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Author's personal copy
J. Anal. Appl. Pyrolysis 80 (2007) 319–324
www.elsevier.com/locate/jaap
Preparation of activated carbon for mercury capture
from chicken waste and coal
Hong Cui *, Yan Cao, Wei-Ping Pan
Institute for Combustion and Science and Environmental Technology, Western Kentucky University, Bowling Green, KY 42101, USA
Received 6 December 2006; accepted 9 April 2007
Available online 19 April 2007
Abstract
Chicken waste and chicken waste blended samples with selected high sulfur coal were used as raw materials for activated carbon preparation.
Raw materials were subjected to the preparation procedures of carbonization in a nitrogen atmosphere and activation in a steam atmosphere. The
basic properties of the raw materials, chars and activated carbons were investigated by components analysis, surface porosity and thermogravimetric analysis. Two activated carbon samples were selected for elemental mercury capture tests in a lab-scale drop tube reactor with air flow.
The current results show that chicken waste is not a suitable raw material for activated carbon production due to its higher contents of volatile
matter and ash. Coal can be used as a carbon carrier for improving the carbon content of products. A low-cost activated carbon was prepared by a
co-process of chicken waste and coal, and examining the high capture efficiency for elemental mercury. It suggests that the coal provides a carbon
carrier or trap for some active species, such as chlorine released from the chicken waste. These active species would likely provide or create the
adsorptive sites on the surface of activated carbon for elemental mercury.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Activated carbon; Chicken waste; Coal; Mercury capture
1. Instruction
Powered activated carbon (PAC or AC) injection technology
upstream of the electrostatic precipitator (ESP) or baghouse is
one of the most promising mercury control technologies for
coal-fired power plants [1]. It has an advantage of high
efficiency and a disadvantage of high sorbent cost, partially due
to the lack of PAC recovery from fly ash. Thus, the cost and
capture capability of PAC play an important role in the
feasibility of carbon injection technology.
Some inexpensive materials with a high carbon content,
such as waste tires [2,3], nutshells [4] and agriculture residues
[5,6] have been used as potential raw materials for activated
carbons production. The preparation generally involves two
steps: carbonization of the raw material in the absence of
oxygen and activation of the carbonized products with water or
CO2. Volatile matters are released in the carbonization step and
* Corresponding author. Present address: Hawaii Natural Energy Institute,
University of Hawaii at Manoa, USA.
E-mail address: hongcui.hawaii@gmail.com (H. Cui).
0165-2370/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jaap.2007.04.002
solid carbon structures, or commonly called char, are remained.
In the activation step which follows, char reacts with activated
agents to form activated carbon with improved pore structure and
surface properties. Each step has an impact on the final
productive yield and properties. In addition, the produced carbon
commonly needs to be modified on the surface by impregnation
with sulfur, chloride, bromine or iodine. These impurities which
function as active sites for mercury adsorption so as to increase
the adsorptive capacity [7–11], but also increase the production
costs [12]. Hence, finding a low cost raw material or developing a
low-cost process to produce highly effective PAC would be very
valuable for carbon injection technology.
Chicken waste has a higher content of chlorine compared
with coal, as shown in Table 1. During the carbonization and
activation partial chlorine components could be kept in the solid
char or activated carbon. This is probably beneficial for
mercury capture via oxidation reaction or chemical adsorption
[7,9,13]. However, the problem is the low char yields when
chicken waste is used alone, due to its high content of volatile
matter and ash. To increase the char yield or solid carbon
content, coal could be selected as an alternative raw material
providing a more solid char carrier.
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Table 1
Basic property for chicken waste, coal and the blended samples
Samplea
CW
C8E2
C5E5
C2E8
E-coal
a
Proximate analysis (as received)
Ultimate analysis (dry basis)
Moisture (%)
Ash (%)
C (%)
H (%)
O (%)
N (%)
S (%)
Cl (ppm)
H/C
O/C
1.36
8.93
7.28
5.49
4.28
28.15
24.35
19.37
12.98
9.14
28.30
36.52
47.45
60.12
67.36
4.97
5.06
5.07
5.13
5.33
34.35
29.89
23.93
17.63
14.11
3.45
3.06
2.49
1.88
1.44
0.78
1.13
1.69
2.26
2.62
11596
5834
5380
1976
162
0.176
0.139
0.107
0.085
0.079
1.214
0.818
0.504
0.293
0.209
C8E2, C5E5 and C2E8 denote the raw sample of chicken waste blending with E-coal with the ratio of 80:20, 50:50 and 20:80, respectively.
The objective of this study is to develop an inexpensive and
effective co-process for activated carbon production from
chicken waste and a selected coal. In this paper, it is concerned
with the preparation of the char and activated carbon. The
yields, surface area, pore size and volume, as well as the
thermal weight loss behaviors for these char and activated
carbon samples were investigated. Finally, two selected
activated carbon samples were injected for elemental mercury
capture and the possible mechanism was proposed.
