Exploring the Role of Imidazoles in Amine-Impregnated Mesoporous Silica for CO₂ Capture

Abstract

A series of efficient adsorbents for CO 2 capture was prepared by a wet-impregnation method. Mesostructured cellular silica foam (MF) was selected as a support and modified with a mixture of tetraethylenepentamine (TEPA) and imidazoles (Ims) to improve the initial and working CO 2 -adsorption capacity. The heat of adsorption was also evaluated. The impact of different amines and the adsorption temperature on CO 2 -adsorption performance was investigated. Some Ims showed a synergistic effect with TEPA regarding adsorption/desorption performance. Impregnating MF with such Ims and TEPA increased CO 2adsorption performance and decreased the heat of absorption compared with those obtained for MF impregnated only with TEPA. MF modified with 30 wt % 4-methylimidazole and 40 wt % TEPA exhibited a high first-pass CO 2 adsorption capacity of 4.88 mmol/g at 100 kPa and 40 °C. Following vacuum regeneration, a working capacity of 4.15 mmol/g was observed for the same conditions.

Effects of Amine Structures on Oxidative Degradation of Amine-Functionalized Adsorbents for CO2 Capture

“…This is in agreement with that observed in the absence of water. The CO 2 adsorption ability of amine-impregnated silica is mainly based on the reaction of CO 2 and primary/secondary amino groups to form carbamate anions and protonated amines, ,,, giving the theoretical maximum amine efficiency of 0.5. The amine efficiency provides an indication of the active ingredient in the adsorption process.…”

“…However, the amine efficiencies of BPEI adsorbents are lower than 0.31, indicating that a significant amount of the amino groups in BPEI was hindered by CO 2 . The low amine efficiencies of the BPEI adsorbents are attributed to the electrostatic interaction between the carbamate anions and protonated amines, which prevents the diffusion of CO 2 to the inner amine active sites, , resulting in a decrease in the amount of adsorbed CO 2 . Additionally, BPEIs are polymers with a high viscosity (Table S2) and thus can regulate the diffusion of CO 2 to active sites, leading to low amine efficiency.…”

“…Amine-containing adsorbents were synthesized by a wet impregnation method. − The amine/methanol/MSU-F mixtures in a ratio of 6 g/200 mL/4 g were agitated for 2 h at 20–25 °C. Subsequently, the adsorbents were obtained by removing methanol in a rotary evaporator.…”

Role of additives in silica-supported polyethylenimine adsorbents for CO2 adsorption

“…Recently, efforts have been made to optimize the amine phase with other additives to obtain adsorbents having higher CO 2 adsorption capacity [14,15]. In this paper, PEI modified SiO 2 aerogels were grafted with different additives from amine functional groups and hydroxyl groups and emphatically the effects of the seven additives on CO 2 adsorption capacity were investigated and evaluated.…”

Enhancement of CO2 Adsorption/Desorption Properties of Solid Sorbents Using Tetraethylenepentamine/Diethanolamine Blends

“… 26 , 27 The effects of amino groups and porous supports on the CO 2 adsorption capacity have been investigated and reported in the literature. Mesoporous silica materials, including hexagonal MCM-41, 19 , 20 , 22 silica aerogels, 23 , 24 SBA-15, 17 , 25 mesoporous silica nanosheets, 28 and mesocellular silica foams (MCFs), 12 , 14 , 26 , 27 , 29 − 33 have been used as supports for amine loading because of their high surface areas and thermal stabilities. Among these supports, MCF has shown the highest CO 2 adsorption performance after wet impregnation with amines owing to its high stability and the presence of three-dimensional wormlike pores, as well as good pore interconnections that promote molecular diffusion.…”