U.S. patent application number 11/820719 was filed with the patent office on 2008-01-17 for microcartridge hydrogen generator.
This patent application is currently assigned to Lynntech, Inc.. Invention is credited to Brad Fiebig.
Application Number | 20080014479 11/820719 |
Document ID | / |
Family ID | 38846185 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080014479 |
Kind Code |
A1 |
Fiebig; Brad |
January 17, 2008 |
Microcartridge hydrogen generator
Abstract
A hydrogen generator (101) is provided which comprises a third
chamber (109) containing a catalyst (121), a first chamber (103)
containing a fluid, a second chamber (105) containing a material
that reacts with the fluid in the presence of the catalyst to
generate hydrogen gas, and a valve (111) movable from a first
position in which the flow of fluid along a pathway including the
first, second and third chambers is enabled, to a second position
in which the flow of fluid along the pathway is prevented.
Inventors: |
Fiebig; Brad; (League City,
TX) |
Correspondence
Address: |
FORTKORT & HOUSTON P.C.
9442 N. CAPITAL OF TEXAS HIGHWAY
ARBORETUM PLAZA ONE, SUITE 500
AUSTIN
TX
78759
US
|
Assignee: |
Lynntech, Inc.
|
Family ID: |
38846185 |
Appl. No.: |
11/820719 |
Filed: |
June 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60815371 |
Jun 20, 2006 |
|
|
|
60834908 |
Aug 1, 2006 |
|
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Current U.S.
Class: |
48/61 ; 429/416;
429/444; 429/515 |
Current CPC
Class: |
Y02E 60/50 20130101;
H01M 8/065 20130101; H01M 8/0631 20130101; Y02E 60/36 20130101;
C01B 3/065 20130101; H01M 8/04208 20130101 |
Class at
Publication: |
429/017 ;
429/019 |
International
Class: |
H01M 8/18 20060101
H01M008/18; H01M 8/04 20060101 H01M008/04 |
Claims
1. A hydrogen generator, comprising: a catalytic chamber containing
a catalyst; a mixture comprising a liquid medium and a
hydrogen-containing material which reacts with said liquid medium
in the presence of said catalyst to generate hydrogen gas; and a
separating means for separating said catalyst and said mixture when
the pressure of hydrogen gas within said catalytic chamber reaches
a predetermined level.
2. The hydrogen generator of claim 1, wherein said catalytic
chamber is equipped with an inlet adapted to admit said mixture
into said catalytic chamber, and wherein said catalytic chamber is
further equipped with a first sub-chamber in communication with
said inlet, and a second sub-chamber which is essentially sealed
off from said first sub-chamber.
3. The hydrogen generator of claim 2, wherein said catalyst is
disposed upon a first member which is withdrawn into said second
sub-chamber when the pressure of hydrogen gas within the first
sub-chamber reaches a predetermined level.
4. The hydrogen generator of claim 2, wherein said catalyst is
disposed upon a cylinder which is withdrawn into said second
sub-chamber when the pressure of hydrogen gas within the first
sub-chamber reaches a first predetermined level.
5. The hydrogen generator of claim 3, wherein said first member is
equipped with a first terminal portion which arrests the movement
of said first member into said second sub-chamber.
6. The hydrogen generator of claim 5, wherein said first member is
further equipped with a second terminal portion which arrests the
movement of said first member into said first sub-chamber.
7. The hydrogen generator of claim 3, wherein said first member is
spring-loaded.
8. The hydrogen generator of claim 3, wherein said catalyst forms a
catalytic surface on said first member, and further comprising a
second member adapted to clean said catalytic surface.
9. The hydrogen generator of claim 8, wherein said second member is
a protrusion which slidingly engages said catalytic surface.
10. The hydrogen generator of claim 1, wherein said catalytic
chamber further comprises an expandable portion which is adapted to
expand when hydrogen gas accumulates in said catalytic chamber.
11. The hydrogen generator of claim 10, wherein said expandable
portion comprises an elastomeric material.
12. The hydrogen generator of claim 10 wherein, when said
expandable portion expands to a predetermined volume, the mixture
within the catalytic chamber is withdrawn from contact with the
catalyst.
13. The hydrogen generator of claim 1, wherein said catalyst is
disposed on the surface of a tortuous pathway, and wherein said
mixture passes through said catalytic chamber by way of said
tortuous pathway.
14. The hydrogen generator of claim 13, wherein said tortuous
pathway comprises a helical tube.
15. The hydrogen generator of claim 13, wherein said tortuous
pathway comprises a helical groove.
16. The hydrogen generator of claim 1, wherein said catalytic
chamber contains first and second major opposing surfaces, and
wherein said catalytic chamber is adapted such that a pressure
build-up of hydrogen gas within said catalytic chamber causes the
first and second major opposing surfaces to move apart from each
other.
17. The hydrogen generator of claim 16, wherein the movement of
said first and second major opposing surfaces apart from each other
terminates the generation of hydrogen gas.
18. The hydrogen generator of claim 17, wherein said catalyst is
disposed as a plurality of bumps on said first major surface.
19. The hydrogen generator of claim 17, wherein said catalyst is
disposed as a continuous coating on said first major surface.
20. The hydrogen generator of claim 17, wherein said catalyst is
disposed as one or more lines on said first major surface.
21. A hydrogen generator, comprising: a catalyst; and a fluid which
reacts in the presence of said catalyst to evolve hydrogen gas;
wherein the hydrogen generator transitions from a first state when
the pressure of hydrogen gas within the hydrogen generator is
P.sub.1, to a second state when the pressure of hydrogen gas within
the hydrogen generator is P.sub.2, wherein P.sub.2>P.sub.1;
wherein the fluid is in contact with the catalyst when the hydrogen
generator is in said first state; and wherein the fluid is
withdrawn from contact with the catalyst when the hydrogen
generator is in said second state.
22. The hydrogen generator of claim 21, wherein said catalyst is
disposed in a chamber, wherein said chamber has a volume V.sub.1
when the hydrogen generator is in said first state, wherein said
chamber has a volume V.sub.2 when said hydrogen generator is in
said second state, and wherein V.sub.2>V.sub.1.
23. The hydrogen generator of claim 22, wherein said chamber
comprises an elastomeric wall.
24. The hydrogen generator of claim 21, wherein P.sub.1 is within
the range of about 2 to about 10 torr.
25. The hydrogen generator of claim 21, wherein P.sub.2 is greater
than about 10 torr.
26. A method for generating hydrogen gas, comprising: providing a
fluid, a catalyst, and a hydrogen-containing material that reacts
with the fluid in the presence of the catalyst to generate hydrogen
gas; creating a mixture of the fluid and the hydrogen-containing
material; when a demand for hydrogen gas exists, contacting the
mixture with the catalyst, thereby generating hydrogen gas; and
when demand for hydrogen gas abates, withdrawing the catalyst from
contact with the mixture.
27. The method of claim 26, wherein the catalyst is disposed in a
chamber, and wherein the catalyst is withdrawn from contact with
the mixture when the pressure of hydrogen gas within the chamber
reaches a predetermined level.
28. The method of claim 27, wherein the catalyst is disposed on a
piston.
29. The method of claim 28, wherein the piston is spring
actuated.
30. The method of claim 27, wherein the chamber has an elastomeric
portion that expands as the pressure of hydrogen gas within the
chamber increases, thereby withdrawing the catalyst from contact
with the mixture.
31. The method of claim 26, wherein the mixture is an aqueous
mixture of sodium borohydride.
32. The method of claim 26, further comprising the step of
separating the generated hydrogen gas from the byproducts of the
hydrogen generation reaction with a hydrogen permeable
membrane.
33. A hydrogen generator, comprising: a source of fluid; a
catalytic element comprising a catalyst disposed on a substrate; a
hydrogen-containing material that reacts with the fluid in the
presence of the catalyst to generate hydrogen gas; and a conduit
for moving a mixture of said fluid and said hydrogen-containing
material from a first location to a second location; wherein said
catalytic element is movable from a first position in which said
catalytic surface is exposed to the mixture disposed within said
conduit, to a second position in which said catalytic surface is
not exposed to the mixture disposed within said conduit.
34. The hydrogen generator of claim 33, wherein the flow of the
mixture through the conduit is enabled when said catalytic element
is in said first position.
35. The hydrogen generator of claim 33, wherein said catalytic
element is equipped with a notch which forms a portion of said
conduit when said catalytic element is in said first position.
36. The hydrogen generator of claim 33, wherein said catalytic
element is adapted to move from said first position to said second
position when the pressure differential between the interior of the
hydrogen generator and the ambient environment exceeds a
predetermined threshold value.
