Process and system for utilizing waste polyester in a continuous polyester polymerization process

Abstract

1. A method for producing a polyester polymer containing waste polyester in a continuous polymerization unit, comprising the steps of: a) providing an intermediate prepolymer stream from the continuous polymerization unit and diverting a portion of the intermediate polymer stream to a centrifugal mixer; b) adding waste polyester to the centrifugal mixer to obtain a homogeneous molten stream; and c) combining the homogeneous molten stream with the remainder of the intermediate polymer stream to form an outlet stream, wherein the waste polyester in step b) is not heated or melted.

Description

[Technical field]

[0001] The present invention relates to an energy efficient method and system for utilizing polyester waste in a continuous polyester polymerization process. In particular, the waste is mixed with a side stream of prepolymer in a centrifugal mixer and returned to the unit to complete the polymerization. [Background technology]

[0002] To meet the global need for a circular economy where plastics are reused and recycled, low-cost processes are needed to recycle these plastics back to the same state as the original virgin plastics. Poly(ethylene terephthalate), PET, is the plastic of choice for use in bottles for water, carbonated soft drinks, and other packaging articles. These bottles and other containers are easily recovered from consumer recycling waste by sorting, granulation, washing, and further classification into a stream of clear polyester granules or flakes (PCR). To meet regulations on the use of polyester for food contact applications, further purification of the PCR is required to remove any absorbed contaminants and to increase the molecular weight to that of standard bottle resins so that the PCR can be reused. Major brand owners of carbonated soft drinks and bottled water have set a target of 50% PCR content in the PET resin they purchase by 2030.

[0003] It is also known that discarded post-consumer (recovered) polyester (PCR) can be chemically depolymerized into their starting materials (monomers) which can then be used to manufacture PET resin. These processes use methanolysis, hydrolysis, or glycolysis reactions to depolymerize waste polyester into base materials such as dimethyl terephthalate, terephthalic acid, glycols, or monomers (bishydroxymethyl terephthalate). All of these processes require additional steps to purify the raw materials or monomers before they can be used as feedstocks to manufacture PET or blended with virgin feedstocks, which leads to increased costs.

[0004] In the methanolysis polyethylene terephthalate (PET) process, waste PET is reacted with methanol to produce the raw materials dimethyl terephthalate (DMT) and ethylene glycol (EG). These reaction products must be purified to meet the same specifications as the virgin feedstock before being used to produce virgin polyester (the polyester formed from that raw material). However, most commercial PET manufacturing facilities use terephthalic acid (TA) rather than DMT, and therefore additional processing is required to convert the DMT to TA.

[0005] PET hydrolysis is the depolymerization of waste PET into TA and EG by reacting it with water. However, it is known that certain contaminants commonly present in waste PET make it very difficult and require additional purification steps to obtain high-purity TA.

[0006] PET glycolysis is the reaction of waste PET with glycols (such as EG) to produce the monomer bishydroxyethyl terephthalate (BHET) and other oligomers. This process has significant advantages over methanolysis or hydrolysis, primarily because BHET may be used as a raw material in either the DMT or TA polyester manufacturing processes without significant and significant modification of the manufacturing equipment. However, BHET must be purified before it can be used to make PET resins with the same quality standards as virgin PET.

[0007] Various processes have been disclosed in which PCR is melted in an extruder and added to the esterification reactor of a continuous polymerization unit. US 2003 / 0134915 discloses a process in which PCR is melted with the addition of ethylene glycol and extruded into an esterification reactor for depolymerization to an oligomeric esterification product, which is then polymerized in a subsequent reactor of a continuous polymerization unit. A vacuum in the final polycondensation reactor ("finisher") removes contaminants absorbed in the PCR. The amorphous pellets can be solid-phase polymerized to the molecular weight required for container applications or polymerized to the final molecular weight in the finisher. Current processes for adding PCR flakes to existing CP lines run at an average recycle content of 25%. Modern installed CP lines have capacities of over 30 tons / day, and retrofitting these lines to add 50% PCR would require extruders capable of operating at 15 tons / hour, which is beyond the speed of current extruder technology. The capital cost of one or more high throughput extruders, as well as the cost of the energy lost in the motors and gearboxes of these extruders, make this technology unattractive.

[0008] In addition, glycols recovered during the continuous PET manufacturing process are recycled to be used with virgin glycol in the initial esterification process with terephthalic acid. Contaminants and decomposition products of adding large amounts of PCR flakes require the recovered glycols to be purified before they can be used as a starting material.

[0009] WO 2019 / 162265 discloses a conceptual process in which PCR flakes are heated and then mixed in a dynamic mixer with an intermediate stream from a PET continuous polymerization unit to depolymerize the PCR and then returned to the continuous polymerization unit to complete their polymerization. The patent application does not provide any examples to support the validation of this process.

[0010] Therefore, there is a need for a more energy efficient and low capital cost process to utilize PCR flakes at up to 75% rate in continuous PET polymerization units. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] US Patent Application Publication No. 2003 / 0134915 [Patent Document 2] International Publication No. 2019 / 162265 Brochure Summary of the Invention [Means for solving the problem]

[0012] According to one embodiment of the present invention, there is provided a method for producing a polyester polymer containing waste polyester in a continuous polymerization unit, comprising the steps of: providing an intermediate prepolymer stream from the continuous polymerization unit and diverting a portion of the intermediate prepolymer stream to a centrifugal mixer; adding waste polyester to the centrifugal mixer to obtain a homogenous melt stream; combining said homogeneous melt stream with a remaining portion of said intermediate polymer stream to form an outlet stream; wherein the waste polyester in step b) is not heated or melted.

