An approach for upgrading bio-oil by using heavy bio-oil co-pyrolyzed with bamboo leached with light bio-oil

The quality of bio-oil produced by conventional pyrolysis of biomass feedstocks is relatively low. In particular, the bio-oil phase separates into light bio-oil (LB) and heavy bio-oil (HB) that are difficult to use. In this study, light bio-oil was used to leach bamboo to remove ash and alkali metals, and then the leached bamboo was co-pyrolyzed with HB. The response surface methodology was used to evaluate the influences of the different experimental conditions (temperature, residence time, and mass ratio) on the properties of the resulting bio-oil. The results highlight that the mass yield and quality of bio-oil produced with HB and bamboo were improved compared to bio-oil produced with only bamboo alone. Under the optimal co-pyrolysis conditions using an HB/raw bamboo mass ratio of 4:1, 640 °C and 25 min, the highest yield of 61.84% was obtained, and the bio-oil had the lowest water content (15.78%) and a higher heating value (HHV) of 27.75 MJ/kg. The yield and HHV were further increased in the bio-oil prepared by co-pyrolysis of HB and bamboo pretreated by the LB leaching process. Moreover, the relative contents of phenols and hydrocarbons in the bio-oil increased, while that of acids decreased because of the synergistic effects of the combined raw materials on the bio-oils produced by co-pyrolysis. Finally, predictive models for the bio-oil yield and properties were established and gave a foundation for the preparation and utilization of bio-oils.