Ti-Si composite glycol salts: depolymerization and repolymerization studies of PET

Area of Science:

• Materials Science
• Chemical Engineering
• Polymer Chemistry

Background:

• Polyethylene terephthalate (PET) recycling remains a significant environmental challenge.
• Existing PET recycling methods often result in material degradation or lower-value products.
• Developing efficient catalysts for PET depolymerization and subsequent repolymerization is crucial for sustainable circular economy models.

Purpose of the Study:

• To synthesize and characterize a novel Ti-Si-ethylene glycol salt (Ti/Si-EG) catalyst.
• To investigate the catalytic activity of Ti/Si-EG for the depolymerization of PET into bis(hydroxyethyl)terephthalate (BHET).
• To optimize the conditions for PET depolymerization and subsequent polycondensation using the Ti/Si-EG catalyst for high-value PET recycling.

Main Methods:

• Synthesis of Ti-Si-ethylene glycol salt (Ti/Si-EG) catalyst.
• Response surface analysis to determine optimal depolymerization conditions (catalyst dosage, temperature, time, reactant ratio).
• Depolymerization of PET using ethylene glycol (EG) and Ti/Si-EG catalyst.
• Polycondensation of BHET using Ti/Si-EG catalyst to synthesize recycled PET.
• Performance testing of synthesized PET and comparison with conventionally produced PET.

Main Results:

• Optimal depolymerization conditions: EG:PET ratio of 4:1, 0.56% catalyst dosage, 203 °C for 3.8 h, yielding 90.10% BHET.
• Successful synthesis of PET from BHET using Ti/Si-EG catalyst with 0.015% catalyst addition.
• Synthesized PET exhibited performance comparable to PET produced via the traditional PTA method.
• Incorporation of Si reduced Ti's catalytic activity and prevented product yellowing.
• The glycol salt catalyst avoided introducing impurity groups into the recycled PET.

Conclusions:

• The Ti/Si-EG catalyst enables efficient, high-value recycling of waste PET through depolymerization and repolymerization.
• The optimized process achieves a high yield of BHET and produces recycled PET with desirable properties.
• The catalyst's composition (Si addition) enhances product quality by preventing yellowing.
• This method offers a sustainable solution for waste PET management, contributing to a circular economy.