[0013] According to another embodiment of the present invention, the method for producing the polyester polymer includes PCR flakes or post-industrial PET as waste polyester.

[0014] According to yet another embodiment of the invention, the process for producing the polyester polymer includes an outlet stream having up to 75% waste polyester.

[0015] According to yet another embodiment of the present invention, the method for producing a polyester polymer as described above, wherein the difference in intrinsic viscosity between the homogenous melt stream and the remainder of the intermediate polymer stream is in the range of about ±0.10 dl / g as measured at 25° C. according to ASTM D4603-96.

[0016] According to yet another embodiment of the present invention, the method for producing a polyester polymer as described above, wherein the difference in intrinsic viscosity between the homogenous melt stream and the remainder of the intermediate polymer stream is in the range of about ±0.05 dl / g as measured at 25° C. according to ASTM D4603-96.

[0017] According to yet another embodiment of the present invention, the method for producing polyester polymer, wherein the residence time of the waste polyester in the centrifugal mixer is less than about 3 minutes.

[0018] According to yet another embodiment of the present invention, the method for producing a polyester polymer as described above, wherein the energy used in the centrifugal mixer is from about 0.69 MJ / kg to about 1.21 MJ / kg.

[0019] In accordance with yet another embodiment of the present invention, the method of making the polyester polymer includes an additional feed stream entering a centrifugal mixer containing a component selected from the group consisting of ethylene glycol, colorants, toners, dyes, release agents, reheat agents, flame retardants, plasticizers, stabilizers, chain extenders, impact modifiers, and combinations thereof.

[0020] According to yet another embodiment of the present invention, the method of producing polyester polymer includes drying the polyester waste in a drying device prior to adding to the centrifugal mixer.

[0021] According to yet another embodiment of the present invention, the method of producing the polyester polymer comprises a ratio of the homogeneous melt stream to the remainder of the intermediate polymer stream in the outlet stream of from about 1:5 to about 2:1.

[0022] According to yet another embodiment of the present invention, the method of producing polyester polymer wherein the amount of said intermediate stream diverted to said centrifugal mixer may be varied based on a desired amount of waste polyester in said outlet stream while maintaining a constant flow rate of said outlet stream to a finisher section of said continuous polymerization unit.

[0023] According to yet another embodiment of the invention, the method of producing the polyester polymer comprises filtering the homogeneous melt stream.

[0024] According to yet another embodiment of the invention, the method of producing a polyester polymer includes a first filtration device and a second filtration device.

[0025] According to yet another embodiment of the invention, the method of producing the polyester polymer includes introducing the outlet stream into a static mixer prior to transferring the outlet stream to the next section of the continuous polymerization unit.

[0026] According to yet another embodiment of the invention, the method of producing the polyester polymer includes introducing the outlet stream into a static mixer prior to transferring the outlet stream to a finisher section of the continuous polymerization unit.

[0027] According to yet another embodiment of the present invention, there is provided a system for producing a polyester polymer, comprising: a centrifugal mixer having at least a first inlet, a second inlet, and an outlet; a first pipe configured to introduce polyester waste into the first inlet of the centrifugal mixer; a prepolymer flow line configured to divert a portion of the prepolymer flow to the second inlet of the centrifugal mixer, the prepolymer flow line allowing a homogenous melt stream to exit the outlet of the centrifugal mixer; a mixing device configured to combine the homogenous melt stream with a remainder of the intermediate polymer stream to form an outlet stream; The waste polyester is not heated or melted prior to entering the centrifugal mixer. A system is provided. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 shows a process flow sheet of one embodiment of the present invention. [Diagram 2] FIG. 2 shows a process flow sheet of the second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention may be more readily understood by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, which form a part of this disclosure. It is to be understood that the present invention is not limited to the specific apparatus (devices), methods, conditions or parameters described and / or illustrated herein, and the terminology used herein is merely for the purpose of describing specific embodiments by way of example, and is not intended to limit the claimed invention. Any and all patents and other publications identified herein are incorporated by reference as if fully set forth herein.

[0030] The ranges described herein are by definition of the ranges, and therefore include both the numbers at the ends of each range and any possible numbers therebetween. Therefore, it is to be understood that the ranges and limits mentioned herein include all ranges (i.e., subranges) located within the stated limits. For example, the range of about 100 to about 200 also includes the ranges of 110 to 150, 170 to 190, 153 to 162, and 145.3 to 149.6. Furthermore, the limit of about 7 also includes, by way of example, the limits of about 5, 3, and about 4.5, as well as ranges within those limits, such as about 1 to about 5, and about 3.2 to about 6.5.

[0031] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weights, reaction conditions, and the like used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.

[0032] As used herein, the terms "comprise," "comprises," "containing," "has," "have," "having," "includes," "include," and "including" are open-ended transitional terms used to transition from the subject matter described before the term to one or more elements listed after the term, and the element or elements listed after the transitional term are not necessarily the exclusive elements that make up the subject matter.

