e.g., a nonvolatile compound) from the amine or diamine (e.g., a volatile compound).D. METHODS FOR DEPOLYMERIZATION OF NYLON 66

[0086] In one aspect, disclosed herein is a method comprising contacting a solid feedstock comprising nylon 66 with water, thereby forming a liquid mixture; reducing a temperature of the liquid mixture, thereby forming a cooled liquid mixture; and contacting the cooled liquid mixture with a reactant comprising an acid or a base, thereby forming a product comprising hexamethylene diamine, adipic acid, a salt thereof (e.g., an adipate salt such as sodium adipate salt or hexamethylene diammonium salt), a derivative thereof, or any combination thereof. In one aspect, the product can comprise at least one of an adipate salt or a hexamethylene diammonium salt). The method can include introducing nylon 66 under high pressure of about 25 MPa to about 100 MPa to water at a temperature of about 250 °C to about 300 °C. In one aspect, the nylon 66 can be introduced to water using an extruder where, for example, the nylon 66 is a nylon 66 melt. The nylon 66 can be dissolved in the water and combined and / or fed at a rate of about 0.1 kg of water to about 10 kg of water per kg of nylon 66. The nylon 66 can be allowed to react with water in a reactor (e.g., a plug flow type reactor) for about O.1 hours to about 15 hours. The homogenous mixture ofwater and nylon 66 can be introduced to a plug flow type reactor that can be designed as a series of pipes or cylindrical vessel. Inserts such as static mixers or mechanical agitators can also used in the reactor to improve heat transfer.

[0087] After reacting or during reacting, the temperature of the reaction mixture can be gradually reduced by about 15% to about 60% or reduced to a temperature of about 125 °C to about 250 °C. The temperature can be reduced at a rate of about 0.1 °C per minute to aboutATTORNEY DOCKET NO. 222204-282015 °C per minute, about 5 °C per minute to about 15 °C per minute, or about 0.1 °C per minute to about 10 °C per minute. In the context of a continuous plug flow type reaction, the temperature gradient in the reactor can be related to the reaction fluids average residence time in the reactor. When the temperature in the reactor is controlled at a gradient, heat can be removed from the reactor by a coolant. In one aspect, the coolant can be vaporizing water. The coolant into the reactor can split between different compartments operating at different pressures allowing different temperatures of coolant in the reactor. In one aspect, vapor generated from the coolant is used as a heat source elsewhere in the process. The controlled lowering of the temperature can also be instantaneous by flashing of the liquid reaction. Here, the pressure of the reacting fluid in the reactor is lowered, vaporizing some water, which lowers the temperature of the reacting fluid. The pressure loss in the reactor can be supplied by friction loss, an orifice, or valve. Vapor generated by the reacting fluid can be vented at different points in the reactor or remain in the reactor.

[0088] The water reacts with nylon 66 forming a low molecular weight mixture of oligomers in the liquid mixture. The solid-liquid equilibrium temperature of the nylon 66 oligomer can decrease with decreasing molecular weight of the oligomer. The temperature of the reaction can be reduced at a rate such that the nylon 66 oligomer remains in solution and does not precipitate. Without wishing to be bound by theory, it can be said that the depolymerization reaction of nylon 66 with water is exothermic and equilibrium favors lower molecular weight oligomers at lower temperatures.

[0089] Following reducing the temperature or during the process of reducing the temperature, a reactant comprising a base or and acid can be added to the cooled reaction mixture at an amount of about 8 moles of reactant to about 20 moles of reactant per kg of nylon 66, wherein moles of reactant refers to the moles of protons that can be donated by the reactant (when it comprises an acid) or accepted by the reactant (when it comprises a base). The acid or base can be added at a single point (e.g., a single feed point into a reactor) or at multiple points (e.g., at multiple points distributed in the reactor). When the acid or base is added at multiple points, the rate can be controlled so the concentration of the acid or base does not exceed about 1 wt% to about 20 wt%, about 1 wt% to about 10 wt%, or about 10 wt% to about 10 wt% of the reaction solution at any point. The reaction following the addition of acid or base, while conceptually described as a separate reaction section, can be a part of the already discussed reactor where the process utilizes a single reactor with acid or base introduced at one or more intermediate points in the reaction. The cooled reaction mixture and acid or base can be allowed to react for about 0.1 hours to about 10 hours, optionally at a temperature of about 100 °C to about 250 °C. The temperature can be maintained isothermally. In one aspect, the temperature of the reaction can be controlled either using a coolant or by flashing the reaction liquid. After reacting, in one aspect, the method can furtherATTORNEY DOCKET NO. 222204-2820comprise reducing the temperature of the mixture to a temperature of about 50 °C to about 175 °C.

[0090] The nylon 66 and water can be combined, mixed, or otherwise allowed to interact. In one aspect, the nylon 66 and water can be combined, mixed, or otherwise allowed to interact in an amount of about 0.1 kg of water to about 10 kg of water, about 0.1 kg of water to about 8 kg of water, about 0.1 kg of water to about 6 kg of water, about 0.1 kg of water to about 4 kg of water, about 0.1 kg of water to about 2 kg of water, about 1 kg of water to about 10 kg of water, about 2 kg of water to about 10 kg of water, about 4 kg of water to about 10 kg of water, about 6 kg of water to about 10 kg of water, about 8 kg of water to about 10 kg of water, about 0.5 kg of water to about 10 kg of water, about 0.5 kg of water to about 8 kg of water, about 0.5 kg of water to about 6 kg of water, about 0.5 kg of water to about 4 kg of water, or about 0.5 kg of water to about 2 kg of water per kg of solid feedstock or nylon 66. In another aspect, the nylon 66 and water can be combined, mixed, or otherwise allowed to interact at a pressure of about 25 MPa to about 100 MPa, about 25 MPa to about 75 MPa, about 25 MPa to about 50 MPa, about 50 MPa to about 100 MPa, about 75 MPa to about 100 MPa, or about 59 MPa to about 75 MPa. In another aspect, the nylon 66 and water can be combined, mixed, or otherwise allowed to interact at a temperature of about 250 °C to about 300 °C, about 250 °C to about 290 °C, about 250 °C to about 280 °C, about 250 °C to about 279 °C, about 260 °C to about 300 °C, about 270 °C to about 300 °C, about 280 °C to about 300 °C, about 260 °C to about 290 °C, about 270 °C to about 290 °C, or about 260 °C to about 280 °C. In another aspect, the nylon 66 and water can be combined, mixed, or otherwise allowed to interact for about 0.1 hours to about 15 hours, about 0.1 hours to about 12 hours, about 0.1 hours to about 10 hours, about 0.1 hours to about 8 hours, about 0.1 hours to about 6 hours, about 0.1 hours to about 4 hours, about 0.1 hours to about 2 hours, about 1 hour to about 15 hours, about 2 hours to about 15 hours, about 4 hours to about 15 hours, about 6 hours to about 15 hours, about 8 hours to about 15 hours, or about 10 hours to about 15 hours.

[0091] After reacting or during the reaction, the temperature of the nylon 66 and water can be reduced by about 15% to about 60%, about 25% to about 60%, about 35% to about 60%, about 45% to about 60%, about 15% to about 50%, about 15% to about 40%, or about 15% to about 30%. In another aspect, the temperature of the nylon 66 and water liquid mixture can be reduced to about 125 °C to about 250 °C, about 125 °C to about 225 °C, about 125 °C to about 200 °C, about 125 °C to about 175 °C, about 125 °C to about 150 °C, about 150 °C to about 250 °C, about 175 °C to about 250 °C, about 200 °C to about 250 °C, about 225 °C to about 250 °C, or about 150 °C to about 220 °C. The cooled liquid mixture (cooled mixture of nylon 66 and water) can include nylon 66 oligomer with a number average molecular weight of about 500 g / mol to about 3000 g / mol, about 1000 g / mol to about 3000 g / mol, about 1500 g / mol to about 3000 g / mol, about 2000 g / mol to about 3000 g / mol, about 2500 g / mol to aboutATTORNEY DOCKET NO. 222204-28203000 g / mol, about 500 g / mol to about 2500 g / mol, about 500 g / mol to about 2000 g / mol, about 500 g / mol to about 1500 g / mol, or about 500 g / mol to about 1000.

[0092] Following reducing the temperature or during the process of reducing the temperature, a reactant comprising a base or an acid can be added to the liquid mixture (the mixture of water and nylon 66) at an amount of about 8 moles of reactant to about 20 moles of reactant, about 9 moles of reactant to about 20 moles of reactant, about 11 moles of reactant to about 20 moles of reactant, about 14 moles of reactant to about 20 moles of reactant, about 17 moles of reactant to about 20 moles of reactant, about 8 moles of reactant to about 17 moles of reactant, about 8 moles of reactant to about 14 moles of reactant, about 8 moles of reactant to about 11 moles of reactant, about 8 moles of reactant to about 15 moles of reactant, 8.8 moles of reactant to about 17 moles of reactant, 8.8 moles of reactant to about 14 moles of reactant, 8.8 moles of reactant to about 11 moles of reactant, or 8.8 moles of reactant to about 15 moles of reactant per kg of nylon 66. In one aspect, the reactant and liquid mixture can be combined, mixed, or otherwise allowed to interact for about 0.1 hours to about 10 hours, about 0.1 hours to about 8 hours, about 0.1 hours to about 6 hours, about 0.1 hours to about 4 hours, about 0.1 hours to about 2 hours, about 1 hours to about 10 hours, about 2 hours to about 10 hours, about 4 hours to about 10 hours, about 6 hours to about 10 hours, about 8 hours to about 10 hours, or about 0.1 hours to about 5 hours. In another aspect, the reactant and liquid mixture can be combined, mixed, or otherwise allowed to interact at a temperature of about 100 °C to about 250 °C, about 100 °C to about 225 °C, about 100 °C to about 200 °C, about 100 °C to about 175 °C, about 100 °C to about 150 °C, about 125 °C to about 250 °C, about 150 °C to about 250 °C, about 175 °C to about 250 °C, about 200 °C to about 250 °C, or about 120 °C to about 220 °C. An acid selected can be a strong acid such as hydrochloric acid, sulfuric acid, nitric acid, the like, or a combination thereof. A base can be a strong base such as potassium hydroxide, ammonium hydroxide, the like or a combination thereof.

[0093] Following reacting the reactant and liquid mixture, the resulting product can be cooled to a temperature of about 50 °C to about 175 °C, about 50 °C to about 150 °C, about 50 °C to about 125 °C, about 50 °C to about 100 °C, about 50 °C to about 75 °C, about 75 °C to about 175 °C, about 100 °C to about 175 °C, about 125 °C to about 175 °C, about 150 °C to about 175 °C, or about 60 °C to about 150 °C. The product yield for the disclosed method (e.g., yield of hexamethylene diamine, adipic acid, a salt thereof, a derivative thereof, or any combination thereof) can range from about 85% to about 100%, about 85% to about 99%, about 85% to about 95%, about 85% to about 90%, about 90% to about 100%, or about 95% to about 100%.

[0094] When the reactant comprises an acid, the product can comprise adipic acid and hexamethylene diamine, a salt thereof, or a derivative thereof. The method can further comprise separating adipic acid (e.g., a non-volatile compound) from hexamethylene diamine,ATTORNEY DOCKET NO. 222204-2820a salt thereof, or a derivative thereof (e.g., a volatile compound). As used herein, a volatile compound refers to a compound that has a relatively high vapor pressure at room temperature. A non-volatile compound refers to a compound that has a relatively low or negligible vapor pressure at room temperature. For example, adipic acid can be crystallized from the product solution and separated as a solid (e.g., crystallized at a temperature of about 5 °C to about 40 °C). Adipic acid can then be further purified (e.g., by one or more additional recrystallization steps). The remaining product solution comprising, for example, a salt of hexamethylene diamine can be neutralized with a base (e.g., a strong base) to convert the salt of hexamethylene diamine to hexamethylene diamine. Hexamethylene diamine can then be evaporated from the solution and, optionally, further purified (e.g., via distillation).

[0095] When the reactant comprises a base, the product can comprise hexamethylene diamine and adipic acid, a salt thereof, or a derivative thereof. The method can further comprise separating adipic acid, a salt thereof, or a derivative thereof (e.g., a non-volatile compound) from hexamethylene diamine (e.g., a volatile compound). For example, hexamethylene diamine can be separated from the product via evaporation and can, optionally, be further purified (e.g., via distillation). The adipic acid, a salt thereof, or a derivative thereof can be dissolved in water and crystallized by adding an acid e.g., crystallized at a temperature of about 5 °C to about 40 °C). This step can convert an adipate salt into adipic acid and form a solid adipic acid, which can then be separated from the remaining solution (e.g., via filtration). Adipic acid can then be further purified (e.g., by one or more additional recrystallization steps).

[0096] As described herein, the initialization of the reaction by dissolving nylon 66 into the liquid phase can eliminate the solid-phase mass transfer resistance of the reaction. Using neutral water can reduce degradation reactions catalyzed by strong acids or bases. The reduction of temperature in the neutral hydrolysis reaction can further reduce degradation reaction rates. This can improve the yield of monomers, reduce yield of degradation byproducts, reduce the consumption of acid and base, reduce the production of salt byproduct, and allows the construction of the reactor with cheaper metallurgy (due to, for example, the use of lower temperatures and lower concentrations of acidic or basic solutions).

