Keywords

Coal, Pyrolysis, Tar

Abstract

Three coals of different rank were pyrolyzed in a drop-tube reactor at a maximum temperature of 900 K and a residence time of 160 ms. The coal and char were analyzed with solid-state ¹³C NMR. The tar was dissolved in deuterated methylene chloride. It was found that the tar was only partially soluble in CD₂Cl₂. The nonsoluble tar portion was analyzed in the same manner as the coal and char, while the soluble tar portion was analyzed using a recently developed high-resolution 13CNMRtechnique developed for liquid phases. The tar structure was found to be significantly different from the structure of the char and coal. The number of bridges and loops per cluster in the tar was up to 65% lower than in the char. In addition, the number of aromatic carbons per cluster in the tar was significantly lower than that found in either the coal or the char. Since the molecular weight per cluster in the tar is lower than reported average tar molecular weights, these data imply that tar is made up of a number of multiple clusters (dimers, trimers, etc.) as well as single clusters (i.e., monomers). The mass of nitrogen per cluster in the tar was found to be significantly lower in the tar than in either the coal or the char. These experimental findings suggest that changes may be necessary in current network devolatilization models to accurately describe the changes in chemical structure.

Original Publication Citation

Watt, M., T. H. Fletcher, S. Bai, M. S. Solum, and R. J. Pugmire, "Chemical Structure of Coal Tar During Devolatilization," Twenty-Sixth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, 3153-3160 (1996).