Determination of the Rate of Contaminant Oxidations by

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Determination of the Rate of Contaminant Oxidations by Powered By Docstoc
					Kinetics of Contaminant Degradation by Permanganate

Rachel Waldemer
Research Associate, OGI School of Science & Engineering

Background


Over 100,000 contaminated sites in the U.S.


~ 80% have contaminated groundwater

http://www.groundwater.org/gi/sourcesofgwcontam.html

2

Options for Groundwater Treatment
 


  

Pump and Treat Monitored Natural Attenuation Air Sparging/Soil Vapor Extraction In Situ Heating In Situ Reduction In Situ Chemical Oxidation
   

Fenton’s Reagent Ozone Permanganate Persulfate

3

ISCO with Permanganate US Projects
• 100’s of successes in the past 5 years • Industrial, government, military

4

Basic Design Features of ISCO with Permanganate
Reagent

Injection Well

Spread of Reagent Residual DNAPL

Monitoring Well

Water Table

Screened Section

Contaminated Aquifer

Groundwater Flow Direction

5

Importance of Kinetic Data

[COC ]  1 1  k"[ MnO4 ] [COC ] t
[COC ] 1  kobs [COC ] t
t1/ 2 ln 2  kobs
6

Kinetic Data Currently Available

7

Analysis by UV spectroscopy
Advantages  Analyzing MnO4- degradation, so this method is independent of the chemical nature of the contaminant.  Permanganate absorbs strongly, so contaminants only need be moderately soluble (~1 mM) and still maintain pseudo-first-order conditions.

Disadvantages  MnO2, the product of MnO4- reduction, also absorbs at 525 nm, the absorption maximum of permanganate.  Doesn’t give information on the reaction products.
8

Beer’s Law

A   bc
x x Ax  [MnO ] MnO  [MnO2 ] MnO

 4

 4

2

MnO2 is a colloidal species, and only behaves according to Beer’s Law of absorbance until scattering properties dominate.  Using phosphate buffer helps prevent the colloidal particles from flocculating  Two approaches are used to identify the region of the reaction for which Beer’s Law is applicable.
9

The Fitting Equation

A525  [CT e

 kobst

]

525 MnO4

 [CT  CT e
0.25

 kobs t

]

525 MnO2

Assumptions:
1) [MnO4-] + [MnO2] = CT 2) Reactions are 1st-order with respect to MnO4A525

0.20

0.15

1.0 mM TCE & 0.1 mM MnO4-

0.10

0.05 0 10 20 30 40 50 60

time (min)
10

Equation fits contaminants with various oxidation rates

0.24 0.20 0.16 0.12

0.25 0.20

0.24 0.20
A525

A525

A525

0.15 0.10

0.16 0.12 0.08

0.08

0.05
0 40 80 time (sec) 120

0

5

10 15 time (hrs)

20

0

40

80 120 time (hrs)

160

3-Chlorophenol 2 minutes

PCE 20 hours

2,4,6-Trinitrophenol (Picric Acid) 6 days
11

Determination of k"

kobs  k"[COC]
0.0030

1

1.6 1.4

0.08
0.0025

kobs x 10 (s )

-1 -5

kobs (s )

-1

kobs (s )

-1

0.06 0.04 0.02

0.0020 0.0015 0.0010 0.0005 0.0000 1.0 2.0 3.0 [TCE] (mM) 4.0 R = 0.98
2

1.2 1.0 0.8 0.6 0.4 50 100 150 200 250 300 [1,4-Dioxane] (mM) R = 0.99
2

R = 0.96 1 2 3 4 5 6 [3-chlorophenol] (mM)

2

12

Permanganate Autodecomposition
0.25 3 replicates of 0.1 mM KMnO4 alone

0.20
A525

0.15

5 mM picric acid and 0.1 mM KMnO4

0.10

0.05 0 20 40 60 80 100 time (hrs) 120 140 160

 Permanganate degrades in solution with no COC present.  Is not significant over the time periods of interest  Any contribution of autodecomposition to k" was neglected.
13

Is MnO4- Reacting with Daughter Products?

