Computational Selection of High-Performing Covalent Organic Frameworks for Adsorption and Membrane-Based CO₂/H₂ Separation

Abstract

Covalent organic frameworks (COFs) have high potential in gas separation technologies because of their porous structures, large surface areas, and good stabilities. The number of synthesized COFs already reached several hundreds, but only a handful of materials were tested as adsorbents and/or membranes. We used a high-throughput computational screening approach to uncover adsorption-based and membrane-based CO 2 /H 2 separation potentials of 288 COFs, representing the highest number of experimentally synthesized COFs studied to date for precombustion CO 2 capture. Grand canonical Monte Carlo (GCMC) simulations were performed to assess CO 2 /H 2 mixture separation performances of COFs for five different cyclic adsorption processes: pressure swing adsorption, vacuum swing adsorption, temperature swing adsorption (TSA), pressure−temperature swing adsorption (PTSA), and vacuum−temperature swing adsorption (VTSA). The results showed that many COFs outperform traditional zeolites in terms of CO 2 selectivities and working capacities and PTSA is the best process leading to the highest adsorbent performance scores. Combining GCMC and molecular dynamics (MD) simulations, CO 2 and H 2 permeabilities and selectivities of COF membranes were calculated. The majority of COF membranes surpass Robeson’s upper bound because of their higher H 2 permeabilities compared to polymers, indicating that the usage of COFs has enormous potential to replace current materials in membrane-based H 2 /CO 2 separation processes. Performance analysis based on the structural properties showed that COFs with narrow pores [the largest cavity diameter (LCD) < 15 Å] and low porosities (ϕ < 0.75) are the top adsorbents for selective separation of CO 2 from H 2 , whereas materials with large pores (LCD > 20 Å) and high porosities (ϕ > 0.85) are generally the best COF membranes for selective separation of H 2 from CO 2 . These results will help to speed up the engineering of new COFs with desired structural properties to achieve high-performance CO 2 /H 2 separations.

Combined GCMC, MD, and DFT Approach for Unlocking the Performances of COFs for Methane Purification

“… 56 Potential parameters of COF atoms were taken from the DRIEDING force field 57 since a good agreement between simulated and experimentally reported CO 2 isotherms of COFs was found in our previous works. 40 , 41 A good agreement between simulations and experimentally measured CH 4 adsorption isotherms of COFs 58 is also seen in Figure S1 of the Supporting Information ( SI ). Using the results obtained from GCMC simulations, we calculated various adsorbent performance evaluation metrics including adsorption selectivity ( S ads ), working capacity (Δ N ), adsorbent performance score (APS), and percent regenerability ( R %), as listed in Table 1 .…”

“… 40 A total of 288 COFs were studied using HTCS methods for CO 2 /H 2 separation at five different operating conditions, and COFs with narrow pores and low porosities were identified as the best-performing candidates for CO 2 separation from H 2 . 41 …”

“…Our group recently screened 295 COFs for CO 2 /N 2 separation at VSA, PSA, and TSA conditions and reported that COFs with pore sizes < 10 Å, 0.6 < porosity < 0.8, and surface area < 4500 m 2 /g are the most promising candidates for flue gas separation . A total of 288 COFs were studied using HTCS methods for CO 2 /H 2 separation at five different operating conditions, and COFs with narrow pores and low porosities were identified as the best-performing candidates for CO 2 separation from H 2 …”

Identification of H2/CO2 Separation Performance of Inorganic Porous Adsorbents via Molecular Simulations

“…Rather than collecting MOF and COF data from separate studies, we aimed to utilize from these computational screening studies and provide the ones with highest adsorption performances. Therefore, the best 20 MOF structures from the study of Avcı et al ( 2018) (Figure 2, red circles), and the best 10 COF structures from the study of Aksu et al (2020) (Figure 2, black square) are included. In these studies, 3,846 MOFs and 286 COFs were examined for CO 2 /H 2 separation.…”

Mechanistic Understanding of CO2 Adsorption and Diffusion in the Imidazole Ionic Liquid–Hexafluoroisopropylidene Polyimide Composite Membrane

“…Membrane capture technology has attracted the attention of most scientists due to its comprehensive advantages in various aspects . Gas composite membranes can generally be divided into three categories: mixed matrix membranes (MMMs), inorganic, and polymeric. , PI membranes are widely used in industrial applications due to their low cost .…”