Producing virgin quality PET and copolyester feedstock from polyester carpet fibers.

Abstract

A method for chemically recycling waste polyethylene terephthalate (PET) carpet fiber, the method comprising the steps of: providing a waste carpet fiber composition comprising at least 75 wt% PET and 6 wt% or less ash; reacting the waste carpet fiber composition with methanol to produce a depolymerized polyester mixture comprising polyester oligomers, dimethyl terephthalate (DMT), and ethylene glycol (EG); and recovering the DMT and EG from the depolymerized polyester mixture.

Description

[Technical field]

[0001] This invention relates generally to the chemical recycling of polyester carpet fibers using methanol. [Background technology]

[0002] National and global efforts are focused on the reuse and recycling of post-consumer and post-industrial materials, specifically polyethylene terephthalate (PET) and PET-like materials (any polymeric material containing a high concentration of terephthalate (TPA)). This includes a range of materials used in a wide range of applications, such as beverage bottles, packaging, textiles, carpets, thermoformed products, multi-layer films, and plasticizers. Some of the more common and less complex materials can be recycled through simple mechanical recycling processes. However, with large and growing brand responsibilities and legislation regarding the use of sustainable or recycled-containing materials, alternative feedstocks that do not fit into existing mechanical recycling streams must be considered to create a viable circular economy.

[0003] One such feedstock is polyester carpet fiber, which is made up of a mixture of PET, heavy colorants, stain guards, polypropylene, inorganic compounds (e.g., TiO 2 ), and other additives, making recycling PET raw material a particularly challenging problem, as it is difficult to properly purify it. Summary of the Invention [Problem to be solved by the invention]

[0004]

[0004] Therefore, there is a need to provide an alternative and / or improved method for producing virgin quality PET feedstock from polyester carpet fibers that can be used in polymer manufacturing. [Means for solving the problem]

[0005]

[0005] The present invention addresses this need, as well as other needs which will become apparent from the following description and the appended claims.

[0006] The invention is as set out in the accompanying claims.

[0006]

[0007] Briefly, in one aspect, the present invention provides a method for chemically recycling waste polyethylene terephthalate (PET) carpet fibers, the method comprising: providing a waste carpet fiber composition comprising at least 75 wt.% PET and 6 wt.% or less ash; reacting the waste carpet fiber composition with methanol to produce a depolymerized polyester mixture comprising polyester oligomers, dimethyl terephthalate (DMT), and ethylene glycol (EG); recovering DMT and EG from the depolymerized polyester mixture; Including, Weight percentage (wt%) is based on the total weight of the waste carpet fiber composition.

[0007]

[0008] In another aspect, the present invention provides a mixture for chemical recycling of waste carpet fibers, the mixture comprising: (a) a waste carpet fiber composition comprising at least 75 wt. % polyethylene terephthalate (PET) and no more than 6 wt. % ash; (b) Methanol comprising the reaction product of The weight percentages are based on the total weight of the waste carpet fiber composition.

[0008]

[0009] In yet another aspect, the present invention provides a method for preparing recycled polyester. In one variation, the method includes: preparing recycled polyester using the purified EG or DMT, or both, obtained according to the present invention; Includes.

[0009]

[0010] In another variation, the method comprises: reacting the purified DMT obtained according to the present invention with water to form recycled terephthalic acid (rTPA); preparing recycled polyester using rTPA and optionally purified EG also obtained according to the present invention; Includes.

[0010]

[0011] In yet another variation, the method comprises: reacting the purified DMT obtained according to the present invention with virgin EG, purified EG also obtained according to the present invention, or both, to form bis(2-hydroxyethyl) terephthalate (BHET) or an oligomer thereof; polycondensing BHET or its oligomers to form recycled PET; Includes. [Brief description of the drawings]

[0011] [Figure 1]

[0012] FIG. 1 shows a flow diagram of an exemplary laboratory methanol decomposition process used in the examples. [Diagram 2]

[0013] FIG. 1 shows a graph of kinetic data for methanol decomposition of several different polyester carpet fiber samples from Example 2. [Diagram 3]

[0014] FIG. 1 shows a graph of kinetic data for methanol decomposition of various mixtures of two polyester carpet fiber samples from Example 2. [Figure 4]

[0015] FIG. 13 shows a graph comparing median MeOH / DMT for control and samples A-D from Example 2 with PET% of the feedstock properties. [Diagram 5]

[0016] FIG. 13 shows a graph comparing the median MeOH / DMT of control and samples A-D from Example 2 with the % Ash of the feedstock properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012]

[0017] Surprisingly, it has been discovered that virgin-quality PET feedstock that can be used for polymer production can be obtained from waste polyester carpet fibers. In various embodiments, mechanical separation, depolymerization, and extensive purification techniques are used to produce virgin-like PET feedstock from waste polyester carpet fibers. Mechanical separation processes can include shredding, screening, settling / floating, grinding, milling, granulation, etc., depending on where the carpet fibers enter the feed stream. After the mechanical processes, the PET depolymerization process uses methanol and an optional transesterification catalyst to break down the PET into building blocks that can be purified. Purification techniques utilize physical properties such as boiling point, solubility, diffusion coefficient, density, surface tension, and particle size in processes such as filtration, centrifugation, and distillation to remove impurities or contaminants in the complex multi-component polyester material. These processes can be combined to remove items commonly found in commercial carpets, such as colorants, stain protectants, polypropylene, and inorganic compounds. The breakdown and purification of such carpets into individual PET building blocks is described below.

[0013]

[0018] As used herein, "PET" or "polyethylene terephthalate" refers to a homopolymer of polyethylene terephthalate or to polyethylene terephthalate that has been modified with one or more acid and / or glycol modifying agents and / or contains residues or moieties other than ethylene glycol and terephthalic acid, such as, for example, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, diethylene glycol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD), cyclohexanedimethanol (CHDM), propylene glycol, isosorbide, 1,4-butanediol, 1,3-propanediol, and / or neopentyl glycol (NPG). Also included within the definition of the terms "PET" and "polyethylene terephthalate" are polyesters having terephthalate repeat units (whether or not they contain ethylene glycol-based repeat units) and one or more residues or moieties of glycols, including, for example, TMCD, CHDM, propylene glycol, or NPG, isosorbide, 1,4-butanediol, 1,3-propanediol, and / or diethylene glycol, or combinations thereof. Examples of polymers having terephthalate repeat units include, but are not limited to, polypropylene terephthalate, polybutylene terephthalate, and copolyesters thereof.

[0014]

[0019] In one aspect, the present invention provides a method for chemically recycling waste polyethylene terephthalate (PET) carpet fibers, the method comprising: providing a waste carpet fiber composition comprising at least 75 wt.% PET and 6 wt.% or less ash; reacting the waste carpet fiber composition with methanol (optionally in the presence of a transesterification catalyst) to produce a depolymerized polyester mixture comprising polyester oligomers, dimethyl terephthalate (DMT), and ethylene glycol (EG); recovering DMT and EG from the depolymerized polyester mixture; Including, The weight percentages are based on the total weight of the waste carpet fiber composition.

[0015] Carpet Fiber Supplies

[0020] There are two potential sources of PET carpet fiber feedstock: post-industrial carpet fiber and post-consumer carpet fiber. Post-industrial carpet fiber is recovered from the manufacturing process prior to tufting, which attaches the PET carpet fiber to the carpet backing. Post-consumer carpet fiber, on the other hand, is removed from the carpet backing by various processes that separate the PET fiber from other carpet components.

[0016]

[0021] Impurities in post-industrial PET carpet fibers can prevent their direct use in mechanical recycling processes outside the textile industry. These impurities can also pose problems in the methanolysis process, as well as in the purification of the recovered monomers, DMT and EG. Some of the contaminants present in post-industrial carpets are listed below: 1. Color bodies and dyes intentionally added to polyester; 2. Dimethyl isophthalate (DMI) - Often used in PET production; 3. Diethylene glycol (DEG) - often a by-product of PET manufacturing; 4. Factory applied stain protectants (e.g., perfluoro compounds); 5. TiO 2 -Added to carpet fibers to give them an opaque sheen.

