Formation of PCDDs and PCDFs during the combustion of polyvinylidene chloride and other polymers in the presence of HCl

Article abstract of DOI:10.1016/j.chemosphere.2003.07.002

PVDC and three non-chlorinated polymers (PP, PET, and PA) were incinerated at 700-850°C in a laboratory-scale quartz tubular furnace in the presence of HCl (ca. 500 ppm?0.8 mg/l), and the gas-phase formation of PCDD/Fs, their putative precursors and their homologue profiles were investigated. The addition of HCl had little or no apparent effect on the level of PCDD/Fs formation during PVDC combustion, and their homologue profiles were quite different from those of the three non-chlorinated polymers. With PVDC, O ₈CDD and particularly O₈CDF were by far most prevalent, apparently as a result of the selective formation of the precursors. With each of the three non-chlorinated polymers, combustion at 800°C or higher in the presence of HCl resulted in PCDD/Fs formation at levels equaling or exceeding those observed with PVDC. In trials made with one of them (PP) under the same conditions but using a large polymer sample (100 mg vs 20 mg in all other trials), the level of PCDD/Fs formation was far higher than with the smaller polymer samples, and thus demonstrated the importance of appropriate combustion conditions for polymer incineration.

Full text of DOI:10.1016/j.chemosphere.2003.07.002

Chemosphere 54 (2004) 1521–1531
www.elsevier.com/locate/chemosphere
Formation of PCDDs and PCDFs during the
combustion of polyvinylidene chloride and
other polymers in the presence of HCl
*
Minoru Ohta , Shozo Oshima, Naoki Osawa, Toshio Iwasa,
Tadashi Nakamura
Conference on Hygiene of Vinylidene Chloride Products, 1-14-7 Nishi-shimbashi, Minato-ku, Tokyo 105-0003, Japan
Received 16 October 2002; received in revised form 9 July 2003; accepted 28 July 2003
Abstract
PVDC and three non-chlorinated polymers (PP, PET, and PA) were incinerated at 700–850 ꢀC in a laboratory-scale
quartz tubular furnace in the presence of HCl (ca. 500 ppm @ 0.8 mg/l), and the gas-phase formation of PCDD/Fs, their
putative precursors and their homologue profiles were investigated. The addition of HCl had little or no apparent effect
on the level of PCDD/Fs formation during PVDC combustion, and their homologue profiles were quite different from
8 8
those of the three non-chlorinated polymers. With PVDC, O CDD and particularly O CDF were by far most prevalent,
apparently as a result of the selective formation of the precursors. With each of the three non-chlorinated polymers,
combustion at 800 ꢀC or higher in the presence of HCl resulted in PCDD/Fs formation at levels equaling or exceeding
those observed with PVDC. In trials made with one of them (PP) under the same conditions but using a large polymer
sample (100 mg vs 20 mg in all other trials), the level of PCDD/Fs formation was far higher than with the smaller
polymer samples, and thus demonstrated the importance of appropriate combustion conditions for polymer inciner-
ation.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Polychlorinated dibenzo-p-dioxins (PCDDs); Polychlorinated dibenzofurans (PCDFs); Polychlorobenzenes (PCBzs);
Polychlorophenols (PCPhs); Polyvinylidene chloride (PVDC); Polypropylene (PP)
1
. Introduction
sent study, we further examined the mechanism of this
PCDD/Fs formation, in terms of the profiles of their
homologues formation and those of their putative pre-
cursors during the PVDC combustion, and investigated
the effects of gas-phase HCl on PCDD/Fs formation
during the combustion of polypropylene (PP), polyeth-
ylene terephthalate (PET), and polyamide (PA), as well
as PVDC.
