The overall objective of this research was to develop and assess a new method, named
remedial extraction and catalytic hydrodehalogenation (REACH), for removing and
destroying soil contaminants. In particular, I considered hydrophobic halogenated
organic compounds (HHOCs). In this research, I developed a closed-loop treatment
process that catalytically destroys the contaminants of concern, and does not generate a
secondary waste stream. Mixtures of water and ethanol appear to be good candidates for
the extraction of 1,2,4,5-tetrachlorobenzne (TeCB) or pentachlorophenol (PCP) from
contaminated soil. Palladium-catalyzed hydrodehalogenation (HDH) was applied for
destroying TeCB or PCP in mixtures of water and ethanol in a batch mode.
The experimental results are all consistent with a Langmuir-Hinshelwood model
for heterogeneous catalysis. Major findings that can be interpreted within the Langmuir-
Hinshelwood framework are as follows: the rate of HDH depends strongly on the solvent
composition, increasing as the water fraction of the solvent increases; the kinetics of the HDH reaction are apparently first-order with respect to the concentration of TeCB in the
solvent; and the HDH rate increases as the catalyst concentration in the reactor
increases. Also, TeCB is converted rapidly and quantitatively to benzene, with only
trace concentrations of 1,2,4-trichlorobenzene appearing as a reactive intermediate. PCP
is transformed to phenol by sequential reductive dehalogenation to tetrachlorophenols,
then to trichlorophenols, then to phenol. The degradation of PCP does not follow firstorder
kinetics, probably because of competitive reactions of intermediate products that
are generated during PCP degradation. Following the batch studies, the REACH
technology was applied in continuous mode under baseline conditions for a span of 7
weeks to treat soils that had been synthetically contaminated by HHOCs in the
laboratory. Extraction of TeCB and PCP from soils was almost completed within two
days by a 50:50 mixture of water and ethanol. Higher reaction rates were observed for
TeCB than for PCP. The activity of the catalyst was slowly lost as contaminant mass
was removed from the soil. The deactivated catalyst was successfully regenerated with a
dilute sodium hypochlorite solution. The results of this research suggest that REACH
could be a viable technology for some contaminated soils.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1280 |
| Date | 15 May 2009 |
| Creators | Wee, Hun Young |
| Contributors | Batchelor, Bill, Cunningham, Jeffrey A. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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