Thermal transformations of nitrogen and sulfur forms in peat related to coalification
- ExxonMobil Research and Engineering Co., Annandale, NJ (United States)
The chemical pathways for nitrogen and sulfur transformations during coalification are elucidated by comparing the chemical forms of unaltered peats, lignites, and coals and pyrolyzed peats using a combination of spectroscopic techniques in unaltered peats, the NMR and XPS spectra are consistent with the presence of amide nitrogen. The spectra indicate that a thermal transformation of amide nitrogen into pyrrolic and pyridinic forms occurs after thermal stress that is roughly equivalent to lignitification. High total nitrogen levels are found in pyrolyzed peats relative to lignites and higher-rank coals, suggesting that some amides initially found in peat are lost via nonthermal pathways during coalification. Lignites contain the highest levels of quaternary nitrogen, and they are associated with protonated pyridinic structures. Most quaternary nitrogen is formed during lignitification as a result of the creation and interaction of basic nitrogen species with acidic functionalities and is lost completely during bitumenization. Sulfur X-ray absorption near-edge structure spectroscopy (S-XANES) of unaltered peats detect the presence of disulfide, mercapto, aliphatic sulfide, and aromatic forms of organically bound sulfur. XPS and S-XANES results show that the relative level of aromatic sulfur increases as the severity of peat pyrolysis increases. The relative level of aromatic sulfur increases through the selective loss of disulfide, aliphatic sulfide, and SO{sub 3} groups and through the transformation of aliphatic sulfur forms. Aliphatic sulfur is present mostly as mercapto and disulfide species in peats and in lignites but not in higher-rank coals. These results indicate that mercapto and disulfide species are lost after lignitification. Organic sulfur in peats exist mainly as aromatic forms, consistent with the level of aromatic sulfur increasing with the increasing degree of coalification. 91 refs., 22 figs., 6 tabs.
- OSTI ID:
- 20741013
- Journal Information:
- Energy and Fuels, Journal Name: Energy and Fuels Journal Issue: 2 Vol. 20; ISSN ENFUEM; ISSN 0887-0624
- Country of Publication:
- United States
- Language:
- English
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