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thesis entitled

Parallel Pathways in the Electrolytic Reduction of
Halogenated Aliphatic Compounds

presented by

Mahesh Rajayya

has been accepted towards fulfillment
of the requirements for

M. 8. degree in ENE

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PARALLEL PATHWAYS IN THE ELECTROLYTIC REDUCTION OF
HALOGENATED ALIPHATIC COMPOUNDS

BY

Mahesh Rajayya

A THESIS

, Submitted to
MICHIGAN STATE UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF

MASTER OF SCIENCE

Department of CNN & Environmental Engineering

1 992

ABSTRACT

PARALLEL PATHWAYS IN THE ELECTROLYTIC REDUCTION OF
HALOGENATED ALIPHATIC COMPOUNDS

BY

Mahesh Ralayya

Halogenated organics are one of the largest single classification of hazardous
chemicals and hazardous wastes. These halogenated aliphatic compounds are
recalcitrant under natural environmental conditions. Reductive dechlorination by
electrolysis can convert highly halogenated molecules into less halogenated spe-
cies that are typically more susceptible to chemical oxidation or biodegradation by
aerobic organisms. Controlled electrolysis in aqueous solutions can be used to
investigate reductive dechlorination in the absence of many-complicating factors.
The compounds chosen for the study are: (1) carbon tetrachloride, (2) chloroform,
(3) 1,1,1 - trichloroethane, (4) tetrachloroethylene and (5) trichloroethylene. The
observed parallel pathways for reductive dechlorination, in terms of, product distri-
bution, are through (1 ) hydrogenolysis (2) a pathway leading to the formation of dis-
solved, dechlorinated carbon and (3) an unknown pathway. It may be possible to
control the pathways of electrolysis by varying the potential applied. Experiments
were conducted to study how variations in the potential applied affect product for-
mation. Hydrogenolysis was found to dominate at higher potentials, whereas the
pathway leading to the formation of other products appears to be independent of

the applied potential over the range investigated.

Dedicated to my thesis advisor and my family

ACKNOWLEDGMENTS

I must first and most importantly thank my advisor, Dr. Craig S. Criddle, for giving
me his guidance, encouragement, and support while completing this research.

Working for him was truly a rewarding experience.

i would also like to acknowledge several people who also helped me with this work.
Dr. Simon Davies and Dr. Susan Masten were very helpful and gave me the assis-
tance in the laboratory when I had questions or problems. I should also thank Doug

Cage who provided help in GC/MS work.

Special thanks also go to my parents, Dr. K. Rajayya and Shadakshari Rajayya,
and sister Dr. Kanchana Prasad. for always encouraging me in my academic stud-
ies and research. I must especially thank my wife Mala Rajayya, for giving me a
valuable support during my research. I must thank Moti Tayal, for being an excel-

lent friend and helping me to complete this work.

This research was financially supported in part, by the State of Michigan Research
Excellence Fund administered through the Center for Microbial Ecology at Michi-
gan State University and, in part, by an Environmental Enhancement Grant from

the Dow Chemical Company.

iv

TABLE OF CONTENTS

Page
Acknowledgments ................................................... ‘ ..................................... i v
List of Figures ............................................................................................... vii
List of Tables ................................................................................................. ix
CHAPTER ....................................................................................................
I. INTRODUCTION ...................................................................... 1
Background ....................................................................... 1
Direct cathodic reduction of C-X bond ........................... 2
Pathways ...................................................................... 3
Carbon tetrachloride .............................................. 3
Chloroform ............................................................. 7
1 ,1 ,1- Trichlororethane ........................................... 8
Trichloroethylene & Tetrachloroethylene ................ 3
Hypothesis ................................ . ........................................ 1 1
ll. MATERIALS & METHODS ...................................................... 12
Electrolysis cell .................................................................. 32
Working electrode ........................................ t ...................... 15
General procedures ........................................................... 18
Analytical methods ............................................................. l9
III. RESULTS & DISCUSSION ..................................................... 2,
Mass balance diagrams ..................................................... 2]
Carbon tetrachloride .......................................................... 22
Chlorofrom ......................................................................... 25
1,1,1 - Trichloroethane ....................................................... 28
Tetrachloroethylene ........................................................... 32
Trichloroethylene ............................................................... 35
IV. CONCLUSIONS .................................................................... 39

Page

V. RECOMMENDATIONS FOR FUTURE WORK ....................... 40
REFERENCES ..................................................................... 4]
APPENDIX ............................................................................ 46

Appendix A OA/OC protocol ...................................... 46
Appendix B Estimation of he .................................... 43
Appendix C Sampling loss calculation for

haloaliphatics ....................................... 50

Appendix D

Appendix E

Appendix F

Calibration constants for volatile
products, chloride and carbon

analysis ............................................... 5]
Statistical test to compare the similarity

between control cell and active cell ...... 53
Raw data .............................................. 54

vi

LIST OF FIGURES

Figure Number
1. Known biotic and abiotic transformations of carbon tetrachloride 5

2. Suggested anaerobic dechlorination and-degradation pathway

for TCA .......................................................................................... 9
3. Suggested anaerobic dechlorination and degradation pathways

for PCE and TCE ............................................................................ to
4. Electrochemical cell for electrolytic studies of reductive dehaloge-

nation in water ................................................................................. 13
5. Carbon tetrachloride electrolysis @ -1.1 V (chlorine balance) ......... 22
6. Carbon tetrachloride electrolysis @ -O.9 V (chlorine balance) ......... 22
7. Carbon tetrachloride electrolysis @ -1.1 V (carbon balance) .......... 24
8. Carbon tetrachloride electrolysis @ -0.9 V (carbon balance) .......... 24
9. Fate of CT in electrolysis cell ...................... 23
10. Chloroform electrolysis @ -1.1 V (chlorine balance) ..................... 26
11 . Chloroform electrolysis @ -0.9 V (chlorine balance) ..................... 26
12. Chloroform electrolysis @ -1.1 V (carbon balance) ....................... 27
13. Chloroform electrolysis @ -0.9 V (carbon balance) ....................... 27
14. Fate of CF in electrolysis cell ........................................................ 23

15. 1,1,1 - Trichloroethane electrolysis @ -1.1 V (chlorine balance) 29
16. 1,1,1 - Trichloroethane electrolysis @ -0.9 V (chlorine balance) 29

17. 1,1,1 - Trichloroethane electrolysis @ -1.1 V (carbon balance) ..... 31

18. 1,1,1 - Trichloroethane electrolysis @ -0.9 V (carbon balance) ..... 3,

19. Fate of TCA in electrolysis cell ...................................................... 30
20. Tetrachloroethylene electrolysis @ -1.4 V (chlorine balance) ....... 33
21. Tetrachloroethylene electrolysis @ -1.2 V (chlorine balance) ....... 33
22. Tetrachloroethylene electrolysis @ -1.4 V (carbon balance) ......... 34
23. Tetrachloroethylene electrolysis @ -1.2 V (carbon balance) ......... 34
24. Fate of PCE in electrolysis cell ...................................................... 35
25. Trichloroethylene electrolysis @ -1.4 V (chlorine balance) ........... 36
26. Trichloroethylene electrolysis @ -1.2 V (chlorine balance) ........... 36
27. Trichloroethylene electrolysis @ -1.4 V (carbon balance) ............. 33
28. Trichloroethylene electrolysis @ -1.2 V (carbon balance) ............. 38
29. Fate of TCE in electrolysis cell ...................................................... 37

LIST OF TABLES

Table Number
1. Characteristics of the electrolysis cell ............................................ 14
2. Typical properties of THORNELL VMA MAT ................................. 16
3. Surface area measurements of THORNELL VMA MAT ................ )7

ix

CHAPTER 1

INTRODUCTION

BACKGROUND:

Toxic or non-biodegradable wastewaters, often containing halogenated
organics, are produced in large quantities by the chemical process industry. Toxic
metals and halogenated organics are two of the most important classes of toxic
compounds found in waste streams (Schmal et al., 1987). Chlorinated compounds
represent 70% of the compounds found in EC list of 129 priority compounds
(Schmal et al., 1987). A variety of commercial techniques are available for the
treatment of halogenated organic wastes, including incineration, chemical oxida-
tion, concentrating techniques, chemical reduction and biological treatment. Incin-
eration, while effective, has several drawbacks including the cost of transporting
waste materials, the cost of large quantities of fuel, and the corrosion of equipment
(Schmal et al., 1986). Polyhalogenated compounds are difficult to destroy using
oxidative technology (Vogel et al., 1987).

Concentration techniques, such as adsorption on activated carbon or res-
ins, membrane separation, and air stripping also suffer from certain drawbacks.
They can be used only in a limited number of cases, and they generate a concen-
trated side stream that requires further treatment (Schmal et al., 1987). Chemical
reduction techniques such as catalytic dehalogenation with hydrogen or other
reducing agents, could be suitable for concentrated waste streams, e.g. haloge-
nated oils (PCB) and solvents (Schmal et al., 1983). Biological treatment of halo-

genated organic waste is under investigation and its limitations are not yet clear.

Electrolflic dehalogenation

Reductive dehalogenation converts highly halogenated molecules into less
halogenated species that are typically more susceptible to chemical oxidation or
biodegradation. However, the transformation products of reductive dehalogenation
may be toxic and in some cases, may be more harmful to human health than the
parent compound. Free radicals generated in the course of reductive transforma-
tion can react in a non-specific manner with constituents of the surrounding milieu.
Consequently, it is important to find means of controlling the transformation path-
way for reductive processes. Controlled electrolysis in aqueous solutions is one
tool that can be used to investigate reductive dehalogenation. Electrolysis makes
it possible to study the principles of reductive dehalogenation in the absence of
many of the complicating factors found in biotic reductive systems (Criddle et al.,
1991 ).

