Chemically activated carbons from olive stones - Peculiarities of pore structure and interpretation of nitrogen adsorption data

Chemically activated carbons were obtained from olive stones either by carb onization with H3PO4 at 300-600 degrees C or by carbonization with ZnCl2 at 600 degrees C. Nitrogen adsorption at 77 K was determined for all the acti vated carbons. The adsorption data were interpreted by considering some con ventional adsorption models. Maximum activation with H3PO4 occurred at 450 degrees C. However, the adsor ption capacities of the ZnCl2-activated carbons were far higher than those of carbons activated with H3PO4. Carbons activated with H3PO4 or ZnCl2 are mainly microporous with the non-micropores representing a small fraction of the total porosity. Although, the nitrogen isotherms are Langmuirian in sh ape, application of the Langmuir equation led to large monolayer capacities of uncertain confidence. The surface areas and micropore volumes determine d by the application of the t-method of de Beer and the alpha(s)-method of Sing were comparable and were slightly higher than those determined by the application of the DR model based on micropore filling. The t-method and th e alpha(s)-method are complementary to each other and would seem to give co nfident values because they are based on standard reference non-porous mate rials. The micropore region may be sub-divided into two sub-regions disting uished by the different filling mechanisms involved.