Structural ordering of coal char during heat treatment and its impact on reactivity

Feng, Bo, Bhatia, Suresh K. and Barry, John C. (2002) Structural ordering of coal char during heat treatment and its impact on reactivity. Carbon, 40 4: 481-496. doi:10.1016/S0008-6223(01)00137-3


Author Feng, Bo
Bhatia, Suresh K.
Barry, John C.
Title Structural ordering of coal char during heat treatment and its impact on reactivity
Journal name Carbon   Check publisher's open access policy
ISSN 0008-6223
Publication date 2002-04-01
Year available 2002
Sub-type Article (original research)
DOI 10.1016/S0008-6223(01)00137-3
Open Access Status Not yet assessed
Volume 40
Issue 4
Start page 481
End page 496
Total pages 16
Place of publication Oxford
Publisher Elsevier
Language eng
Subject C1
250699 Theoretical and Computational Chemistry not elsewhere classified
660101 Coal-electricity
290000 Engineering and Technology
290600 Chemical Engineering
290602 Process Control and Simulation
Abstract The effect of heat treatment on the structure of an Australian semi-anthracite char was studied in detail in the 850-1150degreesC temperature range using XRD, HRTEM, and electrical resistivity techniques. It was found that the carbon crystallite size in the char does not change significantly during heat treatment in the temperature range studied, for both the raw coal and its ash-free derivative obtained by acid treatment. However, the fraction of the organized carbon in the raw coal chars, determined by XRD, increased with increase of heat treatment time and temperature, while that for the ash-free coal chars remained almost unchanged. This suggests the occurrence of catalytic ordering during heat treatment, supported by the observation that the electrical resistivity of the raw coal chars decreased with heat treatment, while that of the ash-free coal chars did not vary significantly. Further confirmatory evidence was provided by high resolution transmission electron micrographs depicting well-organized carbon layers surrounding iron particles. It is also found that the fraction of organized carbon does not reach unity, but attains an apparent equilibrium value that increases with increase in temperature, providing an apparent heat of ordering of 71.7 kJ mol(-1) in the temperature range studied. Good temperature-independent correlation was found between the electrical resistivity and the organized carbon fraction, indicating that electrical resistivity is indeed structure sensitive. Good correlation was also found between the electrical resistivity and the reactivity of coal char. All these results strongly suggest that the thermal deactivation is the result of a crystallite-perfecting process, which is effectively catalyzed by the inorganic matter in the coal char. Based on kinetic interpretation of the data it is concluded that the process is diffusion controlled, most likely involving transport of iron in the inter-crystallite nanospaces in the temperature range studied. The activation energy of this transport process is found to be very low, at about 11.8 kJ mol(-1), which is corroborated by model-free correlation of the temporal variation of organized carbon fraction as well as electrical resistivity data using the superposition method, and is suggestive of surface transport of iron. (C) 2002 Elsevier Science Ltd. All rights reserved.
Keyword Chemistry, Physical
Materials Science, Multidisciplinary
Char
Heat Treatment
Transmission Electron Microscopy, X-ray Diffraction
Reactivity
X-ray-diffraction
Carbonaceous Materials
Combustion Reactivity
Carbons
Gasification
Evolution
Graphitization
Crystallinity
Carbonization
Microscopy
Q-Index Code C1
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Mechanical & Mining Engineering Publications
 
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Citation counts: TR Web of Science Citation Count  Cited 99 times in Thomson Reuters Web of Science Article | Citations
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Created: Wed, 15 Aug 2007, 04:28:49 EST