Permeation and separation properties of CO 2 /H 2 and CO 2 /N 2 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 CO 2 over H 2 or N 2 with CO 2 /H 2 or CO 2 /N 2 mixture feed under the experimental conditions studied. Compared to pure gas permeance data, the presence of the strongly adsorbing CO 2 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 CO 2 /H 2 of close to 5 with a feed CO 2 composition of 82% and a separation factor for CO 2 /N 2 greater than 60 with a feed CO 2 composition of 88% at 445 kPa and 298 K. With the mixture feed, CO 2 permeance increases and N 2 (or H 2 ) permeance decreases, and hence the CO 2 /N 2 (or H 2 ) separation factor increases, with increasing CO 2 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.

SignificanceGas separation by metal-organic framework (MOF) membranes is an emerging research field. Their commercial application potential is, however, still rarely explored due in part to unsatisfied separation characteristics and difficulty in finding suitable applications. Herein, we report "sharp molecular sieving" properties of high quality isoreticular MOF-1 (IRMOF-1) membrane for CO 2 separation from dry, CO 2 enriched CO 2 /CH 4 , and CO 2 /N 2 mixtures. The IRMOF-1 membranes exhibit CO 2 /CH 4 and CO 2 /N 2 separation factors of 328 and 410 with CO 2 permeance of 2.55 3 10 27 and 2.06 3 10 27 mol m 22 s 21 Pa 21 at feed pressure of 505 kPa and 298 K, respectively. High grade CO 2 is efficiently produced from the industrial or lower grade CO 2 feed gas by this MOF membrane separation process. The demonstrated "sharp molecular sieving" properties of the MOF membranes and their potential application in production of valueadded high purity CO 2 should bring new research and development interest in this field.

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