CO₂-Selective Absorbents in Air: Reverse Lipid Bilayer Structure Forming Neutral Carbamic Acid in Water without Hydration

Abstract

Emission gas and air contain not only CO but also plentiful moisture, making it difficult to achieve selective CO absorption without hydration. To generate absorbed CO (wet CO) under heating, the need for external energy to release the absorbed water has been among the most serious problems in the fields of carbon dioxide capture and storage (CCS) and direct air capture (DAC). We found that the introduction of the hydrophobic phenyl group into alkylamines of CO absorbents improved the absorption selectivity between CO and water. Furthermore, ortho-, meta-, and para-xylylenediamines (OXDA, MXDA, PXDA, respectively) absorbed only CO in air without any hydration. Notably, MXDA·CO was formed as an anhydrous carbamic acid even in water, presumably because it was covered with hydrophobic phenyl groups, which induces a reverse lipid bilayer structure. Dry CO was obtained from heating MXDA·CO at 103-120 °C, which was revealed to involve chemically the Grignard reaction to form the resulting carboxylic acids in high yields.

A search for selectivity to enable CO2 capture with porous adsorbents

“…The third important (but so far comparably less considered) scenario is the direct capture (DAC) of CO 2 from air. 4,5,35 CO 2 is abundant everywhere on earth and point sources of emission are accounting only for one third to half of the anthropogenic CO 2 emissions. Direct air capture (DAC) can contribute to a slower increase or even a decrease of the atmospheric CO 2 concentration, especially if applied in closed spaces such aircraft and thermally too well insulated homes.…”

“…7 So far, DAC seems only promising when based on strong adsorption (chemisorption), most often on amine-rich materials. 5,35 However, just like for the previous cases, energy consuming regeneration and especially co-adsorption of H 2 O and O 2 from air remain serious problems for this technology.…”

“…Despite some promising attempts, a DAC process has not been operated on a large scale so far and in the current (materials) scientific literature, it is less visible as compared to CO 2 capture from the point sources of emission. 35,36 The reason for that is simple: the removal of CO 2 from air at very low concentrations (B400 ppm) comes with high selectivity of CO 2 over N 2 and O 2 , with O 2 being potentially even the more challenging subject. In air, the O 2 concentration is obviously more than 500 times higher than the CO 2 concentration, i.e.…”

Controlling the strength of interaction between carbon dioxide and nitrogen-rich carbon materials by molecular design

“…2 Due to the high binding enthalpy of CO 2 , these methods suffer from high energy penalty during regeneration. [5][6][7] Physical adsorption (physisorption) of CO 2 with lower binding enthalpy (in the range of van der Waals forces) is an alternative with less energy intensive regeneration. Great research efforts have been made recently and more and more nanomaterials for selective CO 2 capture have been proposed.…”

Effective and Reversible Carbon Dioxide Insertion into Cerium Pyrazolates

“…CO 2 sorption capacity ca. 3 mmol g À1 at 1 bar) [5] and magnesium-based metal-organic frameworks (ca. 35 wt % or 8 mmol CO 2 g À1 at 1 bar).…”