Coal, surface functional groups

Surface Functional Groups on Minerals and Ores Coal as an... 

A comparison of the data in Fig. 2 (Plate A, filled circles) and Fig. 5 (Plate B, open symbols) reveals that the performance of the heat-treated wood-based carbon, even under some preloading conditions, is similar to single solute TCE uptake by coal-based activated carbons in the absence of preloading [9]. The observed effect may result from some combination of optimum surface acidity, optimal type of surface functional group, and/or pore structure effects. The WVB carbon has a mesoporous pore structure, which has been observed to minimize the impacts of preloading in preliminary comparative experiments designed to isolate this effect (data not shown). Future work will employ carbon surface characterization techniques that will allow identification of functional groups and more accurate correlation with surface reactivity. 

A carbon development program was initiated at the Illinois State Geological Survey (ISGS) and the University of Illinois at Urbana-Champaign (UIUC) to investigate the effects of different carbon types, carbon structures, and carbon surface functional groups on the rate and extent of adsorption of vapor-phase mercury. The results from a study to prepare Illinois coal-based activated carbons are presented. Carbon products were made both in bench- and pilot-scale reactors. 

There is ample evidence in the literature for conversion of reactive hydrocarbons to carbonyl compounds by autoxidation. In coals, the final products of autoxidation under the conditions used in the present study could be a mixture of carbonyl and carboxylic acid surface groups. Under mild oxidation conditions, a different set of functional groups such as ethers as proposed by Liotta et al. or epoxides as suggested in Scheme V could be formed. There are numerous examples of alkoxy radicals rearranging to epoxides . Choi and Stock have shown that ethers can be produced from benzhydrol structures, which are invoked as intermediates in Scheme IV. At higher temperatures, the epoxides and ethers are unstable and may rearrange to carbonyl compounds. 

Sulfide catalysts have been dispersed directly on the coal surface. Very high dispersion on the catalyst may allow direct interactions between the catalyst and solid coal. The first application of this approach utilized molten chloride as the starting material. Later, oil- and water-soluble iron precursors were impregnated or ion exchanged onto the coal surface through the interaction with oxygen functional groups (56 -60). 

Example. A knowledge of the nature and concentration of functional groups on the surfaces of minerals is vital for understanding the response of these minerals to various mineral processing techniques. These functional groups play an important role in adsorption of surfactants used in mineral processing. In recent years, significant research efforts have been made to develop processes to beneficiate coal for recovery at fine sizes. The... 

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). 

Ash fouling appears to be initiated by the formation of a layer of sodium sulfate on the boiler tube. It is thought that thermal decomposition of sodium salts of carboxylic functional groups in the coal is the start of a sequence of reactions leading ultimately to the formation of sodium sulfate in the flame or flue gas. The convective mass transfer diffusion of the sodium-containing species through a boundary layer around the tube results in deposition of sodium sulfate on the tube surface. 

All of the comments above apply to diffusion through solid coal, not through coal s pore structure. Diffusion through the pore network has been studied thoroughly and seems to be understood (8-12). The considerations above are relevant to a reagent penetrating the solid coal to reach a functional group that is not located at a surface. 

Understanding in detail the chemistry of CO and CO-H2O mixtures over metal oxide surfaces has considerable importance for a number of reasons (1) CO-H2O is a more effective reducing medium relative to pure H2 for reduction and depolymerization of low rank coals where metal oxides and other minerals can act as in situ catalysts 48,49,50, 51,52) (2) CO-H2O is better than H2 for the reduction of some organic functional groups (53,54) (3) some metal oxides, especially basic oxides, are used as promotors in Fischer-Tropsch catalytic chemistry and their role is not understood mechanistically (55,56,57) and (4) metal oxides are often used as catalysts for the CO + H2O CO2 + H2 water-gas shift reaction (e.g., see Ref. 58 see also Ref. 59). 

M. Li, Research on Oxygen-Containing Functional Groups on Coal Surface, Taiyuan University of Technology, Taiyuan, Shanxi (2004). 

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