Comparison of Pyrolysis Products from Powdered and Pelletized Woody Biomass

The torrefaction and pyrolysis characteristics of powdered and pelletized woody biomass were systematically compared to elucidate the effect of pelletization on product distribution and volatiles composition. A woody biomass, with and without acid-treatment, was used as feedstock. Pelletization markedly increased bulk density but only slightly affected pyrolysis profiles in thermogravimetric analysis. At the gram scale, however, pelletization enhanced char yield while reducing the formation of condensable volatiles (bio-oil), mainly through secondary condensation and carbonization within dense pellet structures. Acid-washing decreased char yield but greatly promoted the formation of levoglucosan (LGA) with up to eightfold increase compared with the untreated sample. Detailed analysis of bio-oil revealed that pelletization scarcely altered the relative distribution of compounds, though it affected total yields of GC-detectable organics. Tests using cellulose, hemicellulose, and lignin model compounds confirmed that the influence of pelletization on chemical selectivity was minor. These findings demonstrate that pelletization, while enhancing solid fuel density, does not critically suppress the co-production of valuable volatiles such as LGA, suggesting the feasibility of integrated production of black pellets and chemical intermediates from lignocellulosic biomass.