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

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.

Blending Wastes of Marble Powder and Dolomite Sorbents for Calcium-Looping CO2 Capture under Realistic Industrial Calcination Conditions.

The use of wastes of marble powder (WMP) and dolomite as sorbents for CO2 capture is extremely promising to make the Ca-looping (CaL) process a more sustainable and eco-friendly technology. For the downstream utilization of CO2, it is more realistic to produce a concentrated CO2 stream in the calcination step of the CaL process, so more severe conditions are required in the calciner, such as an atmosphere with high concentration of CO2 (>70%), which implies higher calcination temperatures (>900 °C). In this work, experimental CaL tests were carried out in a fixed bed reactor using natural CaO-based sorbent precursors, such as WMP, dolomite and their blend, under mild (800 °C, N2) and realistic (930 °C, 80% CO2) calcination conditions, and the sorbents CO2 carrying capacity along the cycles was compared. A blend of WMP with dolomite was tested as an approach to improve the CO2 carrying capacity of WMP. As regards the realistic calcination under high CO2 concentration at high temperature, there is a strong synergetic effect of inert MgO grains of calcined dolomite in the blended WMP + dolomite sorbent that leads to an improved stability along the cycles when compared with WMP used separately. Hence, it is a promising approach to tailor cheap waste-based blended sorbents with improved carrying capacity and stability along the cycles under realistic calcination conditions.