Direct cathodic reduction of C-X bond

Electrochemical reduction of organic halogenated compounds in aqueous
and non-aqueous media has been studied extensively (Becker, 1983). The reduc-
tive cleavage of organic halides is irreversible (Becker, 1983), and generally inde-
pendent of the pH of the medium.The reduction easily proceeds in the order: RI >
RBr > RCI > RF and tertiary RX > secondary RX > primary RX. Aromatic and vinyl
halides are more difficult to reduce than alkyl halides (Becker, 1983).

Possible mechanisms of electron addition and C-X bond rupture are illus-
trated in the following schemes (Elving, 1979):

Scheme 1. A cleavage of the carbon-halogen bond in a single two-electron
process to yield a carbanion:

(1) RX 4- 26' ———> R’+ X'

3
Scheme 2. A two-step one electron transfer to yield a carbanion:
(2) Fix + e' > n' + x:
(3) n' + e' p n-

 

 

Scheme 3. Formation of a radical anion, which subsequently decomposes
to yield a carbanion: ‘

(4) RX 4- e' ——> [RX]‘

(5) [RX]' ___, n' + X'

 

 

(6) n' + H' a RH
(7) 2n' , R-R
(8) R' + e‘ _ 9'

Scheme 4. Formation of a radical anion followed by addition of electron and
C-X bond cleavage:

(9) RX + e’ __> [RX]'

(10) [RX]' + e’ —-> a: + X'

Scheme 5. Formation of a dianion:

(11) [RX] +2e' _, [RX] 2'

The mechanism provided in scheme 3, is the generally accepted one,
although it has some exceptions that have been observed in some cases. The fol-
lowing section reviews the various possible pathways for reductive dehalogenation
of selected haloaliphatics. The selected compounds are carbon tetrachloride (CT),

chloroform (CF), 1,1,1 trichloroethane (TCA), and tetrachloroethylene (PCE).

Carbon tetrachloride (CT)
Figure 1. summarizes possible pathways possible for the transformation of
CT (Criddle and McCarty, 1991). Most researchers agree that the first step in CT

transformation is a one electron transfer to yield a trichloromethyl radical and a

4

chloride ion, although CT can also undergo direct hydrolysis by an unknown mech-
anism (Wade and Castro, 1973; Bakac and Espenson, 1986; Koster and Asmus,
1971). As illustrated in Fig.1, several pathways can operate simultaneously and

competitively. A discussion of each pathway follows.

Reactign 1. One-electron reduction of CT to the trichloromethyl radical.

(1a) cc:4 + e' __, CCI3' + or

Reaction (1a) is generally considered to be rate-limiting step in alkyl halide
reductions (Wade & Castro, 1973; Bakac and Espenson, 1986). The source of the
electron can be from the reduced species, including certain transition metals,
organics, enzymes and cofactors, or it can be emitted from a cathode or a beta

radiation source (Koster and Asmus, 1971 ).

Reaction 2. Dimerization of trichloromethyl radical to give hexachloroethane.
Andres (1982) shwed that the trichloromethyl radical dimerizes:

(2a) 2 [cc13'1 _, 02016

Reaction 3. Hydrogenolysis. Sequential reductive dehalogenation to chloroform fol-
lowed by further reduction to dichloromethane.
The following reaction sequences have been proposed for hydrogenolysis
of CT (Kubik and Anders, 1981 ; Luke et al. 1987; Egil at al. 1988; Gossett, 1985):
(3a) CCI3' + H* + e' _ CHCI3

 

 

(3b) CCI3' + RH > CHCI3 + 9'
(3c) CCI3' + e' - cc13'
(3d) CCIa. + H+ ’ CHCI3

 

As illustrated in Fig .1, CF and MC are produced from hydrogenolysis reac-

tion of CT. As the degree of chlorination decreases in the series from CT to MC,

4HCI 2H 0
‘ 2

nydrOI‘y'SIS ?

 

carbon tetrachloride - CT

 

. CI C!
O . ‘ '
CI? C'C 5- CI
CI' 4 a
CI CI

 

 

- CI 10/' hexacnloroetnane
R f- R 2 \ o MIND!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

H++e
c1 9"” ' ' C!
\4 l 2 e
C s. 02
4 CI ® (9 CI CI
of CI' ® ‘ ’
4“
cell bound .5 ? CI H
V
4 CI Cl CI
01 \ , chloroform - CF
C
H O \ + .
2 2H 20 C14 O-O - H ‘29 j strong
2HCI _ reauctant
ZHCI CI
'——— HC H
C30 1 n30 Id Cl \ CI CI
0 cac C=O ‘ )
carbon , c! l (C‘
ITIOI'IOXIOB . H H
phosgene
dlchloromethane
H20
2HCI
l_2

 

 

carbon OIOXIOE

Fig 1. Known biotic and abiotic transformations of carbon tetrachloride. Products that

have been detected are shown In boxes. (From Criddle & McCarty, 1991)

 

6

removal of chlorine becomes increasingly more difficult. In general, hydrogenolysis
of CT to CF occurs when reductants of sufficient reducing power are present and
competitive oxidants are not. CF is one of the most difficult compounds to degrade
among Cl alkyl halides (Jeffres et al., 1989). Therefore, it is important to prevent
its formation. There appears to be two possible strategies to prevent the accumu-
lation of CF: in one case, oxidizing conditions could be used to encourage the C02
formation; alternatively, strong reducing conditions could be used to encourage

dichloromethane formation.

Reaction 4. Addition of molecular oxygen to the trichloromethyl radical.

The trichloromethyl radical reacts rapidly with oxygen to give a peroxy radi-
cal (Monig et al., 1983):

(4a) CCI3' + 02 _, CCI3OO'

The mechanism by which peroxy radicals are susequently converted to 002
(Monig et al, 1983) is uncertain. The proposed pathways are illustrated in the fol-

lowing reactions (Asmus et al., 1985; Monlg et al., 1983; Bahnemann et al., 1987).

 

 

 

(4b) colaoo' + RH , CCI300H + R'

(4c) CCI30H + H20 , 0:00:2 + r1202 + HCI
(4d) 2[cc13oo') + 2cc130' + 02

(4e) CCI3o' ‘ , 0=cc12 + or

(at) colao' + in + e' ,, CCI30H

(49) canon > 0=cc12 + HCI

 

(4h) O=CCI2 + H20 ——> C02 + 2HCI
Phosgene (O=CCI2) is an expected intermediate in the aerobic transforma-

tion of CT to 002 as indicated by steps 49 and 4g.

Reaction 5. Two-electron reduction to give dichlorocarbene
Dichlorocarbene (:CCI2) is formed from chloroform under basic conditions,
(Hine, 1950; Andres, 1982; Krimse, 1971; March 1985). Thefollowing reactions

have been suggested as possible sequences leading to its formation from CT:

 

 

 

(5a) cacn, + on: p CCI3' + H20
(5b) CCI3. > :CCI2 + CI.
(5c) cc:4 + 26' > :ccr2 + 2cr

Dichlorocarbene hydrolyzes to give CO and/or formic acid. Using thermody-
namic calculations, Criddle (1989) showed that dichlorocarbene formation from CT
is favorable under less reducing conditions that are required for the one-electron

reduction of CT.

 

 

(5d) :CCI2 + H20 > CO + 2HCI
(5e) :ccr2 + 21120 > HCOOH + 2HCI
Chloroform (CF)

The product distribution is different in the one electron induced degradation
of CF compared to that of CT (Asmus et al., 1985). High yields of HCOOH are
formed. The difference in transformation must be attributed to the existence of the
C-H bond in CF. The initial steps of electron capture and 02 addition are analogous
to reactions 1 and 4a. The CHCIZO radical is formed according to the following

reaction sequence:

 

 

(6a) 011012 + e' > cucrz' + or
(6b) cucuz' + 02 v» cucuzoo'
(6c) 2cucrzoo' .. 2cncrzo' + 02

 

Reductive dechlorination of CF may result in the formation of MC. Reductive

8

dechlorination of MC could result in the formation of free CM. It is also speculated
that in CF metabolism, a dehydrohalogenation/hydration reaction would yield an

aldehyde (Gossett, 1985).

1,1,1 ,- Trichloroethane (TCA)

Pathways for anaerobic transformation of TCA are shown in Fig 2. (Vogel
et. al 1987). The mechanism is believed to be a free radical process reduction sim-
ilar to CT. The similarities in the pathways are; (1) a parallel hydrolytic reaction is
observed. and (2) sequential reduction is observed. A significant difference in the

pathway is the dehydrohalogenation reaction yielding DCE.

Tetrachloroethylene (PCE) and Trichloroethylene (TCE)

Pathways for anaerobic dechlorination are shown in Fig. 3. Anaerobic
dechlorination of PCE has been recently demonstrated (Fathepure and Boyd,
1988). In this pathway, PCE is transformed to TCE, followed by sequential dechlo-
rination. DCE is produced from hydrogenolysis of TCE. As the degree of chlorina-
tion decreases in the series from PCE to DCE. the removal of chlorine becomes
increasingly more difficult under reducing conditions. In general, hydrogenolysis of
PCE to VC occurs when reductants of sufficient reducing power are present and
competitive oxidants are not. Ethylene can be oxidized by aerobic organisms to

yield 002 (Fathepure and Boyd, 1988).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

cu,ccr3
TCA
A
CH2CCIZ cn3cncr2
LLDCE LLDCA
RD RD
V
V
CHZCHCI CH3CH2CI
‘ vc ‘ CA
B
l v
CH3CH20H cn3coon
ETHANOL ACETIC
ACID
i . (.
co2 co2 co2

 

 

 

 

 

 

 

 

 

Fig 2. Suggested anaerobic dechlorination and degradation pathways for 1 ,1,1-
TCA. (RD-reductive dechlorination; A-abiotic; B- biotic; CA-chloroethane;
DCE- dichloroethylene; DCA— dichloroethane (From Vogel et al. 1987.)

cchcch

PCE .

