Investigation on chlorine migration during pyrolysis of medical waste

Large quantities of physiological saline and polyvinyl chloride fragments constitute the primary sources of chlorine within medical waste. During the thermochemical treatment of medical waste, they induce severe corrosion and degradation of product quality. A combined TG-MS-FTIR analysis of 13 representative medical waste types, including plastics, rubber, and cellulose materials, along with their mixtures, revealed a signature five-stage co-pyrolysis process. Free radicals from fibrous dehydration aided plastic scission and lignin cleavage, while polymer melt inhibited secondary fiber reactions. NaCl catalyzed fibrous decarboxylation but hindered hydrocarbons. Fixed-bed tests showed chlorine migration intensely temperature-dependent, with under 500 °C critical for dechlorination. Crucially, 20.06 % of liquid-phase chlorine here existed as chlorinated esters, confirming co-pyrolysis alters speciation via ester exchange. Even at 700 °C, 25.95 % char chlorine remained organic; gas-phase enrichment rose to 44 % by 800℃. Introducing hematite catalyst proved highly effective. Its surface lattice oxygen mediated C-Cl cleavage, reducing chlorinated ester yield by 6.3 % at 500 °C and decreasing chlorine content in the liquid-phase product by 5 %. Hematite also enhanced tar secondary cracking, boosting gas yield and raising renewable gas calorific value by 19.34 %. XRD confirmed stable FeCl₃ formation. By synergizing hematite catalysis with the optimized pyrolysis temperature profile, this study achieved targeted volatile chlorine enrichment and significant suppression of key chlorinated residues. This offers innovative theoretical and technological support for sustainable chlorine pollution mitigation during medical waste pyrolysis resource recovery.