Biochar Structure, Stability, and

Sequestration

Alice BudaiApril 2011

Image from www.nationalgeographic.com

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

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

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

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

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)

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)

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

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

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

Biochars of this project

• Two C4 feedstocks

280 x miscanthus140 x corn cob

Two C4 feedstocks will be utilized

Biochars of this project (continued)

• Three production methods– Slow pyrolysis (including a temperature

gradient)– Flash pyrolysis– Hydrothermal carbonisation

NTNU HNEI MPG

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

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)

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

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

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