Bai, S
1996
Chemical Structure of Coal Tar During Devolatilization
Fletcher, T.H.; Watt, M.; Bai, S.; Solum, M.S. and Pugmire, R.J.
Twenty-Sixth Symposium (International) on Combustion, (in press) 1996. (Also presented at the Twenty-Sixth Symposium (International) on Combustion, Naples, Italy, July, 1996.) Funded by ACERC and US Department of Energy/University Coal Research.
Three coals of different rank were pyrolyzed in a drop tube reactor at a maximum temperature of 900 K and residence time of 160 ms. The coal and char were analyzed with solid state C-13 NMR. The tar was dissolved in deuterated methylene chloride. It was found that the tar was only partially soluble in CD2CL2-. The non-soluble tar portion was analyzed using a recently developed high-resolution C-13 NMR technique 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.
1993
Chemical Structural Features of Pyridine Extracts and Residues of the Argonne Premium Coals Using Solid State C-13 NMR Spectroscopy
Fletcher, T.H.; Bia, S.; Pugmire, R.J.; Solum, M.S.; Woods, S. and Grant, D.M.
Energy & Fuels, 7 (6):734-742, 1993. (Presented at the Spring Meeting of the Western States Section of the Combustion Institute, Salt Lake City, UT, March 1993.) Funded by ACERC.
Soxhlet extractions were performed on the eight Argonne Premium coals using pyridine purged with argon and followed by a novel washing procedure to remove the pyridine. Mass closure (extracts plus residues) on duplicate experiments accounted for 94-96% of the original coal, repeatable to within 2%. Chemical structural features determined from C-13 NMR analyses of the extracts and residues showed more attachments per aromatic cluster for the residues, indicating a greater degree of covalent bonding in the residue than in the extract. H-1 NMR analysis of the extracts showed a gradual increase in the hydrogen aromaticity with rank, along with a maximum in the percentage of a-hydrogen in the high-volatile bituminous coals. Composite chemical features constructed from weighted averages of the features of the residues and extracts agree with many of the features of the parent coal. Chemical structural features of the extracts determined from H-1 NMR analyses agree with similar data reported previously for early coal tars during devolatilization at rapid heating rates.
Chemical Structural Features of Coal Chars, Tars, and Char Extracts During Rapid Pyrolysis Using C-13 and H-1 NMR Spectroscopy
Fletcher, T.H.; Solum, M.S.; Pugmire, R.J.; Grant, D.M.; Bai, S.; Ma, J. and Woods, S.
7th International Conference on Coal Science, Banff, Alberta, Canada, September 1993 (in press). Funded by ACERC.
Structural characteristics have been determined for parent coals and for chars collected at different stages of pyrolysis. Recent work has focused on trying to understand the relationship between chemical structural features of the unreacted coal and the devolatilization and char oxidation phenomena. Models of coal devolatilization have recently related devolatilization behavior to the structure of the parent coal and the initial amount of pyridine extracts. Fong et al. used pyridine extraction methods to quantify the amount of metaplast formed during pyrolysis of a Pittsburgh #8 coal. These experiments demonstrated that under moderate heating conditions (~500 K/s to 873 K), as much as 80% of the initial coal was transformed into a combination of extractable material and volatiles. The work presented here is an examination of the pyridine extraction procedure of the Argonne Premium coal samples and the detailed study of the carbon skeletal structure of the extracts and the extraction residues from these coals. This is the first stage of an experimental program to examine the yield and chemical features of extracts of coal chars collected as a function of time during pyrolysis.
Bai, S
1996
Chemical Structure of Coal Tar During Devolatilization
Fletcher, T.H.; Watt, M.; Bai, S.; Solum, M.S. and Pugmire, R.J.
Twenty-Sixth Symposium (International) on Combustion, (in press) 1996. (Also presented at the Twenty-Sixth Symposium (International) on Combustion, Naples, Italy, July, 1996.) Funded by ACERC and US Department of Energy/University Coal Research.
Three coals of different rank were pyrolyzed in a drop tube reactor at a maximum temperature of 900 K and residence time of 160 ms. The coal and char were analyzed with solid state C-13 NMR. The tar was dissolved in deuterated methylene chloride. It was found that the tar was only partially soluble in CD2CL2-. The non-soluble tar portion was analyzed using a recently developed high-resolution C-13 NMR technique 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.
1993
Chemical Structural Features of Pyridine Extracts and Residues of the Argonne Premium Coals Using Solid State C-13 NMR Spectroscopy
Fletcher, T.H.; Bia, S.; Pugmire, R.J.; Solum, M.S.; Woods, S. and Grant, D.M.
Energy & Fuels, 7 (6):734-742, 1993. (Presented at the Spring Meeting of the Western States Section of the Combustion Institute, Salt Lake City, UT, March 1993.) Funded by ACERC.
Soxhlet extractions were performed on the eight Argonne Premium coals using pyridine purged with argon and followed by a novel washing procedure to remove the pyridine. Mass closure (extracts plus residues) on duplicate experiments accounted for 94-96% of the original coal, repeatable to within 2%. Chemical structural features determined from C-13 NMR analyses of the extracts and residues showed more attachments per aromatic cluster for the residues, indicating a greater degree of covalent bonding in the residue than in the extract. H-1 NMR analysis of the extracts showed a gradual increase in the hydrogen aromaticity with rank, along with a maximum in the percentage of a-hydrogen in the high-volatile bituminous coals. Composite chemical features constructed from weighted averages of the features of the residues and extracts agree with many of the features of the parent coal. Chemical structural features of the extracts determined from H-1 NMR analyses agree with similar data reported previously for early coal tars during devolatilization at rapid heating rates.
Chemical Structural Features of Coal Chars, Tars, and Char Extracts During Rapid Pyrolysis Using C-13 and H-1 NMR Spectroscopy
Fletcher, T.H.; Solum, M.S.; Pugmire, R.J.; Grant, D.M.; Bai, S.; Ma, J. and Woods, S.
7th International Conference on Coal Science, Banff, Alberta, Canada, September 1993 (in press). Funded by ACERC.
Structural characteristics have been determined for parent coals and for chars collected at different stages of pyrolysis. Recent work has focused on trying to understand the relationship between chemical structural features of the unreacted coal and the devolatilization and char oxidation phenomena. Models of coal devolatilization have recently related devolatilization behavior to the structure of the parent coal and the initial amount of pyridine extracts. Fong et al. used pyridine extraction methods to quantify the amount of metaplast formed during pyrolysis of a Pittsburgh #8 coal. These experiments demonstrated that under moderate heating conditions (~500 K/s to 873 K), as much as 80% of the initial coal was transformed into a combination of extractable material and volatiles. The work presented here is an examination of the pyridine extraction procedure of the Argonne Premium coal samples and the detailed study of the carbon skeletal structure of the extracts and the extraction residues from these coals. This is the first stage of an experimental program to examine the yield and chemical features of extracts of coal chars collected as a function of time during pyrolysis.