Formation of chlorinated phenols, dibenzo-p-dioxins, dibenzofurans, benzenes, benzoquinnones and perchloroethylenes from phenols in oxidative and copper (II) chloride-catalyzed thermal process

Article abstract of DOI:10.1016/j.chemosphere.2007.10.036

Formation of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and chlorinated phenols on CuCl₂ from unsubstituted phenol and three monochlorophenols was studied in a flow reactor over a temperature range of 100-425 °C. Heated nitrogen gas streams containing 8.0% oxygen were used as carrier gas. The 0.00024 mol of unsubstituted phenol and 0.00039 mol of each monochlorophenol were passed through a 1 g and 1 cm SiO₂ particle containing 0.5% (Cu by mass) CuCl₂. Chlorination preferentially occurred on ortho-(2, 6) and para-(4) positions. Chlorination increased up to 200 °C, and thereafter decreased as temperature increased. Chlorination of phenols plays an important role in the formation of the more chlorinated PCDD/Fs. Chlorinated benzenes are formed possibly from both chlorination of benzene and chlorodehydroxylation of phenols. Chlorinated phenols with ortho chlorine formed PCDD products, and major PCDD products were produced via loss of one chlorine. For PCDF formation, at least one unchlorinated ortho carbon was required.

Full text of DOI:10.1016/j.chemosphere.2007.10.036

Available online at www.sciencedirect.com
Chemosphere 71 (2008) 1100–1109
www.elsevier.com/locate/chemosphere
Formation of chlorinated phenols, dibenzo-p-dioxins, dibenzofurans,
benzenes, benzoquinnones and perchloroethylenes from phenols
in oxidative and copper (II) chloride-catalyzed thermal process
*
Jae-Yong Ryu
R&D Planning and Management Office, Korea Institute of Environmental Science and Technology (KIEST), 613-2, Bulgwang-Dong,
Eunpyeong-Gu, Seoul 122-706, Republic of Korea
Received 4 April 2007; received in revised form 11 October 2007; accepted 18 October 2007
Available online 3 December 2007
Abstract
Formation of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and chlorinated phenols on
CuCl2 from unsubstituted phenol and three monochlorophenols was studied in a flow reactor over a temperature range of 100–
425 °C. Heated nitrogen gas streams containing 8.0% oxygen were used as carrier gas. The 0.00024 mol of unsubstituted phenol and
0.00039 mol of each monochlorophenol were passed through a 1 g and 1 cm SiO2 particle containing 0.5% (Cu by mass) CuCl2. Chlo-
rination preferentially occurred on ortho-(2, 6) and para-(4) positions. Chlorination increased up to 200 °C, and thereafter decreased as
temperature increased. Chlorination of phenols plays an important role in the formation of the more chlorinated PCDD/Fs. Chlorinated
benzenes are formed possibly from both chlorination of benzene and chlorodehydroxylation of phenols. Chlorinated phenols with ortho
chlorine formed PCDD products, and major PCDD products were produced via loss of one chlorine. For PCDF formation, at least one
unchlorinated ortho carbon was required.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Phenol condensation pathways; Chlorophenols; CuCl2-catalyzed formation; Chlorination; PCDD/F formation mechanism; Thermal process
1. Introduction
CuCl2 is a catalyst. The aromatic molecules are chlorinated
by Cl2 (or Clꢀ ꢀ ꢀCl) as following.
4HCl + O2 ! 2Cl2 + 2H2O
ArH + Cl ꢀꢀꢀCl ! ArCl + HCl
Copper chloride (CuCl2) can lead to aromatic condensa-
tion reactions as well as chlorination reactions of aromatics
at temperatures between 250 and 450 °C. (Stieglitz et al.,
1989; Vogg and Stieglitz, 1989). Condensation reactions
can take place via precursors such as chlorinated phenols
or benzenes. Chlorination also occurs via precursors or
PCDD/Fs (Addink and Olie, 1995; Addink and Altwicker,
1998).
ð1Þ
ð2Þ
Alternatively, direct chlorination of an aromatic mole-
cule can occur by the following direct transfer mechanism
(Stieglitz et al., 1990; Hoffman et al., 1990) noncatalytically.
ArH + CuCl2 ! ArHClÅ + CuCl
ArHClÅ + CuCl2 ! ArCl + CuCl + HCl
ð3Þ
ð4Þ
Two chlorination mechanisms based on copper chloride
have been proposed. First, the Deacon reaction leads to
molecular chlorine formation. In the Deacon reaction,
Born et al. (1993) found that CuCl2 chlorination prefer-
ably occurs on the ortho and para positions of phenol.
The hydroxyl group (OH) is pivotal for adsorption/
chemisorption at the particle surface to enable chlorination.
*
Tel.: +82 2 380 0669; fax: +82 2 380 0699.
