(459c) Chabazite SAPO-34 Zeolite Membranes for Krypton/Xenon Separation: Enhanced Separation Performance and Process Modeling
AIChE Annual Meeting
Wednesday, November 1, 2017 - 8:38am to 8:57am
In the first part of this work, we demonstrate considerable thickness reduction of SAPO-34 membranes. Porous Î±-Al2O3 supports were seeded using steam-assisted conversion (SAC) methods to make a continuous seed layer followed by a conventional hydrothermal reaction for the secondary-growth process. The synthesized membranes showed dense membrane layers with thicknesses as low as 2.4 Âµm. The reduction of membrane thickness led to a large increase in Kr permeance from the previously reported  7.5 GPU to 26.3 GPU with ideal selectivity of 21 at 298 K. Cation-exchanged membranes after thickness reduction showed moderate permeance reduction for both Kr and Xe, but showed large increases (more than 50%) in selectivity. The effects of the type and valency of the exchanged cations is discussed. These membranes were also shown to have excellent Kr selectivity in mixed-gas permeation during ambient and sub-ambient (-18°C) operation. In order to estimate the size of the separation system, process modeling of multistage membrane process was conducted using experimentally obtained permeances and selectivities. The required Xe purity in the retentate of each membrane stage is fixed as 99.9% and the permeate from each stage is sent to the next stage as feed till a Kr purity of 90+% (suitable for waste storage) is reached. Among the cation-exchanged SAPO-34 membranes, K-SAPO-34 membranes showed the best potential which requires a small membrane area (~7 m2) as well as the fewest number (~3) of stages for handling a 1 L/min Kr/Xe feed mixture. Based upon these findings, we conclude that the development of a compact, low cost membrane system for Kr separation is quite feasible.
 Y. H. Kwon, C. Kiang, E. Benjamin, P. Crawford, S. Nair, and R. Bhave, "Krypton-xenon separation properties of SAPO-34 zeolite materials and membranes". AIChE J. 63, 2, 761 (2017).