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• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
  • C08J11/28—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic compounds containing nitrogen, sulfur or phosphorus
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/03—Preparation of carboxylic acid esters by reacting an ester group with a hydroxy group
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C69/00—Esters of carboxylic acids; Esters of carbonic or haloformic acids
  • C07C69/76—Esters of carboxylic acids having a carboxyl group bound to a carbon atom of a six-membered aromatic ring
  • C07C69/80—Phthalic acid esters
  • C07C69/82—Terephthalic acid esters
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/16—Dicarboxylic acids and dihydroxy compounds
  • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
  • C08G63/181—Acids containing aromatic rings
  • C08G63/183—Terephthalic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/14—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with steam or water
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
  • C08J11/22—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
  • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/62—Plastics recycling; Rubber recycling

Definitions

• TITLE IMPROVED PROCESS FOR RECYCLING PET BY ALCOOLYSIS
• the present invention relates to the field of the recycling of plastics of the PET type commonly used for the manufacture of disposable plastic bottles, food trays, textiles, etc. More particularly, it relates to a process allowing the recycling of PET into dimethyl terephthalate or terephthalate of dimethyl (DMT) in a few hours (less than 5h) by carrying out a complete reaction resulting in a product devoid of impurities.
• the depolymerization step takes place in the presence of a monoalcohol as well as an organic base with a guanidine or amidine unit, and a second base which can be either inorganic or an ether oxide. These two bases are present in catalytic quantities relative to the quantity of PET to be treated.
• PET recycling is an important environmental topic and thus represents a business opportunity due to its widespread use, abundance and sustainability.
• recycling plastics is complex and varies by polymer type, packaging design and product type.
• PET can be depolymerized by methanolysis or glycolysis and the monomers thus obtained can be reused to generate new PET polymers called “recycled PET”.
• DMT dimethanolic ester of terephthalic acid
• Document WO2020/128218 describes a process for depolymerizing PET by alcoholysis using a monoalcohol such as methanol or ethanol and a base chosen from sodium methoxide, KOH or NaOH in a stoichiometric quantity with respect to PET.
• a monoalcohol such as methanol or ethanol
• a base chosen from sodium methoxide, KOH or NaOH in a stoichiometric quantity with respect to PET.
• Document US2019/0256450 proposes reacting PET with a base, sodium methoxide in a catalytic quantity, and methanol.
• the process described in document WO2020/188359 is characterized by the sequential addition of methanol and methoxide solutions several times after addition of sodium methoxide. The authors describe high yields of PET production.
• Document US2019/390035 describes another depolymerization approach by adding a glycolate salt; the preparation of this salt includes isolation and drying stages that extend over a week.
• the inventors have developed a new process for depolymerization by alcoholysis under mild conditions for the recycling of the polyethylene terephthalate (PET) polymer into monomers of terephthalate esters and monoethylene glycol (MEG). This is fast and gives access to a product in solid form that is directly reusable due to its purity, in particular DMT in crystalline form.
• PET polyethylene terephthalate
• MEG monoethylene glycol
• This process for recycling waste plastics (PET) into terephthalate ester monomer powder comprises three steps: a. a step of crushing the waste to produce fragments, b. a step of pretreating said fragments to facilitate their depolymerization, c.
• step c. is done: in the presence of an excess of monoalcohol compared to the amount of PET in that said bases are present in a catalytic amount relative to the amount of PET by heating between 25° C. and 80° C. for a period of between 30 minutes and 5 hours.
• the process according to the invention proposes to combine an etheroxide base of the sodium or potassium methoxide type or an inorganic base of the sodium or potassium hydroxide type with an organic base, both in catalytic quantity with respect to PET and a monoalcohol such as methanol, ethanol, propanol or butanol, and reacting them under mild conditions. It has several advantages over the processes described previously, which are set out below:
• the depolymerization reaction is complete, rapid and produces a high purity terephthalate ester. This is particularly advantageous when the PET is depolymerized into DMT because the latter is then easily recyclable.
• the process is fast since the reaction is complete in less than 5 hours, and even in less than 2 hours under optimized conditions.
• the depolymerization reaction is simple. Depolymerization and purification can be done in one and the same step. After completion of the reaction, the product obtained is directly a terephthalate ester (like DMT) in the form of crystals, without being mixed with intermediate or degradation products that would have to be separated from the product of interest.
• a terephthalate ester like DMT
• the yield of the process is high, at least 85% in particular for the depolymerization of PET into DMT.
• the product obtained is 99.9% pure at the end of the reaction (after filtration and washing); there is therefore no need for further purification.
