Method for depolymerizing terephthalic polyester into terephthalate ester at room temperature

Abstract

The present invention relates to the recycling of materials containing terephthalate polyesters, particularly polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), which are commonly used in the manufacture of disposable plastic bottles, food trays, fabrics, insulation composite materials, etc. In particular, it relates to a method for recycling PET into terephthalic diesters and particularly dimethyl terephthalate (DMT) within less than one hour and without a pretreatment step. Furthermore, this method does not use any toxic products. Therefore, it is particularly advantageous from an industrial perspective.

Description

Technology Field

[0001] The present invention relates to the recycling of materials containing terephthalate polyesters, particularly polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), which are commonly used in the manufacture of disposable plastic bottles, food trays, fabrics, insulation composite materials, etc. In particular, it relates to a method for recycling PET into terephthalic diesters and particularly dimethyl terephthalate (DMT) within less than one hour and without a pretreatment step. Furthermore, this method does not use any toxic products. Therefore, it is particularly advantageous from an industrial perspective. Background Technology

[0002] PET recycling is a major environmental issue and therefore presents commercial opportunities due to its widespread use, abundance, and durability. However, the recycling of PET-based materials is complex and depends on the type of polymer, material design, and the type of finished product.

[0003] A major obstacle to the use of recycled plastic materials is the contamination of waste streams by different types of polymers that are incompatible with each other. Consequently, it is often impossible to add recycled PET-type plastics to virgin polymers without compromising specific quality characteristics, such as color, transparency, 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 principles of chemical recycling, PET can be depolymerized by solvent decomposition such as methanol decomposition, sugar decomposition, or hydrolysis, and the monomers obtained thereby can be reused to produce a new PET polymer referred to as "recycled PET."

[0005] In response to industrial demands, specific technologies for manufacturing PET resin rely on the use of dimethyl terephthalate (DMT).

[0006] Furthermore, conventional methanol cracking technologies employ highly energy-intensive and expensive equipment methods; these methods utilize a supercritical phase at temperatures exceeding 300°C and pressures of 5 to 10 bar. Due to extreme reaction conditions in terms of temperature and pressure, these technologies induce isomerization or degradation, particularly as they induce structural changes at the molecular level of PET (U.S. Patent No. 6,706,843, International Publication WO2021 / 126661); consequently, they are unsuitable for the depolymerization of certain PET-based materials, such as multi-fiber fabric materials, because they will produce deformed PET molecules due to "contamination" by residues derived from other components of the fabric. These deformed molecules may be toxic or cause impediments during the manufacture of recycled PET; and they are detrimental to the quality of the depolymerized product for their future applications.

[0007] International Patent WO2020 / 128218 describes a method for depolymerizing PET by alcohol decomposition using a monoalcohol such as methanol or ethanol and a base selected from sodium methoxide, KOH, or NaOH in stoichiometric amounts for PET.

[0008] It is known that using a base in a catalytic amount relative to the mass of PET allows for the production of DMT, but the kinetics of the reaction are considerably slow, the reaction time exceeds 10 hours and 30 minutes, and during this time, the reaction solution is continuously heated. As an example, one may refer to U.S. Patent Application Publication US2019 / 0256450 and International Publication WO2020 / 188359, which describe the depolymerization of PET to DMT in the presence of methanol and an alkoxide, such as sodium methoxide. Such methanol cracking reactions take place at temperatures between 25°C and 100°C. This method necessarily includes a first step of swelling PET with a polar solvent or a chlorinated solvent such as DMSO, DMF, or methanol. U.S. Patent Application Publication US2019 / 0256450 proposes reacting PET with a base, a catalytic amount of sodium methoxide, and methanol. The method described in International Publication WO2020 / 188359 is characterized by the sequential addition of methanol and methylate solutions several times after the addition of sodium methoxide. The authors describe a high PET production yield. U.S. Patent Application Publication US2019 / 390035 describes another approach to depolymerization by the addition of a glycolate salt, the preparation of which includes isolation and drying steps that continue over a period of one week.

