Method for depolymerizing terephthalic polyesters to terephthalate esters at room temperature

Abstract

The present invention relates to the field of recycling materials containing terephthalate polyesters, in particular polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), which are commonly used to manufacture disposable plastic bottles, food trays, textiles, insulation composites, etc. It particularly relates to a method for recycling PET into terephthalic acid diesters, in particular dimethyl terephthalate (DMT), in less than one hour and without pretreatment steps. In addition, this method does not use any toxic products. It is therefore particularly advantageous from an industrial point of view.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to the field of recycling materials containing terephthalate polyesters, in particular polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), which are commonly used to manufacture disposable plastic bottles, food trays, textiles, thermal insulation composites, etc. It particularly relates to a method for recycling PET into terephthalic acid diesters, in particular dimethyl terephthalate (DMT), in less than one hour and without pretreatment steps. In addition, this method does not use any toxic products and is therefore particularly advantageous from an industrial point of view.

[0002] PET recycling is a major environmental issue and therefore a commercial opportunity due to its common use, abundance, and durability. However, recycling of PET-based materials is complex and varies depending on the polymer type, material design, and product type.

[0003] A major obstacle to the use of recycled plastic materials is the contamination of waste streams with different types of polymers that are not compatible with each other. As a result, it is often not possible to add recycled PET-type plastics to virgin polymers without reducing certain quality attributes, such as color, clarity, or impact resistance. For this reason, the ability to replace virgin polymers with recycled PET depends heavily on the purity of the recycled product and the requirements of the final product.

[0004] According to the principle of chemical recycling, PET can be depolymerized by solvolysis or hydrolysis, such as methanolysis or glycolysis, and the monomers thus obtained can be reused to produce new PET polymers, referred to as "recycled PET."

[0005] Due to industrial needs, certain techniques for producing PET resins rely on the use of dimethyl terephthalate (DMT).

[0006] Additionally, conventional methanolysis techniques use highly energy-intensive and equipment-expensive processes. These methods use supercritical phases at temperatures above 300°C and pressures of 5-10 bar. Due to the dramatic reaction conditions in terms of temperature and pressure, these techniques induce structural changes to the molecular units of PET, particularly isomerization or degradation (U.S. Patent No. 6,706,843, WO 2021 / 126661). Therefore, they are not suitable for depolymerizing certain PET-based materials, such as multi-fiber textile materials, because they can result in the production of modified PET molecules due to "contamination" with residues from other components of the textile. These modified molecules can be toxic or can cause destruction during the production of recycled PET, which is detrimental to the quality of the depolymerized product for future applications.

[0007] WO 2020 / 128218 describes a method for depolymerizing PET by alcoholysis using a monoalcohol such as methanol or ethanol and a base selected from sodium methoxide, KOH, or NaOH in a stoichiometric amount relative to the PET.

[0008] While DMT can be obtained by using a catalytic amount of base relative to the mass of PET, the reaction rate is very slow, requiring reaction times longer than 10 hours and 30 minutes, during which the reaction solution is continuously heated. Examples include U.S. Patent Application Publication No. 2019 / 0256450 and International Publication No. 2020 / 188359, which describe the depolymerization of PET to DMT in the presence of methanol and an alkoxide such as sodium methoxide. These methanolysis reactions are carried out at temperatures between 25°C and 100°C. These methods necessarily involve a first step of swelling PET with a chlorinated solvent or a polar solvent such as DMSO, DMF, or methanol. U.S. Patent Application Publication No. 2019 / 0256450 proposes reacting PET with a base, a catalytic amount of sodium methoxide, and methanol. The method described in International Publication No. 2020 / 188359 is characterized by the addition of sodium methoxide followed by several successive additions of methanol and methylate solution. The authors describe high PET production yields. U.S. Patent Application Publication No. 2019 / 390035 describes another approach to depolymerization by adding glycolate salts, the preparation of which involves a week-long isolation and drying process.

