Neopentyl glycol as an alternative solvent for the chemical recycling of complex PET waste

Abstract

The current work reports a novel and effective solvolysis process for the treatment of complex poly(ethylene terephthalate) (PET) waste using neopentyl glycol (NPG) as a depolymerization agent, which to date has not been studied much for chemical recycling. Different complex PET waste samples (multilayers and textiles) were conditioned for glycolysis in the presence of NPG and zinc acetate as a catalyst. The reaction parameters, including temperature and NPG/PET molar ratios, were optimized to maximize the yield of the bis-(hydroxy neopentyl) terephthalate (BHNT) monomer. The reaction progress was gravimetrically determined, and the resulting BHNT monomers were characterized by means of various techniques (FTIR, DSC, and NMR). A novel purification step with active carbon was developed in order to remove dyes and other impurities present in the raw products. The results indicated that an NPG/PET molar ratio of 6 : 1 and a reaction temperature of 200 °C were optimal for achieving high PET conversion and raw BHNT yield. The purification process successfully enhanced the purity of BHNT, increasing the presence of the monomer in the purified samples from 60% to 95% in mol and reducing the oligomer and by-product content. The obtained products have the potential to replace fossil-based NPG in the synthesis of resins or coatings.