February 28, 2007 1

Catalytic Destruction of PCE and Catalytic Destruction of PCE and TCE in Soil Vapor – Laboratory and TCE in Soil Vapor – Laboratory and

Field StudiesField StudiesDepartment of Chemical & Environmental EngineeringDepartment of Chemical & Environmental Engineering

Department of Atmospheric SciencesDepartment of Atmospheric SciencesThe University of Arizona, Tucson, AZThe University of Arizona, Tucson, AZ

Eric BettertonRobert Arnold, Brian Barbaris, Theresa Foley, Ozer Orbay Erik Rupp, Eduardo Sáez, Suzanne Richards,

Marty Willinger

Funded by NIEHS grant # ES04940

February 28, 2007 2

MotivationMotivation

Superfund sites spread throughout the US Often contaminated through commercial ventures

Pose risk to human and ecological health Groundwater contamination

Clean-up methods for contaminated soils Soil-vapor extraction with activated carbon adsorption Pump-and-treat for contaminated groundwater Soil dredging and treatment

February 28, 2007 3

Superfund SitesSuperfund Sites1246 Superfund Sites on National Priority ListCommon Contaminants

Semi-volatile chlorinated organic chemicalsTrichloroethylene (TCE)Tetrachloroethylene (PCE)

These contaminants are present in ~90% of Arizona Superfund sites

February 28, 2007 4

Prevalence of PCE and TCEPrevalence of PCE and TCE

Fraction of samples with detections versus fraction of concentrations less than or equal to the MCL but greater than one-tenth of the MCL (5068 wells sampled). Moran et al., ES &T (2006).Copyright © 2007 American Chemical Society

February 28, 2007 5

Park-Euclid PlumePark-Euclid Plume

Yellow contours representYellow contours representPCE concentration PCE concentration

in groundwater in groundwater from 100 ppb to 1 ppbfrom 100 ppb to 1 ppb

1000 ft

February 28, 2007 6

Contaminant Plume

Activated Carbon AdsorptionActivated Carbon Adsorption

Common Remediation Common Remediation TechnologyTechnology

Requires SVERequires SVEDownsideDownside

Non-destructiveNon-destructive Regeneration/disposal Regeneration/disposal

costscosts

Vapor

Ground Water

Vadose Zone

GAC

Column

Vent to atmosphere

February 28, 2007 7

Catalytic OxidationCatalytic Oxidation

C2Cl4 + 2O2 2CO2+ 2Cl2

2HCl + ½ O2 H2O + Cl2

catalyst

Issues with destruction through oxidationIssues with destruction through oxidation High temperatures (>500High temperatures (>500ooC)C) ClCl22 poisoning occurs above 450 poisoning occurs above 450ooC C

Blocks active Pt sites on catalystBlocks active Pt sites on catalyst Production of furans and dioxinsProduction of furans and dioxins

catalystpoisons

February 28, 2007 8

Schematic (taken from Catalytic Combustion Corporation) showing the major components of the redox catalytic system proposed for pilot-scale testing at the Park-Euclid site. Our system will differ from this in one important way: we propose introducing propane into the catalyst (4) in order to facilitate both reduction and oxidation reactions (not just oxidation), and to prevent catalyst poisoning.

February 28, 2007 9

CC22ClCl44 + 5H + 5H22 CC22HH6 6 + 4HCl + 4HCl

2C2C22ClCl44 + 7H + 7H22 CC22HH66 + 8HCl + 2C + 8HCl + 2C

catalyst

catalyst

Issues with destruction through reductionIssues with destruction through reduction Deactivation through cokingDeactivation through coking High price of HHigh price of H22

Catalytic ReductionCatalytic Reduction

coking

February 28, 2007 10

HypothesisHypothesis Near Stoichiometric Redox ConditionsNear Stoichiometric Redox Conditions

Poisoning reducedPoisoning reducedTemperatures loweredTemperatures lowered

Reduction-Oxidation (Redox) ConditionsReduction-Oxidation (Redox) ConditionsHH22 : O : O22 = 2:1 = 2:1

OO22 + C + C COCO22

HH22 + Cl + Cl22 2 HCl2 HCl

Alternate ReductantsAlternate Reductants PropanePropane Methane, ethane, butaneMethane, ethane, butane