[0017]

[0022] Recycling post-consumer carpet presents different challenges than recycling post-industrial carpet fibers. As with all post-consumer recycled materials, there is inherent variability because the materials are collected from different manufacturers, produced at different times, and used in different parts of the country. Also, the collection process introduces the potential for cross-contamination from other carpet types, such as nylon or polytrimethylene terephthalate (PTT) carpet. CaCO 3 Another complication is the need to remove the PET facing fibers from the carpet backing, as contamination can be introduced from the non-fiber portions of the carpet, such as PET, polypropylene (PP), and adhesives. In addition to this variability in feedstock, there are additional contaminants that are introduced during the life of the carpet, such as cleaners, salt, sand, dirt, and other waste materials. The variability and contamination of post-consumer carpet fibers can render this material unusable for any type of mechanical recycling and can pose problems for methanolysis and monomer purification. A list of contaminants that may be present in post-consumer carpet fibers is given below: 1. Cleaning agents (e.g., surfactants, solvents, etc.); 2. Consumer applied stain protectants (e.g., silicones); 3. Professionally applied stain protectants (e.g., perfluorinated compounds); 4. Road salt (e.g., NaCl, MgCl 2 ); 5. Sand (e.g., SiO 2 ); 6. Earth; 7. Human skin, hair, and body fluids; 8. Pet urine and feces; 9. Food waste; 10. Nylon 6 or Nylon 66 and monomer components; 11. PTT and monomeric components (e.g., 1,3-propanediol); 12. Polypropylene (carpet backing material); 13. CaCO 3 (Carpet backing material); and 14. Adhesives (e.g., styrene-butadiene rubber, low melt PET, polyvinyl butyral (PVB), etc.).

[0018]

[0023] The waste carpet fiber compositions useful in the methods of the present invention may include post-consumer carpet fibers, post-industrial carpet fibers, or both.

[0024] In various embodiments, the waste carpet fiber composition comprises at least 5 wt%, at least 10 wt%, at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 35 wt%, at least 40 wt%, at least 45 wt%, at least 50 wt%, at least 55 wt%, at least 60 wt%, at least 65 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 100 wt%, at least 100 wt%, at least 15 ... In one embodiment, the carpet fiber optics may comprise 75% by weight, at least 80% by weight, at least 85% by weight, or at least 90% by weight, and / or up to 100% by weight, up to 99% by weight, up to 95% by weight, up to 90% by weight, up to 85% by weight, up to 80% by weight, up to 75% by weight, up to 70% by weight, up to 65% by weight, up to 60% by weight, up to 55% by weight, up to 50% by weight, up to 45% by weight, up to 40% by weight, or up to 35% by weight of post-consumer carpet fibers.

[0019]

[0025] In various embodiments, the waste carpet fiber composition comprises at least 5 wt%, at least 10 wt%, at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 35 wt%, at least 40 wt%, at least 45 wt%, at least 50 wt%, at least 55 wt%, at least 60 wt%, at least 65 wt%, at least 70 wt%, at least % or less, and / or up to 100wt%, up to 99wt%, up to 95wt%, up to 90wt%, up to 85wt%, up to 80wt%, up to 75wt%, up to 70wt%, up to 65wt%, up to 60wt%, up to 55wt%, up to 50wt%, up to 45wt%, up to 40wt%, or up to 35wt% of post-industrial carpet fibers.

[0020]

[0026] Waste carpet fiber compositions useful in the methods of the present invention typically contain at least 75 wt%, at least 80 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt%, at least 99 wt%, or 100 wt% PET, based on the total weight of the composition.

[0021]

[0027] When the waste carpet fiber composition includes post-consumer carpet fibers, the PET content of the waste carpet fiber composition may desirably be at least 75 wt%, at least 80 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt%, at least 99 wt%, or 100 wt%, based on the total weight of the composition.

[0022]

[0028] When the waste carpet fiber composition includes post-industrial carpet fibers, the PET content of the waste carpet fiber composition may desirably be at least 90 wt%, at least 95 wt%, at least 99 wt%, or 100 wt%, based on the total weight of the composition.

[0023]

[0029] The PET content can be calculated using the total dicarboxylic acid content in the waste carpet fiber composition. For example, PET may contain some amount of isophthalic acid (IPA) residue in addition to terephthalic acid (TPA) residue, so the PET content can be calculated based on the total content of TPA and IPA.

[0024]

[0030] The waste carpet fiber compositions useful in the methods of the present invention may contain up to 6 wt%, up to 5 wt%, up to 4 wt%, up to 3 wt%, up to 2 wt%, up to 1 wt%, up to 0.5 wt%, up to 0.1 wt%, up to 0.01 wt%, or 0 wt% ash, based on the total weight of the composition.

[0025]

[0031] "Ash" refers to the inorganic residue of the waste carpet fiber composition after it has been subjected to a decomposition ashing procedure, which involves heating a sample of the waste carpet fiber composition at 800°C in air for 3 hours. The residue may come from antiblocking agents, fillers, reinforcing agents, catalysts, colorants, etc., in the waste carpet fiber composition.

[0026]

[0032] In various embodiments, the waste carpet fiber composition may comprise an ash content of greater than 0 up to 6 wt%, greater than 0 up to 5 wt%, greater than 0 up to 4 wt%, greater than 0 up to 3 wt%, greater than 0 up to 2 wt%, greater than 0 up to 1 wt%, greater than 0 up to 0.5 wt%, greater than 0 up to 0.1 wt%, or greater than 0 up to 0.01 wt%, based on the total weight of the composition.

[0027]

[0033] When the waste carpet fiber composition includes post-consumer carpet fibers, the waste carpet fiber composition desirably has an ash content of up to 6 wt%, up to 5 wt%, up to 4 wt%, up to 3 wt%, up to 2 wt%, up to 1 wt%, up to 0.5 wt%, up to 0.1 wt%, up to 0.01 wt%, or 0 wt%, based on the total weight of the composition. In any case, the ash content may be greater than 0.

[0028]

[0034] When the waste carpet fiber composition includes post-industrial carpet fibers, the waste carpet fiber composition desirably has an ash content of up to 1 wt%, up to 0.5 wt%, up to 0.1 wt%, up to 0.01 wt%, or 0 wt%, based on the total weight of the composition. In any case, the ash content may be greater than 0.

[0029]

[0035] The waste carpet fiber compositions useful in the methods of the present invention may contain up to 10 wt%, up to 3 wt%, or 0 wt% residual isophthalic acid, based on the total weight of the waste carpet fiber composition.

[0030]

[0036] When the waste carpet fiber composition includes post-consumer carpet fibers, the isophthalic acid residual content of the waste carpet fiber composition may desirably be up to 10 wt%, up to 3 wt%, or 0 wt%, based on the total weight of the waste carpet fiber composition.

[0031]

[0037] When the waste carpet fiber composition includes post-industrial carpet fibers, the isophthalic acid residual content of the waste carpet fiber composition may also preferably be up to 10 wt%, up to 3 wt%, or 0 wt%, based on the total weight of the waste carpet fiber composition.

[0032]

[0038] The waste carpet fiber compositions useful in the methods of the present invention may contain up to 15 wt%, up to 5 wt%, or 0 wt% 1,3-propanediol residuals, based on the total weight of the waste carpet fiber composition.

[0033]

[0039] When the waste carpet fiber composition includes post-consumer carpet fibers, the 1,3-propanediol residual content of the waste carpet fiber composition may desirably be up to 15 wt%, up to 5 wt%, or 0 wt%, based on the total weight of the waste carpet fiber composition.

[0034]

[0040] When the waste carpet fiber composition includes post-industrial carpet fibers, the 1,3-propanediol residual content of the waste carpet fiber composition may also desirably be up to 15 wt%, up to 5 wt%, or 0 wt%, based on the total weight of the waste carpet fiber composition.

[0035]

[0041] Waste carpet fiber compositions useful in the methods of the present invention may contain up to 5000 ppm, up to 1500 ppm, up to 200 ppm, up to 80 ppm, or 0 ppm nitrogen, based on the total weight of the waste carpet fiber composition.

[0036]

[0042] When the waste carpet fiber composition includes post-consumer carpet fibers, the nitrogen content of the waste carpet fiber composition may desirably be up to 5000 ppm, up to 1500 ppm, up to 200 ppm, up to 80 ppm, or 0 ppm, based on the total weight of the waste carpet fiber composition.

[0037]

[0043] When the waste carpet fiber composition includes post-industrial carpet fibers, the nitrogen content of the waste carpet fiber composition may also desirably be up to 200 ppm, up to 80 ppm, or 0 ppm, based on the total weight of the waste carpet fiber composition.

