Bonding and Structure in BioChar

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Bonding and Structure in BioChar

• Thomas Reed, PhD and Hugh McLaughlin, PhD, PE

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PART I
CHEMICAL BONDING IN BIOCHAR
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BIOCHAR PROPERTIES

• Biochar is an amorphous form of graphite formed
  when biomass, reaching the ignition temperature
  of 275C spontaneously converts to the more
  stable amorphous graphitic bonds, releasing
  gaseous and liquid forms of energy which can be
  harnessed for heat, power and fuels
• Biochar (and Graphite) are biologically inert and
  put the carbon of atmospheric CO2 back in the
  ground, increasing plant growth and reducing the
  excess CO2 from burning fossil fuels
• The Biochar Structure mirrors that of the biomass
  cellular structure

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CHEMICAL BONDING IN BIOMASS
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COVALENT CARBON
Most of the carbon in biomass and fossil fuels
has covalent bonds
?
The three-dimensional structure of cellulose, a
polymer of glucose
Cellulose is a linear polymer of D-glucose units
(two shown here)
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AROMATIC CARBON
Benzene and Lignin have aromatic bonds
BENZENE
LIGNIN
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CHEMICAL BONDING IN BIOCHAR
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GRAPHITIC CARBON

• Graphite is more stable than biomass
• The conversion of covalent or aromatic carbon
  bonds to graphite produces 20 kJ/mole of heat
  which drives the pyrolysis process between 300
  and 400C
• Biomass autopyrolyses in the temperature range
  300-400C producing graphite, gas and liquids

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GRAPHITE BONDS
Graphite is composed of two dimensional sheets of
strongly bonded carbon held together by much
weaker (van der Waals) forces. The sheets can
absorb other molecules
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AMORPHOUS GRAPHITE BIOCHAR
From page
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BIOCHAR FREE RADICALS

• Biochar is formed from the breaking of the
  biomass bonds which must form other more stable
  graphitic bonds or bonds of the volatiles
• At low temperatures (400C) there is no atomic
  mobility for rearrangement of the solid and so
  biochar is highly absorbent and almost amorphous
• At higher temperatures (800C) Biochar can form
  more regular graphite islands, still very
  imperfect but with fewer oxygen functional groups
  
• Fresh charcoal sometimes shows magnetic
  properties, due to the paramagnetism of free
  radicals

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PART 2
STRUCTURE OF BIOCHAR
structure of biomass as modified by heat and
loss of 75 of mass
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STRUCTURE OF BIOCHAR
From http//www.techtp.com/Torrefaction for High
Quality Wood Pellets.pdf, page 7 of 36
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Pyrolysis of Biomass Components (TGA)
100
Cellulose 50
80
60
Lignin 25
Weight remaining -
40
Wood
20
0
100
200
300
400
500
600
700
Temperature - C
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THERMAL REGIONS OF PYROLYSIS
From http//www.techtp.com/Torrefaction for High
Quality Wood Pellets.pdf, page 9 of 36
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QUESTIONS - PART 1 2
THERE IS A POSTER, AND THERE IS A REPRINT
THANK YOU FOR YOUR ATTENTION TBR HSM
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FIGURE 1 Trends on biocarbon properties with
increasing carbonization temperatures
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Page 3 of J. Phys. Condensed Matter 19 (2007)
406208 (17pp)
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Page 3165 Philosophical Magazine, 11 October
2004 Vol. 84, No. 29, 31593167
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Page 3165 Philosophical Magazine, 11 October
2004 Vol. 84, No. 29, 31593167
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BIOCHAR STRUCTURE
Chemically biochar is composed of very small
islands of graphite mirroring the biomass
structure from which it is derived
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