In our previous study (Ohta et al., 2001), it was found
that the combustion of PVDC under appropriate con-
ditions (800 ꢀC or higher, 3 s or more residence time,
sufficient mixing turbulence) resulted in extremely low
levels of polychlorinated dibenzo-p-dioxins/polychlori-
nated dibenzofurans (PCDD/Fs) formation, while com-
bustion at 750 ꢀC or less resulted in higher levels of
PCDDs and particularly PCDFs formation. In the pre-
In municipal incinerators, the combustion gases
generally include HCl at concentrations of several hun-
dred ppm or higher, originating from NaCl and other
chlorides commonly found in waste materials. It is be-
lieved this may lead to the formation of PCDD/Fs
during the incineration of materials having no chlorine
(Lenoir et al., 1991). The formation of PCDD/Fs has
*
Corresponding author. Tel.: +81-3-3591-8126; fax: +81-3-
3591-8127.
E-mail address: vdkyo@oak.ocn.ne.jp (M. Ohta).
0
045-6535/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2003.07.002

1522
M. Ohta et al. / Chemosphere 54 (2004) 1521–1531
Fig. 1. First-stage combustion chamber.
been reported to occur during incineration of the hy-
drocarbons methane, propane, and ethylene in the
presence of HCl (De Fre and Rymen, 1989). It has also
been found to occur during the incineration of poly-
ethylene, polystyrene, and polyurethane at low com-
bustion temperatures (600 ꢀC) in the presence of HCl at
very high concentrations (130 mg/l) (Wirts et al., 1998).
Here we describe the results of our laboratory study
on the combustion of PVDC, PP, PET, and PA in the
presence of HCl at approximately 500 ppm (ca. 0.8 mg/l),
and on the mechanism of PCDD/Fs formation in the
light of their homologue profiles and those of their
presumed polychlorobenzenes (PCBzs) and polychloro-
phenols (PCPhs) precursors.
2.3. Apparatus
As previously reported (Ohta et al., 2001), the ap-
paratus consisted of a two-stage furnace containing a
quartz tube, with a coaxial inner pipe to feed secondary
air containing HCl to the first stage combustion zone
(Fig. 1), and a collection unit comprised of a quench
tube cooled by dry-ice and a tube packed with Amber-
â
lite XAD-2. As shown in Fig. 1, the orifice in the inner
pipe faced upward and was located vertically above the
sample boat, to promote turbulence and thus mixing of
the secondary feed air containing approximately 620
ppm HCl with both the primary feed air and the com-
bustion gas.
2
.4. Experimental conditions
2
. Materials and methods
Sample quantity: 20 mg per test, 50 repetitions per
test run (total 1 g) for each of the four films; for
the PP film also 100 mg per test, 10 repetitions per
test run (total 1 g).
All experiments were performed at the facilities of
Shimadzu Techno-Research Inc. (Kyoto, Japan).
Air quantity: 2.5 l/min (primary, 0.5 l/min; second-
ary, 2.0 l/min).
2
.1. Sample materials
HCl: approximately 500 ppm, calculated as 620
ppm · (2.0 l/2.5 l).
Combustion temperature: heater temperature settings
of 700 ꢀC in the first stage heater and 700, 750, 800,
and 850 ꢀC in the second stage heater.
The sample materials were the following commer-
cially available films, having the indicated thicknesses:
â
PVDC film, approximately 10 lm (Saran Wrap , Asahi
Kasei Corp., Tokyo, Japan); PP film, approximately 20
lm (Daicel Chemical Ind., Ltd., Osaka, Japan); PET
film, approximately 20 lm (Futamura Chemical Ind.
Co., Ltd., Nagoya, Japan); PA film, trilayer film con-
2
.5. Procedure
1
sisting of nylon 6 (5 lm)/MXD (5 lm)/nylon 6 (5 lm)
(
Mitsubishi Chemical Kohjin PAX Corp., Tokyo,
Japan).
Before each test run, the quartz tube with no sample
was held at the target temperature for 30 min with air
feed and next for 30 min with nitrogen feed, and a blank
test run lasting approximately 2 h was then performed at
the target temperature with no sample.
2
.2. HCl
Approximately 620 ppm HCl in air (Takachiho
Chemical Ind., Ltd., Tokyo, Japan).
For each of the four polymers, one test run consisted
of 50 test repetitions with 20 mg of the sample per test
and thus 1 g of sample per test run. For the PP film, a
test run of 10 test repetitions with 100 mg per test, and
thus 1 g per test run, was also performed to investigate
1
MXD: metaxylylenediamine/adipic acid copolymer.

