A Catalyst You Can Filter Out — and Use Thirty Times Over
Professor Jonggeol Na
Department of Chemical Engineering and Materials Science
A joint research team from Ewha Womans University and Sogang University has developed a chemical recycling process for waste PET in which the catalyst can simply be filtered out of the reaction and used again. Because the catalyst leaves no heavy-metal residue, the elaborate purification that has long weighed down PET chemical recycling largely disappears — and with it, much of the cost and carbon. The work was published in Nature Communications on 29 July 2026.
PET accounts for roughly 10–15% of global plastic waste. The most complete way to close its loop is chemical recycling: breaking the polymer back down into its original monomer, bis(hydroxyethyl) terephthalate (BHET), and repolymerizing it into virgin-equivalent material. Glycolysis, which uses ethylene glycol, is the most industrially practical route — it runs at atmospheric pressure and yields a single primary product. The obstacle has been the catalyst. Metal salts such as zinc acetate drive the reaction efficiently but dissolve into the mixture and leave heavy metals behind, requiring six or more recrystallization cycles to remove. The energy spent on that purification cancels out much of the benefit of recycling in the first place.
Led by Professor Hyeong Jun Kim (Department of Chemical and Biomolecular Engineering, Sogang University) and Professor Jonggeol Na (Department of Chemical Engineering and Materials Science, Ewha Womans University), the team first asked a more basic question: when an ionic catalyst is anchored to a polymer chain, does it matter which ion you tie down? It does. Tethering the anion leaves the counter-cation free to reach the ester bonds of PET; tethering the cation sterically blocks it. Polyanion catalysts converted more than 99% of PET with BHET yields up to 96.9%, while their polycation counterparts stalled below 40% conversion. Infrared spectroscopy and kinetic isotope experiments confirmed that catalysis is governed by the interaction between the cation and the ester carbonyl — a question on which the literature had long been divided.
Translating that principle into a process required no new material. The team used sodium polystyrene sulfonate (PSSNa) beads — the same strong-acid ion-exchange resin used in water treatment, available at around $7 per kilogram. What mattered was not the surface but the interior: solid, smooth beads reacted only at the outside and yielded just 4.4% BHET, whereas macroporous beads, with more than twenty times the surface area, reached 94.2%. After the reaction, the beads were recovered by simple filtration and reused 30 times, holding an average yield of 90.7% and 89% of their initial mass.
With no heavy metals to remove, the team replaced repeated recrystallization with a two-stage evaporation that exploits the 120 °C boiling-point gap between BHET and ethylene glycol, cutting steam consumption sharply. The catalyst also held up outside the ideal case: real post-consumer polyester textiles were depolymerized at over 99% conversion to give BHET at 89.4% yield and 95.6% purity, and in mixed plastic streams containing polyethylene and polypropylene, only the PET was broken down. Continuous operation in a stirred-tank reactor sustained a 79.7% yield for more than four hours.
A techno-economic analysis and life-cycle assessment put numbers on the result. The minimum selling price of BHET from this process is $1.02/kg — roughly 24% below the $1.35/kg market price of virgin BHET. Greenhouse gas emissions come to 1.90 kg CO₂-eq per kg of recycled PET, about one third of the 5.35 kg associated with producing virgin PET and incinerating it, and below the 3.45 kg landfill scenario.
“What matters here is not the catalyst alone,” said Professor Na. “We carried it into a real process and checked whether the economics and the carbon actually hold up. We hope this becomes a practical option for accelerating a circular plastics economy.” Professor Kim added that “a choice as seemingly small as which ion you anchor to the backbone turns out to govern catalytic performance — and we were able to draw that principle straight out of an inexpensive resin already used in industry.”