United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-149 Nov. 1984
&ERA Project Summary
Description and Operation of a
Thermal Decomposition Unit-
Gas Chromatographic System
Wayne A. Rubey, Ira B. Fiscus, and Juan L Torres
Controlled high-temperature incinera-
tion is recognized as one of the most
promising methods for the permanent
disposal of industrial organic wastes.
However, before acceptable incineration
procedures can be fully implemented,
information is needed concerning the
thermal decomposition properties of
the immense variety of organic mate-
rials. In response to this need, labora-
tory-scale thermal instrumentation has
been designed and developed for
experimentally determining the high-
temperature gas-phase decomposition
properties of toxic organic substances.
A thermal decomposition unit-gas
chromatographic (TDU-GC) system has
been designed and assembled to provide
data rapidly and safely on the gas-phase
thermal decomposition behavior of
organic substances. This system has
been designed to accommodate a wide
variety of organic materials which
range from pure substances to complex
industrial organic waste mixtures. Data
obtained with the TDU-GC can provide
guidance with respect to the eventual
incineration of numerous industrial
organic wastes.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Cincinnati, OH,
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Numerous procedures have been
proposed for the disposal of the vast
quantities of industrial organic wastes
that are produced annually. One of the
most promising methods for the per-
manent disposal of hazardous organic
wastes is controlled high-temperature
incineration. Before this disposal tech-
nology can be developed fully, more
precise information is needed concerning
the high-temperature decomposition
properties of an immense variety of
organic materials. Accordingly, there are
many advantages to generating such
basic gas-phase thermal decomposition
data in the laboratory, where conditions
can be precisely adjusted and easily
controlled. Once the thermal decomposi-
tion properties of a particular material
have been characterized in the laboratory,
the preliminary decision can be made as
to whether high-temperature incineration
is a viable disposal route for that material.
Appropriate incineration of toxic organic
wastes requires very high temperatures,
sufficient gas-phase residence time,
ample quantities of oxygen, and extensive
gas-phase mixing. With the use of
laboratory-scale instrumentation, a wide
variety of environmentally important
organic compounds can be studied with
respect to their thermal decomposition
behavior. Laboratory-scale studies are
especially suited for identifying and
studying the parameters and variables that
affect gas-phase high-temperature de-
composition behavior.
At the University of Dayton Research
Institute, two thermal decomposition
unit-gas chromatographic (TDU-GC)
systems have been designed and as-
sembled for conducting laboratory-scale
thermal decomposition studies with
various organic materials. Figure 1
shows a block diagram of the TDU-GC
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Thermal Decomposition Unit
Capture of
Effluent Products
Controlled High
Temperature Exposure
Sample Insertion
and Vaporization
Pressure and
Flow Regulation
Compressed Gas
and Purification
High Temperature Transfer
Multifunctional Gas Chromatographic
Instrumentation
Containment or Destruction of
Effluent Products
Figure 1. Block diagram of TDU-GC.
system, and Figure 2 is an artist's
rendering of the system. The TDU-GC has
been designed for measuring the thermal
decomposition properties of a wide range
of organic samples—gases, liquids,
solids, and even polymers. Thermal
decomposition tests can be conducted
relatively easily with the TDU-GC after
suitable familiarization and experience.
The TDU-GC is a continuous system
that can be viewed as two in-line
instrumental stations or units. The
primary function of the thermal decom-
position unit (TDU), that is, the first
station of the system, is to subject gas-
phase molecules to well-defined thermal
exposures. The GC portion of this system,
that is, the second in-line station, serves
to capture, separate, and analyze the
various chemical constituents that have
passed through the TDU.
One of the distinct advantages in
conducting thermal decomposition ex-
periments using the laboratory-scale
TDU-GC is that each molecule is subjected
to essentially the same thermal exposure.
Also, the sample insertion section of the
TDU-GC was designed to be as versatile as
possible and there are numerous modes
for inserting samples into the system.
