A Step in Carbon Capture from Wet Gases: Understanding the Effect of Water on CO₂ Adsorption and Diffusion in UiO-66

Abstract

Understanding the role played by moisture in CO2 sorption is key for designing the next generation of solid sorbents such as metal–organic frameworks, which can be used for carbon capture and conversion as well as for molecular sieving, energy storage, etc. The abundance of water in nature and industrial processes, including in anthropogenic sources of CO2 has been shown to significantly affect commercial adsorbent performances, including their uptake capacity and selectivity. However, less is known about the role of humidity on CO2 diffusion, even though it is crucial for economically viable rapid capture processes. In this work, we have used atomistic simulations and experiments to gain insight into the effect of humidity on CO2 adsorption, diffusion and transport properties in UiO-66­(Zr), here described as a flexible structure. We show that depending on the water concentration adsorbed in the host nanoporosity, the CO2 adsorption can be enhanced or reduced depending on thermodynamic conditions. At low water loading, isolated molecules interact with low-energy sites of the sorbent. At higher loading, nucleation drives water cluster formation, followed by cluster percolation resulting in a sub-nanoporous adsorbing media decreasing the overall CO2 diffusion compared to the dry structures. We finally show that equilibrium parameters such as self-diffusion coefficients and isotherms can be used to describe the CO2 transport in dry and humid structures through the nano-Darcy equation.

Competitive and Cooperative CO2–H2O Adsorption through Humidity Control in a Polyimide Covalent Organic Framework

“…The slower CO 2 diffusion in sub-nanoporous channels created at similar water concentrations has also been observed in MOF UiO-66. 11 As also mentioned in their research, water-enhanced effects at equilibrium can come at the cost of slow kinetics, which shows the importance of fundamentally understanding these processes for rapid separation processes.…”

“…However, initially dry adsorbents are used in these experiments as well as desorption steps at higher temperatures. As a result of such an experimental procedure and the inherent slow diffusion of water in nanoporous materials, an overall lower RH level is likely present in the adsorption column. In another study regarding a novel zinc triazolate oxalate framework, a rare phenomenon of competitive binding of CO 2 over H 2 O was observed .…”

Evaluating degradation of CO2 adsorbents in flue gas from bioenergy with carbon capture and storage

“…Both ZIF-8 and UiO-66 are also considered stable in humid conditions but have some loss of CO 2 capacity in humid feeds as well (Table S7 †). [32][33][34][35] Specically, ZIF-8 is stable in humid environments due to its hydrophobic pore and strong metal-linker bonding. 36,37 However, 5-10 days of exposure to humid 10-20 ppm SO 2 can lead to structural degradation of ZIF-8 through H 2 SO 4 binding to the Zn.…”

Modelling Carbon Capture on Metal-Organic Frameworks with Quantum Computing

“…the Schrödinger equation, are time consuming and remain limited for many-body systems, where solutions in practice do not fully converge. Upscaling simulations based on such techniques yield in some cases spurious isotherm predictions, especially when accounting for ubiquitous moisture 22,29,30 , that cannot be neglected in a screening process because of its critical role in applications 31 .…”