Thin-Sheet Zeolite Membranes

Research and development of thin flat sheet zeolite membranes will be discussed systematically in this presentation from product design concepts, sheet preparation, module fabrication, to applications. The feasibility to put a zeolite membrane on thin porous support sheets of different thermal expansion coefficient from zeolite materials is first studied through stress modeling. A phase-field model is used to generate microstructures of the porous support and the membrane film so that an actual membrane structure is mimicked by the computer model. An iteration method is employed to calculate the stress field in the elastically inhomogeneous structure. The interface de-coherency and cracking are the failure mechanism to reduce the elastic energy. Both the film thickness above the support and penetration depth of the film into the support pore is found as important structural parameters. The maximum stress increases with the penetration depth. However, adequate penetration is necessary for the membrane adhesion. For a given penetration depth, the film thickness does not affect the stress in the film. On the other hand, a thicker film stores more elastic energy from the point view of thermodynamics. It is concluded that thinner film and smaller penetration depth could favor for a more stable film structure.

Preparation of the thin-sheet zeolite membrane is illustrated with deposition of A-type zeolite membranes on a 50 micrometer-thick porous Ni alloy support sheet. Various preparation procedures and conditions are evaluated. The experimental results are consistent with the stress modeling analysis. A stable, crack-free zeolite membrane can be obtained with proper control of the support uniformity and preparation conditions. The resulting zeolite membrane sheet is strong enough to be self-supported and flexible enough to be coiled onto 2-cm diameter tubes. Such a zeolite membrane sheet may be packaged into a separation module of membrane area packing density higher or comparable to the polymeric membranes. Fabrication of cross-flow membrane modules with a channel spacing as small as 0.5 to 1.0mm will be shown.

The thin-sheet zeolite membrane performances for drying of humid gases and for dehydration of alcohol/water mixtures will be presented. The state-of-the-art permeance and selectivity are shown. This zeolite membrane design paves a way for development of low-cost zeolite membranes for a range of significant energy-efficient applications.