2. Experimental
2.1. Raw materials
One chicken waste (CW) and one high sulfur coal (E-coal)
were used in this experiment. Milled samples (below 0.08 mm)
with different ratios of CW and E-coal by weight were
prepared, which were 20:80, 50:50 and 80:20, respectively.
Their basic properties are listed in Table 1.
with 4.0 mg samples and blocked by quartz wool on both ends.
The tube was then connected to a nitrogen supply at a flow rate
of 300 ml/min. After 15 min of purge at ambient temperature
the tube was inserted into the heated furnace. After 60 min of
carbonization time, the tube was taken out of the furnace for
cooling. During the purge, carbonization and cooling stages, N2
flow was always constant to prevent char oxidation. Finally,
char was colleted from the cooling tube and weighed.
The liquid products were swept out of the reactor and passed
through a glass condenser immersed in a mixture of ice and
water. The condensable and gas fractions were not collected or
further analyzed.
The prepared char samples were activated by steam
following the carbonization procedure in the same reactor at
650 and 750 8C for 30 or 60 min, respectively. Water injection
was controlled by a syringe pump at a rate of 0.1 ml/min,
steamed in a pre-heater, and then carried in a flow of N2 at
100 ml/min.
The yields of char or activated char (AC) were calculated by
the equation
2.2. Preparation of char and activated carbon
X ð%Þ ¼
The carbonization and activation of the CW/coal or char
samples were carried out in a horizontal quartz reactor, 50 cm
in length and 2 cm in inner diameter, as shown schematically in
Fig. 1.
Carbonization temperatures between 300 and 550 8C were
selected based on the TGA results. One quartz tube was filled
m
100
m0
where X is char or AC yield (%), m the char or AC mass (g) and
m0 is the raw sample mass (g). The preparation experiments
were done several times to get enough char and AC samples for
further analysis and testing. Thus, X is an average value for the
all effective experiments.
Fig. 1. Schematic of the experimental setup used for CW/coal carbonization or activation.
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H. Cui et al. / J. Anal. Appl. Pyrolysis 80 (2007) 319–324
2.3. Characterization of char and activated carbon
Basic properties were analyzed by ultimate, proximate and
surface porosity analyses.
Thermal weight loss behaviors were examined by thermogravematric analysis (TGA, TA 2950), which was used to
investigate the effect of co-process between coal and CW on
the thermal properties of products, and then to deduce the
possible reaction mechanism. The detailed testing conditions
are listed here: sample mass of 20 mg, N2 gas flow rate of
60 ml/min, heating rate of 20 8C/min and the final temperature
of 1000 8C.
The porous properties including BET surface area, pore
volume and average pore diameters of the raw samples, char
and AC samples were measured by nitrogen or carbon dioxide
adsorption/desorption isotherms with a Micrometritics instrument ASAP 2020.
2.4. Mercury capture test
Mercury capture tests were conducted by using a lab-scale
drop-tube reactor, as shown in Fig. 2.
The main body of the reactor was a stainless steel pipe with
2 in. in i.d., which was reported and verified to be inert to
mercury transformation. The reactor was heated by an electric
furnace, which was temperature controlled by a two-channel
temperature controller, generally at 150 8C to simulate ESP
condition. The whole system was well insulated to keep the
system temperature constant. A custom-made mini stainless
cyclone and inertial probe setup were applied for the gas solid
separation, which had high separation efficiency for particle
diameter of less than 10 mm.
Air or simulated flue gas entered into the reactor from the
top, passing through a heated tube and a sintered metal filter.
Mercury was injected into the gas by contacting carrier gas
(Argon) with an elemental mercury permeation tube in a
Fig. 2. Schematic plot of drop tube reactor for mercury capture tests.
321
temperature-controlled vessel. The mercury concentration was
adjustable by the vessel temperature and the flow rate of the
carrier gas.
Ash sample, colleted from a power plant with the coal
sample, was blended with AC samples to introduce into the
drop tube by a mini-screw feeder at a constant rate. For
simulation of actual injection conditions before ESP at the
utility boiler, the following conditions were performed in this
test: blending ratio of AC to coal ash was 400 mg/5000 mg; the
whole system was kept at 150 8C; the injection rate was set at
6 mg/min resulting in an AC residence time in the reactor of
approximately 1 s.
The simulated gas sample was colleted from the filter
housing and analyzed by a semi-continued mercury monitor
system (PS Analytical SCEM System).