M. Ohta et al. / Chemosphere 54 (2004) 1521–1531
1523
the effects of incomplete combustion with non-chlori-
nated polymers.
show that the formation of PCDD/Fs with PVDC was
very low and nearly equal to those found in the blank
test runs at 800 ꢀC or higher, but with PET and PA it
was clearly higher than the blank test runs.
The interval between test repetitions was approxi-
mately 1.5 min. Residence time in the second stage
furnace was calculated as approximately 3 s at 800 ꢀC,
except in test runs in which a calculated residence time
of approximately 2 s was obtained by using only three
In the test runs at 700 and 750 ꢀC, moreover, the
weight ratio of PCDFs to PCDDs was 300 or more with
PVDC, but 10 or less with PP, PET, and PA (Table 1).
2
of its four heater units. The CO and O concentrations
in the combustion gas were monitored continuously,
throughout the test runs.
3.2. PCBzs and PCPhs formation
The levels of PCBzs (Cl ¼ 3–6) and PCPhs (Cl ¼ 3–5)
formation found during combustion of each of the four
polymers in the presence of HCl are shown in Table 3.
The results for PVDC combustion in air with no HCl
addition, which are also shown for reference, followed
the same basic pattern as those found with PVDC in the
presence of HCl.
2
.6. Analysis
PCDD/Fs entrapped in the quench tube and the
XAD-2 resin were determined by HRGC-HRMS, as
described previously (Ohta et al., 2001).
PCBzs and PCPhs were determined by gas chroma-
tography and mass spectrometry (GC-MS). The GC
column was a DB-5MS (J&W) fused silica capillary
column of 60 m (length), 0.32 mm (i.d.), and 0.25 lm
The level of PCBzs formation with PVDC was high
at 700 ꢀC but declined with increasing combustion
temperature, and at 850 ꢀC was about the same as those
found with the other three polymers, which showed
much less change over the combustion temperature
range of 750–850 ꢀC and were thus much less tempera-
ture dependent.
(
film thickness). The temperature program was 60 ꢀC for
min, next to 110 ꢀC at 5 ꢀC/min, then to 265 ꢀC at 8 ꢀC/
min.
3
The level of PCPhs formation was about the same for
all four polymers over the temperature range of 750–850
3
. Results and discussion
ꢀ
C, and was less temperature dependent than that of
PCBzs.
The ratio of PCBzs to PCPhs was very high (in the
The results of the tests with 20-mg samples and thus
generally complete combustion are presented in Section
.1–3.5. The results of the tests with 100-mg PP samples,
3
range of 100–1000) with PVDC at all temperatures ex-
cept 850 ꢀC, but not far from 1 for the three other
polymers at all temperatures.
which were performed to investigate the effects of in-
complete combustion in the presence of HCl, are pre-
sented in Section 3.6.
3
.3. Homologue profiles
3
.1. PCDD/Fs formation
The homologue profiles of the PCDD/Fs and their
The levels of PCDD/Fs formation in the test runs for
presumed PCBzs/PCPhs precursors, as found in the
combustion test runs with 20-mg samples of each of the
four polymers in the presence of HCl, are shown in Figs.
3 and 4, respectively. Also shown are the profiles ob-
served with PVDC in air alone (for reference) and with
the 100-mg PP samples.
all four polymers are summarized in Tables 1 and 2. The
results clearly show the formation of PCDD/Fs during
the combustion of non-chlorinated PP, PET, and PA in
the presence of HCl. For PVDC, the presence of HCl
had little effect on the PCDD/Fs level, presumably be-
cause the local concentration of HCl generated during
PVDC combustion is itself quite high and thus little
affected by the presence of HCl in the air at several
hundred ppm.
With PVDC, the level of PCDFs generation was
generally higher than that of PCDDs. As shown in Fig.
