Doctoral Dissertations

Date of Award

12-1986

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Gleb Mamantov, Earl L. Wehry

Abstract

Five polycyclic aromatic hydrocarbons (PAHs) were deposited from the vapor phase onto the surfaces of eight different types of coal fly ash. This procedure generated samples of PAH-laden fly ash in a manner which simulated the actual process of adsorption occurring in the gaseous effluent of a coal-fired electric power plant.

Samples were then irradiated with a light source similar in spectral distribution to sunlight. The adsorbed PAHs were extracted from the ash, and the decrease in the PAH concentration on the ash due to irradiation was measured and assumed to be the result of photochemical decomposition. The percentage photochemical decomposition was calculated for each combination of a single PAH compound adsorbed onto a single type of fly ash. The extent of this decomposition was observed to vary from ash to ash. Apparent decomposition of adsorbed PAHs was found to be generally more extensive on ash surfaces which were relatively photo-reflective. In addition, the extent of decomposition was generally suppressed on ashes for which the percentage recovery of pyrene by solvent extraction was lower, and for which the heat of adsorption of pyrene was more exothermic. These results suggested that more strongly adsorbed PAHs were less susceptible to photochemical transformation.

Measurement of the percentage of vapor-deposited pyrene recovered by solvent extraction was obtained with the help of a flame ionization detector to measure the amount of pyrene depositing on the ash. The heat of adsorption was determined by injecting solutions of PAHs onto a gas chromatographic column packed with fly ash, and varying the column temperature for successive injections at the same PAH concentration; results were improved by using small amounts of fly ash and, in most cases, by diluting the ash six-fold with a nonadsorptive solid particulate substrate.

For samples of PAH deposited on fly ash from the solution phase, the percentage recoveries by solvent extraction were frequently larger than the percentage recoveries for samples deposited from the vapor phase, indicating the possibility of competition of solvent with PAH for the most active adsorption sites in "solution deposition" experiments.

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