Process for depolymerizing terephthalate polyesters to terephthalic esters at room temperature

Abstract

The present invention relates to the field of recycling materials which are typically used in the manufacture of disposable plastic bottles, food trays, fabrics, insulating composites and the like, comprising terephthalate polyesters, in particular polyethylene terephthalate (PET) or polybutylene terephthalate (PBT). In particular, the invention relates to a process for recycling PET to diesters of terephthalic acid, in particular dimethyl terephthalate (DMT), in less than one hour and without a pretreatment step. In addition, the method does not use any toxic product. Thus, it is particularly advantageous from the industrial perspective.

Description

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

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

[0003] The main obstacle to using recycled plastic materials is that the waste stream is contaminated with different types of polymers that are incompatible with each other. Therefore, it is usually impossible to add recycled PET-based plastics to virgin polymers without reducing certain quality attributes (such as color, transparency or impact resistance). For this reason, the ability to replace virgin polymers with recycled PET depends largely on the purity of the recycled product and the requirements of the final product.

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

[0005] According to industry needs, some technologies for making PET resins rely on the use of dimethyl terephthalate (DMT).

[0006] In addition, conventional methanolysis techniques use very energy-intensive and equipment-expensive processes; these processes use supercritical phases at temperatures above 300° C. and pressures between 5 and 10 bars. Due to the severe reaction conditions in terms of temperature and pressure, these techniques cause structural changes in the molecular units of PET, in particular isomerization or decomposition (U.S. Pat. No. 6,706,843, WO2021 / 126661); therefore, they are not suitable for the depolymerization of certain PET-based materials (such as multi-fiber fabric materials) because they will result in the production of modified PET molecules due to "contamination" by residues from other components of the fabric. These modified molecules may be toxic or cause damage in the process of producing recycled PET; they are detrimental to the quality of the depolymerization products used for these future applications.

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

[0008] It is known that DMT can be obtained using a catalytic amount of a base relative to the mass of PET, but the kinetics of the reaction are very slow, with a reaction time of more than 10 hours and 30 minutes, during which the reaction solution is continuously heated. By way of example, mention may be made of US2019 / 0256450 and WO2020 / 188359, which describe the depolymerization of PET to DMT in the presence of methanol and an alkoxide such as sodium methoxide. These methanolysis reactions occur at temperatures between 25° C. and 100° C. These methods necessarily include a first stage of swelling the PET with a chlorinated solvent or a polar solvent such as DMSO or DMF or methanol. US2019 / 0256450 proposes reacting PET with a base, a catalytic amount of sodium methoxide and methanol. The method described in WO2020 / 188359 is characterized by the continuous addition of methanol and a methoxide solution several times after the addition of sodium methoxide. The authors describe a high PET yield. US2019 / 390035 describes another method for depolymerization by adding a glycolate, the preparation of which includes a separation and drying step lasting one week.

[0009] WO2021 / 126661 describes an improved process for depolymerizing PET by methanolysis using a catalyst selected from sodium carbonate, magnesium methoxide, DBU and TBD. The process is carried out at a temperature of at least 110°C-140°C by applying a pressure of 15 bar.

[0010] For a person skilled in the art, implementation of the above process clearly presents problems of industrial operability and feasibility with regard to safety aspects in an ATEX environment, such as the safety of methanol under reflux, which requires complex precautions and expensive equipment when introducing flammable products into the process.

[0011] These methods are not satisfactory. It is therefore desirable to have improved methods for recycling PET-based materials which are low-cost and easy to operate industrially in order to promote the promotion of such recycling and to broaden the scope of use of recycled PET and more generally terephthalate polyesters. Summary of the invention

[0012] The inventors have developed a novel process for the particularly efficient depolymerization of terephthalate polyesters, in particular polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), to recycle terephthalate monomers by alcoholysis under mild conditions. The process is very rapid and at the same time more environmentally friendly than the processes of the prior art. The process produces a product in solid form that can be directly reused due to its purity, in particular DMT, DET or BHET in crystalline form.

[0013] The present invention therefore relates to a process for recycling a material comprising terephthalate polyesters to terephthalate esters, the process comprising two steps:

[0014] a. a step of grinding or chopping the material to produce fragments, and

[0015] b. a step of depolymerizing a terephthalate polyester to a terephthalate ester in the presence of:

[0016] (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

[0017] (ii) polar solvents of the cyclic ester or ether oxide type,

[0018] (iii) an alcohol selected from monohydric alcohols or diols,

[0019] Features:

[0020] - said base is present in a catalytic amount relative to the amount of said terephthalate polyester,

[0021] - 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.

