Stability of Supported Amine Adsorbents to SO2 and NOx in Postcombustion CO2 Capture. 1. Single-Component Adsorption

Flue gases from coal-fired power plants typically contain not only CO 2 but other acid-gas impurities such as SO x and NO x that can dramatically influence the CO 2 capture efficiency. Whereas postcombustion CO 2 capture by aminosilica materials has been extensively studied over the past few years because of their high equilibrium CO 2 capacities, the performance of these materials under realistic conditions (in the presence of SO x, NO x, and O 2 ) remains relatively unexplored. In this study, the degree of irreversible binding of SO 2, NO, and NO 2 to four supported amine adsorbents is evaluated to assess the SO 2, NO, and NO 2 adsorption capacities of aminosilica sorbents and their effects on the CO 2 adsorption capacities. Adsorbents constructed using poly(ethyleneimine) and three different silane coupling agents (based on propyltrimethoxysilane linkers) with primary, secondary, and tertiary amines are evaluated. Under the experimental conditions used in this investigation, it is found that primary amines with high amine loadings displayed more affinity toward NO than their secondary and tertiary amine counterparts. However, overall, NO adsorption on the aminosilica adsorbents is low, and therefore, the CO 2 capacities of the adsorbent materials exposed to NO remained almost unchanged after the exposure. In contrast, all materials showed a very high nitrogen dioxide adsorption capacity upon exposure to NO 2 . As a result, all adsorbents treated with NO 2 exhibited a dramatic reduction in CO 2 capacity, which corresponds to the deactivation of amine groups due to the irreversible binding of NO 2 . In addition, our results indicate that SO 2 adsorbed significantly on supported amine adsorbents, resulting in a dramatic loss in CO 2 capacity during CO 2 capture from flue gas. With similar amine loadings, although secondary amines exhibited higher affinity to SO 2, their CO 2 capacity loss after exposure to SO 2 is lower than that of primary amines, indicating that these materials are more stable in the presence of SO 2, which implies that more SO 2 desorbs from secondary amines during the desorption step. These results suggest that for silica-supported amine materials to be useful in practical CO 2 capture applications, it is necessary to significantly reduce the SO 2 and NO 2 concentrations of the flue gas prior to the CO 2 capture process. On the other hand, the capture efficiency of these materials does not change significantly in the presence of NO. This suggests that such materials might be promising for postcombustion CO 2 capture from flue gas streams derived from natural gas combustion, as these streams typically contain reduced SO 2 concentrations but can still have significant NO x concentrations.