Process optimization for catalytic glycolysis of post‐consumer PET wastes

Abstract

BACKGROUND 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. RESULTS 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 H 2 O:BHET ratio was 6.7 mL g -1 . The EG(ethylene glycol)/H 2 O 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.CONCLUSIONS The recirculation of the solid residue from extraction, the separation of EG/H 2 O 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.

Recycling of waste poly(ethylene terephthalate) into flame‐retardant rigid polyurethane foams

“…The methods of the PET depolymerization are hydrolysis, glycolysis, aminolysis, and methanolysis . Comparing with other aforementioned methods, glycolysis of PET waste is a convenient method to recycle polymer because of the relative mild reaction conditions and decent yield of oligomer.…”

Recycling of poly(ethylene terephthalate) – A review focusing on chemical methods

“…They found zinc acetate to be the most effective catalyst (Table 3, 78% BHET), followed by zinc stearate (Table 3, 65% BHET) and finally zinc sulfate (Table 3, 25% BHET). Analogously, Pingale and Shukla [172], Duque-Ingunza and coworkers [203,204,206,212] studied PET-glycolysis using different sodium catalysts with different anions (carbonate, bicarbonate and sulfate). The effectiveness of the sodium catalysts on glycolysis yielding BHET decreased in the following order: sodium bicarbonate > sodium carbonate > sodium sulfate.…”

PET Recycling by Alcoholysis Using a New Heterogeneous Catalyst: Study and its Use in Polyurethane Adhesives Preparation

“…Many catalysts have been applied to PET recycling such as zinc acetate, sodium carbonate or the enzime Candida antarctica lipase B . For this proposal, sodium metasilicate (NaMs) could be used with the advantage of being a low cost and crystalline powder.…”