NMR and 2DNMR analysis of the degradation thermal products of vitrinites in relation to natural hydrogen enrichment and its implications.

Abstract : Natural hydrogen enrichment gives rise to modifications in the macromolecular structure of vitrinite affecting the properties and behaviour of coals. In order to understand these modifications at molecular level it is necessary to study the degradation of the macromolecular network into representative fragments. A preliminary study involving a direct solid state characterization of the coal combined with an analysis of the degradation products obtained by means of flash-pyrolysis has provided very useful information [1]. However, the results obtained through Py-GC/MS only concern the volatile components. NMR studies were also applied to a structural analysis of the volatile components of the soluble fraction obtained from a set of perhydrous coals with different characteristics [2]. By means of Gray-King pyrolysis oil can be obtained for the analysis of both the volatile and the non-volatile components. This analysis was carried out through the qualitative and quantitative NMR study (1H, 13C and 2D proton detected 1H, 13C correlation experiments) of the same set of perhydrous coals as those mentioned above in order to obtain accurate oil/vitrinite relations. A number of reasons support the use of Gray-King pyrolysis as a thermal approach for this purpose. During the pyrolysis of this type of coals high tar yields are obtained (10-31 %). In addition, it has been previously shown [3] that fragmentation processes prevail over condensation reactions. In this work evidence showing that tars can be representative of the parent vitrinite are presented. The strong resemblance between the FTIR spectra of the oils and those of the raw materials justifies an NMR study. Moreover, the volatile fraction of the oils is made up of the same compounds as those identified by Py-GC/MS and close relationships between NMR and Py-GC/MS are presented. An exhaustive compositional study of the low-temperature tars is also important from the technological point of view because perhydrous coals are oil-prone materials which generate oils of a mainly phenolic nature. Phenolic compounds have a peculiar set of chemical properties as a result of which they play a significant role in coal conversion. They also have important environmental implications owing to their carcinogenic and mutagenic activity. References [1] Iglesias, M.J., del Río, J.C., Laggoun-Défarge, F., Cuesta, M.J. and Suárez-Ruiz, I. J. Anal. Appl. Pyrol. 62, 1-34 (2002) and references cited therein. [2] Iglesias, M.J., del Río, J.C., Laggoun-Défarge, F., Cuesta, M.J. and Suárez-Ruiz, I. J. Anal. Appl. Pyrol. 68-69, 387-407 (2003). [3] Arenillas, A., Rubiera, F., Pis, J.J., Cuesta, M.J., Iglesias, M.J., Jiménez, A. and Suárez-Ruiz, I. J. Anal. Appl. Pyrol. 68-69, 371-385 (2003).
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María José Iglesias, María José Cuesta, Fatima Laggoun-Défarge, Isabel Suarez-Ruiz. NMR and 2DNMR analysis of the degradation thermal products of vitrinites in relation to natural hydrogen enrichment and its implications.. 16th International Symposium on Analytical & Applied Pyrolysis, 2004, Alicante, Spain. 1p. ⟨hal-00101391⟩

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