E-mail address: ryujy@kiest.re.kr
0045-6535/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2007.10.036

J.-Y. Ryu / Chemosphere 71 (2008) 1100–1109
1101
Cl
Cl
Cl
Cl
Cl
O O
Cl
OHOH
O
Cl
Cl
Cl
Cl
- Cl
- Cl
Cl
Cl
H
H
3,4,6,7-T4CDF
Cl
2,3-DCP
Cl
- H2O
Cl
OH
O
O
O
(1)
Cl
1,6-DCDD
1,9-DCDD
2
O
O
(2a)
Cl
Cl
Cl
Cl
(2)
- 2H
O
Cl
- Cl
Cl
Cl
Cl
O
Cl
Cl
O
O
Cl
O
Cl
Cl
Cl
Cl
O
1,2,6-T3CDD
1,2,9-T3CDD
O
O
H
Cl
Cl
(2b)
O
O
O
Cl
Cl
Cl
Cl
- Cl
- H
Fig. 1. PCDD/F formation pathways from 2,3-dichlorophenol (DCP).
A chlorinated phenol molecule after chemisorption on the
fly ash can undergo various reactions, such as isomerization,
oxidative breakdown, chlorination and/or condensation,
before distinct products (CO2, CBz, PCDDs) are released.
To illustrate the PCDD/F formation mechanism, gas-
phase pathways from 2,3-DCP are shown in Fig. 1. PCDF
formation most likely occurs by carbon–carbon coupling
of phenoxyl radicals at ortho positions (pathway 1). Such
coupling requires at least one unsubstituted ortho carbon
in each reactant and leads to the keto-tautomer of the
o,o0-dihydroxybiphenyl (DOHB) intermediate. Subsequent
enolizations restore aromaticity to the molecule, producing
the more stable DOHB intermediate. Loss of H2O from
DOHB yields 3,4,6,7-T4CDF with no loss of chlorine.
The formation of PCDD, on the other hand, results via the
coupling of a phenolic oxygen to a chlorinated ortho carbon
of a second phenoxy radical, producing the keto-tautomer of
o-phenoxyphenol (POP) (pathway 2). Subsequent loss of a
chlorine atom produces a resonance-stabilized phenoxy–
phenoxy radical, which can undergo a five-member ring
closure similar to a Smiles rearrangement. Ring expansion
with elimination of a second chlorine atom results in the for-
mation of a pair of 1,6- and 1,9-DCDD isomers (pathway
2a). Also, ring expansion with elimination of the hydrogen
atom results in the formation of a pair of 1,2,6- and 1,2,9-
T3CDD isomers (pathway 2b). A six-member ring closure
with elimination of the chlorine or hydrogen atom leads only
to 1,6-DCDD and 1,2,9-T3CDD congeners.
(3) At what temperatures does phenol condensation
occur to form PCDD/Fs?
(4) What is the effect of chlorine substitution at phenol,
ortho, meta, or para sites on PCDD/F formation?
2. Experimental methods
Experiments were conducted in an electrically heated,
quartz tube flow reactor, 40 cm in length and 1.7 cm in
diameter. A nominal residence time in the quartz tube reac-
tor was 15 s. Separate experiments were performed with
unsubstituted phenol (Ph), 2-chlorophenol (2-CP), 3-chlo-
rophenol (3-CP), and 4-chlorophenol (4-CP). The phenol
reactants were placed in a heated glass vessel and vaporized
in a gas stream consisting of 92% nitrogen and 8% oxygen.
The amounts of reactants used were about 0.00024 mols
for unsubstituted phenol and about 0.00039 mols for each
monochlorophenol. A 1 g particle bed of 1 cm height, con-
sisting of SiO2 (99.6% purity, 325 mesh) and 0.5% (mass)
CuCl2 (anhydrous, 99.999+% purity), was located at the
center of the reactor. Experiments were carried out in
25 °C increments at a gas velocity of 2.7 cm/s over a temper-
ature range from 100 °C to 425 °C for phenol and from
300 °C to 425 °C for each monochlorophenol. Gas flow rate
was changed to keep a constant residence time. The duration
of each experiment was approximately 10 min for unsubsti-
tuted phenol and 20 min for three monochlorophenols.
The entire product gas stream was rapidly quenched and
aromatic tar samples were collected in an ice-cooled dichlo-
romethane trap. Sample and rinse solutions were combined
and filtered, then analyzed by GC/MS (HP 6890 series gas
chromatograph with model 5973 mass selective detector)
equipped with a HP-5MS capillary column. Preliminary
identification of PCDD/PCDF products was based on
published relative retention times for similar columns (Hale
et al., 1985; Ryan et al., 1991). Final identification was
In this paper, results are presented on direct chlorination
and condensation of unsubstituted phenol and the three
monochlorophenols. Questions addressed are as follows.
(1) At what temperatures does chlorination occur?
(2) To what extent does chlorination occur? Is pentachlo-
rophenol (PCP) formed? What is the pattern of
chlorination?

1102
J.-Y. Ryu / Chemosphere 71 (2008) 1100–1109
based on available standards as well as gas-phase synthesis
experiments from single precursors and precursor pairs.
