Method for producing oligomeric PET substrates from PET-containing waste

Abstract

Provided herein is a method for producing an oligomeric PET substrate from post-use PET-containing waste, wherein the oligomeric PET substrate is for use in an rPET manufacturing process. The method comprises the following steps: i) reacting the used PET-containing waste in the presence of ethylene glycol and water in a reaction zone; and ii) producing an oligomeric PET substrate represented by Formula I. Also provided are oligomeric PET substrates from used PET-containing waste wherein the oligomeric PET substrate is represented by Formula I, and also provided are PET polymers made from 5% to 100% rPET, the PET polymers comprising the oligomeric PET substrate.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This International PCT Patent Application claims the benefit of priority to U.S. Patent Application No. 63 / 356,045, filed on June 28, 2022. The above-referenced patent applications are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates to a method for making an oligomeric PET substrate from post-consumer PET-containing waste, an oligomeric PET substrate for use in making recycled PET, and a PET polymer made from 5%-100% recycled PET, the PET polymer comprising the oligomeric PET substrate. Background Art

[0004] PET (polyethylene terephthalate) is a synthetic material that was first produced in the mid-1940s. PET has desirable properties and processing capabilities and is therefore now widely used worldwide for packaging applications in the food and beverage industry and in industrial products and the textile industry.

[0005] Typically, PET has a petrochemical source. Purified terephthalic acid is first formed in a purified terephthalic acid manufacturing facility via aerobic catalytic oxidation of p-xylene in an acetic acid medium. This purified terephthalic acid (PTA) is then reacted with ethylene glycol to produce oligomers (and water) based on PTA, and PET polymers are formed based on the polycondensation of the oligomers of PTA. An alternative approach to preparing PET polymers is the polymerization of bishydroxyethylene terephthalate (BHET) monomers, but this approach is less favorable from a process economic perspective. BHET monomers are formed by the reaction of dimethyl terephthalate (DMT) (diester formed by terephthalic acid and methanol) with ethylene glycol, and then the BHET monomers themselves polymerize to form longer PET chains.

[0006] In the PET manufacturing process, there are three main stages in the melt phase process to prepare the PET polymer: (1) esterification, (2) prepolymerization, and (3) polymerization. When the PET resin is produced, the PET polymer enters an additional solid state (SSP) stage for further changes, which includes increasing the molecular weight of the polymer. In the initial esterification stage, PTA (or DMT) and ethylene glycol are mixed and fed to an esterification unit, where the esterification, which can be catalytic or non-catalytic, is carried out at atmospheric pressure and a temperature in the range of 270°C to 295°C. The water (or methanol in the case of DMT) and excess ethylene glycol produced by the esterification reaction are evaporated. Additives (including catalysts and toners) are usually added to the process between the esterification stage and the subsequent prepolymerization stage. In the prepolymerization stage, the product from the esterification unit is sent to a prepolymerization unit (or upflow prepolymerizer (UFPP)) and reacted with additional ethylene glycol at a temperature in the range of 270°C to 295°C and at a significantly reduced pressure to allow the degree of polymerization of the oligomers to increase. During the polymerization stage, the product from the prepolymerization stage is again subjected to low pressure and a temperature in the range of 270°C to 295°C in a horizontal polymerization unit to further allow the degree of polymerization to increase to about 80-120 repeating units. In embodiments, this is referred to as a finisher or finisher vessel. When preparing PET resins, a fourth solid state polymerization (SSP) stage involving a crystallization step is usually required, wherein the amorphous pellets produced in the melt phase process are converted into crystalline pellets and then further processed depending on the final PET product, which can be as diverse as containers / bottles for liquids and food or industrial products and resins.

[0007] However, the widespread use of PET has caused environmental problems. In particular, the popularity of disposable PET plastic bottles has led to the discarding of these bottles. Although these bottles can be recycled, the vast majority of them end up in landfills, and a considerable number of them end up in the ocean. These discarded disposable PET plastic bottles are not biodegradable and cause damage to marine ecosystems and organisms.

[0008] Obviously, it is desirable to recycle post-use PET waste, especially disposable PET plastic bottles, to reduce the amount of plastic sent to landfills. A known method is to use post-use PET waste (such as PET plastic bottles) and mechanically break it to produce post-use recycling (PCR) flakes. This PCR flake can be glycolyzed to convert it into rBHET. This rBHET can then be used in the PET manufacturing process to prepare recycled PET (rPET; it is called rPET because the oligomers it is based on are derived from post-use PET or PCR, not PTA). This avoids the need to use more PTA from petrochemical sources combined with ethylene glycol to prepare oligomers based on PTA in the vPTA process or to prepare vBHET in the vDMT process. In addition, since the amount of petrochemical products required to prepare recycled PET (rPET) is less than that of new PET (called virgin PET (vPET)), rPET has a lower carbon footprint than vPET. Therefore, rPET is attractive based on its "green" credentials, which themselves may bring economic benefits in certain jurisdictions.

