dnapls: above-ground remediation chang chang yul cha, cha … · 2005-09-14 · @ regeneration rate...

University of Arizona, Prof. Eric A. Betterton

11

DNAPLsDNAPLs: Above: Above--Ground RemediationGround Remediation

ChangChang YulYul Cha, Cha CorporationCha, Cha CorporationEricEric BettertonBetterton, University of Arizona, University of Arizona

Dept. Atmopsheric Sciences 1

22


Microwave Technology for Superfund Site Remediation

National Institute of Dr. C. Y. Cha

Environmental Health Sciences CHA Corporation

Research Triangle Park, NC 27709 Laramie, WY 82072



33

Reaction of Activated CarbonReaction of Activated Carbon to Microwave Energyto Microwave Energy



44

Carbon SparklesCarbon Sparkles


Microwav


55

Advantages of Using MicrowaveAdvantages of Using Microwave EnergyEnergy

•• Rapid Desorption ofRapid Desorption of VOC’sVOC’s

•• Destructive Reaction ofDestructive Reaction of NOx and CarbonNOx and Carbon

•• Microwave DecompositionMicrowave Decomposition of Large Moleculesof Large Molecules

•• Low TemperatureLow Temperature OxidationOxidation

Conventional Heating

e HeatingHeating

Microwave

1) Activated Carbon – VOC desorption

2) NOx & SOx– Chemical Reaction with Carbon

3) Decompose (because of heat) heavy molecules, when contacted with carbon and microwaves. – Waste rocket fuels

4) Carbon mixed with catalyst – causes low temp oxidation, chemical and biological warfare agents (or medical waste).



66

Microwave Induced

Solvent Desorption



77

Small Batch RegeneratorSmall Batch Regenerator

•• 1,100 watt microwave1,100 watt microwave ovenoven



88

Small Batch RegeneratorSmall Batch Regenerator

Carbon Filter

1100 Watt Microwave Oven

Collector

Sweep Gas IN

Sweep Gas OUT



99

Regeneration of GACRegeneration of GAC(Saturated with Gasoline)(Saturated with Gasoline)



1010

MicrowaveMicrowave--Induced DesorptionInduced Desorption

0

5000

10000

15000

20000

25000

30000

0 2 4 6 8 10 12 14 16

Time (minutes)

TH

C C

on

cen

tra

tion

(p

pm

)

300 Watt Applied Power




- 2 inch bed height

- Quartz Tube ID = 7/8 inch

- 10 SCFH nitrogen purge

CHA Corporation



1111

0

100

200

300

400

500

600

700

800

900

1000

0 2 4 6 8 10 12 14 16 18 20

Regeneration Cycle

BE

T S

urf

ace

Are

a, m

2 /g

ram

0.00

5.00

10.00

15.00

20.00

25.00

Ad

sorp

tion

Ca

paci

ty,

g M

EK

/10

0 g

GA

C

Sample 1

Sample 2

GHSV= 20,000 hr -1

Inlet Conc . = 200 ppm

GAC Adsorption/RegenerationGAC Adsorption/Regeneration Cycling for MEKCycling for MEK

CHA Corporation

How many times can you regenerate carbon, without losing adsorption capability.

After about 7 cycles with steam, adsorption capacity decreased enough to replace carbon. Not the case with microwaves, still good after 20 cycles.



Advantages of Microwave UnitAdvantages of Microwave Unit

•• Does not rDoes not reequire a long starquire a long startup periodtup periodDoes not produce any air emission or wastewater•• Does not produce any air emission or wastewater

•• Requires much smaller space than conveRequires much smaller space than convenntionaltional technologiestechnologies

•• Can be easily installeCan be easily installed on a trailer or skidd on a trailer or skid•• Recovers PERC and other sRecovers PERC and other soolvlvents and fuels for recycleents and fuels for recycle•• Eliminate greenhousEliminate greenhouse gas pre gas productionoduction•• CostCost--effective means to replace currently operatingeffective means to replace currently operating

catalytic oxidizerscatalytic oxidizers

1212



Potential ApplicationsPotential Applications

•• Recover gasoline and oRecover gasoline and otther fuel vher fuel vaaporspors generated during the loading of fuel tankers atgenerated during the loading of fuel tankers at bulk fuel terminalsbulk fuel terminals

