Method for ambient temperature depolymerization of terephthalic polyesters to diethyl terephthalate diester

Abstract

The present invention relates to the field of the recycling of materials comprising terephthalate polyester, notably polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) or polytrimethylene terephthalate (PTT), which are commonly used for the manufacture of disposable plastic bottles, food trays, textiles, composite material for insulation, etc. The invention notably relates to a method for recycling PET to a terephthalic diester and notably to dimethyl terephthalate (DMT) in less than one hour and without a pretreatment step. In addition, this method uses products with low environmental impact. It is therefore particularly advantageous from an industrial viewpoint.

Description

[0001] Description

[0002] Title: PROCESS FOR DEPOLYMERIZING TEREPHTHALIC POLYESTERS INTO DIETHYL TEREPHTHALATE DIESTER AT ROOM TEMPERATURE

[0003] The present invention relates to the field of recycling materials containing polyester terephthalate, particularly polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), commonly used in the manufacture of disposable plastic bottles, food trays, textiles, composite insulation materials, etc. It specifically concerns a process for recycling PET into diethyl terephthalate (DET) diester in less than one hour and without any pretreatment steps. Furthermore, this process does not use products with a lower environmental impact than those used in state-of-the-art processes. It is therefore particularly advantageous from an industrial perspective.

[0004] Scope of the invention

[0005] PET recycling is an important environmental issue and therefore represents a commercial opportunity due to its widespread use, abundance, and durability. However, recycling PET-based materials is complex and varies depending on the type of polymer, the material design, and the type of finished product.

[0006] The main obstacle to the use of recycled plastics is the contamination of waste streams with different types of polymers that are incompatible with each other. Consequently, it is often not possible to add recycled PET plastic to virgin polymer without diminishing certain quality attributes, such as color, clarity, or impact resistance. Therefore, the ability to replace virgin polymer with recycled PET depends heavily on the purity of the recycled product and the requirements of the final product. According to the principle of chemical recycling, PET can be depolymerized by solvolysis, such as methoxide or glycolysis, or by hydrolysis, and the resulting monomers can be reused to generate new PET polymers, known as "recycled PET."

[0007] DET obtained by ethanolysis is a monomer of interest because it is easier to dissolve than DMT, produced by methanolysis. DMT requires larger volumes of solvent to maintain its dissolution and thus enable purification operations such as filtration and decolorization. Furthermore, the DET obtained can be oxidized and then used to produce terephthalic acid. For example, document W02007 / 076384 describes an ethanolysis reaction of PET in which PET, or a terpolymer comprising a terephthalate monomer and ethylene glycol monomers, is reacted with ethanol. This reaction produces ethylene glycol and an aromatic diethyl ester, such as diethyl isophlalate and / or diethyl terephthalate. The recovered diethyl components can be subjected to liquid-phase oxidation to produce aromatic carboxylic acid.

[0008] Most PET depolymerization processes begin with a chemical pretreatment step aimed at swelling the material to be treated or a mechanical pretreatment to amorphize the material to be treated.

[0009] It is desirable to have improved, low-cost and easily industrially operable PET-based material recycling processes to facilitate the generalization of this recycling and to broaden the fields of use of recycled PET, and more generally of polyester terephthalate.

[0010] Description of the invention

[0011] The inventors have developed a new, highly efficient depolymerization process by mild ethanolysis for recycling materials containing polyester terephthalate, particularly polyethylene terephthalate (PET), polybutylene terephthalate (PBT), or polytrimethylene terephthalate (PTT), into diethyl terephthalate diester (DET). This process is very rapid and significantly more environmentally friendly than prior art processes. It yields DET in a solid, crystalline form that is directly reusable due to its purity, while minimizing the formation of byproducts.

[0012] Thus, the invention relates to a process for recycling a material comprising a pure or blended polyester terephthalate into a diethyl terephthalate diester, comprising two steps: a. a step of grinding or shredding said material to produce fragments, and b. a step of depolymerizing the polyester terephthalate into diethyl terephthalate diester, in the presence of:

[0013] (i) of a catalyst: a metallic or organic ethoxide base

[0014] (ii) of a polar ester-type solvent of formula A

[0015] [Chem 1] in which R is chosen from an aryl CnEbn, alkyl CnEbn+i or C n H2n-i with n = 1 to 10

[0016] (iii) of an alcohol: ethanol characterized in that: said base is present in catalytic quantity relative to the quantity of said polyester in a mass ratio of at least 5% said depolymerization step is carried out at room temperature or by heating up to 80°C for a period of between 1 minute and 4 hours.

