Preparation and characterization of zeolite thin films and membranes
Abstract (Summary)A novel technique for the fabrication of zeolite thin films and membranes has been developed. The method utilizes colloidal suspensions of zeolite nanocrystals (nanosols) for deposition of precursor-films. These films can be either supported or self-supported. Following the precursor formation, the films are exposed to a controlled hydrothermal seeded growth (secondary growth) which promotes the formation of thin, continuous, and intergrown zeolite layers at the surface of the precursor-film. Decoupling film deposition from crystal growth provided added flexibility for tailoring film microstructure. This technique has been demonstrated for two distinct structure-types: zeolite L (LTL) and silicalite (MFI). For the case of zeolite L, an asymmetric self-supported film was prepared. The film was composed of a thin (200 nm) and intergrown layer of zeolite L crystals at the film surface. The crystal grain size decreased and interzeolitic porosity increased proceeding from the intergrown surface down into the bulk of the film. However, the films were not continuous enough for molecular sieving membrane applications. For silicalite, a thin (500-1500 nm), intergrown, continuous and oriented silicalite membrane was grown on both supported and self-supported precursor films. The microstructure (i.e., thickness, continuity, orientation) of the films was investigated using electron microscopy and x-ray diffraction. The orientation of the crystals at the surface was found to be such that both straight and sinusoidal channel networks run nearly parallel to the membrane surface. Permeation characteristics of both supported and self-supported silicalite membranes were investigated for several single gas and binary mixtures. Several membranes exhibited ideal selectivities for H$\sb2$ over N$\sb2$ as high as 60 at 150$\sp\circ$C and O$\sb2$ over N$\sb2$ as high as 3.5 at 185$\sp\circ$C. Both supported and self-supported membranes demonstrated these trends which are attributed to the microstructure of the thin molecular sieving layer.
School Location:USA - Massachusetts
Source Type:Master's Thesis
Date of Publication:01/01/1998