Hydrolysis in PET Bottle Chemical Recycling

Neutral hydrolysis method for waste polyester without waste liquid discharge. The method involves a two-step process: (1) alcohol treatment with ethylene glycol to partially depolymerize and dissolve impurities in the waste polyester, (2) hydrolysis in ethylene glycol to completely depolymerize and separate the polyester into pure terephthalic acid and ethylene glycol. This allows recycling the polyester without generating waste water. The alcohol treatment reduces polyester molecular weight and impurity content, making hydrolysis milder and more efficient.

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A selective and scalable chemical recycling process for polyethylene terephthalate (PET) waste that avoids the high energy requirements and complex technologies needed for depolymerization of PET. The process involves reacting PET with a nucleophile in excess, catalyzed by a base and alkaline metal salt, to selectively decompose the PET into its monomers. The process conditions are mild compared to existing techniques.

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Method for recycling waste polyester like PET bottles into usable polyester by alcoholysis with ethylene glycol catalyzed by a two-component catalyst of nitrogen-containing polycyclic organic matter and metal salts like zinc acetate. The catalyst synergistically accelerates ester bond cleavage compared to single components. The timing of adding the nitrogen compound is critical to avoid decomposition. The method involves heating crushed PET in ethylene glycol with metal salt, then adding the nitrogen catalyst. The alcoholysis completes when PET disappears. This gives high-purity recycled BHET for repolymerization.

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Method to recycle waste PET into higher value PETG/PCTG copolyester using mixed alcohol depolymerization followed by polycondensation. The recycling process involves alcoholysis of waste PET using a catalyst to break down the polymer into BHET/BHCT monomers and oligomers using a mixture of ethylene glycol (EG) and 1,4-cyclohexanedimethanol (CHDM). These depolymerization products are then polycondensed using a catalyst to make PETG/PCTG copolyester with properties like improved light transmittance, environmental friendliness, and heat resistance compared to virgin PET.

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A double depolymerization method for recycling waste polyester like PET that involves using two different depolymerization techniques in series to improve product yield and purity compared to single methods. The first step is an initial depolymerization using a method like alkaline hydrolysis or methanolysis to partially break down the polyester into monomers or oligomers. The second step is a final depolymerization using a different method like glycolysis or alcoholysis to fully depolymerize the partially broken polymer into monomers. This two-step process allows higher yields and better purification compared to using just one depolymerization method.

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A continuous process for recycling PET plastic waste into high quality regenerated PET. The process involves alcoholysis of the waste PET fragments using ethylene glycol (EG) and a catalyst. The alcoholysis is carried out in two reactors with controlled conditions to depolymerize the oligomers and remove excess EG. The final repolymerization step is done in a separate reactor. The continuous process allows efficient recycling with good economics and high quality regenerated PET. The lower EG to PET ratio and homogeneous reaction conditions in the alcoholysis reactors enable rapid dissolution and depolymerization of the PET fragments.

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A two-component mixed metal catalyst system for efficiently recycling waste polyethylene terephthalate (PET) using alcoholysis. The catalyst contains zinc acetate and an alkali metal hydroxide like sodium or potassium hydroxide. The zinc acetate forms a complex with the highly polar ethylene glycol solvent, and the alkali metal hydroxide provides highly alkaline conditions. This two-component catalyst synergistically improves PET alcoholysis efficiency and yield by enhancing the nucleophilicity of the alcohol solvent and strengthening the hydrogen bonding between the solvent and catalyst.

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A method for recycling waste polyethylene terephthalate (PET) using zinc oxide nanoparticles as a catalyst for alcoholysis. The method involves using a zinc oxide nanoparticle catalyst to convert waste PET into bishydroxyethyl terephthalate (BHET) using ethylene glycol as the solvent. The zinc oxide nanoparticle catalyst is prepared by mixing zinc acetate and sodium hydroxide in water. The catalyst addition, ethylene glycol-to-PET ratio, temperature, and time are optimized to improve the PET conversion and BHET yield.

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Recycling of polyethylene terephthalate (PET) waste into new PET using a two-step process that involves partial depolymerization followed by complete depolymerization. This reduces the time and ethylene glycol required compared to direct depolymerization. The partial depolymerization step involves heating PET with excess ethylene glycol to 200-250°C to produce partially depolymerized PET. This intermediate is then depolymerized with ethylene glycol and catalyst at 170-200°C to form bis(2-hydroxyethyl) terephthalate (BHET). The BHET is purified and polymerized to regenerate PET.

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A method for recycling polyethylene terephthalate (PET) plastic that involves depolymerizing it using an electrolysis cell with an alkali metal glycolate solution. The PET is reacted with the glycolate solution to produce bis-2-hydroxyethyl terephthalate (BHET) at high yields. The method involves using an electrolysis cell with alkali metal glycolate solution instead of acid to depolymerize PET. The cell contains an alkali metal glycolate solution made by electrolysis. This method allows recycling PET into BHET with higher yields and less waste compared to other methods.

