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ABSTRACT
The objective of this study was to assemble a multidisciplinary panel of
experts to recommend 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 which technologies held the most
promise and made suggestions for general areas of research and development
needed to develop collection and destruction technologies.
ii
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CONTENTS
Abstract ii
Tables iv
1. Introduction 1
2. Summary and Recommendations of the Expert Panel 6
Summary of Expert Panel 7
Recommendations of the Expert Panel 13
3. Specific Research Tasks to Address Recommendations 16
4. Conclusions 20
Appendices
A. Meeting Notes (Opening Statements and Discussion) 21
B. Handouts from Expert Panel and Vendor Presentations 36
"Role of Separations Technologies in the Collection
and Destruction of CFCs and Halons," Mr. Jose Bravo 37
"Incineration Technology for the Destruction of
Chlorofluorocarbons, Halons, and Related Chemicals,"
Mr. Ronald D. Bell 47
"Chemical Treatment Methods, Oxidizing Agents,"
Dr. David DeBerry 67
"Biodegradation Technology," Dr. Larry N. Britton 73
"Solar Destruction of Halocarbons," Jim Fish, Rich
Diver, and Hugh Reilly 81
iii
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TABLES
Table Page
1 List of Participants 3
2 Final Agenda 5
3 Summary of Expert Panel Recommendations for Breathable Air Case.. 10
4 Summary of Expert Panel Recommendations for Non-Breathable Air
Case 14
A1 Physical Properties of Chemical Warfare Agents 23
iv
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SECTION 1
INTRODUCTION
BACKGROUND
A family of chemicals known as chlorofluorocarbons (CFCs) have been
implicated in the depletion of stratospheric ozone. A number of adverse
health and ecological effects could result from such depletion. For this rea-
son 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 lev-
els. 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 has the need for new or novel technology to remove and destroy
toxic compounds which may be used in chemical warfare (CW). The current gen-
eration 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.
1
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To this end, the U.S. EPA and 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 "round-table" format to discuss
the proposed technologies. This report presents the results of this meeting
in the sections that follow.
Follow-up work is planned in FY89 to continue the development of CFC
destruction technologies if funds are made available. The follow-up work will
include a better definition of collection technologies for collection of
dilute emissions of CFCs to allow more economical destruction. The research
proposed by the expert panel will be reviewed by the U.S. EPA and Navy, and
the highest priority projects will be selected for initiation in FY89 as
funding permits. Future plans are to develop the ideas generated in the first
phase for destruction of CFCs through small pilot scale evaluations and then
adapt these technologies to the collection and destruction of chemical agents
which may be used in chemical warfare.
OBJECTIVES
The objective of the expert panel was to comment on those technologies
applicable to collection and destruction of CFCs and related compounds. The
panel members discussed their experiences and related them to the compounds at
hand. Also, they identified which technologies held the most promise and made
suggestions for general areas of research and development needed to develop
efficient collection and destruction technologies.
APPROACH
The CFC Destruction Expert Panel was comprised of persons with a wide
variety of expertise. Radian Corporation served as the General Contractor,
and contacted individuals with recognized ability in the area of waste collec-
tion and destruction. The members of the Expert Panel and their relevant area
of expertise are listed in Table 1. It was hoped that at least one industrial
2
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TABLE 1. LIST OF PARTICIPANTS
EXPERT PANEL
Dr. Barry Dellinger
Mr. Jose Bravo
Mr. Don Matter
Mr. Don Oberacker
Mr. Garry Howell
Dr. Norman Plaks
Mr. Joe McSorley
Mr. Ron Bell
Dr. Frank Castaldi
Dr. David DeBerry
VENDOR PARTICIPANTS
Dr. Hugh Reilly
Ms. Kristine Snow
Dr. Larry Britton
OTHER PARTICIPANTS
Mr. Dale Harmon
Dr. Dean Smith
Mr. Bill Rhodes
Mr. Roger Gibbs
Mr. G.E. (Buzz) Harris
Mr. Tom Nelson
Mr. Kirk Hummel
University of Dayton
Research Institute
University of Texas
Rollins Environmental
U.S. EPA/HWERL
U.S. EPA/HWERL
U.S. EPA/AEERL
U.S. EPA/AEERL
Radian Corporation
Radian Corporation
Radian Corporation
Thermal Treatment
Separations
Thermal Treatment
Thermal Treatment
Chemical Treatment
Corona Discharge
Combustion Research
Thermal Treatment
Biological Treatment
Chemical Treatment
Sandia National Laboratory Solar Furnace
Ogden Environmental Circulating Bed
Combustor
Texas Research Institute Biological Treatment
U.S. EPA/AEERL
U.S. EPA/AEERL
U.S. EPA/AEERL
U.S. Navy/NSWC
Radian Corporation
Radian Corporation
Radian Corporation
3
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chemist from a CFC producer would serve on the panel, but all three major U.S.
producers (DuPont, Allied, and Pennwalt) declined to participate.
A "Workbook" containing background material and properties of the com-
pounds of interest was prepared and provided to the members of the panel in
advance of the meeting. Also, Radian contacted several commercial vendors of
waste destruction technology and invited them to send a representative to
discuss their processes (see also Table 1).
The actual panel meeting was held June 23 and 24, 1988 at the Woodfin
Suites Hotel in Austin, TX. One of the vendor participants, Ogden Environmen-
tal, did not attend. The meeting agenda is shown in Table 2.
This report is intended to summarize the information presented at the
meeting, and discuss the conclusions of the expert panel. The report is
divided into the following sections:
• Introduction (containing Background, Objectives, and Approach);
• Summary and Recommendations of Expert Panel;
• Specific Research Tasks to Address Recommendations; and
• Conclusions.
The report also contains appended information on the meeting notes, handouts
from the meeting, and relevant articles.
4
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TABLE 2. FINAL AGENDA
June 23. 1988
8
00AM
8
05AM
8
15 AM
8
25AM
9
00AM
9
15AM
9
30AM
9
45 AM
10:00AK
10:15AM
10:30AM
10:45AM
11:00AM
11:15AM
11:30AM
12:00N-1:30PM
1:30PM
2:00PM
2:30PM
2:45PM
3:15PM
3:30PM-5:00PM
7:00PM
June 24. 1988
8:00AM-10:00AM
10:00AM
10:00AM-12:00N
12:00N-1:30PM
1:30PM-3:30PM
Welcome and Introductions
Opening Statement, U.S. EPA
Opening Statement, U.S. Navy
Workbook Overview
Mr. G.E. Harris
Mr. Dale Harmon
Mr. Roger Gibbs
Mr. Kirk Hummel
Expert Panel Commentary
Expert Panel Commentary
Expert Panel Commentary
Expert Panel Commentary
Morning Break
Dr. Barry Dellinger
Mr. Jose Bravo
Mr. Don Matter
Mr. Don Oberacker
Expert Panel Commentary
Expert Panel Commentary
Expert Panel Commentary
Expert Panel Commentary
Expert Panel Commentary
Expert Panel Commentary
Mr. Garry Howell
Dr. Norman Plaks
Mr. Joe McSorley
Mr. Ron Bell
Dr. Frank Castaldi
Dr. David DeBerry
Lunch Break
Vendor Presentation
Vendor Presentation
Dr. Hugh Reilly
Ms. Kristine Snow
Afternoon Break
Vendor Presentation
"Hazcon" Video Presentation
Open Discussion
Dr. Larry Britton
Dinner
Open Discussion
Morning Break
Ranking of Technologies Discussion
Lunch Break
Conelus ions/Recommendations
5
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SECTION 2
SUMMARY AND RECOMMENDATIONS OF THE EXPERT PANEL
In order to address the issues for EPA and Navy in terms of their partic-
ular interests, it was decided that the expert panel should separately evalu-
ate technologies for collection and for destruction of CFCs, halons, and CW
agents. Therefore, proposed technologies were evaluated for two distinct
classes:
• Technologies capable of collecting, removing, or destroying the com-
pounds 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 com-
pounds from the feed stream with no requirement for a breathable
off-gas (for example, bulk incineration of contaminated CFCs).
The reasons for the division of technologies are fairly simple: the Navy is f
only interested in technologies that generate a breathable airstream. For
collective protection systems used to filter large quantities of contaminated
air entering through ventilation systems and for individual protection systems
(gas masks), the cleansed airstream will be breathed by shipboard personnel.
The U.S. Environmental Protection Agency's main interest was to review
the technologies that are most applicable to the destruction of fully halo-
genated materials such as chlorofluorocarbons and halons. Those materials are
currently being regulated in the United States and elsewhere under the limits
established in the Montreal protocol. The Montreal protocol also allows for
production increases equal to any destruction of the regulated compound. To
date, these destruction techniques have not been identified.
6
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Technologies capable of providing both breathable and non-breathable gas
are of interest to EPA. Although large volumes or high concentrations of CFCs
might be most efficiently destroyed by a technology which would generate a
non-breathable gas (e.g., incineration), CFC emissions from such sources as
flexible foams or solvents might be considered for destruction or recovery by
technologies which would generate breathable air and allow the air to be recy-
cled to the work area or discharged directly to the environment.
SUMMARY OF EXPERT PANEL
The panel reviewed many technologies including thermal, chemical and bio-
logical processes. In most instances biological processes can only be used on
dilute aqueous streams and the biological destruction rate will be very slow.
This is based on experience with highly halogenated PCBs. Therefore, for the
two applications at hand, biological processes were eliminated as possible
candidates.
Breathable Air (CW Defensive Systems)
The overall conclusions of the expert panel for the breathable air situa-
tion was that the use of carbon adsorption as currently done by the Mavy was
the most reasonable, commercially available process. However, carbon adsorp-
tion is limited because high volatility toxic compounds are not strongly held
on carbon, and the reactive impregnants which are added to remove these com-
pounds 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 listed below:
• Inorganic Membranes; These may be either ceramic membranes or carbon
molecular sieves. The current applications for ceramic membranes
i
7
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are in the area of ultrafiltration, so they are not directly
applicable to gas purification. Carbon molecular sieve membranes
are being developed specifically for gas separations. Research into
the materials science aspects of these structures (such as obtaining
reduced pore diameters) could lead to development of sturdy,
chemically resistant separation devices. In the same manner as
other compounds such as silica, alumina, or magnesia, these
inorganic membranes could also serve as supports for catalytic
reaction.
Chemical Scrubbing/Destruction; This technology includes the use of
a highly alkaline, non-aqueous scrubbing liquor to absorb and
destroy the compounds of interest. One example that was cited was
the K-PEG process (KOH is the alkaline component; poly-ethyiene
glycol is the solvent). This process has been used to destroy PCBs,
but has not been developed beyond the bench-scale.
Corona Discharge; This process uses highly energized electrons from
an ionized corona discharge to dissociate the compounds of interest.
Early testing has included using a computer model to.refine the
geometry of the flow path to obtain higher destruction efficiency.
Additional research and testing will be required to determine the
energy requirements and obtain results on other compounds. One
advantage of this process is that it operates at essentially ambient
temperature and pressure.
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 (e.g.,
ZnCl^) which can easily be removed. However, this process has not
been successfully proven beyond the pilot-scale. Further research
will need to address the problem of maintaining an active metal
surface in the presence of air and moisture.
8
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• New Adsorbents; This technology uses tailor-made adsorbents, such as
new zeolites or aluminas, or new polymeric adsorbents, to obtain the
desired separation. One advantage of this technology is that these
compounds have a uniform or well-defined structure which results in
more consistent performance. Also, their properties may be altered
using various pretreatments.
Clearly there will be limitations since these technologies will likely be
tested using a subset of the full spectrum of potential compounds. New com-
pounds could be developed which might defeat these defenses.
Table 3 lists the expert panel's recommendations for those processes
which appear to offer the greatest potential for successful application to the
breathable air case. The listing is in alphabetical order. Listed in the
table is a brief description of the process, potential waste streams to which
it applies, stage of development, and its strengths and weaknesses.
Additional discussion concerning other technologies not listed is contained in
the Appendix (under Meeting Notes).
Non-breathable Air (CFC Destruction)
In the area of destruction of fully halogenated organics without the need
of a breathable off-gas, current thermal destruction processes (i.e., inciner-
ation) may be adequate. Destruction of chlorofluorocarbon wastes is currently
being done in at least one permitted facility (operated by Rollins
Environmental Services). The harsh environment created by the hydrogen
fluoride in the off-gas is one potential cause for concern, as specially
designed internal firebrick and mortars may be required. For example, one
company's experience (Rollins) led them to restrict the destruction of CFCs to
one such specially designed incinerator.
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TABLE 3. SUMMARY OF EXPERT PANEL RECOMMENDATIONS FOR BREATHABLE AIR CASE
Process Name
Description
Phase Status Expressed Advantages
Potential Limitations
BREATHABLE AIR (e.g.
Carbon Adsorption
CW Defensive Systems)
Current Practice
G.L
Simple technology
proven track record
Requires periodic regeneration or
replacement; requires impregnation
for some high volatility chemicals
Inorganic membranes
Ceramic membranes or
Carbon Molecular sieves
G. L
Operation at high tempera- May still require carbon bed
tures, chemically resistant downstream, or metallic salt
impregnants to react with high
volat1lity compounds
Chemical Scrubbing/
Destruction
Highly alkaline, non- G
aqueous scrubbing liquor
Superior to scrubbing
alone, since equilibrium
limitation is removed
Downstream treatment required
to prevent contamination of carbon
bed; may require pretreatment of
inlet air to remove moisture
Corona Discharge
High voltage generates
excited electrons which
dissociate hazardous
wastes
Destruction occurs at
ambient temperatures,
rapid process
May still require carbon bed
downstream; requires high voltage
power supply; may generate ozone
and/or NO
Metals Scrubbing
Active metals such as
zinc or aluminum
G.L B,P Rapid reaction forms
salts (e.g., NaCl) which
/
are easily removed
Uncertain ability to maintain
active metal surface; may require
pretreatment of inlet air to remove
moisture
New Adsorbents
Tailor-made adsorbents,
such as new zeolites or
other aluminas, or poly-
meric adsorbents
G,L (1) Improvement over carbon
with well-defined
structure
New selective adsorbent bed could
conceivably allow some less toxic
compounds through to bo handled by
a cheap carbon bed instead of an
expensive specialty adsorbent bod
G = Gaseous, L = Liquid, S = Solid, B = Bench-scaln, P= prototype, C - Commercial
(1) Some zeolites are commercially available, although for the applications in this study additional
research will probably be needed.
