Characterization of Biochar from Fast Pyrolysis and Gasification Systems

Thermochemical processing of biomass produces a solid product containing char (mostly carbon.) and ash. This char can be combusted for beat and power, gasified, activated for adsorption applications, or applied to soils as a soil amendment and carbon sequestration. agent. The most advantageous use of a given char depends on its physical and chemical characteristics, although the relationship of char properties to these applications is not well understood. Chars from fast pyrolysis and gasification of switch-grass and corn stover were characterized by proximate analysis, CHATS elemental analysis, Brunauer-Emmet-Teller (BET) surface area, particle density, higher beating value (HI-TV), scanning electron microscopy, X-ray fluorescence ash content analysis, Fourier transform infrared spectroscopy using a photo-acoustic detector (FTIR-PAS), and quantitative C-13 nuclear magnetic resonance spectroscopy (NMR) using direct polarization and magic angle spinning. Chars from the same feedstocks produced under slow pyrolysis conditions, and a commercial hardwood charcoal, were also characterized. Switchgrass and corn stover chars were found to have high ash content (32-55 wt %), much of which was silica. BET surface areas were low (7-50 m(2)/g) and HHI/s ranged from 13 to 21 kJ/kg. The aromaticities from NMR, ranging between 8.1 and 94%, appeared to increase with reaction time. A pronounced decrease in aromatic C-H functionality between slow pyrolysis and gasification chars was observed in NMR and FTIR-PAS spectra. ATMR estimates of fused aromatic ring cluster size showed fast and slow pyrolysis chars to be similar (similar to 7-8 rings per cluster), while higher-temperature gasification char was much more condensed (similar to 17 rings per cluster). (C) 2009 American Institute of Chemical Engineers Environ Prog, 28: 386-396, 2009