Examination of the carbonization behavior of coals by using raman sectroscopy and kinetic analysis of hydrogen formation

Abstract

Caking coals, which are main raw materials of metallurgical coke, are carbonized through softening, melting, and subsequent resolidification by heat treatment. The carbonization process after resolidification is poorly understood because of the difficulty of the analysis of the solid amorphous carbons, although it is recognized that the carbonization process affects significantly the strength of coke. In this study, the carbonization process was examined from two aspects: one is the analysis of the hydrogen formation rate during carbonization and the other is the examination of the carbonized coke by the Laser Raman spectroscopy. Formation rate of H2 was analyzed by using the so-called distributed activation energy model to obtain the distribution of activation energy for the hydrogen formation reactions. It was found that the peak activation energy decreased with the increase of the caking property of coal, indicating that the formation of hydrogen is closely related to the caking property of coal. It was proposed to utilize absolute intensity of Raman spectrum for characterizing amorphous carbons. The absolute intensity of Raman spectra for coals carbonized at 600-1300°C decreased with increasing heat treatment temperature. The decrease was well correlated with the amount of H2 produced up to the final temperature, indicating that the absolute intensity decreased by the condensation reaction of aromatic rings and/or cross-linking reactions. It was also found that the peak around 1600cm -1 disappeared and the sharp peak around 1580cm-1 appeared by further heat treatment over 2000°C when Raman spectroscopy was interpreted in terms of absolute intensity. These results show that the Raman spectrum reflects the proceeding of carbonization of coal.