Seventy-four of 75 PCDD congeners and 121 of 135 PCDF
congeners have been synthesized. A universal response fac-
tor was used for PCDDs and PCDFs based on dibenzo-p-
dioxin (DD) and dibenzofuran (DF), respectively.
At 100 °C, the unsubstituted phenol recovery was 98%
and about 1% of the chlorinated phenols and 0.1% of the
chlorinated benzenes were formed. The yield of chlorinated
phenols increased with temperatures up to 200 °C. A max-
imum 6.3% yield of chlorinated phenols was obtained at
200 °C, and then decreased as temperature increased.
PCE was detected at 250 °C, and had a maximum yield
of 0.7% between 350 °C and 425 °C. Chlorinated benzenes
increased with temperature, with a maximum yield of
about 0.15% at 425 °C. Dibenzofuran (DF) was formed
from condensation of unsubstituted phenol pairs. The yield
of DF increased with temperature, with a maximum 0.06%
of yield at 425 °C. Dibenzo-p-dioxin (DD) was formed in
small amounts, with a maximum 0.002% yield at 425 °C.
Monochlorophenol reactant recovery at 300 °C was
73.3%, 71.9%, and 63.4% for each monochlorophenol.
The recovery of monochlorophenol reactants also
decreased with increasing temperature. PCE was produced
in abundant amounts over all the temperature range for
each of the three monochlorophenols. The yield of PCE
increased up to 375 °C, and thereafter decreased as temper-
ature increased. A maximum yield of PCE was about 8%,
11%, and 7.6% for 2-CP, 3-CP and 4-CP, respectively at
3. Results and discussion
3.1. Overall products
Experiments with pure unsubstituted phenol and mono-
chlorophenols were conducted over a temperature range of
100 °C–425 °C for phenol and from 300 °C to 425 °C for
monochlorophenols. Reactant recoveries of phenol and
three monochlorophenols and all other product yields are
shown in Fig. 2. At low temperature, much higher reactant
recoveries were obtained. The recoveries of phenol reac-
tants decreased with increasing temperature. The major
products were chlorinated phenols (CP), perchloroethylene
(PCE), chlorinated benzenes (CBz), chlorinated benzoquin-
nones (CQ), chlorinated dibenzofuran (PCDF), and chlori-
nated dibenzo-p-dioxin (PCDD).
100.00000
100.00000
2-CP
phenol
10.00000
10.00000
PCE
CDDs
1.00000
CP
CP
PCE
1.00000
0.10000
0.10000
CBz
CDFs
0.01000
0.01000
DF
CQ
CBz
0.00100
0.00100
DD
0.00010
0.00010
100
150
200
250
300
350
400
450
275
300
325
350
375
400
425
450
temperature (deg.C)
temperature (deg.C)
100.00000
10.00000
1.00000
0.10000
0.01000
0.00100
0.00010
100.00000
10.00000
1.00000
0.10000
0.01000
0.00100
0.00010
3-CP
4-CP
PCE
PCE
CDFs
CBz
CDFs
CP
CBz
CP
CQ
CQ
CDDs
CDDs
275
300
325
350
375
400
425
450
275
300
325
350
375
400
425
450
temperature (deg.C)
Fig. 2. Phenol reactant recoveries and other product yields.
temperature (deg.C)

J.-Y. Ryu / Chemosphere 71 (2008) 1100–1109
1103
375 °C. A higher amount of PCE was formed but only
0.7% of PCE yield was obtained from unsubstituted phenol
experiment.
(4) sites were observed for unsubstituted and three mono-
chlorophenols. This result is consistent with previous
research by others. Chlorination of phenol has been found
to involve only ortho and para positions (Born et al., 1993).
However, the temperature at which maximum chlorina-
tion occurred was different. Born et al. (1993) found
chlorination was favored at a temperatures range of 350–
450 °C. Different chlorination mechanisms, such as the
Deacon reaction and direct chlorination, may explain the
divergent findings. The direct chlorination reaction by
CuCl2 was found to occur at a much lower temperature
(150 °C) than Deacon controlled (400 °C) chlorination
(Taylor et al., 1998). Gullett et al. (1990) found that the
chlorination of phenols in the gas phase takes place most
effectively in the temperature region of 300–400 °C.
Phenol produced 2-, 4-, 2,4-, 2,6-, 2,4,6- chlorinated phe-
nols. The maximum yield of 2-CP and 4-CP was 4.76% and
1.15%, respectively at 200 °C. The chlorination product
2,4-DCP was preferred over 2,6-DCP. The chlorination
pattern is as follows:
Chlorinated phenol products were formed at 300 °C and
thereafter decreased with increasing temperature. Maxi-
mum yields of chlorinated phenols were 0.77%, 0.40%,
and 0.34%, respectively at 300 °C. In unsubstituted phenol
experiments over a temperature range from 100 °C to
425 °C, the total yield of chlorinated phenol products was
observed to peak at 200 °C. This is consistent with the
results shown in Fig. 2 in which chlorinated phenol yields
decrease with temperatures above 300 °C.