•• Recover and recycle fuel, solvents, and otherRecover and recycle fuel, solvents, and other chemicals from soil vapors produced duringchemicals from soil vapors produced during remediation operations of contaminated sitesremediation operations of contaminated sites including old gas stationsincluding old gas stations

•• Recover and recycle PERC and other solventsRecover and recycle PERC and other solvents used in dry cleaning and part washing as well asused in dry cleaning and part washing as well as painting operationspainting operations

1313



1414

Field Demonstration of Microwave Technology atField Demonstration of Microwave Technology at Former McClellan Air Force Base in SacramentoFormer McClellan Air Force Base in Sacramento

CaliforniaCalifornia(NIEHS SBIR Phase I Program)(NIEHS SBIR Phase I Program)


1515


IC 34/35/37



Specific AimsSpecific Aims

•• OperaOperatte the protoe the protottype microwave uype microwave unnit ait attMcClellan IC 34/35/37 FTO site for two monthsMcClellan IC 34/35/37 FTO site for two months to regenerate carbon onto regenerate carbon on--site and recoversite and recover solvents, fuels and other chemicals contained insolvents, fuels and other chemicals contained in the soil vaporsthe soil vapors

•• Demonstrate that microDemonstrate that microwwave technology can beave technology can be a costa cost--effective solution for the treatment of soileffective solution for the treatment of soil vaporsvapors

1616




1717

Prototype Microwave Reactor System

Sweep Gas

Condenser 1

MicrowaveGeneratorMicrowave

Applicator

QuartzReactor

RotaryValve

Makeup NitrogenContaminated Air from SVE System

Cleaned Air to SVE System's FTO

Pneumatic Conveyor Flow Path

RotaryValve

BlowerExcess Sweep Gas

LEGEND

CARBON

RECYCLE SWEEP

AIR

CarbonFines

Compressor

Condenser 2

KnockoutPot 1

KnockoutPot 2

CompressedNitrogenCylinder

Adsorber

Cyclone

Receiver Hopper

Feed Hopper


1818

Front View of IC 34/35/37 FTO Facility



1919

Overall View of Microwave Reactor System Setup



2020

Adsorber and Pneumatic Conveying System



2121

Multimode-Cavity, Tuning Device and Top Hopper



2222

Bottom Hopper and Multimode-Cavity



Field Demonstration ResultsField Demonstration Results

•• Adsorption Test ResultsAdsorption Test Results–– InitialInitial responresponssee timetime of hyof hydrocarbonsdrocarbons–– TOTO--1155 analyses of influent and effluent gasanalyses of influent and effluent gas samplessamples

2323



Microwave Field Testing Results I n t i a l R e s p o n s e T i m e v s . C y c l e

3 0 . 0 0

2424

0 . 0 0

5 . 0 0

1 0 . 0 0

1 5 . 0 0

2 0 . 0 0

2 5 . 0 0

0 2 4 6 8 1 0 1 2 1 4 C y c le

Re

s p

on

s e

Ti m

e (

hr )

B a t c h A B a t c h B



Field Demonstration ResultsField Demonstration Results

•• Microwave Regeneration TestsMicrowave Regeneration Tests–– Hydrocarbon liquidHydrocarbon liquid recovered fromrecovered from eaeach regeneratch regeneratiionon–– Repeated regenerationRepeated regeneration–– RegRegeenneeratiorationn without sweep gawithout sweep gas recycles recycle

2525



Microwave Field Testing ResultsMicrowave Field Testing ResultsLiquid Recovery vs. Cycle

Liq

uid

Rec

ove

ry (

kg)

