Processes and active catalysts for glycolysis of polyethylene terephthalate (PET)

Abstract

The present invention relates to a method for catalytic glycolysis of polyethylene terephthalate (PET), comprising the steps of: a) mixing PET and ethylene glycol (EG) in a reactor equipped with a catalytic filter to catalyze the depolymerization of PET and heating the mixture to depolymerize PET to form a reaction mixture containing bis(2-hydroxyethyl) terephthalate (BHET) and PET oligomers, b) cooling the reaction mixture obtained in step a) to precipitate BHET and oligomers, and c) at least partially separating the precipitated BHET and oligomers from unreacted EG, the catalytic filter comprising a transesterification catalyst for catalyzing the depolymerization of PET, the catalyst being immobilized on a fiber material. A catalytically active filter for catalytic depolymerization of polyethylene terephthalate (PET), a method for producing the catalytically active filter, and a reactor system for catalytic glycolysis of PET are also provided.

Description

[Technical field]

[0001] The present invention generally relates to the field of catalytic depolymerization of spent polymers into their respective monomers for further processing and utilization. More specifically, the present invention relates to active catalyst product configurations, reactor designs, process layouts, and methods for producing monomeric polymer building blocks by catalytic glycolysis reactions. Thus, the present invention relates to a process for the preparation of highly pure bis(2-hydroxyethyl)terephthalate (BHET) starting from polyethylene terephthalate (PET), which can be recovered from waste using non-toxic materials such as ethylene glycol and water. [Background technology]

[0002] It is known that plastic waste is one of the major problems that we will have to face over the coming decades. Every year, about 300 million tons of plastic waste are generated. The problem is that 75% of the plastic generated becomes waste, much of it released into nature, where it takes about 500-1000 years for plastic to decompose. The problem of plastic waste is further complicated by the process that forms so-called microplastics in nature. Plastic particles are so small that there is concern that they can be incorporated into the biosphere and cause unknown toxic effects.

[0003] It is therefore important that plastics are captured before they are released into the environment. One method of recovering plastics is to burn them and capture the heat, while releasing most of the remaining material into gaseous waste (i.e., CO2). 2 However, it would be even better if plastics could be recycled (i.e. thermally recycled) into new materials, preferably multiple times, before they are finally destroyed.

[0004] Polyethylene terephthalate (PET) is the most common thermoplastic polymer resin of the polyester family and is used in clothing fabrics, liquid and food containers, thermoforming for manufacturing, and in combination with glass fibers for engineering resins. In addition, expanded PET is used as a lightweight building material. PET is well known through its use as food containers, for example the so-called PET bottles.

[0005] Although PET collected or separated into very pure fractions can be directly reused using mechanical recycling, the degree of polymerization and purity of the recycled PET is essentially reduced, affecting its properties. As a result of such sorting and collection, a large fraction of the total post-consumer PET is not recovered and is found in the mixed plastic waste stream. Eventually, further mechanical recycling is not possible and alternative recycling of at least the monomers would be desirable. Preferably, the PET waste is recycled so that it can be reused, for example by chemical recycling. Chemical recycling methods for PET include chemical processes such as acid or base hydrolysis, methanolysis, or glycolysis to recycle the PET monomers.

[0006] US Patent No. 5,399,633 describes a process for preparing bis(2-hydroxyethyl) terephthalate (BHET) by glycolysis, in which waste PET is reacted with excess ethylene glycol in the presence of a transesterification catalyst, and BHET is recovered by crystallization from an aqueous solution. The method is mild and uses non-toxic materials such as ethylene glycol and water.

[0007] However, despite the existence of several different chemical recycling plants in operation, achieving a cost-effective chemical recycling process is difficult. One of the problems faced is impurities in the recycling stream, contaminants and decomposition products generated during processing, all of which can cause problems in the chemical recycling process and lead to a deterioration in the quality of the recycled material.

[0008] Therefore, efficient methodologies and strategies for chemical recycling of recycled polymers such as recycled PET are needed to obtain high purity recycled materials without producing waste liquids that are environmentally harmful and / or difficult to treat, and to allow maximum recycling and reuse of hydrocarbon materials. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] EP0723951A1 Summary of the Invention

[0010] Accordingly, the present invention preferably seeks to mitigate, alleviate or eliminate one or more of the deficiencies and drawbacks of the technology identified above, singly or in any combination, thereby solving at least the above problems by providing a method for catalytic glycolysis of polyethylene terephthalate (PET), the method comprising the steps of: a) mixing PET and ethylene glycol (EG) in a reactor equipped with a catalytic filter to catalyze the depolymerization of PET and heating the mixture to depolymerize the PET to form a reaction mixture comprising bis(2-hydroxyethyl) terephthalate (BHET) and PET oligomers; b) cooling the reaction mixture obtained in step a) to precipitate the BHET and oligomers; and c) at least partially separating the precipitated BHET and oligomers from unreacted EG, wherein the catalytic filter comprises a transesterification catalyst for catalyzing the depolymerization of PET, the catalyst being immobilized on a fibrous material.

