Energy & Fuels 2007, 21, 3735–3739
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Characterization of Activated Carbon Prepared from Chicken Waste and Coal Yan Zhang,† Hong Cui,† Riko Ozao,†,‡ Yan Cao,† Bobby I.-T. Chen,† Chia-Wei Wang,†,§ and Wei-Ping Pan*,† Institute for Combustion Science and EnVironmental Technology, Western Kentucky UniVersity, Bowling Green, Kentucky 42101, SONY Institute of Higher Education, Atsugi, Kanagawa, 243-8501, Japan, and Mingchi UniVersity of Technology, Taipei, Taiwan ReceiVed June 24, 2007. ReVised Manuscript ReceiVed August 13, 2007
Activated carbons (ACs) were prepared from chicken waste (CW) and coal (E-coal) blended at the ratios of 100:0, 80:20, 50:50, 20:80, and 0:100. The process included carbonization in flowing gaseous nitrogen (300 mL min-1) at ca. 430 °C for 60 min and successive steam activation (0.1 mL min-1 water injection with a flow of N2 at 100 mL min-1) at 650 °C for 30 min. Chicken waste is low in sulfur content but is high in volatile matter (∼55 wt %), and ACs with higher specific surface area were more successfully obtained by mixing with coal. The specific surface area of the CW/Coal blend AC can be estimated by SSABET ) -65.8x2 + 158x + 168, where SSABET is the specific surface area in m2 g-1 as determined by the BET method using CO2 as the adsorbent, where x is the coal fraction by weight in the CW/coal blend ranging from 0.0 to 1.0 (e.g., x ) 0.0 signifies the blend contains no coal and x ) 1.0 signifies the blend consists of 100% coal).
Introduction Activated carbons can be produced from virtually any type of carbonaceous materials1 such as coconut shell,2 palm shell,3 nut shell,4 olive stones,5 oil-palm stones,6 agricultural wastes,7,8 and many others. The preparation of activated carbon generally involves two steps: carbonization of the raw material in the absence of oxygen and activation of the carbonized products with water and/or CO2. Volatile matters are released in the carbonization step, and the remaining solid carbon structure is generally called as char. In the following activation step, char reacts with activating agents to form activated carbon (AC) with improved pore structure and surface properties. However, welltailored activated carbon for specific application and having a * Corresponding author: tel +1-270-745-2272; fax +1-270-745-2221; e-mail
[email protected]. † Western Kentucky University. ‡ SONY Institute of Higher Education. § Mingchi University of Technology. (1) Marsh, F.; Rodríguez Reinoso, F. ActiVated Carbon; Elsevier Science: London, 2005. (2) Laine, J.; Yunes, S. Effect of the Preparation method on the Pore Size Distribution of Activated carbon from Coconut Shell. Carbon 1992, 30, 601–604. (3) Daud, W. M. A. W.; Ali, W. S. W.; Salaiman, M. Z. The Effect of Carbonization Temperature on Pore Development in Palm-Shell-Based Activated Carbon. Carbon 2000, 38, 1925–1932. (4) Wang, Z. M.; Kanoh, H.; Kaneko, K.; Lu, G. Q.; Do, D. D. Structure and surface property changes of macadamia nut-shell char upon activation and high temperature treatment. Carbon 2002, 40, 1231–1239. (5) Gonzalez, M. T.; Rodriguez-Reinoso, F.; Garcia, A. N.; Marcilla, A. CO2 Activation of Olive Stones Carbonized under Different Experimental Conditions. Carbon 1997, 35, 159–162. (6) Jia, G.; Lua, A. C. Preparation of Activated Carbons from Oil-PalmStone Chars by Microwave-Induced Carbon Dioxide Activation. Carbon 2000, 38, 1985–1992. (7) Chang, C. F.; Chang, C. Y.; Tsai, W. T. Effect of burn-off and activation temperature on preparation of activated carbon from corn cob agrowaste by CO2 and steam. J. Colloid Interface Sci. 2002, 232, 45–49. (8) Gergova, K.; Petrov, N.; Eser, S. Adsorption properties and microstructure of activated carbons produced from agricultural by-products by steam pyrolysis. Carbon 1994, 32, 693–702.
