Aminopolymer-Impregnated Hierarchical Silica Structures: Unexpected Equivalent CO₂ Uptake under Simulated Air Capture and Flue Gas Capture Conditions

Abstract

Poly(ethyleneimine)-impregnated sorbents are prepared using a hierarchical silica support with bimodal meso-/macroporosity. The sorbents behave unexpectedly during CO 2 adsorption from simulated air and flue gases (400 ppm and 10% CO 2 ) at a fixed temperature, as compared to systems built on commonly studied mesoporous materials. The results demonstrate that (i) impregnation methods influence the efficacy of sorption performance and (ii) the sorbents show almost similar uptake capacities under 400 ppm and 10% dry CO 2 at 30 °C, exhibiting step-like CO 2 adsorption isotherms. These unusual observations are rationalized via control experiments and a hypothesized sorption mechanism. While the sorption performance near room temperature is unexpectedly identical under 400 ppm and 10% CO 2 conditions, there is an optimal temperature at each gas concentration where the uptake is maximized. The maximum sorption capacities are 2.6 and 4.1 mmol CO 2 /g sorbent at the optimized sorption temperatures using 400 ppm and 10% dry CO 2 , respectively. The presence of water vapor under 400 ppm CO 2 conditions further improves the sorption capacity to 3.4 mmol/g sorbent, which is the highest capacity under direct air capture conditions among known amine sorbents impregnated with a similar polymer, to the best of our knowledge.

Drastic enhancement of carbon dioxide adsorption in fluoroalkyl-modified poly(allylamine)

“…The highest DAC capacity recorded to date is 3.36 mmol g -1 in a humidified stream of 400 ppm CO2, Jones and coworkers achieved this outstanding performance using a bimodal meso/macroporous hierarchical silica impregnated with PEI. [15] Single component CO2 adsorption isotherms also demonstrate the ability of PAA-C60 and F-PAA-C60 to capture CO2 at low pressure, as shown in Figure 4. At 0.07 bar, mimicking performance in diluted gas streams, PAA-C60 and F1-PAA-C60 adsorb 0.026 g g -1 and 0.104 g g -1 at 25 °C, respectively (inset of Figure 4a).…”

“…[14a-c, 14f] For example, the three-dimensional interconnected porous structure of hierarchical meso/macroporous silica has been shown to prevent pore blockages when impregnated with the commonly studied poly(ethyleneimine) (PEI). [15] With a PEI loading of 2.62 g PEI/g sorbent (60.8 mmol N/g) the adsorbent displayed the highest CO2 capacity for a supported polyamine adsorbent under simulated air conditions. At 30 °C, under 400 ppm CO2, the capacity was 2.34 mmol CO2 g -1 in dry conditions, increasing to 3.36 mmol CO2 g -1 under a relative humidity of 19%.…”

“…Most of the amines within the bulk of PAA-C60 are not accessible at 30 °C, resulting in low CO2 adsorption, and the presence of strong electrostatic interactions among any surface alkyl ammonium carbamate species is likely to obstruct this access further. [15] This obstruction is overcome at 90 °C, when CO2 diffusion into the bulk of the material, and subsequent CO2 adsorption, is greatly enhanced. This is evidenced in that, at 90 °C, the Qst values are above 100 kJ mol -1 at all investigated CO2 loadings, up to above 100 mg g -1 .…”

“…At 30 °C, under 400 ppm CO2, the capacity was 2.34 mmol CO2 g -1 in dry conditions, increasing to 3.36 mmol CO2 g -1 under a relative humidity of 19%. [15] Although critical, the structural properties of the support are not the only aspect that impacts on efficient amine loading. It has been reported that surface chemistry has a major effect on adsorption behavior, and tuning the chemical properties of the support can affect adsorption capacity.…”

NaNO3‐Promoted Mesoporous MgO for High‐Capacity CO2 Capture from Simulated Flue Gas with Isothermal Regeneration

“…The materials that are often deployed in temperature‐ and/or pressure‐swing separation processes operate in varied temperature and CO 2 pressure regimes. For example, supported amine materials and MOFs can adsorb CO 2 at ambient conditions, whereas some reactive oxide materials (e.g., CaO, MgO) require more elevated temperatures . Additionally, the different types of materials also require different desorption conditions, with temperature ranges varying from <100 °C to >900 °C .…”