Understanding the Role of Mono and Ternary Alkali Metal Salts on CO Uptake of MgO Sorbents.

CO uptake by MgO-based sorbents at intermediate temperatures is attractive for pre- and post-combustion CO capture applications. However, besides the high CO uptake potential of these materials (1.1 g CO g sorbent), in practice, the realistic CO capture is far from that of the theorical values. In this work, the sol-gel method was used to synthetize unsupported and supported MgO sorbents (10% Ca or 10% Ce support, mol) that were impregnated with different fractions (15, 25, and 35; % mol) of a NaNO single salt or a ternary alkali salt (NaNO, LiNO and KNO (18/30/52; % mol)). To understand the role of alkali metal salts (AMSs) in the MgO sorbents' performance, the working and decomposition temperature ranges of AMS under different atmospheres (CO and air) were evaluated. The findings show that the CO uptake temperature range and maximum uptake (20-500 °C, CO atmosphere) of sorbents are correlated. The cyclic CO uptake of the most promising sorbents was tested along five carbonation-calcination cycles. For the first and fifth cycles, respectively, the 15 (Na, K, Li)-MgO sorbents showed the highest carrying capacity, i.e., 460-330 mg CO g sorbent, while for the 15 (Na, K, Li)-MgO-Ca sorbents, it was 375-275 mg CO g. However, after the first cycle, the carbonation occurred faster for the 15 (Na, K, Li)-MgO-Ca sorbents, meaning that it can be a path to overpassing carbonation kinetics limitations of the MgO sorbent, making it viable for industrial applications.