Pyrolysis is an effective way to convert aquatic plants into high-value products. The pyrolysis oil has high energy density but is difficult to utilize. In order to clean and economically convert the acids in pyrolysis oil into high grade esters, improving the quality of pyrolysis oil, this study chose seawater and freshwater reeds as raw materials, upgrading reed pyrolysis oil through catalytic esterification by reed biochar-based solid acid catalyst and comparing the catalytic effect of reed biochar-based solid acid catalysts with commercial 732 and NKC-9 solid acid catalysts. After analyzing the pyrolysis products of two kinds of reeds, seawater reed pyrolysis oil generated from 600°C (has the highest acid content) was chosen as raw oil to upgrade its quality, and biochar generated from 600°C and 700°C was chosen to produce catalysts. The acid content in upgraded oil was significantly reduced, and ester became the main component of upgraded oil. Among the six catalysts, 732-catalyzed upgraded oil had the highest ester content (21.97%). The 700°C freshwater reed biochar-based catalyst has comparable catalytic effect to that of NKC-9, the ester contents of their upgraded oil were 18.71% and 19.98%, respectively. Catalytic effects were proportional to surface sulfonic acid contents of the catalysts. Compared with raw pyrolysis oil, heat value of upgraded oil increased by 15.16%-76.54%, and viscosity decreased from 11.47Pa·s to about 3Pa·s. The commercial catalysts decreased the pH of upgraded oil to a lower value, but the reed biochar-based solid acid catalyst increased the pH value of upgraded oil to about 5, this was attributed to the fact that reed biochar-based solid acid catalyst has a superior thermal stability than that of the commercial catalysts, so that sulfonic acid group was not easily peeled off after being heated. The obtained results could provide a guidance for the relationship between biomass feedstocks, pyrolysis conditions, catalytic activity of biochar-based solid acid catalyst and upgrading effect of pyrolysis oil.
Keywords reed, solid acid catalyst, pyrolysis oil, esterification, upgraded oil