Upgrading of reed pyrolysis oil by using its biochar-based catalytic esterification and the influence of reed sources

[Display omitted] •RBSAC-catalyzed esterification effectively improved the quality of reed pyrolysis oil.•RBSACs prepared with freshwater reed demonstrated better catalytic effects.•Biochar that highly aromatic or rich in electron-donating groups favors SO3H loading.•High inorganic salts contents in seawater reed biochars inhibited their sulfonation.•700FWC was comparable to commercial catalysts in upgrading effect. Biomass pyrolysis oil has a high energy density; however, it cannot be easily utilized owing to its high corrosivity and viscosity. In this study, pyrolysis oil obtained from reed, a type of waste biomass, was upgraded through catalytic esterification to improve the calorific value and reduce viscosity. An inexpensive catalyst, i.e., reed biochar-based solid acid catalyst (RBSAC), was prepared by sulfonating reed biochar, a co-product of pyrolysis oil, to catalyze its esterification process. Seawater reed and freshwater reed were compared to produce RBSACs of better catalytic effects. The RBSACs were then compared with concentrated sulfuric acid and commercial catalysts, 732 and NKC-9, to evaluate their catalytic effects. The results indicate that all the RBSACs can upgrade the pyrolysis oil by replacing its organic acid with ester, thereby increasing its calorific value and pH and significantly reducing its viscosity. The RBSACs prepared with freshwater reed demonstrated better catalytic effects than those prepared with seawater reed. The one prepared with freshwater reed biochar pyrolyzed at 700 °C (700FWC) demonstrated the best upgrading effect; its corresponding upgraded oil had an ester content of 21.85 area% and calorific value of 21.64 MJ/kg. Furthermore, it was found that the characteristics of reed biochar, i.e., large surface area, highly aromatic structure, rich electron-donating surface functional groups, and low inorganic salts content were conducive to obtain a more effective RBSAC. These findings indicate that biochar-based catalysts can be used as an inexpensive catalyst to upgrade biomass pyrolysis oils.