Influence of biomass pretreatment on upgrading of bio-oil: Comparison of dry and hydrothermal torrefaction

[Display omitted] •Dry and hydrothermal torrefaction were compared via batch, quart tube, and auger.•Physical and chemical properties of torrefaction bio-char was investigated.•Batch autoclave and auger promoted the hemicellulose to strip from the CS.•Torrefaction is beneficial for the accumulation of phenols and reduce of acids.•Phenols in bio-oil reaches 60%, the yield is 0.148 g.g−1 with CS/HT sample. The dry and hydrothermal torrefacation of on Camellia Shell (CS) was carried on three different devices- batch autoclave, quartz tube, and auger reactor. The torrefied bio-char products were investigated via TGA, elemental analysis and industrial analysis. Moreover, the pyrolysis and catalytic pyrolysis properties of torrefied bio-char were investigated. The results showed torrefaction significantly influenced the content of hemicellulose in CS. And hydrothermal torrefaction via batch autoclave and dry torrefaction via auger reactors promoted the hemicellulose to strip from the CS. Quartz tube and auger reactor were beneficial for devolatilization and improving heat value of torrefied bio-char. The result showed that the main products were phenols and acids. And hydrothermal torrefaction pretreatment effectively reduced the acids content from 34.5% to 13.2% and enriched the content of phenols (from 27.23% to 60.05%) in bio-oil due to the decreasing of hemicellulos in torrefied bio-char. And the catalyst had slight influence on the bio-oil distribution.