CVD Preparation of Hydrogen Semipermeable Metallic-Ceramic Membrane Composites

本研究试图开发一种用于从气体混合物中高温分离氢的膜。对于高温应用，无机膜是必需的，而钯和钯银合金金属膜对氢的选择性最高。这些金属膜的问题是，温度或压力循环会导致它们破裂，它们的表面可能会被气体混合物中的含硫分子毒化。为了避免开裂，金属膜通常被制造成大厚度，从而赋予结构刚性。然而，较大的膜厚度降低了通量，以至于使用厚膜在经济上变得不具吸引力。为了开发高通量和高选择性的膜，本研究建议在大孔陶瓷衬底的孔内放置金属Pd和Pd/Ag膜。将使用两种类型的多孔陶瓷膜。第一层是一层。第二种是两层盘，由薄(5~7 mm)、小孔(5 Nm)层组成，表面覆盖厚(1-2 mm)、大孔(2~7 mm)的改性氧化铝层。氧化铝载体。金属将通过CVD反扩散过程放置在陶瓷载体中，在该过程中，PdCl2或PdCl2和AgBr2的混合物将从陶瓷载体的一个面通过气孔扩散，而氢将从相反的面扩散。当气体在膜内的某个地方相遇时，还原反应：PdCl2(G)H2(G)-Pd(S)2HCl(G)AgBr1/2H2(G)-Ag(S)Hbr(G)会产生跨越气孔间隙并形成气密层的金属(或金属合金)。由陶瓷膜支撑的层应该更耐用，更不容易受到化学侵蚀。

This study attempts to develop a membrane for use in the high temperature separation of hydrogen from a gaseous mixture. For high temperature applications, inorganic membranes are necessary, and palladium and palladium silver alloy metal membranes exhibit the highest selectivity for hydrogen. The problems with these metallic membranes are that temperature or pressure cycles can cause them to crack, and their surfaces can be poisoned by sulfur containing molecules in the gaseous mixture. To avoid cracking, metallic membranes are usually fabricated to large thicknesses which imparts a structural rigidity. However large membrane thicknesses lower the flux to the point where the use of thick membranes becomes economically unattractive. In order to develop a membrane with high flux and selectivity, the study suggests forming membranes in which metallic Pd and Pd/Ag films have been placed inside the pores of a macroporous ceramic substrate. Two types of porous ceramic membranes will be used. The first is a one layer . alumina disk with a pore diameter in the range of .2 - .7 >m. The second is a two layer disk consisting of a thin (5>m), small pore (5 nm) layer lanthana modified y Al2O3 layer atop a thick (1-2 mm), large pore (.2 - .7 >m) . alumina support. The metal will be placed in the ceramic support by using a CVD counterdiffusion process in which PdCl2 or a mixture of PdCl2 and AgBr will diffuse through the pores from one face of the ceramic support and H2 will diffuse from the opposite face. When the gases meet somewhere inside the membrane, the reduction reactions: PdCl2(g) + H2(g) --- Pd(s) + 2HCl(g) AgBr(g) + 1/2 H2(g) --- Ag(s) + HBr(g) will produce the metal (or metal alloy) which will span the interstitial space of the pore and form a gas tight layer. The layers, supported by the ceramic membrane, should be more durable and less susceptible to chemical attack.