[0011] A catalytically active filter for the catalytic depolymerization of PET is also provided, which comprises a catalyst fused to a fibrous material in the form of a filter so as to be immobilized, said fibrous material being selected from the group consisting of metal fibers, sintered metal fibers, carbon fibers, ceramic fibers, alumina-silicate (alumina)-based fibers, alumina fibers, glass fibers, PTFE fibers, P84 fibers, said catalyst being a catalyst comprising a support having a high internal surface area, such as alumina, titania, ceria, zirconia or mixtures thereof, and a catalytically active metal, such as Cu, Mn, Fe, Zn, Mg, Na, K, oxides of Cu, Mn, Fe, Zn, Mg, Na, K, K(OAc), 2 , Zn(OAc) 2 , Na 2 CO 3 or mixtures thereof, or the fibrous material is a porous ceramic fiber or alumina silicate fiber having a high internal surface area, and the catalyst is a catalytically active metal selected from Cu, Mn, Fe, Zn, Mg, Na, K, an oxide of Cu, Mn, Fe, Zn, Mg, Na, K, K(OAc) 2 , Zn(OAc) 2 , Na 2 CO 3 and the like, or mixtures thereof.

[0012] Further provided is a method for the preparation of a catalytically active filter for the catalytic depolymerization of PET, the method comprising the steps of: a) rendering a fibrous material catalytic by depositing a catalyst on the fiber surface of the fibrous material; and b) fusing the catalyst to the fiber surface to produce an immobilized catalyst, the fibrous material being metal fibers, sintered metal fibers, carbon fibers, ceramic fibers, alumina silicate-based fibers, alumina fibers, glass fibers, PTFE fibers, or P84 fibers; and / or the catalyst being a catalyst comprising a support having a high internal surface area such as alumina, titania, ceria, zirconia or mixtures thereof and a catalytically active metal such as Cu, Mn, Fe, Zn, Mg, Na, K, oxides of Cu, Mn, Fe, Zn, Mg, Na, K, K(OAc), 2 , Zn(OAc) 2 , NaCO 3or a mixture thereof, wherein the catalyst is fused to the fiber surface by heat treatment; or the fiber material is a porous ceramic fiber or an alumina silicate fiber, and the catalyst is a metal catalyst or a metal catalyst precursor that is directly impregnated into the porous ceramic fiber.

[0013] Also provided is a reactor system for catalytic glycolysis of polyethylene terephthalate (PET), the reactor system comprising at least one depolymerization vessel comprising at least one feed inlet for feeding PET and EG to the vessel, at least one outlet for removing BHET and oligomers from the vessel, and at least one catalytic filter disposed downstream of the inlet and upstream of the outlet, the catalytic filter comprising a bound transesterification catalyst for catalyzing the depolymerization of PET, the catalyst being immobilized on a fibrous material. [Brief description of the drawings]

[0014] These and other aspects, features and advantages, which the present invention can realize, will become apparent and will be elucidated from the following description of embodiments of the invention, which proceeds with reference to the accompanying drawings.

[0015] [Figure 1] Schematic diagram of the process of the present invention: (1) PET and EG are placed in a first reactor containing an active catalytic filter system where glycolysis of PET is performed in parallel with removal of insoluble materials. BHET is purified in the following steps: (2) removal of residual insoluble materials and oligomers, (3) final purification of BHET by recrystallization, and (4) polymerization of PET and recovery of EG. [Diagram 2] FIG. 1 is a schematic diagram of the PET glycolysis reaction. [Diagram 3] FIG. 1 is a schematic diagram of a PET glycolysis reactor of the present invention with a fixed fiber section. [Figure 4]1 is a schematic diagram of a reactor system of the present invention with catalytic filter sections and ports for removing particulates and adding additives in the chambers between the catalytic filter chambers. The chambers between the filter sections are designed to have sufficient space to allow for the addition of additives and removal of particulates, and also include a mixing zone to equalize flow variations that may occur at the outlet of one filter section before the liquid flow continues to the next filter section. Additives can act to remove colorants, improve particulate removal, improve dissolution rate, oxidize impurities, and remove colorants. Such additives are known in the art and may include flocculating additives, additives to increase dissolution rate, oxidizers such as ozone, hydrogen peroxide, absorbent materials such as activated carbon to remove colorants, or combinations thereof. Additionally, one or more filter sections may have different mesh sizes in each filter section, which removes smaller particles of insoluble material and increases the residence time of larger particles, including PET. [Diagram 5] FIG. 1 is a schematic diagram of a PET glycolysis reactor of the present invention, in which a fiber-based catalyst is dispersed in the liquid phase, and which consists of a slurry bed reactor equipped with a mechanical filter that separates the fibers from the liquid at the reactor outlet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The following description focuses on embodiments of the invention applicable to active catalyst product configuration, reactor design, and process layout, which in combination provide a method for producing monomeric polymer building blocks via catalytic glycolytic reactions.

