SO2 retention on CaO/activated carbon sorbents. Part III. Study of the retention and regeneration conditions

The retention of SO2 on CaO/activated carbon sorbents is studied. The effect of several variables such as the reaction temperature, partial pressure of SO2 for different calcium loads, and O2 presence are analysed. Additionally, the regeneration and reutilization of spent sorbents is investigated. In all cases presence of well-dispersed CaO in the sorbents improves SO2 retention in comparison with the activated carbon. In absence of O2 in the gas mixture, the amount of SO2 retained does not depend on the SO2 partial pressure in the range of partial pressures studied and, as expected, SO2 physisorption on the activated carbon support occurs at room temperature. SO2 retention occurs in surface CaO between 100 °C and 250 °C, and in bulk CaO above 300 °C. The total calcium conversion is reached at 500 °C. Above 550 °C calcium-catalysed carbon gasification by SO2 occurs. In presence of O2 in the gas mixture, the studied sorbents are very effective for SO2 removal. However, the SO2 retention process in presence of oxygen must be carried out at temperatures lower than 300 °C to avoid carbon gasification by O2. The thermal regeneration of the spent sorbents can be done under inert atmosphere (880 °C) with only 20% activity loss after the first regeneration cycle due to sintering and formation of CaS. No additional activity loss is detected in the subsequent cycles.