[0033] The term "polyester" as used herein is intended to include "copolyester" and is understood to mean a synthetic polymer prepared by the reaction of one or more difunctional carboxylic acids and / or polyfunctional carboxylic acids with one or more difunctional hydroxyl compounds and / or polyfunctional hydroxyl compounds, such as branched comonomers. Typically, the difunctional carboxylic acids can be dicarboxylic acids and the difunctional hydroxyl compounds can be dihydric alcohols, such as glycols and diols. The term "glycol" as used herein includes, but is not limited to, diols, glycols, and / or polyfunctional hydroxyl compounds, such as branched comonomers.

[0034] The term "residue" as used herein means any organic structure incorporated into a polymer by polycondensation and / or esterification reaction from the corresponding monomer. The term "repeating unit" as used herein means an organic structure having a dicarboxylic acid residue and a diol residue linked through a carbonyloxy group. Thus, for example, the dicarboxylic acid residue may be derived from a dicarboxylic acid monomer or its associated acid halide, ester, salt, anhydride, and / or mixtures thereof. Thus, as used herein, the term "dicarboxylic acid" is intended to include dicarboxylic acid and any derivative of dicarboxylic acid including its associated acid halide, ester, half ester, salt, half-salt, anhydride, mixed anhydride, and / or mixtures thereof that are useful in the reaction process with a diol to produce a polyester. As used herein, the term "terephthalic acid" is intended to include terephthalic acid itself and its residues, as well as any derivatives of terephthalic acid, including its associated acid halides, esters, half esters, salts, half salts, anhydrides, mixed anhydrides, and / or mixtures thereof, or residues thereof, that are useful in the reaction process with diols to produce polyesters.

[0035] The polyesters used in the present invention can typically be prepared from dicarboxylic acids and diols that react in substantially equal proportions to be incorporated into the polyester polymer as the corresponding residues. Thus, the polyesters of the present invention can contain substantially equal molar proportions of acid residues (100 mol%) and glycol (and / or multifunctional hydroxyl compound) residues (100 mol%), so that the total moles of repeat units equal 100 mol%. Thus, the mole percentages provided in this disclosure may be based on the total moles of acid residues, the total moles of diol residues, or the total moles of repeat units. For example, a polyester that contains 5 mol% isophthalic acid based on the total acid residues means that the polyester contains 5 mol% isophthalic acid residues out of a total of 100 mol% acid residues. Thus, there are 5 moles of isophthalic acid residues per 100 moles of acid residues. In another example, a polyester that contains 1.5 mol% diethylene glycol out of a total of 100 mol% glycol residues has 1.5 moles of diethylene glycol residues per 100 moles of glycol residues.

[0036] The polyester polymers of the present invention contain ethylene terephthalate repeat units in the polymer chain. The polyester polymers have, based on 100 mole percent of carboxylic acid moiety residues and 100 mole percent of hydroxyl moiety residues in the polyester polymer, (a) a carboxylic acid component comprising at least 90 mole percent, at least 92 mole percent, at least 93 mole percent, or at least 96 mole percent of the residue of terephthalic acid or a derivative of terephthalic acid, or a mixture thereof; (b) a diol component comprising at least 90 mole percent, at least 92 mole percent, at least 93 mole percent, or at least 96 mole percent residues of ethylene glycol; Includes.

[0037] The polyester resin can be optionally modified with up to 10% by weight of a dicarboxylic acid other than terephthalic acid that is useful in forming the resin of the present invention. Suitable diacids can be aliphatic, cycloaliphatic, or aromatic dicarboxylic acids, such as isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, 1,12-dodecanedioic acid; 2,6-naphthalenedicarboxylic acid, bibenzoic acid, oxalic acid, malonic acid, pimelic acid, suberic acid, azelaic acid, maleic acid, fumaric acid, phthalic acid, hemimellitic acid, trimellitic acid, trimesic acid, or mixtures thereof and their equivalents. It is often appropriate to use functional acid derivative equivalents such as dimethyl, diethyl, or dipropyl esters of the above dicarboxylic acids. The preferred modifying dicarboxylic acid is isophthalic acid or 2,6-naphthalenedicarboxylic acid.

[0038] Alternatively, the polyester resin can be optionally modified with up to 10% by weight of one or more different diols other than ethylene glycol. In a typical PET process, about 2 mole percent of diethylene glycol is formed by esterification of ethylene glycol. Such additional diols include, for example, cycloaliphatic diols having 6 to 20 carbon atoms or aliphatic diols having preferably 3 to 20 carbon atoms. Examples of such diols to be included with ethylene glycol are diethylene glycol, triethylene glycol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, 2-methyl-1,3-pentanediol, 2,2-dimethyl-1,3-pentanediol, 2,2,4-trimethylpentane ... Diol-(1,3), 2-ethylhexanediol-(1,3), 2,2-diethylpropanediol-(1,3), hexanediol-(1,3), 1,4-di-(hydroxyethoxy)-benzene, 2,2-bis-(4-hydroxycyclohexyl)-propane, 2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane, 2,2-bis-(3-hydroxyethoxyphenyl)-propane, and 2,2-bis-(4-hydroxypropoxyphenyl)-propane. Preferred modifying diols are diethylene glycol, 1,4-cyclohexanedimethanol, 2-methyl-1,3-pentanediol, and 2,2-dimethyl-1,3-pentanediol.

