Metal-mediated chlorinated dibenzo-p-dioxin (CDD) and dibenzofuran (CDF) formation from phenols

Article abstract of DOI:10.1016/j.chemosphere.2004.08.084

Heterogeneous formation of chlorinated dibenzo-p-dioxins (CDDs) and dibenzofurans (CDFs) on CuCl₂ from three phenols without ortho chlorine and one phenol with two ortho chlorines was studied in a flow reactor over a temperature range of 325-450°C. Heated nitrogen gas streams containing 8% oxygen, 1.5% benzene vapor, and equal amounts of phenol, 3-chlorophenol, 3,4-dichlorophenol and 2,4,6-trichlorophenol vapor (700 ppmv, each) were passed through a 1 g particle bed of silica and 0.5% (Cu mass) CuCl₂. Maximum product yields of greater than 1.4% phenol conversion to CDD and 5.7% phenol conversion to CDF were observed between 400 and 450°C. CDDs formed with loss of one chlorine atom were favored. While total CDD/F yield varied with temperature, CDD/F homologue and isomer distributions did not vary significantly with temperature. Based on the results of experiments with single phenol precursors, phenol precursors could be assigned to all PCDD/F products. Of the chlorinated phenols without ortho chlorine that were studied, 3,4-dichlorophenol was found to have the greatest propensity to form CDFs.

Full text of DOI:10.1016/j.chemosphere.2004.08.084

Chemosphere 58 (2005) 977–988
www.elsevier.com/locate/chemosphere
Metal-mediated chlorinated dibenzo-p-dioxin (CDD) and
dibenzofuran (CDF) formation from phenols
*
Jae-Yong Ryu, James A. Mulholland
Environmental Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0512, USA
Received 13 November 2003; received in revised form 13 August 2004; accepted 27 August 2004
Abstract
Heterogeneous formation of chlorinated dibenzo-p-dioxins (CDDs) and dibenzofurans (CDFs) on CuCl2 from three
phenols without ortho chlorine and one phenol with two ortho chlorines was studied in a flow reactor over a temper-
ature range of 325–450°C. Heated nitrogen gas streams containing 8% oxygen, 1.5% benzene vapor, and equal amounts
of phenol, 3-chlorophenol, 3,4-dichlorophenol and 2,4,6-trichlorophenol vapor (700ppmv, each) were passed through a
1g particle bed of silica and 0.5% (Cu mass) CuCl2. Maximum product yields of greater than 1.4% phenol conversion to
CDD and 5.7% phenol conversion to CDF were observed between 400 and 450°C. CDDs formed with loss of one chlo-
rine atom were favored. While total CDD/F yield varied with temperature, CDD/F homologue and isomer distributions
did not vary significantly with temperature. Based on the results of experiments with single phenol precursors, phenol
precursors could be assigned to all PCDD/F products. Of the chlorinated phenols without ortho chlorine that were stud-
ied, 3,4-dichlorophenol was found to have the greatest propensity to form CDFs.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Chlorinated dibenzo-p-dioxin (CDD); Chlorinated dibenzofuran (CDF); Copper(II) chloride; Chlorinated phenols
1. Introduction
peratures between 250 and 450°C, may involve precur-
sors of similar structure (e.g. chlorinated phenols,
benzenes, and polychlorinated biphenyls) or particulate
carbon (de novo synthesis). Municipal waste incinerator
data from kiln gas and stack samples suggest that the
first route favors the formation of dibenzofuran and less
chlorinated CDD/F congeners, whereas the latter route
favors the formation of highly chlorinated CDD conge-
ners (Hagenmaier et al., 1987; Yamamoto et al., 1989).
The mechanisms of CDD/F formation have been
studied extensively, including gas-phase condensation
of phenoxy radicals (Born et al., 1989) and flyash-medi-
ated, metal-catalyzed formation from phenols (Born
et al., 1993), polycyclic aromatic hydrocarbons (Hell
et al., 1997), and graphitic carbon (Stieglitz et al.,
1989). Nonetheless, there remains much uncertainty
In municipal waste incinerators, chlorinated dibenzo-
p-dioxin (CDD) and dibenzofuran (CDF) byproducts
can be formed by two general pathways: (1) homogene-
ous, gas-phase reactions, and (2) heterogeneous, metal-
mediated reactions. The first route, which is observed
in post-combustion gas at temperatures between 500
and 700°C, occurs via precursors. The second route,
which is observed in particle collection devices at tem-
*
Corresponding author. Tel.: +1 404 894 1695; fax: +1 404
894 8266.
E-mail address: james.mulholland@ce.gatech.edu (J.A.
Mulholland).
0045-6535/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2004.08.084

