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CAER Seminars


Dr. David A. Rockstraw
New Mexico State University
Department of Chemical Engineering
Las Cruces, New Mexico

Thursday, April 23, 1998 3:30 pm
Ben Bandy Conference Center
Center for Applied Energy Research

The Mesilla Valley in Southern New Mexico is famous for the production of pecans. New Mexico is the third largest producer in the country and harvested 42 million of the nearly 300 million pounds of pecans produced in 1997. Thus, annual generation of shell waste is near 20 million pounds in New Mexico alone. When milling, shelling, crushing and sugar processing facilities are considered nationwide, over 100 billion pounds of hulls, shells, cobs and fiber are generated each year from renewable resources.

Practical uses have been sought for the pecan shell, but these markets have not yielded a high value product. Consequently, most of the pecan shell waste is ending up in landfills, thus represent an operating cost to the pecan sheller. Recent work has shown that these shells can represent a potential source of natural adsorbent when converted to activated carbon.

The process developed for making this conversion represents a novel method of carbon manufacture and activation. Activated carbon can be produced either in granular or powdered form. Annual world production of activated carbon in all forms is estimated to be approximately 0.4 millions tons. The adsorption capacity of an activated carbon depends on the type of raw material used and the manner in which the material is activated.

The market price of activated carbon is relatively high when compared to other techniques due to the cost of activation. Moreover, spent carbon can be difficult to reactivation, while discharge and transport of the spent carbon to a reactivation facility represents safety and environmental issues. Many of these concerns have been overcome with the pecan shell-based carbon discussed here.

The activated carbon described in this work is manufactured from pecan shells using a phosphoric acid solution. The carbon has been characterized for its ability to remove copper, strontium, and methylene blue from aqueous solutions. Both the equilibrium and kinetic nature of the carbon are explored.