Submitted to: Biofuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2010
Publication Date: 1/1/2011
Citation: Libra, J.A., Ro, K.S., Kammann, C., Funke, A., Berge, N.D., Neubauer, Y., Titirici, M., Fuhner, C., Bens, O., Kern, J., Emmerich, K. 2011. Hydrothermal carbonization of biomass residuals: A comparative review of the chemistry, processes and applications of wet and dry pyrolysis. Biofuels. 2:71-106. Interpretive Summary: This paper reviews chemistry, processes and application of hydrothermcally carbonized biomass wastes. Hydrothermal carbonization (or wet pyrolysis) of wet biomass waste materials to char (hydrochar) has a high potential to become an environmentally sound conversion process for the production of a wide variety of products. Besides its traditional use for energy and charcoal production, pyrolysis can produce products for use in environmental, catalytic, electronic, and agricultural applications. As an alternative to dry pyrolysis, the wet pyrolysis process opens up the field of potential feedstocks for char production to a range of non-traditional renewable and plentiful wet agricultural and municipal wastes. Its chemistry offers a huge potential to influence product characteristics on demand and produce designer carbon materials. Future uses of these hydrochars may range from innovative materials to soil amelioration, nutrient conservation via intelligent waste stream management and increase of carbon stock in degraded soils.
Technical Abstract: This paper reviews chemistry, processes and application of hydrothermcally carbonized biomass wastes. Potential feedstock for the hydrothermal carbonization (HTC) includes variety of the non-traditional renewable wet agricultural and municipal waste streams. Pyrolysis and HTC show a comparable calorific nature but have significant differences in process design and the energetic requirements to run the process. The solid product from HTC, hydrochar, has substantially different characteristics than char from dry pyrolysis. The characteristics of both products, however, depend highly on feedstock and process conditions. Hydrothermal carbonization usually achieves a higher solid yield than dry pyrolysis. Hydrochar could have soil ameliorating properties when it has a high amount of carboxyl groups; i.e., it may be useful for rising the carbon content of degraded soils and improving plant nutrition. Compared to biochar, however, knowledge on hydrochar use in soils is in its infancy. Thus, possible toxic effects or risks have to be carefully evaluated. Hydrochar may be more stable than normal soil organic matter but less stable than biochar. Knowledge on its property-related long-term stability in soils is lacking. It is unknown to date if hydrochar may reduce emissions of the potent greenhouse gas N2O from soils in the same way than biochar.