Effects of torrefaction on the formation and distribution of dioxins during wood and PVC pyrolysis: An experimental and mechanistic study

Dioxins reduction is crucial for the pyrolysis of municipal solid waste (MSW). In this work, torrefaction was employed as a pretreatment for inhibiting the synthesis of dioxins. A mixture of poplar and polyvinyl chloride (PVC) was used as the model MSW and provided the polycyclic aromatic hydrocarbon (PAH) source and chlorine sources, respectively. A torrefaction-pyrolysis experiment was performed in a tubular furnace system, and the weight loss and chlorine release (mainly in the form of hydrogen chloride) were evaluated. The dioxins distribution in the products were detected by high-resolution mass spectrometry (HR-MS). Thermogravimetric Fourier transform infrared spectroscopy (TG-FTIR) was employed to clarify the chlorination of PAHs. The results showed that torrefaction could reduce 98.63 % of the total amount of dioxins and reduce 99.09 % of the toxic equivalent of volatile dioxins. Since torrefaction cut the Cl participation of MSW (from PVC) by 86.94 %, the overall reaction process was simplified, and the temperature of the maximum conversion rate was increased. In addition, the analysis of the functional groups indicated that most dioxins during pyrolysis was synthesized from 200 ℃ to 400 ℃. This research demonstrated a significant emission reduction, which effected by torrefaction, and provided a new idea for dioxins clean pyrolysis of MSW.