-------
Although CFCs are currently being incinerated, there is very limited data
regarding the destruction efficiency or products of incomplete combustion
(PICs) resulting from these operations. Data is lacking regarding the
quantity and fate of PICs; such compounds may be toxic and/or may pose a
threat to stratospheric ozone.
To summarize the status of incineration of CFCs, this is the only demon-
strated technology which is currently being used, and will likely continue to
be used in the near term. However, the feared potential of corrosive attack
to the refractory and the lack of accurate data on destruction efficiency and
PICs are problems which require solutions.
Other potential technologies which were recommended as good candidates
are listed below:
• Catalytic Thermal Destruction; Metal catalysts have been suc-
cessfully used to destroy dilute hydrocarbon gas streams at reduced
temperature, thereby saving energy and improving the economics of
this control technology. Potential problems with the destruction of
chlorinated hydrocarbons using this technology include low
destruction efficiency due to catalyst deactivation. Catalytic
processes may lose their advantage if high destructive efficiencies
require high temperatures.
• Chemical Scrubbing/Destruction; This process has already been
described for the breathable air case.
• Corona Discharge; This process has already been described for the
breathable air case.
• Metals Scrubbing; This process has already been described for the
breathable air case.
11
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• Pyrolysis; This technology involves thermal treatment in the absence
of air. Since CFCs are destroyed through bond homolysis or
hydrolysis, simple heating without air is sufficient to break the
bonds. Heating without air results in reduced gas flow, because
only the waste decomposition gases are sent to the downstream
scrubbers, in contrast to direct flame incineration where both waste
decomposition gases and fuel combustion gases are treated. Capital
and operating costs of the downstream treatment equipment for
pyrolysis may be less than direct flame incineration because of the
smaller size allowed by the reduced gas flow.
• Supercritical Water Oxidation (SCWO); This process is a modification
of Wet Air Oxidation (WAO) (described below) which involves a
supercritical fluid (water). This new technology features much
higher reaction rates than those achievable in the well known WAO
technology. Furthermore, SCWO operates at very high oxidant
concentrations which enhances the kinetics and produces favorable
equilibria. This technology could be limited by the metallurgy of
the system.
• 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.
R.F. Hein, DuPont Co. - Jackson Laboratory in DuPont's February 1980
Submission to EPA entitled "An Overview of Industry Efforts to Investigate
the Potential for CFC Emission Reduction."
12
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Table 4 lists the expert panel's recommendations for those processes
which appear to offer the greatest potential for successful application to the
breathable air and non-breathable air cases. The listing is in alphabetical
order.
Listed in the table is a brief description of the process, potential
waste streams to which it applies, stage of development, and its strengths and
weaknesses. Additional discussion concerning other technologies not listed is
contained in the Appendix (under Meeting Notes).
RECOMMENDATIONS OF THE EXPERT PANEL
The expert panel agreed that the following areas deserve priority for
further research. These are listed below:
CW Defensive Systems (Breathable Air)
- The panel agreed that future research in this area should begin with
basic fundamentals in order to determine the optimum long-term solution.
- The corona discharge process and the ceramic membrane process were pro-
posed as good potential candidates for initial research.
- Liquid scrubbing with a reactive component (i.e., K-PEG process) may
have application; however, the Navy is concerned with high humidity in the
breathable air.
CFC Destruction (Non-Breathable Air)
- A literature search should be performed to assemble all available data
on previous experience with conventional thermal oxidation (incineration) of
CFCs.
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TABLE 4. SUMMARY OF EXPERT PANEL RECOMMENDATIONS FOR NON-BREATHABLE AIR CASE
Process Name
Description
Phase Status Expressed Advantages
Potential Limitations
NON-BREATHABLE AIR (e.g., CFC Destruction)
Catalytic Thermal
Destruction
Destruction of organlcs
at moderate temperature
over a catalyat bed
G.L
Potential for thermal
destruction at much
lower temperature,
resulting in better
economics
Uncertainty regarding catalyst
resistance to poisoning & attack
Chemical Scrubbing/
Destruction
Highly alkaline, non- G
aqueous scrubbing liquor
Superior to scrubbing
alone, since equilibrium
limitation is removed
May require pretreatment of feed
to remove moisture
Conventional Thermal
Oxidation
(Incineration)
Incineration in direct
flame
G,L,S C Reliable technology,
proven track record
with other hazardous
wastes
Possible difficulty in selecting
materials of construction resistant
to corrosive attack; little actual
data on destruction efficiency and
PICs
Corona Discharge
Blgh voltage generates G
excited electrons which
dissociate hazardous
wastes
Destruction occurs at
ambient temperatures,
rapid process
Requires high voltage
power supply
Metals Scrubbing
Active metals such as
zinc or aluminum
G.L B,P Rapid reaction forms
salts (e.g., HaCl)
which are easily
removed
Uncertain ability to maintain active
metal surface; may require pretreat-
ment of feed to remove moisture
Pyrolysis
Thermal treatment in
the absence of air
G,L,S C Smaller gas flow allows
smaller downstream
treatment equipment
May form larger amounts of PICs;
possible difficulty in selecting
materials of construction resistant
to corrosive attack
Supercritical Water
Oxidation
Treatment with water at L
supercritical conditions
Potentially higher
destruction efflcloncy
than Wet Air Oxidation
Greater energy requirements; not
proven with CFCs; possible metallurgy
limitations; aqueous streams only
Wet Air Oxidation
Treatment with water 1.
at moderate temperature
Process operated at
moderate temperatures
Possible limitation to dilute streams
only; aqueous streams only
G = Gaseous, L - Liquid, S - Solid, B ~ Bench-scale, P ¦=¦ prototype, C - Commercial
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- 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 sta-
bility of CFCs and their basic combustion properties should be studied.
- Inorganic membranes should be studied from a materials science perspec-
tive. Also, new adsorbents should be investigated.
- The chemistry of scrubbing systems which contain a reactive component
(i.e., K-PEG process) should be studied.
- The corona discharge process as it currently exists requires small
scale tests, energy efficiency measurements, and modeling.
- Refractory linings that are resistant to HF should be studied and
tested.
- Potential catalytic materials for catalytic thermal destruction should
be evaluated.
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' SECTION 3
SPECIFIC RESEARCH TASKS TO ADDRESS RECOMMENDATIONS
The following is a. more specific list of possible research activities to
address the expert panel's recommendations.
For the breathable air case, the following research areas are proposed
(listed in alphabetical order of the process):
Ceramic Membranes:
1. Study methods to produce materials with the smallest pore sizes to
allow gas separations;
2. Investigate possible catalytic reactions and use of membranes as a
catalyst support; and
3. Determine how large a pressure drop is required to obtain a good
separation.
Chemical Scrubbing:
1. Determine effect of high humidity air on anhydrous scrubbing liquor;
2. Investigate various alkaline alcoholic agents and solvents (KOH,
NaOH); and
3. Measure destruction and removal efficiency, solubilities of agents
in oils, and vapor pressures of oils. Equilibrium data for agent in
various oils will determine destruction and removal efficiency.
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Corona Discharge:
1. Measure power consumption as a function of destruction efficiency;
2. Establish scaling rules and ability to model corona field; and
3. Investigate properties of ionized bed and reactive pellets.
Metals Scrubbing:
1. Investigate methods to retain active metal surface in the presence
of air or water; and
2. Conduct literature search on Grignard reagents (i.e., zinc and
aluminum).
New Adsorbents:
1. Characterize new materials; and
2. Measure adsorption isotherms with different compounds to determine
uptake.
For the non-breathable air situation, the following research areas are
proposed (listed in alphabetical order of the process) :
Catalytic Thermal Destruction:
1. Conduct laboratory tests using simple plug flow reactor to evaluate
catalytic materials in terms of activity and stability.
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Chemical Scrubbing:
1. See previous discussion for breathable air case; and
2. Determine if CFCs are amenable to treatment with KOH, since
preliminary literature review indicates that this is only effective
in dehydrohalogenation (i.e., a neighboring hydrogen atom is
required).
Corona Discharge:
1. See previous discussion for breathable air case.
Metals Scrubbing:
1. See previous discussion for breathable air case.
Pyrolysis and Conventional Thermal Oxidation (Incineration):
1. Perform a detailed literature review for data on thermal stability
or combustion properties of CFCs.
2. Perform comparative evaluation of these technologies on the
following factors:
Thermodynamic calculations and modeling.
Bench scale testing to obtain experimental data on PICs (using
gas chromatography/mass selective detector (GC/MSD)).
Based on the species identified in the bench scale testing,
compare the toxicity and residual ozone depletion potential of
the PICs from pyrolysis versus thermal oxidation.
18
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3. Evaluate materials of construction suitable for use in this servic
such as:
Refractory development program (to resist high temperature
fluoride attack).
Tail gas clean-up section for acid gases (HF.HCl).
Supercritical Water Oxidation and Wet Air Oxidation:
1. Measure destruction and removal efficiency as a function of
temperature and oxygen concentration; and
2. Conduct literature search to determine what results (if any) have
been obtained in other laboratories.
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SECTION 4
CONCLUSIONS
The expert panel discussions on Che most favorable technologies that war-
rant 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 air onboard a Navy ship;
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 ship-
board 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 refrig-
erants or waste solvents) although materials of construction for the
incinerator and byproducts of combustion should be further
researched; and
4. Sources of dilute emissions of CFCs may require technologies avail-
able in the longer-term. These options, which include technologies
such as catalytic thermal destruction, pyrolysis, or wet air
oxidation, may be source-specific.
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APPENDIX A
MEETING NOTES (OPENING STATEMENTS AND DISCUSSION)
21
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OPENING STATEMENTS BY PANEL MEMBERS
Kr. Dale Harmon, U.S. EPA/AEERL
Mr. Harmon discussed the work of AEERL in areas of global climate
and stratospheric ozone. He mentioned the projects on second generation
chlorofluorocarbon (CFC) substitutes and the current program to determine the
recycleability of used refrigerant from auto air conditioners. He explained
the overlap in Navy's interests regarding generation of breathable air from a
emission control device.
Mr. Roger Gibbs, U.S. Navy/NSWC
Mr. Gibbs discussed his agency's role in developing chemical warfare
defenses. In general, Mr. Gibbs is concerned with protecting ships under
chemical warfare at sea. He described the physical properties of potential
chemical warfare agents (see Table Al). Currently, the Navy uses activated
carbon beds with impregnants added to react with the high volatility hazardous
compounds that are not adsorbed on carbon, such as HCN. They currently use a
cartridge that combines a fixed bed carbon adsorber and a HEPA (High
Efficiency Particulate) filter. CFCs are also not strongly held on carbon, so
this was one tie-in with CFC destruction technology. The Navy will consider
high risk, high payoff technologies. They are interested in corona discharge
and catalytic destruction. The ultimate goal is to eliminate problems with
the carbon beds that include:
• Poor removal of highly volatile compounds such as hydrogen
cyanide or cyanogen chloride;
• Requirement for periodic replacement;
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TABLE Al. PHYSICAL PROPERTIES OF CHEMICAL WARFARE AGENTS
Parameter
ow
Hieh
Molecular Weight
3
Volatility (mg/m )
Vapor Pressure (mmHg)
Boiling Point (°C)
3
Lethality (mg/m -rain)
30
11.22
7.8x10"
¦151
10
364 .
1.28x10
7.97x10
298
15,000
12
23
-------
• The need for a regenerable system due to logistical problems;
arid
• Lack of specificity, e.g., the carbon beds will adsorb other
compounds such as water vapor, jet fuel vapors, and missile
exhaust, thus lowering the available capacity.
Gas masks are used for individual protection.
Don Oberacker (EPA/HWERL) asked about coordination with the Army,
especially regarding destruction of obsolete munitions: Mr. Gibbs responded
saying that the Army is the lead agency for CW and destruction of obsolete
munitions is the Army's program. He said that the Navy and the Army are
required to coordinate, and that the Navy budget is less than l/10th of what
the Army budgets for GW.
Jose Bravo (UT/Separations Research Lab) asked about absorption of
CW agents into paints and other surface coatings. Mr. Gibbs responded by
discussing the Navy's work in the area of strippable coatings.
Dr. Barry Dellinger (Univ. of Dayton/Incineration Research)
Dr. Dellinger spoke from his prepared papers. He discussed the
differences in predicted products of destruction between equilibrium calcula-
tions and kinetics. He stated that it would be better to produce HCl rather
than CI2 because HCl is much easier to scrub out. The formation of HCl or Cl^
would depend on the relative abundance of H and CI; or more generically, H and
X, where X is a halogen. Dr. Dellinger also explained the influence of the
"Deacon reaction" which involves 2HX + 1/2 0^ --> H2O + ¦ For the case of F
and CI, this reaction would promote the formation of HF and Cl^- He described
the flame inhibition problem attributable to halides. Scavenging by halides
results in a reduction of free OH radicals, which are considered the chain
carriers in combustion reactions. He stressed that incineration is a function
24
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of time; real situations cannot be modeled using equilibrium calculations.
His measurements on CFGs have been hampered by poor detector response to
fluorine (doesn't show up well on FID). He showed a model for destruction of
fully-halogenated CFCs (11, 12, 113, etc.) as the initiation being bond
homolvsis. which is the rupture of the carbon-halide bond. He presented some
data for destruction temperatures of various CFCs.
On the subject of products of incomplete combustion ("PICs"), Don
Oberacker asked if brominated compounds (e.g., halons) would produce more
toxic products than fluorine. In either case, he wondered about the formation
of Dioxin-analogs (F or Br instead of CI). Dr. Dellinger explained that it is
very likely that PICs may be higher molecular weight compounds compared to the
parent, (starting) materials. Garry Howell (EPA/HWERL) stated that one of the
reasons that CCl^ fire extinguishers were banned was due to the formation of
phosgene (C0C1). Ron Bell (Radian) asked if the stoichiometry was sub-
stoichiometric as this would affect the PIC/POCH (Principal Organic Hazardous
Constituent) ratio. Dellinger stated that these were sub-stoichiometric due
to real-life mixing problems in commercial incinerators.
Mr. Jose Bravo (Univ. of Texas/Separations Research)
Mr, Bravo spoke about three (3) primary areas for possible applica-
tion:
• Tailor-made or specialty adsorbents; these would include
zeolites, other crystalline aluminas, or possibly ion exchange
resins.