[0009] However, rPET made from rBHET tends to have lower reactivity in the melt phase process and in the solid phase polymerization stage. If rBHET is used in the PET manufacturing process, the amount of rPET produced is about 20% lower than if PTA-based oligomers (i.e., short-chain PET oligomers made by esterification of purified terephthalic acid with ethylene glycol) are used. In addition, rPET made from rBHET tends to be darker (lower L*) and more yellow, mainly due to the presence of impurities in the rPET polymer. Therefore, at present, rPET manufacturing processes using rBHET (a glycolysis product of PET waste) are neither attractive nor competitive compared to vPET processes using PTA-based oligomers or vBHET.

[0010] Therefore, there is a need to produce oligomeric PET substrates that have increased reactivity and therefore increased ability to polymerize to form rPET in order to compete with the process of making vPET. Summary of the invention

[0011] The present disclosure provides, inter alia, a method for producing an oligomeric PET substrate from post-consumer PET-containing waste, wherein the oligomeric PET substrate is for use in a rPET manufacturing process, the method comprising the steps of: i) reacting the post-consumer PET-containing waste in the presence of ethylene glycol and water in a reaction zone; and ii) producing an oligomeric PET substrate represented by Formula I:

[0012]

[0013] wherein R1 is a carboxyl terminal group or a hydroxyl terminal group, R2 is a carboxyl terminal group (COOH) or a hydroxyl terminal group (OH), and n is the degree of polymerization.

[0014] In some embodiments, n is from 1 to 10, preferably from 3 to 7. In some embodiments, the oligomeric PET substrate has a CEG (acid end moles / material te number) of 300 to 1500, preferably from 500 to 1200 and more preferably from 700 to 1100. In a non-limiting embodiment, the oligomeric PET substrate has a hydroxyl end group ratio: carboxyl end group ratio in the range of 1.66 to 6.66, preferably in the range of 2.22 to 4.0.

[0015] In a non-limiting embodiment, ethylene glycol and water are added in either order or together. In a non-limiting embodiment, ethylene glycol in the range of 5 wt % to 50 wt % is added. In a non-limiting embodiment, ethylene glycol in the range of 10 wt % to 40 wt % is added. In a non-limiting embodiment, ethylene glycol in the range of 12 wt % to 18 wt % is added. In a non-limiting embodiment, water in the range of 2 wt % to 20 wt % is added. In a non-limiting embodiment, water in the range of 5 wt % to 10 wt % is added. In a non-limiting embodiment, water in the range of 6 wt % to 8 wt % is added. In a non-limiting embodiment, ethylene glycol in the range of 12 wt % to 18 wt % is added, and the water in the range of 5 wt % to 9 wt % is added.

[0016] In one non-limiting embodiment, the waste is reacted with ethylene glycol and water at a temperature between 120° C. and 300° C. In one non-limiting embodiment, the waste is reacted with ethylene glycol and water at a temperature between 150° C. and 270° C. In one non-limiting embodiment, the waste is reacted with ethylene glycol and water in a reaction zone at a pressure between 3 barg and 30 barg.

[0017] In a non-limiting embodiment, the reaction zone is before the additive is injected. In a non-limiting embodiment, the residence time of the method protected by the claims in the reaction zone is between 30 minutes and 120 minutes. In a non-limiting embodiment, the residence time is between 40 minutes and 50 minutes. In a non-limiting embodiment, the reaction is catalyzed by a catalyst that is already present in the used PET waste or is an exogenously added catalyst. In a non-limiting embodiment, the exogenously added catalyst is a conventional PET catalyst selected from antimony-containing catalysts, titanium-containing catalysts, zinc-containing catalysts, acetate-containing catalysts, manganese-containing catalysts, aluminum-containing catalysts or tin-containing catalysts. In a non-limiting embodiment, the catalyst is any one of antimony trioxide, antimony glycolate, antimony triacetate, titanium alcoholate, zinc acetate or manganese acetate. In another non-limiting embodiment, the reaction is non-catalytic.

[0018] In a non-limiting embodiment, the rPET manufacturing process is a conventional rPET manufacturing process or a modified vPET manufacturing process. In a non-limiting embodiment, the post-consumer PET-containing waste comprises PCR flakes or polyester fibers. In a non-limiting embodiment, the polyester fibers are derived from a waste polyester source such as shirts, bed linens, coats and duvet linings or municipal waste. In a non-limiting embodiment, the oligomeric PET substrate is fed directly or indirectly into the rPET manufacturing process.