 

 

CH.CI.C.C|2

 

‘ TCE

 

 

RD RD

CHZCCIZ CHCICHCI

 

 

1,1-DCE t-l,2-DCE

 

 

 

 

RD

CHCICHCI

 

 

c-l,2-DCE

 

 

RD

 

l

CHZCHCI

 

VC

 

 

 

CHZCHZ

 

 

 

ETHYLENE

 

 

 

l

co2

 

 

 

 

RD 4' H2
RD

 

CH3CH2CI

CA ’

 

 

 

Fig 3. Suggested anaeroboic dechlorination and degradation pathways for PCE
(tetrachloroethylene) and TCE-trichloroethylene. ( RD- reductive dechlorination,
DCE- dichloroethylene (c-cis. t-tans); VC- vinyl chloride; CA-chloroethane).

(From F athepure et al. I 988).

HYPOTHESIS

The underlying hypothesis forthis work is that electrolysis can be used to transform
halogenated aliphatics via various parallel pathways and that the distribution of
products can be controlled by varying the applied potential. Parallel pathways arise
from many factors, including the nature of the electrolyte, the nature of the working
electrode material and the potential applied. This work focuses on the potential
applied. The compounds chosen for the study are: carbon tetrachloride (CT), chlo-
roform (CF), trichloroethylene (TCE), tetrachloroethylene (PCE) and 1,1,1- trichlo-
roethane (TCA). The product distribution for each of these compounds is evaluated
at two different applied potentials.

II

CHAPTER 2
MATERIALS 8: METHODS

Electrolysis Cell

As illustrated in Fig.4, the electrolysis cell (Belco Glass, Inc., \flneland, NJ)
used for this work was a glass vessel consisting of anode and cathode compart-
ments separated by a proton-permeable membrane (Nafion 117R, Dupont Co.,
Wilmington, DE). The cell was also modified to incorporate a reference electrode
(Ag/AgCI, with 1M NaZSO4 filling solution, Fisher Scientific Co., Itasca, IL) a com-
bination chloride electrode (with 1M KNO3 filling solution, Orion Research, Inc.,
Cambridge, MA), a counter electrode, and a working electrode. The counter elec-
trode was an anode made of Ebonex R (Ebonex Co.,). Oxidation at the anode
produces protons, electrons and molecular oxygen (Criddle and McCarty, 1991).
Protons pass through the membrane, to balance the negative charge transferred
via the external circuit. The electrons pass through the external circuit to the graph-
ite electrode where reductions occur. Other cell characteristics are shown in Table
1. The potentiostat (PAR Model 273, EG & G Princeton Applied Research, Trenton,
NJ) automatically adjusts the total voltage between the cathode and anode to
maintain a constant set-point reference potential between the cathode and the ref-
erence electrode. The reference electrode tip was positioned within a few millime-
ters of the cathode surface to avoid any voltage drop due to the solution resistance.

The working electrode consisted of Thornell VMA mat (Amoco Performance
Products, Greenville, SC) mounted in a slide frame. The inner sides of the frame
were coated with silver paint (Structure Probe, Inc., West Chester, PA) to establish
electrical contact. Silver paint was highly effective in establishing electrical contact
between the graphite fibers and a platinum wire exiting the cathode. In the absence
of silver paint, the contact was poor, and little degradation of the organic compound
was observed. Since silver paint used contained some volatile fatty acid ingredi-
ents, background subtraction was done for the dissolved organic carbon due to

12

13

 

 

 

 

 

 

 

 

 

 

Potentlostat Cm“ V rem
setpolnt voltage. Adlust
total voltage across cell

iAV so that v reF setpomt
value
so a. c '1 Vre,
pctentlostat I'ROOOI
‘ ,, 173 I . e'

 

 

 

 

Electrolysis
Cell

 

 

 

 

 

 

 

 

 

 

 

v

 

 

 

I'GIGTOI'ICO
‘ electrode

Ebonex H +‘ "" ' l
anode \ l
(counter .

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. cathode
electrode) 1 I + l j (worklng
N III a n BIOCII’OOBI
Anode membrane Cathode
reaction: reactions:
21120 —I-O 2+ 4H +4.46 ' RX +0 '->R l- X '

nu Hts ""RH

 

2H"'+2e ' --H 2

Fig 4. EleCtrochemicaI cell for electrolytic studies of reductive
dehalogenation in water

I4

Table 1. Characteristics of the elctrolysis cell

Dimensions:

Working cell:

Liquid volume 230 mL
Gas volume 128 mL
’Ebonex’ anode surface area 14.5 cm2
Graphite felt surface area 200 cm2
Nafion memebrane surface area 4.5 cm2
Control cell:

Liquid volume 228 mL
Gas volume 126 mL
Nation membrane size 4.5 cm2
Buffer

N3H2PO4 0.1 M
NaOH 0.06 M

pH 7.0 (without adjustmnet)

IS

leaching of components of the silver paint. TOC (Total Organic Carbon) analyses
indicated that leaching could result in less than 0.2 mg/L of background organic
carbon during an experimental run. Electrical continuity was evaluated with a multi-
meter (Fluke 75 series, John Fluke Mfg. Co., Inc. Everett, WA). Openings of the
electrolysis cell were sealed with Teflon Mininert R valves (Alltech Associates, Inc.,
Deerfield, IL). The lid of each glass compartment was sealed with high vacuum
grease, then clamped to the corresponding glass base.

Working electrode

The physical properties of the electrode are summarized in Table 2. The sur-
face area of the VMA mat , Sf, was computed from the following equation (Kinosh-
ita, et al., 1982).

S, = 4/pd,
where: p is the density(g/cm3) and d is the diameter of the fiber = 8 pm.

The actual surface area of the fibers exposed to the solution was estimated
as follows. The slide frame with the mounted graphite felt was dried upon comple-
tion of an experiment. The fibers inside the window were cut out and weighed. The
actual surface area was computed from S, (1 000cm2/g, from Table 2.). The actual
surface area of the fibers exposed to the solution from each experiment is listed in
Table 3.

Selection of an appropriate working electrode is an important consideration in elec-
trolysis. Thornell VMA mat was chosen for this work. The reasons for selection are
similar to those given by Schmal et al.,(1987) for graphite felt (a very similar mate-
rial).

1) VMA mat has a large specific surface area, reducing the costs of treating low
concentrations of halogenated compounds.

I6

Table 2. Typical properties of THORNELL VMA MAT

 

Density, g/cc 1.90
Fiberdlametemtm 8

Carbon assay, % 98 +

Surface area, m2/g 0.75
Electrical resistivity, u ohm-m 13
Thermal conductivity, W/ m K 22

Porosity 0.9

 

 

 

17

Table 3. Surface area measurement of THORNELL VMA MAT

 

 

Experiment I Surface-area (m 2)
1.CT@-1.0V 0.0184
2. CT @ -0.8 V 0.0189
3. CF @ -1.0 V 0.0191
4. CF @ '0.8 V 0.0187
5. TCA @ -1.1 V 0.0186
6. TCA @ -0.9 V 0.0180
7. PCE @ -1.4 V 0.0188
8. PCE @ -1.2 V 0.0189
9. TCE @ -1.4 V 0.0190
10. TCE @ -1.2 V 0.0188

 

 

 

 

18

2) VMA mat is produced in large quantities, is readily available, and is cheaperthan
most other conductive material.

3) It is less prone to clogging by small particles in waste streams than any other
material.

4) It has relatively high ’overpotential’ for hydrogen evolution, hence the efficiency
of dehalogenation is higher. Mazur et al. (1989) demonstrated that porous amor-
phous carbon felt, which is partially graphitized, demonstrated higher levels of cur-
rent efficiency.

General procedures

The cathode compartment was purged with pure helium to deoxygenate the
solution, while a low potential was applied to remove trace levels of oxygen
present. When the current had fallen less than 5 (M, a known amount of haloge-
nated organic compound was introduced by syringe injection into the cathode com-
partment solution. Sufficient time (15 minutes) was allowed to achieve equilibrium
between gas and liquid phase. To estimate the time required to reach the equilib-
rium, mass transfer experiments were conducted. For a given reactor configura-
tion,k La was estimated for each organic compound at a stirring speed that was
held constant for all the experiments. The measured kLa values for each organic
compound are listed in Appendix B. The mass transfer coefficient was found to be
much smallerthan the first order reaction rate constant, hence the reaction was not
mass transfer controlled. Once equilibrium was achieved, the reference potential
was increased to the desired set point. The experiments were carried out under
potentiostatic mode, under limiting current conditions to avoid excessive H2 pro-
duction. The total voltage across the cell varied from 2510 volts.

A control cell similar to the working cell but lacking electrodes, served as a
control for comparison of physical processes such as sorption or diffusion through
Nafion R membrane. The liquid/gas ratio of the control cell was equal to that of

I9

working cell. The same buffer solution (Table 1) was used in both control cell and
working cell. Known amounts of halogenated organics were injected into the liquid
phase, and allowed to equilibrate. Gas samples (200uL) were drawn by means of
a gas tight syringe equipped with a locking valve.

The control cell also served for calibration of halogenated organic com-
pounds. Calibration was achieved by maintaining the same liquid/gas ratio as in
the active cell. A statistics test (t-test) was performed to confirm that the control
cell can be used for calibration with 99.5% level of confidence. The statistics test is
explained in Appendix E.

