Process for the manufacture of oligomeric polyethylene terephthalate (pet) substrates

Abstract

The invention provides a method for producing an oligomeric polyethylene terephthalate (PET) substrate for use in a recycled PET (rPET) manufacturing process, the method comprising (i) adding recycled bis-hydroxy ethylene terephthalate (rBHET) and an under-esterified purified terephthalic acid (PTA) oligomer to a reaction zone; and ii) reacting the rBHET and the under-esterified PTA oligomer in the reaction zone to produce an oligomeric PET substrate represented by formula (I), wherein 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 (Dp).(I).

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 035,179, filed June 5, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure relates to methods for manufacturing oligomeric polyethylene terephthalate (PET) substrates from recycled dihydroxy terephthalate (rBHET), methods for manufacturing oligomeric PET substrates for use in the manufacture of recycled PET (rPET), and methods for manufacturing PET polymers containing 5%-100% rPET from the oligomeric PET substrates. Background Technology

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

[0005] Typically, PET has petrochemical origins. Purified terephthalic acid is first produced in a purified terephthalic acid manufacturing facility via aerobic catalytic oxidation of p-xylene in an acetic acid medium. This purified terephthalic acid (PTA) then reacts with ethylene glycol to produce PTA-based oligomers (and water), which then undergo condensation polymerization to form PET polymers. An alternative route for preparing PET polymers is via the polymerization of dihydroxy terephthalate (BHET) monomers; however, this route is less economically advantageous. BHET monomers are formed by the reaction of dimethyl terephthalate (DMT) (a diester formed from terephthalic acid and methanol) with ethylene glycol, followed by the self-polymerization of the BHET monomers to form longer PET chains.

[0006] In a typical PET manufacturing process, there are three main stages to make the PET polymer in the melt phase process: (1) esterification, (2) prepolymerization, and (3) polymerization. When making PET resin, the PET polymer goes into a further solid state polymerization (SSP) stage to make 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 into an esterification unit, where the esterification, which can or can not be catalyzed, takes place at atmospheric pressure and temperatures in the range of 270°C to 295°C. The water (or methanol in the case of DMT) and excess ethylene glycol produced from the esterification reaction are evaporated. Additives, including catalysts and colorants, are typically 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 and reacted with additional ethylene glycol at temperatures in the range of 270°C to 295°C and 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 temperatures 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 repeat units. In embodiments, this is referred to as a finisher. When making PET resin, a fourth solid state polymerization (SSP) stage involving a crystallization step is typically required, where the amorphous pellets produced in the melt phase process are converted into crystalline pellets, which are then further processed depending on the final PET product, which can be a wide variety, such as containers / bottles for liquids and food or industrial products and resins.

[0007] Recycling using post-consumer PET-containing waste is desirable to reduce the amount of plastic sent to landfills. One known recycling method is to use post-consumer PET-containing waste to produce post-consumer recycled (PCR) flake. This PCR flake can then be glycolyzed to convert it into recycled bis-hydroxy-ethylene terephthalate (rBHET). This rBHET can then be used in a PET manufacturing process to make recycled PET (rPET; so-called because the oligomers on which it is based originate from post-consumer PET or PCR, not PTA or DMT). This avoids the need to use more PTA of petrochemical origin combined with ethylene glycol to make PTA-based oligomers in a virgin (vPTA) process or virgin (vBHET) in a virgin (vDMT) process. Furthermore, because less petrochemical product is required to make recycled PET (rPET) compared to new PET (known as virgin PET (vPET)), rPET has a lower carbon footprint than vPET. As a result, rPET is attractive based on its ‘green’ credentials, which can in themselves bring economic benefits in certain jurisdictions.

[0008] However, rPET made from rBHET tends to have lower reactivity in the melt phase process and the solid state polymerization stage. If rBHET is used in the PET manufacturing process, the amount of rPET manufactured 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. Additionally, rPET made from rBHET tends to be darker (lower L*) and yellower, primarily due to the presence of impurities in the rPET polymer. Therefore, currently, the rPET manufacturing process using rBHET (a glycolysis product of PET waste) is neither attractive nor competitive compared to the vPET process using PTA-based oligomers or vBHET.