[0009] International Publication WO2021 / 126661 describes an improved method for depolymerizing PET by methanol cracking using a catalyst selected from sodium carbonate, magnesium methoxide, DBU, and TBD. This method is implemented at a temperature of at least 110 to 140°C with a pressure of 15 bar.

[0010] To those skilled in the art, the implementation of the method described above clearly presents issues regarding industrial operability and feasibility in terms of safety in ATEX environments, such as with regard to methanol under reflux, which require complex precautions and expensive equipment when introducing flammable products into the method.

[0011] None of these methods are satisfactory. Therefore, in order to facilitate the generalization of such recycling and to broaden the scope of use for recycled PET and, more generally, terephthalate polyester, it is desirable to have an improved recycling method for PET-based materials that is low-cost and industrially easy to operate.

[0012] The inventors have developed a novel method that is particularly efficient for the depolymerization by alcoholic decomposition under mild conditions for recycling materials containing terephthalate polyesters, particularly polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), into terephthalate ester monomers. This method is much more environmentally friendly and much faster than conventional methods. Due to its purity, it allows access to solid products that can be directly reused, particularly crystalline forms of DMT, DET, or BHET.

[0013] Accordingly, the present invention relates to a method for recycling a material containing terephthalate polyester into terephthalate diester:

[0014] a. A step of manufacturing fragments by milling or crushing the above material and

[0015] b. Terephthalate polyester:

[0016] (i) a catalyst selected from metal or organic ether oxide bases, metal acetates, metal oxides, metal hydroxides, metal esters, or metal carbonates, and

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

[0018] (iii) an alcohol selected from monoalcohols or diols

[0019] The method includes the step of depolymerizing with a terephthalate ester in the presence of,

[0020] It is characterized by the following:

[0021] - The above base is present in a catalytic amount relative to the amount of the above terephthalate polyester.

[0022] - The above depolymerization step is performed at ambient temperature or by heating to a maximum of 70°C for a period of 1 minute to 4 hours.

[0023] Terephthalate polyester-based materials may be plastics, fabrics, or other types of materials containing 100% terephthalate polyester (PET or PBT), or composite materials containing a mixture of terephthalate polyester and other components, such as cotton, polyamide, polyurethane, polyolefin, and fluorinated polymers, such as composite plastics, multi-fiber fabrics, or composite insulation materials.

[0024] Advantages of the invention

[0025] The method according to the present invention proposes associating (i) a catalyst in a catalytic amount for a terephthalate polyester, (ii) an alcohol which is a monoalcohol or diol, and (iii) an ester-type solvent, and reacting them under mild conditions. This has several advantages in relation to the method described above, which are explained below.

[0026] As a first notable advantage, these methods do not require pretreatment that necessitates the use of toxic products. The depolymerization reaction is sufficiently effective to completely depolymerize the material being treated without prior swelling. Therefore, the method according to the present invention is simpler (one less step), more environmentally friendly (no effluent to be treated as there are no toxic products), faster, and less expensive.

[0027] Because the method entails very moderate industrial risk, industrial installations for its implementation can consequently be constructed more easily, and the safety levels of these facilities are less restrictive. Regulatory compliance is simplified during plant installation and throughout the production cycle. Consequently, CAPEX is significantly reduced.

[0028] Although ester-type solvents are preferred, any type of solvent may be used for depolymerization. In fact, these products are non-toxic and are used in food processing, particularly in the field of flavorings.

[0029] Surprisingly, the depolymerization reaction is complete, very fast, and produces high-purity terephthalate esters. This can be applied to PET and also PBT, where it is depolymerized into DMT, DET, or BHET. Subsequently, the latter can be easily recycled and has industrial distribution channels and an recognized market.

[0030] Since the reaction is completed in less than 4 hours at ambient temperature and in less than 20 minutes under optimized heating conditions, particularly 55 to 70°C, the method can be described as "very fast." It is initiated immediately and can complete depolymerization within 1 minute.

[0031] The depolymerization reaction is simple. Depolymerization and purification can be performed in a single step. After the reaction is complete, the resulting product is a terephthalate ester in crystalline form. By washing, it becomes possible to remove intermediates or decomposition products that, under conventional methods, would require distillation operations to separate from the product of interest, which would otherwise require time and effort.

