Molecular structure of coals

Figure 9.19 shows a characteristic molecular structure of coal, featuring an aromatic carbon backbone and a wide range of bond strengths. General plant matter (as distinct from the fruiting bodies that are often used as food and are... 

NMR measurements can distinguish hydrogen In rigid molecular structures of coals, l.e. structures that do not undergo appreciable reorientation and/or translation during time Intervals < 10 s, from hydrogen In mobile structures which possess more rapid molecular motions characteristic of fused or rubbery materials. 

The chemistry of coat liquefaction Is less well understood and how studies of this matter are Interpreted depends to some extent on how the "molecular" structure of coal Is perceived. 

Typical molecular structures of coal, petroleum, and natural gas. 

Curie point pyrolysis mass spectrometry has also been valuable in providing information about the chemical types that are evolved during the thermal decomposition of coal (Tromp et al., 1988) and, by inference, about the nature of the potential chemical types in coal. However, absolute quantification of the product mixtures is not possible, due to the small sample size, but the composition of the pyrolysis, product mix can give valuable information about the metamorphosis of the coal precursors and on the development of the molecular structure of coal during maturation. However, as with any pyrolysis, it is very important to recognize the nature and effect that any secondary reactions have on the nature of the volatile fragments, not only individually but also collectively. 

Davidson, R. M. 1980. Molecular Structure of Coal. Report ICTIS/TR08, International... 

R. M. Davidson, "Molecular Structure of Coal" IEA Coal Research, London, 1980. 

The size and distribution of pores and the size, distribution, and identity of minerals in coal specimens from an eastern Kentucky splint coal and the Illinois No. 6 coal seam were determined by means of transmission electron microscopy (TEM) and analytical electron microscopy (AEM). The observed porosity varies with the macerals such that the finest pores (<2-5 nm) are located in vitrinite, with a broad range of coarser porosity (40-500 nm) associated with the macerals exinite and inertinite. Elemental analyses, for elements of atomic number 11 or greater, in conjunction with selected area diffraction (SAD) experiments served to identify the source of the titanium observed in the granular material as the mineral rutile. Only sulfur could be de-tected in the other coal macerals. Dark-field microscopy is introduced as a means for determining the domain size of the coal macerals. This method should prove useful in the determination of the molecular structure of coal. 

Although the basic chemical features of coal can be qualitatively and in some instances semiquantitatively specified, average-structure models that purportedly reflect statistically preferred molecular structures of coal offer little that advances an understanding of coal. In part, this is due to a continuing paucity of relevant or reliable data and to the procedures used to formulate the constructs. But meaningful representations of molecular structure are currently also precluded by indications that the assumption that underlies average-structure models, namely, that there exists a more or less unique, systematic, rank-dependent, molecular chemistry of coal, is not sustained by the current evidence. Several examples, all drawn from the open literature, are presented to support the view that the chemistry of a coal is heavily influenced by its source materials and early formative history and that coals of similar rank may therefore be chemically much more diverse than is usually supposed. 

Because other means of exploring coal structure at best yield semi-quantitative data, both of these inferences bear importantly on the significance of structural models that purport to reflect the molecular structure of coal. 

ABSTRACT Currently coal and methane outburst disasters still remain seriously. This article aims at looking for the source of methane from the microscopic molecular structure of coal, chemical changes and particle interactions in chemical changes of coal and methane outburst during the impact are theoretically analyzed and a set of electromagnetic radiation experimental scheme is set to research the possibility of fracture and bond of CHj-, CHj = CH- and H- and creating new methane. The basic theory of seam methane disaster prevention through the experiment is innovated. 

There is a much more important aspect of coal composition that must be considered. For example, chemical constituents represent the molecular structure of coal but the form in which these chemical constituents eventually become incorporated into the coal matrix must also be given due consideration. 

There has, however, been a tendency to depart from these types of investigations over the last four decades and to concentrate on the so-called molecular structure of coal (Chapter 10) in the hope that elucidation of this elusive entity will assist in the understanding of the technological behavior of coal. However, as stated earlier, the large number of possible chemical constituents of the source material (Chapter 3) and, in addition, an incomplete knowledge of the prevailing maturation process(es) make the elucidation of the molecular structure (Chapter 9) of coal (if there is such a thing) very difficult, if not impossible. 

In the early years of coal science, one of the prime motives for investigating the oxidation of coal was the production of chemicals from coal. More recently, the oxidation of coal using specific oxidants has become a prime means by which structural entities in coal have been identified. This has, of course, led to postulates of the molecular structure of coal. 

Cronauer, D.C. and Ruberto, R.G. 1911. Report No. EPRI-AF442. Electric Power Research Institute, Palo Alto, CA. Davidson, R.M. 1980. Molecular structure of coal. Report No. ICTIS/TR08. International energy Agency, London, U.K. 

Various attempts to elucidate the molecular structure of humic acids have been reported, but the complex nature of these oxidation products appears to defy resolution. Indeed, the number of potential species that may constitute humic acid lends little assistance to the problem and even complicates the matter still further. Thus, any deductions that have been reported with respect to a molecular structure for humic acids must be open to severe criticism because of the speculation and guesswork that are involved. In fact, as with the studies relating to the molecular structure of coal, such claims are only of very limited value and add to the general confusion that already exists. 

Therefore, for the molecular structure of coal, we should accept and adopt the view of an average molecular structure to build coal molecule structures, which might not represent the entire coal structure, but model one or several aspects of coal [27]. Furthermore, when we construct a suite of concrete models aiming at different coal ranks and coal types related to the practical reaction processes, we are convinced that the models constructed by the above principles are reasonable, exact, and scientific. They can give a reasonable microscopic description, reflect the properties of coal in one or several aspects, and provide reasonable microscopic explanation for the particular and local macroscopic property [28]. 

A number of studies have focused on the molecular structure of coal [29-31]. The structures can be derived using data from a variety of sources, including coal atomic composition, analysis of pyrolysis products, extraction or liquefaction treatments of coal samples, and spectroscopic analyses using GC/MS, NMR, and IR. In our study, the method of Py-GC-MS, which consists of a CDS 5250 pyrolysis autosampler and focus GC-DSQII, has been used to study the pyrolysis of coal in order to obtain information about coal stmcture. 

These are the reasons why the reservoir engineers are not interested in the detailed molecular structure of coals, their attention is rather concentrated on the problem How can flow the methane in the inside structure of coals, that is, they think in micropores, cavities, fractures giving possibility to transport of methane through the coal. It is indifferent to them how these pores, cavities etc. taken shape from the concrete molecular structure. To demonstrate this statement only two examples, from the recent literate, are shown here. King and Ertekin [7] supposed a desorption process from internal coal surfaces then diffusion through matrix and micropores and finally a fluid flow in network (See Figure 3). 

It is believed that the earth s coal deposits were formed as organic matter from prehistoric plant life was subjected to high pressures and temperatures over long periods of time. The molecular structure of coal involves haphazard arrangements of aromatic moieties (highlighted in orange boxes), connected to each other by nonaromatic links (shown in green boxes) ... 

The complete molecular structure of coal is one of the unsolved secrets of nature. Of the various analytical methods available, NMR spectroscopy has proved to be of special importance in coal research. Solid-state NMR techniques allow the structure of coal and coal products to be investigated in a direct and nondestructive way. 

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