Understanding the Role of Mono and Ternary Alkali Metal Salts on CO2 Uptake of MgO Sorbents

Abstract

CO2 uptake by MgO-based sorbents at intermediate temperatures is attractive for pre- and post-combustion CO2 capture applications. However, besides the high CO2 uptake potential of these materials (1.1 g CO2 g−1 sorbent), in practice, the realistic CO2 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 NaNO3 single salt or a ternary alkali salt (NaNO3, LiNO3 and KNO3 (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 (CO2 and air) were evaluated. The findings show that the CO2 uptake temperature range and maximum uptake (20–500 °C, CO2 atmosphere) of sorbents are correlated. The cyclic CO2 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 CO2 g−1 sorbent, while for the 15 (Na, K, Li)-MgO-Ca sorbents, it was 375–275 mg CO2 g−1. 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.