EPA/600/2-86/006
January 1986
PIC FORMATION UNDER PYROLYTIC
AND STARVED AIR CONDITIONS
Barry Dellinger
Douglas L. Hall
John L. Graham
Sueann L. Mazer
Wayne A. Rubey
University of Dayton Research Institute
Dayton, Ohio 45469
and
M. Malanchuk
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
Grant No. CR 81-0783-01
EPA Workplan #01249
Item #4098[A]
Project Officer
Robert E. Mournighan
Thermal Technology Staff
Thermal Destruction Branch
Alternative Technologies Division
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Research Laboratory
Cincinnati, Ohio 45268
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO
EPA/600/2-86/006
l.
3. RECIPIENT'S ACCESSION NO.
b U54227AS
TITLE AND SUBTITLE
PIC Formation Under Pyrolytic and
Starved Air Conditions
5. REPORT DATE
January 1986
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S) ~~
Barry Dellinger, Douglas L. Hall, John L.
Graham, Sueann L. Mazer, Wayne A. Rubey
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
University of Dayton Research Institute
300 College Park
Dayton, OH 45469
10. PROGRAM ELEMENT NO.
D109
11. CONTRACT/GRANT NO.
CR-810783-01-0
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Hazardous Waste Engineering Research Laboratory
26 W. St. Clair St.
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
Progress Oct. 84 - Oct. 85
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A comprehensive program of laboratory studies based on the non-flame mode of
thermal decomposition produced much data on PIC (Products of Incomplete Combustion)
formation, primarily under pyrolytic and starved air conditions.
Most significantly, laboratory results from non-flame studies were compared to
those from various field'tests to evaluate incinerability relationships. Measurement
of gas-phase thermal stability in an atmosphere of low oxygen concentration yielded
results of incinerability ranking that were far more consistent with the findings
from field tests than any one of several common methods applied in the past such as
those that employed heat of combustion, autoignition temperature, etc.
The results of four experimental studies were presented as significant
contributions to developing/expanding the data base on POHC (Principal Organic
Hazardous Constituent) stability and PIC formation for pure compounds and mixtures.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
18. DISTRIBUTION STATEMENT
RELEASE UNLIMITED
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
57
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (R«v. 4-77) PREVIOUS EDITION is OBSOLETE
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
11
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FOREWORD
Today's rapidly developing and changing technologies and industrial
products and practices frequently carry with them the increased generation
of solid and hazardous wastes. These materials, if improperly dealt with,
can threaten both public health and the environment. Abandoned waste sites
and accidental releases of toxic and hazardous substances to the environ-
ment also have important environmental and public health implications. The
Hazardous Waste Engineering Research Laboratory assists in providing an
authoritative and defensible engineering basis for assessing and solving
these problems. Its products support the policies, programs and regula-
tions of the Environmental Protection Agency, the permitting and other
responsibilities of State and local governments and the needs of both large
and small businesses in handling their wastes responsibly and economically.
This report describes the results of various laboratory studies
designed to correlate predictions based on laboratory findings to field
results, with emphasis on Products of Incomplete Combustion (PIC) formation
under pyrolytic and starved air conditions in the laboratory tests.
For further information, please contact the Alternative Technologies
Division/Thermal Destruction Branch of the Hazardous Waste Engineering
Research Laboratory-
David G. Stephan, Director
Hazardous Waste Engineering Research Laboratory
iii
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PIC FORMATION UNDER PYROLYTIC
AND STARVED AIR CONDITIONS
by
Barry Dellinger, Douglas L. Hall,
John L. Graham, Sueann L. Mazer
and Wayne A. Rubey
University of Dayton Research Institute
Dayton, Ohio 45469
and
Myron Malanchuk
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
ABSTRACT
The University of Dayton Research Institute carried out a comprehen-
sive program of laboratory studies based on the non-flame mode of hazardous
waste thermal decomposition. The results of those studies were compared
to those of flame-mode studies and of field tests to evaluate the incin-
eration model proposed. That model was developed upon the premise that
incinerators do not operate continuously at optimum conditions. As a
result, as much, or more, than one percent of the feed and its flame treat-
ment products must undergo further decomposition in the post-flame region
to meet the >99.99% Destruction and Removal Efficiency (DRE) criterion.
Thermal decomposition (non-flame) results were compared to those from
a flame-mode study. That comparison supported a common order of stability
ranking of individual compounds set forth by the findings from both series.
Laboratory results from non-flame studies were compared to those from
various field tests to evaluate incinerability relationships. It was
strongly evident that the results of the laboratory tests where low oxygen
conditions (gas-phase thermal stability at low oxygen concentrations) pre-
vailed, presented a significantly superior incinerability correlation to
field tests than any of the other proposed methods of ranking. Those
methods included heat of combustion, auto-ignition temperature, theoretical
flame-mode kinetics, experimental flame failure modes, ignition delay time,
as well as gas-phase thermal stability at high oxygen concentration.
The results of four experimental studies were presented as support to
developing/expanding the data base on Principal Organic Hazardous Con-
stituent (POHC) stability and Products of Incomplete Combustion (PIC)
formation for pure compounds and mixtures.
Several studies were proposed for further laboratory investigation
of the thermal treatment process.
iv
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CONTENTS
Notice ,„ ii
Foreword iii
Abstract „ . ^ . iv
Tables vi
Figures vii
Introduction 1
Development of an Incineration Model .„ 2
Comparison of Flame and Thermal Decomposition Results - 6
Correlation of Laboratory Predictions and Field Results 13
Discussion 19
Summary and Conclusions...... 20
Expansion of Data Base on POHC Stability and PIC For-
mation for Pure Compounds and Mixtures 21
Thermal Decomposition of CRF Soup-1 21
Formation of PCDFs and Other PICs from PCBs 23
Formation of PICs from Chloroform 33
Formation of PICs from Polychlorinated Phenols 36
Expansion of Pure Compound Kinetic and Thermal
Stability Data Base..... 36
References 46
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TABLES
Number , Page
1 Calculated Destruction Efficiency for Representative Hazar-
dous Organics 4
2 Comparison of Flame and Non-Flame (Thermal) Stability
Ranking of Various Test Compounds 8
3 PICs Found in Diffusion Flame Combustion of Chlorobenzene,
Benzene and HC1 Mixture and Thermal Decomposition of a
Mixture of Carbon Tetrachloride, Toluene, Chlorobenzene,
Trichloroethylene and Freon 113 10
4 Results of Statistical Analyses of Observed vs. Predicted
Thermal Stability Rankings 15
5 Summary of Thermal Decomposition Testing for Components of
Hazardous Waste Mixture #1 22
6 Thermal Reaction Products Observed from the Thermal Decompo-
sition of CRF Soup-1 24
7 Major Thermal Reaction Products Tentatively Identified from
the Thermal Degradation of 2,3',4,4',5-Pentachlorobiphenyl .... 28
8 Maximum Weight Percent Yield of PCDFs as a Function of
Reaction Atmosphere 30
9 Thermal Decomposition Products Observed from Chloroform and
Pentachloroethane 37
10 Thermal Degradation Products from Pentachlorophenol 40
11 Summary of Thermal Decomposition Data 42
12 Summary of First Order Kinetic Results 43
13 Summary of Fractional Reaction Order Calculations 44
vi
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FIGURES
Number Page
1 Comparison of EERC Model Prediction with Predictions of
UDRI Two-Zone Incineration Model for the Acurex Subscale
Boiler 7
2 Concentration vs. Temperature for Propane Oxidation in Air
at a Gas-Phase Residence Time of 2.OS 11
3 Comparison of Flow Reactor Generated Thermal Decomposition
Profile vs. Predicted Results from Computer Modeled Gas-
Phase Free Radical Mechanism for Propane Oxidation 12
4 Thermal Decomposition Behavior of Toluene and Freon 113 27
5 PCDF Formation/Destruction Profiles for = 1.0 and a Gas
Phase Residence Time of 2.OS 31
6 Weight Percent (Normalized to Non-Decomposed Parent Peak) vs.
Temperature for Chloroform and Selected Decomposition
Products (cj> = 0.76, 2.OS Residence Time) 34
7 Weight Percent (Normalized to Non-Decomposed Parent Peak)
vs. Temperature for Pentachloroethane and Its Major
Decomposition Product Tetrachloroethylene (4 = 0.76,
2.OS Residence Time) 35
8 Possible Pathways for the Thermal Decomposition of Chloro-
form 38
9 Thermal Decomposition Profiles for PCP and TCP 39
VII
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PIC FORMATION UNDER PYROLYTIC
AND STARVED AIR CONDITIONS
INTRODUCTION
The University of Dayton Research Institute (UDRI) has addressed
various incineration issues in the first 18 months of the Cooperative
Agreement CR-810783-01-0 and has produced upwards of 15 publications/
presentations based on the several projects during that period. However,
the projects encompassing "PIC Formation Under Pyrolytic and Starved Air
Conditions" is emphasized in the following report.
The ultimate goal of incineration research is to understand the
process of incineration to the extent that one can accurately predict
incinerator emissions and how changing design and operational parameters
affect pollutant emission rates.
Emissions of hazardous organic compounds fall into two general cate-
gories, those compounds in the waste feed which are not totally destroyed
and those compounds formed from the partial degradation of the waste.
