Solubilization techniques, coal

We therefore draw attention to a novel technique which allows solubilization of coal without rupture of covalent bonds. This utilizes the fact that the acidity of low-rank coals, which is largely due to their high -OH contents, can be enhanced by proper choice of a medium. 

The introduction of atomic absorption spectroscopy has resulted in major advances in the rapid analysis of many elements. Initially, atomic absorption was applied only to aqueous systems or to materials that could be readily solubilized. There are methods to analyze major elements in such complex materials as silicates and vitreous siliceous coal ashes (1-5). More recently, lithium metaborate has been reported to be a good fluxing agent (6) and has also been used in conjunction with atomic absorption analysis in silicate analysis (7). This paper describes a lithium tetraborate-atomic absorption analytical technique which is being used to analyze coal ash. 

In the analysis of the glycol-solubilized coal we applied all the techniques used in our studies on coals, SRC and SRL products (4). The effect of the reaction on the aromatic units was shown by comparing selective oxidation products from the coal and its hydrolytic product. These results were compared with the aromaticity of the product deter-... 

Solvent Fractionation. To facilitate later structural analysis, we separated the coal into structural types by solvent fractionation. Some other workers using the phenol depolymerization method to solubilize coal have used gas chroma-tography/mass spectroscopy (GC/MS) techniques to identify individual compounds (11, 13). However, with material containing large amounts of phenol and other polar groups, elaborate preparation and separation schemes have to be used to avoid contamination of the chromatography columns. As the emphasis of the present work was on structural characterization of the whole coal rather than on detailed examination of small parts of it in order to elucidate the chemistry of the phenolation reaction, we used the relatively simple scheme shown in Figure 1. 

The removal of both mineral matter and sulfur species to very low values would provide premium solid fuels and possibly new chemical feedstocks. Several techniques are being explored to achieve these goals. The mineral matter in a physically cleaned coal can be further reduced by the solubilization of the aluminosilicate minerals. This can technically be accomplished with the use of alkaline and then acid treatments. A variety of studies are under way to define the conditions required for effective removal of the mineral matter and establish the amount of sulfur reduction that can be accomplished. Others involve the use of fine grinding to liberate the coal from the mineral matter. Then an agglomerant is used to separate the coal matter from the aqueous phase containing suspended mineral matter. A new approach uses microwave energy to selectively decompose the clays into species that can be solubilized and removed. Still another technique involves treatment with carbon dioxide to reduce the particle size and permit the liberation of the mineral matter. Over the next few years these will be studied further and it is hoped that coal will become available in a form with less of these interesting, but not entirely desirable mineral species. 

Depolymerization of coal is a technique which, it is claimed, solubilizes coal by cleaving methylene bridges in the coal. The methylene chains joining aromatic groups can be cleaved at the ring and the free alkyl group and then alkylate another aromatic substrate (Larsen et al., 1981 Mastral-Lamarca, 1987 Sharma, 1988) ... 

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