United States
Environmental Protection
Agency
Municipal Environmental Research ~
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-091 Dec. 1983
Project Summary
Bromination Process for
Disposal of Spilled Hazardous
Materials
A.J. Darnell
A novel process was tested for oxi-
dizing organic materials, including so-
called "refractory organics" and pesti-
cides. Bromine and water were allowed
to react with such materials at 250° to
300°C to form carbon dioxide and
aqueous hydrobromic acid. The HBr
solution can be electrolyzed at ambient
conditions, using a membraneless
electrolysis cell, to produce hydrogen
and regenerate bromine for recycling.
The byproduct hydrogen can be sold or
used as fuel for the process.
The bromination process has now
been evaluated for the destruction of
hazardous waste spills on both a
laboratory and a pilot-plant scale. Mala-
thion,* the selected model compound,
was successfully treated in an 8-liter,
tantalum-lined autoclave at 300*C as
part of a simulated spill mixture
consisting of the malathion, soil, sand,
humus, and moisture. Essentially
complete destruction of the malathion
(>99.9999%) was achieved.
The aqueous HBr solution resulting
from the oxidation was electrolyzed in
an inclined membraneless cell with
graphite electrodes to yield a solution
containing about 20 wt % HBr and 18
wt % dissolved bromine. Coulombic
efficiency for the electrolysis was about
96%.
A conceptual design for a larger-scale
system was developed on the basis of
the laboratory and pilot-plant results.
This design consisted of batch oxidation
coupled with continuous electrolysis. It
could process hazardous wastes at an
•Mention of trade names or commercial products
does not constitute endorsement or recommendation
for use.
average rate of 7.5 kg/hr. The total
capital cost for such a system installed
at an available site was estimated at
$625.000 in January 1979. Of this
total, $350,000 represented actual
costs for equipment.
Laboratory-scale oxidations using
bromine were also carried out using
two chlorinated hydrocarbons, gamma-
lindane, and heptachlor. Under the
conditions employed, which were not
optimized, decomposition of both of
these compounds was less efficient
than when trichloroethane was the
substrate. The HBr yields for lindane
and heptachlor were 56% and 71%,
respectively.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory, Cincinnati, OH,
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction and Background
The health and safety factors related to
hazardous materials mandate that a high
level technology be used in their disposal
or destruction. Methods used to dispose
of hazardous wastes must also be able to
cope with the nonhazardous materials
that are often present, such as dirt,
vegetation, and water. The variability in
hazardous wastes encountered and the
conditions under which cleanup must be
conducted create unique problems for
response and cleanup personnel.
Rockwell International has developed a
novel process that uses oxidation with
bromine and water to destroy organic
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materials. When allowed to react with
bromine and water at 250° to 300°C in a
closed system, organics (represented by
CH) are oxidized to carbon dioxide and
aqueous hydrobromic acid according to
the general Equation 1:
COi (To Atmosphere)
H2 for Use
or Flare
CH + 2.5 Br2 + 2 H20 -
5HBr(aq. sol.) + CO2
(1)
The carbon dioxide can be released to the
atmosphere after the bromine and
hydrogen bromine vapors have been
stripped. The hydrobromic acid solution
can be electrolyzed, as in Equation 2, to
produce hydrogen and bromine:
SHBr (aq.) electrolytic cell
• >
2.5H2 + 2.5Br2(indil.HBr) (2)
The hydrogen can be sold or used as fuel
for the process, and the bromine can be
recycled to the oxidation process. The
process sequence is shown schematically
in Figure 1.
During the first portion of this program
(designated as Task 1), laboratory investi-
gations were conducted on the bromine
plus water oxidation of three typical
hazardous chemicals—copper acetate,
trichloroethane, and malathion. At the
preferred reaction temperature of 300°C,
destruction of all three compounds was
essentially complete in 1, 3, and 5 hr,
respectively. The chlorine, phosphorus,
and sulfur in the compounds were
converted to hydrochloric, phosphoric,
and sulfuric acid, respectively. The
project demonstrated that the metallic
bromides formed from the copper (and
from other inorganic components that
might be in an actual spilled waste) could
be treated with sulfuric acid to recover
the bromine and reduce the bromide
content of the residue (inorganic sulfates)
to 0.6 ppm.
Task 1 was alsodevoted to developing a
suitable process for the electrolysis of
aqueous HBr solutions. With the constant
boiling, 47% HBr/water azeotrope, a
minimum no-load decomposition poten-
tial of 0.69 volts was measured at 25°C.
Though lower decomposition voltages
can be obtained at higher temperatures,
the nature of hazardous waste disposal is
such that it seemed advisable to carry out
the HBr electrolysis at ambient tempera-
ture and pressure in spite of this penalty.
