Biomass Processing via Thermochemical–Biological Hybrid Processes

Biomass is one of the most interesting sources of organic carbon that can be used for obtaining renewable chemicals. This chapter focuses on the potential offered by a combination of two approaches, which are often considered as an alternative or sometimes even competing: thermochemical processing and biological processing. Understanding of hybrid thermochemical–biological processes requires a steep change in the view of pyrolysis processes. Because most of pyrolysis studies aim to directly obtain a fuel, Pyrolysis Products (PyP) are usually characterized in terms of average fuel proprieties, neglecting details on molecular structures. Microbial Mixed Consortia (MMC) conversions of PyP is something relatively new; thus, some data were back-calculated from experimental results to provide a general indication of the maximum yields and rates obtainable from biological conversions of pyrolysis products with MMC. The metabolic potential of a MMC system can address the conversion of the complex mixture produced by pyrolysis

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

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 and NH , irrespective of the nitrogen content of the feedstock. For hydrochars, a potential increase in availability ofNO ,NH , PO , 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