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Title: Fate of higher-mass elements and surface functional groups during the pyrolysis of waste pecan shell

Author
item JONES, KEITH - State University Of New York (SUNY)
item RAMAKRISHNAN, GIRISH - State University Of New York (SUNY)
item Uchimiya, Sophie
item ORLOV, ALEXANDER - State University Of New York (SUNY)
item CASTALDI, MARCO - State University Of New York- College Of Environmental Science And Forestry
item LEBLANC, JEFFREY - National Institute For Agro-Environmental Sciences
item HIRADATE, SYUNTARO - National Institute For Agro-Environmental Sciences

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2015
Publication Date: 11/23/2015
Citation: Jones, K., Ramakrishnan, G., Uchimiya, M., Orlov, A., Castaldi, M.J., Leblanc, J., Hiradate, S. 2015. Fate of higher-mass elements and surface functional groups during the pyrolysis of waste pecan shell. Energy and Fuels. 29(12):8095-8101.

Interpretive Summary: Thermochemical conversion of agricultural waste will play central role within the food, energy, and water nexus. Pyrolysis kinetics (reaction rate as a function of time) controls the property of conversion products in gas, liquid, and solid phases. This study followed the pyrolysis kinetics of waste pecan shell, and investigated the physical and chemical properties of the products using advanced techniques including synchrotron-based 3D x-ray imaging, nuclear magnetic resonance, and in-situ mass spectrometry. Our findings will help end-users set kinetic conditions appropriate for the specific goals of thermochemical conversion.

Technical Abstract: Thermochemical conversion of agricultural wastes to bioenergy has a potential to play forefront roles within the context of food, energy, and water nexus. Biochar solid product of pyrolysis is a promising tool to manage food crop production and water resources by means of soil amendment. The goal of this study was to understand the fate of surface functional groups and higher atomic mass elements during pyrolysis of pecan shell know to accumulate Ca oxalate. Pecan shell feedstock and biochars were analyzed ex situ using X-ray computed microtomography and solid state 13C cross polarization and magic angle spinning NMR; pyrolysis kinetics was monitored in situ by thermogravimetric-gas chromatography. The NMR indicated the greatest (i) reduction in O/N alkyl functionality and (ii) increase in the aromatic peak between 300 and 500 °C. Primary physical transformation was observed near 400 °C in the tomography slice images and corresponding attenuation coefficients. Key changes in physical structure (microtomography) as well as chemical constituents (solid-state NMR) of pecan shell at 300-500 °C coincided the evolution of gaseous products (hydrogen, methane, carbon monoxide, carbon dioxide, ethylene, and ethane monitored in situ by TGA-GC) occurring at 200-500 °C. These observations followed the reported (i) formation and removal of carboxyl surface functional groups of biochar and (ii) conversion of Ca oxalate to carbonate, both occurring at the key transition temperature near 400 °C.