[0017] The polyester terephthalate-based material can be a plastic, a textile or another type of material containing 100% polyester terephthalate (PET, PBT or PTT) or a composite material containing a mixture of PET and / or PBT and / or PTT with other constituents such as cotton, artificial cotton derivatives, polyamide, polyurethanes, polyolefins and fluorinated polymers, such as a composite plastic, a multifibre textile or an insulation composite material, cellulosic fibers (viscose, lyocell, natural fibers such as flax...).

[0018] Advantages of the invention

[0019] A key advantage is that this process eliminates the need for pretreatment, a step that requires the use of toxic products. The depolymerization reaction is sufficiently efficient to allow complete depolymerization without any pretreatment (chemical or thermomechanical) of the material being processed. Thus, the process according to the invention is simpler (one less step), more environmentally friendly, faster, less expensive, and requires minimal energy input. Reducing the amount of solvents, and potentially alcohol, needed for the reaction and to maintain the monomers in solution results in substantial energy savings during the evaporation stage for solvent recycling.

[0020] Because the process presents a very moderate industrial risk, the industrial facilities required for its implementation can be set up more easily, as the level of safety requirements for these facilities is less stringent. Regulatory compliance is simplified during plant installation and throughout the production cycle. Capital expenditures (CAPEX) are thus significantly reduced.

[0021] The solvent used for depolymerization is an ester. This type of solvent is less toxic than the products used in the prior art; these are products that are notably used in the food industry, in the field of flavorings.

[0022] Remarkably, the depolymerization reaction is very rapid and complete. This applies to PET, PBT, and all other types of terephthalate-patterned polyester, such as PTT, which are thus depolymerized into DET. These are then recyclable and have established industrial applications and a recognized market. The process can be described as "very rapid" since the reaction is complete in less than 4 hours at room temperature, and in less than 20 minutes under optimized heating conditions, particularly between 60 and 80°C. It starts instantly and can lead to complete depolymerization in as little as 1 minute.

[0023] The depolymerization reaction is straightforward. After the reaction is complete, fibrous or coated materials that are not PET-based are easily pre-filtered. The resulting reaction medium contains DET in solution. The DET is then isolated after crystallization.

[0024] This process can be applied to any type of material containing polyester terephthalate, in particular PET, PBT or PTT, pure or mixed, transparent or colored, regardless of its thickness or composition.

[0025] Decolorization is easy and very effective on activated carbon or other absorbent supports such as silica, ion exchange resins, clay... It allows obtaining a very clear, even transparent, reaction medium.

[0026] Those skilled in the art know that composite and multifiber textile materials can be manufactured in various ways. They can be woven and coated in multiple layers, or be non-woven. They are composed of different materials, particularly polyester blended with other materials.

[0027] The nature of "polyester" type materials can differ and, by way of example, can include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polylactic acid (PLA), polycaprolactone (PCL), polyester furanoate (PEE)...

[0028] Other materials blended with polyester may include, but are not limited to, polyamide (Nylon 6,6 or hexamethyldiamine diadipate, Nylon 6 or polycaprolactam, etc.), polyurethanes, natural cellulose-patterned fibers such as cotton; synthetic cotton derivatives such as viscose, Lyocell®, and Tencell®; polyolefins (polypropylene, polyethylene), and fluoropolymers (the latter are generally coated). Fluoropolymers are used for their waterproofing and insulating properties; for example, polytetrafluoroethylene (PTFE). Among polyurethanes, elastane is particularly valued because it provides flexibility and breathability to the fabric, especially in the case of flexible polyurethane elastomers, the two main commercial forms of which are poly(ether)urethanes and poly(ester)urethanes.

[0029] The use of polyamides in varying proportions with PET has many applications in the clothing industry (lingerie and sportswear) as well as in technical textiles due to their highly absorbent and dust-free properties (microfiber wipes for industrial wiping). However, it is currently not possible to recycle a composite material containing elastane, polyamides, or coated materials, which poses a problem in terms of waste management; the process according to the invention provides a solution to this problem.

[0030] Furthermore, the process according to the invention is particularly advantageous for recycling polyester terephthalate-based composite materials because the reaction is selective for polyester terephthalate and does not dissolve other materials. This allows for the easy separation of depolymerized polyester terephthalate in the form of DET monomers from the other components.

