Experimental Study On CO₂ Capture Of Calcium-based Absorbents Modified With Attapulgite In Cement Industrial Flue Gas

Reduction of greenhouse gases emissions such as CO₂ has became the consensus across the world, and China put more efforts to reduce CO₂ emissions. Under high temperature, Calcium-based absorbents can effectively capture CO₂, and became the focus of international and domestic academics. However, Calcium-based absorbents easy to be sintering after multiple times cyclic calcination/carbonation reaction, and resulted in the decrease of porosity and specific surface area, collapse of pore or hole.Thus the effective channel of CO₂ to spread inside disappeared so that cycling carbonation rate（XN） decay rapidly. And fresh absorbent should be replenished continually in the system of CO₂ capture causing waste of resources.This paper adopted the natural mineral-attapulgite to modify the surface of absorbent particles to capture high concentrations CO₂ of flue gas in cement industry. The onedimensional structure of attapulgite could adhere to the surface of the limestone particles and acted as skeleton which effectively reduced the mutual contact between the limestone particles, so that the sintering and fusion of limestone particles can be avoided to some degree during the CCS process. Morphologies and microscopic structures of absorbent modified with attapulgite will be kept after multiple cycles due to the improvement of anti-sintering ability, and carbonation rate（XN） can be enhanced significantly.This paper analyzed the effect of purification processing, additive amount and particle size of attapulgite to modified absorbent’s cyclic carbonation rate（XN）, and the influence of different reaction condition（accumulation state and half suspension state） on absorbent were compared, the main research conclusions are as follows:（1） Under high temperature, attapulgite could absorb a certain amount CO₂ for physical adsorption, the unit mass of attapulgite adsorb 0.0233 g of CO₂. With the different percentage（2wt%¹5wt%） of attapulgite in absorbent, the contribution rate of attapulgite by adsorbing CO₂ to the cyclic carbonation rate（XN） varied between 1.1197% ¹.0354%, therefore the physical adsorption cannot be ignored.（2） Original attapulgite and purified attapulgite both can be used as the modified material, in cyclic calcination/carbonation of 15 times, the cyclic carbonation rate（XN） of calcium-based absorbent modified with original and purified attapulgite were both higher than absorbent modified with nothing, but the effect of purified attapulgite was the best, so this paper chose purified attapulgite as the modified material;（3） The cyclic carbonation rate（XN）of calcium-based absorbent modified with purified attapulgite was higher than the unmodified absorbent, and the improvement degree of absorbent modified with attapulgite was 5wt%>2wt%>10wt%>15wt%. And after modified with attapulgite, the cyclic carbonation rate stability of calcium-based absorbent was better than natural calcium carbonate, after 40 cycling times, cyclic carbonation rate（XN）of absorbent modified with 5wt% purified attapulgite was about 20%, while natural absorbent was only 15%.（4） The research result showed that although the carbonation rate（XN）of larger particle size of calcium-absorbent before modified was the lowest, absorbent modified with the same particle size of purified attapulgite, the effect of particle size larger absorbent was the best;（5） Under the accumulation state and half a suspended state, the microstructure analysis showed that the pore structure and sintering resistance of absorbent modified with purified attapulgite was better than unmodified absorbent;（6） The pore volume distribution of calcium-based absorbent before and after modified with attapulgite after 5, and 15 cycles was both bimodal, but modified absorbent’s pore diameter of bimodal distribution was smaller than unmodified absorbent. Therefore, the small pore of absorbent modified with attapulgite was still relatively abundant than natural absorbent in the process of CO₂ capture.