Strategic use of CO₂ in the catalytic thermolysis of bio-heavy oil over Co/SiO₂ for the enhanced production of syngas

Bio-heavy oil (BHO), a mixture of remaining free fatty acids and glycerides is released as waste materials from biodiesel synthesis process. However, the complexity and impurities in BHO are drawbacks for its valorization due to essential requirement of multiple pretreatment processes. In this study, a direct valorization of BHO into value-added gaseous products was investigated using pyrolysis under CO₂ condition. CO₂ was used to achieve two goals: (1) establishment of environmentally benign platform using a greenhouse gas, and (2) carbon redistribution between CO₂ and BHO to produce more value-added products. Pyrolysis under both CO₂ and N₂ showed the conversion BHO into syngas and CH₄. However, CO₂-mediated pyrolysis had additional CO generation with decrease of the volatile matters from BHO pyrolysis. These resulted from gas phase reaction (GPR) of CO₂ with volatile matters. To further activate the thermal cracking of BHO and GPRs, multi-stage pyrolysis and catalytic pyrolysis was performed with Co catalysts. CO₂-mediated catalytic pyrolysis resulted in both significant formations of CO and H₂ from GPRs and dehydrogenation. Therefore, the proposed technical platform could be considered a viable environmentally benign way for waste valorization.