• Membrane separations; he was not optimistic about the use of
polymeric membranes, but mentioned new developments in the
areas of inorganic membranes. These could include ceramic
materials (aluminas again), or carbon molecular sieve type. He
explained that these could be used as catalyst supports.
25
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• Absorption; he proposed scrubbing processes in conjunction with
chemical reaction.
In another general comment, he emphasized that separations in combination with
chemical reaction was a definite advantage. This type of process would
benefit from the fact that equilibrium limitations would be removed if the
compound of interest could be simultaneously captured and destroyed.
Mr. Don Matter (Rollins Environmental Services/Incineration)
Mr. Matter explained that Rollins has incinerated waste CFCs since
1969. Their incinerators can achieve high destruction and removal efficien-
cies (DREs) of 99.99 to 99.9999%. He cited the example of a test burn in
their New Jersey incinerator with CFC-22 that achieved 99.9994% DRE. The
temperature is over 2000°F with between 2.3 to 2.5 seconds average residence
time. The temperature in the flame front may be as high as 2600°F to 3200°F.
Rollins operates several slagging rotary kilns. He discussed the problems of
incinerating CFCs in terms of the potential for severe scrubber corrosion.
The scrubber section has a drastic temperature change from around 2200°F to
185°F in a short duct. Also he talked about the problems within the incinera-
tor, particularly the refractory lining. They have painstakingly worked to
develop a resistant refractory lining for their New Jersey incinerator. They
currently restrict CFCs to less than 5% of the waste burned in the New Jersey
incinerator and less than 100-200 ppm in the Baton Rouge, LA and Texas incin-
erators. He described the types of CFC wastes that they have destroyed:
• Still bottoms from CFC production which contain 5 ppm
fluorocarbons;
• One ton cylinders of refrigerant; and
• Cases of aerosol cans.
26
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He described their tail gas treatment process: they have plenty of excess ^,
so there is no problem with formation of Cl^ or . Their scrubber sludge is
noticeably heavier when they incinerate CFCs; it contains CaCl^- Disposal
costs for the kiln ash and scrubber sludge are approximately $165 per ton.
Mr. Don Oberacker (U.S.EPA-HWERL/Thermal Treatment)
Mr. Oberacker reviewed the history of EPA's experiences with incin-
eration of hazardous wastes. He also discussed what he felt were the primary
needs for additional information regarding CFC destruction. These needs
included the following:
• More bench scale testing to determine temperatures of destruc-
tion, products formed in the destruction process (breakdown
products or PICs), and possible formation of fluorinated dioxin
analogs.
• Pilot and/or full scale testing with such technologies as the
rotary kiln or liquid injection incinerators. This might be
done at an EPA lab such as the Combustion Research Laboratory
in Arkansas.
He also mentioned the experience with combustion of aluminum pot liner waste;
these wastes contain fluorine, and the offgas contained He mentioned that
in the destruction of ethylene dibromide (EDB), the bromine was controlled by
adding sulfur to form HBr, which could be scrubbed out.
Mr. Matter (Rollins) stated that DuPont knows all about CFC destruc-
tion, but needs the appropriate forum to present such information.
27
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Mr. Garry Howell (U.S.EPA-HWERL/Chemical Treatment)
Mr. Howell discussed his background with destruction of EDB using
the K-PEG process, which uses potassium hydroxide (KOH) in polyethylene glycol
(PEG). This process has been used to destroy PCBs. The PEG serves as a phase
transfer catalyst (to improve solubility in the oil phase). His other sugges-
tions included:
• Zinc (or other active metals) which serve as Grignard reagents
to dehalogenate the compound. He described the reaction
between zinc and trichloroethylene (TCE) as "explosive"; and
• A patented process using a low temperature eutectic mixture of
molten salts. This process uses NaNO^, NaOH, and Na^CO^ to
react with the halocarbon. The NaNO^/NaOH ratio should be
controlled so that NaCl will precipitate out of solution.
To combat the corrosion problem in incinerators, he recommended
zirconia (Z^O^) refractory. He said that this material is used in oxygen
detectors for combustion processes (incinerators).
Dr. Norm Plaks (U.S.EPA-AEERL/Corona Destruction)
Dr. Plaks talked about the development work underway at AEERL on a
corona destruction process. This process uses high voltages of AC or DC
current to generate an ionized corona discharge. The energized electrons are
capable of dissociating the compounds of interest. In order to obtain high
DREs, several stages are connected in series. He discussed modifications to
the basic design such as a fixed bed of high resistance pellets, or a non-
conductive layer. These alternatives may offer the possibility of performing
both a destruction and neutralization process simultaneously.
28
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Mr. Joe McSorley (U.S.EPA-AEERL/Combustion Research)
Mr. McSorley talked about the various programs underway in the area
of combust3ion research. Some of the projects mentioned included:
• Tunnel Furnace used to perforin droplet studies;
• Rotary Kiln used to study the effects of containerized waste
destruction;
• Package Boiler Simulator used to test a low-NQx burner; and
• Circulating Bed Combustor (developed by Ogden Environmental).
Mr. Ron Bell (Radian Corp./Incineration)
Mr. Bell talked about his experiences in incinerator design and
start-up. He mentioned problems with the refractory lining. The point of
waste injection is the coolest spot in the combustion zone and is subject to
thermal stresses. Downstream problems are corrosion related. He stressed the
need to maintain the flue gas above the acid dewpoint to prevent condensation
and resulting corrosive attack. He pointed out that high excess air
(typically used to obtain complete combustion of the waste or fuel) also
results in the potential formation of Clj (instead of the preferred form,
HC1). He described the problems which may occur from acid mists. These
submicron-sized aerosols may be formed upon quenching, and are most difficult
to remove. Special treatment such as "Brinks" mist eliminators or venturi
scrubbers might be required.
29
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Dr. Frank Castaldi (Radian Corp./Biological Treatment)
Dr. Castaldi talked about problems with applying biological
processes to destruction of "refractory" compounds such as CFCs. Since there
are no natural compounds with structures similar to CFCs, naturally occuring
organisms have not developed which could utilize CFCs as a nutrient. Thus, he
felt that organisms which could break down CFCs would have to be genetically
modified for this purpose. He stated that CW agents would be more susceptible
to biological treatment than CFCs. Biological treatment is limited to the
ppm/ppb range only, and is most commonly used on aqueous streams or soil.
Another general limitation is the relatively long time frame for degradation.
Dr. David DeBerry (Radian Corp./Chemical Treatment)
Dr. DeBerry discussed several types of chemical processes:
• Hydroxy (OH) radical attack. This process was not expected to
be successful for CFC destruction, but might be effective at
destroying CW agents;
• Active metals. He described the use of active metals such as
sodium, potassium, aluminum, or zinc to destroy CFCs. Wastes
that contain water and oxygen may pose problems;
• Wet air oxidation is a process which uses a moderately high
temperature (>300°C) aqueous stream with oxygen to destroy
organic compounds. This process may not be effective for CFCs
due to their resistance to oxidation, but might be successful
based on hydrolysis.
Dr. DeBerry also discussed the corrosion problems which might be caused by CFC
destruction. The fluorides and chlorides liberated from CFCs would require
30
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the use of special materials of contruction. Specifically, he noted, that
although titanium materials are resistant to CI, they are attacked by F.
VENDOR PRESENTATIONS
Dr. Hugh Reilly (Sandia National Laboratory/Solar Destruction)
Dr. Reilly (and two other scientists from Sandia) spoke about their
solar furnace development program. Their unit has been tested as a methane
reformer, but they proposed a modification to serve as a thermal destruction
device for CFCs. Many unknowns were identified, such as the relative contri-
butions of thermal, catalytic, and photolytic destruction.
Dr. Larry Britton (Texas Research Institute/Biological Treatment)
Dr. Britton presented material on the biological treatment of
man-made organic compounds. He stated that halogenated compounds are more
resistant to biological degradation than similar alkanes or alkenes. He
explained that halocarbons can be degraded by aerobic or anaerobic conditions.
The organisms degrade these compounds through a "cometabolic transformation".
In other words, the organisms still require a primary nutrient source, but are
also tolerant of the halogenated compounds. The carbon is oxidized to CO^,
and the halogens are converted to their respective salts (e.g., KC1 or NaCl in
the case of chlorine). Chemical warfare agents may be more susceptible to
biological treatment than halocarbons; he cited experience with enzymatic
hydrolysis of organophosphorous compounds.
DISCUSSION
1. CW Defensive Systems for Breathable Air
Mr. Gibbs began by elaborating on their needs for improved CW
defensive systems. The Navy needs a constant air purification system that is
31
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not affected by ^0. Incineration is too energy intensive. Carbon does not
adsorb HCN and CNC1 well, and is also "blinded" (its capacity is reduced) by
H^O. Specific impregnants (silver, copper, and chromium salts) are needed to
react with the HCN/CNC1. However, the impregnants reduce the capacity of the
carbon, are non-selective, and therefore cause difficulty in knowing when the
impregnated carbon needs to be replaced. He stated that the Navy would prefer
a "passive" system; it would be more reliable and require less attention. The
Navy will probably continue to use carbon, but would like to have a device
installed upstream (such as corona destruction or oil scrubbing). He did not
find staged adsorption to be an attractive option. He was also interested in
continuous pressure swing adsorbtion (PSA) using carbon molecular sieves.
One suggestion proposed for the Navy was routing the contaminated
air through the onboard gas turbines or boilers to destroy the CW agents.
Catalysts and pre-heat were also proposed in conjunction with this idea; Mr.
Gibbs said that this type of option would require economic evaluation.
Mr. Bravo was asked to elaborate on the concepts using inorganic
membranes or tailor-made adsorbents. He explained that commercial processes
exist that purify water using either carbon molecular sieves or ceramic
membranes. He felt that the emphasis for development should be on the
materials science aspects and not on process engineering. Inorganic membranes
need improved strength and durability. He discussed the advantages of the MSC
(molecular sieve carbon) over ordinary activated carbon. The MSC (under
development in Israel) has a well-defined pore size distribution, resulting
from the fact that it is produced by pyrolysing a synthetic organic polymer
structure. Only the carbon "skeleton" remains. This offers the advantage of
more controlled and consistent properties compared to coconut-based activated
carbon, for instance. The MSC can be fabricated as a hollow fiber, a cast
sheet, or in pellet or granular form. In general, membranes work best to
concentrate dilute streams. It is more desirable to pass only the small mass
of contaminant through the membrane than to pass the entire bulk flow. In
32
-------
contrast to adsorption systems, the "capacity" of a membrane is very low, it
functions through separation, not retention.
Mr. Bravo also spoke on the subject of new adsorbents (such as
zeolites and aluminas). He cited a recent issue of Chemical Engineering
Progress (February 1988) which was devoted to zeolites.
On the subject of scrubbing processes for CW defensive systems (such
as the K-PEG process), several points were raised. First, the choice of
scrubbing liquid was discussed. The consensus seemed to be that a highly
refined oil with a low vapor pressure would be desirable. Possible candidates
include the silicone or fluorocarbon oils, which may be nonflammable as well.
It was not clear how water would be prevented from entering the scrubber with
the contaminated air, but the alkaline component of this process would not
tolerate much water. Also, it was considered important to prevent entrained
scrubbing liquid from contaminating the downstream carbon bed. Mr. Howell
felt that development of the process for the Navy's application could be a
good research project.
2. CFC Destruction
Mr. Matter was asked again about the types of CFC-containing wastes
that Rollins incinerates. He said that they regularly dispose of by-products
from CFC production processes, still-bottoms which contain residual CFCs
(1,000 to 2,000 gallons per month), waste solvents containing CFCs, and less
frequently, aerosol cans or off-spec refrigerant in large one-ton cylinders.
He repeated that Rollins uses a specialized refractory brick and mortar in the
kiln throat where the temperature difference is greatest. Mr. Matter also
stated that public data already exists on the subject of PICs from CFC-
containing waste incinerators in the RCRA Part B Test Burn Permits.
The possibility was raised of destroying certain CFC emissions (from
solvent cleaning or foam blowing, for example) in existing on-site equipment
33
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such as furnaces or boilers. Mr. Bell discussed some potential problems with
sending CFC-laden gases to on-site boilers:
• If a superheater is used, the tubes in this area may be hot
enough to be attacked directly by acid gases; and
• If an economizer is used, it is possible to cool the flue gases
to the acid dew point, resulting in condensation and localized
corrosion. Mr. Matter added that it is common practice in
Europe to send halocarbons to an available waste heat boiler.
Dr. Dellinger emphasized that PICs from CFC destruction may consist
of olefinic halocarbons. These compounds would have to be tested for toxicity
and possible residual ozone depletion potential. He also stated that combus-
tion was not necessary to destroy CFCs, since they are thermally decomposed.
A pyrolysis process might be smaller and cheaper.
There was a discussion regarding the other types of destruction
processes. Dr. Smith (U.S.EPA/AEERL) mentioned that PIMA (insulation foam
manufacturers trade association) was interested in the possibility of land-
filling old CFC-containing foam. Dr. Castaldi felt that this was not promis-
ing from a biological degradation perspective because of the time scale. The
question arose: "why bother to landfill if you can just incinerate?"
Mr. Howell was asked about his experience with a wet oxidation
process using sodium salts. He stated that acetic acid had been destroyed by
the NaNO^/NaOH mixture, and that a surface catalytic effect with Hastelloy C
was noted. The tests were conducted in an autoclave at 300"C.
Photolysis was proposed as a destruction technology, since this is
the mechanism by which CFCs are decomposed in the upper atmosphere. It seems
that this process is too slow compared to more conventional processes. - The
"LARK" process (which used Hg or Xe arc lamps to generate high intensity
34
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light) was mentioned, but the experiments showed a slow photolysis rate. Dr.
Dellinger felt that photolysis may be enhanced at elevated temperatures.
Regarding the plasma arc processes (for example, Westinghouse Plasma
Systems), Mr. Oberacker cited unfavorable test results showing formation of
PICs in larger than expected amounts. He felt that it would likely require a
downstream afterburner and cleanup systems as well. Thus, the plasma system
begins to look more like a conventional incinerator. Mr. Oberacker also
described his experience with a microwave plasma destruction process. He felt
that the costs were high, and successful operation was "more art than
science."
