United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/105 March 1987
&EPA Project Summary
Report for Non-Flame
Hazardous Waste Thermal
Destruction
A laboratory apparatus, identified as
the Thermal Decomposition Unit-Gas
Chromatograph (TDU-GC) system, has
been used to investigate the impact of
key factors of the post-flame zone in
the combustion process upon the efflu-
ent decomposition products. The re-
sults from thermal treatment of various
organic compounds showed that:
(1) Very good reproducibility under
similar test conditions was obtained for
effluent composition/concentration
from initial thermal treatment tests, of
a solid, pentachloronitrobenzene, and a
volatile organic, chloroform.
(2) Thermal decomposition profiles
of individual organic compounds intro-
duced as the feed material to the sys-
tem provided DE (Destruction Effi-
ciency) values for each compound.
(3) Products of Incomplete Combus-
tion (PICs) were generated, sometimes
in major quantity, that accounted for a
large portion of the elemental composi-
tion of the feed material.
(4) Test series concentrating on the
thermal treatment of chloroform
showed major differences in PIC gener-
ation as a result of different atmos-
pheres (rich oxygen and reduced oxy-
gen). It appeared that several hundred
degrees (°C) higher temperature would
be needed to attain the same degree of
destruction of the more refractory PICs
in the reduced oxygen atmosphere as
was shown in the rich oxygen case.
This Project Summary was devel-
oped by CRA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
In the thermal destruction of haz-
ardous organic waste material, the in-
teractions of the gaseous components
in the post-flame or the non-flame zone
of the combustion process make an im-
portant contribution to the overall re-
sults. The thermal decomposition in
those zones can range from simple py-
rolysis in an oxygen-deficient atmos-
phere as might occur in an incinerator
or a boiler, to a thermal-oxidative treat-
ment with a considerable excess of oxy-
gen as can occur for example in a liquid
injection incinerator supported by a sec-
ondary combustion zone or supply of
air.
A laboratory unit, identified as the
Thermal Decomposition Unit-Gas Chro-
matograph (TDU-GC), has been used to
investigate key thermal decomposition
factors of the post-flame zone, such as
temperature and atmosphere in the re-
actor zone, and their impact upon the
effluent decomposition products. The
TDU-GC was developed at the Univer-
sity of Dayton Research Institute (UDRI)
and has been applied by Institute per-
sonnel over the past several years to
study many organic compounds.
The TDU-GC at EPA's Center Hill Facil-
ity has been used to develop thermal
decomposition profiles for various or-
ganic compounds as well as to study
some of the compounds in depth for the
purpose of evaluating several factors of
the decomposition process and of PIC
(Product of Incomplete Combustion)
formation.
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Experimental Procedure
The principal equipment used in this
study was the Thermal Decomposition
Unit-Gas Chromatograph system, a
closed in-line system consisting of two
basic units, (1) the thermal reactor and
(2) the analyzer, a gas chromatograph.
These units are shown in the basic sche-
matic illustration, Figure 1. The experi-
mental procedure used was as follows:
1. The thermal reactor incorporates a
capillary quartz tube within a furnace
with three heating zones that are inde-
pendently controlled to produce tem-
peratures up to 1150°C in the central
zone for thermally decomposing the
sample compound in its gaseous state.
A tubular quartz extension at the en-
trance of the furnace transfers the feed
gas from the larger-bore sample inser-
tion chamber. That chamber is fitted
with any one of several probes adapted
to handle gas, liquid or solid samples. A
temperature programmer controls the
heating jacket on the insertion chamber,
for converting the liquid and solid sam-
ples to the vapor phase at selected ele-
vated temperatures. The vapor or gas is
conveyed to the reactor by a controlled
flow of carrier gas which is selected ac-
cording to the nature of the atmosphere
required in the high-temperature zone
of the reactor. According to the temper-
ature and pressure measured in the re-
actor tube, the carrier gas flow is regu-
lated at the instrument console to result
in a precise residence time of the vapor-
ized/gaseous sample in the closely con-
trolled high-temperature zone.
The gaseous emission from the reac-
tor pass through a capillary tube into a
in-line tubular trap controlled to sub-
ambient temperatures as low as -50°C
and colder. The trap is located inside the
wall of the gas chromatograph (GC) and
is a very short (several mm) section of
the extension of the GC capillary
column into the 30:1 splitter tubing.