978
J.-Y. Ryu, J.A. Mulholland / Chemosphere 58 (2005) 977–988
about the predominant pathway of CDD/F formation in
combustion systems, particularly in the heterogeneous
environment of particle collection devices.
are consistent with distributions found in samples from
municipal waste incinerator.
Chlorinated phenols that contain only one ortho
chlorine substituent produce both CDDs and CDFs.
In gas-phase pyrolysis of 2-chlorophenol (Yang et al.,
1998) and 2,3-dichlorophenol (Mulholland et al.,
2001), we have shown that yields of CDD products,
formed by loss of both ortho chlorine atoms in the pair
of reacting phenols, are greater than yields of CDF
products, which are formed without chlorine loss. In
gas-phase oxidative environments, on the other hand,
CDFs are the major products (Nakahata and Mulhol-
land, 2000). On particles containing CuCl2, CDD/F for-
mation from chlorinated phenols with only one ortho
chlorine substituent was found to favor CDD formation
with one chlorine loss over CDF formation with no
chlorine loss (Ryu and Mulholland, 2002).
Research in our laboratory has addressed CDD/F
formation from chlorinated phenols, both in the gas
phase and on the surface of copper(II) chloride (CuCl2)
particles. CuCl2 is known to be one of the most active
catalysts in dioxin formation. CDD/F distributions from
chlorinated phenols depend on the distribution of phe-
nol precursors and on the relative rates of formation
from different phenol pairs. We have addressed this
topic by studying three sets of chlorinated phenols those
with both ortho sites chlorinated, those with one ortho
site chlorinated, and those with no ortho chlorinated.
Phenols that have both ortho sites chlorinated pro-
duce only CDDs, which are formed by the loss of two
chlorine atoms from both phenols. We have shown that
CDD isomer distributions produced from these phenols
do not vary significantly over a wide range of reaction
conditions. Total CDD yield and homologue distribu-
tion do vary, however (Mulholland and Ryu, 2001).
Moreover, we found that these CDD isomer patterns
One ortho chlorine is needed to form CDD, whereas
one unchlorinated ortho carbon is needed to form CDF.
For illustration, possible CDD/F formation pathways
from 3,4-dichlorophenol (3,4-DCP) and 2,4,6-trichloro-
phenol (2,4,6-T3CP) are shown in Fig. 1. Pathway (1)
O
O
OHOH
OHOH
O
O
-H O
2
Cl
2,3,7,8-T CDF
4
Cl
Cl
Cl
Cl
Cl
Cl
Cl
HH
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
- 2H
O
O
1,2,7,8-T CDF
4
Cl
HH
Cl
Cl
O
Cl
OHOH
Cl
O
O
1,2,8,9-T CDF
4
HH
Cl
ClCl
Cl
(1)
Cl
ClCl
Cl
Cl
Cl Cl
Cl
-H
-Cl
Cl
O
O
Cl
Cl
O
-2H
1,2,7,9-T CDD
4
Cl
(2)
OH
Cl
H O
Cl
Cl
Cl
Cl
Cl
Cl
Cl
O
O
Cl
Cl
O
Cl
Cl
Cl
O
O
3,4-DCP
Cl
Cl
1,3,7,8-T CDD
4
Cl
O
Cl
Cl
Cl
Cl
Cl
O
O
Cl
OH
Cl
Cl
Cl
Cl
Cl
-2H
Cl
Cl
H O
O
O
O
Cl
2,4,6-T3CP
1,2,6,8-T CDD
4
Cl
Cl
Cl
Cl
(3)
Cl
Cl
O
Cl
-Cl
-Cl
Cl
O
Cl
O
1,3,7,9-T CDD
4
-2H
O
Cl
Cl
Cl
O
O
O
Cl
Cl
Cl
Cl
Cl
Cl
Cl
O
Cl
ClO
Cl
ClCl
Cl
1,3,6,8-T CDD
4
O
Cl
Fig. 1. CDD/F formation pathways from 3,4-DCP and 2,4,6-T3CP.

J.-Y. Ryu, J.A. Mulholland / Chemosphere 58 (2005) 977–988
979
in Fig. 1 depicts three 2,3,7,8-, 1,2,7,8-, and 1,2,8,9-tetra-
chlorodibenzofuran (T4CDF) isomers being formed
without chlorine loss from two 3,4-DCP. Pathway (2)
depicts three 1,2,7,9-, 1,3,7,8-, and 1,2,6,8-tetrachlo-
rodibenzo-p-dioxin (T4CDD) being formed with one
ortho chlorine loss from 3,4-DCP and 2,4,6-T3CP. Path-
way (3) depicts 1,3,6,8- and 1,3,7,9-tetrachlorodibenzo-
p-dioxin (T4CDD) being formed with loss of two
chlorine atoms from two 2,4,6-T3CP.
(Mulholland and Ryu, 2001; Ryu and Mulholland,
2002, respectively), provides a comprehensive experi-
mental investigation of CDD/F formation from phenols
on copper(II) chloride. We do not address the detailed
formation mechanism on CuCl2, which involves adsorp-
tion, reaction, and desorption; other researchers have
proposed reaction mechanisms analogous to the Ull-
mann II reaction (Tuppurainen et al., 1998). Recently,
Lomnicki and Dellinger (2003) have shown a detailed
surface-mediated PCDD/F formation mechanism on
CuO/silica surface.
Here we address CDD/F formation on CuCl2 by
chlorinated phenols without ortho chlorine substituents.
Specifically, we address the following questions. Is CDF
formation favored in a combination of chlorinated
phenols without ortho chlorine substituent? Can chlorin-
ated phenols without ortho chlorine produce CDD prod-
ucts by reacting with chlorinated phenols with ortho
chlorine? Which of these phenols have the greatest pro-
pensity to form CDD/F products? Finally, do CDD/F
isomer distributions provide a fingerprint for CDD/F
formation via this channel? This work, together with re-
sults already published or CDD/F formation from phen-
ols with one and two ortho chorine substituents
2. Experimental
2.1. Methods
The experimental apparatus is shown in Fig. 2.
Experiments were conducted in an electrically heated
quartz tube flow reactor, 40cm in length and 1.7cm in
diameter. Equal molar amounts of phenol (Ph), 3-chlo-
rophenol (3-CP), 3,4-dichlorophenol (3,4-DCP), and
motorized-micro syringe pump
flowmeter
heat tape
vaporizer
quartz tube reactor
particle bed
carrier gas
temperature controller
furnace
exhaust gas
Gas chromatography
Gas chromatography
HP 6890
HP 6890
sample analysis
GC/MS
ice bath with solvent trap
Fig. 2. Apparatus.