35
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APPENDIX B
HANDOUTS FROM EXPERT PANEL AND VENDOR PRESENTATIONS
36
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Mr. Jose Bravo, Separations Consultant, University of Texas
ROLE OF SEPARATIONS TECHNOLOGIES IN THE COLLECTION AND
DESTRUCTION OF CFCs AND HALONS
Separations technologies will play an important role in the collection and
destruction of halocarbons at two different levels; separation of the halo-
carbons themselves from carrier streams for the purposes of decontamination
and purification, and the removal of potentially harmful by-products generated
during destruction of the halocarbons. The role of separations in the purifi-
cation of halocarbons for reuse and recycle will be of lesser importance in
the future; furthermore, the applicable technological concepts (mainly distil-
lation) used for this are very similar to those applied in the manufacture of
the halocarbons and thus is fairly well known and widespread.
The problem of dealing with gaseous or liquid streams that contain small
amounts of halogenated pollutants, particularly CFCs, poses an important
technological challenge in the field of separations. The techniques of choice
should be ones that tend to concentrate and immobilize the contaminants for
easy disposal.
Adsorption onto a solid from either a gaseous or a liquid stream can undoubt-
edly perform the necessary removal from the carrier stream provided the
adsorbent is selected carefully or even tailor made. Adsorption is the
technique that offers the best possibility at this time of producing essen-
tially pure carrier stream. This can be of great importance in military
decontamination applications where breathable air is to be obtained from
contaminated environments.
The technology for manufacturing high-performance, specialty adsorbents is
growing by leaps and bounds. The limiting factor in the applicability of
adsorptive processes for the removal of halocarbons continues to be the
regeneration step. The design of the adsorbent can play a major role in the
ease of regeneration and on the overall applicability of the process. An
excellent combination could be to achieve the regeneration of the adsorbent
with a gaseous fuel so that the pollutant is destroyed when the fuel is
burned.
Membrane technology can also find wide application for the removal of halo-
genated organics from air and water. Membrane selectivity will be the largest
barrier that needs to be overcome and the way to do this is by a materials
science approach. The limiting factor in the application of membrane tech-
nology in the fields where potential exists is in the material science and not
in the process engineering aspects. Combinations of membrane technology with
others, such as stripping and adsorption, can prove to be the most cost-
effective schemes, because the selectivity limitation can be dealt with
through recycle.
37
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New membrane materials, such as carbon molecular sieves and ceramics, can
prove very useful in cases where mechanical and chemical resistance are
imperative. These sturdy materials offer the possibility of effecting a
destruction reaction in conjunction with a membrane separation to favor the
thermodynamics of total destruction. One could even envision a catalytic
membrane that would enhance the rate of reaction and at the same time remove
the products of reaction as they are formed, thus reducing the effect of
equilibrium limitations.
Extraction techniques, in particular, high pressure or supercritical extrac-
tion (SCFE), offer the potential for easy recovery of concentrated halocarbons
from dilute water feed streams. Co-solvent technology can have a great impact
on the ability of SCFE to find industrial implementation in the removal of
CFCs from water.
Still another interesting possibility is that offered by a combination of
absorption and chemical reaction where the pollutant could be removed from a
gaseous stream into an absorbing liquid. Once in the liquid phase, a chemical
reaction, such as a hydrolysis, could render the pollutant harmless and make
it easy to dispose of. Alternatively, the pollutant could be absorbed into a
liquid fuel stream to be sent to a combustion chamber designed to effectively
incinerate the pollutant as the fuel is burned for energy.
Air and steam stripping are proven, cheap methods for dealing with volatile
halocarbons. Combinations of air stripping and gas phase adsorption have
proven to be very effective for the removal of some chlorinated hydrocarbons
from source and supply waters. This could also be the case for dilute streams
of CFCs in water. The interesting research issues in the areas of air and
steam stripping deal with the development of more effective mass transfer
devices.
The complete destruction of CFCs and Halons will produce, in the best of
cases, some environmentally harmful compounds such as hydrogen halides and
halogen oxides. These can be effectively dealt by absorption, followed by
neutralization with a strong sodium or potassium base rendering the halogens
harmless.
38
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United States Patent i^;
Hawellet al.
11 Patent Number:
[45] Date of Patent:
4,497,782
Feb. 5. 1985
[5-q MKTHOD FOR DESTROYING TOXIC
ORGANIC CHEMICAL PRODUCTS
("5] Inventors Samuel G. Howell. »6fio AMon Dr..
Cincinnati. Ohio 4524-1 William R.
Birchall. 555^6 Country Club Rd .
South B
[2fj Appl. No.. 570.853
[22] Filed: Jan. 16. 1984
Related U.S. Application Data
[63J Continuation-in-part of Ser. No. ¦437.434. Oct 28. 1982.
int. a.» COID 3/00
U.S. a. 423/184; 423/659:
423/DIG. 12-. 55/22S
Field of Search 422/D1G 12. 184.659:
55/228
[51]
[52]
[53]
[561
References Cited
U.S. PATENT DOCUMENTS
3,505.01 S 4/1970 Bawaetal 42V653
3.642.583 2/1972 Greenberg ei al. . 203/11
3.647,358 3/1972 Greenberg 55/228
.'oJ'.JS.1 >• DirRnuw ei jl OS/21?''
3.S45.1f Yosim et 4i. 42.''ls4
4.I45..W6 •-!<>"') Grantham 42?/12
OTHER PUBLICATIONS
A.P.C.. Application of Beck. Walter e; al. Scr No.
39J.2J3. published Jj.. 13. l°43
Fukaaa. Shuzo et al. "Cracking Aromatic Chlorinated
Hydrocarbons". Appl. Jan. I0"?, abstracted .n
Chem. Abs. vol. *2. !Q~5, ,TM25Hr
Primary Examiner—John Doll
Assuiani Examiner—Roberi L Stcll
Attorney, .4 gem. or Firm—Wood. Herron i E'. ans
[57] ABSTRACT
A method for destroying toxic organic chemical prod-
ucts. The method is particularly adapted for the de-
struction of polyhaiogenated polvphenyls. especially
polvchlonnated biphenyls (PCBs). The iojuc organic
chemical product is mtimatety contacted and reacted
with a molten mixture of an alkali metal hydroxide and
an alkali metal nitrate, so that it is convened to harmless
products which, in the case of PCBs. include a hahtie
salt, at least one carbon oxide, and water By incorpo-
rating a substantial excess of nitrate in :ne mixture most
of the salt is caused to precipitate and to settle out to the
bottom for easy removal
15 Claims. 2 Drawing Figures
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4.497 732
METHOD FOR DESTROYING TOXIC ORGANIC
CHEMICAL PRODUCTS
RELATED APPLICATION
This application is a continuation-in-part of our co-
pending I S. patent application Ser No 4J".434, Hied
Oa. :"s:.
FIELD OF THE INVENTION
The present invention relates 10 a method for de-
stroying environment-contaminating :oxic organic
chemical products, including polychlorinated biphe-
n> Is.
DESCRIPTION OF THE PRIOR ART
The problem of environmental contamination caused
by toxic materials and the related health nsks to all
forms of life has become of major concern as industrial
societies seem to create ever increasing numbers of
toxic chemical products, particularly organic products.
Environmental contamination may occur by reason of
the toxicity of such a product, per se, or by reason of the
toxicity of by-products formed during the use of such a
product, or by reason of the toxicity of by-products
formed during the manufacture of such a product. The
problem of environmental contamination has become of
such magnitude, in fact, that the federaJ government
and many state governments have established indepen-
dent agencies charged with the responsibility of con-
trolling. or at least minimizing, all forms of environmen-
tal contamination.
Environmental contamination occurs in a number of
ways. It may, for instance, occur when toxic products
resulting from the combustion of petroleum, coal and
other carbonaceous energy sources are released directly
mio the atmosphere, as during the operation of vehicu-
lar engines. Such contamination also occurs at industrial
installations that rely on carbonaceous fuels as energy
sources. At least in the United States, vehicular gasoline
engine emissions are now required by law to be caialyti-
callv oxidized to less obnoxious by-products pnor to
being discharged to the atmosphere. Emissions from
coai and other carbonaceous fuel-burning industrial
installations are similarly treated, or are burned at very
high temperatures in afterburners. Various ether means
and methods have been proposed to treat environment
contaminating emissions of this type. One such proposal
is discussed in Greenberg U S Pat. No 3.647,358 and
involves subjecting industrially generated carbon and
hydrocarbon waste products to the catalytic action of a
molten sail bath at temperatures below the normal com-
bustion temperatures of such waste products, without
chemica. reaction occurring between the waste prod-
ucts and any of the components of the salt bath.
Environmental contamination also occurs when toxic
organic chemical product", that are not the products of
combustion of carbonaceous fuels, enter the environ-
ment. Such toxic organic chemical products may be
primary products, i.e.. those manufactured for a specific
use such as. fur example, a herbicide, pesticide, insecti-
cide. or the like. They may be secondary products, i.e.,
by-products resulting from the manufacture of primary
products. Toxic organic chemical products may enter
the environment in various viays, for example, by re-
lease to the atmosphere during their manufacture, or by
release into water supplies by leaching from agricultural
lands to which they have been applied or from landfills
10
1J
:o
25
30
35
50
55
60
65
into which the\ have beer, deposited without ceiovlV
cation, or by release from other products :n which the>
have been used as components
The toxic organic chemical products above ret'errec
to often take the form of poiynuclear aromatic organic
compound1. which are substituted or, the nucleus -v
halogen, luifur. or phosphorous atoms. Recresen;ju\e
of this !>pe c.f toxic organic chemical products and
those io which :ne method of this invention is particu-
!ariv directed, are polyhalogenjted pclypnenyi com-
pounds ar.a. mere particularly. poi>chionnu:ed bipne-
nyls. often referred io ssmpiy as PCBs PCBs. ano poiy-
halogenated polyphenyis in general, are prepared b>
the direct chlonr.ation of the selected potyphenyl com-
pound which results in a mixture of isomers the bulk of
which, in the case of PCBs. are reported to be the m-
chloro- and tetrachloroisomers. with the balance txmg
the other isomers. The polychlorinated polyphenyis.
including the PCBs. are considered to have excellent
properties of inertness, fire resistance and thermal sta-
bility. ail of which has rendered them highly suited for
use in a variety of areas including varnishes and paints,
copy paper, plasticizers. printing inks, lubricants, and
particularly in electrical transformers and capacitors.
Although PCBs have been known chemically for
many years and have been manufactured and used com-
mercially for quite some time in the several areas noted
above, the significance of their toxicity has only been
recognized more recently. Because of this lack of
knowledge concerning their toxicity, these products
were permitted to enter the environment through un-
controlled burning and direct disposal into public sew-
age systems and landfills without regard to the possible
consequences of these acts. The seriousness of this ear-
lier uncontrolled disposal of PCBs. and related toxic
products, is now recognized in the light of more recent
knowledge that tnese prooucts are very resistant to
biodegradation and will, accordingly, persist in the
environment for long periods of time.
The conventional way to destroy toxic organic chem-
ical compounds has been to subject them to burning at
very high temperatures, as above described with re-
spect to the products of combustion of caroonaceous
fuels. PCBs. however, are known to oe quite resistant to
oxidation, so that when these, and related products, are
subjected to burning in conventional industrial fur-
naces. it often is impossible io maintain the high destruc-
tive temperatures for the required residency time neces-
sary to convert them to carbon dioxide, water and hy-
drogen halide. In order to attain these high destructive
temperatures, i.e.. greater than 1100* C. and to maintain
them for a residence time sufficient to totally destroy
the PCBs. therefore, requires specializes furnace equip-
ment which can be costly to fabricate. Moreover, since
aromatic halogen derivatives such as PCBs have notori-
ously iow fuel v alues, destruction of such products by
burning necessarily requires an e.xtemal heat source n
order to reach and maintain the conversion tempera-
turr- Finally, destruction of PCBs and related haloge-
nated products produces highly corrosive hydrogen
halide acids whicn should be neutralized before dis-
charge. preferably at a point in the procedure designed
to minimize their corrosive effect on the furnace and
allied equipment
Reference was earlier made herein to Greenberg U S
Pat. No 3.647.35S which suggest the use of a molten
salt bath as a cutalvtic oxidizing medium for ihe deMruc-
41
-------
4.4<
3
turn of various industrial^ generated carbon and hydro-
carbon waste products The use of j molten salt bath has
also been proposes in L S Pat. No l.M5-.,06 b> freal-
ine waste materials containing a radioactive cicmcnt
The use of a meit of a hydroxide by us«!f to decompose
PCBs t* taught in Japanese paicni application Ser No
71c><>. filed Jan. 1&. |97_" The use of a moiten sol vent
has also been proposed in L' S Pat. No r-.S45.lW for
the disposal of certain types of organic pesucical com-
pounds. None of these. however. is concernea with the
destruction reaction here invoked, and none enables
the solid reaction product to be so easily removed,
which is an important advantage for continuous opera-
tion.
SUMMARY OF THE INVENTION
Notwithstanding the fact that PCBs are no longer
commercially manufactured in the Untied States and
are totally banned in some areas of the world, the envi-
ronmental hazards of these products continue to exist 20
simply because there are other areas of the world where
PCBs continue to be manufactured and used, albeit
under varying degrees of governmental control in most
instances. Moreover, the most widely applied area of
use for PCBs in the United States has been in electrical 23
transformers and capacitors which have useful lives of
many years, but which, on eventual replacement, must
have their PCB content totally destroyed. Currently,
the only procedures which have been accepted by the
U.S. Environmental Protection Agency for destroying JO
PCBs and related toxic halogenated products are de-
struction by burning, a procedure that has the several
disadvantages noted above, and by treatment with so-
dium metal, an expensive treatment which is limited to
dilute, nonaqueous solution of PCBs. Accordingly, 35
there bas remained a serious need for an improved
method for destroying PCBs and related halogenated
products.
It is a principal object of this invention to provide
such a method. It is a further object of this invention to O
provide a method of destroying PCBs and other toxic
organic chemical products that is total in us effect and
in compliance with the standards established by the
U.S. Environmental Protection Agency. A still further
object of this invention is to provide a method for de-
stroying PCBs and other toxic products that does not
require the excessively high temperatures demanded by
burning. U is also an object of this invention to provide
a method of destroying PCBs and related halogenated
products that does not result in highly corrosive, or
otherwise objectionable, emissions. Another objective
of this invention is to provide a method of destroying
PCBs and related halogenated products that can also be
used effectively to destroy other types of toxic organic
chemical products such as. for instance, organic aro-
matic compounds substituted by sulfur and/or phospho-
rus atoms.