Chlorinated benzene products also started to form at
300 °C and increased with increasing temperature. Maxi-
mum yields of chlorinated benzenes were about 0.11%,
0.20%, and 0.13% for 2-CP, 3-CP, and 4-CP, respectively,
at 400–425 °C.
For PCDD/F formation, 2-CP produced 0.83% yields of
PCDDs and 0.10% yields of PCDFs at 400 °C and 425 °C.
3-CP produced 0.005% yields of PCDDs and 3.4% yields of
PCDFs at 425 °C; 4-CP reactant formed 0.02% yields of
PCDDs and 0.66% yields of PCDFs at 425 °C. Also, chlo-
rinated benzoquinones (CQ) were detected between 325 °C
and 400 °C, which is a little lower than that of a maximum
PCDD/F formation. This compound was not produced
from unsubstituted phenol. A maximum yield of CQ was
0.03% at 350 °C from 2-CP. 3-CP produced 0.02% yield
at 350 °C. 4-CP produced 0.02% of a maximum yield at
325 °C. A possible explanation of the mechanism of CQ
formation will be discussed later.
Phenol ! 2 ꢁ CP > 4 ꢁ CP ! 2; 4 ꢁ DCP > 2; 6 ꢁ DCP
! 2; 4; 6 ꢁ T3CP
In 2-CP experiments, only three chlorinated phenols
(2,4-DCP, 2,6-DCP, 2,4,6-T3CP) were produced. Maxi-
mum yields were observed at 300 °C. 2,4-DCP was favored
over 2,6-DCP at all temperatures except 425 °C.
In 3-CP experiments over temperature range of 300–
425 °C, 2,3-, 2,5-, and 3,4-DCP were derived from ortho/
para chlorination, with 2,5-ꢂ2,3->3,4-DCP. This result
might be explained by a statistical factor.
3.2. Phenol chlorination
3-CP has two ortho sites (2,6) and one para (4) site to
be chlorinated. Chlorination of ortho sites is favored over
chlorination at the para site, with 2,3- and 2,5-DCP
Chlorinated phenol product distributions are shown in
Table 1. Chlorination products at ortho (2,6) and para
Table 1
Yields of chlorinated phenol products (percent phenol conversion)
Reactant
Phenol
Products
Temperature (°C)
100
125
150
175
200
225
250
275
300
325
350
375
400
425
2-CP
4-CP
2,4-DCP
2,6-DCP
2,4,6-T3CP
0.769
0.154
0.006
0.000
0.000
1.639
0.394
0.018
0.000
0.000
3.083
0.694
0.085
0.000
0.000
4.040
0.887
0.201
0.000
0.000
4.761
1.149
0.393
0.004
0.000
3.892
0.998
0.394
0.008
0.006
3.030
0.646
0.223
0.004
0.006
1.841
0.338
0.174
0.003
0.005
0.960
0.066
0.036
0.000
0.001
0.758
0.047
0.016
0.000
0.000
0.413
0.010
0.002
0.000
0.000
0.356
0.008
0.000
0.000
0.000
0.230
0.004
0.000
0.000
0.000
0.041
0.002
0.000
0.000
0.000
2-CP
3-CP
2,4-DCP
2,6-DCP
2,4,6-T3CP
0.379
0.282
0.128
0.312
0.257
0.053
0.282
0.229
0.044
0.280
0.226
0.024
0.238
0.219
0.012
0.204
0.216
0.015
2,5-DCP
2,3-DCP
3,4-DCP
2,4,5-T3CP
2,3,4-T3CP
2,3,6-T3CP
2,3,4,6-T4CP
0.262
0.061
0.044
0.021
0.005
0.006
0.002
0.228
0.055
0.042
0.013
0.004
0.006
0.004
0.227
0.051
0.027
0.011
0.002
0.002
0.002
0.139
0.032
0.019
0.007
0.001
0.002
0.002
0.128
0.030
0.013
0.006
0.001
0.002
0.001
0.110
0.024
0.014
0.004
0.001
0.001
0.000
4-CP
2,4-DCP
2,4,6-T3CP
0.305
0.037
0.238
0.020
0.262
0.007
0.264
0.011
0.266
0.015
0.294
0.009

1104
J.-Y. Ryu / Chemosphere 71 (2008) 1100–1109
produced preferentially over 3,4-DCP. In 4-CP experi-
ments, only two chlorinated phenols were formed, showing
that chlorination is favored at ortho sites.
Thus, the major factors controlling the phenol chlorina-
tion pattern appear to be electronic (electron density) and
statistical (number of equivalent chlorination sites due to
molecular symmetry).
The ratio of ortho/para chlorinated phenol product
yields was calculated at temperatures between 100 and
425 °C for unsubstituted phenol, and between 300 and
425 °C for monochlorophenols. Results are shown in
Fig. 3. Chlorination at ortho site(s) increases with increas-
ing temperature. Chlorination at ortho sites is favored over
chlorination at the para site for unsubstituted phenol and
3-CP. Ratios of ortho/para chlorinated phenols (2-/4-CP)
from phenol chlorination are between 4 and 64, and
between 5 and 10 (2,5-/3,4-DCP) and 1.3 and 2.7 (2,3-/
3,4-DCP) from 3-CP chlorination. But ratios ranged only
from 0.7 to 1.1 (2,6-/2,4-DCP) from 2-CP chlorination.
