ARTICLE pubs.acs.org/IECR
Effect of Microwave Treatment on Structural Changes and Gasification Reactivity of Petroleum Coke Xin Liu, Zhi-jie Zhou,* Bao-shen Zhang, Lu Chen, and Fu-chen Wang Key Laboratory of Coal Gasification, Ministry of Education, East China University of Science and Technology, Shanghai 200237, People's Republic of China ABSTRACT: The gasification reactivity of petroleum coke, which was treated by microwave at different times, powers, and temperatures, was investigated by using thermogravimetric analysis (TGA) at 1473 K at atmospheric pressure. The results showed that the gasification rate of petroleum coke increased with the increase of conversion and then decreased after reaching its maximum; the conversion corresponding to the maximal gasification rate is about x = 0.1. The gasification rate of petroleum coke increased with the increase of microwave irradiation time and irradiation power, but as the irradiation temperature increased, the gasification rate of petroleum coke first increased and then decreased. Petroleum coke before and after microwave treatment was analyzed by X-ray diffraction (XRD), infrared absorption spectroscopy (IR), and the accelerated surface area and porosimetry system (ASAP). The results showed that the crystalline structure of petroleum coke becomes amorphous and the BET surface area and pore volume become larger with increase of microwave irradiation time and irradiation power. As the irradiation temperature increased, the crystalline ordering degree of petroleum coke became weakened and then strengthened and the BET surface area and pore volume increased and then decreased, which agrees with the change in the petroleum coke gasification reaction rate. Results show that microwave treatment is an effective way to change the structure of petroleum coke and promote its gasification reactivity.
1. INTRODUCTION Petroleum coke is the final byproduct during the refining process in delay-coke equipment. With the continuous increase of heavy crude in worldwide supply and the development of the petroleum deep conversion process, the output of petroleum coke is steadily increasing.1,2 Some reports37 on the gasification of petroleum coke have been already published. However, the dull reactivity of petroleum coke is still a problem for industry application mainly because of the high carbon hydrogen ratio, the low content of combustible volatiles, and ash. It is critical to improve the gasification reactivity of petroleum coke. However, most reports have investigated noncatalytic or catalytic gasification of petroleum coke,811 and there are few reports on improving the gasification reaction rate by changing its structural characteristics. As a convenient, efficient, and clean new technology, microwave radiation has the virtues of rapid heating, high thermal efficiency, being clean and pollution-free, and easy automatic control by contrast with conventional heating.12 It can improve the reaction conditions, increase the reaction speed, and increase the yield. In addition, it can promote a number of reactions which were originally difficult to carry out.13,14 The microwave technique has been applied in the determination of moisture, in desulfurization,15 and in the preparation of activated carbon16 in coal gasification. However, there are few reports about the use of the microwave technique in the gasification of petroleum coke by changing its structural characteristics. The purpose of the present work is to study the effect of microwave treatment on structural changes and gasification reactivity of petroleum coke. r 2011 American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Materials. Petroleum coke obtained from Jinling Refinery Plant in Nanjing, China, with a particle size range of 83165 μm was chosen for this study. The WX-4000 microwave digestion system (Shanghai Yiyao Analytical Instruments Corp.) was used for sample preparation. The instrument is mainly composed of a pressure measurement and pressure control system, a temperature measurement and control system, and a high pressure digestion tank. Prepared