TCE
Because parent compound to MnO4ratios are 10:1, reaction with daughter products is not likely to be significant. MnO4-



Carboxylic Acids
MnO4-

CO2
14

Correlation between k" obtained with MnO4- in excess vs. COC in excess

15

Results: Comparison of k" values

Especially good candidates for ISCO with MnO4-

16

Half-life at 10oC

17

Toxicity of permanganate







EPA has a secondary MCL for manganese (Mn) of 0.05 mg/L Extreme levels of Mn (20 mg/m3) have been shown to have neurotoxic effects, in some cases inducing Parkinson-like symptoms No neurotoxic effects have been reported with permanganate’s (MnO4-) use as a chemical oxidant for groundwater remediation

18

Acknowledgements

  

Paul Tratnyek, Oregon Graduate Institute Rick Johnson, Oregon Graduate Institute Phil Vella, Carus Chemical Company

19

Backup

20

Pseudo-First-Order Conditions
 If use the COC in excess, a UV-spectrometer can be used to follow changes in MnO4- concentration over time.

[ MnO4 ] 1  1  k"[COC ] [ MnO4 ] t



[ MnO4 ]  1  kobs [ MnO4 ] t
21



Successive Scans Approach
0.25
0.25

0.20

0.20

Losing the isosbestic point

0.15

0.15

A

0.10

A
0.10

0.05

0.05

0.00 400 450 500 550 600 650
350 400 450

wavelength (nm)

500 550 600 wavelength (nm)

650

700

x x Ax  [MnO ] MnO  [MnO2 ] MnO

 4

At the isosbestic point:

Therefore,

A467  

467 MnO

 4

2

 4

467  MnO2

467 MnO4 / MnO2

 ([MnO ]  [MnO2 ])
22

 4

Determination of Phosphate Buffer Conc.
50 mM is sufficient for most reactions 100 mM is required for others
0.25 0.20 0.15
A

 

A

0.25 0.20 0.15
A

B

0.10 0.05 0.00 400 450 500 550 600 650 wavelength (nm)

0.10 0.05 0.00 400 450 500 550 600 650 wavelength (nm)

MEK with 50 mM PB

MEK with 100 mM PB
23

A525 vs. A418 Approach
525 525 A525  [MnO ] MnO  [MnO2 ] MnO

 4

418 A418  [ MnO2 ]   MnO2

 4

2

525 A525  (MnO

 4

525 MnO  418 MnO

2

525 )  A418  MnO4  CT
constant
0.25 0.20

2

constant
0.25 0.20

A525

0.15 0.10 0.05 0.02 0.04 0.06

A525

0.15 0.10 0.05 0.00

A418

0.010 0.020 0.030 0.040 A418

24

525  MnO Difficulties in determining

2

& [MnO2]

525 525 A525  [MnO ] MnO  [MnO2 ] MnO

 4

 4

2

is determined by graphing different [MnO4-] vs. A and finding the slope.
 4

525  MnO

& [MnO2] are not so easily measured.
2

525  MnO

To determine [MnO2] you would need to know at what point in the reaction all of the MnO4- has been converted to MnO2.
525  MnO may be different for different
2

contaminants.

25

Effects of Common Groundwater Constituents on ko for TCE & MnO46.5 6.0
7.0
kobs x 10 (s )
-1 -4

kobs x 10 (s )

5.5 5.0 4.5 4.0 3.5 3.0 0 400 800 1200 1600 concentration of bicarbonate (mg/L) 7.0

-1

-4

6.0 5.0 4.0

0 200 400 600 800 1000 concentration of nitrate (mg/L)

6.5

kobs x 10 (s )

6.0 5.5 5.0 4.5 4.0 3.5 0 200 400 600 800 1000 concentration of sulfate (mg/L)

-4

-1

No effect on kobs for TCE & MnO4- under natural conditions.
26

Effects of NOM on kobs for TCE & MnO4-

0.0022 0.0020 0.0018 0.0016

kobs (s )

