Nutshell Www.ars.Usda.gov is AR Archive Sep99 pdf
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14 Agricultural Research/September 1999 6 A new kind of recycling is under way in the Com- modity Utilization Re- search Unit located at the Southern Regional Re- search Center (SRRC) just outside down- town New Orleans. But don’t expect to find crushed soda cans, plastic water bottles, or musty-smelling newspapers heaped at this high-tech facility. A team of chemists there led by Wayne E. Marshall is recycling trash of the agricultural kind—like discarded soybean hulls and the shells of various edible nuts. About 50 million tons of these and other assorted agricultural wastes are generated each year. The pecan industry, for example, gen- erates about 59,500 tons of shells from its harvests. Growers and processors ab- sorb some of the cost of shell disposal by grinding them up and selling them as livestock bedding, mulch, or other low- value commodities. The shells alone bring in a pittance: about $2 a ton. But Marshall’s group is on the verge of delivering what could amount to an economic boom. Since 1993, they have been perfecting an ar- ray of techniques to make charcoal-like substances called activated carbons from pecan, almond, and most recently , mac- adamia nut shells. “We’re looking at creating new uses and value-added products from these commodities,” says Lynda H. Wartelle. She and Marshall are with USDA’s Ag- ricultural Research Service. Their waste- recycling unit is operated by the SRRC. Today’s usual activated carbons are made from coal, peat, coconut shells, and wood, says Mars hall. W orking like char- coal “sponges,” they adsorb from the air or water many types of organic com- pounds—like benzene, toluene, and ac- etonitrile, as well as metals such as lead. Carbon uses run the gamut: from fish tank filters and tap water purifiers to wastewater treatment and air pollution monitoring and control. In the United States, such applications consume over 300 million pounds of ac- tivated carbons annually—about half the 600 million pounds used worldwide. “One of the selling points for this ap- proach is that we’re looking to make use of very low-value agricultural wastes. In this case, we’re using a waste to clean up other wastes,” says Christopher A. T oles, formerly with ARS but now with Northeastern University in Boston, Mas- sachusetts. “And the nutshells we’re working with are renewable on a yearly basis.” The team, looking to collaborate with industry, recently negotiated a coopera- tive agreement with a Georgia-based firm to test granular forms of the nutshell carbons. Their work has also sparked interest from commercial nut growers and trade groups like the Almond Hullers and Pro- cessors Association. Under a special grant, that California-based organizatio n supplies the scientists with large amounts of shells for their research. The team sees other potential avenues for their emerging technology: electro- pating companies, mining operations, and jewelry makers. All are industries that use activated carbons to help remove contaminants in the wastewater they gen- erate. A Tough Nut To Crack Marshall’s team is now testing acti- vated carbons made from macadamia shells supplied to them by a Hawaiian nut processor. The shells derive their density and strength from two components—lignin and cellulose. Density and strength are key to the shell’s conversion to carbons. That’s because they must withstand grinding and exposure to temperatures of up to 900 o C in combination with steam, certain gases, or acids. Such treatment activates, or opens, millions of microscopic pores in the car- bonized shells, enabling them to hold onto chemical molecules like benzene. Another step, called oxidation, confers a negative charge to the shells that helps capture metal ions, such as those in so- lution. So porous are today’s activated car- bons, notes Toles, that a single gram can have over 900 square meters of surface area. A pound can have up to 465,000 square meters—owing to the materials’ micro-, meso-, and macro-sized pores. Of the nutshell carbons examined thus far, macadamias adsorb the broadest range of organic molecules. “We’re still trying to figure out what makes the mac- adamia’s nutshell carbons so effective in this regard,” says Wartelle. She also com- pares the nutshell carbons to commercia l organic adsorbents made from natural and synthetic materials. Chalk It Up to Charcoal In one comparative study with six commercial adsorbents, use of activated macadamia shells led to a three- to four- fold increase in the ability of a standard Environmental Protection Agency air Some “Trash-Talk” Worth Listening to— Activated Carbons in a Nutshell A Scanning electron micrograph shows the effect activation has on the gross structure of nutshell carbon granules. While it is impossible to see active micro- and meso- pores, the large pits are significant evidence of gasification. Magnified about 40x. CHRISTOPHER TOLES Chemists Wayne Marshall and Lynda Wartell e air-sample vo latile organic compounds to determine the adsorptive properties of nutshell carbons.
