High-Throughput Screening of MOF Adsorbents and Membranes for H₂ Purification and CO₂ Capture

Abstract

Metal organic frameworks (MOFs) have emerged as great adsorbent and membrane candidates for separation of CO2/H2 mixtures. The main challenge is the existence of thousands of MOFs, which requires computational screening methods to identify the best materials prior to experimental efforts. In this study, we performed high-throughput computational screening of MOFs to examine their adsorbent and membrane performances for CO2/H2 separation. Grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations were used to compute various adsorbent and membrane performance metrics of 3857 MOFs. CO2/H2 adsorption selectivities of MOFs at pressure swing adsorption (PSA) and vacuum swing adsorption (VSA) conditions were calculated to be in the range of 2.5–25 000 and 2.5–85 000, respectively, outperforming many zeolite adsorbents. Correlations between the ranking of MOF adsorbents at the PSA and VSA conditions were examined. H2/CO2 selectivities and H2 permeabilities of MOF membranes were computed as 2.1 × 10–5–6.3 and 230–1.7 × 106 Barrer, respectively. A high number of MOF membranes was identified to surpass the upper bound defined for polymers due to high gas permeabilities of MOFs. Structure–performance relations revealed that MOFs with narrow pore sizes and low porosities are the best adsorbent materials for separation of CO2 from H2, whereas MOFs with large pore sizes and high porosities are the best membrane materials for selective separation of H2. Our results will guide the selection of MOF adsorbents and membranes for efficient H2 purification and CO2 capture processes.

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

“…We previously showed that MOFs with high APSs generally suffer from low R %. 55 Figure S2a shows that most COFs (244 out of 288) have R % > 85%, but those with high APSs (>100 mol/kg) have a low R % under PSA conditions. On the other hand, Figure S2b shows that all COFs have R % > 85% as the lowest R % was computed as 95% under PTSA conditions.…”

“…The results revealed that many COFs have better/similar performances than/to zeolites and hMOFs under PSA conditions, whereas MOFs generally have higher selectivities than COFs. 55 , 68 , 76 , 77 …”

“…We recently showed that a large number of MOFs can outperform zeolites and polymers in CO 2 /H 2 separation processes. 55 Similarity of COFs with MOFs in terms of structural properties makes COFs also potential adsorbents and membranes for CO 2 /H 2 separation. Therefore, a comprehensive work aiming to unlock CO 2 /H 2 separation performances of experimentally synthesized COFs is strongly needed to guide the selection of the best COF adsorbents and membranes for future studies.…”

Do New MOFs Perform Better for CO2 Capture and H2 Purification? Computational Screening of the Updated MOF Database

“… 26 Grand canonical Monte Carlo (GCMC) simulations were performed for CO 2 /H 2 :40/60 mixture in 358 400 hMOFs and CO 2 /H 2 selectivities up to 300 and CO 2 working capacities up to 35 mol/kg were reported at 40 bar, 313 K. 27 These studies focused on hypothetical MOF structures, however performing molecular simulations on experimentally synthesized, readily available MOF structures is also important since there are already >88 000 existing MOFs. 28 531 real MOFs were screened and the top MOF was identified to have CO 2 working capacity of 6.0 mol/kg and CO 2 /H 2 selectivity of 83 for CO 2 /H 2 separation at 20 bar, 313 K. 26 Our group 29 recently screened 3857 experimentally synthesized MOFs obtained from the Cambridge Structural Database (CSD) and identified the top MOF adsorbents and membranes outperforming zeolites and polymers due to their high CO 2 /H 2 selectivities. Many more MOFs have been deposited into the CSD since then and computation-ready MOF database has been updated.…”

Revealing the effect of structure curations on the simulated CO2 separation performances of MOFs

“…Many highthroughput computational screening studies used either of the databases to investigate the gas storage and/or gas separation potentials of MOF materials. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Simon et al 27 recently provided an excellent review on molecular simulations of MOFs and discussed some shortcomings of computation-ready MOF databases. For example, the method used for solvent removal from MOFs could be too aggressive so that (i) the structural integrity of some MOFs without solvents may become questionable or (ii) the MOF could relax into a different form after the solvent removal or (iii) performing automatic solventremoval on large numbers of MOFs can lead to chemically inaccurate structures by accidentally removing an essential part such as the ligand or CBIs of the framework.…”