[0017] In this invention, it has been found that many of the problems faced in chemical recycling processes are related to two main challenges. The first challenge is that the process requires a catalyst that is sufficiently active, overcomes the mass transfer limitations inherent in liquid reaction systems, and does not contaminate the product or effluent stream. A homogeneous catalyst provides sufficient catalytic activity, overcomes the mass transfer limitations, and can be separated from the product by crystallization. However, homogeneous catalysts will inevitably contaminate the water or EG effluent stream, or both. When using conventional heterogeneous catalysts, the size of the catalyst must be in the micrometer or nanometer range, which makes such catalysts difficult to recycle when used in the glycolysis of waste plastic feedstocks, as the catalyst material is mixed with non-PET polymers and non-polymeric residues. Furthermore, the size of the impure starting materials and the mechanically different starting materials will result in different temperatures and non-uniform reaction conditions, all of which reduce the efficiency of chemical recycling and the purity of the recycled end product.

[0018] It was hypothesized that the use of a fiber-supported catalyst in a fixed structure in the glycolysis reactor could solve some of these problems. The fiber-supported catalyst has a large exposed catalyst surface to overcome external mass transfer resistance, a fiber diameter in the micrometer range to reduce mass transfer resistance within the material, and does not contaminate the product or effluent streams because the catalyst is immobilized within the reactor. Furthermore, by configuring the fiber material as a filter bed and flowing the reactants and products through the filter in the reaction chamber, a residence time distribution of the undissolved fragments is achieved, which results in a longer residence time, and therefore reaction time, for the larger fragments compared to the smaller fragments and the dissolved PET molecules.

[0019] To prove this concept, a glycolytic process for processing PET into BHET was used, as described in EP0723951A1 and shown in Figure 2, in which waste PET is reacted with excess EG in the presence of a transesterification catalyst. The method is mild and uses non-toxic materials such as EG and water.

[0020] During testing, an active catalytic filter material was developed that could reliably select the PET fragments suitable for the active catalyst, here the glycolysis of PET to BHET. An overview of the complete reaction from recycled PET to repolymerized PET is shown in Figure 1.

[0021] The filter provides a 3D mesh network to which the active catalyst binds. Thus, the filter separates the reaction starting materials (such as recycled PET particles) by size, while ensuring that the correct materials react selectively, i.e., within the active filter material. Once the reaction has taken place, the small end products (i.e., the resulting monomeric polymer building blocks, e.g., BHET) exit the filter and do not remain in the active catalytic environment any longer than necessary. This helps to prevent unwanted side reactions of the reactants and products.

[0022] The following filter characteristics have been found to be most suitable for such a reaction:

[0023] The diameter of the fiber material is a trade-off between maximizing the external surface, minimizing the internal diffusion length, and mechanical strength. An active catalytic filter should preferably be composed of one or multiple filter beds with catalytic fiber material diameters between 5 and 200 micrometers, preferably between 5 and 50 micrometers, and most preferably between 5 and 10 micrometers.

[0024] The fiber material may be metal fiber, sintered metal fiber, carbon fiber, ceramic fiber, alumina silicate based fiber, alumina fiber, glass fiber, PTFE fiber, P84 fiber, etc. The fibers are catalyzed by attaching a catalytic material to the fibers and then bonding or fusing the catalyst to the filter surface at high temperature. The catalytic material may be a support having a high internal surface area such as alumina, titania, ceria, zirconia or mixtures thereof, and a catalytically active metal such as Cu, Mn, Fe, Zn, Mg, Na, K, oxides of Cu, Mn, Fe, Zn, Mg, Na, Na, K, K(OAc), etc. 2 , Zn(OAc) 2 , Na 2 CO 3and mixtures thereof.

[0025] The catalytic fibers may further be porous ceramic fibers or alumina silicate fibers which support and immobilize a catalytically active component or mixture of components, preferably with a high internal surface area. The catalytic fibers may be formed of catalytically active metals such as Cu, Mn, Fe, Zn, Mg, Na, Na, K, oxides of Cu, Mn, Fe, Zn, Mg, Na, K, K(OAc), etc. 2 , Zn(OAc) 2 , Na 2 CO 3 or mixtures thereof, followed by drying and treatment at elevated temperatures (ie, heat treatment) to attach or fuse the catalyst to the fibrous material.

[0026] Porous ceramic or alumina silicate fibers with large internal surface area are 20 cm 2 / g or more, for example, 20 to 800 cm 2 / g of surface area.