In chlorination, the ortho/para directing OH group of
phenol is explained by the electrophilic aromatic substitu-
tion mechanism (Luijk et al., 1994). Electron densities at
each carbon of the phenols were calculated using the
semi-empirical molecular orbital method (PM3) with opti-
mal conformation. Results are shown in Table 2. The bold
figures in Table 2 represent the highest electron density at
each atom that can be chlorinated. Chlorination is favored
at carbons with high electron density. For example, phenol
has three carbons with high electron density: the two ortho
(2,6) carbons and one para (4) carbon. Moreover, 2- and 6-
carbons have the same electron density, which is higher
than the density of the 4-carbon. This is consistent with
results in the phenol experiment in which 2-CP produced
more than 4-CP.
Weber and Hagenmaier (1999a) reported that the most
abundant chlorophenols are ortho and para chlorinated
phenols such as 2,4-DCP, 2,4,6-T3CP, 2,3,4,6-T4CP, and
PCP. This distribution could be explained from ortho/para
chlorination of unsubstituted phenol. The concentration of
unsubstituted phenol in the gas effluent of MWI (municipal
waste incinerators) is more than 100 times higher than that
of chlorinated phenols (Weber and Hagenmaier, 1999b).
Therefore, phenol chlorination is a possible source of
abundant chlorinated phenols.
Yamamoto and Inoue (1990) reported that the major
chlorinated phenols found in municipal waste incinerators
are the congeners with ortho and para sites (2, 4, 6 carbons)
chlorinated: namely, 2,4,6-T3CP, 2,3,4,6-T4CP and PCP.
3.3. PCDD/Fs formation
Results, shown in Table 3, indicate total PCDD/F yield
and isomer distribution from phenol reactants over all tem-
perature ranges. The primary CDD/F products are DF
(phenol), DD/1-MCDD/4,6-DCDF (2-CP), 1,7/3,7/1,9-
DCDF (3-CP), 2,8-DCDF (4-CP), respectively. The gas-
phase PCDD/F formation pathway is shown in Fig. 4.
Small amounts of secondary PCDD/F products were
produced from chlorinated phenol products. 1,3/1,7/1,8-
DCDD isomers are formed from 2-CP and 2,4-DCP, and
1,6/1,9-DCDD isomers are formed from 2-CP and 2,6-
DCP by the loss of one chlorine (Ryu and Mulholland,
2002) or two 2,6-DCP by the loss of two chlorine (Mulhol-
land and Ryu, 2001). Condensation of 2-CP and 2,4,6-T3CP
by the loss of one chlorine or 2,6-DCP and 2,4,6-T3CP by
the loss of two chlorine produced 1,3,6-T3CDD isomer. 3-
CP also produced secondary PCDD/F products, 2,7/2,8/
1,7/1,8-DCDD isomers from 3-CP and 2,5-DCP by one
chlorine loss, only 1,2,7/2,3,9-T3CDF from 3-CP and 3,4-
DCP that can form 1,2,7/2,3,9/2,3,7/1,29-T3CDF isomers.
Secondary PCDD/F, 2,7/2,8-DCDD, 1,3,7/1,3,8-T3CDD
and 2,4,8-T3CDF were produced from reactant 4-CP and
2,4-DCP or two 2,4-DCP formed from chlorination.
100
10
phenol ==> 2-/4-CP
3-CP ==> 2,5-/3,4-DCP
3-CP ==> 2,3-/3,4-DCP
tho/pra
1
2-CP ==> 2,6-/2,4-DCP
Three monochlorophenols have different chlorine substi-
tution patterns called ortho, meta, and para. Each of the
three different chlorine substitution patterns shows a differ-
ent propensity for PCDD/F formation. A maximum yield of
PCDD/F from 2-CP reactant was 1.53% phenol conversion
on PCDD at 400 °C and 0.1% phenol conversion at 425 °C.
3-CP produced a maximum yield of 0.005% phenol conver-
sion on PCDD, and 3.38% phenol conversion on PCDF at
425 °C. 4-CP produced a maximum 0.019% PCDD yield
of phenol conversion, and 0.66% of phenol conversion on
PCDF at 425 °C. 2-CP has the greatest propensity to form
PCDD, but is likely the least inclined to form PCDF prod-
ucts. 3-CP has the greatest propensity to form PCDF, but is
the least to form PCDD products.
0.1
50
100
150
200
250
300
350
400
450
temperature (deg.C)
Fig. 3. Ortho/para ratios of chlorinated phenol products.