[0038]

[0044] The waste carpet fiber compositions useful in the methods of the present invention may include waste carpet fibers that have not been densified.

[0045] Alternatively, the waste carpet fiber compositions useful in the methods of the present invention may comprise waste carpet fibers that have been densified, such as by melt extrusion (e.g., pelletizing), molding (e.g., briquetting), or agglomeration (e.g., by externally applied heat, heat generated by frictional forces, or by the addition of one or more adhesives). As used herein, the term "densified" refers to a bulk density of at least 0.20 g / cm. 3 The term refers to a material that has undergone one or more processing steps to increase its quality.

[0039]

[0046] In one or more embodiments, the densified waste carpet fibers have a bulk density of at least 0.22, at least 0.25, at least 0.27, at least 0.30, at least 0.32, or at least 0.35 g / cm. 3 , and / or 0.50 g / cm 3 Below, 0.47g / cm 3 Below 0.45g / cm 3 Below, 0.42g / cm 3 Below 0.40g / cm 3 or less than 0.37g / cm 3 The densified waste carpet fibers may be subjected to one or more processing steps including, for example, cutting, chopping, or other size reduction, separation of two or more different types of components, heating (and optionally melting), and pelletizing or solidifying.

[0040]

[0047] In one or more embodiments, the densified waste carpet fibers may comprise particulates, pellets, granules, agglomerates, or particles having a D90 particle size of at least 0.1, at least 0.5, at least 1, at least 1.5, at least 2, at least 2.5, at least 3, at least 3.5, at least 4, at least 4.5, or at least 5 mm, and / or 10 mm or less, 8 mm or less, 6 mm or less, 5 mm or less, 3 mm or less, 2 mm or less, 1 mm or less, or 0.5 mm or less.

[0041]

[0048] In one or more embodiments, the waste carpet fiber composition may comprise at least 80, at least 85, at least 90, at least 95, at least 98, at least 99, at least 99.5, or at least 99.9 wt% waste carpet fiber, based on the total weight of the waste carpet fiber composition.

[0042]

[0049] In one or more embodiments, the waste carpet fiber composition may comprise at least 80, at least 85, at least 90, at least 95, at least 98, at least 99, at least 99.5, or at least 99.9 wt% densified waste carpet fiber, based on the total weight of the waste carpet fiber composition.

[0043]

[0050] The waste carpet fiber composition useful in the method of the present invention may include any combination of the parameters described herein. For example, the waste carpet fiber composition may include any combination of the PET and ash content described herein; PET, ash, and / or IPA content; PET, ash, IPA, and / or 1,3-propanediol content; PET, ash, IPA, 1,3-propanediol, and / or nitrogen content.

[0044]

[0051] In various embodiments, the waste carpet fiber composition comprises post-consumer carpet fibers and, based on the total weight of the waste carpet fiber composition, comprises 75-100 wt.% PET, 0-10 wt.% IPA residue, 0-6 wt.% ash, 0-15 wt.% 1,3-propanediol residue, and 0-5000 ppm nitrogen.

[0045]

[0052] In various other embodiments, the waste carpet fiber composition comprises post-consumer carpet fibers and, based on the total weight of the waste carpet fiber composition, comprises 90-100 wt.% PET, 0-3 wt.% IPA residue, 0-3 wt.% ash, 0-5 wt.% 1,3-propanediol residue, and 0-1500 ppm nitrogen.

[0046]

[0053] In various embodiments, the waste carpet fiber composition comprises post-industrial carpet fibers and, based on the total weight of the waste carpet fiber composition, comprises 90-100 wt.% PET, 0-10 wt.% IPA residue, 0-1 wt.% ash, 0-15 wt.% 1,3-propanediol residue, and 0-200 ppm nitrogen.

[0047]

[0054] In various other embodiments, the waste carpet fiber composition comprises post-industrial carpet fibers and, based on the total weight of the waste carpet fiber composition, comprises 95-100 wt.% PET, 0-3 wt.% IPA residue, 0-0.5 wt.% ash, 0-5 wt.% 1,3-propanediol residue, and 0-80 ppm nitrogen.

[0048]

[0055] The waste carpet fiber compositions useful in the method of the present invention can be commercially obtained from waste carpet fiber reclaimers. Alternatively, in the case of post-industrial carpet fibers, they can be obtained directly from carpet manufacturers. In the case of post-consumer carpet fibers, the waste carpet fiber compositions can be obtained by removing fibers from carpet backings by various techniques such as shearing, and optionally subjecting the fibers to one or more processing techniques such as chopping, screening, settling / floating, grinding, milling, granulation, etc.

[0049] Methanol Decomposition

[0056] The method of the present invention involves providing a waste carpet fiber composition suitable for chemical recycling, and then subjecting the composition to methanolysis. During methanolysis, the waste carpet fiber composition is reacted with methanol (optionally in the presence of a transesterification catalyst) to produce a depolymerized polyester mixture comprising polyester oligomers, dimethyl terephthalate (DMT), and ethylene glycol (EG).

[0050]

[0057] Depending on the composition of the waste carpet fibers, other monomers such as 1,4-cyclohexanedimethanol (CHDM), diethylene glycol, dimethyl isophthalate, and 1,3-propanediol can also be produced.

[0051]

[0058] The process of methanolysis is well documented throughout the literature and is effective for producing DMT from PET materials. Some representative examples of PET methanolysis include those described in U.S. Patent Nos. 3,321,510, 3,776,945, 5,051,528, 5,298,530, 5,414,022, 5,432,203, 5,576,456, and 6,262,294, which are incorporated herein by reference. These examples can be used in the method of the present invention.

[0052]

[0059] One example of a suitable methanol decomposition process can be illustrated with reference to the disclosure of U.S. Pat. No. 5,298,530, which describes a method for recovering EG and DMT from scrap polyester (or in the present case, waste polyester carpet fiber). The method includes dissolving scrap polyester in an oligomer of EG and terephthalic acid (TPA) or DMT and passing superheated methanol through the mixture. The oligomer may include any low molecular weight polyester polymer of the same composition as the scrap material used as the starting component, such that the scrap polymer dissolves into the low molecular weight oligomer. DMT and EG are recovered from the methanol vapor stream exiting the depolymerization reactor.

[0053]

[0060] In the above process, scrap PET can be conveyed by a loading system to a dissolver containing terephthalate oligomers. The loading system can be any conventional system known to those skilled in the art, such as a screw feeder, an extruder, or a batch adder. The dissolver is equipped with an agitator and heating means, which can include a jacket, tracing, internal heating coils, and / or an external heat exchanger. At start-up, polyester monomers or oligomers, such as EG and / or DMT, can be introduced into the dissolver and heated to a temperature of 110°C to 305°C. For example, the temperature range can be 230°C to 290°C. The scrap PET and oligomers can be agitated in the dissolver for a time sufficient for the scrap PET to mix with the oligomers to form a start-up melt. Typically, the time required for mixing can range from 5 minutes to 60 minutes.

[0054]

[0061] The start-up melt can be passed through a strainer and transferred by a pump to the depolymerization reactor, or all or a portion of the start-up melt can be returned to the dissolver, which is useful during start-up, as well as after start-up if desired, to feed molten polyester to the top of the dissolver to begin melting of the fresh polyester scrap feed.

[0055]

[0062] Superheated methanol vapor can then be passed through the contents of the depolymerization reactor to heat the reactor contents to form a melt containing low molecular weight polyester oligomers, monohydric alcohol terminated oligomers, glycols, and DMT. Conventional systems, such as the methanol feed and recovery loop described in U.S. Patent No. 5,051,528, can be used to heat and feed the methanol to the reactor and recover the methanol for reuse.

[0056]

[0063] Instead of, or in addition to, superheated methanol vapor, methanol in liquid form, saturated methanol vapor, and / or supercritical methanol can be introduced into the depolymerization reactor.

[0057]

[0064] Typically, an excess of methanol is passed through the depolymerization reaction mixture. For example, a weight ratio of methanol to PET of 1.1:1 to 10:1 can be used.

