Use of chemical and physical
characteristics to investigate trends
in biochar feedstocks
Fungai Mukome, Xiaoming Zhang, Lucas C.R. Silva, Johan
Six, and Sanjai J. Parikh
University of California, Davis
US Biochar Conference, Rohnert Park, CA
July 2012
What is Biochar?
Walnut shell
Fly ash
carbon-negative.us
Wood chips
Rice Husks
Manure
Corn stover
Orange peels
Wood
All biochars are not created equal….
(McLaughlin et al. 2009)
• Differ on
– Cation exchange capacity (CEC)
– pH
– H/C ratio
– Surface area
– C/N ratio
– Ash content
– Water holding capacity
• All a function of pyrolysis temperature (highest
treatment temperature-HTT), pyrolysis method,
residence time and feedstock
Objectives
1. To characterize physical and chemical
properties of various biochars (mostly
commercially available)
2. To determine if trends exist for biochar
properties that can be related to feedstock
material, which can serve to develop
guidelines for biochar use.
Objectives 1
Twelve biochars were analyzed
• Physical properties: • Chemical properties:
– Moisture content
– Elemental content
– Ash content
– H and C content
– BET Surface area
– pH
– Surface
– Cation exchange capacity
morphology
– Surface basicity and acidity
– Surface functionality (ATR-FTIR
and Raman)
Physical properties
Char
Source Material
BC_ A
BC_Bb
Turkey litter
Walnut shell
700-800
900
64
40.4
21.8
227.1
BC_C
Inoculated material
unavailablec
15.5
95.9
Ps. II (H4)
BC_D
Soft wood
600-700
2.4
25.2
Ps. II (H4)
BC_E
Wood + Algal digestate
Wood
Wood
Wood chips
Wood chips
Wood chips
Wood chips
Wood chips
600-700
510
410
500-650
unavailable
unavailable
unavailable
unavailable
6.4
3
2.6
17
5
2.8
5.5
4.2
2
165.8
2.8
4.9
164.1
153.1
154.4
301.6
Ps. II (H3)
Ps. II (H4)
Ps. II (H3)
Ps. II (H3)
Ps. II (H4)
Ps. II (H4)
Ps. II (H4)
Ps. II (H4)
BC_F
BC_G
BC_H
BC_I
BC_J
BC_K
BC_L
a
Ps.II = Pseudo Type II
b Unknown, not willing to provide or proprietary
c Not commercially available
Ash
(wt %)
Type
BET Surface
Area (m2/g) (Hysteresis)
Pyrolysis
Temp (°C)
aPs.
II (H3)
Ps. II (H4)
Wood
Non-wood
Scanning Electron Microscopy analysis
a) BC_G
60µm
b) BC_F
100µm
c) BC_B
10µm
SEM images of three biochars showing a) a char with type H3 hysteresis loop b) a char with type H4
hysteresis loop and c) a char with high ash content.
Type II isotherms - capillary non-porous or macroporous adsorbents and
represent monolayer-multilayer adsorption.
Lower surface areas (BC_J,BC_H, BC_A and BC_G) - Type H3 hysteresis loops lack of microporosity, plate-like particles and slit shaped pores.
