Effect of amine double-functionalization on CO2 adsorption behaviors of silica gel-supported adsorbents

Amine double-functionalized adsorbents were fabricated using silica gel as supports and their capabilities for CO₂ capture were examined. Aminopropyltrimethoxysilane (1N-APS), and N¹-(3-trimethoxysilylpropyl)diethylenetriamine (3N-APS) were used as grafted amine compounds, and tetraethylenepentamine and polyethyleneimine were used as impregnated species. The influence of double-functionalization method on the CO₂ adsorption performance and textural properties of adsorbents was investigated. The adsorption capacity, the amine efficiency, and the thermal stability of double-functionalized sorbents depend strongly upon molecular variables associated with two different functional states (i.e., chemically grafted and physically impregnated amines). The temperature dependence of adsorption isotherms reveals that the CO₂ adsorption behavior in the double-functionalized adsorbents follow the diffusion limitation model proposed by Xu et al. (Energy Fuels 16:1463–1469, 2002) where the CO₂ adsorption is helped by the diffusion of impregnated amines. It is also found that the adsorption isotherm in the double-functionalized sorbent system with a proper choice for grafted and impregnated amines is nearly independent of temperature, which may offer a novel means to fabricate practically useful sorbents that can be used in a wide range of temperature without loss of CO₂ adsorption capacity.