Krypton‐xenon separation properties of SAPO‐34 zeolite materials and membranes

Abstract

Separation of the radioisotope 85Kr from 136Xe is an important target during used nuclear fuel recycling. We report a detailed study on the Kr and Xe adsorption, diffusion, and membrane permeation properties of the silicoaluminophosphate zeolite SAPO‐34. Adsorption and diffusion measurements on SAPO‐34 crystals indicate their potential for use in Kr‐Xe separation membranes, but also highlight competing effects of adsorption and diffusion selectivity. SAPO‐34 membranes are synthesized on α−alumina disk and tubular substrates via steam assisted conversion seeding and hydrothermal growth, and are characterized in detail. Membrane transport measurements reveal that SAPO‐34 membranes can separate Kr from Xe by molecular sieving, with Kr permeabilities around 50 Barrer and mixture selectivity of 25–30 for Kr at ambient or slight sub‐ambient conditions. The membrane transport characteristics are modeled by the Maxwell‐Stefan equations, whose predictions are in very good agreement with experiment and confirm the minimal competing effects of adsorption and diffusion. © 2016 American Institute of Chemical Engineers AIChE J, 63: 761–769, 2017

One-Pot Synthesis of High-Flux b-Oriented MFI Zeolite Membranes for Xe Recovery

“…The preferential adsorption of Xe by MFI zeolite (Figure S12) would compromise CO 2 transport through the membranes, leading to much lower permeance than in the case of single gas. 45,58 As the mixed gas selectivity factor is higher than the ideal gas selectivity, the CO 2 -selective separation is attributed to the high CO 2 diffusivity in MFI zeolite as demonstrated by breakthrough studies. 4,58 This is further supported by the slight increase of separation factor with temperature, which is the result of a stronger reduction in Xe adsorption because of its higher heat of adsorption than that of CO 2 .…”

“…The ideal selectivity of CO 2 /Xe could be as high as ∼500 for the benchmark eight-member-ring zeolite membranes, for example, SAPO-34; 45 however, the gas permeance would be significantly deteriorated by the mixed gas. For example, the permeance was merely 11.5 GPU 45 and 17.1 GPU 54 for Kr/Xe mixtures.…”

“…The ideal selectivity of CO 2 /Xe could be as high as ∼500 for the benchmark eight-member-ring zeolite membranes, for example, SAPO-34; 45 however, the gas permeance would be significantly deteriorated by the mixed gas. For example, the permeance was merely 11.5 GPU 45 and 17.1 GPU 54 for Kr/Xe mixtures. The same situation occurred for carbon molecular sieving membranes 46 and polymeric membranes [e.g., polymer inclusion membrane (PIM), PIM-1 47 and PIM-7, 47 and polydimethylsiloxane (PDMS) 48 for the separation of CO 2 /Xe.…”

Efficient Kr/Xe separation from triangular g-C3N4 nanopores, a simulation study

“…1,2 Addressing this would reduce by ten times the storage volume of 85 Kr, and therefore reduce also associated risks. 3,4 Moreover, Xe recovered in a pure form or with negligible 85 Kr contamination can nd applications in ash and arc lamps, as propellants for ion thrusters in satellites, and as general anesthetics. [5][6][7][8] Currently, the separation of non-hazardous Kr/Xe mixtures is carried out predominantly by cryogenic distillation, relying on the relative volatility of liquid Kr and Xe.…”

Surface-gel-conversion synthesis of submicron-thick MFI zeolite membranes to expedite shape-selective separation of hexane isomers

“…Alternative to hydrothermal synthesis, dry-gel conversion exhibits several advantages; for example, a small quantity of gel is needed for the membrane synthesis, zeolites are crystallized in high yields, and no liquid/solid wastes are disposed [18][19][20][21][22]. However, defects or cracks are prone to form in the membrane due to volume shrinkage in the gel-to-zeolite crystallization [18][19][20][21][22][23]. To acquire acceptable selectivity, the membranes have to be grown thick, which inevitably decreases the flux [21,24].…”