980
J.-Y. Ryu, J.A. Mulholland / Chemosphere 58 (2005) 977–988
2,4,6-trichlorophenol (2,4,6-T3CP) were dissolved in
benzene. The benzene/chlorinated phenol solution was
injected into a heated glass vessel by micro-syringe pump
(Sage Instruments, model 341B-Boston, MA) at a rate of
10ll/min. The reactant stream was immediately vapor-
ized in a gas stream of 92% nitrogen and 8% oxygen.
The resulting gas stream contained 1.5% benzene vapor
and 700ppmv of each phenol (2800ppmv total). A 1g
particle bed of 1cm height, consisting of SiO2 (99.6%
purity, 325 mesh) and 0.5% (by Cu mass) CuCl2 (anhy-
drous, 99.999+% purity), was located at the center of the
reactor. The SiO2/CuCl2 particle bed was prepared by
mechanical mixing. This method has been shown to pro-
vide repeatable results (Mulholland and Ryu, 2001; Ryu
and Mulholland, 2002). Experiments were carried out
over a temperature range of 325–450°C, in 25°C incre-
ments, at a gas velocity of 2.7cm/s (0.3s of contact time).
Experiments were run for approximately 20min to col-
lect enough samples, with the entire product gas stream
rapidly quenched and soot and aromatic tar samples col-
lected in an ice-cooled dichloromethane trap.
of 28 trichlorodibenzofurans (T3CDFs), 34 of 38
tetrachlorodibenzofurans (T4CDFs), 22 of 28
pentachlorodibenzofurans (P5CDFs), 12 of 16 hexachlo-
rodibenzofurans (H6CDFs),
2 of 4 heptachloro-
dibenzofurans (H7CDFs), and octachlorodibenzofuran
(OCDF). CDD isomer peak separation was as follows:
2 peaks for 2 monochlorodibenzo-p-dioxin (MCDD)
isomers,
7 peaks for 10 dichlorodibenzo-p-dioxin
(DCDD) isomers, 10 peaks for 14 trichlorodibenzo-p-di-
oxin (T3CDD) isomers, 15 peaks for 22 tetrachlo-
rodibenzo-p-dioxin (T4CDD) isomers, 12 peaks for 14
pentachlorodibenzo-p-dioxin (P5CDD) isomers, 7 peaks
for 10 hexachlorodibenzo-p-dioxin (H6CDD) isomers, 2
peaks for 2 heptachlorodibenzo-p-dioxin (H7CDD) iso-
mers. A universal response factor was used for CDDs
and CDFs based on dibenzo-p-dioxin (DD) and dib-
enzofuran (DF), respectively.
3. Results and discussion
3.1. Overall product distributions
2.2. Instrumental analysis and identification
Experiments with the benzene solution containing
four phenols (Ph, 3-CP, 3,4-DCP, 2,4,6-T3CP) were
conducted over a temperature range of 325–450°C.
Yields of overall product groups are shown in Table
1. Chlorinated benzene (CBz) yields were observed to
peak at 21.7% (percent of phenol input, carbon basis)
at 400°C. By chlorination, a maximum total chlorinated
phenol (CP) product yield of 1.7% was observed at
325°C. A maximum perchloroethylene (PCE) yield of
3.6% was observed at 375°C. Total chlorinated quinone
(CQs) yields were very small, about 0.1% between
325°C and 375°C, and decreased with increasing tem-
perature. Optimum formation temperatures for these
compounds are consistent with results of similar exper-
iments with chlorinated phenols with one ortho chlorine
atom described elsewhere (Ryu and Mulholland, 2002).
A maximum total CDD yield of 1.4% was observed at
425°C; a maximum CDF yield of 5.7% was observed
at 425°C. CDF formation was favored over CDD
formation.
Sample solutions were filtered and then analyzed by
GC/MS (HP 6890 series gas chromatograph with model
5973 mass selective detector-EI type) with autosampler
equipped with a HP-5MS capillary column with length
30m, i.d. 0.25mm and phase 0.25lm film of crosslinked
5% PH ME siloxane (J&W Scientific, CA). A GC was
carried out with splitless injection and He as carrier
gas. For identification, the mass spectrometer was oper-
ated in the scan mode, and for quantification, in selected
ion mode (SIM). Preliminary identification of CDD/F
products was based on published relative retention times
for similar columns (Hale et al., 1985; Ryan et al., 1991).
Final identification was based on available standards
and gas-phase synthesis experiments from single precur-
sors and precursor pairs. Seventy-four of 75 CDD con-
geners and 121 of 135 CDF congeners have been
synthesized from phenol pairs. All four mono-
chlorodibenzofuran (MCDF) isomers were separated,
as were 13 of 16 dichlorodibenzofurans (DCDFs), 25
Table 1
Overall product yields (percent of phenol input, carbon basis, except where noted)
325°C
350°C
375°C
400°C
425°C
450°C
CDDs
CDFs
CPs
CBz*
PCE
CQs
*
0.061
0.13
1.67
0.63
0.82
0.113
0.067
0.36
1.05
1.95
2.90
0.134
0.20
1.25
0.82
2.80
3.56
0.125
0.55
2.83
0.95
3.41
2.59
0.037
1.36
5.72
0.78
2.92
1.47
0.019
0.48
5.04
0.78
2.72
0.80
0.008
CBz yields are based on percent of phenol and benzene input.