Decomposition voltage was also found to
depend on HBr concentration, with
higher voltages required for 20% and
65% HBr than for 47% HBr.
Carbonaceous -^
Waste
Water —
Concentrated
Hydrogen Bromide
(Aqueous)
Electric
'Power
Ash or
Inorganic
Residue
Bromine + Dilute Hydrogen
Bromide (Aqueous)
Figure 1.
Schematic flow diagram for disposal of carbonaceous wastes by the bromination
process.
The results of Task 1 of this program
were reported in the Proceedings of the
1978 National Conference on Control of
Hazardous Material Spills, Miami Beach,
Florida, 1978. p. 221. Hazardous Materials
Control Research Institute, Rockville, MD
(now in Silver Spring, MD).
Experimental Procedures
and Results
Laboratory Oxidations Using
Bromine
Parameters affecting the oxidation
reaction were evaluated by carrying out a
series of experiments, first with pure
malathion in water and then with a
simulated spill mixture containing 70 wt
% malathion, 10 wt % sand, 10 wt %
sand, 5 wt % humus, and 5 wt %
moisture. The bromine was supplied first
as a solution of bromine and water and
later as a solution in aqueous hydrobromic
acid, as might be produced from the
electrolysis. The test apparatus consisted
of a 600-ml glass ampule that was sealed
and placed inside a 2000-ml steel
autoclave. The autoclave was heated to
300°Cand maintained at that temperature
for up to 5 hr. After the required time, the
autoclave was chilled in liquid nitrogen to
condense the carbon dioxide in the
reaction ampule, and the ampule seal
was broken.
Analyses for malathion residues were
carried out on the gas phase, the liquid
phase, and (if present) the solid residue
from the reaction using gas chromatogra-
phy with a flame photometric analyzer
sensitive to phosphorus. An electron
capture detector was later substituted to
achieve increased sensitivity. Liquid
samples were extracted with petroleum
ether before analysis. Solid residues
obtained when the simulated spill mixture
was used were filtered to separate the
solids, which were then extracted by
refluxing in aqueous hydrobromic acid at
127°C for 30 min. The liquid was then
extracted with petroleum ether to obtain
a sample for analysis.
The first three experiments were
intended to demonstrate that changes
from Task 1 conditions would not affect
the results of subsequent experiments.
These experiments were as follows:
1) A control experiment was conducted
under the same conditions as in Task 1,
except that reactant quantities were
increased about tenfold. The same size of
ampule was used (600-ml), which meant
that the pressure developed from carbon
dioxide would be about 10 atm instead of
1 atm.
2) An experiment was done in which
bromine dissolved in 22 wt % hydrobromic
acid was substituted for the bromine/wa-
ter reagent. This test was necessary,
since the plan was to reuse the recovered
solutions from the electrolysis as the
source of bromine in the bromination
reaction.
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3) An experiment was conducted
using the simulated spill mixture of
malathion with soil, sand, humus, and
moisture and bromine dissolved in 22 wt
% hydrobromic acid.
The change did not adversely affect the
results in any of the three experiments.
After reaction at 300°C for 5 hr, no
organo-phosphorus residue was detected
in the gaseous, liquid, or solid phases of
the reaction mixture. Based on the
sensitivity of the analytical procedures,
the bromination reaction effectively
destroyed more than 99.9998% of the
malathion.
An experiment was then carried out to
assess the effect of agitation on reaction
time. Agitation, which was accomplished
by rocking the autoclave and furnace
assembly at 3 cycles/min, had a clearly
beneficial effect on the destruction rate
(Table 1).
Reaction of the simulated spill mixture
with bromine and water for 5 hr required
more bromine than malathion alone
required, since each of the added
materials (particularly the humus) also
consumed some bromine. Table 2 summa-
rizes some of the data on bromine
consumption by the other constituents in
the mixture.
Table 1. Effect of Agitation on Reaction of
Malathion with Bromine and Water!*)
Amount of Malathion Used
Reaction
Time
Ihr)
1
2
2
5
Without
Agitation
1%)
85ft)
89ft)
>99 999ft)
With
Agitation
ss
(*IReaction with an initial Br2/H£)/malathion mole
ratio of 40/600/1
ftlFrom analyses of HBr. HiSOt. and Hz POt formed
ft)From analysis of malathion residuals by gas
chromatography
Table 2. Amount of Bromine that Reacted with
Debris in 5 hr at 300°C
Component
Sand
So/I
Humus
Bromine Reacted*
Ig Bromine/ g of
Debris Component)
004
0 11
4.74
"For comparison, the reaction used IS.Sg of bromine
for each gram of malathion consumed
Tests were also carried out in the
laboratory apparatus at 300°C for 1 hr
using lindane (gamma-CeHeCU) and
heptachlor (CioHsCI?). With the production
of HBr as a measure of oxidation, it was
clear that both of these cyclic chlorinated
compounds were considerably more
resistant to bromine oxidation than was
trichloroethane. The yields of HBr were
56% for li ndane and 71 % for the heptachlor,
but reaction conditions had not been
optimized.
