Synthesis of Amine Modified Mg-Al LDH and their CO₂ Adsorption Characteristics

A series of amine modified layered double hydroxides (LDHs) were prepared using 3-aminopropyltrimethoxysilane (N1) and N-aminoethyl-γ-aminopropyltrimethoxysilane (N2) as grafting agents, and these LDHs were characterized by X-ray diffraction (XRD), Flourier Transform Infrared spectroscopy (FT-IR), elemental analysis (EA) and thermogravimetric analysis (TG). Effects of amine loading on CO₂ adsorption were investigated and the amine modified LDH with excellent adsorption performance was selected. Effects of adsorption temperature on adsorption and recycling performance were further investigated. The results indicate that the composite amine modification method overcomes the shortcoming of conventional amine modified methods such as exfoliation and anionic surfactant methods which are difficult to further improve amine loading. LDH with high amine loading was obtained. CO₂ adsorption increases with the increase of amine loading. Mg-Al N2 with amine loading of 6.20 mmol∙g^-1 has an adsorption capacity of 2.26 mmol∙g^-1 at 30℃ and 0.1 MPa. CO₂ adsorption capacity reduces when temperature increases from 30℃ to 90℃. Moreover, CO₂ can be completely desorbed at 140℃ and the structure and performance of the adsorbent remains unchanged after five adsorption-desorption cycles.