Study Of π-Complexation Adsorbent For Removal Of Trace Amount Of C₂H₄ From CO₂

Recovery of CO₂ is significant for both reduction in a greenhouse gas and best utilization of carbon resource. However, a captured CO₂ stream is not easy to be deep-purified because some impurities, such as C₂H₄, in the CO₂ stream are difficult to be removed. Techno-economic adsorption-separation approach might be a promising alternative. The purpose of this study is to develop efficient adsorbents for removing C₂H₄ impurity from CO₂ stream with an adsorptive approach by using a quantum-chemistry computation and an experimental approach.Molecular orbital (MO) theory calculation based on quantum mechanics has been used to study the nature of adsorption, and also used to investigate the feasibility of deep removal of C₂H₄ from a CO₂ stream by using AgNO₃ modified silica-alumina zeolites. The adsorption type and adsorption strength of C₂H₄ on metal ion depend on the orbital symmetry, orbital occupancy and orbital energy. Both cations (Ag⁺, Cu⁺) and anions (F^-, Cl^-, Br^-, I^-) have great effects on the adsorption of C₂H₄ on metal ion. Cations affect Ï€-complexation directly, and anions play their roles through effect a change in cations. The calculation predicts that AgNO₃ modified silica-alumina zeolite, through Ag⁺ forming Ï€-complexation with C₂H₄, might be deeply remove C₂H₄ species from the CO₂ stream.The fixed-bed adsorption, frontal chromatographic adsorption and desorption experiment, associated with XRD, TGA/DTA, UV-Vis, TEM, C₂H₄-TPD, NH₃-TPD and ICP have been performed to investigate the adsorbents. It shows that there is an intense competition between CO₂ and C₂H₄ on the weak-site adsorption, so the unmodified zeolites can not remove C₂H₄ from CO₂. And the AgNO₃ modified NaY and HY, through Ag⁺ active sites forming stronger Ï€-complex with C₂H₄, can deeply remove C₂H₄ species from the CO₂ stream(≤1 ppmv), the saturated adsorbent can be effectively regenerated at a temperature no more than 280℃, and N₂, CO₂ and dry air can be used as purge gases. The AgNO₃ modified HZSM-5 also get a high purity (≤1 ppmv), but it need about 400℃ for complete regeneration due to its part stronger adsorption sites.Ag⁺ are active sites on AgNO₃ modified zeolites, so whether the silver phase keeps its valence state as Ag⁺ is a key problem. When HY is impregnated with the AgNO₃ aqueous solution, Ag⁺ ions exchange with the H⁺ ions on the cation sites, so the AgNO modified HY...