ObjectivesObjectives

February 28, 2007 11

Lab Process Flow DiagramLab Process Flow Diagram

February 28, 2007 12

Lab – HLab – H22/O/O2 2 EffectEffect

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

50 100 150 200 250 300 350 400 450 500

Catalyst Temperature (oC)

% R

em

ov

al

of

PC

E

H2/O2 2.15H2/O2 1.18H2/O2 0.67H2/O2 0.26H2/O2 0.0

• 0.5 Lpm Flow Rate • 5% O2 (vol)

•Varying H2

•N2 Remainder

•0.50 sec Residence Time

•800 ppm PCE

February 28, 2007 13

Propane as ReductantPropane as Reductant

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

325 350 375 400 425 450 475

Catalyst Temperature (oC)

% R

em

ov

al

of

PC

E

0.0% C3H80.2% C3H80.4% C3H80.6% C3H80.8% C3H81.0% C3H8

•1.0 Lpm flow rate • 5% O2 (vol)

•Varying C3H8

•N2 Remainder

•0.25 sec residence time

•200 ppm PCE

C3H8 + 5O2 3CO2 + 4H2O

February 28, 2007 14

Reactor ModelReactor Model

Assumptions Reaction is first order Adsorption represented

by Langmuir isotherm Fast

adsorption/desorption No interspecies

competition for sites

k = 1st order reaction constantr = reaction rate = reactor residence timex = target compound conversionC = concentration of target compoundC0 = initial concentrationb = equilibrium constant

0

00

1

)1ln(

1

C

Cx

kbCb

xxC

r

dC

bC

bC

kr

PCE

PCE

PCE

PCE

PCEPCE

PCEPCE

February 28, 2007 15

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

0 50 100 150 200 250 300 350 400 450 500

PCE Concentration (ppm)

Pe

rce

nt

Re

mo

va

l o

f P

CE

b = 0.025 ppm-1

k = 1067 ppm s-1

1.0 L/min 1.3% O2

2.7% H2

N2 remainder 0.25 s residence time 200 oC

Lab – Effect of HLab – Effect of H22/O/O22

February 28, 2007 16

Alkane ReductantsAlkane Reductants (weakest) C-H bond dissociation energy: butane < propane < ethane < methane

Honeycomb Temperature vs Percent Removal of PCE, 1 L/min total flow, 130-180 ppm of PCE

0

10

20

30

40

50

60

70

80

90

100

300 350 400 450 500 550 600

Honeycomb Temperature (C)

% R

emo

val

Control

2% Methane

5% Methane

2% Ethane

3% Ethane

1% Propane

1.5% Butane

February 28, 2007 17

Field Process Flow DiagramField Process Flow Diagram

February 28, 2007 18

Catalytic ConverterCatalytic Converter

2 alumina honeycomb 2 alumina honeycomb monolith support s (2" long x monolith support s (2" long x 4.7" major axis 3.15" minor 4.7" major axis 3.15" minor axis). axis).

Pt/Rh or Pd/Rh with Pt/Rh or Pd/Rh with cerium/zirconium oxygen cerium/zirconium oxygen storage additives.storage additives.

Surface area = 4400 mSurface area = 4400 m22

Normal automotive flow rate: Normal automotive flow rate: 20 cfm to 300 cfm. 20 cfm to 300 cfm.

Minimum temperature for Minimum temperature for 50% activity = 415 50% activity = 415 00CC

February 28, 2007 19

Park-Euclid Field SitePark-Euclid Field Site

Propane

SVE pump

Catalytic converters

Effluent stream

Heater control

Catalytic converters

Effluent stream

100 L/min through each reactor (3.5 cfm)100 L/min through each reactor (3.5 cfm)

Scrubber

February 28, 2007 20

2 Alumina supported Pt/Rh catalysts2 Alumina supported Pt/Rh catalysts 2" long x 4.7" major axis; 3.15" minor axis

450 – 650450 – 650ooC Temperature RangeC Temperature Range25 – 200 ppmv PCE25 – 200 ppmv PCE

