Valorization of oily sludge with coal gasification slag via catalytic pyrolysis

The treatment of oily sludge (OS) and coal gasification slag (CGS), which are abundant hazardous solid wastes in the energy industry, is still challenging. Herein, we demonstrate the CGS catalyzed OS pyrolysis in a fixed-bed reactor, and the effect of CGS to OS ratios on the product distribution was investigated at temperatures of 400-800 °C. Importantly, both coal gasification coarse slag (CGCS) and coal gasification fine slag (CGFS) can effectively catalyze the pyrolysis of OS with increased yields of methane, H₂ and liquid hydrocarbons but suppressed formation of CO₂ and sulfur-containing gases. Specifically, CGCS exhibited higher activity for gaseous product formation, whereas CGFS proved more effective in enhancing liquid oil production. Thermogravimetric results reveal that the OS pyrolysis proceeds in three stages, i.e., dehydration, light-component volatilization, and heavy-component/mineral decomposition, the kinetics of which can be optimally described by the distributed activation energy model. For both CGCS and CGFS, the activation energy decreased for the light-component decomposition but increased for heavy fractions, which is consistent with complex reaction pathways revealed from the Master plot analysis. These results not only validate the simultaneous valorization of CGS and OS, but also demonstrate the CGS catalyzed OS pyrolysis a promising waste-to-resource pathway.