Effect of biochar structure on the selective adsorption of heavy components in bio-oil

In this study, biochars with different structures were prepared through HNO₃ oxidation and secondary pyrolysis to study the relationship between the structure of biochar and its selectivity for the adsorption of light and heavy aromatics in bio-oil. The results showed that the adsorption rates of biochar with different structures ranged from 2.90 to 4.00 g bio-oil per g biochar. The influence of pore structure was dominant, followed by the influence of O-containing functional groups and the degree of graphitization. The higher the adsorption capacity of biochar for bio-oil, the smaller the concentrations of the light aromatic model compounds in the absorbed bio-oil (ABO). Among the five light aromatics, biochar has the best adsorption selectivity for dihydroxybiphenyl and the worst for eugenol and propyl phenol. This is attributed to the diphenyl ring structure of dihydroxybiphenyl, which makes it more susceptible to adsorption, and other light model compounds only have one benzene ring. In summary, biochar demonstrates better adsorption selectivity for heavy aromatics than light aromatics. The more developed the pore structure is, the more enriched O-containing functional groups are, and the higher the graphitization degree of biochar is, the better the selective adsorption of aromatic compounds in bio-oil.