Energy & Fuels 2007, 21, 881-890
881
Factors That Influence the Extraction of Polycyclic Aromatic Hydrocarbons from Coal Jian Xue,† Guijian Liu,*,†,‡ Zhiyuan Niu,† Chen-Lin Chou,§ Cuicui Qi,† Liugen Zheng,† and Haoyuan Zhang† CAS Key Laboratory of Crust-Mantle Materials and EnVironments, School of Earth and Space Sciences, UniVersity of Science and Technology of China, Hefei 230026, China, Key Laboratory of Loess and Quaternary Geology, Institute of Earth and EnVironment, CAS, Xi’an, 710075 Shanxi, China, and Illinois State Geological SurVey (Emeritus), Champaign, Illinois 61820 ReceiVed NoVember 16, 2006. ReVised Manuscript ReceiVed January 24, 2007
Coal samples and carbonaceous mudstone were collected from the Huaibei coalfield, China, and experiments investigating the factors influencing the extraction of the sixteen US EPA (Environmental Protection Agency) priority polycyclic aromatic hydrocarbons (PAHs) were carried out. Different extraction times, solvents, and methods were used. Major interest was focused on finding optimum conditions for extracting the PAHs from coal. We conclude that (1) coal composition, including the H/C and O/C ratios, is an important factor for the distribution of PAHs in coals; (2) the total amount of EPA priority PAHs increases with increasing extraction time, 30 min being suitable for ultrasonic-assisted extraction and 24 h for Soxhlet extraction; (3) CS2 is effective in extracting low molecular weight PAHs, while CH2Cl2 is better for extracting high molecular weight PAHs (both are excellent extraction solvents vs hexane); (4) both Soxhlet and ultrasonic extraction showed a similar PAH concentration profile, but the ultrasonic method is less efficient.
1. Introduction The US Environmental Protection Agency1 has designated 16 polycyclic aromatic hydrocarbons (PAHs) as priority pollutants (Table 1). They were chosen for this study because (1) more information is available on these compounds than others; (2) they are potentially more harmful than other PAHs, and they exhibit harmful effects that are representative of the PAHs; (3) there is a greater chance of being exposed to these PAHs than to others in the environment; (4) of all the PAHs analyzed, these were the ones in the highest concentration at NPL (national priorities list) hazardous waste sites. In China, nine PAHs including benzo[a]pyrene were defined as priority PAHs by the State Environmental Protection Administration.2 The world consumption of coal is ca. 5800 million tons annually, of which ca. 75% is used for electricity generation and the remainder is used for industrial and domestic fuel. China is the largest coal producing and consuming country.3-4 Coal accounts for ca. 67% of the energy consumption,5 and more than 400 million people in China rely on it for domestic energy needs, such as heating and daily cooking. Due to the limited * Corresponding author. Tel.: +86-551-3603714. Fax:+86-551-3621485. E-mail address:
[email protected]. † University of Science and Technology of China. ‡ Institute of Earth and Environment. § Illinois State Geological Survey (Emeritus). (1) Code of Federal Regulation, Title 40, Part 60, subparts D, Da, Db, Dc; Environmental Protection Agency: Washington, DC, 1997; p 44. (2) Yue, M.; Gu, X.; Zou, H.; Zhu, R.; Su, W. J. Capital Normal UniV. (Nat. Sci. Ed.) 2003, 24, 40-44. (3) Liu, G. J.; Wang, G. L.; Zhang, W. Study on EnVironmental Geochemistry of the Trace and Minor Elements in Coal; China University of Mining and Technology Press. 1999. (4) Liu, G. J.; Peng, Z. C.; Wang, G. L.; Yang, P. Y.; Chou C. L. AdV. Earth Sci. 2002, 17, 53-62. (5) Chen, Y. J.; Bi, X.; Mai, B. X.; Sheng, G. Y.; Fu, J. M. Fuel 2004, 83, 781-790.