[0027] Such porous ceramic fiber materials have a length of 20 to 280 mm. 2 / g and a surface area of ​​0.05-0.8 cm 3 / g of pore volume.

[0028] The most preferred catalyst material is a support (mainly alumina) and an active metal oxide (ZnO or Fe 2 O 3 ), or mixtures thereof.

[0029] The catalyst may be fused to the fibrous material.

[0030] The high temperature treatment (ie, heat treatment to bond or fuse the catalyst to the fiber surface) is preferably carried out at a temperature between 200 and 600 degrees Celsius.

[0031] Some catalysts, such as oxides of Cu, Mn, and Fe, may require additional treatment at elevated temperatures in a calcination / decomposition step to produce the active catalyst components. The temperatures required for such calcination / decomposition depend on the particular catalyst species, but may range from 200 to 600°C.

[0032] Catalytic filters include fibrous materials in the form of woven fibers, felted fibers, fibers formed using a webbing process, or fibers bonded together with a binder using vacuum forming.

[0033] In the present invention, a method for producing a catalytically active filter for catalytic depolymerization of PET polymers is presented, the method comprising the steps of a) rendering a textile material catalytic by depositing a catalyst on the fiber surface of the textile material, and b) fusing the catalyst to the fiber surface to produce an immobilized catalyst.

[0034] The method of manufacturing a catalytically active filter may further comprise the step of c) forming the fibrous material into the form of a filter. Further, the fibrous material may be arranged to form a catalytic filter reactor.

[0035] The fiber-based catalyst configuration produces an immobilized catalyst product, so that the process does not pollute the product or wastewater and glycol streams. This can in principle also be achieved by using pellet- or fragment-based heterogeneous catalysts. However, due to the high mass transfer resistance of such catalyst structures, studies have shown that micrometer- and nanometer-sized particulates are necessary (see Journal of Cleaner Production, 225 (2019) 1052-1064. Section 2.5.4 and table 6; Yonghwan Kim et.al., Polymers 2022, 14, 656. https: / / doi.org / 10.3390 / polyml4040656). Separating such catalyst particles from the liquid therefore represents a major technical challenge and costly negative impact for the process. The fiber-based catalyst product configuration produces a catalyst that is immobilized and therefore does not require separation from the liquid, has a large external surface to overcome external mass transfer limitations between the fiber and the bulk liquid phase, has a mass transfer diffusion length of a few micrometers or less, and does not pollute water or EG effluent from the process.

[0036] During testing with activated filter catalysts, it was found that filters enabled new reactor designs and improved PET glycolysis processes that were developed concurrently with this invention.

[0037] The present invention is a process in which BHET is produced by catalytic decomposition of PET using an active fiber-based filter catalyst. The catalytic filter contains a transesterification catalyst that catalyzes the depolymerization of PET, and the catalyst is immobilized on a fiber material. The process consists of several steps:

[0038] a) PET is mixed with ethylene glycol (EG) and heated to an appropriate temperature. The mixture is mixed or fed into a reactor and contacted with a fiber-based catalyst. The mixture is heated to depolymerize the PET, thereby forming a reaction mixture containing bis(2-hydroxyethyl) terephthalate (BHET) and PET oligomers.

[0039] EG is preferably in stoichiometric excess.

[0040] The ratio of PET to EG is preferably 1:3 to 1:9, more preferably 1:3.7 to 1:6, and most preferably 1:4 to 1:5.

[0041] The preferred operating temperature is 150-300°C, more preferred is 180-280°C, and most preferred is 190-260°C.

[0042] The reaction mixture obtained in step a) may be filtered to remove oligomers and non-PET materials. The filtration may be performed by a catalytic filter and / or an additional filter material. Thus, the catalytic filter can prevent insoluble particles such as dirt and non-polyester components from entering the downstream process (i.e., step b).

[0043] b) The liquid phase is cooled, preferably to ambient temperature, thereby precipitating the BHET and oligomers.

[0044] c) At least partially separating the precipitated BHET and oligomers from unreacted EG, for example by filtration.

[0045] The BHET and PET oligomers of step c) may be separated by any suitable separation method, such as filtration or centrifugation.

[0046] The solid separated in step c) may be dissolved in water followed by precipitation, recrystallization and filtration at a specific temperature to obtain pure BHET.

[0047] In step b), the reaction mixture may be cooled to a temperature of 60-90°C, preferably 65-75°C, by adding water. The amount of water added may affect the ease of the subsequent steps of the process and the overall cost of BHET, and may vary in ratios of 1:0.1 to 1:10 (wt / wt), preferably 1:0.5 to 1:2, depending on the reaction mixture. Temperature control is important at this stage, since BHET needs to be dissolved in the aqueous solution, while oligomers (which would otherwise co-crystallize with BHET and prevent the formation of sufficiently large BHET crystals and contaminate BHET) must remain in suspension.