[0097] FIGS. 1 , 2, 3, 4A, and 4B provide illustrative examples of the disclosed methods, using nylon 66 as an example. The use of the following illustrative examples does not exclude other steps or aspects that are consistent with the principles disclosed by the following illustrative examples.

[0098] FIG. 1 depicts one aspect of the disclosed method where a proton accepting base is used in the depolymerization reaction and follows known downstream processes to produce hexamethylene diamine and adipic acid products. Following FIG. 1 , the process begins with a mixture of nylon 66, 101, that may be size reduced to flakes and washed in upstreamATTORNEY DOCKET NO.222204-2820processes or bulk pieces entering a mixing unit, 050. The nylon 66, 101, may be postconsumer or post-industrial in source and consist of automotive parts, carpeting, textiles, or electronics components. The nylon 66, 101, may contain glass fibers or cellulose fibers. The mixing unit, 050, can contact the nylon 66, 101 , with water, 353, at a rate of 0.5 kg - 8 kg per kg nylon 66 (a rate of 0.5 kg to 8 kg per kg nylon 66). The mixing unit pressurizes the nylon 66, 101, between 50,000 kPa and 75,000 kPa and operates at a temperature between 260 °C - 290 °C where nylon 66 dissolves in the water. The mixing unit, 050, can be designed as an extruder, as a series of two tanks, or other methods of creating a homogenous mixture of water and nylon 66 melt. Heat is supplied to the mixing unit either by heating the water, 353, between 260 °C - 330 °C, jacketed heating, an external heat exchanger, electrical energy from an extruder, or any combination thereof.

[0099] The homogenous mixture of water and nylon 66, 051 , enters a neutral hydrolysis section of a plug flow type reactor, 100. The reactor can be designed as a series or pipes, a cylindrical vessel, or other type of plug flow type design known in the art. The use of static mixers or mechanical agitation inside the reactor can be used to enhance heat transfer. The reaction solution is progressively cooled in this section of the reactor, 100, from a feed temperature 260 °C - 290 °C to an outlet temperature of 140 °C - 220°C. A coolant can be used to achieve a reduced temperature profile in the reactor wherein the coolant can be a vaporizing liquid and the generated vapor can be used to supply heat elsewhere in the process. The temperature in the neutral hydrolysis section, 100, can be reduced by flashing of liquid in the reactor either from hydraulic loss in the reactor or by pressure drop through valves or orifices. The reaction temperature profile in the neutral hydrolysis section, 100, can be designed to maintain a homogeneous solution and avoid precipitation of nylon 66 oligomer. The neutral hydrolysis section, 100, can designed to provide a total residence time between 0.25 hours - 10 hours. The partially depolymerized nylon 66 mixture, 102, exits the neutral hydrolysis section, 100, between 140 °C -220 °C and the number average molecular weight of the nylon 66 oligomer between 500 - 3,000 and enters the alkaline hydrolysis section of the reactor, 150.

[0100] The neutral hydrolysis section, 100, and the alkaline hydrolysis section, 150, can be designed as separate vessels or part of a single plug flow type reactor with the alkaline hydrolysis section, 150, defined by the point where alkaline hydroxide, 151, is added to the reaction. The base can be an alkaline hydroxide such as sodium hydroxide or potassium hydroxide and, without wishing to be bound by theory, can react with carboxylate acid end groups on the nylon 66 oligomers forming carboxylate salts. The alkaline hydroxide, 151, can be a liquid containing between 20 wt% - 80 wt% alkaline hydroxide and can be fed to the reactor at a temperature between 25 °C - 220°C. The alkaline hydroxide, 151, can be fed at a rate of 8.8 moles - 20 moles alkaline hydroxide per kg nylon 66. The alkaline hydroxide canATTORNEY DOCKET NO. 222204-2820be introduced at a single point in the reactor or distributed at multiple points in the alkaline hydrolysis section, 151 , of the reactor to limit the concentration of alkaline hydroxide in the reaction mixture below 1 wt% -20 wt%. The alkaline hydrolysis section, 100, can be designed to provide a total residence time between 0.5 hours - 10 hours. The yield of sodium adipate salt and hexamethylene diamine at the end of the reaction can both be between 85% - 99%. The depolymerization product, 152, can then be subjected to further processing to produce a purified hexamethylene diamine and adipic acid product with general process for a polymer reacted with alkaline hydroxide.

[0101] Referring to FIG. 1 , the reaction product, 152, can be cooled between 60 °C - 150 °C and solids or precipitating materials, 202, can be filtered, 200. The filtered product, 201 , goes to an evaporation unit, 300, where volatile products, 302, such as water and hexamethylene diamine are separated from the adipate salt product, other salts, alkaline hydroxide, and nonvolatile impurities, 301, and can be designed as a precipitation vessel, evaporator, or some combination of devices to perform this separation.

[0102] The volatile vapor product, 302, goes to a distillation system, 350, comprising one or more distillation columns, producing a purified hexamethylene diamine product, 351; a water product, 352, that can be recycled to the mixing section, 050; and separates impurities, 355. The impurities outlet, 355, is shown as a single outlet for simplicity but can consist of one or more outlets for high volatility impurities such as CO2, NH3, and cyclopentanone, intermediate volatility impurities such as amines and intermediate volatility degradation byproducts, and low volatility impurities such as oligomers, and heavy degradation byproducts. Most of the water, 353, from the distillation system, 350, is recycled to the mixing section, 050, accumulating water from the addition of alkaline hydroxide is purged as wastewater, 354. The salt product, 301, from the evaporator, 300, can go to an organic wash section, 400, where the salt is contacted with an organic solvent, 402, such as toluene to remove low volatility organic impurities. The solvent with extracted organic impurities, 403, can be separated from the salt product and the solvent recovered and separated from the impurities in downstream separation.

[0103] The salt product, 401 , from the organic wash unit, 400, goes to a dissolution unit, 500, to dissolve the salt, 401 , in water, 501. The dissolved salt product can pass through an adsorption unit, 510, to remove remaining impurities, 512. The dissolved product, 511 , from the adsorption unit, 510, can go to a reactive crystallization unit, 520, where an acid, 521 , such as hydrochloric acid, sulfuric acid, or nitric acid is added to the adipate salt solution, reacting to form adipic acid and an inorganic salt such as sodium chloride or sodium sulfate. The acid, 521, can be added at a rate to maintain the pH of the reactive crystallization between 0 - 3. The reactive crystallization unit, 520, temperature can be maintained between 5 °C - 40 °C and adipic acid precipitates as it is formed. Some water can leave the reactive crystallizer,ATTORNEY DOCKET NO. 222204-2820523, if flash cooling is used. Liquid containing solid adipic acid, 522, can be withdrawn from the reactive crystallizer, 520, and filtered, 530, to separate solid adipic acid, 531 , and a solution primarily of water and salt, 532.

[0104] The solid adipic acid, 531, can then be dissolved, 540, in water, 541, at elevated temperature between 70 °C - 120 °C for recrystallization. The dissolved adipic acid solution, 542, can be fed to a crystallizer, 550, where some water can exit as a vapor, 552, when flash crystallization is used to crystallize at a temperature between 5 - 40°C. A solution containing solid adipic acid, 551 , can be withdrawn from the crystallizer, 550, and can be filtered to separate solid adipic acid, 561 , from the solvent, 562, containing water, adipic acid and a small concentration of impurities, which can be recycled to the upstream reactive crystallization unit, 520. The solid adipic acid product, 561 , can be dried, 570, using vapor such as air, 571 , producing a dried adipic acid product, 572, with the moisture containing vapor, 573, vented.

[0105] The solvent, 532, from the reactive crystallization filter, 530, contains water, salt, and residual adipic acid and impurities. The salt can be recovered by evaporative crystallization, 600, where water is progressively vaporized, 602. The salt crystallizes and a solution of solid salt and solvent, 601 , can be withdrawn and filtered, 610. The solid salt, 611, can be dried, 620, using vapor, 621 , such as air, producing a dried salt product, 622, and venting moisture containing vapor, 623. The filtered solvent, 612, from the salt crystallization filter, 610, contains a saturated solution of salt, adipic acid, and some impurities and can be recycled to the reactive crystallizer, 520, with some purged and processed as waste.

[0106] FIG. 2 depicts one aspect of the disclosed method where a proton donating acid is used in the depolymerization reaction and follows known downstream processes to produce hexamethylenediamine and adipic acid products. Following FIG. 2, the process begins with a mixture of nylon 66, 1101 , that can be size reduced to flakes and washed in upstream processes or bulk pieces entering a mixing unit, 1050. The nylon 66, 1101, can be postconsumer or post-industrial in source and consist of automotive parts, carpeting, textiles, or electronics components. The nylon 66, 1101 , can contain glass fibers or cellulose fibers and does not change the innovation of this disclosure. The mixing unit, 1050, can contact the nylon 66, 1101, with water, 1353, at a rate of 0.5 kg - 8 kg per kg nylon 66. The mixing unit pressurizes the nylon 66, 1101, between 50,000 and 75,000 kPa and operates at a temperature between 260 - 290°C where nylon 66 dissolves in the water. The mixing unit, 1050, can be designed as an extruder, as a series of two tanks, or other methods of creating a homogenous mixture of water and nylon 66 melt. Heat can be supplied to the mixing unit either by heating the water, 1353, between 260 °C - 330 °C, jacketed heating, an external heat exchanger, electrical energy from an extruder, or any combination thereof.

[0107] The homogenous mixture of water and nylon 66, 1051 , enters a neutral hydrolysis section of a plug flow type reactor, 1100. The reactor can be designed as a series or pipes, aATTORNEY DOCKET NO. 222204-2820cylindrical vessel, or other type of plug flow type design known in the art. The use of static mixers or mechanical agitation inside the reactor may be used to enhance heat transfer. The reaction solution is progressively cooled in this section of the reactor, 1100, from a feed temperature 260 °C - 290 °C to an outlet temperature of 140 °C - 220°C. A coolant can be used to achieve reducing temperature profile in the reactor with the coolant being a vaporizing liquid and the generated vapor being used to supply heat elsewhere in the process. The temperature in the neutral hydrolysis section, 1100, can be reduced by flashing of liquid in the reactor either from hydraulic loss in the reactor or by pressure drop through valves or orifices. The reaction temperature profile in the neutral hydrolysis section, 1100, can be designed to maintain a homogeneous solution and avoid precipitation of nylon 66 oligomer. The neutral hydrolysis section, 1100, can be designed to provide a total residence time between 0.25 hours - 10 hours. The partially depolymerized nylon 66 mixture, 1102, exits the neutral hydrolysis section, 1100, between 140 °C - 220 °C and the number average molecular weight of the nylon 66 oligomer between 500 - 3,000 and enters the acid hydrolysis section of the reactor, 1150.

[0108] The neutral hydrolysis section, 1100, and the acid hydrolysis section, 1150, can be designed as separate vessels or part of a single plug flow type reactor with the acid hydrolysis section, 1150, defined by the point where acid, 1151 , is added to the reaction. The acid is can be a strong acid such as hydrochloric acid, sulfuric acid, or nitric acid, and, without wishing to be bound by theory, can react with amine end groups on the nylon 66 oligomers forming ammonium salts. The acid, 1151 , can be a liquid containing between 20 wt% - 100 wt% acid and is fed to the reactor at a temperature between 25 - 220 °C. The acid, 1151 , is fed at a rate of 8.8 moles - 20 moles of donated acidic protons per kg nylon 66. The acid, 1151, can be introduced at a single point in the reactor or distributed at multiple points in the acid hydrolysis section, 1151 , of the reactor to limit the concentration of acid in the reaction mixture below 1 wt% - 20 wt%. The acid hydrolysis section, 1100, can be designed to provide a total residence time between 0.5 hours - 10 hours. The yield of hexamethylene diammonium salt and adipic acid at the end of the reaction can both be between 85% - 99%. The depolymerization product, 1152, is then subjected to further processing to produce a purified hexamethylene diamine and adipic acid product.

[0109] In FIG. 2 the reaction product, 1152, can be cooled between 60 °C - 150 °C and solids or precipitating materials, 1202, can be filtered, 1200. The filtered product, 1201 , goes to a crystallization unit, 1520, temperature can be maintained between 5 °C - 40 °C and adipic acid precipitates. Some water, 1523, leaves the crystallizer, 520, if flash cooling is used. Liquid containing solid adipic acid, 1522, can be withdrawn from the crystallizer, 1520, and filtered, 1530, to separate solid adipic acid, 1531, and a solution primarily of water and hexamethylene diammonium salt, 1532.ATTORNEY DOCKET NO. 222204-2820

[0110] The solid adipic acid, 1531 , can then be dissolved, 1540, in water, 1541 , at elevated temperature between 70 °C - 120°C for recrystallization. The dissolved adipic acid solution, 1542, can be fed to a crystallizer, 1550, where some water exits as a vapor, 1552, when flash crystallization is used with crystallization at a temperature between 5 °C - 40°C. A solution containing solid adipic acid, 1551 , can be withdrawn from the crystallizer, 1550, and can be filtered to separate solid adipic acid, 1561 , from the solvent, 1562, containing water, adipic acid and a small concentration of impurities, which can be recycled to the upstream crystallization unit, 1520. The solid adipic acid product, 1561 , can be dried, 1570, using vapor such as air, 1571 , producing a dried adipic acid product, 1572, with the moisture containing vapor, 1573, vented.