These various objects are met in accordance with this
invention by providing a method of destruction that
comprises reacting the toxic organic product with a
molten mixture of an alkali metal hydroxide and an
alkali metal nitrate to form an alkali meial salt, under
conditions such that the salt is precipitated from the
molten mixture and settles out. More particularly, in a
specific embodiment the method of this invention com-
prises intimately mixing PCBs. or related halogenated
products, with a molten alkali metal hydroxide-alkali
metal nitrate mixture, under such conditions of temper-
7.782
4
aturc. time, and melt composition as will cause the total
destruction oi the i'CBs by converting the haloger.
content so an alkali metal halide salt which is precipi-
tated. and b\ convening ihe carpon and hvurogen con-
5 tent to carbon dtuxide and water, which are released in
vapor form.
While it ib not the intention to restrict this invention
by any particular theory of operation. it would appear
:nai the method invokes ihe reaction of ihe PCHs K|.
tu :he alkali metal hydroxide to form ihe corresponding
alkali metal haiide. one or more carcon oxides, and
water. Notwithstanding the property of unusual inert-
ness that PCBs are known to possess. >t has. neverthe-
less. been reported in the literature that under very
* extreme conditions PCBs will react with sodium hy-
droxide to form a dehalogenated biphenyl as an nrgamc
secondary reaction product ("Chlorinated Biphenyis
and Related Compounds" by R. E. Hatton. Encyciopt-
dta of Chemical Technology. Kirk-Othmer. Wiley Inter-
science Publications. Wiley 4 Sons. 1st Ed.. Vol 5, pp.
844-848). The dehalogenated biphenyl resulting from
the alkali metal hydroxide reduction is then apparently
oxidized by the alkali metal nitrate, principally to water
and carbon dioxide, the alkali metal nitrate being re-
duced in the latter reaction to the alkali metai nuntc. In
further consideration of the theory of operation, prac-
tice of the method of the invention appears to have
shown some apparent evidence of a synergistic effect of
the two component molten bath, since a melt of either
component alone fails to produce the same degree of
destruction. In any event, whatever the theory, destruc-
tion of PCBs and related halogenated products by the
method of this invention is complete in an environmen-
tal sense so as to comply with the standards established
by the United States Environmental Production
Agency for these products.
The proportion of nitrate and hydroxide should be
sufficient to stoichiometncally react with the toxic feed.
Beyond that, however, it has surprisingly been found
desirable to maintain a substantial excess of nitrate over
the stoichiometric proportion actually needed to oxi-
dize the organic secondary reaction product, e.g.. the
dehalogenated biphenyis It has been determined that
use of a substantially higher proportion of nitrate than
required for reaction reduces the solubilitv ot the reac-
tion product salt in the meit. and thereby facilitates
precipitation of salt from the liquid phase. Moreov er, it
has further been found thai increasing the proportion of
nitrate reduces the viscosity of the mixture, thereby
enabling the precipitated salt panicles to settle out from
the melt and to collect at the bottom This greaily facili-
tates removal of salt from the reaction sue. and is espe-
cially useful in a continuous or semi-ccnunuous process.
The mol amount of nitrate to be used shouid be at
least twice that of the hydroxide present. In respect to
the salt, the amount of nitrate should be such as to cause
the salt to exceed its solubility limit ana so to precipi-
tate. The optimum proportions depend on melt temper-
ature, the nature and concentration of the salt, and other
factors. For a given set of circumstances the optimum
proponion can be determined by a series of compara-
tive tests, in which the amounts of hydroxide and salt
are held constant and the proportion of nitrate is gradu-
ally increased. An NOj/OH mol ratio of about 3:1 is
preferred where the nitrate is regenerated and reused,
and where the OH/I'CB ratio is near unity Ai very-
high ratios of nitrate to hydroxide it appears that salt
solubility begins to increase, so thai above that level salt
42
-------
4,497,782
is not so readily precipitated from the met: At present,
it appears that NaNOi/NaOH/PCB ratios of ji leaM
M.I will usuallv accomplish salt precipitation, and
substantially higher ratios are preferred.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. I ss a scnemauc view illustrating a system for
carrying out the method of this invention, wnsrein the
toxic product is in liquid form:
FIG. 2 is a schematic view illustrating the presently
preferred continuous method for the practice of the
invention, wherein the toxic product is vaporized.
DETAILED DESCRIPTION
Referring now to FIG I. there is schematically rep-
resented an enclosed chemical reaction vessel 10
adapted to hold the hydroxide-nitrate molten baih :n
which the destruction of a toxic organic chemicai prod-
uct. such as PCBs, is to be carried out. Reference nu-
meral 11 indicates a hydroxide-nitrate mix storage
hopper from which the mix is fed by mix feeder 12
through mix feed column 13 into reaction vessel 10,
wherein it is kept in an agitated condition by agitator
blade 14. Surrounding reaction vessel 10 is a heating
enclosure IS provided with a heating element 16 by
means of which the hydroxide-nitrate mix is maintained
in a molten state. Provided at the top of heating enclo-
sure S is an exhaust vent 17 for discharge of the heating
element products of combustion, while at the bottom of
heating enclosure 15 and associated with reaction vessel
10 is a salt discharge valve 18 through which alkali
metal halide can be withdrawn. Reference numeral 19
indicates a toxic product storage Lank from which the
product intended for destruction is fed by means of
pump 20 into reactor 10 through toxic product feed
column 21. the lower end of which extends beneath the
surface of the hydroxide-nitrate molten bath. The upper
. end of toxic product feed column 21 extends through
the enclosed top of reaction vessel 10 into the upper
section of heating enclosure IS from which it communi-
cates with reflux condenser 22 on the exterior of heating
enclosure 15. Reflux condenser 22 is provided with
exhaust means 23 for venting uncondensed reaction
vapors from reaction vessel 10 to the atmosphere, and a
condensate line 24 for refiu.xing concerned reaction
vapors from reaction vessel 10 back to toxic product
feed column Z1 The upper end of a nurue oxidizing
column 25 extends through the enclosed top of reaction
vessel 10 and communicates with a demister 26 in the
upper section of heating enclosure 15. from which it
communicates directly with reaction vessel 10 through
toxic feed column 21 and indirectly therewith through
reflux condenser 22. Surrounding reaction vessel 10 is a
heat exchanger 27 for preneatmg air passing from air
compressor 28 into nitrite oxidizing column 25 through
air valve 29
In carrying out the method of this invention using the
apparatus of FIG. 1. the hydroxide-nitrate mix selected
to constitute the melt is conveyed from hydroxide-
nitrate storage lank II into reaction vessel 10 via feeder
12 and mixer 13. The metal-based components of the
mix may be any member selected from the class of alkali
metals but. for purposes of the method of this invention,
the hydroxides and nitrates of sodium and potassium are
preferred as a practical matter because of their common
industrial availability. Whether or not the metal-based
components of the hydroxide and nitrate are the same as
or different than one another appears to be immaterial
from the standpoint of the efficacy of the method but. as
j practical matter, they will usually hi- the same
In the case of PCBs. wnh respect to which further
description will be directed, the amount cf metal h\ ¦
5 droxide present in the mix must be sufficient to essen-
tially completely convert 'ne chlorine content of the
PCBs lo the meul chloride salt. *hiie the alkali metal
nitrate must be present in lufHcient amount io essen-
tially completed ovidize the carbon and hydrocarbon
i0 content of the PCBs to a carbon oxide and water, and to
cause salt precipitation and senlinc. Since the isomer
mix can vary from situation to situation in the chlorina-
tion of biphenyl. u is desirable to analyze the PCBs so
that appropriate hydroxide-nitrate quantities and mol
15 rattoscan be provided to effect the intended destruction
and precipitation. The mol amount of nitrate should he
substantially higher than that of the hydroxide to cause
the salt to be readily precipitated and to settle out
Reaction vessel 10 is heated by means of heating
20 element 16 so as to convert the hydroxidenitrate mix to
a molten bath which serves as the medium in w hich the
destruction of the PCBs will take place. The tempera-
ture of the molten bath can range from a minimum of
about 2J0" C. to as high as 800" C.. or even higher. The
25 exact temperature in any particular situation will be
determined by the heat required to maintain the hydrox-
ide-nitrate mix in a molten state without decomposition
of either component, and by the heat required to carry
out the destructive reactions of the PCBs. For most
30 purposes, it has been found that a melt temperature of
about 273* C. to 450" C. maintained in the reaction zone
will be effective in attaining the desired destruction,
when the PCBs are in the liquid phase in the melt.
Once the molten alkali metai hydroxide-alkali metal
J5 nitrate bath has been formed and the intended reaction
temperature established, a stream of PCBs to be de-
stroyed is introduced into reaction vessel 10 from stor-
age lank 19 The normal physical form of PCBs may-
vary from liquids to solids of varying crystallinity de-
¦W pending upon the isomer mix. Any of these may be
treated by the method of this invention in their normal
physical form. For ease of injection into the molten bath
the PCBs should be in a liquid form. Introduction of the
PCBs into reaction vessel 10 is made preferably beneath
•i5 the surface of the molten nydrcxide-nitrate bath by
injecting the liquid PCBs slowly into a flowing stream
of air or oxygen.
As the PCBs are slowly added to the hydroxideni-
trate melt, the destructive reactions commence. Alkali
50 metal chloride is formed which is only partially soluble
in the melt and which, if the nitrate concentration is
high enough, precipitates toward the bottom of reaction
vessel 10 from which it can eventually be withdrawn
through salt discharge valve 18. Gaseous reaction prod-
55 ucts formed by the nitrate oxidation of the dechlon-
nated biphenyl residue accumulate in reaction vessel 10
and are passed through reflux condenser 22. Any con-
densate drawn o(T frum reflux condenser 22 is returned
as a reflux in toxic product feed column 21. L'ncon-
60 densed vapors in reflux condenser 22. comprising prin-
cipally carbon dioxide and water, are discharged to the
atmosphere The reaction time required to attain com-
plete destruction of the PCBs. or other produci. as the
case may be, will vary from situation to situation de-
65 pending upon the composition of the toxic product and
the quantity of loxic product lo be destroyed. The
needed reaction time in each situation can best be esiab-
lished by simple tests.
43
-------
¦i.49"
7
During (he destructive reactions of the PCBs. a
stream of the mnlten bath. no« containing alkali metal
nitrite a* a product of the -.urate reduction. may bo
withdrawn from the body of the bath and passed
through nitrite oxidizing coiumn 25. Alkali metal nitrate !
can be regenerated by contacting the stream of ni-
tritcbcaring melt in nitrite o*:dizing column IS wun
preheated air introduced through air valve 29 The
oxidized stream of meit nu» bearing at least some re-
generated alkali metal nitrate is passed through demister
26 for removal of droplets, anc is returned to reaction
vessel 10 through toxic product feed column 21. H>-
droxidc is consumed by reaction with the toxic product,
and should be replaced as needed Although the nitrate
can be regenerated in the bath, some is earned out as
sait is removed. Replacement nitrate should tnerefore
be added to maintain the desired proportions.
In order to provide belter contacting, columns 13. 21
and 25 are desirably provided with baffle plates or agi-
tating means as shown in the drawing. Use of motor
driven agitating means (such as shown in column 13) is
preferred.
Although not essential to ihe efficacy of the method
of this invention, an oxidation catalyst such as ammo-
nium molybdate can be incorporated in the hydro*- ^
idennrate melt. Similarly, injection of air into the react-
ing hydroxide-nitrate melt can be continued after addi-
tion of the PCBs is completed for all or a pan of the
reaction period, to oxidize the nitrate that are formed.
FIG. 2 shows a presently preferred method for carry- JO
ing out the method of the invention on a continuous or
semi-continuous basis, wuh the toxic product in a gase-
ous phase. In this apparatus, which is not claimed herein
and which is to be the subject of a separate patent appli-
cation. the nitrate-hydroxide liquid mixture is contacted 35
with PCB vapor in countercurrent flow relation. The
nitrate and hydroxide are charged to a tank or reservoir
35 wherein they arc initially meited by an external heat
source means, i.e.. a gas flame or heater tubes 33. lo
produce a liquid melt. The meit is then delivered from *0
the reservoir 35 by a pump 36o. through a line 36. to the
top of a reaction column 37 The lower end 34 of col-
umn 37 extends below the liquid level 51 The moiten
hydroxide-nitrate mixture is distributed over tne inter-
nal cross-sectional area it the top of the column, as b> •»?
a spray head 38. and makeup reagents are added
through line 53 and trickles downwardly over a series
of pacKing sections 40 in the column. These plates may
comprise corrugated steel sheets. Desirably four verti-
cally spaced packing sections 40 are provided. The 50
toxic product ,s carried by an air stream in a line 41. and
is supplied :n;acolumn 37 near the lower end thereof,
above the melt surface 51 The feed may comprise liq-
uid droplets. This feed falls onto the melt, the tempera-
ture of which is above the boiling point of the material 55
to be destroyed, so as to vaporize it. (The boiling points
of PCBs are in the range of about 2?5*-50Q* C.. depend-
ing on the particular compound.) The toxic product is
vaporized, and it and the vapor of its decomposition
products rise upwardly in column 37, in countercurrent 60
flow to the falling streams of hydro.xide-nitrate mixture.
The composition of the reacting mass varies greatly
along the column; the toxic product reacts near ihe
bottom to form secondary organic products which then
react in the higher packing sections. The nitrate and t>i
hydroxide concentration is high at the top of the col-
umn but becomes progressively lower toward the bot-
tom. Once initialed, the destruction process is highly
,782
8
exothermic and large quantities of heat must be re-
moved in order to maintain a steads temperature. Desir-
ably this :s earned out, as shown in the drawing. 3>
cooling cot is 45 between the respective packing sec
uons 40 A coolant is passed through the con* 45 to
maintain the reaction mass at the desired temreraiore
level If necessars. pump uptlow line 36 can aisc 3e
cooled
The !ov.c product vapor reacts with the moiien mix-
10 ture in the packing section and produces sa.i wmcn ;s
earned downwardly in the column b\ the meit streams
Provided the proportion of nitrate in the tank is suffi-
ciently high, the salt is precipitated and the panicles
settle out in the melt pool in the tank 35, to the bottom
15 46. The tank is provided with drag bar conveyor 48
which scrapes the salt panicles from the bottom of the
tank and sleeps :hem over an apron 49 for easy re-
moval. The gaseous reaction products, i.e.. carbon diox-
ide and water vapor, pass through a mist eliminator 52
20 and a vent 53 at the top of the column.