Designations for these classes have been borrowed from the regulatory
designations of Principal Organic Hazardous Constituents (POHCs) and Pro-
ducts of Incomplete Combustion (PICs). Since regulation of incineration
will always require some type of testing or monitoring of the actual in-
cinerator, a desirable product of research would be information that can be
used to reduce the testing burden and ensure that the proper emissions and
operating parameters are being monitored that will ensure environmentally
safe waste disposal. This has been the goal of the research program con-
ducted by UDRI.
The complexity of the incineration process, the differences in inciner-
ator designs, and the difficulties in monitoring changing operating con-
ditions makes the accurate prediction of absolute incineration performance
an essentially impossible task. A more reasonable goal is to be able to
predict the relative destruction efficiency of POHCs and the relative
emission rate of PICs for a given incinerator. This is a goal which is
consistent with the goal of reducing the need for incinerator testing,
since one could then simply conduct tests focusing on the least "inciner-
able" POHCs and the PICs of greatest yield as predicted by laboratory
testing and research. If these compounds are found to meet regulatory
requirements then presumably so would the other POHCs and PICs. Of course,
one 'must have sufficient knowledge of the effect of incineration parameters
on POHC and PIC emissions to correctly define the conditions for the labora-
1.
-------
tory and field studies and allow for subsequent changes in these conditions
on the incinerator. Laboratory and field testing under "worst" case con-
ditions would appear to be the best means of assuring continuing incinera-
tor compliance. Once initial compliance has been established, a method of
monitoring for continuing compliance is also necessary. This defines a.
second goal of our research program which is to identify appropriate species
or operating parameters for continuous compliance monitoring.
DEVELOPMENT OF AN INCINERATION MODEL
The first step in determining which incinerator parameters signifi-
cantly affect POHC and PIC emission is to develop a simple, qualitative
incineration model that can be used to determine major effects.
In determining the destruction efficiency of hazardous organic
materials by incineration, chemical reactions occuring in condensed
phases may effectively be neglected. This is true due to mass and heat
transfer considerations. Thus, we may primarily concern ourselves with
gas-phase chemistry although the nature of the passage of material from
condensed phase into the gas-phase by physical processes may be impor-
tant.
Once in the gas phase, there exists more than one mode of destruction
of the material and it is necessary to address the factors affecting these
destruction modes. Two modes are clearly evident and they may be designated
as direct flame and thermal (non-flame) decomposition.
Both flame mode and thermal decomposition studies indicate that any
known organic waste can be destroyed in an incinerator to greater than
99.99% destruction efficiency (DE) if it is operating under theoretically
optimum (Conditions (1-3). Thermal decomposition can be expected at less
than 1000C in flowing air at a mean residence time of 2.0 seconds. Flame
^destruction of waste droplets may occur in flames operating in excess of
850C.
Excursions, or fault modes, are probably the controlling phenomena
for incineration efficiency. Four parameters (atomization inefficiency,
mixing inefficiency, thermal failure, and quenching) have been identified
as failure modes in flames (2). Laboratory studies have shown that rela-
tively small excursions from ideality for these parameters can easily drop
measured flame destruction efficiencies from greater than 99.99% to 99% or
even less than 90% (three orders of magnitude). Non-flame upset parameters
can be conveniently classified in terms of distributions of oxygen, resi-
dence time, and temperature (1-4).
The key to understanding the significance of upset conditions is that
only a very small fraction of the total volume of the waste needs to ex-
perience these less than optimum conditions to result in significant devi-
ations from the targeted destruction efficiencies. To illustrate how
2.
-------
laboratory thermal decomposition testing relates to upset modes and can
potentially be used to predict observed emissions from full scale facili-
ties, let us examine a specific example.
Previous research has shown that the destruction kinetics of typical
hazardous organic compounds can be described satisfactorily using simple
pseudo-first order kinetics (1). Although different or more complex models
may be used, the actual model used is not important for the scope of this
discussion.
We will first examine the case of a simple one-stage combustor where a
waste feed mixture is fed directly into a turbulent flame and the hot gases
evolving from the flame pass on through a relatively long, high temperature
hold-up zone prior to exiting from the system. Representative reaction
conditions for the flame can be chosen as an average residence time of 0.1
second and a bulk flame temperature of 1700K. For the post-flame zone, we
may choose a mean residence time of 2.0s and a bulk gas-phase temperature
of HOOK. Although a range of residence times and temperatures are actual-
ly experienced by the individual molecules, the values chosen are typical
effective residence times and temperatures.
As mentioned in the previous paragraphs, several destruction failure
modes have been identified for the flame. In this model, we will assume
that only 1% of the waste feed avoids experiencing the bulk reaction con-
ditions in the flame. This might be caused by a reduced gas-phase resi-
dence time from an improperly operating nozzle or from experiencing a
reduced temperature as a result of being sealed in particulate matter. A
third cause might be reduced time at temperature from quenching by cold
gases or poor mixing with oxygen.
This one percent of the waste feed enters the post-flame zone. The
overall measured destruction efficiency at the stack is the weighted aver-
age of the destruction efficiencies of the flame and post-flame zones. The
results of these calculations for hazardous waste of a range of thermal
stabilities are shown in Table 1. From examination of the table, it is
apparent that each of the compounds is destroyed to essentially the same
efficiency in the flame, i.e., greater than 99.99%. In the post-flame
region, significant differences in thermal stability are observed.
From examination of the last column of the table, it is apparent that
the overall destruction efficiency parallels the destruction efficiency in
the post-flame region. The principal value of the overall DE is 99% in all
cases, with the variations in DE occurring to the right of the decimal.
The destruction achieved in the flame determines the principal value, while
the non-flame destruction efficiency determines the approach to four nines.
The overall destruction efficiencies quoted in the table are typical
of preliminary results reported for studies on full-scale incinerators.
The measured destruction efficiencies for essentially all full-scale sys-
tems have exceeded or approached 99.99% for most compounds. Variations
have been in the third, second, or in some cases, the first decimal place.
3.
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TABLE 1. CALCULATED DESTRUCTION EFFICIENCY FOR REPRESENTATIVE
HAZARDOUS ORGANICS
Calculated Destruction Efficiencies
DE
DE
DE
Compound
(s"1) (kcal/mole) (Flame) (Post-Flame) (Overall)
Acetonitrile
Benzene
Chloroform
Tetrachlorobenzene
Tetrachloroethylene
Trichlorobenzene
4
2
2
1
2
2
.7xl07
.8xl08
.9xl012
.9xl06
.6xl06
.2xl08
40
38
49
30
33
38
99
99
99
99
99
99
.999+
.999+
.999+
.999+
.999+
.999+
66.357
99
99
98
77
99
.999+
.999+
.556
.127
.968
99.
99.
99.
99.
99.
99.
664
999+
999+
986
771
999+
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A further observation has been that most Incinerators can achieve a
DE of 99.99% for essentially all waste feeds when operating optimally.
However, optimum operation cannot be attained on a continuous basis. If
an incinerator could be sampled on a continuous basis, one would probably
find that at least 90% of the hazardous organic emissions occur in the
fraction of time when the incinerator experiences an upset. Such upsets
could be loss of flame, an overload of waste feed, or a failure of a spray
nozzle. It is during these system upsets that a large percentage of the
feed material can escape flame mode destruction and the reaction conditions
in the post-flame zones can be degraded from their steady-state operating
values. Under upset conditions, the difference in waste incinerability may
be magnified, the non-flame zone destruction comes to even greater promi-
nence, and the performance of the incinerator fails to achieve four nines
for a greater number of components of the waste feed.
Poor mixing of waste and oxygen in the afterburner gives rise to a
certain fraction of the waste being subjected only to low oxygen condi-
tions. Numerous laboratory studies have shown that destruction of the feed
material is much slower under these conditions and PIC formation is en-
hanced. We again have the case where although most of the waste experi-
ences oxidizing conditions and is destroyed, the small fraction of the feed
experiencing the pyrolytic conditions may be responsible for the emission.
The observation in field and laboratory studies that most reaction products
are pyrolysis type products (e.g., benzene, toluene, naphthalene) tends to
confirm this hypothesis.
Although the conclusion that a subfraction of a fraction of the waste
feed is responsible for most hazardous organic emissions may be surprising
at first, the same process is generally responsible for emission of most
air pollutants. One is not really concerned with the major chemistry, such
as in a power plant which forms carbon dioxide and water; but instead the
minor reaction pathways which form sulfur dioxide, sulfuric acid, and
nitrogen oxides. These pathways are responsible for less than 0.1 to 1% of
the stack emissions but are the reactions of interest in pollutant forma-
tion.
The applicability of this qualitative model has recently been con-
firmed by a more complex model of hazardous waste incineration developed by
the Energy and Environmental Research Corporation (EERC) [5,6]. This model
includes considerations of furnace heat transfer, flow, mixing, injection,
tracking, and kinetics. UDRI pseudo-first order thermal decomposition
kinetics were used as inputs for the model. Thus far, modeling results for
three pilot-scale hazardous waste thermal destruction systems have been
reported. These systems are the Controlled Temperature Tower (CTT), the US
EPA's Combustion Research Facility's (CRF) rotary kiln system, and the
Acurex subscale boiler. The CTT was modeled under several modes of opera-
tion and failure modes including standard, cooled, insulated, backheated,
fast quench, and various droplet vaporization points. The CRF system was
modeled for varying loads, different excess air levels, and kiln or after-
burner flameout. The Acurex subscale boiler was modeled for various fuel
heating values, heat removal rates, excess air rates, waterwall/nonwater-
wall modes, various droplet vaporization points, and temperature profiles.