J.-Y. Ryu, J.A. Mulholland / Chemosphere 58 (2005) 977–988
981
3.2. Chlorinated phenol formation
4-CP. 3-CP chlorination produced 2,3-, 2,5- and 3,4-
DCP. From a pure 3-CP experiment, more 2,5-DCP
was produced than 2,3-DCP and 3,4-DCP. 3,4-DCP
chlorination produced 2,4,5- and 2,3,4-T3CP, with much
more 2,4,5-T3CP produced than 2,3,4-T3CP. These re-
sults suggest that both steric and electronic factors gov-
ern phenol chlorination. Pentachlorophenol (PCP) was
also produced in small amounts, showing that chlorina-
tion can occur at meta (3,5) sites as well.
Phenol reactant recovery and chlorinated product
yields are shown in Fig. 3. The highest recovery was
unreacted 2,4,6-T3CP; the least recovered was 3,4-
DCP. Phenol reactant recovery decreased with increasing
temperature. Chlorination product yields were greatest
at low temperatures (325–350°C).
Chlorination products at ortho (2,6) and para (4)
sites were favored over chlorination at meta (3,5) sites.
Chlorination of phenol at 352–452°C has been found
to involve only ortho and para positions (Born et al.,
1993), and this was explained by the electrophilic aro-
matic substitution mechanism for the ortho/para-direct-
ing OH group of phenol (Luijk et al., 1994).
3.3. Chlorinated benzene formation
From phenol and benzene experiments on copper(II)
chloride, we observed that chlorinated benzenes (CBz)
can be formed from chlorinated phenols (CP) either by
chlorodehydroxylation or by chlorination of benzene.
Phenol chlorodehydroxylation leads to specific benzene
products; e.g. 3,4-DCP chlorodehydroxylation produces
Phenol chlorination produced 2-, 4-chlorophenols
and then 2,4- and 2,6-dichlorophenols. From a pure
phenol experiment, more 2-CP was produced than
50
40
30
20
10
Reactants
2,4,6-T3CP
Ph
3-CP
3,4-DCP
Products
1
2,4,5-T3CP
2-CP
2,3,4-T3CP
0.1
2,5-DCP
2,3,4,6-T4CP
2,4-DCP
2,3-DCP
0.01
2,3,6-T3CP
2,6-DCP
PCP
0.001
300
325
350
375
400
425
450
475
temperature (deg.C)
Fig. 3. Phenol reactant recovery and phenol chlorination product yields.

