Influence of Zeolite Protective Overlayer on the Performances of Pd Thin Film Membrane on Tubular Asymmetric Alumina Supports

Abstract

The role of zeolite overlayer in the performance of Pd thin film membranes on asymmetric alumina tubular supports is analyzed. These novel multilayer membranes have a ceramic base support (asymmetric α-Al2O3 tubes) on which a crack-free Pd dense thin film was deposited by electroless plating deposition followed by creation of a further zeolite (titanium silicalite, TS-1) membrane compact layer on the top of the Pd thin film. The TS-1 layer was prepared by a two-step procedure: (i) the preseeding with TS-1 nanocrystals by dip-coating, eventually assisted by a polymer (PEI or PDADMAC), followed by (ii) a secondary growth. The composite membranes are crack-free and homogeneous, and show good mechanical properties, in terms of adhesion between metallic film and substrate, and between the zeolitic film and Pd thin film. The composite membranes were evaluated in terms of H2 permeance with respect to bare Pd membrane. The zeolite overlayer induces a change in the rate-limiting step in H2 transport, due to the partial coverage of Pd surface by zeolite, compensated by an increase in the sticking coefficient of H2 adsorption. These materials were tested to protect Pd from deactivation by propylene, for use in catalytic membrane reactors for propane dehydrogenation.

Deposition of TS-1 zeolite film on palladium membrane for enhancement of membrane stability

“…On the other hand, the H2 permeation flux increases with temperature and activation energies of 15.4 and 13.7 kJ mol -1 were obtained for the palladium membrane and resulted TS-1-Pd composite membrane, respectively. These values are comparable to that reported in other publications [34,46]. zeolite regrowth at various temperatures and pressure differences.…”

“…Fig.7 shows that the hydrogen flux is linearly proportional to the pressure difference across the membrane at different temperatures, reflecting the n value=1. Factually, the pressure exponent often deviated from 0.5, as reported by many researchers [31,37,38,46], the differences of n-values would be attributed to the differences in the preparation method, surface activity, membrane microstructure and mass transfer resistance for palladium composite membranes. It is believed that the existence of TS-1 film decreases the surface which may be reached by H2, because part of the palladium membrane is shielded from the deposited zeolite crystals.…”

“…This is attributed to the higher transport resistance across the compact TS-1 zeolite film. Yu et al [46] reported that the presence of an additional zeolite film on top of the palladium membrane markedly decreased its hydrogen permeance. In addition, Ti element was introduced to synthesize TS-1 zeolite film.…”

“…This sandwich-like structure significantly improved the membrane stability. Abate et al [46] reported that a TS-1 zeolite film was fabricated on the palladium membrane by secondary growth technique, including seeding of palladium membrane with TS-1 nanocrystals followed by hydrothermal synthesis.…”

Interlayer Properties of In-Situ Oxidized Porous Stainless Steel for Preparation of Composite Pd Membranes

“…The properties of supports have a clear influence on the membrane performance, despite an ideal solution is not adopted. In general, ceramic supports with a smooth surface and narrow pore sizes provide a better surface for the membrane preparation [28][29][30] but the limited mechanical resistance and diverse thermal expansion coefficient to that of palladium jeopardize the membrane lifespan [18]. On the other hand, metallic supports present an exceptional mechanical resistance that ensures good sealing and suitable integration in conventional stainless steel devices [31,32], although the rougher surface with relatively large pore sizes hinders the preparation of a thin and free-defect Pd film [31,33].…”