[0111] The solvent, 1532, from the crystallization filter, 1530, contains water, acid, hexamethylene diammonium salt, and residual adipic acid and impurities and goes to a neutralization and crystallization unit, 1600. The neutralization and crystallization unit adds a base, 1601, such as sodium hydroxide or potassium hydroxide, to convert hexamethylene diammonium salt to hexamethylene diamine and a salt such as sodium chloride or sodium sulfate and evaporates, 1603, the water and hexamethylenediamine from the solvent to crystallize the salt. The neutralization and crystallization unit, 1600, can be configured as separated vessels for neutralization and crystallization, a single vessel, or use a different method of separating the salt byproduct from hexamethylenediamine. Liquid containing solid salt, 1602, can be withdrawn from the neutralization and crystallization unit, 1601 , and can be filtered, 1610. The solid salt, 1611, can be dried, 1620, using vapor, 1621 , such as air, producing a dried salt product, 1622, and venting moisture containing vapor, 1623. The filtered solvent, 1612, from the salt crystallization filter, 1610, contains a saturated solution of salt, adipic acid, and some impurities in predominantly hexamethylenediamine, which can be recycled to the neutralization and crystallization unit, 1600, or the crystallizer, 1520, with some purged and processed as waste.

[0112] The vapor, 1603, from the neutralization and crystallization unit, 1600, can go to a distillation system, 1350, consisting of one or more distillation columns, producing a purified hexamethylene diamine product, 1351 , a water product, 1352, that can be recycled to the mixing section, 1050, and separates impurities, 1355. The impurities outlet, 1355, is shown as a single outlet for simplicity but can consist of one or more outlets for high volatility impurities such as CO2, NH3, and cyclopentanone, intermediate volatility impurities such as amines and intermediate volatility degradation byproducts, and low volatility impurities such as oligomers, and heavy degradation byproducts. Most of the water, 1353, from the distillation system, 1350, is recycled to the mixing section, 1050, accumulating water from the addition of alkaline hydroxide is purged as wastewater, 1354.

[0113] FIG. 3 depicts two different aspects of the disclosed methods for mixing water andATTORNEY DOCKET NO. 222204-2820nylon 66. In one aspect, an extruder, 2050, can be used to produce a homogenous mixture of water and nylon 66. Here a feed of solid nylon 66, 2101, can be fed into an extruder, 2050, by normal means with the extruder supplying energy to melt the polymer and heat it between 270 °C - 290 °C and pressurize the melt between 50,000 kPa - 75,000 kPa. A portion of the water feed, 2353a, can be fed directly into the extruder, 2050, to reduce melt viscosity and provide good contact and mixing of the water and nylon 66. A portion of the water feed, 2353b, can be introduced downstream of the extruder, 2050, to reduce its volumetric throughput. The mixture of water and nylon 66 melt, 2051, can then go to the neutral hydrolysis reaction section, 2100. It can be understood that the neutral hydrolysis reaction occurs inside of extruder when water is introduced into the extruder, 2050, and part of the neutral hydrolysis reaction, 2100, can be intentionally carried out here.

[0114] In another aspect, two tanks can be used to produce a homogenous mixture of water and nylon 66. In this method, solid nylon 66, 3101, can be mixed with a portion of water, 2343a, in an atmospheric tank, 3050a, with water, 2343a, fed at a temperature between 30 °C - 100 °C. Water, 2343a, can be added at a rate to create a slurry between 30 wt% - 80 wt% water that can be pumped, 3060, to a pressure between 50,000 kPa - 75,000 kPa, feeding a melt tank, 3050b. An additional portion of water, 2343b, can be added to the melt tank, 3050b, to control the water rate for the neutral hydrolysis reaction, 3100. The additional water, 2343b, can be added at a temperature between 270 °C - 330°C. Heat is supplied to the melt tank, 3050b, to maintain a temperature of the mixture between 260 °C -290°C using jacketing, heat from the water addition, 2343b, an external heat exchanger and circulation loop, or some combination thereof. The hold up time of the melt tank, 3050b, can be designed to allow complete dissolution of nylon 66 in the water and is between 0.1 hours - 2 hours. The homogenous mixture of nylon 66 and water, 3051 , from the melt tank, 3050b, can be fed to the neutral hydrolysis reactor, 3100.

[0115] FIG. 4A and FIG. 4B depict two different aspects of the disclosed methods for controlling temperature in the nylon 66 depolymerization reaction. The reactors, 4100 and 4150 in FIG. 4A and 5100 and 5150 in FIG. 4B, can be operated in the same way as the reactors described in FIG. 1, 100 and 150, and FIG. 2, 1100, and 1150. In the first aspect, in FIG. 4A, a homogenous mixture of water and nylon 66, 4051 , from an upstream mixing unit, 4050, can enter a plug flow type neutral hydrolysis section, 4100, with cooling of the reaction and control of the reaction temperature profile by a coolant, 4103 and 4105. The coolant can be a liquid and can exit, 4104 and 4106, the reactor heat transfer element as a vapor. The coolant, 4103 and 4105, can be water at a pressure between 300 kPa - 3,500 kPa. The temperature of the neutral hydrolysis section of the reaction, 4100, reduces from 260 °C - 290 °C to 140 °C - 220 °C. Two or more coolant segments with vaporizing liquid can be used at different pressures, providing different coolant temperature. FIG. 4A shows two coolantATTORNEY DOCKET NO. 222204-2820sections for the neutral hydrolysis reactor, 4100, where the early stage coolant, 4103, is at higher pressure than the later stage coolant, 4105. This can allow for easier control of the reaction temperature profile and can recover higher temperature heat when the vapor from the coolant is used elsewhere in the process.

[0116] The outlet of the neutral hydrolysis section, 4100, can be mixed with either an acid or alkaline hydroxide, 4151, and can enter the acid or alkaline section of the reactor, 4150. This reaction is exothermic and coolant, 4153, can be required to maintain either an isothermal reaction or further cool the reaction to between 80 °C - 220°C. A coolant can be used, 4153, such as water at a pressure between 100 kPa - 1 ,000 kPa and can generate a vapor, 4154, that can supplies heat elsewhere in the process. The reaction product, 4152, from the acid or alkaline reactor, 4150, can go to downstream processing units, 4200.

[0117] The acid or alkaline hydroxide, 4151, can be distributed to multiple points, 4153, in the reactor sections, 4100 and 4150. This can be done because as the reaction progresses more acid or basic end group on nylon 66 oligomers are produced. The added acid or base reacts with these end groups consuming the added acid or base. Careful addition of the acid or base at multiple locations can limit the required concentration of the acid or base to a maximum concentration between 1 wt% - 20 wt%. This reduces degradation reactions catalyzed by strong acids or bases and lower corrosivity of the reaction mixture, allowing for the use of less expensive metallurgy. When a small amount of acid or base is added in the neutral hydrolysis section, 4100, it can increase the depolymerization rate in this section.

[0118] In a second aspect, in FIG. 4B, a homogenous mixture of water and nylon 66, 5051 , from an upstream mixing unit, 5050, can enter a plug flow type neutral hydrolysis section, 5100, which is cooled by progressively reducing the pressure in the neutral hydrolysis section, 5100, between 350 kPa - 25,000 kPa, which reduces the reaction temperature from 260 °C -290 °C to 140 °C - 220 °C by vaporizing some water in the reactor. The neutral hydrolysis section, 5100, can contain sections of progressively increasing pipe diameter to account for the increased volumetric flow rate from vapor in the reactor. Pressure loss in the neutral hydrolysis section, 5100, can be from hydraulic loss in the reactor, or by controlled pressure drop at specific section(s) of the reactor, 5110, such as orifices or valves. A plug flow type reaction system where temperature and pressure are controlled by hydraulic losses, generating some water vapor, and having multiple diameters is described for the application of continuous nylon 66 polymerization by US Patent Application No. 2,689,839. Vapor generated from vaporizing water in the neutral hydrolysis section, 5100, can be separated from the liquid phase at one or more points, 5120, with the liquid, 5102, continuing in the neutral reaction section, 5100, or acid or alkaline reaction section, 5150. The heat to condense vapor, 5103, from the separator, 5120, can be used to supply heat elsewhere in the process.

[0119] The outlet of the neutral hydrolysis section, 5100, can be mixed with either an acid orATTORNEY DOCKET NO. 222204-2820alkaline hydroxide, 5151, and enters the acid or alkaline section of the reactor, 5150. This reaction is exothermic and the temperature can be maintained isothermally by controlling a temperature profile in the acid or alkaline section of the reactor, 5150, by controlling the pressure between 100 kPa - 25,000 kPa and allowing some water in the reactor to vaporize. Pressure loss in the acid or alkaline hydrolysis section, 5150, can be from hydraulic loss in the reactor, or by controlled pressure drop at specific section(s) of the reactor such as orifices or valves. The acid or alkaline hydrolysis section, 5150, can contain sections of progressively increasing pipe diameters to account for the increased volumetric flow rate from vapor in the reactor. Vapor generated from vaporizing water in the acid or alkaline hydrolysis section, 5150, can be separated from the liquid phase at one or more points, 5160, with the liquid, 5152, continuing in the acid or alkaline reaction section, 5150, or continue to downstream processing sections, 5200. The heat to condense vapor, 5153, from the separator, 5160, can be used to supply heat elsewhere in the process.

[0120] The acid or alkaline hydroxide, 5151, can be distributed to multiple points, 5153, in the reactor sections, 5100 and 5150. This can be done because as the reaction progresses more acid or basic end group on nylon 66 oligomers are produced. The added acid or base reacts with these end groups consuming the added acid or base. Careful addition of the acid or base at multiple locations can limit the required concentration of the acid or base to a maximum concentration between 1 wt% - 20 wt%. This reduces degradation reactions catalyzed by strong acids or bases and lower corrosivity of the reaction mixture allowing the use of less expensive metallurgy. When a small amount of acid or base is added in the neutral hydrolysis section, 5100, it can increases the depolymerization rate in this section.E. ASPECTS

[0121] The following listing of exemplary aspects supports and is supported by the disclosure provided herein.

[0122] Aspect 1. A method, comprising: contacting a solid feedstock comprising nylon 66 with water, thereby forming a liquid mixture; reducing a temperature of the liquid mixture, thereby forming a cooled liquid mixture; and contacting the cooled liquid mixture with a reactant comprising an acid or a base, thereby forming a product comprising hexamethylene diamine, adipic acid, a salt thereof, a derivative thereof, or any combination thereof.

[0123] Aspect 2. The method of aspect 1 , wherein contacting the solid feedstock with water is done at a rate of about 0.1 kg of water per kg of the solid feedstock to about 10 kg water per kg of the solid feedstock.

[0124] Aspect 3. The method of aspect 1 or aspect 2, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react at a pressure of about 25 MPa to about 100 MPa.ATTORNEY DOCKET NO.222204-2820

[0125] Aspect 4. The method of any one of aspects 1-3, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react at a reaction temperature of about 250 °C to about 300 °C.

[0126] Aspect 5. The method of any one of aspects 1-4, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react for about 0.1 hours to about 15 hours.

[0127] Aspect 6. The method of any one of aspects 1-5, wherein reducing the temperature of the liquid mixture comprises reducing the temperature of the liquid mixture by about 15% to about 60%.

[0128] Aspect 7. The method of any one of aspects 1-5, wherein reducing the temperature of the liquid mixture comprises reducing the temperature of the liquid mixture to a reduced temperature of about 125 °C to about 250 °C.

[0129] Aspect 8. The method of any one of aspects 1-7, wherein the cooled liquid mixture comprises a nylon 66 oligomer with a number average molecular weight of about 500 g / mol to about 3,000 g / mol.

[0130] Aspect 9. The method of any one of aspects 1-8, wherein the cooled liquid mixture is contacted with the reactant at a rate of about 8 moles to about 20 moles of reactant per kg of the nylon 66.

[0131] Aspect 10. The method of any one of aspects 1-9, wherein contacting the cooled liquid mixture with the reactant further comprises allowing the cooled liquid mixture and the reactant to react at a second reaction temperature of about 100 °C to about 250 °C.

[0132] Aspect 11. The method of any one of aspects 1-10, wherein contacting the cooled liquid mixture with the reactant further comprises allowing the cooled liquid mixture and the reactant to react for about 0.1 hours to about 10 hours.

[0133] Aspect 12. The method of any one of aspects 1-11, wherein the reactant comprises the acid selected from hydrochloric acid, sulfuric acid, nitric acid, and a combination thereof.

[0134] Aspect 13. The method of any one of aspects 1-12, wherein the reactant comprises the base selected from potassium hydroxide, ammonium hydroxide, and a combination thereof.

[0135] Aspect 14. The method of any one of aspects 1-13, wherein the method results in a product yield of about 85% to about 100%.

[0136] Aspect 15. The method of any one of aspects 1-14, wherein the method further comprises reducing a temperature of the product.

[0137] Aspect 16. The method of aspect 15, wherein the method further comprises reducing the temperature of the product to a second reduced temperature of about 50 °C to about 175 °C.