5.
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In each reported case the predicted relative destruction efficiencies
correlated almost perfectly with the values for 199.99(1) (temperature for
99.99% destruction at 1.0 sec. residence time) of the test compounds. For
the CTT, the agreement was essentially perfect for every case. For the six
test compounds modeled for the CRF, only methane exhibited a moderate
deviation from the behavior predicted by purely pseudo-first order post-
flame kinetics. For the Acurex boiler, of the eight compounds modeled,
only acetonitrile showed significant deviation (see Figure 1).
The excellent agreement between the ranking according to 199^99 (1)
and the EERC model are as predicted by our two-zone incineration model,
illustrating the importance of post-flame reaction kinetics. Although
quantitative predictions are available from the EERC model, accurate pre-
dictions for complex incineration systems will require many years of model
development and refinement. However, the significance of post-flame
chemistry in controlling relative POHC DEs has been clearly con-
firmed.
Thus, improvements of model accuracy can best be accomplished by more
refined post-flame kinetics. Detailed flame kinetics are of less value
since waste compounds subjected to the flame environment will essentially
be totally destroyed. Post-flame kinetics can be improved by addressing
the effect of varying oxygen levels and waste feed composition for mixtures.
Most importantly, the development of data on formation of PICs is essen-
tial.
Comparison of UDRI generated laboratory flow reactor (non-flame) data
with laboratory flame-mode data, illustrates the similarity in the reaction
mechanisms for both zones, i.e., a free—radical degradation mechanism.
These results suggest that many PICs can be formed from simple feed mix-
tures and the POHC DEs and PIC yields may be very dependent upon the waste
composition and oxygen level of the reaction atmosphere. A detailed com-
parison of field and laboratory studies further indicates the importance of
PIC emissions in determining incinerator performance and how laboratory data
can be used to predict PIC formation.
COMPARISON OF FLAME AND THERMAL DECOMPOSITION RESULTS
With our flow reactor systems at UDRI, we have generated thermal
decomposition data on nearly 100 different hazardous organic compounds.
The experimental difficulties in generating similar flame data has resulted
in a very limited data base for comparison. However, a recently reported
study has furnished some data for comparison (7).
Thirteen compounds of interest to hazardous waste incineration were com-
busted in a laboratory diffusion flame. The relative burning rates of these
compounds were determined based on their flame front velocities. A listing
of these compounds and their rankings based on non-flame thermal degradation
studies is shown in Table 2. For the six compounds for which thermal decom-
position data is available, the non-flame rankings are indicated. Further-
more, the flame-mode rankings for the remaining compounds are basically as
one would predict for the thermal degradation of untested compounds.
6.
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r\J
r\J
o
ro
_c
o
(V)
en
-10
CO
LO
CO
CO
en
n
o
C.J
o
o
UJ
no
O
i
CD
LOG (FRflCTIQN UNREflClEO)
1,2,3,4-tetrachlorobeniene
ethane
carbon tetrachloride O
acetonitrile O
acrylonlt rile
tetrachloroethylene
Figure 1. Comparison of EERC model prediction with predictions of
UDRI two-zone incineration model for the Acurex Subscale
Boiler. The results indicate the control of overall
relative destruction efficiencies of test compounds by
post-flame chemical kinetics.
7-
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TABLE 2. COMPARISON OF FLAME AND NON-FLAME (THERMAL) STABILITY
RANKING OF VARIOUS TEST COMPOUNDS
Compound
Relative Burning UDRI Thermal
jlate (Flame)[7] Stability (Non-Flame) Ranking
1,2, 4-Trichlorobenzene
m-Dichlorobenzene
o-Dichlorobenzene
1 , 6-Dichlor ohexane
Chlorobenzene
1-Chlor ohexane
Benzene
Dichloroisopropylether
1 , 2-Dichloropropane
n-Hexane
1,1, 1-Trichloroethane
Epichlorohydrin
1 , 2-Dichloroethane
10.9
13.5
12.6
25.6
28.4
34.7
60.0
87
219
736
844
1142
1500
ll
2
3
4
5
6
-"•Ranking of 1 is most stable
8.
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In a second flame experiment, various combinations of dichlorobenzene,
benzene, and hydrogen chloride (HC1) were combusted at 40% of stoichio-
metric air. The identity and yield of these products were found to be
essentially invariant as long as the ratios of chlorine, hydrogen, carbon,
and oxygen were constant. The observed PICs are listed in Table 3.
Recently completed was a study of PIC formation from the thermal de-
composition of a mixture of carbon tetrachloride, toluene, chlorobenzene,
trichloroethylene, and Freon 113 (4). Those PICs resulting from this
mixture that were also found in the flame combustion of chlorobenzene are
also noted in Table 3.
The agreements between relative POHC stability and PIC production for
flame and non-flame studies is striking, particularly for PIC production.
Most of the differences in observed PICs are the lack of higher chlorinated
compounds from the thermal degradation studies. This is probably due to the
fact that the chlorine content of the thermal degradation mixtures was only
6 mole percent while it was 50 mole percent for the flame study, the latter
favoring formation of higher chlorinated species. The only other real
discrepancy was the lack of formation of biphenylene and chloroacetylene in
the thermal decomposition study, although the presence of chloroacetylene
was suspected from Gas Chromatograph (GC) analysis but could not be con-
firmed by Gas Chromatograph-Mass Spectometer (GC/MS) due to experimental
limitations.
The similarity in results obviously suggests that similar reactions
are occurring, i.e., a gas-phase free-radical mechanism. It is well docu-
mented that hydrocarbon reactions proceed by mechanisms based primarily on
attack of molecular species at low temperature (3,8). At temperatures
between 250 and 450C, a peroxide-dominated mechanism appears to be active.
Above 450C, transition to a free-radical mechanism usually occurs.
The "knee" in the thermal decomposition profiles generated on the IDAS
(Thermal Decomposition Analytical System) and TDU-GC (Thermal Decomposition
Unit-Gas Chromatograph) denotes the region of transition from a relatively
slow to a much faster reaction mechanism, e.g., transition from a peroxide
to a free-radical mechanism (see Figure 2 for example). Detailed kinetic
calculations for propane indicate a rapid increase in the concentration of
the free-radical pool, predominantly OH, 0, and H, in the temperature range
of the knee (see Figure 2). We have also performed pseudo-equilibrium
calculations for other more complex molecules, which also demonstrate a
rapid increase in radical concentration in this region. This temperature
range of 500C to 700C is also appropriate for unimolecular decomposition
reactions to become significant.
Some resarchers have questioned the contributions of surface reactions
or "wall effects" on flow reactor studies. We have compared the results of
the extended gas-phase kinetic model for propane oxidation with results
from the TDU-GC. This kinetic model has previously been compared to re-
sults from shock-tube studies and shown to be in excellent agreement (9).
As can be seen from the graph In Figure 3, the agreement between this
purely gas-phase kinetics model and our flow reactor study is excellent,
9.
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TABLE 3. PICs FOUND IN DIFFUSION FLAME COMBUSTION OF CHLOROBENZENE,
BENZENE, AND HC1 MIXTURE AND THERMAL DECOMPOSITION OF A MIXTURE
OF CARBON TETRACHLORIDE, TOLUENE, CHLOROBENZENE,
TRICHLOROETHYLENE, AND FREON 113
PICs From:
Flame-Mode Combustion
Thermal Decomposition
Mixture 1
Mixture 2
Anthracene
Benzofuran
Biphenyl
Biphenylene or Acenaphthalene
Chloroace tylene
Chloroanthracene
Chlorobenzene
Chlorobiphenyl
Chlorobiphenylene
Chloronaphthalene
Chlorophenylacetylene
Chlorostyrene
Chlorotoluene
Dichloroanthracene
Dichlorobenzene
Dichlorobiphenyl
Dichloronaphthalene
Dichloromethylstyrene
Dichlorostyrene
Dichloroacetylene
Dibenzofuran
Fluoroanthene
Methylnaphthalene
Naphthalene (or Azulene)
Phenylacetylene
Phenol
Phenylnaphthalene
Pyrene
Styrene
Tetrachloribiphenyl
Trichlorobiphenyl
Trichlorobenzene
Toluene
x
x
x
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
10.
-------
-3
-5
1/3
LJ
_J
O
21
CD
O
-9
-11
13
100
D -
A - CK
-f- - o
800
900 1000
TEHPERRTURE IK )
1100
1200
Figure 2. Concentration vs. temperature for propane oxidation
in air at a gas-phase residence time of 2.0 seconds.
-------
NJ
CD
ct
T.
UJ
LJ
cr.
CD
o
-3
-M
Experimental
Computer Prediction
500
600 "700 800
TEMPERRTURE 10
300
1000
Figure 3. Comparison of flow reactor generated thermal decomposition
profile versus predicted results from computer-modeled gas-
phase free-radical mechanism for propane oxidation.
-------
especially in predicting the 199.99(2). The slightly faster rate of
decomposition predicted by the model in the knee of the curve is likely
due to inaccuracies in the model in accounting for reactions involving
peroxides. This is not unexpected since the model was developed for a
higher temperature region, where free-radical mechanisms dominate. The
agreement between the flow reactor study and the gas-phase free-radical
kinetic model indicates that the mechanism of propane degradation in the
TDU-GC is truly a gas-phase, free-radical pathway at higher tempera-
tures .