[0039] The polyester of the present invention may also include at least one chain extender. Suitable chain extenders include, but are not limited to, polyfunctional (including but not limited to difunctional) isocyanates, polyfunctional epoxides, including epoxidized novolacs, and phenoxy resins. In certain embodiments, the chain extender may be added at the end of the polymerization process or after the polymerization process. If added after the polymerization process, the chain extender may be incorporated by compounding or by addition during a conversion process such as injection molding or extrusion. The amount of chain extender used may vary depending on the specific monomer composition used and the physical properties desired, but is generally about 0.1 to about 5 wt % or about 0.1 to about 2 wt % based on the total weight of the polyester.

[0040] In addition, the polyester compositions and polymer blend compositions useful in the present invention may also contain any amount of at least one additive, such as 0.01 to 2.5% by weight of the total composition of common additives, such as, but not limited to, colorants, dyes, mold release agents, flame retardants, reheat additives, plasticizers, UV stabilizers, thermo-oxidative stabilizers and / or reaction products thereof, stabilizers, chain extenders, and impact modifiers. Examples of thermo-oxidative stabilizers include phosphorus compounds and primary and secondary antioxidants commercially available for use in polyester resins. Examples of typical commercially available impact modifiers well known in the art and useful in the present invention include, but are not limited to, ethylene / propylene terpolymers, functionalized polyolefins, such as those containing methyl acrylate and / or glycidyl methacrylate, styrenic block copolymer impact modifiers, and various acrylic core / shell impact modifiers. Examples of chain extenders include, but are not limited to, multifunctional (including but not limited to difunctional) isocyanates, multifunctional epoxides, including epoxidized novolacs, and phenoxy resins. Residues of such additives are also contemplated as part of the polyester composition.

[0041] In addition, certain agents that tone the polymer can be added to the polycondensation process. A bluing toner can be used to reduce the yellowness of the resulting polyester polymer melt phase product. Such bluing agents include cobalt salts, blue inorganic and organic toners, etc. In addition, red toner(s) can be used to adjust the redness. Organic toners can be used, such as blue and red organic toners. The organic toner can be supplied as a premix composition. The premix composition can be a neat blend of red and blue compounds, or the composition can be dissolved or slurried in one of the polyester raw materials, such as ethylene glycol.

[0042] The total loading of the toner components depends on the amount of inherent yellow color in the base polyester and the effectiveness of the toner. Generally, concentrations of up to about 15 ppm of mixed organic toner components and a minimum concentration of about 0.5 ppm are used, with the total loading of the bluing additive typically ranging from about 0.5 ppm to about 10 ppm.

[0043] Polymerization Process The polyesters of the present invention are produced by a continuous process. A continuous process typically consists of four major process units: (i) a slurry preparation vessel in which dicarboxylic acids and diols are mixed, (ii) an esterification unit, (iii) a prepolymerization (or oligomerization) unit, and (iv) a high polymerizer or finisher unit. In most designs, melt phase polymerization is carried out in one or more esterification reactors, one or more prepolymerizers, and one or two high polymerizers. In some designs, esterification and prepolymerization are carried out in one vessel.

[0044] The terms "esterifier", "prepolymerizer", "higherpolymerizer" or "finisher" as used in the specification and claims are intended to mean both single and multiple reactors in each unit. A typical polyesterification process includes one or more stages and is commercially carried out in one of two general routes. In processes using direct esterification in the early stages of the process, dicarboxylic acids are reacted with one or more diols at temperatures of about 200°C to about 270°C to form macromonomer structures and small condensate molecules of water. Since the reaction is reversible, water is continuously removed to drive the reaction towards the desired first stage product. Similarly, when diesters (instead of diacids) are used, transesterification processes are used to react the ester groups of the diesters and the diols with certain well-known catalysts such as manganese acetate, zinc acetate, or cobalt acetate. After completion of the transesterification reaction, these catalysts are scavenged with phosphorus compounds such as phosphoric acid to prevent decomposition during the polycondensation process.

[0045] Then, in the second stage of the reaction, either the macromonomer structure (direct esterification product) or the exchanged moiety (transesterification product), usually described as an oligomeric esterification product, undergoes a polycondensation reaction to form a polymer.

[0046] The reactants from the esterification stage are then continuously transferred to a prepolymerizer having a slight vacuum, preferably less than about 200 mm absolute mercury (Hg) and operating at a temperature in the range of about 240-300°C for about 30-75 minutes. This prepolymerizer can be an integral part of the esterification process. At this stage, the prepolymer has a molecular weight in the range of about 0.2 to about 0.3 dl / g, as measured by its intrinsic viscosity (IV). This prepolymer is then continuously transferred to an intermediate polymerizer or directly to a high polymerizer, in which the vacuum is increased to less than about 10 millimeters absolute mercury, preferably less than about 5 mm, and the temperature is about 260-300°C for about 45-90 minutes. The diol is continuously removed in the prepolymerizer and high polymerizer and recycled to the esterifier.

[0047] The polymerization reaction is stopped when the required / target molecular weight is achieved and / or the maximum molecular weight for the equipment design is reached. The polyester is extruded through a die into strands which are quenched and chopped into pellets or chopped underwater to form pellets. If necessary, the polyester pellets can be further polymerized to higher molecular weight by well-known solid state polymerization processing techniques.

[0048] Catalysts commonly used in polycondensation reactions are compounds containing antimony, germanium, aluminum, titanium or other catalysts known to those skilled in the art, or mixtures thereof. The specific additives used and their introduction points during the reaction are known in the art and do not form part of the present invention. Any conventional system may be used, and those skilled in the art can select from a variety of commercially available systems for the introduction of additives to achieve optimal results.