samples with water as polar medium were poured into the digestion tank, with the volume from nearly one-third to one-half of the tank, and then were put into the microwave digestion system. The experiment was carried out after setting different microwave irradiation times (12, 14, 16 min), temperatures (373, 388, 398 K), and powers (300, 500, 700 W). The treated samples were used for gasification after drying at 378 K to take out the moisture content. The proximate and ultimate analyses of petroleum coke before and after microwave treatment are shown in Table 1. Table 1 shows that petroleum coke after microwave treatment still has characteristics of high carbon content, high sulfur content, low ash content, and low volatiles content in comparison with coal. 2.2. Physical Gas Adsorption. The specific surface area of the samples studied was measured by means of the adsorptive method. The adsorption of N2 at liquid nitrogen temperature (77 K) was achieved for samples in ASAP2020 Micromeritics Received: April 7, 2011 Accepted: June 20, 2011 Revised: May 27, 2011 Published: June 20, 2011 9063
dx.doi.org/10.1021/ie2007328 | Ind. Eng. Chem. Res. 2011, 50, 9063–9068
Industrial & Engineering Chemistry Research
ARTICLE
Table 1. Proximate and Ultimate Analyses of Petroleum Cokea proximate analysis/(%, d) treatment conditions
a
ultimate analysis/(%, d)
A
V
FC
C
H
O
N
S
untreated
0.46
14.01
85.53
86.17
5.92
2.18
1.36
4.36
373 K/12 min/300 W
0.25
14.10
85.65
86.16
4.84
3.25
1.37
4.38
373 K/14 min/300 W
0.33
14.17
85.50
85.86
5.47
2.75
1.38
4.54
373 K/16 min/300 W
0.29
13.38
86.33
86.15
4.94
2.97
1.39
4.56
373 K/12 min/500 W
0.41
13.99
85.60
86.23
4.40
3.44
1.42
4.51
373 K/12 min/700 W
0.36
13.77
85.87
86.15
4.70
3.24
1.38
4.52
388 K/12 min/300 W
0.43
13.94
85.63
85.83
4.12
3.88
1.38
4.80
398 K/12 min/300 W
0.42
15.33
84.25
86.10
5.93
1.90
1.36
4.70
A, ash; V, volatiles; FC, fixed carbon; d, dry basis.
(Micromeritics Instrument Corp.). The SBET values were calculated from the linear form of the BrunauerEmmettTeller equation,17 and the pore diameter, pore volume, and its distribution were calculated by the BarrettJoynerHalenda (BJH)18 calculation method. 2.3. FTIR Spectroscopy. All Fourier transform infrared spectroscopy (FTIR) was conducted by use of a NEXUS6700 spectrometer manufactured by the American Nicolet Co. The samples were mixed with potassium bromide for quantitative analyses. 2.4. X-ray Diffraction (XRD) Analysis. Aromatic structure analyses of petroleum coke were performed by means of an X-ray diffraction (XRD) spectrometer with monochromatic Cu KR radiation (40 kV, 100 mA) and a step size of 0.1° over the angular 2θ range 1080° and a scan rate of 2°/min. The mean interlayer spacing of the aromatic sheets following the Bragg law (eq 1), the height of aromatic layers (Lc) deduced from the Scherrer formula (eq 2), and the crystallite size (La) deduced from the Scherrer formula (eq 3) were calculated from band (002): d002 ¼
λ 2 sinðθ002 Þ
ð1Þ
0:94λ Lc ¼ β002 cosðθ002 Þ
ð2Þ
1:84λ β002 cosðθ002 Þ
ð3Þ
La ¼
where θ is the Bragg angle of the diffraction maximum, λ = 1.5418 Å; β represents the angular width of the (002) band at half-height corrected for the natural angular breadth of the line for a well-crystallized specimen.19 2.5. Gasification Reactivity. The gasification reactivity of the petroleum coke was determined using a thermogravimetric analyzer (TGA) at 1473 K. The sample was heated in N2 at a constant rate of 25 K/min, and then N2 was replaced by CO2 when the desired temperature was reached. After internally compensating for the thermal expansion of the balance arm and for buoyancy, the results of each TGA test were saved in the form of a data-logging file. In this file, the weight value in milligrams was tabulated as a function of time. The conversion is defined as m0 m ð4Þ X ¼ m0 ð1 Aad Þ
Figure 1. XRD spectra of petroleum coke treated at different conditions: (a) untreated; (b) 373 K/12 min/300 W; (c) 373 K/14 min/300 W; (d) 373 K/16 min/300 W; (e) 373 K/12 min/500 W; (f) 373 K/12 min/700 W; (g) 388 K/12 min/300 W; (h) 398 K/12 min/300 W.
