Energy Fuels 2009, 23, 5284–5286 Published on Web 09/22/2009
: DOI:10.1021/ef900563e
Release of Organonitrogen and Organosulfur Compounds during Hydrotreatment of Pocahontas No. 3 Coal Residue over an Activated Carbon Lin-Bing Sun,*,†,‡ Xian-Yong Wei,*,‡,§ Xiao-Qin Liu,† Zhi-Min Zong,‡ and Wen Li§ † State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009, China, ‡Key Laboratory of Coal Processing and Efficient Utilization, China University of Mining and Technology, Xuzhou 221008, Jiangsu, China, and §State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
Received June 2, 2009. Revised Manuscript Received September 10, 2009 Understanding the mode of occurrence of organonitrogen and organosulfur compounds (ONCs and OSCs) and efficiently removing them from coals are both important topics of interest and challenging subjects in clean coal conversion.1 Many coals contain a significant amount of organic nitrogen and/or sulfur; they are finely distributed and bound strongly to the coal matrix.2,3 A variety of attempts have been made to clarify the structures of ONCs and OSCs, for example, by X-ray photoelectron spectroscopy, X-ray absorption near edge structure, and nuclear magnetic resonance.4-7 Unfortunately, the identification of ONC and OSC structures at the molecular level is quite difficult from these inseparable methods. Use of a separable and nondestructive strategy [combining fractional extraction and gas chromatography-mass spectrometry (GC/MS) analysis], the molecular-level determination for organohalogens8 and ONCs9 in coals was recently reported. Coals themselves usually contain a solvent-soluble portion to different extents. Many organic compounds have been detected in the solvent-soluble portion of several coals.10 The concentration of ONCs and OSCs in coals is often much lower than that of hydrocarbons, which leads to the difficulty in determining ONC and OSC structures in coals. To avoid the disturbance of hydrocarbons, a solvent-insoluble fraction (that is, a residue) was used as reactant and the release of ONCs11 and OSCs12 was observed during hydrotreatment. It should be noted that the catalysts used for hydrotreatment were transition metals, such
Figure 1. Extraction procedure for the reaction mixtures from the hydrotreated coal residue.
as Ni and Pd. Taking into account that these transition-metal catalysts are quite active, some side reactions are possible to occur;13 as a result, the detected compounds may differ from their original existing forms in coal. Carbon materials, such as activated carbon (AC) and carbon black, have been found as efficient catalysts for the hydroconversion of various model compounds.14-16 Fascinatingly, the AC can selectively catalyze the hydrogenation of some aromatic rings and the cleavage of C-C bridges in diarylmethanes.14,15 These facts indicate that the AC may be promising for the selective release of nitrogen- and/or sulfur-containing compounds, because the C-N and C-S linkages are weaker than the C-C one. Here, for the first time, we used the AC as catalyst for the hydrotreatment of Pocahontas No. 3 (P3) coal residue. The release of ONCs and OSCs from the residue was subsequently examined by the separable and nondestructive strategy. Table 1 shows the proximate and ultimate analyses of P3 coal. The residue used was tetrahydrofuran (THF)/CS2 (volume ratio of 2:1)-insoluble fraction from the coal. The extraction was carried out under a nitrogen atmosphere in a modified Soxhlet extractor, as reported previously.17 The extraction temperature was controlled at boiling point of THF. The extraction was conducted for at least 10 days, aiming at reaching an exhaustive
*To whom correspondence should be addressed. Telephone: þ86-(25)8358-7177. Fax: þ86-(25)-8358-7191. E-mail:
[email protected] (L.-B.S.); Telephone/Fax: þ86-(516)-8388-4399. E-mail:
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(13) Wei, X. Y.; Ni, Z. H.; Zong, Z. M.; Zhou, S. L.; Xiong, Y. C.; Wang, X. H. Energy Fuels 2003, 17 (3), 652–657. (14) Sun, L. B.; Zong, Z. M.; Kou, J. H.; Zhang, L. F.; Ni, Z. H.; Yu, G. Y.; Chen, H.; Wei, X. Y.; Lee, C. W. Energy Fuels 2004, 18 (5), 1500– 1504. (15) Sun, L. B.; Zong, Z. M.; Kou, J. H.; Liu, G. F.; Sun, X.; Wei, X. Y.; Zhou, G. J.; Lee, C. W. Energy Fuels 2005, 19 (1), 1–6. (16) Farcasiu, M.; Smith, C. Energy Fuels 1991, 5 (1), 83–87. (17) Wei, X. Y.; Lee, C. W.; Wang, J.; Wang, X. H.; Zong, Z. M.; Han, S. Y.; Park, J. N.; Eum, M.; Li, C. Q.; Takanohashi, T. Proc. 8th Japan-China Symp. Coal C1 Chem., Kitakyushu, Fukuoka, Japan, 2003; pp 51-52.
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Energy Fuels 2009, 23, 5284–5286
: DOI:10.1021/ef900563e
Table 1. Proximate and Ultimate Analyses of P3 Coala proximate analysis (wt %)
ultimate analysis (wt %, daf)
Mad
Ad
Vdaf
C
H
N
S
Ob
0.65
4.77
19.53
91.81
4.48
1.34
0.51
1.86
a
M, moisture; A, ash; V, volatile matter; ad, air-dried basis; d, dry (namely, moisture-free) basis; daf, dry and ash-free basis. b By difference.
extraction. After extraction, THF and CS2 remaining in the residue were extracted with acetone. No compounds except for THF, CS2, and acetone were detected with GC/MS in the extraction solution, indicating that the exhaustive extraction was achieved. The residue was dried in vacuum at 100 °C for 4 h to remove the remaining solvents from extraction. All of the solvents were purchased from Aldrich and were purified by distillation prior to use. The AC (Darco KB-B,
