Investigating activated carbons for SO2 adsorption in wet flue gas

Abstract

The removal of sulfur dioxide from flue gas is an important process for the mitigation of acid rain. Activated carbons have a low affinity for water and a high affinity for polarizable molecules, such as sulfur dioxide, making them good candidates for selective adsorbents for flue gases. This work presents results on the multicomponent adsorption of N2/CO2/SO2 and N2/CO2/SO2/H2O flue gas mixtures on four activated carbons prepared from petroleum coke, and one carbon black. Multicomponent adsorption was measured at T = 30, 60, 90 °C. All five activated carbons had a high affinity and selectivity for SO2 in both the presence and absence of water. The activated carbons prepared with KOH (P_K) and NaOH (P_Na) showed the highest capacity for SO2 under wet conditions with thermal swing regeneration (P_K: nadsSO₂ = 0.148 ± 0.002 mmol g−1, P_Na: nadsSO₂ = 0.13 ± 0.01 mmol g−1). In pressure swing experiments of the wet flue gas mixture, the activated carbon prepared with a K2CO3 and KOH (P_CK) (nadsSO₂ = 0.077 ± 0.002 mmol g−1) and P_K (nadsSO₂ = 0.064 ± 0.005 mmol g−1) activated carbons had the highest SO2 capacities. Of the activated carbon, P_K had the greatest SO2/H2O selectivity for the thermal swing adsorption (T = 30 °C, SSO₂/H₂O = 3.0 ± 0.2) and pressure swing adsorption (T = 90 °C, SSO₂/H₂O = 3.9 ± 0.6) experiments. It was observed that activated carbons with higher carbon fraction were less likely to have a difference in SO2 adsorption from dry versus wet conditions. After the wet SO2 multicomponent adsorption, no change in the adsorption performance of any activated carbons was observed after 10 cycles.