Oxidized coal, definition

Natural coal and oil contain many compounds of nitrogen. One of the worst products of their combustion is the acidic oxide of nitrogen, NO. At once, we are startled by this terminology, because the Lowry-Brpnsted definition of an acid involves the release of a proton, yet nitrogen monoxide NO has no proton to give. 

If it is also recalled that alkali soluble material (humic acid) builds up much more slowly than acidity (and always markedly dependent on T and [O]), and that the distinctly acidic parent coal is effectively insoluble in alkali, it becomes evident that acidity and alkali solubility are not necessarily covariant, and that accepted definitions of humic acid are, chemically speaking entirely arbitrary. Under the conditions of this study the oxidation appears to involve two simultaneous but seemingly unrelated reactions which result in the development of acidity and in molecular (skeletal) breakdown, respectively, and this suggests that alkali solubility is mainly a consequence of degradation which is only coincidentally connected with the formation of acidic functional groups. Figure 20 illustrates this concept qualitatively and leads to the inference that the wide spread in molecular weights of humic acids reported... 

The SO2 thus formed can then be used to make H2SO4, can be treated with limestone, or can be converted to elemental sulfur. The conversion to elemental sulfur can be achieved either by the Claus process or by treating SO2 with a reductant such as carbon (Trail/Resox process). An attractive way of recovering sulfur is by reacting the SO2 with iron sulfide itself to form iron oxide and elemental sulfur. Thus, if the SO2 formed by the oxidation of iron sulfide is recirculated, elemental sulfur can be produced in a single step. The problem with this scheme is that the elemental sulfur needs to be separated from the exit stream by cooling, and the SO2 needs to be reheated. Karr, et al. ( ) and Schrodt and Best (7) carried out experiments to test the feasibility of this scheme. The latter authors, using coal ash as the sorbent material, concluded that sulfur recovery by this method is both technically and economically unattractive. The same may not be true for the iron oxide-silica sorbent. More studies are necessary before a definite conclusion can be drawn. 

The definition of environmental chemistry given above is illustrated for a typical environmental pollutant in Figure 2.3. Pollutant sulfur dioxide is generated in the anthrosphere by combustion of sulfur in coal, which has been extracted from the geosphere. The S02 is transported to the atmosphere with flue gas and oxidized by chemical and photochemical processes in the atmosphere to sulfuric acid. The sulfuric acid, in turn, falls as acidic precipitation, where it may have detrimental effects, such as toxic effects, on trees and other plants in the biosphere. Eventually the sulfuric acid is carried by stream runoff in the hydrosphere to a lake or ocean, where its ultimate fate is to be stored in solution in the water or precipitated as solid sulfates and returned to the geosphere. 

Figure 2.3 Illustration of the definition of environmental chemistry by the example of pollutant sulfuric acid formed by the oxidation of sulfur dioxide generated during the combustion of sulfur-containing coal. 

Since in some processes with coal feedstock (e.g., the Lurgi Process) the reaction according to Equation (61) may proceed to a considerable extent, they are more often referred to as coal gasification rather than as partial oxidation, but this is just a matter of definition. 

Many oxidative degradations also have been carried out to break coal down into simpler species (10, 18-21) however, isolation and identification of phenols such as p-hydroxybenzene (I), vanillic (II), and syringic (III) derivatives, which are considered as characteristic lignin oxidation products (1, 4, 17, 22, 23), have not yet been confirmed definitely. 

It is, in fact, apparently contradictory observations of this type (where, more often than not, direct comparisons of the experimental conditions are difficult, if not impossible) that also add many complications to coal chemistry. Of course, the apparent contrasting nature of the data is dependent upon the definition of extractable matter. Organic nonpolar material that is extractable by organic solvents might be expected to decrease with oxidation. On the other hand, polar material such as humic adds that are produced by coal oxidation should be expected to decrease. It may be, after all, a matter of definition. 

FIGU RE 1.1 Illustration of the definition of environmental chemistry exemplified by the life cycle of a typical pollutant, sulfur dioxide. Sulfur present in fuel, almost always coal, is oxidized to gaseous sulfur dioxide, which is emitted to the atmosphere with stack gas. Sulfur dioxide is an air pollutant that may affect human respiration and may be phytotoxic (toxic to plants). Of greater importance is the oxidation of sulfur dioxide in the atmosphere to sulfuric acid, the main ingredient of acid rain. Acidic precipitation may adversely affect plants, materials, and water, where excessive acidity may kill fish. Eventually, the sulfuric acid or sulfate salts end up in water or in soil. 

Ammonia decomposition over Fe, Cu, Ag, Au, and Pt Hydrolysis of starch to glucose catalyzed by acids Mixture of coal gas and air makes a platinum wire white hot Measurements on the rate of H2O2 decomposition Selective oxidation of ethanol to acetic acid over platinum Comprehensive paper on the H2 + O2 reaction on platinum foils, including reaction rates, deactivation, reactivation, and poisoning Definition of catalysis, catalyst, and catalytic force First quantitative analysis of reaction rates Systematic studies on the concentration dependence of reaction rates First concise monograph on chemical kinetics Definition of order of reaction Arrhenius equation k = u exp (-Ea/RT)... 

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