| Global warming is unequivocal due to greenhouse effect, majorly caused by increasing concentration of carbon dioxide in the atmosphere. Using metal oxide sorbents, such as calcium oxide, is one of the most potent ways to separate CO2 in contrast to existing or emerging technologies today. Unlike other technologies, calcium-based separation can be applied easily above 550°C for capturing CO2.;Calcium-based sorbents were prepared first using inorganic and organometallic precursors (OMP) by calcination or wet chemistry. Sorbent performance was tested using a thermogravimetric analyzer (TGA). Amongst all, the sorbents prepared from calcium propionate and calcium acetate exhibited the highest capacity to uptake CO2, converting from calcium oxide to calcium carbonate. These two sorbents possessed higher BET surface area and larger pore volume than the other sorbents. Thermal decomposition of these two OMPs resulted in the maximum evolution of heat, which could eventually lead to the generation of larger macropores, thus explaining the resultant CO 2 uptake capacity demonstrated.;The sorbents originated from OMPs and involved more heat during formation of calcium carbonate exhibited better performance. Therefore, flame technique, which involves with combustion of OMPs, was applied to synthesis sorbents. Scalable flame spray pyrolysis (FSP) is unique in making controllable sized nanoparticles. Such flame-made sorbents consisted of nanostructured calcium oxide and calcium carbonate with high specific surface area (40-90 m 2/g), exhibiting faster and higher CO2 uptake capacity than non FSP-made sorbents. In multiple carbonation/decarbonation cycles, the nanostructured sorbents demonstrated relatively stable, reversible and high CO2 uptake capacity sustaining molar conversion at about 50% after 60 such cycles. The high performance of flame-made sorbents is best attributed to their nanostructure (30-50 nm grain size) that allows operation in the reaction-controlled carbonation regime, rather than in the diffusion-controlled one when sorbents made with larger particles are employed. To further boost durability of the FSP-made sorbents, refractory dopants (Si, Ti, Cr, Co, Zr, and Ce) were applied, aiming at developing sorbents with better mechanical strength. Amongst all, FSP-made Zr-doped CaO sorbents exhibited the best CO 2 capture performance. The effect of Zr-dopant concentration on sorbent characteristics and performance was investigated in detail. A Zr/Ca = 3:10 atomic ratio resulted in the most robust nanosorbent for dozens of multi-cyclic operation. This sorbent retained, unchanged, its ability to capture CO 2 during extended cycles and also demonstrated excellent stability in water vapor (10 vol. %).;To understand sorbent tolerance for capturing CO2 in the presence of sulfur dioxide, three sets of experiments were carried on M/Ca sorbents, namely carbonation and sulfation, both separately and simultaneously. The results show that the capacity of the sorbents for capturing CO2 is reduced in the presence of SO2, due to reaction competition between carbonation and sulfation. TGA and X-ray photoelectron spectroscopy results indicate that the carbonation was totally reversible, while this is not the case with the sulfation. The Ce/Ca sorbent gave the best for CO 2 capture and is the most SO2 tolerant. On the other side, the Mn/Ca promoted one has the strongest affinity for SO2, resulting the most permanent weight gain after sulfation. |