[0009] WO 2021 / 126661 describes an improved method for depolymerizing PET by methanolysis using a catalyst selected from sodium carbonate, magnesium methoxide, DBU, and TBD. The method is carried out at a temperature of at least 110-140°C by applying a pressure of 15 bar.

[0010] For those skilled in the art, the implementation of the above described process clearly presents industrial operability and feasibility problems with regard to safety aspects in ATEX environments, for example, those of methanol under reflux, which require complex precautions and expensive equipment when introducing flammable products into the process.

[0011] None of these methods are satisfactory, and it would therefore be desirable to have an improved method for recycling PET-based materials that is inexpensive and easily operable industrially, in order to facilitate the generalization of this recycling and to broaden the range of uses for recycled PET, and more generally terephthalate polyester. Summary of the Invention

[0012] The present inventors have developed a novel method that is particularly efficient for alcoholytic depolymerization under mild conditions to recycle materials containing terephthalate polyesters, particularly polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), into terephthalate ester monomers. This method is very rapid, yet much more environmentally friendly than state-of-the-art methods. This method provides access to solid forms of the product, particularly crystalline forms of DMT, DET, or BHET, which can be directly reused due to their purity.

[0013] Accordingly, the present invention provides a method for recycling materials comprising terephthalate polyesters into terephthalate esters, the method comprising two steps: a. grinding or shredding the material to produce fragments; b. terephthalate polyester, (i) a catalyst selected from a metal or organic ether oxide base, a metal acetate, a metal oxide, a metal hydroxide, or a metal carbonate; and (ii) polar solvents of the cyclic ester or ether oxide type, (iii) depolymerizing to terephthalate esters in the presence of an alcohol selected from a monoalcohol or a diol; the base is present in a catalytic amount relative to the amount of the terephthalate polyester; the depolymerization step is carried out at ambient temperature or by heating to 70°C for a period of between 1 minute and 4 hours.

[0014] The terephthalate-polyester based material can be a plastic, fabric, or another type of material containing 100% terephthalate polyester (PET or PBT), or a composite material containing a mixture of terephthalate polyester with other components such as cotton, polyamide, polyurethane, polyolefin, and fluorinated polymers, for example, a composite plastic, a multi-fiber fabric, or a composite insulating material.

[0015] Advantages of the invention The process according to the invention proposes to combine (i) a catalytic amount of a catalyst with a terephthalate polyester, (ii) an alcohol, either a monoalcohol or a diol, and (iii) an ester-type solvent, and react them under mild conditions. The present invention has several advantages over the process described above, which are discussed below.

[0016] A first notable advantage: the method does not require pretreatment, a step that requires the use of toxic products. The depolymerization reaction is sufficiently effective to allow complete depolymerization without prior expansion of the material being treated. Therefore, the method according to the invention is simpler (one less step), more environmentally friendly (no toxic products and therefore no wastewater to be treated), faster, and cheaper.

[0017] Since this method involves a very moderate industrial risk, industrial facilities for its implementation can consequently be set up more easily and the level of security of these facilities is less restrictive. Compliance with regulations is simplified during plant installation and throughout the entire production cycle. CAPEX is therefore significantly reduced.

[0018] Any type of solvent can be used for the depolymerization, but ester-type solvents are preferred. In fact, these products do not have any toxicity and are used in the field of flavorings, especially in food processing.

[0019] Remarkably, the depolymerization reaction goes to completion, is very fast, and produces high-purity terephthalate esters. This is also applicable to PET and PBT, which are depolymerized to DMT, DET, or BHET, the latter of which are readily recyclable and have industrial outlets and recognized markets.

[0020] This method can be described as "very fast" because the reaction is complete in less than 4 hours at ambient temperature and in less than 20 minutes under optimized heating conditions, particularly at 55-70°C. It initiates instantly and can result in complete depolymerization within one minute.

[0021] The depolymerization reaction is simple. Depolymerization and purification can be carried out in one and the same step. After completion of the reaction, the product obtained is directly terephthalate ester in crystalline form. Washing allows for the removal of intermediate products or decomposition products, which in conventional methods would require laborious distillation operations to separate them from the product of interest.

