Influence Mechanisms of Torrefaction on Syngas Production from Bio-Waste Molten Salt Thermal Treatment

•Torrefaction promotes higher gas yield from bio-wastes in molten salts.•The elevation of lignin in the torrefied bio-wastes greatly enhances the CO yield.•Anions in the molten salt are more involved in the torrefied bio-wastes reaction.•Increase in lignin content and decrease in oxygen-containing groups delay reaction.•Sugarcane bagasse is highly graphitised after torrefaction at 280 ℃ and hardly react.