[0065] A portion of the reactor melt may then be returned from the reactor to the dissolver where it reacts with and equilibrates with the molten scrap polyester chains, shortening the average chain length of the dissolver contents and thereby significantly reducing the viscosity. Thus, the initial oligomer introduction into the dissolver is usually required just at start-up. After start-up, the process of the present invention can be run continuously without further introduction of external polyester chain shortening material to the dissolver. The dissolver can be run at atmospheric pressure with almost no methanol present, thereby greatly reducing the risk of methanol leakage and improving the safety of the process. Simple solids handling equipment such as rotary airlocks can be employed since more elaborate sealing equipment is not required. The viscosity of the melt transferred from the dissolver is low enough that inexpensive pumping means can be used and the reactor can be operated at pressures significantly above atmospheric pressure.

[0058]

[0066] The return of the reactor melt from the depolymerization reactor to the dissolver is determined by the flow rates of material into and out of the dissolver, and can be adjusted to a rate selected based on the desired ratio of molten reactor contents to molten scrap polyester in the dissolver. For example, the ratio of reactor melt to scrap polyester can be 5-90 wt%. In another example, the ratio of reactor melt to scrap polyester can be 20-50 wt%. If desired, the recovery step (described below) can be omitted while the reactor melt is being transferred to the dissolver, e.g., during standby operation when the feed of scrap polyester to the dissolver is interrupted, during plant start-up, or while the melt in the dissolver is being brought up to an operating level.

[0059]

[0067] The depolymerization reactor can be run at a higher pressure than the dissolver, thereby eliminating the need for pumping means to transfer the reactor melt from the reactor to the dissolver. Auxiliary pumping means may be optionally provided, if desired. The operating pressure of the depolymerization reactor can be from 0 kPa gauge (0 psig) to 689.5 kPa gauge (100 psig). The reactor is typically operated at pressures from 206.8 kPa gauge (30 psig) to 344.7 kPa gauge (50 psig).

[0060]

[0068] The temperature of the melt in the depolymerization reactor is typically maintained above the boiling point of methanol at the pressure in the reactor, or above its critical temperature (about 239°C) to keep the methanol in a vapor state and easily exit the reactor. For example, the melt temperature in the depolymerization reactor can be 100°C to 320°C, 180°C to 305°C, or 250°C to 290°C.

[0061]

[0069] To facilitate depolymerization, a transesterification catalyst, such as zinc, titanium, manganese, lithium, potassium, and / or magnesium, can be added to the dissolver and / or reactor. In various embodiments, the transesterification catalyst can be a mixture of two or more catalytic metals. The catalytic metals can be introduced in the form of a salt with an anion, such as acetate, carbonate, hydroxide, oxide (especially soluble oxides), methoxide, fluoride, chloride, bromide, iodide, phosphate, sulfate, nitrate, etc.

[0062]

[0070] In one or more embodiments, the transesterification catalyst may be zinc acetate, titanium(IV) isopropoxide, lithium acetate, manganese(II) acetate, magnesium methoxide, and / or potassium carbonate.

[0063]

[0071] The catalyst can be used in the range of 0-800 parts by weight of catalytic metal per million parts by weight of solid polyester introduced into the dissolver / reactor. Other catalyst amounts can include 30-300 ppm or 30-100 ppm.

[0064]

[0072] In one or more other embodiments, the transesterification catalyst excludes tin, zinc, and / or titanium. In various embodiments, the amount of tin, zinc, and / or titanium in the depolymerization reactor melt is 200 ppm or less, 150 ppm or less, 100 ppm or less, 50 ppm or less, 25 ppm or less, 10 ppm or less, or 1 ppm or less, based on the weight of solid polyester introduced into the dissolver / reactor.

[0065]

[0073] The transesterification catalyst can also be used with a cocatalyst, such as sodium hydroxide. The cocatalyst can be used in the range of 0-800 parts by weight of cocatalyst metal per million parts by weight of solid polyester introduced into the dissolver / reactor. Other cocatalyst amounts can include 30-300 ppm or 30-100 ppm.

[0066]

[0074] To further promote the depolymerization, a glycoxide or methoxide may be added to the reaction mixture. The glycoxide or methoxide includes a glycoxide or methoxide anion and a cation, and may be selected from an alkali metal glycoxide or methoxide, an alkaline earth metal glycoxide or methoxide, a metal glycoxide or methoxide, an ammonium glycoxide or methoxide, or a combination thereof. Examples of cations include lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, aluminum, and ammonium. In various embodiments, the glycoxide or methoxide may be sodium glycoxide or methoxide, such as monosodium glycoxide. The glycoxide or methoxide may be generated by adding an alkali metal, an alkaline earth metal, or a metal to monoethylene glycol (MEG). In various embodiments, the glycoxide may be generated by adding sodium hydroxide to MEG, or the methoxide may be generated by adding sodium hydroxide to methanol.

[0067]

[0075] In various embodiments, the molar ratio of glycoxide or methoxide to methanol can range from 0.05:1 to 0.5:1, such as about 0.2:1.

[0076] In various embodiments, the molar ratio of glycoxide or methoxide to PET may range from 1:2 to 1:20, or from 1:10 to 1:15.

[0068]

[0077] In one or more embodiments, the average residence time of the waste carpet fiber composition in the reaction zone may be at least 1, 2, 5, 10, or 15 minutes, and / or no more than 12, 11, 10, 9, 8, 7, 6, 5, or 4 hours.

[0069]

[0078] In one or more embodiments, at least 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 99 wt% of the total weight of PET introduced into the methanolysis reaction zone is decomposed when it exits the zone.

[0070]

[0079] In one or more embodiments, a reactor purge stream may be continuously or periodically removed from the reaction zone. The reactor purge stream may have a boiling point higher than the boiling point of DMT.

[0071]

[0080] In one or more embodiments, the reactor purge stream may comprise at least 25, at least 30, at least 35, at least 40, at least 45, at least 50, at least 55, at least 60, at least 65, at least 70, at least 75, at least 80, at least 85, at least 90, at least 95, or at least 99 wt% DMT, based on the total weight of the stream. In one or more embodiments, the reactor purge stream may comprise no more than 25 wt%, no more than 20 wt%, no more than 15 wt%, no more than 10 wt%, no more than 5 wt%, no more than 2 wt%, or no more than 1 wt% of components having a boiling point higher than that of DMT. Additionally or alternatively, the reactor purge stream may have a melt temperature at least 5, at least 10, at least 15, at least 20, or at least 25° C. above the temperature of the reactor, and / or 50° C. or less, 45° C. or less, 40° C. or less, 35° C. or less, 30° C. or less, 25° C. or less, 20° C. or less, or 15° C. or less.

[0072]

[0081] The reactor purge stream may contain at least 100 ppm and up to 25 wt. % of one or more non-DMT solids, based on the total weight of the stream. In one or more embodiments, the total amount of non-DMT solids in the reactor purge stream is at least 150, at least 200, at least 250, at least 300, at least 350, at least 400, at least 500, at least 600, at least 700, at least 800, at least 900, at least 1000, at least 1500, at least 2000, at least 2500, at least 3000, at least 3500, at least 4000, at least 5000, at least 6000, at least 7000, at least 8000, at least 90 ...000, at least 1000, at least 1500, at least 2000, at least 2500, at least 3000, at least 4000, at least 5000, at least 100 at least 4000, at least 4500, at least 5000, at least 5500, at least 6000, at least 7000, at least 8000, at least 9000, at least 10,000, or at least 12,500 ppm, and / or 25 wt% or less, 22 wt% or less, 20 wt% or less, 18 wt% or less, 15 wt% or less, 12 wt% or less, 10 wt% or less, 8 wt% or less, 5 wt% or less, 3 wt% or less, 2 wt% or less, or 1 wt% or less.

[0073]

[0082] In one or more embodiments, the reactor purge stream comprises at least 100, at least 250, at least 500, at least 750, at least 1000, at least 1500, at least 2000, at least 2500, at least 3000, at least 3500, at least 4000, at least 4500, at least 5000, at least 5500, at least 6000, at least 6500, at least 7000, at least 7500, at least 8000, at least 8500, at least or at least 9000, at least 9500 ppm by weight, or at least 1, at least 2, at least 5, at least 8, at least 10, or at least 12 wt%, and / or a total solids content of 25 wt% or less, 22 wt% or less, 20 wt% or less, 17 wt% or less, 15 wt% or less, 12 wt% or less, 10 wt% or less, 8 wt% or less, 6 wt% or less, 5 wt% or less, 3 wt% or less, 2 wt% or less, or 1 wt% or less, or 7500 ppm or less, 5000 ppm or less, or 2500 ppm or less.

