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QUARTERLY PROGRESS REPORT
Date: April 15, 1993
Reporting Period: December 1, 1992 - February 28, 1993
Project Title: Silica Membranes for Hydrogen Separation from Coal Gas
Identification Number: DE-FG22-92PC92525
Institution: California Institute of Technology DOE/PC/9 2525--T2
Principal Investigator: G. R. Gavalas DE 9 3 013 612
I. Project Objectives
The project objectives are (1) to explore new silylation reagents and reaction
conditions with the purpose of reducing the thickness and increasing the permeance of
silica membranes, (2) to delineate mechanism and kinetics of silica deposition, (3) to
measure the permeability of silica layers at different extents of deposition and (4) to
mathematically model the relationship of permeability and membrane structure.
II. Work Performed During Reporting Period
1. New Silylation Reagents and Reactions
A new reactor system was constructed which can be used for CVD of SiO2 layers on
porous Vycor tubes. The system is suitable for the usual one-sided deposition and for
alternating (or layer-by-layer) deposition whereby the silylating agent and water are
passed one at a time in alternating periods. The main advantage of alternating deposition
is that it allows membrane deposition using silica precursors for which the homogeneous
hydrolysis is fast. As we have demonstrated in earlier work, fast homogeneous reaction
interferes with membrane formation. The disadvantage of alternating deposition is the
longer time required for membrane formation.
Figure 1 is a schematic of the new reactor constructed for homogeneous deposition.
In each silylation period the space inside and outside of the support tube is evacuated and
a small and accurately controlled amount of reactant (e.g. SiCL4) is allowed to flow from
a storage glass flask 4 into the reactor annulus by opening valve 5 for a few seconds. The
silylation reaction is allowed to proceed for the desired time interval (about one minute)
after which the reactor is evacuated and flow of water vapor commences by opening
valve 7. After the completion of one cycle of silylation and hydrolysis, the nitrogen
permeance of the support tube is measured by the techniques used in our earlier work
(bubble flow meter or pressure transducer). After the nitrogen permeance has decreased
by a specified factor (about thirty) from its initial value, the reactions are terminated and
the membrane is annealed at 700"C for about ten hours after which the nitrogen and
hydrogen permeances are measured at several temperatures.
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Gavalas, G. R. Silica Membranes for Hydrogen Separation From Coal Gas, report, April 15, 1993; Pasadena, California. (https://digital.library.unt.edu/ark:/67531/metadc1187947/m1/1/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.