Coalified wood

Survival of Lignin-Derived Structural Units in Ancient Coalified Wood Samples... 

In an attempt to delineate the degree of preservation of lignin in pre-Tertiary coal, we examined numerous coalified wood samples ranging in age from Carboniferous to Cretaceous. The samples were initially screened by solid-state l C nuclear magnetic resonance to detect the possible presence of methoxyl carbon. Once such carbons were detected, the samples were subjected to analytical pyrolysis to determine the relative yields of methoxyphenols which would provide an indication of the state of preservation of the lignin-derived structu units. We report here on the identification of lignin-derived methoxyphenols in the coalified wood samples selected for analytical pyrolysis. 

Table 1. Elemental compositions (dry mineral-matter free) for coalified wood samples...

All the coalified wood samples examined in this report were of lignite rank, as determined by their elemental compositions (Table 1). The one sample from the Moscow Basin was not analyzed for its elemental composition but was collected from a well-known Carboniferous lignite deposit. Figure 1 shows the solid-state 13c NMR data for some of the samples. Though the spectra show a large, broad... 

The phenol, the cresol isomers, and the dimethylphenols, major pyrolysis products in e Moscow wood sample, are probably also derived frt>m lignin precursors that have been altered through coalification reactions. Hatcher [fr] have shown that an increase is observed in the relative proportion of phenols and cresols as rank of coaHfred wood samples increases to subbituminous coal. Comparing the distribution of pyrolysis products from the Moscow wood to that of other coalified wood samples of Hatcher allows us to deduce that the... 

Moscow wood is more similar to coalified wood of subbituminous rank than it is of coalified wood of lignite rank, assuming that its lignin was originally similar to lignin in Cretaceous or younger woods. 

Figure 4. Py/gc/ms traces of coalified wood from the Moscow Basin.a) total ion chromatogram, b) mass chromatogram m/z=109, c) mass chromatogram m/z=138.

Dr. Spackman Several different, coalified, cell wall products have been described. In some instances the source walls were anatomically similar, and similar coalified products resulted. In other cases, the source walls were anatomically distinct and each type yielded a distinct coalified product. Moreover, the walls of each cell type seemed to respond consistently to coalification. When the walls of a particular cell type were compared with their analogs in coalified wood of a different plant genus, sometimes the products were similar, but instances were observed in which the coaly products were quite dissimilar. The latter was inferred to reflect an initial and heretofore, unrecognized difference in the nature of the source materials involved. 

Hatcher P. G. (1990) Chemical structural models for coalified wood (vitrinite) in lowrankcoal. Org. Geochem. 16,959-968. 

Hatcher P. G., Wenzel K. A., and Cody G. D. (1994) The coalification reactions of vitrinite derived from coalified wood transformations to the rank of bituminous coal. In Vitrinite Reflections as a Maturity Parameter (eds. P. K. Mukhopadhyay and W. G. Dow). American Chemical Society, Washington, DC, pp. 112-135. 

Several authors (9,12,14,16,30) have pointed out that the reaction involved in the TMAH/pyrolysis scheme is one of chemolysis rather than pyrolysis. Because the procedure is more likely a thermally-assisted chemolysis or "thermochemolysis", subpyrolysis temperatures of 300°C have also been found to effectivelly produce a suite of products similar to that observed at higher pyrolysis temperatures (16,21). Moreover, in a recent paper by McKinney et al. (31), a procedure was outlined for the characterization of lignin at subpyrolysis temperatures of 300°C in the presence of TMAH using sealed pyrex tubes. Since then, this technique has been extended to the characterization of lignin in fresh and degraded woods (52) and in coalified woods (33). 

Sample preparation. Core samples were washed with cold tap water and a stiff wire brush, then air-dried. Coalified wood fragments were scraped from bedding-plane surfaces. Elemental analyses and JC NMR spectra for these coal samples were obtained without further preparation. 

Elemental compositions. Coalified wood fragments, which indisputably represent terrestrial material, have the following moisture-and-ash-free average elemental compositions ... 

The spectrum for the coalified wood from sample WV-5 (Figure 3) shows less aromatic carbon than that of the wood fragment from the Connellsville Sandstone Member. If higher aromaticity is an indication of higher rank in coal (25). then this wood is of lower rank than the Waynesburg log, which is a... 

Figure 4. Carbon aromaticities, fa, for coalified wood fragments in Upper Devonian shales of the Appalachian basin.

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