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Spectroscopic investigation into oxidative degradation of silica-supported amine sorbents for CO(2) capture.

ABSTRACT: Oxidative degradation characteristics of silica-supported amine sorbents with varying amounts of tetraethylenepentamine (TEPA) and polyethylene glycol (PEG; P(200) or P(600) represents PEG with molecular weights of 200 or 600) have been studied by IR and NMR spectroscopy. Thermal treatment of the sorbents and liquid TEPA at 100 °C for 12 h changed their color from white to yellow. The CO(2) capture capacity of the TEPA/SiO(2) sorbents (i.e., SiO(2)-supported TEPA with a TEPA/SiO(2) ratio of 25:75) decreased by more than 60 %. IR and NMR spectroscopy studies showed that the yellow color of the degraded sorbents resulted from the formation of imide species. The imide species, consisting of NH associated with two C=O functional groups, were produced from the oxidation of methylene groups in TEPA. Imide species on the degraded sorbent are not capable of binding CO(2) due to its weak basicity. The addition of P(200) and P(600) to the supported amine sorbents improved both their CO(2) capture capacities and oxidative degradation resistance. IR spectroscopy results also showed that TEPA was immobilized on the SiO(2) surface through hydrogen bonding between amine groups and the silanol groups of SiO(2). The OH groups of PEG interact with NH(2) /NH of TEPA through hydrogen bonding. Hydrogen bonds disperse TEPA on SiO(2) and block O(2) from accessing TEPA for oxidation. Oxidative degradation resistance and CO(2) capture capacity of the supported amine sorbents can be optimized through adjusting the ratio of hydroxyl to amine groups in the TEPA/PEG mixture.

SUBMITTER: Srikanth CS

PROVIDER: S-EPMC3561697 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature

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Spectroscopic investigation into oxidative degradation of silica-supported amine sorbents for CO(2) capture.

Srikanth Chakravartula S CS Chuang Steven S C SS

ChemSusChem 20120628 8

Oxidative degradation characteristics of silica-supported amine sorbents with varying amounts of tetraethylenepentamine (TEPA) and polyethylene glycol (PEG; P(200) or P(600) represents PEG with molecular weights of 200 or 600) have been studied by IR and NMR spectroscopy. Thermal treatment of the sorbents and liquid TEPA at 100 °C for 12 h changed their color from white to yellow. The CO(2) capture capacity of the TEPA/SiO(2) sorbents (i.e., SiO(2)-supported TEPA with a TEPA/SiO(2) ratio of 25:7 ...[more]

PMID: 22744858

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Project description:Rising CO2 emissions are responsible for increasing global temperatures causing climate change. Significant efforts are underway to develop amine-based sorbents to directly capture CO2 from air (called direct air capture (DAC)) to combat the effects of climate change. However, the sorbents' performances have usually been evaluated at ambient temperatures (25 °C) or higher, most often under dry conditions. A significant portion of the natural environment where DAC plants can be deployed experiences temperatures below 25 °C, and ambient air always contains some humidity. In this study, we assess the CO2 adsorption behavior of amine (poly(ethyleneimine) (PEI) and tetraethylenepentamine (TEPA)) impregnated into porous alumina at ambient (25 °C) and cold temperatures (-20 °C) under dry and humid conditions. CO2 adsorption capacities at 25 °C and 400 ppm CO2 are highest for 40 wt% TEPA-incorporated γ-Al2O3 samples (1.8 mmol CO2/g sorbent), while 40 wt % PEI-impregnated γ-Al2O3 samples exhibit moderate uptakes (0.9 mmol g-1). CO2 capacities for both PEI- and TEPA-incorporated γ-Al2O3 samples decrease with decreasing amine content and temperatures. The 40 and 20 wt % TEPA sorbents show the best performance at -20 °C under dry conditions (1.6 and 1.1 mmol g-1, respectively). Both the TEPA samples also exhibit stable and high working capacities (0.9 and 1.2 mmol g-1) across 10 cycles of adsorption-desorption (adsorption at -20 °C and desorption conducted at 60 °C). Introducing moisture (70% RH at -20 and 25 °C) improves the CO2 capacity of the amine-impregnated sorbents at both temperatures. The 40 wt% PEI, 40 wt % TEPA, and 20 wt% TEPA samples show good CO2 uptakes at both temperatures. The results presented here indicate that γ-Al2O3 impregnated with PEI and TEPA are potential materials for DAC at ambient and cold conditions, with further opportunities to optimize these materials for the scalable deployment of DAC plants at different environmental conditions.

Project description:Aminopolymer-based sorbents are preferred materials for extraction of CO2 from ambient air [direct air capture (DAC) of CO2] owing to their high CO2 adsorption capacity and selectivity at ultra-dilute conditions. While those adsorptive properties are important, the stability of a sorbent is a key element in developing high-performing, cost-effective, and long-lasting sorbents that can be deployed at scale. Along with process upsets, environmental components such as CO2, O2, and H2O may contribute to long-term sorbent instability. As such, unraveling the complex effects of such atmospheric components on the sorbent lifetime as they appear in the environment is a critical step to understanding sorbent deactivation mechanisms and designing more effective sorbents and processes. Here, a poly(ethylenimine) (PEI)/Al2O3 sorbent is assessed over continuous and cyclic dry and humid conditions to determine the effect of the copresence of CO2 and O2 on stability at an intermediate temperature of 70 °C. Thermogravimetric and elemental analyses in combination with in situ horizontal attenuated total reflection infrared (HATR-IR) spectroscopy are performed to measure the extent of deactivation, elemental content, and molecular level changes in the sorbent due to deactivation. The thermal/thermogravimetric analysis results reveal that incorporating CO2 with O2 accelerates sorbent deactivation using these sorbents in dry and humid conditions compared to that using CO2-free air in similar conditions. The in situ HATR-IR spectroscopy results of PEI/Al2O3 sorbent deactivation under a CO2-air environment show the formation of primary amine species in higher quantity (compared to that in conditions without O2 or CO2), which arises due to the C-N bond cleavage at secondary amines due to oxidative degradation. We hypothesize that the formation of bound CO2 species such as carbamic acids catalyzes C-N cleavage reactions in the oxidative degradation pathway by shuttling protons, resulting in a low activation energy barrier for degradation, as probed by metadynamics simulations. In the cyclic experiment after 30 cycles, results show a gradual loss in stability (dry: 29%, humid: 52%) under CO2-containing air (0.04% CO2/21% O2 balance N2). However, the loss in capacity during cyclic studies is significantly less than that during continuous deactivation, as expected.

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Spectroscopic investigation into oxidative degradation of silica-supported amine sorbents for CO(2) capture.

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Spectroscopic investigation into oxidative degradation of silica-supported amine sorbents for CO(2) capture.

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