[0138] Aspect 17. The method of any one of aspects 1-16, wherein the solid feedstockATTORNEY DOCKET NO. 222204-2820comprises a nylon 66 melt.

[0139] Aspect 18. The method of any one of aspects 1-18, wherein the product comprises a solid precipitate and an aqueous solution, further comprising: separating the solid precipitate from the aqueous solution, wherein the aqueous solution comprises volatile compounds and non-volatile compounds; and separating the volatile compounds from the non-volatile compounds, thereby forming a volatile product and a non-volatile product; wherein the volatile product comprises hexamethylene diamine, a derivative thereof, a salt thereof, or any combination thereof; and wherein the non-volatile product comprises adipic acid, a derivative thereof, a salt thereof, or any combination thereof.

[0140] Aspect 19. The method of aspect 18, wherein the non-volatile product comprises a derivative of adipic acid or a salt of adipic acid, further comprising: contacting the non-volatile product with water, thereby forming a first aqueous solution; and contacting the first aqueous solution with an acid, thereby forming an acid-treated mixture comprising a second aqueous solution and a solid residue, wherein the solid residue comprises adipic acid.

[0141] Aspect 20. The method of aspect 19, wherein the non-volatile product is washed with an organic solvent prior to contacting the non-volatile product with water.

[0142] Aspect 21. The method of any one of aspects 18-20, wherein the volatile product comprises hexamethylene diamine, further comprising: distilling the volatile product, thereby forming a distillate comprising hexamethylene diamine.

[0143] Aspect 22. The method of aspect 18, wherein the non-volatile product comprises adipic acid, further comprising: contacting the non-volatile product with water, thereby forming a first aqueous solution; and crystalizing the first aqueous solution, thereby forming a crystalized mixture comprising a second aqueous solution and a second solid residue, wherein the second solid residue comprises adipic acid.

[0144] Aspect 23. The method of aspect 18 or aspect 22, wherein the volatile product comprises a derivative of hexamethylene diamine or a salt of hexamethylene diamine, further comprising: contacting the volatile product with a base, thereby forming a base-treated mixture; evaporating the base-treated mixture, thereby forming a vapor and an evaporation residue; and distilling the vapor, thereby forming a distillate comprising hexamethylene diamine.

[0145] Aspect 24. A method, comprising: contacting a solid feedstock comprising nylon with water, thereby forming a liquid mixture; reducing a temperature of the liquid mixture, thereby forming a cooled liquid mixture; and contacting the cooled liquid mixture with a reactant comprising an acid or a base, thereby forming a product comprising at least a monomer or a salt thereof, wherein the at least one monomer comprises a carboxyl group, an amine, or a combination thereof.

[0146] Aspect 25. The method of aspect 24, wherein the at least one monomer comprises aATTORNEY DOCKET NO.222204-2820carboxylic acid, a primary amine, ora combination thereof.

[0147] Aspect 26. The method of aspect 24, wherein the at least one monomer is selected from a carboxylic acid compound, a dicarboxylic acid compound, an amine compound, a diamine compound, a salt thereof, and any combination thereof.

[0148] Aspect 27. The method of aspect 24, wherein the at least one monomer is selected from adipic acid, dodecanedioic acid, 11-aminoundecanoic acid, w-aminolauric acid, 1,4-diaminobutane, hexamethylene diamine, a salt thereof, a derivative thereof, and any combination thereof.

[0149] Aspect 28. The method of any one of aspects 24-28, wherein contacting the solid feedstock with water is done at a rate of about 0.1 kg of water per kg of the solid feedstock to about 10 kg water per kg of the solid feedstock.

[0150] Aspect 29. The method of any one of aspects 24-29, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react at a pressure of about 25 MPa to about 100 MPa.

[0151] Aspect 30. The method of any one of aspects 24-30, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react at a reaction temperature of about 250 °C to about 300 °C.

[0152] Aspect 31. The method of any one of aspects 24-31, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react for about 0.1 hours to about 15 hours.

[0153] Aspect 32. The method of any one of aspects 24-32, wherein reducing the temperature of the liquid mixture comprises reducing the temperature of the liquid mixture by about 15% to about 60%.

[0154] Aspect 33. The method of any one of aspects 24-32, wherein reducing the temperature of the liquid mixture comprises reducing the temperature of the liquid mixture to a reduced temperature of about 125 °C to about 250 °C.

[0155] Aspect 34. The method of any one of aspects 24-34, wherein contacting the cooled liquid mixture with the reactant further comprises allowing the cooled liquid mixture and the reactant to react at a second reaction temperature of about 100 °C to about 250 °C.

[0156] Aspect 35. The method of any one of aspects 24-35, wherein contacting the cooled liquid mixture with the reactant further comprises allowing the cooled liquid mixture and the reactant to react for about 0.1 hours to about 10 hours.

[0157] Aspect 36. The method of any one of aspects 24-36, wherein the reactant comprises the acid selected from hydrochloric acid, sulfuric acid, nitric acid, and a combination thereof.

[0158] Aspect 37. The method of any one of aspects 24-37, wherein the reactant comprises the base selected from potassium hydroxide, ammonium hydroxide, and a combination thereof.ATTORNEY DOCKET NO. 222204-2820

[0159] Aspect 38. The method of any one of aspects 24-38, wherein the method results in a product yield of about 85% to about 100%.

[0160] Aspect 39. The method of any one of aspects 24-39, wherein the method further comprises reducing a temperature of the product.

[0161] Aspect 40. The method of aspect 40, wherein the method further comprises reducing the temperature of the product to a second reduced temperature of about 50 °C to about 175 °C.

[0162] Aspect 41. The method of any one of aspects 24-41, wherein the solid feedstock comprises a nylon melt.

[0163] Aspect 42. The method of any one of aspects 24-42, wherein the product comprises a solid precipitate and an aqueous solution, further comprising: separating the solid precipitate from the aqueous solution, wherein the aqueous solution comprises volatile compounds and non-volatile compounds; and separating the volatile compounds from the non-volatile compounds, thereby forming a volatile product and a non-volatile product; wherein the volatile product comprises an amine compound, a diamine compound, a salt thereof, or any combination thereof; and wherein the non-volatile product comprises a carboxylic acid compound, a dicarboxylic acid compound, a salt thereof, or any combination thereof.

[0164] Aspect 43. The method of aspect 43, wherein the non-volatile product comprises the salt of the carboxylic acid compound or the salt of the dicarboxylic acid compound, further comprising: contacting the non-volatile product with water, thereby forming a first aqueous solution; and contacting the first aqueous solution with an acid, thereby forming an acid-treated mixture comprising a second aqueous solution and a solid residue, wherein the solid residue comprises the carboxylic acid compound or the dicarboxylic acid compound.

[0165] Aspect 44. The method of aspect 44, wherein the non-volatile product is washed with an organic solvent prior to contacting the non-volatile product with water.

[0166] Aspect 45. The method of any one of aspects 43-45, wherein the volatile product comprises the amine compound or the diamine compound, further comprising: distilling the volatile product, thereby forming a distillate comprising an amine compound or a diamine compound.

[0167] Aspect 46. The method of aspect 43, wherein the non-volatile product comprises the carboxylic acid compound or the dicarboxylic acid compound, further comprising: contacting the non-volatile product with water, thereby forming a first aqueous solution; and crystalizing the first aqueous solution, thereby forming a crystalized mixture comprising a second aqueous solution and a second solid residue, wherein the second solid residue comprises the carboxylic acid compound or the dicarboxylic acid compound.

[0168] Aspect 47. The method of aspect 43 or aspect 47, wherein the volatile product comprises the salt of the amine compound or the salt of the diamine compound, furtherATTORNEY DOCKET NO. 222204-2820comprising: contacting the volatile product with a base, thereby forming a base-treated mixture; evaporating the base-treated mixture, thereby forming a vapor and an evaporation residue; and distilling the vapor, thereby forming a distillate comprising the amine compound or the diamine compound.

[0169] Aspect 48. The method of any one of aspects 24-47, wherein the nylon is an aliphatic nylon.

[0170] From the foregoing, it will be seen that aspects herein are well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure.

[0171] While specific elements and steps are discussed in connection to one another, it is understood that any element and / or steps provided herein is contemplated as being combinable with any other elements and / or steps regardless of explicit provision of the same while still being within the scope provided herein.

[0172] It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

[0173] Since many possible aspects may be made without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings and detailed description is to be interpreted as illustrative and not in a limiting sense.

[0174] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.

[0175] Now having described the aspects of the present disclosure, in general, the following Examples describe some additional aspects of the present disclosure. While aspects of the present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit aspects of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the present disclosure.F. EXAMPLES

[0176] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and / or methods claimed herein are made and evaluated, and are intended to be purely exemplary of the disclosure and are not intended to limit the scope of what the inventors regard as their disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should beATTORNEY DOCKET NO. 222204-2820accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric.1. NYLON 66 DEPOLYMERIZATION

[0177] There is incentive to recycle step-growth polymers such as nylon 66 because the reversible chemistry allows convenient conversion to monomers, which enable purification pathways that expand the scope of recyclable waste. Despite the higher value of nylon 66 polymer and chemical similarity to nylon 6, it is more challenging to recycle. Part of the challenge recycling nylon 66 can be attributed to lower thermal stability of nylon 66 compared to nylon 611 12, coupled with the higher melt temperature, 270°C, where thermal degradation during polymerization is known to occur13"15. The other challenge is that the monomers of nylon 66, hexamethylene diamine (HMDA) and adipic acid (AA), form a salt complex (FIG. 5) under neutral conditions, making it difficult to isolate them for purification.

[0178] Nylon Polymerization 66 Chemistry. The polymerization chemistry of nylon 66 is important to understanding chemical depolymerization pathways. Nylon 66 is a polyamide and grows by condensation reaction where carboxylic acid and amine end groups react to form an amide linkage and water. Nylon 66 is an AABB-type polymer where the reactive groups (A, B) are present on separate monomers. The two monomers used for the polymerization of nylon 66 are the dicarboxylic acid, adipic acid (AA), and the diamine, hexamethylene diamine (HMDA). FIG. 5 summarizes nylon 66 polymerization chemistry.

[0179] AABB reactions require equimolar feed of the monomers to achieve high conversion and molecular weight. The polymerization of nylon 66 begins with the preparation of a salt solution of HMDA and AA concentrated to ~50 wt% in water17. FIG. 5 shows the salt formed between HMDA and AA. Nylon 66 can be formed directly from the monomer salt without water, but is not done industrially because of processing difficulties and inability to control the reaction temperature17.

[0180] The monomer salt is preheated to a temperature of ~200°C and the pressure is increased to keep water in the liquid phase16 18. The polymerization reaction is rarely catalyzed16 17. The condensation reaction is reversible and limited by equilibrium. Water is removed as it is formed during the reaction to increase the molecular weight of the polymer. The reaction temperature is slowly ramped above the nylon 66 melt temperature, while water concentration is controlled by the reaction pressure to keep the polymer in solution.

[0181] Once the final reaction temperature setpoint is reached, it is slowly depressurized. In some cases, vacuum pressure or non-volatile stripping gas is used to further improve polymer molecular weight1618. The reaction is held at the final temperature and pressure to allow the polymerization reaction to approach equilibrium, before the polymer is extruded or spun. FIG.6 and 7 show a general phase boundary and operation profile for batch nylon 66 polymerization. The reaction must avoid precipitating salt solution or freezing of the polymerATTORNEY DOCKET NO. 222204-2820and minimizes time at elevated temperature and reduced pressure where degradation occurs17.

[0182] There is almost no information on nylon 66 chemical recycling as indicated by the recent reviews by Clark and Sharver2and Liu and Ma22. There have been some reports, mostly industrial patents, on hydrolysis pathways using water as a reactant to drive the reverse condensation reaction and ultimately produce HMDA and AA23 33. Hydrolysis pathways rely on the addition of an acid or base to isolate one monomer and subsequent neutralization to isolate the other monomer. These pathways utilize either a proton- donating acid or a protonaccepting base. The first monomer is generally isolated, and the solution is neutralized to yield the second monomer and salt byproduct.

[0183] Other chemical recycling pathways have been investigated producing products other than AA and HMDA. The ammonolysis process developed by DuPont using ammonia as a reactant is the best documented example34 35. FIG. 8 shows the two-step reaction where ammonia reacts to form amide and amine end groups. The amide end groups then dehydrate, forming nitrile end groups. Ammonolysis is operated as a stripping reaction where vapor ammonia is introduced to the polymer melt. The volatile monomers, HMDA and adiponitrile (ADN), are stripped from the melt, driving the reaction towards these products.

[0184] Other chemical recycling pathways use acetic or formic acid as a reactant to form AA and a di-acetamide or di-formamide monomer product36, use acetamide and ammonia to form a di-acetamide and adipamide38, use hydrogen to produce of HMDA and hexanediol41 42, or use ethylene glycol to form HMDA and a diol derivative of AA43.

[0185] There is a clear gap in the literature and reviews regarding chemical recycling of nylon 66, despite the economic potential of this process and attention received by similar chemistries.

[0186] Discussed in this Example is the development of an activity based kinetic model necessary for the non-ideal liquid phase in neutral hydrolysis of nylon 66 and estimation of degradation reactions to include byproducts in process modeling. Also discussed is the development of first process model for chemical recycling of nylon 66 using alkaline hydrolysis that leverages innovations from PET alkaline hydrolysis, and demonstrates heat integration and process intensification configurations.

