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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. [ABSTRACT FROM AUTHOR]

Densification is widely considered as a means to improve the bulk energy density and transportation efficiency of biomass, while the durability and fuel quality of densified biomass often need to be further improved by the addition of binders. In this study, the heavy fractions of bio‐oils from slow pyrolysis (HBO‐SP) and hydrothermal treatment (HBO‐HT) of rice husk (RH) are used as bio‐binders for RH densification. Optimal parameters are determined based on Taguchi methods. They are: densification temperature 130 °C, densification pressure 200 MPa, bio‐binder content 8%, particle size 0.4–0.6 mm, and using HBO‐HT as the binder. The obtained pellets showed a high drop resistance of 99.8% and the binding mechanism is governed by solid bridges between particles. Heavy bio‐oils are deformed and re‐solidified and function as a binder for RH densification. The RH/HBO‐HT pellets showed lower activation energy for pyrolysis as well as lower ignition temperature (292.81 °C compared with 298.34 °C for RH pellets). The higher heating value of pellets was increased from 14.99 to 16.29 MJ kg−1 with 8 wt% HBO‐HT. The co‐densification of heavy bio‐oils and RH provides an approach for producing more qualified solid biofuels from agriculture wastes. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]