Bioresources and Bioprocessing
Application of modern biomass pyrolysis methods for production of biofuels and biochar is potentially a significant approach to enable global carbon capture and sequestration. To realize this potential, it is essential to develop methods that produce biochar with the characteristics needed for effective soil amendment.
Biochar materials were produced from peanut hulls and pine wood with different pyrolysis conditions, then characterized by cation exchange (CEC) capacity assays, nitrogen adsorption–desorption isotherm measurements, micro/nanostructural imaging, infrared spectra and elemental analyses.
Under a standard assay condition of pH 8.5, the CEC values of the peanut hull-derived biochar materials, ranging from 6.22 to 66.56 cmol kg−1, are significantly higher than those of the southern yellow pine-derived biochar, which are near zero or negative. The biochar produced from peanut hulls with a steam activation process yielded the highest CEC value of 66.56 cmol kg−1, which is about 5 times higher than the cation exchange capacity (12.51 cmol kg−1) of a reference soil sample. Notably, biochar produced from peanut hulls with batch barrel retort pyrolysis also has a much higher CEC value (60.12 cmol kg−1) than that (12.45 cmol kg−1) from Eprida’s H2-producing continuous steam injection process. The CEC values were shown to correlate well with the ratios of oxygen atoms to carbon atoms (O:C ratios) in the biochar materials. The higher O:C ratio in a biochar material may indicate the presence of more hydroxyl, carboxylate, and carbonyl groups that contribute to a higher CEC value for the biochar product. In addition, the increase in surface area can also play a role in increasing the CEC value of biochar, as in the case of the steam activation char.
Comparison of characterization results indicated that CEC value is determined not only by the type of the source biomass materials but also by the pyrolysis conditions. Biochar with the desirable characteristics of extremely high surface area (700 m2/g) and cation exchange capacity (> 60 cmol kg) was created through steam activation.
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Original Publication Citation
Lee, J. W., Hawkins, B., Kidder, M. K., Evans, B. R., Buchanan, A. C., & Day, D. (2016). Characterization of biochars produced from peanut hulls and pine wood with different pyrolysis conditions. Bioresources and Bioprocessing, 3(1), 1-10, Article 15. https://doi.org/10.1186/s40643-016-0092-x
Lee, James W.; Hawkins, Bob; Kidder, Michelle K.; Evans, Barbara R.; Buchanan, A. C.; and Day, Danny, "Characterization of Biochars Produced From Peanut Hulls and Pine Wood with Different Pyrolysis Conditions" (2016). Chemistry & Biochemistry Faculty Publications. 256.