The following content is copied from an open access paper (https://doi.org/10.3390/ijerph7083129).
“Calcium aluminate-based pellets are new and one of the most efficient and inexpensive solid sorbents for CO2 capture [31]. They can help in mitigation of sorbent sintering, attrition, and consequent elutriation. All of these shortcomings are considered to be mitigated by means of reactivation/pelletization of fresh/spent/elutriated sorbent before or during its utilization. It has been shown that the use of appropriate binders is necessary and calcium aluminate cement is the most efficient binder [50]. It is also a source of alumina compounds desirable in the CaO structure, which enhance micro- and nano-porosity of the sorbent. However, like other CaO-based sorbents, aluminate-based pellets lose their activity, which is especially pronounced at higher temperatures [44] necessary during sorbent regeneration in order to produce concentrated CO2 streams.”
“The reactivation of aluminate-based pellets by steam or water to recover their activity during capture cycles has also been investigated [45]. Moreover, these pellets can be reshaped after reactivation by water, which is another advantage. A photograph of pellets is presented in Figure 6. A test involving 300 cycles in a tube furnace, followed by reactivation and reshaping of the pellets, was continued for a further 350 cycles in the TGA. During this series of 350 cycles, a steam reactivation step was applied after 210 cycles. The CO2 capture activity of pellets was determined in a TGA apparatus, and Figure 7 presents TGA results from this 350-cycle test. These results illustrate the superior performance of aluminate-based pellets, with the added important property that they can be reactivated/reformed, resulting in high average conversions, >35%, in series of hundreds of CO2 capture cycles.”
“Figure 6. Photograph of calcium aluminate-based pellets.”
“Figure 7. Carbonation conversion of reformed aluminate-based pellets (1 mm) enhanced by steam reactivation (5 min at 100 °C in saturated steam). Pellets were prepared with 10% CA-14 cement and 90% Cadomin limestone [31]. Calcination at 950 °C in 100% CO2; carbonation at 700 °C in 20% CO2 (N2 balance) for 30 min.”
“The morphology of pellets was observed by a SEM and obtained images at magnifications of 2,500× and 20,000× are presented in Figure 8. The images were taken from the interior of broken pellet spheres after 30 CO2 cycles. It can be seen that two types of pores are present: large macropores on the 1 μm scale and mesopores on the 10–100 nm scale. These nano-sized pores, which did not disappear during cycles, are responsible for carbonation conversion because they are the main contributor to the sorbent surface area and to the micro- and meso- porosity necessary for storage of more voluminous product, CaCO3.”
“Figure 8. Morphology of aluminate-based pellets (SEM).”