TY - JOUR

T1 - Towards Biochar and Hydrochar Engineering—Influence of Process Conditions on Surface Physical and Chemical Properties, Thermal Stability, Nutrient Availability, Toxicity and Wettability

AU - Dieguez-Alonso, Alba

AU - Funke, Axel

AU - Anca-Couce, Andrés

AU - Rombolà, Alessandro Girolamo

AU - Ojeda, Gerardo

AU - Bachmann, Jörg

AU - Behrendt, Frank

N1 - Funding information: Acknowledgments: The authors thank Susanne Hoffmann, Hernán Almuina Villar, Alba Domínguez Yebra, Alberto García Rueda and Christina Eichenauer (Technische Universität Berlin) for their support with the analytic characterization of biochars and hydrochars. The authors also thank the Leibniz Institute for Agricultural Engineering and Bioeconomy (Potsdam, Germany) for preparation of hydrochar samples. The authors acknowledge support by the German Research Foundation and the Open Access Publication Funds of Technische Universität Berlin.

PY - 2018/2/27

Y1 - 2018/2/27

N2 - 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 ofNO- 3 ,NH+ 4 , PO3- 4 , 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. c 2018 by the authors. Licensee MDPI, Basel, Switzerland.

AB - 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 ofNO- 3 ,NH+ 4 , PO3- 4 , 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. c 2018 by the authors. Licensee MDPI, Basel, Switzerland.

KW - Biochar engineering

KW - Hydrothermal carbonization

KW - Nutrients

KW - Polycyclic aromatic hydrocarbon (PAH)

KW - Porosity

KW - Pyrolysis

UR - http://www.scopus.com/inward/record.url?scp=85050252031&partnerID=8YFLogxK

U2 - 10.3390/en11030496

DO - 10.3390/en11030496

M3 - Article

AN - SCOPUS:85050252031

VL - 11

JO - Energies

JF - Energies

SN - 1996-1073

IS - 3

M1 - 496

ER -