[0019] Another aspect of the present invention relates to an oligomeric PET substrate produced from post-consumer PET-containing waste, wherein the oligomeric PET substrate is represented by Formula I:

[0020]

[0021] R1 is a carboxyl end group or a hydroxyl end group, R2 is a carboxyl end group or a hydroxyl end group, and n is the degree of polymerization, wherein the oligomeric PET substrate is represented by any two of the following characteristics: i) n is a degree of polymerization of 1-10; ii) CEG (acid end moles / material te number) is between 300 and 1500; or iii) a hydroxyl end group:carboxyl end group ratio is in the range of 1.66 to 6.66, and wherein the oligomeric PET substrate is used in the synthesis of a polymer comprising 5%-100% rPET.

[0022] Another aspect of the present invention relates to a PET polymer made from 5%-100% rPET, which is produced from an oligomeric PET substrate represented by Formula I and represented by any two of the following characteristics: i) a degree of polymerization of n from 1 to 10; ii) a CEG (acid end moles / material te number) between 300 and 1500; or iii) a hydroxyl end group:carboxyl end group ratio in the range of 1.66 to 6.66, and wherein the oligomeric PET substrate is used in the synthesis of a polymer comprising 5%-100% rPET.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs. Although methods and materials similar or equivalent to those described herein can be used to implement the present invention, suitable methods and materials are described below. In the event of a conflict, the present specification (including definitions) shall prevail.

[0024] In addition, the materials, methods and examples are illustrative only and are not intended to be limiting. The details of one or more embodiments of the invention are set forth in the following drawings and description. Other features, objects and advantages of the invention will become apparent from the description and drawings, as well as from the claims. According to standard practice in patent law, the word "comprising" in a claim may be replaced with "consisting essentially of" or "consisting of".

[0025] Unless otherwise specifically stated or apparent from the context, the term "about" as used herein is to be understood as being within the normal tolerance range in the art, such as within 2 standard deviations of the mean. Approximately can be understood as being within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of a specified value. Unless the context indicates otherwise, all numerical values ​​provided herein are modified with the term "about". BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the claimed process showing a reaction zone in which spent PET-containing waste is reacted with ethylene glycol and water. DETAILED DESCRIPTION

[0027] Disclosed herein are methods for producing oligomeric PET substrates from post-consumer PET-containing waste, oligomeric PET substrates for use in making rPET, and PET polymers made from 5%-100% recycled PET, the PET polymers comprising the oligomeric PET substrates. In the methods of the present invention, post-consumer PET-containing waste is mixed with ethylene glycol and water to produce the oligomeric PET substrate.

[0028] Thus, the methods disclosed herein solve the problems known in the art regarding the need to produce oligomeric PET substrates with increased reactivity, and therefore increased ability to polymerize to form rPET, in order to compete with processes for making vPET.

[0029] The term "PET" or "PET polymer" means polyethylene terephthalate.

[0030] The term "PTA" means purified terephthalic acid.

[0031] The term "vPTA" refers to PTA synthesized via aerobic catalytic oxidation of p-xylene in an acetic acid medium.

[0032] As used herein, "PTA-based oligomers" refers to short-chain PET oligomers synthesized by a process requiring the esterification of purified terephthalic acid with ethylene glycol. Purified terephthalic acid (PTA) is reacted with ethylene glycol to produce PTA-based oligomers (and water), which are polycondensed to form PET polymers. When PTA is reacted with ethylene glycol, short-chain PTA-based oligomers are formed, which are characterized by Dp (degree of polymerization or number of repeating units) and CEG (or carboxylic acid end group concentration). The degree of polymerization (Dp) is calculated from the number average molecular weight Mn by the following formula: Dp = (Mn-62) / 192, where Mn is calculated by rearranging the IV (intrinsic viscosity) following correlation: IV = 1.7e-4(Mn) 0.83 . The intrinsic viscosity (IV) of polyesters can be measured by melt viscosity techniques equivalent to ASTM D4603-96. Typically, for PTA-based oligomers formed by reacting PTA with ethylene glycol, the degree of polymerization is typically between 3 and 7, and the CEG is typically between 500 and 1200 (acid end moles / material te number). The ratio of hydroxyl end groups (HEG) to carboxyl end groups (CEG) is determined by rearrangement of the CEG measurement and the following Mn calculation: Mn = 2e6 / (CEG+HEG).

[0033] As used herein, "PET manufacturing process" refers to a facility that produces PET. Such a facility may be integrated with a PTA manufacturing process, or may be completely independent.

[0034] As used herein, "post-consumer PET-containing waste" refers to any waste stream that contains at least 10% PET waste. Thus, post-consumer PET-containing waste may contain from 10% to 100% PET. Post-consumer PET-containing waste may be municipal waste, which itself includes at least 10% PET waste, such as PET plastic bottles or PET food packaging or any post-consumer recycled PET-containing waste, such as waste polyester fibers. Sources of waste polyester fibers include items such as clothing items (shirts, pants, dresses, coats, etc.), bedding, duvet linings, or towels. "Post-consumer PET-containing waste" may also include post-consumer recycled (PCR) flakes, which are waste PET plastic bottles that have been mechanically broken into small pieces for use in the recycling process.

