An Introduction To Biochar With An Emphasis On Its Properties

An Introduction to Biochar with an Emphasis on its Properties and Potential for Climate Change Mitigation Jim Amonette Pacific Northwest National Laboratory Richland, WA 99352 USA PNW Biochar Initiative Meeting 21 May 2009

PNNL-SA-66736

Outline What is Biochar? How is it Made? Pyrolysis and Hydrothermal Carbonization Processes Feedstocks Yields

What are its Properties? Physical Chemical

How can it be Used? Energy Soil Fertility Carbon Sequestration

Where does it fit in the Environmental Technology Landscape? Summary

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What is Biochar? “Biochar is a fine-grained charcoal high in organic carbon and largely resistant to decomposition. It is produced from pyrolysis of plant and waste feedstocks. As a soil amendment, biochar creates a recalcitrant soil carbon pool that is carbon-negative, serving as a net withdrawal of atmospheric carbon dioxide stored in highly recalcitrant soil carbon stocks. The enhanced nutrient retention capacity of biochar-amended soil not only reduces the total fertilizer requirements, but also the climate and environmental impact of croplands.” (International Biochar Initiative Scientific Advisory Committee)

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What is Biochar? Product Solid product resulting from advanced thermal degradation of biomass

Technology Biofuel—process heat, bio-oil, and gases (steam, volatile HCs) Soil Amendment—sorbent for cations and organics, liming agent, inoculation carrier Climate Change Mitigation—highly recalcitrant pool for C, avoidance of N2O and CH4 emissions, carbon negative energy, increased net primary productivity (NPP)

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How is Biochar Made? Major Techniques: Slow Pyrolysis traditional (dirty, low char yields) and modern (clean, high char yields) Flash Pyrolysis modern, high pressure, higher char yields Fast Pyrolysis modern, maximizes bio-oil production, low char yields Gasification modern, maximizes bio-gas production, minimizes bio-oil production, low char yields but highly recalcitrant Hydrothermal Carbonization under development, wet feedstock, high pressure, highest “char” yield but quite different composition and probably not as recalcitrant as pyrolytic carbons

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Slow Pyrolysis—Continuous Auger Feed Exhaust gas and heat Generator

Gas turbine Air

Electricity

Lignocellulosic feedstock

Gas cleaner and separator

Mill

Hopper

Flue gas

Steam Dryer

Motor

Pyrolysis gases

Pyrolysis reactor

Feeder

Cyclone

Combustor

Char

Heat Air Biochar storage

courtesy Robert Brown JE Amonette 24Apr2009

Fast Pyrolysis Fluidized Bed Reactor Lignocellulosic feedstock

Pyrolysis gases Vapor, gas,

Mill

Flue

char

gas

products

Cyclone Quencher

Hopper

Pyrolysis

Bio -oil storage

Char

reactor Motor

Biochar storage

Feeder

Fluidizing gas Combustor

Air Brown (2009)

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Bio-oil

Pyrolysis Competition between three processes as biomass is heated: Biochar and gas formation Liquid and tar formation Gasification and carbonization

Relative rates for these processes depend on: Highest treatment temperature (HTT) Heating rate Volatile removal rate Feedstock residence time

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Competition Among Pyrolysis Processes Spruce Wood, Slow Pyrolysis, Vacuum (Demirbas, 2001)

Factors favoring biochar formation

In general, process is more important than feedstock in determining products of pyrolysis

80

Yield, wt%

70

Char Gas Tar+Liquid

60 50 40 30 20 10 0 200

300

400

500

600

700

800

900

High Heating Temperature, C

Eastern Red Maple Wood, Fast Pyrolysis, High Purge Rate (Scott et al., 1988) 90 80 70 Yield, wt%

Lower temperature Slower heating rates Slower volatilization rates Longer feedstock residence times

90

Char Gas Liquid

60 50 40 30 20 10 0 200

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300

400

500

600

High Heating Temperature, C

700

800

900

Wood Char Yields from Pyrolysis

Figure from Amonette and Joseph (2009) showing data of Figueiredo et al. (1989), Demirbas (2001), Antal et al. (2000), Scott et al. (1988), and Schenkel (1999) as presented by Antal and Gronli (2003),.