[0049] The terephthalic acid and / or ethylene glycol are preferably derived from a biomass feedstock, rather than a petroleum-based feedstock. In addition, the use of chemically recycled terephthalic acid (or dimethyl terephthalate) and ethylene glycol from post-consumer polyester waste is also preferred for the polyesters of the present invention.

[0050] Addition of PCR flakes The process of the present invention is based on three principles to minimize thermal degradation of PCR flakes, reduce capital costs, avoid contamination of the internal recycle EG, and reduce the energy losses associated with the addition of up to 75% of PCR flakes to a continuous polymerization (CP) line.

[0051] The first principle recognizes that the throughput of a CP unit for the polymerization of polyesters is limited by the design of the finisher for the target molecular weight (intrinsic viscosity). The reaction rate of polycondensation is governed by the diffusion of ethylene glycol by-product from the molten mass. In this final stage of polymerization, the viscosity of the polyester increases rapidly with increasing molecular weight, and these reactors are agitated by horizontal agitators with disks or cages that lift the molten polymer and create a thin film from which ethylene glycol can diffuse into the high vacuum inside the reactor. The spacing of the disks increases along the axis of the reactor based on the increase in viscosity to ensure that a thin film is created on these disks and does not form bridges between successive disks. As a result, the design of the finisher reactor is based on the difference between the inlet molecular weight and the final desired molecular weight. A typical design for a disk-ring reactor is disclosed in U.S. Pat. No. 3,248,180, and a typical design for a cage reactor is disclosed in U.S. Pat. No. 5,599,507. The process of the present invention provides the same nominal molecular weight of prepolymer entering the finisher vessel with PCR recycle rates of up to about 50%, thus maintaining the throughput of the CP line to reach its target molecular weight.

[0052] The second principle is to reduce the energy losses and capital costs associated with adding the PCR flakes to the CP unit by melting them in a high throughput extruder, and the third principle is to minimize any thermal degradation associated with adding the PCR flakes and to segregate any volatile organic compounds from entering the CP process.

[0053] Both of these aforementioned principles are accomplished in the method of the present invention by adding the PCR flakes as a solid, without melting or heating, to a side stream of prepolymer in a centrifugal mixer with a residence time of less than about 3 minutes, and directing this molten stream of mixed PCR flakes and prepolymer, having nominally the same molecular weight as the prepolymer, back into the prepolymer stream that was not diverted to the mixer and toward the finisher.

[0054] Centrifugal Mixer Centrifugal mixers are commonly used in the refining of cocoa-containing products such as chocolate. WO 2007 / 066362 describes such a mixer, for example. In this case, the material to be treated is guided in a drum, preferably arranged substantially horizontally. The drum has a rotating shaft at least partially equipped with pins arranged helically to move the material along the drum. This rotating shaft is operated at a high rotational speed which throws the material against the inner wall of the drum by the action of centrifugal forces.

[0055] The introduced substance or mixture is constantly mixed by the pins. The density of the pins can vary along the shaft. The pins can be similar, for example with a round cross-sectional area of ​​the same diameter. Alternatively, different types of pins, for example with different cross-sectional areas (polygonal, elliptical, circular) or different diameters, can be arranged on the shaft. Preferably, the pins are cylindrical. By rotation of the pins, the energy input to the mixture occurs in a thin layer formed by the centrifugal force, this energy input being relatively uniform over the entire volume of the mixture.

[0056] Centrifugal mixers are ideally suited to mix the PCR flakes with the molten flow of prepolymer. The walls of the drum, and optionally the rotating shaft, are heated, which, together with the friction of this mixture against the inner walls of the drum, provides sufficient energy to melt the PCR flakes and form a homogeneous molten mixture. Open centrifugal mixers are preferred for the present invention, as they provide free discharge of the molten mixture without any restrictions that could cause stagnation and degradation of the mixture.

[0057] The rotating shaft operates at high speed, preferably greater than about 250 revolutions per minute (rpm), more preferably greater than about 500 rpm. The centrifugal mixer has an inlet for the molten prepolymer and one or more inlets for the PCR flakes, the shaft supported at the inlet end and driven by a motor. The residence time for melting the PCR flakes and mixing them homogeneously with the prepolymer is less than about 3 minutes. The residence time is set in part by the length of the barrel, the angle of the internal pin, and can be controlled by the rotational speed of the shaft. Melting the PCR flakes at atmospheric pressure with a short residence time minimizes motor load, minimizes thermal degradation of the PCR flakes, if any, by eliminating losses in the gearbox and the energy required to compress the melt at the exit of the extruder, and reduces energy losses compared to melting the PCR flakes in the extruder.

[0058] PCR flakes The preferred PCR flakes are obtained from the recycling of PET bottles obtained by mechanical recycling processes. Typically, bottles are collected from four main collection methods: curbside, store drop-off, buy back, and deposit refund programs. The first step in the mechanical recycling process is to sort and separate the plastics from the metals in the waste stream. Next, non-rigid plastics are separated from the rigid plastics, which are then washed to remove labels and other surface contaminants. The rigid plastics are shredded or crushed into flakes ranging in size from approximately 9 to 12 mm in maximum dimension.

