Journal
FUEL
Volume 90, Issue 1, Pages 376-383Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.fuel.2010.08.010
Keywords
Coal combustion; Fly ashes; Fluorine forms; Carbon forms; Surface oxygen species
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Funding
- Ministry of Education, Science, Sports and Culture, Japan
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The functionalities of the fluorine and carbon present in fly ashes formed in pulverized coal combustion have been studied with X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) techniques. The ash samples include 20-130 mu g/g-dry and 0.4-4.1 mass%-dry of fluorine and carbon elements, respectively, and these components are enriched at the outermost layer of the ash surface. The F consists of both inorganic and organic functionalities, and the proportion of the latter is as high as 84-98 mol%. The C has different types of surface oxygen species, such as carboxyl, lactone/acid anhydride and phenolic groups, and most of these groups decompose to CO(2) or CO up to 700 degrees C to yield carbon active sites. When the amount of the O-functional forms increases, the content of organic C-F forms tends to increase almost linearly. On the basis of the above results, it may be speculated as one possibility that the formation of covalent C-F bonds takes place mainly through secondary reactions between gaseous F-containing compounds (HF and/or F(2)) in flue gas and carbon active sites produced below 700 degrees C downstream of coal-fired boilers. (C) 2010 Elsevier Ltd. All rights reserved.
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