Temperature and reaction atmosphere effects on the properties of corn stover biochar

Abstract

Biochar properties can vary widely depending on feedstock and processing conditions, which can make meaningful comparisons between biochars difficult. Clear trends can be observed in slow pyrolysis biochar properties over a 300–800°C range of highest treatment temperatures (HTT). These trends, however, are much less consistent for biochars made under slightly oxidizing conditions, such as in gasification and internally‐heated kiln carbonization processes. In this study, slow pyrolysis biochars were produced from corn stover under either pure nitrogen or nitrogen + 5% oxygen atmospheres over a 200–800°C HTT range. For the biochars made at 300 and 400°C, the presence of oxygen in the reaction environment resulted in biochars with properties similar to those of biochars produced at higher HTTs in pure nitrogen. Addition of oxygen has only minor effects on biochar bulk oxygen content or abundance of surface oxygenated functionalities. Thermogravimetric analysis with mass spectroscopy (TGA‐MS) indicated that the apparent increase in HTT for chars made in the O2 environment at 300 and 400°C resulted in the removal of methyl and higher alkyl functionalities in the biomass feedstock. Advanced solid state 13C nuclear magnetic resonance spectroscopy (NMR) methods to quantify carbon functional group abundance and aromaticity supported this observation. Overall, addition of oxygen to the pyrolysis atmosphere will increase pyrolysis process severity but will not create oxygenated groups on biochar surfaces as biochar aging does. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 696–707, 2017

Sorption of ammonium and nitrate to biochars is electrostatic and pH-dependent

“…Red oak ( Quercus rubra ) and corn stover (Zea mays) feedstocks were slow-pyrolyzed at 400, 500 and 600 °C to produce a total of six biochars. Slow pyrolysis was conducted in a N 2 -purged muffle furnace (Thermo-Scientific; Lindberg/Blue M Moldatherm box furnace) 32 . About 500 g of each air-dry feedstock (particle size < 2 mm) was placed into a steel box (24 cm × 14 cm × 15 cm) within the muffle furnace; an N 2 purge line was inserted through the furnace and into the box, and the box was purged for 30 min at 1500 mL min −1 .…”

“…About 500 g of each air-dry feedstock (particle size < 2 mm) was placed into a steel box (24 cm × 14 cm × 15 cm) within the muffle furnace; an N 2 purge line was inserted through the furnace and into the box, and the box was purged for 30 min at 1500 mL min −1 . For the pyrolysis reaction, the purge rate was decreased to 40 mL min −1 , the furnace was initially heated at 10 °C min −1 to a temperature 100 °C below the target temperature (300 °C, 400 °C or 500 °C), held for 2 hr, and then heated to the final temperature (e.g., 400, 500 and 600 °C) at 0.5 °C min −1 32 . The highest treatment temperature was held for 2 hr, then the furnace was allowed to cool overnight under N 2 -purge (40 mL min −1 ).…”

Biochar soil amendments for increased crop yields: How to design a “designer” biochar

“…Gai et al reported similar trends but lower values of surface areas that only reach a maximum of 70 m 2 /g at 700°C . On the other hand, the CEC of biochars, one of the better predictors of their adsorption capacity, declines with increasing temperature as the more severe pyrolysis conditions strip the biochar surface of O‐ and H‐containing functional groups …”

Mitigation of Gaseous Emissions from Swine Manure with the Surficial Application of Biochars

“…Highly alkaline and porous biochar (HAP) is a result of the addition of 95% of N2 and 5% of O2 during a pyrolysis process [32]. HAP has a high pH, which potentially can be effective in mitigating emissions of H2S and volatile fatty acids (VFAs).…”