Coalification process

The high-volatile Liddell bituminous coal (Figure 2 (E)) shows little indication of thermally-activated molecular mobility below 500 K. There is some fusion between 500 and 600 K followed by a major fusion transition above 600 K which appears very similar to the high temperature transition of the Amberley coal. This Liddell coal, however, has only 6% liptinite, has a crucible swelling number of 6.5 and exhibits considerable Gieseler fluidity. We therefore attribute this high temperature fusion event to the aromatic-rich macerals of the coal and associate it with the thermoplastic phenomenon. This implies that a stage has been reached in the coalification processes at which aromatic-rich material becomes fusible. 

Another proof of the importance of temperature is the fact that there is often a strict relationship between the run of isovols and the run of isotherms in deep profiles, both being influenced no doubt by the varying thermal conductivity of the different rocks. The strong influence of temperature on the rank of coal is obvious in the case of contact-metamorphic coals, whose rank increases distinctly when approaching the intrusive body. Apart from these geological observations, all experiments on artificial coalification have shown that temperature is the decisive factor in the coalification process. Thermodynamic and reaction kinetic considerations (9) also support this opinion. 

Time generally is considered to have relatively small influence on the coalification process. To prove this it is usual to offer the example of the Mississippian lignites from the Moscow Basin which, despite their great geological age, still lack bituminous characteristics. These coals, however, were never buried to any great depth. 

Figure 16. The run of isovols depends on the relationship in time of the coalification process and folding (schematic)...

Pressure of the overburden does not cause chemical reactions which lead to a higher rank. Experiments have shown that static pressure even retards coalification processes. By contrast, pressure affects the physical properties, notably the porosity and moisture content in low rank coals. Further, the optical anisotropy of vitrinites (which is a tension anisotropy) is caused by pressure. Shearing movements have influenced the chemical coalification only occasionally and locally in the foredeeps that we have studied (for instance in the immediate vicinity of overthrusts). In such cases the tectonic movements probably were so quick that the friction heat and the shearing could operate. Shearing in no way can account for the gradual increase in coal rank with depth. 

Dr. Berkowitz I must question the validity of Dr. Teichmiiller s rather definite conclusions about the relative roles of time, temperature, and pressure in the coalification process. From an examination of Ruhr coals, Dr. Teich-miiller said that only temperature plays a significant role. I suggest that conclusions drawn from data for coals in other areas (e.g., Alberta and Pennsylvania) would lead to the conclusion that pressure rather than temperature was the determining variable therefore, I doubt whether Dr. Teichmiiller s quite unqualified statements could have general validity. Indeed, from first principles one would deduce a rather complex and variable situation. Thermodynamically, one could perhaps rule out time as an important parameter since, unless one accepted the concept of a "tunnelling factor, time alone will not... 

Douglas S. Montgomery. Dr. Hacquebard stated that in his experience there was no more fusinite in anthracite than in low rank coals, and fusinite therefore did not, in his opinion, result from the coalification process. Could the same statement be made concerning the semifusinite ... 

Extended discussion of these speculative relationships is unwarranted until more critical information is available. The multilinear aspect of coalifi-cation described previously (3, 6) appears to be well illustrated by the Brandon woods. It seems evident that from a single plant tissue various dissimilar materials may result as products of coalification. Those described represent macerals related to the vitrinite, micrinite, and resinite maceral series. Because of the position of these materials in their respective series—i.e., only slightly metamorphosed and anatomically relatable to the woods of extant plants— their detailed study using appropriate chemical and physical methods should reveal useful information concerning the basic composition of coals of both higher and lower rank and simultaneously add to our knowledge of the coalification process. 

The authors agree with Dr. Given that initial physical structure and initial chemical composition both influence the course of coalification. The materials described should be studied further to clarify the significance of each and to evaluate the suggestion that the coalification processes have involved saturation of cell wall residues with foreign, flavonoid pigments. 

Coal is mainly composed of carbon, hydrogen and oxygen and is formed from plants by a coalification process. During this process the oxygen, constituting about 40% of the plant material, is split off as, for example, H20 and C02. The process can be... 

Fig. 88b. The change of naphthenic and aromatic rings during the coalification process, according to Meijs. R/C=number of rings per carbon atom.

Lignite is an early stage in the coalification process and thus could be expected to retain some characteristics of wood. This relationship is illustrated by the electron micrographs shown as Figures 1 and 2. Pieces of plant debris, presumably twigs or rootlets, can be seen in Figure 1. Remains of the woody cellular structure are visible in Figure 2. This structure is similar to that of a softwood (5). 

Solid-state NMR has proved to be an extremely useful tool for examining the major changes in organic matter occurring during the coalification process (Hatcher et al., 1982, 1989a, b Botto, 1987 WUson, 1987). Studies of coals of... 

Hatcher P. G., Wilson M. A., Vassallo A. M., and Lerch H. E. (1989b) Studies of angiospermous wood in Australian brown coal by nuclear magnetic resonance and analytical pyrolysis new insights into the early coalification process. Int. J. Coal Geol. 13, 99-126. 

Three hypotheses have been considered to explain the origin of the rods found during this work (1) bacterial remains (2) plant cell remains (3) artifacts formed during phase separation in the coalification process. 

Peat is formed from degradative remains of plant material, mainly of the peat mosses Sphagnum and Hypnum. Peat types are categorized by botanical composition and degree of coalification. In peat, the coalification process is only beginning, and lignin,... 

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