[0032] Accordingly, by the present method, DMT, DET, or BHET can be obtained depending on whether the depolymerization of PET or PBT is carried out by methanol hydrolysis, ethanol hydrolysis, or sugar hydrolysis, respectively.

[0033] This method can be applied to any type of material, including pure or blended, transparent or colored terephthalate polyesters, particularly PET or PBT, regardless of its thickness or composition.

[0034] Those skilled in the art know that composite fabrics and multifiber materials can be manufactured in different ways. They can be woven and coated in the form of several layers or non-woven fabrics. They consist of different materials, in particular polyester materials blended with other materials.

[0035] The properties of "polyester" type materials may vary, and in non-strict terms, the latter may be polyethylene terephthalate (PET); polybutylene terephthalate (PBT), polylactic acid (PLA), polycaprolactone (PCL), etc. The material that can be recycled by the method according to the present invention comprises at least one terephthalic polyester of the PET or PBT type.

[0036] Other materials combined with polyester may, in a non-limiting manner, be polyamides (such as nylon 6,6 or hexamethylene diamine diadifate, nylon 6 or polycaprolactam), polyurethanes, cotton, polyolefins (polypropylene, polyethylene), and fluorinated polymers (the latter are generally coated). Fluorinated polymers; for example, polytetrafluoroethylene (PTFE) is used due to its sealing and thermal insulation properties. Among polyurethanes, elastane is particularly recognized because it provides elasticity and breathability to fabrics, and especially when it is an elastic elastomer polyurethane, the two main commercially available forms are poly(ether)urethane and poly(ester)urethane.

[0037] The use of polyamide in variable proportions together with PET has numerous applications in the clothing sector (lingerie and sportswear) as well as in industrial fabrics (microfiber wipes for industrial wiping) due to their high absorbency and dustproof properties. However, it is currently impossible to recycle composite materials or coated materials containing elastane and polyamide, which pose many problems in terms of waste management; the method according to the present invention provides a solution to this problem.

[0038] Furthermore, the method according to the present invention is advantageous for recycling terephthalate-polyester composite materials, particularly due to the fact that the reaction is selective for terephthalate polyester and does not modify other selective components; thus, separation between the depolymerized terephthalate polyester in monomeric form and other components is easy; the latter can be recovered by simple filtration and washing. Next, after a possible bleaching step in the case of fabric, the cooled mixture is allowed to precipitate the terephthalate ester. Washing is sufficient to obtain DMT, DET, or BHET that can be used directly. The washing solvent is advantageously the alcohol used during depolymerization.

[0039] Another distinct advantage of the method is that it enables the separated material of terephthalate polyester in an unchanged form to be upcycled after its depolymerization. Polyamide (polyamide 6; polyamide 6,6) elastane and cotton are specific examples of this in the field of fabrics. The method described in this patent enables the isolation of the terephthalate polyester and the components initially blended with it to a purity that allows for their subsequent recycling. It may be noted that one of the highly innovative applications of this method is to recover elastane or polyamide from terephthalate polyester-based composite materials and reuse them in novel applications.

[0040] The yield of the method is high, at least 85%, especially in the case of depolymerization of PET to DMT. In addition, the material blended with polyester is completely restored.

[0041] 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 subsequent purification is required. DMT can be used directly after washing with methanol. Given its level of purity, it can be used in various applications for remanufacturing PET or any other type of industrial resin containing this monomer. The selection of reagents and the implementation of mild conditions ensure that isomerization reactions do not occur and that degradation products detrimental to the quality of the resulting product are not formed. Since the presence of these secondary molecules interferes with the polymerization reaction, purification of the unpurified DMT is required before use. This can be generalized to the depolymerization of PET and PBT to any type of terephthalate ester monomer (DMT, DET, and BHET).

[0042] This method is more economical and environmentally friendly than existing methods due to the fact that the base (catalyst) is used in a catalytic amount relative to the amount of recycled terephthalate polyester, the reaction temperature is less than 80°C and is generally included in ambient temperature (approximately 25°C) to 60°C, and the reaction time is significantly reduced compared to that of PET depolymerization methods described in the literature.

