Effect of gas-pressurized torrefaction on the upgrading and pyrolysis characteristics of corn stalk

Corn straw was torrefied under at different temperatures and the torrefied products were characterized by proximate analysis, ultimate analysis, FT-IR, TGA and pyrolysis experiments; the effect of gas-pressurized torrefaction on the upgrading and pyrolysis characteristics of corn stalk was investigated. The results indicate that the deoxidation efficiency and energy density of torrefied products under both atmospheric pressure (AP) and gas pressured (GP) conditions increase with the increase of torrefaction temperature. The temperature required for GP torrefaction is almost 40 °C lower than that for AP torrefaction to obtain the same mass yield. The energy yield, carbon yield, deoxidation efficiency and the energy density of GP-torrefied corn straw are 1.125, 1.142, 1.539 and 1.131 times higher than those of AP-torrefied one, respectively. The GP-torrefied corn straw shows better hydrophobicity and is easier to dehydrate. In addition, the pyrolysis of GP-torrefied corn straw produces significantly higher fractions of CH₄ and H₂ in the gaseous product than the pyrolysis of AP-torrefied one; meanwhile, the relative content of phenols in the liquid products for the pyrolysis of GP-torrefied samples also increases up to 51.11%, whereas the contents of furans and acids decrease considerably. All these suggest that GP torrefaction performs better in biofuel upgrading than AP torrefaction under the same temperature.