There is clearly a demonstrated correlation between flame-mode
and non-flame flow reactor POHC and PIC data. This is due to free-
radical, decomposition reactions being operational in both instances.
The marked agreement in PIC identities, even for dissimilar feed mix-
tures, further illustrates the importance of the free-radical mechanism.
The majority of the products are due to recombination of free-radical
fragments or radical addition to aromatic substrates. The lack of
oxygen-containing products even under oxidative conditions suggests that
abstraction of H by OH and 0 dominate over addition reactions. Alter-
nately, addition products such as phenols may be very reactive and rapidly
undergo further degradation.
The main experimental difference in the flow reactor and flame studies
is the higher temperature in the flame which accelerates the overall reac-
tion rate, but apparently does not result in a change of mechanism. Thus,
relative POHC DEs and PIC identities are very similar for both cases.
CORRELATION OF LABORATORY PREDICTIONS AND FIELD RESULTS
Of course the ultimate test of the study of the utility of laboratory
research is the degree of agreement between experimental or theoretical
predictions and actual field results.
It was felt that a comparison of various proposed scales of inciner-
ability with recently available field test results would be useful. If
areas of agreement or disagreement could be identified, then consider-
able guidance could be gained for the direction of future research. This
study, which required considerable time and effort, was quite successful.
A summary of the results are reported in the following paragraphs.
Six methods of ranking the relative incinerability of hazardous
organic compounds have been previously proposed (1,2,4,7,10-14).
" Heat of Combustion (AHc/g)
* Auto-Ignition Temperature (AIT)
* Theoretical Flame-Mode Kinetics (TFMK)
" Experimental Flame Failure Modes (EFFM)
* Ignition Delay Time (IDT)
* Gas-Phase Thermal Stability [Tgg(2) (99% destruction at 2 seconds
residence time), TSH102 (High oxygen concentration), TSLo02 (Low
oxygen concentration)]
13.
-------
The gas-phase thermal stability method has been proposed based on the
results of flow reactor studies- One method of ranking that has been pre-
viously proposed is based on laboratory-determined thermal stability speci-
fied by the temperature required for 99% or 99.99% destruction at 2.0 seconds
reactor residence time in an atmosphere of flowing air [Tgg (2)] (1,14).
This scale was originally developed for pure compounds in flowing air. How-
ever, recently generated data have shown that relative stability varies as
a function of the composition of the waste feed and oxygen concentration
[4]. This has led to modification of the rankings to account for the thermal
stability of individual POHCs fed as a mixture in both an oxygen-rich
(TSHi02) and an oxygen deficient (TSLo02) environment. These three hier-
archies along with the predictions of the other five, have been applied to
predicting results of studies described in the following paragraphs.
Intercomparison of field and laboratory data should be conducted with
extreme caution. While laboratory studies are usually conducted under
precisely controlled well-defined conditions, field studies generally are
not (2,4, 14,15). Upon examination of field study reports, it is obvious
that the quantitative intercomparison of the performance of the facilities
with respect to operational parameters is not viable. However, relative
ORE data for POHCs within a waste feed at a given facility can be analyzed
with proper data validation guidelines. To ensure a valid comparison of
predicted and observed results, the following data validation and reduction
criteria were used:
* only compare POHC DREs (Destruction and Removal Efficiencies) for
a given incinerator
* only compare POHC DREs when they are fed to the system
at a common point
* use averages of DREs when no significant run-to-run variation
in relative POHC ORE is observed
only use data where the majority of the POHC DREs are less than
99.995%
include data from non-concurrently fed POHCs if other key para-
meters are held constant
conduct the correlation of observed field vs. predicted results on
a rank/order basis with a minimum of four data points.
The observed incinerability rankings of the test compounds at each
source were compared with the prediction of each proposed hierarchy using a
rank/order correlation approach (16). This method was judged to be superi-
or to a linear regression analysis since the latter judges the agreement of
the data with a best-fit straight line while the former simply determines
if a statistically significant relationship exists between the observed and
predicted rankings. The rank-correlation coefficient, rs, was used to
judge if a correlation existed at the 90% confidence level for a number of
test compounds, N.
14.
-------
TABLE 4. RESULTS OF STATISTICAL ANALYSES OF OBSERVED VERSUS
PREDICTED THERMAL STABILITY RANKINGS
Study
A
B
C
D
E
F
G
H
I
J
// Of
// Of
H
-0.
-0.
-0.
-0.
0.
0.
0.
-0.
-0.
-0.
Successes
Failures
% Success*
r/g
300/51
190/8
500/5
100/9
589/7*
343/15
400/4
333/7
077/10
291/10
1
9
10
AIT
-0
0
-0
0
0
0
-0
0
.200/4
.200/4
—
.060/
.428/6
.571/7*
—
.457/6
.262/8
.147/8
1
8
11
TFMK
—
—
—
—
-0.100/5
—
—
0.600/4
0.800/4*
1
2
33
Helrarchy
EFFM
—
—
—
—
—
—
—
0.600/4
0.600/4
0
2
0
IDT
—
—
—
—
—
—
-0.300/4
-0.100/5
-0.100/5
0
3
0
T99(2)
-0.057/6
0.500/5
-0.800/4
-0.300/5
-0.425/9
0.800/4*
-0.161/7
-0.217/9
-0.202/9
1
8
11
TSH102
0.
0.
0.
0.
0.
0.
0.
-0.
-0.
-0.
000/5
533/10*
400/5
386/9
425/8
041/15
800/4*
036
318/11
114/11
2
8
20
TSLoO?
0.900/5*
0.529/10*
0.600/5
0.493/9*
0.429/8
0.073/15
0.900/4*
0.655/8*
0.536/11*
0.523/11*
7
3
70
Correlation was statistically significant at the 90% confidence level
-------
Results of this analysis are summarized in Table 4 for ten studies
judged to meet the data validation criteria (15,17-22). Of the eight
proposed ranking methods, only£Hc/g, AIT, T99 (2), TSHi02, and TSLo02
had a sufficient data base to make predictions for a significant number of
sources. Of these, only the experimentally predicted order under low oxy-
gen conditions, TSLo02 met with a reasonable success, i.e., 70%. The other
four methods only correlated with field observations 10-20% of the time.
More importantly, it was apparent after detailed examination of the indi-
vidual data plots that certain trends were occuring that could not be ex-
plained by simple application of the ranking methods. In particular, the
compounds that deviated in stability from predictions of the TSLo02 hier-
archy were often the same for the various studies. In many cases, this
deviation could be explained using other available information.
The paragraphs that follow discuss the data from the specific sources
in a manner that demonstrates how the field-scale observations can be re-
liably predicted with modifications to the TSLo02 hierarchy.
Study A. The test compounds followed the order of stability: toluene
> methyl ethyl ketone > 1,1,1-trichloroethane > Freon 113. The observed
order was the same as predicted by TSLo02 except for reversal of 1,1,1-
trichloroethane and Freon 113. In actuality, both of these compounds are
predicted to be relatively very fragile under low 02 conditions, and the
predicted rankings could have been easily reversed. The predicted rankings
as pure compounds in flowing air or in a mixture of high 02 were quite
different and did not correlate with the observations. This is consistent
with the low 02 levels noted in the field study reports.
Study B. The predictions of the TSLo02 method and the observed sta-
bilities agreed quite well with only a few exceptions. Chlorobenzene and
dichlorobenzene were observed to be reversed from the predicted order.
This is readily explained by the observation that significant levels of
chlorobenzene were detected in the scrubber make-up waste and could be
stripped out and into the stack gases. This would result in an apparent
chlorobenzene DRE lower than actually achieved by thermal destruction and
account for the disparity with the TSLo02- A major deviation was observed
for bis-2-ethyl-hexyl phthalate, which appeared more stable than predicted.
Although the predicted stability of phthalate is questionable due to lack
of laboratory data, phthalates are ubiquitous and detected levels may be
due to out-gassing of plastics in the system and not from undecomposed
feed. High levels of phthalates are commonly found in ambient environments
and for this reason should probably be excluded from all data sets (23).
Bis-2-ethyl-hexyl phthalate was found at high levels in the scrubber water.
Stripping from the water by the effluent gas could account for its observed
emissions.
Two other major outliers were aniline and trichloroethylene. These
compounds were significantly more fragile than predicted. Neither aniline
nor trichloroethylene would be expected to be a major thermal reaction
product from this test sample. This is in contrast to chloroform, carbon
tetrachloride, and phosgene, which unexpectedly surpassed aniline and tri-
chloroethylene in apparent stability. The apparent thermal stabilities of
16.
-------
carbon tetrachloride, chloroform, and phosgene may be due to their forma-
tion as products from other components of the waste as opposed to their
stability as POHCs. Furthermore, these compounds are quite volatile and
could be present in the ambient air as fugitive emissions. Either forma-
tion as a product or as an ambient air contaminant could explain the un-
expected reversal in thermal stability.
