Virtuous utilization of biochar and carbon dioxide in the thermochemical process of dairy cattle manure

The huge generation of livestock manures has been raised due to the dramatically increasing protein demand. In this study, dairy cattle manure (DCM) was valorized through a pyrolysis platform using CO₂ as a co-feedstock, suggesting the conversion of manure to value-added chemicals in a sustainable and renewable way. This work demonstrated that biocrude derived from DCM involves high contents of N-containing hetero-hydrocarbons and aromatic compounds. Because they are not desirable chemicals to be used as fuels due to the challenges during combustion processes, they were further transformed into syngas. CO₂ and DCM-derived biochar signified the conversion of biocrude into syngas at ≤ 600 °C, where no gasification reaction works. The gas phase reactions of CO₂ with gas phase biocrude led to enhanced CO formation. In addition, alkaline metal(oxide)s in biochar promoted gas phase reactions and chemical bond scissions of biocrude, resulting in more than 5 times higher H₂ and CO formations with 3 g DCM biochar than non-catalytic pyrolysis. To evaluate the performance of DCM biochar, pyrolysis of DCM was done with Ni and Co catalysts. The promotion effect of DCM biochar for syngas formation was better than that of equivalent amount of Co catalyst. The performance of DCM biochar was higher than Ni when the additional amount of biochar was used. Considering that DCM is emitted as an agricultural waste material, it is inferred that the waste derived biochar has more economic viability than metal catalysts. Therefore, this study provides that the CO₂-driven pyrolysis with DCM biochar could be an environmentally benign means for syngas generation with an economic benefit. Copyright © 2021 Elsevier B.V.