[0022] The method thus makes it possible to obtain DMT, DET or BHET, depending on whether the depolymerization of PET or PBT is carried out by methanolysis, ethanolysis or glycolysis, respectively.

[0023] The method can be applied to any type of material, including terephthalate polyesters, especially PET or PBT, pure or blended, clear or colored, regardless of their thickness or their composition.

[0024] Those skilled in the art know that composite fabrics and multi-fiber materials can be produced in different ways: they can be woven, coated in the form of several layers, or of non-woven nature, and they consist of different materials, in particular polyester materials blended with other materials.

[0025] The nature of the materials of the "polyester" type can be different and, in a non-inclusive term, the latter can be polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polylactic acid (PLA), polycaprolactone (PCL), etc. The materials that can be recycled by the method according to the invention comprise at least one terephthalic polyester of the PET or PBT type.

[0026] Other materials blended with polyesters can be, but are not limited to, polyamides (such as nylon 6,6 or hexamethylenediamine diadipate, nylon 6 or polycaprolactam), polyurethanes, cotton, polyolefins (polypropylene, polyethylene), and fluorinated polymers (the latter are generally coated). Fluorinated polymers are used for their sealing and insulating properties, such as polytetrafluoroethylene (PTFE). Among polyurethanes, elastane is particularly valued for providing flexibility and breathability to textiles, especially when it is a flexible elastomeric polyurethane, the two main commercial forms of which are poly(ether)urethane and poly(ester)urethane.

[0027] The use of polyamides in various proportions with PET has many applications not only in the field of clothing (lingerie and sportswear) but also in industrial textiles (microfiber wipes for industrial wiping) due to their high absorbency and dust-free properties. However, it is currently not possible to recycle composite materials containing elastane, polyamide, or coated materials, which is a problem in terms of waste management. The method according to the present invention provides a solution to this problem.

[0028] Additionally, the method according to the present invention is particularly advantageous for recycling terephthalate-polyester composites due to the fact that the reaction is selective for terephthalate polyester and does not modify other optional components. Therefore, separation of the depolymerized terephthalate polyester in monomer form from other components is easy. The latter can be recovered by simple filtration and washing. Then, after a possible bleaching step in the case of textiles, the cooled mixture precipitates the terephthalate ester monomer. Washing is sufficient to obtain DMT, DET, or BHET, which can be used directly. The washing solvent is preferably the alcohol used during depolymerization.

[0029] Another advantage over this method is that it allows the separated material of terephthalate polyester to be upcycled in an unchanged form after its depolymerization. Polyamide (polyamide 6; polyamide 6,6), elastane, and cotton are specific examples of this in the textile field. The method described in this patent allows the isolation of components initially blended with terephthalate polyester in a purity that allows for subsequent recycling. It should be noted that one of the highly innovative applications of this method allows the recovery of elastane or polyamide from composites based on terephthalate polyester and their reuse in new applications.

[0030] The yield of this method is high, at least 85%, especially for the depolymerization of PET to DMT. In addition, materials blended with polyester are completely restored.

[0031] In the specific case of depolymerizing PET to DMT using methanol, the resulting product is 99.9% pure at the end of the reaction (after filtration and washing). Therefore, no further purification is necessary. DMT can be used directly after washing with methanol. Given its purity level, DMT can be used in many applications to regenerate PET or any other type of industrial resin containing this monomer. The choice of reagents and the implementation of mild conditions mean that no isomerization reactions occur and no degradation products are formed that are detrimental to the quality of the resulting product. If present, these secondary molecules to the reaction would interfere with the polymerization reaction, and therefore, purification of the crude DMT is necessary before it can be used. This can be generalized to the depolymerization of PET and PBT to any type of terephthalate ester monomer (DMT, DET, and BHET).

[0032] This method is more economical and environmentally friendly than existing methods due to the fact that the base (catalyst) is used in catalytic amounts relative to the amount of terephthalate polyester being recycled, the reaction temperature is below 80°C, generally between ambient temperature (about 25°C) and 60°C, and the reaction time is significantly reduced compared to that of PET depolymerization methods described in the literature.