[0009] Therefore, there is a need to produce an oligomeric PET substrate that has increased reactivity, and thus, the ability to increase polymerization to form rPET, in order to compete with the process of making vPET. SUMMARY

[0010] The present disclosure provides, among other things, a method for producing an oligomeric PET substrate for use in a rPET manufacturing process, the method comprising the steps of: i) adding recycled bis-hydroxy ethylene terephthalate (rBHET) and under-esterified purified terephthalic acid (PTA) oligomers to a reaction zone; and ii) reacting the rBHET and under-esterified PTA oligomers in the reaction zone to produce an oligomeric PET substrate represented by Formula I:

[0011] (I)

[0012] wherein 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 a degree of polymerization (Dp).

[0013] In some embodiments, n is 1 to 10, preferably 3 to 7, and more preferably n is 6. In some embodiments, the oligomeric PET substrate has a CEG of 300 to 1500 acid end moles per material te, preferably 500 to 1200 acid end moles per material te, and more preferably 700 to 1100 acid end moles per material te. In some embodiments, 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. In some embodiments, the under-esterified PTA oligomers are in the range of 5 wt% and 50 wt%, preferably in the range of 20 wt% to 40 wt%.

[0014] In some embodiments, the rBHET is reacted with the under-esterified PTA oligomers at a temperature between 120°C to 300°C, preferably 150°C to 270°C. In some embodiments, the reaction zone comprises a residence time between 30 minutes to 120 minutes, preferably 40 minutes to 50 minutes. In some embodiments, the rBHET is reacted with the under-esterified PTA oligomers at a pressure between 3 barg to 20 barg. In some embodiments, rBHET is fed to the esterifier in addition to PTA and ethylene glycol. In some embodiments, the rBHET is fed to the esterifier at a ratio in the range of 40 wt% to 55 wt%, preferably in the range of 45 wt% to 51 wt%.

[0015] In some embodiments, the rBHET is reacted with the under-esterified PTA oligomers using an exogenously added catalyst selected from the group consisting of antimony-containing catalysts, titanium-containing catalysts, zinc-containing catalysts, acetate-containing catalysts, manganese-containing catalysts, germanium-containing catalysts, aluminum-containing catalysts, tin-containing catalysts, and combinations thereof. In some embodiments, the catalyst comprises at least one of antimony trioxide, antimony glycolate, antimony triacetate, titanium alcoholate, zinc acetate, or manganese acetate. In some embodiments, the oligomeric PET substrate is fed directly or indirectly into the rPET manufacturing process.

[0016] The present disclosure also provides an oligomeric PET substrate represented by Formula I

[0017] (I)

[0018] wherein 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 a degree of polymerization, and wherein the oligomeric PET substrate comprises at least two of the following characteristics: i) n is a degree of polymerization of 1-10; ii) CEG (acid end molar number per metric ton (te) of material) is 300 to 1500; and iii) a hydroxyl end group: carboxyl end group ratio is in the range of 1.66 to 66.6. In some embodiments, the oligomeric PET substrate is used to synthesize a polymer comprising 5%-100% rPET.

[0019] The present disclosure also provides a PET polymer made from 5%-100% rPET produced from an oligomeric PET substrate as represented by Formula I. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1A is a schematic diagram showing a system according to one aspect of the present disclosure, wherein rBHET and under-esterified PTA oligomers are reacted to produce an oligomeric PET substrate.

[0021] Figure 1BA graph showing trimmer pressure as a function of oligomer OH:COOH ratio for the simulated process for producing PET according to Example 1.

[0022] Figure 2 A graph showing trimmer pressure as a function of oligomer OH:COOH ratio for the simulated process for producing PET according to Example 1.

[0023] Figure 3 A graph showing plant rate as a function of oligomer OH:COOH ratio for the simulated process for producing PET according to Example 1.

[0024] Figure 4 A graph showing trimmer pressure as a function of COOH esterifier ratio for the simulated process for producing PET according to Example 3.

[0025] Figure 5 A graph showing trimmer pressure versus oligomer OH:COOH for the simulated process for producing PET according to Example 3 with a BHET feed of 50%.

[0026] Figure 6 A graph showing trimmer pressure as a function of COOH esterifier ratio for the simulated process for producing PET according to Example 3 with a BHET feed of 30%.

