CO₂ generated from coal combustion is the main cause of the greenhouse effect, and it is urgent to reduce its CO₂ emissions. CO₂ capture is the key to Carbon Capture, Utilization and Storage (CCUS) technology. Silicon-based materials are commonly used as carriers for adsorbents, but their CO₂ adsorption capacity is weak, and chemical reagents need to be supported. At present, there is little research on the stability of different diamine adsorbents and adsorbents in the presence of impurity gases. Therefore, it is necessary to prepare silicon-based amine adsorbents and explore their adsorption mechanism and the influence of various factors. In this paper, a variety of organic amines are loaded onto silicon-based materials, aiming to prepare various silicon-based amine adsorbents. The influence mechanism of adsorption temperature, amine types, and gas components (SO₂, NO_x, H₂O) on CO₂ adsorption are carefully investigated.

Using P123 as the template agent and Na₂SiO₃ as the silicon source, the silicon-based mesoporous material SM was prepared. Then, tetraethylenepentamine (TEPA), polyethyleneimine (PEI) and 2-amino-2-methyl-1-propanol (AMP) were supported on SM to obtain the silicon-based amine adsorbents.

CO₂ adsorption mechanism of the silicon-based amine adsorbents was explored through pore structure analysis, infrared spectroscopy analysis and thermogravimetric analysis. CO₂ adsorption experiments of the silicon-based amine adsorbents were carried out by using a fixed-bed analyzer and a thermogravimetric analyzer.

Pore structure analysis shows that due to the filling of organic amines, the porosity decreases and the average pore diameter increases. Infrared analysis indicates that the modification of organic amines does not damage the silicon-based carrier skeleton. Some Si—OH groups form bonds with organic amines, and new characteristic peaks appear after loading, which proves the successful loading of organic amines. Thermogravimetric analysis reveals that the weight loss of the adsorbent occurs in two stages, and the silicon-based amine adsorbent exhibits good thermal stability. In terms of adsorption performance, the modification of organic amines enhances the CO₂ adsorption capacity of SM. Modification with diamines is more effective, as CO₂ reacts with amino groups to form specific products. Adsorption kinetics studies find that the adsorption of CO₂ by SM is mainly physical adsorption, and the adsorption of the three diamine adsorbents is jointly affected by physical and chemical adsorption. Regarding the cyclic performance, after 10 cycles of 30PEI-30AMP/SM, the CO₂ adsorption capacity can reach 95% of the initial capacity, and the synergistic effect of the mixed amines improves the regenerability of the adsorbent. As for the influence of gas components, SO₂ reduces the CO₂ adsorption capacity, water vapor enhances it, and NO has a relatively minor effect.

The main conclusions of this work are summarized as follows: 1) A silicon-based mesoporous material was prepared by using P123 as the template and Na₂SiO₃ as the silicon source. By impregnating with TEPA, PEI and AMP, nine monoamine adsorbents and three diamine adsorbents were synthesized. Among them, the CO₂ adsorption performance of the silicon-based diamine adsorbents is better. 2) The macromolecular amine PEI can significantly occupy the pore space, causing a significant decrease in the specific surface area and pore volume, and a relative increase in pore diameter. The small molecular amines like TEPA and AMP can maintain a higher porosity and specific surface area while filling the pores. The combination of diamines can effectively utilize the characteristics of different amines, and significantly improve the pore structure through intermolecular interactions and spatial arrangements. 3) TEPA and PEI contain a large number of primary amine groups, which can react with CO₂. However, their high viscosity limits their dispersion in the carrier. AMP, a steric hindrance amine with hydroxyl groups, forms an additional network structure, improving the thermal stability of the adsorbent. Different types of amines in the diamine adsorbents can cooperate with each other to enhance their CO₂ adsorption performance. 4) SO₂ in coal-fired flue gas will compete with CO₂ for the limited adsorption sites in the adsorbent, preferentially reacting chemically with the amine groups on the surface of the adsorbent, reducing the adsorption sites for CO₂. Moreover, the generated sulfates will also block the pores, increasing the diffusion resistance of CO₂ and resulting in a decrease in the CO₂ adsorption performance of the adsorbent. An appropriate amount of water vapor can improve the utilization efficiency of amino groups and enhance the CO₂ adsorption performance of the adsorbent.