Wet and dry torrefaction of corncobs was conducted in high-pressure reactor and tube-type reactor,
respectively. Effect of wet and dry torrefaction on chemical structure and pyrolysis behavior of corncobs
was compared. The results showed that hemicellulose could be effectively removed from corncobs by torrefaction.
However, dry torrefaction caused severe degradation of cellulose and the cross-linking and
charring of corncobs. X-ray diffraction analysis revealed that crystallinity degree of corncobs was evidently
enhanced during wet torrefaction, but reduced during dry torrefaction as raising treatment temperature.
In thermogravimetric analysis, wet torrefied corncobs produced less carbonaceous residues
than raw corncobs, while dry torrefied corncobs gave much more residues owing to increased content
of acid insoluble lignin. Pyrolysis–gas chromatography/mass spectroscopy analysis indicated that wet
torrefaction significantly promoted levoglucosan yield owing to the removal of alkali metals. Therefore,
wet torrefaction can be considered as a more effective pretreatment method for fast pyrolysis of biomass.