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Feedstocks Essentially all forms of biomass can be converted to biochar Preferable forms include: forest thinnings, crop residues (e.g., corn stover, alfalfa stems, grain husks), yard waste, paper sludge, manures, bone meal Trace element (Si, K, Ca, P) and lignin contents vary Lignin content can affect char yields

Lignin Content, Temperature, and Char Yield Slow Pyrolysis, Vacuum (Demirbas, 2001) 50

y = 0.39x + 26.76 R2 = 0.99

45 Char Yield, wt%

40

Husks, Shells, Kernels

35 30

Corn Cob Wood

25

y = 0.33x + 15.29 R2 = 0.96

20 15

Char (277 C) Char (877 C)

10 5 0 0

10

20

30

40

Biomass Lignin Content, wt% JE Amonette 24Apr2009

50

60

What are the Properties of Biochar? Pine Wood Char

Oak Wood Char

Corn Cob Char

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Gas

Fast

Slow

Physical Properties

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Physical Properties Change with HTT a )

b )

Downie et al., 2009

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Kercher and Nagle, 2003

Physical Structure and Chemical Properties Depend on Carbon Bonding Network

Radovic et al., 2001 13C

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CP-MAS NMR Amonette et al., 2008

X-ray Diffraction Analysis

Gasification and Fast Pyrolysis Chars

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Slow Pyrolysis and Hydrothermal Chars (steam present) Combustion Char (high mineral content)

Gas

Fast

Slow

Chemical Properties

Slow Pyrolysis chars produced in presence of steam at 475°C tend to be acidic (carboxylic acid groups activated) Fast Pyrolysis chars produced in absence of steam at 500°C tend to be slightly basic Gasification chars produced in presence of steam at 700°C tend to be very basic and make good liming agents JE Amonette 24Apr2009

Surface Chemistry 1200

NaOH Analyte

Slow Pyrolysis (steam)

Na2CO3 Analyte

1000

NaHCO3 Analyte Fast Pyrolysis (no steam)

HCl Analyte

800

Gasification (steam) 

600

400

200

0 OKEB ‐200

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PBEB

PCEB

PCN

OAK

PNNL‐M PNNL‐P

PNNL‐S

HW

OK (CSA) 

WS 

CSB 

pH-Dependent Exchange Capacities Oak Feedstock 1000 Slow Pyrolysis (steam), 475°C

OKEB

Ion Sorption Capacity, meq/kg

800

OAK OK (CSA)

600

400 Fast Pyrolysis, 500°C 200

Gasification (steam), 700°C

0 0

2

4

6

8

-200 -400

-600

pH

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10

12

14

How can Biochar Technology be Used? Generate Carbon-Negative Energy Soil Amendment Carbon Sequestration

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Comparison of Biochar Production Methods Carbonization Method

Products

Net Energy Released, GJ/t C

Fossil C (Coal) Offset Efficiency

Solid C Production Efficiency

Fast Pyrolysis

CH4, CO2, BioOils, H2O, Char

22.0

0.65

0.15

Slow Pyrolysis

Char, tars, CH4, CO2, H2O

17.7

0.53

0.5

“lignite”, H2O

5.5

0.16

1.0

CO2, H2O

38.4

0.97

0.01?

Hydrothermal Conversion

Combustion

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The Biofuel N2O Problem Recent work (Crutzen et al., 2007, Atmos.Chem. Phys. Disc. 7:11191; Del Grosso, 2008, Eos 89:529) suggests that globally, N2O production averages at 4% (+/- 1%) of N that is fixed IPCC reports have accounted only for field measurements of N2O emitted, which show values close to 1%, but ignore other indicators discussed by Crutzen et al. If 4% is correct, then combustion of biofuels except for high cellulose (low-N) fuels will actually increase global warming relative to petroleum due to large global warming potential of N2O Biochar avoids this issue Ties up reactive N in a stable pool Eliminates potential N2O emissions from manures and other biomass sources converted to biochar Decreases N2O emissions in field by improving N-fertilizer use efficiency and increasing air-filled porosity JE Amonette 24Apr2009