[0048] During the separation of the oligomers in step c), the aqueous solution is slowly cooled to precipitate BHET, whose solubility in water varies with temperature. To obtain a high yield of BHET, the final temperature must reach -10 to +30°C, preferably 5 to 15°C.

[0049] The BHET crystals are separated from the aqueous solution containing most of the excess EG by filtration or centrifugation. The recovered solid is dissolved again in hot water until a temperature of 70-100°C is reached, and then cooled to a temperature of 0-30°C, preferably 5-15°C, to obtain highly pure BHET crystals that are easy to filter.

[0050] In this second crystallization step, the ratio of the amount of water to BHET is 1:4-1:10, preferably 1:6-1:8. The BHET in crystalline form is recovered by filtration and further polymerized to form PET and EG. The produced EG may be sold or recycled to the glycolysis process.

[0051] During development, it was found that not only does this method work, but in test experiments benchmarked against current state-of-the-art methods, BHET yields were improved using the method of the present invention, as shown in Example 1.

[0052] In the glycolysis process of processing PET to BHET, the PET material is a solid that is solvated by EG, so after solvation, the PET, EG reactant, and BHET product constitute a homogenous liquid that can then be pumped through a reactor packed with a fiber-based catalyst.

[0053] The process can be operated without flow, such as in a batch mode, in a closed reactor in which the products and reactants contact the fiber-based catalyst by natural or forced convection within the reactor. Such forced convection can be achieved by stirring or by moving the fiber-based catalyst through a liquid phase containing the reactants and products, or the products and reactants can flow through the reactor containing the fiber-based catalyst.

[0054] The reactor may be in the form of a tubular reactor, ie, a tubular reactor configuration, in which the fiber-based catalyst is immobilized within the reactor and the products and reactants flow through the reactor.

[0055] The reactor may include at least two catalytic filters, the downstream filter having a different permeability and density and / or a different catalyst formulation than the first upstream filter.

[0056] Similarly, the reactor contains at least two catalytic filters, with subsequent filters downstream of the first filter having the same catalyst formulation as the first filter, but with successively finer mesh sizes to further remove smaller particles and insoluble material and to increase the residence time of larger PET particles and PET oligomers.

[0057] The fibrous material may further be in the form of a filter, i.e. may form a catalytically active filter.

[0058] By utilizing one or more catalytic filters with different permeabilities and densities, and possibly different catalyst formulations, separation of contaminants and catalytic conversion of PET can be achieved simultaneously.

[0059] This filter provides a longer residence time for larger PET pieces or material where the PET becomes mixed or fused with impurities such as multi-layer films and fabrics which are known to have a lower effective rate of reaction.

[0060] Yonghwan Kim et. al. (Polymers 2022, 14, 656, https: / / doi.org / 10.3390 / polyml4040656) clearly show that longer residence times for solvation do not adversely affect the yield of BHET. By holding the PET-containing material for longer periods, the dissolution of less accessible PET into the reaction solution does not have a significant negative effect on the overall yield. Conversely, more of the PET in the feedstock is glycolyzed and converted to BHET, improving the overall yield. This allows for a glycolysis process that is significantly more efficient than current technologies for processing waste PET.

[0061] In the present invention, a reactor system is developed that includes at least one depolymerization vessel containing at least one feed inlet for feeding PET and EG to the vessel, at least one outlet for removing BHET and oligomers (and excess EG) from the vessel, and at least one catalytic filter disposed downstream of the inlet and upstream of the outlet.

[0062] The depolymerization vessel may have two feed inlets for feeding PET and EG to the vessel. Such a system is shown in FIG.

[0063] The depolymerization vessel may be in the form of a reactor, with the catalytic filter fixed within the reactor and the products and reactants flowing through the reactor.

[0064] The catalytic filter prevents insoluble materials (such as dirt and non-polyester components) from entering downstream process steps and provides a residence time distribution that provides larger PET particles and larger particles that contain PET but are retained in the solid phase because other polymers are not dissolved, while smaller particles flow through the filter more quickly. This provides a mechanism for longer residence times for less reactive feed materials and shorter residence times for more reactive feed materials (higher PET content or smaller size fragments). Essentially, this results in a uniform product distribution, higher yields, and reduced formation of undesirable by-products.

[0065] The reactor system may include at least two catalytic filter sections, each with a different mesh size, with successively finer mesh sizes to further remove smaller particles of insoluble material and increase the residence time of larger particles, including PET.

[0066] The reactor system may further include at least one catalytic filter section and at least one non-catalytic filter section.

