Diffusion kinetics of CO₂ in amine‐impregnated MIL‐101, alumina, and silica adsorbents

Abstract

CO 2 sorption kinetics of poly(ethylenimine) (PEI)-impregnated MIL-101, γ-alumina, and UVM-7 silica were investigated by the zero-length column technique for the purpose of understanding the effect of amine content, adsorbent porosity, and adsorption temperature on CO 2 sorption rates. Each of the adsorbents was impregnated with three different amine contents (20, 35, and 50 wt%) and the effective diffusion time constants were determined at 25 C. For each respective adsorbent, it was found that increasing the amine content results in diminished diffusion rates. Additionally, it was found that the pore size of the support has a profound effect on diffusional kinetics, where microporous MIL-101 yielded substantially slow desorption rates upon amine-functionalization compared to mesoporous γ-alumina. PEIimpregnated UVM-7 silica was further investigated at 50 and 75 C in order to provide insight into the effect of temperature on sorption kinetics. The results indicated that PEI-impregnated UVM-7 exhibited faster sorption kinetics at higher temperatures. Upon desorption, PEI-UVM-7 silica exhibited two distinct regions of masstransfer control that occur at different sorption times. This is best explained by first the occurrence of surface diffusion followed by diffusion out of the bulky PEI polymer chains. The findings of this study provide novel kinetic characterizations on promising amino-adsorbents for carbon capture applications. K E Y W O R D S γ-alumina, CO 2 capture, diffusion time constant, MIL-101, UVM-7 silica, ZLC technique 1 | INTRODUCTION The rapid rise of anthropogenic CO 2 emissions resulting from fossil fuel combustion has been widely identified as the primary cause to the increase in global temperatures, due to the deleterious effects of this greenhouse gas. 1 Hence, development of cost-effective carbon capture processes is essential for mitigation of CO 2 emissions. 1-4 Aqueous monoethanol amine absorption is regarded as the benchmark technology for post-combustion CO 2 capture, but suffers from high-energy penalties upon solvent regeneration. 3 Alternatively, the direct removal of CO 2 from ambient air has arisen as an attractive option in recent years that could be implemented in residential areas to mitigate emissions resulting from transportation sources. 4,5 Therefore, solid-state adsorbents have been intensively studied as a viable, cost-effective alternative to absorption-based amine scrubbing for practical carbon capture applications. Solid adsorbents, traditionally including zeolites, carbon molecular sieves, activated carbons, activated alumina, and metal-organic frameworks (MOFs), are physical adsorbents and have been extensively studied due to their high efficiency, low regeneration requirements, and long-term stability. 6 However, these adsorbents suffer from inferior capture capacities compared to aqueous amine-scrubbing, as well as reduced working capacities in humidified conditions. 7 Therefore, recent research has focused on the incorporation of amine moieties

Insights into the Critical Role of Abundant-Porosity Supports in Polyethylenimine Functionalization as Efficient and Stable CO2 Adsorbents

“…Similar phenomena could be observed based on several previous investigations. ,,,,,,,− We summarized the maximum CO 2 adsorption capacities and the corresponding optimal adsorption temperatures of the reported PEI-functionalized adsorbents all with around 50% loadings in these studies, as presented in Figure f. Thereinto, various adsorbents were divided into PEI/SiO 2 , PEI/Al 2 O 3 , PEI/AC, and PEI/resin, according to the selected porous supports.…”

“…To this end, the amine efficiency, the ratio of the adsorbed CO 2 to the modified amine groups (mmol CO 2 /mmol N), was commonly proposed to evaluate the accessibility of CO 2 –amine binding in the functionalized adsorbents . Notably, the reaction of CO 2 and primary/secondary amines with a 1:2 ratio gave the efficiency of 0.5, whereas the theoretical maximum amine efficiency was generally lower and about 0.38 because of the presence of tertiary amines in PEI. , As displayed in Figure , at a lower adsorption temperature of 30 °C, 30%PEI/HP20 and 30%PEI/XAD4 exhibited the highest amine efficiencies of 0.36, close to the theoretical maximum value, indicating that the functionalized 30% PEI was basically available for CO 2 adsorption. In contrast, the amine efficiencies of 30%PEI/SiO 2 , 30%PEI/Al 2 O 3 , and 30%PEI/AC were just 0.26, 0.18, and 0.24 at 30 °C, respectively.…”

Diffusion Kinetics of CO2, CH4, and their Binary Mixtures in Porous Organic Cage CC3

“…A plot of ln­( C/C 0 ) versus time will yield a long-time asymptote with a slope of π 2 D c / r c 2 . More extensive overviews of the micropore ZLC theoretical model are detailed in previous studies. ,,,− …”

“…Our results revealed ethylene diffusion is hindered by strong surface resistance effects occurring between ethylene double bonds and the external crystalline surfaces of MOFs ZIF-7 and Ni­(bdc)­(ted) 0.5 . Following this study, our group then utilized the ZLC technique to investigate the diffusion kinetics of CO 2 through amine-functionalized MIL-101, γ-alumina, and UVM-7 silica adsorbents . Results revealed high loadings of polyethylenimine on UVM-7 silica can achieve both elevated adsorption capacities and accelerated diffusion kinetics at postcombustion capture temperatures.…”

High‐performance oxygen transport membrane reactors integrated with IGCC for carbon capture

“…[7][8][9] The high-temperature gasification (1,200-1,400 C) and low-temperature CO 2 separation (25-400 C) make heat integration inefficient, and lead to excessive exergy loss. H 2 /CO 2 separation and CC based on the state-of-the-art absorption (e.g., amine and ammonia) 10 or adsorption processes (e.g., zeolites, 11,12 activated carbon 13 ) consume much energy and significantly decreases the net output of the power plants.…”