Soil Amendment Biochar typically increases cation exchange capacity, and hence retention of NH4+, K+, Ca2+, Mg2+ N from original biomass, however, may not be readily available P, on the other hand, is generally retained and available Liming agent Enhanced sorption of organics (herbicides, pesticides, enzymes) (Good? Bad?) Some evidence for increased mycorrhizal populations, rhizobial infection rates Used as carrier for microbially-based environmental remediation Lowers bulk density

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Identification of best biochar type for soil application Criteria Near-neutral pH High ion exchange capacities (CEC and AEC) Moderate hydrophobicity to retain organics High stability to oxidation Low volatile content Pre-treated with NH4+ to avoid induced N deficiency

Recommendation Steam-activated Carbonized (i.e., treated to higher temperature to remove volatiles) Slow pyrolysis probably better

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Carbon Sequestration Why? Decrease atmospheric GHG levels Stop acidification of oceans by CO2 absorption We only have one Earth

Atmosphere 597 + 211

7. 2

Vegetation, Soil, and Detritus 2477 - 34

How? Create stable C pool using biochar Use energy to offset fossil-C emissions Avoid emissions of N2O and CH4 Increase net primary productivity (NPP) JE Amonette 24Apr2009

Fossil Fuels 3700 - 319

Surface Ocean 900 + 22

Intermediate and Deep Ocean 37100 + 120

Pre-industrial values (1750) Anthropogenic changes (2005)

Adapted from IPCC AR4 WGI with updated inventory and flux data

Observed and Projected Global Warming

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IPCC (2007) WG1-AR4, SPM, p. 6, 14

Factors Affecting Global Warming (100-year timeframe)

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IPCC (2007) WG1-AR4, p. 136

Properties of Key Greenhouse Gases Atmos. Half-life, yr

Relative Radiative Efficiency

Global Warming Potential (20-yr)

Global Warming Potential (100-yr)

Global Warming Potential (500-yr)

CO2

30-325*

1

1

1

1

CH4

8.3

26

72

25

7.6

N2O

79

214

289

298

153

CFC12

69

23000

11000

10900

5200

H2O

~0.011

~0.4

Due to its short half-life (precipitation!), H2O is a feedback gas, rather than forcing warming

*Decay rate has several pathways with different rates. About 22% of the CO2 is very long lived. The first two half-lives are 30 yr and 325 yr. IPCC (2007) WG1-AR4, SPM, p. 3 JE Amonette 24Apr2009

2500

Atmospheric concentration of CO2, ppm 1250

2000

850

1500

600

1000

A2 21 00

A1 B 21 00

B1 21 00

st an t

280

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Co n

17 50

0

Irreversible warming threshold?

379

500

20 05

Cumulative Anthropogenic C in Atmosphere (GtC)

Projected Atmospheric Carbon Levels and Associated Global Warming

IPCC (2007) WG1-AR4, SPM, p. 14, modified to show zone where irreversible warming of Greenland ice sheet is projected to occur (ibid., p. 17)

What to do . . . Eliminate the C-positive, accentuate the C-negative! Minimize fossil fuel inputs Improve energy efficiency Point-source capture/sequestration of CO2 Replace with biofuels, nuclear (???$$$)

Maximize terrestrial sink (diffuse capture/sequestration) Afforestation Low-input and perennial cropping systems

Implement C-negative energy technologies Biomass combustion with CO2 sequestration Biomass pyrolysis with biochar production/CO2 sequestration JE Amonette 24Apr2009

Creating a Stable Carbon Pool with Biochar

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Human-Appropriated Net Primary Productivity 29% of all C fixed by photosynthesis aboveground (ca. 10.2 GtC/yr) is currently used by humans! Of this 1.5 GtC/yr is unused crop residues, manures, etc. An additional 1.8 GtC/yr) is not fixed due to prior human activities (e.g., land degradation) and current land use Current fossil-C emissions are ca. 8 GtC/yr Increased productivity and expanded use of residues from biochar production could have a significant impact on global C budget

Haberl et al., PNAS 2007 JE Amonette 24Apr2009

Carbon Sequestration using Biochar

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Estimates of Half-life in Soils (Slow Pyrolysis Biochars) 1400 Cheng et al. (2008) 1200 Kuzyakov et al. (2009)