3. Result and discussions
3.1. Thermal analysis of CW and CW blended samples with
coal
Fig. 3 shows weight loss profiles for CW, E-coal and their
blended samples in a nitrogen atmosphere. The volatile
releasing temperature is around 300 8C for CW and around
450 8C for E-coal, at which points the devolatilization rate
reach their maximum. For the blended samples, two peaks
appear near 300 and 450 8C on the TGA/DTG curves, which
correspond to those of CW and coal. Increasing the coal content
in the blended samples causes the peak around 300 8C to shrink,
while the peak around 450 8C increases in size. The blended
samples have both characteristics of coal and CW, and more
CW content results in more volatile matters emission at low
temperature. The cooperation effect was not found for the
blended samples in this investigation.
Considering the devolatilization behavior of CW, coal and
their blended samples, carbonization temperatures were
selected intentionally between 300 and 550 8C. At this
temperature range, different groups of volatile matter can be
eliminated with different characteristic char samples left.
Fig. 3. Thermal properties for coal, CW and the blended samples in N2
atmosphere.
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H. Cui et al. / J. Anal. Appl. Pyrolysis 80 (2007) 319–324
Fig. 4. Char yields with varied blending ratios at 316, 427 and 538 8C.
3.2. Carbonization
Fig. 4 shows the char yields with different CW/coal ratios
carbonized at 316, 427 and 538 8C for 60 min in a nitrogen
stream. It is found that char yields decrease with increasing
carbonized temperature for the same raw samples, and also
decrease with more CW contents for the blended samples at the
same carbonized temperatures.
Based on the char yields of pure coal and pure CW sample,
as well as the blending ratios, char yields of blended samples at
427 8C can be calculated and predicted, as shown in Fig. 5. The
calculated data are very close to the experimental results, which
indicate that an additive effect appears on the char yields by cocarbonization of coal and chicken waste under the experimental
conditions. Similar results are also found on the char samples
prepared at 316 and 538 8C.
Temperature-programmed TGA analysis provides an effective tool to evaluate the char preparation by investigating the
char’s thermal properties, as shown in Fig. 6.
For the char samples prepared at 316 8C (Fig. 6a), E-coalchar maintained its devolatilization behavior so that the main
DTG peak appears at around 450 8C, the same as the original
coal. The blended samples also have this DTG peak and its size
varies with coal contents. More coal contents result in a bigger
Fig. 6. Thermal properties for char samples in N2 atmosphere (char prepared at:
(a) 316 8C, (b) 427 8C and (c) 528 8C).
Fig. 5. Comparison of actual and predicted char yields.
DTG peak. This peak was also presented for the CW-char
sample, and no difference was found for the other blended
sample-chars. It can be suggested that this DTG peak is
contributed by both coal and chicken waste, in which their chars
have the volatile matters with the same releasing temperatures.
After 800 8C, another DTG peak appears for CW-char and
increases with CW content increasing in the blended samplechars.
For the char samples prepared at 427 8C (Fig. 6b) and 528 8C
(Fig. 6c), the DTG peaks (around 450 8C) disappear and
indicate that the dominative volatile matters were almost
released. The two DTG peaks presenting at around 700 and
950 8C indicated some heavy volatile matters remained in these
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323
Table 2
Basic properties for char samples prepared at 427 8C (dry basis)
Sample
C (%)
H (%)
O (%)
N (%)
S (%)
Cl (ppm)
Ash (%)
CW-char
C8E2 char
C5E5 char
C2E8 char
E-coal char
28.43
41.10
54.32
67.15
70.91
1.40
1.96
2.45
3.04
3.38
8.76
4.77
5.49
4.89
7.86
2.67
2.62
2.29
1.92
1.73
1.20
1.72
2.07
2.28
2.40
22617
17747
9290
2630
180
57.54
47.84
33.39
20.73
13.71
Table 3
Yields of char and activated carbons (AC)
Sample
Char
yield (%)
AC yield (%)
(based on char)
AC yield (%)
(based on raw
material)
CW
C8E2
C5E5
C2E8
E-coal
45.4
50.4
57.4
63.3
68.5
72.0
74.2
75.0
76.0
83.0
32.7
37.4
43.1
48.1
72.0
Char was prepared at 427 8C for 60 min; AC was prepared at 650 8C for 30 min.
char samples, which contents would be more with the blended
samples of higher CW/coal ratio.
The basic properties of the char samples prepared at 427 8C
are listed in Table 2. It should be noticed that the blended-chars
have higher C and S contents with lower ash content than CWchar, and also have higher Cl contents than coal-char. It
indicates that blended-chars are more suitable raw materials for
activated carbon production than CW-char.
3.3. Activation
Table 3 lists the yields of char samples prepared at 427 8C
for 60 min, and the yields of AC samples prepared at 650 8C for
30 min, based on char or raw materials. For the CW sample, the
yields of char and activated carbon are the lowest at 45.4 and
72%, respectively, compared with coal and the blended
samples. The total yield of CW–AC is 32.7% based on the
raw material, and the ash content is high up to 90%. It indicates
CW–AC is a low quality activated carbon with a low yield and
high ash content. For the blended samples, the AC samples’
yields can be increased at 37.4 and 48.1%, when 80 and 20%
CW were used, respectively.
