SO2 retention on CaO/activated carbon sorbents. Part II: Effect of the activated carbon support

The present paper analyses the role of the activated carbon (AC) properties on the SO2 uptake capacity of CaO/AC sorbents prepared by AC impregnation or ionic exchange with calcium acetate water solutions. Gas adsorption and mercury porosimetry have been used for textural characterization of the AC and surface oxygen groups have been characterized by temperature programmed desorption (TPD). Thermogravimetry has been used for SO2 retention tests and CO2 chemisorption at 300 °C for CaO dispersion (d) determinations. The results show that the surface calcium on CaO/AC samples, determined as “Ca loading · CaO dispersion” (parameter Ca(%) · d), governs the SO2 uptake. The surface oxygen content is the AC property that mainly controls both the calcium loading and surface calcium on CaO/AC samples, which could be explained by the fact that the surface oxygen lowers the hydrophobic character of the AC supports therefore favouring the interaction with the calcium acetate water solutions. The combination of high calcium loading and dispersion leads to SO2 uptakes up to 123 mg SO2/g. The textural properties of the supports have some influence in the calcium loading. However, the effect is masked by the blockage of AC porosity by the calcium loaded.