Higher surface area - (BC_L, BC_K, BC_J, BC_I, BC_F) - Type H4 hysteresis loopsnarrow slit-like pores
Chemical properties
Char
C
N
H
O
PO4-P
K
(wt %) (wt %) (wt %) (wt %) (wt %) (wt %)
S
(ppm)
Fe
(ppm)
pHw
(1:2)
Acidity Basicity
cmol/kg (meq/g) (meq/g)
CECa
BC_A
15.6
0.78
0.83
4.4
6.61
7.05
10720
9191
10.9
24.4
0.08
4.92
BC_Bb
55.3
0.47
0.89
1.6
0.64
9.32
940
1981
9.7
33.4
-
11.71
BC_C
53.3
1.96
3.7
24.3
0.47
1.2
5920
1109
6.8
44.5
1.22
1
BC_D
68.2
0.51
3.66
26.8
0.13
0.26
370
1934
7.5
26.2
1.24
1.02
BC_E
58.1
0.41
4.16
31.7
0.08
0.19
685
3370
6.8
67
1.56
1.22
BC_F
83.9
0.36
1.88
19.8
0.02
0.13
110
505
7.3
12
0.27
0.93
BC_G
65.7
0.21
4.38
23.5
0.02
0.12
50
248
7.1
10
0.83
0.4
BC_H
71.2
0.91
2.88
11.6
0.08
0.72
480
3517
7.9
3.2
0.79
1.01
BC_I
87.3
0.59
2.15
7.4
0.07
0.85
140
203
9.2
9.1
0.41
0.84
BC_J
88
0.44
2.55
14.8
0.02
0.33
60
79
9.5
14.9
0.49
0.87
BC_K
85.4
0.55
2.37
8.9
0.07
0.48
140
606
8.8
3.6
0.6
0.94
BC_L
82.5
0.49
1.64
5.6
0.06
1.02
160
473
9.5
16.5
0.36
1.21
aCEC
= Cation exchange capacity
b Not commercially available
Wood
Non-wood
BC_A
BC_B
FTIR: Fourier Transform
Infrared Spectroscopy
BC_C
13
80
Aromatic
10
29
BC_D
Absorbance
BC_E
BC_F
BC_G
C=C
C-H
Aliphatic/Functionalized
C-O, C-H
C-O
BC_H
C=O
BC_I
BC_J
1800
1600
75
0
80
4
16
95
87
0
15
87
BC_K
BC_L
1400
1200
1000
-1
Wavenumber (cm )
800
600
Greater aromaticity
in wood derived
biochar
xAromatic
C-H
(744cm-1)
xAliphatic
ether
(1029cm-1)
xAliphatic
CH3
(1417cm-1)
xAromatic
C=C
(1587cm-1)
Char
xAromatic
carbonyl
(1690cm-1)
BC_A
-
2.9
1
0.21
0.02
BC_B
-
1.1
2.2
-
-
BC_C
0.53
3.6
0.38
0.69
0.39
BC_D
0.63
2.67
2.46
2.6
1.2
BC_E
0.27
2.83
2.2
2.05
0.94
BC_F
1.2
2.09
1.7
2.3
0.28
BC_G
1.2
2.16
0.83
1.5
0.4
BC_H
1.12
1
1.71
1.78
0.41
BC_I
1
1.2
1.83
1.98
0.38
BC_J
0.71
1.67
0.27
1.41
0.36
BC_K
1.05
1.17
1.6
1.9
0.36
BC_L
1.1
1.01
1.05
1.22
0.12
x. Ratios of peak intensities relative to the aromatic C-H stretch at 870cm-1 common to all spectra
BC_B
BC_D
BC_E
BC_G
BC_H
BC_K
BC_C
BC_F
BC_I
BC_L
BC_J
Intensity
BC_A
Char
Aliphatic ether
(1029cm-1)
BC_A
BC_B
BC_C
BC_D
BC_E
BC_F
BC_G
BC_H
BC_I
BC_J
BC_K
BC_L
2.9
1.1
3.6
2.67
2.83
2.09
2.16
1
1.2
1.67
1.17
1.01
yRaman
Id/Ig
0.4
0.34
0.76
0.58
0.65
0.4
0.25
0.83
0.68
0.72
0.59
0.71
y. Ratio of peak intensities of the Carbon D (1350cm1) and G (1690cm-1) bands in Raman spectra
1000
1200
D band
G band
(aromatic)
(aliphatic
& olefinic)
1400
-1
Wavenumber (cm )
1600
• ID - sp2 disordered C atoms in
aromatic ring structures
• IG - sp2 disordered C atoms in
aliphatic and olefinic molecules
•Approximates sp2: sp3 ratio in
amorphous carbon
1800
Objective 2
2.0
A algae
G grass
L hull
M manure
N nutshell
P pomace
W wood
1.8
1.6
H/C atomic ratio
1.4
W
W
G
W
W
G W
P
P
y = 2.182x + 0.198
2
R = 0.88 M
1.0
G
L
0.6
GL
0.4
0.2
G
G
1.2
0.8
Literature
Study biochar (inset)
N
GN G
W
W WWG
W
WGW
WW
W
W W
WG
G
W
G
W
W
W
G
P
WG
W W
P WG
L
G
G
G
P
A
0.5
0.2
L
0.2
G
D
H
I
B
K
L
J
F
0.1
n= 85
0.1
0.7
0.3
0.0
0.0
0.0
0.0
E
C
0.4
P
P
0.9
0.6
P
W
G
1.0
0.8
G
P
NW
0.3
0.4
0.1
0.5
y = 1.805x + 0.190
2
R = 0.83
0.2
0.3
0.6
0.4
0.7
0.5
0.8
O/C atomic ratio
van Krevelen diagram of a) selected biochar (from literature) and b) 12
study biochar (inset)
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80
A
G
L
M
N
P
W
70
60
A
algae
grass
hull
manure
nutshell