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14 Agricultural Research/September 1999
A
new kind of recycling is
under way in the Com-modity Utilization Re-
search Unit located at theSouthern Regional Re-
search Center (SRRC) just outside down-town New Orleans. But don’t expect to
find crushed soda cans, plastic waterbottles, or musty-smelling newspapersheaped at this high-tech facility.
A team of chemists there led byWayne E. Marshall is recycling trash of the agricultural kind—like discarded
soybean hulls and the shells of variousedible nuts.
About 50 million tons of these andother assorted agricultural wastes aregenerated each year.
The pecan industry, for example, gen-
erates about 59,500 tons of shells fromits harvests. Growers and processors ab-sorb some of the cost of shell disposalby grinding them up and selling them aslivestock bedding, mulch, or other low-value commodities.
The shells alone bring in a pittance:
about $2 a ton. But Marshall’s group ison the verge of delivering what couldamount to an economic boom. Since1993, they have been perfecting an ar-ray of techniques to make charcoal-likesubstances called activated carbons frompecan, almond, and most recently, mac-adamia nut shells.
“We’re looking at creating new usesand value-added products from thesecommodities,” says Lynda H. Wartelle.She and Marshall are with USDA’s Ag-
ricultural Research Service. Their waste-recycling unit is operated by the SRRC.
Today’s usual activated carbons aremade from coal, peat, coconut shells, andwood, says Marshall. Working like char-coal “sponges,” they adsorb from the air
or water many types of organic com-pounds—like benzene, toluene, and ac-etonitrile, as well as metals such as lead.
Carbon uses run the gamut: from fishtank filters and tap water purifiers towastewater treatment and air pollution
monitoring and control.
In the United States, such applicationsconsume over 300 million pounds of ac-tivated carbons annually—about half the
600 million pounds used worldwide.“One of the selling points for this ap-
proach is that we’re looking to make use
of very low-value agricultural wastes. Inthis case, we’re using a waste to cleanup other wastes,” says Christopher A.Toles, formerly with ARS but now withNortheastern University in Boston, Mas-sachusetts. “And the nutshells we’re
working with are renewable on a yearlybasis.”
The team, looking to collaborate with
industry, recently negotiated a coopera-tive agreement with a Georgia-based
firm to test granular forms of the nutshellcarbons.
Their work has also sparked interest
from commercial nut growers and tradegroups like the Almond Hullers and Pro-
cessors Association. Under a specialgrant, that California-based organizationsupplies the scientists with large amountsof shells for their research.
The team sees other potential avenuesfor their emerging technology: electro-
pating companies, mining operations,and jewelry makers. All are industriesthat use activated carbons to help remove
contaminants in the wastewater they gen
erate.
A Tough Nut To Crack Marshall’s team is now testing acti
vated carbons made from macadamiashells supplied to them by a Hawaiiannut processor.
The shells derive their density andstrength from two components—ligninand cellulose. Density and strength are
key to the shell’s conversion to carbonsThat’s because they must withstandgrinding and exposure to temperatureof up to 900 oC in combination with
steam, certain gases, or acids.Such treatment activates, or opens
millions of microscopic pores in the carbonized shells, enabling them to holdonto chemical molecules like benzeneAnother step, called oxidation, confera negative charge to the shells that helpcapture metal ions, such as those in solution.
So porous are today’s activated carbons, notes Toles, that a single gram canhave over 900 square meters of surfacarea. A pound can have up to 465,000square meters—owing to the materialsmicro-, meso-, and macro-sized pores.