[0022] Terephthalate-polyester based materials can be plastics, fabrics or another type of material containing 100% terephthalate polyester (PET or PBT), or composite materials such as composite plastics, multi-fiber fabrics or composite insulation materials containing a mixture of terephthalate polyester with other components (such as cotton, polyamides, polyurethanes, polyolefins and fluorinated polymers).

[0023] Advantages of the invention

[0024] The process according to the present invention proposes to mix together (i) a catalytic amount of a catalyst relative to terephthalate polyester, (ii) an alcohol as a monohydric alcohol or a diol and (iii) an ester solvent and react them under mild conditions. The present invention has several advantages over the above process, as will be explained below.

[0025] First significant advantage: the method does not require pretreatment, i.e. steps requiring the use of toxic products. The depolymerization reaction is sufficiently efficient to achieve complete depolymerization without the need for preswelling of the material to be treated. The method according to the invention is therefore simpler (one less step), more environmentally friendly (no toxic products and therefore no effluent to be treated), faster and less expensive.

[0026] Since the method has a very modest industrial risk, it is easier to build industrial plants for implementing the method, and the safety level of these facilities is less constrained. Regulatory compliance during plant installation and throughout the production cycle is simplified. CAPEX is thus significantly reduced.

[0027] Any type of solvent can be used for the depolymerization, but ester solvents are preferred. These products have virtually no toxicity and are used in food processing, particularly in the field of flavorings.

[0028] It is noteworthy that the depolymerization reaction is complete, very fast and produces high purity terephthalates. This applies to PET, but also to PBT, to depolymerize them into DMT, DET or BHET. DMT, DET or BHET are then easily recycled and have industrial distribution channels and recognized markets.

[0029] The process 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 between 55° C. and 70° C.). The reaction starts immediately and can lead to complete depolymerization within 1 minute.

[0030] The depolymerization reaction is simple. Depolymerization and purification can be carried out in the same step. After the reaction is completed, the product obtained is directly terephthalate in the form of crystals. Intermediates or degradation products can be removed by washing, while in conventional methods, laborious distillation operations are required to separate intermediates or degradation products from the product of interest.

[0031] Therefore, the method is able to obtain DMT, DET or BHET depending on whether the depolymerization of PET or PBT is carried out by methanolysis, ethanolysis or glycolysis, respectively.

[0032] The process can be applied to any type of material comprising terephthalate polyesters, in particular PET or PBT, pure or blended, transparent or pigmented, regardless of its thickness or its composition.

[0033] The skilled person knows that composite fabrics and multi-fiber materials can be manufactured in different ways. They can be in the form of woven and coated with several layers, or of non-woven nature. They are composed of different materials, in particular polyester materials blended with other materials.

[0034] The nature of the "polyester" class of materials may vary, in non-exhaustive terms the polyesters may be polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polylactic acid (PLA), polycaprolactone (PCL), etc. The material that can be recycled with the aid of the process according to the invention comprises at least one terephthalate polyester of the PET or PBT type.

[0035] Other materials blended with polyester in a non-limiting manner may be polyamides (nylon 6,6 or hexamethylenediamine diadipate, nylon 6 or polycaprolactam, etc.), polyurethanes, cotton, polyolefins (polypropylene, polyethylene), fluorinated polymers (these materials are usually coated). Fluorinated polymers, for example, polytetrafluoroethylene (PTFE) are used for their sealing and insulating properties. Among polyurethanes, elastic fibers are particularly preferred because they provide flexibility and breathability properties to the fabric, especially when it is a flexible elastomeric polyurethane, the two main commercially available forms of which are poly(ether)urethane and poly(ester)urethane.

[0036] Polyamides used in variable ratios with PET have many applications in the field of clothing (lingerie and sportswear) and also in technical textiles due to their high absorbency and dust-free properties (microfiber wipes for industrial wiping). However, it is currently not possible to recycle composite materials containing elastane fibers, polyamide or sheathing materials, which is problematic in terms of waste management; the method according to the invention provides a solution to this problem.