It is a highly desirable feature of the invention that
the sail is segregated in the bath at the bottom and can
be easily removed in crystal form. This avoids the accu-
mulation of dissolved or suspended sait in the meit, and
greatly facilitates continuous operation. It also insures
that the concentration of reaciants remains high, to
drive the reaction toward completion.
By way of demonstrating the etTect of a high propor-
tion of nitrate m causing the reaction product salt to
precipitate, the following senes of comparative tests
was run.
A. Salt was gradually added to a clear men of
NaNOj at a temperature of 400* C. When the sail con-
tent of the mixture reached approximately 6^- ("r by
weight of the total) grains of salt were visible, indicating
that the solubility limit of the salt was reached. The salt
did not dissolve but remained as undissolved salt grains.
B. NaOH was added to the 6% NaCl melt of A.
above, to provide a 3:1 moi ratio of N'aNOj to NaOH.
The viscosity of the melt did not change greatly, but the
salt grains dissolved. This shows that salt is more solu-
ble in a NaNOj/NaOH melt than in NaNO; aione
C. Salt was gradually added to the NaNOj/NaOH,'•
NaCl mixture of B. At about 149r NaCl. by weight of
the totai mixture, the solubility limr. of the sait wis
again reached and the salt grams remained undissolved
in the melt.
D. Salt was added to a 400' C. melt of NaNO; and
NaOH in 5:'. mol ratio. The solubility limit of the salt
was reached at only about &%. This shows that the
higher proportion of nitrate facilitates precipitation of a
larger proportion of sait from the melt.
E. When the melt of D is cooled from 400* C. to
about 35C' C . the cloudiness of the melt increases, thus
indicating further precipitation of the salt from solution.
When the mall is cooled to about 275*. it becomes thick
and grainy, indicating heavy salt precipitation This
indicates the desirability of cooling the melt containing
the reaction product salt, in order to facilitate its precip-
!U**'on. For this reason it is preferred to run the destruc-
tion reaction at about 400" C.. then to cool the meit
containing the salt to assist in salt precipitation.
F If a salt crystal growth promoting agent such as
manganese dichlonde. MnClj. is added to the melt,
viscosity is reduced, salt crystals grow and settle out
still more readily. It is known that manganese salts such
as the dichlonde. as well as lead and cadmium salts, will
assist in the precipitation of salt from water (see A'irk
44
-------
4.497,
9
Othmcr. 2d ed. Vol IS. p 4S0V but so far as is known
such agents hase not heretofore been used to assist tn
the precipitation of ^all from molten solutions.
The method of;hi*, invention is further descncea by
the following Examples which are illustrative oniv and 5
not intended to be restrictive. Unless otherwise indi-
cated. all pans arc by weight,
EXAMPLE 1
A mixture of 33 5 pans by weight (0.34 moll of so- 10
mum hydroxide and 34} parts (4.0 moi) of sodium ni-
trate (corresponding to a NaNO-./NaOH mcl ratio of
about 4 S) were introduced into a closed steel reaction
vessel equipped with a dip lube and a condenser After
the hydroxide-nitrate mixture has been converted to a 15
molten bath b> application of heat. 50 parts of poly-
chlorinated biphenvl were introduced. This corre-
sponds :o a NaOH/PCB mot ratio of 1.1 and a Na-
NOj/PCB mol ratio of 1.1 The PCD was fed beneath
the surface of the molten bath by allowing it to drip 2Q
slowly into a stream of nitrogen passing through the dip
tube. The quantities of NaOH and NaNOj were in ap-
proximately 10% excess of that needed stoichiometn-
cally to convert all the PCB to NaCJ. CO2 and water,
however the nitrate was not regenerated by addition of 25
external air during the reaction. PCB injection into the
molten bath was continued over a period of about 30
minutes during which period the temperature of the
bath was maintained at a temperature of 338* C.-340" C.
Follow ing completion of injection of the PCB. the tern- 30
perature of the molten bath was raised to 345' C. and
maintained at that temperature for one additional hour.
The reaction vessel was then opened and the molten
bath removed and allowed to solidify by cooling. 0 04
part of a brown. waxy material was removed from the 35
resultant cake by washing with toluene. On analysis by-
gas chromatography, the waxy material was shown to
contain 1000 ppm of PCB. This indicated a 99.99 — %
destruction of the PCB injected into the reaction vessel.
The amount of NaCl formed in this reaction was inefTi- 40
cient to judge its solubility in the melt, but some grarnie-
ness was evident, indicating incipient precipitation.
EXAMPLE 2
The procedure of Example 1 was repeated. 50 parts 45
of an askarel comprised of 70% Monsanto Chemical
Company AROCLOR 1254 brand of PCB and 30% of
tnchlorobenzene. was injected into the molten bath
over a two hour period, using air instead of nitrogen as
the earner and purge gas in the dip tube. The air flow 50
rate was 1 L./min.. which was sufficient to reoxidize the
nitrite formed The average meit temperature was about
;45" C. A temperature of 340* C. was maintained for an
additional one hour after addition of PCB had stopped,
after which the reaction vessel was opened and the 55
molten bath removed and permuted to solidify 0 155
part of a waxy suDstance was extracted by toluene
washing from the resultant cake and was found, on
analysis, to contain 9750 parts of PCB. This represented
a 99 5% destruction of the PCB injected into the reac- 60
lion xessel. The air stream helreC to regeneraie and
maintain lhc proportion of nitrate.
EXAMPLE 3
The procedure of Example 1 was repealed except 65
that 6S.6 parts (0.81 mol) of sodium nitrate were used in
the hydroxide-nuraie mix. This represented an approxi-
mate I I nitraie to hydroxide rjtio 5C parts of the PCB-
782
10
containing askarel were injected into the meit by means
of an air siream over a period of one nour 11 a tempera-
ture of 270* C. The amount of NaSO; was less than that
required stoichiometncally to convert the dehaloge-
nated biphenvl secondary reaction product tc CO; The
hydroxide-nitrate molten bath temperature was main-
tained at 270* C. for an additional hour while the injec-
tion of air into the bath was continued. On separation 0!
the molten bath and solidification. 2.55 parts ot" a light
tan waxy substance were recovered which, analysis,
was found to contain 4.2% PCB. This represented a
S9.78% destruction of the PCB injected into the reac-
tion vessel. This example illustrates that less complete
destruction is attained as temperature is decreased.
EXAMPLE 4
The procedure of Example 1 was repeated using
114.4 parts (1.35 moi) of sodium nitrate in the hydrox-
ide-nitrate mix together with 0 18 pans of ammonium'
molybdate as a catalyst- The NO5/OH ratio was about
1.6. 50 parts of the askarel were injected into the hy-
droxide-nitrate molten bath by means of an air siream-
Injection time and subsequent reaction time totalled 6.5
hours at a temperature of 410" C. The salt did not pre-
cipitate. as its solubility limit was not excetded. The
solidified molten bath was white in color, exhibited no
exudation, and no PCB could be washed from it. 5.75
parts of condensate collected from the condenser were
found to contain 22 ppm of PCB on analysis. This repre-
sented a 99.995% destruction of the PCB injected into
the furnace, but the NaNOj proportions used were too
low for salt removal.
To. show the criticality of using the hydroxide and
nitrate together in the method of this invention, the
following Examples 5 and 6 were conducted in which
the nitrate and hydroxide components of the mix-were
used, in the absence of each other.
EXAMPLE 5
The procedure of Example 1 was repeated except
that the molten bath consisted of 67 parts of sodium
hydroxide together wtth 0.35 pan of ammonium moiyb-
daie as a catalyst. The molten bath contained no alkali
metal nitrate. Addition of 100 pans of PCS-containing
askarel into the molten bath by means of an air stream
was made over a period of "0 minutes while maintaining
a temperature of 340* C. The injection of air was contin-
ued for an additional hour while continuing to maintain
a 340" C. temperature. On opening the reaction vessel,
it was found that the bath was substantially solid rather
than liquid. Salt remained suspended in the melt. Grainy
deposits of an orange-red color were found in the upper
reaches of the reaction vessel. Deposits also pamally
blocked the condenser. 15 parts of condensate were
collected from the condenser which, when analyzed,
showed a PCB content of 29 6%. This represented a
91.1% destruction of the PCB injected into the reaction
vessel, a level low as not to be useful in a practical sense.
EXAMPLE 6
The procedure cf Example 1 wai repeated except
that (he molten bath consisted of 312 parts of sodium
nitrate together with 0.18 part of ammonium molybdate
as a catalyst. The molten bath contained no alkaii metal
hydroxide. Addition of 50 pans of PCB-containmg
askarel into the molten bath by an air stream was made
over a period of 1.75 hours while maintaining a temper-
ature of 400" C. The injection of air wis conttnued for
45
-------
4.497.'
11
jn jddiiional hour while maintaining a 3C0* C icmpera-
ture. On opening of the reaction vessel. the bacn najs
founu (O he biac«. with a carbonaceous suhsiance On
solidificaiion of the molten bath, a gummy exudate;
formed on the surface On extraction with solvent, this 5
exud-ile w-as found to contain substantial particulate
carlxrn The level of destruction of the PCBs was much
lower than in Examples 1-5
EXA.MPLE7 i0
The procedure of Example I is repeated except that
the hvdroxide-nitraic mi.i comprises 33.5 parts of potas-
sium hydroxide and 343 parts of potassium nitrate. All
other conditions of Example I remain the same. Per-
centage of destruction of PCBs is essentially the same as I!
thai ootained in Example I This demonstrates that
other alkali metals can be used instead of sodium.
The description of the method of this invention has
thus far been directed principally to the destrucnon of
polyhalogenated polyphenyls. and particularly to poly- 20
chlorinated biphenyls with respect to which it has been
found to be especially effective. The method of this
invention is, however, equally applicable to (he destruc-
tion of other toxic halogen containing products, as well
as to the destruction of sulfur and phosphorus contain- 25
ing toxic products. Representative of these types of
products are. dichlorodiphenyltrichloroethane (DDT),
gamma hexachlorocyclohexane (LINDANE); ortho-»-
bromo-2.5-dichlorophenyl-omethylphenyl phos-
phorothionate (LEFTOPHOS); iexachlorobenzene: JO
2,4-dichlorophenoxyacetic acid (2.4 D); 2.4,5-tnehloro-
phenoxyacetic acid (2,4,5 T); 2,3,7,Stetrachlorodiben-
zop-dioxin (AGENT ORANGE); 2,2-dichloroethenyl
dimethyl phosphate (DJCHLOROPHOS); 0,0-
dimethyl dithiophosphate of diethyl mercapiosuccir.ate 35
(MALATHION); ethylene dibromide and other halo-
gencontaining toxic organic products. The destruction
of a phosphorous and sulfurcontaining toxic organic
chemical compound is shown in the following example.
40
Example 8
The reaction vessel described in Example 1 was
charged with 65 parts NaOH. 130 pans of NaNO:-, and
0 25 parts of ammonium molybdate. The mixture was
melted and heated to 440" C. After temperature equili- ¦»<
braiion. 50 parts of Ortho Malathion 50 Insect Spray.
50% solution (Chevron Chemical Company) were
added over a one-hour period. The reactor was opened
and was found to contain partly solidified saJls. Analysis
of the salts showed a phosphate content of 2-98(as 50
PiOs) and a sulfate content of 11.8%. The S/P ratio of
the salts was approximately the same as that of the
Malathion, which indicated complete destruction.
It snould be noted that a further advantage of the
invention is that the reaction mixture is non-corrosive to 55
steel, in contrast to a reaction mass which coniains
hydroxice but not nitrate. Inspection of the reaction
vessel after use shows a shiny hard black oxide coating,
without rusting or corrosion. This greatly reduces the
cost of the reactor that would otherwise be required. 60
Having described the invention, what is claimed is:
I. Jn a method for destroying a toxic organic chemi-
cal product wherein said to*ic product is coniacted
with a molten mixture of an alkali metal hydroxide and
an alkali metal nitrate to form an alkali metal salt as a 65
product of reaction with said hydroxide, an organic
intermediate reaction product also being produced.
'82
12
ihe improvement which comprises.
maintaining a mitl rauo of saic curat; 'o *Jid hydros-
ide in said molten mixture of at .east 2 !. the pro-
portion of said nitrate in said mixture furt.ier being
sufficiently high to provide ; lost viscosity of sxd
mixture so ihat a aree portion of said aikali metal
sail settles js suiid salt particles io ihe bottom of
saiQ molten mixture.
reacting said organic intermediate recfion prrd'.ict
with said nitrate to form CO CO;, or a mixture
thereof, ana siaier. and
removing said solid salt particles from said mnlter.
mixture at the bottom thereof
2. The method of claim 1 wherein the mol ratio of
nitrate to said hydroxide is in the ranee of 2.'; to M
3 The method of claim I wherein ihe moi ia;io of
nitrate to said hydroxide to said toxic product is in the
ranee of about 2.1.1 ;o about 5:1.1.
4. The method of claim 3 wherein said toxic organic
chemical product is a polyhalogenateo polypheny!
product.
5. The method according to claim 4 in which the
polyhalognenated polyphenyl product is contactec in
gaseous form with said molten mixture.
6. The method of claim 1 further wherein a portion of
said nitrate is removed from the bottom of said moiten
mixture along with said solid salt panicles, and
additional mitrate is added to maintain the proportion
of said nitrate in said mixture sufficiently high ihat
said solid salt panicles continue to settle to the
bottom of said molten mixture.
7. The method of claim I wherein said mixture is
initially melted by heat from an external source, and
wherein said mixture is thereafter maintained in molten
condition by heat of reaction
8. The method of claim 1 including the further step of
removing heat of reaction from said molten mixture, as
said destruction proceeds, to maintain a substantially
constant temperature.
9. The method according to claim 1 in which the
toxic organic chemical product has a substituent any of
halogen, sulfur o phosphorous atoms.
10. The method according to claim 1 :n which saiu
molten mixture is at a lemperature which is above the
boiling point of said toxic product.
11. The method according to claim 1 in which said
nitrate is reduced to the corresponding nitrite by reac-
tion with said intermediate reaction product, and at
least a portion of said molten mixture :s contacted with
a stream of oxygen-containing gas. to oxidize the nitrite
back in. the nitrate
12. The method according to claim 1 in which addi-
tional alkali metal hydroxide and nitrate are added to
the mixture to at least partially replace that which re-
acted in the destruction of said product.