1000 Time, years

Slow pyrolysis biochars are highly recalcitrant in soils with half-lives of 100-900 years Sensitivity analysis suggests that half lives of 80 years or more are sufficient to provide a credible C sink Recent evidence using 14C-labeled biochar shows no evidence for enhanced rates of soil humic carbon degradation in agricultural soils (Kuzyakov et al., 2009) No evidence for polyaromatic hydrocarbon (PAH) contamination has been seen Down-side risks seem very small

800 600 400 200 0 5

10

15

20

25

Mean Annual Temp, C

30

35

IBI Estimates of Global Biochar Impact

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The last resort ? To balance the C cycle, annual human harvest of fixed biomass would have to double from about 8.2 Gt C currently (Haberl et al., 2008) to more than 15 Gt C. This would amount to harvesting about 40% of above-ground biomass C, and is comparable to levels of biomass C appropriation seen in India today (Haberl et al., 2008). The annual diversion of 11.3% of global biomass carbon (7 Gt C, roughly one-fifth of all above-ground biomass C produced) to a pyrolysis industry would have a profound impact on the global ecology and would be considered a last resort. JE Amonette 24Apr2009

See James Lovelock Interview http://www.guardian.co.uk/science/video/2009/ apr/22/james-lovelock-gaia-space-biochar

Methane and Traditional Methods Woody Biomass No Energy Recovery 36% Biochar Yield 30% Biochar Yield

600

20% Biochar Yield 10% Biochar Yield

500 Global Warming Mitigaion Potential, g CO2-Ceq/kg dry biomass

Traditional methods without energy recovery generate methane Some decrease in mitigation potential results Difference in biochar yield is far more important These methods still yield a positive result

Modern Slow Pyrolysis

400

300

200

Traditional kilns w/ no energy recovery

100

0 0.0

0.5

1.0

1.5

2.0

CH4 Emissions (Percent of all C Emissions)

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2.5

3.0

Impact of Energy Recovery

600

500 Global Warming Mitigaion Potential, g CO2-Ceq/kg dry biomass

Recovery of energy released during pyrolysis improves mitigation potential significantly Modern pyrolysis methods should be implemented wherever possible Economic decision

All Sustainable Biomass 70% Pyrolysis Energy Recovery Efficiency

Modern Slow Pyrolysis

400

300

200

36% Biochar Yield 30% Biochar Yield 20% Biochar Yield 10% Biochar Yield

100

Traditional kilns w/ no energy recovery

0 0.0

0.5

1.0

1.5

2.0

CH4 Emissions (Percent of all C Emissions)

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2.5

3.0

Where does Biochar Fit? Offers a flexible blend of biofuel energy, soil fertility enhancement, and climate change mitigation Limited by biomass availability and, eventually, land disposal area How much biomass can be made available for biochar production vs. other uses? Crop-derived biofuels cannot supply all the world’s energy needs Maximum estimates suggest 50% of current, 33% of future Biodiversity (HANPP)? N2O?

Perhaps best use of harvested biomass is to make biochar to draw down atmospheric C levels and enhance soil productivity, with energy production as a bonus (but not the driving force). This will require government incentives (C credits/taxes?) and a change in the way we value cropped biofuels

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Further Information and Acknowledgments International Biochar Initiative (www.biochar-international.org)

New book: Biochar for Environmental Management: Science and Technology, Earthscan, 2009 (in press) North American Biochar Conference 2009 University of Colorado at Boulder, August 9-12, 2009 Research supported by USDOE Office of Fossil Energy through the National Energy Technology Laboratory USDOE Office of Biological and Environmental Research (OBER) through the Carbon Sequestration in Terrestrial Ecosystems (CSiTE) project. Research was performed at the W.R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility at the Pacific Northwest National Laboratory (PNNL) sponsored by the USDOE-OBER. PNNL is operated for the USDOE by Battelle Memorial Institute under contract DE AC06 76RL01830. JE Amonette 24Apr2009

