Oxygen in coal

Figure 8. Percent oxygen converted vs. rank (2-5 min) (%), percent oxygen lost as CO or C02 (X), percent oxygen in coal as carboxyl or carboxyl groups.

It has been often proposed that the units of coal structure are linked by ether linkages. Recently, Ruberto and his coworkers (7,8), Ignasiak and Gawlak (9) concluded that a significant portion of the oxygen in coal occurs in ether functional groups. 

For many years, no satisfactory method existed for the direct determination of oxygen in coal. In practice, in the expression of the ultimate analysis it is customary to deduct from 100.0 the sum of the percentages of moisture, ash, carbon, hydrogen, nitrogen, and sulfur (ASTM D-3176) ... 

Several other methods for the direct determination of oxygen have met with some success when applied to coal and therefore deserve mention here, because it is conceivable that at some future date one of these methods (or a modification thereof) could find approval as a recognized standard method for the direct determination of oxygen in coal. 

Another method for the determination of oxygen in coal involves reduction of the coal by pyrolysis in the presence of hydrogen, whereupon the oxygen is converted catalytically to water. However, the procedure is relatively complex and the catalyst may be poisoned by sulfur and by chlorine. 

The use of gas chromatography to determine oxygen in coal is considerably faster than the methods just described. The oxygen produced from coal pyrolysis in a vacuum was converted to carbon monoxide catalytically, and the total quantity of gas was measured. Gas chromatography was then used to measure the concentration of carbon monoxide in the gas. 

British Carbonization Research Assoc iatioriTBCRA), "An Infrared Spectroscopic Study of the Influence of Oxygen in Coal on the Plastic Stage of the Coking Process", Carbonization Research Report 64, 1979, 22 pp. 

Kinetic Experiments. The technique of Charged Particle Activation Analysis (CPAA) for analysis of oxygen in coal has been described previously (J3). In the experiments to study the adsorption of oxygen onto the coal, a slight modification of this procedure has been used. Small lumps of coal were transferred in... 

Klosek, J., Smith, R. S., and Solomon, J., The role of oxygen in coal gasi cation, paper presented at 8th Annual Industrial Energy Technology Conference, Houston, June 1986. 

The lack of a satisfactory direct method for determining oxygen in coal and similar carbonaceous materials has dictated, historically (some would say hysterically), that oxygen be determined by subtracting the sum of the other components of ultimate analysis from 100 (ASTM, 2011p) ... 

However, in spite of the reliance on the difference method, over the last two decades the direct determination of oxygen in coal has been achieved by use of neutron activation (Volborth, 1979a,b Mahajan, 1985 Volborth et al., 1987). The concentration of oxygen is determined by measuring the radiation from the sample. The method is nondestructive and rapid, but if only the organic oxygen is to be determined, then the sample must first be demineralized. 

In general, fresh (unweathered) higher-rank (bituminous and anthracite) coals appear to contain little, or no, aliphatic hydroxyl, carboxyl, or methoxyl functions while brown coals are reputed to contain aliphatic hydroxyl groups. Furthermore, there have been suggestions that, except for lignites, virtually all of the oxygen in coal can be accounted for as carboxyl. 

A great deal of information about the location of oxygen in coal has been derived from infrared spectroscopic investigations. However, infrared spectroscopic data tend to suffer from their inability to be quantitative and can, at best, be used to illustrate trends throughout the progression from low-rank coals to high-rank coals (Table 10.11). 

Hinckley, C.C, et ah, Carbon monoxide detection of chemisorbed oxygen in coal and other carbonaceous materials. Fuel, 69(1), 103-109(1990). 

Carbon may be a potential candidate for such reference, but it presents in coal in a fixed form and as a part of volatiles, making such normalization doubtful. Such conclusion is confirmed by the fact that C emission intensity is strongly influenced by volatiles quantity. Oxygen in coal also exists as component of organics and as different oxides of inorganic elements (Si, Al, Mg, Ca) and also may occur as results of air breakdown on the surface of the samples. From the other side, the contents of nitrogen N are usually low in coal and still the N(I) line doublet (744.2... 

Volatiles produced on pyrolysis burn with oxygen in coal combustion processes either immediately as the volatiles leave the particles or after the volatile Jets break thro a a distance from the particle. The rate of the volatile combustion is controlled in the immediate combustion by rate of pyrolysis while in the delayed combiistion by the rate of mixing with oxygen. Information on the kinetics volatile combiastion is very limited. 

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