3, all of the PCDF homologues (tetrachloro- to octa-
chlorodibenzofuran; T
4
CDF to O
8
CDF) were generated
8
CDF generation was
The temperature dependence of the PCDD/Fs for-
mation with PVDC was clearly different from that with
the other three polymers (Fig. 2). The levels of forma-
tion with PVDC were clearly higher than with the other
polymers during combustion at 700 and 750 ꢀC, but
about the same or lower than with the other three at 800
and 850 ꢀC. With the three non-chlorinated polymers,
particularly PET and PA, higher levels of PCDD/Fs
formation than the blank test runs were observed even at
in large quantities at 700 ꢀC, but O
far larger than that of the other homologues at both 750
and 800 ꢀC. With the other three polymers, all of the
PCDD/F homologues were generated at all of the
combustion temperatures.
A similar trend was observed among the homologues
of the precursor PCBzs and PCPhs, as shown in Fig. 4.
With PVDC, the generation of the PCBz homologue
6
hexachlorobenzene (H CBz) was far larger than that of
any of the other PCBz and PCPh homologues. With PP,
8
00 ꢀC or higher. The results expressed in TEQ (Table 2)

Table 1
PCDD/Fs formation (pg/g sample) during PVDC, PP, PET, and PA combustion
700 ꢀC
750 ꢀC
800 ꢀC
850 ꢀC
PCDDs
PCDFs
DFs/DDs
wt ratio
PCDDs
PCDFs
DFs/DDs
wt ratio
PCDDs
PCDFs
DFs/DDs
wt ratio
PCDDs
PCDFs
DFs/DDs
wt ratio
PVDC
5300
1 730 000
(196 000)
230
(99)
150 000
(130 000)
21
(12)
1500
(1300)
180
(42)
880
(210)
3
26
48
652
405
71
17
4:5
20 mg · 50 (520)
in air
r.t. ¼ 2 s
4600
1 600 000
(190 000)
420
(270)
170 000
(150 000)
38
(23)
640
(540)
28
(18)
300
(220)
3
11
(510)
PVDC
1800
560 000
(170 000)
490
(360)
150 000
(140 000)
97
(80)
9500
(9100)
57
(11)
150
(49)
311
355
308
306
260
319
98
38
15
2:6
4:8
5:7
20 mg · 50 (830)
in HCl gas
r.t. ¼ 3 s
3100
1 100 000
(340 000)
500
(430)
130 000
(130 000)
63
(50)
2400
(2300)
19
(8)
91
(66)
(1300)
2600
800 000
(180 000)
310
(220)
99 000
(90 000)
68
(56)
1000
(930)
30
(14)
170
(87)
(1000)
PP
1900
10 000
(4900)
2700
(1800)
11 000
(5700)
690
(470)
2500
(1500)
140
(47)
850
(220)
5
:3
4:1
1:7
3:6
3:1
6:1
5:4
20 mg · 50 (1300)
in HCl gas
r.t. ¼ 3 s
810
4200
(970)
2100
(380)
3500
(1100)
830
(600)
2600
(1500)
94
(46)
510
(170)
5:2
(430)
PP
100
15 000
(4500)
130 000
(23 000)
8700
(1800)
87 000
(12 000)
23 000
(6000)
200 000
(32 000)
52 000
(14 000)
470 000
(68 000)
8
:7
:6
10
14
8:7
9:0
mg · 10 in
HCl gas
11 000
95 000
(18 000)
4500
(750)
63 000
(6600)
10 000
(2100)
130 000
(16 000)
27 000
(7400)
310 000
(58 000)
8
13
11
(3200)
r.t. ¼ 3 s
PET
18 000
81 000
(29 000)
4100
(2800)
22 000
(14 000)
2300
(1800)
13 000
(9400)
730
(330)
4300
(1100)
4
:5
:9
5:4
3:9
5:7
5:9
5:9
5:4
20 mg · 50 (11 000)
in HCl gas
r.t. ¼ 3 s
6300
31 000
(15 000)
1000
(510)
3900
(2400)
270
(120)
1600
(450)
540
(190)
2900
(570)
4
(3900)
PA
1900
18 000
(7000)
1200
(690)
9800
(5800)
2900
(2100)
18 000
(12 000)
1100
(820)
6000
(3700)
9
:5
:8
8:2
5:8
6:2
4:9
5:5
4:4
20 mg · 50 (1000)
in HCl gas
r.t. ¼ 3 s
3100
21 000
(8000)
1400
(870)
8100
(5400)
1400
(760)
6800
(3400)
360
(190)
1600
(900)
6
(2000)

M. Ohta et al. / Chemosphere 54 (2004) 1521–1531
1525
PET, and PA, both H
6
CBz and pentachlorophenol
5
(P CPh) were generated in relatively large quantities, but
the other precursor homologues were also generally
observed.