Study C. The waste was spiked with theroretically stable POHCs which
had an observed order of stability: acetonitrile > benzene > trichloro-
ethylene > chlorobenzene > carbon tetrachloride. This was as expected
except for benzene which was considerably more stable than predicted based
purely on thermal stability. It is possible that benzene was formed as a
product from chlorobenzene (or the auxiliary fuel). This hypothesis is
supported by two independent observations. First, a simulated waste stream
very close in composition to the actual waste was subjected to thermal
decomposition in the laboratory. Under low 02 conditions, benzene would
actually have been predicted as a reaction product resulting in a low
apparent DRE for benzene as a POHC. Secondly, the waste stream was also
fed to the full-scale incinerator without benzene in the feed. Roughly
equivalent levels of benzene were found in the stack effluent, thus con-
firming the hypothesis that its emission was due to sources other than
residual POHC from the waste feed.
Study D. Field test results were in basic agreement with prediction
for low oxygen conditions. The exceptions were phthalates, which were
discussed previously, and tetrachloroethylene, which was predicted to be
the most stable component but was observed to be less stable than benzene,
toluene, naphthalene, carbon tetrachloride, and methyl ethyl ketone.
Laboratory studies have demonstrated or strongly suggested that each of
these compounds can be a significant reaction product from various pre-
cursors (A,17,24). Dichloromethane and chloroform were also found in the
source emissions, suggesting the formation of chlorinated methanes as
thermal reaction products. Thus, the apparently greater stability of these
compounds than tetrachloroethylene may be due to their formation as pro-
ducts in the incineration process.
Study E. A. correlation was observed between predicted and observed
rankings but there was significant scatter. The fragile nature of 1,1,2-
trichloroethane, 1,1,1-trichloroethane, and methyl ethyl ketone were
correctly predicted (DREs all at 99.999% or greater). The observed sta-
bility of these three compounds were permuted from their predicted value
contributing to the poor correlation coefficient.
Methylene chloride, and to some extent, carbon tetrachloride appeared
more stable than predicted. It should be noted that high levels of other
halogenated methanes were found in the stack effluent indicating a source of
carbon tetrachloride and methylene chloride emissions other than residual
POHC (i.e., either incomplete combustion products or a result of stripping
of these volatiles from the scrubber water). The most unexpected behavior
was exhibited by tetrachloroethylene, which was predicted to be the most
stable POHC but was observed to be very fragile.
17.
-------
Study F. Although this facility exhibited the lowest correlation of
predicted and observed emissions, the results are extremely informative.
Two distinct groups were evident, one consisting of primarily chlorinated
aromatics and olefins, and a second consisting of primarily halogenated
aliphatics along with bis-2-ethyl-hexyl phthalate and hexachlorocyclobuta-
diene.
Methylene chloride and chloroform were found in the scrubber make-up
water which could readily account for their observed emission levels. The
other halogenated compounds (in the second group) are also very volatile
and have been found in the ambient air surrounding such facilities (pre-
sumably due to fugitive emissions) (15). As previously discussed, phthal-
ate emissions are consistently high at most sources. Finally, there is
some question concerning the accuracy of the predicted ranking for hexa-
chlorocyclopentadiene due to lack of laboratory data. Its low stability
prediction was based on possible strain of the five numbered ring structure,
but could well be in error. If the six compounds in question are eliminated
from the data set and a correlation is performed with the remaining nine
compounds, a statistically significant rank correlation coefficient of 0.89
is obtained.
Study G. The observed stability is as predicted under low Q£ con-
ditions except for carbon tetrachloride which appeared more stable than
chlorobenzene. This is not surprising since chloroform, which was also
present in the mixture of carbon tetrachloride, has been established as a
thermal reaction product of chloroform by laboratory studies.
Study H. The POHCs in this test essentially followed the predicted
order except for tetrachloroethylene and trichloroethylene, which appeared
less stable than benzene and toluene, contrary to predictions. This type
of result has been observed in other studies and is ascribed to the propen-
sity for formation of toluene and benzene as reaction products. It is also
interesting to note that carbon tetrachloride emissions were also quite
high (average of 173 g/s) which tends to confirm its prevalence as a reac-
tion product from incineration of chlorinated wastes.
Study I. The observed POHC stabilities followed predicted trends
except for benzene, carbon tetrachloride, and 1,2-dichloroethane. Benzene
and carbon tetrachloride are again expected to be products of thermal
degradation (primarily from chlorobenzene/toluene and methylene chloride
respectively). The 1,2-dichloroethane is a volatile compound that is
commonly found in scrubber water or in the ambient air as a fugitive
emission, factors which could account for its elevated emission level (15).
The emission level of 1,1,1-trichloroethane, also sometimes found as a
fugitive emission or in scrubber makeup water, was also slightly elevated.
Study J. The observed deviations from the predicted rankings were
similar to those observed for the previous nine cases. Benzene, toluene,
and carbon tetrachloride emissions were higher than expected, an observa-
tion which is attributed primarily to product formation.
18.
-------
Discussion of Laboratory/Field Comparisons
The degree of success, as indicated by the results reported in Table
4 and the subsequent discussions of predicting the relative thermal
stabilities of hazardous organics through laboratory flow reactor studies
may appear somewhat surprising considering the complexity of the incinera-
tion process. However, the development of the two-zone incineration model,
which was discussed earlier illustrates how post-flame chemistry controls
incinerator emissions and is sufficient to explain general agreement between
laboratory-based predictions and field results. However, none of the
previously presented incinerability hierarchies directly address the issue
of PIC emissions as they are only concerned with thermal stability of the
POHCs in the feed material.
PICs resulting from the incineration of hazardous waste are not
currently regulated by the USEPA. However, the previously discussed field
data and results of other laboratory, pilot, and full-scale testing pro-
grams have shown that toxic products can be formed and are emitted from
incinerators (3,4,17-24). Many observed PICs are also potential POHCs,
consequently, it is entirely possible that a PIC may also be a POHC in the
original mixture. Three documented examples are: the formation of carbon
tetrachloride from chloroform, and from hexachlorobenzene from hexachloro-
cyclopentadiene, and benzene from chlorobenzene or toluene (4,17,24).
In the previous discussion of field results many such cases were
identified. This gave rise to low apparent DRE for the POHC. Since this
effect would be more important when the input concentration of the POHC is
low, the result would be an apparent dependence of DRE on input POHC con-
centration (i.e., the higher the input concentration, the greater the
apparent DRE). The true effect, however, is that the emission concentra-
tion is constant, since the emissions are probably due to product formation
from other waste components.
The observation of an apparent DRE dependence on concentration has
been made for hazardous waste incinerators and attributed to greater than
first order kinetics for indivudal POHCs (15). While such an effect could
be possible for combustion of a pure compound, it is highly improbable when
the POHC is only a small portion of a complex waste. The reaction chemistry
is determined by the overall waste and fuel composition as opposed to pure
compound kinetics. Volatile POHCs in the ambient air as a result of fugi-
tive emissions, volatile POHCs stripped from scrubber waters, and out-gas-
ing of phthalate-containing materials would also give rise to apparent
concentration dependencies since their emission levels would be constant
while the POHC input rate varies. Specifically; it has been shown earlier
that most of the observed deviations from laboratory predicted rankings of
incinerability may be attributed to product formation or "contamination" of
the stack effluent by volatile POHCs that did not pass through the destruc-
tion zones of the incinerator.
As if predicting POHC stability were not difficult enough, we must now
predict product formation. This can be accomplished perhaps by laboratory
thermal decomposition testing of the actual waste stream to be incinerated,
19.
-------
or a very close simulation. As indicated by the agreement of laboratory
predictions based on low C>2 conditions, these studies should be conducted
under pyrolytic conditions.
An excellent example of this approach is Study C. The incinerability
ranking based purely on POHC ORE was successful for four out of the five con-
stituents of the waste, only benzene being apparently more stable than the
other components. However, laboratory testing was performed on a very similar
waste stream and under pyrolytic conditions; significant levels of benzene
were were observed. Thus, when product formation is included, laboratory
testing of a simulated waste stream could correctly predict the observed
field results.
Summary And Conclusions Regarding Laboratory/Field Comparisons
The results of comparison of ten field studies with thermal stability
predictions indicates that no ranking based on pure compound properties can
provide an appropriate scale of incinerability. However, a ranking based on
predicted POHC stability in complex mixtures under low oxygen conditions gave
a statistically significant correlation with field results in seven of ten
cases. More importantly, analysis of results gives strong reason to believe
that formation of "POHCs" in the incineration process as PICs may be respon-
sible for their observed DREs.
Pending further confirmatory comparisons with field results, the
following conclusions are proposed.
• Measured POHC DREs and relative stabilities of all but the most
stable compounds are due to formation as products from other com-
ponents of the waste fuel or feed.
* Only DREs for very stable POHCs, or POHCs difficult to form as
reaction products (e.g., acetonitrile), are expected to be unaffec-
ted by PIC formation and these stabilities are predictable from
pure compound thermal decomposition kinetics.
The stack emissions and observed DREs of the very volatile com-
pounds (e.g., methylene chloride, chloroform, di- and trichloro-
ethanes) may be dominated by fugitive emissions in the ambient air
or stripping of these compounds from contaminated scrubber water.
Thermal decomposition, not in-flame destruction determines relative
POHC DREs and the identity and yield of products of incomplete com-
bustion.
* Pyrolytic conditions in the incinerator are responsible for most
emissions and control the relative DREs of POHCs and the formation
of products.
Predictions from laboratory thermal decomposition testing of
pure compounds and mixtures can be effectively used to predict
relative POHC DREs.
20.
