Characterization of coals and coal oxidation by magic-angle 13C n.m.r. spectroscopy

✍ Scribed by John R. Havens; Jack L. Koenig; Deborah Kuehn; Carol Rhoads; Alan Davis; Paul C. Painter

• Publisher: Elsevier Science
• Year: 1983
• Tongue: English
• Weight: 651 KB
• Volume: 62
• Category: Article
• ISSN: 0016-2361
• DOI: 10.1016/0016-2361(83)90165-5

✦ Synopsis

Magic-angle

13C n.m.r. spectra have been obtained for a series of vitrinite concentrates. Proper modification of the cross-polarization pulse sequence allows separation of protonated and nonprotonated carbon resonances. This technique is used to determine the relative fraction of nonprotonated aromatic carbons for each of the vitrinites, a parameter observed to decrease with increasing rank. Another parameter, related to the aromatic hydrogen content, is also calculated from these data and the results correlate with those from Fourier transform i.r. spectroscopy. The methods used for analysis of the vitrinite concentrates were then applied to the low-temperature oxidation of coal. The fractional aromaticity as determined by n.m.r. increases with longer oxidation times, indicating preferential attack on aliphatic structures. Here the FT-i.r. results are in quantitative agreement with those from n.m.r. Finally, the advantages of using various pulse sequences to extend the range of magic-angle n.m.r. and of combining FT-i.r. and n.m.r. results are discussed in the context of their potential for coal science.