[0043] In particular, the alcohol is used in a ratio of 0.25 to 16 molar equivalents to the terephthalate polyester; preferably 0.6 to 9 molar equivalents to the terephthalate polyester; more precisely, in a ratio of 1.1 to 4.9 molar equivalents to the terephthalate polyester, which is a significant improvement over conventional methanol decomposition techniques that require a ratio of 25 molar equivalents.

[0044] The ratio of the acetate-type polar solvent is also reduced to a range of at least 1:1.5 to 1:10 relative to the volume of the terephthalate polyester mass:solvent mixture.

[0045] From an ecological perspective, it should be noted that the depolymerization vessel containing the solvent can be reused for a new processing cycle once the product is filtered. The vessel can be used at least twice without affecting the effectiveness of the reaction. When the reaction is finished, the solvent can be recovered by simple low-energy distillation, considering its low boiling point. Specific details for implementing the invention

[0046] The present invention relates to a method for recycling a material containing terephthalate polyester into terephthalate diester:

[0047] a. A step of manufacturing fragments by milling or crushing waste and

[0048] b. The above polyester:

[0049] (i) a catalyst selected from metal or organic ether oxide bases, metal acetates, metal oxides, metal hydroxides, metal carbonates, or metal esters and

[0050] (ii) Polar solvents of the cyclic ester or ether oxide type

[0051] (iii) an alcohol selected from monoalcohols or diols

[0052] The method includes the step of depolymerizing with a terephthalate ester in the presence of,

[0053] It is characterized by the following:

[0054] - The above base is present in a catalytic amount relative to the amount of the above polyester.

[0055] - The above depolymerization step is performed at ambient temperature or by heating to a maximum of 70°C for a period of 1 minute to 4 hours.

[0056] In a preferred embodiment, the present invention relates to a method for recycling a material containing polyethylene terephthalate into a terephthalate ester monomer:

[0057] a. A step of manufacturing fragments by milling or crushing waste and

[0058] b. PET:

[0059] (i) a catalyst selected from metal or organic ether oxide bases, metal acetates, metal oxides, metal hydroxides, metal carbonates, or metal esters and

[0060] (ii) Polar solvents of the cyclic ester or ether oxide type

[0061] (iii) an alcohol selected from monoalcohols or diols

[0062] The method comprises the step of depolymerizing with terephthalate ester and monoethylene glycol (MEG) in the presence of,

[0063] It is characterized by the following:

[0064] - The above base exists in a catalytic amount relative to the amount of PET.

[0065] - The above depolymerization step is performed at ambient temperature or by heating to a maximum of 70°C for a period of 1 minute to 4 hours.

[0066] It is known to those skilled in the art that the depolymerization of terephthalate polyesters produces DMT and diols corresponding to polyesters, namely monoethylene glycol from PET and butanediol from PBT.

[0067] Materials containing terephthalate polyester may be composed of 100% terephthalate polyester (e.g., plastic or fabric) or may be composed of a mixture of terephthalate polyester and other components, such as cotton, polyamide, elastane, PTFE, polyethylene, and polypropylene (e.g., composite plastic, multi-fiber fabric, or thermal insulation composite panel).

[0068] When a material containing terephthalate polyester is composed of 100% terephthalate polyester, this material is converted into terephthalate ester. This can be recovered by simple filtration and precipitated by cooling, as described below and exemplified in the experimental section.

[0069] Terephthalate polyester is selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

[0070] When a material containing terephthalate polyester is a composite material containing terephthalate polyester blended with other components, the recycling method produces terephthalate ester (DMT) by depolymerizing the terephthalate polyester, while the other components of the material remain in an unchanged form in the reaction mixture. Since these other components are more abundant than DMT, they can be separated from the latter by simple filtration.

[0071] The composite material comprises a terephthalate polyester selected from polyethylene terephthalate and polybutylene terephthalate, blended with another component selected from cotton, polyamide, polyurethane, polyolefin, and fluorinated polymer.

[0072] Accordingly, in a specific embodiment in which the material containing PET is a composite material containing PET blended with other components, the PET can be converted (recycled) to DMT by a recycling method and the other components (which can also be recycled) can be released.

