CO2-assisted co-pyrolysis of textile dyeing sludge and hyperaccumulator biomass: Dynamic and comparative analyses of evolved gases, bio-oils, biochars, and reaction mechanisms

[Display omitted] •CO2-assisted co-pyrolysis of sludge and hyperaccumulator was conducted.•CO2-assisted atmosphere increased volatiles and CO evolution.•CO2-assisted co-pyrolysis enhanced the temperature sensitivity of C = O in biochar.•CO2-assisted co-pyrolysis was more efficient than the N2 atmosphere co-pyrolysis.•50 % CO2 atmosphere had the similar pyrolysis effect as the pure CO2 atmosphere. The CO2-activated co-pyrolysis technology presents promising potential to mitigate the environmental pollution and climate change. The dynamic analyses of evolved syngas, bio-oils, biochars, interaction effects, and reaction mechanisms of the co-pyrolysis of textile dyeing sludge (TDS) and Pteris vittata (PV) (hyperaccumulator biomass) were characterized and quantified comparatively in the three atmospheres. In the CO2-assisted atmosphere, the gasification of PV began to prevail between 600 and 900 °C, while in the N2 atmosphere, PV and TDS were stable at 750 °C. The CO2-assisted co-pyrolysis reduced the apparent activation energy. The higher CO2 concentration during gasification led to the higher activation energy. The CO emission level of the CO2 and mixed atmospheres was almost 20 and 14 times that of the N2 atmosphere, respectively. The CO release from the CO2 atmosphere was 1.4 times that from the mixed atmosphere. CO2 significantly changed the production pathway of biochar in the N2 atmosphere, as was evidenced by the enhanced temperature sensitivity of O–C = O/hydroxy (−OH) in ester. Our findings research can provide new insights into the effectiveness of the CO2-assisted co-pyrolysis associated with reduced costs and hazardous wastes.