specific surface area of 500 m2 g-1 or larger cannot be easily obtained by simply carbonizing the carbonaceous materials or biomass above, and because of its ready availability and stability in production, much study has been done on coal for the industrial production of activated carbon.9–12 In the case of coal-fired power plants, powdered activated carbon (PAC) is injected upstream of the electrostatic precipitator (ESP) or baghouse to control mercury emission.13 Although PAC injection has an advantage of high efficiency, it has a disadvantage of high sorbent cost, partially due to the lack of PAC recovery from fly ash. Moreover, the AC commonly need to be impregnated with sulfur, chlorides, bromine, or iodine to enhance Hg adsorptive capacity.14–18 Thus, the cost and capture capability of PAC play an important role in the feasibility of (9) Munõz-Guillena, M. J.; Illan´-Gom ´ ez, M. J.; Martin´-Martin´ez, J. M.; Linares-Solano, A.; Salinas-Martin´ez de Lecea, C. Activated Carbons from Spanish Coal. 1. Two-Stage CO2 Activation. Energy Fuels 1992, 6, 9–15. (10) Centeno, T. A.; Stoeckli, F. The Oxidation of an Asutrian Bituminous Coal in Air and Its Influence on Subsequent Activation by Steam. Carbon 1995, 33, 581–586. (11) Kovacik, G.; Wong, B.; Furimsky, E. Preparation of Activated Carbon from Western Canadian High Rank Coals. Fuel Proc. Technol. 1995, 41, 89–99. (12) Teng, H.; Ho, J.-A.; Hsu, Y.-F.; Hsieh, C.-T. Preparation of Activated Carbons from Bituminous Coals with CO2. Ind. Eng. Chem. Res. 1996, 35, 4043–4049. (13) Pavlish, J. H.; Sondreal, E. A.; Mann, M. D.; Olson, E. S.; Galbreath, K. C.; Laudal, D. L.; Benson, S. A. Application of sorbents for mercury control for utilities burning lignite coal. Fuel Process. Technol. 2003, 82–89. (14) Zeng, H.; Jin, F.; Guo, J. Removal of elemental mercury from coal combustion flue gas by chloride-impregnated activated carbon. Fuel 2004, 83, 143–146. (15) Granite, E. J.; Pennline, H. W.; Hargis, R. A. Novel Sorbents for Mercury Removal from Flue Gas. Ind. Eng. Chem. Res. 2000, 39, 1020– 1029. (16) Korpiel, J. A.; Vidic, R. D. Effect of Sulfur Impregnation Method on Activated Carbon Uptake of Gas-Phase Mercury. EnViron. Sci. Technol. 1997, 31, 2319–2325. (17) Vidic, R. D.; Siler, D. P. Vapor-phase elemental mercury adsorption by activated carbon impregnated with chloride and chelating agents. Carbon 2001, 39, 3–14.