[0037] Furthermore, the process according to the invention is particularly advantageous for recycling terephthalate-polyester based composites, since the reaction is selective with respect to the terephthalate polyester and does not modify other optional components; therefore, the separation between the depolymerized terephthalate polyester in monomeric form and the other components is easy; the other components can be recovered by simple filtering and washing. Next, after a possible bleaching step in the case of fabrics, the cooled mixture allows the terephthalate monomers to precipitate. Washing is sufficient to obtain DMT, DET or BHET which can be used directly. The washing solvent is advantageously the alcohol used in the depolymerization process.

[0038] Another advantage over this method is that the present invention enables the upcycling of the separated terephthalate polyester material in unchanged form after depolymerization. In the textile field, polyamides (polyamide 6, polyamide 6,6), elastane and cotton are specific examples thereof. The method described in this patent enables the separation of the components originally blended with the terephthalate polyester in a purity that allows their subsequent recycling. It should be noted that one of the highly innovative applications of this method is to allow the recovery of elastane or polyamide from composite materials based on terephthalate polyester and their reuse in new applications.

[0039] The process has a high yield: at least 85%, in particular for the depolymerization of PET to DMT. In addition, the material blended with the polyester is fully recovered.

[0040] In the specific case of depolymerizing PET to DMT using methanol, the product obtained at the end of the reaction (after filtration and washing) is 99.9% pure; therefore, no subsequent purification is required. DMT can be used directly after washing with methanol. Considering its level of purity, it can be used in many applications for the regeneration of PET or any other type of technical resin involving 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 product obtained. When present, these secondary molecules of the reaction interfere with the polymerization reaction, so purification of the crude DMT is required before use. This can be extended to the depolymerization of PET and PBT to any type of terephthalate monomers (DMT, DET and BHET).

[0041] The process is more economical and more environmentally friendly than existing processes, since the base (catalyst) is used in catalytic amounts relative to the amount of terephthalate polyester to be recycled, and the reaction temperature is below 80° C., typically between ambient temperature (about 25° C.) and 60° C., and the reaction time is greatly shortened compared to the PET depolymerization processes described in the literature.

[0042] In particular, the alcohol is used in a ratio ranging from 0.25 molar equivalents to 16 molar equivalents relative to the terephthalate polyester; preferably 0.6 molar equivalents to 9 molar equivalents relative to the terephthalate polyester; more precisely 1.1 molar equivalents to 4.9 molar equivalents relative to the terephthalate polyester, which is a substantial improvement over conventional methanolysis technology (in which a ratio of 25 molar equivalents is necessary).

[0043] The proportion of acetate type polar solvents is also reduced, ranging from a minimum of 1:1.5 terephthalate polyester mass:solvent mixture volume ratio to 1:10 terephthalate polyester mass:solvent mixture volume ratio.

[0044] From an ecological point of view, it should be noted that the depolymerization bath containing the solvent can be reused for a new treatment cycle after filtering the product. The bath can be used at least twice without affecting the effectiveness of the reaction. At the end of the reaction, the solvent can be recovered by a simple low-energy distillation, given its low boiling point. DETAILED DESCRIPTION

[0045] The present invention relates to a process for recycling a material comprising terephthalate polyesters to terephthalate esters, the process comprising two steps:

[0046] a. a step of grinding or shredding the waste to produce fragments, and

[0047] b. the step of depolymerizing the polyester to terephthalate in the presence of:

[0048] (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

[0049] (ii) polar solvents of the cyclic ester or ether oxide type,

[0050] (iii) an alcohol selected from monohydric alcohols or diols,

[0051] Features:

[0052] - said base is present in a catalytic amount relative to the amount of said polyester,

[0053] 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.

[0054] In a preferred embodiment, the present invention relates to a process for recycling a material comprising polyethylene terephthalate to terephthalate monomers, the process comprising two steps:

[0055] a. a step of grinding or shredding the waste to produce fragments, and

[0056] b. a step of depolymerizing PET into terephthalate and monoethylene glycol (MEG) in the presence of:

[0057] (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

[0058] (ii) polar solvents of the cyclic ester or ether oxide type,

[0059] (iii) an alcohol selected from monohydric alcohols or diols,

[0060] Features:

[0061] - said base is present in a catalytic amount relative to the amount of PET,

[0062] - 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.