20

18

16

14

12

10

8

6

4

2

0

0 2 4 6 8 10 12

Note: Cycle 11A and B were regenerated twice prior to readsorption in cycle 12. The liquid recovery presented is the sum recovered in both regeneration cycles

2626

14

Cycle

Batch A Barch B



2727

Liquid Recovered During MicrowaveLiquid Recovered During Microwave RegenerationRegeneration



Recovered LiquidRecovered Liquid

•• Trichloroethane = 3.2 mole%Trichloroethane = 3.2 mole%•• HydrocarbonsHydrocarbons

•• C5C5 –– C8 =C8 = 2211.3 mole.3 mole%%•• C8C8 –– C1C10+0+ == 75.575.5 mole%mole%

•• Specific GrSpecific Gravity = 0.787avity = 0.787•• JP fuel Specific Gravity = 0.75JP fuel Specific Gravity = 0.75 –– 0.800.80

2828



GAC Balance

GAC Added Batch A Batch B 9/24/2003 200 lb 9/27/2003 200 lb

10/16/2003 24.92 lb 11/20/2003 15.25 lb

Total 215.25 lb 224.92

GAC Removed Batch A Batch B Fines 7.83 6.72 End of Testing 208.47 216.24

Total 216.22 222.96

Difference 0.45% -0.87%

2929



Tests After Field TestingTests After Field Testing

•• MeasMeasure Adsorption Capacure Adsorption Capaciity of GAty of GAC after 13C after 13thth

Adsorption/Regeneration CycleAdsorption/Regeneration Cycle•• DeterminDetermine the the Effect of Sweep Ge Effect of Sweep Gaas Velocity ons Velocity on

the GAC Regeneration Efficiencythe GAC Regeneration Efficiency•• Determined Size DistriDetermined Size Distribution of GAC after 13bution of GAC after 13thth

Adsorption/Regeneration CycleAdsorption/Regeneration Cycle

3030



Adsorption Capacity (gHC/100g carbon)Adsorption Capacity (gHC/100g carbon)

•• Batch A after 1Batch A after 133thth RegeRegenerationeration = 2n = 222..00•• Batch BBatch B after 1after 133thth RegeRegenerationeration = 2n = 222..00•• Fresh Carbon = 29.0Fresh Carbon = 29.0

3131


2.36” Quartz Tube

3-kW Microwave Generator


3232

Note: Chemicals used for adsorption tests were collected during Field Demonstration at McClellan Air Force Base

GAC Regeneration Efficiency @ Regeneration Rate of 26-38lb/hr

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80 90

N2 Sw e ep Gas Flow Rate , scfh

Ad

so

rpti

on

Ca

pa

city

(%

of

Ori

gin

al

Ad

sorp

tio

n C

apa

cit

y)



GAC Size AnalysisGAC Size Analysis

Sieve AnalysisSieve Analysis

Fresh GACFresh GAC Batch ABatch A Batch BBatch B

+20 mesh+20 mesh 0.1%0.1% 3.9%3.9% 3.6%3.6%

+10 mesh+10 mesh 99.6%99.6% 95.9%95.9% 96.3%96.3%

+3 mesh+3 mesh 0.4%0.4% 0.1%0.1% 0.1%0.1%

3333



NIEHS SBIR Phase II ProgramNIEHS SBIR Phase II Program

•• Design and Construct a 50Design and Construct a 50--kg/hr Mkg/hr Moobilebile Microwave UnitMicrowave Unit

•• Field Demonstration of MoField Demonstration of Mobile Microwave Unitbile Microwave Unit–– Chlorinated Solvent Contaminated SiteChlorinated Solvent Contaminated Site–– Fuel Contaminated Site (FFuel Contaminated Site (Fuel depot or gasuel depot or gas station)station)–– Dry Cleaning FacilDry Cleaning Facilityity

•• CharCharacterize and Purifyacterize and Purify Recovered Solvents andRecovered Solvents and FuelsFuels

3434


3535


Mobile 50Mobile 50--kg/hr Microwave Carbon Regeneratorkg/hr Microwave Carbon Regenerator



