Polyethylene terephthalate depolymerization

Depolymerization, e.g., polyethylene terephthalate and cellulose hydrolysis Hydrothermal oxidation of organic wastes in water Crystallization, particle formation, and coatings Antisolvent crystallization, rapid expansion from supercritical fluid solution (RESS)... 

Polyethylene terephthalate also has the tendency, because it is produced by a condensation polymerization process, to depolymerize under high pressure and temperatures in the presence of water. Although this is usually a negative attribute, it can be utilized to regenerate pure monomers which can be repolymerized to make fresh polymer. This avoids the issues experienced by reprocessing resins, as the new resin has not experienced a previous heat history. A major drawback to this process is the requirement that the monomers used in polymerization processes must be highly pure, Unfortunately, this process is extremely costly and not performed on a commercial scale. 

Claims of perpetual motion create moments of mirth and consternation for those knowledgeable in the laws of thermodynamics. Yet, is it only hyperbole when a responsible journal such as the European Plastics News [1] proclaims that depolymerization of polyethylene terephthalate (PET) can be repeated indefinitely The second law of thermodynamics brings us back to reality. The depolymerization of PET does not operate at 100% yields, but does offer the opportunity for near-stoichiometric recovery of the monomers used to make the polyester. With high yields of potentially valuable monomers, the commercial potential for polyester depolymerization to regain feedstocks must be considered. 

Manufacture. The manufacture of 1,4-cyclohexanedimethanol can be accomplished by the catalytic reduction under pressure of dimethyl terephthalate in a methanol solution (47,65). This glycol also may be prepared by the depolymerization and catalytic reduction of linear polyesters that have alkylene terephthalates as primary constituents. Polyethylene terephthalate) may be hydrogenated in the presence of methanol under pressure and heat to give good yields of the glycol (see Polyesters) (66,67). 

Chemical depolymerization of polyesters has been mainly applied to polyethylene terephthalate (PET), the most common polyester on the market. Chemo-lysis of PET by a variety of methods has been known for many years. In fact, the chemical depolymerization of PET can be considered the starting point of plastic chemical recycling. 

Second, a molecule or molecular fragment can also be split which is called decomposition. To recycle bottles made of polyethylene terephthalate (PET) catalytic depolymerization is used to split the PET in valuable components. ... 

There is also uncertainty in the regulatory status of tertiary recycling when it does not result in the direct production of monomers suitable for polymerization into new plastic. The European Commission has at times supported the chemical recycling (depolymerization) of condensation polymers such as polyethylene terephthalate back to monomer (e.g., dimethyl terephthalate) as recycling for the purpose of government-mandated plastics recycling rate calculations, but not the liquefaction of polyolefin plastics back to petrochemical feedstocks for reprocessing in a refinery. Discussions around these types of definitional issues, and their environmental and economic implications, are likely to continue for many years to come. 

Hydrolysis reactions have been widely reported in NCW for low-molecular-weight molecules as well as for polymeric materials. Mandoki reported a process for depoly-merizing condensation polymers using NCW without addition of bases or acids. More particularly, polyethylene terephthalate, polybutene terephthalate, nylon 6, and nylon 66 were hydrolytically depolymerized (Fig. 9.25). 

Yal9inyuva, T. Kamal, M.R. Lai-Fook, R.A. Ozgiuniis, S. Hydrolytic Depolymerization of Polyethylene Terephthalate by Reactive Extrusion. Intern. Polymer Processing. 2000,15,137-146. 

As reported by Fukushima et al., TBD was used as catalyst to depolymerize polyethylene terephthalate (PET) leading to bis(2-hydroxyethyl)terephthalate (BHET) (Scheme 16). The... 

AIST A process for converting PET (polyethylene terephthalate) into virgin plastic. The scrap PET is first depolymerized by heating with ethylene glycol and a metal salt catalyst. 

It can be obtained by depolymerization and hydrogenation of polyethylene terepb-thalate in the presence of methanol, but it is produced industrially by Tenttessee Eastman from dimethyl terephthalate. 

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