Characterization and thermal conversion of charcoal derived from fluidized-bed fast pyrolysis oil production of switchgrass

The charcoal coproduct associated with pyrolysis oil (bio-oil) production can add economic value to the process operation if it can be successfully employed as an activated biochar for soil amendment applications or can be used as a combustion fuel to power the pyrolysis process or as a gasifier feedstock. Although proposed, none of these have been extensively studied. In this submission, the surfaces and interfaces of the charcoal produced from making pyrolysis oil from switchgrass in a fluidized bed were characterized to establish its usefulness as an adsorbent material. Its reactivity in air and in CO2 were also determined to establish its potential as combustion fuel or gasification feedstock. It was found that the surface areas were low, typically 7.7 and 7.9 m(2)/g, 2 orders of magnitude of the areas encountered in activated charcoal. Compounding this was high surface crystallinity of the structure as measured by X-ray diffraction, thereby suggesting poor characteristics as a sorption agent without further activation. However, this does not preclude its use for other soil applications including carbon storage and as a nutrient delivery substrate. Upon further pyrolysis in helium, the charcoal yielded equal amounts of CO and CO2, exhibiting reaction kinetics similar to that of coal pyrolysis. Furthermore, reactivity in CO2 and in air atmosphere resulted in activation energies of 8 411 and 11487 J/mol, respectively. It appears that the charcoal could be better used as combustion fuel or gasification feedstock than as an activated charcoal applied for metal sorption for the fact that the latter application will require higher surface and interfacial areas than measured.