Characterization studies in microporous silica membranes

Current efforts to design more efficient gas
separation membranes are hampered by an incomplete
understanding of material structure and of the
microscopic features that control gas diffusion in
membranes. In this study we seek to develop
techniques to characterize these features, and to
study the effects of thermal treatment on the
properties of
microporous silica membranes. We make the important
distinction between traditional characterization
techniques, which characterize void space, and size
exclusion experiments that probe the small subset of
features that actually control diffusion. The
results of size exclusion, gas adsorption, 129Xe NMR,
and transport experiments are combined to propose a
model of the amorphous microporous silica structure.
Thermal treatment is found to have almost no effect
on void space, while profoundly affecting transport
rates. We attribute the transport changes to the
removal of water from the system, which increases
pore interconnectivity thereby allowing alternate
diffusion pathways.

Autorentext

Larry Wagg is a research engineer with Matheson Tri-Gas Inc. inLongmont, Colorado. His interests include Fiats, woodworking,Ultimate Frisbee, and Cygnus (see photo). J. Douglas (Doug) Wayis a Professor of Chemical Engineering at the Colorado School ofMines where he has been a faculty member since 1993.

Klappentext

Current efforts to design more efficient gasseparation membranes are hampered by an incompleteunderstanding of material structure and of themicroscopic features that control gas diffusion inmembranes. In this study we seek to developtechniques to characterize these features, and tostudy the effects of thermal treatment on theproperties ofmicroporous silica membranes. We make the importantdistinction between traditional characterizationtechniques, which characterize void space, and sizeexclusion experiments that probe the small subset offeatures that actually control diffusion. Theresults of size exclusion, gas adsorption, 129Xe NMR,and transport experiments are combined to propose amodel of the amorphous microporous silica structure.Thermal treatment is found to have almost no effecton void space, while profoundly affecting transportrates. We attribute the transport changes to theremoval of water from the system, which increasespore interconnectivity thereby allowing alternatediffusion pathways.