One major requirement with respect to
sample handling with the TDU-GC is that
substances leaving the sample insertion
chamber must be in the gas phase.
Therefore, TDU-GC samples are either
volatilized or thermally degraded in the
sample insertion chamber. Also, the rate
at which molecules are admitted into the
high-temperature reactor is an important
factor in thermal decomposition studies.
In addition to the sample handling
requirements, there are three basic
criteria that must be met for proper
transport of gas-phase samples. Material
inertness and uniformity are important,
and, therefore, fused quartz was used as
the tubing material for sample transport
in the TDU-GC. The second basic require-
ment for good transport involves the
continual gas sweeping of the transfer
tubing. The selection of transport tem-
perature and the maintenance of uniform
temperature along the transport path
constitutes the third criterion for proper
transfer of sample. Each of these criteria
was given special attention in the design
of the TDU-GC system.
One of the most important components
of the TDU-GC system is the high-
temperature reactor. The design con-
siderations and the thermal reactor
assembly details are found in a previous
report on the development of a thermal
decomposition analytical system (see
EPA-600/2-80-098). Using the multiple
folded racetrack reactor design, as shown
in Figure 3, sample molecules encountet
essentially isothermal conditions during
their traverse through the reactor due to
the averaging of the existing subtle
longitudinal temperature gradients. A
temperature versus time profile for gas-
Data
Terminal
Gas Thermal
Chromatograph Reactor
Glove Box
Instrumentation
Console
Figure 2. Artist's rendering of assembled TDU-GC.
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70mm by
0.43mm ID
Connecting Tubing
70 mm by 0.43 mm ID
2.1 cm Radius
886 mm by 1.1 mm ID
Figure 3. Detail of Quartz Tube Reactor
phase molecules is shown in Figure 4.
The high-temperature unit selected for
heating the quartz thermal reactor
assembly employed a three-zone furnace
of hinged construction that was designed
for continuous operation at temperatures
up to 1200°C.
In the TDU-GC, the effluent from the
high-temperature reactor is swept through
the heated exit transfer line after which it
is cryogenically cooled. The entire
flowpath is then purged with an inert
carrier gas, where upon the collected
sample is subsequently passed into a
high-resolution gas chromatograph.
The assembled TDU-GC system in-
cludes a versatile modular instrumenta-
Temperature Variations
Cyclic Over Seven
Cycles
tion console which is used to monitor and
control the many experimental variables,
such as reactor temperature, gas flow rate,
transport temperatures, and pressure.
The gas flow control module of this
console is an especially important
component as it has direct interaction
with the high-temperature reactor.
Laboratory-scale thermal decomposition
experiments rely strongly on the analysis
of the chemical compounds that emerge
from the high-temperature reactor.
Accordingly, the primary function of the
GC located in the TDU-GC assembly is to
separate the constituents of the various
complicated chemical mixtures. Another
vital function of the TDU-GC separation
column is to trap cryogenically the
condensable products that emerge from
the high-temperature reactor.
Test samples that are to be introduced
into the TDU-GC can be prepared in their
final form within the confines of the glove
box that surrounds the entrance to the
sample insertion region of the TDU-GC.
Sampling procedures have been deve-
loped for gaseous samples, highly volatile
liquid samples, low volatility liquid
samples, and also solid organic samples.
For low volatility organic samples, a
microiiter syringe can be used for sample
introduction; however, in most cases, the
±2.0° @ 1200°K
t, = 2.00 sec.
— <5 ms
Figure 4. Square wave profile of gas-phase temperature versus time.
sample of interest will have to be diluted
with a suitable solvent.
With the TDU-GC system, precise
thermal decomposition experiments can
be conducted using a wide assortment of
pure organic substances or highly
complex industrial organic waste mix-
tures. Figure 5 shows a chromatogram of
an extremely complex organic waste
mixture which was examined using a
TDU-GC. The skeletal chromatogram
presented in Figure 6 gives an indication
of the relatively few stable compounds
from that complex sample which survived
a 2 0 second 690°C exposure while in a
flowing air atmosphere.
