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Thermodynamic Separation of 1-Butene from 2-Butene in Metal–Organic Frameworks with Open Metal Sites
preprintrevised on 24.09.2019, 17:07 and posted on 26.09.2019, 14:57 by Brandon Barnett, Surya Parker, Maria V. Paley, Miguel I. Gonzalez, Naomi Biggins, Julia Oktawiec, Jeffrey R. Long
Most C4 hydrocarbons are obtained as byproducts of ethylene production or oil refining, and complex and energy-intensive separation schemes are required for their isolation. Substantial industrial and academic effort has been expended to develop more cost-effective adsorbent- or membrane-based approaches to purify commodity chemicals such as 1,3-butadiene, isobutene, and 1-butene, but the very similar physical properties of these C4 hydrocarbons makes this a challenging task. Here, we examine the adsorption behavior of 1-butene, cis-2-butene and trans-2-butene in the metal–organic frameworks M2(dobdc) (M = Mn, Fe, Co, Ni; dobdc2− = 2,5-dioxidobenzene-1,4-dicarboxylate) and M2(m-dobdc) (m-dobdc4− = 4,6-dioxido-1,3-benzenedicarboxylate), which all contain a high density of coordinatively-unsaturated M2+ sites. We find that both Co2(m-dobdc) and Ni2(m-dobdc) are able to separate 1-butene from the 2-butene isomers, a critical industrial process that relies largely on energetically demanding cryogenic distillation. The origin of 1-butene selectivity is traced to the high charge density retained by the M2+ metal centers exposed within the M2(m-dobdc) structures, which results in a reversal of the cis-2-butene selectivity typically observed at framework open metal sites. Selectivity for 1-butene adsorption under multicomponent conditions is demonstrated for Ni2(m-dobdc) in both the gaseous and liquid phases via breakthrough and batch adsorption experiments.
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in Journal of the American Chemical Society