[0031] Another differentiating advantage of the process is that it allows for the recovery of materials separated from polyester terephthalate after its depolymerization, in an unaltered form. Polyamide (polyamide 6; polyamide 6,6), elastane, and cotton are concrete examples in the textile industry. The process described in this patent makes it possible to isolate the components initially mixed with polyester terephthalate with a degree of purity that allows for their subsequent recycling. It is worth noting that one of the highly innovative applications of this process is enabling the recovery of elastane or polyamide from polyester terephthalate-based composite materials and their reuse in new applications.

[0032] The process yields a high rate: at least 70%, particularly for the depolymerization of PET into DET. Furthermore, the material mixed with polyester is fully recovered.

[0033] For the depolymerization of PET to DET by ethanolysis using the ester solvent combined with ethanol and a metal or organic ethoxide (second-order solvent and base), the resulting product can be up to 99.9% pure at the end of the reaction. Given its level of purity, it can be used in numerous applications, for the regeneration of DMT or other diesters; PET; or any other type of technical resin involving this monomer. The choice of reagents and the implementation of mild conditions ensure that any degradation products or isomers formed that could compromise the quality of the final product can be separated using well-established techniques such as recrystallization, distillation, etc.When present, secondary reaction molecules - considered as degradation products or by-products - can disrupt reactions in which DET is used, such as polymerization, and purification of raw recycled DET is therefore necessary before its use.

[0034] This process is more economical and environmentally friendly than existing processes because the bases (catalysts) are used in smaller, or even significantly reduced, quantities relative to the amount of polyester terephthalate to be recycled, and because the reaction temperatures are below 100°C, generally between ambient temperature (around 25°C) and 80°C, and the reaction times are much shorter than those of PET depolymerization processes described in the literature. Furthermore, ethanol is an alcohol with very low toxicity (unlike methanol, which is commonly used for PET depolymerization).

[0035] In particular, ethanol is used in proportions ranging from 0.25 to 14 molar equivalents relative to polyester terephthalate; preferably from 1.1 to 5 molar equivalents relative to polyester terephthalate, which is a substantial improvement compared to conventional methanolysis technologies in which proportions of 25 molar equivalents are required, but also compared to methanolysis processes described to date.

[0036] The proportions of the polar ester-type solvent are also reduced, with a minimum ratio of 1:1.5 in terms of the mass of polyester terephthalate to the volume of the solvent mixture. Preferably, this ratio is at least 1:3, or even 1:4, or 1:5, and even more preferably 1:6. From an environmental perspective, it should be noted that the depolymerization bath containing the solvent can be reused for a new treatment cycle once the product has been filtered. The bath can be used at least twice without affecting the efficiency of the reaction. Once the reaction is complete, the solvents can be recovered by simple, energy-efficient distillation, given their low boiling point.

[0037] DETAILED DESCRIPTION OF THE INVENTION

[0038] The invention relates to a process for recycling a material comprising a pure or blended polyester terephthalate into a terephthalate diester, comprising two steps: a. a step of grinding or shredding the waste to produce fragments, and b. a step of depolymerizing said polyester into a terephthalate diester in the presence of:

[0039] (i) of a catalyst selected from a metal or organic ethoxide base

[0040] (ii) of a polar solvent which is an ester of formula A

[0041] [Chem 1] in which R is chosen from an aryl C n H2n, alkyl C n H2n+i or C n H2n-i with n = 1 to 10

[0042] (iii) of an alcohol is ethanol characterized in that: said base is present in a catalytic quantity relative to the quantity of said polyester in a mass ratio of at least 5%; said depolymerization step is carried out at room temperature or by heating up to 80°C for a duration of between 1 minute and 4 hours. This process is applicable to the recycling of all types of terephthalate-patterned polyester, the most commonly used of which are PET and PBT.

[0043] Materials containing polyester terephthalate can be composed of 100% polyester terephthalate (e.g., plastics or textiles) or be composed of a mixture comprising polyester terephthalate and other components such as cotton, cellulosic fibers (viscose, lyocell, natural fibers like flax, ...), polyamide, elastane, PTFE, polyethylene, polypropylene (e.g., composite plastics, multifiber textiles or composite insulation panels).

[0044] When the material containing polyester terephthalate is made up of 100% polyester terephthalate, this material is transformed into terephthalate diester.

[0045] Terephthalate polyester is preferably chosen from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), which are commonly used polymers. However, it can be any other type of terephthalate-patterned polyester such as triethylene terephthalate (PTT), polylactic acid (PLA), polycaprolactone (PCL), polyethylene furanoate (PEE)...

