Fly ash is a by-product from the combustion of coal. The 1985 annual US production was estimated to be about 1 x 108 metric tons. The utilization of fly ash during the 1980s remained stable at about 25% per year. Because of its pozzolanic properties, nearly 50% of the utilized fly ash is consumed in the production of cement and concrete. The vast quantity of fly ash that is not being used and its availability throughout the country and worldwide have motivated research for new uses in commerce and industry. Little is known of the organic adsorbent properties of fly ash. However, if they are found to be favorable, the potential commercial applications of the adsorptive characteristics of fly ash could include its use as an adsorbent sandwich for organics in combination with landfill or other dump-site liners, in traps for organics in waste waters, in filters for organics in process air streams, and as a stabilizer for organic wastes in drums. Variables that may affect the adsorbability of the fly ash towards organics in water include temperature; solution pH; and interactions between solute molecules and fly ash, and between solvent molecules and fly ash. Thus, there is an essential need to characterize each coal fly ash type to enable potential correlation between coal fly ash structural properties and the effectiveness of the adsorption characteristics of coal fly ash for immobilizing organic hazardous waste compounds. The composition and properties of pulverized fly ash depend on the type of coal burned and the nature of the combustion process. Thus, fly ashes from different origins may have significantly different sorption properties towards organic compounds of environmental interest. Eastern and western coal fly ashes differ significantly in their physical and chemical properties. The major minerals found in coal fly ash are α-quartz (SiO2), mullite (3A12O3 ·2SiO2), hematite (Fe2O3), magnetite (Fe3O4), lime (CaO), and gypsum (CaSO4·2H2O). Little is known of the coordination state and distribution of siliceous and aluminous material in coal fly ashes. Most siliceous and aluminous materials in fly ash are amorphous and thus are not detected or quantified by X-ray techniques.
The hydrogen spin−lattice relaxation time in the rotating frame was measured for three whole asphalts at temperatures ranging from 20 to −45 °C. These data were used to calculate the apparent activation energies for the molecular motion of the aromatic and aliphatic components found in asphalt. The measured activation energies ranged from 8.8 to 9.8 kJ/mol for the aliphatic components in the three asphalts and were attributed to rapid methyl rotation of the terminal and branched methyl groups on the long carbon chainlength alkanes. The apparent activation energies measured for the molecular motion of the aromatic components in the three asphalts ranged from 6.5 to 7.2 kJ/mol. The low barrier to molecular motion observed for the aromatic constituents can be explained by two mechanisms. The first mechanism is spin−diffusion interaction of the aromatic ring hydrogens with the aliphatic hydrogens of the rapidly rotating methyl substituents on aromatic rings. The second mechanism is the in-plane rotation of relatively small polycondensed aromatic molecules and torsional oscillations of pendant phenyl groups as guest molecules within a nanopore matrix of rigid-amorphous aliphatic components.
Abstract Size exclusion chromatography was used to separate an asphalt into nine fractions, and these fractions were then investigated by 1H and 13C NMR. From the integration of the spectra, various molecular structural parameters were calculated. The aromatic carbon to nitrogen and the aromatic carbon to sulfur ratios were determined for six of the fractions. The catenation (linear and circular) of the aromatic ring structure was determined for six fractions. It appears that circular catenation is more probable for the high molecular weight fraction. For the lower molecular weight fraction, both linear and circular catenation are equally probable.
Solid- and liquid-state 13C NMR measurements have been made on the residues and liquids produced during hydrous pyrolysis experiments conducted on Almond and Lance Formation coals from the Upper Cretaceous Mesaverde Group in the Greater Green River Basin. The NMR spectra of the residues showed a decrease in aliphatic carbon fraction, a partial resolution of aliphatic carbons attached to aromatic rings, a narrowing of the aromatic carbon resonance band, and a loss of carboxylate functionality with increasing temperature. These changes are indicative of aromatization reactions, cleavage of alkyl substituents on aromatic rings and evolution of CO2 occurring during hydrous pyrolysis. Only a small percentage of the total carbon (13%) was converted to volatile products for both coals during hydrous pyrolysis. An accounting of the aliphatic carbons was obtained by comparing the aliphatic carbons in the gas, oil, water, and residue products with that of the starting coals. The amount of aliphatic carbons in the products was not sufficient to account for the total amount of aliphatic carbons that disappeared. From this it was inferred that 41 and 50% of the aliphatic carbons aromatized during hydrous pyrolysis of the Almond and Lance coal, respectively. NMR spectra were obtained on Almond coal samples taken from different depths of burial. These spectra had characteristics similar to the hydrous pyrolysis residues generated at different temperatures.