Pilot-Plant Bromine Oxidation
The pilot-plant apparatus consisted
of an 8-liter, tantalum-lined autoclave
plus all the auxiliary equipment for
stirring, heating, and temperature and
pressure monitoring. A simulated spill
mixture composed of 35 g malathion, 5
g sand, 5 g soil, 2.5 g humus, and 2.5 g
moisture was allowed to react with a 5
wt % excess of bromine at 300°C for 2
hr. When the reaction was complete and
the autoclave was cool, the residual
pressure from carbon dioxide was 1208
kPa. Since the calculated carbon dioxide
pressure for complete reaction was 1159
kPa, the reaction of the malathion plus
debris mixture was essentially complete.
No malathion residue was detected in the
gaseous, liquid, or solid products.
Laboratory Electrolysis
Since the electrolyzed solution was to
be reused as the source of bromine,
electrolysis was carried out with solutions
that would be produced from copper
acetate, chlorinated organics and mala-
thion (copper (II), chloride, sulfate and
phosphate). These tests were carried out
in a cell containing graphite electrodes
(surface area - 14 cm ) and an aluminum
oxide, fibered-felt membrane separator.
Electrolyzing the hydrobromic acid
solution from a copper acetate reaction
required a lower decomposition voltage
than when copper-free hydrobromic
acid was used, possibly because of the
increased ion concentration in the
solution. At a voltage of 3.2V, copper was
also observed to plate out on the cathode.
During electrolysis of the 47% hydro-
bromic acid solution from the trichloroe-
thane reaction (which also contained
hydrochloric acid), the decomposition
voltage was about 10% lower than with
the control. Note that no chlorine
evolution was detected, since the decom-
position voltage for hydrochloric acid is
about 0.5 V higher than that of hydrobro-
mic acid.
When malathion was the organic being
oxidized, 2 moles of sulfuric acid and 1
mole of phosphoric acid were formed for
each 64 moles of hydrobromic acid.
Electrolysis of this reaction solution
required a higher decomposition voltage
than the control. Several explanations
are offered for this observation.
Pilot-Scale Electrolysis
The electrolysis apparatus used in the
laboratory experiments was first scaled
up about tenfold in electrode surface
area. With this equipment a noticeable
decrease in coulombic efficiency was
observed when the hydrobromic acid
solution contained large amounts of
dissolved bromine. The efficiency of
electrolysis was also reduced, and
diffusion of bromine through the membrane
increased significantly. Since the plan
was to use an HBr solution that would be
rich in bromine, these observations were
quite serious.
A search of the literature indicated that
a membraneless electrolysis cell such as
the mercury cell used in salt electrolysis
could overcome these difficulties. Based
on this review, the design selectedf or the
pilot-scale electrolysis cell consisted of
graphite electrodes separated by Teflon
spacers. The upper electrode was the
cathode. When current is passed through
a cell of this design, the hydrogen formed
at the cathode rises and escapes from
ports at the upper surface. The bromine
formed at the anode combines with HBr
to form HBra, which is more dense than
HBr and flows out ports at the lower end
of the cell. Tilting the assembly so that the
gas exit at the cathode was only slightly
above the horizontal (3°) improved the
coulombic efficiency significantly (Table
3). These results may reflect reduced
turbulence and mixing of the denser HBra
The inclined, membraneless cell was
then used as part of a regeneration
system. Concentrated hydrobromic acid
electrolyte was pumped at 2 ml/min from
a reservoir to the upper end of the cell,
and the product solution of bromine and
dilute hydrobromic acid was removed at
the lower end. The hydrogen byproduct
gas was scrubbed with water and sodium
bromide solution to remove bromine and
HBr vapors. The scrubbed exit gas
contained less than 2 ppm of combined
bromine and HBr. The bromine/bromide
content could be further reduced to 0.1
ppm by the addition of a 10% sodium
hydroxide scrubber to the train.
Decomposition voltages for electrolysis
of the 38% HBr solution from a malathion
bromination essentially paralleled those
obtained in the 4-liter membrane cell, but
the coulombic efficiency of the membrane-
less, flow-through cell was much higher.
The voltage (energy) requirements were
also considered to be several-fold higher
than expected by comparison with other
electrolysis processes. In an effort to
reduce the needed voltage, the graphite
cathode was coated with 5.5 mg/cm2 of
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Table 3. Coulombic Efficiency of Membraneless Cell
Electrode Current
Density
Milliamps/crr?