[0027] Figure 7 A graph showing trimmer pressure versus oligomer OH:COOH for the simulated process for producing PET according to Example 3 with a BHET feed of 30%.

[0028] Figure 8 A graph showing trimmer pressure versus esterifier residence time for the simulated process for producing PET according to Example 3 with a BHET feed of 50%.

[0029] Figure 9 A graph showing trimmer pressure versus oligomer OH:COOH for the simulated process for producing PET according to Example 3 with a BHET feed of 50%. DETAILED DESCRIPTION

[0030] Disclosed herein are methods of producing oligomeric PET substrates from rBHET, methods of producing oligomeric PET substrates for use in manufacturing rPET, and methods of producing PET polymers made from oligomeric PET substrates. In the methods of the present disclosure, rBHET and under-esterified PTA oligomers are added to a reaction zone and reacted in the reaction zone under conditions effective to produce oligomeric PET substrates. The degree of esterification (De) is determined by calculating the percent molar conversion of terephthalic acid, for example: 90% conversion of 100 g of terephthalic acid will release ((100*0.9) / 166) *2*18 = 19.52 g of water.

[0031] The methods disclosed herein address the recognized problem in the art that rBHET has lower reactivity in the manufacture of PET oligomers compared to vBHET, and therefore, PET oligomers made from rBHET have lower yields compared to PET oligomers made from vBHET or PTA. In particular, the present disclosure provides a method of increasing rPET manufacturing efficiency by reacting BHET with under-esterified PTA oligomers during the manufacturing process. These methods increase the ability of practitioners to make PET from recycled starting materials in a manner that is economically competitive with methods for making virgin PET.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the present application, suitable methods and materials are described below. In case of conflict, the present specification, including definitions, will control. Other features, objects, and advantages of the present application will be apparent from the description and drawings, and from the claims.

[0033] In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. The details of one or more embodiments of the application are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the application will be apparent from the description and drawings, and from the claims. As used in the description and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Under the patent statutes, the word "comprising" can be replaced with the phrases "consisting essentially of' or "consisting of."

[0034] The term "about" as used herein, unless otherwise indicated or unless the context clearly dictates otherwise, is understood to be within the normal tolerances of the art, for example within 2 standard deviations of the mean. About can be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the indicated value. Unless the context indicates otherwise, all numerical values provided herein are modified by the term "about."

[0035] The term "PET" or "PET polymer" refers to polyethylene terephthalate.

[0036] The term "PTA" refers to purified terephthalic acid.

[0037] The term "vPTA" refers to PTA synthesized via aerobic catalytic oxidation of p- xylene in acetic acid media.

[0038] As used herein, "PTA-based oligomer" refers to a short chain PET oligomer synthesized by a process that requires esterification of purified terephthalic acid with ethylene glycol. Purified terephthalic acid (PTA) is reacted with ethylene glycol to produce a PTA- based oligomer (and water), which is polycondensed to form a PET polymer. When PTA is reacted with ethylene glycol, a short chain PTA-based oligomer is formed, which is characterized by Dp (degree of polymerization or number of repeat units) and CEG (or carboxylic end group concentration). The degree of polymerization (Dp) is calculated from the number average molecular weight Mn according to the following formula: Dp = (Mn - 62) / 192, where Mn is calculated by rearranging the IV (intrinsic viscosity) dependence below: IV = 1.7e-4(Mn) 083 The intrinsic viscosity (IV) of a polyester can be measured by the melt viscosity technique 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). The ratio of hydroxyl end groups (HEG) to carboxylic end groups (CEG) is determined from the CEG measurement and rearrangement of the following Mn calculation: Mn = 2e6 / (CEG + HEG).

[0039] As used herein, "PET manufacturing process" refers to a facility that produces PET. Such a facility can be integral to a PTA manufacturing process, or can be completely independent.

[0040] As used herein, "post-consumer PET-containing waste" refers to any waste stream containing at least 10% PET waste. Thus, post-consumer PET-containing waste can comprise from 10% to 100% PET. Post-consumer PET-containing waste can be municipal waste, which itself comprises 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 articles such as clothing articles (shirts, pants, dresses, coats, etc.), bedding, duvet inners, or towels. Post-consumer PET-containing waste can also include post-consumer recycled (PCR) flake, which is waste PET plastic bottles that have been mechanically shredded into small pieces for use in a recycling process.

