Thermochemical processing of biomass produces a solid product containing char (mostly carbon) and ash. This char can be combusted for heat 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 switchgrass and corn stover were characterized by proximate analysis, CHNS elemental analysis, BrunauerEmmet-Teller (BET) surface area, particle density, higher heating value (HHV), scanning electron microscopy, X-ray fluorescence ash content analysis, Fourier transform infrared spectroscopy using a photo-acoustic detector (FTIR-PAS), and quantitative 13 C 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 HHVs ranged from 13 to 21 kJ/kg. The aromaticities from NMR, ranging between 81 and 94%, appeared to increase with reaction time. A pronounced decrease in aromatic CÀ ÀH functionality between slow pyrolysis and gasification chars was observed in NMR and FTIR-PAS spectra. NMR estimates of fused aromatic ring cluster size showed fast and slow pyrolysis chars to be similar ($7-8 rings per cluster), while highertemperature gasification char was much more condensed ($17 rings per cluster).

No abstract

One factor limiting the understanding and evaluation of biochar for soil amendment and carbon sequestration applications is the scarcity of long-term, large-scale field studies. Limited land, time, and material resources require that biochars for field trials be carefully selected. In this study, 17 biochars from the fast pyrolysis, slow pyrolysis, and gasification of corn stover, switchgrass, and wood were thoroughly characterized and subjected to an 8-week soil incubation as a way to select the most promising biochars for a field trial. The methods used to characterize the biochars included proximate analysis, CHNS elemental analysis, Brunauer-Emmett-Teller surface (BET) area, photo-acoustic Fourier transform infrared spectroscopy, and quantitative 13 C solid-state nuclear magnetic resonance (NMR) spectroscopy. The soil incubation study was used to relate biochar properties to three soil responses: pH, cation exchange capacity (CEC), and water leachate electrical conductivity (EC). Characterization results suggest that biochars made in a kiln process where some oxygen was present in the reaction atmosphere have properties intermediate between slow pyrolysis and gasification and therefore, should be grouped separately. A close correlation was observed between aromaticity determined by NMR and fixed carbon fraction determined by proximate analysis, suggesting that the simpler, less expensive proximate analysis method can be used to gain aromaticity information. Of the 17 biochars originally assessed, four biochars were ultimately selected for their potential to improve soil properties and to provide soil data to refine the selection scheme: corn stover low-temperature fast pyrolysis (highest amended soil CEC, information on high volatile matter/ O-C ratio biochar), switchgrass O 2 /steam gasification (relatively high BET surface area, and amended soil pH, EC, and CEC), switchgrass slow pyrolysis (higher-amended soil pH and EC), and hardwood kiln carbonization (information on slow pyrolysis, gasification and kilnproduced differences). AbbreviationsBET Brunauer-Emmett-Teller (surface area) CEC Cation exchange capacity CP Cross polarization DP Direct polarization EC Electrical conductivity FTIR Fourier transform infrared spectroscopy Electronic supplementary material The online version of this article (

No abstract

No abstract

No abstract

No abstract

A potential concern about the use of fast pyrolysis rather than slow pyrolysis biochars as soil amendments is that they may contain high levels of bioavailable C due to short particle residence times in the reactors, which could reduce the stability of biochar C and cause nutrient immobilization in soils. To investigate this concern, three corn ( L.) stover fast pyrolysis biochars prepared using different reactor conditions were chemically and physically characterized to determine their extent of pyrolysis. These biochars were also incubated in soil to assess their impact on soil CO emissions, nutrient availability, microorganism population growth, and water retention capacity. Elemental analysis and quantitative solid-state C nuclear magnetic resonance spectroscopy showed variation in O functional groups (associated primarily with carbohydrates) and aromatic C, which could be used to define extent of pyrolysis. A 24-wk incubation performed using a sandy soil amended with 0.5 wt% of corn stover biochar showed a small but significant decrease in soil CO emissions and a decrease in the bacteria:fungi ratios with extent of pyrolysis. Relative to the control soil, biochar-amended soils had small increases in CO emissions and extractable nutrients, but similar microorganism populations, extractable NO levels, and water retention capacities. Corn stover amendments, by contrast, significantly increased soil CO emissions and microbial populations, and reduced extractable NO. These results indicate that C in fast pyrolysis biochar is stable in soil environments and will not appreciably contribute to nutrient immobilization.