10.1021/ef700358z CCC: $37.00 2007 American Chemical Society Published on Web 09/28/2007
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Table 1. Summary of Proximate Analysis, CHN, S, and Gross Calorific Value of the Samples sample
moisture (wt %)
ash (wt %)
volatile matter (wt %)
C (wt %)
N (wt %)
H (wt %)
O (wt %)
S (wt %)
calorific value (Btu lb-1)
CW C8E2 E5C5 E8C2 E-coal
10.6 9.7 8.4 7.1 6.2
26.6 23.2 18.0 12.8 9.4
54.7 50.6 44.5 38.3 34.2
29.1 36.7 48.2 59.6 67.2
3.4 3.0 2.5 1.9 1.5
5.1 5.2 5.3 5.3 5.4
35 30.8 24.4 18.0 13.8
0.8 1.2 1.8 2.4 2.8
5166 6556 8642 10727 12118
the PAC injection technology. A solution for overcoming the problem of cost is to use an inexpensive material with high carbon content, such as industrial or agricultural wastes. The authors have prepared coal-like material from apple pomace19 and also reported on the preparation of chicken waste woodceramics, i.e., a so-called inexpensive c/c composite produced from plant-originated carbon, which showed good potential of capturing mercury.20 Recently, chicken waste was characterized by proximate, absolute, and elemental analyses, and furthermore, the decomposition in nitrogen and combustion were studied using evolved gas analysis.21,22 The results also showed that chicken waste is a raw material candidate for activated carbon; i.e., it is a carbonaceous material high in calcium content that may be suitable for providing activated carbon sites to trap mercury. Furthermore, woodceramics produced from chicken waste showed selectivity in adsorption behavior, which suggested chicken waste to favor dominance of chemical adsorption.23 However, to the authors’ knowledge, no activated carbon has been produced from chicken wastes. Accordingly, the present study is concerned with the preparation of AC from chicken waste (CW) and coal by the carbonization in a nitrogen atmosphere followed by activation in a steam atmosphere. The yields, specific surface area, pore volume, and pore size of the products are determined. The effects of carbonization and activation temperature on these properties are also studied. Thermal weight loss behaviors of char and AC samples were investigated and used to deduce the formation of char or AC at varied preparation conditions. The specific surface area is obtained as a function of the CW/coal blend ratio. Experimental Section Sample Preparation. Chicken waste (CW) (below 0.08 mm in particle size, which was prepared by drying, grinding, and sieving with 200-mesh sieve21) and high-sulfur coal (E-coal) were used as the starting material, and CW was blended with coal at different ratios by weight of 2:8, 5:5, and 8:2 to obtain samples C2E8, C5E5, and C8E2, respectively. The samples were characterized using the American Society for Testing and Materials (ASTM) method D5373 for carbon, hydrogen, and nitrogen using a LECO CHN-2000. Likewise, sulfur was determined instrumentally using a LECO SC(18) Lee, J. L.; Seo, Y. C.; Jurng, J.; Lee, T. G. Removal of gas-phase elemental mercury by iodine- and chlorine-impregnated activated carbons. Atmos. EnViron. 2004, 30, 4887–4893. (19) Ozao, R.; Pan, W.-P.; Whitely, N.; Okabe, T. Coal-like Thermal Behavior of a Carbon-Based Environmentally Benign New Material: Woodceramics. Energy Fuels 2004, 18, 638–643. (20) Ozao, R.; Okabe, T.; Nishimoto, Y.; Cao, Y.; Whitely, N.; Pan, W.-P. Gas and Mercury Adsorption Properties of Woodceramics Made from Chicken Waste. Energy Fuels 2005, 19, 1729–1734. (21) Whitely, N.; Ozao, R.; Cao, Y.; Pan, W.-P. Multi-utilization of Chicken Litter as a Biomass Source. Part II. Pyrolysis. Energy Fuels 2006, 20, 2666–2671. (22) Whitely, N.; Ozao, R.; Artiaga, R.; Cao, Y.; Pan, W.-P. Multiutilization of chicken litter as biomass source. Part I. Combustion. Energy Fuels 2006, 20, 2660–2665. (23) Ozao, R.; Okabe, T.; Arii, T.; Nishimoto, Y.; Cao, Y.; Whitely, N.; Pan, W.-P. Gas adsorption properties of woodceramics. Mater. Trans. 2006, 46, 2673–2678.
