Effects of wet torrefaction on the physicochemical properties and pyrolysis product properties of rice husk

•Wet torrefaction of rice husk prior to pyrolysis was applied.•Wet torrefaction has the dual advantages of dry torrefaction and demineralisation.•Wet torrefaction at the mild reaction condition promoted the production of bio-oil.•Biochar produced can be used as the feedstock for preparation of nanosilica. Wet torrefaction in the temperature range from 150 to 240°C for 60min was applied on rice husk sample prior to pyrolysis process in this work. Its effects on the physicochemical properties and pyrolysis product properties were evaluated. The analysis results of physicochemical properties of raw and pretreated samples indicated that wet torrefaction not only improved the fuel characteristics but also removed a large amount of alkali and alkaline earth metal species with the dual advantages of dry torrefaction and demineralisation. On the basis of pyrolysis experiment results, it was found that wet torrefaction at the mild reaction condition had a positive impact on bio-oil production, but more severe wet torrefaction condition was not reasonable. The highest relative content of levoglucosan (57.2%) was obtained from pyrolysis of rice husk sample after wet torrefaction at 210°C, which was about 6.2 times higher than that of raw rice husk. The results of biochar analysis suggested that biochar produced from sample after wet torrefaction and pyrolysis seems not a desirable solid fuel, it can be used as the feedstock for preparation of nanosilica.