3
.4. Characteristics of PCDD/Fs formation with PVDC
It is known that in combustion processes resulting in
the generation of PCDD/Fs, the level of PCDFs for-
mation generally tends to be higher than that of PCDDs
formation. With PVDC, this tendency was particularly
strong, presumably as a result of the large quantity of
PCBzs formed in combustion of this polymer. In other
words, a high level of PCBzs formation leads to a high
level of PCDFs formation.
Among the PCDD/F homologues generated with
PVDC, the ratios of formation were relatively large for
O
8
CDD and O
the extremely high level of H
8
CDF. This is presumably attributable to
CBz and, among the PCPh
6
5
homologues, the relatively high level of P CPh forma-
tion.
3
.5. PCDD/Fs formation with PP, PET, and PA
In the presence of HCl, the combustion of PP and
particularly PET and PA resulted in levels of PCDD/Fs
formation that were clearly higher than those of the
blank test runs, even at 800 ꢀC or higher. The reasons
for this are not entirely clear, but the overall reac-
tion pathway presumably consist of (1) formation of
low-molecular-weight hydrocarbons and aromatics, as
thermal decomposition products of the polymers (2)
formation of precursors (PCBzs, PCPhs) by chlorina-
tion, molecular growth reactions, and cyclization of the
hydrocarbons and by chlorination of the aromatics, and
(
3) formation of PCDD/Fs from these precursors. The
time required for completion of this chain of reactions is
relatively long, in comparison with PVDC, and the time
remaining for their decomposition in our test furnace
may therefore have been insufficient. These results ap-
pear to underline the importance of both the pathway
and the location of the PCDD/Fs formation in the
combustion gas stream.
The differences which were observed between the
levels of PCDD/Fs formed at various temperatures with
PP and those formed with PET and PA may be related
to the presence of the aromatic ring in PET and PA and
its absence in PP, leading to higher levels of PCDD/Fs
formation with the PET and PA.
3
.6. PCDD/Fs formation with 100-mg PP
Although the level of PCDD/Fs formation was gen-
erally low in the combustion test runs with 20-mg PP
samples in air containing HCl, it became far higher with

1526
M. Ohta et al. / Chemosphere 54 (2004) 1521–1531
Table 2
PCDD/Fs formation (pg-TEQ/g sample) during PVDC, PP, PET, and PA combustion
7
00 ꢀC
750 ꢀC
800 ꢀC
850 ꢀC
Note
a
PVDC 20 mg · 50
6800
39
5.6
0.44
In air r.t. ¼ 3 s
PVDC 20 mg · 50
PVDC 20 mg · 50
PP 20 mg · 50
12 000, 12 000
4000, 6600, 5600
110, 62
180, 180
100, 87, 95
91, 72
1.8, 1.0
4.1, 1.0, 1.1
15, 18
20, 0.83
2.3, 0.1, 1.4
16, 7.0
In air r.t. ¼ 2 s
In HCl (500 ppm) r.t. ¼ 3 s
In HCl (500 ppm) r.t. ¼ 3 s
In HCl (500 ppm) r.t. ¼ 3 s
In HCl (500 ppm) r.t. ¼ 3 s
In HCl (500 ppm) r.t. ¼ 3 s
In HCl (500 ppm) r.t. ¼ 3 s
PP 100 mg · 10
PET 20 mg · 50
PA 20 mg · 50
2400, 1700
870, 270
220, 250
1700, 1300
140, 31
68, 52
4300, 2700
50, 22
9800, 6100
77, 53
42, 17
100, 75
8.4, 3.2
b
Blank
4.8, 14
17, 13
5.6, 4.0
Multiple data represent the results of two or three test runs.
a
Details of the results are shown in the previous report (Ohta et al., 2001).