432 in accordance with ASTM D4239. Instrumental procedures for proximate analysis were used following the ASTM method D5142 and utilizing a LECO TGA-601. The gross calorific value was determined using a LECO AC-350 bomb calorimeter following ASTM D5865. A Rigaku RIX-3001 XRF was used to determine the major and minor elemental composition following ASTM D4326. Preparation of Char and Activated Carbon. The temperatures for carbonization, preoxidation, or activation of the CW/coal or char samples were determined in the range between 300 and 550 °C based on the results obtained by TGA runs and kinetic analysis thereof.21 The experimental setup24 consisted of a 15 in. tube with 13/16 in. inside diameter inserted into an electric furnace. The weighed sample was put into this tube with quartz wool on both sides. The tube was heated to the desired temperature by the electric furnace via a temperature controller. For carbonization experiments, the weighed sample sat in a 427 °C nitrogen atmosphere for about 60 min. Similarly, the solid residues were tested on a TGA. On starting the carbonization, the furnace was set at a desired temperature. One quartz tube was filled with around 4.0 mg samples and blocked by quartz wool on the both sides. Before putting the tube into the heated furnace for carbonization, it was purged first by N2 flow (300 mL min-1) for around 15 min. After 60 min of carbonization, the tube was drawn out of the furnace, and gaseous N2 was flown through for cooling. Finally, char was collected 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. However, the condensable and gases fraction were not collected since the yields were very small. Thus-prepared char samples were activated by steam following the same procedure in the same reactor at 650 and 750 °C for 60 min. The water injection rate was 0.1 mL min-1 with a flow of N2 at 100 mL min-1. For mass production of activated carbon, however, further study is necessary using a scaled-up furnace using, e.g., a rotary kiln and the like. SEM Observation. The texture and pore structure were observed under a JEOL JSM 5400-LV scanning electron microscope (SEM). Thermogravimetric Analysis (TGA). To evaluate the thermal stability properties, about 20 mg each of the samples was subjected to TGA runs at a heating rate of 20 °C min-1 using a TA Instruments Hi-resolution TGA 2950 under air (Airgas compressed air (breathing grade), type I, grade D, 21% O2 certified) at a flow rate of 60 mL min-1. X-ray Diffraction (XRD) Analysis. The XRD analysis on the thus-prepared samples was made using a SCINTAG X’TRA AA85516 (ThermoARL) X-ray diffractometer equipped with a Peltier cooled Si solid detector. Monochromatized Cu KR1 (0.150 54 nm) was used as the radiation. Diffraction patterns were collected at 45 kV–40 mA, at 0.01° step and count time of 0.500 s over a range of 1.00°–90.00° (2θ), at a step scan rate of 1.20° min-1. Pore Structure Analysis. Specific surface area based on the Brunauer–Emmett–Teller model (SSABET) and the adsorption and desorption isotherms were obtained using nitrogen gas as adsorbate at 77 K or carbon dioxide gas at 273 K (ASAP 2020 accelerated surface area and porosimetry analyzer, Micromeritics Instrument Corp.). The total pore volume, V0, was calculated from the amount (24) Cui, H.; Cao, Y.; Pan, W.-P. J. Anal. Appl. Pyrolysis 2007, 80, 319–324.
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Figure 1. TGA curves and derivative weight curves for E-coal, CW, and their blended samples in a N2 atmosphere at a heating rate of 20 deg min-1. Table 2. Basic Composition for Char Samples Prepared at 427 °C (Dry Basis) sample
C, %
H, %
O, %
N, %
S, %
Cl, ppm
ash, %
CW char C8E2 char C5E5 char C2E8char 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
of gas adsorbed at relative pressure of 0.95, and the specific surface area, SSABET, was calculated using multipoint BET equation in the relative pressure range of 0.05–0.35.
