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GC/MS Analysis of Water-Soluble Products from the Mild Oxidation of Longkou Brown Coal with H2O2 Zhen-Xue Liu and Ze-Chang Liu School of Chemical and Environment Engineering, Shandong University of Science and Technology, Jinan 250031, Shandong, China
Zhi-Min Zong and Xian-Yong Wei* School of Chemical Engineering, China University of Mining and Technology, Xuzhou 221008, Jiangsu, China
Jun Wang† and Chul Wee Lee Advanced Chemical Technology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong, Daejeon 305-600, Republic of Korea Received March 21, 2002
Longkou brown coal was oxidized by H2O2 at 40 °C for 10 h. Water-phase fraction from the reaction mixture was extracted with chloroform to afford chloroform-soluble, chloroform-insoluble but water soluble (CIWS) and solid subfractions. A series of heteroatom(s)-containing organic compounds were detected with GC/MS from the CIWS subfraction. The heteroatoms included O, N, S, and Cl.
Many attempts have been made for obtaining organic acids from coals by oxidation in alkali or acid solution.1-3 Oxidation was also used as a pretreatment for the study on coal structure.4 Since severe oxidation of coals usually leads to the formation of a large amount of CO2 and is thereby unfavorable both to the production of organic acids and to the study on coal structure, mild oxidation was recently paid great attention for coal investigation and utilization. Miura et al.5,6 reported that the oxidation of low-rank coals with H2O2 under mild conditions afforded small molecule fatty acids, such as malonic acid, glycolic acid, formic acid, acetic acid, and oxalic acid, in high yield and selectivity. Mae et al.7 found large amounts of oxalic acid, acetic acid, and isobutylic acid from the water-soluble fraction of an oxidized Australian brown coal. Recently, we investigated the H2O2 oxidation of a series of coals, finding * Corresponding author. Present address: Advanced Chemical Technology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong, Daejeon 305-600, Korea. E-mail:
[email protected]. † On a study leave from Department of Chemical Engineering, Nanjing University of Technology, Nanjing 210009, China. (1) Kamiya, Y. Kogyo Kagaku Zasshi 1956, 59, 197-202. (2) Kamiya, Y.; Nakano, Y. Kogyo Kagaku Zasshi 1959, 62, 15711573. (3) Deno, N. C.; Gregger, B. A.; Stroud, S. G. Fuel 1978, 57 (8), 455459. (4) Mae, K.; Maki, T.; Okutsu, H.; Miura, K. Fuel 2000, 79 (3-4), 417-425. (5) Miura, K.; Mae, K.; Okutsu, H.; Mizutani N. Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem. 1999, 44 (3), 734-738. (6) Miura, K.; Mae, K.; Okutsu, H.; Mizutani, N. Energy Fuels 1996, 10 (6), 1196-1201. (7) Mae, K.; Shindo, H.; Takahashi, K.; Miura, K. In Prospects for Coal Science in the 21st Century; Li, B. Q., Liu, Z. Y., Eds.; Shanxi Science and Technology Press: Taiyuan, China, 1999; pp 901-904.
Table 1. Proximate and Ultimate Analyses of Longkou Brown Coala proximate analysis/wt %
ultimate analysis/wt %, daf
Mad
Ad
Vdaf
C
H
N
Cl
H/C
10.51
4.16
37.81
73.22
4.36
1.75
0.024
0.710
a
Data for proximate and ultimate analyses except for Cl content were obtained with Leco Mac-400 thermogravimetric analyzer and Leco CHN-2000 elemental determinator, respectively, and Cl content was obtained according to a standard procedure.8
some other products from the oxidized coals. In this communication, we report the analytical results of water-soluble subfraction from oxidized Longkou brown coal. Longkou brown coal was pulverized to pass through 200 mesh screen and dried in a vacuum at 80 °C for 24 h before use. Table 1 shows the proximate and ultimate analyses of the coal sample. About 6.0 g of the coal sample was added to a 100 mL, round-bottom flask, which was kept in a water bath at a constant temperature of 40 °C, then 20 mL of 30% H2O2 aqueous solution was dropped slowly to the flask from a funnel. The gases released from the reaction system were collected with a prevacuumized gasbag. After the reaction was carried out for 10 h, the flask with the reaction mixture was rapidly cooled to room temperature in a cold water bath. About 20 mmol of gases (total five gases, including ca. 6 mmol CO2 in GC) was produced from the reaction system. The reaction mixture in the flask was separated to solid- and water-phase fractions by filtration through a membrane filter with 0.8 µm of pore size. The water-phase fraction was subsequently separated to chloroform-soluble (0.060 g), chloroform-
10.1021/ef020071e CCC: $25.00 © 2003 American Chemical Society Published on Web 02/06/2003
Oxidation of Longkou Brown Coal
Energy & Fuels, Vol. 17, No. 2, 2003 425
Figure 1. Total ion chromatogram of the CIWS subfraction.