[0046] When the material containing polyester terephthalate is a composite material comprising polyester terephthalate mixed with other components, the recycling process 1) produces polyester terephthalate esters (DET) by depolymerizing the polyester terephthalate, and 2) recovers the other components of the material in an unaltered solid form within the reaction mixture. These other components, being in solid form, can be separated from the DET in solution by filtration. The recovery of these components allows for their reuse; some of these "recycled" components constitute a sought-after raw material for industry.

[0047] The composite material comprises polyester terephthalate selected from polyethylene terephthalate and polybutylene terephthalate, mixed with another constituent selected from cotton, artificial cotton derivatives, cellulosic fibers (viscose, lyocell, natural fibers such as flax...) polyamide, polyurethanes, polyolefins and fluorinated polymers.

[0048] Thus, in a particular embodiment in which the material comprising PET is a composite material comprising PET mixed with other components, the recycling process enables the transformation (recycling) of PET into DET and the release of the other components (which can also be recycled).

[0049] The invention also relates to a recycling process for a composite material comprising a polyester terephthalate blend with other components as defined above, wherein the component(s) recovered after depolymerization for reuse are selected from polyethylene terephthalate, polybutylene terephthalate, cotton, artificial cotton derivatives, cellulosic fibers (viscose, lyocell, natural fibers such as flax), polyamide, polyurethanes, particularly elastane, polyolefins, and fluoropolymers. Indeed, it is possible to recover the component(s) of interest, which may be a polyester or another component.

[0050] Thus, the process according to the invention provides alternatively, for example, a process for recycling elastane from a composite material comprising elastane mixed with PET.

[0051] The catalyst is an ethoxide base chosen from, for example, lithium ethoxide, sodium ethoxide, potassium ethoxide, magnesium ethoxide, barium ethoxide, titanium ethoxide.

[0052] The catalyst is present in a molar ratio of less than 35% relative to the terephthalate polyester, preferably between 0.5 and 20%.

[0053] The ester-type solvent preferably conforms to formula A:

[0054] [Chem 1] in which R is chosen from an aryl CnFOn, alkyl CnFOn+i or CnFOn-i with n = 1 to 10

[0055] In a preferred embodiment, the polar solvent is ethyl acetate, a solvent of low toxicity.

[0056] In a preferred embodiment of the invention, the mass ratio of polyester terephthalate to solvent volume is between 1:1.5 and 1:10. Preferably, this ratio is at least 1:3, or even 1:4, or even 1:5 and even more preferably 1:6.

[0057] The alcohol used during the depolymerization step is ethanol.

[0058] The amount of ethanol involved in the depolymerization reaction is variable. The alcohol can be supplied either by the base in solution (in an alcohol) or added directly to the reaction mixture. The ethanol can therefore be in excess, in equal quantity, or insufficient relative to the amount of polyester terephthalate. This parameter will be adjusted by a person skilled in the art.

[0059] Ethanol is present in a ratio of between 0.25 and 16 molar equivalents relative to polyester terephthalate. In another preferred embodiment of the invention, the ethanol:polyester terephthalate molar ratio is between 0.5 and 14; preferably between 0.6 and 9; more preferably precisely between 1.1 and 5.

[0060] Advantageously, the process is carried out by applying a mass ratio of polyester terephthalate to volume of solvent of between 1:1.5 and 1:10, preferably between 1:1.5 and 1:6, and a molar ratio of ethanol to polyester terephthalate of between 0.25 and 10. In a particular embodiment, the process is carried out by applying a mass ratio of polyester terephthalate to volume of solvent of between 1:1.5 and 1:6 and a molar (equivalent) ratio of ethanol to polyester terephthalate of between 0.25 and 6.

[0061] A key feature of the invention is the use of an alcohol, an ester, and a base of the same order (i.e., order 2) in the depolymerization reaction. This combination has the advantage of enabling a complete and highly efficient depolymerization reaction, yielding pure products. The terephthalate monomers are thus solubilized into DET. Cooling the solution is sufficient to precipitate them and recover a purified solid product.

[0062] If the material contains a mixture of polyester terephthalate and other non-polyester-based components, the latter will not be modified, will remain in suspension and will be easily removed by filtration.

[0063] In a preferred embodiment of the invention, the depolymerization of the terephthalate polyester is obtained in the presence of ethanol, ethyl acetate and sodium ethoxide.