[0035] As used herein, "vPET" refers to virgin PET, which is PET synthesized by a process requiring the esterification of purified terephthalic acid with ethylene glycol. Purified terephthalic acid (PTA) is reacted with ethylene glycol to produce PTA-based oligomers (and water), which are polycondensed to form PET polymers. Alternatively, vPET can be formed by reacting dimethyl terephthalate (DMT), a diester formed from terephthalic acid and methanol, with ethylene glycol. BHET monomers are formed by reacting dimethyl terephthalate (DMT), a diester formed from terephthalic acid and methanol, with ethylene glycol, which then polymerizes itself to form longer PET chains.

[0036] As used herein, "rPET" refers to recycled PET, which is PET made entirely or at least in part from oligomers that have been derived from post-consumer PET-containing waste. rPET can be synthesized from 100% oligomers derived from post-consumer PET-containing waste. Alternatively, rPET can be synthesized from a combination of oligomers that include those derived from post-consumer PET-containing waste, and those from vBHET or PTA-based oligomers used to prepare vPET. In one non-limiting embodiment, rPET includes at least 5% oligomeric PET substrate derived from post-consumer PET-containing waste. In another non-limiting embodiment, rPET includes at least 50% oligomeric PET substrate derived from post-consumer PET-containing waste. In yet another non-limiting embodiment, rPET includes at least 80% oligomeric PET substrate derived from post-consumer PET-containing waste.

[0037] As used herein, "rPET manufacturing process" refers to both manufacturing processes and facilities that have been specifically designed and constructed to synthesize recycled PET (rPET), i.e., PET made from substrates including those derived from any post-consumer PET-containing waste in addition to virgin substrates (i.e., vBHET or PTA-based oligomers), and manufacturing processes and facilities that have been constructed to synthesize vPET, but which have been modified or refitted to allow for the production of rPET. The changes that need to be made to a vPET facility in order to produce rPET are generally not structurally major, but require extensive process changes.

[0038] The term "BHET" refers to bis(hydroxy)ethylene terephthalate (C 12 H 14 O6), including all structural isomers, characterized by the absence of carboxyl end groups, i.e., the carboxylic acid end group concentration (CEG) is zero. The chemical structure of the para-isomer of the BHET monomer is shown below:

[0039]

[0040] In order to produce PET, BHET reacts with itself in a polycondensation reaction to prepare a longer chain, thereby forming polyethylene terephthalate, and releasing ethylene glycol in the process. BHET, i.e., BHET monomer, is usually formed by the reaction of dimethyl terephthalate (DMT) with ethylene glycol, but it is also a minor component of the oligomer made by PTA plus ethylene glycol, i.e., a part of the oligomer molecular weight distribution. When PTA reacts with ethylene glycol, an oligomer based on short-chain PTA is formed, characterized in that Dp (degree of polymerization or the number of repeating units) and CEG (or carboxylic acid end group concentration). Typically, for oligomers based on PTA formed by reacting PTA with ethylene glycol, the degree of polymerization is usually between 3 and 7 or between 25 and 35, and CEG is usually between 500 and 1200 or between 150 and 190 (acid end mole number / material te number).

[0041] The term "vBHET" refers to native BHET, which is a BHET monomer formed by the reaction of dimethyl terephthalate (DMT) and ethylene glycol.

[0042] The term "rBHET" refers to recycled BHET, which is a BHET molecule produced by glycolysis of PET. Post-consumer PET-containing waste, such as PET plastic bottles, is mechanically broken down to produce post-consumer recycled (PCR) flakes. This PCR flake is then glycolyzed to convert it into rBHET.

[0043] As used herein, "oligomeric PET substrate" refers to a molecule according to Formula I:

[0044]

[0045] Either end of Formula I can be a carboxyl end group (COOH) or a hydroxyl end group (OH). Thus, R1 or R2 can be a carboxyl end group or a hydroxyl end group. The optimal ratio of hydroxyl end groups: carboxyl end groups (HEG:CEG) in the oligomeric PET substrate is generally between 1.66 and 6.66. Formula I polymerizes with itself in an esterification reaction, wherein the carboxyl end groups react with the hydroxyl end groups to form ester bonds, releasing water. "n" represents the degree of polymerization (Dp) or the number of repeating units of Formula I present in the oligomeric PET substrate, and can be, for example, between 3 and 7 or between 25 and 35. In addition to being characterized by the degree of polymerization (Dp), the oligomeric PET substrate is also characterized by its carboxylic acid end group concentration (referred to herein as CEG). The CEG (in units of moles of acid ends / number of material te) can be, for example, between 500 and 1200 or between 700 and 1100.