-------
Laboratory testing under pyrolytic conditions on actual waste
streams or closely simulated waste streams is an effective
and reliable method for predicting relative POHC stabilities
and PIC emissions.
EXPANSION OF DATA BASE ON POHC STABILITY AND PIC FORMATION FOR PURE
COMPOUNDS AND MIXTURES
The success in predicting the results of field studies from labora-
tory experimentation shows the utility of the laboratory approach but also
points out the need for a larger data base from which to predict the effect
of changing reaction atmosphere and waste composition.
The results of four early experimental studies are detailed in the
following paragraphs.
Thermal Decomposition of "CRF Soup - 1"*
In our most ambitious laboratory study to date, the thermal
degradation of a mixture of five hazardous organic compounds under a
variety of conditions was investigated. The mixture was studied in three
reaction atmospheres: oxygen-starved, stoichiometric oxygen, and oxygen-
rich. The behavior of the components in the mixture was compared to their
behavior when tested as pure compounds and the thermal reaction products
were identified. Thermal decomposition behavior was analyzed and related
to elementary chemical reaction kinetics.
The observed thermal stabilities for the test compounds for each
experimental condition are summarized in Table 5. As can be seen from
these results, considerable differences in absolute and relative thermal
stabilities were observed as a function of both oxygen content (specified
as the equivalence ratio,
-------
TABLE 5. SUMMARY OF THERMAL DECOMPOSITION TESTING FOR
COMPONENTS OF HAZARDOUS WASTE MIXTURE #1
T99 (2) ("O
T99 (2) (°C) for HWM-1 Pure Compounds
POHC A Hr/g j>-0.06 <|)=1.0 Pyrolysis
Freon 0.11
Carbon tetrachlori.de 0.24
Trichloroethylene 1.74
Chlorobenzene 6.60
Toluene 10.14
770
670
730
730
670
780
680
780
800
750
780
680
920
>1000
820
780
750
800
900
820
780
750
780
700
680
22.
-------
measured thermal stabilities will also vary with changing reaction atmos-
sphere. The lower concentration of H atoms (and somewhat lower reactivity
versus OH and 0) results in slower destruction rates for the three aromatic
compounds at reduced oxygen levels, while Freon 113 and carbon tetrachlor-
ide are relatively unaffected. For these reasons, relative POHC thermal
stabilities are observed to change as a function of .
Benzaldehydes, phenols, and benzofurans were the only observed oxidation
products under oxidative or pyrolytic conditions while numerous complex
pyrolysis type products were observed (see Table 6). This indicates that
most products result from recombination of radical fragments and OH and 0
addition products are not significant. The lack of addition products
suggests that OH and 0 may be more likely to participate in abstraction
reactions at high temperatures or that the intermediate addition products
are not very stable. This is clearly an area for further research.
In that same study, the thermal degradation of carbon tetrachloride and
Freon 113 were observed to be independent of the oxygen content of the re-
action atmosphere, while trichloroethylene, monochlorobenzene, and toluene
decomposed more readily as the oxygen concentration was increased (see
Figure 4 for example). This behavior is predictable based on chemical
kinetic considerations as previously discussed. It is also interesting to
note that Freon 113 (a previously proposed tracer) was not observed to be
very stable. The relatively fragile nature of Freon 113 has recently been
confirmed by pilot and field studies [30,31].
Formation of PCDFs and other PICs from PCBs
The thermal degradation of a single PCB isomer was conducted under
four reaction atmospheres at a constant gas-phase residence time of 2.0
seconds. The isomer selected for study was 2,3 ' ,4,4',5-pentachloro-
biphenyl (2,3 ' ,4,4 ' ,5-PCB). The oxygen availability in the reaction atmo-
sphere was again described using the equivalence ratio . The values of $
used in this study were 3.0, 1.0, 0.2, and 0.05 which range from oxygen
starved to very oxygen rich conditions as the values of become progres-
sively smaller. Thermal degradation experiments were conducted at various
temperatures ranging from 500-1000C.
Table 7 lists the major thermal reaction products tentatively iden-
tified for the thermal degradation of 2,3',4,4',5-PCB. A variety of pyro-
lysis and partial oxidation products were formed, with polychlorinated
dibenzofurans (PCDF) congeners representing the majority of the oxidative
products. Significant quantities of partially dechlorinated biphenyl
congeners were formed along with dichlorobenzenes and trichlorobenzenes.
Tetrachlorobiphenylene isomers were also observed. These are of particular
interest due to their suspected toxicity. The formation of trichloronaph-
thalene is important because of its apparent thermal stability. At 1000C
for |> = 1-0, the reaction product tentatively identified as tetrachloro-
naphthalene exceeded the concentration of the remaining parent PCB. As one
might expect, the yield of pyrolysis products decreased with increasing
oxygen levels. However, the increase in PCDF concentration with increase in
oxygen concentration was far more striking.
23.
-------
TABLE 6. REACTION PRODUCTS OBSERVED FROM
THE THERMAL DECOMPOSITION OF CRF SOUP-1
Formula
CHC13
C2H3C1F2
C2H2C12
C2C13F
C2C14
^-*4 4 2
C^HA
C6H6
C6H60
C6H5F
C6H5C10
C6H4C12
C6H4C12
C7H80
C7H7C1
C7Hg02
C7H60
C8H].o
C8H8
C8H7C1
C8H6
C8H6C12
C8H6C1F
C8H6F2
C8H60
C8H5C1
C8H5C13
C8H5C10
C8H5F3
C9Hg
C9H8C12
C9H80
C9H7C13
C9H7C10
C9H60
C10H8
Identification =0.06 <|>=1.0
Tri chlor ome thane
Chlorodifluoroethane
1 , 1-Dichloroethene
Trichlorof luoroethene
Tetrachloroethene
Dichlorobutadiene
Benzene
1,5-Hexadiyne
1 , 5-Hexadi en-3-yne
Phenol
Fluorobenzene
Chlorophenol
Dichlorohexadiyne
Dichlorohexadiene-yne
Dichlorobenzene
Methylphenol
Chloromethylbenzene
Hydroxy-benzaldehyde
Benzodioxol
Benzaldehyde
Ethylbenzene
Ethenylbenzene (Styrene)
Chloroethenylbenzene
Ethynylbenzene
Dichloro-ethenylbenzene
Chloroethenyl-chlorobenzene
Di Chloroethenylbenzene
Chloro-f luoroethenyl-benzene
Difluoro-ethenylbenzene
Benzof uran
Chloro-ethenylbenzene
Trichloroethenylbenzene
Chlorobenzofuran
?
IH-indene
Dichloro-propenylbenzene
Dichloropropylbenzene
Chlor opropenylchlorobenzene
Phenyl-propenal
?
Chi orome thy Ibenzof uran
Phenylpropynone
Azulene
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Pyrolysis
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Naphthalene
Methylene-lH-indene
24.
-------
TABLE 6. - Continued
Formula
Identification
ij)=0.06 «)>=1.0 Pyrolysis
C10H8C1F
C10H7C1
C10H6C12
C10H5C13
C11H10
C11H10
C11H10
C13H802
C14H14
Cl4H12
C14H12
C14H10
C14H100
C14H9F
C15H2
C16H12
C16H12
Chloronaphthalene
Dichloronaphthalene x
Trichloronaphthalene x
1-Methyl-naphthalene
2-Methyl-naphthalene
Methyl-naphthalene
Biphenyl
Dibenzofuran x
1,1-Methylene(bis)-benzene
9H-Fluorene
Diphenylmethanone x
9H-Xanthen-9-one x
1,!'-(!,2-ethanediyl)(bis)-
benzene x
MethyIfluoroene
1,!'-(!,2-ethenediyl)(bis)-
(E)-benzene
Dihydrophenanthrene x
1,!'-(!,2-ethynediyl)(bis)-
(z)-benzene
1,!'-(!,2-ethynediyl)(bis)-
benzene x
Phenanthrene
9-Methylene-9H-fluoroene
Anthracenone x
Penanthrenol
Fluoro-l,l'-(12,-ethyne-
diyl)(bis)-benzene
Fluorophenanthrene
Fluoromethylene-9H-fluoroene
7
Methyl-anthracene
Methyl-phenanthrene
2-Phenyl-lH-indene
9-Ethylidene-9H-fluoroene
1,4-Dihydro-l,4-ethenoanthracene
1-Phenyl-naphthalene
5-Methylene-5H-dibenzo[a,d] cyclo-
heptene
2-Phenyl-naphthalene
Fluorophenylnaphthalene
Fluoro-5-me thylene-5H-dibenzo[a, d ]-
cycloheptene
Fluoro-1,4-dihydro-l,4-etheno-
anthracene
x
x
x
X
X
X
X
X
X
X
X
X
X
x
x
x
25.
-------
TABLE 6. - Continued
Formula Identification £=0.06 <|)=1.0 Pyrolysis
^16^11*" Fluorophenylnaphthalene
C16H10 Pyrene x
Fluoroanthene
C16H10C1F ? x
Fluoropyrene x
Fluorofluoroanthene
HH-Benzo[a]fluorene x
HH-Benzo [b]f luorene
26.
-------
100
CD
LU
10
o.i
LU
0.01
TOLUENE
' * 1.0
° PYROLYSIS
0 200 400 600 800 1000
TEMPERATURE (°C)
100
CD
LU
0
S2 O.I
LU
0.01
FREON 113
= 0.66)
and stoichiometric air (([> = 1.0), and
absolute pyrolytic conditions for gas-
phase residence times (tr) of 2.0 seconds
27.