[0064] The base involved in the depolymerization reaction is in catalytic quantity relative to the quantity of polyester terephthalate to be treated.

[0065] The term "catalytic quantity" refers to a non-stoichiometric amount of base, i.e., in a molar ratio of 1% to 49% relative to the amount of polyester terephthalate being treated. The term "catalytic" also applies to a reactant that is recovered in its initial form at the end of the reaction (catalyst).

[0066] In a preferred embodiment of the invention, said base is present in a catalytic quantity at a ratio of 5 to 12% by mass relative to the amount of said polyester, preferably at a ratio of 6 to 9% by mass, and more preferably at a ratio of 6 to 8% by mass relative to the amount of said polyester. Extended reaction times can be applied to further reduce this quantity, thereby reducing the cost of the reaction.

[0067] The reaction temperature can vary. The reaction medium can be heated up to 80°C. The mixture can advantageously be heated between 60°C and 80°C, preferably below 70°C, i.e., between 60°C and 70°C. Heating reduces the reaction time. However, it is very interesting to note that the reaction proceeds very well at room temperature (around 25°C) and is rapid, with complete depolymerization achieved in 3 to 4 hours. Not heating the reaction simplifies implementation and reduces costs.

[0068] The invention also relates to the use of DET obtained according to the process of the invention (referred to as recycled DET) to manufacture polyester, polyethylene terephthalate (PET), thermoplastic resins, thermosetting resins, alkyd resins, plasticizers, and surfactants. These products can be used in the manufacture of various articles.

[0069] Among these items we can list textiles, clothing, upholstery fabrics, carpets and rugs, sewing threads and rope, synthetic fibers, plastic films and packaging, water, beverage or oil bottles, food trays, industrial paints and varnishes, inks, adhesives, insulating films, electronic component supports, shoes, composite materials, particularly for boats, surfboards, car bodies, aircraft or train components, wind turbine blades.

[0070] The invention also relates to the use of DET obtained according to the process of the invention (referred to as recycled DET) to manufacture DMT (dimethyl terephthalate), BHET (bishydroxyethyl terephthalate), or terephthalic acid. DMT and BHET are obtained by transesterification. Terephthalic acid is obtained by hydrolysis. The invention also relates to the use of said DMT and BHET to manufacture the aforementioned chemicals and articles.

[0071] The process of the invention offers the advantage of valorizing the materials separated from the terephthalate polyester (called co-materials) after the depolymerization of the latter.

[0072] The invention also relates to the use of the co-material obtained according to the process of the invention (called recycled co-material) to manufacture the aforementioned chemicals and articles. The materials separated from the polyester terephthalate, called co-materials, are polyamides such as nylon 6,6 or hexamethylnediamine diadipate, nylon 6 or polycaprolactam, polyurethanes, in particular elastane, natural fibers with a cellulosic pattern such as cotton, artificial cotton derivatives such as viscose, Lyocell®, Tencell®, polyolefins such as polypropylene and polyethylene, and fluorinated polymers such as polytetrafluoroethylene (PTFE).

[0073] The present invention will be better understood by reading the following examples, which are provided by way of illustration and should in no way be considered as limiting the scope of the present invention.

[0074] EXPERIMENTAL SECTION

[0075] EXAMPLE 1: Depolymerization of 100% PET by ethanolys

[0076] A quantity (500 g) of PET fragments from various sources (textiles, food trays, water bottles, etc.) is introduced into a solution containing 2 L of ethyl acetate and 99 mL of a sodium ethoxide solution (21% in ethanol), corresponding to a molar ratio of 15% sodium ethoxide (which corresponds to sodium ethoxide) to PET. The reaction starts instantly. After 45 minutes of reaction at 70°C, all the PET fragments have disappeared, leaving behind a homogeneous reaction mixture, colored in the case of textiles. The crude reaction mixture is filtered using a Buchner funnel to retain the unreacted material. The recovered mixture contains DET, monoethylene glycol (a product of the depolymerization reaction), the base initially used in the reaction, and the solvent mixture.After decolorization using activated carbon, the DET (423 g) is recovered as a pasty solid following evaporation of the solvents and cooling of the reaction mixture. Finally, this mixture is washed with ethanol. The reaction yield is 73%.