where m0 is the initial mass of sample, m is the mass of sample at gasification time t, and Aad is the content of ash in the sample. r ¼
dx dt
ð5Þ
3. RESULTS AND DISCUSSION 3.1. Effect of Microwave Treatment on Microcrystalline Structure of Petroleum Coke. Due to the high ratio of C/H,
petroleum coke is composed of polycyclic aromatic hydrocarbons and is rich in aromatics with many rings.20 The compounds in petroleum coke are varied according to the different amounts of rings in the aromatics. Figure 1 shows the XRD spectra of petroleum coke treated at different irradiation times, powers, and temperatures. The effect of microwave irradiation on the degree of graphitization of petroleum coke before and after microwave treatment can be seen. The crystal parameters are analyzed and calculated by the Scherrer equation,21 which has been confirmed to be suitable for graphite-like materials.22 It can be concluded that the change in the diffraction peak (002) is small; interplanar crystal spacing is all close to 3.352 Å, the interplanar crystal spacing of amorphous graphite. Figure 2 shows that, with the increase of microwave irradiation time and power, the diffraction peak (002) shifted to low angle which indicated that the layer structure of petroleum coke has 9064
dx.doi.org/10.1021/ie2007328 |Ind. Eng. Chem. Res. 2011, 50, 9063–9068
Industrial & Engineering Chemistry Research
ARTICLE
Figure 2. Crystal structure parameters of petroleum coke at different treatment conditions: (a) crystal structure parameters at different microwave irradiation times; (b) crystal structure parameters at different microwave irradiation powers; (c) crystal structure parameters at different microwave irradiation temperatures.
Table 2. BET Surface Area and Pore Volume of Petroleum Coke at Different Treatment Conditions treatment conditions
SBET/(m2 3 g1) Vp/(103 cm3 3 g1) pore size/(nm)
untreated
1.182
5.95
21.816
373 K/12
1.625
8.43
21.045
373 K/14
1.675
8.77
21.817
min/300 W 373 K/16
1.764
9.26
21.793
1.623
8.00
20.610
1.778
8.14
19.191
388 K/12
1.794
9.49
22.063
min/300 W 398 K/12
1.738
8.92
21.408
min/300 W
min/300 W 373 K/12 min/500 W 373 K/12 min/700 W
min/300 W
changed and intermolecular forces weaken in the direction of d002. As the treatment time and power increases, the interplanar crystal spacing becomes larger, and the Lc and La decrease, which shows that the structure of petroleum coke trends to an amorphous state. However, as the microwave irradiation temperature increased, the interplanar crystal spacing first increased and then decreased, and Lc and La decreased and then increased, which indicates that the crystalline ordering
Figure 3. FTIR spectra of petroleum coke treated at different conditions: (a) untreated; (b) 373 K/12 min/300 W; (c) 373 K/14 min/300 W; (d) 373 K/16 min/300 W; (e) 373 K/12 min/500 W; (f) 373 K/12 min/700 W; (g) 388 K/12 min/300 W; (h) 398 K/12 min/300 W.
degree of petroleum coke became weakened and then strengthened. 3.2. Effect of Microwave Treatment on BET and Pore Structure of Petroleum Coke. Table 2 shows that microwave irradiation can increase the BET surface area and enlarge the pore volume of petroleum coke. As the microwave irradiation time and power increased, the BET surface area and pore volume increased. It is well-known that the microwave activation rate is fast; as a result, the microwave treatment can develop the porous structure. Microwave irradiation time and power are both propitious to pore formation. However, the BET surface area and pore volume at a microwave irradiation temperature of 388 K 9065
dx.doi.org/10.1021/ie2007328 |Ind. Eng. Chem. Res. 2011, 50, 9063–9068
Industrial & Engineering Chemistry Research are larger than at other microwave irradiation temperatures. The reason is that micropores may appear with an increase of microwave irradiation temperature, but with a further increase of microwave irradiation temperature, the formed micropores and mesopores collapsed and became larger, resulting in a decrease of BET surface area and shrinking of pore volume. Hence, 388 K is a more suitable temperature compared to other temperatures for the pore structural change of petroleum coke. The structure of petroleum coke became fluffy and pore volume increased, which resulted in oxidants being possibly easier to enter the macromolecular structure of petroleum coke, and an increased effective contact area between petroleum coke and oxidants, leading to the increase in the chance of chemical reactions.23 3.3. Effect of Microwave Treatment on Functional Groups of Petroleum Coke. In order to understand the effects of
Figure 4. Gasification rate (r) vs conversion (x) of petroleum coke with different treatment methods.