-------
TABLE 7. MAJOR REACTION PRODUCTS TENTATIVELY IDENTIFIED FROM
THE THERMAL DEGRADATION OF 2,3',4,4',5-PENTACHLOROBIPHENYL
Number of
Product Class Major Peaks
Tetrachlorodibenzofurans 2
Trichlorodibenzofurans 2
Pentachlorodibenzofurans 1
Tetrachlorobiphenyls 5
Trichlorobiphenyl 1
Trichlorobenzene 1
Dichlorobenzene 1
Trichloronaphthalene 1
Tetrachloronaphthalene 1
Trichlorophenylethyne 2
Dichlorophenylethyne 1
Tetrachlorobiphenylenes 2
C9H8OC1 1
C10H3C13 1
28.
-------
Table 8 presents the yields of observed PCDFs at various equivalence
ratios. As the oxygen concentration increased by a factor of 60, the yield
of total PCDFs increased by a factor of 7. The percentage of total PCDFs
identified as tetra isomers ranged from 62-72%. Thermal formation/
destruction profiles for observed PCDFs for = 1.0 are depicted in Figure
As can be seen from the data in Figure 5 the degradation rate of
2,3',4,4',5-PCB rapidly increases above approximately 750C. This is in
the region where one would expect a transition from a peroxide-dominated
reaction mechanism to a free-radical mechanism. Pseudo-equilibrium calcu-
lations of the concentration of small reactive species indicate that the
concentration of reactive radicals increases rapidly between 700C and 900C.
Since incorporation of oxygen is necessary for the formation of PCDFs from
PCBs, OH and 0 are implicated as the predominant reactive species responsi-
ble for PCDF formation.
For all but the most fuel-rich systems and temperatures between 700C
and 1000C, the OH concentration is calculated to be roughly a factor of 10
greater than the 0 concentration, which is in turn a factor of 1000 to
10,000 greater than the H concentration. Thus, OH would appear to be the
major reactive radical under either stoichiometric or oxygen-rich con-
ditions. When the equivalence ratio increases, the OH and 0 concentrations
decrease as the H atom concentration increases. This shift in equilibrium
to non-oxygen containing radicals results in a decreased yield of oxygen-
ated products such as PCDF. Thus, for large equivalence ratios, larger
yields of pyrolysis products (e.g., polychlorinated benzenes, PCB congen-
ers, chlorinated naphthalenes, chlorinated biphenylenes, etc.) are obser-
ved. Although H atoms are usually considered to be the dominant reactive
radical in hydrocarbon systems under pyrolytic conditions, the large con-
centration of Cl atoms in PCB systems may result in Cl being the dominant
reactive species. Additional research on the role of Cl atoms is strongly
suggested.
For the range of oxygen levels studied, the PCDF yield decreased with
equivalence ratio. Although not addressed directly in this study; one
might expect the yields of PCDFs to start to eventually decrease with
increasing oxygen concentration due to enhanced destruction of the PCDF
product as it is oxidized to simpler products including carbon monoxide and
carbon dioxide. The shift in the temperature for maximum yield of PCDFs as
a function of equivalence ratio is a reflection of the competition between
oxidation of PCB to form PCDF and oxidation of the PCDF itself. The obser-
vation that the highest temperature of maximum PCDF yield is for <}> = 1.0
and decreases for <}> = 3.0 or = 2.0, may well be due to the shifting con-
centrations of the species responsible for PCDF formation and destruction.
Potentially important elementary reactions for PCDF formation by OH
attack are shown in reactions 1 through 3.
29.
-------
TABLE 8. MAXIMUM WEIGHT PERCENT YIELD OF PCDFs
AS A FUNCTION OF REACTION ATMOSPHERE
Temperature of Weight % Yield
>j) Maximum Yield (C) Tri-CDFS Tetra-CDFS Penta-CDFS Total PCDFS
0.05 750 0.66 4.3 2.0 6.9
0.2 800 0.34 1.7 0.56 2.6
1.0 900 0.13 1.3 0.25 1.7
3.0 850 0.068 0.71 0.21 0.99
30.
-------
100
o
cr
UJ
CL
10
O.I
O.OI
2, 3 ' ,4,4• .5-PC3
TOTikL-PCDFS
TE7RA-COFS
PENTA-CDFS
TRI-CDFS
500 6OO 70O 800
EXPOSURE TEMPERATURE,°C
900
IOOO
Figure 5. PCDF formation/destruction profiles for
=1.0 and a gas-phase residence time of
2.0 seconds.
31.
-------
:D
ci
4- H
(2)
(2'
(3)
H 0
A mechanism involving reactions 1 and 2 would correspond to an HC1
elimination mechanism, while as mechanisms involving reactions 1, 2, and 3,
would correspond to an H2 elimination mechanism. Reaction 1 is shown as a
substitution reaction but may actually be an addition followed by H atom
elimination.
Similar reaction mechanisms may be drawn for 0 atom attack. Reactions
4 and 5 would also result in H2 elimination.
(4)
(5)
Reaction schemes involving CI atom loss through addition or substitution
reactions would be expected to be energetically less favorable with lower
yields of PCDFs. This would account for the lower observed yields of PCDFs
formed through a mechanism involving Cl2 elimination.
The changes in yields of various products as a function of oxygen
level and temperature is very important for understanding the results of
PCS degradation. For example, internal arcing in a sealed capacitor would
result in heating of PCBs in an oxygen-deficient environment. Under these
conditions, one would predict a shift of yields towards pyrolysis products
such as other PCBs, polychlorinated benzenes (PCBzs), and polynuclear aro-
32.
-------
matics^(PNAs) rather than PCDF. However, higher temperatures are required
to achieve conversion which may not be reached. On the other hand, open
burning or combustion of the PCBs would occur in an environment with more
available oxygen which would favor the formation of oxidative products such
as PCDFs. However, even under fire conditions, oxygen-starved conditions
can also exist resulting in formation of pyrolysis products.
During incineration, one would expect that oxygen-deficient combustion
conditions would control the composition of the stack effluent. For ther-
mal destruction processes that involve both flame combustion and thermal
oxidation, it is contended that only the fraction of the organic waste
which escapes the flame and thus undergoes degradation in an oxygen-defici-
ent environment is responsible for most emissions. Therefore, a well-
defined relationship for temperature and oxygen concentration effects on
PCB degradation and product formation can be used to guide the environmen-
tally safe incineration of PCB-containing wastes.
Formation of PICs from Chloroform
The thermal decomposition profile of chloroform and the thermal
generation/decomposition profiles for two of its thermal reaction products
are plotted in Figure 6. Pentachloroethane as a product is shown due to
its possible role in the chloroform thermal decomposition pathway. Tetra-
chloroethylene is shown because of its high yields, exceptional thermal
stability, and toxicity.
As shown in Figure 6, chloroform is a relatively thermally fragile
compound. In a recent study by our laboratory, chloroform ranked second
from the last in terms of thermal stability (1). It has also been shown to
be considerably less stable than dichloromethane and carbon tetrachloride.
Based on decomposition via homolysis of a C-C1 bond, chloroform would be
expected to be more stable than carbon tetrachloride.
Studies by Shilov and Sabirova at temperatures ranging from 485-599C
led to the conclusion that the initial step of chloroform decomposition was
not simply C-C1 bond homolysis, but the direct loss of HC1 to form an
intermediate biradical dichlorocarbene (25). The dichlorocarbene may then
further react with chloroform through insertion in the C-H bond to form
pentachloroethane (26). Another proposesd reaction of dichlorocarbene is
its combination with another dichlorocarbene to form tetrachloroethylene.
The thermal decomposition profile of pentachloroethane and the
generation/decomposition profile for the product tetrachloroethylene are
shown in Figure 7. As shown, pentachloroethane and chloroform are of
comparable thermal stability. The conversion of pentachloroethane to tetra-
chloroethylene is very favorable and most likely occurs through the concerted
elimination of HC1 (27). If chloroform decomposition does proceed via the
formation of pentachloroethane, then subsequent HC1 elimination from the
pentachloroethane would certainly contribute to the high yields of tetra-
chloroethylene observed.
The products identified (tentative structural assignments) from the
33.
-------
100
C2HCL5
0.01
300
500 70O
Temperature (°C)
900
Figure 6. Weight percent (normalized to non-decomposed parent
peak) vs. temperature for chloroform and selected
decomposition products ( = 0.76, 2.0 seconds
residence time).
-------
100 Q
10.0
U)
Ln
g> 1.00
(D
0.10
0.01
D
A
0
L
C2CL4
1
300
Figure 7.
500 700
Temperature (°C)
900
Weight percent (normalized to non-decomposed parent
peak) vs. temperature for pentachloroethane and its
major decomposition product tetrachloroethylene
( = 0.76, 2.0 seconds residence time).
-------
thermal reaction of chloroform and pentachloroethane are listed In Table
9. The similarity of the products supports the hypothesis of common
decomposition pathways. Based on the observed products as well as the
previously mentioned studies, decomposition pathways as shown in Figure 8
may be envisioned. Products listed in Table 9 which are not shown may be
generated by further elimination of HC1 and/or radical reactions.
