Geology topics

T.V. Verheyen

Publications and source records attributed to T.V. Verheyen.

3 recordsLinked to original sources

USGS1990

Organic geochemical studies of the transformation of gymnospermous xylem during peatification and coalification to subbituminous coal

Organic geochemical investigations of peatified and coalified xylem from gymnosperms have provided useful information on the organic transformational processes collectively known as coalification. The combined use of solid-state 13 C nuclear magnetic resonance (NMR) and pyrolysis/gas chromatography/mass spectrometry (py/gc/ms) has allowed us to examine the organic composition of peatified and coalified xylem on both a bulk (average) compositional basis and on a detailed molecular basis. We conclude from our studies that coalification of gymnospermous xylem involves the following processes1. (1) early selective removal of cellulosic materials so that lignin, a primary constituent of xylem, is transformed to macromolecular aromatic components in coal;2. (2) modification of gymnospermous lignin by demethylation to form catechol-like structures, and by condensation reactions to induce a high level of cross-linking at an early stage of coalification; and (3) dehydroxylation during increasing coalification to subbituminous coal, the resultant xylem becomes more phenolic in character as the catechol-like structures decrease.

International Journal of Coal Geology↗

USGS1989

Solid-state 13C nuclear magnetic resonance studies of coalified gymnosperm xylem tissue from Australian brown coals

We report here on the use of solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy to contrast the average chemical composition of modern degraded gymnosperm woods with fossil gymnosperm woods from Australian brown coals (Miocene). We first established the quantitative nature of the NMR techniques for these samples so that the conventional solid-state 13 C NMR spectra and the dipolar dephasing NMR spectra could be used with a high degree of reliability to depict average chemical compositions. The NMR results provide some valuable insights about the early coalification of xylem tissue from gymnosperms. Though the cellulosic components of wood are degraded to varying degrees during peatification and ensuing coalification, it is unlikely that they play a major role in the formation of aromatic structures in coalified woods. The NMR data show that gynmosperm lignin, the primary aromatic contribution to the coal, is altered in part by demethylation of guaiacyl-units to catechol-like structures. The dipolar dephasing NMR data indicate that the lignin also becomes more cross-linked or condensed.

Organic Geochemistry↗

USGS1988

Pyrolysis g.c.-m.s. of a series of degraded woods and coalified logs that increase in rank from peat to subbituminous coal

Xylem tissue from degraded wood and coalified logs or stems was examined by pyrolysis g.c.-m.s. to improve understanding of the coalification process. The pyrolysis data, when combined with solid-state 13 C n.m.r. data for the same samples, show several stages of evolution during coalification. The first stage, microbial degradation in peat, involves the selective degradation of cellulosic components and preservation of lignin-like components. As coalification increases, the lignin structural units undergo a series of defunctionalization reactions. The first of these involve loss of methoxyl groups, with replacement by phenolic hydroxyls such that catechol-like structures are produced. As the xylem tissue is converted to subbituminous coal, the persistence of phenols and methylated phenols in pyrolysis g.c.-m.s. data of subbituminous coal suggests that the catechol-like structures are being converted to phenol-like structures. The ability to discern detailed changes in the chemical structural composition of a genetically and histologically related series of samples provides an ideal method for developing models of coal structure, especially that of low-rank coal.

Fuel↗