(472c) Microporous Silica Coatings on Mesoporous SiO2 and ZrO2 Supports: Membranes for High Temperature Gas Separation Applications

Abstract

Fossil fuel combustion emissions
are now considered directly responsible for the increase in global temperatures
due to high global CO₂ concentrations [1]. As a result, CO₂
capture has become a topic of great industrial interest in recent years owing
to the huge environmental and economic implications associated with CO₂
emissions.  The cost effective separation of CO₂ from hot exhaust
gases, is therefore an important economic and scientific challenge and one made
all the more complex by the difficult demands placed on materials used in the
hot exhaust gas environments. Inorganic membranes may provide a solution to
this as they can be used for applications whereby high temperatures and
corrosive conditions exist.

Previous experimental and
theoretical work [2, 3] has shown promising permselectivity
results for porous inorganic membranes fabricated through chemical vapour
deposition (CVD) of ultra-thin (≈5?25 nm) microporous dense films onto
mesoporous supports. The main problem however with films produced by
thermal CVD methods relates to the variability of the deposited coating thickness
and chemistry.  Plasma based deposition processes provide better control of film
thickness, density and film chemistry [4], and therefore offer the possibility
of producing superior membranes.

In this work, composite
asymmetric membranes are prepared by magnetron sputtering deposition (MS), and
atmospheric pressure plasma chemical vapour deposition (APCVD) of SiO_x
films onto flat mesoporous SiO₂ and ZrO₂. The deposition
conditions for both coating types were systematically controlled to determine
their effect on the deposited coating architecture (morphology, porosity and
thickness) and stoichiometry using scanning electron microcopy (SEM), atomic
force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), ellipsometry,
X-ray diffraction (XRD) and optical profilometry. These methods were used to provide
an accurate depiction of the membrane coating physical and chemical properties.
In addition, permeation measurements were made on all membranes in order to
assess their perm-selectivity and suitability for membrane applications. Thus, separation
of N₂/O₂ and CO₂/N₂ mixtures both
at room temperature and 450⁰C are reported and an assessment made on
the use of plasma based processes for the production of CO₂-selective
membranes.

References

1.    IPCC,
2007: The Physical Science Basis. Contribution of Working Group I to the Fourth
Assessment Report of the Intergovernmental Panel on Climate Change [Solomon,
S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L.
Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

2.    J.M.D.
MacElroy, Molecular simulation of kinetic selectivity of a model silica system,
Mol. Phys. 100 (2002) 2369.

3.    Laurence
Cuffe, J.M. Don MacElroy, Matthias Tacke, Mykola
Kozachok, Damian A. Mooney The development of nanoporous membranes for of
carbon dioxide at high temperatures, J. Membr Sci 272 (2006) 6?10

4.     
Hugh, O Pierson, Handbook of Chemical Vapour
Deposition, Noyes Publications, (1999).