\ I /
United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711 //
Research and Development
EPA/600/S2-89/037 Aug. 1989
f/EPA Project Summary
Potential Technologies for
Collection and Destruction of
CFCs, Halons, and Related
Compounds
Kirk E. Hummef and Thomas P. Nelson
This report gives recommen-
dations of a multidisciplinary panel of
experts on new or novel technologies
(or modifications of existing
technologies) which show the most
promise for the collection and
destruction of chlorofluorocarbons
(CFCs) and related compounds. The
panel members met in a "roundtable"
format to discuss their experiences
and relate them to the compounds of
interest. The panel identified
technologies that held the most
promise and suggested general
areas of research and development
needed to develop collection and
destruction technologies.
This Project Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park, NC, 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
A family of chemicals known as
chlorofluorocarbons (CFCs) has been
implicated in the depletion of
stratospheric ozone. A number of adverse
health and ecological effects could result
from such depletion. For this reason a
number of strategies or options for
controlling the release of these
compounds are being evaluated by
governments and industry worldwide.
Existing technological means have not
been conclusively demonstrated as
suitable for curtailing CFC emissions
from certain sources to acceptable levels.
Because of their great chemical stability,
CFCs are very difficult to break down. In
order to be destroyed, the CFC would
first have to be collected. Thus, EPA felt
a program was needed to evaluate
various existing and new or novel
technologies for the collection and
destruction of CFCs.
The Navy needs new or novel
technology to remove and destroy toxic
compounds which may be used in
chemical warfare (CW) The current
generation of shipboard CW defensive
systems are based on activated carbon
adsorption. These devices are
considered effective against high
molecular weight, low volatility chemicals
such as "nerve agents" which are
strongly adsorbed. However, in order to
deal with high volatility, weakly adsorbed
toxic compounds (such as hydrogen
cyanide, HCN), a reactive impregnant has
been added to the carbon. It is known
that some CFCs are not strongly held on
carbon, so it was assumed that (if a
technology could be developed for
collection and/or destruction of CFCs) it
might be possible to modify such a
process for shipboard use as a CW
defensive system.
To this end, the U.S. EPA and the
Navy proposed assembling a multi-
disciplinary panel of experts to
recommend new or novel technologies
(or modifications of existing technologies)
-------
which show the most promise for future
development. The panel would then meet
in a "roundtable" format to discuss the
proposed technologies. This report gives
results of this meeting.
Summary of Expert Panel
To address the issues for the EPA and
the Navy in terms of their particular
interests, the technologies were
evaluated for two distinct classes:
Technologies capable of collecting,
removing, or destroying the
compounds from the feed stream
and providing an off-gas or effluent
suitable for breathing air (for
example, shipboard CW defense);
and
Technologies capable of collecting,
removing, or destroying the
compounds from the feed stream
with no requirement for a breathable
off-gas (for example, bulk
incineration of contaminated CFCs).
The panel reviewed many
technologies including thermal, chemical,
and biological processes. In most
instances biological processes can be
used only on dilute aqueous streams and
the biological destruction rate is very
slow. This is based on experience with
highly halogenated polychlorinated
biphenyls (PCBs). Therefore, for the two
applications at hand, biological processes
were eliminated as possible candidates.
The overall conclusions of the expert
panel for the breathable air situation was
that the use of carbon adsorption as
currently done by the Navy was the most
reasonable, commercially available
process. However, carbon adsorption is
limited because high volatility toxic
compounds are not strongly held on
carbon, and the reactive impregnants
which are added to remove these
compounds are non-specific (they react
with a host of other contaminants) and of
limited capacity. Furthermore, there is
currently no method to determine when
the carbon needs to be replaced.
The potential candidates to replace
the present carbon adsorption system
are:
Inorganic Membranes: These may
be either ceramic membranes or
carbon molecular sieves. Inorganic
membranes operate at high
temperatures and are chemically
resistant. A carbon bed may still be
required downstream or metallic
salt impregnants may be needed to
react with high volatility com-
pounds.
Chemical Scrubbing/Destruction:
This technology includes the use of
a highly alkaline, non-aqueous
scrubbing liquor to absorb and
destroy the compounds of interest.
This is superior to scrubbing alone,
since equilibrium limitation is
removed. Downstream treatment is
required to prevent contamination
of the carbon bed. Pretreatment of
the inlet air may be required to
remove moisture.
Corona Discharge: This process
uses highly energized electrons
from an ionized corona discharge to
dissociate the compounds of
interest. This process operates at
essentially ambient temperature
and pressure. A carbon bed may
still be required downstream. A
high voltage power supply is
required and ozone and/or NOX
may be generated.
Metals Scrubbing: This technology
uses an active metal such as zinc
or aluminum to react with the
compounds of interest. It is known
that active metals can rapidly
destroy halogenated organics such
as PCBs. One advantage is that a
solid salt may be formed which can
easily be removed. Pretreatment of
the inlet air may be required to
remove moisture since there may
be a problem in maintaining an
active metal surface in the
presence of air and moisture.
New Adsorbents: This technology
uses tailor-made adsorbents, such
as new zeolites, and aluminas, or
polymeric adsorbents, to obtain the
desired separation. These com-
pounds have a uniform or well-
defined structure which results in
more consistent performance. Also,
their properties may be altered
using various pretreatments. A new
selective adsorbent bed could
conceivably allow some less toxic
compounds through to be handled
by a cheap carbon bed instead of
an expensive specialty adsorbent
bed.