Analytical methods

Volatile products

To identify and quantify the products formed during experiment, gas samples (200
uL) were injected onto a PE 8500 gas chromatograph equipped with a flame ion-
ization detector and a 10% squalene, 80/100 Chromsorb W AW column (5 ft. x 1/
8 in; Supelco, Inc., Bellefonte, PA). The volatile products formed during experiment
were confirmed with JEOL AX 505 model, double focussing mass spectrometer
equipped with a HP 5890 gas chromatograph, where porplot U fused silica column
(25 mt. X 0.32 mm; Chrompack, Rearintan, NJ) was directly intefaced via heated
inlet into mass spectrometer ion source.

Chloride analysis

Chloride analysis was done using a two-electrode system consisting of a chloride
ion selective electrode (Orion Research, Inc., Cambridge, MA) and a reference
electrode (Fisher, Scientific Co., ltsaca, IL) with 1M NaZSO4 used as filling solution.
External calibration standards were prepared by using the same buffer solution to
eliminate any background interferences present. The detection limit for chloride
analyses was 1 mg/L.

20

Carbon analysis

Organic carbon analyses were performed on a TOC (Total Organic Carbon) Ana-
lyzer (TOO-500 model, Shimadzu Corporation, Kyoto, Japan). Liquid samples (1
mL) were drawn periodically from the electrolysis cell and saved into a glass vial.
The samples and the external standard was acidified (pH <2) with 0.5 N HCI and
purged with helium gas to remove carbon-dioxide. During purging all VOCs are
completely removed from the samples. Calibration standards were prepared in the
same buffer used in the experiment. The detection limit for TOC was 0.1 mg/L
Background TOC was computed from triplicate samples of buffer after electrolysis
of a solution not containing halogenated aliphatics.

CHAPTER 3

RESULTS 8: DISCUSSION

Mass balance diagrams

Chlorine and carbon mass balances were calculated for each of the exper-
iments conducted. Mass balance diagrams for chlorine and carbon were con-
structed using the data obtained for volatile organics, free chloride and dissolved
organic carbon. All measurements were corrected for background chlorine and
carbon measured in the control cell. Some general features of the mass balance
diagrams should be noted. The upper horizontal line on top of the diagram repre-
sents the mean value of the amount of chemical injected in the control cell (from
triplicate samples). The error bar outside the diagram shows the 95% confidence
interval for the original mass of the chemical injected at the beginning of the exper-
iment. Chlorine mass balance diagrams were constructed from the measured con-
centrations of the volatile products and aqueous free chIOride. Carbon mass
balance diagrams were constructed using the data for parent compounds, volatile
products and dissolved organic carbon in aqueous phase. The mass loss due to
aqueous sampling was also accounted for in these diagrams, and the calculations

are provided in Appendix C. Sampling of gas phase resulted in <0.2% of the total

mass of the chemical.

Carbon tetrachloride (CT)
Chlorine balance

The chlorine mass balances obtained when CT was reduced at two different
reduction potentials (-1.1 V and -0.9 V) over a 3 hour period are illustrated in fig-

ures 5 and 6. In this experiment, CT was reduced to CF, MC, CM and methane.

21

pmoles as chlorine

pmoles as chlorine

22

 

EL 95% C. I

  
   

60° TTF—Sr—‘ — CM

550 , I’ll/[WWW NC

500 San'lpling loss
45° ,, , ;';‘,,;,-4,;/,;','///

4m 1’ [I . /////z I

350 , . ,. ..

        

 

 

 

 

 

 

 

 

 

 

    

 

 

    
   
  
   
    

 
   
   

      
      

 

   
  

  
 
    
   
     

  

 
     

      
  

     
  
    

 

 

  
 
      

   
  

   
  
        
   
   
  

 

  
     
 
   
 

 

   
 
 

  

[I] Free cnlonde '_
1 :/ .
o . , » . . . . ,
o 20 40 so so 100 120 140 160 180
Time (rnmutesl
Figure 5. CT electrolysis at -1.1 V (-0.88 V vs SHE)
750
700 _-
650 ..
600 =,_ 959'. or
"W W . ,
550 7,2,, » ' [I’ll/MM . WWW/{4 fl Samollng 105‘
flVVK/Jgf/qx/ki' ’/4 . ,”,' :1; (a, m
7// I. (421/; /% , /'/////////////;x/////
400 / x 77; . :{/’/{////// / %;;;/;;i/;
W /, ”VA,” / ,9, ,
300 ///////;//j////////
250 .927, 22"".2/ ’ f‘
, . //:////’,¢///////x//////Z
20° ',.I :g. 7/ .2 ’ :7 / ”Zfr/gc/l/ y/{j/{g/
150 ' " 7 //2 /.’///// . , ////y//// ’ 32%
/,{¢//%/¢6//7i/////U //,¢/{”/’;///////I/%
‘00 22727,,” fifi/Afffy’flfifl, w;/§’Z////V/ZI’///// 1”” ”
so 1/4’3224l/4fiZ4’7/7/ ////”/'////” H l “
gay/{f (CD Free chlonoe
o I. I IIIII‘IlllllIlIllllllllll

 

t . r I I fi—
0 20 4O 60 80 100 120 140 160 180

Time (minuteSI

Figure 6. CT electrolysis at -0.9 V (-0.68 V vs SHE)

23

The disappearance rate of CT was faster at the higher reducing potential (-1.1 V).

At the higher reducing potential (-1.1 V), the rate of formation of hydrogenolysis

products was also greater than the rate which occurred at the less reducing poten-

tial (-0.9 V).

Carbon balance

The carbon mass balance for CT at the two different reducing potentials are illus-

trated in Figures 7 and 8. The mass of dissolved organic carbon and sampling loss

adjustments are indicated. The final dissolved organic carbon (determined at the

completion of the experiment) did not vary much at the two different reducing

potentials.

The distribution of products formed by electrolytic reduction of CT are

shown in Figure 9.

 

 

 

 

 

 

 

 

CT
@ -1.1 V (19%) (66%) (15%)
@ -O.9 V (24%) (44%) (32%)
i r r
Unknown pathway Hydrogenolysis Dissolved organic carbon
products products products

Figure 9. Fate of CT in electrolysis cell

Figure 9 indicates that the hydrogenolysis is favored at higher reducing

potentials when compared to other pathways. The results of the experiments agree

with previous studies (Criddle and McCarty, 1991; Horanyi and Torkos, 1982). In

umoles ac carbon

umoles as carbon

200

24

 

180--l

 

160-

 

140

120

100

80

60

40

20

 

TOO
Sampling loss
CM
NC

lot

[I] Methane

20 40 60 80 100 120 I40 160 180

Time (rrimtes)

Figure 7. CT electrolysis at -1.1 V (-0.88 V SHE)

 

 

Tm

Wuf ”’lI/IIW /////__/////// -

Sampling loss
OM
MC

20 40 60 80 100 120 140 160 180
Time(minutes)

Figure 8. CT elctrolysis at -0.9 V (-0.68 V vs SHE)

25

methanogenic systems, it has been suggested that coenzyme F 430 is involved in
the reduction of CT and the products formed are CF, MC, CM and methane (Krone
et al., 1989).

Chloroform (CF)
Chlorine balance

The chlorine mass balance for two different reducing potentials (-1.1 V and
-0.9 V) are shown in Figures 10 and 11 respectively. The potentials chosen for the
CF experiment were the same as for the CT experiments. The products of hydro-
genolysis such as MC, CM and methane were produced in larger quantities at
higher reducing potential (-1.1 V) compared to lower reducing potential (09 V).
Krone et al., (1989) showed that coenzyme F430 (Krone et al., 1989) show that the
reductive dehalogenation products of CF transformation are MC, CM, methane

and some unidentified nonvolatile compounds.

Carbon balance

The carbon mass balance for CF at two different reducing potentials are
illustrated in Figures 12 and 13 respectively. At the higher reducing potential, more
dissolved organic carbon was produced, but it still constituted a small fraction of
the products. At the higher reducing potential, the formation of hydrogenolysis
products were faster when compared to lower reducing potential. The hump in the
TOC data shown can be either due to a transformation of the aqueous phase car-

bon products during the course of the transformation or to analytical error.

The distribution of products formed by electrolytic reduction of CF are shown in Fig-

ure 14. Figure 14 indicates that the hydrogenolysis is most likely to be favored at

pmoles as chlorine

pmoles as chlorine

600 f

550
500
450
400
350
300
250
200
1 50
I 00

50

26

 

 

95% C. l

«l/x/I/x/Il/fl/WWW/é r.

Sampling loss
CM

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ICU Free cnlonde
lllllllll‘lllllIlllllll
20 4O 60 80 10° 120 140 160 180

Time (minutes)

Figure 10. CF electrolysis at -1.1 V (0.88 V vs SHE)

 

 

, éW/Zéfixz’m ,
/"{//7 '
a/i’”, A
/ly -

Free cnlonde

0 20 40 60 80 100 120 140 160 180
Timelrrtimrtes)

Figure 11. CF elcectrolysis at —0.9 V (-0.68 V vs. SHE)

PRIOIBS as carbon

Paroles as carbon

27

 

20017
95%C.I

180 ,

160

140

      
       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12° :1}, 4 "I,lll/I////”/””/’l///
’: W
100 WW 71. Samplingloss
so Elli? CM
60 ,
40 [I] Methane
o I ‘ l l ‘ I
o 20 40 60 80 too 120 140 160 180
Time (minutes)
Figure 12. CF elctrolysis at -1.1 V (-0.88 V vs SHE)
220
200 95560 I
180 «
160 TCI:
14o Samplrngloss
CM
120 a m

/

// 47/,7//
// 1 /
/« //

llllllllllllllllll
I

A I I Y I I
O 20 4O 60 80 100 120 I40 160

I
180

Time (minutesl

Figure 13. CF electrolysis at -0.9 V (-o.68 V vs SHE)

28
higher reducing potential when compared to other pathways. The pathway leading

to the formation of dissolved organic carbon is least affected by varying potential.

