Mechanism of biochar-gas-tar-soot formation during pyrolysis of different biomass feedstocks: Effect of inherent metal species

Abstract

The thermal behavior and evolution profiles of major volatile fragments from each biomass pyrolysis (i.e., rice husk, sawdust, cornstalk) have been discussed in depth, while paying close attention to the impact and contributions of inherent metal species on the raw material pyrolysis. It is found that high temperature would promote the conversion of tar to soot. The insertion of O atoms increases the size of microcrystalline structure of soot. The formation of soot mainly comes from the polymerization reaction between the cracked products of macromolecular precursors produced by devolatilization. And inherent metal species can inhibit the formation of soot. Before 500 °C, the pyrolysis of biomass has basically been completed. The inherent metal species would promote the biomass pyrolysis reaction, according to the kinetic results. The inherent metal species decrease the O atoms of tar component, increase its complexity and reduce the degree of polymerization. In homogeneous transformation, the inherent metal species would promote the cracking of tar precursors into gases, and inhibit the polymerization of aromatic compounds. In heterogeneous transformation, the inherent metal species could promote the production of small molecular gases. This research could lay the foundation for further analysis of the homogeneous/heterogeneous conversion of biomass pyrolysis and provide theoretical support for the process optimization of biomass utilization technology.