[0046] Aspects of the present disclosure provide methods for making oligomeric PET substrates from post-consumer PET-containing waste. Methods for producing rPET typically employ a process in which PET (or a waste source containing PET such as PCR flakes) is glycolyzed using, for example, ethylene glycol to produce bis(hydroxy)ethylene terephthalate (rBHET) monomers. This conventional method for producing rPET uses rBHET and polymerizes it to produce rPET. However, the rBHET has a lower reactivity than PTA-based oligomers formed by the esterification reaction of purified terephthalic acid with ethylene glycol. Therefore, when used to prepare rPET, for a similar process, rBHET produces an amount of rPET that is reduced by approximately 20% compared to the amount of vPET made using PTA-based oligomers (formed by the esterification reaction of purified terephthalic acid with ethylene glycol).

[0047] In the present disclosure, it was unexpectedly discovered that a combination of hydrolysis and glycolysis can be used to produce an oligomeric PET substrate having increased reactivity compared to rBHET (formed by glycolysis of PET-containing waste such as PCR flakes). In particular, ethylene glycol and water are added to PET-containing waste and an oligomeric PET substrate is produced. The oligomeric PET substrate is represented by Formula I:

[0048]

[0049] Oligomeric PET substrates such as represented by Formula I are shown to have increased reactivity compared to unmodified oligomers such as rBHET.

[0050] One aspect of the present invention therefore provides a method for producing an oligomeric PET substrate.

[0051] In embodiments, water and ethylene glycol are added together simultaneously to allow the corresponding reactions to occur. However, in alternative embodiments, water may be added before ethylene glycol is added, or ethylene glycol may be added before water is added. In other embodiments, water and / or ethylene glycol may be added partially, followed by more water and / or ethylene glycol, etc.

[0052] The optimal ratio of carboxyl end groups: hydroxyl end groups of the oligomeric PET substrate (Formula I) is generally between 0.15 and 0.6, and preferably between 0.25 and 0.45, as described in US 3551386 A. The degree of polymerization (Dp) of the oligomeric PET substrate (Formula I) or the number of repeating units present in the oligomeric PET substrate is generally between 3 and 7. In addition to being characterized by the degree of polymerization (Dp) and the ratio of carboxyl end groups: hydroxyl end groups, the oligomeric PET substrate is also characterized by its carboxylic acid end group concentration (referred to herein as CEG). The CEG (in units of acid end moles / material te number) is generally between 300 and 1500 and preferably between 500 and 1200 or between 700 and 1100.

[0053] It was found that the benefits associated with an optimized end group ratio come from a balance of reaction rates for esterification versus polycondensation, the relative partial pressures of the condensation products, i.e., water and ethylene glycol, and the balance of chemical equilibrium constants for esterification versus polycondensation. This balance yields a natural optimum in the range of 0.25 to 0.45, as previously described.

[0054] In a non-limiting embodiment, ethylene glycol is added in the range of 5 wt % to 50 wt %. A non-limiting example of a preferred range of ethylene glycol is in the range of 10 wt % to 40 wt %. Another non-limiting example of a preferred range of ethylene glycol is in the range of 12 wt % to 18 wt %.

[0055] In a non-limiting embodiment, water in the range of 2 wt % to 20 wt % is added. A non-limiting example of a preferred range of water is in the range of 5 wt % to 10 wt %. Another non-limiting example of a preferred range of ethylene glycol is in the range of 6 wt % to 8 wt %.

[0056] In one non-limiting embodiment, ethylene glycol and water are added together, specifically 12 wt%-18 wt% ethylene glycol is added and 5 wt% to 9 wt% water is added.

[0057] In one non-limiting embodiment, ethylene glycol and water are reacted with post-consumer PET-containing waste at a pressure between 3 barg and 30 barg. This pressure is typically generated in a reaction zone commonly referred to as an esterification unit.

[0058] In another non-limiting embodiment, the residence time for the reaction of ethylene glycol and water with post-consumer PET-containing waste in the esterification unit is between 30 minutes and 120 minutes. Another non-limiting example of a preferred range of residence time is between 40 minutes and 50 minutes.

[0059] The spent PET-containing waste is reacted with ethylene glycol and water in a reaction zone early in the PET manufacturing process and usually before the linear reactor (at this stage additives are added to the process).