[0041] As used herein, “vPET” refers to virgin PET, which is PET synthesized through a process that requires 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 PTA-based oligomers are polycondensed to form the PET polymer. Alternatively, vPET can be formed by reaction of dimethyl terephthalate (DMT), a diester formed from terephthalic acid and methanol, with ethylene glycol. BHET monomers are formed by reaction of dimethyl terephthalate (DMT), a diester formed from terephthalic acid and methanol, with ethylene glycol, which BHET monomers then polymerize themselves to form longer PET chains.

[0042] As used herein, “rPET” refers to recycled PET, which is PET made entirely or at least partially from oligomers that have originated from post-consumer PET-containing waste. rPET can be synthesized from 100% oligomers that have originated from post-consumer PET-containing waste. Alternatively, rPET can be synthesized from a combination of oligomers, including those that have originated from post-consumer PET-containing waste, as well as those from vBHET or PTA-based oligomers used to make vPET. In one non-limiting embodiment, rPET includes at least 5% oligomeric PET substrate that has originated from post-consumer PET-containing waste. In another non-limiting embodiment, rPET includes at least 50% oligomeric PET substrate that has originated from post-consumer PET-containing waste. In yet another non-limiting embodiment, rPET includes at least 80% oligomeric PET substrate that has originated from post-consumer PET-containing waste.

[0043] As used herein, “rPET manufacturing process” refers to manufacturing processes and facilities that have been specifically designed and constructed to synthesize recycled PET (rPET), i.e., PET made from substrates that include those originating from any post-consumer PET-containing waste in addition to virgin substrates (i.e., vBHET or PTA-based oligomers), as well as manufacturing processes and facilities that have been constructed to synthesize vPET, but which have been modified or retrofitted to allow production of rPET. The changes required to vPET facilities to produce rPET are typically not major in structure, but require extensive process changes.

[0044] The term “BHET” refers to bis-hydroxy terephthalic acid ethylene glycol monomer (C 12 H 14 O6), including all structural isomers, characterized by the absence of carboxyl end groups, i.e., a carboxylic acid end group concentration (CEG) of zero. The chemical structure of the para isomer of BHET monomer is shown below:

[0045]

[0046] To produce PET, BHET reacts with itself in a polycondensation reaction to make longer chains, forming polyethylene terephthalate and releasing ethylene glycol in the process. BHET, i.e., BHET monomer, is typically formed by the reaction of dimethyl terephthalate (DMT) with ethylene glycol, but it is also a minor component of the oligomers made from PTA plus ethylene glycol, i.e., part of the oligomer molecular weight distribution. When PTA is reacted with ethylene glycol, an oligomer based on short chain PTA is formed, characterized by Dp (degree of polymerization or number of repeat units) and CEG (or carboxylic acid end group concentration). 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).

[0047] The term “vBHET” refers to virgin BHET, which is BHET monomer formed by the reaction of dimethyl terephthalate (DMT) with ethylene glycol.

[0048] The term “rBHET” refers to recycled BHET, which is a BHET molecule produced by the glycolysis of PET. Post-consumer PET-containing waste, such as PET plastic bottles, is mechanically broken down to produce post-consumer recycled (PCR) flake (PCR flake). This PCR flake is then glycolyzed to convert it to rBHET.

[0049] As used herein, “oligomeric PET substrate” refers to a molecule according to Formula I:

[0050] Formula I

[0051] Either end of Formula I can be a carboxylic acid end group or a hydroxyl end group. Thus, R1or R2may be a carboxylic acid end group or a hydroxyl end group. The optimal ratio of hydroxyl end groups: carboxylic acid end groups in the oligomeric PET substrate is typically between 1.66 and 6.66. Formula I polymerizes with itself in an esterification reaction, where the carboxylic acid end groups react with the hydroxyl end groups to form ester linkages, releasing water. “n” represents the degree of polymerization (Dp) or the number of repeat units of Formula I present in the oligomeric PET substrate, and can be, for example, between 3 and 7. 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 (units are acid end moles / material te) can be, for example, between 500 and 1200.