 

 

 

 

 

 

 

 

CF
@ -1.1 V (20%) (51%) (28%)
@ -0.9 V (25%) (45%) (30%)
i v v
Unknown pathway Hydrogenolysis Dissolved organic carbon
products products products

Figure 14. Fate of CF in the electrolysis cell

1,1,1- Trichloroethane
Chlgrine balangg I

The chlorine mass balance for TCA electrolysis are shown in Figures 15 and
16 respectively. The potentials chosen for the experiment were the same as those
used in the CT and CF experiment. At the higher reducing potential, the reduction
of TCA was complete after 2 hours. Reduction of TCA resulted in the formation of
DCA, CA and ethane via hydrogenolysis. Anaerobic degradation of TCA yielded
products such as DCA and DOE (Gossett, 1985). Previous electrolytic studies with

TCA yielded DCA and other fully dechlorinated products (Criddle and McCarty,
1991).

pmoles as chlorine

”moles as chlorine

29

 

 

   

500
450
40° '5'" I .jt'jjfl”"”””””‘WW///////x///////////////////////e

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time (minutes)

Figure 15. TCA electrolysis at -1.1 V (-0.88 V vs SHE)

soo

 

450

 

 

350

300

25° TCA '

[fl] Free cnlonde

“2,,11, “Hill

I ' I ‘7 I ' I

0 20 40 60 80 100 120 I40 160 180

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time (minutes)

Figure 16. TCA electrolysis at -0.9 V (-0.68 V vs SHE)

E 95% C. I

CA

" \fl Sampling loss

DCA

95% C. I

Sampling loss
CA
DCA

30

Cafln balance

The carbon mass balance for TCA at two different reducing potentials are
shown in Figures 17 and 18 respectively. The quantity of dissolved organic carbon
produced at the higher reducing potential was nearly the same as the quantity pro-
duced at the lower potential. It is worth noting that the total dissolved organic car-
bon measured was much larger for TCA than for the other alkanes studied. The
unidentified portion of the carbon balance diagram could be due to the formation
of unknown products. Possible explanations for the formation of aqueous phase
dissolved organic carbon are hydrolysis or hydrolytic reduction. Hydrolysis reaction
of TCA would yield acetate and hydrolytic reduction might yield acetaldehyde by
the following reaction (Criddle and McCarty, 1991):

CH3CCI3 + H20 + 29- CH3CHO + H+ + 3CI-
The distribution of products formed by electrolytic reduction of TCA are

shown in Figure 19.

 

 

 

 

 

 

 

 

TCA
@ -1.1 V (31%) (33%) (35%)
@ -O.9 V (47%) (20%) ‘ (33%)
v v t
Unknown pathway Hydrogenolysis Dissolved organic carbon
products products products

Figure 19. Fate of TCA in the electrolysis cell

pmoles as carbon

pmoles as carbon

3i

 

 

95% C. I

250

 

     

'/1 Samplinglosa
I CA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I " DOA
so [I] Ethane
. . , , , . lllllllllllllll , ,
o 20 40 so so 100 120
iime(mrnutesl
Figure 17. TCA electrolysis at -1.1 volts (088 V vs SHE)
350
300 SI: 95%c.r
250 ..
200 L-
150 E TOC
10° Samplingloss
TCA I CA
so
DCA
0 (m III] Ethane

 

I

0 20 40 60 80 100 120 I40 160 180

Time (minutes)

Figure 18. TCA electrolysis at -0.9 V (-0.68 V vs SHE)

32

Tetrachloroethylene
Chlorine balance

Chlorine mass balances for PCE at two different reducing potentials are
shown in Figures 20 and 21 respectively. The potential required for the reduction
of chlorinated alkanes was considerably more negative than that required for the
reduction of alkanes. The rate of hydrogenolysis product formation was faster at
the higher reducing potential. The formation of TCE, t-DCE, ethylene and trace
amounts of VC was faster at higher reducing potential. Gossett (1985) showed that
the anaerobic degradation of PCE resulted in the formation of TCE, c-DCE, and t-
DCE. Reductive dechlorination of PCE by vitamin 8,2 resulted in the formation of

TCE and c—DCE (Gantzer and Wackett, 1991).

Carbon balance
Carbon mass balance for PCE at two different reducing potentials are
shown in figures 22 and 23 respectively. The aqueous phase dissolved carbon was

less for PCE than for the other alkanes studied.

Figure 24 illustrates the fate of PCE in electrolysis cell. The distribution of
the products differ from those of alkanes (CT,CF and TCA) with respect to hydro-
genolysis and the pathway leading to the formation of the dissolved organic car-
bon. Alkenes require more energy for dechlorination when compared to alkanes.
At lower potential, little PCE removal was observed. It is evident from the Figure 28

that hydrogenolysis is the dominant pathway.

pruoles as Chlorine

pmoles as Chlorine

33

 

l...

   

 

55° -. r—L 35". C.I
500 ":,,,,lm W 1% . Samoungloss

r

I. rDCE

   

/‘/‘ l1]!

ree cnlonde l

 

 

 

 

 

 

 

F
I I . I '

l I
0 20 ~10 60 80 100 120 140 160 180
Time(mrrutes)

 

 

 

  

Figure 20. PCE electrolysis at -1.4 V (-1.18 V vs SHE)

 

650
600

“ I 95% c. I
550 7/;;',;\' ., ’ _' x 23’!”

 
   
 
    
   

./ ..

III/III/Il/MWW

\s‘i
\. \

/( 7{{/
50° 7 ZQ/z/yfi’l / E2! Sampling loss

 

, /7/////////////////// .
/ / //,~ . ‘
4 // /////////f/7//

%////,///x//

. ../VA{£/T’f'/ /
///////////’/ y
// // . . ////

/7

    

- ..,.

I-DCE

\\
\\
-
\

 

   
 

   

3:
a
. \\ \\\

   
       
    
   
 
  
   

/// //

m
at
O
\x\ \\
{SEX
\\

O
8
_. is;

5/
Z/
/

/
42 .. V/ 4/2/ n
, -, ‘ ,v'/// ’

 

.
\
.\\

  
 
 

  
   

 

   

/
/
/,/////

/

 

4/l

 

Free cnlonde l
. llllllllllllxllllllllllllj
0 40 60 80 100 120 140 160 180

Time (minutes)

Figure 21. PCE electrolysis at -1.2 V (-0.98 V vs SHE)

pmoles as carbon

,umoles as carbon

34

 

 

 

     

 

 

 

     

 

  

 

300 1
35% c. I
250
1%,
—. /
20,, ; =——i:’//////////
' : Sampling loss
t-DCE
150
100
50
o ’ l | I lllllllllllrllllllll
o 20 40 so so too 120 140 160 180
Time (rmmtes)
Figure 22. PCE electrolysis at -1.4 V (-1.18 V vs SHE)
300
I 95% 0.1
25° ~ .’,’.’_’””///////////// —?__——
‘ “ amollng less
200 ~ .
, , // I coca
”I" 1‘} /,_////,,/ /// / 7 ' _/
' / ,- "/IIII/l'7////¢//:///
‘5° / .; ’=- ' fl//%
'1; zen/{MM /
.00 ”557/; 5% graze/rec %’27///%//// -:
// ’ :24 ' f//%’%%/%.
,,, /A/éf//%////Z
//, ,/’ / _/
50 H / 2%W/Z
. ,, / ,.
gW/fl // EII'IYIOHO
o l I I ‘I1 I l Ifi'fi—

I
0 20 4D 60 80 100 120 140 160 180

Time (rnirutes)

Figure 23. PCE electrolysis at -1.2 V (-0.98 V vs SHE)

35

 

 

 

 

 

 

 

 

PCE
@ -1.4 v (23%) (63%) ’ (14%)
@ -1 .2 V '(30%) V (53%) V (17%)
Unknown pathway Hydrogenolysis Dissolved organic carbon
products products products

Figure 24. Fate of PCE in electrolysis cell

Trichloroethylene

Chlorine balance

. Of all the compounds studied, TCE was the most difficult to reduce under
the experimental conditions used. Figures 25 and 26 show the chlorine mass bal-
ance for TCE electrolysis experiment. The products of hydrogenolysis of TCE are
t-DCE, ethylene and trace amounts of VC. Gossett (1985) showed that the anaer-
obic dechlorination of TCE resulted in the formation of DCE, c-DCE and VC . The
dechlorination by vitamin B12 yielded 1,1-DOE, c-DCE and t-DCE, whereas the
dechlorination by coenzyme F430 resulted in the formation of c-DCE and t-DCE
(Gantzer and Wackett, 1991). The chloride measured was also significantly lower
when compared with other compounds. The rate of formation of DCE was much

slower when compared with that of PCE.

pmoles as chlorine

lJITIOIeS as chlorine

36

 

300

   

7. Sampling less
250 w t-DCE

200
I 50
IOO

SO

ll'fl Free cnlonde
1 IIIIIIIIIII'll‘llIIIIIIII

' m"")
0 20 40 60 80 100 120 I40 160 180

 

Time (minutes)

Figure 25. TCE electrolysis at -1.4 V (-1.18 V vs SHE)

 

 

95% C. I

/// ,/// ?)///// a?” ,(////////// /,’ ‘

/ //////,/ / //I a Sampling 1°55
// / ///////

1% 9)” / /’//’/

/.
//// 7////%/; //,j'/
///;’/// ’fl'ig/
' /

 

U] Free cnlonde
I

I I I Ifi
0 20 40 60 80 100 120 I40 160 180

Time (ITIII’IUIES)

Figure 26. TCE electrolysis at -1.2 V (-0.98 V vs SHE)

37

Carbon balance

The carbon balance for TCE electrolysis are shown in Figures 27 and 28,
respectively. Since the rate of dehalogenation was slower, the measured dissolved
organic carbon was small. The products of hydrogenolysis were present in larger
amounts at higher negative potential (-1.4 V) when Compared to lower potential (-
1.2 V). Hydrogenolysis appeared to be the favored pathway for TCE transforma-
tion.