ARTICLE
microwave treatment on functional groups of petroleum coke, treated and untreated cokes were measured by FTIR spectroscopy. From the results of Figure 3, it can be seen that there are mainly five peak districts in the spectrum of petroleum coke:2426 (1) OH stretching vibration peak around 3400 cm1, (2) aromatic CH stretching vibration peak between 3000 and 3100 cm1, (3) aliphatic CH symmetric and asymmetric stretching vibration peak between 2800 and 3000 cm1, (4) oxygen-containing functional groups and the functional groups such as the CC skeleton in benzene ring absorption peak between 1000 and 1800 cm1, and (5) CH deformation vibration absorption peak between 750 and 880 cm1. Figure 3a shows that, as an important part of petroleum coke, the aromatic structure is mainly around 3030 cm1 on the aromatic CH skeleton stretching vibration absorption peak, 1600 cm1 around the aromatic CdC stretching vibration absorption peak, and 750880 cm1 of the aromatic face of the CH outside the absorption peaks of deformation. Although NH2 groups also have absorbed in the region around 3400 cm1, they have little effect on results because the nitrogen content in petroleum coke is very low. The absorption peak around 2020 and 2851 cm1 is CH2 and CH3 stretching vibration absorption. As time, power, and temperature increased, the OCO absorption peak around 1160 cm1 emerged, which is ether linkage; it builds the structural complexity of petroleum coke. It also can be seen that microwave irradiation cannot provide enough energy to break up typical chemical bonds, such as the CC, CO, or CH bonds. The OH stretching vibration peak is sharper with the increase of irradiation time and power, which indicates that the petroleum coke is composed of dimer hydroxide, without long chains of polymer ordered structure, and showing a certain disordered
Figure 5. Gasification rate (r) vs conversion (x) of petroleum coke treated under different conditions at 1473 K: (a) gasification treatment at different microwave irradiation times; (b) gasification treatment at different microwave irradiation powers; (c) gasification treatment at different microwave irradiation temperatures. 9066
dx.doi.org/10.1021/ie2007328 |Ind. Eng. Chem. Res. 2011, 50, 9063–9068
Industrial & Engineering Chemistry Research
Figure 6. Pore change of petroleum coke (373 K, 12 min, 300 W) treated at different conversions.
state. Some studies27 suggest that microwave irradiation treatment can remove some oxygen-containing functional groups in the form of CO or CO2, with lots of active center remaining, which is easier to contact with a gasifying agent. Therefore, it is an effective way to treat petroleum coke by microwave radiation, which can provide energy and contact area for petroleum coke and amboceptor. 3.4. Effect of Microwave Treatment on Gasification Reactivity of Petroleum Coke. In order to exclude the water heated effect on the petroleum coke, the petroleum coke was heated by water at a temperature of 388 K using a conventional heating method under the same experimental conditions. We make a comparison with the results using microwave heating. The gasification reactivity curve of untreated petroleum coke is essentially coincident with that of the water heated petroleum coke. The results of Figure 4 show that the water heated method has almost no effect on the gasification of petroleum coke. It can be seen from Figure 5 that microwave treatment has improved the gasification reactivity of petroleum coke at different irradiation times, powers, and temperatures. Also, the gasification reactivity of petroleum coke increased with the increase of microwave irradiation time and microwave irradiation power, but as the irradiation temperature increased, the gasification rate first increased and then decreased. Figure 5a shows that the longer the irradiation time is, the faster the gasification rate is. Probably the enhanced amorphous state of treated petroleum coke promoted the gasification reactivity rate from the results of XRD and FTIR spectroscopy. Otherwise, the treated petroleum coke has a larger BET surface area and pore volume than untreated