2
b
h duration was taken as equivalent to test run with 1 g of sample.
Fig. 2. PCDD/Fs formation (pg/g sample) during combustion of four polymers (20-mg samples) based on the mean value from the two
or three test runs.
1
00-mg PP samples under the same conditions, and
formation. It presumably contained no metals (e.g., Cu
or Fe) which would exert a catalytic effect, and would
therefore be expected to have little or no role in de novo
synthesis of PCDD/Fs. It may be noted, however, that
some studies have indicated the possibility that soot it-
self may have a catalytic effect (Luijk et al., 1994).
showed a clear tendency to increase with increasing
combustion temperature (Tables 1 and 2). Under these
incomplete combustion conditions, the formation of
their precursor PCBzs and PCPhs also increased, par-
ticularly at the higher combustion temperatures (Table
3
). This may be due to the rapid combustion rate which
causes the increase of the extent of incomplete com-
bustion. The increased precursor formation was thus
directly related to the large quantities of PCDD/Fs
formed with the 100-mg samples.
3.7. Pathways to PCDD/Fs formation with PVDC
Many studies have been reported on the generation
and emission of PCDD/Fs in municipal incineration and
other combustion of plastic resins, involving either ho-
mogeneous gas-phase reactions or post-furnace pro-
cesses involving fly ash.
Soot formation was observed in the combustion with
the 100-mg PP sample, but it is not clear whether the
soot played any role in the increased levels of PCDD/Fs

Table 3
PCBzs (Cl ¼ 3–6) and PCPhs (Cl ¼ 3–5) formation (ng/g sample) during PVDC, PP, PET, and PA combustion
Sample
700 ꢀC
750 ꢀC
800 ꢀC
850 ꢀC
Note
PVDC
PCBzs
PCPhs
250 000 (110 000)
1100 (310)
230
96 000 (95 000)
100 (62)
960
4800 (4700)
44 (44)
110
240 (240)
30 (30)
8.0
In air
r.t. ¼ 2 s
20 mg · 50
a
Ratio
PVDC
0 mg · 50
PCBzs
PCPhs
150 000 (100 000)
365 (170)
415
76 800 (76 000)
111 (42)
692
6450 (6400)
48 (14)
134
208 (190)
142 (35)
1.5
In HCl (500 ppm)
r.t. ¼ 3 s
2
a
Ratio
PP
PCBzs
PCPhs
280 (180)
610 (350)
0.46
180 (130)
170 (110)
1.1
74 (68)
27 (27)
2.7
71 (63)
<20 (<20)
>3.6
In HCl (500 ppm)
r.t. ¼ 3 s
20 mg · 50
a
Ratio
PP
PCBzs
PCPhs
540 (190)
810 (290)
0.67
350 (130)
760 (200)
0.46
880 (300)
570 (200)
1.5
2600 (690)
1700 (650)
1.5
In HCl (500 ppm)
r.t. ¼ 3 s
100 mg · 10
a
Ratio
PET
PCBzs
PCPhs
400 (280)
510 (320)
0.8
150 (120)
160 (130)
0.94
100 (86)
150 (110)
0.67
100 (77)
72 (26)
1.4
In HCl (500 ppm)
r.t. ¼ 3 s
20 mg · 50
a
Ratio
PA
PCBzs
PCPhs
250 (160)
230 (130)
1.1
150 (110)
110 (71)
1.4
180 (140)
150 (110)
1.2
110 (89)
100 (56)
1.1
In HCl (500 ppm)
r.t. ¼ 3 s
20 mg · 50
a
Ratio
Figures in parentheses show H
a
6
CBz or P
5
CPh (ng/g sample).
PCBzs (Cl ¼ 3–6)/PCPhs (Cl ¼ 3–5) wt ratio.