[0073] The catalyst is a base selected from the following:

[0074] (i) Ether oxide of the type of sodium methoxide, magnesium methoxide, potassium methoxide, or ammonium methoxide,

[0075] (ii) Metal carbonates of the sodium carbonate or potassium carbonate type,

[0076] (iii) metal hydroxides of the type of sodium hydroxide or potassium hydroxide, and

[0077] (iv) zinc acetate Zn(OAc)2 or sodium acetate NaOAc type or potassium acetate KOAc gold acetate,

[0078] (v) metal oxide,

[0079] (vi) Metal esters of the type titanium ester Ti(OiPr)4, manganese ester Mn(OR)2, or antimony ester Sb(OR)2.

[0080] In a preferred embodiment of the present invention, the catalyst is selected from sodium methoxide, magnesium methoxide, potassium methoxide, or ammonium methoxide.

[0081] The catalyst is present in a molar ratio of less than 35%, preferably 1 to 20%, with respect to the terephthalate polyester.

[0082] The ester-type solvent can be a monoester, diester, or tryster.

[0083] The ester-type solvent preferably satisfies chemical formula A:

[0084] [Chemistry 1]

[0085]

[0086] Ether oxide type solvents preferably satisfy chemical formula B:

[0087] [Chemistry 2]

[0088]

[0089] In the above formula, R1 and R2 are the same or different, and aryl C n H 2n , alkyl C n H 2n+1 , or C n H 2n-1 Selected (independently) from, where n is 1 to 10.

[0090] In a preferred embodiment, the polar solvent is of the ester type because it is non-toxic. The ester type solvent may be selected from methyl acetate, ethyl acetate, propyl, butyl, and isopropyl.

[0091] Table 2 (experimental section) describes different embodiments of the present invention depending on the base used.

[0092] The solvent can also be of the cyclic ether oxide type, such as dioxane.

[0093] In a preferred embodiment of the present invention, the terephthalate polyester:solvent ratio is 1:1.5 to 1:10.

[0094] The amount of alcohol included in the depolymerization reaction is variable. The alcohol can be supplied as a base in the solution (alcohol) or added directly into the reaction medium. Accordingly, the alcohol may be in excess, equivalent, or deficient relative to the amount of terephthalate polyester. This parameter will be controlled by a person skilled in the art.

[0095] 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 present invention, the molar ratio of alcohol to terephthalate polyester is 0.5 to 16; preferably 0.6 to 9; more preferably 1.1 to 3.

[0096] Advantageously, the present invention is implemented by applying a terephthalate polyester:solvent mixture ratio of 1:1.5 to 1:10 and an alcohol:terephthalate polyester molar ratio of 0.25 to 10. In a specific embodiment, the present invention is implemented by applying a terephthalate polyester:solvent mixture ratio of 1:1.5 to 1:5 and an alcohol:terephthalate polyester molar ratio of 0.25 to 3.

[0097] The alcohol used during the depolymerization step is preferably a monoalcohol or diol selected from methanol, ethanol, propanol, or butanol, such as ethylene glycol.

[0098] In a specific embodiment of the present invention, alcohols and esters of the same rank are used during the depolymerization reaction.

[0099] This combination of alcohol and ester of the same grade has the advantage of allowing a complete depolymerization reaction. Thus, the terephthalate monomer is solubilized. It is sufficient to cool the solution to precipitate them and recover a high-purity product (at least 99%).

[0100] If the material contains a mixture of terephthalate polyester and other components, the latter will not be deformed, will remain in the suspension, and will be easily removed by filtration.

[0101] For example, methanol and methyl acetate can be combined to obtain DMT (methanol decomposition reaction) or ethanol and ethyl acetate to obtain DET (diethyl terephthalate diester) (ethanol decomposition reaction). If diethylene glycol is used, BHET (bis(2-hydroxyethyl) terephthalate) is obtained (sugar decomposition reaction).

[0102] The advantages of DET are exemplified, for example, in the document International Publication WO2007 / 076384, which describes the ethanol decomposition reaction of PET. It is stated that the production of DET is advantageous due to the fact that DET is easier to dissolve than DMT. The obtained DET can be oxidized and subsequently used to produce terephthalic acid.