petroleum coke, and with the increase of microwave irradiation time, the BET surface area and pore volume increased, which also explains the gasification rate trends. Figure 5b shows that the greater the irradiation power is, the faster the gasification rate is. It is wellknown that enhanced power is in favor of chemical reactions. Therefore, the experimental phenomenon is due to the heating rate increasing with the microwave irradiation power; meanwhile, the pyrometric effect is more evident. The results of XRD, FTIR spectroscopy, and adsorption correspond with gasification experimental results. Figure 5c shows that as the irradiation temperature increased, the gasification rate first increased and then decreased, but all were superior to those for untreated petroleum coke. From the results of XRD and ASAP, it could be seen that the amorphous state was enhanced and the pore structure flourished with the increase of microwave temperature between 373 and 388 K. However, the degree of
ARTICLE
ordering was enhanced, pores collapsed, and the pore volume decreased because of a certain degree of heat expansion of the microcrystalline structure when the temperature exceeded 388 K. In order to avoid experimental error and to maintain the quality of the observation, the sample was prepared and then tested three times. The experiment shows that microwave irradiation temperature has an obvious effect on the gasification reaction rate of petroleum coke, and 388 K is the most suitable temperature for microwave irradiation of petroleum coke. Figure 5 shows that the gasification rate of coke increased with the increase of coke conversion and then decreased after reaching its maximum. The conversion corresponding to the maximal gasification rate is about x = 0.1. Some researchers28,29 have investigated that the gasification rate is closely related to the pore structure of particles. They claim that the occurrence of the maximal gasification rate can be explained by a low initial porosity. In the initial stage, the opened pores which were first isolated in the solid are becoming accessible during the coke consumption; thus an increase of accessible surface area causing the increase of gasification rate with gasification conversion is observed. However, the pore increment cause pore collapse and the decrease of surface area and pore volume, resulting in the decrease of gasification rate. The small initial porosity of petroleum coke shown in Table 2 is in good agreement with the explanation of previous research, which is the main reason for the occurrence of maximal gasification rate. Treated petroleum coke has the same experimental phenomena as untreated petroleum coke. In order to confirm the experimental results, the pore structural change of microwave-treated petroleum coke at different gasification conversions was tested, and the results are shown in Figure 6. It can be seen that the BET surface area and pore volume reach a maximum at the conversion x = 0.1, which is in accordance with the change of gasification rate. Microwave irradiation can open closed pores and cause the formation of new micropores.30,31 However, a mass of closed pores are still not opened, and the gasification rate reaches its maximum when the BET surface area and pore volume of treated petroleum coke reach their maximum.
4. CONCLUSIONS 1. Microwave irradiation is a potential way for promoting gasification of petroleum coke. The degree of amorphous state and pore volume increased with the increase of microwave irradiation time and power, but first increased and then decreased with the increase of microwave irradiation temperature. 2. The gasification activity of petroleum coke increased with the increase of microwave irradiation time and power, but as the irradiation temperature increased the gasification rate increased and then decreased while the temperature exceeded 388 K. The gasification rate of petroleum coke increased with the increase of coke conversion and then decreased after reaching its maximum; the conversion corresponding to the maximal gasification rate is about x = 0.1. It is closely due to the pore structure of petroleum coke during the gasification process. In brief, longer microwave irradiation time and higher power are in favor of gasification, but high microwave irradiation temperature does not contribute to gasification of petroleum coke. ’ AUTHOR INFORMATION Corresponding Author