[0074]

[0083] Examples of non-DMT solids can include, but are not limited to, non-volatile catalytic compounds. In one or more embodiments, the reactor purge stream may contain at least 100, at least 250, at least 500, at least 750, at least 1000, at least 1500, at least 2000, at least 2500, at least 3000, at least 3500, at least 4000, at least 4500, at least 5000, at least 7500, at least 10,000, or at least 12,500 ppm, and / or no more than 60,000 ppm, no more than 50,000 ppm, no more than 40,000 ppm, no more than 35,000 ppm, no more than 30,000 ppm, no more than 25,000 ppm, no more than 20,000 ppm, no more than 15,000 ppm, or no more than 10,000 ppm of non-volatile catalytic metals. Examples of non-volatile catalytic metals include, but are not limited to, titanium, zinc, manganese, methoxide compounds, alkali metals, alkaline earth metals, tin, residual esterification or transesterification catalysts, residual polycondensation catalysts, aluminum, depolymerization catalysts, and combinations thereof.

[0075]

[0084] A vapor stream containing DMT, EG, and methanol can be removed from the depolymerization reactor. Depending on the composition of the polyester carpet fiber, other monomers (such as diethylene glycol, triethylene glycol, dimethyl isophthalate, 1,4-cyclohexanedimethanol, 1,3-propanediol, and / or methyl hydroxyethyl terephthalate) may also be present in the methanol vapor stream. In addition to being a depolymerization reactant, the methanol vapor helps remove other vapors from the reactor by acting as a carrier gas stream and by stripping other gases from the solution. The effectiveness of superheated methanol to heat the reactor contents and strip gases depends on its volumetric flow rate. Thus, the rate of depolymerization in the reactor depends on the methanol flow rate into the reactor. The methanol vapor stream exiting the depolymerization reactor can be transferred to a distillation unit to separate most of the methyl hydroxyethyl terephthalate from the vapor stream. The recovered methyl hydroxyethyl terephthalate may be transferred to a dissolver and / or reactor where it serves as a low molecular weight oligomer to reduce the average polyester chain length and to reduce the viscosity of the melt in the dissolver / reactor.

[0076]

[0085] The vapor stream can then be transferred to a second distillation unit that separates the methanol from the other vapor stream components. The methanol can be recovered for further use as described in U.S. Patent No. 5,051,528, which is incorporated herein by reference. The remaining recovered vapor stream components can be transferred to other separation units, such as distillation columns and crystallizers, where the DMT, EG, and optionally other monomers can be separated.

[0077]

[0086] The methanol decomposition process can be carried out as a semi-continuous or continuous process. After the initial start-up, it is not necessary to feed the above-mentioned start-up oligomers to the process from an external source, i.e., the melt fed to the dissolver from the depolymerization reactor and / or the methylhydroxyethyl terephthalate fed to the dissolver from the optional distillation of the methanol vapor stream can sufficiently shorten the average polyester chain length and reduce the melt viscosity in the dissolver.

[0078]

[0087] Most of the contaminants in the scrap or waste PET carpet fiber composition can be removed from the melt in the dissolver before the melt is introduced into the depolymerization reactor. For example, inorganic contaminants such as metals or sand can be removed by straining the melt from the dissolver. Polyolefins such as polyethylene, polystyrene, and polypropylene and other contaminants tend to float to the top of the melt in the dissolver and can be passed through a separator and removed, and the polyolefin-free melt can be returned to the dissolver. Soluble contaminants can accumulate in the melt in the dissolver and can be purged with oligomers from the depolymerization reactor in the usual manner. Alternatively, they can be removed from the melt that flows back from the reactor to the dissolver.

[0079]

[0088] In addition to or in combination with waste carpet fiber compositions, the methanolysis reaction step according to the present invention can accept a wide array of other PET-containing waste materials, such as textiles, bottle flakes, reclaimer waste, or combinations thereof, to produce recycled monomer feedstock for repolymerization into polyester.

[0080]

[0089] The rate at which the methanolysis reaction proceeds can be assessed by calculating the molar ratio of MeOH consumed to DMT produced (MeOH / DMT molar ratio) over time. Lower values ​​indicate less methanol was used to produce one mole of DMT, and are therefore more efficient and desirable. In various embodiments, the reaction steps of the present invention can provide MeOH / DMT molar ratios of 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, or 4 or less throughout the reaction period. The denominator of the MeOH / DMT molar ratio includes DMT derivatives such as methyl hydroxyethyl terephthalate (MHET).

[0081] Recovery and purification

[0090] The DMT and EG in the depolymerized polyester mixture produced during the methanolysis reaction can be recovered and purified by crystallization, filtration, distillation, or a combination thereof. Additional techniques for recovering and purifying the monomers include adsorption (e.g., with activated carbon, charcoal, silica gel, etc.), anion or cation exchange, and / or liquid extraction. Other monomers that may be present in the waste carpet fiber composition, such as dimethyl isophthalate, 1,4-cyclohexanedimethanol, dimethyl 1,4-cyclohexanedicarboxylate, 1,3-propanediol, diethylene glycol, etc., can also be recovered by the techniques mentioned above and repolymerized into polyester.

[0082]

[0091] In various embodiments, the methanol vapor stream exiting the depolymerization reactor may include a gas phase stream containing DMT, EG, methanol, and small amounts of impurities. The amount of impurities in the methanol vapor stream depends on the relative volatility of the impurities and DMT. If the volatility of the impurities is low enough, some of the impurities will be carried out of the reactor in significant concentrations.

[0083]

[0092] In various embodiments, the methanol vapor stream can be cooled and condensed to form a condensate containing DMT dissolved in methanol. The temperature of this stream can then be reduced and a portion of the methanol removed to precipitate the dissolved DMT as crystals. The solids can then be separated by a suitable separation method, such as filtration and / or centrifugation. The crystals can then be washed to remove most of the EG and other contaminants and can be further separated and purified. The crude DMT can then be distilled to obtain a polymer grade material suitable for the preparation of polyesters similar or equivalent to those prepared from virgin materials.

[0084]

[0093] Other methods for separating and purifying DMT and various glycol components from polyester depolymerization products are described, for example, in U.S. Pat. Nos. 5,364,985, 5,391,263, 5,498,749, 5,712,410, 5,912,275 (Dupont), 6,706,843 (Teijin), 7,078,440, and 10,808,096, all of which are incorporated herein by reference.

[0085]

[0094] Briefly, in various embodiments, to facilitate recovery of methanol, an azeotroping agent, such as methyl benzoate and / or methyl p-toluate, can be added to the mixture containing methanol and / or EG following the methanol decomposition reactor to facilitate separation of the methanol and / or EG from the DMT.

[0086]

[0095] If solid foreign matter is present in the reaction mixture, (A) a portion of the solid foreign matter floating on the surface of the mixture can be removed by flotation separation, (B) a portion of the remaining solid foreign matter that did not float to the surface can be removed by solid / liquid separation, (C) a portion from step (B) can be distilled and concentrated to recover distilled EG, (D) the distillation residue from step (C) can be mixed with a transesterification catalyst and methanol to cause a transesterification reaction between the distillation residue and methanol to produce DMT and EG, the reaction mixture can then be subjected to a recrystallization process and then centrifugation to separate the reaction mixture into a DMT cake and a mixed solution, the cake can be purified by distillation to recover high purity distilled DMT, (E) the mixed solution from step (D) can be subjected to a distillation process to recover distilled methanol, and (F) the distillation residue from step (E) can be subjected to a distillation process to recover distilled EG.

[0087]

[0096] Foreign matter may include polyesters other than PET, polyvinyl chloride, polyvinylidene chloride, polyolefins, polystyrene, polyamides, polycarbonates, polyurethanes, polylactic acid, acrylics, rayon, acetates, polyvinyl alcohol, natural plant fibers, natural animal fibers, metals, pigments, oils, inorganic compounds, sand, paper, wood, glass, asbestos, carbon black, dyes, and / or insulating materials.

[0088]

[0097] Polyesters other than PET may include copolymerized PET, polyethylene naphthalate, polytrimethylene terephthalate, and / or polybutylene terephthalate.

[0098] The foreign polyolefin may include polyethylene and / or polypropylene.

[0089]

[0099] The EG recovered in step (C) can be recycled to step (A).