Of the nutshell carbons examined thufar, macadamias adsorb the broadesrange of organic molecules. “We’re stiltrying to figure out what makes the macadamia’s nutshell carbons so effective inthis regard,” says Wartelle. She also compares the nutshell carbons to commerciaorganic adsorbents made from naturaand synthetic materials.
Chalk It Up to Charcoal
In one comparative study with sixcommercial adsorbents, use of activatedmacadamia shells led to a three- to fourfold increase in the ability of a standardEnvironmental Protection Agency ai
Some “Trash-Talk” Worth Listening to—
Activated Carbons in a Nutshell
A
Scanning electron micrograph shows the
effect activation has on the gross structureof nutshell carbon granules. While it isimpossible to see active micro- and meso-
pores, the large pits are significant evidenceof gasification. Magnified about 40x.
CHRISTOPHER TOLES
Chemists Wayne Marshall and LyndaWartelle air-sample volatile organiccompounds to determine the adsorptiveproperties of nutshell carbons.
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Agricultural Research/September 1999 15
SCOTT BAUE R (K8326-5)
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16 Agricultural Research/September 1999
shell carbons can be used over and overagain for laboratory sampling.”
The same properties that make the
nutshell carbons so promising for industrial cleanup might also lend themselveto more mundane applications, like purifying tap water.
“Ultimately,” says Toles, “we think imight be interesting to devise a taste andodor nutshell carbon to supplement charcoal carbons already on the market fo
water purification.”Now, that’s not such a nutty idea.—
By Jan Suszkiw, ARS.This research is part of New Uses
Quality, and Marketability of Plant Products, an ARS National Program de
scribed on the World Wide Web at http:
/www.nps.ars.usda.gov/programs/
cppvs.htm.
Wayne E. Marshall and Lynda H
Wartelle are in the USDA-ARS Commod
ity Utilization Research Unit, Southern
Regional Research Center, 1100 Rober
E. Lee Blvd., New Orleans, LA 70124
phone (504) 286-4207, fax (504) 286
4367, e-mail
Raw macadamia nut shells placed in a special oven by chemist Chris Toles will becarbonized and activated at temperatures above 800 oC.
SCOTT BA UER (K8327-3)
Macadamia shell pieces before and aftercarbonization.
ar-spling procedure to detect benzene atconcentrations of 100 parts per billion.Benzene is used in fuels, dyes, solvents,and many other prod-ucts but becomes a
contaminant uponescape into the envi-ronment.
The nutshell car-
bon also worked wellin small-scale studiesto remove copper fromindustrial wastewater.
Wartelle is particular-ly encouraged by the car- b o n ’ s
potential as an adsorbent material for gaschromatographic analysis of air.
Right now, the cost for such analyti-cal carbons can run as high as $13 pergram, she reports. Eventually, the mac-adamia shells might supplement this spe-
cialty market.“We also hope to do more work with
some of the other harder nutshells, likethose of hazelnuts, black walnuts, andBrazil nuts, and to try to investigate theproperties that make them a good air
sampling carbon,” says Wartelle.
SCOTT BAUER (K8328-1 )
Nut Just a Pipe Dream
To foster commercial collaboration,the team has applied for patent protec-
tion on its activation procedures. Use of these methods, Toles estimates, could
yield about 3,000 tons of activatedcarbon material from the 14,600tons of macadamia shells now avail-able.
Marshall stresses that the idea isto supplement—not displace—exist-ing carbon resources.
“Coal and coconut shells are tworeally big resources,” Toles says. “But
when you make carbons from
coal, you’re competingwith people who use it for
energy.”Coal also generatesconsiderable ash andsulfur. But the nutshells,
when activated, releasevery little. “We’re hopingthat making activated car-bons from nutshells will cre-ate a slightly ‘greener’ technology thanmaking them from coal,” Toles says.
And like many standard commercialcarbon products, Wartelle adds, “the nut-
