CO₂ Absorption over Ion Exchange Resins: The Effect of Amine Functional Groups and Microporous Structures

Abstract

The moisture-swing sorbent of amine-based anion exchange resins is one of the most promising materials for direct carbon capture from ambient air to alleviate excessive emissions of CO 2 . In this study, how the physical and chemical properties of amine-based anion exchange resins affect their carbon capture performances is studied systematically, through different kinds of resins. Contrary to previous understandings, the effect of the chemical functional groups on the overall capture performance is found to far outweigh that of the physical properties. It is found that the main property that determines the absorption capacity is the chemical one, i.e., the amine functional groups, while properties dominating the absorption kinetics are the physical ones, i.e., particle size and microporous structures. The absorption capacity of resins loaded with strong amine groups is strikingly higher than that with weak amine groups. The mechanism is explored by a combination of molecular dynamics and quantum chemical calculations. The most superior sorbent is the macro-porous strong base resin due to its strong amine groups and large inner pore sizes. The present study provides new insights into selecting suitable absorbents or preparing better ones for enhanced direct air capture of CO 2 .

Carbon Dioxide-Mediated Desalination

“…This process overall completes the removal of sodium and chloride ions without external energy input. Considering that CO2 had been utilized as a regenerant for cation exchange resins, we believe that the CO2 can be a sole input in complete desalination, at least, from low salinity brine solutions 32,33 . To provide conceptual feasibility of our desalination solution, we synthesized a diamine-modified resin (Fig 5C ) for continuous ion-exchange process in a one-litre column (Fig 5D).…”

Recent advances in direct air capture by adsorption

“…Recent work revealed the working mechanism of moisture swing adsorbents as free energy change of the chemical reaction. [158][159][160][161][162][163][164][165][166][167] The influence of pore size, cation spacing, and surface hydrophobicity of the adsorbent on the CO 2 capture efficiency was elucidated. Potential supports for moisture-driven sorbents have also been extended to covalent organic frameworks (COFs), zeolites, silica, graphene oxides, functionalized carbon black, and MOFs.…”

Isotherm model for moisture-controlled CO2 sorption

“…3 The digital data was obtained by digitizing the figures in the original paper. The value of y was recalculated based on our definition of y (see eqn (22)) in this paper.…”

“…This description is supported by various numerical simulations on the atomistic level that indeed reproduce the moisture-swing effect. [21][22][23] In developing a continuum model we therefore start from a description which is very similar to that used to describe an aqueous solution of an alkali cation but assumes that the modification of the property of water inside the strong-base AEM makes different equilibrium constants. This model is very different from those derived by treating CO 2 binding as a surface adsorption effect, i.e., a surface complexation model, 24 such as Van Cappellen's model.…”

“…This description is supported by various numerical simulations on the atomistic level that indeed reproduce the moisture-swing effect. 21–23…”