[0063] It is known to those skilled in the art that depolymerization of terephthalate polyesters produces DMT and the diols corresponding to the polyester, namely monoethylene glycol from PET and butanediol from PBT.

[0064] Materials containing terephthalate polyester can be composed of 100% terephthalate polyester (e.g., plastics or fabrics), or can be composed of a mixture containing terephthalate polyester and other components such as cotton, polyamide, elastane, PTFE, polyethylene, polypropylene (e.g., composite plastics, multi-fiber fabrics or composite insulation panels).

[0065] When the terephthalate polyester-containing material consists of 100% terephthalate polyester, the material is converted to the terephthalate ester. This can be recovered by simple filtration and precipitated by cooling, as described below and illustrated in the experimental section.

[0066] The terephthalate polyester is selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

[0067] When the material comprising terephthalate polyester is a composite material comprising terephthalate polyester blended with other components, the recycling process produces terephthalate polyester (DMT) by depolymerization of the terephthalate polyester, and the other components of the material are present in unchanged form in the reaction mixture. Because these other components are larger than DMT, they can be separated from DMT by simple filtration.

[0068] The composite material comprises a terephthalate polyester selected from polyethylene terephthalate and polybutylene terephthalate blended with another component selected from cotton, polyamides, polyurethanes, polyolefins and fluorinated polymers.

[0069] Thus, in certain embodiments in which the material comprising PET is a composite material comprising PET blended with other components, the recycling process enables the conversion (recycling) of the PET into DMT and release of the other components (which can also be recycled).

[0070] The catalyst is a base selected from:

[0071] (i) ether oxides of the sodium methoxide, magnesium methoxide, potassium methoxide or ammonium methoxide type,

[0072] (ii) a metal carbonate of the sodium carbonate or potassium carbonate type,

[0073] (iii) a metal hydroxide of the sodium hydroxide or potassium hydroxide type, and

[0074] (iv) metal acetates of the type zinc acetate Zn(OAc)2 or sodium acetate NaOAc or potassium acetate KOAc,

[0075] (v) metal oxides,

[0076] (vi) Metal esters of the titanium ester Ti(OiPr)4, manganese ester Mn(OR)2 or antimony ester Sb(OR)2 type.

[0077] In a preferred embodiment of the present invention, the catalyst is selected from sodium methoxide, magnesium methoxide, potassium methoxide or ammonium methoxide.

[0078] The catalyst is present in a molar ratio of less than 35%, preferably between 1% and 20%, relative to the terephthalate polyester.

[0079] The ester solvents may be monoesters, diesters or triesters.

[0080] The ester solvent preferably satisfies formula A:

[0081] [Compound 1]

[0082]

[0083] The ether oxide solvent preferably satisfies Formula B:

[0084] [Compound 2]

[0085]

[0086] wherein R1 and R2 are the same or different and are (independently) selected from aryl C n H 2n , alkyl C n H 2n+1 or C n H 2n-1 , where n=1 to 10.

[0087] In a preferred embodiment, the polar solvent is of ester type because it is non-toxic. The ester solvent can be selected from methyl acetate, ethyl acetate, propyl, butyl, isopropyl.

[0088] Table 2 (experimental part) describes different embodiments of the invention according to the base used.

[0089] The solvent may also be of the cyclic ether oxide type, such as dioxane.

[0090] In a preferred embodiment of the present invention, the terephthalate polyester:solvent ratio is between 1:1.5 and 1:10.

[0091] The amount of alcohol involved in the depolymerization reaction is variable. The alcohol can be provided by the base in solution (in the alcohol) or added as is to the reaction medium. Thus, the alcohol can be in excess, equal or insufficient relative to the amount of terephthalate polyester. This parameter will be adjusted by those skilled in the art.

[0092] The alcohol is present in a ratio between 0.25 and 16 molar equivalents relative to the terephthalate polyester. In another preferred embodiment of the invention, the alcohol:terephthalate polyester molar ratio is between 0.5 and 16; preferably between 0.6 and 9; more preferably between 1.1 and 3.

[0093] Advantageously, the process is carried out by applying a terephthalate polyester:solvent mixture ratio between 1:1.5 and 1:10 and an alcohol:terephthalate polyester molar ratio between 0.25 and 10. In a particular embodiment, the process is carried out by applying a terephthalate polyester:solvent mixture ratio between 1:1.5 and 1:5 and an alcohol:terephthalate polyester molar ratio between 0.25 and 3.