[0067] This allows for a (less preferred) system design where the catalytic filter section consists of a fiber-based catalyst slurry suspended in the reactor, which is then retained in the reactor by filtration in the non-catalytic filter section. During such testing, the fiber-based catalyst slurry may form a filter cake in the non-catalytic filter section (downstream of the filter slurry), resulting in two filter sections. An example of such a system is shown in Figure 5.

[0068] A catalytic filter-based reactor may consist of multiple filter sections, with each filter having a different mesh size. An example of such a setup is shown in Figure 4. For example, the coarsest filter mesh may allow particles up to 2 mm in size to pass through the filter, while the finest mesh size may only allow fine particles up to 5 micrometers to pass through the filter. In between the coarsest and finest filter sections, numerous filter sections can be installed, and these sections can be designed to have mesh sizes that allow fine particulate material between 2 mm and 5 micrometers to pass through such filter sections.

[0069] The fibrous material of the catalytic filter section in the reactor can be supported between metal (or other material capable of withstanding the reaction temperatures and chemical composition of the liquid in the reactor) mesh structures to form reactor internals in which the fibrous material is compressed to reach the desired material bulk density, permeability, and residence time.

[0070] In one embodiment of the present invention, the catalytic filter fiber material is dispersed at the feed inlet and collected on a filter cake along with the unconverted material, which may be further configured as multiple reactors and / or combined with catalytic filters to optimize BHET yield and impurity removal.

[0071] Desired material bulk density, permeability, and residence time can also be achieved by vacuum forming to form rigid structures from fibrous materials and binders, as is well known, for example, in the manufacture of high temperature insulating components for furnaces and other process equipment in the glass making and steel industries.

[0072] Heating and / or cooling can be applied between fiber-based catalyst sections to provide optimal conditions for pollutant removal and / or enhanced BHET yield.

[0073] The reactor system includes at least two catalytic filter sections, preferably with additives being able to be injected between the sections, and preferably with solid material being able to be removed before or between the sections.

[0074] An additional EG flow can be injected between the fiber-based catalyst sections to provide optimal conditions for pollutant removal and / or BHET yield.

[0075] Solid adsorbents and / or flocculants and / or precipitation agents can be injected between the fiber-based catalyst sections to remove contaminants prior to the subsequent reaction step.

[0076] Additional catalytic materials can be injected between the fiber-based catalyst sections to provide optimal conditions for pollutant removal and / or BHET yield. Catalytically active materials include Cu, Mn, Fe, Zn, Mg, Na, K, oxides of Cu, Mn, Fe, Zn, Mg, Na, Na, K, K(OAc) 2 , Zn(OAc) 2 , Na 2 CO 3 and the like, or mixtures thereof, and other homogeneous catalysts known in the art.

[0077] Activated carbon can be used to remove colorants and other contaminants, and 2 O 2 , O 3 It is well known that pollutants and colorants can be decomposed using various oxidizing agents such as [WO2021124149A1], and therefore these measures can be carried out during the section of the fiber-based catalyst product or as a post-treatment of the liquid.

[0078] The reactor design of the present invention may be a tubular reactor with fixed catalyst internals, which provides significantly improved reaction conditions compared to batch, semi-batch, or continuous tank reactors, since the optimum PET / EG ratio and optimum catalyst space velocity can be maintained throughout the reactor.

[0079] A further advantage compared to utilizing homogeneous catalyst technology is that in homogeneous catalyst the reactor continues to react during the cooling stage before the first crystallization step is performed, whereas in the present invention the reaction stops when the liquid stream exits the reactor since there is no catalyst outside the reactor.

[0080] Research (Yonghwan Kim et. Al. Polymers 2022, 14, 656. https: / / doi.org / 10.3390 / polyml4040656) shows that the BHET yield is directly related to the amount of catalyst used, i.e., there is an optimal catalyst loading and too much catalyst promotes competing reactions that do not form BHET.

[0081] Example 1 – Fiber-based catalysts and state-of-the-art catalysts Experiments were carried out in 150 ml reactors (2 pcs) using 10 g of PET (Invista new feedstock "RT20") and 50 ml of ethylene glycol (technical quality 98%). The amount of catalyst in the experiments with fiber-based catalyst products was 20 wt.% relative to the amount of PET loaded in the reactor. For more efficient mixing, three inert ceramic beads (diameter 3-4 mm) were added per reactor.

[0082] The reactor was mounted on a rotating holder (30 rpm) in an oven heated to a temperature of 230° C. The heating time of the reactor was assumed to be about 10 min. The reaction time was set to 60 min.

[0083] Isolation of the monomers was achieved following standard procedures involving filtration, crystallization, and recrystallization.

[0084] The yield (weight of BHET) and the weight of the material collected on the filter paper were determined.

[0085] Glycolysis was performed using the catalytic filter product and the state-of-the-art catalyst, but under otherwise identical conditions. The yields obtained are shown in Table 1. As can be seen, the method using the catalytic filter not only worked, but also showed better BHET yields than the current state-of-the-art method.