37. The hydrogen generator of claim 33, wherein said catalytic
element is adapted to move from said first position to said second
position when the pressure differential between the pressure
experienced by the catalytic element and the ambient environment
exceeds a predetermined threshold value.
38. The hydrogen generator of claim 33, wherein said catalytic
element is disposed within a chamber equipped with a static
pressure port.
39. The hydrogen generator of claim 38, wherein said chamber is
equipped with a spring which deforms as the pressure differential
between the pressure experienced by the catalytic element and the
ambient environment increases.
40. The hydrogen generator of claim 39, wherein the deformation of
said spring allows the catalytic element to move from the first
position to the second position.
41. The hydrogen generator of claim 33, further comprising an
interface at which said mixture of said fluid and said
hydrogen-containing material is formed.
42. The hydrogen generator of claim 41, wherein said interface
includes a helical flow path.
43. The hydrogen generator of claim 42, further comprising a source
of said hydrogen containing material, and wherein said fluid and
said hydrogen-containing material are in contact with each other
along the entire course of said helical flow path.
44. A hydrogen generator, comprising: a catalytic reactor equipped
with (a) first and second chambers which are separated from each
other by a wall having an opening therein, and (b) a retractable
member which extends through said opening and which has a catalyst
disposed on a surface thereof; a first compartment containing a
liquid; and a second compartment containing a hydrogen-generating
material which reacts with said liquid in the presence of said
catalyst to generate hydrogen gas.
45. The hydrogen generator of claim 44, wherein said member is
essentially rod-shaped, and wherein said catalyst is disposed on an
axial surface thereof.
46. The hydrogen generator of claim 45, wherein said member is
equipped with a first stopper on a first end thereof, and a second
stopper on a second end thereof.
47. The hydrogen generator of claim 44, further comprising a spring
housed in said first chamber.
48. The hydrogen generator of claim 44, wherein said second chamber
is equipped with an inlet and an outlet.
49. A hydrogen generator, comprising: a catalytic reactor
containing a catalytic element, wherein said reactor is adapted to
receive a mixture comprising a hydrogen-containing material which
is disposed in a liquid medium, wherein the hydrogen-containing
material is adapted to react with said liquid medium in the
presence of said catalytic element to generate hydrogen gas, and
wherein said reactor contains a wall which is adapted to expand as
hydrogen gas accumulates in the reactor, thereby increasing the
volume of the reactor.
50. The hydrogen generator of claim 49, wherein said wall comprises
an elastomeric material.
51. The hydrogen generator of claim 49, wherein the expansion of
said wall separates said mixture and said catalytic element.
52. The hydrogen generator of claim 49, wherein said catalytic
element has a catalytic surface, and wherein said catalytic element
is movable from a first position in which the catalytic surface is
in the flow path of the mixture entering the reactor, to a second
position in which the catalytic surface is removed from contact
with the mixture entering the reactor.
53. The hydrogen generator of claim 52, wherein said catalytic
element has a notch defined therein, and wherein the surface of
said notch contains said catalytic surface.
54. The hydrogen generator of claim 53, wherein said notch forms
part of the flow path of the mixture entering the reactor when the
catalytic element is in the first position.
55. The hydrogen generator of claim 53, wherein said catalytic
element blocks the flow path of the mixture entering the reactor
when the catalytic element is in the second position.
56. The hydrogen generator of claim 49, wherein said catalytic
element comprises a catalytic surface encased in a material which
is permeable to said mixture.
57. The hydrogen generator of claim 56, wherein said material is a
porous material.
58. The hydrogen generator of claim 56, wherein said material is
selected from the group consisting of porous plastic and porous
glass.
59. The hydrogen generator of claim 56, wherein said material is
hydrophobic.
60. The hydrogen generator of claim 49, wherein said catalytic
element comprises a catalytic surface disposed within a cage.
61. The hydrogen generator of claim 60, wherein said cage is
essentially spherical, and wherein said catalytic surface is
disposed in essentially the center of said cage.
62-128. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Ser. No.
60/815,371, filed on Jun. 20, 2006 and entitled "MICROCARTRIDGE
HYDROGEN GENERATOR", and to U.S. Ser. No. 60/834,908, filed on Aug.
1, 2006 and entitled "MICROCARTRIDGE HYDROGEN GENERATOR", both of
which are incorporated herein by reference in their entirety.
FIELD OF THE DISCLOSURE
[0002] The present disclosure relates generally to hydrogen
generators, and more specifically to hydrogen generators that may
be incorporated into hand-held devices.
BACKGROUND OF THE DISCLOSURE
[0003] Hydrogen generators are devices that generate hydrogen gas
for use in fuel cells, combustion engines, and other devices, often
through the evolution of hydrogen gas from chemical hydrides,
borohydrides or boranes. Sodium borohydride (NaBH.sub.4) has
emerged as a particularly desirable chemical hydride for use in
such devices, due to the molar equivalents of hydrogen it generates
(see EQUATION 1 below), the relatively low mass of NaBH.sub.4 as
compared to some competing materials, and the controllability of
the hydrogen evolution reaction:
NaBH.sub.4+2H.sub.2ONaBO.sub.2+4H.sub.2 (EQUATION 1)
[0004] The hydrolysis of hydrogen-generating materials in general,
and sodium borohydride in particular, as a method of hydrogen
generation has received significant interest in the art, due to the
high gravimetric storage density of hydrogen in these materials and
the ease of creating a pure hydrogen stream from the hydrolysis
reaction. However, in some applications, such as when hydrogen
generators are used in combination with hydrogen fuel cells to
power laptops or handheld devices and electronics, the inability to
adequately control the generation of hydrogen gas is a drawback
from a system perspective. Ideally, in such an application, the
hydrogen generator should be able to produce a stream of hydrogen
gas promptly when the gas stream is needed, and should likewise be
able to promptly terminate the flow of hydrogen gas when it is no
longer needed.
[0005] In reality, however, most hydrogen generators currently
available display a significant lag time from the point of time at
which the demand for hydrogen commences, and the point of time at
which the flow of hydrogen gas is suitable to meet that demand.
Perhaps more significantly, the flow of hydrogen in most currently
available hydrogen generators does not cease with demand, and may
even proceed until the hydrogen generating material has been
depleted. The generation of hydrogen gas in excess of demand is
problematic for hydrogen generators in general, and for small
hydrogen generators (of the type designed for incorporation into
laptop PCs and hand-held devices) in particular. Aside from the
danger of fire or explosion, the excess gas creates pressure spikes
that can damage the generator and its components.
[0006] Moreover, the need to accommodate such pressure spikes and
to store excess hydrogen gas requires hydrogen generators to be
heavier, bulkier, stronger, and more complicated than would
otherwise be the case. Since space and weight are typically at a
premium in laptop computers and hand-held devices, this is a
serious drawback in hydrogen generators. Venting excess hydrogen
gas is typically not an option in these devices due to the obvious
fire risks and, in any event, is undesirable in that it reduces the
effective yield of the hydrogen generator.
[0007] There is thus a need in the art for a hydrogen generator
that offers fast response time to the need for hydrogen so that a
supply of hydrogen is available on demand. There is also a need in
the art for a hydrogen generator that effectively halts the
production of hydrogen gas when the demand for hydrogen abates, so
that excess hydrogen is not generated. There is further a need in
the art for a hydrogen generator with minimum dimensions, weight
and space requirements. These and other needs are met by the
devices and methodologies disclosed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an illustration of a particular, non-limiting
embodiment of a hydrogen generator in accordance with the teachings
herein;
[0009] FIG. 2 is an illustration of a particular, non-limiting
embodiment of a separator for the hydrogen generator of FIG. 1;
[0010] FIG. 3 is an illustration of a particular, non-limiting
embodiment of a catalytic reactor of the hydrogen generator of FIG.
1 shown in a first state in which hydrogen is being actively
generated;
[0011] FIG. 4 is an illustration of the catalytic reactor of FIG. 3
shown in a second state in which the generation of hydrogen has
been terminated;
[0012] FIG. 5 is an illustration of a particular, non-limiting
embodiment of a shut-off valve for the hydrogen generator of FIG.