[0033] In particular, the alcohol is used in a proportion ranging from 0.25 to 16 molar equivalents relative to the terephthalate polyester, preferentially from 0.6 to 9 molar equivalents relative to the terephthalate polyester, more precisely from 1.1 to 4.9 molar equivalents relative to the terephthalate polyester, which is a substantial improvement over conventional methanolysis techniques, where a proportion of 25 molar equivalents is required.

[0034] The proportion of acetate-type polar solvent is also reduced from a minimum of 1:1.5 by weight of terephthalate polyester to volume of solvent mixture to a range of 1:10 by weight of terephthalate polyester to volume of solvent mixture.

[0035] From an ecological point of view, it should be noted that the depolymerization bath containing the solvent can be reused for a new processing cycle once the product has been filtered. The bath can be used at least twice without affecting the effectiveness of the reaction. Once the reaction is complete, the solvent can be recovered by simple, low-energy distillation, taking into account its low boiling point. [Mode for Carrying Out the Invention]

[0036] The present invention provides a method for recycling materials containing terephthalate polyesters into terephthalate esters, the method comprising two steps: a. grinding the waste material to produce fragments; b. The polyester (i) a catalyst selected from a metal or organic ether oxide base, a metal acetate, a metal oxide, a metal hydroxide, a metal carbonate, or a metal ester; and (ii) polar solvents of the cyclic ester or ether oxide type, (iii) depolymerizing to terephthalate esters in the presence of an alcohol selected from a monoalcohol or a diol; the base is present in a catalytic amount relative to the amount of polyester; wherein the depolymerization step is carried out at ambient temperature or by heating to 70°C for a period of 1 minute to 4 hours.

[0037] In a preferred embodiment, the present invention provides a method for recycling polyethylene terephthalate-containing materials into terephthalate ester monomers, the method comprising two steps: a. grinding the waste material to produce fragments; b.PET, (i) a catalyst selected from a metal or organic ether oxide base, a metal acetate, a metal oxide, a metal hydroxide, a metal carbonate, or a metal ester; and (ii) polar solvents of the cyclic ester or ether oxide type, (iii) depolymerizing the terephthalate esters to monoethylene glycol (MEG) in the presence of an alcohol selected from a monoalcohol or a diol; the base is present in a catalytic amount relative to the amount of PET; the depolymerization step is carried out at ambient temperature or by heating to 70°C for a period of between 1 minute and 4 hours.

[0038] It is known to those skilled in the art that depolymerization of terephthalate polyesters produces DMT and the corresponding diols of the polyester, i.e., monoethylene glycol from PET and butanediol from PBT.

[0039] Materials comprising terephthalate polyester can consist of 100% terephthalate polyester (e.g., plastics or fabrics) or can consist of blends (e.g., composite plastics, multi-fiber fabrics, or insulating composite panels) that include terephthalate polyester and other components such as cotton, polyamide, elastane, PTFE, polyethylene, polypropylene, and the like.

[0040] When the material containing terephthalate polyester consists of 100% terephthalate polyester, the material is converted to terephthalate esters, which can be recovered by simple filtration and precipitated by cooling, as described below and illustrated in the experimental section.

[0041] The terephthalate polyester is selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

[0042] When the material containing terephthalate polyester is a composite material containing terephthalate polyester blended with other components, a recycling method involves depolymerizing the terephthalate polyester to produce terephthalate ester (DMT), while the other components of the material remain unchanged in the reaction mixture. Because these other components are larger than DMT, they can be separated from the DMT by simple filtration.

[0043] The composite material includes a terephthalate polyester selected from polyethylene terephthalate and polybutylene terephthalate blended with another component selected from cotton, polyamide, polyurethane, polyolefin, and fluorinated polymer.

[0044] Thus, in certain embodiments where the material comprising PET is a composite comprising PET blended with other components, the recycling method allows for the PET to be converted (recycled) into DMT and the release of the other components, which may also be recycled.