• DMT can be used directly after washing with methanol. Given its level of purity, it can be used in many applications, to remake PET or any other type of technical resin involving this monomer.
• the choice of reagents and the fact that the reaction conditions are mild means that no isomerization reaction occurs, nor the formation of degradation products which affect the quality of the product obtained. When present, these Molecules secondary to the reaction disturb the polymerization reaction and purification of the raw DMT is therefore necessary before it can be used.
• the pretreatment step can be carried out in the presence of an aprotic solvent, as an alternative to controversial solvents with regard to environmental standards, without this affecting the efficiency of the reaction, in particular the time of reaction.
• 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.
• a process for recycling waste polyethylene terephthalate (PET) plastics into terephthalate ester monomer powder comprising three steps: a. a step of crushing the waste to produce fragments, b. a step of pretreating said fragments to facilitate their depolymerization, c. a step of depolymerizing the PET into a terephatalate and monoethylene glycol (MEG) ester, in the presence (i) of an organic base comprising an amidine or guanidine unit and (ii) of an etheroxide base of the sodium methoxide or methylate methoxide type potassium, or inorganic of the sodium hydroxide or potassium hydroxide type, characterized in that step c.
• PEG waste polyethylene terephthalate
• catalytic quantity within the meaning of the invention, is meant a non-stoichiometric quantity of base, that is to say in a molar ratio of 1% to 49% relative to the quantity of pretreated PET.
• catalytic also applies to a reagent that is found in its initial form at the end of the reaction (catalyst).
• the catalytic amount of each of the bases is an amount less than 30%, 25% and 20% relative to the amount of PET. More preferably, it is less than 15%, or even 10%. Most preferably, it is less than 5%, in particular between 1 and 3%, for example 1.5%.
• the monoalcohol can be chosen for example from methanol, ethanol, propanol and butanol.
• the terephthalate ester obtained will depend on the monoalcohol used.
• DMT dimethyl terephthalate
• DET diethyl terephthalate
• DPT dipropyl terephthalate
• DBT dibutyl terephthalate
• the method makes it possible to obtain DMT.
• the product of the reaction is a powder of DMT with a high purity of the order of 99%, in the form of crystals, which can be filtered and washed at the end of the polymerization stage.
• this process is characterized by the fact that the depolymerization and the purification are carried out in a single step.
• the recovery of DMT monomers is done simply by filtering the solid present in the solvent bath, followed by washing with methanol.
• the depolymerization step is preceded by a pretreatment in order to facilitate the depolymerization reaction, and the access of the bases to the polymers.
• This pretreatment can be carried out in different ways, described in the state of the art and well known to those skilled in the art.
• the pretreatment step may consist of soaking without dissolution in a container providing continuous agitation of the PET fragments in a solvent solution.
• solvent solution Different types of solvent can be used, alone or as a mixture, chosen from:
• Polar aprotic solvents such as DMAc (dimethyl acetamide), DMF (dimethyl formamide), dimethyl sulfoxide (DMSO), 2-butanone or MEK (Methyl Ethyl Ketone), phenolic esters;
• Apolar solvents such as biphenyl ethers or chlorinated solvents such as dichloromethane, dichloroethane, tetrachloroethane or chlorobenzene.
• the solvent is an aprotic non-chlorinated solvent chosen from DMAc, DMF, 2-butanone (or MEK) and is used at a temperature below 50° and for a shorter time. at 18 hours.
• the soaking stage is followed by a settling stage and a spin cycle.
• the pretreatment step is essential for the depolymerization reaction to take place correctly and that it gives the expected results under the reaction conditions described below.
• the depolymerization step is carried out in the presence of two bases.
• the first is an organic base with an amidine unit, such as l,8-diazabicyclo[5.4.0]undec-7-ene (DBU), l,5-Diazabicyclo(4.3.0)non-5-ene (DBN ) or with a guanidine motif such as triazabicyclodecene (TBD), 1,1,3,3-Tetramethylguanidine (TTMG), guanidine hydrochloride.
• the second is an etheroxide base of the sodium methoxide type, or an inorganic base of the sodium hydroxide or potassium hydroxide type.
• this set of bases has the advantage of being able to contribute to renewing the formation of the depolymerization catalyst to ensure rapid solvolysis.
• the use of the organic base alone in the presence of a monoalcohol does not allow the reaction to progress.
• the use of the methoxide base alone at catalytic amounts does not allow the reaction to be completed within the reaction times cited above for this process.
• the association of this basic set is therefore essential and has not been reported anywhere else.
• the pattern of the organic base is represented by formula (I) below:
• the amount of DBU base is less than 2% relative to the molar amount of PET.
