Structure of coals

Coals (the plural is deliberately used because coal has no defined, uniform nature or structure) are fossil sources with low hydrogen content. The structure of coals means only the structural models depicting major bonding types and components relating changes with coal rank. Coal is classified, or ranked, as lignite, subbituminous, bituminous, and anthracite. This is also the order of increased aromaticity and decreased volatile matter. The H C ratio of bituminous coal is about 0.8, whereas anthracite has H C ratios as low as 0.2. 

FIGURE 18.16 A highly schematic representation of a part of the structure of coal. When coal is heated in the absence of oxygen, the structure breaks up and a complex mixture of products—many of them aromatic—is obtained. 

Mott, R. A. Contribution to Discussion, "Proc. Conf. on Ultra-fine Structure of Coals and Cokes , British Coal Utilization Research Association, 1944, pp. 156-159. 

The Effect of Catalyst Concentration, Temperature, and Residence Time on the Chemical Structure of Coal Hydropyrolysis Oils... 

While, oxygen containing structures of coal must be playing important parts in the course of coal liquefaction. It will be key points that what kinds of oxygen containing structure are decomposed and what kinds of structure are formed in the course of reaction. It has been proposed (5,6) and recently stressed (2-11) that the units of coal structure are linked by ether linkage. 

The Thermal Decomposition of Aromatic Ethers. According to the results of Table I, the bond scission of oxygen containing polynucleus aromatic structure of coal at liquefaction temperature of 450°C seems to occur mainly at methylene or ether structures. Therefore, it will be very important to study the... 

Diaryl ether must be one of the important structures responsible for the liquefaction of coal among various oxygen-containing organic structures of coal. 

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... 

Much of the research pursued by the authors of this paper and by their associates has involved studies of the catalytic hydrogenation of coals in the absence of solvent. The technique has been used to elucidate the mechanisms of catalytic coal liquefaction and to provide simultaneously some insight into the structure of coals. Peter Given was directly instrumental in providing the incentive for this research which has extended since 1983. Previous findings were disseminated through several publications (4-8. In this paper, some of the earlier data have been collated with more recent results (9) to provide an account of the relevance of these studies to the two-component concept. 

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. 

CAMD modeling has been used in this study to compare and partially to differentiate several postulated bituminous coal models based on their physical structures, minimum energies, and other characteristics. It is clear from the folding of the CAMD structures after molecular dynamics (especially in Figures 3c and 4c) that simple two-dimensional representations cannot adequately represent the structure of coal. Inter-cluster bonding has a powerful influence on coal structure when three-dimensional models are employed. 

For the above reaction to occur, the aromatic nuclei in compound 1 should carry activating groups, such as hydroxyl, alkoxy, or fused ring aromatics". As a result of reaction with BF3 and phenol, the macromolecular structure of coal should undergo rupture at the aliphatic bridges, and these bridges are transferred to phenol molecules to produce bisphenols. Analysis of the bisphenols should provide information on the aliphatic bridges present in coal structure. 

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. 

Coconut-shell-based GACs These have a high portion of micropores and present surface areas generally over 1000 m2/g and apparent densities of about 0.50 g/cm3. Being manufactured mainly from vegetative material, they do not exhibit the fully developed pore structure of coal-based carbons. They are used in both vapor- and liquid-phase applications. Coconut shell-based carbon is slightly more expensive to produce than coal-based GAC, since about only 2% of the raw material is recoverable as GAC, versus 8-9% for coal-based carbons. In Table 4.1, the basic properties of common materials used in the manufacture of activated carbon ate presented. 

This introduction to the geochemistry of coal includes discussions of the origin and the physical and chemical structure of coal in addition to a discussion of the composition of coal. 

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

Dunningham, A. C., Proc. Conf. Ultra-Fine Structure of Coals and Cokesy British Coal Utilisation Research Assoc. 1944, 57. 

Marie Mackowsky. Have you ever recognized an influence of the electronic beam on the structure of coal Nemetschek and I observed that the energy of the electronic beam can graphitize the coal, especially if one uses high magnification. 

In 1933, Francis (4) measured the rate of the alkaline permanganate oxidation of coal at screen cuts of through 60 on 100 and through 100 on 200 mesh. He found that the rate of reaction was directly proportional to the external area of the different coal samples, thus inferring that there is little internal area available for reaction. In 1936 Cauzelin and Crussard (8) reached the same conclusion in similar experiments. Since 1933 a vast and complicated pore structure of coal has been discovered. However, the discovery of this pore structure does not invalidate the experimental results of Francis as some authors (19) have suggested. 

While the high energy, short duration irradiation of coal produced a simple mixture of low molecular weight gases, it gave little information concerning the chemical structure of coal. 

Triazine is a good solvent for solvent-refined coals. This may prove to be exceptionally important in spectrometric studies on the structures of coals (81MI22000). 

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