Tetraethylenepentamine-modified MCM-41/silica gel with hierarchical mesoporous structure for CO2 capture

MCM-41, with relatively small mesopores centered at 2.7 nm and 3.7 nm, and silica gel (Gel), with relatively large mesopores centered at 8.8 nm, were physically mixed to act as a support layer. Tetraethylenepentamine (TEPA) was used to modify the support to prepare the sorbents for CO2 capture. The effects of the weight ratios of Gel to MCM-41, amine loadings, adsorption temperatures, and CO2 partial pressures at different temperatures were investigated in a self-assembled fixed bed reactor. The adsorption thermodynamics was studied using the Langmuir isotherms, and kinetics was modeled using three kinetic models and the intraparticle diffusion model. The saturated CO2 adsorption capacity of 4.27 mmol-CO2/g-sorbent was obtained at 55 °C and 15 vol.% CO2/85 vol.% N2 when the weight ratio of Gel to MCM-41 was 1:1 and the TEPA loading was 50%. The experimental data fit well with the Langmuir model and the isosteric heat of adsorption at relatively high adsorbate coverage was 57 kJ/mol, indicating the homogeneity of the adsorption sites and the chemisorption characteristics. The well fitting of Avrami model with the experimental data suggested that multiple reaction pathways occurred during the CO2 adsorption process. The intraparticle diffusion prediction showed that boundary layer diffusion was the rate-controlling step. In addition, GMCM-41-TEPA50% exhibited good regenerability after ten adsorption-desorption cycles.