3636

Preliminary Process Flow DiagramPreliminary Process Flow Diagram



Experimental Work Required to Build aExperimental Work Required to Build a 5050--kg/hr Mobile Unitkg/hr Mobile Unit

•• Conduct a series of experiments toConduct a series of experiments to devdeveeloplop the design for microwave reactorthe design for microwave reactor configuration capable of regenerating 50configuration capable of regenerating 50--kg/hr activated carbonkg/hr activated carbon

•• Design and construct supporting syDesign and construct supporting systems onstems on the trailerthe trailer

3737



3838

New Slotted WaveguideNew Slotted Waveguide



3939

Slotted Waveguide In Mailbox CavitySlotted Waveguide In Mailbox Cavity



4040

Inside View of New Applicator SystemInside View of New Applicator System



Advantages of New Applicator SystemAdvantages of New Applicator System

•• Slotted Waveguide Distributes Energy Along theSlotted Waveguide Distributes Energy Along the Length of the TubeLength of the Tube

•• CurvCurved Ced Caavity Wvity Waallll ReflectsReflects EnerEnergy Back Towardgy Back Toward the Tubethe Tube

4141



4242

ScaleScale--up Test Systemup Test SystemCompleted Test SystemCompleted Test System



4343

Laboratory AdsorberLaboratory Adsorber



Scale Up Testing ResultsScale Up Testing ResultsTestTest

(lb/hr)(lb/hr)1A1A 3535 33 9090 98981B1B 3535 33 6060 96962A2A 3535 3.53.5 9090 99992B2B 4040 3.53.5 8585 97973A3A 4040 3.53.5 7070 98983B3B 4040 4.54.5 8080 98984A4A 4040 44 8080 1011014B4B 4545 44 7070 98985A5A 4545 4.54.5 8585 1021025B5B 5050 4.54.5 5555 1091096A6A 5050 55 8080 1011016B6B 5050 55 3535 1081087A7A 5050 55 8080 102102

“Note” %Recovery = (Fresh GAC wt./Reg. GAC wt.)x100

4444

Carbon RateCarbon Rate Power (kW)Power (kW) Sweep Gas (SCFH)Sweep Gas (SCFH) % Recovery% Recovery



Scale Up Regenerator Performance 120%

4545

70%

80%

90%

100%

110%

600 650 700 750 800 850 900 950

Microwave Power (J/g GAC dry basis)

% r

ec

ov

ery

Carbon Mass Recovery



4646

Additional Field Testing At McClellanAdditional Field Testing At McClellan Air Force Base (IC19 and OUD Site,Air Force Base (IC19 and OUD Site,

Chlorinated Solvents)Chlorinated Solvents)



Annual Cost Savings, dollarsAnnual Cost Savings, dollars

ItemItem Quantity SavingsQuantity Savings Cost savings, $Cost savings, $

Natural GasNatural Gas 188,431188,431 thermtherm 131,902131,902

ElectricityElectricity 418,522418,522 kwhkwh 37,66737,667

WastewaterWastewater 4.756 M gallons4.756 M gallons 10,60810,608

Utility waterUtility water 5.675.67 M gallonsM gallons 3,0613,061

GACGAC changeoutschangeouts 120,000120,000

Labor and suppliesLabor and supplies 100,740100,740

Total Annual SavingsTotal Annual Savings 403,978403,978

4747



Prepare Field Testing at FormerPrepare Field Testing at Former McClellan AFBMcClellan AFB

•• Build a SBuild a Shhelelter to protect microwave equipter to protect microwave equipmmentent from rainfrom rain

