Characteristics of activated carbon from peanut hulls in relation to conditions of preparation

Powdered dried peanut hulls were treated by one-step procedures to get activated carbon using chemical activation by H3PO4, ZnCl2, KOH and thermal activation by steam pyrolysis. Products were characterized by adsorption. of NZ at 77 K and methylene blue (MB) from aqueous solution. Simple carbonization at 700-900 degreesC yields low adsorbing microporous carbons. Steam pyrolysis at 600 degreesC generates porosity in the mesopore range. KOH activation results in carbons of low surface area similar to steam pyrolysis, but with much developed. mesoporosity, whereas ZnCl2 activation yields a moderate adsorbing carbon, essentially microporous. Treatment with H3PO4 at increasing impregnation ratios creates abundant microporosity with extended surface area attaining a maximum at a ratio of 1.0. Considerable loss in porosity accompanies additional activating acid indicating the governing action of the amount of activant. A 50% diluted H3PO4 acid results in a carbon with considerable reduction in the internal porosity. Highest removal capacity of MB appears with H3PO4-activated carbons, whereas KOH- activated carbons show the weakest uptake for the dye. (C) 2002 Published by Elsevier Science B.V.