Coal-derived materials characterization

Characterization of Coal-Derived Materials by Matrix Isolation Spectroscopy... 

The identification and quantitative determination of specific organic compounds in very complex samples is an area of intense current research activity in analytical chemistry Optical spectroscopy (particularly UV-visible and infrared absorption and molecular fluorescence and phosphorescence techniques) has been used widely in organic analysis. Any optical spectroscopic technique to be used for characterization of a very complex sample, such as a coal-derived material, should exhibit very high sensitivity (so that trace constituents can be determined) and extremely great selectivity (so that fractionation and separation steps prior to the actual analysis can be held to the minimum number and complexity). To achieve high analytical selectivity, an analytical spectroscopic technique should produce highly structured and specific spectra useful for "fingerprinting purposes," as well as to minimize the extent of overlap of spectral bands due to different constituents of complex samples. 

The material presented herein was meant to provide an indication of the utility of ESR and ENDOR spectrometries as probes to characterize the free radicals in coals and coal-derived materials. The results suggest that, in addition to their use in characterization studies, the techniques may have potential in helping to elucidate the mechanism of coal liquefaction. They further suggest that coals may be heat-treated directly in the cavity of an ESR spectrometer with the assurance that reliable data will be obtained provided simple precautionary measures are taken to avoid unwanted effects. Similar in situ ESR measurement of coals under liquefaction conditions remains a possibility, although considerable... 

Only a limited number of coal-derived pitches were examined by H NMR because of their low solubility in solvents commonly used m conventional proton magnetic resonance. Table 12 reports the distribution of hydrogen for three of the pitches. Unlike coal-tar pitches, which typically have over 85% of the hydrogen bonded to aromatic carbon, the materials listed in Table 12 are characterized by a high content of aliphatic hydrogen. 

Coal is used in processes such as combustion (Chapters 14 and 15), carbonization (Chapters 16 and 17), liquefaction (Chapters 18 and 19), and gasification (Chapters 20 and 21). The products derived from coal are used as precursors of other materials and in the production of chemicals (Chapter 24). Thus, a coal must be characterized before it is used, whether as a single or blended coal, in order to find out the properties of a coal, to determine its quality, and to predict its technological behavior (Chapters 4, 8, and 9). 

Cherepy et al. (2005) conducted a more thorough examination of the dependence of anode rate at fixed polarization. The carbon materials included a variety of charred vegetable material, furnace and thermal blacks, calcined petroleum and charred coal-derived pitch, and fine graphite particles. The structure of these materials was characterized with use of a crystallinity index after Fugimoto (1994). This index is a... 

Under the optical microscope the texture of products derived from the three coals studied show an anisotropy of the type which already has been described for similar materials (I, 4, 9). The texture of the l.t. pitch coke is entirely isotropic, whereas the h.t. pitch coke is characterized by a pronounced anisotropy in bands. The anisotropy of the carbonization products of mixtures of l.t. and h.t. pitches varies linearly as a function of the composition of the mixture (8). 

All of the papers in this book deal with the chemistry and characterization of coal macerals and, as such, recognize the heterogeneous nature of coal. Coal is, in fact, a rock derived from a variety of plant materials which have undergone a variety of physical and chemical transformations. While a number of chemical studies of coal have found the concept of a single "coal molecule" useful, the papers in this book are aimed at characterizing in some way the various macromolecules that comprise the many kinds of coal macerals. 

Bituminous materials are dark brown or black, semi-solid or liquid, thermoplastic mixtures of hydrocarbons derived from natural or synthetic processes in which hydrocarbon mixtures have lost their volatile components leaving a denser residue. Natural bitumens come from exposed and weathered petroleum and rock deposits. Synthetic bitumens come from the residue remaining after the distillation of petroleum, coal tar, and other organic materials like wood and peat. The complexity of the high molecular weight hydrocarbon oils and resins bitumens contain make complete chemical characterization impossible. The terms bitumen, tar (8007-45-2), pitch (61789-60-4), and asphalt (8052-42-4) apply to any of these substances, although pitch and tar also describe the sticky resins that exude from various trees. 

Coal and its derivative products are used in a range of nonenergy applications such as the production of carbon anodes for the aluminum industry, graphite electrodes for the steel industry, and as a component for a number of other carbon-based materials and chemicals. Because coal is a heterogeneous material that is made of up organic and inorganic components, it must be characterized before it is used, to understand its properties, determine its quality, and predict its technological behavior. 

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