Towards biochar and hydrochar engineering-influence of process conditions on surface physical and chemical properties, thermal stability, nutrient availability, toxicity and wettability

Alba Dieguez-Alonso*, Axel Funke, Andrés Anca-Couce, Alessandro Girolamo Rombolà, Gerardo Ojeda, Jörg Bachmann, Frank Behrendt

*Corresponding author for this work

Research output: Contribution to journalArticle

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 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.

Original languageEnglish
Article number496
JournalEnergies
Volume11
Issue number3
DOIs
Publication statusPublished - 25 Feb 2018

Keywords

  • Biochar engineering
  • Hydrothermal carbonization
  • Nutrients
  • Polycyclic aromatic hydrocarbon (PAH)
  • Porosity
  • Pyrolysis

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Energy Engineering and Power Technology
  • Energy (miscellaneous)
  • Control and Optimization
  • Electrical and Electronic Engineering

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