[0045] The catalyst is (i) ether oxides of the sodium methoxide, magnesium methoxide, potassium methoxide, or ammonium methoxide type; (ii) metal carbonates of the sodium or potassium carbonate type, (iii) metal hydroxides of the sodium hydroxide or potassium hydroxide type, and (iv) metal acetates of the zinc acetate Zn(OAc)2 or sodium acetate NaOAc type, or potassium acetate KOAc, (v) metal oxides, (vi) A base selected from metal esters of the titanium ester Ti(OiPr)4, manganese ester Mn(OR)2, or antimony ester Sb(OR)2 type.

[0046] In a preferred embodiment of the present invention, the catalyst is selected from sodium methoxide, magnesium methoxide, potassium methoxide, or ammonium methoxide.

[0047] The catalyst is present in a molar ratio of less than 35%, preferably 1 to 20%, relative to the terephthalate polyester.

[0048] The ester-type solvent can be a monoester, a diester, or a triester.

[0049] The ester-type solvent preferably satisfies formula A: [ka]

[0050] The ether-oxide solvent preferably satisfies formula B: [ka] wherein R1 and R2 are the same or different, and n H 2n , alkyl C n H 2n+1 or C n H 2n-1 are (independently) selected from, where n=1 to 10.

[0051] In a preferred embodiment, the polar solvent is an ester type because it is non-toxic. The ester type solvent can be selected from methyl acetate, ethyl acetate, propyl, butyl, and isopropyl acetate.

[0052] Table 2 (experimental part) illustrates different embodiments of the invention depending on the base used.

[0053] The solvent may also be of the cyclic ether oxide type, such as dioxane.

[0054] In a preferred embodiment of the present invention, the terephthalate polyester:solvent ratio is 1:1.5 to 1:10.

[0055] The amount of alcohol involved in the depolymerization reaction is variable. The alcohol can be provided by a base in solution (in alcohol) or added directly to the reaction medium. Thus, the alcohol can be in excess, equal, or insufficient relative to the amount of terephthalate polyester. This parameter can be adjusted by those skilled in the art.

[0056] The alcohol is present in a ratio of 0.25 to 16 molar equivalents relative to the terephthalate polyester. In another preferred embodiment of the invention, the alcohol:terephthalate polyester molar ratio is 0.5 to 16, preferentially 0.6 to 9, and more preferentially 1.1 to 3.

[0057] Advantageously, the process is carried out by applying a ratio of terephthalate polyester:solvent mixture of 1:1.5 to 1:10 and a molar ratio of alcohol:terephthalate polyester of 0.25 to 10. In a particular embodiment, the process is carried out by applying a ratio of terephthalate polyester:solvent mixture of 1:1.5 to 1:5 and a molar ratio of alcohol:terephthalate polyester of 0.25 to 3.

[0058] The alcohol used during the depolymerization step is preferably a monoalcohol selected from methanol, ethanol, propanol, or butanol, or a diol such as ethylene glycol.

[0059] In certain embodiments of the present invention, alcohols and esters of the same rank are used during the depolymerization reaction.

[0060] This combination of alcohol and ester of the same rank has the advantage of allowing a complete depolymerization reaction. The terephthalate monomers are thus solubilized. Cooling the solution is sufficient to precipitate them and recover a high-purity product (at least 99%).

[0061] When the material comprises a blend of terephthalate polyester with other components, the latter is unmodified and remains in suspension, easily removed by filtration.

[0062] For example, methanol and methyl acetate can be combined to give DMT (methanolysis reaction), or ethanol and ethyl acetate to give DET (diethyl terephthalate diester) (ethanolysis reaction). If diethylene glycol is used, BHET (bis(2-hydroxyethyl) terephthalate) is obtained (glycolysis reaction).

[0063] The interest in DET is illustrated, for example, in document WO 2007 / 076384, which describes the ethanolysis reaction of PET. The DET production is explained as being advantageous due to the fact that DET is more soluble than DMT. The resulting DET can be oxidized and then used to produce terephthalic acid.

