SO2 retention on CaO/activated carbon sorbents. Part I: Importance of calcium loading and dispersion

Sorbents for SO2 retention at low temperature consisting of CaO supported on activated carbons have been prepared by different methods (physical mixing, incipient wetness impregnation, rotary evaporator impregnation, complex formation and ionic exchange). Ca(OH)2, CaCO3, CaO, Ca(CH3COO)2 and Ca(C2H5COO)2 have been used as calcium precursors. The preparation method affects calcium loading as well as calcium dispersion. SO2 retention depends both on the calcium loading and on the calcium dispersion. The best preparation method, among those tested, was impregnation of the activated carbon with calcium acetate. Similar calcium loading can be obtained by the physical mixing method but the resulting calcium dispersion is low. On the contrary, samples with higher calcium dispersion were obtained by the complex formation method, presenting the disadvantage of the low calcium loading reached. The molar calcium conversion results are much higher than values reported for unsupported calcium compounds.