[0059] At this stage, the flakes contain plastics from closures, usually polyethylene or polypropylene, as well as flakes from bottles of green, blue and other colors. The polyolefins are removed in a caustic washing process because these polymers float to the surface while PET and other plastics that are heavier than water, such as polystyrene, polyvinyl chloride, sink to the bottom. These flakes are then sorted by optical scanning to separate the colored flakes from the clear flakes. This stream of clear flakes is then sorted by NIR to remove most of the other flakes, leaving a stream of PCR PET flakes. Preferred specifications for PCR flakes that can be used in the present invention are listed in Table 1, without limiting the meaning of PCR to these specifications.

[0060] [Table 1]

[0061] In addition to using PCR flakes in the process of the present invention, it is contemplated that post-industrial PET, such as off-spec resins, can be used in conjunction with or in place of the PCR flakes in the process of the present invention.

[0062] process As shown in FIG. 1, PCR flakes are stored in a feed hopper 100 and fed through a pipe 40 to a gravimetric weighing device 110 connected to the inlet of a centrifugal mixer 300. Molten prepolymer 10 from the CP unit is fed through a polymer pump 200 to a three-way valve 210. This three-way valve 210 is set to divert a portion of the prepolymer stream to a pump 220 that feeds another inlet of the centrifugal mixer 300. The barrel of the centrifugal mixer 300 is heated by a heat transfer fluid to a temperature in the range of about 275° C. to about 290° C., and the rotating shaft of the mixer can also be heated to the same temperature range. The shaft is rotated at a speed in the range of about 250 to about 1000 rpm. The energy used in the centrifugal mixer 300 is about 0.7 to about 1.2 MJ·kg -1The homogeneously mixed melt stream consisting of PCR flakes and prepolymer leaves the centrifugal mixer 300 through pipe 45 to the screw pump 310 which feeds the coarse filter 320. The coarse filter 320 is used to extend the life of the screen changer filter or fine filter 340 and typically has a filtering accuracy of 1000 microns (1000 μm). The outlet of the coarse filter 320 is pumped through pipe 55 to the degasser 325 which removes any volatile products present in the PCR flakes or formed during the mixing process, through pipe 85 to the gas scrubber 500, and the volatile organic chemicals are exhausted through pipe 90. The outlet of the degasser 325 is connected through pipe 58 to a polymer pump 330 which feeds the molten stream through pipe 60 to a fine filter 340 having a filtering accuracy of about 60 to about 100 microns (about 60 to about 100 μm) to remove any remaining contaminants from the PCR flakes. The outlet of the fine filter 340 is directed through pipe 65 to a three-way valve 360. The molten prepolymer bypassed from the centrifugal mixer by the three-way valve 210 provides a stream 70 to the other inlet of the three-way valve 360, the outlet stream of which is passed through a static mixer 400 and then through pipe 80 to the finisher of the CP unit.

[0063] FIG. 2 shows an alternative process to the above process, where a dryer 105 is placed between the PCR feed hopper 100 and the gravimetric weighing device 110. This is used when the PCR flakes have high moisture, which may hydrolyze the PCR as it is melted in the centrifugal mixer 300, causing the molten mixture of PCR and prepolymer stream exiting the centrifugal mixer 300 to have a lower molecular weight than the desired IV. In addition, the process shown in FIG. 2 has an additional feed stream 95 to the inlet of the centrifugal mixer 300. This feed stream may consist of ethylene glycol, which glycolizes the molten mixture in the centrifugal mixer in situations where the molecular weight of the PCR is high and needs to be lowered for the desired IV of the mixed polymer stream 45 exiting the centrifugal mixer 300. This feed stream 95 may also be used to add toner to adjust the color of the mixture of PCR flakes and prepolymer and other additives required in the final product.

[0064] The ratio of the amount of prepolymer stream 15 diverted to inlet 25 of centrifugal mixer 300 via three-way valve 210 to the amount of PCR flakes provided to inlet 40 of the centrifugal mixer can be in the range of about 1:5 to about 2:1.

[0065] The IV and temperature differences between prepolymer stream 10 diverted to the mixing and filtration process by stream 20 through three-way valve 210 and outlet stream 65 which returns it to undiverted prepolymer stream 70 through three-way valve 350 should be within the range of about ±0.10 dl / g, preferably about ±0.05 dl / g, and about ±5° C., respectively.

[0066] For a desired % PCR content in the final resin, this process offers the flexibility to divert different amounts of prepolymer to the centrifugal mixer 300 while maintaining a constant rate of the above mixture to the finisher section of the CP unit. This allows the process to be adjusted depending on the IV of the PCR flakes to meet the requirement that the IV of the prepolymer stream does not change significantly with the addition of PCR flakes. This is shown in Table 2, where for a constant rate of prepolymer material to the finisher section (normalized to a dimensionless number of 100), the relative amount of prepolymer diverted to the centrifugal mixer can be adjusted to give the same amount of PCR flakes in the final polymer.

[0067] [Table 2]

[0068] It is also contemplated that the process of the present invention can be used to add PCR flakes in other stages of the CP process, for example, using the oligomer stream from the esterification section, a diverted stream of this oligomer stream is mixed into a centrifugal mixer to mix and homogenously melt the PCR flakes, and the resulting stream is pumped together with the undiverted stream to the first stage of the polycondensation unit. Alternatively, for a CP process that includes multiple finishers, a portion of the outlet stream from one finisher can be diverted into a centrifugal mixer to mix and homogenously melt the PCR flakes, and the resulting stream can be pumped together with the undiverted stream to the next finisher unit.

