Staged pyrolysis of medical waste for high-value product generation: Impact of inter-component interactions on chlorine migration and light compounds formation

Medical waste is highly hazardous, with its volume increasing annually. Staged pyrolysis is a pyrolysis technique that can improve the quality of pyrolysis products while reducing the generation of pollutants, which shows enormous potential for efficient disposal and resource recovery of medical waste. However, medical waste exhibits a highly complex composition. Interactions occur during the co-pyrolysis of multi-component feedstocks, significantly influencing pyrolysis behavior and product distribution. Therefore, this study investigated the interaction mechanisms during the low-temperature dechlorination stage (Stage I) and dechlorinated semi-char re-pyrolysis stage (Stage II) of medical waste staged pyrolysis, providing a theoretical basis for the clean and sustainable treatment of medical waste. In the low-temperature dechlorination stage, HCl interacted with gauze in the gas phase, lowering its decomposition temperature and releasing significant oxygenated volatiles. HCl also promoted the breakdown of plasticizers, producing chlorinated hydrocarbons. Gas-solid interactions partially inhibited HCl release, leading to adsorption and fixation on semi-char. In the dechlorinated semi-char re-pyrolysis stage, gas-phase interactions accelerated the denitrogenation of nitrogen-containing aromatics. In contrast, gas-solid interactions reduced the release of oxygenated functional groups, weakening CO and CO₂ production. Additionally, gas-phase and gas-solid interactions promoted the removal of organic chlorine from oil and char, generating CH₃Cl, with the gas-solid interactions having a more significant impact. This study revealed the impact of inter-component interactions on chlorine migration and light compounds formation during staged pyrolysis of medical waste, offering theoretical and technical support for efficient waste treatment and high-value product generation.