PET-Polyesterproduktion durch Polykondensation
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Übersicht
Polyethylene terephthalate (PET) is produced by polycondensation of ethylene glycol with terephthalic acid (PTA). PET is the world's most recycled plastic, used for beverage bottles, food packaging, and polyester textile fibers. The two-stage process involves esterification followed by melt polycondensation under vacuum. Global PET production exceeds 90 million tons annually, with approximately 70% used for fibers and 30% for packaging.
Chemischer Prozess
Purified terephthalic acid (PTA) is esterified with ethylene glycol (EG) at 240-260 degrees C to form bis(2-hydroxyethyl) terephthalate (BHET). The BHET undergoes melt polycondensation at 270-290 degrees C under high vacuum (<1 mbar) using antimony trioxide catalyst, removing ethylene glycol to build molecular weight. Solid-state polymerization (SSP) further increases IV for bottle-grade resin.
Rohstoffe
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Purified terephthalic acid (PTA, C₈H₆O₄) — Oxidation of p-xylene (Diacid monomer)
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Ethylene glycol (C₂H₆O₂) — Hydration of ethylene oxide (Diol monomer)
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Antimony trioxide (Sb₂O₃) — Mining and smelting (Polycondensation catalyst)
Endprodukte
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PET resin (chips/pellets) — Bottles, packaging, polyester fibers (IV 0.60-0.84 dL/g depending on grade)
Environmental Impact
PET is the most recycled plastic with established mechanical and chemical recycling infrastructure. However, production from fossil feedstocks contributes to CO₂ emissions. Antimony catalyst traces in PET have raised health concerns. Microfiber shedding from polyester textiles is a growing environmental issue.
Sicherheitshinweise
- ⚠ High-temperature melt processing (270-290 degrees C)
- ⚠ Ethylene glycol is toxic if ingested
- ⚠ Vacuum systems require rigorous maintenance
- ⚠ Antimony trioxide is a suspected carcinogen
Neuere Innovationen
Bio-based PET using plant-derived ethylene glycol and furandicarboxylic acid (PEF) as a drop-in replacement is in commercial development.
Enzymatic depolymerization by PETase enzymes enables closed-loop chemical recycling under mild conditions.
Produktionsmaßstab
90000000
Tonnen/Jahr
$55 billion
Marktwert
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