Moisture- and Temperature-Responsive Polyglycerol-Based Carbon Dioxide Sorbents—The Insight into the Absorption Mechanism for the Hydrophilic Polymer

Abstract

This article reports the preparation and characterization of CO 2 sorbents based on hyperbranched polyglycerol containing trimethylammonium hydroxide groups. The influence of humidity and temperature on the capture/release properties of the sorbents is presented. The presence of humidity showed to be critical for the absorption of carbon dioxide. The full sorption capacity was achieved for a moderate relative humidity of 20−40%. Investigated materials were capable of capturing up to 42 mg of CO 2 per gram in the form of bicarbonate moieties. Approximately 20% (up to 8.2 mg/g) of this amount could be then reversibly desorbed and absorbed under various conditions. The typical size of the humidity or temperature swing was estimated to be in the range of 0.9−1.1 mg of CO 2 per 1 g per hour. In the case of humidity swing, the absorption and desorption times were on comparable levels. In the case of thermal desorption, a short temperature impulse was only needed to fully regenerate the bed. The presented results show that the release of captured CO 2 is also possible under dry conditions, which supports the old bicarbonate/ carbonate-exchange mechanism. For humid conditions, both old and recently published new mechanisms may be applied, showing that the nature of this process is more complex than expected and depends on many inter-related factors. The investigated sorbents showed to be stable for several capture/release cycles and are promising materials for CO 2 capture.

Polymeric Materials Based on Carbon Dioxide: A Brief Review of Studies Carried Out at the Faculty of Chemistry, Warsaw University of Technology

“…Since the thermal desorption of CO 2 may be expensive and not environmentally friendly, we developed systems based on hyperbranched polyglycerols containing trimethylammonium groups capable of the reversible capture/release of CO 2 under humidity control (Figure 3) [78]. Usually, the full sorption capacity of such sorbents is achieved for a moderate relative humidity level (20-40%).…”

Carbon Capture Beyond Amines: CO2Sorption at Nucleophilic Oxygen Sites in Materials

“…It was originally proposed that desorption is triggered by shifting the equilibrium in Figure 7 from two adjacent bicarbonates to one carbonate and free CO 2 [13,143,146,152] . Although this is counterintuitive – water lies on the product side of this equilibrium – it is likely that CO 3 2− hydrogen‐bonds with nanoconfined water more strongly than HCO 3 − , favoring CO 3 2− formation (and CO 2 desorption) in the presence of water [153–158] . One downside of this proposed mechanism is that the sorbent's working capacity (∼0.19 mmol/g in the case of Excellion I‐200), [132] or the amount of CO 2 that can be cycled on and off, is less than half of the theoretical capacity, as the CO 3 2− species do not desorb during the moisture‐swing process [146] .…”

“…[13,143,146,152] Although this is counterintuitive -water lies on the product side of this equilibrium -it is likely that CO 3 2À hydrogen-bonds with nanoconfined water more strongly than HCO 3 À , favoring CO 3 2À formation (and CO 2 desorption) in the presence of water. [153][154][155][156][157][158] One downside of this proposed mechanism is that the sorbent's working capacity (~0.19 mmol/g in the case of Excellion I-200), [132] or the amount of CO 2 that can be cycled on and off, is less than half of the theoretical capacity, as the CO 3 2À species do not desorb during the moisture-swing process. [146] That being said, recent in situ SS NMR studies have called the formation of CO 3 2À species into doubt, suggesting that the critical equilibrium may simply be between OH À and HCO 3 À (Figure 6).…”

“…[162] Unfortunately, the best material still required approximately 3 h to saturate at a capacity of 0.4 mmol/g under fast air flow (1 L/min). [162] Efforts to incorporate IERs into porous hybrid structures by Matyjaszewski and others include growing polymers inside carbon black, [132,163] engineering IERs into porous electrospun fibers, [164] impregnating quarternized hyperbranched polyglycerols into silicas, [154] and preparing hybrid structures with polyether sulfone (PES). [160,165] Hydroxide-rich polymers can also be formed into porous structures by using colloidal crystals of polymethyl methacrylate (PMMA) as a template, [132,166] preparing high internal phase emulsion (HIPE) polymers, [132,167] and functionalizing mesoporous polystyrene resins.…”

Quaternary Ammonium-Functionalized Poly(Arylene Ether Sulfone) Random Copolymers for Direct Air Capture

“…However, comprehensive investigations are still required to better understand the mechanism, develop faster kinetics, increase the loading capacity, and enhance the selectivity for CO 2 . Porous polymers, ammonium-based anion exchange resins, ammonium-functionalized ionic liquids, cellulose and chitosan/PVA aerogels, ammonium-modified silica, colloidal crystal templates, and sorbent-containing electrospun fibers have been evaluated as sorbents. ,− He and co-workers tested three QA-functionalized porous materials and reported CO 2 uptake between 0.13 and 0.49 mmol/g when cycling the relative humidity between 20 and 95% . Song and co-workers investigated QA chitosan/PVA and reported a maximum uptake of 0.18 mmol/g at room temperature while varying the relative humidity between 3 and 95% .…”