[0086] [Table 1]

[0087] Example 2 - Effect of catalyst product composition and reactor design The impact of catalyst product composition and reactor design is summarized in Table 2 below.

[0088] [Table 2]

[0089] For a 20,000 ton PET recycling plant, utilizing the present invention would allow for 200,000 ton water streams to be free from contamination by any homogeneous catalyst and 80,000 ton ethylene glycol to be free from contamination by any homogeneous catalyst.

[0090] Thus, the present invention makes it possible to reduce the costs of refining the important effluent streams of water and ethylene glycol.

[0091] Although the present invention has been described above with reference to specific embodiments, it is not intended that the present invention be limited to the specific forms described herein. Rather, the present invention is limited only by the scope of the appended claims, and other embodiments than the specific embodiments described above are equally possible within the scope of these appended claims, e.g., different from the embodiments described above.

[0092] In the claims, the term "comprising" does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Furthermore, although individual features may be included in different claims, they may be advantageously combined where possible, and the inclusion of different claims does not imply that a combination of features is not feasible and / or advantageous. Moreover, singular references do not exclude a plurality. The terms "one", "one", "first", "second", etc. do not exclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be interpreted as limiting the scope of the claims in any way.

Claims

1. A catalytic glycolysis method for polyethylene terephthalate (PET), a) A step of mixing PET and ethylene glycol (EG) in a reactor equipped with a catalytic filter to catalyze the depolymerization of PET, and heating the mixture to depolymerize PET, thereby forming a reaction mixture containing bis(2-hydroxyethyl) terephthalate (BHET) and PET oligomers, b) A step of precipitating BHET and oligomers by cooling the reaction mixture obtained in step a), c) A step of separating the precipitated BHET and oligomer from the unreacted EG, The catalyst filter comprises a transesterification catalyst that catalyzes the depolymerization of PET, and the catalyst is immobilized on a fibrous material.

2. The method according to claim 1, wherein the catalyst is fused to the fiber material.

3. The method according to claim 1 or 2, wherein the catalyst filter comprises a fibrous material in the form of woven fibers, felted fibers, fibers formed using a webbing process, or fibers bonded together with a binder using vacuum forming.

4. The method according to claim 1 or 2, wherein the fiber material is a porous ceramic fiber or alumina silicate fiber with a large internal surface area, on which a catalytically active component or a mixture of components is supported and immobilized.

5. The method according to claim 1 or 2, wherein the fibrous material is arranged to constitute a catalytic filter reactor.

6. The method according to claim 1 or 2, wherein the preferred ratio (weight / weight) of PET to EG in step a) is 1:3 to 1:9, preferably 1:3.7 to 1:6, and more preferably 1:4 to 1:

5.

7. The method according to claim 1 or 2, wherein in step a), the heating is carried out to a temperature of 150 to 300°C, preferably 180 to 280°C, and more preferably 190 to 260°C.

8. The method according to claim 1 or 2, wherein in step b), the reaction mixture is cooled to a temperature of 60 to 90°C, preferably 65 to 75°C, by adding water, and the water is added in a mass-to-mass ratio of 1:0.1 to 1:10, more preferably 1:0.5 to 1:2 (reaction mixture:water).

9. The method according to claim 1 or 2, wherein the temperature in step c) is -10 to +30°C, preferably 5 to 15°C.

10. The method according to claim 1 or 2, wherein the BHET and PET oligomer in step c) are separated by filtration or centrifugation.

11. The method according to claim 1 or 2, wherein the BHET and PET oligomer separated in step c) are dissolved in water, subsequently precipitated, recrystallized, filtered or centrifuged to obtain high-purity BHET.

12. The method according to claim 11, wherein, in order to obtain high-purity BHET crystals, the temperature during dissolution is 70 to 100°C, and the temperature during precipitation and crystallization is 0 to 30°C, preferably 5 to 15°C.

13. The method according to claim 11, wherein the ratio (weight / weight) of water to BHET during precipitation and crystallization is in the range of 1:4 to 1:10, preferably 1:6 to 1:

8.

14. The method according to claim 1 or 2, wherein the catalyst filter prevents insoluble particles such as dirt and non-polyester components from entering the downstream process step b).

15. The method according to claim 1 or 2, wherein the reactor comprises at least two catalyst filters, the downstream filters having different permeability and density and / or different catalyst formulations than the first upstream filter.

16. The method according to claim 1 or 2, wherein the reactor includes at least two catalyst filters, the subsequent filters downstream of the first filter having the same catalyst composition as the first filter, but with progressively finer mesh sizes to further remove smaller particles and insoluble materials, and to increase the residence time of larger PET particles and PET oligomers.