[0187] Herein is proposed a reaction scheme where nylon 66 is initially depolymerized under neutral hydrolytic conditions to a homogenous aqueous oligomer, followed by the addition of an acid or base at mild temperature to drive the reaction to monomers. This route can be benefited by mild temperatures, improving product selectivity and allowing cheaper metallurgies. The homogeneity of the reaction means that excess acid is not required to solubilize the polymer, and the alkaline hydrolysis reaction is not limited by solid-phase mass transport. The polymer chemistry of nylon 66 makes the production of hundreds of differentATTORNEY DOCKET NO. 222204-2820monomers feasible, but not all reaction pathways are commercially attractive or practical. Depolymerization routes must have competitive yields, valuable products, and with feasible and convenient purification methods available.

[0188] The polymer chemistry of nylon 66 makes the production of hundreds of different monomers feasible, but not all reaction pathways are commercially attractive or practical. Depolymerization routes must have competitive yields, valuable products, and with feasible and convenient purification methods available.

[0189] Nylon 66 Degradation Reactions. Degradation is well-investigated for nylon 66 polymerization systems, because end group degradation is a problem at polymerization reaction temperatures and is discussed in several nylon 66 polymer books and reviews14 1718 60. Nylon 66 degradation reactions in this work are assumed to estimate the yield and species of possible degradation byproducts.

[0190] Schafer et al. explain the hypothesized end group degradation mechanism where acid end groups, [-COOH], dehydrate to cyclopentanone ring containing end groups, referred to as stabilized end groups, [SE]61. The formation of [SE] leads to decrease in [-COOH] concentration. It is proposed the [SE]-forming reaction is reversible, inhibited by water, supported by data from Wiloth15. The increase in amine end group concentration, [-NH2], is proposed to come from the decomposition of acid amide linkages, [R-COOH], to [SE] and [-NH2], since water is not present to hydrolyze amide groups and cause the amine group concentration increase61. Cyclopentanone (CP), a commonly detected byproduct60, is hypothesized to form from the hydrolysis of [SE] forming [-NH2], CO2, and CP61. FIG. 9 summarizes the hypothesized acid group decomposition reactions.

[0191] Ammonia is a commonly reported nylon 66 degradation product indicating decomposition of amine groups. One ammonia-forming reaction occurs where amine end groups react to form a secondary amine group and ammonia shown in FIG. 10. This secondary-amine-containing linkage yields bis(hexamethylene) triamine (BHTMA) upon depolymerization.

[0192] The work of Schafer et al. is used herein, which quantifies NH3, CO2, CP, and BHMTA formation to estimate degradation rates61. More complex degradation byproducts have been reported such as pyridines, Schiff base, or cyclopentanone derivatives at unquantified and presumably lower rates14 61. The rates of byproduct formation to end group concentrations demonstrate that the formation rate of BHMTA appears to be 3rdorder with respect to amine end group concentration61, which may result from catalytic effects. Ammonia formation appears to be first order with respect to amine end group concentration. CO2and CP rates appear independent of end group concentration with CO2rate sensitive to water concentration in the melt and CP rate relatively invariant of composition. CO2and CP rates are assumed to be first order with respect to the total concentration of acid segments, whichATTORNEY DOCKET NO. 222204-2820is consistent with invariance to end group concentration.

[0193] These general relationships are used to estimate degradation reaction rates for nylon 66 depolymerization. Since the NH3rate reported by Schafer et al.61is not entirely accounted for by the BHMTA-forming reaction, the remaining NH3is assumed to come from a generic reaction with a non-volatile byproduct. CO2 rates appear inversely correlated to water concentration and are possibly negligible in a water-rich depolymerization system. For simplification, the entire CO2 yield is assumed to come from the CP-forming reaction.

[0194] Without wishing to be bound by theory, it is possible that degradation reactions evaluated under polymerization conditions of low water content do not necessarily extent to water-rich depolymerization systems, and it could be expected that the assumed degradation rates are conservatively high. The purpose of including degradation reactions is to account for likely byproducts that define separations and purification steps in the depolymerization process. It is possible degradation products are introduced to the process from degraded linkages in the waste nylon 66 feed, even if depolymerization degradation rates are low.

[0195] Adipic Acid Purification. Adipic acid is almost exclusively purified by crystallization. Acid hydrolysis patents describe the crystallization of adipic acid in acidic solution in the presence of the diammonium salt between 1 - 30°C followed by recrystallization and optional activated carbon treatment26 27 29 31. Basic hydrolysis patents by Miller25and Thorburn32describe reactive crystallization where adipic acid is precipitated from aqueous sodium adipate solution by adding an acid to decrease pH to ~1. Seeliger reports converting sodium adipate to adipic acid by electrolysis and then crystallizing by cooling the electrolyzed solution28. Wiest describes the use of a methanol solvent in which sodium adipate is insoluble and precipitates33. The sodium adipate is dissolved in water and acid is added to form solid AA by reactive crystallization33. Conventional adipic acid processes describe a crude crystallization step in the presence of nitric acid, water, and some byproducts from cyclohexane oxidation between 5 - 20°C75’77followed by recrystallization in water78. Some patents describe the use of acetic acid or mixtures with water as recrystallization solvent79 80. There are considerable solid-liquid equilibrium data available for adipic acid in various solvents to model crystallization81’83.

[0196] Process Design. An alkaline nylon 66 hydrolysis processes is modeled to provide some insights into the general design, operation, utility demands, and explore heat integration and process intensification innovations. The alkaline hydrolysis process separates HMDA first and AA and the salt byproducts are crystallized in a purely aqueous system where solid-liquid equilibrium is supported by experimental data. The alkaline hydrolysis process also conveniently resembles the PET alkaline hydrolysis process in terms of the reaction and processing steps and can be compared against this process as a benchmark.

[0197] Table 1 summarizes the assumed nylon 66 feed composition in this work. A relativelyATTORNEY DOCKET NO. 222204-2820clean nylon waste feed that is saturated with water (~8 wt%) from upstream washing steps is assumed. The number-average molecular weight of the nylon 66 feed is assumed to be 11 ,300, although the depolymerization kinetics are relatively insensitive to feed molecular weight. Non-volatile soluble impurities such as dyes, additives, or non-volatile monomers from reacting polymer impurities, such as nylon 66 or PET is assumed. The presence of some nylon 6 is assumed, which is expected to depolymerize to 80% caprolactam (CL) and 20% cyclic dimer (CD) based on other work6. NaOH and HCI are purchased at commercially available concentrations of 50 wt% and 38 wt% respectively.Table 1. Summary of feed and product specifications for design case study.<>

[0198] We assume degradation reactions described above forming CO2, NH3, CP, and BHMTA. A non-volatile degradation byproduct (HEAVY) is defined to account for the stoichiometric mass balance of the ammonia- forming reaction. We define the HMDA purification specification as 100 ppmw water and 100 ppmw non-water impurities. Adipic acid is assumed to be purified by two-stages of crystallization. Product purification is going to be largely influenced by real waste feed composition and degradation products, and specifications are defined in this study mainly to provide consistency between cases when evaluating the effect of design variables.

[0199] We use the same utility assumptions for steam and refrigeration described in our prior work6. All simulations are modeled using Aspen Plus. We use the POLYNRTL thermodynamic model for reaction modeling of the polymer system. We use the ENRTL model for the electrolytic section of the design. NRTL binary parameters are taken from Aspen Plus databanks or regressed from experimental data where available. Missing binary parameters are taken from a machine-learning model by Winters et al.89where available and remaining parameters are estimated by UNIFAC. We provide a list of binary interaction parameters further down. We present a complete mass and energy balance for each case study further down. We refer the reader to our recent work for our assumptions and methodology for accounting for CO2emissions from utilities within the Aspen Plus simulation7.

[0200] FIG. 11 illustrates a simplified process diagram of the alkaline hydrolysis process which we describe in more detail later. Conceptually, this process is similar to PET alkaline hydrolysis processes which we describe in our prior works5 7. The process begins with nylon 66 being introduced to the hydrolysis reactor near its melt temperature, 270°C, by an extruderATTORNEY DOCKET NO. 222204-2820and is mixed with water in a plug-flow type reactor. The nylon 66 partially depolymerizes in the neutral hydrolysis reactor and is progressively cooled to 180°C and NaOH is introduced to the reactor. The NaOH addition drives the reaction to the monomer products HMDA and sodium adipate. The product is filtered to separate solids following the reaction. The filtration can be done close to the reaction temperature or at ~80°C-90°C to allow non-reacting polymers to precipitate. After the filtration, the reaction product is evaporated to separate water and HMDA from salts, sodium adipate and excess NaOH. The HMDA and water are separated from impurities in a distillation section with HMDA yielded as a product and water recycled to the hydrolysis reactor.

[0201] We propose an organic solvent wash step following the evaporation of volatiles from the salt product to remove organic heavy impurities that can be solubilized in an organic solvent such as toluene. The solvent washes the salt product and goes to a recovery unit that evaporates the solvent and concentrates the heavy impurities. The washed salt goes to the crystallization section where the salt is dissolved in water. An adsorbent is used to remove the remaining impurities in the aqueous salt solution. The aqueous salt solution enters a reactive crystallization unit operating at ~20°C with HCI added to convert sodium adipate to AA. The formed AA precipitates and is separated by filtration. We consider a second crystallization stage to increase the purity of AA with solid AA dissolved in water at an elevated temperature and crystallized at ~20°C. The solid AA is filtered from the second-stage crystallizer and dried to produce a solid AA product.

[0202] The filtrate from the reactive crystallization contains the NaCI byproduct and soluble AA. NaCI is recovered by flash crystallization at 60°C. The solid NaCI is filtered, dried, and collected as a byproduct. The filtrate from the NaCI crystallizer contains a mixture of AA and NaCI that is recycled to the reactive crystallizer to recover AA. Accumulating impurities are purged from this stream.

[0203] FIG. 12 shows the envisioned configuration of the alkaline hydrolysis reactor. The purpose of the neutral hydrolysis reaction is to initialize the reaction in the melt state to avoid solid-phase mass transport limitations, allowing the alkaline hydrolysis reaction to proceed at a lower temperature. The homogenous reaction takes advantage of more efficient and less expensive plug-flow designs. Static mixers in the plug-flow reactor can resolve temperature gradients and keep non-polymeric solids suspended. The hydrolysis reaction is fast at the melt temperature and the temperature can be rapidly reduced once the polymer is solubilized. The neutral hydrolysis reaction and alkaline hydrolysis reaction take place in the same reactor divided by one or more points in the plug-flow reactorwhere NaOH is added, as shown in FIG.12. The motivation to add NaOH after neutral hydrolysis is to mitigate degradation reaction catalyzed by an alkaline environment claimed above 220°C25and use less expensive metallurgy. Expensive nickel alloys are used for alkaline systems at high temperature andATTORNEY DOCKET NO. 222204-2820NaOH concentration can be replaced with less expensive stainless steel if temperatures and NaOH concentration are mild44.

[0204] The data from Ogata52allow us to demonstrate that starting at the melt temperature of ~270°C, the reaction temperature can be rapidly lowered below 200°C before adding NaOH. We define the alkaline hydrolysis reaction to be at 180°C based on alkaline hydrolysis processes25 28 33. We do not have data to model the alkaline hydrolysis reaction, so we only model the neutral hydrolysis reaction and assume the addition of NaOH converts the unreacted amide linkages. We assume for our case study that 99% of the polymer following the neutral hydrolysis section is converted to monomers. NaOH is added at 25% stoichiometric excess relative to AA yield.

[0205] FIG. 13A shows the reactor temperature profile used for the case study where temperature is lowered linearly from 270°C to 200°C in 1.5 hours and from 200°C to 180°C over -7.5 hours, which we use for our case study evaluation. This design shows MWN is below 2,000 when the reaction is at ~250°C (FIG. 13B) and is expected to remain homogenous. We set the reactor size and residence time of the hydrolysis reaction to achieve 20% conversion of amide linkages (-650 MWN). The target conversion for the neutral hydrolysis reaction is arbitrary, since the primary objective is homogeneous reaction at low temperature. Higher neutral hydrolysis conversion is going to decrease the reaction time for the alkaline hydrolysis section.

[0206] FIGS. 14A-14C compare an isothermal hydrolysis reaction at270°C (a) to the reaction where the temperature is ramped to 200°C in 1.5 hours (b) and the reaction where the temperature is ramped to 200°C in 1.5 hours and linearly to 180°C for the duration of the reaction (c). We report the hydrolysis reaction in terms of amide linkage conversion, which is the fraction of amide linkages in the reacting polymer hydrolyzed. Equilibrium limits the amide conversion to -30% with monomer yields less than 10%. While the degradation rates are only a rough estimate, FIG. 14A demonstrates how end group degradation reactions, such as the ammonia forming reaction, increase rapidly as the polymer molecularweight decreases. FIGS.14B and 14C show that ramping down reaction temperature substantially reduces degradation yield. The hydrolysis reaction is exothermic in water and the lower temperature improves the equilibrium conversion, allowing the lower temperature reaction to have similar conversion after 5-6 hours.

