**3. Results**

*3.1. Raw Sorbents*

3.1.1. Dolomite

The simulation of the CaL process for dolomite showed an initial weight loss of the sorbent (calcination) amounting to 45.06% of its weight (Figure 4), which means that the sorbent was composed of almost pure CaMg(CO3)2. The dolomite derivatogram reveals that two reactions registered on the DSC curve as two adjacent endothermic effects at 740 and 870 ◦C. The first is responsible for the CO2 release from MgCO3, and the second from CaCO3; the sample mass losses are 23.59 and 21.47%, respectively. During carbonation, the CO2 capture was obtained, causing the sample mass changes in the range from 18.77% (first cycle) to 10.30% (10th cycle) (Figure 5). The gas capture efficiency decreased with increasing number of CaL cycles, which may be related to the decreasing active surface of the sorbent due to sintering.

It is worth noting that the carbonation process was not completed within the assumed time of 10 min. This is evident in the sample mass change (TGA) graph, which shows the rapid rise (reaction step—line 1) smoothly moving through the transition (line 2) towards the diffusion step (line 3). According to the SCM model, such effects are connected with the increasing thickness of the CaCO3 layer surrounding the unreacted CaO core. However, this last step was not fully completed, as shown by the line 3, which is tangent to a portion of the mass loss curve still deviates from the horizontal position. This means that in the case of dolomite sorbent, carbonation could be carried out for a longer time than assumed in the analyzed simulation. This is justified by the observation of the occurrence of a segmen<sup>t</sup> typical for the diffusion that was visible at the time of about 10 min after closing the CO2 flux to the reaction chamber of the furnace, when the atmosphere was not fully replaced with the protective gas (N2). In this case, the extension of the carbonation time may be associated with a potential reduction in the economics of the capture process, as the recorded increase in uptake by diffusion was only 0.29% in the first cycle, and in the next, it was about 1% of the sorbent sample mass (Figure 5). This issue would require further tests with extended carbonation time in order to calculate the amount of CO2 bound by the sorbent through the diffusion process.

**Figure 4.** TGA and DSC curves for dolomite.

**Figure 5.** Relative mass changes for dolomite in the CaL process (the solid black line marks the section of the surface reaction, and the dashed line marks the section possibly corresponding to diffusion).

3.1.2. Saint Anne Mountain Limestone

The initial weight loss of the sorbent was observed (dehydration and calcination) to amount to 42.89% of its weight (Figure 6), which means that the sorbent was composed of almost pure calcium carbonate. Carbonation caused the sample mass changes in the range from 30.49% (first cycle) to 12.42% (10th cycle) (Figure 7).

**Figure 6.** TGA and DSC curves for limestone from Saint Anne Mountain.

**Figure 7.** Relative mass changes for the limestone from Saint Anne Mountain.

The gas capture efficiency clearly decreased after the first cycle—to 24.28%—which may be related to the reduction in the active sorbent surface due to sintering. In subsequent cycles, this decline showed a downward trend. It should be noted that the reaction segmen<sup>t</sup> (visible as a steep mass increase) was shortened more and more in subsequent steps. At the same time, the elongation of the transition section was noticeable—this proves the increasing role of diffusion and confirms the sintering phenomenon. At the end of the assumed carbonation stage, a slightly inclined section of the sample mass increase was formed, which proves the diffusion process at that time (Figure 6). In addition, within about 5 min after closing the CO2 supply, small, unsystematic fluctuations in the mass of the sample are revealed (from −0.71% to +0.06%), followed by rapid calcination.