[0052] Aspects of the present disclosure provide methods of producing an oligomeric PET substrate. Methods of producing rPET generally employ a process of glycolysis of PET (or a waste source having PET) using, for example, ethylene glycol to produce bis-hydroxylethylene terephthalate (rBHET). This method of producing rPET uses rBHET and polymerizes it to produce rPET. However, the rBHET has a lower reactivity compared to PTA-based oligomers formed by esterification of purified terephthalic acid with ethylene glycol. Thus, when used to make rPET, rBHET produces about 20% less amount of rPET compared to the amount of vPET made using PTA-based oligomers (formed by esterification of purified terephthalic acid with ethylene glycol) for a similar process.

[0053] In the present disclosure, it was surprisingly found that rBHET can react with under-esterified PTA oligomers to produce an oligomeric PET substrate having increased reactivity compared to unmodified rBHET. Specifically, under-esterified PTA oligomers are reacted with rBHET to produce an oligomeric PET substrate. This oligomeric PET substrate shows increased reactivity compared to unmodified oligomers, i.e., rBHET, as shown in the Examples section. Thus, aspects of the present disclosure relate to methods for producing an oligomeric PET substrate by reacting rBHET with under-esterified PTA oligomers.

[0054] The oligomeric PET substrate is represented by Formula I:

[0055]

[0056] In embodiments, either end of Formula I can be a carboxyl end group or a hydroxyl end group. Thus, R1or R2may be a carboxyl end group or a hydroxyl end group. As described herein, the optimal ratio of hydroxyl end groups:carboxyl end groups of Formula I is generally between 1.66 and 6.66, preferably between 2.22 and 4.0. The degree of polymerization (Dp) or the number of repeating units present in the oligomeric PET substrate can be between 1 and 10, more typically between 3 and 7, and preferably 6. In addition to being characterized by the degree of polymerization (Dp) and the ratio of hydroxyl end groups:carboxyl end groups, the oligomeric PET substrate is also characterized by its carboxylic acid end group concentration (referred to herein as CEG). The CEG (units are acid end moles / material te) is generally between 300 and 1500 and preferably between 500 and 1200 or even between 700 and 1100.

[0057] In one non-limiting embodiment, the oligomeric PET substrate includes a ratio of hydroxyl end groups:carboxyl end groups between 1.66 and 6.66, a Dp between 4 and 7, and a CEG between 700-1100 acid end moles / material te.

[0058] The benefits found to be associated with the optimized end group ratio arise from a balance of the reaction rate of esterification versus polycondensation, the relative partial pressure of the condensation products, i.e. water and ethylene glycol, and the chemical equilibrium constant of esterification versus polycondensation. This balance results in a natural optimum in the range of 2.22 to 4.0, as previously described.

[0059] In one non-limiting embodiment, the rBHET is in powder form and is melted prior to addition to the reaction zone. This melted form of rBHET is added to the process prior to the injection of the additive into the reaction zone containing under-esterified PTA oligomers.

[0060] In one non-limiting embodiment, the under-esterified PTA oligomers are in the range of 5 wt% to 50 wt% and preferably in the range of 20 wt% to 40 wt%.

[0061] In one non-limiting embodiment, the rBHET and under-esterified PTA oligomers are reacted at a temperature between 120 °C and 300 °C and preferably between 150 °C and 270 °C.

[0062] In one non-limiting embodiment, the residence time in the reaction zone can be between 30 minutes to 120 minutes and preferably between 40 minutes to 50 minutes.

[0063] In one non-limiting embodiment, the rBHET and under-esterified PTA oligomers are reacted at a pressure of 3 barg to 20 barg.

[0064] In an alternative embodiment, an alternative under-esterification process is used in which about 50 wt% of rBHET is added to the usual PTA / EG slurry into a smaller esterifier, thereby reducing the residence time and limiting the extent of the PTA esterification reaction.

[0065] In one non-limiting embodiment, the rBHET is fed to the esterifier at a ratio in the range of 40 wt% to 55 wt% and preferably in the range of 45 wt% to 51 wt%.

[0066] In one non-limiting embodiment, the rBHET and under-esterified PTA oligomers are reacted at a temperature in the range of 180 °C to 300 °C and preferably in the range of 240 °C to 300 °C.

[0067] In one non-limiting embodiment, the rBHET and under-esterified PTA oligomers are reacted in the esterifier with a residence time of 60 minutes to 100 min and preferably 85 minutes to 95 minutes.