The distribution of the products formed by electrolytic reduction of TCE are
shown in Figure 29. The rate of dehalogenation could be enhanced by applying
more negative potential, but such a measure would lead to significant heating. By
making the reference voltage more negative, the temperature of the solution would
increase, and, this will change the electrode thermodynamics and Henry’s constant

leading to errors in the experimental procedure.

 

 

 

 

 

 

 

 

TCE
@ -1 .4 V (17%) (65%) (18%)
-1 .2 V 76% 13% 11%
@ vl ) V ( ) V ( )
Unknown pathway Hydrogenolysis Dissolved organic carbon
products products products

Figure 29. Fate of TCE in electrolysis cell

pmoles as carbon

)imoles as carbon

38

 

 

 

250

225 + -
J—\_¢I 35v. C.l

zoo M_'—T'——'—"

   

175

Sampling loss
t-DCE

150

100

75

50

25 , //// [1,] . ,,,,,,, we” 54/6/9W/é

/ 57/4;

I 9/17/r ,

   

 

I l i i 1 *fi
0 20 4o 60 80 100120140160180
Time(minutes)

Figure 27. TCE electrolysis at -1.4 V (-1.18 V vs SHE)

 

   
 

 

  
     
        
   
   
  
 
 

 

250
.
225 1' 95% C. I
' 0",l’l' u
-' . . ’IIIII
/ us I
200 ’I’,’”’III’IIIII -

 

 

/Zé?/////7,j;*‘; ’ .,, .. , i
44’; ,M//// // w x .-

175

   

Sampling loss

  

    
 

  
 
 
    
  
  
     
  

/,,-~-', , _,,(l .
. j ,IVz/zyiu/z/ Wyy/lxa/v;;;li/u;;.

/ __ ’7/7/ ’////////,/,////////////1

125 ' . jagg/g/y///,¢/I////////// //
W /////,;////////;//,//// %

—' 974,2714/¢2,.o%// //

1 0° /. ://// é/fl'jV/V/ /

 

   

-//./ //////////.
I; [2,: ZI'W ,,l M g/ ’/%///I/’/////’ /f/ /,
/”mxx . //////Z{////:’/////////é///
-' ////;-r,,, '4 ,., :04, ///7//////

o 20 40 so 80 100 120 140 160 180
Time(mtnutes)

”“1 xx;
0,7,

    
      

      
  
  

  
  
   

               
      
  
     

\
\

  

 
   

U] Ethylene

        

     

Figure 28. TCE electrolysis at -1.2 V (-o.98 V vs SHE)

CHAPTER 4

CONCLUSIONS

Halogenated aliphatics undergo parallel transformation reactions by hydrogenoly-
sis and reduction to soluble dechlorinated products. Hydrogenolysis is an impor-
tant pathway for the transformation of compounds in many instances. Reduction of
chlorinated alkenes require the application of a higher negative potential than is
required for chlorinated alkanes. The fate of chlorinated alkanes was altered by
varying the applied potential. This is possible because of the fact that hydrogenol-
ysis seems to vary with applied potential. Hydrogenolysis pathway appears domi-

nant at higher negative potentials.

The pathway leading to the formation of dissolved carbon appears to be
independent of applied potential. The pathway leading to the formation of dechlo-
rinated, dissolved carbon may be more acceptable from an environmental stand-
point than hydrogenolysis. The former pathway, through hydrolysis or hydrolytic

reduction, may produce products that are easily biodegradable.

39

CHAPTER 5
RECOMMENDATIONS FOR FUTURE WORK

The fate of approximately one fourth of the carbon remains unknown, hence
additional experiments are recommended to identify these substances. Further
experiments will be useful to characterize the form of carbonaceous material
present in the aqueous phase. The effect of dissolved oxygen, pH and nature of
the electrolyte should be studied to Optimize conditions for the dechlorination of
acceptable products. For instance, in CT transformation, addition of molecular oxy-
gen might alter the reaction pathway to form peroxy radical from trichloromethyl
radical, resulting in C02 as the end product (Figure 1). By varying the pH, the
hydrolysis pathway could be altered.

Replacing the Nation membrane with ion-exchange beads will reduce the
treatment cost considerably. Modifications of the cathode material to enhance the
electron transfer should be investigated. Recently, considerable attention has been
devoted to "chemically modified electrodes", and these electrodes are electrocat-
alayzed (Kerr et al., 1980). It has also been reported that chemically altering an
electrode with vitamin B12 catalyzed the electroreduction of alkylhalides in non-
aqueous media when vitamin 812 are absorbed on a graphite electrode (Zagal et
al., 1987). Additional experiments to evaluate the efficiency of reducing mixtures
of aliphatics are strongly recommended. The rate of dehalogenation for alkenes
could be enhanced by employing adequate temperature controls to maintain the
isothermal conditions. Cathode materials which sorb haloaliphatics and are electri-

cally conductive may be particularly desirable, and should be investigated.

REFERENCES

Andres, M. W.1982. Aliphatic halogenated hydrocarbons. Chapter 2 in: Metabolic

Basis of Detoxication: Metabolism of Functional Grougs. W. B. Jakoby, J. R. Bend,
and J. Caldwell, ed., Academic Press, New York, NY.

Asmus, K.-D., D. Bahnemann, K. Krischer, M. Lal, and J. Monig. 1985. One -elec-
tron induced degradation of halogenated methane and ethanes in oxygenated and

anoxic aqueous solutions. Life Chemistry Reports 3: 1-15.

Bahnemann, D. W., C.-H. Fischer, M. R. Hoffmann, A.P. Hong, J. Monig. and C.
Kormann. 1987. Mechanistic study of photocatalytic decomposition of organic
compounds on semiconductor particles. Preprint extended abstract. Presented at
the Meeting of Division of Environmental Chemistry, American Chemical Society,

New Orleans, Lousiana, Aug 30-Sept 4, 1987.

Bario-Lage, G., F. 2. Parsons, R. S. Nassar, and P. A. Lorenzo.1986. Sequential

dehalogenation of chlorinated ethenes. Environ. Sci. Technol. 20: 96-99.

Becker, J. Y. 1983. Electrochemical oxidation, reduction and formation of the C-X
bond direct and indirect processes. In: The Chemistry of Functional Groups, Sup-
plement D. Edited by S. Patai and Z. Rappoport, John Wiley & Sons Ltd., NY, New
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Bouwer, E. J. and P. L. McCarty. 1983 a. Transformations of 1- and 2- carbon halo-

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4|

42

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Criddle, C. S. and P. L. McCarty. 1991. Electrolytic model system for reductive

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Criddle, C. S. 1989. Reductive dehalogenation and electrolytic model systems. EL

D. Thesis Dissertation, Stanford Univeristy.

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New York, NY.

Direnzo, A. B., A. J. Gandolfi, l. G. Sipes. and K. Brendel. 1984. Effect of 02 ten-
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Elgi, C., T. Tschan, R. Scholtz, A. M. Cook and T. Leisinger. 1988. Transformation
of tetrachloromethane and 1.2-dichloromethane to degrade products by pure cul-

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Fathepure, B. Z., J. M. Tidjie, and S. A. Boyd. 1988. Anaerobic bacteriataht dechlo-
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43

Freedman, D. L., and J. M. Gossett. 1989. Biological reductive dechlorination of

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Electroanal. Chem. 140: 329-346.

Jeffers, P. M., L. M. Ward, L. M. Woytowitch, and N. L. Wolfe. 1989. Homogeneous
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44

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45

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min B12 adsorbed on a graphite electrode. J. Electroanal. Chem. 237: 145-148.

APPENDIX A

QA/QC Protocol

The following techniques were employed to ensure a proper QA/QC technique.

Calibration and standardization
* Five point calibration were generated for each compound. The concentrations of

the standards bracket the concentrations quantified.

* Five point calibration curves were also prepared for chloride measurements.

* The same buffer solution was employed for DOC (dissolved organic carbon), free
chloride calibration and in actual experiments.

* The same buffer solution was employed in the control and working cells.

* The liquid/gas ratio of the working cell was equal to that of the control cell.

* Triplicates electrolysis experiments were conducted to show that the electrolysis
of the blank buffer solution did not give rise to any incorrect measurements of dis-
solved organic carbon. This served as a tool to account for silver paint leaching.

"’ All the liquid samples for DOC analyses were pre-filtered through a 5 pm syringe

filter to avoid possible contamination due to the breakdown of the VMA mat.

mm

* Initial sampling intervals were every 10 minutes for 1 hour period followed by a
20 minute sampling period after 1 hour.

* Triplicate samples were employed to estimate the 95% C. l. of the original mass

of the halogenated organic compound injected in the control cell.

46

47
Record Keeging
* All the chromatograms were saved.
" All the results were entered in a bound lab. note-book in pen.

" Statistical analysis to estimate the regression coefficients was done by using
PLOTIT software package (Scientific Programming Enterprises, Hasslett, Ml).

