Understanding the thermochemical conversion of biomass to overcome biomass recalcitrance

Abstract

Partial oxidative pyrolysis of red oak was studied in a laboratory-scale, continuous fluidized bed reactor. The concentration of oxygen in sweep gas was between 0.525 % and 8.40 % (v/v), corresponding to equivalence ratios of 0.034 to 0.539. The influence of oxygen on the distribution and properties of pyrolysis products was investigated using various analytical methods, including GC-MS/FID, IC, HPLC and FT-IR. It was found that total biooil yield was not affected by varying oxygen concentration (61.2-64.8 g/100 g biomass) although the water content of the bio-oil increased. The elemental carbon content of bio-oil and biochar decreased with increasing oxygen concentration, being converted to noncondensable gases mainly CO and CO2. As expected, the presence of high concentration of oxygen in the sweep gas stream had detrimental effects on the pyrolysis products, including increase in water and oxygen content. However, the results also revealed that a small amount of oxygen in the sweep gas (0.525 to 1.05 %, v/v) improved the yield of hydrolyzable sugars and total yield of phenolic monomers. The bio-oil produced under oxidative pyrolysis also contained less acid and pyrolytic lignin. Oxygen increased the surface area of biochar. The results of this study suggest that carefully controlled partial oxidative pyrolysis can improve 16 the quality of bio-oil from fast pyrolysis, increasing the content of sugars and phenolic monomers.

Characterization of free radicals by electron spin resonance spectroscopy in biochars from pyrolysis at high heating rates and at high temperatures

“…Radicals generated from the primary pyrolysis reactions can be trapped in the polyaromatic matrix of lignin [56], and stabilized by the delocalized unpaired electrons [57,58]. The major products from cellulose pyrolysis (levoglucosan and other light oxygenates) do not have unpaired electrons [59], and therefore, the radical concentrations in the char from the decay stage are low. The char prepared from softwood lignin at 1000 C with 1 s holding time showed a higher concentration of radicals than the wheat straw lignin char.…”