982
J.-Y. Ryu, J.A. Mulholland / Chemosphere 58 (2005) 977–988
Table 2
Chlorinated benzene yields
Yield (percent total phenol/benzene conversion)
Isomer fraction
325°C
350°C
375°C
400°C
425°C
450°C
Avg
St.dev.
MCBz
0.694
0.009
2.14
0.044
3.01
3.60
0.133
2.98
0.149
2.68
0.166
1,3-DCBz
1,4-DCBz
1,2-DCBz
1,3,5-T3CBz
1,2,4-T3CBz
1,2,3-T3CBz
1,2,3,5-T4CBz
1,2,4,5-T4CBz
1,2,3,4-T4CBz
PCBz
0.071
0.126
0.133
0.0003
0.014
0.013
0.0084
0.0013
0.0056
0.0113
0.0051
0.254
0.329
0.416
0.017
0.470
0.513
0.515
0.067
0.418
0.056
0.155
0.102
0.015
0.162
0.176
0.098
0.020
0.116
0.031
0.012
0.070
0.080
0.108
0.221
0.098
0.237
0.105
0.262
0.0000
0.0017
0.0055
0.0016
0.0001
0.0028
0.0028
0.0018
0.0000
0.0054
0.0124
0.0045
0.0006
0.0046
0.0080
0.0037
0.0010
0.0212
0.0174
0.0101
0.0014
0.0068
0.0102
0.0039
0.0014
0.0294
0.0158
0.0120
0.0013
0.0056
0.0065
0.0027
0.0020
0.0324
0.0197
0.0100
0.0016
0.0069
0.0052
0.0014
HCBz
1,2,4-T3CBz. Born et al. (1993) also reported that CBz
could be produced from chlorinated phenols by chloro-
dehydroxylation. Chlorination of benzene is favored at
sites ortho and para to other chlorine substituents. Chlo-
rinated benzene yields based on benzene and phenol
reactant feeds are shown in Table 2. Monochloroben-
zene (MCBz) was the major product, with chlorinated
benzenes observed through hexachlorobenzene (HCBz).
Ratios of CBz formed by chlorodehydroxylation and
by benzene chlorination are shown in Fig. 4. The ratio of
1,3- and 1,2-CBz was almost constant, and less than 1.
This result indicates that formation of 1,2-CBz formed
by benzene chlorination was greater than formation
of 1,3-CBz formed from 3-CP chlorodehydroxylation.
The ratios 1,2,4-/1,2,3-T3CBz and 1,2,3,5-/1,2,3,4-
T4CBz increased with increasing temperature. At low
temperatures, 1,2,3-T3CBz and 1,2,3,4-T4CBz produced
from benzene chlorination were greater than 1,2,4-
T3CBz and 1,2,3,5-T4CBz produced from chlorodehyd-
roxylation of 3,4-DCP and 2,4,6-T3CP reactants. These
results show that benzene chlorination is dominant at
low temperatures, but phenol chlorodehydroxylation in-
creases with temperature. Weber and Hagenmaier (1999)
measured isomer distributions of chlorinated benzenes
from municipal solid waste incinerator. They reported
the favored formation of 1,2-/1,2,3-/1,2,3,4-CBz, which
is similar to benzene chlorination patterns.
3.4. PCE and CQ formation
The production of PCE from phenols and benzene
was already reported (Ryu and Mulholland, 2002). A
maximum perchloroethylene (PCE) yield of 3.6% based
on chlorinated phenol input was observed at 375°C.
Above 375°C, yield decreased as shown in Table 1. Born
et al. (1993) suggested that PCE very likely results from
ring opening oxidative breakdown of chlorinated
phenols.
Chlorinated quinone (CQ) products, which included
dichlorinated and trichlorinated quinones, were formed
in very small amounts, about 0.1% based on chlorinated
phenol input between 325°C and 375°C. Above these
temperatures, CQ yield decreased (Table 1). A mecha-
nism of benzoquinone formation by removal of the
chlorine atom during electrochemical incineration of
4-chlorophenol has been proposed by Johnson et al.
(1999). Basu and Wei (2000) also proposed that di-
chlorobenzoquinone compounds were formed from
2,4,6-trichlorophenol in the aqueous phase FentonÕs
reagent (aqueous solution of hydrogen peroxide and
ferrous ion). The two dichlorobenzoquinones were 2,6-
dichloro-1,4-benzoquinone and 3,5-dichloro-1,6-benzo-
quinone; which one occurs depends on which chlorine
is removed. Recently, Lomnicki and Dellinger (2003)
also have shown a detailed CQ formation mechanism
from 2-CP on a CuO/silica surface.
2.5
2.0
1.5
1,2,3,5/1,2,3,4-T CBz
4
1,2,4-/1,2,3-T CBz
3
1.0
0.5
0.0
1,3-/1,2-DCBz
300
325
350
375
400
425
450
475
Fig. 4. Ratio of chlorinated benzenes from phenol chlorode-
hydroxylation and benzene chlorination.

J.-Y. Ryu, J.A. Mulholland / Chemosphere 58 (2005) 977–988
983
3.5. CDD/F formation
patterns as fingerprints for the CDD/F formation by the
phenol precursor mechanism.
Total yields for CDD/F homologues are shown in Fig.
5. CDF product yields were greater than CDD product
yields. DF through P5CDF products were observed. Peak
CDF yields also occurred at 425°C, but CDF yields re-
mained high above this temperature. DCDF products
were greatest at all temperatures. CDF homologue distri-
bution varied little with temperature. CDD products
from dibenzo-p-dioxin (DD) through penta (P5CDD)
were observed. Highest peak yields of DD through
P5CDDs were observed at 425°C. The T4CDD fraction
was highest at all temperatures. There was little variation
in the CDD homologue distribution with temperature.
To assess which phenol combinations produce the
most CDDs and CDFs, isomer distributions were exam-
ined. The dependence of the isomer patterns on temper-
ature is examined to assess the potential for using these
3.6. CDF isomer distributions
Isomer yields for CDF products, shown in order of
decreasing yields, are listed in Table 3 as percent of total
phenol conversion. CDF isomers that could not be sep-
arated are listed in groups. CDF congeners formed
based on pathway 1 (Fig. 1) are listed.
All major CDF products are formed from chlorin-
ated phenol reactants that lack ortho chlorine. These
are 1,2-DCDF, 1,2,7-/2,3,9-T3CDF, 1-MCDF, 1,7-
DCDF, 1,2,7,8-T4CDF, 3-MCDF, 2,3-DCDF, DF,
2,3,7-T3CDF, 1,2,9-T3CDF, 3,7-DCDF, 2,3,7,8-
T4CDF, 1,2,8,9-T4CDF, and 1,9-DCDF. CDF products
in lower yields are also produced from phenol chlorina-
tion products.
CDD
T4CDD
0.6
0.4
0.2
T3CDD
DCDD
P5CDD
MCDD
DD
0.0
3.0
CDF
DCDF
2.5
2.0
1.5
1.0
0.5
0.0
T3CDF
MCDF
P5CDF (very small)
T4CDF
DF
300
325
350
375
400
425
450
475
Fig. 5. CDD/F homologue yields.