17. A catalytically active filter for catalytic depolymerization of PET, It includes a catalyst that is fused to a fibrous material in the form of a filter so as to be immobilized, The fiber material is selected from the group consisting of metal fibers, sintered metal fibers, carbon fibers, ceramic fibers, alumina silicate fibers, alumina fibers, glass fibers, PTFE fibers, and P84 fibers. The catalyst consists of a support with a large internal surface area such as alumina, titania, ceria, zirconia, or mixtures thereof, and catalytically active metals such as Cu, Mn, Fe, Zn, Mg, Na, and K, oxides of Cu, Mn, Fe, Zn, Mg, Na, and K, and K(OAc). ２ , Zn (OAc) ２ Na ２ CO ３ It includes acetate salts such as, or mixtures thereof, Or, The fibrous material is a porous ceramic fiber or alumina silicate fiber with a large internal surface area, and the catalyst is a catalytically active metal selected from Cu, Mn, Fe, Zn, Mg, Na, K, an oxide of Cu, Mn, Fe, Zn, Mg, Na, K, or K(OAc). ２ , Zn (OAc) ２ Na ２ CO ３ A catalytically active filter, which is an acetate salt or a mixture thereof.

18. The catalyst-activated filter according to claim 17, wherein the fibrous material has a fiber diameter of 5 to 200 micrometers, preferably 5 to 50 micrometers, and most preferably 5 to 10 micrometers.

19. The porous ceramic fiber material has a surface area of 20 to 280 m ２ / g and a pore volume of 0.05 to 0.8 cm ３ / g, and the catalytic activity filter according to claim 17.

20. A method for producing a catalytically active filter for catalytic depolymerization of PET, a) A step of making the fiber material catalytic by attaching a catalyst to the fiber surface of the fiber material, b) A step of fusing the catalyst to the surface of the fiber to produce an immobilized catalyst, The fiber material is a metal fiber, a sintered metal fiber, a carbon fiber, a ceramic fiber, an alumina silicate fiber, an alumina fiber, a glass fiber, a PTFE fiber, or a P84 fiber, and / or The catalyst comprises a support with a large internal surface area such as alumina, titania, ceria, zirconia, or mixtures thereof, and catalytically active metals such as Cu, Mn, Fe, Zn, Mg, Na, and K, oxides of Cu, Mn, Fe, Zn, Mg, Na, and K, and K(OAc). ２ , Zn (OAc) ２ Na ２ CO ３ The catalyst comprises acetates such as, or mixtures thereof, and the catalyst is fused to the fiber surface by heat treatment. Or, A method for manufacturing a catalytically active filter, wherein the fiber material is porous ceramic fiber or alumina silicate fiber, and the catalyst is a metal catalyst or metal catalyst precursor, which is directly impregnated into the porous ceramic fiber.

21. The method for producing a catalytically active filter according to claim 20, wherein the catalytic fiber material has a fiber diameter of 5 to 200 micrometers, preferably 5 to 50 micrometers, and most preferably 5 to 10 micrometers.

22. The method for producing a catalyst-activated filter according to claim 20 or 21, wherein the heat treatment is performed at a temperature of 200 to 600°C.

23. This includes an additional calcination step to generate the active catalyst component, The method for producing a catalyst-activated filter according to claim 20 or 21, wherein the catalyst is treated at a high temperature of 200 to 600°C.

24. A method for producing a catalytically active filter according to claim 20 or 21, further comprising step c) forming the fibrous material into the form of a filter.

25. A reactor system for catalytic glycolysis of polyethylene terephthalate (PET), It includes at least one depolymerization vessel, the depolymerization vessel is The container has at least one supply inlet for supplying PET and EG, The container comprises at least one outlet for removing BHET and oligomers, It includes at least one catalytic filter located downstream of the inlet and upstream of the outlet, The catalyst filter comprises a bonded transesterification catalyst that catalyzes the depolymerization of PET, and the catalyst is immobilized on a fibrous material in the reactor system.

26. The reactor system according to claim 25, wherein the depolymerization vessel includes two supply inlets for supplying PET and EG to the vessel.

27. The reactor system according to claim 25 or 26, wherein the depolymerization vessel is in the form of a reactor, the catalyst filter is fixed within the reactor, and the product and reactants flow through the reactor.

28. The reactor system according to claim 25 or 26, comprising at least two catalyst filter sections, wherein an additive can be injected between the sections, and a solid material can be removed before or between the sections.

29. The reactor system according to claim 25 or 26, wherein the reactor system comprises at least two catalyst filter sections with different mesh sizes for each filter.

30. The reactor system according to claim 25 or 26, wherein the reactor system comprises at least one catalytic filter section and at least one non-catalytic filter section.

31. The reactor system according to claim 25 or 26, wherein the fiber-based catalyst comprises a slurry of suspended fibers that are subsequently retained in the reactor by filtration.

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