0.0014 0.0012 0.0010 0.0008 0.0006 0.0004
5 6 7 8 9 2 3 4 5 6 7 8 9 2 3 4 5

-1

1

10 Concentration of NOM (mg/L)

27

Cost Comparison
Fenton’s: $1.10/lb (includes amendments for pH control and ferrous iron) Permanganate: $4.75/lb Ozone: $3.90/lb (assumes $32,000 initial cost for 10 lb/day ozone generator that requires 10 Kw-hr at $0.10 per Kw-hr) *Remember that Fenton’s requires closely spaced injection wells (~1 – 7 yards apart) and ozone sparging systems have a limited radius of influence, while permanganate is stable enough to diffuse away from the injection wells to the location of the COC.
www.2the4.net/html/chemoxwp.htm

Overall costs of ISCO projects of ~100ft2 in size tend to be on the order of $200K - $800K
EPA, 1998: 28 http://www.caruschem.com/pdf/Hazardous%20Remediation/Field%20Applications%20of%20In%20Situ%20Technologies%20(EPA).pdf

Temperature dependence of k" data
 Experiments in this study were at 25oC, but most groundwater temperatures range from ~ 5-15oC.  k" can be adjusted for temperature using the Arrhenius equation:

k  Ae

 EA / RT

29

Application to a plume with more than 1 COC


As long as MnO4- is in excess, the rate of degradation of each COC should be independent of one another and can be determined from its respective rate law.
[TCE]  [TCE]i e
 k "[ MnO4 ]t
 k "[ MnO4 ]t

[cis  DCE]  [cis  DCE]i e


The total time it takes to degrade the plume is therefore limited by the contaminant with the lowest k" and highest initial concentration*.

* Assumes rate of oxidation, not mass transport from NAPL, is rate limiting
30

Distribution of fitted values of

525  MnO
 kobs t

2

A525  [CT e

 kobst

]

525 MnO4

 [CT  CT e

]

525 MnO2

31

ETBE does not seem to fit the kinetic model
0.30 0.25

A

ETBE fit allowing 525 MnO2 to float.



0.20
A525

2 = 3.7 x 10-4 KMnO4 = 2.46 ± 0 MnO2 = -3.5 ± 0.5
CT kobs = 0.1 ± 0 = 0.073 ± 0.008 hrs
-1

0.15 0.10 0.05 0.00 0 1 2 3 time (hrs)

40 mM ETBE + 0.1 mM KMnO4 50 mM Phosphate Buffer, pH 7, 25 C
4 5 6
o

ETBE fit holding 525 at the MnO2 mean of all positive 525 values of MnO2 .

0.30 0.25 0.20
A525



B

2 = 5.6 x 10-3 KMnO4 = 2.46 ± 0 MnO2 = 0.376 ± 0
CT kobs = 0.1 ± 0 = 0.31 ± 0.01 hrs
-1



0.15 0.10 0.05 0.00 0 1 2 3 time (hrs)

40 mM ETBE + 0.1 mM KMnO4 50 mM Phosphate Buffer, pH 7, 25 C
4 5 6 32
o

MTBE does fit kinetic model
0.25

0.20

2 = 2.4x10-5 KMnO4 =2.46 ± 0 MnO2
CT kobs = 0.192 ± 0.006 = 0.097 ± 8.5x10
-5 -1

0.15

A

= 0.0186 ± 0.0001 hrs

0.10

0.05 0 20 40 time (hrs) 60 80 100

MTBE

 ETBE could contain an impurity  Steric effect?
MTBE TBA ETBE33

Other negative values for
0.25 0.20
A525

525  MnO

2
 = 3.26x10-5 KMnO4 = 2.46 ± 0
2

A

2,4-Dinitrophenol 525 fit allowing MnO2 to float.



MnO2= -0.44 ± 0.06
CT = 0.1 ± 0 = 0.00168 ± 5x10
-5

0.15 0.10 0.05 0 100 200 time (min)
0.25

kobs

300

400

500

B

2,4-Dinitrophenol fit 525 holding MnO2 to the mean of positive 525 values of MnO2 .

