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

Michael Mc Cann1, Amsarani Ramamoorthy1, Mahfujur Rahman1, Damian A. Mooney1, Denis Dowling2, and J. M. Don MacElroy1. (1) UCD School of Chemical and Bioprocess Engineering, Belfield, Dublin, 4, Ireland, (2) UCD School of Electrical, Electronic and Mechanical Engineering, Belfield, Dublin, 4, Ireland

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 (525 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 SiOx 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) 610

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