[0068] In one non-limiting embodiment, the rBHET is reacted with the under-esterified PTA oligomers in an esterifier at a pressure of 0.05 barg to 2 barg.

[0069] The reaction can be catalyzed or non-catalyzed, depending on the composition of the PCR flake used to make the rBHET. In one non-limiting embodiment, the rBHET and the under-esterified PTA oligomers are reacted in the presence of an exogenously added catalyst. Post-consumer PET waste or PCR flake, due to its manufacturing process, can contain a latent catalyst. Thus, in some embodiments, the rBHET derived from PCR flake can have sufficient endogenous catalyst. However, additional exogenous catalyst can be added if desired. Non-limiting examples of catalysts that can be added to the reaction include antimony-, titanium-, zinc-, manganese-, germanium-, aluminum-, and tin-containing catalysts. These can be selected from an antimony-containing catalyst, a titanium-containing catalyst, a zinc-containing catalyst, an acetate-containing catalyst, a manganese-containing catalyst, a germanium-containing catalyst, an aluminum-containing catalyst, or a tin-containing catalyst. These can be, for example, antimony trioxide, antimony glycolate, antimony triacetate, titanium alkoxide, zinc acetate, or manganese acetate. Such catalysts are added to the reaction zone, which is commonly referred to as the esterification unit. Titanium-containing catalysts are typically added at 2-100 ppm, and preferably about 10 ppm, relative to the final PET polymer. All other catalysts (except titanium-containing catalysts) are typically added at 40 ppm-300 ppm, preferably about 240 ppm.

[0070] In some non-limiting embodiments, the oligomeric PET substrate is used in an rPET manufacturing process that was previously designed for the synthesis of vPET, but has been retrofitted for a process to make rPET. In an alternative non-limiting embodiment, the oligomeric PET substrate is used in an rPET manufacturing process that was specifically designed from the outset for the production of rPET.

[0071] One aspect of the present disclosure also relates to an oligomeric PET substrate produced by or obtainable by a process as described herein. In one non-limiting embodiment, the present disclosure relates to an oligomeric PET substrate produced by using rBHET derived from PCR flake.

[0072] In some embodiments, the oligomeric PET substrate has a structure according to Formula I:

[0073] (I)

[0074] wherein R1is a carboxyl end group or a hydroxyl end group, R2is a carboxyl end group or a hydroxyl end group, and n is a degree of polymerization, and wherein the oligomeric PET substrate is represented by two or more of the following characteristics:

[0075] i) n is a degree of polymerization of 1 to 10;

[0076] ii) CEG (molar number of acid ends / material te number) of 300 to 1500; and

[0077] iii) The ratio of hydroxyl end group to carboxyl end group in the range of 1.66 to 6.66.

[0078] In some embodiments, the oligomeric PET substrate is characterized by: (i) a degree of polymerization of n from 1 to 10 and (ii) a CEG (molar number of acid ends / te number of materials) of 300 to 1500. In some embodiments, the oligomeric PET substrate is characterized by: (i) a degree of polymerization of n from 3 to 7 and (ii) a CEG (molar number of acid ends / te number of materials) of 700 to 1100.

[0079] Another aspect of this disclosure relates to PET polymers manufactured using oligomeric PET substrates produced by or obtainable through the methods described herein during polymerization. The PET polymers can range from 5% to 100% rPET. Therefore, the PET polymers can comprise a mixture of vPET and rPET.

[0080] refer to Figure 1A A system 100 according to one aspect of this disclosure is shown for producing oligomeric PET substrates from rBHET powder stored in a hopper 110. In the illustrated system 100, rBHET powder is fed from the hopper 110 into a melting vessel 120, where the rBHET powder is melted and stirred. The molten rBHET is then mixed with under-esterified PTA oligomers. Under-esterification is achieved from existing esterifiers by operating under conditions such as lower T, lower EG:TA molar ratio, and lower stock levels. The mixture is supplied to a reaction zone 130, also referred to as a linear reactor 130. The linear reactor 130 provides a residence time at the temperature at which the reaction of rBHET with the under-esterified oligomers is completed. For example, this refers to the oligomer retention period. The reaction zone 130 is maintained under conditions that allow the rBHET to catalytically react with the under-esterified oligomers to produce oligomeric PET substrates. The effluent from reaction zone 130 is then fed into prepolymerization container 150 and then into trimmer container 160 to increase the degree of polymerization of the monomer.

