Kinetic study of SO2 removal over lignin-based activated carbon

Abstract

Adsorption of SO2 on an activated carbon obtained by chemical activation of kraft lignin with zinc chloride was studied in a laboratory column. The presence of oxygen and water vapor in the inlet stream increases the SO2 adsorption capacity of the carbon, due to the surface oxidation of the SO2 to SO3 and the subsequent hydration to H2SO4. Desorption of the SO2 chemisorbed at temperatures in the range of 150–300 °C produces carbon gasification, forming oxygen surface groups that decompose mainly as CO at higher temperatures (>−500 °C). The presence of CO2 in the inlet gas decreases the SO2 adsorption capacity of the carbon. However, the presence of NO does not produce any significant change in the adsorption of SO2, at the studied conditions. The breakthrough curves of the SO2 adsorption are predicted adequately by a rigorous mathematical model that takes into account the catalytic oxidation of SO2 by an Eley-Rideal mechanism and the reaction between adsorbed SO3 and water vapor to produce H2SO4, followed by the elution of the adsorbed H2SO4 that releases the active sites.