*Tel.: +86 21 6425 2974. Fax: +86 21 6425 1312 E-mail:
[email protected]. 9067
dx.doi.org/10.1021/ie2007328 |Ind. Eng. Chem. Res. 2011, 50, 9063–9068
Industrial & Engineering Chemistry Research
’ ACKNOWLEDGMENT The research is supported by the National Key State Basic Research Development Program of China (973 Program, 2010 CB 227000), the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT-IRT 0620), and the Shanghai Outstanding Academic Leaders Subsidy Scheme (08 XD 1401300). X.L. would like also to thank Fu Wang for conducting experiments. ’ REFERENCES (1) Wang, J.; Anthony, E. J.; Abanades, J. C. Clean and Efficient Use of Petroleum Coke for Combustion and Power Generation. Fuel 2004, 83, 1341–1348. (2) Zhan, X. L.; Jia, J.; Zhou, Z. J.; Wang, F. C. Influence of Blending Methods on the Co-Gasification Reactivity of Petroleum Coke and Lignite. Energy Convers. Manage. 2011, 52 (4), 1810–1814. (3) Ginter, D.; Somorjai, G.; Heinemann, H. Factors Affecting the Reactivity of Chars and Cokes During Low-Temperature Steam Gasification. Energy Fuels 1993, 7 (3), 393–398. (4) Revankar, V.; Gokarn, A.; Doraiswamy, L. Studies in Catalytic Steam Gasification of Petroleum Coke with Special Reference to the Effect of Particle Size. Ind. Eng. Chem. Res. 1987, 26 (5), 1018–1025. (5) Zou, J. H.; Zhou, Z. J.; Wang, F. C.; Zhang, W.; Dai, Z. H.; Liu, H. F.; Yu, Z. H. Modeling Reaction Kinetics of Petroleum Coke Gasification with CO2. Chem. Eng. Process. 2007, 46 (7), 630–636. (6) Zou, J. H.; Yang, B. L.; Gong, K. F.; Wu, S. Y.; Zhou, Z. J.; Wang, F. C.; Yu, Z. H. Effect of Mechanochemical Treatment on Petroleum Coke-CO2 Gasification. Fuel 2008, 87 (6), 622–627. (7) Trommer, D.; Steinfeld, A. Kinetic Modeling for the Combined Pyrolysis and Steam Gasification of Petroleum Coke and Experimental Determination of the Rate Constants by Dynamic Thermogravimetry in the 500-1520 K Range. Energy Fuels 2006, 20 (3), 1250–1258. (8) Yoon, S. J.; Choi, Y. C.; Lee, S. H.; Lee, J. G. Thermogravimetric Study of Coal and Petroleum Coke for Co-Gasification. Korean J. Chem. Eng. 2007, 24 (3), 512–517. (9) Fermoso, J.; Arias, B.; Plaza, M. G.; Pevida, C.; Pis, J. J.; Garcia-Pena, F.; Casero, P. High-Pressure Co-Gasification of Coal with Biomass and Petroleum Coke. Fuel Process. Technol. 2009, 90, 926–932. (10) Lee, S. H.; Choi, C. S. Chemical Activation of High Sulfur Petroleum Cokes by Alkali Metal CompoundsJ. Fuel Process. Technol. 2000, 64, 141–153. (11) Zhan, X. L.; Zhou, Z. J.; Wang, F. C. Catalytic Effect of Black Liquor on the Gasification Reactivity of Petroleum Coke. Appl. Energy 2010, 87 (5), 1710–1715. (12) Ma, L. H.; Paul, D. L.; Pothecary, N.; Railton, C.; Bows, J.; Barratt, L.; Mullin, J.; Simons, D. Experimental Validation of a Combined Electromagnetic and Thermal FDTD Model of a Microwave Heating Process. IEEE Trans. Microwave Theory Tech. 1995, 43 (11), 2565–2572. (13) Chen, H.; Li, J. W.; Lei, Z.; Ge, L. M. Microwave-assisted Extraction of Shenfu Coal and its Micromolecule Structure. Min. Sci. Technol. 2009, 19, 19–24. (14) Lester, E.; Kingman, S. The Effect of Microwave Pre-heating on Five Different Coals. Fuel 2004, 83, 1941–1947. (15) Yang, Y. Q.; Cui, L. Y.; Mi, J. Analysis of Organic Sulfur Forms in Coals by Extraction under Ultrasonic and Microwave. Coal Convers. 2006, 29, 8–11. (16) He, X. J.; Lei, J. W.; Geng, Y. G.; Zhang, X. Y.; Wu, M. B.; Zheng, M. D. Preparation of Microporous Activated Carbon and Its Electrochemical Performance for Electric Double Layer Capacitor. J. Phys. Chem. Solids 2009, 70, 38–744. (17) Yan, J. M.; Zhang, Q. Y. Adsorption and Agglomeration. Solid Surface and Pore; Science Press: Beijing, 1986 (18) Barrett, E. P.; Joyner, L. G.; Halenda, P. P. The Determination of Pore Volume and Area Distributions in Porous Substances. Computations from Nitrogen Isotherms. J. Am. Chem. Soc. 1951, 73 (1), 373–380.