[0064] Alternatively, another embodiment according to the present invention can be achieved by combining alcohols and esters of different ranks. For example, two commonly used reagents, ethyl acetate and methanol, can be combined. The PET depolymerization reaction is efficient and complete, yielding the majority of the product corresponding to the alcohol used, in this case DMT due to the presence of methanol, but also secondary products such as DET and other terephthalate monomers.

[0065] The base participating in the depolymerization reaction may be in a catalytic amount relative to the amount of terephthalate polyester being treated.

[0066] "Catalytic amount" means a non-stoichiometric amount, i.e., a molar ratio of 1% to 49% relative to the amount of terephthalate polyester being treated. The term "catalytic" also applies to the reagent (catalyst) found in its initial form at the end of the reaction.

[0067] In a preferred embodiment of the present invention, the catalytic amount of ether oxide base is less than 35 mol%. The catalytic amount of ether oxide base can vary from 1 mol% to 35 mol%, preferably from 1 mol% to 20 mol%, or even from 5 mol% to 20 mol%. To further reduce this amount, extended reaction times can be applied, which makes it possible to reduce the cost of the reaction.

[0068] The reaction temperature can vary. The reaction medium can be heated to 70°C. The mixture can be particularly advantageously heated to temperatures between 50°C and 70°C, preferably below 60°C. However, it is very interesting to note that the reaction is fast, since complete depolymerization is obtained in 3-4 hours, yet it works very well at room temperature (about 25°C). The fact that the reaction is not heated simplifies its implementation and reduces costs.

[0069] The invention will be better understood on reading the following examples, which are provided by way of illustration and are not to be considered in any way as limiting the scope of the invention.

[0070] Experimental part Example 1: PET depolymerization by methanolysis A quantity (500 g) of polyethylene terephthalate (PET) chips from different sources (food trays, water bottles, etc.) is introduced into 2 L of methyl acetate. 120 mL of sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide relative to the amount of PET introduced, and 200 mL of methanol are added to the chips. The reaction begins instantly. After 30 minutes of reaction at 55 °C, all PET chips have disappeared, and a slight white solid is suspended in the solution. To retain the unreacted material, the crude reaction mixture is filtered through a Buchner filter. The recovered medium gels almost instantly. It contains DMT, monoethylene glycol produced by the depolymerization reaction, as well as the initially reacted base and solvent. The white solid (DMT) is recovered (410 g, 82%) and washed with methanol.

[0071] Example 2: PET depolymerization by methanolysis A quantity (500 g) of PET fragments from different sources (food trays, water bottles, etc.) is introduced into 2 L of methyl acetate. 210 mL of sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 35% sodium methoxide relative to the amount of PET introduced, is added to the fragments. The reaction begins instantly. After 30 minutes of reaction at 55 °C, all PET fragments have disappeared, and a slight white solid is suspended in the solution. To retain the unreacted material, the crude reaction mixture is filtered through a Buchner filter. The recovered medium gels almost instantly. It contains DMT, monoethylene glycol produced by the depolymerization reaction, as well as the initially reacted base and solvent. The white solid (DMT) is recovered (400 g, 80%) and washed with methanol.

[0072] Example 3: Depolymerization of 100% PET Fabric by Methanolysis A quantity (500 g) of 100% PET colored fabric pieces is introduced into 2 L of methyl acetate. 119 mL of sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide relative to the amount of PET introduced, is added to the pieces. The reaction begins instantly. After 120 minutes of reaction at 55 °C, all PET pieces have depolymerized, and a slight amount of colored solid is suspended in the solution. A bleaching step is carried out by adding activated carbon to obtain white DMT. The crude reaction mixture is filtered through a Buchner filter to retain unreacted materials and the activated carbon. The recovered medium gels almost instantly. It contains DMT, monoethylene glycol produced by the depolymerization reaction, and the initially reacted base and solvent. The white solid (DMT) is recovered (350 g, 70%) and washed with methanol.

