Development of macroporosity in activated carbons by effect of coal preoxidation and burn-off

The effects of different treatments-preoxidation, pyrolysis and extent of burn-off-on the textural properties of activated carbons prepared from a semianthracite were studied. The materials obtained in the different steps were characterised by mercury porosimetry, nitrogen adsorption and scanning electron microscopy. Coal was preoxidised at 543 K for different periods of time up to 7 days. Carbonisation of fresh and oxidised coal samples was carried out under nitrogen at 1123 K at a heating rate of 60 K/min and a soaking time of 1 h. A significant development of macroporosity was obtained in the pyrolysis step, being more important in the case of the char produced from the unoxidised coal. Activation of the chars obtained after carbonisation of the oxidised coals was carried out by gasification in steam at 1123 K. Activation produced high macropore volumes mainly in the 800-2000 nm radius interval in the activated materials. The total pore volumes increased with burn-off, reaching values close to those of commercial activated carbons. (C) 1998 Elsevier Science Ltd. All rights reserved.