•• Modify previous microwave unit to allowModify previous microwave unit to allow –– Carbon transportation fromCarbon transportation from/to the/to the portable adsorbportable adsorberer–– Higher recyclHigher recycle gae gas flow rates flow rate–– Isolate theIsolate the ssyystestemm frofromm the adthe adsorption unitsorption unit–– Install the automatic shuInstall the automatic shuttdowndown system in thesystem in the microwavemicrowave

generatorgenerator

4848



4949

Microwave Unit at McClellan AFBMicrowave Unit at McClellan AFB



5050

Volume of VOCs Recovered

0

2

4

6

8

10

12

14

16

18

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Regeneration Number (Cycle)

Vo

lum

e R

eco

vere

d (

L)

OU D Vessel A

OU D Vessel B



5151

Breakthrough at OU D VGAC Vessels

0%

25%

50%

75%

100%

125%

150%

0 2 4 6 8 10 12 14

Days

Per

cen

t B

reak

thro

ugh

Drum A Cycle 1 Drum B Cycle 1 Drum A Cycle 2 Drum B Cycle 2 Drum A Cycle 3 Drum B Cycle 3 Drum A Cycle 4 Drum B Cycle 4 Drum A Cycle 5 Drum B Cycle 5



Dry Cleaning FacilityDry Cleaning Facility

•• PurposePurpose–– To remove PTo remove PEERC by thRC by the ae acctivtivaated carbted carbon from dryon from dry cleaner’scleaner’s

vented airvented air–– ToTo demondemonsstrate the featrate the feassibilibility ofity of recovering PERCrecovering PERC from saturatedfrom saturated

carbon by microwavescarbon by microwaves

•• Test LocationTest Location–– Deluxe CleanDeluxe Cleaneers andrs and TailorsTailors

1614 House Ave.1614 House Ave.Cheyenne, WYCheyenne, WY

5252



5353



Carbon RegenerationCarbon RegenerationFresh GAC, kgFresh GAC, kg 37.237.2 37.737.7

GAC afterGAC after 49.549.5 44.144.1saturation, kgsaturation, kg

GAC afterGAC after 38.438.4 37.037.0regeneration, kgregeneration, kg

Liquid recovered,Liquid recovered, 5.655.65 4.964.96kgkg

5454



5555

Recovered PERC After WaterRecovered PERC After Water Extraction (PERC is Bottom Layer)Extraction (PERC is Bottom Layer)



5656

Questions?Questions?



5757

Innovative Technologies forInnovative Technologies for Destruction of ChlorinatedDestruction of Chlorinated

SolventsSolventsDepartments of Chemical & Environmental EngineeringDepartments of Chemical & Environmental Engineering

Atmospheric SciencesAtmospheric SciencesThe University of Arizona, Tucson, AZThe University of Arizona, Tucson, AZ

• Dr. Robert Arnold • Dr. Eric Betterton • Dr. Wendell Ela • Dr. Eduardo Saez

• Brian Barbaris • Kate Candillo • Xiumin Ju • Cary Leung • Ozer Orbay • Lei Wang • Rohit Tripathi



Systems SummarySystems SummaryZero-valent metals Complete, e.g., Env. Sci. Technol., 34,

804-811 (2000)

Electrolytic reduction (conventional cell) Complete, e.g., Ind. Eng. Chem. Res., 43 (25), 7965 -7974 (2004); Ind. Eng. Chem. Res. 43, 913-923 (2004 )

Electrolytic oxidation (conventional cell) Complete, e.g., J. Appl. Electrochem., 961–970, 29 (1999)

Continuous-flow electrolytic reactor (1-dimensional) Complete, manuscript prepared

Continuous-flow electrolytic reactor (2-dimensional) In progress - manuscript in preparation

Modified fuel cell reactor In progress, e.g., Env. Sci. Technol., 35, 4320-4326 (2001)

Photo-initiated dehalogenation in 2-solvent system Complete, e.g., Env. Sci. Technol., 34, 1229-1233 (2000); Water Res. 38, 27912 (2004); Environ. Sci. Technol., 39, 2262-2266 (2005)

Membrane air stripping reactor Complete, e.g., J. Env. Eng. 130, 12321241 (2004)