[0207] Reaction and Distillation Section. FIG. 15 shows the process diagram for the reaction and distillation sections of the process. Nylon 66 feed enters an extruder, EX-101, which heats the polymer to its melt temperature and is mixed with water at 270°C. The mixture enters the plug-flow type hydrolysis (R-100A) and alkaline (R-100B) reactors, whose operating conditions are elsewhere herein. The hydrolysis reaction is mildly exothermic, and reducing the reaction temperature requires heat removal. We assume that heat removal is provided byATTORNEY DOCKET NO. 222204-2820generating steam, which is used to heat the water feed to the reactor. It is also possible for the reaction temperature to be controlled by the pressure of the reaction and flashing water.

[0208] Following the reactors, R-100A and R-100B, we separate a portion of the water by mechanical vapor recompression (MVR). The evaporator E-200 operates at 100 kPa and is heated by condensing vapor compressed by C-201 to 170 kPa. The heat load of the condensing vapor from C-201 exceeds the duty of E-200, and a parallel condenser, E-203 condenses the remaining vapor, generating LP steam. A solids filtration unit can be placed between R-100B and E-200 to separate solids.

[0209] The HMDA concentrated liquid from E-200 enters an evaporation unit E-204, which operates at 20 kPa and 160°C. This unit separates the volatile HMDA product from the nonvolatile sodium adipate product. It is depicted as a single heater but can be a combination of evaporator, precipitation vessel, or a mechanically agitated heater to separate volatiles from precipitating salt products. The temperature and pressure of this step recover over 99% of HMDA in the product. The solid from E-204 goes to the organic solvent wash unit. The vapor from E-204 goes to the water column, T-300, to separate water from HMDA at 20 kPa. The bottom product from T-300 contains 100 ppmw water relative to HMDA and the distillate contains 100 ppmw HMDA.

[0210] The bottom of T-300 goes to the HMDA column, T-310, to separate HMDA from heavies. This column operates at 6 kPa, similar to the literature62, and produces a HMDA product with 100 ppmw of heavy impurity, primarily CL. The distillate temperature is 113°C and we assume the condenser generates LP steam. The column is operated to recover 99.5% of HMDA in the feed. At these conditions, the bottom of T-300 contains ~17 wt% HMDA, 58 wt% CL, and 24 wt% BHMTA and is 146°C. The presence of some CL in the heavy waste aids in the recovery of HMDA, since the relative volatility is high enough to be easily separated, but low enough to be distilled at mild temperature. CL also aids in solubilizing the heavy product, decreasing the likelihood of precipitation fouling in the T-310 reboiler.

[0211] Water from the distillate of T-300 is split, some water evaporated by E-305 as stripping steam in the organic wash section, some is combined with condensed vapor from C-201, and the rest is purged as wastewater. All the impurities in the water (NH3 and CP) distill light relative to water. CP has a lower volatility than water, but is hydrophobic, becoming light in the presence of water. A light column, T-320, is operated to separate light impurities from water at 100 kPa. The column is operated to separate 99% of CP to the distillate and controls water in the distillate at 20 wt%. The light waste contains ~70 wt% NH3and ~10 wt% CP and is left in the vapor phase to be incinerated. The rate of degradation impurities is relatively low, so the light column is partially bypassed to control the impurity concentration in the recycle water and reduce the energy demand. We use 500 ppmw NH3in water for this case study, which allows ~75% of the recycled water to bypass T-320.ATTORNEY DOCKET NO.222204-2820

[0212] None of the impurities assumed in this evaluation have intermediate volatility between water and HMDA, which reduces the complexity of the distillation section. We selected degradation reactions that have been observed for nylon 66, but it is likely for degradation products or impurities with intermediate volatility to exist. The distillation section design is particularly sensitive to impurities that have a similar volatility to that of HDMA or are slightly less volatile than HMDA. Close-volatility impurities cause particular difficulties in conventional HDMA purification62.

[0213] We consider mechanical vapor recompression (MVR) to reduce the energy demand of the water separation in the process. We take advantage of the large difference in volatility between HMDA and waterto separate a large fraction of the water in a single stage. The vapor is compressed so that the condensing temperature of the vapor provides a driving force for vaporization. The amount of water vaporized in this step is limited by the amount of HMDA that volatilizes with the water. There is a tradeoff between increasing fraction of water separated in the MVR evaporation step and the concentration of HMDA that evaporates and ends up in the recycle water to the depolymerization reactor.

[0214] FIGS. 16A-16C demonstrate the tradeoff where thermal duty of the process (primarily MP steam) is drastically reduced by increasing the fraction of water separated by MVR by allowing more HMDA in recycle water with the increased electrical duty from compression being comparatively small. The process generates LP steam at a temperature of ~105°C from the T-310 condenser and the E-203 condenser. Increasing the fraction of water separated by MVR substantially increases the amount of LP steam generated from E-203. We select 2,000 ppmw HMDA in recycle water as the control target for the MVR configuration in this case study.

[0215] We compare the performance of the MVR design to a more conventional configuration where the reactor product is flashed at atmospheric pressure and vaporized by E-204. FIG.17A compares the MVR configuration to the conventional design and FIGS. 17B and 17C compare the two designs and impact of the water rate on process. The MVR design is particularly effective at mitigating energy impact for high water rates with MP steam duty practically constant over the range of evaluated water rates, while LP steam rate generated increases. Electrical duty for the MVR design increases by 129 kJ / kg water. The MP steam duty for the conventional design increases by 2,060 kJ / kg water and without E-203, the conventional design generates only a small amount of LP steam. The primary benefit of increased water rates are reduced reaction times and higher HMDA yields. The conventional design has better yield compared to the MVR design because there is practically no HMDA in the water recycle.

[0216] MVR is not the only intensified design that can be applied. FIG. 18 demonstrates a combination of MVR with single stage multi-effect evaporation. A second evaporator, E-210,ATTORNEY DOCKET NO. 222204-2820is added and operates so that the condensing vapor from E-210 supplies heat to E-200. Heat is supplied to E-210 by condensing the compressed vapor from C-201. Since water is separated over two stages instead of a single stage, more water can be separated with an equivalent concentration of HMDA in the recycle water. This reduces MP steam duty compared to the MVR case. Less LP steam is generated, but the higher compression ratio allows the LP steam for the multi-effect case to be 115°C instead of 105°C. The multi-effect configuration consumes slightly more electricity from C-201. We demonstrate multi-effect evaporation in our previous studies that can also be applied6 7. The point is that numerous process intensification methods can be applied to the water-HMDA separation to drastically reduce energy demand.

[0217] We consider an organic solvent wash step following the precipitation of the salt product based on a similar step described for alkaline hydrolysis of PET by Crippa90. The purpose is to remove low volatility hydrophobic impurities that are difficult to separate in the downstream aqueous crystallization section. These impurities are expected to be present regardless of how the salt product is isolated. The heavy organic impurities in our model include nylon 6 cyclic dimer, BHMTA, nylon 66 oligomers, and the generic heavy soluble nonvolatile impurity assumed in the feed, which could be additives or organic dyes.

[0218] We choose toluene as the solvent for our model because of its commercial availability, negligible solubility of salts, ability to phase-separate from water, and better ability to solubilize slightly polar molecules such as amines compared to alkane solvents. The purpose of including this unit operation in the evaluation is to demonstrate the relatively low energy impact and convenient mass balance of the organic solvent wash step.

[0219] As illustrated in FIG. 19, the wash section begins with salt from E-250 being contacted with toluene at a rate of 1 kg per kg solid. We have depicted W-400 as a displacement wash unit, but the solvent-contacting section can be designed as a stirred tank and filtration unit, or any other convenient unit for contacting the solvent with the salt. The salt from E-250 is not cooled, so the mixture is above 100°C, which helps dissolve organic impurities. We assume the extraction removes 90% of non-salt components. The real separation efficiency is dependent on several factors relating to the wash design, rate, and composition of impurities. A separation efficiency greater than 80 - 90% is likely necessary to justify the organic solvent wash. Excess toluene and extracted impurities exit W-400 and toluene is evaporated in E-420 at 40 kPa using MVR where the vapor is compressed to 100 kPa with the condensing vapor supplying heat to the evaporator. The recovery of toluene by MVR is limited by large difference in relative volatility between toluene and the heavy impurities causing evaporator temperature to increase as toluene content in the liquid is reduced. It is likely necessary to keep some content of toluene in the liquid phase to maintain a soluble, processible liquid. The fraction of toluene vaporized in E-420 is limited by the temperature approach of the condensing vaporATTORNEY DOCKET NO. 222204-2820from C-421 and the temperature of E-420. Using a C-421 compression ratio is 2.5 results in a toluene concentration in the liquid exiting E-420 of ~40 wt%. Lower compression ratio results in a higher toluene content in the E-420 liquid.

[0220] Treatment of the liquid from E-420 is case-dependent. The liquid can be directly incinerated, but results in loss of toluene at a rate of -0.02 kg / kg nylon 66 in this evaluation. Alternatively, toluene can be recovered by feeding the residue from E-420 to a drum S-430 with steam stripping. Steam is effective to separate toluene from the residue and allows near complete recovery of toluene. Since the extracted non-volatile residue is likely hydrophobic, recovering toluene by steam stripping is likely to result in solid precipitation or phase separation. Either option for the heavy liquid from E-420 is viable, and dependent on a more detailed understanding of the rate and composition of heavy residue. We consider the recovery of toluene using stripping in S-430 to limit the toluene loss to 0.005 kg / kg nylon 66.

[0221] The solid from W-400 contains some toluene solvent stuck to the solids. This amount is dependent on the design and operation of W-400. We assume 10 wt% of solvent on the solid from W-400. The solid goes to a dryer DR-203 which operates at 15 kPa and 100°C. Introducing steam at the end of the dryer reduces the concentration of toluene in the solids. We set the steam rate such that concentrations in the solid from DR-203 is 1 ppmw. The vapor from the dryer is condensed by E-411. The liquids from E-422, E-431 , and E-411 are combined in drum S-440, which separates an aqueous and toluene-rich liquid. The aqueous product is returned to the reaction and distillation section. The toluene-rich product is combined with make-up toluene and recycled to W-400.

[0222] FIG. 20A demonstrates the utility demands related to the organic solvent extraction section over a broad range of solvent wash rates. We consider the effect of the fraction of toluene on solid after W-400 over a range typical in solid-liquid separations and find a relatively small effect on LP steam duty. We compare the MVR design shown in FIG. 19 to a conventional design where toluene is recovered by an evaporator using LP steam (FIG. 20B). The effect of toluene rate for the MVR case is 45 kJ / kg toluene for LP steam and 37 kJ / kg toluene for electrical duty compared to the conventional design with 429 kJ / kg toluene LP steam duty and 5.5 kJ / kg toluene electrical duty. Even considering high rates of toluene wash, the utility demand of the solvent wash is small compared to the distillation and reaction sections and can utilize LP steam generated in the reaction and distillation sections. We show organic solvent extraction as a method to remove non-volatile hydrophobic impurities that are particularly challenging to separate by aqueous crystallization with relatively low energy demand and without influencing the downstream or upstream processes.

[0223] The crystallization section separates and purifies AA and NaCI. We model the crystallization from a mass and energy balance (MEB) standpoint using the following assumptions generally valid for crystallization91.ATTORNEY DOCKET NO. 222204-2820• The solute crystallizes as a pure solid• Impurities remained dissolved in solvent• Impurities on the solid come from solvent entrained in the solid either from inclusions in the crystal or solvent stuck to the surface of the crystal

[0224] We additionally make the following assumptions for simplification.• The solute is in equilibrium with the solvent• Filtration separates 100% of solids

[0225] We model the solid-liquid equilibrium of AA in water using data from the literature as discussed herein. Solid-liquid equilibrium for NaCI is modeled using database parameters available in Aspen Plus. The final parameter that impacts the mass balance and purification provided by a crystallization unit is solvent on the solid after filtration, which is the source of impurity on the solid. This is claimed by Genk to range between 2 - 10 wt% of the filtered product, but is strongly dependent on the filtration unit design, solvent, and crystal characteristics91. We use 10 wt% as the base design value in this case study.

[0226] We also consider modeling the washing of crystals following filtration. As stated previously, the source of impurity on a crystal product is from solvent adhered to the crystal. It is common practice to improve crystal purity by displacing the impurity-containing solvent with clean solvent. We assume for modeling washing the total solvent on the solid is the same following the wash step. The two remaining parameters to model washing from a MEB standpoint are the flow rate of wash solvent and the fraction of impurity containing solvent removed by washing. The rate of wash solvent is typically reported on a rate basis relative to the solvent on the solids91 92. We assume the wash efficiency, or the fraction of solvent displaced by washing, is 90% and the wash ratio of 3. These values are conservatively low and high, respectively, compared to examples from the literature to avoid overly optimistic estimation of wash performance91 92.

[0227] We introduce the organic wash section to reduce the rate of impurities entering the crystallization unit. We can model the separation of the two precipitating solids, AA and NaCI. Concentration of AA in the solvent for NaCI crystallization and NaCI concentration in solvent for AA crystallization are going to be higher than any other impurity. Provided that all impurities in the crystallization unit are solubilized in water, NaCI in the AA product and AA in the NaCI product represent the highest impurity concentration in each product. Knowing this we can then evaluate the crystallization section by the general MEB of the process and sensitivity of the solid product purities to crystallization and wash design variables.