PNNL-SA-64398

References Cited Amonette, J. E., and Joseph, S. 2009. Characteristics of biochar: Micro-chemical properties. Chapter 3 in (J. Lehmann and S. Joseph, eds.) Biochar for Environmental Management: Science and Technology. Earthscan, London, UK and Sterling, VA. Amonette, J. E., Dai, S. S., Hu, Y., Schlekewey, N., Shaff, Z., Russell, C. K., Burton, S. D., and Arey, B. W. 2008. ‘An exploration of the physicochemical diversity of a suite of biochars.’ Eos Trans. AGU 89(53), Fall Meet. Suppl., Abstract B31G-0379. Poster presentation. Antal, M. J. Jr. and Grønli, M. 2003. ‘The art, science, and technology of charcoal production’, Industrial and Engineering Chemistry Research, vol 42, pp1619-1640 Antal, M. J. Jr., Allen, S. G., Dai, X.-F., Shimizu, B., Tam, M. S. and Grønli, M. 2000. ‘Attainment of the theoretical yield of carbon from biomass’, Industrial and Engineering Chemistry Research, vol 39, pp4024-4031 Brown, R. 2009. Biochar production technology. Chapter 7 in (J. Lehmann and S. Joseph, eds.) Biochar for Environmental Management: Science and Technology. Earthscan, London, UK and Sterling, VA. Cheng, C-Hsin, Lehmann, J., Thies, J. E., and Burton, S. D. 2008. ‘Stability of black carbon in soils across a climatic gradient.’ J. Geophys. Res. 113:G02027. Crutzen, P. J., Mosier, A. R., Smith, K. A., and Winiwarter, W. 2007. ‘N2O release from agro-biofuel production negates global warming reduction by replacing fossil fuels.’ Atmos. Chem. Discuss. 7:11191-11205. Del Grosso, S. J., Wirth, T., Ogle, S. M., and Parton, W. J. 2008. ‘Estimating agricultural nitrous oxide emissions.’ Eos 89(51):529-530. Demirbas, A. (2001) ‘Carbonization ranking of selected biomass for charcoal, liquid and gaseous products’, Energy Conversion and Management, vol 42, pp1229-1238 Downie, A., Crosky, A, and Munroe, P. 2009. Physical properties of biochar. Chapter 2 in (J. Lehmann and S. Joseph, eds.) Biochar for Environmental Management: Science and Technology. Earthscan, London, UK and Sterling, VA. Figueiredo, J. L., Valenzuela, C., Bernalte, A. and Encinar, J. M. 1989. ‘Pyrolysis of holm-oak wood: influence of temperature and particle size’, Fuel, vol 68, pp1012-1017 Haberl, H. Heinz Erb, K., Krausmann, F., Gaube, V., Bondeau, A., Plutzar, C., Gingrich, S., Lucht, W., and Fischer-Kowalski, M. 2007. ‘Quantifying and mapping the human appropriation of net primary production in earth’s terrestrial ecosystems.’ Proc. Natl. Acad. Sci. 104:12942-12947. Kercher, A. K. and Nagle, D. C. 2003. ‘Microstructural evolution during charcoal carbonization by X-ray diffraction analysis’, Carbon, 41:15-27. Kuzyakov, Y., Subbotina, I., Chen, H-Q, Bogomolova, I., and Xu, X-L. 2009. ‘Black carbon decomposition and incorporation into soil microbial biomass estimated by 14C labeling’. Soil Biol. Biochem. 41:210-219. Radovic, L. R., Moreno-Castilla, C. and Rivera-Utrilla, J. 2001. ‘Carbon materials as adsorbents in aqueous solutions’, Chemistry and Physics of Carbon: A Series of Advances, vol 27, pp227-405 Schenkel, Y. 1999. ‘Modelisation des flux massiques et energetiques dans la carbonisation du bois en four cornue’, PhD thesis, Université des Sciences Agronomiques de Gembloux, Gembloux, Belgium Scott, D. S., Piskorz, J., Bergougnou, M. A., Graham, R. and Overend, R. P. 1988. ‘The role of temperature in the fast pyrolysis of cellulose and wood’, Industrial and Engineering Chemistry Research, vol 27, pp8-15

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