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Energy & Fuels 2003, 17, 1244-1250
Quantitative Analysis of Hydrogen in Carbonaceous Materials: Hydrogen in Anthracite Hiromi Aso, Koichi Matsuoka, and Akira Tomita* Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku Sendai, 980-8577 Japan Received December 13, 2002
The accurate determination of elemental composition is the first step to elucidate the chemical structure of carbonaceous materials. However, it is generally not easy to obtain reliable data for hydrogen content, especially in hydrogen-lean materials. We attempt to establish a reliable method to determine not only the total hydrogen content, but also the distribution mode of hydrogen in various moieties in carbonaceous materials. As the first example, the hydrogen distribution in Chinese anthracites is determined in this study. In the temperature-programmed oxidation, H2O evolved in two temperature ranges from 50 to 500 °C and from 500 to 800 °C. The H2O evolution in the low-temperature region was assigned to the desorption of adsorbed water. The dehydration of mineral matter was seen in the high-temperature region, but the quantity was very small. The majority of H2O evolution in the high-temperature region was the result of the oxidation of the polyaromatic hydrocarbon moiety in anthracite. Oxidation of anthracite accompanied CO and CO2 evolution. The H/C atomic ratio of organic moiety in the sample can thus be known from the amount of evolved H2O, CO, and CO2. The ratio obtained for the demineralized samples are 0.08, 0.13, and 0.18 for SWZ, MTG, and GEZ anthracite, respectively. This ratio is directly related to the chemical structure of anthracite, and the above result indicates quite different nature of three anthracites. The hydrogen content determined by the ultimate analysis includes not only organic hydrogen but also hydrogen in adsorbed water and mineral matter, and therefore the H/C ratios calculated from the ultimate analysis data are quite different from the above values. The ratios are 0.15, 0.15, and 0.16 for respective anthracites. There is almost no difference among the three anthracites.
Introduction The ultimate analysis data are the most important information to deduce chemical structure of any molecule: inorganics or organics, low molecular weight or high molecular weight, and pure compound or mixture. This holds true for understanding the chemical structure of oil and coal, and Brown and Ladner, for example, proposed a methodology to analyze these complex hydrocarbon materials.1,2 This method was based on the ultimate analysis data and NMR data. The analysis of hydrocarbon compounds with more carbon and less hydrogen is difficult compared with that of oil and coal. In fact, little attention has been paid to the ultimate analysis of carbon-rich materials. This is partly because the carbon content is overwhelmingly high and the contents of minor elements are too small to analyze accurately. However, reliable data on hydrogen content are essential to deduce the chemical structure of carbonaceous materials. Hydrogen in coal and anthracite is present in several forms. Hydrogen in adsorbed water and that in mineral matter can be classified as inorganic hydrogen, while * Corresponding author. Tel: +81-22-217-5625. Fax: +81-22-2175626. E-mail:
[email protected]. (1) Brown, J. K.; Ladner, W. R.; Sheppard, N. Fuel 1960, 39, 7986. (2) Brown, J. K.; Ladner, W. R. Fuel 1960, 39, 87-96.
hydrogen in the polyaromatic hydrocarbon moiety can be termed as organic hydrogen. There are many forms of organic hydrogen; for example, aromatic hydrogen, aliphatic hydrogen, hydrogen in the hydroxyl group, hydrogen in the pyrrol group, and many others. The hydrogen content from ultimate analysis includes more or less all of these forms of hydrogen and it is not directly related to the chemical structure of the organic moiety of carbonaceous material under study. Therefore, it is definitely necessary to have reliable ultimate analysis data on the organic portion of the material. Many structural studies on coal and anthracite have been made using XRD,3,4 NMR,5-7 FT-IR,8 HRTEM,9 and others,10,11 but these approaches are indirect ones. If we can determine the content of each element in the organic moiety, our understanding of the structure of (3) Hirsch, P. B. Proc. R. Soc. A 1954, 226, 143-169. (4) Bratek, K.; Bratek, W.; Gerus-Piasecka, I.; Jasienko, S.; Wilk, P. Fuel 2002, 81, 97-108. (5) Marzec, A.; Jyrkiewicz, A.; Pislewski, N. Fuel 1983, 62, 996998. (6) Given, P. H.; Marzec, A.; Barton, W. A.; Lynch, L. J.; Gerstein, B. C. Fuel 1986, 65, 155-163. (7) Shinn, J. H. Fuel 1984, 63, 1187-1196. (8) Ibarra, J. V.; Miranda, J. L. Vib. Spectrosc. 1996, 10, 311-318. (9) Sharma, A.; Kyotani, T.; Tomita, A. Energy Fuels 2000, 14, 1219-1225. (10) Blom, L.; Edelhausen, L.; van Krevelen, D. W. Fuel 1957, 36, 135-153. (11) Larsen, J. W.; Lee, D.; Shawver, S. E. Fuel Process. Technol. 1986, 12, 51-62.
10.1021/ef020285w CCC: $25.00 © 2003 American Chemical Society Published on Web 07/18/2003
Analysis of Hydrogen in Carbonaceous Materials
Energy & Fuels, Vol. 17, No. 5, 2003 1245
Table 1. Ultimate Analysis of Raw Anthracites ultimate analysis (wt %, dafa) sample
code
C
H
N
S
Ob
Si Wang Zhang Men Tou Gou Guo Er Zhuang
SWZ MTG GEZ
94.0 95.7 96.3
1.2 1.2 1.3
0.6 0.3 0.7
0.3 0.2 0.3
4.0 2.7 1.5
a
Dry ash free. b By difference. Table 2. Ash and Moisture Content of Raw and Demineralized Anthracites sample
ash (wt %, dba)
moisture (wt %, mebb)
SWZ-rawc SWZ-demd MTG-raw MTG-dem GEZ-raw GEZ-dem
12.7 1.6 5.4 0.4 12.0 1.0
2.0 2.4 4.7 5.4 5.3 5.6
a Dry basis. b Moisture-equilibrated sample basis. c Raw anthracite. d Demineralized anthracite.
carbon-rich materials would be much deeper. Among all elements, accurate quantification of hydrogen is a key issue. The present project attempts to determine hydrogen content of carbonaceous materials as accurately as possible. Furthermore, we attempt to separately quantify different forms of hydrogen. In this paper, we selected three anthracites as the first examples. To the best of the authors’ knowledge, no careful study on the hydrogen content of anthracite has been reported. We determine the hydrogen distribution in anthracite by temperature-programmed oxidation (TPO). H2O that evolved during TPO is analyzed by gas chromatography (GC) and mass spectroscopy (MS). Experimental Section Samples. The ultimate analysis of three Chinese anthracites (