Table 1. Sixteen US EPA Priority PAHs ab
PAHs
rings
ab
PAHs
rings
Nap Acpy Acp Flu PHE Ant FL Pyr
naphthalene acenaphthylene acenaphyhene fluorine phenathrene anthracene fluoranthene pyrene
2 3 3 3 3 3 4 4
BaA CHR BbF BkF BaP IND DBA BghiP
benz[a]anthracene chrysene benzo[b]fluoranthene benzo[k]fluoranthene benzo[a]pyrene indeno[1,2,3,-cd]pyrene dibenz[a,h]anthracene benzo[ghi]perylene
4 4 5 5 5 6 6 6
petroleum and natural gas reserves and significant coal reserves (1000 billion tons) in China, it is likely that this coal-based, relatively cheap energy structure will continue for the foreseeable future.6-10 Because of incomplete combustion, a large amount of PAHs is emitted from coal. These PAHs can enter the human body via breathing polluted air or through the food chain. Various forms of PAHs in coals or from coal combustion may affect humans, especially with respect to indoor combustion. In industrial use, PAHs in coal can reduce or even poison the activity of catalysts in refineries, giving the stockpile of liquid products undesirable features (such as being allochromatic or showing color change, odor, etc.)11-13 Ezatti et al.14 estimated (6) Liu, G. J.; Yang, P. Y.; Peng, Z. C.; Chou, C. L. J. Asian Earth Sci. 2004, 23, 491-506. (7) Liu, G. J.; Zhang, H. Y.; Gao, L. F.; Zheng, L. G.; Peng, Z. C. Fuel Process. Technol. 2004, 85, 1635-1646. (8) Ni, B. Acta Geol. Sin. 2000, 74, 311-314. (9) Xu, X. C.; Chen, C.; Qi, H. Fuel Process. Technol. 2000, 62, 153160. (10) Zhong, T.; Yang, W. Fuel Process. Technol. 2000, 62, 137-141. (11) Chen, Y. J.; Sheng, G. Y.; Bi, X.; Feng, Y. L.; Mai, B. X.; Fu, J. M. EnViron. Sci. Technol. 2005, 39, 1861-1867. (12) Naikwadi, K. P.; Karasek, F. W.; Hatano, H. J. Chromatogr., A 1990, 511, 281-290. (13) Liu, G. J.; Zheng, L. G.; Duzgoren-Aydin Nurdan, S.; Gao, L. F. ReV. EnViron. Contam. Toxicol. 2007, 189, 89-106.
10.1021/ef0605753 CCC: $37.00 © 2007 American Chemical Society Published on Web 02/22/2007
882 Energy & Fuels, Vol. 21, No. 2, 2007
that, in 2000, global mortality due to indoor air pollution from using solid fuels (such as wood, charcoal, and crop residues, but mainly coal) would be >1.6 million. This lead of mortality, together with combustion-induced diseases such as pneumoconiosis, dermatosis, and other related diseases, indicates an urgent need to take immediate action to reduce indoor air pollution, especially in developing countries. Some research15-18 found that PAH emissions from coal combustion were one of the most important sources of PAHs in the environment. So, pollution, including PAHs, released from coal utilization processes are an important hindering factor for China’s economic and social development as well as for human health. Two problems need to be solved before approaching the study. The first one was how to extract PAHs from coal and coal combustion products. Up to now, traditional extraction methods have been used,19-25 including ultrasonic, Soxhlet, and other more modern techniques (supercritical fluid extraction, microwave extraction, etc.). For example, Purushothama et al.24 carried out an extraction of coal ash. The results showed that the highest recoveries were obtained using the reflux slurry extraction procedure with CH2Cl2 