Table 2
Electron densities of chlorinated phenol carbon atoms
PM3
C-1
C-2
C-3
C-4
C-5
C-6
Phenol
2-CP
3-CP
4-CP
3.9013
3.8988
3.8875
3.9002
4.1702
4.1725
4.1480
4.1585
4.0611
4.0683
4.0863
4.0613
4.1444
4.1314
4.1471
4.1657
4.0611
4.0596
4.0450
4.0613
4.1702
4.1858
4.1988
4.1585
Calculated by PM-3 method.

J.-Y. Ryu / Chemosphere 71 (2008) 1100–1109
1105
Table 3
PCDD/F yield (percent phenol conversion) and isomer distributions from phenols
Reactants
CDD/F products
Temperature (°C)
Isomer avg
Fraction st. dev.
250
275
300
325
350
0.0104
0.0001
0.0110
375
0.0097
0.0001
0.0117
400
0.0631
0.0009
0.0137
425
Phenol
DF
0.0010
0.0000
0.0000
0.0020
0.0000
0.0000
0.0009
0.0000
0.0000
0.0037
0.0000
0.0000
0.0399
0.0015
0.0383
DD
DD/DF
2-CP
DD
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0024
0.0000
0.0000
0.0000
0.0000
0.0000
0.0024
0.0000
0.0672
0.0152
0.3293
0.0045
0.0036
0.0042
0.0001
0.0000
0.4206
0.0036
0.6217
0.0317
0.5349
0.0157
0.0412
0.0061
0.0000
0.0006
1.2106
0.0412
29.41
0.6915
0.0411
0.7511
0.0327
0.0369
0.0077
0.0000
0.0014
1.5254
0.0369
41.35
0.2863
0.0318
0.4778
0.0191
0.1006
0.0050
0.0000
0.0004
0.8204
0.1006
8.15
2-MCDD
1-MCDD
13-DCDD
46-DCDF
16/17/18-DCDD
19-DCDD
136-T3CDD
total CDD
total CDF
CDD/CDF
0.0482
0.9518
0.7327
0.0258
0.0258
0.1324
0.2644
0.0029
0.1264
0.0064
115.54
3-CP
17-DCDF
37-DCDF
19-DCDF
27/28-DCDD
17/18-DCDD
127/239-T3CDF
Total CDD
Total CDF
CDD/CDF
0.0013
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0013
0.0000
0.0048
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0048
0.0000
0.1150
0.0027
0.0007
0.0000
0.0000
0.0008
0.0000
0.1193
0.0000
0.2629
0.0104
0.0041
0.0003
0.0000
0.0014
0.0003
0.2788
0.0010
1.3967
0.0913
0.0355
0.0023
0.0004
0.0028
0.0027
1.5262
0.0018
2.9331
0.3679
0.0698
0.0036
0.0011
0.0062
0.0047
3.3771
0.0014
0.9297
0.0576
0.0128
0.9012
0.0988
0.0529
0.0470
0.0088
0.1188
0.1188
4-CP
28-DCDF
0.0000
0.0020
0.0000
0.0000
0.0020
0.0000
0.0125
0.0021
0.0000
0.0000
0.0021
0.0125
0.1690
0.0337
0.0021
0.0000
0.0000
0.0021
0.0337
0.0629
0.0758
0.0057
0.0000
0.0000
0.0057
0.0758
0.0748
0.2256
0.0125
0.0000
0.0008
0.0133
0.2256
0.0589
0.6606
0.0185
0.0001
0.0007
0.0192
0.6607
0.0291
27/28-DCDD
248-T3CDF
137/138-T3CDD
Total CDD
Total CDF
CDD/CDF
Only phenols with chlorine in the ortho position are
capable of forming PCDD. But ortho chlorine is not avail-
able in either 3- or 4-CP, and these have a higher probabil-
ity of forming PCDF products. In Table 3, the ratio of
total PCDD/F product shows that 4-CP has a much higher
propensity to form PCDD products compared to 3-CP.
The PCDD/F ratio decreased as temperatures increased.
This result is consistent with the gas-phase experiment.
Weber and Hagenmaier (1999a), reported that ortho/para
chlorinated phenols are very reactive to form POP (phen-
oxyphenol), intermediate for PCDD and meta chlorinated
phenols favored the formation of DOHB (dehydroxybiphe-
nyls), intermediate for PCDF. This finding is also consis-
tent with previous gas-phase results (Nakahata and
Mulholland, 2000), which suggested that chlorine substitu-
tion at phenol meta carbons (3 and 5) favors PCDF forma-
tion over chlorine substitution at the para carbon (4).
are shown Table 4. Bold figures represent the most abun-
dant homologue and isomer groups.
Phenol produced monochlorobenzene (MCBz) in the
most abundant amount, showing 95% of chlorobenzene
homologue group. Dichlorobenzene (DCBz) was the most
abundant homologue group, about a 70% fraction, of all
chlorinated benzenes, from three monochlorophenols and
the most abundant DCBz isomers were different depending
on the substitution pattern. 1,2-DCBz isomer was about
97% from 2-CP, and 1,3-DCBz isomer was about 99%
from 3-CP, and 1,4-DCBz was about 99% from 4CP. Thus,
MCBz, 1,2-, 1,3-, and 1,4-DCBz were likely produced by
chlorodehydroxylation of phenol, 2-CP, 3-CP, and 4-CP,
respectively. Born et al. (1993) also reported polychlori-
nated benzenes are formed by chlorodehydroxylation of
chlorinated phenols.
