Note: Descriptions are shown in the official language in which they were submitted.
~IL08~979
This inven-tion relates to the storage of hydro~en,
In view o~ the increasing importance of hydrogen
as a source o~ energy, i-t i~ now a ~requent requirement
to store hydrogcn in an accessible form. The conventional
method ~or the storage of hydrogen on a small scale involves
the use of tilick-walled pressurlsed cylinders which are
weighty and bulky, and in certain circumstances constitute
an explosion hazard. On a larger scale it is more conven-
ient to store hydrogen in the liquid state, but this may
only be achieved by the use of cryogenic techniques
involving expensive lique-faction equipment, It is known
that some metals will absorb hydrogen to a lesser or greater
e~tent, resulting in potentially very compact stores, but
in most cases -the hydrides formed are too stable to be of
application as hydrogen storage media,
Certain intermetallic compounds, however, have pressure-
composition-temperature relationships-which are suitable
for the absorption and thus storage of hydrogen,
, ~,
; A limitation in the use o~ such intermetallic
compounds, however, arises ~rom the fac-t that in addition to
the propensity for hydrogen absorption, the hydride
~orming metal component inevitably forms compounds o~ high
., ~ .1 .
thermodynamic stability wlth many other gaseous molecules
1 such as 2~ H20, N2, CO and CO2 etc. The formation of these
`' high stability compounds is an irrevers~le effect in the
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~ 33~75~
hydrogen storage material and in practice results in progressiVe de-
terioration or "poisoning" of the store. The source of these poison~
ing elements is normally from impurities in the hydrogen bein~ stored
and these impurities are, from a practical point of view, almost un-
avoidable in hydrogen obtained from commercial sources. It is, there-
fore, one object of the present invention to provide an apparatus and
method for the storage o hydrogen which may contain i-mpurities.
According to one aspect of the present invention appara-
tus for the storage of hydrogen comprises a membrane constructed from
a metallic material containing a major proportion of palladium in gas-
tight connection with a gas-tight heat-exchange chamber containing an
intermetallic compound capable of reversibly absorbing hydrogen.
According to a second aspect of the present invention a
method for storing hydrogen comprises:
(a) causing hydrogen to diffuse into a gas-tight
chamber through a membrane constructed from a
metallic material containing a major proportion
of palladium, and
(b) contacting the so-diffused gas with a compound
-'~ 20 within said chamber capable of reversibly ab-
sorbing hydrogen.
Preferably, the palladium containing membrane is constructed
;, from pure palladium, 20% by weight silver-palladium or another alloy
containing a major proportion
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~0~3~9
by weight of palladi. um .
The chamber containing the intermetallic compound
is capable of acting as a heat~exchanger by the provision
internally or externally surrounding the chamber, of a
heating elemen-t or heat-exchange tubes for the passage of
a heat~exchange fluid.
Examples of intermetallic compounds which are .
suitable ~or use in the present invention are LaNi5 which
may be used at 1-3 atmospheres pressure and near ambient
temperature and TiFe alloys. Another suitable inter- .
metallic compound is Mg2Ni operating at 250C.
The invention will now be described by way of
example ~ith reference to the iaccompanyinj~ drawings, in
which:-
Figure 1 shows in diagrammati.c form, a diffusion and
storage apparatus according to the present invention; "
Figures 2 and 5 show two different types of
, .
dif~usion membrane assemblies having a plurality of :
rectilinear membranes;
Figure 4 is a sec-tion throllgh an apparatlls aocording to .
the present invention utilising tubular membranes; and,
~.,,
Figure 5 shows an alternative embodiment of the
present invention
In Figure 1 a diffusion membrane 2 made ~rom a palladiw~
;~, alloy is i.n planar form and is mounted in a vessel V.
Impure hydrogen is -fed via an lnlet pipe 1 to the upstream
side of the membrane 2 and waste products are removed via a
li bleed 3. A storage compound 5 is located in the vessel
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"" ` ~01~3~79
adjacent to the membrane 2 and a valved outlet 6 is provided
for controlling exit o-f the s.tored gas.. Palladium alloy
membranes in such applications will only opera-te efficiently
at elevated temperatures oE 150 - 400C, and it is,
therefore, essential to use a storage compound which is
compatible with these operating conditions. The titanium-
iron materials already mentioned are, consequently,
appropriate as also is the compound Mg2Ni, but the method
can equally be applied to any storage substance having
the required pressure - composition - relationships with
respect to hydrogen.
A heater 4 which may either be external to or housed
within the system serves to.maintain the diffusion
membrane and compound at the operating tempera-ture.
~i
.~ In the diffusion membrane assemblies o-E Figures 2 and 3,
~.