1;
[0013] FIG. 6 is an illustration of a particular, non-limiting
embodiment of a catalytic reactor useful in a hydrogen generator of
the type depicted in FIG. 1, shown in a first condition in which a
steady demand for hydrogen gas exists;
[0014] FIG. 7 is an illustration of the catalytic reactor depicted
in FIG. 6, and shown in a second condition in which the demand for
hydrogen gas has abated;
[0015] FIG. 8 is an illustration of a particular, non-limiting
embodiment of a catalytic reactor useful in the hydrogen generators
described herein;
[0016] FIG. 9 is an illustration of a particular, non-limiting
embodiment of a catalytic reactor useful in the hydrogen generators
described herein;
[0017] FIG. 10 is an illustration of a particular, non-limiting
embodiment of a hydrogen generator in accordance with the teachings
herein;
[0018] FIG. 11 is an illustration of a particular, non-limiting
embodiment of a catalytic reactor useful in the hydrogen generators
described herein;
[0019] FIG. 12 is a cross-sectional view of the catalytic reactor
of FIG. 11 taken along the line 12-12, and shown in a first state
in which a steady demand for hydrogen gas exists;
[0020] FIG. 13 is a cross-sectional view of the catalytic reactor
of FIG. 11 taken along the line 12-12, and shown in a second
condition in which the demand for hydrogen gas has abated;
[0021] FIG. 14 is an illustration of a particular, non-limiting
embodiment of a catalytic reactor useful in the hydrogen generators
described herein, depicted in a first state in which hydrogen gas
is being generated;
[0022] FIG. 15 is an illustration of the catalytic reactor of FIG.
14, depicted in a second state in which the generation of hydrogen
gas has been terminated;
[0023] FIG. 16 is a side view of the catalytic reactor of FIG.
14;
[0024] FIG. 17 is an illustration of a particular, non-limiting
embodiment of a hydrogen generator in accordance with the teachings
herein;
[0025] FIG. 18 is an exploded view of the hydrogen generator of
FIG. 17;
[0026] FIG. 19 is an illustration of the chassis of the hydrogen
generator of FIG. 17;
[0027] FIG. 20 is an illustration of the hydrogen generator of FIG.
17 with the chassis removed;
[0028] FIG. 21 is an exploded view of the hydrogen generator of
FIG. 17 with the chassis removed;
[0029] FIG. 22 is an exploded view of the hydrogen generator of
FIG. 17 with the chassis removed;
[0030] FIG. 23 is an exploded view of the fluid manifold of the
hydrogen generator of FIG. 17;
[0031] FIG. 24 is a view of the fluid manifold of the hydrogen
generator of FIG. 17 with some of the layers thereof rendered
transparent;
[0032] FIG. 25 is an exploded view of the fluid manifold of the
hydrogen generator of FIG. 17;
[0033] FIG. 26 is a partially exploded view of the hydrogen
generator of FIG. 17;
[0034] FIG. 27 is a partially exploded view of the hydrogen
generator of FIG. 17;
[0035] FIG. 28 is a partially exploded view of the hydrogen
generator of FIG. 17;
[0036] FIG. 29 is a partially exploded view of the hydrogen
generator of FIG. 17;
[0037] FIG. 30 is an illustration showing the fluid path in the
fluid manifold of the hydrogen generator of FIG. 17;
[0038] FIG. 31 is an illustration showing the hydrogen path in the
fluid manifold of the hydrogen generator of FIG. 17;
[0039] FIG. 32 is an illustration of a pressure regulator valve in
the hydrogen generator of FIG. 17;
[0040] FIG. 33 is an illustration of the catalytic reactor in the
hydrogen generator of FIG. 17;
[0041] FIG. 34 is an illustration of the catalytic reactor in the
hydrogen generator of FIG. 17;
[0042] FIG. 35 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17;
[0043] FIG. 36 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17;
[0044] FIG. 37 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17;
[0045] FIG. 38 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17;
[0046] FIG. 39 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17;
[0047] FIG. 40 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17;
[0048] FIG. 41 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17;
[0049] FIG. 42 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17;
[0050] FIG. 43 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17;
[0051] FIG. 44 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17; and
[0052] FIG. 45 is an illustration of a step in the manufacture of
the hydrogen generator of FIG. 17.
DETAILED DESCRIPTION
[0053] In one aspect, a hydrogen generator is provided herein which
comprises (a) a fluid; (b) a catalytic chamber containing a
catalyst; (c) a hydrogen-containing material that reacts with the
fluid in the presence of the catalyst to generate hydrogen gas; and
(d) an inlet adapted to input a mixture of the fluid and the
hydrogen-containing material into the reaction chamber. The
catalytic chamber is adapted to withdraw the catalyst from the
mixture when the pressure of hydrogen gas within the catalytic
chamber reaches a predetermined level.
[0054] In another aspect, a hydrogen generator is provided which
comprises a catalyst, and a fluid which reacts in the presence of
said catalyst to evolve hydrogen gas. The hydrogen generator
transitions from a first condition when the pressure of hydrogen
gas within the hydrogen generator is P.sub.1, to a second condition
when the pressure of hydrogen gas within the hydrogen generator is
P.sub.2, wherein P.sub.2>P.sub.1. When the hydrogen generator is
in the first state, the fluid is in contact with the catalyst. When
the hydrogen generator is in the second state, fluid is withdrawn
from contact with the catalyst.
[0055] In still another aspect, a hydrogen generator is provided
which comprises (a) a catalyst; (b) a fluid; (c) a
hydrogen-containing material; (d) a mixing chamber adapted to form
a mixture of said fluid and said hydrogen-containing material; and
(e) a reaction chamber adapted to react said mixture in the
presence of said catalyst to generate hydrogen gas; wherein the
hydrogen generator transitions from a first condition when the
pressure of hydrogen gas within the reaction chamber is P.sub.1, to
a second condition when the pressure of hydrogen gas within the
reaction chamber is P.sub.2, where P.sub.2>P.sub.1; wherein the
mixing chamber is adapted to generate said mixture when said
hydrogen generator is in said first state; and wherein said mixing
chamber is adapted to cease generation of said mixture when said
hydrogen generator is in said second state.
[0056] In another aspect, a hydrogen generator is provided which
comprises (a) a catalyst; (b) a fluid; (c) a hydrogen-containing
material; and (d) a reaction chamber adapted to react a mixture of
said fluid and said hydrogen-containing material in the presence of
said catalyst to generate hydrogen gas, and being further adapted
to separate the generated hydrogen gas from reaction
byproducts.
[0057] In a further aspect, a hydrogen generator is provided which
comprises a third chamber containing a catalyst, a first chamber
containing a fluid, a second chamber containing a material that
reacts with the fluid in the presence of the catalyst to generate
hydrogen gas, and a valve movable from a first position in which
the flow of fluid along a pathway including the first, second and
third chambers is enabled, to a second position in which the flow
of fluid along the pathway is prevented.
[0058] In yet another aspect, a hydrogen generator is provided
which comprises a fluid reservoir containing a fluid; a first
chamber having a hydrogen-containing material disposed therein,
said first chamber being adapted to input a flow of said fluid from
said fluid reservoir and to output a mixture of said fluid and said
hydrogen-containing material; a reaction chamber containing a
catalyst, said reaction chamber being adapted to input said mixture
and to react said mixture, in the presence of said catalyst, to
evolve hydrogen gas, and being further adapted to output said
hydrogen gas and the byproducts of the hydrogen evolution reaction;
a separation chamber, downstream from said reaction chamber, which
is adapted to separate the hydrogen gas from the reaction
byproducts; and a valve movable from a first position in which the
flow of fluid along a pathway including the fluid reservoir and the
first chamber is enabled, to a second position in which the flow of
fluid along the pathway is prevented.
[0059] In still another aspect, a hydrogen generator is provided
which comprises (a) a catalyst; (b) a first compartment containing
a hydrogen-containing material and being equipped with a porous
member against which the hydrogen-containing material is pressed;
(c) a second compartment containing a fluid that forms a mixture
with said hydrogen-containing material, wherein said mixture reacts
in the presence of said catalyst to evolve hydrogen gas; and (d) a
first channel providing a flow of fluid from said first compartment
to said porous member, said first channel being equipped with a
valve; wherein the valve is movable from an open position to a
closed position when the pressure of hydrogen gas within the
generator reaches a predetermined level.
[0060] In a further aspect, a method for generating hydrogen gas is
provided. In accordance with the method, a fluid, a catalyst, and a
hydrogen-containing material that reacts with the fluid in the
presence of the catalyst to generate hydrogen gas are provided.
[0061] A mixture of the fluid and the hydrogen-containing material
is then created. When a demand for hydrogen gas exists, the mixture
is contacted with the catalyst, thereby generating hydrogen gas.
When demand for hydrogen gas abates, the catalyst is withdrawn from
contact with the mixture.
[0062] In yet another aspect, a method for forming a reactor for a
hydrogen generator is provided. In accordance with the method, a
core is provided which comprises a first material and having at
least one groove in the surface thereof. The groove is then covered
with a second material so as to form a passageway between the core
and the second material, wherein said passageway has a hydrogen
generation catalyst disposed on a surface thereof.