In a previous study (Ryu, Ph.D, Dissertation, 2002), the
formation of chlorinated benzenes shows the following pat-
terns: MCBz, 1,2-DCBz, 1,2,3-T3CBz, 1,2,3,4-T4CBz.
Chlorinated benzenes could be formed from either chlori-
nation of major DCBz isomers or from chlorodehydroxyla-
tion of chlorinated phenol products.
3.4. (Chloro-) benzenes formation
In this section, chlorinated benzene homologue and iso-
mer distributions are addressed to identify the mechanism
of chlorinated benzenes. Average homologue and isomer
fractions of chlorinated benzenes with standard deviation
For the 2-CP experiment, the isomer fraction of 1,2,4-
T4CBz and 1,2,3-T3CBz is 0.62 and 0.38. 1,2,4-T3CBz

1106
J.-Y. Ryu / Chemosphere 71 (2008) 1100–1109
OH
O O
-2H
HO
OH
O
2
O
O
-H2
H H
DF
phenol
DOHB Keto-tautomer
O O
Cl
Cl
Cl
Cl
Cl
HO
Cl
OH
Cl
O
-H2
H H
DOHB Keto-tautomer
4,6-DCDF
O
OH
-2H
-Cl
Cl
O
2
-Cl
O
O
DD
2-CP
Cl
Cl
O
O
O
Cl
O
Phenoxyphenol
H
O
O
O
O
Cl
Cl
-H
1-MCDD
O
-H2
O
O
OH HO
Cl
O
3,7-DCDF
O
Cl
Cl
Cl
Cl
Cl
Cl
Cl
-2H
H H
OH
O
O
OH
Cl
HO
HO
2
Cl
Cl
HH
Cl
3-CP
Cl
1,7-DCDF
O
O
OH
O
H
H
Cl Cl
DOHB
Cl
Cl
1,9-DCDF
Cl
Cl
DOHB Keto-tautomer
-2H
O
O
OH
HO
OH
O
2
O
-H2
Cl
Cl
H H
DOHB Keto-tautomer
Cl
Cl
Cl
Cl
Cl
4-CP
2,8-DCDF
DOHB
Fig. 4. Pathways of PCDD/F formation from phenols.
could formed from chlorinated phenol products, 2,4-DCP
and 1,2,3-T3CBz from 2,6-DCP, by chlorodehydroxyla-
tion, and 1,2,3-T3CBz also could be from chlorination of
1,2-DBz. 1,2,3,5-T4CBz is formed from 2,4,6-T3CP, and
1,2,3,4-T4CBz is produced from chlorination of either
1,2,4-T3CBz or 1,2,3-T3CBz (2,3,6-T3CP is not available
for 1,2,3,4-T4CBz formation by chlorodehydroxylation).
3-CP produced about 70% of 1,2,4-T3CBz and 30% of
1,2,3-T3CBz. 1,2,4-T3CBz is formed from 2,5- and 3,4-
DCP. 1,2,3-T3CBz is formed from either 2,3-DCP or chlo-
rination of 1,3-DCBz already formed. 1,2,4,5-T4CBz is
formed from 2,4,5-T3CP. 1,2,3,4-T4CBz is formed from
2,3,4- and 2,3,6-T3CP or chlorination of 1,2,3-T3CBz.
4-CP produced 1,2,4-T3CBz that is possibly formed
from 2,4-DCP. 1,2,3,5-T4CBz is formed from 2,4,6-T3CP
and 1,2,3,4-T4CBz is formed from chlorination of 1,2,4-
T3CBz. Isomer distributions of chlorinated benzene from
phenol are very similar to that of the chlorinated benzene
formed from benzene only chlorination discussed in a pre-
vious study (Ryu, Ph.D. Dissertation, 2002). But here, 1,2-

J.-Y. Ryu / Chemosphere 71 (2008) 1100–1109
1107
Table 4
Chlorinated benzene average homologue and congeners distributions
Homologues
Phenol
Avg.
2-CP
Avg.
3-CP
Avg.
4-CP
Avg.
St. dev.
St. dev.
St. dev.
St. dev.
