A new upgrading platform for livestock lignocellulosic waste into syngas using CO₂-assisted thermo-chemical process

This study valorized a lignocellulosic livestock waste into energy intensive platform chemical, syngas (H₂ and CO), and biochar via pyrolysis process as an environmentally sustainable manner for disposal of waste released from livestock industry. To construct a more sustainable valorization platform for the livestock waste, this work also laid stress on the possible use of CO₂ as a co-reactant in pyrolysis. In pyrolysis of livestock waste, CO₂ itself was reduced into CO, simultaneously oxidizing volatile matters (VMs) from the thermolysis of livestock waste through the gas phase reactions (GPRs). In short, CO₂ played a critical role as an additional source of oxygen, and such mechanistic role opens a new opportunity to use CO₂ as a raw feedstock during the valorization process of livestock waste. Nonetheless, the temperature window enabling the GPRs in line with CO₂ was experimentally determined at ≥510 °C, and the reaction kinetics for the GPRs was not fast to convert the majority of VMs derived from the thermolysis of livestock waste into syngas. In an effort to improve the reaction kinetics of GPRs, this study particularly employed biochar produced from pyrolysis of livestock waste (that was fabricated at 650 °C for 1 h) as a catalyst. In catalytic pyrolysis under the CO₂ environment, livestock waste biochar served as a role to expedite the reaction kinetics for GPRs. This led to the significant enhancement of the formation of syngas proportional to the amount of biochar catalyst loading. In reference to non-catalytic pyrolysis, catalytic pyrolysis of livestock waste over its biochar showed 3 times more syngas production.