Upgrade of natural gas in rhozeolite-like metal–organic framework and effect of water: a computational study

Abstract

A computational study is reported for the upgrade of natural gas (CO₂/CH₄ mixture) in rhozeolite-like metal–organic framework (ZMOF) and the effect of water on upgrade efficiency. CO₂ is adsorbed predominantly over CH₄, attributed to the strong electrostatic interactions of CO₂ with ionic framework and extraframework Na⁺ ions. With increasing pressure, Na⁺ ions are coordinated and solvated increasingly by CO₂ molecules. The distance between CO₂ molecules becomes shorter with increasing pressure, while the distance between Na⁺ and CO₂ remains more or less constant. Compared with other MOFs and nanoporous materials reported to date, rho-ZMOF exhibits exceptionally high selective adsorption for CO₂/CH₄ mixture. The selectivity is up to 3800 at infinite dilution and 80 at ambient condition. With a trace amount of H₂O added into CO₂/CH₄ mixture, the interaction between CO₂ and Na⁺ is reduced. Consequently, CO₂ adsorption drops but CH₄ adsorption is not discernibly affected, and the selectivity decreases by one order of magnitude. This work reveals that rho-ZMOF is a promising candidate for the separation of natural gas and H₂O has a significant effect.