pomace
wood
M
G
M
M
G A
G
M
50
A
G
M
M
40
N
M
A
30
W
A
G
G
W
G A LG
L
W
W
P
G
N
L WL
G
N
G
W
N
N
W
P
W
P
W
P
W
M W
P
W
P W
P N
W
W P W
P P W
W
W
W
W
20
10
0
0
100
200
300
400
500
600
700
800
30
W
900
1000
o
Temperature ( C)
H
25
H Hardwood
S Softwood
20
Change in ash content as a
function of pyrolysis temperature
of biochar derived from hard and
softwood
Ash content (%)
Ash content (%)
Change in ash content as a
function of pyrolysis temperature
of biochar
G
15
H
H
HS
10
S
5
0
S
S
S
H
H
S
100
200
300
400
H
S
S
500
o
Temperature ( C)
S
600
700
W
1000
W
W
W
W
W
W
N
W
W
W
J ratio
M
100
G
G
G
G G M
G
G
W W PG
W
P
P P P L
P
L
W
W
W
W
WW W
W
WG
W
M
W
algae
grass
hull
manure
shell
pumice
wood
Change in the C/N ratio as a function of
pyrolysis temperature of biochar
W
N
M G
M
W
M
G
G G W
L
W
W G
G
W
P
G
P M P
L
L
L
W
M
10
A
G
L
M
N
P
W
W
N
G
M
M
M
M A
A
A
A
A
A
S
0
100
200
300
400
500
600
700
800
900
1000
S
1000
S
S
S
S
S
o
J ( C)
H
S
hardwood
softwood
S S
H
S
C/N ratio
Change in the C/N ratio as a function of
pyrolysis temperature of biochar
derived from hard and softwood.
S
H
H
S
S
S
S
H
100
H
H
H
H
200
300
H
H
10
0
100
400
500
O
Temperature ( C)
600
700
W
G
W
M
G
N
P
N
P
W
G
W
W
W
G
W
G
W
G
W
1
M
G
G
W
W
W
G
G
W
L
W
G
W
100
200
Change in the surface area as a
function of pyrolysis temperature of
biochar
G
P
G
P
W
G
G
10
N
W
P
W
P
G
W
P
G
W
P
G
W
W
N
S
300
400
500
600
700
800
W
Temperature
W
Change in surface area as a
function of pyrolysis temperature
of biochar derived from hard and
softwood
900
S
1000
S
S
2 -1
P
W
W
G
LW
P
2 -1
(Surface area (m g )
100
grass
hull
manure
nutshell
pumice
wood
(Surface area (m g )
G
L
M
N
P
W
H Hardwood
S Softwood
100
H
S
10
H
H
H
S
S
S
S
H
H
S
1
S
H
100
200
300
400
500
o
TemperatureS ( C)
600
700
Box plots showing differences in a) ash content and b) C/N ratios, but not in c) surface area across the
different feedstocks. The grey boxes show the range from first to third quartiles, with the median dividing
the interquartile range, into two boxes for the second and third quartiles. Letters show significant
differences (p<0.05) according to a one-way ANOVA followed by Tukey (HSD) multiple means comparison
Suggested guidelines
Property
Agroecosystem consideration
Ash content
Hydrophobicity and retention of agrochemicals
C/N ratio
Initial Immobilization of soil N
Sorption of pesticides, herbicides and heavy metals, sites
for fungal and microbial colonization
Surface area
Characteristic
Suggested guideline
Ash content
grass ≈ manure >> nut shells, pomace and wood
(hard wood > soft wood)
C/N ratio
Surface area
wood >> grass> pomace> manure
(soft wood > hard wood)
temperature dependent
(soft wood > hard wood)
Acknowledgements
•
•
•
•
•
Xiaoming Zhang
Lucas C.R. Silva
Johan Six
Sanjai J. Parikh
UC Davis Agricultural Sustainability Institute
(ASI) Junior Faculty Award
• David and Lucile Packard Foundation
Email:fmukome@ucdavis.edu
Effects of biochar
• Improves
–
–
–
–
–
water holding capacity
nutrient retention
soil fertility
agricultural yield
greenhouse emission (GHG) mitigation
• However many other studies have shown
– no increase in crop yields,
– increased GHG emissions,
– unintended “liming” of soils.
• Results often linked to the properties of the biochar
used, application rate, soil type and climate.