Activated carbons by pyrolysis of coffee bean husks in presence of phosphoric acid

Activated carbons (Acs) were prepared by pyrolysis of coffee bean husks in presence of phosphoric acid (chemical activities). Husks from Colombian coffee beans were impregnated with aqueous solutions of H3PO4 following a variant of the incipient wetness method. Diffenent concentrations were used to produce impregnation ratios of 30, 60, 100 and 150 wt.%. Activation was carried out under argon flow by heating to 723 K with 1 h soaking time. The porous texture of the obtained ACs was characterized by physical adsorptions of N-2 at 77 K and CO2 at 273 K. The impregnation ration had a strong influence on the pore structure of these Acs, which could be easily controlled by simply varying the proportion of H3PO4 used in the activation. Thus, low impregnation ratio led to essentially microporous Acs. At intermediate impregnation ratios, ACs with wider pore size distribution (from micropores to mesopores) were obtained. Finally, high impregnation ratios yielded essentially mesoporous carbons with high surface area and pore volume. (C) 2002 Elsevier Science B.V. All rights reserved.