In the area of destruction of fully
halogenated organics without the need of
a breathable off-gas, current thermal
destruction processes may be adequate.
CFC wastes are currently being
destroyed in at least one permitted
facility. The harsh environment created
by the hydrogen fluoride (HF) in the off-
gas is one potential cause for concern;
specially designed internal firebrick and
mortars may be required.
Although CFCs are currently b
incinerated, there are very limited
regarding the destruction efficient
products of incomplete combus
(PICs) resulting from these operati
Data are lacking regarding the qus
and fate of PICs; such compounds
be toxic and/or may pose a three
stratospheric ozone.
To summarize the status
incineration of CFCs, this is the
demonstrated technology whic!
currently being used, and will li
continue to be used in the near I
However, the feared potential of corr<
attack to the refractory and the lac
accurate data on destruction effici
and PICs are problems which re<
solutions.
Other technologies which \
recommended as good candidates v
there is not a need for breathable air
Catalytic Thermal Destruc
Metal catalysts have t
successfully used to destroy i
hydrocarbon gas stream
reduced temperature, the
saving energy and improvmc
economics of this coi
technology. Potential problem;
the destruction of chlorir
hydrocarbons using this techn
include low destruction effic
due to catalyst deactivation.
Chemical Scrubbing/Destru<
This process has already
described for breathable air.
Corona Discharge: This pn
has already been describe
breathable air.
Metals Scrubbing: This proces
already been describee
breathable air.
Pyrolysis: This technology in<
thermal treatment in the absei
air. Since CFCs are dest
through bond homolysi
hydrolysis, simple heating v
air is sufficient to break the I
Heating without air resu
reduced gas flow which can
smaller downstream trea
equipment. Potential prol
include the possibility of coi
attack and the formation of
amounts of PICs.
Supercritical Water Oxk
(SCWO): This is a modifica
Wet Air Oxidation (WAO
scribed below) which invo
supercritical fluid (water). Th
technology features much
reaction rates than those ach
-------
in the well-known WAO technology.
Furthermore, SCWO operates at
very high oxidant concentrations
which enhance the kinetics and
produce favorable equilibria.
Potential problems are greater
energy requirements and possible
metallurgical limitations.
Wet Air Oxidation (WAO): This
process uses a high temperature
(>300°C) aqueous stream and
oxygen to destroy many organic
compounds. Since CFCs do not
contain a hydrogen atom or a
double bond, they are expected to
be resistant to oxidation. However,
CFCs are susceptible to hydrolysis
during incineration, so a high
temperature aqueous treatment
could be effective.
Recommendations of the
Expert Panel
The expert panel agreed that several
areas deserve priority for further
research.
CW Defensive Systems (Breathable
Air)
The panel agreed that future
research in this area should begin
with fundamentals in order to
determine the optimum long-term
solution.
The corona discharge process and
the ceramic membrane process
were proposed as good potential
candidates for initial research.
Liquid scrubbing with a reactive
component may have application;
however, the Navy is concerned
with high humidity in the breathable
air.
CFC Destruction (Non-Breathable Air)
A literature search is needed to
assemble all available data on
previous experience with
conventional thermal oxidation
(incineration) of CFCs.
Products of incomplete destruction
(PICs) should be identified for
residual ozone depletion potential
and toxicity In particular, the
formation of F and Br analogs of
dioxin should be investigated. Also,
the thermal stability of CFCs and
their basic combustion properties
should be studied
Inorganic membranes should be
studied from a materials science
perspective. Also, new adsorbents
should be investigated.
The chemistry of scrubbing
systems which contain a reactive
component should be studied.
The corona discharge process as it
currently exists requires small scale
tests, energy efficiency measure-
ments, and modeling.
Refractory linings that are resistant
to HF should be studied and tested.
Potential catalytic materials for
catalytic thermal destruction should
be evaluated.
Conclusions
The expert panel discussions on the
most favorable technologies that warrant
future development for CFC destruction
and naval CW defense lead to the
following conclusions.
1. There do not appear to be any new
near-term technologies which are
as capable as activated carbon in
removing a broad spectrum of toxic
CW agents from shipboard air.
2. Longer-term options such as the
corona discharge process and the
ceramic membrane process should
be pursued as research projects
where these options could lead to
improved technologies for
shipboard CW defense compared
to conventional carbon adsorbers.
3. Thermal incineration appears to be
feasible in the near-term for the
destruction of bulk quantities of
CFCs (such as contaminated
refrigerants or waste solvents),
although materials of construction
for the incinerator and byproducts
of combustion should be further
researched.
4. Sources of dilute emissions of
CFCs may require technologies
available in the longer-term. These
options, which include technologies
such as catalytic thermal
destruction, pyrolysis, or wet air
oxidation, may be source-specific.
-------
Kirk E. Hummel and Thomas P. Nelson are with Radian Corporation, Austin, TX
78720-1088.
Dale L. Harmon is the EPA Protect Officer (see below).
The complete report, entitled "Potential Technologies for Collection and
Destruction of CFCs, Halons, and Related Compounds," (Order No. PB
89-219 968/AS; Cost: $15.95 subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
\PENALty I l/.S.POSTdGf ji
jPRiV'A'.T I ji
/USE -300|' ;< (1 n f- -j,
*i - u .1 b -j
e s".-"i ;'
Official Business
Penalty for Private Use $300
EPA'600/S2-89/037
000085833 PS
0 S ENVIB PROTECTION
REGION 5 LIBRARX
230 S DEABBOfiS STREET
CHICAGO IL 60604
------- |