[0063] In still another aspect, a method for forming a reactor for
a hydrogen generator is provided. In accordance with the method, a
core is provided having a hydrogen generation catalyst disposed on
a surface thereof. A conduit is also provided which has at least
one opening along its length. The conduit is then disposed about
the core so that the opening is sealed by the core.
[0064] In a further aspect, a hydrogen generator is provided herein
which comprises (a) a source of fluid; (b) a catalytic element
comprising a catalyst disposed on a substrate; (c) a
hydrogen-containing material that reacts with the fluid in the
presence of the catalyst to generate hydrogen gas; (d) a conduit
for moving a mixture of said fluid and said hydrogen-containing
material from a first location to a second location; wherein said
catalytic element is movable from a first position in which said
catalytic surface is exposed to the mixture disposed within said
conduit, to a second position in which said catalytic surface is
not exposed to the mixture moving through said conduit.
[0065] It is now been found that the aforementioned needs may be
met by the devices and methodologies disclosed herein. In
particular, a hydrogen generator is disclosed herein which, in some
embodiments, provides hydrogen on demand by rapidly commencing and
terminating the hydrogen evolution reaction. Preferably, this is
achieved by removing the catalyst (if one is utilized) or one of
the reactants from the reaction chamber as hydrogen demand abates,
and reintroducing the removed element when hydrogen demand
increases.
[0066] The hydrogen generator may be configured as a small, compact
unit, and may be further configured so that, as reactants are
exhausted and the space used to store them is freed up, that space
may be utilized for the storage of reaction byproducts. In some
embodiments, the hydrogen generator may be configured as a passive
unit which is sufficiently small so that it can be placed on the
back of the handheld device or incorporated into a laptop
computer.
[0067] FIG. 1 illustrates a first specific, non-limiting embodiment
of a hydrogen generator made in accordance with teachings herein.
The hydrogen generator 101 comprises a first chamber 103 which
contains a fluid that is preferably maintained under a positive
pressure, a chamber reservoir 105 which houses a
hydrogen-containing material and which is in fluidic communication
with the first chamber 103 by way of a shutoff valve 107, a
catalytic reactor 109, a separator 111, and a third chamber 113 for
holding the byproducts of the hydrogen-generation reaction. The
shutoff valve 107 is transformable between a first orientation in
which the first chamber 103 is in open communication with the
second chamber 105, and a second orientation in which the first
chamber 103 is no longer in communication with the second chamber
105.
[0068] In use, when the shutoff valve 107 is placed into the first
orientation, water flows from the first chamber 103 into the second
chamber 105, where it forms a (preferably aqueous) solution or
slurry with the hydrogen-generating material. This slurry is then
conducted into the catalytic reactor 109 where it undergoes a
reaction to evolve hydrogen gas. The hydrogen gas so generated is
then conducted to the separator 111, where it is separated from any
reaction byproducts, unreacted materials, or solids or liquids that
may have contaminated the hydrogen gas stream. The hydrogen gas
then exits the separator 111 by way of a suitable outlet, and any
reaction byproducts, unreacted materials, solids or liquids that
have been separated from the hydrogen gas stream are transported to
the third chamber 113. In some embodiments, backflow of hydrogen
gas between the third chamber 113 and the separator may be
permitted to accommodate the continued reaction or decomposition of
hydrogen-containing materials stored therein. Thus, for example,
the third chamber 113, the separator 111, and/or a conduit
connecting these elements may be equipped with a one-way flow
mechanism which permits a backflow of hydrogen gas but prevents the
backflow of liquids or solids. Such a mechanism may comprise, for
example, a one-way flow valve in which the valve comprises a
hydrogen-permeable material.
[0069] In the preferred embodiment, the first chamber 103 contains
water. The water may be present as an aqueous solution which may
also contain suitable pH adjusting agents, anti-foaming agents,
surfactants, solvents, co-solvents or the like, and which may also
contain other materials or compounds such as methanol, ethanol or
other alcohols. The first chamber 103 is preferably capable of
undergoing a volumetric reduction as fluid is withdrawn from the
reservoir to accommodate expansion in the third chamber 113 as the
amount of reaction byproducts accumulates. This may be
accomplished, for example, by forming the first and/or third
chambers out of flexible or elastomeric materials, or through the
use of elastic bands, springs, or the like to apply pressure to the
first and/or third chambers. In some embodiments, these chambers
may be disposed adjacent to each other, and one of these chambers
may be used to apply pressure to the other.
[0070] FIG. 2 shows the separator 111 of the hydrogen generator of
FIG. 1 in greater detail. In the particular embodiment depicted,
the separator 111 comprises a first compartment 121 which is in
communication with the reactor chamber 109 (see FIG. 1) by way of
an inlet 127, and a second compartment 123 which is separated from
the first compartment 121 by a suitable boundary 125 which is
selectively permeable to hydrogen gas. The stream entering the
separator 111 will typically comprise hydrogen gas, byproducts from
the hydrogen evolution reaction, unreacted materials, and water. As
the stream enters the separator 111, the hydrogen gas component
flows into the second compartment 123 by way of the boundary 125,
and is thus separated from the stream. The hydrogen gas is
withdrawn from the second compartment 123 by way of outlet 129. The
remaining components of the stream are forced out of outlet 131 and
into the third chamber 113. This may be accomplished, for example,
by the pressure created by the hydrogen gas evolved in the reaction
chamber 109, through gravity, or through other suitable means.
[0071] In some embodiments, the shape of the first compartment 121
may be selected to promote plug flow in the separator. Such flow
can be advantageous in that it can permit direct contact between
the hydrogen gas and the boundary 125. This, in turn, can provide
almost instantaneous egress of the hydrogen gas through the
boundary 125.
[0072] The boundary 125 in the separator may comprise various
materials which are selectively permeable to hydrogen gas, and
which are preferably impermeable to the reaction byproducts,
reactants, and/or water. These include, but are not limited to,
porous or mesh materials comprising ceramics, plastics, polymers,
non-wovens, wovens, textiles, fabrics, carbons, carbon-fibers, ion
exchange resins, metals, alloys, wires, meshes, foamed glass, glass
frits, and combinations thereof. Preferably, the porous or mesh
material is in the form of a sheet or flat membrane which may
include, for example, nylon screens and stainless steel screens.
Preferably, the porous or mesh material comprises expanded
polytetrafluoroethylene.
[0073] FIGS. 3-4 show the catalyst reactor 109 of the hydrogen
generator of FIG. 1 in greater detail. The catalytic reactor 109
comprises a housing having first 131 and second 133 chambers which
are in communication with each other by way of a central aperture
equipped with a seal 135. A piston 137 is provided which comprises
a first plug 139 disposed in the first chamber 131 to which is
attached a catalytic rod 141. The catalytic rod 141 terminates in a
second plug 143. The piston is suspended from a spring 145 which is
housed in (and preferably attached to a wall of) the first chamber
131. The second chamber 133 of the housing is provided with an
inlet 147 and an outlet 149.
[0074] In use, when the generation of hydrogen gas is desired, the
catalytic rod 141 is disposed in an orientation in which it is
extended into the second chamber 133 as shown in FIG. 3. The first
plug 139 arrests the movement of the piston 137 at the appropriate
point of this operation, and the spring 145 provides a suitable
force to hold the piston 137 in place. In this position, the active
surface of the catalytic rod 141 contacts the fluidic stream which
enters the second chamber 133 of the catalytic reactor 109 by way
of inlet 147 and which comprises a mixture or slurry of the liquid
from the first chamber 103 (see FIG. 1) and the hydrogen-containing
material from the second chamber 105. The fluidic stream reacts in
the presence of the catalyst to generate hydrogen gas and reaction
byproducts. The hydrogen gas and reaction byproducts then exit the
second chamber 133 of the catalytic reactor 109 by way of outlet
149.
[0075] When the demand for hydrogen gas ceases, the flow of gas
from the hydrogen generator 101 is terminated. This may be
accomplished, for example, through the provision of a valve or
other suitable device downstream from the outlet 129. As a result,
pressure from accumulating hydrogen gas begins to rise in the
second chamber 133 of the catalytic reactor 109. As the pressure
rises, the catalytic rod 141 is pushed into the first chamber 131
of the catalytic reactor 109 as shown in FIG. 4, thereby
terminating the evolution of hydrogen gas. The second plug 143
arrests the movement of the piston 137 at the appropriate point of
this operation. The spring 145 disposed in the first chamber 131 of
the catalytic reactor 109 provides a restoring force to the piston
137 when pressure abates, so that the generation of hydrogen gas
can resume.