[0103] Alternatively, another embodiment according to the present invention may consist of combining different grades of alcohol and ester. For example, two commonly used reagents, ethyl acetate and methanol, may be combined. The PET depolymerization reaction is carried out effectively and completely, and a major product corresponding to the alcohol used is obtained, and in this example, due to the presence of methanol, secondary products such as DET as well as other terephthalate monomers are obtained.

[0104] The base included in the depolymerization reaction may be a catalytic amount relative to the amount of terephthalate polyester being treated.

[0105] "Catalytic amount" refers to a non-stoichiometric amount, that is, a molar ratio of 1% to 49% with respect to the amount of terephthalate polyester being treated. The term "catalytic" also applies to a reagent (catalyst) found in its initial form at the end of the reaction.

[0106] In a preferred embodiment of the present invention, the catalytic amount of the ether oxide base is less than 35 mol%. The catalytic amount of the ether oxide base may vary from 1 mol% to 35 mol%, preferably from 1 mol% to 20 mol%, or even from 5 mol% to 20 mol%. An extended reaction time may be applied to further reduce this amount, which enables a reduction in reaction costs.

[0107] The reaction temperature may vary. The reaction medium may be heated to 70°C. The mixture may be heated to a temperature between 50°C and 70°C, preferably below 60°C, which is particularly advantageous. However, interestingly, the reaction proceeds very well at room temperature (about 25°C), and since complete depolymerization is obtained within 3 to 4 hours, the reaction is rapid. The fact that the reaction is not heated simplifies implementation and reduces costs.

[0108] The present invention will be better understood by interpreting the embodiments provided as follows and will not be construed as limiting the scope of the invention in any way.

[0109] Experimental section

[0110] Example 1: PET Depolymerization by Methanol Decomposition

[0111] A predetermined amount (500 g) of polyethylene terephthalate (PET) pieces derived from different sources (food trays, water bottles, etc.) is 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 molar ratio of 20% sodium methoxide to the introduced PET, are added to the pieces. The reaction is initiated immediately. After reacting at 55°C for 30 minutes, all PET pieces have disappeared, and a white solid slightly suspended in the solution remains. To retain the unreacted material, the unrefined reaction mixture is filtered through a Buchner funnel; the recovered medium gels almost immediately. This contains DMT, monoethylene glycol, and the initially reacted base and solvent produced by the depolymerization reaction. The white solid (DMT) (410 g, 82%) is recovered and washed with methanol.

[0112] Example 2: PET Depolymerization by Methanol Decomposition

[0113] A predetermined amount (500 g) of PET pieces derived from different sources (food trays, water bottles, etc.) is introduced into 2 L of methyl acetate. 210 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 35% sodium methoxide to the introduced PET, is added to the pieces. The reaction is initiated immediately. After reacting at 55°C for 30 minutes, all PET pieces have disappeared, and a white solid slightly suspended in the solution remains. To retain the unreacted material, the unrefined reaction mixture is filtered through a Buchner funnel; the recovered medium gels almost immediately. This contains DMT, monoethylene glycol, and the initially reacted base and solvent produced by the depolymerization reaction. The white solid (DMT) (400 g, 80%) is recovered and washed with methanol.

[0114] Example 3: Depolymerization of 100% PET fabric by methanol decomposition

[0115] A predetermined amount (500 g) of colored fabric pieces of 100% PET is introduced into 2 L of methyl acetate. 119 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide to the introduced PET, is added to the pieces. The reaction is initiated immediately. After reacting at 55°C for 120 minutes, all PET pieces were depolymerized, leaving a colored solid slightly suspended in the solution. A bleaching step was performed by adding activated carbon to obtain white DMT. The unrefined reaction mixture was filtered through a Buchner funnel to retain the unreacted material and activated carbon; the recovered medium gels almost immediately. This contains DMT produced by the depolymerization reaction, monoethylene glycol, and the initially reacted base and solvent. The white solid (DMT) (350 g, 70%) is recovered and washed with methanol.