2. The gas chromatograph is fitted
with a fused silica capillary column
leading to a flame ionization detector
(FID). Heating the trap transfers, via the
30:1 splitter, the smaller stream of
trapped emissions sample to the front
end of the capillary column which itself
is at the sub-ambient temperature.
Upon injection of the sample into the
GC, as initiated by the switch on the
supporting computer, the temperature
program for the capillary column con-
trols the separation of the components
of the reactor emissions sample and
their ensuing detection and measure-
ment by the FID.
Helium
Filtration
Control
Air
1 Heated
. Transfer \
/ \
f Quartz Tube
Insertion 1 1 lift, j—-
Chamber mm; •'
\
•il i lu.
luiii
r ~
Cryogenic
Trap
Gas
Chromatograph
Figure 1. Basic schematic of TDU-GC system.
The computer, coupled with a
recorder, provides a means of storing
the output from the FID and of depicting
it in a chromatogram as well as in a tab-
ulation of the various peak areas.
3. The Principal Organic Hazardous
Constituent (POHC) material under in-
vestigation was introduced into the in-
sertion chamber as a gas, liquid or solid.
The more volatile, low molecular
weight compounds were generally fed
by syringe to the TDU-GC system as
gaseous samples prepared at known
concentrations.
For various organic liquids, nanoliter
quantities were injected directly into the
insertion chamber where the sample
was converted to the vapor form by a
programmed temperature increase that
provided transfer by the carrier gas into
the thermal reactor.
4. Samples of organic solids were de-
posited as measured amounts in solu-
tion onto the end of the "solids" probe.
Evaporation of the solvent left a residue
which in the confines of the insertion
chamber was transformed to the vapor
state for transfer into the thermal reac-
tor by the carrier gas.
Results
Thermal decomposition profiles were
obtained for various organic com-
pounds. In the process of the thermal
decomposition of the POHC (feed) ma-
terial, various PICs formed and in turn
decomposed with temperature increase
in the reactor. In some cases, the major
PICs were identified and then quantified
through subsequent calibration runs.
Where unidentified PICs were included
in the plots, for lack of calibration runs
that would help quantify those compo-
nents, their peak area counts obtained
from the analysis step were treated as
being equivalent to the counts of the
POHC material in the plot presentations.
Through a major effort expended oi
the study of the thermal treatment c
chloroform, the effects of atmospher
(rich oxygen and reduced oxygen) type
were presented in plots, percent cor
centration vs. temperature. Th
changes in PIC formation—peak leve
temperature of DE, and rates of forme
tion/decomposition—were readily de
picted through comparison of the plot
for the different reactor atmospheri
conditions.
In most every case, the temperatur
range investigated extended beyon
the point for 99.99% DE (Destruction E
ficiency) of the POHC (feed) material.
Discussion
The early test runs, with per
tachloronitrobenzene (PCNB) and wit
pure chloroform, were made primaril
to check for inter-laboratory reproduc
bility. The PCNB results from th
present study yielded a decompositio
curve for PCNB that closely matche
that reported by UDRI; the formatioi
decomposition profile of the PIC, he)
achlorobenzene, also closely matche
that reported by UDRI. The results fc
the thermal treatment of chloroforr
showed very good agreement wit
those presented by UDRI as reported fc
some of their earlier work with toxic o
ganic compounds. The three major PIC
of the current study, which were ident
fied as hexachloroethane, tetrf
chloroethylene and carbon tetrachlt
ride apparently were the same as th
three unidentified PICs presented in th
UDRI plot.
In a study of a chloroform-heptar
mixture (3 weight percent chloroform
the effective masking of the GC peal
for chloroform and its products by tr
heptane source pollutants limited th
results to simply a decomposition pn
file for heptane, with a Tg90(2) of 675'
-------
(temperature for 99.0 percent destruc-
tion of heptane at 2.0 seconds residence
time).
Thermal treatment of monochloro-
benzene, trichloroethylene and Freon-
113 indicated a 199.99(2) of 850, 875, and
810°C, respectively, for those com-
pounds.
