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Autumn 2007 Seminar Series
Friday, September 28 , at 3:30 p.m. in room 264 MacQuigg Labs
S. Ted Oyama
Department of Chemical Engineering
Virginia Polytechnic Institute & State University
Blacksburg, Virginia, 24061-0211
Nanostructure of a High-Permeability, Hydrogen-Selective Inorganic Membrane
Abstract
In this work we report the preparation of an inorganic membrane with permeability for H2 higher than palladium and with over 99.9% selectivity over larger species like CO, CO2 and CH4. The membrane is a composite formed by the deposition of a thin, 20 nm SiO2 layer on a specially designed alumina support. The alumina support is obtained by the deposition of boehmite sols of controlled size on top of a porous substrate, so as to create a graded structure with increasingly small pore sizes. The permeation of the small gas species, H2, He, and Ne through the silica layer is analyzed in detail in order to obtain insight about the transport mechanism and the structure of the silica. The order of permeance through the silica layer is highly unusual, He > H2 > Ne, following neither molecular weight nor size. The order of permeation is quantitatively explained using a theory derived from statistical mechanics, which takes into consideration the density of solubility sites for the various species and the vibrational frequency of the species within the sites. The theory allows obtention of the vibrational frequency (1.2x1013 s-1), solubility site density (3.7x1026 m-3 for H2) and the average distance between sites (0.84 nm) in the membrane. This is the first time an inorganic membrane has been described in detail at the nanometer level.
The antagonistic effects of pressure on reaction equilibrium and permeability were also studied for the first time in a membrane reactor. The reaction employed was the dry-reforming of methane (CH4 + CO2 ↔ 2 CO + 2 H2) which produces a net increase in moles and is disfavored by high pressure. The studies were conducted at non-equilibrium conditions in a membrane reactor (MR) containing a hydrogen-selective ceramic membrane and a packed-bed reactor (PBR) at various pressures (1-20 atm) and temperatures (873 K and 923 K) using a Rh/Al2O3 catalyst. Because of the concurrent and selective removal of hydrogen from the reaction in the MR significant enhancements over the PBR in the yields for H2 (> 170%) and CO (> 130%) in the reaction products were obtained. However, as pressure was increased the enhancement in H2 and CO yields in the MR went through a maximum and then declined. This occurred because, although the rate of hydrogen separation increased with increasing pressure, the conversions of the reactants decreased with increasing pressure. Thus, the maximum was due to a tradeoff between a transport property (hydrogen separation) and a thermodynamic quantity (hydrogen production) which had opposing pressure dependencies.
Bio
S. Ted Oyama, a native of Tokyo, Japan, was raised in South America and earned his degrees at American universities. He double-majored in chemistry and in engineering & applied science at Yale University and earned his PhD degree in chemical engineering at Stanford University in 1981. He first worked as a research engineer and project leader at Catalytica, Inc. and then joined the Clarkson University faculty in 1988 as an associate professor. He moved to Virginia Tech in 1993, where he is currently a chaired full professor of chemical engineering.
Ted Oyama is an editor of the Journal of Catalysis, the flagship journal in the field, and is on the editorial board of the J. of Natural Gas Chemistry, and the Emirates J. of Engineering. He served as Chairman of the ACS Northern New York Section between1990-1993, and has been a member of the Program Committee of the ACS Petroleum Division from 1991-present. He has received recognition for teaching from Omega Chi Epsilon in 1993 and 1995, and in research by the Deans Award in Research in 2003, and a Japan Society for the Promotion of Science Fellowship in 2007. Ted Oyama is the author of over 170 peer-reviewed, scientific papers, and has edited or written 7 books.
Ted Oyama's research deals with pressing environmental problems of a world-wide scope. He has three main areas of concentration: 1) the processing of clean-burning fuels, 2) the reduction of greenhouse gas emissions, and 3) the conversion and utilization of ozone. He is a member of a number of professional organizations including the American Association for the Advancement of Science, the American Chemical Society, the American Institute of Chemical Engineers, the Material Research Society, and the Chemical Society of Japan.
Please join our speaker for refreshments in room 479 Watts Hall following the talk.