[0077] EXAMPLE 2: Depolymerization of PET-based textiles by ethanolysis. A quantity (500 g) of PET / Elastane 69 / 31% textile fragments is introduced into a solution containing 2.4 L of ethyl acetate, 600 mL of ethanol, and 131 mL of a sodium ethoxide solution (21% in ethanol), corresponding to a molar ratio of 20% sodium ethoxide to the PET present. The reaction starts instantly. After 60 minutes of reaction at 70°C, all the PET has disappeared, leaving undegraded elastane fragments. The crude reaction mixture is filtered using a Buchner funnel to retain 154 g of unreacted material. This material is washed and dried. The recovered filtrate contains DET, monoethylene glycol (a product of the depolymerization reaction), the base initially used in the reaction, and the solvent mixture.After bleaching with activated carbon, the DET (359 g) is recovered as a pasty solid following solvent evaporation and cooling of the reaction mixture. This solid is then washed with ethanol. The reaction yield is 73% of the initial amount of PET contained in the textile.

[0078] The examples below have shown that using catalysts based on either a metal ethoxide or an organic ethoxide prevents the formation of undesirable byproducts. The appearance of such undesirable byproducts compromises the purity of the final product and necessitates additional purification steps, thereby increasing the costs and complexity of the process during scale-up.

[0079] EXAMPLE 3: Depolymerization of a 100% PET blue textile by ethanolysis

[0080] A quantity (50 g) of 100% blue PET textile fragments was introduced into 200 mL of ethyl acetate. 15.08 mL of a sodium ethoxide solution (21% in ethanol), corresponding to a molar ratio of 15% sodium ethoxide to the PET introduced, and 30 mL of ethanol were added to the fragments. The reaction started instantly. After 30 minutes of reaction at 70°C, all the textile fragments had disappeared, leaving behind a white solid slightly suspended in a blue reaction medium. After two hours of reaction, a few milliliters of the reaction medium were taken and added to a known mass of ethyl acetate. GC-FID analysis determined the total mass of 1,4-diethyl terephthalate (DET) in the reaction medium. The reaction medium contained 57 g of DET (99%). GC-FID analysis did not detect either by-product (SP) or 1,4-dimethylterephthalate (DMT).Comparative EXAMPLE 1: Depolymerization of a 100% PET blue textile by ethanolysis in the presence of sodium methoxide.

[0081] This comparative example was carried out according to the protocol of example 3, with the difference that sodium ethoxide was replaced by sodium methoxide.

[0082] A quantity (50 g) of 100% blue PET textile is introduced into 200 mL of ethyl acetate. 12 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide to the PET introduced, and 30 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, leaving behind a white solid slightly suspended in a blue reaction medium. After two hours of reaction, a few milliliters of the reaction medium are taken and added to a known mass of ethyl acetate. GC-FID analysis allows for the determination of the total mass of 1,4-diethyl terephthalate (DET), an unidentified byproduct (SP), and 1,4-dimethyl terephthalate (DMT) contained in the reaction medium. The reaction medium contains 52 g of DET (91%) and 0.8 g of SP by-product (1.4%).The appearance of such a by-product is not satisfactory because it leads to additional purification operations, thus increasing the costs and complexity of the process when scaling up.

[0083] EXAMPLE 4: Depolymerization of a textile made of 70% PET and 30% elastane by ethanolysis

[0084] A quantity (50 g) of white textile (70% PET and 30% elastane) was introduced into 200 mL of ethyl acetate. 20.14 mL of a sodium ethoxide solution (21% in ethanol), corresponding to a molar ratio of 29% sodium ethoxide to the PET introduced, and 30 mL of ethanol were added to the textile pieces. The reaction started instantly. After 30 minutes of reaction at 70°C, all the PET pieces had disappeared, leaving behind a white solid slightly suspended in a beige-orange reaction medium. After two hours of reaction, a few milliliters of the reaction medium were taken and added to a known mass of ethyl acetate. GC-FID analysis determined the total mass of 1,4-diethyl terephthalate (DET) in the reaction medium. The reaction medium contained 39 g of DET (97%). GC-FID analysis did not detect either by-product (SP) or 1,4-dimethylterephthalate (DMT).Comparative EXAMPLE 2: Depolymerization of a textile 70% PET and 30% elastane by ethanolysis in the presence of sodium methoxide.

[0085] This comparative example was carried out according to the protocol of example 4, with the difference that sodium ethoxide was replaced by sodium methoxide.