[0094] 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.

[0095] In a particular embodiment of the invention, the same grade of alcohol and ester are used during the depolymerization reaction.

[0096] This combination of alcohol and ester of the same grade has the advantage of allowing a complete depolymerization reaction. The terephthalate monomers are thus dissolved. Cooling the solution is sufficient to precipitate them and recover a high purity product (at least 99%).

[0097] If the material comprises a blend of terephthalate polyester and other components, the other components will not be modified, will remain suspended and will be easily removed by filtration.

[0098] By way of example, methanol and methyl acetate may be combined to obtain DMT (methanolysis reaction) or ethanol and ethyl acetate to obtain DET (diethyl terephthalate) (ethanolysis reaction). If diethylene glycol is used, BHET (bis(2-hydroxyethyl) terephthalate) (glycolysis reaction) is obtained.

[0099] The interest in DET is illustrated, for example, in document WO 2007 / 076384, which describes the ethanolysis of PET. The production of DET is described as advantageous because DET is more soluble than DMT. The DET obtained can be oxidized and then used to produce terephthalic acid.

[0100] Alternatively, another embodiment according to the invention may consist in combining different grades of alcohols and esters. For example, two common reagents, ethyl acetate and methanol, may be combined. The PET depolymerization reaction proceeds efficiently and completely and obtains the main product corresponding to the alcohol used, in this example DMT due to the presence of methanol, but also minor products such as DET and other terephthalate monomers.

[0101] The base involved in the depolymerization reaction may be a catalytic amount relative to the amount of terephthalate polyester to be treated.

[0102] "Catalytic amount" means a non-stoichiometric amount, that is to say a molar ratio of 1% to 49% relative to the amount of terephthalate polyester to be treated. The term "catalytic" also applies to the reagent (catalyst) which is present in its initial form at the end of the reaction.

[0103] In a preferred embodiment of the invention, the catalytic amount of the ether oxide base is less than 35 mol%. The catalytic amount of the ether oxide base can vary between 1 mol% and 35 mol%, preferably 1 mol% to 20 mol%, or even 5 mol% to 20 mol%. Extended reaction times can be applied to further reduce this amount, thereby enabling the cost of the reaction to be reduced.

[0104] The reaction temperature can vary. The reaction medium can be heated to 70° C. The mixture can be particularly advantageously heated between 50° C. and 70° C., preferably to a temperature below 60° C. However, it is very interesting to note that the reaction proceeds very well at room temperature (about 25° C.), while being rapid, since complete depolymerization is obtained within 3 to 4 hours. The fact that the reaction does not require heating simplifies implementation and reduces costs.

[0105] The present invention will be better understood by reading the following examples, which are provided by way of illustration and are in no way to be considered as limiting the scope of the present invention.

[0106] Experimental Section

[0107] Example 1: Depolymerization of PET by methanolysis

[0108] A certain amount (500 g) of polyethylene terephthalate (PET) flakes from different sources (food trays, water bottles, etc.) were introduced into 2 L of methyl acetate. 120 mL of a sodium methoxide solution (25% in methanol) and 200 mL of methanol corresponding to a 20% sodium methoxide molar ratio relative to the PET introduced were added to these flakes. The reaction started immediately. After 30 minutes of reaction at 55° C., all the PET flakes had disappeared, leaving a white solid slightly suspended in the solution. The crude reaction mixture was filtered through a Büchner filter in order to retain the unreacted material; the recovered medium gelled almost immediately. It contained DMT, monoethylene glycol produced by the depolymerization reaction, and the base and solvent of the initial reaction. The white solid (DMT) was recovered (410 g, 82%) and washed with methanol.

[0109] Example 2: Depolymerization of PET by methanolysis

[0110] A certain amount (500 g) of PET flakes from different sources (food trays, water bottles, etc.) were introduced into 2 L of methyl acetate. 210 mL of a sodium methoxide solution (25% in methanol) corresponding to a sodium methoxide molar ratio of 35% relative to the PET introduced was added to these flakes. The reaction started immediately. After 30 minutes of reaction at 55° C., all the PET flakes had disappeared, leaving a white solid slightly suspended in the solution. The crude reaction mixture was filtered through a Büchner filter in order to retain the unreacted material; the recovered medium gelled almost immediately. It contained DMT, the monoethylene glycol produced by the depolymerization reaction, and the base and solvent of the initial reaction. The white solid (DMT) was recovered (400 g, 80%) and washed with methanol.