Redox catalysis In progress

5858



5959

ParkPark--Euclid WQRF Site: PCE, TCEEuclid WQRF Site: PCE, TCE and Dieseland Diesel

Typical Soil Vapor Analysis

PCE ≈ 300 ppmv

TCE ≈ 30 ppmv

cis-1,2-DCE ≈ 3 ppmv

O2 ≈ 18% v/v



Redox Catalytic Destruction:Redox Catalytic Destruction: Oxidative and Reductive DehalogenationOxidative and Reductive Dehalogenation

•• PCE + 5PCE + 5HH22catalyst

CC22HH66 + 4HCl+ 4HCl

catalyst•• 2PCE + 3C2PCE + 3C33HH88 2C2C22HH66 + 2HCl + 9C+ 2HCl + 9Ccatalyst

•• CC22HH66 ++ 3/23/2OO22 2CO2CO22+ 3H+ 3H22OOcatalyst

•• 2H2H22 + O+ O22 2H2H22OOcatalyst

•• 2HCl + ½ O2HCl + ½ O22 HH22O + ClO + Cl22

6060



6161

Redox Catalytic Destruction:Redox Catalytic Destruction:Laboratory WorkLaboratory Work



6262

Catalytic ConverterCatalytic Converter

•• 2 alumina honeycomb monolith2 alumina honeycomb monolith support s (2" long x 4.7" majorsupport s (2" long x 4.7" major axis 3.15" minor axis).axis 3.15" minor axis).

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

•• Surface area = 4400 mSurface area = 4400 m22

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

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



6363

Ceramic Honeycomb SupportCeramic Honeycomb Support



6464

PCE Removal: Laboratory T and H2/O2 Ratio

(500 mL/min, 1.2 s retention)

0

20

40

60

80

100

120

0 50 100 150 200 250 300 350 400 450

Honeycom b temperature (C)

PC

E %

rem

ov

ed

5.17 3.2 2.75 2.27 1.55 0.95 0.36 0.36



6565

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

0 50 100 150 200 250 300 350 400

Time (min)

Co

nc

. (m

ole

/L)

0

100

200

300

400

500

Tem

p.

(C)

Ethane PCE Total C Furnace T Honeycomb T

PCE Removal: Laboratory T vs.PCE Removal: Laboratory T vs. EthaneEthane

(8.64 mL/min H2, 25 mL/min O2, 500 T mL/min, 1.2 s retention)



6666

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

0 100 200 300 400 500 600 700 800

Time (min)

Co

nc

. (m

ole

/L)

0

50

100

150

200

250

300

350

400

450

Te

mp

. (C

)

Ethane out

PCE out

Furnace T

Honeycomb T

PCEin

Redox Catalyst: PCE DestructionRedox Catalyst: PCE Destruction(300 C; 500 mL/min total flow, 50 mL/min H2, 25 mL/min O2, 1.2 s retention time



6767

0

20

40

60

80

100

120

0 4 8 12

% Hydrogen

PC

E %

rem

ove

d

0

100

200

300

400

500

Ho

ney

com

b (

C)

PCE

PCE @ 400 C

Catalyst T

Redox Catalyst: PCE Reduction HRedox Catalyst: PCE Reduction H--EffectsEffects



6868

0

20

40

60

80

100

120

0 5 10 15 20 25

% H2

% R

emo

ved

0

1

2

3

4

5

% O

2 i

n −

% O

2 o

ut

TCE PCE O2 in - O2 out

PCE Removal: ParkPCE Removal: Park--EuclidEuclid((H2 and O2)



6969

Catalyst Poisoning: OxidativeCatalyst Poisoning: Oxidative450 0C, O2 =21%, Pd/Rh Catalyst

0

5

10

15

20

25

30

0 5 10 15 20

Time (h)

PC

E %

Rem

ova

l



7070

Catalyst Poisoning: Reductive (propane, O2= 0 %; residence time:1.08 s, run time:410 min

0

20

40

60

80

100

380 400 420 440 460 480 500 520 540

Honeycomb Temp. (C)

