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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]

It remains challenging to develop a techno-economically feasible method to remove alkali and alkaline earth metal species (AAEMs) from rice husk (RH), which is a widely available bioresource across the world. In this study, the AAEMs leaching effect of aqueous phases of both bio-crude prepared by hydrothermal liquefaction (AP-HT) and bio-oil prepared by pyrolysis (AP-Pyro) of RH were systematically investigated. The results indicated that although the acidity of AP-HT and AP-Pyro are much lower than that of HCl, they performed a comparable removal efficiency on AAEMs (Na: 56.2%, K: 96.7%, Mg: 91.0%, Ca: 46.1% for AP-HT, while Na: 58.9%, K: 96.9%, Mg: 94.0%, Ca: 86.3% for AP-Pyro) with HCl. The presence of phenolics in bio-oil could facilitate the penetration of water and organic acids into the inner area of RH cells, thus enhancing the AAEMs removal via chelate reactions. The thermal stability of leached RH during thermochemical conversions was studied via TG and Py-GC-MS. The results showed that the heat conduction efficiency in leached RH was enhanced with a high pyrolysis rate, resulting in a narrow carbon chain distribution (C5–C10) of derived chemical compounds. [ABSTRACT FROM AUTHOR]