[0111] Example 3: Depolymerization of 100% PET Fabric by Methanolysis

[0112] A certain amount (500 g) of 100% PET colored fabric pieces were introduced into 2 L of methyl acetate. 119 mL of sodium methoxide solution (25% in methanol) corresponding to a 20% sodium methoxide molar ratio relative to the introduced PET was added to these pieces. The reaction started immediately. After 120 minutes of reaction at 55° C., all PET pieces had been depolymerized, leaving a colored solid slightly suspended in the solution. A bleaching step was performed by adding activated carbon to obtain white DMT. The crude reaction mixture was filtered through a Büchner filter to retain unreacted material and activated carbon; the recovered medium gelled almost immediately. It contained DMT, monoethylene glycol produced by the depolymerization reaction, and the base and solvent of the initial reaction. The white solid (DMT) (350 g, 70%) was recovered and washed with methanol.

[0113] Example 4: Depolymerization of 85% / 15% PET / Spandex Blend Fabric Material by Methanolysis

[0114] A certain amount (500 g) of PET / spandex blended fabric pieces containing different percentages of spandex consisting of 85% colored PET and 15% colored spandex 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 20% sodium methoxide molar ratio relative to the introduced fabric was added to these pieces. The reaction started immediately. After 80 minutes of reaction at 55°C, all PET-based fabric pieces had been depolymerized, leaving unreacted spandex pieces and colored solids slightly suspended in the solution. A pre-filtration step was performed to retain the spandex (75 g, 15%) and unreacted materials. The next step was bleaching by adding activated carbon to the crude reaction mixture in order to obtain white DMT. The crude reaction mixture was filtered through a Büchner filter in order to retain the activated carbon; the recovered medium gelled almost immediately. It contained DMT, monoethylene glycol produced by the depolymerization reaction, and the base and solvent of the initial reaction. A white solid (DMT) (280 g, 66%) was recovered and washed with methanol.

[0115] Example 5: Depolymerization of PET / cotton (80% / 20%) blended fabric by methanolysis

[0116] A certain amount (500 g) of PET / cotton blended fabric pieces consisting of 80% colored PET and 20% colored cotton were introduced into 5 L of methyl acetate. 119 mL of sodium methoxide solution (25% in methanol) corresponding to a 20% sodium methoxide molar ratio relative to the introduced fabric was added to these pieces. The reaction started immediately. After 210 minutes of reaction at 55° C., most of the PET fabric pieces had decomposed, leaving unreacted cotton pieces and colored solids slightly suspended in the solution. A pre-filtration step was performed to retain cotton (165 g, 20%) and unreacted materials. The next step was to bleach by adding activated carbon to the crude reaction mixture in order to obtain white DMT. The crude reaction mixture was filtered through a Büchner filter in order to retain the activated carbon; the recovered medium gelled almost immediately. It contained DMT, monoethylene glycol produced by the depolymerization reaction, and the base and solvent of the initial reaction. The white solid (DMT) (245 g, 61%) was recovered and washed with methanol.

[0117] Example 6: Depolymerization of PET / polyamide (90% / 10%) blended fabric by methanolysis

[0118] A certain amount (500 g) of colored PET / PA blended fabric pieces were introduced into 5 L of methyl acetate. 119 mL of sodium methoxide solution (25% in methanol) corresponding to a 20% sodium methoxide molar ratio relative to the introduced fabric was added to these pieces. The reaction started immediately. After 120 minutes of reaction at 55°C, all fabric pieces had been degraded, leaving unreacted PA pieces and colored solids slightly suspended in the solution. A pre-filtration step was performed to retain PA (50 g, 10%) and unreacted materials. The next step was bleaching by adding activated carbon to the crude reaction mixture in order to obtain white DMT. The crude reaction mixture was filtered through a Büchner filter in order to retain the activated carbon; the recovered medium gelled almost immediately. It contained DMT, monoethylene glycol produced by the depolymerization reaction, and the base and solvent of the initial reaction. The white solid (DMT) (350 g, 70%) was recovered and washed with methanol.

