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Recapturing Methyl Bromide Emissions
One way to help solve an important part of the methyl bromide
emissions problem is to recapture, in an environmentally acceptable way,
the chemical that escapes into the air from commodity and quarantine
fumigations. Several groups in the United States and abroad are working on
ways to effectively and efficiently recapture methyl bromide. Under a
Cooperative Research and Development Agreement, James Leesch, ARS research entomologist, is working
with GFK Consulting, Ltd., of San Clement, California, on one such
approach to capture the methyl bromide and reuse its bromine content as a
raw material.
"With our process, methyl bromide could be used for commodity and
quarantine fumigations without damaging the stratospheric ozone
layer," Leesch says. "If packinghouse, exporters, importers, and
other commodity fumigators were to use this recapture technique, methyl
bromide emissions could be reduced by as much as 95 percent." He is
with the ARS Horticultural Crops Research Laboratory in Fresno,
California.
Leesch says the process has some obvious pluses: It minimally affects
the environment and does not alter established fumigation procedures.
Leesch and Gary Knapp of GFK Consulting, trap the methyl bromide
with activated carbon.
"We're essentially talking about putting a gas mask on fumigation
chambers to prevent the release of methyl bromide to the atmosphere,"
Leesch says.
Instead of venting the gases from the fumigation enclosure directly
into the atmosphere, as is done now, they plan to pass the air containing
the methyl bromide through a transportable container filled with activated
carbon. This activated carbon will trap 95 percent of the methyl bromide.
Once the activated carbon has reached its adsorption capacity, it will be
shipped to a central location where the carbon will be regenerated by
flushing it with hot air or steam. The flushing removes the methyl
bromide, which is thermally, or catalytically, converted to hydrogen
bromide (HBr), carbon dioxide, and water. Then the HBr, either as it is or
after chemical conversion to bromine, will be reused as a raw material.
The regenerated carbon and its container are returned to another location,
ready for further recapture of methyl bromide.
Advantages of this methyl bromide recapture process include the
following:
- It does not affect the treated commodity or the fumigation
process. There will be virtually no change in fumigation procedures and
100 percent virgin methyl bromide will always be used. Protocol will be
maintained with no change in methyl bromide concentration, fumigation
time, temperature, or relative humidity.
- It can be used at many locations with minimal impact on cost.
The only equipment needed at each location is the ducting, the blower, and
the controls to connect the fumigation enclosure to the transportable
carbon container. Bromine recovery and carbon regeneration will be done
at a single location, regardless of the number of fumigation
locations.
- The spent carbon is not an RCRA (Research Conservation and
Recovery Act) hazardous waste under 40 CFR 261. In fact, activated carbon
is considered an excellent adsorbent for cleaning up and eliminating
hazards, should methyl bromide be spilled accidentally.
- Thermal recovery of bromine from byproducts or from waste is
common practice in the bromine industry; waste is eliminated, and bromine
is recovered. Methyl bromide flushed during regeneration of activated
carbon is typical of waste that is already being treated.
In the first phase of their research project, Leesch and Knapp built
and tested a bench-scale carbon adsorber to determine how methyl bromide
concentration, type of carbon, temperature, and relative humidity affect
adsorption capacity. They have done initial lab tests of the desorption
process, and presented some of their results at the Methyl Bromide
Conference in San Diego in November 1995. Leesch presented the work at the
annual meeting of the Georgia Entomological Society, Savannah, Georgia, in
March 1996 and will discuss it at the International Controlled Atmosphere
and Fumigation Conference in Nicosia, Cyprus, in April 1996.
The current, second phase, focuses on repeated recapture of methyl
bromide in the bench-scale column followed by regeneration with hot
air.
"This will confirm the carbon's ability to adsorb methyl bromide
and it will also show any decrease in adsorption capacity over time.
Significant decreases in capacity require makeup carbon, which in turn
adds costs to the overall process," Leesch says.
For the third, and final phase, Leesch and Knapp will build adsorbers
to hold 150 pounds of carbon that, each minute, will treat 100 cubic feet
of exhaust streams from commercial fumigation operations.
"These adsorbers will be big enough to warrant transporting them
back to a prototype facility where the carbon can be regenerated and the
bromine recovered," Knapp says. "And the bromine recovery for
these experiments will be done in cooperation with the Great Lakes
Chemical Company that has already provided part of the equipment needed
for the study."
Knapp estimates the cost for a fumigator to use the overall process to
be no more than about $15 per pound of methyl bromide. This price, he
says, would include delivery and removal of the actvated carbon container
and regeneration of the activated carbon. "The fumigator would need
to supply the ducting, blower, and controls to connect his exhaust to the
containers," he says.
Leesch and Knapp expect the final phase of the project to be completed
some time this summer.
[April 1996 Table of Contents]
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Last Updated: October 15, 1996
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