[0060] The reaction can be catalytic or non-catalytic, depending on the composition of the post-consumer PET-containing waste. Due to its manufacturing process, the post-consumer PET-containing waste contains potential catalysts, because the waste PET contains catalysts. In the embodiment where the PCR flakes are used entirely as post-consumer PET-containing waste, it may not be necessary to add an exogenous catalyst, because the catalyst required for the reaction of ethylene glycol and water with the post-consumer PET-containing waste (in this embodiment, the PCR flakes) is already present. However, additional catalysts can be added if necessary. However, in the embodiment where the PCR flakes are not used entirely as post-consumer PET-containing waste, but are used in combination with polyester fibers derived from a waste polyester source (such as shirts, bed fabrics, coats and duvet linings or urban garbage), so that the content of the PET substrate is lower than when the PCR flakes are used entirely as post-consumer PET-containing waste, it is necessary to add an exogenous catalyst. The catalyst may be present in such a waste polyester source in an amount of about 150ppm to 200ppm. It is preferred to increase the amount of the catalyst to about 180ppm to 320ppm, and preferably 240ppm to 280ppm. Non-limiting examples of catalysts that can be added to the reaction include catalysts containing antimony, titanium, zinc, manganese, germanium, aluminum or tin. These can be, for example, antimony trioxide, antimony glycolate, antimony triacetate, titanium alcoholate, zinc acetate or manganese acetate. Such catalysts are added to the reaction zone commonly referred to as the esterification unit. Titanium-containing catalysts are typically added at 2ppm-100ppm, and preferably at about 10ppm. All other catalysts (except titanium-containing catalysts) are typically added at 40ppm-300ppm, preferably at about 240ppm.

[0061] In one non-limiting embodiment, the present invention is directed to a method for synthesizing an oligomeric PET substrate from post-consumer PET-containing waste, wherein the post-consumer PET-containing waste essentially comprises PCR flakes derived from waste PET plastic bottles.

[0062] In one non-limiting embodiment, the PCR flakes are reacted with ethylene glycol and water to produce an oligomeric PET substrate. In some non-limiting embodiments, the oligomeric PET substrate is used in a rPET manufacturing process that was previously designed for the synthesis of vPET but has been adapted for the production of rPET. In an alternative non-limiting embodiment, the oligomeric PET substrate is used in a rPET manufacturing process that was specifically designed from the outset for the production of rPET. The oligomeric PET substrate can be fed directly or indirectly into the rPET manufacturing process.

[0063] In a non-limiting embodiment, the post-consumer PET-containing waste can be PCR flakes or polyester fibers. The polyester fibers can be derived from waste polyester sources such as shirts, bed linens, outerwear and duvet linings or municipal waste.

[0064] Another aspect of the present invention also relates to an oligomeric PET substrate produced by or obtainable by the method as described herein. In a non-limiting embodiment, the present invention relates to an oligomeric PET substrate produced by using a PCR flake.

[0065] Another aspect of the invention also relates to PET polymers made from 5%-100% rPET and made using in the polymerization process an oligomeric PET substrate produced or obtainable by the process as described herein. The claimed PET polymers may therefore include both rPET and vPET.

[0066] Example

[0067] Aspects of the present disclosure are demonstrated through process modeling examples of continuous polymerization (CP) operations showing the predicted impact of the combination of hydrolysis and glycolysis on a PCR flake.

[0068] Additionally, the present invention has also been demonstrated on a 20 L (liter) semi-plant scale batch reactor using the following experimental protocol.

[0069] Typically, under ambient conditions, 8kg of oligomers based on PTA or 10.58kg of BHET are loaded into the reactor together with enough antimony trioxide catalysts to obtain 280ppm Sb (as element), cobalt acetate tetrahydrate is loaded to obtain 40ppm Co (as element), and triethyl phosphate is loaded to obtain 20ppm P (as element). According to the following detailed examples, other additives are added as described. The reactor is then separated under a nitrogen blanket and heat is applied. The reactor temperature setting point is then set to 260°C, and as the content temperature increases, the reactor pressure naturally increases according to volatiles (mainly water and ethylene glycol) vapor pressure. During this time and throughout the initial time period, the content is stirred with 50rpm-1200rpm. Once 260°C has been reached, the reactor is kept for a predetermined time, typically 30 minutes to 60 minutes, then the pressure is released to atmospheric pressure, and a sample of oligomeric liquid is taken out. The steam released during the decompression is condensed and collected in a receiving vessel. Once the oligomeric sample is collected, vacuum is gradually applied to the reactor in steps of 250mbara, 15 minutes per step, from 1000mbara to full vacuum, usually less than 2mbara. At the same time, the reactor temperature setting value is increased to 290°C. The reactor temperature setting value is usually reached at the end of the vacuum drop; usually after 60 minutes. The following time period is called the polycondensation time when the contents are maintained at 290°C, full vacuum and stirred at 100rpm. These conditions are maintained until the agitator torque reaches a predetermined value of 1.5Nm, which is associated with an intrinsic viscosity (iV) of 0.54dl / g, at which time the vacuum is released and the agitator is stopped to degas the resulting polymer. Throughout the process, volatiles are condensed and collected as described above. When degassing is completed, usually after 10 minutes, the molten polymer is discharged by 2bar overpressure and granulated through a cooling tank.

[0070] The resulting polymer was then subjected to various standard PET analysis procedures for metal content including IV, carboxyl end group analysis (COOH), diethylene glycol analysis (DEG), CIE color analysis, and X-ray fluorescence (XRF) analysis.

