Stability of amine-based hollow fiber CO2 adsorbents in the presence of NO and SO2

Abstract

Comparative studies of the cyclic stability of primary, secondary, and tertiary amine-grafted silica/polymer composite fiber adsorbents upon exposure to simulated flue gas are reported. A simulated dry flue gas mixture with 200ppm NO does not cause degradation of the amine grafted fiber adsorbents and all fibers retain their CO2 capacity in the presence of NO. In contrast, upon exposure to dry flue gas in the presence of 200ppm SO2 at 35°C, the primary amine containing adsorbent, CA–S–APS, shows a CO2 capacity reduction of 55% over 120 cyclic adsorption–desorption runs. As the initial SO2 induced degradation occurs in this adsorbent, the amine sites first irreversibly adsorb SO2 and then begin to gradually adsorb SO2 reversibly, as evidenced from a quantitative comparison of the amount of adsorbed SO2 to the amount of desorbed SO2. The secondary amine containing adsorbent, CA–S–MAPS, exhibits an improved stability and approximately 25% CO2 capacity loss is observed during cycling in the presence of SO2. Therefore, the secondary amine based CA–S–MAPS adsorbent demonstrates some degree of tolerance to SO2 in comparison to the CA–S–APS sample. Under humid conditions, SO2 imposes significant detrimental impacts on the two adsorbents, as a result of increased SO2 adsorption capacities in the presence of moisture. Although the CO2 uptake is nearly zero in the tertiary amine adsorbent, CA–S–DMAPS, the SO2 capacity of this adsorbent reaches 0.43mmol/g under humid conditions and this material has the highest SO2/N ratio of the fiber adsorbents studied. More importantly, this CA–S–DMAPS sample demonstrates reversible SO2 adsorption, as indicated from the SO2 cyclic adsorption experiments. The tertiary amine based fiber adsorbents have good potential for flue gas desulfurization, with advantageous characteristics of high SO2/N ratio, excellent reversibility, low CO2 adsorption and relatively low regeneration temperature.