Highly selective molecularly imprinted poly[acrylamide-co-(ethylene glycol dimethacrylate)] polymer particles (MIPs) for CO capture were synthesized by suspension polymerization via oil-in-oil emulsion. Creation of CO-philic, amide-decorated cavities in the polymer matrix led to a high affinity to CO. At 0.15 bar CO partial pressure, the CO/N selectivity was 49 (corresponding to 91% purity of the gas stream after regeneration), and reached 97 at ultralow CO partial pressures. The imprinted polymers showed considerably higher CO uptakes compared to their nonimprinted counterparts, and the maximum equilibrium CO capture capacity of 1.1 mmol g was achieved at 273 K. The heat of adsorption was below 32 kJ mol and the temperature of onset of intense thermal degradation was 351-376 °C. An increase in monomer-to-cross-linker molar ratio in the dispersed phase up to 1:2.5 led to a higher affinity toward CO due to higher density of selective amide groups in the polymer network. MIPs are a promising option for industrial packed and fluidized bed CO capture systems due to large particles with a diameter up to 1200 μm and irregular oblong shapes formed due to arrested coalescence during polymerization, occurring as a result of internal elasticity of the partially polymerized semisolid drops.
Silica-supported tetraethylenepentamine (TEPA/SiO 2 ) sorbents for CO 2 adsorption were prepared by incipient impregnation method, in which porous silica was loaded with TEPA and alkanolamines or alcohols as dopants. Both CO 2 adsorption capacity and amine utilization efficiency of these sorbents were evaluated in a self-assembled fixed-bed reactor. The results show that the introduction of alkanolamines or alcohols, especially those with higher amine and hydroxyl densities, into TEPA/SiO 2 notably improves their CO 2 adsorption performance. The maximum CO 2 adsorption capacity (4.14 mmol/g) was obtained over a doped TEPA/SiO 2 loaded with 30% TEPA and 30% diethanolamine. The interaction between hydroxyl and amino groups, leading to the improved dispersion of TEPA phase on the surface of SiO 2 , was investigated by N 2 adsorption−desorption measurements, scanning electron microscopy, and X-ray photoelectron spectroscopy. The calculation based on density functional theory shows that the existence of the hydroxyl group in the doped TEPA/SiO 2 sorbents increases the CO 2 adsorption energy, which is the key factor to achieve the optimized CO 2 adsorption capacity and amine utilization efficiency.
The series of polyethylenimine (PEI)-based solid sorbents were prepared by the wet-impregnation of PEI (M w = 600) on the surface of six porous materials, i.e., mesoporous silicas (MCM-41, SBA-15, and KIT-6), mesoporous carbon (CMK-3), protonated titanate nanotube (PTNT), and fumed silica (FS). The resultant materials, denominated PEI/supports, were characterized by N 2 adsorption/desorption at 77 K, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). CO 2 adsorption on the PEI/supports was evaluated using 2 vol % CO 2 in flowing air on a self-assembled fixed bed reactor. The observations made here show that relative to the other four sorbent counterparts, PEI/PTNT and PEI/FS exhibit better performance of CO 2 adsorption, mainly attributed to their more abundant secondary macropores, together with more homogeneous PEI surface dispersion. For all the PEI/ supports, the adsorption data of CO 2 at various pressure equilibriums were modeled by the Langmuir dual-site isotherms. And the values of the fitted model parameters offer some hints that both chemisorption and physisorption are synchronously involved in these sorbent systems, one of which will govern the CO 2 adsorption process, dependent on the nature of the supports used.
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