Abstract/Details

Reductive dehalogenation of gas-phase trichloroethylene using heterogeneous catalytic and electrochemical methods


2005 2005

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Abstract (summary)

The first part of this work investigates catalytic hydrodechlorination (HDC) of gas-phase trichloroethylene (TCE) using 0.5 wt.% Pt/γ-Al 2O3 and 0.0025 wt.% Pt/SiO2 in packed-bed reactors. TCE was efficiently transformed on the platinum surface using H2 as reducing agent. The main products of the reaction were ethane and chloroethane. In the case of Pt/Al2O3, more than 94% TCE conversion efficiency was maintained for over 700 hours of operation at 100°C at a residence time of 0.37 seconds. At 22°C, severe catalyst deactivation was observed. Catalyst deactivation was attributed to coking and chlorine poisoning. A series of treatments including (i) hydrogen gas addition at high temperature (oxygen free) to remove chlorine and (ii) oxygen addition at 500°C to remove coke were attempted to regenerate the deactivated catalyst. Only hydrogen treatment partially restored catalyst activity. When using Pt/SiO2, catalyst deactivation was severe even at 100°C, probably due to low surface area of Pt and the silica support. Adding KOH to the packed Pt/SiO2 catalyst during (otherwise) normal operation slowed catalyst deactivation. Adding O2 to the influent improved catalyst activity and slowed deactivation.

The second part of this research involves the destruction of gas-phase TCE using an electrochemical reactor similar in design of a polymer electrolyte membrane (PEM) fuel cell. With a proton-conducting membrane in the middle, the anode and cathode comprised of carbon cloth and carbon-black-supported Pt were hotpressed together to form a membrane electrode assembly (MEA). TCE contaminated gas streams were fed to the cathode side of the fuel cell, where TCE was reduced to ethane and hydrochloric acid. The results suggest that TCE reduction occurs via a catalytic reaction with atomic hydrogen that is reformed on the cathode’s surface rather than an electrochemical reduction via direct electron transfer. Substantial conversion of TCE was obtained, even in the presence of molecular oxygen in the cathode chamber. The process was modeled successfully by conceptualizing the cathode chamber as a plug flow reactor with a continuous source of H2 (g) emanating from the boundary.

Indexing (details)


Subject
Environmental engineering
Classification
0775: Environmental engineering
Identifier / keyword
Applied sciences; Dehalogenation; Hydrodechlorination; Platinum
Title
Reductive dehalogenation of gas-phase trichloroethylene using heterogeneous catalytic and electrochemical methods
Author
Ju, Xiumin
Number of pages
128
Publication year
2005
Degree date
2005
School code
0009
Source
DAI-B 66/09, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
0542330970, 9780542330971
Advisor
Arnold, Robert G.
University/institution
The University of Arizona
University location
United States -- Arizona
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3190601
ProQuest document ID
305026234
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/305026234
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