APPENDIX B

Estimation of kLa

Plot ln (1- AG/ A; ) vs time, where AG = GC area units at time t, and A; = GC
area units at equilibrium. Mass transfer coefficients kLa can be computed by the

following formula:

kLa = -slope/ (VG/VL +1/HC)

The value of VG and VL of electrolysis cell are: 0.118 L and 0.240 L respectively.
HC is the dimensionless Henry's constant ; HC = CG /C._, where CG is the equilib-
rium gas phase concentration, and CL is the equilibrium liquid phase concentration.
The values of dimensionless Henry’s constant at 21.5 0 C for the haloapliphatics of

interest are as follows (Gossett. 1985):

 

 

Chemical Hc
CT 0.987
CF 0.117
MC 0.072
CM 0.278
TCA 0.559
DCA 0.182
CA 0.389
PCE 0.563
TCE 0.305
DCE 0.306
VC 0.145

 

 

 

 

as

Measured kLa values for haloaliphatics in active electrolysis cell

 

 

 

Chemical kLa (h '1) calibration constants

b0 . b1 .. '2
CT 17.521 0.350 -0.194 0.965
CF 48.65 -0.751 -0.089 0.961
TCA 39.04 -0.117 -0.285 0.980
PCE 31.55 0.144 -0.232 0.971
TCE 46.03 0.759 -0.231 0.966

 

 

 

 

 

* b0 is the intercept of the linear calibration curve

** b1 is the slope of the linear calibration curve

iii

r2 is the coefficient of correlation of the linear calibration curve.

Note: The raw data for In (1- A / A; ) vs time is provided in Appendix F.

 

APPENDIX C

Sampling loss calculation for haloaliphatics

All mass balances were corrected for the mass removed during sampling

with the following expressions.

AM = V sample * CL (1)
CL=MT/(VL+HcVG) (2)
Where,

AM = mass of sample removed at a given time, MT = total mass (umoles),
VL = volume of liquid phase, VG = volume of gas phase, Hc = Henry’s con-
stant, V sample = 0.002 L. Values for VL, VG and HC are given in Appendix B.

Substituting these values into equation (1) gives,

AM = 0.002 MT/ (0.24 + 0.118 Re)

For example:

CI‘@ -1.1 V, when time = 10 minutes,

M1- = 499.44 umoles as Cl‘

Hc = 0.987

AM = 0.002 * 499.44/ (0.24 + 0.117) = 2.80 umoles of CT removed.

50

APPENDIX D

Calibration constants for volatile products, chloride and carbon analysis

 

 

 

Target compond Analytes Calibration constants
b0. b1" r2...
CT 1 .95 0.841 0.997
CF 062 0.525 0.998
MC -1 .25 0.532 0.997
CT CM -1 .18 3.043 0.992
Methane -4.31 8.349 0.993
Chloride 182.35 -56.01 0.999
Dissolved carbon 465.03 29.467 0.999
CF -1.52 0.487 0.997
MC 0.74 0.561 0.999
CF CM -2.22 6.458 0.997
Methane -3.15 10.367 0.995
Chloride 182.78 -55.85 1.000
Dissolved carbon 465.03 29.467 0.999
TCA 0.54 4.459 0.999
DCA 2.35 8.762 0.995
CA -1 .76 20.82 0.997
TCA Ethane -2.01 11.266 0.996
Chloride 183.25 -55.78 1.000
Dissolved carbon 465.03 29.467 0.999

 

51

 

 

 

52

 

 

 

Target compound Analytes Calibration constants
b0. b1" r2...

PCE -5.33 2.256 0.998

TCE 1 .20 2.624 0.998

PCE DCE -1.67 7.876 0.997
Ethylene -1.50 11.279 0.998

Chloride 180.67 -55.06 1.000

Carbon 465.03 29.467 0.999

TCE 4.61 3.647 0.998

DCE -11.04 7.999 0.994

TCE VC -3.56 8.345 0.996
Ethylene 3.73 ‘ 12.536 0.999

Chloride 181.76 -55.56 0.999

Carbon 465.03 29.467 0.999

 

 

 

 

 

" b0 is the intercept of the linear calibration curve

“ b1 is the slope of the linear calibration curve

if.

r2 is the coefficient of correlation of the linear calibration curve

APPENDIX E

Statistical test to compare the similarity between control cell and active cell
Hypothesis

Ho:8=0vs H126>0

The model compound chosen was CF, and the data for active and control cell are

shown in the table below:

 

 

 

 

 

Volume of the chemical 0 5 10 12 15 20
(11L)

Active cell area units (X) 0 43.65 94.25 114.42 138.75 169.25
Control cell area units (Y) 0 42.42 96.52 115.52 137.92 170.85
c1i = (Y-X) o -1.23 2.27 1.1 -0.83 1.6
(6,) 2 o 1.512 5.153 1.21 0.689 2.56

 

d= Edi/n=2.91/6=0.485
sd = (11.124/5)"2 =1.492
t= a * (n) "2 /sd = 0.485'2.449 /1.492=0.796

Assuming (1 =0.005, the one-sided rejection region is t > t 0.005 = 4.032, and the
observed ’t’ does not fall in the rejection region. Hence, the null hypothesis is

accepted with 99.5% level of confidence.

53

APPENDIX F

54

CT electrolysrs @ -1.1 V Sun. Mar 29. 1992 15:36

Time (minutes) Methane IUt‘l'll CM as carbon (um) MC as carbon (urn) CF ascemon CT as carbon mm
0.00 3.00 0.00 0.00 0.00 165.05
10.00 2.46 0.57 0.80 14.32 124.86
20.00 4.39 0.83 1.25 20.51 99.69
30.00 9.83 1.08 1.81 35.21 74.86
45.00 13.36 1.32 2.10 35.58 55.95
60.00 18.33 1.51 2.38 35.15 42.60
80.00 22.81 1.81 2.63 37.37 32.11
100.00 27.45 1.93 3.47 39.57 23.40
120.00 31.32 2.11 3.83 38.35 14.75
140.00 33.51 2.16 4.82 35.43 8.59
160.00 36.13 2.22 4.12 35.78 6.10
180.00 37.55 2.23 4.09 33.26 5.22

CT electrolysis @ -1.1 V
Free cnlonde (um) :‘OC (um) Total loss as chlonnelum) Control Cell as CI (11111)

0.00 0.00 0.00 650.98
78.11 5.23 4.53 650.34
145.45 4.12 9.14 648.32
182.37 6.78 13.58 647.35
248.75 11.12 17.80 646.55
280.30 10.95 22.47 646.89
319.71 21.71 27.42 645.78
353.11 28.56 32.13 644.34
367.41 22.45 36.98 643.21
380.78 28.55 41.40 643.09
395.03 22.55 46.38 641.98
408.91 22.37 51.31 640.97

.4.

”soomwmmuwm-

.4

Time (minutBSI

0.00
10.00
20.00
30.00
45.00
60.00
80.00
100.00
120.00
140.00
160.00
180.00

Free cnlonde (um)

0.00
14.59
31.47
39.54
48.66
53.77
60.87
70.45
78.22
84.56

--92.25

99.56

Methane (umi

0.00
1 35
1.83
2.40
2.74
3.07
3.50
3.89
4.28
4 71
4 82
5.18

TOC (urn)

0.00
3.65
5.03
7.24
7.81
14.66
18.31
21.79
25.34
28.76
32.25
35.77

CT electrorysrs @ -0.9 V

CM as carbon (um)

0.00
0.61
0.68
0.74
0.76
0.71
0.71
0.78
0.82
0.81
0.82
0.80

55

0.00
3.74

7.24
10.91
14.37
18.32
22.12
25.73
29.43
33.15
37.81
41.23

MC as carbon turn)

0.00
0.12
0.67
0.97

_‘fi—‘d—J—l—Ju—L

.37
.04
.42
.26
.41
.44
.26
.24

CT electrolysis @ -0.9 V

CF as carbon

0.00
71.50
8.82
10.53
11.81
12.23
13.98
14.64
15.83
16.85
17.76
18.21

Total loss as chlonnetum) CT in control cell as Cl-

650.98
650.34
648.32
647.35
646.55
646.89
645.78
644.34
643.21
643.09
641.98
640.97

Sun. Mar 29. 1992

158.13
148.42
132.89
123.92
121.28
116.87
112.01
108.72
107.11
102.81
100.05
98.49

15:35

CT as carbon (um)

~d°@m\;0)m4-WI\J

_A ..o .._0

Time imrnutesl

0.00
10.00
20.00
30.00
45.00
60.00
80.00
100.00
120.00
140.00
160.00
180.00

TOC Iuml

0.00

7.86

13.25
16.31
17.49
24.46
47.27
52.23
49.96
33.55
40.83
49.05

Methane tum)

9.00
‘1.99
21.66
28.78
37.25
43.35
52.18
55.47
61.22
62.52
63.80
64.45

56

CF electrolysis @ -1.1 V

0.00
0.57
0.83
1.09
1.32
1.51
1.81
1.93
2.10
2.16
2.22
2.23

CF electrolysrs @ -1.1 V

Total loss as cnlorme

0.00
4.38
8.61
12.85
17.42
21.84
26.17
30.64
34.82
39.18
43.54
47.97

CM as carbon (urn) MC as carbon turn)

0.00
16.28
22.74
24.74
29.15
32.41
36.98
37.88
41.12
41.52
41.59
41.62

CF in contror cell as CI-

578.87
578.25
577.56
577.45
576.23
575.45
572.21
574.34
574.45
573.89
573.35
572.98

CF ascamon

187.60
133.17
93.84
82.68
65.32
51.45
37.57
26.09
19.03
13.41
10.42
6.58

Sun. Mar 29. 1992

0.00
1 10.00
190.31
245.35
285.30
320.65
365.70
390.24
409.20
422.36
429.36
434.80