Results and Discussion Sample Description. As described above, E-coal, a sulfurrich coal having particle size below 0.08 mm, was blended with CW at mixing ratios of 2:8, 5:5, and 8:2 by weight to obtain mixed samples denoted as E8C2, E5C5, and E2C8, respectively. The proximate analysis, CHN, S, and gross calorific value of E-coal and CW are given in Table 1 together with the blended samples. Figure 1 shows mass loss profiles for CW/coal samples in a N2 atmosphere.24 It is found that volatile releasing temperature is around 300 °C for CW and around 450 °C for coal, at which point the devolatilization rate reaches its maximum. For blended samples, two peaks appear near 300 and 450 °C on the DTG curves. Increasing the coal content in the blending samples causes the peak around 300 °C to shrink, while the peak around 450 °C increased in size. The blending samples have the both characteristics of coal and CW, so that more CW content results more volatile matters emission at low temperature. By TGA, the cooperation effect was also not found for the mixture of CW/coal in a N2 atmosphere. The basic composition of char samples prepared at 427 °C are listed at Table 2. With increasing CW contents in the blending samples, ash, N, and Cl contents of char samples increase. It shows that char samples remain the original characteristics after carbonization either from coal or chicken waste. Less carbon content and increased ash content indicate that CW char is not a suitable precursor for activated carbon. However, a certain amount of coal blended with CW can increase carbon content and decrease ash content. Increasing coal content also increases the content of S while decreasing that of Cl. Specific surface area as obtained according to BET model, SSABET, of CW, which was 3.90 m2 g-1 as measured at 77 K
Figure 2. (a) SEM photograph of carbonized E-coal (magnification 200×). (b) SEM photograph of carbonized E-coal (magnification 10000×).
using N2 as adsorbate, increased to 7.79 m2 g-1 by carbonization. However, the SSABET of the char obtained from E-coal decreased from 8.55 to 0.50 m2 g-1. This is due to insufficient evolution of volatiles as above described. The pore structure and size vary depending on the conditions of activation.25 By using steam as the activating agent for thermal activation, the porous structure of the char is enhanced according to the following reaction: C + H2O ) CO + H2. The activation temperature was determined on the TG and DTG curves of the carbonized samples obtained by heating in N2 at 427 °C for 60 min. Generally, the reactivity of the char is partly attributed to the change in surface area and increases with the O/C ratio of the precursor. Thus, the highest rate of reaction as observed on DTG curve was 600 °C for blended samples and around 700 °C for the CW sample.24 Since no great difference was observed among the temperature conditions of 650 and 750 °C, the activation temperature was set to 650 °C. Parts a and b of Figure 2 show the SEM photograph at 200× and 10 000× magnification, respectively, of the activated carbon obtained from E-coal. Carbonization and activation of coal result in fine particles that are adhered on the surface of larger particles. This can be explained by referring again to Figure 1. The coal pyrolysis occurs rapidly with gas evolution at a higher temperature, thus destroying partially the original coal structure. On the other hand, volatiles are gradually released at a lower and wider temperature range. Thus, the sample consists of larger particles that are partly porous, as shown in the SEM photographs of parts a and b of Figure 3, which are obtained at 200× (25) Mui, E. L. K.; Ko, D. C. K.; McKay, G. Production of active carbons from waste tyres––a review. Carbon 2004, 42, 2789–2805.
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Figure 5. Adsorption isotherm of N2 on C5E5 at 77 K.
Figure 6. Specific surface area (m2 g-1) (as determined by BET using N2 as the adsorbent), SSABET, as a function of the coal fraction, x. Table 3. Specific Surface Area (BET Method Using N2 and CO2 as Adsorbent at 273 K) and Average Pore Diameter of the Activated Carbons Figure 3. (a) SEM photograph of carbonized C5E5 (magnification 200×). (b) SEM photograph of carbonized C5E5 (magnification 10 000×).