and a relatively fast (20 °/min) GC temperature ramp to 310 °C. Hageman et al.21 used water extraction and conventional extractions. Quantitative determination (recovery typically ranging from ∼60% to 140% as compared to conventional solvent extraction) of PAHs from soil and air particulate matter was achieved using a 250 °C extraction step and isotopically labeled PAHs as internal standards. The second problem is how to detect PAHs in the extraction. In earlier studies, extraction was performed using column chromatography with ultraviolet detection. Then came packed GC column techniques using Dexsil and poly(dimethylsiloxane).26-29 Since the 1990s, analytical methods have been changing progressively. UV-visible absorption spectrometry was utilized as a general technique for analysis of organic particulate material in ambient samples.30 At the same time, the technique of fluorescence spectrometry was developed for PAH determination31. Then, liquid chromatography has been (14) Ezzati, M.; Lopez, A. D.; Rodgers, A.; Vander Hoorn, S.; Murray, C. J. Lancet 2002, 360, 1347-1360. (15) Durlak, S. K.; Biswas, P.; Shi, J. Mernhard, M. J. EnViron. Sci. Technol. 1998, 32, 2301-2307. (16) Mastral, A. M.; Calle´n, M. S. EnViron. Sci. Technol. 2000, 34, 3051-3056. (17) Su, M.-C.; Christensen, E. R.; Karls, J. F. EnViron. Pollut. 1998, 98, 411-419. (18) Simcik, M. F.; Eisenreich, S. J.; Lioy P. J. Atmos. EnViron. 1999, 33, 5071-5079. (19) Chen, C. S.; Suresh, P.; Rao, C.; Lee, L. S. Chemosphere 1996, 32, 1123-1132. (20) Claessens, H. A.; Rhemrev, M. M.; Wevers, J. P.; Janssen, A. A. J.; Brasser, L. J. Chromatographia 1991, 31, 569-574. (21) Hageman, K. J.; Mazeas, L.; Grabanski, C. B.; Miller, D. J.; Hawthorne, S. B. Anal. Chem. 1996, 68, 3892-3898. (22) Lee, M. L.; Novotny, M.; Bartle, K. D. Analytical Chemistry of Polycyclic Aromatic Compounds; Academic Press: New York, 1981. (23) Leonhardt, E.; Stahl, R. Anal. Chem. 1998, 70, 1228-1230. (24) Purushothama, S.; Pan, W.-P.; Riley, J. T.; Lloyd, W. G. Fuel Process. Technol. 1998, 53, 235-242. (25) Stephens, D. L.; McFadden, T., Jr.; Heath, D. O.; Mauldin, R. F. Chemosphere 1994, 28, 1741-1747. (26) Colier, A. R.; Rhead, M. M.; Trier, C. J.; Bell, M. A. Fuel 1995, 74, 362-367. (27) Hanson, R. L.; Carpenter, R. L.; Newton, G. J.; Rothenberg, S. J. J. EnViron, Sci. Health A 1979, 14, 223. (28) Hauser, T. R.; Pattison, J. N. EnViron. Sci. Technol. 1972, 6, 549557. (29) Wise, S. A.; Schantz, M. M.; Benner, B. A.; Hays, M. J.; Schiller, S. B. Anal. Chem. 1995, 67, 1171-1178. (30) Kister, J.; Pieri, N.; Alvarez, R.; Diez, M. A.; Pis, J. J. Energy Fuels 1996, 10, 948-957. (31) Nie, S.; Dadoo, R.; Zare, R. N. Anal. Chem. 1993, 65, 3571-3575.
Xue et al.
Figure 1. Location of the Huaibei mining district, Anhui province, China.