[0090] Chemical recycling mixture of waste carpet fibers

[0100] In another aspect, the present invention provides a mixture for chemical recycling of waste carpet fibers, the mixture comprising: (a) a waste carpet fiber composition comprising at least 75 wt. % polyethylene terephthalate (PET) and no more than 6 wt. % ash; (b) Methanol comprising the reaction product of The weight percentages are based on the total weight of the waste carpet fiber composition.

[0091]

[0101] The waste carpet fiber composition in the mixture may have any of the characteristics / parameters described herein.

[0102] The methanol may be in liquid or vapor form, or both.

[0092]

[0103] In one or more embodiments, the methanol may be a saturated vapor.

[0104] In one or more embodiments, the methanol may be superheated or supercritical.

[0093]

[0105] In one or more embodiments, the methanol may be superheated vapor.

[0106] The mixture may have a mass ratio of methanol to PET of 1.1:1 to 10:1.

[0107] The mixture may also include other PET-containing waste materials, such as textiles, bottle flakes, reclaimer waste, or combinations thereof.

[0094]

[0108] In one or more embodiments, the mixture includes up to 95, up to 90, up to 85, up to 80, up to 75, up to 60, up to 50, up to 40, up to 30, up to 20, up to 10, up to 5, or up to 1 wt % other PET-containing waste, based on the total weight of the mixture.

[0095]

[0109] The mixture may include a transesterification catalyst.

[0110] Examples of transesterification catalysts include zinc acetate, lithium acetate, manganese(II) acetate, titanium(IV) isopropoxide, magnesium methoxide, and potassium carbonate.

[0096]

[0111] In one or more embodiments, the mixture comprises from 0 to 800 ppm, from 30 to 300 ppm, or from 30 to 100 ppm of transesterification catalyst, based on the total weight of the mixture.

[0097]

[0112] The mixture may further include a transesterification cocatalyst.

[0113] An example of a transesterification cocatalyst is sodium hydroxide.

[0114] In one or more embodiments, the mixture comprises from 0 to 800 ppm, from 30 to 300 ppm, or from 30 to 100 ppm of transesterification co-catalyst, based on the total weight of the mixture.

[0098]

[0115] The mixture may further include dimethyl terephthalate, an oligomer, or both.

[0116] The mixture may also include methoxy 2-hydroxyethyl terephthalate; bis(2-hydroxyethyl) terephthalate; diethylene glycol; dimethyl isophthalate; residual catalytic metals from PET, such as antimony, titanium, aluminum, etc.; dyes; colorants, inert solids, and / or dirt from the PET supply.

[0099] Method for preparing recycled polyester

[0117] In yet another aspect, the present invention provides a method for preparing recycled polyester. In one variation, the method includes: preparing recycled polyester using the purified EG and / or DMT obtained according to the present invention; Includes.

[0100]

[0118] In another variation, the method comprises: reacting the purified DMT obtained according to the present invention with water to form recycled terephthalic acid (rTPA); preparing recycled polyester using rTPA and optionally purified EG obtained according to the present invention; Includes.

[0101]

[0119] In yet another variation, the method comprises: reacting the purified DMT obtained according to the present invention with virgin EG, purified EG also obtained according to the present invention, or both, to form bis(2-hydroxyethyl) terephthalate (BHET) or an oligomer thereof; polycondensing BHET or its oligomers to form recycled PET; Includes.

[0102]

[0120] Various methods are known for preparing polyesters from EG, DMT, or both. For example, DMT can be reacted with EG to produce an esterification product. The esterification product is then polycondensed at reduced pressure in the presence of a polycondensation catalyst to obtain PET.

[0103] General Provisions

[0121] For the avoidance of any doubt, the present invention includes, expressly contemplates and discloses, any and all combinations of the embodiments, features, properties, parameters, and / or ranges set forth herein, i.e., the subject matter of the present invention may be defined by any combination of the embodiments, features, properties, parameters, and / or ranges set forth herein.

[0104]

[0122] It is contemplated that any component, ingredient, or step not specifically named or identified as part of the present invention may be explicitly excluded.

[0123] Any process / method, apparatus, compound, composition, embodiment, or component of the invention may be modified by the transitional terms "comprising," "consisting essentially of," or "consisting of," or variations of these terms.

[0105]

[0124] As used herein, the indefinite articles "a" and "an" mean one or more, unless the context clearly indicates otherwise. Similarly, the singular form of a noun includes the plural and vice versa, unless the context clearly indicates otherwise.

[0106]

[0125] Although efforts have been made to ensure accuracy, the numerical values ​​and ranges set forth herein can be considered approximate. These values ​​and ranges may vary from the stated numbers depending on the desired properties sought to be obtained by the present disclosure as well as variations resulting from standard deviations found in measurement techniques. Moreover, the ranges set forth herein are intended and specifically contemplated to include all subranges and values ​​within the stated ranges. For example, a range of 50-100 is intended to include all values ​​within the range, including subranges such as 60-90, 70-80, etc.

[0107]

[0126] Any two numbers of the same property or parameter reported in the examples can define a range, and these numbers can be rounded to the nearest four decimal places, three decimal places, two decimal places, one decimal place, one digit, ten digit, or hundred digit to define the range.

[0108]

[0127] The contents of all documents cited herein, including patents as well as non-patent literature, are incorporated herein by reference in their entirety. To the extent that any incorporated subject matter conflicts with any disclosure herein, the disclosure herein shall take precedence over the incorporated content.

[0109]

[0128] The present invention can be further illustrated by the following examples, which are included for illustrative purposes only and are not intended to limit the scope of the invention. EXAMPLES

[0110] Example 1 feedstock

[0129] Various carpet fiber feedstocks were analyzed for PET content (calculated using IPA and TPA), ash content, 1,3-propanediol, nitrogen, and metals. The control sample (Control) was a high-grade colored rPET flake suitable for mechanical recycling, refined in a PET reclaimer. Other samples were post-industrial (PI) carpet fibers (Samples A, D, E, F), post-consumer (PC) carpet fibers (Samples B, C, H-O), and a combination of post-industrial carpet and carpet pad (Sample G). For laboratory evaluation, all samples were densified by either melt extrusion or agglomeration.

[0111]

[0130] To determine the TPA and IPA content, the feedstock was analyzed by hydrolysis liquid chromatography as described in [Anal. Chem. 1991, 63, pp. 1251-1256]. This test has an error limit of ±3%. To calculate %PET and to correct for water added during the hydrolysis procedure, the sum of %TPA and %IPA (if measured) was divided by 0.864. If IPA was not measured, the value of %IPA was assumed to be 0.

[0112]

[0131] To determine the ash content, 1 g of sample was heated at 800°C in air for 3 h and then analyzed gravimetrically.

[0132] To quantitatively determine total nitrogen, samples were ground and measured by chemiluminescence using an NSX-2100H trace elemental analyzer.

[0113]

[0133] Propanediol was determined by hydrolysis gas chromatography. Samples were prepared for analysis by using hydrolysis reaction and silylation. Sample solutions were chromatographed on a DB-5 column using split injection and flame ionization detection. Weight percent concentrations of sample components were calculated from integrated chromatograms using the internal standard quantification method.

[0114]

[0134] Other metals, halogens, and nonmetals were qualitatively determined by X-ray fluorescence on a Malvern / PANalytical Zetium XRF using the Omnian software package.

[0115]

[0135] The results are shown in Table 1.

[0116] [Table 1-1]

[0117] [Table 1-2]

[0118] Example 2 Methanol Decomposition Reaction and Purification in the Laboratory

[0136] The samples from Example 1 were screened in a laboratory-scale methanol decomposition reactor and monomer purification system as shown in FIG.

[0119]

[0137] Each methanol decomposition reaction was carried out by adding the initial charges of PET carpet fiber feedstock, catalyst, and ethylene glycol to a 2 L reactor having dimensions of 11 inches deep and 4 inches in diameter. Ethylene glycol was added to aid in melting the PET feedstock in the batch laboratory scale reactor and was stripped from the reactor within the first few hours of the procedure.

[0120]

[0138] The reactor was heated to 260°C to form a melt, and then the melt was sparged with superheated methanol at 305°C at a rate of 10 mL / min. The content level in the reactor was checked every hour. When the level dropped below 7 inches, 100 g of PET carpet fiber feedstock and the appropriate level of catalyst were added to the reactor. The initial charge and subsequent charge charges were recorded every 8 hours and reported in Table 2. The crude products of DMT, EG, and MeOH were collected in a receiving flask / tank for purification.