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Process for depolymerizing PET plastics into BHET using sodium or potassium glycolate obtained by reactive distillation. The process involves reacting glycol with alkali metal alcoholate like sodium or potassium ethoxide in a reactive distillation column. This produces a crude product stream containing glycolate, water, alcohol, and unreacted alcoholate. The glycolate can then be separated and used for depolymerizing PET to BHET. The reactive distillation provides higher yields of BHET compared to using glycolate directly. After depolymerization, the BHET can be polymerized again into PET if desired. This provides a recycling loop for PET plastics.

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Mild, efficient and selective recycling method for waste polyester materials that involves hydrolysis to break down the polyester into monomers. The process involves mixing the waste polyester with glycol, water, a polar aprotic solvent or ether, and an alkaline catalyst. The reaction forms acidic degradation products that precipitate out. This selective hydrolysis allows gentle and efficient recycling of complex waste polyester materials like bottles and textiles, compared to incineration or landfilling.

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Selective depolymerization of waste polyester like PET using aqueous metal salts to produce depolymerized monomers and oligomers. This allows recycling of waste plastics into new polymers without significant degradation. The process involves heating waste polyester in metal salt solution to break down the polymer. The depolymerized products can then be polymerized again to make renewable polyesters. The metal salt residue is removed. This selective depolymerization avoids the energy-intensive separation steps of conventional methods.

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Mild and selective depolymerization of waste polyester and its blended textiles to recover the polyester without degrading the non-polyester fibers. The process uses a solvent mixture of alcohols and aprotic solvents, catalyzed by alkaline bases, to hydrolyze or alcoholysis decompose the polyester selectively. This avoids harsh conditions that degrade other fibers. The undepolymerized non-polyester fibers are separated and recycled, while the polyester decomposes into recoverable monomers.

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Catalyzing low-temperature degradation of waste polyethylene terephthalate (PET) into terephthalic acid and ethylene glycol using alkaline earth metal hydroxides or oxides as catalysts. The catalyst allows controlled degradation of PET melt at temperatures as low as 230-350°C. Adding water after catalytic degradation hydrolyzes the intermediate monovinyl terephthalate to generate the final products. This method recovers terephthalic acid and ethylene glycol from waste PET using simple, low-energy, and catalyst-recoverable degradation.

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Recovering waste polyester like PET bottles by alcoholysis using ionic liquids as catalysts instead of metal catalysts. This provides a green and efficient method to recycle waste PET into new polyester products without degrading the quality. The ionic liquids catalyze the reaction of waste PET with ethylene glycol at mild conditions to produce BHET, the main component of PET. The ionic liquid catalysts like 1-butyl-3-methylimidazolium acetate have better performance compared to metal catalysts in terms of PET conversion rate and BHET productive rate.

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Chemical recycling method for waste polyester like old PET bottles and textiles to produce high-purity polyester chips. The method involves pretreating the waste polyester to remove impurities, followed by depolymerization using a mixture of diols and alkane solvents. The depolymerization is catalyzed by an initiator. The resulting polyester monomer is crystallized, filtered, and dried to make high-purity polyester chips. This yields over 97% compared to traditional methods that struggle to exceed 70%. The pretreatment removes heavy metals, pigments, and other impurities, ensuring high-quality recycled polyester chips.

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A method to degrade polyester plastics like PET into high-purity monomers and esters using organic acids as solvent and catalyst. The degradation reaction involves mixing waste polyester with an organic acid like acetic acid to depolymerize the polyester into terephthalic acid (TPA) and esters like ethylene glycol diacetate (EGDA) and ethylene glycol monoacetate (EGMA). The degradation products can be purified and used for repolymerization or other applications. The organic acid solvent allows efficient depolymerization and recovery of the monomers and esters compared to water-based methods.

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A method to recycle high-viscosity PET like water bottle containers without using solvents. The method involves melting the PET, adding an alkali slurry with ethylene glycol, and reacting the melted PET in-situ to form alkali terephthalate. This is done continuously in an extruder-like reactor. The alkali terephthalate is then dissolved in water and further reacted with acid to produce terephthalic acid. The extruder-based in-situ reaction avoids the need for solvents to decompose high-viscosity PET.

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Recovering high-quality BHET (bisphenol A ethylene terephthalate) from waste polyester products like old textiles and bottles using the unique phase transition properties of BHET crystals. The method involves alcoholysis to convert waste PET into BHET, followed by decompression sublimation and condensation to separate and purify the BHET crystals from impurities. This allows efficient recycling of waste PET into high-value BHET without needing expensive decolorization steps.

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