PC

E %

Re

mo

va

l



7171

Redox Catalyst: PCE with propaneRedox Catalyst: PCE with propane (21% O2)

0

20

40

60

80

100

380 430 480 530 580

Honeycomb temp(C)

%p

ce r

emo

val

2% propane

4%propane

0% propane



7272

Redox Catalyst: Methane vs.Redox Catalyst: Methane vs. Propane and TPropane and T

(21% O2)

0

10

20

30

40

50

60

70

80

90

100

340 360 380 400 420 440 460 480 500 520

Honeycomb temp(C)

Rem

ova

l per

cen

t

2% methane

1% propane



7373

Redox Catalyst: PCE and TCE withRedox Catalyst: PCE and TCE with HH22/O/O22 ratioratio

(410 0C)

0

10

20

30

40

50

60

70

80

90

100

0 0.05 0.1 0.15 0.2

H2/O2 ratio

Rem

ova

l p

erce

nt

PCE

TCE



Fuel CellFuel Cell

H2 PEM O2

anode

CC

cathode 2H+ +2 e O2 + 4 H+ + 4 e− 2H2OH2

l4 + H+ + 2e− CHCl3 + Cl−

Pt-black on carbon cloth

PEM: Nafion proton-exchange membrane

7474


Valve

N2

water

TCEGC

Anode Cathode

Flow meter

H2

water

discharge

potentiostat

lveAnode Cathode

Flow meter

discharge

potentiostat

lveAnode Cathodet

Flow meter

discharge


7575

Va

N2

water

TCE GC

H2

water Va

N2

water

TCEGC

Anode Ca hode

H2

water

potentiostat

flow meter

val ve

Fuel Cell Experimental Set upFuel Cell Experimental Set up



TCE ReductionTCE Reduction –– Fuel Cell PotentialFuel Cell Potential(room temp., Patm, 18 mL/min, res. time = 2.3 s)

0.0

0.5

1.0

1.5

2.0

2.5

Mol

ar F

low

Rat

e (µ

mol

/min

)

0.1 -0.1 -0.5-0.3

Cell Potential (V)

TCE effl. Ethane Effl.

TCE + Ethane (effl.) TCE infl.

7676

This slide showed an experiment conducted under room temperature, atmospheric pressure, inlet flow rate 18 ml/min, TCE concentration of 2500ppmv. The left graph showed TCE and reaction product concentration in the effluent. TCE concentration was reduced monotonically with respect to cell potential. Ethane as the product of TCE degradation increased to a maxima, and then decreased with respect to cell potential. This was caused by increase of flow rate due to hydrogen evolution in the cathode. No Chlorinated intermediates were detected.

The right graph showed the molar flow rate of TCE and ethane and the sum of two in the effluent. The solid red line represented the inlet TCE molar flow rate. We can see that a good mass balance was obtained here, and thus proved that ethane was the major product of TCE degradation. The variation of effluent data around inlet data probably due to experimental error.



7777

TCE ReductionTCE Reduction –– Fuel CellFuel Cell Current EfficiencyCurrent Efficiency

(room temp., Patm, 18 mL/min, res. time = 2.3 s)

0.0

0.2

0.4

0.6

0.8

1.0

-0.5-0.3-0.10.1

Cell Potential (V)

Co

nve

rsio

n a

nd

cu

rre

nt

eff

icie

ncy

conversion

current efficiency

Here in this graph the current efficiency was plotted with respect to cell potential, and TCE conversion was also plotted. Current efficiency here is defined as the ratio of the current used for TCE reduction to total current. As you can see, the current efficiency is relatively low due to large amount of hydrogen generated.