[0121]

[0139] For purification, the product was crystallized in a stirred tank, and then the crystallized product was filtered. The filter cake was then purified by batch column distillation to produce purified DMT.

[0140] Purified ethylene glycol can be produced by first removing methanol from the filtrate in a methanol stripping column, followed by purification by column distillation.

[0122] [Table 2-1]

[0123] [Table 2-2]

[0124] [Table 2-3]

[0125] Speed ​​Data

[0141] The rate at which the reaction proceeded was assessed by calculating the molar ratio of MeOH / DMT at each time point and is shown in Table 3. Higher values ​​indicate more methanol was used to produce one mole of DMT and are therefore less desirable. The amount of methanol used was calculated from the rate of methanol addition and the time that methanol was sparged into the reactor (Table 2). The amount of DMT produced was calculated by weighing the product in the receiving tank and quantifying the DMT concentration in the product using gas and liquid chromatography.

[0126] [Table 3]

[0127]

[0142] The rate data from Table 3 are shown graphically in Figures 2 and 3. MeOH / DMT is used as a proxy for reaction rate, where lower values ​​of MeOH / DMT indicate fewer moles of MeOH required to produce 1 mole of DMT.

[0128]

[0143] As seen in Figure 2, higher PET content in the feedstock correlated with lower MeOH / DMT values. Some feedstocks, especially those containing post-consumer carpet fibers, showed a correlation where lower PET content resulted in higher ash content and therefore higher MeOH / DMT values ​​due to the way the samples were prepared. For example, comparing the three post-consumer samples (B, C, and D), sample D had the lowest PET% (76.5 wt%) and highest ash% (6.92 wt%) and proceeded with the highest MeOH / DMT value. Sample B had intermediate levels of PET% and ash% (89.7 wt% and 4.4 wt%, respectively) and proceeded with an intermediate MeOH / DMT rate. Sample C had the highest PET% (94.2 wt%) and lowest ash% (1.9 wt%) and proceeded with the lowest MeOH / DMT value. Also, feedstocks with higher ash content tended to slow down over time as the inorganic content filled the reactor with inert material.

[0129]

[0144] Sample A, the post-industrial carpet fiber sample, had the lowest level of % ash (0.18 wt%) and the highest % PET (100.7 wt%). This feedstock had very similar % PET and % ash to the control sample, and therefore very similar kinetics.

[0130]

[0145] Figures 4 and 5 are graphs comparing the median MeOH / DMT values ​​for the control and samples A-D with the feedstock properties PET% and Ash%, respectively. As can be seen from these graphs, the MeOH / DMT values ​​were surprisingly not a linear function of either PET% or Ash%. The median MeOH / DMT values ​​were calculated using the results from time points 24-64 hours (time points 8 and 16 hours were omitted). The initial time points, 8 hours, and 16 hours, were often noisy due to lack of equilibrium in the reaction.

[0131]

[0146] Figure 3 shows the kinetic data for the control sample, sample B, and various mixtures of the two. The trends observed in Figure 2 were carried over to Figure 3.

[0147] Additionally, as seen in Figure 3, the sample diluted to 15% surprisingly performed nearly identically to the sample diluted to 25%. These results suggest a non-linear response to PET% in the carpet fiber feedstock. Additionally, it was surprising to find that, in general, pure DMT was obtained from carpet fiber samples that contained all of the impurities listed above.

[0132] Purified DMT

[0148] The DMT from each carpet sample was isolated from the reactants in the receiving flask and then purified by crystallization, filtration, and distillation as described above. The impurities in the DMT after distillation are reported in Table 4. The total assay of DMT was determined by gas chromatography and the metals present were detected by X-ray fluorescence. Portions of the samples were collected as two fractions from the distillation.

[0133]

[0149] For comparison, commercially available virgin DMT (denoted as distilled DMT) was redistilled in the same manner as the methanol cracking feedstock. The impurities after distillation are also reported in Table 4.

[0150] In Table 4, MHET is methyl hydroxyethyl terephthalate, MHT is monohydroxyethyl terephthalate, BHET is bis(hydroxyethyl) terephthalate, and DMI is dimethyl isophthalate.

[0134] [Table 4]

[0135] Example 3 Copolyester Synthesis

[0151] A portion of the purified recycled DMT (rDMT) from Example 2 was screened for suitability for use in producing copolyesters by synthesizing an amorphous copolyester with 2,2,4,4-tetramethyl-1,3-cyclobutenediol (TMCD) and 1,4-cyclohexanedimethanol (CHDM). All copolyesters were produced using the second fraction from the batch distillation described above. rDMT (77.68 g), CHDM (38.05 g), and a TMCD / MeOH solution (35 wt% TMCD, 67.11 g solution) were weighed into a 500 mL one-neck flask. To the monomers was added a catalyst solution in n-butanol containing phosphorus and tin compounds to a final catalyst concentration of 125 ppm Sn and 8 ppm P. The flask was equipped with a motorized stirring system, a side-arm condenser, a condensate receiving flask, a dry ice-acetone trap, and an inert (N 2 The flask was equipped with a manifold to achieve a vacuum atmosphere and a pressure gauge. Heating of the flask was achieved by lowering it into a bath of molten metal in contact with a heating mantle. An automated program was used to control the temperature, pressure, and stirring rate throughout the reaction.

[0136]

[0152] Atmospheric pressure N 2The flask was gradually heated under vacuum from 220° C. to 245° C. over 25 minutes and then held at 245° C. for 40 minutes. The pressure was then reduced to 250 torr and the temperature increased to 265° C. over 18 minutes. The pressure was then reduced to 1.5 torr and the temperature increased to 277° C. over 8 minutes and then held there for 37 minutes. After this sequence was completed, the flask was returned to atmospheric conditions and the polymer was removed for analysis.

[0137]

[0153] The properties of the resulting copolyester were measured and are reported in Table 5.

[0138] [Table 5]

[0139]

[0154] In Table 5, the rPET control, Sample A (post-industrial carpet fiber), and Sample B (post-consumer carpet fiber) polymers were synthesized from rDMT produced by lab methanolysis and purification. As noted above, the distilled DMT control was commercially available virgin DMT that was redistilled by the same means as the methanolysis feedstock.

[0140]

[0155] As can be seen in Table 5, all polymers had similar IV and end group composition, indicating that the rDMT samples produced by methanolysis were of sufficient purity to produce commercial grade copolyesters. The yellowness and haze of the base were measured because impurity concentrations too small to be measured can often cause quality issues, and therefore these values ​​are indicative of the ability of rDMT to make high quality copolyesters. Since the rPET control and sample A and B polymers were both within reasonable ranges of the distilled DMT control polymer, the rDMT obtained by methanolysis of waste PET carpet fibers can be considered for commercial production of high quality copolyesters.

[0141]

[0156] The invention has been described in detail with particular reference to certain embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

[0157] One aspect of the present invention is a mixture for chemical recycling of waste carpet fibers, the mixture comprising: (a) a waste carpet fiber composition comprising at least 75 wt. % polyethylene terephthalate (PET) and no more than 6 wt. % ash; (b) Methanol comprising the reaction product of The weight percentages are based on the total weight of the waste carpet fiber composition.

[0142]

[0158] One embodiment of this aspect is one in which the waste carpet fiber composition comprises at least 90 wt%, at least 95 wt%, or 100 wt% PET.

[0159] One embodiment of this aspect and the previous embodiment is one in which the waste carpet fiber composition comprises 3 wt.% or less, 1 wt.% or less, 0.5 wt.% or less, or 0 wt.% ash.

[0143]

[0160] In one embodiment of this aspect and the previous embodiments, the waste carpet fiber composition comprises an ash content of greater than 0 to 6 wt%, greater than 0 to 3 wt%, greater than 0 to 1 wt%, or greater than 0 to 0.5 wt%.

[0144]

[0161] One embodiment of this aspect and the previous embodiments is one in which the waste carpet fiber composition includes post-industrial carpet fibers, post-consumer carpet fibers, or both.