[0071] Comparative Example 1 :

[0072]

[0073]

[0074] In this case, 8.0 kg of rPET derived BHET was polymerized at 290°C. As can be seen in the table, the polymer produced had a COOH number of 30.7 microequivalents / g, an iV of 0.549 dl / g, an L color of 45.61, and a b color of 11.5. The oligomer COOH numbers quoted in the table are for the starting material. The polymerization time was 75 minutes.

[0075] Comparative Example 2 :

[0076]

[0077]

[0078] In Comparative Example 2, 8.0 kg of a commercial scale of PTA-based oligomer was polymerized at 290°C. As can be seen in the table, the polymer produced had a COOH value of 26.4 microequivalents / g, an iV of 0.541 dl / g, an L color of 63.99, and a b color of 9.89. The oligomer COOH numbers quoted in the table are for the starting material. The polymerization time was 95 minutes.

[0079] Comparative Example 3 :

[0080]

[0081]

[0082] In this case, 6.92 kg of vPTA was reacted with 3.62 kg of ethylene glycol at 246°C for nine hours. The pressure of the sealed autoclave naturally increased as esterification occurred, but was periodically vented from 9 bar to 4 bar to allow the release of water. When no further increase in pressure was observed, i.e. when esterification was complete, the vessel was cooled and the additives were charged as in the previous examples. The resulting oligomer was then polymerized at 290°C. As can be seen in the table, the COOH number of the polymer produced was 30.9 microequivalents / g, iV was 0.535 dl / g, L* color was 59.45, and b* color was 12.56. No oligomer COOH number is available for this example. The polymerization time was 75 minutes.

[0083] Embodiment 4:

[0084] parameter value unit PCR slice 5.0 kg H2O 0.38 kg EG 0.63 kg CoAc.4H2O 40 ppm TEP 20 ppm Oligomer COOH 564 Micro equivalent / g Low polymer retention temperature 259 ℃ pressure 9.0 barg time 60 min polymerization temperature 290 ℃ pressure 1.8 mbara time 90 min iV 0.582 dl / g COOH 23.2 Micro equivalent / g Sb 298 ppm P 8.6 ppm Co 18.2 ppm L 44.3 CIE b 12.62 CIE

[0085] In this case, 0.38 kg of water and 0.63 kg of ethylene glycol were added to 5.0 kg of post-consumer recycled PET flakes and maintained at 259°C for 60 minutes. During this time, the agitator torque dropped from an initial 18 Nm to 0.1 Nm, indicating that glycolysis had occurred. The oligomer was then polymerized at 290°C as in the previous examples. As can be seen in the table, the polymer produced had a COOH number of 23.2 microequivalents / g, an iV of 0.582 dl / g, an L* color of 44.3, and a b* color of 12.62. The COOH number of the oligomer of 564 microequivalents / g is significantly higher than that of the starting material, indicating that hydrolysis has occurred. The polymerization time was 90 minutes.

[0086] Example 5 :

[0087] The following and subsequent examples take the form of a process model simulation of a three-vessel CP process operating at 450 metric tons / day to produce a typical bottle resin grade PET. The reactor train includes an esterifier, UFPP, and a trimmer vessel. The process conditions used for the simulation are described as follows:

[0088]

[0089]

[0090] The key parameters of interest are the oligomer OH:COOH value of 3.63 and the trimmer pressure of 2.29 mmHg. Within the simulation, as we increase the esterifier feed molar ratio, the effect is to change the oligomer OH:COOH upwards and this affects the reactivity and therefore the predicted trimmer vacuum requirements as described in US 3551386 A. We can see the effect of this prediction in the figure below.

[0091]

[0092] Another way to represent this is to simulate the plant rate or plant capacity as a function of oligomer OH:COOH while maintaining a constant trimmer vacuum. This is shown in the graph below.

[0093]

[0094] The change in oligomer OH:COOH from about 3.1 to about 3.6 apparently corresponds to about 5% of the plant's production capacity.

[0095] Embodiment 6:

[0096] The following is a predictive example of the same three-vessel CP process operated at 450 metric tons / day as in Example 5, making the same typical bottle resin grade PET, but this time using a BHET feed.

[0097]

[0098]

[0099] The key parameters of interest are the very high (508) oligomer OH:COOH and the greatly reduced trimmer pressure requirement of 1.58 mmHg. This oligomer OH:COOH is so large that it exceeds the above capacity chart, in which case, in order to increase the trimmer pressure to 2.3 mmHg, as in Example 5, we must reduce the plant rate to 390 tpd, which represents a reduction in capacity of approximately 20%. The degradation of L* color is also significant.

