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WSRC-MS-2002-00558
Separation Membrane Development
(Separation Using Encapsulated Metal Hydride)
L. Kit Heung
Westinghouse Savannah River Company
Aiken, SC 29808, USA
Goals and Objectives
The goal of this work is to develop an efficient hydrogen separation process based on a new
type of composite material. There are two main objectives: The first is to produce a sol-gel
encapsulated metal hydride packing material that will a) absorbs hydrogen selectively and
reversibly, b) not break down to fines, and c) be resistant to reactive impurities. The second
objective is to evaluate the hydrogen separation properties of these composite samples in a
laboratory scale separation column.
Status of Progress
Several composite samples have been produced and two of them tested in a small-scale
separation column for separating hydrogen from a hydrogen-nitrogen mixture. Separation tests
using other gaseous mixtures have been planned will be conducted soon.
Background
For a hydrogen economy to become a reality, hydrogen production will have to be greatly
increased from what it is today. According to U.S. DOE 1994 fuel use numbers, U.S. household
transportation fuel use is a hydrogen equivalent of 0.55 billion lb/day. This is about 6 times the
total U.S. hydrogen use of 0.1 billion lb/day today. Where will all the hydrogen come from?
Definitive answer to this question is not yet known. One probable answer may be that hydrogen
must come from multiple sources. These sources will include renewable (solar, wind, hydro,
biomass and etc.) and non-renewable (fossil, nuclear and etc.) One sure thing is that hydrogen
will have to be recovered from all kinds of gas streams. Many of them will contain low levels of
hydrogen and undesirable impurities. Today's hydrogen recovery processes include the most
commonly used pressure swing adsorption process, the cryogenic process, and the membrane
process. Their use for low concentration feeds and to reach high recovery are not efficient. New
hydrogen recovery process is still needed. This work is targeted at a new hydrogen recovery
process that will be suited for hydrogen recovery from low concentration gas streams.
Metal Hydrides for Hydrogen Absorption
When hydrogen content in a feed stream is high (more than about 50%), it is efficient to adsorb
the impurities separating them from the hydrogen. This is the principle of the pressure swing
adsorption process. When the hydrogen concentration is low (less than about 50%). It will be
more efficient to absorb the hydrogen instead. However, a practical absorbent for hydrogen is
not yet available. In the 1970s metal hydrides became a very well known group of material for
they absorb hydrogen reversibly at moderate conditions. One example is LaNi4.25Ao.75:2 LaNi4.25A1075+ 5 H2 ++ 2 LaNi4.25Ao75H5
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Heung, L.K. Separation Membrane Development (Separation Using Encapsulated Metal Hydride), report, June 13, 2002; South Carolina. (https://digital.library.unt.edu/ark:/67531/metadc741984/m1/2/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.