[0076] It will be appreciated that, in various embodiments made in
accordance with the teachings herein, the second plug 143 may be
replaced by other features which accomplish a similar end. Thus,
for example, in some embodiments, the longitudinal dimension of the
catalytic rod 141 may be selected to be slightly longer than the
height of the first chamber 131 so that the catalytic rod 141
cannot be withdrawn completely into the first chamber 131. In other
embodiments, the catalytic rod 141 (or a portion thereof) may be
wedge-shaped, and the first chamber 131 may be equipped with a
complimentary-shaped aperture into which the catalytic rod 141 is
withdrawn. The surfaces of the aperture will then abut the surfaces
of the catalytic rod 141 when the catalytic rod 141 is withdrawn
sufficiently far into the aperture, thereby arresting its further
progress.
[0077] It will be appreciated from the foregoing that, in some
embodiments, a sufficiently good seal may be desired between the
first 131 and second 133 chambers so that a sufficient pressure
differential will exist to drive the piston 137 in response to the
pressure within the first chamber 131. In some embodiments, a
suitable seal may be provided through the provision of an
elastomeric material, an o-ring, or a lubricant. In some
embodiments, the seal and/or the adjacent features of the housing
may be further adapted to remove or abrade materials adhering to
the surface of the catalytic rod 141 so that a fresh catalytic
surface will be provided when the resumption of hydrogen generation
is desired. In other embodiments, this function may be performed by
a separate blade or protrusion disposed within the catalytic
reactor 109 which preferably slidingly engages the catalytic
surface.
[0078] In various embodiments, the first chamber 103, the second
chamber 105, and/or the third chamber 113 may all be equipped with
means to apply pressure to the contents therein. In the case of the
first chamber 103, a positive pressure within this chamber is
desirable in order to provide a ready flow of liquid into the
second chamber 105. Similarly, it will frequently be desirable to
subject the hydrogen-containing material disposed in the second
chamber to pressure so as to force that material against the
interface used to mix the liquid from the first chamber 103 with
the hydrogen-containing material disposed in the second chamber
105. In various embodiments of the hydrogen generators disclosed
herein, this pressure may be provided by various means, including
springs, elastic bands, elastomeric materials, aerosols, or the
like.
[0079] FIG. 5 depicts the details of the shut-off valve 107. The
shut-off valve 107 comprises a first compartment 153 within which
is seated a membrane 155. The first compartment is equipped with an
opening 157 to the ambient environment. A plug 159 is attached to
the membrane 155, and is housed within a second compartment 161
equipped with an inlet 163. The housing 151 is likewise equipped
with an outlet 165 which is in fluidic communication with the inlet
163 when the valve 107 is in the open state (that is, when the plug
159 is dislodged from the opening 158). Similarly, the outlet 165
is no longer in fluidic communication with the inlet 163 when the
valve 107 is in the closed state (that is, when the plug 159 is
seated on the opening 158). By operating in this manner, the valve
107 provides for a unidirectional flow of fluidic whenever the
pressure at the inlet 163 exceeds the pressure at the outlet
165.
[0080] FIGS. 6-7 illustrate another particular, non-limiting
embodiment of a catalytic reactor made in accordance with the
teachings herein. The catalytic reactor 209 depicted therein
comprises a housing 233 which terminates in an elastomeric portion
234. The housing is equipped with an inlet 247 to deliver reactants
into the reactor 209. The reactants react in the presence of a
catalyst 241 to generate hydrogen gas. The housing 233 is also
equipped with an outlet 249 to remove reaction byproducts and
hydrogen gas from the reactor 209.
[0081] In use, when a demand for hydrogen gas exists, a fluidic
flow of reactants is maintained within the catalytic reaction
chamber 209, and the elastomeric portion 234 of the reaction
chamber 209 remains at a minimum volume as shown in FIG. 6. When
the demand for hydrogen gas begins to abate, the pressure within
the catalytic reaction chamber 209 begins to rise, and the
elastomeric portion 234 of the reaction chamber 209 begins to
expand as shown in FIG. 7. Eventually, when the flow rate of fluid
at the outlet 249 drops sufficiently low in comparison to the rate
at which hydrogen gas is being generated, the expansion of the
elastomeric portion 234 of the reaction chamber 209 withdraws the
fluid flow from contact with the catalyst 241, thereby arresting
the hydrogen evolution reaction. It will be appreciated that, when
the demand for hydrogen gas increases again, the volume of the
elastomeric portion 234 of the reaction chamber 209 decreases from
the withdrawal of hydrogen gas to the point where the reactants are
once again in contact with the catalyst 241, and the generation of
hydrogen gas resumes. It will further be appreciated that the
reactor design provides a ready supply of hydrogen gas at all times
after initial start-up, thus accommodating the need for hydrogen on
demand.
[0082] One skilled in the art will appreciate that a wide number of
variations are possible to the embodiments depicted in FIGS. 6-7.
For example, while the expandable portion 234 of the catalytic
reaction chamber 209 is depicted as being spherical in the device
of FIGS. 6-7, a similar effect can be achieved with expandable
portions that are of various other geometries. For example, rather
than being spherical, the expandable portion could be tubular or
could have a bellows-like configuration. Also, various embodiments
are possible wherein the catalyst is attached to one or more
surfaces of the expandable region 234 and is withdrawn from the
fluid flow as the expandable portion expands under the accumulation
of hydrogen gas. Moreover, while the inlet 247 and outlet 249 are
arranged on opposing sides of the reaction chamber 209, it will be
appreciated that embodiments are possible wherein the inlet 247 and
outlet 249 are arranged on the same side of the reaction chamber
209.
[0083] In other variations of the embodiment depicted in FIGS. 6-7,
the catalyst may be suspended within a cage which is disposed
within the expandable region 234 such that the cage separates the
catalyst from any surface the cage is resting upon by a certain
minimum distance. The cage may be permitted to move freely within
the catalytic reaction chamber 209. In such an embodiment, when the
expandable portion 234 expands under the influence of accumulating
hydrogen gas, the increased volume of the reaction chamber 209 will
withdraw the fluid containing the reactants from contact with the
catalyst, thus halting the hydrogen generation process. Conversely,
as hydrogen gas is withdrawn from the reaction chamber 209 as
demand increases again, the reducing volume of the reaction chamber
209 will again bring the fluid into contact with the catalyst.
Preferably, the reaction chamber 209 in such an embodiment is
essentially spherical in shape, and has an outlet which is covered
with a hydrogen-permeable, water-impermeable membrane.
[0084] In variations of the foregoing embodiment, a porous and/or
liquid permeable material may be used in place of the cage. This
material is preferably adapted to permit a mixture of a
hydrogen-containing material and a liquid medium to contact the
catalyst, while spacing the catalyst apart from the surface of the
reaction chamber the material is resting on. Thus, for example, the
catalyst may be suspended, embedded or encapsulated within a porous
and/or liquid permeable medium, such as, for example, foamed glass
or foamed plastic. In a preferred embodiment of this type, the
catalyst is disposed at the center of a sphere comprising the
porous and/or liquid permeable material. The material may be
hydrophobic or hydrophilic.
[0085] FIG. 8 illustrates another particular, non-limiting
embodiment of a catalytic reaction chamber 209 suitable for use in
the hydrogen generators described herein. The catalytic reaction
chamber 209 is equipped with a tortuous pathway so as to subject
the reactants to an extended residence time during which they are
in contact with the catalyst 241. In the particular embodiment
depicted, the outlet from the reaction chamber is in fluidic
communication with a helical winding of tubing 251 that terminates
inside of the catalytic reaction chamber 209. A portion of the wall
of the tubing is open to the catalyst. As fluid is drawn out of the
inlet 249, it flows through the helical winding 251 and, in so
doing, is subjected to extended contact with the catalyst 241. This
helps to ensure that the hydrogen evolution reaction is driven to
completion.
[0086] FIG. 9 illustrates another particular, non-limiting
embodiment of a catalytic reaction chamber 209 equipped with a
tortuous pathway so as to subject the reactants to an extended
residence time during which they are in contact with the catalyst
241. The catalytic reaction chamber of FIG. 9 is similar in most
respects to the catalytic reaction chamber of FIG. 8, except that,
rather than using a helical winding of tubing to increase fluid
residence time, a series of helical grooves 269 are employed for
this purpose. The grooves 269 are sealed off from one side with a
layer 271 of a suitable material to form closed passageways. The
surfaces of the helical windings and/or the layer 271 are coated
with a suitable catalyst to promote the hydrogen evolution
reaction.
