PNNL

Abstract

The demand for Xe/Kr separation continues to grow due to the industrial significance of high-purity Xe gas. Current separation processes rely on energy intensive cryogenic distillation. Therefore, there is a need to develop less energy intensive alternatives such as physisorptive separation using porous materials. Here we show that an underexplored class of porous materials called hybrid ultramicroporous materials (HUMs) based upon inorganic and organic building blocks affords new benchmark selectivity for Xe separation from Xe/Kr mixtures. The isostructural materials, CROFOUR-1-Ni and CROFOUR-2-Ni, are coordination networks that exhibit coordinatively saturated metal centres and two distinct types of micropores, one of which is lined by CrO42- (CROFOUR) anions and the other is decorated by the functionalized organic linker. These nets offer unprecedented selectivity towards Xe, and also address processing and stability limitations of existing porous materials. Modelling experiments indicate that the extraordinary selectivity of these nets is tailored by synergy between the pore size, which is just above the kinetic diameter of Xe, and the strong electrostatics afforded by the CrO42- anions. Column breakthrough experiments demonstrate the potential of the practical use of these materials in Xe/Kr separation at low concentrations at the levels relevant to Xe capture from air and in nuclear fuel reprocessing. B.S. acknowledges the National Science Foundation (Award No. CHE-1152362), including support from the Major Research Instrumentation Program (Award No CHE-1531590), the computational resources that were made available by a XSEDE Grant (No. TG-DMR090028), and the use of the services provided by Research Computing at the University of South Florida. We (P.K.T) thank the US Department of Energy (DOE), Office of Nuclear Energy for adsorption and breakthrough measurements. We (P.K.T) particularly thank J. Bresee, Kimberly Gray, T. Todd (Idaho National Laboratory), John Vienna (PNNL), B. Jubin (Oak Ridge National Laboratory) and D.M. Strachan (Strachan LLC) for providing programmatic support and guidance. Pacific Northwest National Laboratory is a multi-program national laboratory operated for the US Department of Energy by Battelle Memorial Institute under Contract DE-AC05-76RL01830. M.J.Z. gratefully acknowledges Science Foundation Ireland (Award 13/RP/B2549) for support. This research used Beamline 17-BM of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.