[0081] refer to Figure 1B An alternative system 100a according to one aspect of this disclosure is shown for producing oligomeric PET substrates from rBHET powder stored in a hopper 110. In the illustrated system 100a, rBHET powder is fed from the hopper 110 into a melting container 120, where the rBHET powder is melted and stirred. Figure 1AIn contrast, molten rBHET is mixed with ethylene glycol and PTA in a scaled-down esterifier 140, thereby reducing residence time and limiting the extent of PTA esterification.

[0082] Example

[0083] The aspects of this disclosure are demonstrated through process modeling examples of continuous polymerization (CP) operations, which illustrate the expected effects of adding BHET to under-esterified PTA-based oligomers.

[0084] Example 1:

[0085] The following and subsequent examples use a process model simulation of a three-vessel CP process operating at 450 metric tons / day to produce typical bottle-grade PET. The reactor series includes an esterifier, a UFPP reactor, and a trimmer vessel. The process conditions used for the simulation are described below:

[0086]

[0087] As shown in the table above, the key parameters of interest are the oligomer OH:COOH value of 3.63 and the dresser pressure of 2.29 mmHg. Increasing the esterifier feed molar ratio upwards alters the oligomer OH:COOH value and affects reactivity, thus allowing for the prediction of the dresser vacuum requirement. The predicted effects are as follows: Figure 2 As shown.

[0088] An alternative way to represent this situation is to simulate the plant rate or plant capacity based on the variation of oligomer OH:COOH, while maintaining a constant dresser vacuum. This is in Figure 3 As shown in the figure, it can be seen that the change in oligomer OH:COOH from about 3.1 to about 3.6 is equivalent to an increase in plant production capacity of about 5%.

[0089] Example 2:

[0090] The following is an example of a three-container CP process operating at 450 metric tons / day as in Example 1, producing the same typical bottle-grade resin PET, but this time using BHET feed.

[0091]

[0092] As shown in the table above, the key parameters of interest are the very high 508 oligomer OH:COOH and the significantly reduced 1.58 mmHg dresser pressure requirement. This oligomer OH:COOH is so high that, as in Example 1, to increase the dresser pressure to 2.3 mmHg, the plant rate would drop to 390 tpd, representing a reduction in production capacity of approximately 20%. The degradation of L* color is also significant.

[0093] Example 3:

[0094] In this embodiment, the process parameters of Example 2 were kept constant, but now 50% BHET feed was added and the esterification conditions were changed to intentionally under-esterify the feed. As a result, the COOH content of the esterifier product increased, and its Dp decreased, thereby producing oligomers with different OH:COOH ratios. When it reacts with BHET, the following set of results is expected:

[0095]

[0096] like Figure 4 As shown, a clear optimum is observed at approximately 3500 ppm of the esterifier COOH, which corresponds to the maximum value predicted in the dresser vacuum requirements. Furthermore, Figure 5 The vacuum requirements for the trimmer are shown for the resulting oligomer OH:COOH. For example... Figure 5 As shown, for a 50% BHET feed, an optimal esterifier OH:COOH ratio of approximately 7:1 was achieved. Clearly, given the increased vacuum requirements of the dresser, using this optimized esterifier to esterify under-esterified products allows the plant to return to full capacity of 450 tpd.

[0097] The following table shows a set of predictions using a 30% BHET feed:

[0098]

[0099] Figure 6 The required dresser pressure for the COOH in the esterifier is shown. Figure 6 As shown, a clear optimum is observed at approximately 2200 esterifier COOH, which is represented by the maximum value of the predicted dresser vacuum requirement.

[0100] Figure 7 The vacuum requirements for the dresser of the esterifier products are shown. For example... Figure 7 As shown, for a 30% BHET feed, an optimal esterifier OH:COOH ratio of approximately 5:1 was achieved. Clearly, given the increased vacuum requirements of the dresser, using this optimized esterifier to esterify under-esterified products allows the plant to return to full capacity of 450 tpd.

