Characterization of biochar from fast pyrolysis and gasification systems

Abstract

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).

Biochar as a Substitute for Vermiculite in Potting Mix for Hybrid Poplar

“…Finally, it has been established that biochars derived from different feedstocks and under different pyrolysis conditions have unique physical and chemical properties [36,37]. As such, additional testing with a variety of biochars is needed to compare how the selection of feedstocks and processes affect the ability of different biochars to serve as a renewable substitute for vermiculite.…”

Review Paper: The Fundamentals of Biochar as a Soil Amendment Tool and Management in Agriculture Scope: An Overview for Farmers and Gardeners

“…The chemical environment of the fixed carbon can be investigated or probed by a diversity of solid phase C13 nuclear magnetic resonance mechanisms or techniques [58] [59] [60]. Biochar chemistry and surface functionality can be evaluated by different methods and techniques including spectroscopically by vibrational techniques such as infrared [58] [59], electron energy loss [61] spectroscopies and titrimetrically [62].…”

Biochar: Pyrogenic Carbon for Agricultural Use - A Critical Review

“…In spite of its particular importance for bio-oil, fast pyrolysis produces 10 to 15 % of solids, which can be used as biochar, raw or pelleted charcoal. Since fast pyrolysis is usually performed at high temperatures (above 500 °C), the aromaticity of the resulting biochar is generally higher (Brewer et al, 2009;Kim et al, 2012) and O/C atomic ratio lower than by slow pyrolysis for the same residence time. The O/C ratio is an important indicator of stability and functionality of biochar and can range from 0.2 (highly stable) to 0.6 (highly functional) (Spokas, 2010).…”

“…The first step of gasification is drying followed by pyrolysis. The process produces gas, vaporized tars and oils and a char residue, consisting of typically 5 to 10 % of the original feedstock mass (Brewer et al, 2009).…”

“…As the process can involve such high temperatures, gasification is used to produce biochars with a high concentration of aromatic structures. Brewer et al (2009), comparing chemical properties of chars produced by different processes, showed that gasification char had similar aromaticity to slow-pyrolysis char, but a larger cluster size of the fused ring systems. According to these authors, aromatic cluster size seems to be more controlled by the reaction temperature than by duration.…”