[0086] A quantity (50 g) of white textile (70% PET and 30% elastane) was introduced into 200 mL of ethyl acetate. 12 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 29% sodium methoxide to the PET introduced, and 30 mL of ethanol were added to the textile pieces. The reaction started instantly. After 30 minutes of reaction at 70°C, all the PET pieces had disappeared, leaving a white solid slightly suspended in a beige reaction medium. After two hours of reaction, a few milliliters of the reaction medium were taken and added to a known mass of ethyl acetate. GC-FID analysis determined the total mass of 1,4-diethyl terephthalate (DET), an unidentified byproduct (SP), and 1,4-dimethyl terephthalate (DMT) contained in the reaction medium. The reaction medium contains 38 g of DET (95%) and 1 g of SP by-product (2.7%).The appearance of such a by-product is not satisfactory because it leads to additional purification operations, thus increasing the costs and complexity of the process when scaling up.

[0087] EXAMPLE 5: Depolymerization of a PET / cotton textile by ethanolys

[0088] A quantity (50 g) of textile (65% PET and 35% green cotton) was introduced into 200 mL of ethyl acetate. 20.14 mL of a sodium ethoxide solution (21% in ethanol), corresponding to a molar ratio of 31% sodium ethoxide to the PET introduced, and 30 mL of ethanol were added to the textile pieces. The reaction started instantly. After 30 minutes of reaction at 70°C, all the PET pieces had disappeared, leaving behind a white solid slightly suspended in a green reaction medium. After two hours of reaction, a few milliliters of the reaction medium were taken and added to a known mass of ethyl acetate. GC-FID analysis determined the total mass of 1,4-diethyl terephthalate (DET) in the reaction medium. The reaction medium contained 37 g of DET (100%). GC-FID analysis did not detect either by-product (SP) or 1,4-dimethylterephthalate (DMT).Comparative EXAMPLE 3: Depolymerization of a textile 65% PET and 35% cotton by ethanolysis in the presence of sodium methoxide.

[0089] This comparative example was carried out according to the protocol of example 5, with the difference that sodium ethoxide was replaced by sodium methoxide.

[0090] A quantity (50 g) of textile (65% PET and 35% green cotton) was introduced into 200 mL of ethyl acetate. 12 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 31% sodium methoxide to the PET introduced, and 30 mL of ethanol were added to the textile fragments. The reaction started instantly. After 30 minutes of reaction at 70°C, all the PET fragments had disappeared, leaving behind a white solid slightly suspended in a green reaction medium. After two hours of reaction, a few milliliters of the reaction medium were taken and added to a known mass of ethyl acetate. GC-FID analysis determined the total mass of 1,4-diethyl terephthalate (DET), an unidentified byproduct (SP), and 1,4-dimethyl terephthalate (DMT) contained in the reaction medium. The reaction medium contains 34 g of DET (90%) and 0.5 g of SP by-product (3.7%).The appearance of such a by-product is not satisfactory because it leads to additional purification operations, thus increasing the costs and complexity of the process when scaling up.

[0091] EXAMPLE 6: Depolymerization of PET by ethanolys

[0092] A quantity (50 g) of PET fragments from various sources (food trays, water bottles, etc.) is introduced into 200 mL of ethyl acetate. 20.14 mL of a sodium ethoxide solution (21% in ethanol), corresponding to a molar ratio of 20% sodium ethoxide to the added PET, is added to the fragments. The reaction begins instantly. After 30 minutes of reaction at 70°C, all the PET fragments have disappeared, leaving behind a white solid slightly suspended in a beige reaction medium. After two hours of reaction, a few milliliters of the reaction medium are taken and added to a known mass of ethyl acetate. GC-FID analysis allows us to determine the total mass of 1,4-diethyl terephthalate (DET) contained in the reaction medium. The reaction medium contains 48 g of DET (85%). GC-FID analysis did not detect either by-product (SP) or 1,4-dimethylterephthalate (DMT).Comparative EXAMPLE 4: Depolymerization of PET-based textiles by ethanolysis in the presence of sodium methoxide.

[0093] This comparative example was carried out according to the protocol of example 6, with the difference that sodium ethoxide was replaced by sodium methoxide.