[0116] Example 4: Depolymerization of 85% / 15% PET / elastane blend fabric material by methanol decomposition

[0117] A predetermined amount (500 g) of a PET / elastane blend fabric piece, consisting of 85% colored PET and 15% colored elastane containing different percentages of elastane, was introduced into 3.2 L of methyl acetate and 0.8 L of methanol. 119 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide to the introduced fabric, was added to the piece. The reaction was initiated immediately. After reacting at 55°C for 80 minutes, all PET-based fabric pieces were depolymerized, leaving colored solids and unreacted elastane pieces slightly suspended in the solution. A pre-filtration step was performed to retain the elastane (75 g, 15%) and unreacted material. The next step is bleaching by adding activated carbon to the crude reaction mixture to obtain white DMT. To retain the activated carbon, the crude reaction mixture was filtered through a Buchner funnel; The recovered medium gels almost immediately. It contains DMT, monoethylene glycol, and the initially reacted base and solvent produced by the depolymerization reaction. A white solid (DMT) (280 g, 66%) is recovered and washed with methanol.

[0118] Example 5: Depolymerization of PET / Cotton (80% / 20%) Blend Fabric by Methanol Decomposition

[0119] A predetermined amount (500 g) of a PET / cotton blend fabric piece, consisting of 80% colored PET and 20% colored cotton, is introduced into 5 L of methyl acetate. 119 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide to the introduced fabric, is added to the piece. The reaction is initiated immediately. After reacting at 55°C for 210 minutes, the majority of the PET fabric piece deteriorated, leaving a colored solid slightly suspended in the solution and unreacted cotton pieces. A pre-filtration step was performed to retain the cotton (165 g, 20%) and unreacted material. The next step is bleaching by adding activated carbon to the crude reaction mixture to obtain white DMT. To retain the activated carbon, the crude reaction mixture is filtered through a Buchner funnel; the recovered medium gels almost immediately. This contains DMT, monoethylene glycol, and the initially reacted base and solvent produced by the depolymerization reaction. A white solid (DMT) (245 g, 61%) is recovered and washed with methanol.

[0120] Example 6: Depolymerization of PET / polyamide (90% / 10%) blend fabric by methanol decomposition

[0121] A predetermined amount (500 g) of colored PET / PA blend fabric pieces is introduced into 5 L of methyl acetate. 119 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 20% sodium methoxide to the introduced fabric, is added to the pieces. The reaction is initiated immediately. After reacting at 55°C for 120 minutes, all fabric pieces decomposed, leaving colored solids and unreacted PA pieces slightly suspended in the solution. A pre-filtration step was performed to retain the PA (50 g, 10%) and unreacted material. The next step is bleaching by adding activated carbon to the crude reaction mixture to obtain white DMT. To retain the activated carbon, the crude reaction mixture is filtered through a Buchner funnel; the recovered medium gels almost immediately. This contains the DMT produced by the depolymerization reaction, monoethylene glycol, and the initially reacted base and solvent. A white solid (DMT) (350 g, 70%) is recovered and washed with methanol.

[0122] Example 7: Depolymerization of 100% PET Composite Insulation Panels by Methanol Decomposition

[0123] A predetermined amount (500 g) of white 100% PET foam pieces is introduced into 1.5 L of methyl acetate. 71.43 mL of a sodium methoxide solution (25% in methanol), corresponding to a molar ratio of 12% sodium methoxide to the introduced PET, is added to the pieces. The reaction is initiated immediately. After reacting at 55°C for 20 minutes, all the insulation panel pieces decomposed, leaving a pale yellow solid slightly suspended in the solution. To retain the unreacted material, the unrefined reaction mixture is filtered through a Buchner funnel; the recovered medium gels almost immediately. This contains DMT, monoethylene glycol, and the initially reacted base and solvent produced by the depolymerization reaction. The white solid (DMT) (360 g, 72%) is recovered and washed with methanol.