[0119] Example 7: Depolymerization of 100% PET Composite Insulation Panels by Methanolysis

[0120] A certain amount (500 g) of 100% PET white foam pieces were introduced into 1.5 L of methyl acetate. 71.43 mL of sodium methoxide solution (25% in methanol) corresponding to a 12% sodium methoxide molar ratio relative to the introduced PET was added to these pieces. The reaction started immediately. After 20 minutes of reaction at 55°C, all the insulating panel pieces had degraded, leaving a light yellow solid slightly suspended in the solution. The crude reaction mixture was filtered through a Büchner filter in order to retain unreacted material; the recovered medium gelled almost immediately. It contained DMT, monoethylene glycol produced by the depolymerization reaction, and the base and solvent of the initial reaction. The white solid (DMT) (360 g, 72%) was recovered and washed with methanol.

[0121] Example 8: Depolymerization of PET by ethanolysis

[0122] A certain amount (500 g) of PET flakes from different sources (food trays, water bottles, etc.) was introduced into 2 L of ethyl acetate. 28.12 g of sodium methoxide and 300 mL of ethanol corresponding to a 20% sodium methoxide molar ratio relative to the introduced PET were added to these flakes. The reaction started immediately. After 30 minutes of reaction at 70° C., all PET flakes had disappeared, leaving a white solid slightly suspended in the solution. The crude reaction mixture was filtered through a Büchner filter in order to retain unreacted material, and the recovered medium contained DET, monoethylene glycol produced by the depolymerization reaction, and the base and solvent of the initial reaction. After evaporation of the reaction solvent, DET (400 g) was recovered in the form of a pasty solid and washed with ethanol.

[0123] Example 9: Changes in conversion rate as a function of time and temperature

[0124] Table 1 shows the effects of reaction time and temperature on the conversion of PET to DMT.

[0125] The following reaction conditions were used: 10 g of PET was incubated in a sodium methoxide solution (diluted to 25% in MeOH) in the presence of 45 mL of methyl acetate at a 20% ratio (moles of sodium methoxide: moles of PET).

[0126] [Table 1]

[0127]

[0128] Table 1: Effect of time / temperature on conversion

[0129] Example 10: Changes in conversion rate depending on the type of solvent and alcohol

[0130] Table 2 shows the effect of reaction time and temperature on the conversion of PET to DMT.

[0131] The reaction conditions were the same as those of Example 4.

[0132] Ester solvents have the formula:

[0133] [Compound 1]

[0134]

[0135] [Table 2]

[0136]

[0137] Table 2: Effect of changing solvent / alcohol type on conversion.

Claims

1. A process for recycling a material comprising terephthalate polyesters into terephthalate diesters, the process comprising two steps: a. a step of grinding or chopping the material to produce fragments, and b. the step of depolymerizing the polyester to terephthalate in the presence of: (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) an alcohol selected from monohydric alcohols or diols, Features: - said base is present in a catalytic amount relative to the amount of said 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. The method of claim 1, wherein the material consists of a 100% terephthalate polyester selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

3. 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. The method according to claim 3 , wherein the polyurethane is an elastic fiber.

5. The process according to claim 1 , wherein the catalyst is selected from (i) ether oxides of the sodium, potassium, magnesium 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, (iv) or metal esters, or (i) metal esters of the titanium ester type.

6. The process according to claim 5, wherein the catalyst is a metal ester selected from titanium ester, manganese ester, antimony ester, or zinc acetate, sodium acetate or potassium acetate.

7. The process according to one of the preceding claims, wherein the catalyst is present in a molar ratio of less than 35% relative to the terephthalate polyester.

8. The process according to claim 1, wherein the polar solvent satisfies one of the formulas A or B: [Compound 1] [Compound 2] wherein R1 and R2 are the same or different and are selected from aryl C n H 2n , alkyl C n H 2n+1 or C n H 2n-1 , where n=1 to 10.

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

10. The process according to one of the preceding claims, wherein the terephthalate polyester:solvent ratio is between 1:1.5 and 1:

10.

11. The process according to one of the preceding claims, wherein the monohydric alcohol is selected from methanol, ethanol, propanol or butanol, and the diol is ethylene glycol.

12. The process according to one of the preceding claims, wherein the alcohol:terephthalate polyester molar ratio (equivalent) is between 0.25 and 16.

13. The process according to one of the preceding claims, wherein the same grade of alcohol and ester are used for the same depolymerization reaction.

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