A525



 = 5.8x10-5 KMnO4 = 2.46 ± 0
2

0.20 0.15 0.10 0.05 0 100 200 time (min) 300

MnO2= 0.376 ± 0
CT kobs = 0.1 ± 0 = 0.00273 ± 4x10
-5



400

500

34

Determination of slow rates
0.24 0.20 120 mM dichloromethane 50 mM 1,4-dioxane 75 mM 1,2-dichloroethane

We know that k" for 1,4dioxane is 8.7E-05. These other compounds appear to have rates of reaction that are slower than or equal to 1,4dioxane. Therefore, k" for these compounds should be 10-4.
0.25

A525

0.16 0.12 0.08 0
0.12 0.11 0.10

40 80 time (hrs)

120

7mM 1,4-dioxane 7 mM 1,1,1-TCA

3.5 mM 1,4-dioxane 3.5 mM CCl4

0.24 0.23
A525

A525

0.09 0.08 0.07 0 10 20 30 40 50 time (hrs) 60 70

0.22 0.21 0.20 0 10 20 30 time (hrs) 40 5035

Proposed mechanism with BTEX

36

First-Order Appearance Curves

A) 1 mM m-cresol and B) 1 mM 2-chlorophenol. The intermediate reactions (occur on the order of minutes to hours) include C) 1 mM TCE and D) 1mM PCE. The slow reactions (occur on the order of days) include E) 50 mM MTBE and F) 4mM toluene. 37

Reaction of NOM only & MnO4
0.26 0.24 0.22 0.20
A525

MnO4- & 10 mg/L NOM only

0.18 0.16 0.14 0.12 0.10 0 2 4 6 8 time (hrs) 10 12

38

Structures

aldicarb

RDX

dichlorvos
39

COCs that also absorb light
0.30 0.25 0.20 0.15 0.10 0.05 0.00 400 450 500 550 600 wavelength (nm) 650
5 mM picric acid

A

0.30 0.25 0.20 0.15 0.10 0.05 0.00
A

A

0.30 0.25 0.20 0.15 0.10 0.05 0.00
A

B

450

500 550 600 wavelength (nm)

650

450

500 550 600 wavelength (nm)

650

40

Alternate Method 1: Run Rxn to Completion to get accurate 525 value for

 MnO

2

Rxn is assumed to be complete when spectrum no longer shows MnO4- absorbance peaks.
x x Ax  [MnO4 ] MnO  [MnO2 ] MnO
 4 2

[MnO4 ]v  ( A   A / ) /  [ MnO4 ]v  ( A  A A / A ) / 
 525 v 525 v 525 418 MnO2 v 525 418 f v

525 525 [ MnO4 ]v  ( Av525   MnO2 [ MnO2 ]v ) /  MnO  
4

418 525 MnO2 MnO4 418 525 f MnO4

where v= any time f = final time

Lee and Perez-Benito, Can. J. Chem 1985

Allows [MnO4-] to be determined without having to estimate (or fit)  525
MnO2

Could then get k from conc vs time data.
41

Alternate Method-2: Estimate absorbance 525 spectrum of  MnO
2
x x Ax  [MnO4 ] MnO  [MnO2 ] MnO
 4 2

y x AMnO2  Q  AMnO2 [ MnO4 ]  x y  MnO2  Q   MnO4 

y MnO Q x MnO

2

2

y AMnO2  x AMnO2

Assumes: All absorbance in the ranges 438 – 478 nm and 598 – 638 nm is due almost entirely to MnO2 (black squares in figure). Fits a third order polynomial to the absorbance over both these ranges after 2-3 half-lives so that MnO2 Absorbance may be calculated at any wavelength and Give the ratio Q of absorbances for any 2 wavelengths. Generate: Four rate constants at 4 pairs of wavelengths and average them to get the reported value. 526 526 546 546 450 494 450 494
42

K. Gardner, pH.D. dissertation

Alternate method-2: A necessary modification for environmental conditions

0.25

0.20

Gardner MnO2 absorbance range MnO2 absorbance range appropriate to these conditions Polynomial fit to appropriate MnO2 range Absorbance scan for the reaction of 4 mM toluene and 0.1 mM KMnO4 at 144 hours

0.15
A

0.10

0.05

0.00 350 400 450 500 550 wavelength (nm) 600 650 700

43

Alternate Method 2: Comparison of spectrums

4 mM toluene, 0.1 mM KMnO4 50 mM Phosphate Buffer pH 7 25C 44

Alternate method -2: Reproduction of their conditions gives similar spectrum.
0.5

