Catalytic Pyrolysis of Swine Manure Using CO2 and Steel Slag

Pyrolysis of swine manure (SM) was conducted as a case study to establish an environmentally sound management of livestock manure. To build a more renewable pyrolysis platform for SM, this study selected carbon dioxide (CO2) as the reaction medium. In addition, CO2 was used in pyrolysis of SM to restrict the formation of toxic compounds, such as benzene derivatives and polycyclic aromatic hydrocarbons (PAHs). A series of thermo-gravimetric analysis (TGA) tests was done to understand the thermolysis of SM in the CO2 environment. The TGA tests elucidated no occurrence of heterogeneous reactions between the SM sample and the CO2. Moreover, the TGA tests of SM suggested that SM contains more volatile matter (VM) than lignocellulosic biomass. Non-catalytic transesterification of SM lipids confirmed that the dried SM sample contained 8.85 ± 0.05 wt.% of lipids. This study also confirmed that the mechanistic role of CO2 was realized through the gas phase reactions between volatile pyrolysates evolved from the thermolysis of SM and CO2. In summary, CO2 donates O, enhancing the generation of CO through homogeneous reactions. In parallel, this study confirmed that CO2 suppress dehydrogenation. Therefore, the identified gas phase reactions between volatile pyrolysates and CO2 led to the compositional modifications in the condensable pyrolysates. However, such mechanistic features arising from CO2 only initiated at ≥ 520 °C. To expedite the reaction kinetics of the homogeneous reaction triggered by CO2, steel slag (SS) was used as a catalyst. Hence, the reaction kinetics associated with the mechanistic role of CO2 were substantially enhanced (up to 80%) when SS was used as a catalyst. Therefore, all experimental findings strongly suggest that CO2 can be utilized as a raw material in a thermo-chemical process. More importantly, all observations suggest that CO2 lopping can also be achieved in a thermo-chemical process. Lastly, this study shows that the high Cu content in SM was effectively immobilized through pyrolysis. Conclusively, this study experimentally proved that CO2 could be promising for restricting the formation of toxic pollutant in the thermo-chemical treatment in that CO2 offers an innovative and strategic means for controlling the ratio of C to H. Note that aromaticity and toxicity of chemical compounds are highly contingent on the ratio of C to H.