1528
M. Ohta et al. / Chemosphere 54 (2004) 1521–1531
Fig. 3. PCDD/F homologue profiles of four polymers.
Fig. 4. PCBz/PCPh homologue profiles of four polymers.

M. Ohta et al. / Chemosphere 54 (2004) 1521–1531
1529
Various studies have reported on post-furnace for-
mation, since Lustenhouwer et al. (1980) first proposed
mechanisms for PCDD/Fs formation. Many of these
have focused on formation from precursors (Dickson
and Karasek, 1987; Karasek and Dickson, 1987; Born
et al., 1989; Dickson et al., 1989; Dickson et al., 1992;
Born et al., 1993; Addink et al., 1995; Cains et al., 1997).
Others have investigated de novo synthesis from carbon,
organic fragments, and organic or inorganic chloride
compounds (Stieglitz et al., 1989a,b; De Leer et al.,
order of chlorination. The large quantities of highly
chlorinated benzenes (H CBz) and phenols (P CPh) may
6
5
be the result of chlorine rearrangement reactions and
thermal decomposition of homologues with lower-order
chlorination. In the homologue profiles specific in this
study to PVDC combustion at 750 and 800 ꢀC, O
was predominant and among PCDD homologues,
CDD was highest (Table 1, Fig. 3). These profiles
8
CDF
O
8
correlated closely with the patterns of precursor for-
mation that were also found to be specific to PVDC
1
989; Jay and Stieglitz, 1991). In their extensive review
combustion at these temperatures, in which H
counted for nearly all of the PCBzs formation and the
ratio of P CPh formation to that of other PCPhs was
6
CBz ac-
of reports then available, Huang and Buekens (1995)
discussed the rates and mechanisms of post-combustion
PCDD/Fs formation. Weber and Hagenmaier (1999b)
performed an extensive investigation of the isomer dis-
tribution patterns of PCDD/Fs, PCBzs, and PCPhs
in the flue gas, stack gas, and fly ash of fluidized
bed incinerators, and concluded that the mechanism of
PCDDs and PCDFs formation essentially consists of
condensation reactions between PCPhs and between
PCPhs and PCBzs respectively.
5
also very high (Table 3). In the PVDC combustion at
700 ꢀC, in contrast, all of the tri- to hexa-chlorobenzene
homologues were detected (T
lg/g; P CBz, 110 lg/g; H
the tri- to penta-chlorophenol homologues (T
lg/g; T CPh, 0.41 lg/g; P CPh, 0.31 lg/g), and forma-
tion of the T CDF to O CDF homologues found in this
3
CBz, 13 lg/g; T
CBz, 110 lg/g), as were all of
CPh, 0.30
4
CBz, 16
5
6
3
4
5
4
8
experiment is most likely attributable to reactions be-
tween these PCBzs and PCPhs.
A model mechanism of homogeneous gas-phase
formation of PCDDs from PCPhs was first proposed by
Shaub and Tsang (1983). Ballschmiter and Swerev
In this light, the experimental results suggest that the
formation of PCDFs in the combustion of PVDC
throughout the temperature range of 700–800 ꢀC is the
result of chlorophenoxy radical-chlorobenzene reac-
tions. This is in contrast to the conclusions of other
studies which did not specifically consider PVDC com-
bustion, that PCDFs formation occurs primarily by
ortho–ortho coupling of chlorophenoxy radicals (Mul-
holland et al., 2001; Wiater-Protas and Louw, 2001;
Louw and Ahonkhai, 2002).
(
1987) and Ballschmiter et al. (1988) subsequently re-
ported on the mechanisms of PCDD/Fs formation by
gas-phase reaction, in which they proposed PCBzs and
PCPhs, and also polychlorobiphenyls and polychloro-
diphenyl ether, as the main precursors.
Young and Voorhees (1991) discussed the mecha-
nisms of incomplete combustion product formation in
their investigation on pyrolysis of 1,2-dichlorobenzene.