[0087] In some cases, the catalytic reactor 261 of FIG. 9 may offer
greater ease of manufacturability, due to the ease with which
catalyst may be deposited directly on the surfaces that defined the
tortuous pathway. For example, the core of the catalytic rod can be
readably made from moldable plastics. Once formed, catalyst can be
deposited on the surfaces of the helical windings through, for
example, solution-based deposition processes that are well known in
the art. Alternately or in conjunction with the foregoing, catalyst
may be deposited on the surface of the layer 271 through various
processes known to the art. This layer may then be disposed about
the outer surfaces of the core in a variety of ways. For example,
the layer 271 may be formed as the tape which is wound around the
core, and which may be hydrogen permeable. The layer 271 may also
be formed as a skirt of heat-shrinkable plastic or other suitable
material which is then shrunk into place about the core through
exposure to a suitable heat source.
[0088] FIG. 10 depicts a further particular, non-limiting
embodiment of a hydrogen generator made in accordance with the
teachings herein. The hydrogen generator 301 comprises a central
chamber 303 which is charged with sodium borohydride 305 or another
suitable hydrogen-containing material. A piston 307 is provided on
one end of the chamber and exerts a compressive force against the
sodium borohydride 305. In the particular embodiment depicted, the
piston 307 is spring driven, though one skilled in the art will
appreciate that the piston 307 may be driven pneumatically or by
any other suitable means as is known to the art.
[0089] The compressive force exerted against the sodium borohydride
305 by the piston 307 causes the sodium borohydride 305 to be
pressed against a porous frit 309 disposed on an opposing side of
the central chamber 303 from the piston 307. The frit 309 is in
combination with a water reservoir 311 by way of a valve 313. In
the particular embodiment depicted, the water reservoir 311 is
cylindrical and forms the outer surface of the device. However, one
skilled in the art will appreciate that water reservoirs of a wide
variety of geometries and configurations may be utilized in the
device depicted and in variations thereof. A layer of catalyst 315
is provided on the surface of the frit 309 opposite the sodium
borohydride 305.
[0090] In use, when a demand for hydrogen exists, water is
withdrawn from the reservoir 311 by way of the valve 313 and wicks
across the porous frit 309, where it dissolves a portion of the
sodium borohydride 305. The sodium borohydride solution then reacts
in the presence of the catalyst 315 to generate hydrogen gas. In
some embodiments, the layer of catalyst 315 and/or the porous frit
309 may be serpentine in shape to increase the residence time of
the solution during which it is in contact with the catalyst 315,
thereby helping to ensure that the hydrogen evolution reaction runs
to completion. In other embodiments, a similar result may be
achieved through proper selection of the dimensions of the device.
In still other embodiments, the catalyst may be combined or
incorporated into the porous frit 309.
[0091] As the reacted solution exits the porous frit 309, it flows
along a channel 317 provided along one wall of the device. The
channel 317 is an open communication with a compartment 319 of the
device that houses the spring 321. As the sodium borohydride is
depleted, this compartment 319 increases in volume, thus providing
a suitable storage location for the reaction byproducts.
[0092] A hydrogen-permeable membrane 323 is provided on one end of
the hydrogen generator 301. As hydrogen gas is generated, it flows
through the channel 317 and exits the device via an outlet 325
controlled by a valve 327. In some embodiments, the hydrogen
generator 301 may also be adapted to permit the flow of hydrogen
gas across the porous frit 309 and through the piston 307, where it
again exits the device via the hydrogen-permeable membrane 323. In
such embodiments, the piston 307 may itself be a hydrogen-permeable
membrane.
[0093] When hydrogen demand abates, or if the valve 327 is closed,
hydrogen gas begins to accumulate in the device. The valve 313 is
adapted such that the back pressure created by the accumulating
hydrogen gas closes the valve 313 when a sufficient pressure is
attained. This, in turn, results in the cessation of water flow,
and the accompanying termination of the hydrogen evolution
reaction. In some embodiments, one or more compartments of the
device may be equipped with an expandable volume to accommodate the
increased pressure.
[0094] FIGS. 11-13 depict a further particular, non-limiting
embodiment of a catalytic reactor in accordance with the teachings.
The catalytic reactor 401 depicted therein comprises a flat
rectangular housing 403 equipped with an inlet 405 and an outlet
407. A plurality of catalytic bumps 409 are provided upon one major
surface of the catalytic reactor (note that the opposing surface
has been removed for illustration purposes). In the particular
configuration depicted therein, the catalytic bumps 409 are
arranged in a staggered fashion to ensure sufficient exposure to
the catalyst of the fluid flowing through the reactor 401.
[0095] When a sufficient demand for hydrogen exists, the catalytic
reactor 401 is in the state depicted in FIG. 12, in which the two
major opposing surfaces of the reactor 401 are sufficiently close
so as to ensure exposure of the fluid flowing through the reactor
401 to the catalyst 409, thereby ensuring the continuing evolution
of hydrogen gas. By contrast, when the demand for hydrogen gas
abates, the pressure of the accumulating gas causes the two major
surfaces of the reactor 401 to move apart from each other, thereby
removing the contact between the catalyst bumps 409 and the fluid
flow, and terminating the hydrogen evolution reaction.
[0096] One skilled in the art will appreciate that numerous
variations are possible to the embodiment depicted in FIGS. 11-13.
For example, in the embodiment depicted therein, the major surface
devoid of catalyst bumps is depicted as the surface that undergoes
deformation to withdraw the catalyst from contact with the fluid
stream. However, it will be appreciated that either or both of
these major surfaces may undergo suitable deformation to accomplish
this end. It will further be appreciated that the catalyst may be
disposed within the reactor in various ways. For example, the
catalyst may be disposed as one or more lines upon one or both
major surfaces of the reactor. The catalyst may also be disposed is
a uniform coating on one or both major surfaces of the reactor.
[0097] FIGS. 14-16 illustrate another particular, non-limiting
embodiment of a catalytic reactor in accordance with the teachings
herein. The catalytic reactor 501 depicted therein comprises a
moveable wall 503 which encloses the interior of the reactor 501
and which is disposed about a stationary plug 505. An inlet 507 for
introducing a reactant solution into the reactor 501, and an outlet
508 for removing byproducts from the reactor 501, are disposed on
opposing sides of the plug 505. A layer of catalyst 509 is disposed
on the wall 503 between the inlet 507 and the outlet 508.
[0098] FIG. 14 shows the catalytic reactor 501 in a first
orientation in which the movable wall 503 has been placed such that
the layer of catalyst 509 is apart from the plug 505. In this
orientation, as liquid reactant enters the reaction chamber, it is
forced by the plug 505 and the movable wall 503 to flow along a
first course that brings it into contact with the catalyst 509. The
liquid reactant reacts in the presence of the catalyst 509 to
generate hydrogen gas. Hence, the first orientation corresponds to
the "on" position of the reactor 501.
[0099] FIG. 15 shows the catalytic reactor 501 in a second
orientation in which the movable wall 503 has been moved such that
the plug 505 is in contact with the layer of catalyst 509. In this
orientation, as liquid reactant enters the reaction chamber, it is
forced by the plug 505 and the movable wall 503 to flow along a
second course that prevents it from coming into contact with the
catalyst 509. The liquid reactant is thus unable to react to
generate hydrogen gas. Hence, the second orientation corresponds to
the "off" position of the reactor 501.
[0100] FIG. 16 shows a cross-sectional view of the catalytic
reactor 501 of FIG. 14 taken along the LINE 16-16. As seen therein,
the top of the reactor 501 is equipped with a hydrogen permeable
membrane 511 that allows the hydrogen to exit the reactor, while
leaving the reaction byproducts behind. Hence, a pure stream of
hydrogen is extracted across the membrane. Various conduits and
other such devices may be provided to collect and/or route the
extracted hydrogen to a desired location.
[0101] It will be appreciated from the above that the reactor 501
depicted in FIGS. 14-16 operates to control the hydrogen evolution
reaction by exposing the catalyst 509 to the liquid reactant when
the generation of hydrogen gas is desired, and by essentially
removing the catalyst 509 from the reaction chamber when it is
desired to cease the generation of hydrogen gas. The catalytic
reactor 501 may be incorporated into a hydrogen generator or other
such device which provides other functionalities, such as control
over the flow of liquid reactant.
[0102] In several of the embodiments described above, pressure from
accumulating hydrogen gas is utilized to remove the catalyst from
the reactant solution, thereby arresting the evolution of hydrogen
gas. However, one skilled in the art will appreciate that a similar
technique may be utilized to remove one of the other components
necessary to the hydrogen evolution reaction to achieve a similar
effect. For example, such a technique may be utilized to physically
remove the hydrogen-containing material from the reaction zone.