15:48

Free chlonds luml

57

CF electrolysis @ -0.9 V Sun. Mar 29. 1992 15:48

DONOUIJIUN“

N-‘O

$72.98

Time rmrnutesi Methane rum) CM as carbon tum) MC as earoon turn) CF ascaroon Free chloride turn)
0.00 0.00 0.00 0.00 188.31 0.00
10.00 4.14 0.66 1.62 184.15 3.93
20.00 7.59 0.85 2.31 181.27 14.78
30.00 11.24 1.03 2.93 173.35 32.68
45.00 12.98 1.28 4.35 163.99 60.82
60.00 13.67 1.53 4.92 154.16 83.29
80.00 14.67 1.73 6.19 140.36 117.61
100.00 15.23 1.89 6.49 129.97 134.64
120.00 17.56 2.09 6.73 120.99 153.28
140.00 19.66 2.18 8.08 110.64 173.56
160.00 23.55 2.52 8.38 101.81 192.30
180.00 26.77 2.83 9.65 95.93 205.62

CF electrolysis @ -0.9 v

TOC (um) Total loss as Chlorine CF in control cell as Cl.
0-00 0.00 578.87
“-22 4-40 578.25
5.79 8.98 577.56
8.87 13.72 577.45
16.09 18.41 576.23
‘8'“ 23.11 575.45
25.17 27.62 572.21
28.23 32.15 574.34
18.28 36.60 574.45
28.79 41.08 573.89
14.72 45.41 573.35
33.87 49.81

oomwmmburx)“

ommwmwhwma

-‘

58

TCA electrotysls @ -1.1 V Sun. Mar 29. 1992 16:28

Time lmlnuteSI Ethhae ruml

CA as C (um) DCA as C (um) TCA as C lum) Free cnlonde (um)
0.00 0.00 0.00 0.00 294.59 0.00
5.00 8.45 1.10 8.52 249.31 48.76
10.00 16.16 2.24 13.84 190.24 120.55
20.00 25.64 3.90 18.22 123.32 210.42
30.00 28.19 4.38 19.64 67.07 278.55
45.00 30.24 5.08 20.44 27.31 344.89
60.00 33.56 5.28 20.33 9.27 363.45
80.00 34.34 4.11 19.04 2.78 368.95
100.00 34.49 4.82 19.70 1.54 372.25
120.00 34.89 4.70 19.76 1.18 275.51
TCA electrotysls @ -1.1 V

TOClum1 Total 1055 as chlorine TCA in control cell as Cl-

0.00 0.00 456.35

26.78 2.79 455.45

39.78 6.48 455.23

52.62 10.72 454.34

68.45 14.23 454.89

83.33 17.17 453.31

85.52 21.83 452.23

93.65 25.68 451.45

89.58 29.28 451.57

91.67 34.02 450.95

1

2
3
4
5
6
7
8
9
0
1
2

_.a..4-e

QmeUIbUN‘

Time (minutes)

0.00
10.00
20.00
30.00
45.00
60.00
80.00
100.00
120.00
140.00
160.00
180.00

TOC (urn)

0.00
10.87
33.26
40.32
56.43
70.56
79.01
72.72
70.37
71.85
78.66
70.03

Ethnae tum)

0.00
1.70
3.08
4.62
6.46
8.28
10.46
12.28
14.78
16.54
18.51
21.61

Total loss as cnlonne

0.00

4.09

7.41
11.49
14.16
18.87
23.50
27.56
30.78
24.65
39.08
42.56

59

TCA electrorysls @ -0.9 V

CA as C (um)

0.00
0.28
0.48
0.72
1.06
1.43
1.81
2.11
2.56
2.85
3.17
3.38

DCA as c 1......

0.00
0.54
1.10
1.98
2.46
3.10
3.31
4.66
6.04
6.78
6.96
7.62

TCA electrolysis @ -0.9 V

TCA in control cell as CI-

456.35
455.45
455.23
454.34
454.89
453.31
452.23
451.45
451.57
450.95
449.67
449.32

TCA as C (uml

292.55
259.37
236.04
214.29
193.96
170.51
133.33
116.12
90.77
72.60
59.43
45.72

Sun. Mar 29. 1992

0.00
35.29
65.79

102.67
130.30
166.89
197.06
230.35
256.59
273.26
285.43
293.45

16:37

Ere. chloride (UMI

60

PCE electrotysls @ .14 V Sun. Mar 29. 1992 15:55

\JmmS-UJN-

4010a:

doomwmmhuma

PCE electrolysrs @ .14 V

TOC (um) Total cnlorrne loss (umi PCE in control cell as Cl-
0.00 0.00 572.35
5.54 5.19 571.25
12.23 10.15 570.29
24.19 15.09 569.35
18.52 19.91 588.45
18.65 23.69 568.78
14.45 28.77 568.12
16.23 33.64 587.23
23.23 38.21 566.78
35.53 42.69 568.34
34.88 46.79 566.21

Time lmlnutesl Ethylene luml t-DCE as C (um) TCE as C (um) PCE as C (umi Free cnlonde (uml
0.00 0.00 0.00 0.00 280.30 0.00
10.00 0.88 0.25 5.94 245.72 42.26
20.00 1.99 1.54 27.54 221.06 55.20
40.00 3.02 2.53 39.62 189.88 75.62
60.00 4.99 2.26 52.73 160.22 97.55
80.00 7.86 4.30 69.93 127.58 141.76
100.00 9.91 6.58 89.67 72.92 199.59
120.00 13.05 7.92 103.53 51.76 212.91
140.00 14.44 8.86 105.67 28.30 259.27
160.00 16.98 9.36 108.27 20.18 282.01
180.00 18.78 10.22 108.41 17.48 284.28

61

PCE electrohrsls @ -1.2 V Sun. Mar 29. 1992 15:57

doomwmmpwm

AoomwmmpuN-e

PCE electrolysls @ -1.2 V

TOC (urn) Total cnlorlne loss luml PCE in control cell as CI-
0.00 0.00 572.35
4.20 3.49 571.25
4.03 7.80 570.29
8.83 12.15 569.35
10.86 17.50 588.45
9.28 21.09 568.78
7.35 25.75 588.12
10.03 30.71 567.23
10.97 34.61 588.78
15.35 38.85 588.34
18.20 42.72 $66.21

Time lmlnutesl Ethylene luml t-DCE as C tum) TCE as C (um) PCE asC (0011 Free cnlonde luml
0.00 0.00 0.00 0.00 282.19 0.00
‘0.00 0.45 0.12 4.41 268.93 20.82
20.00 1.25 0.56 9.23 252.98 33.53
40.00 2.34 3.06 15.91 235.56 58.99
60.00 3.11 2.18 24.63 213.06 77.03
80.00 3.44 2.84 26.93 208.26 84.99
700.00 3.96 2.42 30.60 197.41 94.51
120.00 4.59 2.66 34.88 183.48 103.79

140.00 4.86 2.85 37.16 172.28 118.07
160.00 5.47 3.03 40.61 161.38 123.48
180.00 5.86 3.31 42.48 152.81 134.04

_soromxlmmpwro»

.solomxlmuns-uN—r

J...

62

TCE electrolysis @ -1.4 V Sun. Mar 29. 1992 16:24
Time lmlnutesl Ethylene lumi t-DCE as C (um) TCE as C (um) Free cnlonde T00 (0011

0.00 3.00 0.00 210.65 0.00 0.00
10.00 1.05 0.00 199.38 3.12 2.83
20.00 2.13 0.15 191.27 11.22 4.34
40.00 3.96 0.89 184.35 19.09 7.89
60.00 5.69 4.64 178.37 30.78 7.57
80.00 6.66 4.56 170.53 44.87 10.35
100.00 8.12 4.94 165.54 53.54 9.43
120.00 9.40 5.88 158.78 71.85 7.95
140.00 10.82 5.84 148.91 82.75 8.25
160.00 12.04 6.24 143.41 89.52 12.65
180.00 13.03 6.34 138.05 103.41 9.97

TCE electrolysls @ -1.4 V

Total chlorlne loss tum) TCE in control cell as Cl-

0.00 322.45
2.54 322.14
7.08 321.90
10.13 320.98
14.46 320.56
18.66 320.55
21.17 320.12
23.84 319.54
27.18 319.88
29.18 318.76

32.45 317.99

doomwmmuuN—O

doomummauma

63

TCE electrorysls @ .12 V Sun. Mar 29. 1992 16:03
Time lmlnutesl Ethylene lUlTll :-DCE as C lum) TCE as C (uml Free cnlonde TOC lum)

0.00 3.00 0.00 221.19 0.00 0.00
10.00 3.09 0.05 217.75 1.02 1.99
20.00 3.46 0.09 212.70 3.83 3.45
40.00 3.82 0.12 207.54 11.28 3.87
60.00 3.94 0.15 198.90 20.27 5.49
80.00 ' 44 0.23 191.38 27.45 5.36
100.00 1 62 0.22 185.99 34.42 6.03
120.00 '. 74 0.29 180.85 38.85 6.36
140.00 1.95 0.34 178.63 40.35 5.01
160.00 2.10 0.39 177.47 43.56 4.88
180.00 2.08 0.44 172.65 46.68 3.65

TCE electrolySls @ -1.2 V

Total chlorine 1088 (um TCE in control cell as Cl-

0.00 322.45
2.67 322.14
4.51 321.90
5.29 320.98
8.46 320.56
11.23 320.55
17.15 320.12
19.88 319.54
23.29 319.88
25.81 318.76

28.71 317.99

Time

(minutes)
0
3
6
1 0
1 3
1 5
1 8

10.5
14.5
17.5
18.5

\IUO

10

13
16.5
19.5

-In

(I-CIC')

.367
.695
1.082
1.76
2.303
3.955

.547
2.125
2.256
2.667
3.411
5.449

1.124
2.053
2.696
3.380
3.732
5.809

.872
1.437
2.012
2.821
4.341
4.828

.69
1.556
2.480
2.689
3.322
4.456

64

Mass Transfer Data Fri, Apr 3, 1992 1:20

Chemical: CF

Chemical: CT

Chemical: TCA

Chemical: TCE

Chemical: PCE

MICHIGAN STATE UNIV. LIBRARIES
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
31293008957239