Table 3
Likely CDF precursors and CDF congener yields
Furan products
Reactants (pathway 1)
Reactant + CP product (pathway 1)
Yield (percent phenol conversion)
Isomer fraction
325°C
350°C
375°C
400°C
425°C
450°C
Avg
St.dev.
1,2
1,2,7/2,3,9
ph + 3,4
3 + 3,4
ph + 3
0.050
0.028
0.019
0.143
0.084
0.450
0.334
0.175
0.082
0.065
0.024
0.021
0.030
0.015
0.010
0.022
0.002
0.014
0.0035
0.0028
0.0005
0.0000
0.0007
0.0023
0.0000
0.0006
0.0002
0.0000
0.0000
0.937
0.711
0.415
0.220
0.152
0.077
0.061
0.063
0.045
0.033
0.025
0.012
0.019
0.019
0.0079
0.0058
0.0059
0.0086
0.0091
0.0032
0.0006
0.0014
0.0000
0.0006
1.804
1.334
0.885
0.505
0.315
0.161
0.139
0.109
0.106
0.087
0.045
0.029
0.039
0.036
0.028
0.020
0.021
0.016
0.014
0.0114
0.0097
0.0021
0.0018
0.0017
1.533
1.108
0.789
0.410
0.243
0.240
0.195
0.161
0.106
0.062
0.039
0.047
0.024
0.017
0.014
0.013
0.018
0.0084
0.0043
0.0083
0.0004
0.0004
0.0010
0.0000
0.767
0.836
0.871
0.144
0.901
0.129
0.043
0.083
0.064
0.077
0.050
0.086
0.077
0.026
1
1,7
0.049
0.018
3 + 3
3,4 + 3,4
ph + 3
0.0039
0.0089
0.0000
0.0007
0.0051
0.0008
0.0000
0.0000
0.0000
0.0104
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
1,2,7,8
0.016
0.006
3
2,3
ph + 3,4
ph + ph
3 + 3,4
3 + 3,4
0.004
0.011
DF
2,3,7
0.0012
0.0002
0.018
0.079
0.046
0.032
0.007
0.028
0.011
0.034
0.023
0.003
0.003
0.022
0.013
0.006
0.813
0.001
0.187
0.098
0.026
0.034
0.008
0.023
0.010
0.028
0.023
0.004
0.003
0.021
0.014
0.009
0.225
0.002
0.225
1,2,9
1,8
3 + 4
3,7
1,2,8
3 + 3
0.0000
0.0101
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
4 + 3,4
ph + 2,4,5
1,2,4
2,3,7,8
3,4 + 3,4
3,4 + 3,4
3 + 3
1,2,8,9
1,9
1,4
1,2,4,7
ph + 2,5
3 + 2,4,5
1,2,6,7
1,2,6,8/1,4,6,7/1,4,7,8
1,2,4,6,7
2,3 + 3,4
3,4 + 2,4/2,3 + 2,5/3,4 + 2,5
2,3 + 2,4,5
2,4,6,7/2,3,4,9/1,4,6,9
2,3,4,8,9
2,3 + 2,4/3 + 2,3,4/2,5 + 2,5
3,4 + 2,3,4

J.-Y. Ryu, J.A. Mulholland / Chemosphere 58 (2005) 977–988
985
CDF isomer patterns were largely independent of
temperature, even though total CDF yield varied signif-
icantly. This is evidenced by the small standard devia-
tion in isomer fractions for the six experiments.
DCP > phenol + 3-CP > 3-CP + 3-CP > 3,4-DCP + 3,4-
DCP > phenol + phenol.
3.7. CDD isomer distributions
The relative propensity of the chlorinated phenol
reactants studied to form CDFs was ascertained by iden-
tifying the phenol precursors for each product. The re-
sults, shown in Fig. 6, indicate the following ranking
of CDF formation potential for the three chlorinated
phenol reactants: 3,4-DCP > 3-CP > phenol. Thus, 3,4-
DCP is most likely to form CDF products, whereas it
was found to be least likely to form CDD products. In
gas phase oxidative environments at higher tempera-
tures, on the other hand, phenol had the highest propen-
sity to form CDF products (Nakahata, 2001).
Product yields for CDD congeners, with isomer frac-
tions, shown in order of decreasing yields, are listed in
Table 4 as a percent of total phenol conversion. CDD
isomers that could not be separated are listed in groups.
CDD congeners formed based on the pathways 2 (one
chlorine loss) and 3 (two chlorine loss) of Fig. 1 are listed.
As shown in Table 4, CDD products formed from
chlorinated phenol reactants were favored over CDD
products that were formed from chlorinated phenol
reactant and product, with the exception of 1,2,7,9-
T4CDD. The most abundant CDD products were
1,3,6-T3CDD, 1,3-DCDD, 1,3,6,8-, 1,3,7,8-, 1,3,7,9-
T4CDD, 1,3,9-T3CDD, 1,2,6,8-, and 1,2,7,9-T4CDD.
The ranking of CDF formation potential from
phenol combinations for the three chlorinated phenol
reactants is as follows: phenol + 3,4-DCP > 3-CP + 3,4-
18
16
14
12
10
8
3,4-DCP
ph
3-CP
6
4
2
0
4
ph+3,4-DCP
3
2
1
0
3-CP+3,4-DCP
ph+3-CP
3-CP+3-CP
3,4-DCP+3,4-DCP
ph+ph
300
325
350
375
400
425
450
475
temperature (deg.C)
Fig. 6. CDF formation propensity of phenol, 3-CP, and 3,4-DCP.

