Co-pyrolysis of light bio-oil leached bamboo and heavy bio-oil: Effects of mass ratio, pyrolysis temperature, and residence time on the biochar

•Bamboo is treated with a new deashing method using light bio-oil leaching.•Biochar preparation method from co-pyrolysis of heavy bio-oil and bamboo is proposed.•Effect of mass ratio, temperature, and time on the biochar property is investigated.•The synergistic effect of heavy bio-oil and leached bamboo promotes biochar yield.•Best fitting models for yield and HHV of biochar are quadratic regression equations. Light fraction of bio-oil (LB) has high contents of water and organic acids with good liquidity and is a promising leaching agent for deashing of biomass. Heavy fraction of bio-oil (HB) contains more amounts of phenols and pyrolytic lignin, has poor fluidity, and is easy to carbonize when heated. In this study, a novel method for preparation of biochar from co-pyrolysis of HB and LB leached bamboo (LB-bamboo) has been proposed. Effects of three experimental variables, namely, mass ratio (1:0–0:1), pyrolysis temperature (400–700 °C), and residence time (5–30 min), on the mass yield and properties of biochar were investigated, based on response surface methodology. Results showed that co-processing of HB and bamboo by pyrolysis synergistically improved the yield and higher heating value (HHV) of biochar. Under typical co-pyrolysis conditions (mass ratio 1:1, 550 °C, and 17.5 min), the experimentally determined yield (25.97%) and HHV (29.43 MJ/kg) of biochar from co-pyrolysis of HB and raw bamboo were 1.61% and 1.01 MJ/kg higher than the corresponding theoretically predicted values. The ash and metallic species in bamboo were significantly removed by LB leaching pretreatment, leading to a more synergistic effect observed during the subsequent co-pyrolysis. The experimentally determined yield (24.63%) and HHV (30.62 MJ/kg) of biochar from co-pyrolysis of HB and LB-bamboo were 2.40% and 1.57 MJ/kg higher than the corresponding theoretical values. Ultimately, the regression equations between the biochar properties and the three experimental variables were established. The best fitting models for yield and HHV of biochar were quadratic regression equations.