1. 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

2. What is Biochar? Walnut shell Wood chips Rice Husks Manure Corn stover
Orange peels
Fly ash
carbon-negative.us
Wood

3. All biochars are not created equal…. (McLaughlin et al. 2009)
Differ on pH
Surface area
Ash content
Water holding capacity
Cation exchange capacity (CEC)
H/C ratio
C/N ratio
The top 3 are usually proprietary
Feedstock choice based on locally available resources – airborne loss, transportation costs and reduced carbon footprint
All a function of pyrolysis temperature (highest treatment temperature-HTT), pyrolysis method, residence time and feedstock

4. Objectives
To characterize physical and chemical properties of various biochars (mostly commercially available)
To determine if trends exist for biochar properties that can be related to feedstock material, which can serve to develop guidelines for biochar use.

5. Objectives 1 Twelve biochars were analyzed Physical properties:
Moisture content
Ash content
BET Surface area
Surface morphology
Chemical properties:
Elemental content
H and C content pH
Cation exchange capacity
Surface basicity and acidity
Surface functionality (ATR-FTIR and Raman)

6. Physical properties Char Source Material Pyrolysis Temp (°C)
Ash (wt %)
BET Surface Area (m2/g)
Type (Hysteresis)
BC_ A
Turkey litter 64
21.8
aPs. II (H3)
BC_Bb
Walnut shell
900
40.4
227.1
Ps. II (H4)
BC_C
Inoculated material
unavailablec
15.5
95.9
BC_D
Soft wood
2.4
25.2
BC_E
Wood + Algal digestate
6.4 2
Ps. II (H3)
BC_F
Wood
510 3
165.8
BC_G
410
2.6
2.8
BC_H
Wood chips 17
4.9
BC_I
unavailable 5
164.1
BC_J
153.1
BC_K
5.5
154.4
BC_L
4.2
301.6
Separate into
a Ps.II = Pseudo Type II
b Unknown, not willing to provide or proprietary
c Not commercially available
Wood
Non-wood

7. Scanning Electron Microscopy analysis
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.
c) BC_B
a) BC_G
b) BC_F
10µm
100µm
60µm
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 loops- narrow slit-like pores

8. Chemical properties aCEC = Cation exchange capacity
Char
C (wt %)
N (wt %)
H (wt %)
O (wt %)
PO4-P (wt %)
K (wt %)
S (ppm)
Fe (ppm)
pHw (1:2)
CECa
cmol/kg
Acidity (meq/g)
Basicity (meq/g)
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
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
0.19
685
3370 67
1.56
BC_F
83.9
0.36
1.88
19.8
0.02
110
505
7.3 12
0.27
0.93
BC_G
65.7
0.21
4.38
23.5
0.12 50
248
7.1 10
0.4
BC_H
71.2
0.91
2.88
11.6
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
0.84
BC_J 88
0.44
2.55
14.8
0.33 60 79
9.5
14.9
0.49
0.87
BC_K
85.4
0.55
2.37
8.9
0.48
606
8.8
3.6
0.6
0.94
BC_L
82.5
1.64
5.6
0.06
160
473
16.5
1.21
High C in wood derived biochar
aCEC = Cation exchange capacity
b Not commercially available
Wood
Non-wood

9. Greater aromaticity in wood derived biochar
FTIR: Fourier Transform Infrared Spectroscopy
Aromatic
C=C
C-H
Aliphatic/Functionalized
C-O, C-H
C-O
C=O
Greater aromaticity in wood derived biochar

10. xAliphatic ether (1029cm-1) xAromatic carbonyl (1690cm-1)
Char
xAromatic C-H (744cm-1)
xAliphatic ether (1029cm-1)
xAliphatic CH3 (1417cm-1)
xAromatic C=C (1587cm-1)
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
2.05
0.94
BC_F
2.09
1.7
2.3
0.28
BC_G
2.16
0.83
1.5
0.4
BC_H
1.12
1.71
1.78
0.41
BC_I
1.83
1.98
BC_J
0.71
1.67
1.41
0.36
BC_K
1.05
1.17
1.6
1.9
BC_L
1.01
1.22
0.12
x. Ratios of peak intensities relative to the aromatic C-H stretch at 870cm-1 common to all spectra