Table 4
Likely CDD precursors and CDD congener yields
Dioxin products
Reactants (pathway 2 or 3)
Reactant + CP product (pathway 2)
Yield (percent phenol conversion)
Isomer fraction
325°C
350°C
375°C
400°C
425°C
450°C
Avg
St.dev.
1,3,6
1,3
3 + 2,4,6
0.018
0.018
0.019
0.011
0.051
0.041
0.131
0.120
0.312
0.284
0.135
0.142
0.867
0.939
0.354
0.343
0.246
0.079
0.030
0.050
0.019
0.650
0.885
0.027
0.018
0.010
0.023
0.036
0.024
0.052
0.0080
0.0053
0.011
0.022
0.010
0.176
0.133
0.022
0.011
0.011
ph + 2,4,6
Two 2,4,6
3,4 + 2,4,6
Two 2,4,6
3 + 2,4,6
1,3,6,8
1,3,7,8
1,3,7,9
1,3,9
0.0056
0.015
0.012
0.016
0.033
0.039
0.024
0.090
0.088
0.243
0.172
0.058
0.061
0.0032
0.0006
0.0004
0.0008
0.0003
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0065
0.0016
0.0004
0.0000
0.0005
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.063
0.013
0.161
0.029
0.041
0.012
0.0044
0.0015
0.0009
0.0005
0.0034
0.0003
0.0035
0.0004
0.0000
0.0000
0.0017
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
1,2,6,8
2,3
3,4 + 2,4,6
0.0085
0.0063
0.0045
0.0060
0.0042
0.0022
0.0028
0.0023
0.0023
0.0020
0.0008
0.0013
0.0000
0.0014
0.0000
0.0007
0.0002
0.0004
0.0007
0.025
0.024
0.0054
0.0083
0.0047
0.0009
0.0051
0.0014
0.0020
0.0004
0.0043
0.0001
0.0000
0.0000
0.0007
0.0005
0.0016
0.0005
0.0000
0.0000
0.0000
2 + 3,4
1,2,7,9
1,2,4,6,8/1,2,4,7,9
2
3,4 + 2,4,6
0.017
0.012
0.011
2,4,5 + 2,4,6
2 + 3
1,2,6
2,3,7
3 + 2,3,4
3 + 2,4,5
ph + 2,3,4,6
ph + 2
0.0087
0.0119
0.0087
0.0056
0.0071
0.0057
0.0048
0.0047
0.0032
0.0032
0.0022
0.0023
0.0007
0.0018
1,2,3
DD
1,2,3,6,8
1,2
2,3,4 + 2,4,6
2 + 3,4
0.235
0.0060
0.080
0.095
0.0084
0.096
1,2,3,7,9
2,7/2,8
1,2,3,7/1,2,3,8
1
2,3,4 + 2,4,6
3 + 2,5
0.0049
0.0033
0.115
0.0070
0.0025
0.133
2,5 + 2,3,4
2 + 3
1,2,7,8
2,3,7,8
1,3,6,9
1,2,4,7,8
3,4 + 2,4,5
3,4 + 2,4,5
2,5 + 2,4,6
3,4 + 2,3,4,6
0.0023
0.0011
0.0007
0.035
0.0016
0.0017
0.0008
0.041

J.-Y. Ryu, J.A. Mulholland / Chemosphere 58 (2005) 977–988
987
These CDD products can be formed by pathway 2 (one
chlorine loss) or pathway 3 (two chlorine loss). 3-CP and
2,4,6-T3CP can form 1,3,6-, 1,3,9-, 1,3,7-, 1,3,8-T3CDD,
but 1,3,7-, 1,3,8-T3CDD was not detected. The 1,3,6,8-
and 1,3,7,9-T4CDD pair is formed by two chlorine loss
that occurs in the reaction of two 2,4,6-T3CP precursors.
The 1,3,7,8-, 1,2,6,8-, and 1,2,7,9-T4CDD pair is formed
by the loss of one chlorine in the combination of 3,4-
DCP and 2,4,6-T3CP precursors. These results demon-
strate that CDD products are formed by the loss of
one chlorine from combination of chlorinated phenol
precursors without ortho chlorine (phenol, 3-CP, 3,4-
DCP) and with two ortho chlorine (2,4,6-T3CP). The
2,4,6-T3CP is known as most reactive precursor to form
CDD products between chlorinated phenols with two
ortho chlorine (Mulholland and Ryu, 2001). Results
shown here indicate 2,4,6-T3CP also readily forms
CDD products by combination with phenols without
ortho chlorine, such as phenol, 3-CP and 3,4-DCP.
Chlorinated phenol products are likely responsible for
some CDD products formed in low yields.
Little variation in the CDD isomer distributions with
temperature was observed, even though the total CDD
yield did vary significantly. This is also evidenced by
the small standard deviation in isomer fractions for the
six experiments.
Chlorinated phenol precursor pairs were assigned to
each major CDD product. To assess the relative CDD
formation propensities of the chlorinated phenol reac-
tants studied. The result, shown in Fig. 7, indicates the
ranking of CDD formation potential for the four chlo-
rinated phenol reactants is as follows: 2,4,6-T3CP ꢀ 3-
CP > phenol > 3,4-DCP.
The bottom panel of Fig. 7 indicates the reactivity of
phenol, 3-CP and 3,4-DCP to produce CDD products
by combination with 2,4,6-T3CP. The CDD formation
6
5
2,4,6-T CP
3
4
3
ph
2
3-CP
1
3,4-DCP
0
2.0
two 2,4,6-T3CP
1.5
1.0
0.5
0.0
ph+2,4,6-T3CP
3-CP+2,4,6-T3CP
3,4-DCP+2,4,6-T3CP
300
325
350
375
400
425
450
475
Fig. 7. CDD formation propensity of phenol, 3-CP, 3,4-DCP, and 2,4,6-T3CP.