Figure 2. Mass spectrum of compound 17#. Table 2. Yields of the Compounds Identified with GC/MS from the CIWS Subfraction
peak
compound
yield, µg/g coal, daf
1 2 3 4 5 6 7 8
[Z]-2-butenedioic acid butenedioic anhydride chloroacetic acid 2-chloropropanoic acid 4-chlorobutanoic acid 4-chloro-1-butanol 3-methylene butanedioic anhydride butanedioic anhydride
9.9 0.6 198.0 0.6 0.6 52.3 3.3 30.8
insoluble but water-soluble (CIWS, 0.631 g) and solid subfractions (0.041 g) by extraction with chloroform. After evaporating water at 80 °C under reduced pressure, the CIWS subfraction was dissolved in acetone and analyzed with GC/FID (HP 6890) and GC/MS (HP 6890/ 5973). A series of authentic compounds purchased from Aldrich Chemical Co., Inc., were used for the confirmation and quantification of the compounds identified with GC/MS. Figure 1 shows the total ion chromatogram of the CIWS subfraction. Corresponding compounds identified along with their yields are listed in Table 2. Sixteen peaks were identified by comparing their mass spectra with NIST library data, and most of them were further confirmed with corresponding authentic compounds. All of the compounds identified contain heteroatom(s), including eight carboxylic acids, three anhydrides, one alcohol, one aldehyde, one ketone, one ester, and one thiophene. It is noteworthy that seven organochlorines were detected, including mono-, di-, and tetrachlorides. Dichloroacetic acid is the most abundant among the organochlorines. A series of blank tests indicate that no
peak
compound
yield, µg/g coal, daf
9 10 11 12 13 14 15 16
3-methylpentanal 1,1,3,3-tetrachloro-2-propanone 4-chloro-1-butanol acetate dichloroacetic acid 2-isopropyl-5-(2-methylbutyl)thiophene hexadecanoic acid [Z,Z]-9,12-octadecadienoic acid octadecanoic acid
22.0 2.2 11.6 277.2 1.1 55.0 211.2 44.0
Figure 3. Presumed structure of compound 17#.
reactions occurred during the extraction with chloroform for separating the water-phase products, indicating the organochlorines should result from the coal itself. The compound 17# is the most abundant among the compounds detected in the CIWS subfraction, but neither corresponding authentic mass spectrum nor authentic compound is available. According to its mass spectrum shown in Figure 2, we presume the compound is 5,6-indenono[1,2]-1,2-pyreno[3,4]pyrrole, as shown in Figure 3. The compound should not be easily dissolved in water according to its structure. We consider that its appearance in the CIWS subfraction may be related to
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the strong interaction (mainly as hydrogen bond) between the compound and other organics. As is well-known, many sulfur-, nitrogen-, and chlorinecontaining organic compounds are very harmful to the environment during coal combustion but are valuable as chemicals. Although a number of methods 9-11 have been tried to investigate the contents, modes of occurrence, and origin of chlorine in coals, to our knowledge, no reports have been issued on molecular structures of organochlorines in any coals. Our experiments provide (8) Jiang, X.-G.; Xu, X.; Yan, J.-H.; He, J.; Chi Y.; Cen K.-F. J. China Coal Soc. 2001, 26 (6), 667-670. (9) Huggins, F. E.; Huffman, G. P. Fuel 1995, 74 (4), 556-559. (10) Jimenez, A.; Martinez-Tarazona, M. R.; Suarez-Ruiz, I. Fuel 1999, 78 (13), 1559-1565. (11) Vassilev, S. V.; Eskenazy, G. M.; Vassileva, C. G. Fuel 2000, 79 (8), 903-921.
Liu et al.
the first access to organochlorines in coal on the molecular level. In summary, a series of heteroatom(s)-containing organic compounds, especially organochlorines, were identified with GC/MS in a water-soluble subfraction from mild oxidation of Longkou brown coal with H2O2. Acknowledgment. We thank the Research Fund for the Doctoral Program of Higher Education (Grants 98029016 and 20020290007), the Special Fund for Major State Basic Research Project (Grant G1999022101), National Natural Science Foundation of China (Grant 20076051), and Brain-Pool Program of the Korean Federation of Science and Technology Societies. EF020071E
