For the extrusion of PET, it is necessary to achieve higher temperatures
than those used for the extrusion of other polymers, such as
polyethylene (PE) and polypropylene (PP).
A single medium-sized food packaging factory, for instance,
produces about 8 ton monthly of parings of multilayer films containing
PET. These films are gathered in the factory or turned
into waste. Thus, the future of multilayer packages has become a
great environmental concern. The separation of polymers before
recycling would be an interesting method to overcome the limitations
presented by extrusion-recycling of multilayer films.
Numerous processes for PET depolymerization have been
performed with different depolymerizing conditions. The most
used processes are glycolysis, hydrolysis and alcoholysis. The
glycolysis process using ethylene glycol depolymerizes PET to
bis-(hydroxyethyl) terephthalate (BHET) [9–11]; the hydrolysis
processes under acidic or basic conditions produce terephthalate
acid (TPA) [12–17], and the alcoholysis processes using supercritical
methanol and supercritical ethanol in PET depolymerization
have as products dimethyl terephthalate (DMT) and diethyl terephthalate
(DET), respectively [17–20]. All of these processes present
both advantages and drawbacks. Supercritical fluids are very
striking means for running chemical reactions, mainly because
relatively minor changes in either temperature or pressure into
the system can modify appreciably and continuously the solvent
and the transport properties of a single solution [21,22].
For the extrusion of PET, it is necessary to achieve higher temperaturesthan those used for the extrusion of other polymers, such aspolyethylene (PE) and polypropylene (PP).A single medium-sized food packaging factory, for instance,produces about 8 ton monthly of parings of multilayer films containingPET. These films are gathered in the factory or turnedinto waste. Thus, the future of multilayer packages has become agreat environmental concern. The separation of polymers beforerecycling would be an interesting method to overcome the limitationspresented by extrusion-recycling of multilayer films.Numerous processes for PET depolymerization have beenperformed with different depolymerizing conditions. The mostused processes are glycolysis, hydrolysis and alcoholysis. Theglycolysis process using ethylene glycol depolymerizes PET tobis-(hydroxyethyl) terephthalate (BHET) [9–11]; the hydrolysisprocesses under acidic or basic conditions produce terephthalateacid (TPA) [12–17], and the alcoholysis processes using supercriticalmethanol and supercritical ethanol in PET depolymerizationhave as products dimethyl terephthalate (DMT) and diethyl terephthalate(DET), respectively [17–20]. All of these processes presentboth advantages and drawbacks. Supercritical fluids are verystriking means for running chemical reactions, mainly becauserelatively minor changes in either temperature or pressure intothe system can modify appreciably and continuously the solventand the transport properties of a single solution [21,22].
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