0.4

absorbance

0.3

0.2

0.1

0.0 400 440 480 520 560 600 640

wavelength (nm)

4 mM toluene + 0.1 mM KMnO4 4 mM Phosphate Buffer, pH 7 75 C

45

NOM

0.0022 0.0020 0.0018 0.0016

0.0022 0.0020 0.0018 0.0016

kobs (s )

kobs (s )

-1

-1

0.0014 0.0012 0.0010 0.0008 0.0006 0.0004
6 8 2 4 6 8 2 4

0.0014 0.0012 0.0010 0.0008 0.0006 0.0004

1 10 Concentration of NOM (mg/L)

0

10 20 30 40 50 Concentration of NOM (mg/L)

Log scale

Linear scale
46

Permanganate Mechanism for TCE

47

Ozone Mechanisms: Direct Ozonation

Beltran, 2003 48

Decomposition of Ozone produces HO•

49

Fenton’s Reactions Fe2+ + H2O2  Fe3+ + OH• + OH-

50

Hydroxyl Radical Mechanisms

Hydroxyl radical addition to unsaturated systems (e.g. double bonds):

Hydrogen abstraction (typically from alkyl or hydroxyl groups):

Direct electron transfer:

51

Persulfate Reactions

52

Proposed Persulfate Mechanisms

>C

C< + SO4

-•

>C

C< + SO42-

+

ArH + SO4-•

[ArH]+• + SO42-

53

Background for QSARs--1



Benefits of QSARs
 



Can be used for predictive purposes Evidence for a correlation (or lack of one) can provide insight on mechanisms Can determine consistency among the data

54

Background for QSARs--2




For a successful QSAR, the compounds must have similar reaction mechanisms or structurally similar reaction centers A descriptor variable that relates to the reaction mechanism or reaction center must be identified


Energetics descriptors:





E1/2 IP EHOMO EGap k" ozone
55



Stability descriptor:




Substituent effect descriptor:




Cross-correlation descriptor:


QSAR—all
 QSAR not necessarily expected.
log k" KMnO4

EHOMO (PM5/H2O)

 k" ozone is the
best descriptor • Implies similar mechanisms
EGap (PM5/H2O)

IP

BTEX & Related Compounds Carboxylic Acids Oxygenates & Related Compounds Substituted Phenols Chloroform Chlorinated Ethylenes

log k" Ozone

56

QSAR—Chlorinated Ethylenes
k" is controlled by # of Cl substituents & steric effects, not energetics
log k" KMnO4

EHOMO (PM5/H2O)

EGap (PM5/H2O) ozonide IP 2,3-Dichloropropene trans-DCE cis-DCE 1,1-DCE TCE PCE

# of Cl on double bond

log k" Ozone

57

Phenols
log k"total KMnO4

EHOMO (PM5/H2O)

EGap (PM5/H2O)

E1/2



pKa Nitrophenols Chlorophenols Cresols

log k"total Ozone

58

Calculations for Separate Correlations of Phenols and Phenolates

k " phenol 

k "total , pH 7

0

k "phenolate 

k "total , pH 7

1
59

Phenols Only
log k"phenol KMnO4 *


*
 

*


*

*


EHOMO (PM5/H2O)

EGap (PM5/H2O)

E1/2



pKa Nitrophenols * Picric Acid  2,4-Dinitrophenol Chlorophenols Cresols

log k"phenol Ozone

60

Phenolates Only
log k"phenolate KMnO4 EHOMO (PM5/H2O) EGap (PM5/H2O)

E1/2



pKa Nitrophenols Chlorophenols Cresols

log k"phenolate Ozone

61

Oxygenates
log k" KMnO4

EHOMO (PM5/H2O)

EGap (PM5/H2O)

IP

Ketones and Diketones Ethers Glycol Aldehyde Alcohols and Diols

log k" Ozone

62

BTEX
log k" KMnO4

EHOMO (PM5/H2O)

EGap (PM5/H2O)

IP

Ethylbenzene Benzaldehyde Isopropylbenzene Xylenes Toluene

log k" Ozone

63


				
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