CO2 capture on polyethylenimine-impregnated hydrophobic mesoporous silica: Experimental and kinetic modeling

CO2 adsorption measurements for polyethylenimine (PEI)-impregnated pore-expanded MCM-41 were conducted by gravimetry to investigate the effects of (i) amine loading, (ii) CO2 partial pressure, (iii) adsorption and desorption temperatures. Amine impregnation was conducted on ethanol-extracted pore-expanded MCM-41, referred to as PME which is a mesoporous silica whose internal surface is laden by a layer of cetyltrimethylammonium cations (CTMA). The well-dispersed PEI inside the PME hydrophobic channels exhibited a CO2 adsorption capacity at 75 °C as high as 206 mg/g for 55 wt.% PEI loading. Moreover, the current PEI-impregnated PME materials had high CO2 adsorption efficiency (g CO2/g PEI) than any other PEI-containing adsorbent reported in the literature. In contrast to most PEI-impregnated materials reported in the literature, which because of diffusion resistance showed little or no CO2 adsorption at room temperature, the PEI-impregnated PME material showed high potential for CO2 removal at ambient temperature. Also a new adsorption kinetic model was proposed to describe the adsorption of CO2 over amine-impregnated materials. The model was found to be in good agreement with experimental data under a wide range of conditions including different PEI loadings, CO2 pressures and adsorption temperatures.

► Well-dispersed PEI inside on mesoporous silica with hydrophobic channels exhibit high CO2 adsorption efficiency (g CO2/g PEI) at all temperatures.
► At low temperature, e.g. 25 °C; it is more efficient to use adsorbents with relatively low PEI content rather than highly loaded materials to take full advantage of the increased adsorption rate due to diminished diffusion.
► A new adsorption kinetic model is proposed to describe the adsorption of CO2 over amine-impregnated materials.