¦ hydrogen from any convenient source is passed under pressure
~ to inlet 1 oE a diffusion unit employing a plurality of
,3 rectilinear membranes 2 made from palladium, palladium-
/~ silver or another alloy of palladium The ingoing hydrogen-
containing gas may be of comparatively low purity and
;l normally completely unacceptable as a hydrogen storage
ource, :Eor example directly Erom the ca-talyt:Lc re:Eorming oE
~, a hydrocarbon fuel. The hydrogen is separated from this
ingoing gas by di:Efusion through the palladium alloy
:;
~,~i membranes and issues from the membranes with a very low
.' impurity content, usually a smali fraction o-f one par-t per
:'I
million by volume The impurities or waste products are
i removed from a "bleed" orifice 3 of the diffusion unit.
.
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~83979
The high purity hydrogen issues f'rom the di~fusion
membranes a-t a pressure less than the partial pressure of'
hydrogen in -the input gas, Preferably the heater (4 in Figure
1) is in the form of` a heat exchange chamber containi.ng
intermetallic compQund surrounding the di~fusion membranes
so that the diff'used gas lS then in contact with the inter-
metallic compound 5. The chamber will have previously
been exposed to high pressure hydrogen or some other
activating proce~ure during its manufacture to ensure that i'
the compound is converted into the activated condition
necessary f'or rapid hydrogen ad~forption and desorption.
Hydrogen will be absorbed by the compound resulting in
the well-known exothermic reaction and the heat liberated is
removed by the heat-exchanger part of' the chamber,
In the di~-fusion UIlit of' Figure 4 the diffusion
membranes 3 of palladium alloy are o~ tubular ~orm, Impure
hydrogen is ~ed to an inlet 1 f'itted with a valve iA on the
upstream side o~ the membranes and waste products are
removed via "b].eed" orifice 3 as in the case o~ the apparatus
~hown in Figures 2 and 3. The intermetallic storage
¢ompound 5 is located in a heat-e~changer chamber adjacent
to the tubular membranes 2. A valved outlet 6 for the
stored gas is provided as indica-ted. Palladi.wm alloy
i:
membranes in such applications will only operate
ef'f'iciently at elevated temperatures o~, say, 150-500QC,
and it is, theref'ore, essential to use a storage compound
' which is compatible with these operating conditions.
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39~9
The titanilml-ir~on materia:Ls alrea~y mentionecl previous].y
are consequently appropriate, as.also is the compound
Mg2Ni, but the method herein described can equally be
~ applied to any storage substance having the required
: press-ure-composition-relationships.with respect to hydrogén.
Some form of heater 4/4A which may either be'éxternal to or
contained in the system is included to maintain the diffusion
membrane and compound at the operating temperature.
When the store is fully charged, the inlet valve
~; lA is closed and the store is ready fo~ use. 1~l0n hydrogen
is required, the outlet valve 6 is opened. Dehydrogenation
of the intermetallic compound is an endothermic process and
heat will be supplied as required vi.a the heat-exchange
element 4 or tubes 4A, 'rhis heat requirement may be employed
as a controllable factor in removing hydrogen from the store,
only the quantity of.heat (conveniently as electrical
power) necessary to "boil o-ff" the requisite quantity of
' hydrogen from the intermetallic compound being supplied at
any one time
' When the store is depleted of hydrogen, va].ved outlet 6
is closed and the cycle repeated Due to the extremely
' high purity of the hydrogen stored in'the combined
diffusion cell storage vessel system, poison.Lng effects
. will be negligible over many cycles and a long operating
'~ life for the store will result.
.1
An alternative embodiiuent of the present invention
is illustrated in ~igure 5. The storage intermetallic ~
is contained in a.multiplicity of thin-walled palladium alloy
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~L0~3979
"
containers 2~. These may be formed f`rom palladium - 23/~
silver foil ~.002 in. thick, folded and welded on three
sides to ~orm-small "ravioli-like" units or envelopes
shown encircled in Figure 5. Alternative units may equally
well be forme~ by other means such as packing the compound
into thin-walled tubes, or vapour depositing or plating
the palladium base envelope onto the storage ~edium, provided
the compound is physically separated by the hydrogen permeable
membrane from the impure gas. In operation of -the apparatus,
the hydrogen from a source is supplied to the vessel V via
inlet 1 and was~ products removed via a valved "bleed" 3.
For discharging -the store the source should be disconnected9
and the hydrogen passed via valved outlet valve 6 -to a user.
In this embodiment, during the discharge cycle it is
necessary for the hydrogen to be desorbed by the inter~
metallic compound and subsequently, permeate in a reverse
direction through the thin palladium alloy walls or membranes
before being available at the outlet 6. Heating is provided
as previously described at 1~. It is ~urther desirable that
the upstream volume or volume not fi].led ~ith encapsula-ted
.compound be l~ept to a minimum in the unit sho~n in F:L~ure
5 to ensure that any impur:Lty oarryover in the issuing gas
is also kept to a minimum. Alternatively, this free volume
may be purged ~ith pure hydrogen before attempting -to dis-
charge the store.
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