10 – 50 ppmv TCE

100 Lpm total flow rate100 Lpm total flow rate 0.2 sec Residence Time

1.0 – 2.0% propane by volume1.0 – 2.0% propane by volume

Field ConditionsField Conditions

February 28, 2007 21

Field – Propane EffectField – Propane Effect

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.8% 1.0% 1.2% 1.4% 1.6% 1.8% 2.0% 2.2%

% Propane by Volume

% R

em

ov

al

of

Ta

rge

t C

om

po

un

d

Propane

PCE

TCE

DCE

100 L/min SVE Gas1-2% C3H8 (vol)0.2 s residence time20-200 ppm PCE 450-650 oC

February 28, 2007 22

Field – Extended OperationField – Extended Operation 100 L/min SVE gas 2% C3H8 (vol) 0.2 s residence time~520 oC

0

10

20

30

40

50

60

70

80

90

100

110

120

0 20 40 60 80 100 120 140 160 180 200 220 240

Elapsed Time (days)

Co

nc

en

tra

tio

n (

pp

m)

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

% R

em

ov

al

of

Ta

rge

t C

om

po

un

d

PCE Inlet Conc.

TCE Inlet Conc.

PCE Removal

TCE Removal

February 28, 2007 23

Treatment CostsTreatment Costs

Catalytic ConverterCatalytic Converter 200 ppm PCE200 ppm PCE 10106 6 L soil vapor treatedL soil vapor treated 2% v/v propane @ $1.70/gal (DOE, 2005) 2% v/v propane @ $1.70/gal (DOE, 2005) Propane-only treatment costsPropane-only treatment costs

$10/lb PCE destroyed (PCE-dependent)

Granular Activated CarbonGranular Activated Carbon 100 ppmv PCE, 50 cfm, 85 100 ppmv PCE, 50 cfm, 85 FF GAC-only treatment costs:GAC-only treatment costs:

$3.50/lb PCE absorbed (Siemens Water Technologies, Sept. 2006)

February 28, 2007 24

Future Directions Field WorkFuture Directions Field Work

SBIR Phase I ($100k/6 months)SBIR Phase I ($100k/6 months)SBIR Phase II ($750k/2 y)SBIR Phase II ($750k/2 y)

Hydro Geo ChemHydro Geo Chem Improved scrubber designImproved scrubber design Larger flow rates (150 cfm; Phoenix area)Larger flow rates (150 cfm; Phoenix area) UA Page Ranch (relocate existing system; Freon 11, 12; UA Page Ranch (relocate existing system; Freon 11, 12;

solar)solar)

Provisional patent application - Dec. 2006Provisional patent application - Dec. 2006

February 28, 2007 25

ConclusionsConclusions

Catalytic destruction w/ redox conditions Catalytic destruction w/ redox conditions viable remediation technologyviable remediation technology Available for long term applicationsAvailable for long term applications Resolves previous issues with catalytic destructionResolves previous issues with catalytic destruction

Propane an effective alternate to Propane an effective alternate to hydrogen gas as reductanthydrogen gas as reductant

Works under wide range of conditionsWorks under wide range of conditions

February 28, 2007 26

Stoichiometry andStoichiometry andBond Dissociation Energy Bond Dissociation Energy

4 2 2 2

2

4

2 6 2 2 2

2

2 6

3 8 2 2 2

2

2 2

1 2 ...

1 9.5 ...

. .,10.5%

3.5 2 3

1 3.5 ...

1 16.7 ...

. ., 6.0%

5 3 4

1 5 ...

1 23.8 ...

. ., 4.

CH O CO H O

mol mol O

mol mol air

i e CH in air

C H O CO H O

mol mol O

mol mol air

i e C H in air

C H O CO H O

mol mol O

mol mol air

i e

3 8

4 10 2 2 2

2

4 10

2%

6.5 4 5

1 6.5 ...

1 30.9 ...

. ., 3.2%

C H in air

C H O CO H O

mol mol O

mol mol air

i e C H in air

439.3 kJ/mol

420.5 kJ/mol

410.5 kJ/mol CH3CH2CH3

411.1 kJ/mol CH3CH2CH2CH3

February 28, 2007 27

Thank You

After viewing the links to additional resources, please complete our online feedback form.

Thank You

Links to Additional ResourcesLinks to Additional Resources