[0228] FIG. 21 illustrates the crystallization section process diagram considered in this case study. Salt from the organic wash section dryer DR-203 enters a dissolution tank, S-500. Water is added to control the solute concentration at 30 wt%. The dissolved solution is pumped through and adsorbent bed AD-501, which we assume removes all remaining organic impurities. The solution enters the reactive crystallizer CR-510, which operates at 2 kPa andATTORNEY DOCKET NO. 222204-2820~21 °C. HCI is added to convert sodium adipate to AA, which crystallizes. 1.5% excess HCI is added to maintain the pH at ~1.5. Solid AA is filtered by FL-513 and washed in W-514. Washed crude AA from W-514 enters a dissolution tank heated to 95°C. Water is added to maintain a solute concentration of 25 wt%. The dissolved solution enters a partial crystallization vessel, CR-530, operating at 10 kPa and 45°C. The vapor from CR-530 is condensed with cooling water at 45°C. The slurry of partially crystallized AA goes to crystallization vessel, CR-540, which operates at 2 kPa and 18°C. The AA solution from CR-540 is filtered by FL-542 and washed in W-543. The washed AA crystal from W-543 is dried in DR-550 using air at 75°C to reduce moisture content on the solid below 100 ppmw. The filtrate from FL-542 is used for dissolution in S-500.

[0229] The NaCI-rich filtrate from CR-510 is preheated by E-600, and goes to NaCI crystallizer, CR-610, which operates at 60°C and 15 kPa. Heat is supplied to the CR-610 crystallization solvent loop by MVR from compressor, C-611 , which compresses the vapor from CR-610 to 72 kPa. NaCI crystallizes by evaporating water from CR-610. Solid NaCI is filtered from the solvent by FL-614 and washed in W-615. Washed NaCI crystals from W-615 are dried in DR-660 using air at 75°C to reduce moisture content on solid below 100 ppmw. Filtrate from FL-614 is withdrawn from the CR-610 solvent loop and fed to CR-510 to keep the concentration of AA in the solvent below 8 wt%. A portion of this stream can be purged to remove accumulating impurities.

[0230] The second AA crystallization is to reduce NaCI concentration in AA product. NaCI concentration in the CR-510 solvent is -23 wt%. The concentration of NaCI in crude AA after filtration and wash is -2,000 ppmw. Even with different design variables or crystallization performance, it is unlikely that a single crystallization produces sufficiently pure AA product. The NaCI concentration on AA after the second crystallization and wash is -10 ppmw. The same issue applies to NaCI crystallization where AA concentration accumulates to 8 wt% in CR-610. AA concentration in the NaCI product is -900 ppmw. A second crystallization stage for NaCI can be added if higher purity is desired.

[0231] We design the AA crystallizers CR-510 and CR-540 to operate at the same pressure and we assume a common condenser. Refrigeration is required to condense the vapor at ~15°C, which we model with a 5°C ammonia refrigeration unit. Refrigeration temperature is necessary because of the relatively high solubility of AA in water, which is just under 2 wt% at 20°C. We add CR-530 to reduce the refrigeration duty of the process, but this unit can be eliminated if the added capital does not justify the reduction in utility cost. The reactive crystallizer CR-510 is expected to release CO2, which is converted to NaCO3 from the alkaline hydrolysis reaction and released after the addition of HCI. It may be effective to strip CO2 before the alkaline hydroxide addition if the evolution of CO2 in CR-510 causes issues with the vacuum system.ATTORNEY DOCKET NO. 222204-2820

[0232] We consider the impact of some of the primary variables in the crystallization section have on the process. These include the rate of water added in the first dissolution, S-500, the water added to dissolve AA in S-520, and the rate of water purged in the CR-610 solvent loop, which controls the concentration of AA accumulating in the solvent. FIG. 22A shows the effect of solute concentration in the first dissolution, S-500, where increasing water rate primarily increases electrical duty through the MVR unit. The LP steam duty, which is from the dryer air heater and heat input for S-520, is unaffected. AA purity is higher with lower solute concentration, since the NaCI concentration in CR-510 is lower. The minimum water concentration in S-500 is dictated by the solubility of NaCI, which can co-precipitate in CR-510. The concentration of NaCI in CR-510 with S-500 controlling solute concentration to 30 wt% is ~23 wt%, compared to its solubility of ~27 wt% in CR-610. Sodium adipate solubility may also factor into the minimum water rate, but its solubility in water is ~36 wt% at 20°C93.

[0233] FIG. 22B shows the effect of the CR-610 solvent purge rate. From a mass balance perspective, the NaCI-rich solution from CR-510 entering CR-610 has two outlets where water can only exit as a vapor and NaCI can only exit as a solid. AA present at ~1.8 wt% complicates the separation since it cannot exit as a vapor and contaminates the NaCI product exiting as a solid. The purge stream from CR-610 is recycled to CR-510 to recover the concentrated AA solution. Increasing the purge rate lowers AA concentration but increases the circulation rate between CR-510 and CR-610. This has a relatively small impact on utility demand over the range considered. The purity of NaCI increases by lowering AA concentration in CR-610, and AA purity slightly decreases from the recycling of saturated NaCI to CR-510. The minimum purge rate from CR-610 is defined by the solubility of AA in CR-610. We chose 60°C as the operating temperature to increase AA solubility to ~11 wt%. It is possible to operate CR-610 at the same pH as CR-510 to keep AA in the acidic form or to add NaOH to convert AA to sodium adipate. We do not consider the second option, since the saturation limit of sodium adipate in saturated NaCI where co-precipitates occurs is unknown, and this option consumes additional NaOH and HCI.

[0234] FIGS. 25A and 25B demonstrates the effect of solute concentration in the second dissolution, S-520, on utility demand and product purity. Increasing water rate increases the rate of filtrate yielded from CR-540. The only outlet for the filtrate is S-500. When the water rate to S-520 is high enough the rate of filtrate from CR-540 exceeds the rate to control the solute concentration in S-500, which we show in FIG. 23A. Before this point, increasing water rate primarily increases LP steam duty for S-520. When the rate of filtrate from CR-540 exceeds the water rate to S-500 the control for the first stage solute concentration is lost and electrical duty increases similarly to what is shown in FIG. 22A for the decrease in solute concentration in S-500. Solute concentration in the second dissolution has a linear correlation with AA purity, and practically no effect on NaCI purity. The temperature to dissolve AA in S-ATTORNEY DOCKET NO. 222204-2820520 is also affected by water concentration with higher water concentration requiring a lower temperature for dissolution.

[0235] We consider the impact of the assumed crystallization and wash parameters. FIG.24A-24C show the impact of solvent on filtered solids, the wash separation efficiency, and the wash ratio. The solvent content on filtered solids has the largest impact on both product purity and utility demand of these parameters. Utility demand increases primarily from the drying air rates, since drying air requires both compression and heating. The wash ratio and wash separation efficiency are codependent variables where the separation efficiency is a function of the wash ratio for a real system. We separate the variables to demonstrate the impact of separation efficiency on the product purity and wash ratio on the utility demand. The wash ratio has a relatively small impact on utility demand since the rates of solvent on solids being washed are tiny in comparison to the total rate of solvent in the crystallization system. We emphasize that while the performance of the crystallization systems has a relatively small impact on the energy balance, it can have drastic impact on the purity of the crystallized product.

[0236] We consider the use of MVR to remove water in CR-610, which is the largest energy demand in the crystallization section. MVR is commonly employed for salt crystallization. The compression ratio (4.78) is higher than for the other MVR applications in this design, and we assume a two-stage centrifugal compressor. FIG. 25 shows details of the MVR design and comparison to conventional design using LP steam for E-601. MVR requires ~1 ,000 kJ / kg nylon 66 electrical duty but reduces LP steam duty by ~ 7,000 kJ / kg nylon 66.

[0237] We provide a final evaluation of one design variable, which is the rate of NaOH added during the alkaline hydrolysis reaction, which can impact the entire process. This value impacts the hydrolysis reaction and is going to be selected based on the tradeoff between monomer yield and cost of NaOH addition. FIGS. 26A and 26B demonstrate the impact of the NaOH on utility demand and associated feed and product rates. Higher NaOH rates slightly increase the MP steam duty and electrical duty, but more importantly increase the consumption of NaOH and HCI. We demonstrate the large energy demand associated with the electrolysis process to regenerate a salt byproduct in our associated work7. This energy, 7,200 - 7,600 kJ / kg NaOH94, drives cost of NaOH and HCI and has to be factored into life cycle analysis. Some value can be recovered by selling NaCI as a product, but the value is lower than the respective prices of HCI and NaOH. This applies to nearly any acid combination used with NaOH where the salt is of a lower value than the corresponding acid and base. Wastewater comes from water in the NaOH and HCI at commercially available concentrations. Wastewater produced can be reduced by either electrolyzing NaCI, purchasing solid NaOH and diluting in the process, or using acids such as H2SO4, which can be purchased at higher concentrations.ATTORNEY DOCKET NO. 222204-2820

[0238] Conclusion. We report the case study results for our base evaluation using the base design variables described in the previous sections in Table 2 compared to the PET alkaline hydrolysis process evaluated in our prior work7. We note the process generates LP steam using the base design variables. Further optimization can be done to balance LP steam demand, so the net LP steam duty is 0. The results provide an order-of-magnitude estimate of energy demand, energy related CO2 emissions, feed requirements, and products. We demonstrate the sensitivity of the energy balance and product yields to design variables. We also demonstrate several instances where process intensification by MVR can be applied and the substantial reduction and thermal energy demand it provides. Overall, we find that the total thermal duty of the nylon 66 alkaline hydrolysis process to compare favorably to the PET alkaline hydrolysis process. The fact that nylon 66 monomers are higher value than TPA and EG and that alkaline hydrolysis processes are being actively developed for commercialization present a strong case for the economic viability of nylon 66 alkaline hydrolysis5 7.Table 2. Comparison of nylon 66 alkaline hydrolysis process results for the base design in our case study compared to results from the similar PET alkaline hydrolysis process evaluated in our prior work7. EG is short for ethylene glycol, TPA is short for terephthalic acid. We consider the PET alkaline hydrolysis case where NaCI is crystallized for comparative analysis.

[0239] In addition to the process case study, we have developed a kinetic model incorporating activity coefficients for neutral hydrolysis of nylon 66 applicable to non-ideal liquid environments with high water concentration, and we include degradation and side reactions, and byproduct formation from depolymerization. This model can be extended to modeling nylon 66 polymerization kinetics with new experimental data. We additionally provide an overview of different chemical recycling pathways for nylon 66 and the different purificationATTORNEY DOCKET NO. 222204-2820methodologies for depolymerization products.2. ADDITIONAL DATA

[0240] We summarize the degradation reactions discussed in Example 1. FIG. 27 shows the three assumed degradation reactions. Equations 1 - 3 show the rate equations assumed for each degradation reaction. Here we use azepane as a ‘generic’ heavy component to satisfy the mass balance for the ammonia forming reaction. We set the volatility for ‘azepane’ to zero in the model, so it behaves as a non-volatile heavy component. We assign the degradation reactions to consume HMDA and AA respectively to simplify assigning reactions consuming segments. This is not going to significantly impact the condensation reaction kinetics as the condensation reaction rates are an order of magnitude faster than the degradation reactions. Table 3 summarizes the kinetic rate constants used for the three degradation reactions regressed from data by Schafer et al14.TDEG = kDEGi X [HMDA] + 0.5[T - HMDA])3(1) rDEG2 = kDEG2 X ([HMDA] + 0.5[T - HMDA]) (2)rDEG3=^DEG3x([AA] + [T — AA] + [ / ? — AA]) (3) Table 3. Summary of kinetic rate parameters for degradation reactions.

[0241] FIGS. 28A and 28B show the change in the condensation equilibrium constant and apparent heat of reaction as a function of water composition and temperature. Heat of reaction is estimated from the temperature dependency of the equilibrium constant and Van’t Hoff equation. We can capture the change in apparent reaction enthalpy that occurs at ~7 wt% water composition. The reason for the inversion in reaction enthalpy is from the difference in enthalpy of the end groups in the ionic and molecular form. Under aqueous conditions the acid and amine groups completely dissociate into their ionic forms lowering the enthalpy. The heat of dissociation is large at ambient conditions (~-5kJ / mol AA9596and ~-115 kJ / mol HMDA9798), about -60 kJ / mol assuming similar dissociation enthalpy for nylon 66 end groups as the monomers. At low water concentrations the end groups lose their ionic characteristic and take on a more molecular form, which is an exothermic reaction based on heats of combustion of the monomers and polymer99.

[0242] Regression of the binary parameters and rate constants for the system is challenging because of the large number of regression parameters available. There are 16 total considering the four kinetic parameters and 12 binary parameters. We have found duringATTORNEY DOCKET NO. 222204-2820regression using different initial values or including all parameters in the regression results in drastically different results, while maintaining a roughly equivalent objective function value. This indicates co-linearity of the parameters, which is why we reduced the number in the regression to 8, using vapor-liquid equilibrium data from Ogata52to determine binary parameters between the amide group and water. We attempted to include additional data such as the equilibrium data from Ogata at high temperature and low water content52, data from Wiloth15100, or data from Giori and Hayes10, but these typically resulted in inconsistent results for interpolated and extrapolated predictions. The nature of the activity coefficient in the model makes it sensitive to overfit, such as the change in the apparent heat of reaction for the 200°C case at high water concentration.