50
100
50
100
Electrode Angle
(Degrees from Horizontal)
16
16
3
3
Coulombic
Efficiency
(Percent)
66
64
96
92
platinum by electrochemical deposition.
This modification resulted in a significant
(more than 50%) decrease in the decom-
position voltages at comparable current
densities. For example, at lOOmilliamps/
cm2, the decomposition voltage was
reduced from 2.95 to 1.24 V. In addition,
this value did not deteriorate over the 4 hr
of the test, during which time coulombic
efficiency was about 97%.
Design Study
A review of the magnitude of reported
spills suggested that a unit capable of
treating 22.7 kg of hazardous chemical
would be suitable for field use. This figure
was used as the basis for the design of a
field-scale system. Batch bromination
coupled with continuous electrolysis for
bromine regeneration were selected as
the least costly scenario. The design
reflected the laboratory and pilot-plant
results indicating that 2 hr at 300° and
8500 kPa were the maximum conditions
needed. Also considered were the
reactivity of other debris and the need to
remove solids after reaction. The tantalum
lining of the reactor was retained.
The electrolysis unit (to be operated
continuously once a reserve of hydrobro-
mic acid liquor was generated) would
operate at 25°C and atmospheric pressu re
and convert the bromination reactor
effluent to a final recyclestream containing
22% HBr and 16% bromine.
The completed design is shown sche-
matically in Figure 2. A total capital cost
of $299,800 was estimated from vendor
quotes and other sources. Piping, overhead,
construction costs, etc., resulted in a total
installed cost (1979) at an available site of
$625,000 (Table 4). The system is
capable of processing about 7.5 kg/hr of
hazardous chemicals.
Table 4. Cost Summary for 7.5-kg/hr
Disposal System*
Item
Major equipment
Minor equipment
Installation
Piping
Total
Cost
$299,800
50,000
150,000
125,000
$624,800
*1979 dollars.
CO2
Makeup
Water
Nz Purge
Spill
Charge
Bromine Dissolved in Dilute HBr
— — — — Dashed Lines Indicate Flow During Shutdown
Figure 2. Block diagram of a conceptual disposal system.
4
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Conclusions
Pilot-plant testing demonstrated that
an organic hazardous chemical such as
malathion can be completely destroyed
(99.9999%) by an oxidation process usi ng
bromine, even in a simulated spill
mixture. Bromine and/or hydrobromic
acid also react with other organic and
inorganic components of such mixtures
to a limited extent during the process.
Some inorganic materials form metallic
bromides that consume bromine, but the
bromine can be recovered readily by
treating these residues with sulfuric acid.
The concentrated, aqueous hydrobromic
acid effluent from the bromine oxidation
process can be electrolyzed to make the
bromine available for reuse. Based on
pilot-plant studies, the electrolysis can be
carried out in a single pass at ambient
temperature and pressure using a mem-
braneless electrolysis cell. The addition of
small amounts of a platinum catalyst to
the graphite cathode reduces the electrical
power requirements by more than 50%.
A full-scale system capable of treating
7.5 kg/hr of hazardous waste had an
estimated installed capital cost of about
$650,000 in January 1979.
Recommendations
The oxidation of hazardous wastes by
bromine should be considered as an
option for the destruction of hazardous
chemcials, even when these are mixed
with nonhazardous debris.
Further studies should be done to
include the use of catalysts and to
accelerate the oxidation reaction or
reduce the required temperature. Similar-
ly, techniques should be explored to
increase the reactivity with other chlorin-
ated hydrocarbons such as lindane and
heptachlor, which may be encountered in
spill cleanup situations.
The amount of platinum required on
the graphite cathode to catalyze the
electrolysis of aqueous hydrobromic acid
should be better defined. Alternative
methods of activating the electrodes and
catalyzing the electrolysis (such as the
reported use of nitric acid) should be
investigated.
A unit capable of destroying 8 to 10
kg/hr of hazardous wastes should be
constructed for larger-scale confirmation
of the pilot-plant results and for possible
field testing.
The full report was submitted in partial
fulfillment of Contract No. 68-03-2493 by
Rockwell International under the sponsor-
ship of the U.S. Environmental Protection
Agency.
A. J. Darnell is with Rockwell International, Canoga Park, CA 91304.
John E. Brugger is the EPA Project Officer (see below).
The complete report, entitled "Bromination Process for Disposal of Spilled
Hazardous Materials," (Order No. PB 83-263 806; Cost: $10.00. subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Oil and Hazardous Materials Spill Branch
Municipal Environmental Research Laboratory-Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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