High-throughput computational screening of 137953 metal–organic frameworks for membrane separation of a CO2/N2/CH4 mixture

Abstract

As an environmentally benign energy source, natural gas needs to be upgraded by separating impurities (e.g. CO₂ and N₂) from CH₄. In the current upgrading technology, CO₂ and N₂ are separated via multiple energy-intensive steps. Herein, we report a computational study to high-throughput screen 137953 metal–organic frameworks (MOFs) for a single-step membrane separation of a CO₂/N₂/CH₄ mixture. The screening strategy consists of four stages. First, the pore limiting diameters (PLDs) are calculated and 17257 MOFs with a PLD of 3–4 Å are selected. Second, the Henry's constants, diffusivities and permeabilities of CO₂, N₂, and CH₄ in the 17257 MOFs are estimated at 298 K and infinite dilution by Monte Carlo and molecular dynamics simulations. Their quantitative relationships with the PLD are established. Third, based on permselectivity versus permeability plots, 24 MOFs are prescreened for both CO₂/CH₄ and N₂/CH₄ separation. Finally, the adsorption, diffusion, and permeation of a three-component CO₂/N₂/CH₄ mixture are simulated in the 24 prescreened MOFs at 298 K and 10 bar, and the 5 best MOFs are identified for the membrane separation of CO₂ and N₂ from CH₄. This computational study reveals that the PLD and a new structural parameter (the percentage of pore size distribution) are key factors governing diffusion and permeation, provides quantitative structure–property relationships from the bottom up and would facilitate the development of new membranes for the upgrading of natural gas.