Ethylene production from chlorinated organic hazardous wastes by thermal plasma pyrolysis

Chlorinated organic hazardous wastes (COHW) from the chemical industry threaten human health and environment due to persistent toxicity and resistance to degradation. Conventional treatments often suffer from incomplete degradation or poor resource recovery. This work proposed an efficient COHW conversion to ethylene (C₂H₄) for dual COHW treatment and chemical production. Tetrachloroethylene (C₂Cl₄), a representative of COHW, was selected to develop a hydrogen thermal plasma pyrolysis reaction kinetic model, which was validated through experiments. The particle evolution in the reactor was investigated, and the cascade reaction pathway of C₂Cl₄ = > acetylene (C₂H₂) = > C₂H₄ was unveiled, providing a theoretical foundation for product composition regulation. To address the trade-off between low carbon black (C(B)) formation and high C₂H₄ selectivity in the pyrolysis with conventional single-stage quenching, a novel two-stage quenching strategy was proposed: rapid quenching (above 1300 K) suppresses C₂H₂ to C(B) conversion, followed by appropriate slow quenching (below 1300 K) intensifying C₂H₂ hydrogenation to C₂H₄. This coupling enhances the C₂H₄ selectivity and yield. The optimized experiments achieved 100 % chlorine removal, a C(B) yield reduction of 94 %, a C₂H₄ selectivity of 43.3 %, and a C₂H₄ yield of 40.2 %, making a 110 % improvement over single-stage quenching and surpassing all reported COHW-derived C₂H₄ yields.