Process optimization for catalytic glycolysis of post-consumer PET wastes
Glycolysis has been the subject of increased interest as a valuable feedstock recycling for poly(ethylene terephthalate) (PET). However, there are no reports in the technical literature that deal with the design and optimization of the global process.
Conversion into bis(2-hydroxyethyl) terephthalate (BHET) of the non-glycolyzed solid was feasible, carried out in the presence or absence of fresh PET. The yield varied between 63 and 80%. The monomer was recovered by extraction with hot water followed by crystallization at 4 °C. The optimized H2O:BHET ratio was 6.7 mL g-1. The EG(ethylene glycol)/H2O mixture was effectively separated by vacuum distillation and EG of 99.6% purity was recovered, which could be used again. Finally, the highly active catalytic role of sodium carbonate salt for glycolysis was evident not only for transparent PET wastes but also for complex wastes.
The recirculation of the solid residue from extraction, the separation of EG/H2O mixture from crystallization and the subsequent refeeding of the organic reactant into the reactor, the minimization of the amount of water to efficiently recover the monomer and the suitability of the chemical recycling of complex PET wastes are operational aspects that significantly increased the global efficiency. © 2013 Society of Chemical Industry