[0145]

[0162] One embodiment of this aspect and the previous embodiments is where the waste carpet fiber composition is at least 5 wt%, at least 10 wt%, at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 35 wt%, at least 40 wt%, at least 45 wt%, at least 50 wt%, at least 55 wt%, at least 60 wt%, at least 65 wt%, at least 70 wt%, based on the total weight of the waste carpet fiber composition. %, at least 75% by weight, at least 80% by weight, at least 85% by weight, or at least 90% by weight, and / or no more than 100% by weight, no more than 99% by weight, no more than 95% by weight, no more than 90% by weight, no more than 85% by weight, no more than 80% by weight, no more than 75% by weight, no more than 70% by weight, no more than 65% by weight, no more than 60% by weight, no more than 55% by weight, no more than 50% by weight, no more than 45% by weight, no more than 40% by weight, or no more than 35% by weight of post-consumer carpet fibers.

[0146]

[0163] One embodiment of this aspect and the previous embodiments is where the waste carpet fiber composition is at least 5 wt%, at least 10 wt%, at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 35 wt%, at least 40 wt%, at least 45 wt%, at least 50 wt%, at least 55 wt%, at least 60 wt%, at least 65 wt%, at least 70 wt%, based on the total weight of the waste carpet fiber composition. , at least 75% by weight, at least 80% by weight, at least 85% by weight, or at least 90% by weight, and / or no more than 100% by weight, no more than 99% by weight, no more than 95% by weight, no more than 90% by weight, no more than 85% by weight, no more than 80% by weight, no more than 75% by weight, no more than 70% by weight, no more than 65% by weight, no more than 60% by weight, no more than 55% by weight, no more than 50% by weight, no more than 45% by weight, no more than 40% by weight, or no more than 35% by weight of post-industrial carpet fibers.

[0147]

[0164] In one embodiment of this aspect and the previous embodiments, the waste carpet fiber composition comprises up to 10 wt%, up to 3 wt%, or 0 wt% residual isophthalic acid, based on the total weight of the waste carpet fiber composition.

[0148]

[0165] In one embodiment of this aspect and the previous embodiments, the waste carpet fiber composition comprises up to 15 wt%, up to 5 wt%, or 0 wt% residual propanediol, based on the total weight of the waste carpet fiber composition.

[0149]

[0166] An embodiment of this aspect and the previous embodiments is one in which the waste carpet fiber composition comprises up to 5000 ppm, up to 1500 ppm, up to 200 ppm, up to 80 ppm, or 0 ppm nitrogen, based on the total weight of the waste carpet fiber composition.

[0150]

[0167] In one embodiment of this aspect and the previous embodiments, the waste carpet fiber composition comprises densified waste carpet fibers.

[0168] An embodiment of this aspect and the previous embodiments further include a transesterification catalyst and optionally a transesterification cocatalyst.

[0151]

[0169] An embodiment of this aspect and the previous embodiments further include dimethyl terephthalate, an oligomer, or both.

[0170] An embodiment of this aspect, as well as the previous embodiments, further comprises the reaction product of one or more other PET-containing waste materials with methanol.

[0152]

[0171] In one embodiment of this aspect and the previous embodiments, the other PET-containing waste material includes textiles, bottle flakes, reclaimer waste, or combinations thereof.

Claims

1. A method for chemically recycling waste polyethylene terephthalate (PET) carpet fibers, comprising: providing a waste carpet fiber composition comprising at least 75 wt. % PET and no more than 6 wt. % ash; reacting the waste carpet fiber composition with methanol to produce a depolymerized polyester mixture comprising polyester oligomers, dimethyl terephthalate (DMT), and ethylene glycol (EG); recovering the DMT and the EG from the depolymerized polyester mixture; Including, The method wherein said weight percentage is based on the total weight of the waste carpet fiber composition.

2. The method of claim 1 , wherein the waste carpet fiber composition comprises at least 80 wt %, at least 85 wt %, at least 90 wt %, at least 95 wt %, or 100 wt % PET.

3. 3. The method of claim 1 or 2, wherein the waste carpet fiber composition comprises 3 wt.% or less, 1 wt.% or less, 0.5 wt.% or less, or 0 wt.% ash.

4. 3. The method of claim 1 or 2, wherein the waste carpet fiber composition comprises an ash content of greater than 0 and up to 6 wt%, greater than 0 and up to 3 wt%, greater than 0 and up to 1 wt%, or greater than 0 and up to 0.5 wt%.

5. 3. The method of claim 1 or 2, wherein the waste carpet fiber composition comprises post-industrial carpet fibers, post-consumer carpet fibers, or both.

6. The waste carpet fiber composition comprises at least 5 wt%, at least 10 wt%, at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 35 wt%, at least 40 wt%, at least 45 wt%, at least 50 wt%, at least 55 wt%, at least 60 wt%, at least 65 wt%, at least 70 wt%, at least 75 wt%, or a smaller amount of the waste carpet fiber composition, based on the total weight of the waste carpet fiber composition.

3. The method of claim 1 or 2, comprising at least 80 wt%, at least 85 wt%, or at least 90 wt%, and / or no more than 100 wt%, no more than 99 wt%, no more than 95 wt%, no more than 90 wt%, no more than 85 wt%, no more than 80 wt%, no more than 75 wt%, no more than 70 wt%, no more than 65 wt%, no more than 60 wt%, no more than 55 wt%, no more than 50 wt%, no more than 45 wt%, no more than 40 wt%, or no more than 35 wt% post-consumer carpet fibers.

7. The waste carpet fiber composition comprises at least 5 wt%, at least 10 wt%, at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 35 wt%, at least 40 wt%, at least 45 wt%, at least 50 wt%, at least 55 wt%, at least 60 wt%, at least 65 wt%, at least 70 wt%, at least 75 wt%, or less, based on the total weight of the waste carpet fiber composition.

3. The method of claim 1 or 2, wherein the carpet fiber comprises at least 80 wt%, at least 85 wt%, or at least 90 wt%, and / or no more than 100 wt%, no more than 99 wt%, no more than 95 wt%, no more than 90 wt%, no more than 85 wt%, no more than 80 wt%, no more than 75 wt%, no more than 70 wt%, no more than 65 wt%, no more than 60 wt%, no more than 55 wt%, no more than 50 wt%, no more than 45 wt%, no more than 40 wt%, or no more than 35 wt% post-industrial carpet fibers.

8. 3. The method of claim 1 or 2, wherein the waste carpet fiber composition comprises up to 10 wt%, up to 3 wt%, or 0 wt% of residual isophthalic acid, based on the total weight of the waste carpet fiber composition.

9. 3. The method of claim 1 or 2, wherein the waste carpet fiber composition comprises up to 15 wt%, up to 5 wt%, or 0 wt% of 1,3-propanediol residues, based on the total weight of the waste carpet fiber composition.

10. 3. The method of claim 1 or 2, wherein the waste carpet fiber composition comprises at most 5000 ppm, at most 1500 ppm, at most 200 ppm, at most 80 ppm, or 0 ppm nitrogen, based on the total weight of the waste carpet fiber composition.

11. The method of claim 1 or 2, wherein the waste carpet fiber composition comprises densified waste carpet fibers.

12. 3. The method of claim 1 or 2, wherein the reacting step is carried out in the presence of a transesterification catalyst and optionally a transesterification cocatalyst.

13. 3. The method of claim 1 or 2, wherein the methanol is superheated or supercritical.

14. 3. The method of claim 1 or 2, wherein the molar ratio of methanol consumed to DMT produced throughout the reaction step is 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, or 5 or less.

15. 10. The method of claim 1, wherein the DMT, the EG, or both are purified by crystallization, filtration, distillation, or a combination thereof.

16. 3. The method of claim 1 or 2, which produces virgin quality EG, virgin quality DMT, or both.

17. 3. The method of claim 1 or 2, wherein the reacting step is carried out in the presence of one or more other PET-containing waste materials.

18. 18. The method of claim 17, wherein the other PET-containing waste comprises textiles, bottle flakes, reclaimer waste, or combinations thereof.

19. 1. A method for preparing recycled polyester, comprising:

16. The method of claim 15, comprising the step of preparing recycled polyester using purified EG or DMT, or both. or reacting the purified DMT from the method of claim 15 with water to form recycled terephthalic acid (rTPA); preparing a recycled polyester using the rTPA and optionally the purified EG; A method comprising:

20. 1. A method for preparing recycled polyethylene terephthalate (rPET), comprising: reacting purified DMT from the method of claim 15 with virgin EG, the purified EG, or both to form bis(2-hydroxyethyl) terephthalate (BHET) or an oligomer thereof; polycondensing the BHET or its oligomer to form the rPET; A method comprising:

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