7878

ElectrolysisElectrolysis -- Annular AnodeAnnular Anode

V

anolyte

Porous electrode (copper foam)

Anode (carbon cloth)

Reference electrode

Potentiostat

Catholyte (influent)

Nafion membrane

+− +→− HOeOH 2 2

12 22

Anode Reaction

−−+ +→++ ClCHeHCCl 484 44

−− +→+ OHHeOH 22 2

1

Cathode Reaction



7979

ElectrolysisElectrolysis –– Cu foamCu foam



8080

Conductivity = 0.067 S/m (tap water)

0 5 10 15 20 25 0.0

0.2

0.4

0.6

0.8

1.0

E = -0.2V E= -0.4V

C/C

0

Distance (cm)

Conductivity = 2.7 S/m

0 5 10 15 20 25 0.0

0.2

0.4

0.6

0.8

1.0

E = -0.2V E = -0.4V

C/C

0

Distance (cm)

CT Electrolysis: Applied Potential andCT Electrolysis: Applied Potential and ConductivityConductivity

(velocity = 0.0349 cm/s, cathode = 22.5 cm)(velocity = 0.0349 cm/s, cathode = 22.5 cm)



8181

CT Electrolysis: Applied PotentialCT Electrolysis: Applied Potential and Conductivityand Conductivity

cathode = 22.5 cm; -0.4 V; 0.05 S/m; solid and dashed lines correspond to mathematical model

Residence time (min)

Cbin--Inlet concentration. Cb—Bulk concentration



8282

Electrochemical CT Reduction: pHElectrochemical CT Reduction: pH(Ni foam)



8383

Photochemical Treatment at ParkPhotochemical Treatment at Park--Euclid SiteEuclid Site



8484

0

20

40

60

80

100

250 300 350 400 450

Wavelength (nm)

% T

ran

smit

tan

ce a

nd

% R

efl

ecta

nc

e

0

0.5

1

1.5

2

En

erg

y (

W/m

2 nm

)

Acetone % Reflectance 2-Propanol Glass Energy

Photochemical Treatment: PCE atPhotochemical Treatment: PCE at ParkPark--Euclid Spectral PropertiesEuclid Spectral Properties



Photochemical MechanismPhotochemical Mechanism

H H H

O Me OH (2) Me OHhvO

H H Me Me

acetone photon excited actone 2-propanol 2-propanol

radical radical

Acetone in its excited state, extracts a hydrogen atom from a suitable donor, such as 2-propanol, producing a highly reduced 2-propanol radical that is capable of reducing a variety of halogenated targets.

OH Cl Cl H OH Cl Cl Cl Cl

Me Me OHHOH MeMe OHMe Cl Cl Me

Me Cl Cl

PCE 2-propanol

MeMe Me Cl Cl

2-propanol 3,3,4,4-tetrachloro- 2-propanol radical 2-methyl-butan-2-ol radical

1. Alkene-radical chemistry suggests that the 2-propanol radical may add to the chlorinated alkene to produce a chloro-methyl alcohol (3,3,4,4-tetrachloro-2-methyl-butan-2-ol).

2. Data also support electron donation to PCE and/or the chloro-methyl alcohol by the 2-propanol radical accompanied by chloride elimination, similar to carbon tetrachloride mechanism (Betterton et al., ES&T 2000).

8585



8686

0

0.5

1

0 10 20 30 40 50 60 70 80 90 100 110 120

Exposure Time (min)

Rel

ativ

e C

on

cen

trat

ion

15-Mar

20-Mar

23-Mar

24-Apr

25-Apr

30-May

31-May

20-Sep

28-Sep

PCE Photochemical Treatment:PCE Photochemical Treatment: ParkPark--EuclidEuclid



SummarySummary

• Catalyzed thermochemical reduction is feasible – H2 costs may be high but propane may be viable substitute.

• Electrolytic reduction of chlorinated solvents appears feasible using annular anode/cathode – even in low-conductivity water.

• Gas-phase treatment of solvents is fast using fuel cell – system requires scale up/additional design work.

• Photocatalytic system effective but scale up for volatile liquids may be unattractive.

8787



8888

Thank YouThank You

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

Thank You

Links to Additional Resources


dnapls: above-ground remediation chang chang yul cha, cha … · 2005-09-14 · @ regeneration rate...

Documents