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Energies 2018, 11(3), 496; https://doi.org/10.3390/en11030496

Towards Biochar and Hydrochar Engineering—Influence of Process Conditions on Surface Physical and Chemical Properties, Thermal Stability, Nutrient Availability, Toxicity and Wettability

1
Institute of Energy Engineering, Technische Universität Berlin, Chair for Energy Process Engineering and Conversion Technologies for Renewable Energies, Fasanenstr. 89, 10623 Berlin, Germany
2
Institute of Catalysis Research and Technology (IKFT), Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
3
Institute of Thermal Engineering, Graz University of Technology, Inffeldgasse 25b, 8010 Graz, Austria
4
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
5
Ecological and Forestry Applications Research Centre (CREAF), 08193 Cendanyola del Vallès, Spain
6
Institute of Soil Science, Leibniz University of Hannover, Herrenhaeuser Str. 2, 30419 Hannover, Germany
*
Author to whom correspondence should be addressed.
Received: 31 December 2017 / Revised: 11 February 2018 / Accepted: 11 February 2018 / Published: 27 February 2018
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications Ⅱ)
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Abstract

The impact of conversion process parameters in pyrolysis (maximum temperature, inert gas flow rate) and hydrothermal carbonization (maximum temperature, residence time and post-washing) on biochar and hydrochar properties is investigated. Pine wood (PW) and corn digestate (CD), with low and high inorganic species content respectively, are used as feedstock. CD biochars show lower H/C ratios, thermal recalcitrance and total specific surface area than PW biochars, but higher mesoporosity. CD and PW biochars present higher naphthalene and phenanthrene contents, respectively, which may indicate different reaction pathways. High temperatures (>500 °C) lead to lower PAH (polycyclic aromatic hydrocarbons) content (<12 mg/kg) and higher specific surface area. With increasing process severity the biochars carbon content is also enhanced, as well as the thermal stability. High inert gas flow rates increase the microporosity and wettability of biochars. In hydrochars the high inorganic content favor decarboxylation over dehydration reactions. Hydrochars show mainly mesoporosity, with a higher pore volume but generally lower specific surface area than biochars. Biochars present negligible availability of NO 3 and NH 4 + , irrespective of the nitrogen content of the feedstock. For hydrochars, a potential increase in availability of NO 3 , NH 4 + , PO 4 3 , and K + with respect to the feedstock is possible. The results from this work can be applied to “engineer” appropriate biochars with respect to soil demands and certification requirements. View Full-Text
Keywords: pyrolysis; hydrothermal carbonization; biochar engineering; porosity; nutrients; polycyclic aromatic hydrocarbon (PAH) pyrolysis; hydrothermal carbonization; biochar engineering; porosity; nutrients; polycyclic aromatic hydrocarbon (PAH)
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Dieguez-Alonso, A.; Funke, A.; Anca-Couce, A.; Rombolà, A.G.; Ojeda, G.; Bachmann, J.; Behrendt, F. Towards Biochar and Hydrochar Engineering—Influence of Process Conditions on Surface Physical and Chemical Properties, Thermal Stability, Nutrient Availability, Toxicity and Wettability. Energies 2018, 11, 496.

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