Date of Award

12-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Science

Advisor

Schlautman, Mark A

Committee Member

Carraway , Elizabeth R

Committee Member

Freedman , David L

Abstract

Abiotic electron transfer mediated reductive dechlorination reactions have been studied extensively in the past decade. Porphyrins and metalloporphyrins are common electron transfer mediators used. Past studies have shown that some metalloporphyrins play a key role in increasing the rate of reaction in the presence of cosolvents. There have also been suggestions that organic cosolvents enhance the rate of reduction by increasing the solubility of metalloporphyrins.
The primary objective of this project was to examine the effect of cosolvents on the metalloporphyrin-catalyzed reductive dechlorination of tetrachloroethylene (PCE). Subsequently, experiments were also conducted to test the hypothesis that metalloporphyrin solubility is linked to the rate of degradation of PCE. PCE degradation mediated by iron tetraphenyl porphyrin chloride [Fe (III)-Cl TPP] was studied using various volume concentrations (0, 1, 2, 5 and 10%) of dimethylformamide (DMF) and methanol. The rate of PCE degradation increased with increase in cosolvent concentration up to 5% but decreased considerably when the cosolvent concentration was 10%. The increase in reaction rate up to 5% DMF or methanol may be due to an increase in solubility of the Fe (III)-Cl TPP with increasing cosolvent concentration. The decrease in reaction rate from 5 to 10% cosolvent concentration however was not consistent with the expected enhanced solubility of Fe (III)-Cl TPP.
The solubility of metalloporphyrins was investigated using absorbance measurements and the Beer-Lambert Law. Fe (III)-Cl TPP absorbance was expected to increase with increasing cosolvent concentration marking an increase in concentration of metalloporphyrin with increasing solubility. However, the absorbance values did not show the expected trend and formation of flocs were noticed in all the samples. These flocs may be related to dimers which are known to form when Fe (III)-Cl TPP is present in a mixture of water and an organic solvent. The increase in dechlorination reaction rate up to 5% cosolvent concentration might be attributed to the catalytic activity of dimers.
Although the reason for the increase in PCE dechlorination reaction rate with increasing DMF and methanol concentration up to 5% and then subsequent decrease at 10% could not be experimentally established, sufficient evidence was obtained in this study which precludes Fe (III)-Cl TPP solubility as being solely responsible for the 'solubility hypothesis' advanced by Dror and Schlautman.

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