• the organic base is DBU and the ether oxide base is sodium methoxide in an amount less than 5% relative to the molar amount of PET.
• the organic base is DBU and the inorganic base is potassium hydroxide; preferably the two bases are used in an amount less than 5% relative to the molar amount of PET.
• the depolymerization reaction takes place in the presence of a monoalcohol as a solvent.
• the monoalcohol is present in excess relative to the amount of PET.
• the amount of monoalcohol is at least 4 times (or even 5 times) greater in mass ratio than the amount of PET, typically between 4 times and 20 times, or even between 5 and 20 times.
• the monoalcohol is methanol
• the end product is therefore DMT.
• the monoalcohol is ethanol, propanol, or butanol
• the end products are DET, DPT, and DBT, respectively.
• the depolymerization reaction is carried out by heating between 25°C and 80°C, preferably between 50°C and 75°C, most preferably between 60°C and 70°C.
• the reaction time will depend on the temperature and the relative quantity of the reagents involved in relation to the quantity of PET. A person skilled in the art knows how to adapt these parameters. Thus, the reaction time will generally be between 30 minutes and 5 hours and preferably between 1h30 and 3h, even more preferably from 2 to 3h.
• reaction time will be from 2h to 3h and the temperature from 55°C to 70°C.
• the process according to the invention takes place at atmospheric pressure.
• the process will be carried out under the following conditions: in the presence of sodium methoxide in a molar ratio of 5% relative to PET, of DBU in a molar ratio of 1.5% relative to ratio to PET, and methanol has a mass ratio of 5 times by heating for 4 hours at 70° C.; in the presence of sodium methoxide and DBU, the two bases being in a molar ratio of 15% relative to PET, and of methanol in a mass ratio of 10 times by heating for 3 hours at 70° C.; in the presence of potassium hydroxide in a molar ratio of 15% relative to PET, of DBU also in a molar ratio of 15% relative to PET, and of methanol at a mass ratio of 20 times by heating for 3h at 70 °C; in the presence of sodium methoxide in a molar ratio of 15% relative to PET, of DBU in a molar ratio of 1.5% relative to PET, and of methanol at a mass ratio of 10 times by heating for
• the yields obtained under these conditions are at least 80%.
• the DMT can be directly recovered by filtration and washing of the cake obtained. It is 99% pure and can be directly used to generate PET again by reaction with ethylene glycol.
• the quality of the DMT regenerated by this process and then of the recycled PET obtained from this DMT allows use in applications where high quality is required, for example in a mixture with virgin PET or other polymers when the presence of contaminants would be detrimental to quality criteria, such as color, clarity or impact resistance.
• the pieces of PET introduced contain impurities consisting of metal, wood debris, plastics of different types (Polypropylene, Polyethylene, PVC, etc.), it is possible to resort to the use of a sieve whose porosity is at an intermediate size allowing the passage of the crystal powder (in particular of DMT) but preventing that of the impurities mentioned above, which will not have reacted given the selectivity of the process with respect to PET screws only.
• a sieve with a porosity ranging from 0.5 to 1 mm could allow this operation.
• EXAMPLE 1 Recycling of PET into DMT in the presence of sodium methoxide and of DBU in a catalytic quantity, and of methanol
• EXAMPLE 2 Recycling of PET into DMT in the presence of potassium hydroxide and DBU in a catalytic quantity, and of methanol
• DMAc Dimethylacetamide
• the PET pieces treated are drained, optionally washed with an alcohol and dried before being transferred into a glass reactor of 50 mL in volume. 15 mL of anhydrous methanol are added to the pretreated pieces followed by 0.44 mL sodium methoxide (25% in methanol) corresponding to a molar ratio of 30% relative to the PET introduced.
• EXAMPLE 4 Recycling of PET to DMT in the presence of sodium methoxide and of TBD in a catalytic quantity, and of methanol
• DMAc Dimethylacetamide
• DMAc Dimethylacetamide
• the DMT obtained was repolymerized using conventional PET synthesis routes and made it possible to obtain very satisfactory technical specifications in comparison with a commercial DMT.

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• Life Sciences & Earth Sciences (AREA)
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• Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 2020
  • 2020-11-24 FR FR2012085A patent/FR3116532B1/fr active Active
• 2021
  • 2021-11-24 KR KR1020237021316A patent/KR20230129010A/ko unknown
  • 2021-11-24 CN CN202180078952.3A patent/CN116685572A/zh active Pending
  • 2021-11-24 WO PCT/FR2021/052085 patent/WO2022112715A1/fr active Application Filing
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