[0124] Example 8: PET Depolymerization by Ethanol Decomposition

[0125] A predetermined amount (500 g) of PET pieces derived from different sources (food trays, water bottles, etc.) is introduced into 2 L of ethyl acetate. 28.12 g of sodium methoxide and 300 mL of ethanol, corresponding to a molar ratio of 20% sodium methoxide to the introduced PET, are added to the pieces. The reaction is initiated immediately. After reacting at 70°C for 30 minutes, all PET pieces have disappeared, and a white solid slightly suspended in the solution remains. To retain the unreacted material, the unrefined reaction mixture is filtered through a Buchner funnel, and the recovered medium contains DET, monoethylene glycol produced by the depolymerization reaction, and the initially reacted base and solvent. DET (400 g) is recovered in the form of a paste solid after the reaction solvent evaporates and is washed with ethanol.

[0126] Example 9: Conversion rate as a function of time and temperature

[0127] Table 1 shows the effect of reaction time and temperature on the conversion rate of PET to DMT.

[0128] The following reaction conditions were used: 10 g of PET was incubated in a sodium methoxide solution (diluted to 25% in MeOH) at a ratio of 20% (mol:PET mol) in the presence of 45 mL of methyl acetate.

[0129] [Table 1]

[0130]

[0131] [Table 1] Effect of Time / Temperature on Conversion Rate

[0132] Example 10: Conversion rate as a function of solvent and alcohol type

[0133] Table 2 shows the effect of reaction time and temperature on the conversion rate of PET to DMT.

[0134] The reaction conditions are the same as those of Example 4.

[0135] Ester-type solvents have the following chemical formula:

[0136] [Chemistry 1]

[0137]

[0138] [Table 2]

[0139]

[0140] [Table 2] Effect of Solvent / Alcohol Type Change on Conversion Rate

Claims

Claim 1 A method for recycling a material containing a terephthalate polyester into a terephthalate diester, comprising: a. milling or crushing the material to produce fragments; and b. depolymerizing the polyester into a terephthalate ester 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) a polar solvent of the cyclic ester or ether oxide type; and (iii) an alcohol selected from a monoalcohol or a diol, wherein: - the base is present in a catalytic amount relative to the amount of the polyester; and - the depolymerization step is performed at ambient temperature or by heating to a maximum of 70°C for a period of 1 minute to 4 hours. Claim 2 A method according to claim 1, wherein the material is composed of a 100% terephthalate polyester selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Claim 3 The method according to 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. Claim 4 In paragraph 3, the method wherein the polyurethane is elastane. Claim 5 A method according to any one of claims 1 to 4, wherein the catalyst is selected from (i) an ether oxide of the type of sodium methoxide, potassium methoxide, magnesium methoxide, or ammonium methoxide; (ii) a metal carbonate of the type of sodium carbonate or potassium carbonate; (iii) a metal hydroxide of the type of sodium hydroxide or potassium hydroxide; (iv) a metal acetate of the type of zinc acetate or sodium acetate or potassium acetate; (v) a metal oxide (vi) or a metal ester; or (vii) a metal ester of the type of titanium ester. Claim 6 In claim 5, the method wherein the catalyst is a metal ester selected from titanium ester, manganese ester, antimony ester, or zinc acetate, sodium acetate, or potassium acetate. Claim 7 A method according to any one of claims 1 to 4, wherein the catalyst is present in a molar ratio of less than 35% with respect to the terephthalate polyester. Claim 8 In any one of claims 1 to 4, the polar solvent satisfies one of chemical formulas A or B: [Chemistry 1] [Chemistry 2] In the above formula, R1 and R2 are the same or different, and aryl C n H 2n , alkyl C n H 2n+1 , or C n H 2n-1 A method selected from, where n is 1 to 10. Claim 9 In claim 8, the method wherein the ester is selected from methyl acetate, ethyl acetate, propyl, butyl, and isopropyl. Claim 10 A method according to any one of claims 1 to 4, wherein the terephthalate polyester:solvent ratio is 1:1.5 to 1:

10. Claim 11 A method according to any one of claims 1 to 4, wherein the monoalcohol is selected from methanol, ethanol, propanol, or butanol, and the diol is ethylene glycol. Claim 12 A method comprising, in any one of claims 1 to 4, an alcohol:terephthalate polyester molar ratio (equivalent) of 0.25 to 16. Claim 13 A method according to any one of claims 1 to 4, wherein alcohols and esters of the same rank are used in the same depolymerization reaction.

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