Quantifying pyrogenic carbon from thermosequences of wood and grass using hydrogen pyrolysis |
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| Institution: | 1. School of Earth and Environmental Sciences and Centre for Tropical Environmental and Sustainability Science, James Cook University, Cairns, QLD 4879, Australia;2. Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Garmisch-Partenkirchen, Germany;3. Department of Geography, University of Zurich, Switzerland;1. Department of Earth, Environmental, and Planetary Science, Brown University, Providence, RI 02912, USA;2. Institute at Brown for Environment and Society, Brown University, Providence, RI 02912, USA;3. Departamento de Química, Universidade Federal de Sergipe, São Cristóvão, Sergipe SE 491000-000, Brazil;1. School of Earth and Environmental Sciences and Centre for Tropical Environmental and Sustainability Science, James Cook University, Cairns, Queensland 4870, Australia;2. Australian Nuclear Science and Technology Organisation (ANSTO), Kirrawee DC, NSW 2232, Australia;3. Scottish University Environmental Research Centre (SUERC), Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride G75 0QF, UK;4. Department of Chemical and Environmental Engineering, Faculty of Engineering, University of Nottingham, NG7 2RD, UK;5. EPSRC Solid-State NMR Service, Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK;1. Department of Chemistry “Giacomo Ciamician”, C.I.R.I. Energia Ambiente and C.I.R.S.A., Università di Bologna, Ravenna Campus, Via S. Alberto 163, 48123, Ravenna, Italy;2. Department of Chemical and Environmental Engineering, University of Nottingham, Nottingham NG7 2RD, United Kingdom;3. Institute of Energy Engineering, Technische Universität Berlin, Fasanenstrasse 89, 10623 Berlin, Germany |
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| Abstract: | Previously studied thermosequences of wood (chestnut) and grass (rice straw) biochar were subjected to hydrogen pyrolysis (hypy) to evaluate the efficacy of the technique for determining pyrogenic carbon (CP) abundance. As expected, biochar from both wood and grass produced at higher temperature had higher CP amount. However, the trend was not linear, but more sigmoidal. CP/CT ratio values (CT = total organic carbon) for the wood thermosequence were ?0.03 at biochar production temperature (TCHAR) ? 300 °C. They increased dramatically until 600 °C and remained relatively constant and near unity at higher biochar production temperature. Grass biochar was similar in profile, but CP/CT values rose dramatically after 400 °C. The findings are consistent with the hypothesis that hypy residues contain polycyclic aromatic hydrocarbons (PAHs) with a degree of condensation above at least 7–14 fused rings, with labile organic matter and pyrogenic PAHs below this degree of condensation removed by hypy.Both wood and grass thermosequences displayed δ13CP values that decreased with increased TCHAR, indicating that recalcitrant carbon compounds (pyrogenic aromatic PAHs with a relatively high degree of condensation) were first formed from structural components with relatively high δ13C values (e.g. cellulose). Relatively constant δ13C values at TCHAR ? 500 °C suggested the dominant pyrolysis reaction was condensation of PAHs with no additional fractionation. Comparison of hypy with benzene polycarboxylic acid (BPCA), ‘ring current’ NMR and pyrolysis gas chromatography–mass spectrometry (GC–MS) results from the same suite of samples indicated a consistent overview of the structure of CP, but provided unique and complimentary information. |
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