Fig. 7. Thermal properties for AC samples in N2 atmosphere (AC prepared at
427 8C for 60 min).
Fig. 7 shows TGA analysis results for the blended-ACs. The
DTG peak at around 900 8C becomes large with an increase of
CW/coal ratio in the raw samples. It likely shows that carbon
structures derived from CW still remain in the AC samples, are
also indicates the AC samples are stable thermally before
600 8C.
As a good activated carbon, it should have a large surface
area and developed pore structure. Activation plays this role by
the reactions between char and steam. Table 4 lists the surface
properties of raw samples, char samples and AC samples at
varied conditions. For example, the C5E5 (blended sample with
the ratio of 50:50) has a surface area of 4.06 m2/g. After
carbonization at 427 8C for 60 min, its surface area remained
almost constant at 3.33 m2/g. However, its surface area was
dramatically increased to 168.6 m2/g after activation at 650 8C
for 30 min, which was attributed to the development of
micropore structure. This indicates that the char’s pore structure
cannot be improved by carbonization; however, it can be
dramatically improved by activation. Higher coal content in
blended samples is of benefit to the formation of activated
carbon with high surface area and pore volume.
3.4. Mercury capture test results
Two AC samples prepared from C8E2 and CW were used for
the mercury capture test. The test results are listed in Table 5.
Table 4
Properties of raw samples, chars and activated carbons
Sample
CW
C8E2
C5E5
C2E8
E-coal
a
b
Raw samplesa
Chara (427 8C, 60 min)
ACb (650 8C, 30 min)
Surface area
(m2/g)
Vo
(cm3/g)
Pore diameter
(nm)
Surface
area (m2/g)
Vo
(cm3/g)
Pore diameter
(nm)
Surface
area (m2/g)
Vo
(cm3/g)
Pore diameter
(nm)
3.90
–
4.06
–
8.55
0.0082
–
0.0083
–
0.013
8.37
–
8.14
–
6.12
7.79
–
3.33
–
0.50
0.028
–
0.012
–
0.001
14.25
–
14.70
–
8.32
164.2
203.6
(168.6)a
247.0
263.9
0.043
0.065
(0.117)a
0.021
0.089
1.04
1.27
(2.78)a
1.30
1.35
Measures at 77 K using N2 as absorbate.
Measures at 273 K using CO2 as absorbate.
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Table 5
Elemental mercury Hg(0) capture efficiency by ash, C8E2–AC and CW–AC samples
Sample
Inlet Hg(0) (ng/m3)
Outlet Hg(0) (ng/m3)
Retention of Hg(0) (ng/m3)
Capture efficiency (%)
Net efficiency (%)
Ash
C8E2–AC + ash
CW–AC + ash
8316
7663
9444
7111
2589
5841
1205
5074
3603
14.5
66.2
38.2
0
51.7
23.7
More than 51.7% of the mercury was removed by C8E2–AC
(AC produced from the blended sample with a ratio of CW to Ecoal at 8:2) and just 23.7% net removal efficiency was obtained
by CW–AC (AC produced from the CW alone). The mercury
removal efficiency can be realized at a maximum of 66.2% for
C8E2–AC sample, if the removal contribution by ash is
included.
The current results verify the mercury capture efficiency of
C8E2–AC is higher than that of CW–AC. It means that the coal
blending with chicken waste could improve the quality of
activated carbon, which is suitable for mercury capture. The
reason, we suggest, that coal provides a carbon carrier or trap
for some active species, such as chlorine released during the
chicken waste carbonization. These active species would likely
provide or create the active sites on the AC surface for mercury
bonding [14,15].
4. Conclusion
The objective of this study was to develop an inexpensive
and effective activated carbon from chicken waste and a
selected coal for mercury capture. Test results indicate that
chicken waste is not a suitable raw material for activated carbon
production due to its high contents of volatile matter and ash.
Coal can be used as a carbon carrier for improving the carbon
contents of products. The char’s pore structure cannot be
improved by carbonization; however, it can be improved by
activation. More coal contents are of benefit to the formation of
activated carbons with high surface area and pore volume.
Higher mercury removal capability of the activated carbon
prepared from chicken waste and coal was obtained. It suggests
that the coal provide a carbon carrier or trap for some active
species, such as chlorine released from the chicken waste.
These active species would likely provide or create the
adsorptive sites on the AC surface for elemental mercury.
Currently, no more evidence is provided to explain this result. It
needs more detailed study and analysis on the surface chemistry
properties of activated carbon to verify the current testing
results.
Acknowledgement
This work is supported by the USDA-ARS Project No. 640612630-002-02S.
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