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
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1 1 Illlil

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    (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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