[0243] Steppan et al.54attempt to use the data from Giori and Hayes10, which is incorrect, since this data is for a nylon 6 system that includes CL. Data from Wiloth100shows that while similar, nylon 6 and nylon 66 equilibrium are different. Trying to force a fitting using mixed data is likely to result in poor extrapolative ability using the activity coefficient kinetic model. The best way to improve the extrapolative and predictive capability using this model is to conduct more detailed analysis of the kinetics of the broader range. This includes studies at water concentrations higher than 50 wt% and at lower temperature for depolymerization and higher temperature studies with low water concentration for polymerization. Equilibrium at polymerization conditions is complicated by decomposition reactions that must be accounted for.

[0244] The component BHMTA does not exist in Aspen Plus. We define this component using estimation methods in Aspen Plus to define necessary thermodynamic properties for modeling. Table 4 provides scalar properties defined for BHMTA. Table 5 summarizes methods to calculate properties in Aspen Plus.ATTORNEY DOCKET NO.222204-2820Table 4. Summary of scalar values defined for BHMTA. DHFORM is enthalpy of formation for ideal gas at 25°C, DGFORM is Gibbs free energy of formation of ideal gas at 25°C, PC is critical pressure, TC is critical temperature, NBT is normal boiling temperature, MW is molecular weight.Table 5. Methods used to estimate properties for BHMTA in Aspen Plus.

[0245] Equations 4-7 provide the temperature dependent forms for vapor pressure, ideal gas heat capacity, and heat of vaporization for BHMTA. Table 6 provides the respective parameters. The temperature is in Kelvin, Tc is critical temperature. C1 parameter was modified to match reported boiling point temperature between 163-165°C at 4 Torr pressure reported101.< <<ATTORNEY DOCKET NO.222204-2820Table 6. Temperature dependent property parameters for equations S4-S7. Estimated by methods indicated in Table 5.

[0246] Table 7 shows the following thermodynamic parameters defined in the Aspen Plus model to match data. AA(s) thermodynamic parameters are regressed from experimental data8283. NA2AA thermodynamic parameters regressed to data from Rozaini and Brimblecombe15. Adipic acid anion thermodynamic parameters defined using pKa data from Dash and Mishra95. Van Krevelen parameters set for nylon 66 segments so that the heat of reaction from nylon 66 to molecular form AA and HMDA is endothermic (~26 kJ / mol amide) and the net alkaline hydrolysis reaction is exothermic (~-22 kJ / mol amide) consistent with Skuratov and Bonetskaya".Table 7. Summary of user defined thermodynamic parameters. DHSFORM is solid enthalpy of formation at 25°C. DGSFORM is solid Gibbs energy of formation at 25°C. DHAQFORM is aqueous enthalpy of formation at infinite dilution at 25°C. DGAQFORM is aqueous Gibbs energy of formation at infinite dilution at 25°C. DHVKFORM is Van Krevelen heat of formation for polymer segments.G. REFERENCES

[0247] References are cited herein throughout using the format of reference number(s) superscripted corresponding to one or more of the following numbered references. For example, citation of references numbers 1 and 2 immediately herein below would be indicated in the disclosure as1 2.

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[0349] It will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Other aspects of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.

Claims

ATTORNEY DOCKET NO.222204-2820CLAIMSWhat is claimed is:

1. A method, comprising:contacting a solid feedstock comprising nylon 66 with water, thereby forming a liquid mixture;reducing a temperature of the liquid mixture, thereby forming a cooled liquid mixture; andcontacting the cooled liquid mixture with a reactant comprising an acid or a base, thereby forming a product comprising hexamethylene diamine, adipic acid, a salt thereof, a derivative thereof, or any combination thereof.

2. The method of claim 1 , wherein contacting the solid feedstock with water is done at a rate of about 0.1 kg of water per kg of the solid feedstock to about 10 kg water per kg of the solid feedstock.

3. The method of claim 1 or claim 2, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react at a pressure of about 25 MPa to about 100 MPa.

4. The method of any one of claims 1-3, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react at a reaction temperature of about 250 °C to about 300 °C.

5. The method of any one of claims 1-4, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react for about 0.1 hours to about 15 hours.

6. The method of any one of claims 1-5, wherein reducing the temperature of the liquid mixture comprises reducing the temperature of the liquid mixture by about 15% to about 60%.

7. The method of any one of claims 1-5, wherein reducing the temperature of the liquid mixture comprises reducing the temperature of the liquid mixture to a reduced temperature of about 125 °C to about 250 °C.

8. The method of any one of claims 1-7, wherein the cooled liquid mixture comprises a nylon 66 oligomer with a number average molecular weight of about 500 g / mol to about 3,000 g / mol.ATTORNEY DOCKET NO. 222204-28209. The method of any one of claims 1-8, wherein the cooled liquid mixture is contacted with the reactant at a rate of about 8 moles to about 20 moles of reactant per kg of the nylon 66.

10. The method of any one of claims 1-9, wherein contacting the cooled liquid mixture with the reactant further comprises allowing the cooled liquid mixture and the reactant to react at a second reaction temperature of about 100 °C to about 250 °C.

11. The method of any one of claims 1-10, wherein contacting the cooled liquid mixture with the reactant further comprises allowing the cooled liquid mixture and the reactant to react for about 0.1 hours to about 10 hours.

12. The method of any one of claims 1-11 , wherein the reactant comprises the acid selected from hydrochloric acid, sulfuric acid, nitric acid, and a combination thereof.

13. The method of any one of claims 1-12, wherein the reactant comprises the base selected from potassium hydroxide, ammonium hydroxide, and a combination thereof.

14. The method of any one of claims 1-13, wherein the method results in a product yield of about 85% to about 100%.

15. The method of any one of claims 1-14, wherein the method further comprises reducing a temperature of the product.

16. The method of claim 15, wherein the method further comprises reducing the temperature of the product to a second reduced temperature of about 50 °C to about 175 °C.

17. The method of any one of claims 1-16, wherein the solid feedstock comprises a nylon 66 melt.

18. The method of any one of claims 1-18, wherein the product comprises a solid precipitate and an aqueous solution, further comprising:separating the solid precipitate from the aqueous solution, wherein the aqueous solution comprises volatile compounds and non-volatile compounds; andseparating the volatile compounds from the non-volatile compounds, thereby forming a volatile product and a non-volatile product;wherein the volatile product comprises hexamethylene diamine, a derivative thereof, a salt thereof, or any combination thereof; andwherein the non-volatile product comprises adipic acid, a derivative thereof, a salt thereof, or any combination thereof.ATTORNEY DOCKET NO.222204-282019. The method of claim 18, wherein the non-volatile product comprises a derivative of adipic acid or a salt of adipic acid, further comprising:contacting the non-volatile product with water, thereby forming a first aqueous solution; andcontacting the first aqueous solution with an acid, thereby forming an acid-treated mixture comprising a second aqueous solution and a solid residue, wherein the solid residue comprises adipic acid.

20. The method of claim 19, wherein the non-volatile product is washed with an organic solvent prior to contacting the non-volatile product with water.

21. The method of any one of claims 18-20, wherein the volatile product comprises hexamethylene diamine, further comprising:distilling the volatile product, thereby forming a distillate comprising hexamethylene diamine.

22. The method of claim 18, wherein the non-volatile product comprises adipic acid, further comprising:contacting the non-volatile product with water, thereby forming a first aqueous solution; andcrystalizing the first aqueous solution, thereby forming a crystalized mixture comprising a second aqueous solution and a second solid residue, wherein the second solid residue comprises adipic acid.

23. The method of claim 18 or claim 22, wherein the volatile product comprises a derivative of hexamethylene diamine or a salt of hexamethylene diamine, further comprising:contacting the volatile product with a base, thereby forming a base-treated mixture; evaporating the base-treated mixture, thereby forming a vapor and an evaporation residue; anddistilling the vapor, thereby forming a distillate comprising hexamethylene diamine.

24. A method, comprising:contacting a solid feedstock comprising a nylon with water, thereby forming a liquid mixture;reducing a temperature of the liquid mixture, thereby forming a cooled liquid mixture; andcontacting the cooled liquid mixture with a reactant comprising an acid or a base,ATTORNEY DOCKET NO. 222204-2820thereby forming a product comprising at least one monomer or a salt thereof, wherein the at least one monomer comprises a carboxyl group, an amine, or a combination thereof.

25. The method of claim 24, wherein the nylon is an aliphatic nylon.

26. The method of claim 24 or claim 25, wherein the at least one monomer comprises a carboxylic acid, a primary amine, or a combination thereof.

27. The method of claim 24 or claim 25, wherein the at least one monomer is selected from a carboxylic acid compound, a dicarboxylic acid compound, an amine compound, a diamine compound, a salt thereof, and any combination thereof.

28. The method of claim 24 or claim 25, wherein the at least one monomer is selected from adipic acid, dodecanedioic acid, 11-aminoundecanoic acid, w-aminolauric acid, 1 ,4- diaminobutane, hexamethylene diamine, a salt thereof, a derivative thereof, and any combination thereof.

29. The method of any one of claims 24-28, wherein contacting the solid feedstock with water is done at a rate of about 0.1 kg of water per kg of the solid feedstock to about 10 kg water per kg of the solid feedstock.

30. The method of any one of claims 24-29, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react at a pressure of about 25 MPa to about 100 MPa.

31. The method of any one of claims 24-30, wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react at a reaction temperature of about 250 °C to about 300 °C.

32. The method of any one of claims 24-31 , wherein contacting the solid feedstock with water further comprises allowing the solid feedstock and water to react for about 0.1 hours to about 15 hours.

33. The method of any one of claims 24-32, wherein reducing the temperature of the liquid mixture comprises reducing the temperature of the liquid mixture by about 15% to about 60%.

34. The method of any one of claims 24-32, wherein reducing the temperature of the liquid mixture comprises reducing the temperature of the liquid mixture to a reduced temperature of about 125 °C to about 250 °C.ATTORNEY DOCKET NO.222204-282035. The method of any one of claims 24-34, wherein contacting the cooled liquid mixture with the reactant further comprises allowing the cooled liquid mixture and the reactant to react at a second reaction temperature of about 100 °C to about 250 °C.

36. The method of any one of claims 24-35, wherein contacting the cooled liquid mixture with the reactant further comprises allowing the cooled liquid mixture and the reactant to react for about 0.1 hours to about 10 hours.

37. The method of any one of claims 24-36, wherein the reactant comprises the acid selected from hydrochloric acid, sulfuric acid, nitric acid, and a combination thereof.

38. The method of any one of claims 24-37, wherein the reactant comprises the base selected from potassium hydroxide, ammonium hydroxide, and a combination thereof.

39. The method of any one of claims 24-38, wherein the method results in a product yield of about 85% to about 100%.

40. The method of any one of claims 24-39, wherein the method further comprises reducing a temperature of the product.

41. The method of claim 40, wherein the method further comprises reducing the temperature of the product to a second reduced temperature of about 50 °C to about 175 °C.

42. The method of any one of claims 24-41, wherein the solid feedstock comprises a nylon melt.

43. The method of any one of claims 24-42, wherein the product comprises a solid precipitate and an aqueous solution, further comprising:separating the solid precipitate from the aqueous solution, wherein the aqueous solution comprises volatile compounds and non-volatile compounds; andseparating the volatile compounds from the non-volatile compounds, thereby forming a volatile product and a non-volatile product;wherein the volatile product comprises an amine compound, a diamine compound, a salt thereof, or any combination thereof; andwherein the non-volatile product comprises a carboxylic acid compound, a dicarboxylic acid compound, a salt thereof, or any combination thereof.

44. The method of claim 43, wherein the non-volatile product comprises the salt of the carboxylic acid compound or the salt of the dicarboxylic acid compound, further comprising:ATTORNEY DOCKET NO.222204-2820contacting the non-volatile product with water, thereby forming a first aqueous solution; andcontacting the first aqueous solution with an acid, thereby forming an acid-treated mixture comprising a second aqueous solution and a solid residue, wherein the solid residue comprises the carboxylic acid compound or the dicarboxylic acid compound.

45. The method of claim 44, wherein the non-volatile product is washed with an organic solvent prior to contacting the non-volatile product with water.

46. The method of any one of claims 43-45, wherein the volatile product comprises the amine compound or the diamine compound, further comprising:distilling the volatile product, thereby forming a distillate comprising an amine compound or a diamine compound.

47. The method of claim 43, wherein the non-volatile product comprises the carboxylic acid compound or the dicarboxylic acid compound, further comprising:contacting the non-volatile product with water, thereby forming a first aqueous solution; andcrystalizing the first aqueous solution, thereby forming a crystalized mixture comprising a second aqueous solution and a second solid residue, wherein the second solid residue comprises the carboxylic acid compound or the dicarboxylic acid compound.

48. The method of claim 43 or claim 47, wherein the volatile product comprises the salt of the amine compound or the salt of the diamine compound, further comprising:contacting the volatile product with a base, thereby forming a base-treated mixture; evaporating the base-treated mixture, thereby forming a vapor and an evaporation residue; anddistilling the vapor, thereby forming a distillate comprising the amine compound or the diamine compound.

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