Co-pyrolysis of cellulose/lignin and sawdust: Influence of secondary condensation of the volatiles on characteristics of biochar

Abstract

The major compounds of cellulose and lignin in biomass could have varied contributions on distribution and properties of pyrolysis products by generating the volatiles of different structures via pyrolysis. In this paper, the co-pyrolysis of cellulose or lignin with sawdust were investigated, aiming to probe the impacts of volatiles from lignin or cellulose pyrolysis on evolution of products. The results indicated that the interactions between volatiles from cellulose or lignin with that of sawdust did exist. The co-pyrolysis of sawdust with cellulose tended to promote the bio-oil production, while the co-pyrolysis with lignin enhanced the formation of biochar. The cross-polymerization of light species (i.e. radicals) from cellulose pyrolysis with heavier ones from lignin pyrolysis transformed the precursors of gases into condensable liquid, bio-oil. In comparison, the interaction of heavy species between lignin and those from sawdust produced more carbonaceous solid, biochar. Additionally, the biochar from co-pyrolysis of sawdust with cellulose possessed more oxygen-containing functionalities (i.e. CO), higher oxygen content, while lower thermal stability, while that from co-pyrolysis with lignin was opposite. The in situ Diffuse Reflection Infrared Fourier Transform Spectra (DRIFTS) analysis suggested that the volatiles from cellulose reacted with that from sawdust formed more aliphatic structures.