Some remarkable differences in PIC
emissions concentrations were noted
when chloroform was exposed to high
temperatures under highly oxidative
(Figure 2) and under reduced oxygen
(Figure 3) atmospheres:
(1) Tetrachloroethylene, C2CI4, was
far more refractory under the reduced
oxygen condition. Its presence per-
sisted in large amount throughout the
higher temperatures investigated. At
the 850°C level, there still was about 15
mol percent of the compound present in
the emissions, in sharp contrast to the
mere 0.4 percent in the rich oxygen at-
mosphere case.
(2) Carbon tetrachloride, CCI4, also
persisted through the higher tempera-
tures much more in the reduced oxygen
atmosphere.
(3) Hexachloroethane, C2CI6, was
more readily formed in the high oxygen
atmosphere than in the reduced oxygen
case.
(4) Pentachloroethane, C2HCI5, ap-
peared in trace amounts in the reduced
oxygen runs, but was not detected in
the rich oxygen series.
(5) The POHC chloroform had a
slightly higher value of about 635°C for
the 99.99% DE point in the reduced oxy-
gen atmosphere as compared to about
610°C in the rich oxygen case.
Only perchlorinated compounds were
being formed in significant/detectable
amounts in the reduced oxygen atmos-
phere, with both tetrachloroethylene
and carbon tetrachloride persisting
through the higher temperatures.
Tetrachloroethylene was also pro-
duced in considerable quantity as a PIC
when carbon tetrachloride was exposed
as a feed, to high temperature treat-
ment.
Conclusions and
Recommendations
The Thermal Decomposition Unit-Gas
Chromatograph (TDU-GC) system has
been used to evaluate the non-flame
thermal decomposition of various or-
ganic compounds associated with the
incineration of toxic/hazardous organic
waste substances.
3
§
0.01
300
400
500
700
Temperature, °C
800
900
1000
Figure 2. Thermal treatment of chloroform CHCIs (vapor feed, air carrier gas).
|7, = 2.0 seel
j 0 = ~ 0.05J
The system has been used success-
fully to demonstrate reproducibility of
results consistent with the findings of
other investigations using similar
equipment.
From the experience with heptane as
a component in the feed, it appears nec-
essary, for accurate measurement of
the effects of feed composition, to limit
mixtures for study to a very few, per-
haps only two, compounds that are indi-
vidually "clean" in any GC analysis.
In the study of oxygen/organic-
compound ratio, the oxygen in a large
amount had a very significant effect
upon the composition of the emissions
under the test conditions used. Perchlo-
rinated compounds were totally domi-
nant in the reduced oxygen atmos-
phere; in the rich oxygen atmosphere,
those compounds were far more readily
being eliminated. It appears that a tem-
perature several hundred degrees (°C)
higher is needed in a reduced oxygen
atmosphere to obtain the same destruc-
tion level of PICs that was observed for
the oxygen-rich atmosphere. Also, the
generation/production levels of the PICs
varied with the oxygen concentration
levels. Clearly, the mechanisms/rates
for PIC formation were different in those
different atmospheres. In the oxygen-
rich atmosphere, there were no
hydrogen-containing organic com-
pounds detected in significant amounts.
For more fully characterizing the ther-
mal reactor emissions with respect to
PICs, more extensive procedures in-
volving additional instrumentation is
needed to identify and quantify PIC
compounds. A Mass Selective Detector
(MSD) dedicated to the TDU-GC system
is the instrument of choice, both for ac-
curacy of determinations and for vol-
ume of work (data) that can be expe-
dited.
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100
50
JO
5
ss
5f ,
0.5
0.1
0.05
— l_-.r._: —
, _
-~=L-.r=-,
__ _
— ~~ ^--"
—
.. ecu
_ CjWC/s'
]
300 400 500 600 700 800 900 WO
Temperature. °C
Figure 3. Thermal treatment of chloroform CHCI3 ["'• = 2- ° sec 1
The EPA author, Myron Malanchuk. is with the Hazardous Waste Engineering
Research Laboratory. Cincinnati, OH 45268.
The complete report, entitled "Report for Non-Flame Hazardous Waste Thermal
Destruction,"(Order No. PB 87-130 274/AS; Cost: $ 11.95, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA author can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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