13. The method according to claim 1 in which the
mixture is cooled after said salt has formed therein,
thereby further decreasing the solubility of said salt in
the mixture and increasing us precipitation from said
mixture.
14. The method according to claim 1 further wherein
a salt crystal growih promoting agent is aiso present in
said mixture, to promote growth of salt crystals in the
molten mixture
IS The method of claim 14 wherein said salt crystal
growth promoting ageni is manganese chloride.
• * • • •
46
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INCINERATION TECHNOLOGY FOR
THE DESTRUCTION OF
CHLOROFLUOROCARBONS, HALONS, AND
RELATED CHEMICALS
Prepared for:
CONFERENCE ON CFCs, HALONS, AND RELATED CHEMICALS
COLLECTION AND DESTRUCTION
Auscin, Texas
23-24 June 1988
Prepared by:
RADIAN CORPORATION
RONALD D. BELL
47
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TABLE OF CONTENTS
1.0 INTRODUCTION 49
2.0 INCINERATION TECHNOLOGY OPTIONS 49
2 .1 Rotary Kiln 49
2.2 Fluidized Bed 50
2.3 Liquid Injection
2.4 Emerging Technologies 5^
3.0 QUENCHING TECHNOLOGIES 52
3.1 Air Injection 53
3.2 Evaporative Water Cooling 53
3.3 Waste Heat Recovery 53
4.0 AIR POLLUTION CONTROL TECHNOLOGIES 54
4.1 Wet Electrostatic Precipitators 55
4.2 Fabric Filters (Baghouse) 56
4.3 Venturi" Scrubbers 56
4.4 Packed Bed Scrubbers 56
4.5 Sorbent Injection (Semi-dry Scrubbing) 57
48
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1.0
INTRODUCTION
The problem of how to dispose of toxic chemicals has been an
important environmental issue for over 50 years in the United States.
Development of environmentally acceptable methods for disposal of these
materials, however, has been fully addressed in the past 10 years as a result
of pressure caused by such regulatory acts as the Resource Conservation and
Recovery Act (RCRA) and the Toxic Substances Control Act (TSCA). One method
that has found acceptance by the regulatory agencies for treatment of toxic
and hazardous wastes is incineration coupled with air pollution control
devices which remove acid gases and particulates that are formed in the
combustion process.
This presentation presents an overview of the incineration
technologies which are suitable for treatment of chlorofluorocarbons, halons,
cyanides, organo-phosphates and other related chemicals.
2.0 INCINERATION TECHNOLOGY OPTIONS
The incineration technologies best suited for these applications are
rotary kiln (RK), fluidized bed combustion (FBC), and liquid injection (LI).
Each of these technologies is currently being operated in commercial
facilities for incineration of these types of wastes. Other emerging
technologies that have not been used commercially but are capable of treating
some of the wastes under consideration are electromelt, plasma arc, molten
salt, and wet air oxidation. All of the technologies have relative advantages
and disadvantages. Such factors as flexibility, reliability, operability, and
cost must be considered in selecting the optimum incinerator technology.
2.1 Rotary Kiln
Rotary kiln incinerators are thermal treatment devices which utilize
a rotating refractory lined cylinder as the primary combustion chamber for
49
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combusting ar.d/or devolatilizir.g solids. The major components of a rotary
kiln system include a solids feed system, the rotary kiln, a secondary
combustion chamber, and air pollution control devices. The kiln is operated
at temperatures in the 1500-1800°F range with residence times of 1-2 seconds
for gases and minutes to hours for the solids. Products of combustion from
the kiln enter the secondary combustion chamber and are exposed to
temperatures in excess of 2000"F with sufficient excess air and residence time
to obtain the required destruction efficiency.
2.2 Fluidized Bed
Fluidized bed incinerators use a bed of granular material, such as
sand, which is fluidized by the upflow of combustion air to create turbulence
which enhances the combustion process. As waste material is injected into the
bed, heat is transferred into the waste feed. As the waste material oxidizes,
the energy released is transferred back into the bed material to provide
preheat for incoming wastes. These units are operated at temperatures in the
1500-1800°F temperature range with residence times of 1-2 seconds for the
products of combustion. The bed depth for most conventional fluidized bed
combustors is 3 feet when not fluidized and 6 feet during actual operation.
These systems are limited to wastes such as sludges and solids that have
fairlv uniform shapes and small diameters.
A variation in fluidized bed technology allows for the bed material
to be circulated through the combustion chamber, collected, and returned to
the bed. This is referred to as circulating bed combustion and offers some
advantages over stationary bed units by allowing higher gas flows and
utilizing more of the combustion chamber for destruction efficiency.
Fluidized bed combustors offer high destruction efficiencies and do not
require secondary combustion chambers. Use of limestone as the fluidizing
media allows in situ removal of acid gases, thus minimizing the need for air
pollution control devices.
-------
2.3 Liquid Injection
Liquid injection involves spraying the waste into a refractory lined
combustion chamber with air and auxiliary fuel. The secondary combustion
chamber included in other incinerator technologies (i.e., rotary kiln and
electric infrared furnace) is actually a liquid injection incinerator which
provides additional residence time for the products from the primary
combustion device. It is limited to waste streams that are liquids that can
be atomized. The typical operating temperature is 2000-22QQ°F with residence
times that are in the 1-2 second range. High destruction efficiencies are
achieved, but solids and most sludges cannot be treated in a liquid injection
incinerator.
2 .4 Emerging Technologies
New technologies which can be used for the destruction of
chlorofluorocarbons and related compounds are plasma arc, electromelt furnace,
molten salt, and wet air oxidation. None of these is currently being used in
commercial incineration facilities, but all have been proven operationally.
These systems are limited in their application but do offer advantages for
certain types of wastes.
Plasma arc systems offer a means of achieving extremely high
temperatures for the destruction of compounds that are difficult to oxidize.
The process involves introducing wastes into the discharge of a plasma arc
torch where temperatures as high as 9000°F are achieved. The wastes are
atomized and pass into the main reaction chamber where they recombine to form
nonhazardous products of combustion.
The electromelt furnace and the molten salt are similar in their
methods of heat transfer to the waste feed streams. Both use molten liquids
to provide a high temperature for pyrolysis of the wastes. In the case of the
electromelt furnace, electrical energy melts constituents that form a molten
glass phase into which the waste materials are fed. The molten glass phase
51
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croduces a constant infrared heat flux at 22CC°F to provide for the ignition
and pyrolysis of the waste materials. Additional air is injected above the
molten pool to provide for oxidation of the combustible materials. The molten
salt incinerator operates under the same principle but uses a salt with a high
melt point to provide the heat flux.
Wet air oxidation units use air dissolved in water at high pressures
(50C-3000 psi) to oxidize wastes than can be dissolved in the water. This
reaction occurs at temperatures much lower than those required for thermal
oxidation, usually in the 250-530"? range. This technology is limited to
liquids, and the concentration of combustibles must be maintained at levels
low enough to prevent excessive heat build-up in the water. Auxiliary fuel is
minimized by cross heat exchange between the treated discharge and the inlet
feed stream.
3.0 QUENCHING TECHNOLOGIES
Since virtually all incinerator applications involve treating wastes
that will produce particulates and acid gases, flue gas treatment is required
before combustion products can be discharged to the atmosphere. The process
steps required to remove particulates and acid gases cannot be achieved at the
temperatures required for oxidation. Therefore, a flue gas cooling step
referred to as quenching is required.
Quenching technologies used to cool flue gas prior to flue gas
treatment include air injection, evaporative cooling by water injection, and
waste heat recovery. The quench step can have one or more stages whicn can
employ combinations of the quench mechcds listed above. Important factors in
the evaluation of a quench system include availabilitv of quench medium, ease
and reliability of operation, and cost of equipment.
52
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Air Iniecciori
Air injection involves the introduction of ambient air directly into
the flue gas stream to provide direct contact cooling upon mixing of the two
streams. This method is quite reliable and offers no inherent operating
difficulties. It does have the disadvantage of requiring a large amount of
quench medium relative to flue gas. In general, the flue gas is cooled from
temperatures in the 2200°F range down to the 170°F range. This means that the
air will be heated from about 70°F to 170°F, resulting in about 14 parts of
cooling air being required for each part of flue gas. This large increase in
mass flow will require all of the downstream air pollution control equipment
to increase in size to accommodate the added flow.
3,2 Evaporative Water Cooling
This method of quenching is also accomplished by direct contact with
the hot flue gas. Water is spray atomized into the flue gas stream and
provides cooling primarily through vaporization of the water droplets.
Although this method of injection requires additional energy in che form of
hydraulic head and atomization media such as compressed air or steam, che
quantity of quench medium required is greatly reduced because the heat of
vaporization of the liquid provides che heat sink. Only about 0.5 part of
water is required per part of flue gas to achieve the same level of quenching
as outlined above with air injection. The injection of water dees create the
possibility ot corrosion if acid gases are present ir. the flue gas stream.
Proper design and material selection for the quench system can minimize the
pocential for corrosion. This method of cooling does not affect downstream
equipment sizing co tne extent that air injection does and, in general, is
more economical.
3 . 3 w'aste Heat Recovery
For the other methods of quenching discussed above, che energy
expended cc obtain che temperature necessary for the required destrue:ion
53
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efficiency in Che incinerator was lose cue Che stack. To maximize energy
utilization, a waste heat boiler can be used to provide flue gas cooling and
to generate usable energy in the form of steam. The major disadvantage is the
potential for corrosion and plugging due to corrosives and particulates
present in most incineration flue gas streams. Care must be taken in the
design of the waste heat recovery system to minimize these potential sources
of operational difficulties. Preconditioning by air injection to solidify
molten salts is often used in conjunction with soot blowing to minimize
fouling of the boiler tubes. Proper design and material selection can
minimize the potential for corrosion. The cost of the equipment is greater
for this method than for air or water quench, but waste heat recovery is the
most economical method because of the recovery of usable energy.
4.0 AIR POLLUTION CONTROL TECHNOLOGIES
The flue gas treatment system for an incineration process should
provide for the removal of particulates, acid gases, and heavy metal
contaminants. Since much of the particulate matter in the flue gas stream was
formed by condensation of constituents that were in the vapor state at the
operating temperature of the incinerator, the resulting particle size
distribution will be mostly in the micron to sub-micron range. Because acid
gases tend to form aerosols upon condensing, the technologies suited for
particulate removal must be able to remove sub-micror. particulates including
aerosols formed as the flue gas is cooled. The technologies which are proven
for these applications include both wet and dry techniques. Dry removal
methods include electrostatic precipitators and fabric filters or baghouses.
Wet methods include packed bed scrubbers, venturi scrubbers, and wet
electrostatic precipitators. Their use is categorized in Table 4-1.
54
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TABLE 4-1. AIR POLLUTION CONTROL TECHNOLOGIES
Pollutants Controlled
Technology Particulates Acid Gases Metals
ESP (wet)
Venturi Scrubber
Packed Bed Scrubber
Baghouse
Sorbent Injection
1-prime removal technology
2-secondary removal technology
3-not applicable
1 1 2
1 1 1
3 1 3
1 2 1
3 1 3
4 . 1 Wet Electrostatic Precipitators
Wet electrostatic precipitators use electrically charged plates to
collect liquid droplets that are passed through an electrical field and
separate them from the flue gas stream. These devices must operate at low gas
velocities in order to achieve the separation. As a result, the pressure drop
across the ESP is quite low when compared to other methods of removal. The
main disadvantage, however, is trie tact that ESPs are large vessels requiring
increased capital costs. When exposed to acid gases in the flue gas scream,
potential for corrosion is increased. The vet system is utilized to remove
acid gases from the flue gas, but requires special materials of construction
due to the corrosive environment.
55
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4 . 2 Fabric Filters t'Bag'nouse)
Fabric filters, commonly referred to as bag filters or baghouses.
collect particulates from the flue gas by allowing the dusc-laderi gas to pass
through a fabric sock which provides surface area to filter ouc the
parciculates. Bag materials limit the use of this technology to a maximum
temperature of 400"F. Bag filters offer high removal efficiencies with low to
moderate pressure drops. Particulates are removed by pulsing the bags with a
back flow of compressed air or by actually reversing the flow through the bags
to dislodge the collected particles. The major disadvantages of this method
of removal are the possibility of bag rupture allowing particulate emissions
and the exposure to corrosion of the casing by acid gas dew point corrosion.
4.3 Venturi Scrubbers
Venturi scrubbers are wet scrubbing devices that provide fcr the
removal of particulates by intimate contact with a liquid stream. The flue
gas stream is accelerated through the throat of the venturi. The high
velocity gas stream atomizes the liquid into small droplets which are
penetraced by the particulates. The entrapped particles in the liquid
droplets are coagulated and recovered from the flue gas stream. This method
requires high pressure crops relative to cry removal methods such as ESFs and
Dag filters. The main advantages are its low capital investment, high degree
of reliability, and ease of operation. This type of scrubber will also remove
acid gases if they are present in the flue gas.
L.4 Packed Bed Scrubbers
Packed bed scrubbe rs utilize a packing mate rial to provide contact
surface for absorpcion and neutralization of acid gases. The exhaust gases
from the incinerator are cooled to saturation and then flew up through the
packing material. A liquid reagent is introduced at the top of the scrubber
and flows countercurrentLy down over the packing. Acid gases are absoroed
56
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Into the liquid and neutralized by a chemical reaction wich the reagent. This
method of scrubbing achieves high removal efficiencies with low to moderate
pressure drops. Material of construction must be chosen that are compatible
with the acids that may be formed if they are not totally neutralized by the
reagent.
4 . 5 Sorber.t Inlection (Semi-dry Scrubbing)
Sorbenc injection involves the injection of a solution or dry-
reagent to adsorb and neutralize acid gases in the gas stream. It is usually
injection by spray atomization if in solution form, rotating cup if a slurry,
or pneumatic conveying if a dry solid. The temperature should be
approximately 600°F for optimum removal efficiencies with the point of
injection downstream of the incinerator. The resultant salt is recovered in a
baghouse or ES? along with the removed particulates. The major advantage of
this method is that acid gases are neutralized and their resulting salts are
recovered dry without the need for additional equipment if particulate
recovery is required. The main disadvantage is the limited removal efficiency
compared with packed bed scrubbers.
