Catalytic co-pyrolysis of sewage sludge and rice husk over biochar catalyst: Bio-oil upgrading and catalytic mechanism

In this study, the effects of different biochar catalysts on the quality of bio-oil derived from the co-pyrolysis of sewage sludge (SS) and rice husk (RH) are explored. Catalysts include SS biochar (SWC), RH biochar (RHC), mixed SS and RH biochar (SRC), and RH ash (RHA). The quality of bio-oil was evaluated based on the results of gas chromatography-mass spectrometry (GC-MS; including the contents of hydrocarbons and N-species), oxygen content, higher heating value, and pH. The GC-MS analysis results illustrated that N-species content in the bio-oil reduced with the addition of the biochar catalyst, while the hydrocarbons content increased from 15.51% for co-pyrolysis to 38.74-61.84% for different biochar catalysts at a catalytic temperature of 650 degrees C. RHC exhibited the best catalytic effect in terms of decreasing the content of N-species by 58.79% and increasing the content of hydrocarbons by nearly four times compared to co-pyrolysis. The higher heating value of bio-oil raised from 25.75 to 34.67 MJ/kg, while oxygen content decreased from 31.1 to 8.81 wt%, and the pH increased from 4.06 to 5.48. Moreover, the catalytic mechanism of catalytic co-pyrolysis over RHC, including the hydrocarbon generation pathway and nitrogen removal, is also discussed here. High specific surface area of RHC provides sufficient active sites (e.g. O-containing and N-containing functional groups) for the catalytic reaction of pyrolytic intermediates. (C) 2020 Elsevier Ltd. All rights reserved.