EFFECT OF GASIFICATION ON THE POROUS CHARACTERISTICS OF ACTIVATED CARBONS FROM A SEMIANTHRACITE

Activated carbons with degrees of burn-off between 20% and 80% have be en prepared from a semianthracite char by gasification in steam at 112 3 K. The adsorption isotherms of nitrogen at 77 K and CO2 at 273 K hav e been determined. The pore size distribution has been calculated from t plots, and helium and mercury densities. The ungasified char has a narrow pore size distribution and mainly consists of very fine micropo rosity. The pores have constrictions that do not allow adsorption of n itrogen, but the microporosity can be measured by the adsorption of CO 2 at 273 K. S-mic and CO2 (D-R) surface areas of the ungasified char a re about the same. The gasification of the char broadens the micropore distribution. The small microporosity calculated from t plots increas es with burn-off between 20%-35%. Gasification to higher degrees of bu rn-off causes burning of the walls between the adjacent pores and elim inates pore constrictions. This results in widening the micropores, cr eating meso and macroporosity and decreasing microporosity. When the d egree of gasification is 80%, the small microporosity disappears almos t completely, although the total porosity has been increased almost th ree times. While the nitrogen surface area increases with burn-off, th e CO2 surface area decreases at higher degrees of burn-off.