57
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INCINERATION TECHNOLOGY
for the
DESTRUCTION OF CHLOROFLUOROCARBONS,
HALONS, AND RELATED CHEMICALS
yjy
oo
Presented by
RADIAN CORPORATION
Ronald D. Bell
-------
WASTE FEEDS
/ S /
INCINERATION SYSTEM
COMBUSTION FLUE GAS COOLING FLUE GAS TREATMENT
TREATED FLUE GAS
TO ATMOSPHERE
FLYASH
AND SALT
FLYASH
SLAG
DRY BULK SOLIDS
PUMPABLE LIQUIDS
AND SLUDGES
DRUMMED
NON-PUMPABLES
SOLIDIFICATION
ENGINEERED LANDFILL
PHYSICAL/CHEMICAL
TREATMENT
AQUEOUS ORGANIC
RESIDUES
SOLID RESIDUES WITH
ORGANICS
WET SCRUBBER
SPRAY DRYER WITH
FABRIC FILTER
PROCESSES
AIR INJECTION
WASTE HEAT
RECOVERY BOILER
WATER SPRAYS
PROCESSES
ROTARY KILN
INCINERATOR WITH
SECONDARY
COMBUSTION
CHAMBER
FLUIDIZED BED
COMBUSTOR
LIQUID INJECTION
PROCESSES
SCHEMATIC ILLUSTRATION OF INCINERATION SYSTEM
-------
INCINERATION TECHNOLOGY OPTIONS
• Rotary kiln
• Fluidized bed
• Liquid injection
• Emerging technologies
plasma arc
electromelt
molten salt
wet air oxidation
-------
Combustion
Waste
Liquids
Combustion
Auxiliary
Fuel
Auxiliary
Fuel
1500 - 1800 °F
Secondary
Combustion Chamber
2000 - 2200 °F
Waste
Solids
Ash
Rotary Kiln Incinerator
-------
Discharge
Solids
Feed
Liquid
Sludge
Feed
ON
to
Fluidizing
Combustion
Air
Ash Bed
Removal
dud ~~~~;~
Preheat
Burner
xwwwww
x^WNWWW
\
1500 - 1800 °F
Fluidized
Sand or
Alumina
Auxiliary
Fuel
Air
\ Distribution
Manifold
Fluidized Bed Incinerator
-------
Discharge
Aqueous
Waste
Refractory
ON
Auxiliary
Fuel
Liquid Waste
Atomizing
Steam or Air
Steam
2000 - 2200 °F
,/
/
/
/
/
v
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
Primary
Combustion
Air
Liquid Injection Incinerator
-------
QUENCH TECHNOLOGIES
• Air injection
• Evaporative water cooling
• Waste heat recovery
-------
AIR POLLUTION CONTROL TECHNOLOGIES
• Wet electrostatic precipitators
• Venturi scrubbers
• Packed bed scrubber
• Sorben injection (semi-dry scrubbing)
with fabric filters (bag house)
-------
AIR POLLUTION CONTROL TECHNOLOGIES
POLLUTANTS CONTROLLED
TECHNOLOGY PARTICULATES ACID GASES METALS
ON
ESP (Wet) 1 1 2
Venturi Scrubber 1 11
Packed Bed Scrubber 3 1 3
Baghouse 1 2 1
Sorbent Injection 3 13
1 - prime removal technology
2 - secondary removal technology
3 - not applicable
-------
Dr. David DeBerry, Radian Corporation
Chemical Treatment; Methods
Oxidizing Agents
Low (ambient) temperature chemical or photochemical oxidation
processes have been used to destroy a number of organic
compounds.
Many 'high-powered' processes work mainly by generation of
hydroxyl radicals, e.g.:
H202 + hv > 2 "OH
03 + H20 + hv > 2 H202
0, + 2 H-0- > 2 'OH + H_0 +2 0,
3 2 2 2 t
Fe2 + f H202 > Fe3+ + 0H~ -h 'OH
However, even hydroxyl radicals may not be reactive with CFC's,
as most of the mechanisms involve abstraction of a H atom or
adding to an aromatic system or double bond. For a rough
comparison, rate constants for reaction of several organic
compound with ozone are shown below.
Compound k (M^sec-1)
benzene 2
methylene chloride o.l
carbon tetrachloride <0.005
The CFC's are most likely resistant to electrochemical oxidation
except under extreme potentials in nonaqueous solvents.
Reagents and/or power sources are usually expensive for these
processes.
67
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Reaction with Active Metals
Halogenated hydrocarbons are known to react with metals such as
sodium and potassium. Metals such as aluminum and zinc may also
be fairly reactive.
An example reaction is:
3 CC1_ F_ t 8 A1 > Al„C- - 2 A1F- + 2 A1C1-
2 2 -t J ^ J
The aluminum carbide is said to decompose in the presence of
water to give alumina and methane.
Cost of the active metals could be a consideration. For the
above example the cost for aluminum alone is about $0.46/lb
{CFC-12) if none of the aluminum can be recovered. CFC-12 costs
about $0.68/lb.
Would need to remove water, oxygen from waste streams. Materials
of construction could be a problem.
Thermodynamics of process need to be investigated.
68
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Wet Air Oxidation
Uses high temperature ( >3 00 °C) aqueous stream and oxygen to
destroy many organic compounds.
Oxidation will probably not be effective (for same reasons as
given above), but combination with high temperature hydrolysis
might give conditions similar to incineration (DuPont reference).
May be possible to catalyze process.
Thermodynamics of hydrolysis need to be investigated.
69
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Corrosion
Destruction of CFC's can produce compounds which are corrosive to
the equipment used for treatment.
Chlorides induce pitting and other forms of localized corrosion
or stress corrosion cracking of many metals, including 'exotic'
alloys.
Fluorides can attack materials which are resistant to chloride
attack, eg: titanium. Ceramic materials (liners, etc) are
susceptible to attack by HF and fluorides.
Potential corrosion problems should be considered when estimating
the cost and the acceptability and reliability of the treatment
processes.
70
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CFC Summary
There a number of problems associated with chemical treatment
methods for CFC's.
Thermodynamic calculations and directed literature surveys could
clear up part of the uncertainty. Actual reactivities, degrees
of conversion, kinetics would have to be determined
experimentally.
Many fluoride salts are toxic and secondary disposal problems
should be considered.
Possible corrosion problems and increased costs due to need for
exotic materials of construction should be considered.
Since there are many fairly small sources of CFC's, it might be
worth investigating processes whereby CFC's are adsorbed onto
some support at the source, then transported to a central
location for disposal (e.g., an incinerator).
71
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CW Applications
Hydroxyl radical generating processes are quite applicable zo
most CW agents. Reactions are fast and complete. The reagents
can be stored, but rapidly deployed.
Could also consider an adsorbent system which is periodically
dosed with a strong oxidizing agent to make sure the surface is
always 'active.*
72
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BIODEGRADATION
TECHNOLOGY
Presented by:
Larry N. Britton, Ph.D. .
Director, Environmental Sciences
Texas Research Institute, Inc.
9063 Bee Caves Road
Austin, TX 78733
(512) 263-2102
73
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What makes man-made organic
compounds biodegradable?
Parameters to be fulfilled:
• Ability of microbial enzymes to metabolize
compounds with structures similar to, but not
identical with chemicals found in nature
(fortuitous metabolism)
• Ability of man-man compounds to induce or
derepress the synthesis of the necessary
degradative enzyme(s) in microorganisms
• The presence of an appropriate environment (e.g.,
presence or absence of oxygen; the availability of
nutrients; adequate pH; temperature; etc.)
74
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Can microorganisms be used
to destroy CFCs?
Problems:
• Halogenation increases the recalcitrance of
organic compounds to biodegradation (e.g.,
methane vs. dichloro-difluoromethane; biphenyl
vs. polychlorinated biphenyls)
• \folatility low boiling point of many CFCs
• Slow degradation rates compared to other
technologies (no publications on CFC
biodegradation)
• No advantages except for possible restoration of
contaminated soil and water
75
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How do microorganisms
transform halomethanes?
• Studies primarily with chlorinated methanes
(methyl chloride, methylene chloride, chloroform,
carbon tetrachloride)
?
»
H > F > CL > BR
• Anaerobic and aerobic mechanisms reported
Anaerobic = reductive dehalogenations
under methanogenic
conditions
Aerobic = Oxidative dehalogenations
reported in soil & water microbes
and in mammalian liver systems
• Cometabolic transformations. Energy for growth
derived from other organic compounds
• Pathways not yet determined
76
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How do microorganisms transform
haloethanes and haloethenes?
• Studies primarily with chlorinated ethanes and
ethenes
• Anaerobic degradation under methanogenic
conditions. Aerobic degradation by methane
oxidizing (methanotrophic) bacteria
• Cometabolic transformation
• Pathways for haloethenes:
Anaerobic: PCE —~ TCE —^ DCE —~ VC * » CQ2
Dichloroacetic acid
CO2
Aerobic: TCE
CO2
Glyoxyl —Glyoxylic
chloride acid
X
TCE Diol
• Pathways for haloethanes:
Anaerobic: Dichloroethane —Chloroethane—^C02
Aerobic: Dichloroethane —*~ 2-chloroacetaldehyde
2-chloroacetate —Glyoxylic
acid
77
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Can microorganisms degrade
chemical warfare agents?
• HCN: Yes. Cyanide degraders are commonly
found in soil and cyanide-containing industrial
wastes
• Cyanogen chloride: ?
• Mustards: HD (sulfur mustard): Probably
HN (nitrogen mustard): Probably
• Organophosphorous (nerve) agents: Yes
Ri — P — X
R2
Z = Oxygen or sulfur
X = Easily displacable group (F, CN, SCH2CH2NR)
Rl/ R2 = Alkyl,alkoxy, or amino
78
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Can microbial enzymes be used
to hydrolyze G and V agents?
• DFP hydrolase from squid axon and bacteria
• Parathion hydrolase from pseudomonas
f, , PAR S
CH3-CH2-o"^OH .
ch2-ch3 ch,- ch,
23 PNP
PAR
79
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Are biotechnology methods useful
for CW agent destruction?
• Yes, if soil and water remediation is required.
Probably not if bulk disposal of CW agents is
required
• Possible novel decontamination methods
80
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Sandia Laboratories
Soteiir Edwus/
SOLAR DESTRUCTION OF HALOCARBONS
Sandia National Laboratories
Solar Energy Department
Jim Fish
Rich Diver
Hugh Reilly
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Sandia Laboratories AGENDA
SOLAR DESTRUCTION OF HAZARDOUS WASTES
o Overview
o Approach
o Status
o Planned Activities
SOLAR DESTRUCTION OF CFCs
o Approach
oIssues
SUMMARY
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Solar Destruction of Hazardous Wastes
OVERVIEW
Objective
Use solar energy to destroy hazardous wastes.
Process must achieve:
-High DRE
-Cost Effectiveness
Scope
-Direct Catalytic Absorption Receiver (DCAR) Development
-Laboratory Experiments
-Field Experiments
-Modeling
-Systems Analysis
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Sandia laboratones Solar Destruction of Hazardous Wastes
APPROACH
- Catalytic Steam Reforming of Halocarbons
- Direct Catalytic Absorption Receiver (DCAR)
- Water Quench
- Neutralization of Acidic Product Gases
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C2CI3F3
Qv (1.05 kW)
H20
(2.883 gm/sec,
Qv (7.58 kW)
Vaporizer
Steam
Generator
H20
(2.883 gm/sec,
22.85 Ib/hr)
400 K
7.688 gm/sec
a>
cn
Qhe «
(23.183 kW)
AssMmptions
Pressure = 1 atm with no pressure drop
Equilibrium Conversion at 1,200 K
Partial Pressure of water at 6 = 0.031 atm
No C02 dissolved in quench
Wp -0
SOLAR DESTRUCTION OF HAZARDOUS WASTES
Energy and Mass Balance
(Freon 113, C2CI3F3: 1,1,2-Trichloro-1,2,2-Trifluoroethane)
Receiver/Reactor
state 3, 1,200 K
[CO] = 0.03937
[C02] = 0.13856
[HCI] = 0.26689
[HF] = 0.26689
[H2] = 0.04959
[H201 = 0.23870
We ~0
State 4
(5.409 gm/sec)
|H2] = 0.2801
[HCI] = 0.3600
[HF] = 0.3601
Fl are
©
State 6 & 7, 298 K
(2.279 gm/sec)
[CO] = 0.1677
[C02] = 0.5901
[H2] = 0.2112
[H20] = 0.0310
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| Sandia Laboratories
| S©ia(r
Solar Destruction of Hazardous Wastes
WHY SOLAR?
COMBUSTION
- Fuel Required
" Oxygen Required
- Products of Incomplete Combustion
- NOx
- Flue Gas Cleanup
SOLAR
- Concentrated Effluent
- Potential for High DRE at Lower Temperature
- NOx Free
- Potentially Effective at Smaller Scale
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Sanclia Laboratories
Test Setup
Test Results to Date
Solar Destruction of Hazardous Wastes
STATUS
-------
00
00
Sandia laboratories Solar Destruction of Hazardous Wastes
li
TEST RESULTS
Preliminary Tests Indicate Equilibrium Conversion
of C02 / CH4 and H20 / CH4
- Temperatures in the range 1000 - 1200K
- Pressures in the range 0.5 - 0.7 atm
- Solar power absorbed by chemicals in the range 1-4 kW
- Less than 1% CII4 at outlet (in agreement with equilibrium
predictions)
- Reactor matrix and catalyst not optimized
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Sanrtia Laborator.es Solar Destruction of Hazardous Wastes
I
I Sdlaor
PLANNED ACTIVITIES
Continued Testing to Include Chlorinated Hydrocarbons
Conceptual Design of System for Chlorinated Hydrocarbons
DCAR Reactor Modeling
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Sandia laboratories Solar Destruction of CFCs
li
APPROACH
Catalytic Steam Reforming / Acid Neutralization
Small-scale Material Compatibility Experiments
Demonstrate at 3 kW Scale on Fresh CFC
-------
Sandia laboralo.ies Solar Destruction of CFCs
fir Emm
ISSUES
Material Handling
o Hydrofluoric Acid
o Contaminants in Spent CFCs
Proof-of-Concept Tests (Very Stable Compounds)
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Sandia Laboratories
i Solar IGimom
I
Solar Destruction of Halocarbons
SUMMARY
DEMONSTRATED PERFORMANCE ON HYDROCARBONS
o High Extent of Reaction
o 3-5 kW Level
o Achieved Matrix Temperature of 1300K
CHLORINATED HYDROCARBONS NEXT
FLUORINATED HYDROCARBONS NOT IN CURRENT SCOPE
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