Coconut Carbon Can Trap a Used Fumigant

By Marcia Wood
April 7, 1998

Bits of activated carbon made from crushed and superheated coconut shells can capture methyl bromide left over from fumigating crops at packinghouses or other facilities. The fumigant kills insects that can damage fruits, nuts, grains, and other commodities.

The activated carbon, housed in a steel container, trapped up to 95 percent of the methyl bromide in air vented to it in studies led by entomologist James G. Leesch. He's with USDA's Agricultural Research Service in Fresno, Calif. The researchers used carbon granules crushed to about the size of pea gravel.

The Fresno research will offer packinghouse managers and others the first proven, practical method for keeping methyl bromide out of the stratosphere. U.S. production of methyl bromide is scheduled to be eliminated in 2001 because it is thought to damage the earth's protective ozone layer.

The idea of using activated carbon to trap methyl bromide is not new. But the new system also recycles activated carbon and yields a useful chemical by-product. Leesch is testing the technology under a cooperative research and development agreement between ARS and GFK Consulting, Ltd., San Clemente, Calif., and Great Lakes Chemical Corp., West Lafayette, Ind.

Earlier, ARS and GFK Consulting scientists found that, for trapping methyl bromide, use, coconut-shell-carbon is superior to peat or bituminous coal carbons. The scientists have tested the activated carbon in conditions typical of the air-tight fumigation chambers.

Heating the spent activated carbon--with nitrogen, steam or air--reactivates it for re-use and also drives off the trapped methyl bromide. Further heating breaks down the methyl bromide into carbon dioxide, water and hydrogen bromide that can be converted into a compound suitable for making fire retardants and other chemicals.

Last fall, researchers completed preliminary pilot tests of a prototype carbon-filled container at a California fig-packing plant. They plan new experiments this spring at a portside facility.

Scientific contact: James G. Leesch, ARS Horticultural Crops Research Laboratory, 2021 S. Peach Ave., Fresno, CA 93727. Phone (209) 453-3090, fax (209) 453-3088, jleesch@qnis.net.