Influência do SO2 na captura do CO2 em condições de pós-combustão

Abstract

Flue gases consist of a complex gaseous mixture resulting mainly from the burning of fossil fuels. Most of its components, among which carbon dioxide is the one emitted in greater quantities, are considered atmospheric contaminants whose emissions must be minimized and controlled. Several technologies have been proposed to perform the separation and capture of CO2, with adsorption being one of the most promising technologies for this purpose. However, the presence of other contaminants, such as sulfur dioxide, tends to interfere in the process through different mechanisms. In that sense, understanding how the presence of SO2 impacts the efficiency of CO2 capture systems is fundamental for the design and optimization of the separation process. Thus, the present dissertation aimed to evaluate the effects of SO2 on the CO2 retention capacity through fixed bed tests and simulations under typical conditions found in the post-combustion scenario. The evaluation was performed using a commercial activated carbon referred to as C141-S, which was chosen because this class of material presents more suitable selectivity values for the purpose explored in this study. The breakthrough curves obtained for the binary system CO2/SO2 showed that SO2 has a higher adsorption affinity to C141-S in relation to CO2 in all cases evaluated, even at low partial pressures. On the other hand, the results suggest that SO2 has little influence on the CO2 retention capacity at typical post-combustion flue gas conditions, with the impacted limited to a 11 % decrease of the CO2 retention capacity. The results also demonstrate that both components are captured during the process and completely desorbed through suitable regeneration methods, pointing to the feasibility of using C141-S in cyclic adsorption/desorption processes. In effect, there are indications that these components can be separated and removed using a single step/equipment, eliminating the need for a pre-treatment unit to remove SO2. The results also suggest that the IAST and Langmuir Extended models are not suitable for determining the adsorption selectivity of systems containing strongly interacting molecules, since the models do not account for two factors affecting the theoretical estimates: the competition for the adsorption sites and the condensation of sulfur dioxide in the pores of the adsorbent.