Although the TDU-GC is especially
suited for complex organic mixtures it can
also be used to:
a) establish the thermal decomposition
profile of a substance;
b) determine the residence time effects
and associated kinetic behavior;
c) investigate different gaseous atmos-
pheres, pressure effects, and other
related thermal decomposition vari-
ables;
d) collect data for prediction of thermal
decomposition behavior; and
e) provide guidance for larger scale
thermal disposal operations.
The TDU-GC system that is located in
the Environmental Chemistry Laboratory
at the University of Dayton has been in
operation since early 1982. Maintenance
and troubleshooting procedures have been
established for the TDU-GC systems.
Conclusions
The TDU-GC laboratory system has the
following specific features incorporated
into its design:
• With the closed continuous design
concept and the gloved-boxed sample
entry of this system, toxic samples
can be safely tested.
• Samples can be subjected to a very
precise thermal exposure in the
TDU-GC. At selected reactor tem-
peratures ranging from 200°C to
1150°C, the maximum temperature
variation is less than ±2°C
• The TDU-GC is capable of subjecting
a sample to a precise mean residence
time ranging from 0.25 to 5.0
seconds. In addition, this system
provides a narrow Gaussian resi-
dence time distribution.
• With the flexibility designed into the
TDU-GC, thermal decomposition
studies can be conducted using pure
organic substances or complex
organic mixtures, and only small
quantities of sample are needed
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10
20
30
40
50
60
70
70 80 90 WO 110 120
Retention Time (minutes)
Figure 5. HRGC chromatogram of composited waste sample.
130
140
I
c
o
a — Benzene
b — Toluene
c — Dibenzofuran
d— o.p'-DDE
e — Hexachlorobenzene
f — Decachlorobiphenyl
:
,1
b
1
1 1 Illlil
I
e
c d
\\ hill Illl 1,11 1. . I, III!
|
\
!
\
,
f
1
I
(micrograms). Samples can be
either gases, liquids, or solids. In (
addition, these samples can be
subjected to thermal decomposition
studies in any of a wide variety of
atmospheres.
• Analyses of the thermal decomposi-
tion products are performed through
the use of a versatile high-resolution
gas chromatograph and a variety of
sensitive detectors.
• The TDU-GC can provide funda-
mental thermal decomposition data
rapidly and economically.
Recommendations
In view of the numerous industrial
organic compounds and mixtures that
need to be subjected to permanent
disposal, it is recommended that the
high-temperature gas-phase thermal
decomposition behavior of these organic
materials be evaluated using the labora-
tory-scale thermal decomposition unit-
gas chromatographic (TDU-GC) system.
This thermal instrumentation system has
been designed for the efficient examina-
tion and safe handling of a wide variety of
organic substances. It is recommended
that laboratory-scale data be obtained
prior to subjecting large quantities of
complex organic mixtures to controlled
high-temperature incineration. i
It is further recommended that the
TDU-GC be utilized for data base genera-
tion such as studying the thermal
decomposition behavior of hazardous
organic compounds and determining the
formaton of products of incomplete
combustion (PICs). As many variations in
conditions can occur throughout the
various areas of a large incineration
system, it is recommended that the
effects of different incineration variables
be studied using the TDU-GC system.
to
Time •
Figure 6. Skeletal TDU-GC chromatogram of the composited waste effluent.
4
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W. Rubey, I. Fiscus, and J. Torres are with the University of Dayton Research
Institute, Dayton. OH 45469.
Ft/chard A. Carries is the EPA Project Officer (see below).
The complete report, entitled "Description and Operation of a Thermal Decompo-
sition Unit-Gas Chromatographic System." (Order No. PB 84-246 362; Cost:
$16.00, 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 Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
^USGPO: 1984 — 559-111/10727
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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