[0103] FIG. 17 illustrates a further particular, non-limiting
embodiment of a hydrogen generator 601 made in accordance with the
teachings herein. In the particular embodiment depicted, the
hydrogen generator is essentially rectangular in shape. In a
typical embodiment, this hydrogen generator has a height of about 3
inches, a width of about 2 inches, and a thickness of about 0.5
inches. Of course, one skilled in the art will appreciate that the
hydrogen generator may be made in a variety of shapes and sizes, as
taught herein. Hydrogen is produced on demand within the hydrogen
generator 601, and is emitted from a hydrogen outlet 603 disposed
on the top of the hydrogen generator 601. Various conduits and
connectors (not shown) may be attached to the outlet 603 to conduct
the generated hydrogen gas to the point of use.
[0104] The details of the hydrogen generator 601 of FIG. 17 may be
further appreciated with respect to the exploded few of FIG. 18. As
seen therein, the hydrogen generator 601 comprises a fluid manifold
605, a fluid bladder 607, a fluid bladder motivator 609, a residual
hydrogen vent 611, a chemical hydride 613 (it is to be noted that
this term is used here as shorthand for any of the various
hydrogen-containing materials described herein), a spring 615, a
piston 617, a chassis 619, and a base 621. Each of these components
is described in greater detail below.
[0105] FIG. 19 shows the chassis 619 in greater detail. As seen
therein, in this particular embodiment, the chassis 619 comprises a
first cylindrical compartment 623 which houses the chemical hydride
613, and a second rectangular compartment 625 which houses the
fluid bladder 607, the fluid bladder motivator 609, and the
residual hydrogen vent 611. It will be appreciated that, in other
embodiments, the chassis 619 may have any number of compartments,
and the shape and construction of each of these compartments may be
adapted or optimized for their intended contents. Thus, for
example, the geometry of the first compartment 623 may be modified
to compliment the geometry of the chemical hydride 613 or the
piston 617, either of which may have a wide varieties of
geometries. Similarly, the second compartment may be further
subdivided to provide a separate compartment for the residual
hydrogen vent 611, and may be pressurized with air or a suitable
gas to maintain pressure on the fluid bladder 607.
[0106] FIGS. 20-22 illustrate the assembly of the various
components of the hydrogen generator 601. The chassis 619 (see FIG.
18) has been deleted from FIGS. 20-23 for clarity of illustration.
As seen therein, the base 621 is provided with a cylindrical
aperture 631 (see FIG. 22) which provides a seat for one end of the
spring 615. The piston 617 is mounted on the opposing end of the
spring 615 and applies compressive force against one end of the
chemical hydride 613. The opposing end of the chemical hydride 613
engages a hydride/water interface 633 (see FIG. 21) disposed on one
surface of the fluid manifold 605. The chemical hydride 613 is
maintained in proper alignment with respect to the hydride/water
interface 633 by virtue of the complimentary shaped first
cylindrical compartment 623 of the body 619 (see FIG. 19).
[0107] The base 621 is also provided with a rectangular aperture
635 (see FIG. 22) which seats one end of the fluid bladder 607 and
the fluid bladder motivator 609. In some embodiments, the base may
provide some of the functionalities typically provided by the fluid
manifold 605, such as the residual pressure relief subsystem.
[0108] The fluid bladder 607, the fluid bladder motivator 609 and
the residual hydrogen vent 611 are housed together in the
rectangular compartment 625 (see FIG. 19) of the chassis 619 and
are thus maintained in contact with each other, thereby allowing
the fluid bladder motivator 609 to exert a compressive force
against the fluid bladder 607.
[0109] The fluid bladder motivator 609 exerts force on the fluid
bladder 607, preferably in a direction parallel to the force
exerted by the generated gas pressure. In some embodiments, as in
embodiments in which a water pumping mechanism is used within the
fluid manifold, the fluid bladder motivator 609 may be deleted. The
fluid bladder motivator 609 may be, for example, a compressed
open-cell polymeric foam, a telescoping cylinder with aerosol or
compressed gas, or an elastomeric component acting as a compression
spring or extension spring (such as, for example, a rubber band
constricting the water bladder). In some embodiments, the fluid
bladder 607 itself can act as a motivator. Thus, for example, in
some embodiments, the fluid bladder 607 may be fashioned as an
expanded balloon which provides a contracting force on its
contents.
[0110] As best seen in FIG. 21, the fluid bladder 607 is equipped
with an outlet 641 which engages a port 643 in the fluid manifold
605 to provide for the flow of fluid from the fluid bladder 607
into the fluid manifold 605. Also, as described in greater detail
below with respect to FIG. 31, the fluid manifold 605 is equipped
with a port 645 (seen in greater detail in FIG. 44) which is in
communication with the residual hydrogen vent 611 (see FIG. 20) and
which provides a means by which residual hydrogen (generated by
reaction byproducts or incompletely reacted materials) may be
eliminated from the system. This may occur, for example, through
reaction with oxygen in the ambient environment (preferably in the
presence of a catalyst) or with an internally stored oxidant to
form water vapor (which may be released to the environment or
reused in the hydrogen generation reaction), by chemically fixing
the hydrogen to a substrate to render it relatively non-reactive,
or by passing the hydrogen to a shorted fuel cell membrane
electrode assembly to be converted into water.
[0111] The fluid manifold 605 controls the flow of fluid to the
chemical hydride 613, and also controls the rate of hydrogen
generation. The fluid manifold 605 further accomplishes
hydrogen/borate separation, and provides a means through which
internal system pressure due to residual hydrogen generation may be
relieved.
[0112] The construction of the fluid manifold 605 may be
appreciated with respect to FIGS. 23-31. As seen in FIG. 23, the
fluid manifold 605 in this particular embodiment is a laminate
comprising molded plastic components and thin layers of filtration
media and elastomers. Thus, the fluid manifold 605 comprises a base
plate 651, a separator layer 653, a mid plate 655, an elastomer
layer 657, and a top plate 659. As explained in greater detail
below, the base plate 651 is equipped with a plurality of valves
(such as fluid forward pressure regulator valve 661) which control
the flow of both fluid and hydrogen gas through the fluid manifold
605, and is further equipped with a reactor 673 where the
generation of hydrogen gas occurs.
[0113] The top plate 659 is equipped with a hydrogen gas outlet
603, an active heater and water pump electrical access port 663, a
static pressure port 665, a water shutoff actuator access 667,
water vapor vents 669, and a static pressure port 671. The top
plate 659 may be constructed of thermally insulating material, such
as suitable plastics or fiberglass, and provides interfaces with
external devices that utilize a hydrogen gas such as, for example,
fuel cells and gas chromatographs.
[0114] The elastomer layer 657 may comprise various suitable
elastomeric materials. These include, without limitation, silicone
and EPDM. The elastomer layer 657 provides a barrier between the
ambient environment and reactants or byproducts disposed within the
hydrogen generator 601, while allowing communication between the
internal and external pressure. The elastomer layer 657 also serves
as a seal between the top plate 659 and mid plate 655.
[0115] The midplate 655 preferably comprises high thermal
conductivity, low thermal mass materials such as, for example,
thermally conductive particles or fiber filled plastics, carbon or
carbon composites, and metals. The midplate 655 provides fluid
manifolding and thermal conduction to the reactants and/or
byproducts.
[0116] The separator layer 653 preferably comprises a laminate
which includes a filtration media capable of separating hydrogen
from an alkaline solution (such filtration media may include,
without limitation, expanded polytetrafluoroethylene (PTFE) or
non-woven polyethylene fabric), adhesives, or elastomers. The
separator layer 653 also serves as a sealing and/or adhesion layer
between the midplate 655 and the base plate 651.
[0117] The base plate 651 preferably comprises a high thermal
conductivity, low thermal mass material (such as those described
above) or a composite consisting primarily of a thermally
insulating material with an inclusion of thermally conductive
material positioned between the catalytic reaction zone and the
hydride/water interface zone. The base plate 651 provides fluid
manifolding and thermal conduction to the reactants and/or
byproducts. The base plate 651 also provides sites for liquid
pressure regulator and shutoff valves, gas shutoff valves, and
liquid pumps.
[0118] Though not specifically illustrated, it will be appreciated
that the fluid manifold 605 may include various other layers and
elements. For example, in some embodiments, the fluid manifold 605
may include appropriate circuitry to control the various valves and
other devices that may be incorporated into the manifold. Such
circuitry may be advantageously incorporated into the fluid
manifold as one or more layers of flexibly circuitry, or may be
disposed on one or more dies or printed circuit boards incorporated
into the manifold. The manifold may also be wired for control by
one or more external devices.