988
J.-Y. Ryu, J.A. Mulholland / Chemosphere 58 (2005) 977–988
the formation and decomposition of PCDD/Fs. Environ.
Sci. Technol. 21, 1080.
potential of phenol, 3-CP, and 3,4-DCP was much less
than that of two 2,4,6-T3CP. Thus, CDD formation by
one chlorine loss occurs at much lower rate than CDD
formation by two chlorine loss from chlorinated phenols
that have two ortho chlorines.
Hale, M.D., Hileman, F.D., Mazer, T., Shell, T.L., Noble,
R.W., Brooks, J.J., 1985. Mathematical modeling of tem-
perature programmed capillary gas chromatography reten-
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4. Conclusion
Johnson, S.K., Houk, L.L., Feng, J., Houk, R.S., Johnson,
D.C., 1999. Electrochemical incineration of 4-chlorophenol
and the identification of products and intermediates by mass
spectrometry. Environ. Sci. Technol. 33, 2638.
The formation of CDD and CDF products on cop-
per(II) chloride (CuCl2) from phenol, 3-CP, 3,4-DCP,
and 2,4,6-T3CP was observed. CDF formation is fav-
ored over CDD formation. CDD products are formed
by loss of one chlorine from chlorinated phenols with-
out ortho chlorine with chlorinated phenols with two
ortho chlorine. CDD/F isomer patterns are largely
independent of temperature; therefore, the isomer pat-
terns may provide a fingerprint for CDD/F formation
by this mechanism. Phenol chlorination by CuCl2 is
also controlled by steric and electronic factors and
plays an important role in higher chlorinated CDD/F
formation and in much broader CDD/F isomer
formation.
Lomnicki, S., Dellinger, B., 2003. A detailed mechanism of the
surface-mediated formation of PCDD/F from the oxidation
of 2-chlorophenol on a CuO/silica surface. J. Phys. Chem. A
107, 4387.
Luijk, R., Dorland, C., Smit, P., Jansen, J., Govers, H.A.J.,
1994. The role of bromine in the de novo synthesis in a
model fly ash system. Chemosphere 28, 1299.
Mulholland, J.A., Ryu, J.-Y., 2001. Formation of polychlorin-
ated dibenzo-p-dioxins by CuCl2-catalyzed condensation of
2,6 chlorinated phenols. Combust. Sci. Technol. 169, 107.
Mulholland, J.A., Umesh, A., Yang, Y., Ryu, J.-Y., 2001.
Temperature dependence of DCDD/F isomer distributions
from chlorophenol precursors. Chemosphere 42, 719.
Nakahata, D.-T., Mulholland, J.A., 2000. Effect of dichloro-
phenol substitution pattern on furan and dioxin formation.
Proc. Combust. Inst. 28, 2701.
Results reported here and two previous publications
(Mulholland and Ryu, 2001; Ryu and Mulholland,
2002) provide a complete experimental investigation of
CDD/F formation by phenol condensation on particles
containing copper(II) chloride.
Nakahata, D.-T., 2001. Determination of Relative Formation
Rates of Dibenzofurans via Gas-phase Condensation of
Phenols. Ph.D. Thesis, Georgia Institute of Technology,
Atalnta, USA.
Acknowledgment
Ryan, J.J., Conacher, H.B.S., Panopio, L.G., Lau, B.P.-Y.,
Hardy, J.A., 1991. Gas chromatographic separations of all
136 tetra- to octa-polychlorinated dibenzo-p-dioxins and
polychlorinated dibenzofurans on nine different stationary
phases. J. Chromatogr. 541, 131.
The authors gratefully thank the National Science
Foundation (CTS-9457028), the Research Foundation
for Health and Environmental Effects, and the Environ-
mental Protection Agency (QT-OH-99-000537) for
financial support.
Ryu, J.-Y., Mulholland, J.A., 2002. Dioxin and furan forma-
tion on CuCl2 from chlorinated phenols with one ortho
chlorine. Proc. Combust. Inst. 29, 2455.
Stieglitz, L., Zwick, G., Beck, J., Bautz, H., Roth, W., 1989.
Carbonaceous particles in fly ash––a source for the de-novo-
synthesis of organochlorocompounds. Chemosphere 19,
283.
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