Gas separation properties of metal organic framework (MOF-5) membranes

Permeation and separation properties of CO₂/H₂ and CO₂/N₂ mixtures for high quality, thin (∼14 μm) MOF-5 membranes prepared by the secondary growth method were studied at different temperatures, feed pressures, and feed composition. The MOF-5 membranes offer selective permeation for CO₂ over H₂ or N₂ with CO₂/H₂ or CO₂/N₂ mixture feed under the experimental conditions studied. Compared to pure gas permeance data, the presence of the strongly adsorbing CO₂ in the binary mixture separation suppresses less adsorbing H₂ or N ₂, similar to what was observed for zeolite membranes. The MOF-5 membranes exhibit a separation factor for CO₂/H₂ of close to 5 with a feed CO₂ composition of 82% and a separation factor for CO₂/N₂ greater than 60 with a feed CO₂ composition of 88% at 445 kPa and 298 K. With the mixture feed, CO₂ permeance increases and N₂ (or H₂) permeance decreases, and hence the CO₂/N₂ (or H₂) separation factor increases, with increasing CO₂ partial pressure (through the change of composition or feed pressure). It is consistent with the trend predicted by the molecular simulation reported in the literature. The sharp increase in separation factor for MOF-5 membranes with increasing feed pressure is a phenomenon unobserved for other microporous inorganic membranes.