Oxidation of coal

The combustion of coal may be simply represented as the staged oxidation of coal carbon to carbon dioxide... 

Partial oxidation of coal to form either synthetic fuel, syngas, or synthetic natural gas represents a potential use of oxygen (see Fuels, synthetic). 

Neither benzenepentacarboxylic acid nor mellitic acid are manufactured commercially, but synthetic mellitic acid can be purchased as a laboratory chemical (99). Both can be synthesized by oxidizing the corresponding methylbenzenes or other substituted benzenes, and both are present in trace amounts after oxidation of coal or coal-like substances. 

A search for alternative energy supplies has triggered efforts to develop efficient homogeneous catalysts for Fischer-Tropsch-type syntheses via hydrogenation of carbon monoxide, a likely future key material available, for example, through oxidation of coal (33, 327, 328, 417, 418). Metal cluster systems have been used in attempts to emulate the presently used heterogeneous catalysts. The important reactions are methanation,... 

This process (usually with addition of steam) can also be used to generate gas mixtures from partial oxidation of coal for synthetic gasoline production (see (4), above). Fluidized beds offer convenience for continuous handling of the feed solids. 

Several important chemical reactions for the conversion of coal to methane are shown in Table 2. Steam conversion involves the reaction of coal with steam to produce hydrogen and carbon monoxide. Hydrogen conversion is a reaction in which coal and hydrogen react to form methane. Oxygen conversion produces hydrogen and carbon monoxide by partial oxidation of coal. Methan-ation involves a reaction in which methane and water are produced from carbon monoxide and hydrogen. The water gas shift reaction between carbon monoxide and steam produces carbon dioxide and hydrogen. 

Air oxidation of coal causes a significant decrease in the concentration of aliphatic bridges as determined by acid-catalyzed transalkylation of coal with phenol. Infrared analysis of the raw and oxidized coals indicate that the hydrocarbon bridges are converted to carbonyl groups. Plausible explanations have been offered for the formation of carbonyl groups from aliphatic bridges. 

The compound is obtained from the spent oxide of coal gas purifiers. In the laboratory it may be prepared by treating ferrous sulfate solution with a solution of potassium cyanide ... 

An aromatic compound which is employed along with glycerol in the production of alkyd resins is phthalic anhydride. The conventional process for the manufacture of this chemical has been from the catalytic oxidation of coal tar naphthalene, and annual production of the anhydride in recent years has been around 150,000,000 pounds. In 1946 production was started (4) in a plant of the Oronite Chemical Co. at Richmond, Calif., to produce phthalic anhydride by the oxidation of o-xylene produced in a hydroformer unit of the adjacent Standard Oil Co. of California refinery. The Oronite plant was reported to have a design capacity of 7,000,000 to 8,000,000 pounds per year of 99.7% pure phthalic anhydride. 

Growth of the 1700 cm.-1 band is accompanied by reduction in the intensity of all absorptions associated with nonaromatic C-H groups. Currently held views are that aliphatic structures are destroyed during the oxidation of coal, and the changes in absorption pattern support this. 

This equation will be referred to as the correlation between rank and reactivity. In this paper the various correlations between rank and reactivity in the literature will be compared with the correlation presented here for liquid phase oxidation of coal with molecular oxygen in alkali. 

All the available data on the rate of liquid phase oxidation of coal have been taken in batch reactors. Interpreting this data is complicated by the homogeneous oxidation of the intermediate organic acids formed and the con-... 

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. 

The availability of the pores for reaction is a difficult problem in any gas or liquid phase reaction with coal. Liquid phase oxidation of coal in alkali... 

Concurrent studies in these laboratories (15) indicate that humic acids heated to temperatures around 300°C. (or higher) will, even in the presence of oxygen, tend to lose their acidic functional groups and revert to an essentially coal-like material. In view of this and observations made in the course of the investigations reviewed here, the overall reactions occurring during dry oxidation of coal can be put in the form ... 

Pretreatment mild oxidation of coal to eliminate caking (agglomeration) tendencies. 

Infrared Spectroscopy can be used to gain important information about functional groups on surfaces of minerals, but quantitative determinations have been difficult. For complex materials, like coal, the spectra are still not resolved fully for example, there is great deal of uncertainty about the 1600cm-1 band which is the dominant feature of all coal spectra. Fourier-transform infrared spectroscopy, which is a considerable improvement in this technique, has recently been used to investigate low-temperature oxidation of coal (13). 

Although the selective oxidation of coal has been extensively studied (31-33, surprisingly little has been reported about sulfur species in the oxidation products. Even less is known about the distribution of organic sulfur species between different coal macerals despite the fact that this information is important for the development of any future desulfurization technology. 

Oxidation of Coal and Coal Macerals. Extraction residues were oxidized as outlined in the experimental section. Two oxidation procedures were adopted - i). excess oxidant oxidation and ii). oxidant starved oxidation (partial oxidation). 

Bearse, A. E. Cox, J. L. Hillman, M. Production of Chemicals by Oxidation of Coal. Battelle Energy Program Rep., Columbus, Ohio, 1975. 

Carbon molecular sieves are produced by controlled pyrolysis and subsequent oxidation of coal, anthracite, or organic polymer materials. They differ from zeolites in that the micropores are not determined by the crystal structure and there is therefore always some distribution of micropore size. However, by careful control of the manufacturing process the micropore size distribution can be kept surprisingly narrow, so that efficient size-selective adsorption separations are possible with such adsorbents. Carbon molecular sieves also have a well-defined bi-modal (macropore-micropore) size distribution, so there are many similarities between the adsorption kinetic behavior of zeolitic and carbon molecular sieve systems. 

Oxidation of Coal Particles—It is important in combustion engineering to have available data on the oxidation of coal particles. The relationships between oxidation-rate and temperature and particle-size here described, while specifically limited to carbonaceous materials,... 

Both the initial oxidation and the effect this oxidation has on the processing characteristics of the coal have been an area of interest for many years (1). In the last few years there has been a renewed interest in tTTe oxidation of coal and several new analytical techniques have been applied to this problem (2-6). Several salient features of the process have been revealed including the chemical forms the oxygen takes when bound to the coal. It has been noted that the oxidation is not uniform throughout the particle as evidenced by the formation of a discoloration of the coal near the surface (7). This "oxidation rim" is directly related to the behavior of the coal. 

Several salient features have emerged from work done in other laboratories on the low temperature oxidation of coal. 

Apart from its thermochemical and catalytic activities, it. seems very probable that pyrites can assist in the oxidation of coal in a purely mechanical manner as well, inasmuch as it tends to swell on oxidation and thus to increase the mechanical disintegration of the coal, thereby exposing larger surfaces to aerial attack.4... 

Moisture accelerates the oxidation of coal, but an excess of water retards it, partly because it enters the pores and thereby renders it less accessible to the atmosphere and partly also because its evaporation tends to keep down the temperature. Oxidation proceeds in the absence of bacteria.9... 

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