ACTIVATED CARBONS AS ADSORBENTS OF SO2 IN FLOWING AIR - EFFECT OF THEIR PORE TEXTURE AND SURFACE BASICITY

Activated carbons used as adsorbents were prepared from a Spanish lignite char by CO2 activation. Activated carbons so prepared were characterized by N2 and CO2 adsorption at 77 and 273 K, respectively, by adsorption of molecular probes at 303 K, and in terms of their mercury and helium densities. Molecular probe and CO2 adsorption data were analyzed by the Dubinin-Radushkevich equation, in order to obtain the micropore volume filled by different adsorptives, their characteristic adsorption energy, and the micropore dimensions. Adsorption Of SO2 in flowing air on these activated carbons was carried out at 358 K and was followed in a thermogravimetric analyzer. The SO2 adsorption capacity and the maximum rate of the adsorption process were obtained for the first and subsequent adsorption cycles, after desorption at 673 K in a N2 flow. These parameters were correlated with the pore texture of the activated carbons and with their total surface basicity as measured by HCl titration. Thus, the SO2 adsorption capacity and the maximum adsorption rate depend on the micropore volume accessible to either benzene or n-hexane. The SO2 adsorption capacity decreases and the adsorption rate increases from the first to the subsequent adsorption cycles, which was interpreted as due to a blockage of the narrower micropores by the SO2 molecules not desorbed. Finally, an increase in the total surface basicity increases the SO2 adsorption capacity, although an adequate microporosity was the most influential parameter in the samples used.