ARTICLE
(19) Jimenez, A.; Iglesias, M. J.; Laggoun, D. F.; Suarez, R. I. Effect of the Increase in Temperature on the Evolution of the Physical and Chemical Structure of Vitrinite. J. Anal. Appl. Pyrolysis 1999, 50 (2), 117–148. (20) Bayram, A.; Muezzinoglu, A.; Seyfioglu, R. Presence and Control of Polycyclic Aromatic Hydrocarbons in Petroleum Coke Drying and Calcination Plants. Fuel Process. Technol. 1999, 60 (2), 111–118. (21) Feng, B.; Bhatia, S. K.; Barry, J. C. Variation of the Crystalline Structure of Coal Char during Gasification. Energy Fuels 2003, 17 (3), 744–754. (22) Shi, H.; Reimers, J.; Dahn, J. Structure-Refinement Program for Disordered Carbons. J. Appl. Crystallogr. 1993, 26 (6), 827–836. (23) Tran, K. N.; Bhatia, S. K.; Tomsett, A. Air Reactivity of Petroleum Cokes: Role of Inaccessible Porosity. Ind. Eng. Chem. Res. 2007, 46 (10), 3265–3274. (24) Ibarra, J. V.; Munoz, E.; Moliner, R. FTIR Study of the Evolution of Coal Structure During the Coalification Process. Org. Geochem. 1996, 24, 725–735. (25) Painter, P. C.; Snyder, R. W.; Starsinic, M.; Coleman, M. M.; Kuehn, D. W.; Davis, A. Concerning the Application of FT-IR to the Study of Coal: A Critical Assessment of Band Assignments and the Application of Spectral Analysis Programs. Appl. Spectrosc. 1981, 35 (5), 475–485. (26) Chen, C.; Gao, J. S.; Yan, Y. J. Observation of the Type of Hydrogen Bonds in Coal by FTIR. Energy Fuels 1998, 12 (3), 446–449. (27) Wang, T. X.; Zong, Z. M.; Zhang, J. W.; Wei, Y. B.; Zhao, W.; Li, B. M.; Wei, X. Y. Microwave-assisted Hydroconversions of Demineralized Coal Liquefaction Residues from Shen and Shengli Coals. Fuel 2008, 87, 498–507. (28) Oboirien, B. O.; Engelbrecht, A. D.; North, B. C.; Cann, V. M.; Verryn, S.; Falcon, R. Study on the Structure and Gasification Characteristics of Selected South African Bituminous Coals in Fluidised Bed Gasification. Fuel Process. Technol. 2011, 92 (4), 735–742. (29) Sahimi, M.; Tsotsis, T. T. Statistical Modeling of Gas-Solid Reaction with Pore Volume Growth: Kinetic Regime. Chem. Eng. Sci. 1988, 43 (1), 113–121. (30) Liu, Q. S.; Zheng, T.; Wang, P.; Guo, L. Preparation and Characterization of Activated Carbon from Bamboo by MicrowaveInduced Phosphoric Acid Activation. Ind. Crops Prod. 2010, 31 (2), 233–238. (31) Deng, H.; Yang, L.; Tao, G. H.; Dai, J. L. Preparation and Characterization of Activated Carbon from Cotton Stalk by Microwave Assisted Chemical Activation—Application in Methylene Blue Adsorption from Aqueous Solution. J. Hazard. Mater. 2009, 166, 1514–1521.
9068
dx.doi.org/10.1021/ie2007328 |Ind. Eng. Chem. Res. 2011, 50, 9063–9068