MCBz
DCBz
T3CBz
T4CBz
P5CBz
H6CBz
0.9506
0.0331
0.0149
0.0005
0.0004
0.0006
0.0693
0.0512
0.0228
0.0010
0.0009
0.0020
0.0467
0.7066
0.1514
0.0501
0.0191
0.0261
0.0761
0.0654
0.0872
0.0326
0.0205
0.0342
0.0288
0.7474
0.1469
0.0465
0.0238
0.0066
0.0465
0.0976
0.0741
0.0236
0.0206
0.0070
0.0466
0.7578
0.1282
0.0475
0.0173
0.0025
0.0578
0.0289
0.0445
0.0334
0.0171
0.0031
Isomers
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
0.0189
0.0630
0.9180
nd
nd
1.0000
nd
0.0302
0.1176
0.1112
nd
nd
0.0000
nd
0.0239
nd
0.0324
nd
0.9961
0.0024
0.0014
0.0002
0.6992
0.3006
0.1226
0.4010
0.4764
0.0070
0.0041
0.0030
0.0007
0.1181
0.1181
0.0682
0.1474
0.0957
0.0015
0.9985
nd
nd
1.0000
nd
0.8694
0.0011
0.1295
0.0030
0.0030
nd
nd
0.0000
nd
0.1050
0.0031
0.1047
0.9761
0.0004
0.6181
0.3815
0.8199
nd
0.0324
0.0012
0.0873
0.0872
0.0939
nd
nd
1.0000
nd
0.0000
0.1801
0.0939
0.04
0.03
0.02
0.01
0.00
DCBz is 92% of total DCBz, while it was only 55% in ben-
zene chlorination. This high formation of 1,2-DCBz is
attributed to higher formation of 2-CP than 4-CP. 1,2-
DCBz is formed from 2-CP and 1,4-DCBz is produced
from 4-CP by chlorodehydroxylation.
dichloro-
trichloro-
3.5. Perchloroethylene (PCE) formation
The yield of PCE from phenols was higher from three
monochlorophenols than from phenol (Fig. 2). Born
et al. (1993) also reported comparable quantities of PCE
are formed at 427 °C. They mentioned that the PCE
product very likely results from ring opening oxidative
breakdown of chlorinated phenols. Furthermore, they
suggested that PCE should be monitored in municipal
waste incinerator effluent gases as a possible indicator of
PCDD/F emissions. Other researchers also have mentioned
PCE formation in fly ash catalyzed reactions (Jay and Stie-
glitz, 1991; De Leer et al., 1989). Little research has been
done on the mechanism of PCE formation and more study
is needed.
phenol
2-CP
3-CP
4-CP
Fig. 5. Yields of chlorinated quinones from monochlorophenols at
350 °C.
O
O
O
O
O
O
Cl
O
Cl
Cl
O
Cl
Cl
2
Cl
3
2
trichlorobenzoquinone
dichlorobenzoquinone
3.6. Chlorinated benzoquinones formation
Fig. 6. Molecular structures of chlorinated quinone compounds.
Chlorinated benzoquinone compounds were detected in
very small amounts over the temperature range 325–400 °C
in the 2-CP, 3-CP and 4-CP experiments (Fig. 5). Unsubsti-
tuted phenol produced no chlorinated benzoquinone com-
pounds. Each monochlorophenol produced a dichlorinated
benzoquinone (e.g. 2,6-dichloro-1,4-benzoquinone). In
addition, 3-CP produced a small amount of another tri-
chlorobenzoquinone. Possible molecular structures of chlo-
rinated quinone products are shown in Fig. 6.
formation occurred by removal of the chlorine atom during
electrochemical incineration of 4-chlorophenol, as shown
in Fig. 7.
Basu and Wei (2000) proposed that dichlorobenzoqui-
none compounds were formed from 2,4,6-trichlorophenol
in the aqueous phase Fenton’s reagent (aqueous solution
of hydrogen peroxide and ferrous ion). The two dic-
hlorobenzoquinones were 2,4-dichloro-1,6-benzoquinone
and 3,5-dichloro-1,6-benzoquinone; which one occurs
depends on which chlorine is removed. It was impossible
Quinone compounds were produced from chlorinated
phenols in another study (Johnson et al., 1999). The
researchers proposed that the pathway to benzoquinone

1108
J.-Y. Ryu / Chemosphere 71 (2008) 1100–1109
was favored on ortho and para carbon (2,4,6-) of phenols.
OH
OH
Cl
OH
At 200 °C, a maximum yield of chlorinated phenols was
observed, yielding about 6.3% conversion. Controlling fac-
tors for chlorination appear to be electronic and statistical.
Chlorinated benzenes are formed by chlorodehydroxyla-
tion of chlorinated phenols. Perchloroethylene and chlori-
nated benzoquinones are also formed from chlorinated
phenols. A maximum yield of PCDD and PCDF formation
was obtained at temperatures between 400 and 425 °C.
Ortho and para chlorinated phenols have a greater propen-
sity to form PCDD products and meta chlorinated phenols
have a greater propensity to form PCDFs.
Cl
4-chlorophenol
4-chlorocatechol
OH
O
O
OH
hydroquinone
benzoquinone
Acknowledgements
Fig. 7. Proposed pathway of benzoquinone formation from 4-CP (John-
son et al., 1999).
Support from the Research Foundation for Health and
Environmental Effects and the Environmental Protection
Agency (QT-OH-99-000537) is gratefully acknowledged.
to distinguish between these two in the mass spectra
because of their similar structure and identical molecular
weights.
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