In a very early work, Buser (1979) described the for-
mation of PCDD/Fs and PCPhs in PCBzs gas-phase
pyrolysis (620 ꢀC), and reported the formation of PCBz
with higher-order chlorination than the starting PCBz,
and PCDFs in quantities larger than those of PCDDs.
Menad and Bj o€ rkman (2000) have reviewed both the
gas-phase and the fly ash formation of PCDD/Fs from
precursors, in the light of the reports available to that
time.
In the combustion experiments with PP, PET, and
PA, on the other hand, the quantity of PCBzs detected
was extremely small (Table 3), indicating that the
PCDD/Fs formation with these non-chlorinated resins
was the result of gas-phase reaction between the pre-
cursor chlorophenoxy radicals.
4. Conclusion
In the past several years, in particular, various studies
have stressed the importance of radical/radical reactions
by PCPhs in the gas-phase formation of PCDD/Fs
In the combustion of PVDC at 750 and 800 ꢀC in air
with or without HCl addition, the PCDD/F homologues
(
Weber and Hagenmaier, 1999a; Wiater and Louw,
O
8
CDD and particularly O
highest quantities, apparently as a result of the high level
of their precursor PCBz/PCPh homologues H CBz and
5
P CPh. This PCDD/F homologue profile was specific to
8
CDF were formed in the
1
2
999; Wiater et al., 2000; Wiater-Protas and Louw,
001; Louw and Ahonkhai, 2002).
Other recent studies on the mechanism of gas-phase
6
PCDD/Fs formation from PCPhs suggest that chloro-
phenoxyl radical/radical recombination reactions play
an important role, and an elementary reaction-kinetic
model has been developed (Evans and Dellinger, 2003;
Khachatryan et al., 2003a,b).
PVDC, and was not found to occur in the combustion of
any of the other polymers under the same conditions.
These results indicate that in gas-phase reactions of
PVDC combustion at high temperatures (700–850 ꢀC),
the formation of PCDD/Fs occurs via the formation of
PCBzs, PCPhs, and perhaps other precursors.
In the present study on gas-phase PCDD/Fs forma-
tion, PVDC combustion resulted in the formation of
large quantities of PCBzs, particularly those with a high
PCDD/Fs were also found in the combustion of PP,
PET, and PA in the presence of HCl under similar

1530
M. Ohta et al. / Chemosphere 54 (2004) 1521–1531
conditions. Under inappropriate combustion conditions,
as shown by the results of the combustion tests using
De Fre, R., Rymen, T., 1989. PCDD and PCDF formation
from hydrocarbon combustion in the presence of hydrogen
chloride. Chemosphere 19, 331–336.
1
00-mg samples of PP, the incineration of non-chlori-
De Leer, E.W.B., Lexmond, R.J., de Zeeuw, M.A., 1989. ‘‘De
novo’’-synthesis of chlorinated biphenyls, dibenzofurans
and dibenzo-p-dioxins in the fly ash catalyzed reaction of
toluene with hydrochloric acid. Chemosphere 19, 1141–
nated polymers in the presence of HCl even at temper-
atures of 800 ꢀC or higher may result in high levels of
PCDD/Fs formation. It is therefore important to meet
the three essential combustion conditions of appropriate
temperature, residence time, and air mixing, in the in-
cineration of non-chlorinated plastics as well as PVDC.
The results of the experiments with PP, PET, and PA
in the presence of HCl indicate that PCPhs play the
primary role in the formation of PCDD/Fs during
combustion of these non-chlorinated polymers, in con-
trast to the results with PVDC.
1
152.
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of polychlorinated dibenzo-p-dioxins produced on munici-
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dibenzofurans during incineration. Chemosphere 19, 277–
2
82.
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solid waste incinerator postcombustion conditions. Environ.
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Acknowledgements
We are grateful to Shimadzu Techno-Research Inc.
for the use of their facility for the combustion experi-
ments, and for the invaluable suggestions and guidance
of Mr. Norihito Umezu and Mr. Takumi Takasuga re-
lating to the planning of the experiments, operation of
the facility, and evaluation of the results.
Evans, C.S., Dellinger, B., 2003. Mechanisms of dioxin forma-
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