(402c) Measuring Competitive CO2/H2o Adsorption Equilibria on Milligram Quantities of CO2 Capture Metal-Organic Frameworks

CO₂ capture from industrial exhaust flue gases is one of the solutions to mitigate climate change. CO₂ capture by adsorption has the potential to reduce energy, cost and corrosion compared to the well-known CO₂ capture by absorption. Among the many materials studied for this application, Metal-Organic Frameworks (MOFs) have shown great promise¹. Most studies focusing on post-combustion CO₂ capture report the adsorption behavior of CO₂ and N₂. However, water, always present in the flue gas, can harm the adsorbent’s ability to capture CO₂. Hence, quantifying the effect of CO₂ capture in the presence of H₂O is essential. This measurement is complicated, especially for early-stage adsorbents available only in milligram quantities.

The main purpose of this study is to develop experimental techniques to measure the competitive adsorption of CO₂ and H₂O on a host of MOFs that have shown promise for CO₂ capture. A micro-scale dynamic column breakthrough apparatus (𝜇-DCB) is built to measure unary H₂O and binary CO₂/H₂O isotherms². In this study, CALF-20, the first MOF commercialized for CO₂ capture, is investigated. Competitive equilibrium data for a range of CO₂ compositions and temperatures are presented. The effect of water on CO₂ adsorption, and as importantly, the effect of CO₂ on H₂O adsorption is elucidated. In addition, two other MOFs, Al-Fumarate and CAU-10-H are considered. All three MOFs show a S-shaped isotherm for H₂O and a Langmuirian isotherm for CO₂. The interaction of these two isotherms results in unforeseen effects on the competitive equilibria, which are unique to each MOF. These effects are reflected in the unique shapes of the breakthrough curves that provide vital insights into the propagation of composition fronts. These results will be presented and analyzed using the local equilibrium theory.

References:

1. J. M. Kolle et al., Understanding the effect of water on CO2 adsorption, Chemical Reviews, vol. 121, 7280-7345 (2021)

2. N.S Wilkins et al., A quantitative microscale dynamic column breakthrough apparatus for measurement of unary and binary adsorption equilibrium on milligram quantities of adsorbent, Ind. Chem. Res., 61, 20, 7032-7051 (2022)