Assessment of the Effect of Process Conditions and Material Characteristics of Alkali Metal Salt-Promoted MgO-Based Sorbents on Their CO2 Capture Performance

CO 2 capture using alkali metal salt (AMS)-promoted MgO-based sorbents at intermediate temperatures (300 – 500 °C) has gained increased interest recently. The prospects of such materials for CO 2 capture were assessed in this work. We investigated the most reactive MgO-based sorbents that have been reported in the literature, i.e., MgO promoted with a combination of various AMS (incl. NaNO 3 , LiNO 3 , K 2 CO 3 and Na 2 CO 3 ), and examined how particle size (from powder to pelletized 500 μm particles) and reaction conditions (calcination/carbonation temperature, and partial pressure of CO 2 ) affect the cyclic CO 2 uptake using a thermogravimetric analyzer (TGA) at ambient pressure. The TGA results showed that the CO 2 uptake of the sorbents decreased significantly after pelletization, losing 74 % of its initial capacity. However, the CO 2 uptake capacity of the pelletized sorbents continued to increase over 100 cycles and reached a value (~ 0.46 g CO2 /g sorbent ) close to that of the powdery sample (~ 0.53 g CO2 /g sorbent ). Analysis via X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscope (SEM) and N 2 physisorption suggests that the increase in CO 2 uptake was related to a change of the nature of the alkali species within the molten phase that is reflected by their re-crystallization behavior when cooling them down to room temperature, and appeared to be affected by the CO 2 partial pressure present during carbonation. Finally, the CO 2 capture performance of the best-performing sorbents was evaluated in a packed bed reactor, in order to assess whether the most reactive sorbents are capable of removing a significant amount of CO 2 from a gas stream at ambient pressure. The CO 2 uptake of the sorbents in the packed bed experiments was very close to that in the TGA experiments; however, the CO 2 capture efficiency was less than 10 %, which currently appears too low for an industrial post-combustion CO 2 capture process to be viable. New material developments should not only focus on improving the rate of formation of MgCO 3 from MgO, but also assess whether CO 2 removal with such sorbents is actually feasible.