[0094] A quantity (50 g) of PET fragments from various sources (food trays, water bottles, etc.) was introduced into 200 mL of ethyl acetate. 12 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide to the PET introduced, was added to the fragments. The reaction started instantly. After 30 minutes of reaction at 70°C, all the PET fragments had disappeared, leaving behind a white solid slightly suspended in a beige reaction medium. After two hours of reaction, a few milliliters of the reaction medium were taken and added to a known mass of ethyl acetate. GC-FID analysis allowed us to determine the total mass of 1,4-diethyl terephthalate (DET), an unidentified byproduct (SP), and 1,4-dimethyl terephthalate (DMT) contained in the reaction medium. In the reaction medium, we find 39 g of DET (69%), 0.4 g of DMT (0.8%) and 8 g of SP (16%). The appearance of such by-products is unsatisfactory because they lead to additional purification operations, thus increasing the costs and complexity of the process during scale-up. The reaction yield is 69%, which is significantly lower than that of Example 6.

Claims

DEMANDS 1. A process for recycling a material comprising pure or blended polyester terephthalate into terephthalate diester, comprising two steps: a. a step of grinding or shredding said material to produce fragments, and b. a step of depolymerizing said polyester into terephthalate ester in the presence of: (i) of a catalyst selected from a metal or organic ethoxide base (ii) of a polar solvent of the ester type with formula A: [Chem 1] in which R is chosen from an aryl C n H2n, alkyl CnFOn+i or C n H2n-i with n = 1 to 10 (iii) of an alcohol: ethanol characterized in that: said base is present in catalytic quantity relative to the quantity of said polyester in a mass ratio of at least 5% said depolymerization step is carried out at room temperature or by heating up to 80°C for a period of between 1 minute and 4 hours.

2. A method according to claim 1 wherein said material is composed of 100% polyester terephthalate selected from polyethylene terephthalate, polybutylene terephthalate and polytrimethylene terephthalate.

3. A method according to claim 1 wherein said material is a composite material comprising polyester terephthalate selected from polyethylene terephthalate, polybutylene terephthalate and polytrimethylene terephthalate mixed with another constituent selected from cotton, artificial cotton derivatives, polyamide, polyurethanes, polyolefins and fluorinated polymers.

4. A method according to claim 3 wherein said polyurethane is elastane.

5. A process according to any one of claims 1 to 4 wherein said catalyst is an ethoxide selected from lithium ethoxide, sodium ethoxide, potassium ethoxide, magnesium ethoxide, barium ethoxide, titanium ethoxide.

6. A process according to any one of claims 1 to 5 wherein said catalyst is sodium ethoxide or potassium ethoxide.

7. A method according to any one of claims 1 to 6 wherein said catalyst is present in a mass ratio of between 0.5 and 20% relative to the terephthalate polyester.

8. A method according to any one of the preceding claims wherein said polar ester-type solvent corresponds to formula A and is ethyl acetate.

9. A process according to any one of the preceding claims wherein the mass ratio of polyester terephthalate to volume of solvent is between 1:1.5 and 1:

10.

10. A method according to any one of the preceding claims wherein the (equivalent) molar alcohol: terephthalate polyester ratio is between 0.25 and 6.

11. A recycling process according to claim 3, wherein the material recovered after depolymerization for reuse is selected from polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, cotton, and derivatives. artificial cotton, polyamide, polyurethanes, especially elastane, polyolefins and fluorinated polymers.

12. Use of the terephthalate diester obtained according to the process of claims 1 to 11 for manufacturing polyester, polyethylene terephthalate (PET), thermoplastic resins, thermosetting resins, alkyd resins, plasticizers, surfactants.

13. Use of the terephthalate diester obtained according to the process of claims 1 to 11 for the manufacture of textiles, clothing, upholstery fabrics, carpets and rugs, sewing threads and ropes, synthetic fibers, plastic films and packaging, bottles of water, beverages or oil, food trays, industrial paints and varnishes, inks, adhesives, insulating films, electronic component supports, footwear, composite materials, in particular for boats, surfboards, motor vehicle bodies, aircraft or train components, wind turbine blades.

14. Use of the terephthalate diester obtained according to the process of claims 1 to 11 for manufacturing DMT (dimethyl terephthalate), or BHET (bishydroxyethyl terephthalate), or terephthalic acid.

15. Use of cotton, artificial cotton derivatives, polyamide, polyurethanes, polyolefins or fluorinated polymers obtained according to the process of claim 3 for the manufacture of textiles, clothing, upholstery fabrics, carpets and rugs, sewing threads and ropes, synthetic fibers, plastic films and packaging, water, beverage or oil bottles, food trays, industrial paints and varnishes, inks, adhesives, insulating films, electronic component supports, footwear, composite materials, in particular for boats, surfboards, motor vehicle bodies, aircraft or train components, wind turbine blades.

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