N2
pore specific pore specific coal surface area: diameter surface area: diameter (nm) SSABET (m2/g) (nm) sample fraction SSABET (m2/g) CW C8E2 C5E5 C2E8 E-coal
Figure 4. XRD patterns of the AC samples.
and 10 000× magnification, respectively. Since CW is higher in volatile content, volatiles are evolved at a lower temperature than pure coal, and these gases likely form pores with complicated structure. Figure 4 shows the XRD patterns of the AC samples. E-coal and CW both contain silica as the mineral matter (e.g., (101) diffraction peak observed at 2θ ) 26.6° and (100) at 2θ ) 21.0°). CW furthermore has sharp peaks at 2θ ) 28.2°, 31.2°, 40.2°, and 49.9°, which may be attributed to boehmite (alumina monohydrate) or calcite. Figure 5 shows an adsorption–desorption isotherm of N2 on C5E5 at 77 K. The isotherm is typical of type V and exhibits hystheresis due to filling the pores by capillary condensation in mesopores.26 Thus, the activated carbon not only has micropores
CO2
0 0.2 0.5 0.8 1
128 203 235 248 250
2.78 2.27 2.23 1.30 1.68
164.2 203.6 230.0 247.0 263.9
1.04 1.27 1.30 1.30 1.35
(pores with internal width of less than 2 nm) but also mesopores (pores with internal width between 2 and 50 nm). The original C5E5 had a specific surface area of 4.06 m2 g-1. After carbonization at 427 °C for 60 min, its surface area remained almost constant at 3.33 m2 g-1. However, its specific surface area was dramatically increased to 235 m2 g-1 after activation at 650 °C for 30 min, which was attributed to the development of microporous and mesoporous structure. Accordingly, the average pore diameter increased from the original 8.14 to 14.7 nm by carbonization but decreased to 2.23 nm with the development of micro- and mesopores. Table 3 summarizes the pore properties of the activated carbon samples. The specific surface area of the ACs increase with increasing E-coal. The AC produced from E-coal consist of fine particles, as stated above, and this may account for a larger specific surface area. Furthermore, CW contain additional mineral matter, and this may partly account for decreasing the specific surface area of the ACs prepared from CW. Since CO2 molecules are accessible to micropores having wedgelike structure, the specific surface area is increased for (26) Sing, K. S. W.; Everett, D. H.; Haul, R. A.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Reporting Physisorption data for gas/solid systems with special reference to the determination of surface area and porosity. Pure Appl. Chem. 1985, 57, 603–619.
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m2 g-1. This provides an empirical estimation of SSABET for CW/coal blend activated carbons according to the following equation: (1) SSABET ) -65.8x2 + 158x + 168 2 -1 where SSABET is the specific surface area in m g as determined by BET method using CO2 as the adsorbent, and x is the coal fraction by weight in the CW/coal blend ranging from 0.0 to 1.0 (e.g., x ) 0.0 signifies the blend contains no coal, and x ) 1.0 signifies the blend consists of 100% coal). Conclusions 2
-1
Figure 7. Specific surface area (m g ) (as determined by BET using CO2 as the adsorbent), SSABET, as a function of the coal fraction, x.
all the samples by using CO2 as the adsorbent. The pore diameter as obtained with N2 as the adsorbent is larger for CW but is smaller for E-coal. However, this trend is reversed in case CO2 is used as the adsorbent. This indicates that pores with complicated structure is formed in ACs using CW, which may be beneficial for capturing smaller molecules. Figure 6 shows the specific surface area (m2 g-1) (as determined by BET using N2 the adsorbent), SSABET, as a function of the coal fraction, x. Similarly, Figure 7 shows SSABET obtained by using CO2 adsorbent as a function of the coal fraction, x. The values are indicated with an allowance1 of (25
Activated carbons (ACs) were prepared from chicken waste and coal by carbonization in nitrogen atmosphere at ca. 430 °C for 60 min and successive steam activation at 650 °C for 30 min. Because chicken waste is low in sulfur content but is high in volatile matter (∼55 wt %), ACs with higher specific surface area were more successfully obtained by mixing with coal. The specific surface area of CW/coal blend AC can be estimated by SSABET ) -65.8x2 + 158x + 168, where SSABET is the specific surface area in m2 g-1 as determined by the BET method using CO2 as the adsorbent, where x is the coal fraction by weight in the CW/coal blend ranging from 0.0 to 1.0. Acknowledgment. This work is supported by the USDA-ARS Project No. 6406-12630-002-02S. EF700358Z