[0100] Example 7 :

[0101] In this example, we run a typical PCR feed of 0.76 iV, 27.4 COOH through a pressurized CSTR glycolysis simulation at 3000 mmHg pressure, 260°C, and 64 minutes residence time with 450 tpd PET resin. Varying the amount of water and ethylene glycol to the feed, we predict the following results:

[0102]

[0103] Or for example, the resulting oligomeric OH:COOH and Dp relative to the % H2O at 6% ethylene glycol addition are shown below:

[0104]

[0105] Re-feeding these oligomers forward through the CP process as described in Example 6, we obtain the following set of predictions:

[0106]

[0107] Or the required trimmer pressure relative to the H2O% at 6% EG addition is shown below:

[0108]

[0109] A clear optimum is seen at approximately 2.5% H2O at 6% EG, which is indicated by the maximum in the predicted trimmer vacuum requirement. Likewise, the trimmer vacuum requirement for oligomer OH:COOH is plotted below:

[0110]

[0111] Now we see an optimum oligomer OH:COOH of approximately 3.3:1. It is clear that based on the increase in trimmer vacuum requirements, plant operation can be restored to full capacity of 450 tpd when the optimized glycolytic / hydrolytic oligomers are added to the process.

Claims

1. A method for producing an oligomeric PET substrate from post-consumer PET-containing waste, wherein the oligomeric PET substrate is for use in a rPET manufacturing process, the method comprising the steps of: i) reacting post-consumer PET-containing waste in the presence of ethylene glycol and water in a reaction zone; and ii) producing an oligomeric PET substrate represented by formula I: wherein R1 is a carboxyl terminal group or a hydroxyl terminal group, R2 is a carboxyl terminal group or a hydroxyl terminal group, and n is the degree of polymerization.

2. The method according to claim 1, wherein n is 10, preferably 3 to 7.

3. The method according to claim 1, wherein the oligomeric PET substrate has a CEG (acid end moles / material te number) of 300 to 1500, preferably 500 to 1200 and more preferably 700 to 1100.

4. A method according to any one of the preceding claims, wherein the oligomeric PET substrate has a hydroxyl end group:carboxyl end group ratio in the range of 1.66 to 6.66, preferably in the range of 2.22 to 4.

0.

5. A method according to any preceding claim, wherein the ethylene glycol and water are added in either order or together.

6. The method according to any preceding claim, wherein the ethylene glycol is added in the range of 5 to 50 wt%, preferably in the range of 10 to 40 wt% and more preferably in the range of 12 to 18 wt%.

7. A method according to any preceding claim, wherein the water is added in the range of 2 to 20 wt%, preferably in the range of 5 to 10 wt% and more preferably in the range of 6 to 8 wt%.

8. A method according to any preceding claim, wherein the ethylene glycol is added in the range of 12 to 18 wt% and the water is added in the range of 5 to 9 wt%.

9. A method according to any preceding claim, wherein the waste material is reacted with ethylene glycol and water at a temperature in the range of 120°C to 300°C, preferably in the range of 150°C to 270°C.

10. A process according to any preceding claim, wherein the waste material is reacted with ethylene glycol and water in the reaction zone at a pressure of between 3 barg and 30 barg.

11. The method of claim 1 , wherein the reaction zone precedes additive injection.

12. The process according to claim 1, comprising a residence time in the reaction zone of between 30 and 120 minutes, preferably between 40 and 50 minutes.

13. The process of claim 1, wherein the reaction is catalyzed by a catalyst that is already present in the post-consumer PET-containing waste or is an exogenously added catalyst.

14. The method according to claim 13, wherein the exogenously added catalyst is a common PET catalyst selected from antimony-containing catalysts, titanium-containing catalysts, zinc-containing catalysts, acetate-containing catalysts, manganese-containing catalysts, aluminum-containing catalysts or tin-containing catalysts.

15. The method of claim 14, wherein the catalyst is any one of antimony trioxide, antimony glycolate, antimony triacetate, titanium alkoxide, zinc acetate, or manganese acetate.

16. The method of claim 1, wherein the rPET manufacturing process is a conventional rPET manufacturing process or a modified vPET manufacturing process.

17. The method of claim 1, wherein the post-consumer PET-containing waste comprises PCR flakes or polyester fibers.

18. The method of claim 1, wherein the oligomeric PET substrate is fed directly or indirectly into the rPET manufacturing process.

19. An oligomeric PET substrate produced from post-consumer PET-containing waste, wherein the oligomeric PET substrate is represented by Formula I: R1 is a carboxyl terminal group or a hydroxyl terminal group, R2 is a carboxyl terminal group or a hydroxyl terminal group, and n is the degree of polymerization, wherein the oligomeric PET substrate is represented by any two of the following characteristics: i) a degree of polymerization wherein n is 1 to 10; ii) CEG (acid end moles / material te number) between 300 and 1500; or iii) a hydroxyl end group:carboxyl end group ratio in the range of 1.66 to 6.66, And wherein the oligomeric PET substrate is used to synthesize a polymer comprising 5%-100% rPET.

20. A PET polymer made from 5% to 100% rPET produced from the oligomeric PET substrate according to claim 19.

Images