[0073] Example 4: Depolymerization of 85% / 15% PET / Elastane blended textile material by methanolysis A certain amount (500 g) of PET / elastane blend fabric pieces, consisting of 85% pigmented PET and 15% pigmented elastane containing different proportions of elastane, was introduced into 3.2 L of methyl acetate and 0.8 L of methanol. 119 mL of sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide relative to the amount of fabric introduced, was added to the pieces. The reaction started instantly. After 80 minutes of reaction at 55 °C, all PET-based fabric pieces were depolymerized, leaving unreacted elastane pieces and a slight suspension of colored solids in the solution. A prefiltration step was performed to retain the elastane (75 g, 15%) and unreacted materials. The next step was bleaching by adding activated carbon to the crude reaction mixture to obtain white DMT. The crude reaction mixture was filtered through a Buchner filter to retain the activated carbon. The recovered medium gelled almost instantly. It contains DMT, monoethylene glycol produced by the depolymerization reaction, and the base and solvent originally reacted in. The white solid (DMT) is recovered (280 g, 66%) and washed with methanol.

[0074] Example 5: Depolymerization of PET / cotton (80% / 20%) blended fabric by methanolysis A quantity (500 g) of PET / cotton blend fabric pieces, consisting of 80% colored PET pieces and 20% colored cotton, was introduced into 5 L of methyl acetate. 119 mL of sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide relative to the amount of fabric introduced, was added to the pieces. The reaction started instantly. After 210 minutes of reaction at 55 °C, most of the PET fabric pieces had degraded, leaving unreacted cotton pieces, and a small amount of colored solids suspended in the solution. A prefiltration step was performed to retain the cotton (165 g, 20%) and unreacted materials. The next step was bleaching by adding activated carbon to the crude reaction mixture to obtain white DMT. The crude reaction mixture was filtered through a Buchner filter to retain the activated carbon. The recovered medium gelled almost instantly. It contained DMT, monoethylene glycol produced by the depolymerization reaction, and the base and solvent initially reacted. The white solid (DMT) is collected (245 g, 61%) and washed with methanol.

[0075] Example 6: Depolymerization of PET / Polyamide (90% / 10%) Blended Fabric by Methanolysis A quantity (500 g) of colored PET / PA blend fabric pieces was introduced into 5 L of methyl acetate. 119 mL of sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide relative to the amount of fabric introduced, was added to the pieces. The reaction started instantly. After 120 minutes of reaction at 55 °C, all fabric pieces had decomposed, leaving only small pieces of unreacted PA, and a slight suspension of colored solids in the solution. A prefiltration step was performed to retain the PA (50 g, 10%) and unreacted materials. The next step was bleaching by adding activated carbon to the crude reaction mixture to obtain white DMT. The crude reaction mixture was filtered through a Buchner filter to retain the activated carbon. The recovered medium gelled almost instantly. It contained DMT, monoethylene glycol produced by the depolymerization reaction, and the initially reacted base and solvent. The white solid (DMT) was recovered (350 g, 70%) and washed with methanol.

[0076] Example 7: Depolymerization of 100% PET Composite Insulation Panels by Methanolysis A quantity (500 g) of white 100% PET foam pieces is introduced into 1.5 L of methyl acetate. 71.43 mL of sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 12% sodium methoxide relative to the amount of PET introduced, is added to the pieces. The reaction begins instantly. After 20 minutes of reaction at 55 °C, all of the insulation panel pieces have decomposed, and a slight amount of pale yellow solid is suspended in the solution. To retain the unreacted material, the crude reaction mixture is filtered through a Buchner filter. The recovered medium gels almost instantly. It contains DMT, monoethylene glycol produced by the depolymerization reaction, as well as the initially reacted base and solvent. The white solid (DMT) is recovered (360 g, 72%) and washed with methanol.