11. ID - sp2 disordered C atoms in aromatic ring structures
Char
Aliphatic ether (1029cm-1)
yRaman Id/Ig
BC_A
2.9
0.4
BC_B
1.1
0.34
BC_C
3.6
0.76
BC_D
2.67
0.58
BC_E
2.83
0.65
BC_F
2.09
BC_G
2.16
0.25
BC_H 1
0.83
BC_I
1.2
0.68
BC_J
1.67
0.72
BC_K
1.17
0.59
BC_L
1.01
0.71
y. Ratio of peak intensities of the Carbon D (1350cm-1) and G (1690cm-1) bands in Raman spectra
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
D band
(aromatic)
G band
(aliphatic & olefinic)

12. Objective 2
van Krevelen diagram of a) selected biochar (from literature) and b) 12 study biochar (inset)
1. Sharma et al. Fuel 2004, 83,
2. Keiluweit et al. Environmental Science & Technology 2010, 44,
3. Zheng et al. Journal of Hazardous Materials 2010, 181,
4. Cao, X. et al. Bioresource Technology 2010, 101,
5. Özçimen et al. Renewable Energy 2010, 35,
6. Jindarom et al. Chemical Engineering Journal 2007, 133,
7. Chan et al. Soil Research 2008, 46,
8. Azargohar et al. Applied Biochemistry and Biotechnology 2006, 131,
9. Wu et al. Industrial & Engineering Chemistry Research 2009, 48,
10. Toles et al. Bioresource Technology 2000, 71,
11. Van Zwieten et al. Plant and Soil 2010, 327,
12. Chen, B. and Chen, Z. Chemosphere 2009, 76,
13. Major et al. Plant and Soil 2010, 333,
14. Argudo, M. et al. Carbon 1998, 36,
15. Hammes et al. Applied Geochemistry 2008, 23,
16. Chun et al. Environmental Science & Technology 2004, 38,
17. Mahinpey et al. Energy & Fuels 2009, 23,
18. Rondon et al. Biology and Fertility of Soils 2007, 43,
19. Abdullah, H. and Wu, H. Energy & Fuels 2009, 23,
20. Cheng, C.-H and Lehmann, J. Chemosphere 2009, 75,
21. Spokas et al. Chemosphere 2009, 77,
22. Steiner et al. J. Environ. Qual. 2009, 39,
23. Busscher et al. Soil Science 2010, 175,
24. Brewer et al. Environmental Progress & Sustainable Energy 2009, 28,
25. Novak et al. Annals of Environmental Science 2009, 3,
26. Novak, J. M. and Reicosky, D. C. Annals of Environmental Science 2009, 3,
27. Singh et al. J. Environ. Qual. 2010, 39,
A algae
G grass
L hull
M manure
N nutshell
P pomace
W wood
Challenges
n= 85

13. Change in ash content as a function of pyrolysis temperature of biochar
Change in ash content as a function of pyrolysis temperature of biochar derived from hard and softwood
Wood material has lower ash content
Greater ash content in hard wood compared to softwood

14. Change in the C/N ratio as a function of pyrolysis temperature of biochar
Change in the C/N ratio as a function of pyrolysis temperature of biochar derived from hard and softwood.

15. Change in the surface area as a function of pyrolysis temperature of biochar
Change in surface area as a function of pyrolysis temperature of biochar derived from hard and softwood

16. 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

17. Suggested guidelines Property Agroecosystem consideration Ash content
Hydrophobicity and retention of agrochemicals
C/N ratio
Initial Immobilization of soil N
Surface area
Sorption of pesticides, herbicides and heavy metals, sites for fungal and microbial colonization
Characteristic
Suggested guideline
Ash content
grass ≈ manure >> nut shells, pomace and wood
(hard wood > soft wood)
C/N ratio
wood >> grass> pomace> manure
(soft wood > hard wood)
Surface area
temperature dependent

18. 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

19. Effects of biochar Improves However many other studies have shown
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.