Hydrocarbon separations in metal-organic frameworks

Owing to their high surface areas, tunable pore dimensions, and adjustable surface functionality, metal-org. frameworks (MOFs) can offer advantages for a variety of gas storage and gas sepn. applications. In an effort to reduce the major energy requirements for the sepn. of mixts. of light hydrocarbons via cryogenic distn., we are developing new MOFs with a high capacity for the selective adsorption of unsatd. hydrocarbons at higher temps. In particular, the compds. M2(dobdc) (M = Mg, Mn, Fe, Co, Ni; dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate), featuring open M2+ cation sites, have been evaluated for their performance in the fractionation of mixts. of C1-C3 hydrocarbons at 45 °C. The results indicate that these materials have significant potential for applications in adsorption-based processes for natural gas purifn. and olefin/paraffin spearations. In addn., it will be shown that certain structural features possible within MOFs, but not in zeolites, can enable the fractionation of hexane isomers according to the degree of branching or octane no.