[0077] Example 8: PET depolymerization by ethanolysis A certain amount (500 g) of PET fragments from different sources (food trays, water bottles, etc.) is introduced into 2 L of ethyl acetate. 28.12 g of sodium methoxide, corresponding to a molar ratio of 20% sodium methoxide relative to the amount of PET introduced, and 300 mL of ethanol are added to the fragments. The reaction begins instantly. After 30 minutes of reaction at 70 °C, all the PET fragments have disappeared, and a slight white solid is suspended in the solution. To retain the unreacted material, the crude reaction mixture is filtered through a Buchner filter. The recovered medium contains DET, monoethylene glycol produced by the depolymerization reaction, as well as the base and solvent initially reacted. After evaporation of the reaction solvent, DET (400 g) is recovered in the form of a pasty solid and washed with ethanol.

[0078] Example 9: Conversion as a function of time and temperature Table 1 shows the effect of reaction time and temperature on the conversion of PET to DMT.

[0079] The following reaction conditions are used: 10 g of PET are incubated in a 20% ratio (mol:mol of PET) of sodium methoxide solution (diluted to 25% in MeOH) in the presence of 45 ml of methyl acetate. [Table 1]

[0080] Example 10: Conversion as a function of solvent and alcohol type Table 2 shows the effect of reaction time and temperature on the conversion of PET to DMT.

[0081] The reaction conditions were the same as those in Example 4.

[0082] Ester-type solvents have the formula: [ka] [Table 2]

Claims

1. 1. A method for recycling materials comprising terephthalate polyesters into terephthalate diesters, the method comprising two steps: a. grinding or shredding the material to generate fragments; b. (i) a catalyst selected from a metal or organic ether oxide base, a metal acetate, a metal oxide, a metal hydroxide, a metal ester, or a metal carbonate; (ii) polar solvents of the cyclic ester or ether oxide type; (iii) depolymerizing to terephthalate esters in the presence of an alcohol selected from a monoalcohol or a diol; the base is present in a catalytic amount relative to the amount of polyester; - the depolymerization step is carried out at ambient temperature or by heating up to 70°C for a period of between 1 minute and 4 hours.

2. 10. The method of claim 1, wherein the material is composed of 100% terephthalate polyester selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

3. 10. The method of claim 1, wherein the material is a composite material comprising a terephthalate polyester selected from polyethylene terephthalate and polybutylene terephthalate blended with another component selected from cotton, polyamide, polyurethane, polyolefin, and fluorinated polymer.

4. The method of claim 3 wherein the polyurethane is elastane.

5. 2. The method of claim 1, wherein the catalyst is selected from (i) ether oxides of the sodium methoxide, potassium methoxide, magnesium methoxide, or ammonium methoxide type, (ii) metal carbonates of the sodium or potassium carbonate type, (iii) metal hydroxides of the sodium or potassium hydroxide type, (iv) metal acetates of the zinc or sodium or potassium acetate type, (v) metal oxides (vi) or metal esters, or (vii) metal esters of the titanium ester type.

6. 6. The method of claim 5, wherein the catalyst is a metal ester selected from titanium esters, manganese esters, antimony esters, or zinc acetate, sodium acetate, or potassium acetate.

7. 10. The method of claim 1, wherein the catalyst is present in a molar ratio of less than 35% relative to the terephthalate polyester.

8. the organic base satisfies one of formulas A or B: 【Chemistry 1】 【Chemistry 2】 In the formula, R １ and R ２ are the same or different, and aryl C ｎ H ２ｎ , alkyl C ｎ H ２ｎ＋１ or C ｎ H ２ｎ－１ 2. The method of claim 1, wherein n is selected from the group consisting of:

9. 9. The method of claim 8, wherein the ester is selected from methyl acetate, ethyl acetate, propyl, butyl, isopropyl acetate.

10. 10. The method of claim 1, wherein the terephthalate polyester:solvent ratio is from 1:1.5 to 1:

10.

11. 2. The method of claim 1, wherein the monoalcohol is selected from methanol, ethanol, propanol, or butanol, and the diol is ethylene glycol.

12. 10. The method of claim 1, wherein the alcohol:terephthalate polyester molar ratio (equivalents) is comprised between 0.25 and 16.

13. 13. The method according to any one of claims 1 to 12, wherein alcohols and esters of the same rank are used in the same depolymerization reaction.

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