Oxidative pyrolysis of organic ion exchange resins in the presence of metal oxide catalysts

Pretreatment of the organic ion exchange resins by oxidative pyrolysis is effective for volume reduction before vitrification. In this work, pyrolysis of two nuclear-grade resins, Purolite NRW100 (cationic) and NRW400 (anionic), was examined using a laboratory-scale theromgravimetric analyzer (TGA) in air. It was shown that the cationic resin was harder to degrade and was less volatile compared to anionic resin. Off-gas data revealed the presence of SO₂, CO₂, CO, and H₂O during oxidative pyrolysis of cationic resin from 30 to 800°C. Trimethylamine, CO₂, CO, and ethyl formate were found in the case of anionic resin. In addition, oxidative pyrolysis of the mixed resins (50/50wt.%) showed the existence of the gases nearly at the temperatures where the gases would evolve if the results of two different resins were superimposed. Several metal salts including CuSO₄·5H₂O, CuO, and FeSO₄·7H₂O, as well as the ions Cu²⁺ pre-loaded on the resins had a catalytic effect on the oxidative pyrolysis of cationic resins, in which the decomposition of functional groups and polymer matrices was enhanced. Such catalytic effect was highlighted by a large decrease in activation energy calculated according to a degradation mechanism involving four consecutive reactions.