widely applied to the determination of PAHs.29,32-34 In addition, liquid chromatographic-electrochemical detector (LC-ED),34-35 supercritical fluid chromatography (SFC),36-37 Fourier transform infrared (FTIR),30 two-step laser MS38, high-resolution MS,39 and capillary electrophoresis with fluorescence detection31 were also used to determine PAHs and other organic compounds. Recent studies have used GC-MS to determine PAHs.5,40-44 At present, research on coal-related PAH pollution is mainly focused on their emissions during combustion or the factors involved, e.g., burning temperature and its effect on emissions during combustion.45-48 Studies on PAHs extracted from raw coal are rare.5,49 In this study, efforts were aimed toward (32) Qian, K.; Hsu, C. S. Anal. Chem. 1992, 64, 2327-2333. (33) Manoli, E.; Samara, C. Chromatographia 1996, 43, 135-142. (34) Garcia, P.; Perez, J. L.; Moreno, B. Anal. Chem. 1994, 66, 874881. (35) Murayama, M.; Dasgupta, P. K. Anal. Chem. 1996, 68, 1226-1232. (36) Heaton, D. M.; Bartle, K. D.; Clifford, A. A.; Myers, P.; King, B. W. Chromatographia 1994, 39, 607-611. (37) Vayisoglu-Giray, E. S.; Johnson, B. R.; Fere, B.; Gizir, A. M.; Bartle K. D.; Clifford A. A. Fuel 1998, 77, 1533-1537. (38) Kovalenko, L. J.; Maechling, C. R.; Clement, S. J.; Philippoz, J. M.; Zare, R. N.; Alexander, C. M. Anal. Chem. 1992, 64, 682-690. (39) Chasey, K. L.; Aczel, T. Energy Fuels 1991, 5, 386-394. (40) Gao, L. F.; Liu, G. J.; Xue, J.; Zhang, H. Y.; Zheng, L. G. EnViron. Chem. 2006, 25, 498-502. (41) Xue, J.; Liu, G. J.; Zhang, H. Y.; Niu, Z. Y. EnViron. Sci. Res. 2006, 19 (5), 23-27. (42) Zhang, H. Y.; Liu, G. J.; Xue, J. J. Chin. Coal Soc. 2005, 30, 97101. (43) Zhang, H. Y.; Liu, G. J.; Xue, J. EnViron. Chem. 2005, 5, 613616. (44) Wang, X.; Xue, W.; Zhu, J.; Gu, Y.; Sheng, G.; Fu, J. J. Fuel Chem. Technol. 1994, 22, 196-202. (45) Liu, K.; Han, W.; Pan, W.; Riley, J. T. J. Hazard. Mater. 2001, 84, 175-188. (46) Masclet Fuel 1987, 66, 556-562. (47) Okuda, T.; Kumata, H.; Naraoka, H.; Takada, H. Org. Geochem. 2002, 33, 1737-1745. (48) Pisupati, S. V.; Ronald, S. W.; Alan, W. S. J. Hazard. Mater. 2000, 74, 91-107.
Extraction of PAHs from Coal
Energy & Fuels, Vol. 21, No. 2, 2007 883 Table 2. Composition of Coals and Amount of Total PAHs Extracted
samples
C (%)
H (%)
O (%)
N (%)
S (%)
ash (%)
H/C (mol) a
O/C (mol)b
total PAHs (Ul 20 minc, µg/g)
total PAHs (So 48 hd, µg/g)
Hz4-1 Hz4-2 Hz4-3 Hz4-4 Hz4-5 Hz4-7 Hz4-9 Hz4-10 HZ5-1 Hz5-2 Hz5-3 Hz5-6 Hz5-7 Hz5-8
79.4 64.8 72.2 70.8 65.5 76.1 71.2 67.3 76.0 72.0 74.1 73.0 72.4 73.8
3.19 1.17 2.25 2.68 3.08 3.37 3.00 2.64 3.35 3.12 3.39 4.10 3.94 4.27
2.427 4.325 3.025 3.571 3.960 2.792 3.537 4.307 2.504 2.598 2.470 3.970 3.812 3.415
1.51 0.83 1.32 1.41 0.85 1.33 1.41 0.94 1.40 1.33 1.20 1.35 1.36 1.88
0.853 0.228 0.500 0.574 0.494 0.432 0.541 2.46 0.884 0.826 0.669 0.486 0.456 0.496
12.62 28.65 20.71 20.97 26.12 15.98 20.31 22.35 15.86 20.13 18.17 17.09 18.03 16.14
0.480 0.217 0.374 0.454 0.564 0.532 0.506 0.471 0.529 0.520 0.549 0.675 0.653 0.695
0.023 0.050 0.031 0.038 0.045 0.028 0.037 0.048 0.025 0.027 0.025 0.041 0.039 0.035
10.23 0.40 0.93 3.44 8.88 9.08 23.96 4.10 12.41 5.19 13.38 24.20 15.07 17.41
11.02 0.55 1.70 4.04 15.98 17.20 40.63 5.72 17.84 14.81 22.18 69.64 34.30 34.67
a
H/C molar ratio. b O/C molar ratio. c Ultrasonic-assisted extraction for 20 min. d Soxhlet extraction for 48 h. Table 3. Concentration (µg/g) of US EPA Priority PAHs in CH2Cl2 Extracts vs Extraction Time Using Ultrasonic Extraction 10 min
20 min
30 min
PAH
Hz4-1
Hz5-3
Hz5-6
Hz5-9
Hz4-1
Hz5-3
Hz5-6
Hz5-9
Hz4-1
Hz5-3
Hz5-6
Hz5-9
Nap Acpy Acp Flu PHE Ant FL Pyr BaA CHR BbF BkF BaP IND DBA BghiP ∑PAHs (except Nap)
0.29