Formation of PICs from Polychlorinated Phenols
The thermal decomposition of chlorophenols is of intense
interest because of the potential formation of polychlorinated dibenzo-
dioxins (PCDDs) as incomplete combustion products. Thermal decomposition
data was obtained using the TDU-GC for pentachlorophenol (PCP) in nitrogen,
pentachlorophenol in air, and 2,4,5-trichlorophenol (2,4,5-TCP) in nitrogen.
Thermal decomposition profiles for these compounds are presented in Figure 9.
The extrapolated Tgg(2) is 640C for PCP in nitrogen, 630C for PCP in air,
and 775C for 2,4,5-TCP in nitrogen.
Major products of incomplete combustion were identified for PCP in
nitrogen and in air using the TDAS. These partial combustion products,
along with their temperatures of maximum formation, are given in Table 10.
The similarity between the thermal stability of PCP in air and nitro-
gen suggests that unimolecular decomposition is a significant degradation
mechanism. The oxygen-hydrogen bond energy in phenol is relatively low (88
kcal/mole) and may be lower in 2,4,5-TCP and lower yet in PGP- Of course,
oxygen is available in the reaction atmosphere as a degradation product of
PCP and TCP, probably in the form of OH. One would expect the hydroxyl
hydrogen to be susceptible to abstraction by OH. From profiling the
combustion products, it was observed that all were formed at approxi-
mately equal concentrations (within a factor of 10), at their temperatures
of maximum yield. It was also observed that the formation maxima for PICs
generally peaked at about 630C-650C for pentachlorophenol in air and 725-
775C for pentachlorophenol in nitrogen. This is interesting in light of
the fact that the parent material exhibited a maximum decomposition rate
between 625C and 650C in both cases. This may have occurred because in air
PICs were forming directly from the parent material, while in nitrogen the
principal PICs may have evolved through thermal decomposition of other PICs.
Table 10 includes only the major PICs observed at selected reaction
temperatures on the TDAS. It should be noted that the production of octa-
chlorodibenzo-p-dioxin (OCDD) was tentatively identified by retention time
on the TDU-GC, and that this identification was confirmed by examining low-
level peaks on the TDAS. The maximum yield in air (— 1%) was observed at
500C, while the maximum yield in nitrogen (^1.5%) was seen at 550C.
Expansion of Pure Compound Kinetic and Thermal Stability
Data Base
We have also generated additional pure compound thermal decomposition
kinetic data. Tables 11 through 13, are a complete listing of compounds
for which we have measured pseudo-first order oxidation kinetic parameters.
36.
-------
TABLE 9. THERMAL DECOMPOSITION PRODUCTS
OBSERVED FROM:
CHLOROFORM
(CHCl.Q
CC14
C2HC13
C2HC15
C2C12
C4C14
PENTACHLOROETHANE
CHC13
CC14
C2H2C14
C2HC13
C2C12
C3H6C12
C3C14
C4H2C16
37.
-------
CHCL3 £
CCL2 + HCL
.CHCL
HCL
C2HCL5
CL-, C9HCLa- + CCLv CHCLo-
I
CHCL3 +
C2CL5 + C2HCL5
HCL
C2HCL3
Figure 8. Possible pathways for the thermal
decomposition of chloroform.
38.
-------
I I
100 r
10
o
z
UJ
o:
H
z
UJ
o
-------
TABLE 10. THEHHAL DEGRADATION PRODUCTS FROM PENTACHLOROPHENOL3
Tentative Identification Tentative Structure
Dichlorobutadiyne
Temperature of
Maximum Formation (C)
In N? In Air
800
ND
Tetrachloroethylene
Tetrachloropropyne
Ck
Cl
Cl
Cl
I
Cl
ND
ND
650
630
Trichlorofuran
l,l,2,4-tetrachloro-l-buten-3-
yne
Tetrachlorofuran
Trichlorobenzene
Cl
-0
Cl
Cl H
Cl
I ..Cl
C'^P^CI
Cl Cl
x^v cu
ND
ND
625
630
725 630
650
630
Tetrachlorobenzene
Pentachlorobenzene
CL
CI5
775
725
630
630
Hexachlorobenzene
725
ND
40.
-------
TABLE 10. (Continued)
Tentative Identification
Tentative Structure
Temperature of
Maximum Formation (C)
In N-
In Air
Octachlorostyr
ene
725
ND
Hexachlorodihydronaphthalene
-CI4
725
630
Unknown chlorinated compound
Molecular Weight 400
725
ND
aldentifications are based on mass spectra alone and are strictly tentative.
Standards were not analyzed to confirm these identifications, and in some cases,
library spectra were not available for comparison.
bND=«not detected on TDAS, with a detection limit of about 2% conversion of parent
41.
-------
TABLE 11. SUMMARY OF THERMAL DECOMPOSITION DATA
Compound
Acetonitrile
Tetrachloroethylene
Acrylonitrile
Methane
Hexachlorobenzene
1,2,3, 4-Tetr achlorobenzene
Pyridine
Dichlorome thane
Trichloroethylene
Carbon Tetrachloride
Hexachlorobutadiene
1 , 2 ,4-Trichlorobenzene
1 , 2-Dichlorobenzene
Ethane
Benzene
Aniline
Monochlorobenzene
Nitrobenzene
Hexachloroe thane
Chloroform
1,1, 1-Trichloroethane
Triallate
Trifluralin
Empirical
Formula
C2H3N
C2C14
C3H3N
CH4
CfrCIft
C6H2C14
C5H5N
CH2C12
C2HC13
CC14
C4C16
C6H3C13
C6H4C12
C2H6
^6^6
C6H7N
C6H5C1
C6H5N02
C2Clg
CHC13
C2H3C13
C10H16NSOC13
CnHifiNiiOAF*
onset ^}
(C)
760
660
650
660
650
660
620
650
600
600
620
640
630
500
630
620
540
570
470
410
390
360
360
T99 (2)
(C)
900
850
830
830
820
800
770
770
765
750
750
750
740
735
730
730
710
670
600
590
570
470
440
T99.99 (2)
(C)
950
920
860
870
880
850
840
780
935
820
780
790
780
785
760
750
780
700
640
620
600
525
477
42.
-------
TABLE 12. SUMMARY OF FIRST ORDER KINETIC RESULTS
Compound
Trichloroethylene
Aery lonit rile
Ace tonit rile
Tetrachloroethylene
Methane
Hexachlorobenzene
1,2,3, 4-Tetrachloro benzene
Ethane
Carbon Tetrachloride
Mono chloro benzene
Dichloromethane
1,2, 4-Trichlorobenzene
Pyridine
1, 2-Dichlorobenzene
Hexachlorobutadiene
Benzene
Aniline
Nitrobenzene
Hexachloroethane
Chloroform
1,1,1-Trichloroethane
Trial late
Trifluralin
ACs-1) E (kcal/mole
4.2xl03
1.3xl06
4.7xl07
2.6xl06
3.5xl09
2.5xl08
1.9xl06
1.3xl05
2.8xl05
8.0xl04
3. 0x10 13
2.2xl08
1-lxlO5
3.0xl08
6. 3x10 12
2. 8x10 8
9. 3x10 15
1.4xl015
1.9xl07
2. 9x10 12
1.9xl08
6.8xl08
2. 7x10 7
18
31
40
33
48
41
30
24
26
23
64
39
24
39
24
38
71
64
29
49
32
31
25
Temperature
) Range
600-700
750-810
800-850
725-825
700-800
710-785
700-765
675-725
680-730
600-670
700-755
675-725
700-750
685-725
700-750
685-715
650-700
600-650
500-600
520-585
475-550
360-460
360-430
Calculated
TQQ(2)(°C)
913
910
908
900
874
845
834
830
824
810
796
789
767
766
763
757
726
672
641
606
601
516
483
43.
-------
TABLE 13. SUMMARY OF FRACTIONAL REACTION ORDER CALCULATIONS
Compound
Acetonitrile
Acrylonitrile
Aniline
Benzene
Carbon Tetrachloride
Chloroform
1, 2-Dichloro benzene
Dichlorome thane
Ethane
Hexachlorobenzene
Hexachlorobutadiene
Hexachloroethane
Methane
Monochlorobenzene
Nitrobenzene
Pyridine
1,2,3, 4-Tetrachlorobenzene
Tetrachloroethylene
Trial late
1,2, 4-Trichlorobenzene
1,1, 1-Trichloroethane
Trichloroethylene
Trifluralin
Temperature
(C)
850
810
700
720
730
585
725
752
725
785
730
600
800
670
650
750
740
825
460
725
550
700
430
Reaction
Order
a
1.1
1.6
1.1
1.1
1.5
1.1
1.3
0.9
1.0
0.9
1.0
1.2
1.2
1.6
1.1
1.3
1.3
1.1
1.4
1.4
1.2
1.3
1.3
r2
1.00
0.98
1.00
0.90
1.00
0.98
1.00
0.50
0.98
1.00
0.99
0.97
0.93
0.89
1.00
0.99
0.90
0.99
0.99
0.99
0.96
0.99
0.99
44.
-------
of fl i| ranks the compounds by their experimental Tgg (2) in an atmosphere
owing air. Table 12 presents the Ea and A values for the compounds
ranked by calculated T99 (2). Table 13 summarizes the calculated fractional
on orders for the compounds, which can be used to estimate the concen-
tration dependence of the destruction efficiency of the pure compounds.
Ihe theoretical formalism and experimental design for these studies is
available from other reports to which the reader is referred for additional
information (1).
45.
-------
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