Field Testing of Palladium-Catalyzed Hydrodehalogenation for Chlorinated
Hydrocarbon Removal from Groundwater
Principal Investigators
Martin Reinhard and Paul V. Roberts
Stanford University
(Supported by R2D2 Program)
E-mail: reinhard@stanford.edu
Goal
This project aims to:
- Establish the viability of the hydrogen/palladium
system by determining the catalyst lifetime and reaction kinetics in a
continuous-flow packed bed reactor;
- Identify competitors/inhibitors in the
process and minimize their effects;
- Quantify hydrogen consumption and
determine effective supply methods;
- Scale up, optimize and implement the
process at the field-scale.
Rationale
Palladium has been demonstrated to catalyze the reduction of
halogenated hydrocarbons to alkanes by hydrogen. Batch studies with palladium
indicate a rate of reaction several orders of magnitude higher than in the
zero-valent iron system (another method currently under study). Chlorinated
ethenes, including PCE and vinyl chloride, were completely removed from tap water
within ten minutes at room temperature by 0.5% palladium on alumina at 0.1 atm of
hydrogen pressure. (Schreier and Reinhard, Chemosphere, 31(6) pp 3475-3487,
1995.) This quick reaction time demonstrates palladium's great potential for
application in pump-and-treat groundwater remediation. Although palladium has
been used as a reduction catalyst for years in organic chemistry applications,
the system has not yet been well characterized for groundwater treatment.
Approach
This project entails construction of several parallel bench-scale
continuous-flow reactors. These reactors enable simultaneous study of several
water sources: a controlled supply of contaminated deionized water, groundwater
from Livermore, California, and groundwater from the California Central Valley.
This study seeks to ensure adequate residence time and catalyst life and to
determine the effects of any competitors or inhibitors. Initial characterization
tests are conducted with nitrate solutions and are followed by more detailed
tests using TCE and DBCP solutions. Once the parameters have been quantified at
the bench scale, a pilot-scale reactor is constructed and optimized. This design
is then scaled up to a field-scale model and tested.
Status
The first year of the field-scale demonstration employing a reactive well equipped with a Pd-reactor has been completed at LLNL. The
results have been reported by McNab et al. In ES&T, Vol. 34, No. 1, 2000, p. 149-153. The demonstration unit utilized a packed-bed column
and a microporous hollow fiber membrane hydrogen supply module. Removals were 99% or better for PCE, TCE, and 1,1-DCE, 98% for
carbon tetrachloride, 91% for chloroform, and 0% for 1,2-Dichloroethane. These removals are consistent with previously reported laboratory
studies. Periodic aeration and shut-downs was necessary for maintaining catalyst activity. On going studies aim to improve the overall
efficiency of the reactor and to determine the cost-effectiveness of the approach.
Copyright © Georgia Tech Research Corporation, 2000. All Rights
Reserved.
Make comments to: mark.hodges@gtri.gatech.edu
Last modified on: March 16, 2000.
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