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Biochar Structure, Stability, and
Sequestration
Alice BudaiApril 2011
Image from www.nationalgeographic.com
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Outline
• Motivation behind Biochar Research– Why focus on Stability?
• Not all chars are created equal• Biochar characterization
– Objectives– Hypotheses
• Biochars of the project– Feedstock and pyrolysis methods
• Characterization Methods• Methods of stability estimation
Image from www.forskning.no
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The CO2 problem
Figure from Wikipedia and Dr. Pieter Tans
• Atmospheric concentrations of carbon dioxide have increased from 280 to 390 ppm
• The rate of change of CO2 in the atmosphere is increasing over time
• Only 50% of anthropogenic CO2 emissions are naturally sequestered
• Anthropogenic sequestration could be applied to pick up the slack
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Carbon Cycle Perspective
Estimated fluxes
• Fosslil fuel combustion(+6,3 Gt/yr)
• Net ocea and land uptake (-3,1 Gt/yr)
• Atmospheric Accumulation (-3.2 Gt/yr)
• Estimated flux from soil (50-60 Gt/yr)
Image from: Rice University, based on data from Prentice IC, et al (2001), The Carbon Cycle and Atmopheric Carbon Dioxide, in Climate Change 2001,The Scientific Basis. Contributions of Working Group 1 to Third Assessment Report of the IntergovernmentalPanel on Climate Change, edited by J. T. Houghton, et al.,Cambridge University Press, Cambridge, UK
Soils have a great potential to sequester carbon
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The CO2 solution
• By pyrolyzing biomass it becomes more recalcitrant and can be used to store carbon in soil
• How much CO2 could be sequestered using purposeful biochar production and application to soil?
Images from www.news.cornell.edu and Adam
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Not all Biochars are created Equal Biochar properties are determined by the biomass
• Pore size and distribution is determined by the feedstock (cell) structure
• Surface area and internal volume are thus determined
• Mineral-contents vary among feedstocks
Images from www.airterra.com and ”Biochar: Environmental Management” (edited by Lehmann and Joseph, 2009)
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Not all Biochars are created EqualBiochar properties are determined by pyrolyis conditions
• Prominent Factors:– Temperature
• HTT, rentention– Pressure– Fluidizing agent– Degree of oxidation
• Mechanisms:– O, H, C, and minerals (K, Ca, N, P, Al, S,…) are
volatilized at different rates– The remaining C molecules rearrange
Image from ”Biochar: Environmental Management” (edited by Lehmann and Joseph, 2009)
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Characterizing Chars
According to Structure
Physical and chemical
characterisitics
According to Function
Phenomenological abilities to improve plant growth and
microbial processes
Ability to store carbon
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Main Objectives
• To detect structural (chemical) differences in biochars using advanced analysis techniques
• To detect structural (chemical) changes after incorporation into soil using advanced analyses
• To measure the stability of biochars using laboratory incubation and natural abundance carbon isotopes
• To link the structure of biochar to its stability in soil, and to identify a proxy for stability
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Hypotheses
• The production method (carbonization/pyrolysis) influences biochar’s stability and structure
– Higher temperature chars are expected to be more recalcitrant, consisting of aromatic rings instead of O-alkyl carbon, affecting surface properties of the biochar and its behavior in soil
– More intensive pyrolysis methods will lead to more stable biochars
– Structural characteristics will affect stabilization behavior of the char (binding to organic matter and clay)
– An incubation study of biochar with soil over 1,5 years will reflect the ratio of labile to recalcitrant carbon
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Biochars of this project
• Two C4 feedstocks
280 x miscanthus140 x corn cob
Two C4 feedstocks will be utilized
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Biochars of this project (continued)
• Three production methods– Slow pyrolysis (including a temperature
gradient)– Flash pyrolysis– Hydrothermal carbonisation
NTNU HNEI MPG
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Characterization Methods
• Elemental Analysis– Weight % of C, H, O, N, S
• Proximate Analysis– Moisture content– Volatile content– Free carbon remaining– Ash (mineral content)TG– Mass change of a material as a function of
temperatureDSC– Thermal stability and decomposition
Figure from Morten Grønli
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Characterization Methods (..continued..)
• CEC– Ability of the material surface to bind ions
• BET– Surface area of the material
• SEM– Surface topography– Composition– Other, electrical conductivity
Image from ”Biochar: Environmental Management” (edited by Lehmann and Joseph, 2009)
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Characterization Methods (..continued)
• Spectrometry (NMR and NIR/MIR)– Chemical structure
Charcoal shown in red,
forest soil shown in blueand green
• BPCA– Degree of condensation of the aromatic
rings
Sources: Brennan et al, 2001 and Line Tau Strand
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Elucidating Stability through Stable Isotopes
• The isotopic signature of carbon in biochar produced from C4 plants is noticeably different from that of organic matter in Norwegian soil
– This natural abundance labeling will be used to identify the source of respired CO2 during incubation
• It will be assumed that biochar is composed of a labile and recacitrant carbon pool
• Based on the kinetics and d13C of CO2 respired, and changes in biochar structure over time, the stability and size of the reacalcitrant pool will be estimated
Image from www.picarro.com
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Summary of main objectives
• Identification of a proxy (measurable chemical property) for biochar stability
• Development of a fast/easy characterization method that could be used to control the quality of biochars on the market