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Title: New applications of x-ray tomography in pyrolysis of biomass: biochar imaging

item JONES, KEITH - Brookhaven National Laboratory
item RAMAKRISHNAN, GIRISH - State University Of New York (SUNY)
item Uchimiya, Sophie
item ORLOV, ALEXANDER - State University Of New York (SUNY)

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2015
Publication Date: 1/19/2015
Citation: Jones, K., Ramakrishnan, G., Uchimiya, M., Orlov, A. 2015. New applications of x-ray tomography in pyrolysis of biomass: biochar imaging. Energy and Fuels. 29(3):1628-1634.

Interpretive Summary: Large (micrometer-sized) pores play a dominant role in water uptake/retention and release by soils. Biochar, a heat treated biomass, became a popular soil amendment in the past years. It is partly because of biochar’s high porosity. However, conventional analytical techniques are only able to measure very small pores that are not accessible to plant roots. This study employed advanced 3D x-ray imaging techniques to understand how the pore structure of agricultural waste change by heating without air. Significant (>20%) micrometer-sized porosity developed at a relatively low temperature (350C) treatment of agricultural waste (cottonseed hulls). 3D imaging visualized networks of pores as well as accumulation of metals. Obtained 3D images are a promising tool to understand the water flow through the pore networks, and the availability of held water for crop growths.

Technical Abstract: We report on the first ever use of non-destructive micrometer-scale synchrotron computed microtomography for characterization of biochar materials as a function of pyrolysis temperature. Using this innovative approach we have observed an increase in marcropore fraction of the sample, resulting in 29% sample porosity. This is an important result for two reasons. First, conventional BET measurements do not detect the macropores. Second, since water retention by biochars in soils is controlled by the macropores, application of tomography can be a unique analytical method in the future. Complementing our data with SEM, EDX and XRF characterization techniques allowed us to develop a better understanding of mechanistic aspects of biochar development. These results have significant implications for using biochar as soil additive and can also assist in developing a comprehensive understanding of biofuels production by pyrolysis. Our results can be also very beneficial in development of highly tunable biochar properties, where surface chemistry and porosity can be modified by adjusting the biomass pyrolysis conditions.