Gas Separation Properties of Metal Organic Framework (MOF-5) Membranes

Permeation and separation properties of CO2/H-2 and CO2/N-2 mixtures for high quality, thin (similar to 14 mu m) 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 H-2 or N-2 with CO2/H-2 or CO2/N-2 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 H-2 or N-2, similar to what was observed for zeolite membranes. The MOF-5 membranes exhibit a separation factor for CO2/H-2 of close to 5 with a feed CO2 composition of 82% and a separation factor for CO2/N-2 greater than 60 with a feed CO2 composition of 88% at 445 kPa and 298 K. With the mixture feed, CO2 permeance increases and N-2 (or H-2) permeance decreases, and hence the CO2/N-2 (or H-2) 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.