COAL CHARACTERIZATION RESEARCH PROGRAM

John C. Crelling - Department of Geology - Southern Illinois University, Carbondale

Coal characterization research has been the major research effort of the Department of Geology at Southern Illinois University for the last twenty years. The focus of this research is in three laboratories, the Coal Characterization Laboratory in operation since 1972, the Maceral Separation Laboratory in operation since 1984, and the Organic Geochemistry Laboratory in operation since 1987. The overall objective of the coal characterization research program is to apply an integrated approach to better understand the origin, occurrence and properties of coal in order to best utilize this resource. Two full time faculty in geology, occasional visiting professors and post-doctoral researchers, one full-time technician, and various graduate students conduct the research. The integrated research approach involves a range of levels, sub-disciplines and techniques. A good example of the integrated approach is the current work on sulfur in Illinois coal:

At the seam level, coals have been sampled and mapped to study the geological controls on the distribution of sulfur within seams.
At the maceral level, using density gradient centrifugation, macerals have been separated and analyzed for organic and inorganic sulfur.The results of this work have shown for the first time that the organic sulfur content in coal is maceral specific.
At the molecular level, work has shown that organic sulfur occurs in different forms in different macerals. The results of this integrated approach at the various levels are leading to the development of new desulfurization methods.

At this time the main research efforts are in five specific areas:

1. Petrographic Characterization of Coal and Coal Macerals - an ongoing program of separation and advanced petrographic characterization of whole coals, coal lithotypes, and single coal macerals.

2. Fluorescence Spectrophotometry - the design, construction, and operation of an unique diode array microscope system and an ongoing program of coal fluorescence research including spectral analysis.

3. Chemistry and Petrology of Sulfur and Nitrogen in Coal - a long range program detailing the chemical nature of organic sulfur and nitrogen in coal and coal macerals.

4. Reactivity of Coal and Coal Macerals - a unique program studying the combustion properties and char reactivity of single coal macerals.

5. Properties of Cokes, Chars, Carbons, and Graphites - a program of determining the technologically important properties of these materials using state-of the-art techniques of separation, microscopy, and chemical analysis.

To date this program has been very productive and successful. Since 1975 the research in this program has resulted in:

76 Master of Science degrees.
7 Ph. D. degrees (the Ph. D program was just recently initiated).
Over 100 articles published in professional journals, proceedings, and books.
Over 50 research grants received totalling over 4 million dollars.

Coal Characterization Research

Coal is an extremely complex heterogeneous material that is difficult to characterize. Coal is a rock formed by geological processes and is composed of a number of distinct organic entities called macerals and lesser amounts of inorganic substances - minerals. However, coal is not a uniform mixture of these substances. The macerals and minerals occur in distinct associations called lithotypes and each lithotype has a set of physical and chemical properties which also affect coal behavior.

Coal seams, the basic units in which coal occurs, are composed of layers of coal lithotypes, and individual coal seams may also have their own set of physical and chemical properties. For example, even if two coal seams have the same maceral and mineral composition, the seams may have significantly different properties if the lithotypes in the two seams are different. Because coal seams always occur in association with other strata, the enclosing rocks immediately above and below a coal can also affect the properties of the coal seam. This aspect is of particular importance in mine design, production, and strata control.

Thus, the compositional characterization of a coal seam must take place at a number of levels including:

the macerals,
the lithotypes,
the entire seam, and
the association of the seam with its enclosing strata.

The research program at the Coal Characterization Laboratory involves research projects of all of these levels.

In addition to compositional factors, coal properties also change with the rank or the degree of coalification of a given sample of coal. Coal is part of a metamorphic series ranging from peat, through lignite, subbituminous and bituminous coal to anthracite. The geologic factors of temperature, pressure, and time alter the original precursors of coal through this metamorphic series. As the rank of the coal changes, the properties of the coal macerals change progressively and, therefore, so also do the properties of lithotypes and the entire seam.

Because of these factors, coal characterization requires a detailed knowledge of both the maceral composition and rank of coal. All coal properties are ultimately a function of these two factors. At this time, with the rapidly expanding interest in coal and with the increasingly sophisticated uses contemplated for this abundant natural resource, the principle purpose of coal characterization research must be to adequately delimit the properties of coal macerals and rank, such that it is possible to predict the behavior of coal in any physical, chemical, biological and technological process of interest.

Maceral Characterization

Each of the various coal macerals and minerals have a unique set of physical and chemical properties which control the overall behavior of coal. Although much is known about the properties of minerals in coal, for example, the crystal chemistry, crystallography, magnetic, and electrical properties, surprisingly little is known about the properties of individual coal macerals. Two of the main reasons for this lack of knowledge about the properties of coal macerals is that they are extremely difficult to separate from coal and that they are not non-crystalline organic compounds and, therefore, not good subjects to analyze with such standard methods as x-ray diffraction or electron-microprobe analysis. The most successful characterization of coal macerals to date has been by petrographic methods, in which the individual macerals do not have to be separated. In the steel industry, for example, petrographic techniques have proven so successful in allowing the prediction of the coking properties of coal that most major steel companies have now established petrographic laboratories. To expand the usefulness of coal characterization for other processes such as coal gasification and liquefaction, the properties of the individual macerals must be better understood. This improved understanding requires the separation of pure maceral concentrates which can be analyzed with modern chemical techniques of coal analysis.

In summary, the complete characterization of coal must include the characterization of individual coal macerals. Because the macerals have proven to be difficult to separate from coal, the most successful ways of characterizing macerals have been in situ techniques including the standard petrographic methods of maceral and reflectance, the recently introduced techniques of fluorescence spectral analysis, and the experimental techniques developed at SIUC of laser time-domain microscopy and photoacoustic microscopy.

There are three established methods of maceral separation. The standard techniques of hand-picking and sink-float have been widely used but have never given petrographically verifiable single maceral concentrates. However, the technique of density gradient centrifugation (DGC) has provided much better maceral concentrates that can be analyzed with modern chemical techniques such as NMR and Pyrolysis Mass Spectrometry.

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