The Challenge of Water Competition in Physical Adsorption of CO₂ by Porous Solids for Carbon Capture Applications – A Short Perspective

Abstract

With ever‐increasing efforts to design sorbent materials to capture carbon dioxide from flue gas and air, this perspective article is provided based on nearly a decade of collaboration across science, engineering, and industry partners. A key point learned is that a holistic view of the carbon capture problem is critical. While researchers can be inclined to value their own fields and associated metrics, often, key parameters are those that enable synergy between materials and processes. While the role of water in the chemisorption of CO2 is well‐studied, in this perspective, it is hoped to highlight the often‐overlooked but critical role of water in assessing the potential of a physical adsorbent for CO2 capture. This is a challenge that requires interdisciplinarity. As such, this document is written for a general audience rather than experts in any specific discipline.

Abnormal CO2 and H2O Diffusion in CALF-20(Zn) Metal–Organic Framework: Fundamental Understanding of CO2 Capture

“…Thanks to its stability to humidity, its ability to capture CO 2 from wet flue gases (in the presence of other harsher contaminants, NO x and SO x ), and its rather simple and cheap synthesis, CALF-20 was demonstrated to be a robust alternative sorbent to the currently used zeolite 13X, even in the presence of relative humidity below 40%. From a process perspective, this observation paves the way toward the implementation of CALF-20 in a moisture swing or humidity swing technology, as already proposed by the company Svante in their rapid TSA process. , However, so far, there is still a lack of understanding of the mechanisms at the origin of this excellent level of performance . Therefore, this calls for an in-depth atomistic exploration of the thermodynamics and kinetics of both CO 2 and H 2 O in CALF-20.…”

“…2,32 However, so far, there is still a lack of understanding of the mechanisms at the origin of this excellent level of performance. 33 Therefore, this calls for an in-depth atomistic exploration of the thermodynamics and kinetics of both CO 2 and H 2 O in CALF-20. To address this objective, we deployed a combination of force field-based grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) approaches that revealed rather unusual adsorption and diffusion mechanisms for both guests.…”

Engineering of an Isoreticular Series of CALF-20 Metal–Organic Frameworks for CO2 Capture

“…A similar hydrogen-bond network (from water cluster multimers to wired hydrogen-bond network structures) was reported for CALF-20 recently by Magnin et al This water organization constrains CO 2 molecules to occupy only the pore center of SquCALF-20 in a manner similar to that in the scenario of CALF-20 (see the snapshot in Figure a,b) and therefore leads to a gradual reduction of the CO 2 uptake for RH > 30%. A similar adsorption mechanism of CO 2 under water humidity (with the ranges of % RH) in pristine CALF-20 was also reported recently. − These studies evidenced (i) the association of H 2 O in the vicinity of the CALF-20 pore wall through hydrogen bonds with the MOF atoms and (ii) the formation of water–water hydrogen bonds that repels CO 2 molecules in the middle of the confined pore of CALF-20. − …”

How Can (or Why Should) Process Engineering Aid the Screening and Discovery of Solid Sorbents for CO2 Capture?

“…Although predicting CO 2 /N 2 behavior on MOFs seems to be relatively easier, recent works show how the choice of force fields, even for simpler molecules such a CO 2 , is not straightforward and can have a substantial impact on predicted process performance . Further, the adsorption of H 2 O and its impact on CO 2 adsorption is poorly understood, and very little experimental and simulation data are available to validate atomistic simulations . For real materials, very often, data on kinetics, competitive adsorption, and heat capacities, among others, are seldom available to make reasonable predictions.…”