[0101] An alternative to insufficient esterification involves feeding approximately 50 wt% rBHET along with the usual PTA / EG slurry into a smaller esterifier, thereby reducing residence time and limiting the extent of PTA esterification. The following simulation uses a three-vessel CP process similar to Example 1, operating at 450 tons / day, but with a 50 wt% BHET feed and a much smaller esterifier to obtain resin-grade PET. As shown in the table below, the esterifier residence time is now approximately 90 min, compared to 200 min in Example 1. To further slow down the PTA esterification rate, the temperature and feed molar ratio were reduced. The process conditions used for the simulation are described in the table below:

[0102]

[0103] In the implementation scheme, for these conditions, the oligomer OH:COOH value is observed to be 4.05, resulting in a desired dresser vacuum requirement of 2.3 mmHg. The table below shows that if the esterifier volume and therefore residence time are adjusted, the following set of predictions can be generated.

[0104]

[0105] Figure 8 The optimal esterifier residence time of approximately 95 minutes is shown to minimize the trimmer vacuum requirement.

[0106] Alternatively, Figure 9 The results show that, under the same data, the optimal oligomer OH:COOH value of approximately 4.1 minimizes the trimer vacuum requirement.

Claims

1. A method for producing oligomeric polyethylene terephthalate (PET) substrates for use in the manufacture of recycled PET (rPET), the method comprising: i) Add recycled ethylene dihydroxy terephthalate (rBHET) and under-esterified PTA oligomers to the reaction zone; as well as ii) React the rBHET and the under-esterified PTA oligomer in the reaction zone to produce an oligomeric PET substrate represented by Formula I: (I) Where R1 is a carboxyl or hydroxyl terminal group, R2 is a carboxyl or hydroxyl terminal group, and n is the degree of polymerization (Dp), where n is from 1 to 10. The rBHET mentioned therein is a glycolysis product of PET waste.

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

3. The method according to claim 1, wherein n is 6.

4. The method of claim 1, wherein the oligomeric PET substrate has a CEG of 300 to 1500 acid term moles / material te number.

5. The method of claim 1, wherein the oligomeric PET substrate has a CEG of 500 to 1200 acid term moles / material te number.

6. The method of claim 1, wherein the oligomeric PET substrate has a CEG with an acid end molar number of 700 to 1100 per material te number.

7. The method of claim 1, wherein the oligomeric PET substrate has a hydroxyl end group to carboxyl end group ratio in the range of 1.66 to 6.

66.

8. The method of claim 1, wherein the oligomeric PET substrate has a hydroxyl end group to carboxyl end group ratio in the range of 2.22 to 4.

0.

9. The method of claim 1, wherein the under-esterified PTA oligomer is in the range of 5% to 50% by weight.

10. The method of claim 1, wherein the under-esterified PTA oligomer is in the range of 20% to 40% by weight.

11. The method of claim 1, wherein the rBHET reacts with the under-esterified PTA oligomer at a temperature between 120°C and 300°C.

12. The method of claim 1, wherein the rBHET reacts with the under-esterified PTA oligomer at a temperature between 150°C and 270°C.

13. The method of claim 1, wherein the reaction zone includes a residence time of 30 minutes to 120 minutes.

14. The method of claim 1, wherein the reaction zone includes a residence time of 40 to 50 minutes.

15. The method of claim 1, wherein the rBHET reacts with the underesterified PTA oligomer at a pressure of 3 barg to 20 barg.

16. The method of claim 1, wherein, in addition to PTA and ethylene glycol, the rBHET is also fed into the esterifier.

17. The method of claim 16, wherein the rBHET is fed into the esterifier at a rate ranging from 40% to 55% by weight.

18. The method of claim 16, wherein the rBHET is fed into the esterifier at a ratio ranging from 45% to 51% by weight.

19. The method of claim 1, wherein the rBHET is reacted with the under-esterified PTA oligomer using an exogenously added catalyst, the exogenously added catalyst being selected from antimony-containing catalysts, titanium-containing catalysts, zinc-containing catalysts, acetate-containing catalysts, manganese-containing catalysts, germanium-containing catalysts, aluminum-containing catalysts, tin-containing catalysts, and combinations thereof.

20. The method according to claim 19, wherein the catalyst comprises at least one selected from antimony trioxide, antimony glycolate, antimony triacetate, titanium alkoxide, zinc acetate, or manganese acetate.

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

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