Upgrading biochar from bio-oil distillation residue by adding bituminous coal: Effects of induction conditions on physicochemical properties

In this study, biochar was produced by co-pyrolysis of bio-oil distillation residue and bituminous coal under different induction temperature and gas flow rate in a tube furnace. Central composite design was introduced to explore the combined effects of experimental conditions on biochar. The physicochemical properties of biochar from different induction conditions were comprehensively evaluated by elemental analysis, Fourier transform infrared spectrometry (FTIR) and Raman spectroscopy based on response surface methodology. The results showed that bituminous coal was beneficial to the increase in biochar yield, whereas temperature had the opposite effect and the effect of gas flow rate was not obvious. Moreover, C/O ratio increased with the increase of pyrolysis temperature and bio-oil distillation residue in feedstocks, while C/H ratio increased only with increasing temperature. Gas flow rate had a more pronounced descent effect on C/H compared with C/O. In addition, induction conditions caused a relative weakening of CC stretching vibration and the relative enrichment of CH in biochar. Bituminous coal, temperature and gas flow rate all contributed to the conversion of small aromatic rings of biochar to large aromatic rings during the co-pyrolysis process.