Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2002
Publication Date: 5/12/2003
Citation: Ng, C., Marshall, W.E., Rao, R.M., Bansode, R.R., Losso, J.N. 2003. Activated carbon from pecan shell: process description and economic analysis. Industrial Crops and Products. 17(3):209-217. Interpretive Summary: Pecan shells are high volume, low cost, renewable agricultural waste that can be converted to value added products such a granular activated carbon. The utility of pecan shell carbon toward the adsorption of metals and organic compounds that pollute the environment has been amply demonstrated. Because of their potential use as a commercial product, there is a need to determine the cost to manufacture pecan shell carbon in order to determine whether this product can compete with commercial carbons in the marketplace. Our cost analysis has determined that pecan shell carbon can be manufactured for about $1.30/lb. This cost includes constructing a completely new production facility with all new equipment. This cost compares to about $2.00-10.00/lb for the selling price of comparable commercial carbons. Therefore, there may be room between our production cost and a commercial selling cost to make a profit manufacturing pecan shell carbons.
Technical Abstract: Granular activated carbons derived from pecan shells have been shown to adsorb a variety of metal and organic species in various processing wastewaters. Their effectiveness is equivalent to or exceeds comparable commercial carbons in this regard. The objectives of this study were to develop process flow diagrams for the large-scale production of pecan shell-based carbons derived from steam or phosphoric acid activation and to carry out an economic evaluation to estimate the cost to manufacture these carbons. On the basis of laboratory investigations with pecan shell-based carbons, process flow diagrams were established for scale-up, and an economic evaluation of carbon production costs was determined. Process flow diagrams were developed for steam and phosphoric acid activation of pecan shells. Major unit operations included shell preparation for pyrolysis, pyrolysis/activation, washing/drying and collection of the final product. Process parameters were calculated for a production facility processing 10,000 kg/day of shells. Final product yields were 13.7% for steam activation and 24.3% for phosphoric acid activation. Therefore, 1,370 kg of steam-activated and 2,964 kg of acid-activated pecan shell carbon could be produced per day. Mass losses were incurred during milling (20%), during pyrolysis/activation (82% for steam and 55% of acid), during washing/drying (13%) and during sieving (5%) of the final product. Based on an annual production cost of $1.22 million and an annual production of 448,000 kg of carbon, steam-activated carbon would cost about $2.72/kg. For the phosphoric acid activation process, annual production costs were estimated at $2.78 million and annual production at 960,000 kg. Therefore, the estimated cost for acid-activated carbon would be $2.89/kg.