[0069] Test Method intrinsic viscosity Intrinsic viscosity was measured at 25° C. according to ASTM D4603-96.

[0070] color CIELAB color index (L * , a * and b *) was measured in reflectance mode with d / 8 illumination using a Konica Minolta spectrometer model CM-5 according to ASTM D6290-05. A D65 illuminant was used with a CIE 1964 10° standard observer. L * is a measure of brightness, and a * is a measure of redness (+) or greenness (-), and b * is a measure of yellowness (+) or blueness (-). EXAMPLES

[0071] The prepolymer was obtained by extruding a portion of the polymer stream through the drain from the outlet of the prepolymerizer before the finisher of a continuous polymerization unit producing a standard bottle-grade amorphous resin with an IV of 0.62 dl / g. The molten prepolymer was collected in a steel pan under nitrogen and, after cooling, crushed into flakes.

[0072] PCR flakes were obtained from Wellman France Recyclage SAS. The properties of the prepolymer and PCR flakes are summarized in Table 3.

[0073] [Table 3] 1 Not measured, the prepolymer was ground to a different size than the PCR flakes.

[0074] Testing was carried out in a pilot scale centrifugal mixer (Lico SpA). The prepolymer was melted in an extruder at a melt temperature of 285°C and fed at a controlled rate into one inlet of the mixer. The PCR was metered into the other inlet without melting or drying. The output from the mixer was quenched in air and then solidified in a steel pan under nitrogen and, after cooling, ground into flakes.

[0075] Tests were performed with %PCR flake in the final product from 0% to 98%, at different mixer shaft rotation speeds from 142 to 767 rpm, and throughputs from 27 to 249 kg / h. The temperature of the melt leaving the mixer and the energy used in the mixer were recorded, and the IV and color index of the final product were measured. The results of these tests are summarized in Table 4.

[0076] [Table 4] 1 The polymer from test 1 was not measured as it was ground to a different size compared to all other tests.

[0077] Tests 2, 3 and 4 were carried out with PCR flake contents of 25%, 50% and 75%, respectively, at a constant throughput of 100 kg / h and a shaft rotation speed of 615 rpm. The IV and color index of the homogeneously mixed prepolymers indicate that this process can produce satisfactory products polymerized in the finisher over a wide range of PCR contents. In addition, the power (electricity) required to mix this range of PCR flake contents was in the range of about 1.1±0.1 MJ / kg.

[0078] Tests 5-8 were performed at a constant PCR flake content of 50% and a constant throughput of 100 kg / h, mixed at progressively increasing shaft rotation speeds and barrel temperatures. As with the previous tests, these tests demonstrate the flexibility of this process to homogeneously melt and mix PCR flakes with the molten prepolymer stream over a range of process parameters that can be selected to optimize the properties of the molten mixture of PCR flakes and prepolymer to meet the requirements of the finisher unit to polymerize the molten mixture of PCR flakes and prepolymer to the target properties of the final amorphous polymer.

[0079] Tests 9 and 10 were carried out at 50% PCR content at higher throughputs of 150 and 200 kg / h compared to the previous tests. The lower energy required to deliver a satisfactory mixed PCR flake / prepolymer melt stream to the finisher of the continuous polymerization unit compared to the 100 kg / h run demonstrates the low energy required in this inventive process.

[0080] Tests 11 and 12 were carried out at nominal 25 kg / h and 250 kg / h and 50% PCR flake content. By increasing the shaft rotation speed at high throughput, the IV and color index of the PCR and prepolymer mixture demonstrate the flexibility of the process of the present invention to be operated over a range of throughputs to suit the specific throughput of the continuous polymerization unit.

[0081] Tests 13 and 14 again demonstrate the flexibility of the process of the present invention to mix PCR contents ranging from 1% to 98% with the prepolymer stream to provide a satisfactory product that is polymerized in the finisher of the CP unit.

[0082] These tests show that the centrifugal mixer can be used over a range of conditions to mix PCR flakes with a portion of the prepolymer flow from the CP unit while maintaining the IV at the mixer outlet within ±0.05 dl / g of the inlet prepolymer. The flow from the mixer can be combined with the remainder of the prepolymer stream after filtration and before the finishing section of the CP unit without affecting the throughput of the CP unit.

[0083] While the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those skilled in the art that other embodiments and examples may perform a similar function and / or achieve similar results. All such equivalent embodiments and examples are within the spirit and scope of the present invention and are intended to be covered by the appended claims.

Claims

1. 1. A process for producing a polyester polymer containing waste polyester in a continuous polymerization unit, comprising the steps of: a) providing an intermediate prepolymer stream from said continuous polymerization unit and diverting a portion of said intermediate prepolymer stream to a centrifugal mixer; b) adding waste polyester to the centrifugal mixer to obtain a homogenous melt stream; c) combining said homogeneous melt stream with a remaining portion of said intermediate prepolymer stream to form an outlet stream; wherein the waste polyester in step b) is not heated or melted before being added to the centrifugal mixer.

2. 2. The method of claim 1, wherein the waste polyester is PCR flake or post-industrial PET.

3. 10. The method of claim 1, wherein said outlet stream contains up to 75% waste polyester.

4. 10. The method of claim 1, wherein the difference in intrinsic viscosity between said homogeneous melt stream and said remaining portion of said intermediate prepolymer stream is in the range of about ±0.10 dl / g as measured at 25° C. according to ASTM D4603-96.

5. 2. The method of claim 1, wherein the difference in intrinsic viscosity between said homogeneous melt stream and said remaining portion of said intermediate prepolymer stream is in the range of about ±0.05 dl / g as measured at 25° C. according to ASTM D4603-96.

6. 10. The method of claim 1, wherein the residence time of the waste polyester in the centrifugal mixer is less than about 3 minutes.

7. 10. The method of claim 1, wherein the energy used in the centrifugal mixer is from about 0.69 MJ / kg to about 1.21 MJ / kg.

8. 10. The method of claim 1 further comprising an additional feed stream entering said centrifugal mixer containing components selected from the group consisting of ethylene glycol, colorants, toners, dyes, release agents, flame retardants, plasticizers, stabilizers, chain extenders, impact modifiers, and combinations thereof.

9. 10. The method of claim 1 further comprising the step of drying the waste polyester in a drying device prior to adding to the centrifugal mixer.

10. 10. The method of claim 1, wherein the ratio of said homogeneous melt stream to said remaining portion of said intermediate prepolymer stream in said outlet stream is from about 1:5 to about 2:

1.

11. 10. The method of claim 1, wherein the amount of said intermediate prepolymer stream diverted to said centrifugal mixer may be varied based on a desired amount of waste polyester in said outlet stream while maintaining a constant flow rate of said outlet stream to a finisher section of said continuous polymerization unit.

12. The method of claim 1 further comprising the step of filtering the homogeneous melt stream.

13. 10. The method of claim 1 further comprising filtering the homogeneous melt stream through a first filter and a second filter.

14. 10. The method of claim 1 further comprising the step of: conducting said homogeneous melt stream to a degasser for removing any volatile products in said homogeneous melt.

15. 10. The method of claim 1 further comprising the step of introducing said outlet stream into a static mixer prior to transferring said outlet stream to a next section of said continuous polymerization unit.

16. 10. The method of claim 1 further comprising the step of introducing said outlet stream into a static mixer prior to transferring said outlet stream to a finisher section of said continuous polymerization unit.

17. 1. A system for producing a polyester polymer containing waste polyester, comprising: a centrifugal mixer having at least a first inlet, a second inlet, and an outlet; a first pipe configured to introduce waste polyester into the first inlet of the centrifugal mixer; a prepolymer flow line configured to divert a portion of an intermediate prepolymer stream to the second inlet of the centrifugal mixer, the prepolymer flow line exiting the outlet of the centrifugal mixer with a homogenous melt stream; a mixing device configured to combine the homogenous melt stream with a remaining portion of the intermediate prepolymer stream to form an outlet stream; wherein the waste polyester is not heated or melted prior to entering the centrifugal mixer.

18. 18. The system of claim 17, wherein the waste polyester is PCR flake or post-industrial PET.

19. 20. The system of claim 17, wherein the outlet stream contains up to 75% waste polyester.

20. 18. The system of claim 17, wherein the difference in intrinsic viscosity between said homogeneous melt stream and said remaining portion of said intermediate prepolymer stream is in the range of about ±0.10 dl / g as measured at 25° C. according to ASTM D4603-96.

21. 18. The system of claim 17, wherein the difference in intrinsic viscosity between said homogeneous melt stream and said remaining portion of said intermediate prepolymer stream is in the range of about ±0.05 dl / g as measured at 25° C. according to ASTM D4603-96.

22. 20. The system of claim 17, wherein the residence time of the waste polyester in the centrifugal mixer is less than about 3 minutes.

23. 20. The system of claim 17, wherein the energy used in the centrifugal mixer is from about 0.69 MJ / kg to about 1.21 MJ / kg.

24. 20. The system of claim 17, further comprising an additional feed stream pipe configured to introduce an additional feed stream containing components selected from the group consisting of ethylene glycol, colorants, toners, dyes, release agents, flame retardants, plasticizers, stabilizers, chain extenders, impact modifiers, and combinations thereof, into the centrifugal mixer.

25. 20. The system of claim 17, further comprising a drying device for drying the waste polyester prior to addition to the centrifugal mixer.

26. 18. The system of claim 17, wherein a ratio of said homogeneous melt stream to said remaining portion of said intermediate prepolymer stream in said outlet stream is from about 1:5 to about 2:

1.

27. 20. The system of claim 17, wherein the amount of the intermediate prepolymer stream diverted to the centrifugal mixer may be varied based on a desired amount of waste polyester in the outlet stream while maintaining a constant flow rate of the outlet stream to a finisher section of a continuous polymerization unit.

28. 20. The system of claim 17, further comprising a filtration device for filtering the homogenous melt stream.

29. 20. The system of claim 17, further comprising a first filtration device and a second filtration device for filtering the homogenous melt stream.

30. 20. The system of claim 17, further comprising a degasser for removing any volatile products in the homogeneous melt.

31. 20. The system of claim 17, further comprising a static mixer for mixing said outlet stream prior to transferring said outlet stream to a next section of a continuous polymerization unit.

32. 20. The system of claim 17, further comprising a static mixer for mixing said outlet stream prior to transferring said outlet stream to a finisher section of a continuous polymerization unit.

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