[0119] With reference to FIG. 24, the fluid manifold 605 is further
provided with a fluid forward pressure regulator valve 661, a 20
PSI check valve 675, an externally actuated fluid shut-off valve
677, a fluid pump 679 (described in greater detail below), and a
hydrogen recombiner 681. FIGS. 25-29 further illustrate the
construction and individual features of each of the laminate
layers, as well as their assembly into the completed fluid manifold
605.
[0120] FIG. 30 illustrates the flow path of the fluid (which may be
water or any of the various aqueous solutions described herein)
employed in the hydrogen generator of FIG. 16 as it travels through
the fluid manifold 605. As seen therein, fluid enters the fluid
manifold 605 from the fluid bladder (not shown) by way of port 643.
While fluid forward pressure regulator valve 661 is in an open
position, the fluid passes through the fluid manifold 605 to the
fluid shut-off valve 677. While the fluid shut-off valve 677 is in
an open position, the fluid passes onto the water/hydride interface
683. There, the fluid dissolves a portion of chemical hydride (not
shown), and the resulting solution or slurry passes into the
catalytic reactor 673. In the catalytic reactor, the solution or
slurry reacts in the presence of a suitable catalyst to generate
hydrogen gas. The liquid byproducts from the hydrogen generation
reaction flow out of the catalytic reactor 673 and exit the fluid
manifold 605 by way of an aperture 685 (see also FIG. 21) and into
the rectangular compartment 625 (see FIG. 19) of the chassis
619.
[0121] FIG. 31 illustrates the fluid flow path of hydrogen gas in
the hydrogen generator of FIG. 17 as it travels through the fluid
manifold 605. As seen therein, primary and secondary flow paths are
created for hydrogen gas in the fluid manifold 605. The primary
flow path extends from the catalytic reactor 673 to the hydrogen
outlet 603, and is the path taken when the hydrogen generator is
actively evolving hydrogen gas.
[0122] A first portion of the secondary flow path for hydrogen gas
extends from the primary flow path to outlet 687, which is in open
communication with the residual hydrogen vent 611 (see FIG. 18).
This portion of the secondary flow path provides a means for
releasing hydrogen gas (and thus reducing hydrogen gas pressure in
the fluid manifold 605) which may accumulate in the rectangular
compartment 625 of the chassis (see FIG. 19) or in the primary flow
path upstream from the catalytic reactor 673 when the reactor is
shut down. It will be appreciated that, in some embodiments, the
residual hydrogen vent 611 may be designed to permit hydrogen gas
to reenter the primary flow path by way of outlet 687 and the
secondary flow path when demand for hydrogen resumes.
[0123] A second portion of the secondary flow path extends from the
residual hydrogen vent 611 and is controlled by check valve 675.
This portion of the secondary flow path provides a means for
relieving pressure due to accumulating hydrogen gas in the
rectangular compartment of the chassis 619 (see FIG. 19). The check
valve 675 may be adapted to vent hydrogen gas at a predetermined
pressure threshold such as, for example, 20 psi. In some
embodiments, the hydrogen gas may be vented to the atmosphere,
while in other embodiments, the hydrogen gas may be reacted with a
catalyst and converted into water, or may be rendered less reactive
through chemical bonding to a substrate. The later two types of
embodiment are preferred in applications where the vented hydrogen
gas might pose a risk of fire or explosion.
[0124] FIG. 32 illustrates the pressure regulator valve 661 in
greater detail. As seen therein, the fluid pressure regulator valve
661 comprises a spring 703 disposed in a first compartment 705, a
spring loaded valve stem 707 disposed in a second compartment 709,
and a valve body 711 which physically connects the spring 703 to
the spring loaded valve stem 707. The valve body 711 is disposed
within the fluid flow path 713 (see FIG. 30). When the fluid
pressure regulator valve 661 is in the open position, fluid flows
around the valve stem 707 and along the flow path 713. When the
fluid pressure regulator valve 661 is in the closed position, the
valve stem 707, which preferably comprises a resilient material
such as, for example, a fluoroelastomer, is compressed against the
opening between the second compartment 709 and the fluid flow path
713, thereby sealing off the fluid flow path and arresting the flow
of fluid therethrough. Static pressure port 671 allows for control
of the fluid pressure regulator valve 661 through the pressure
differential between the interior of the fluid bladder 607 (see
FIG. 20) and the ambient environment.
[0125] FIGS. 33-34 illustrate the catalytic reactor 673 in greater
detail. As seen therein, the catalytic reactor 673 in this
particular embodiment is situated downstream from the fluid/hydride
interface 683 (shown in greater detail in FIG. 44) such that fluid
in the fluid flow path (see FIG. 30) flows into the fluid/hydride
interface 683 by way of fluid flow channel 714, dissolves a portion
of chemical hydride at the fluid/hydride interface 683, and flows
from the fluid/hydride interface 683 to the catalytic reactor 673
via fluid flow channel 716.
[0126] As seen in FIG. 34, the catalytic reactor 673 in this
particular embodiment comprises a cylindrical body 733 with a
radial notch 735 defined therein. When the catalytic reactor 673 is
in active mode (that is, when hydrogen gas is being actively
generated), the catalytic reactor 673 is positioned such that the
radial notch 735 places fluid flow channel 716 into fluidic
communication with separator channel 727. Consequently, hydride
solution flows through the radial notch 735 by way of fluid flow
channel 716 and reacts in separator channel 727 (separator channel
727 is annular, as seen in FIG. 40) with a catalyst disposed on the
exterior of the cylindrical body 733 of the catalytic reactor 673.
The hydrogen gas exits the separator channel 727 by way of a
separator vent 731. The flow of hydrogen gas in this process is
depicted in FIG. 31.
[0127] When the catalytic reactor 673 is in passive mode (that is,
when the active generation of hydrogen gas has been terminated),
the catalytic reactor 673 is positioned (as by moving upward into
compartment 723) such that the catalytic surface disposed on the
exterior of cylindrical body 733 is no longer exposed to the
hydride solution, thereby terminating the hydrogen generation
reaction. Static pressure port 665 ensures that the catalytic
reactor 673 will assume this position anytime the pressure
differential between fluid flow channel 716 and the ambient
environment exceeds a predetermined threshold value. Static
pressure port 665, in combination with spring 721 (and possibly
elastomeric layer 657), further ensures that the catalytic reactor
673 will resume the position depicted in FIG. 33 when the pressure
differential drops below the threshold value. This threshold value
may be determined, at least in part, by the spring constant of
spring 721 and/or the resiliency of elastomeric layer 657. Hence,
this feature allows the hydrogen generator to shut off
automatically when hydrogen production exceeds demand, and to
automatically resume hydrogen production when demand increases.
[0128] FIGS. 35-44 illustrate one particular, non-limiting
embodiment of a fabrication process that may be used to manufacture
a hydrogen generator of the type depicted in FIG. 17. The steps in
this process may be best understood in the context of FIGS. 23-29,
which show various views of the completed assembly, it being noted
that, while FIGS. 23-29 show the assembly from a top perspective,
FIGS. 34-35 illustrate the fabrication of the assembly from bottom
and side perspectives.
[0129] As shown in FIGS. 35-36 (which are, respectively, side and
bottom views of the top plate 659), the process begins with the
formation of top plate 659, which is preferably constructed from a
suitable polymeric material and which may be fabricated by
injection molding or through various other suitable molding
processes. The top plate 659 contains a hydrogen gas outlet 603
which is in fluidic communication with an aperture 805 provided at
the bottom of the top plate 659. A rectangular indentation 807 and
first 809 and second 811 cylindrical indentations are provided in
the bottom of the top plate 659. The rectangular indentation 807 is
in open communication with water vapor vents 669, and the first 809
and second 811 cylindrical indentations are in open communication
with static pressure ports 665 and 671, respectively (see FIG. 23).
The top plate 659 is also provided with a water pump electrical
access port 663 and water shutoff actuator access 667.
[0130] Referring now to FIG. 37, hydrogen recombiner 681, which is
typically a sheet of porous material, is placed into rectangular
indentation 807, and springs 721 and 815 are placed into first 809
and second 811 cylindrical indentations, respectively. As seen in
FIG. 33, spring 721 forms part of the catalytic reactor assembly
and, as seen in FIG. 24, spring 815 forms part of fluid forward
pressure regulator valve 661.
[0131] Referring now to FIG. 38, elastomeric layer 657 is applied
to the bottom surface of the top plate 659. The elastomeric layer
657, which may be attached to the substrate through welding or with
suitable adhesives (such as, for example, pressure sensitive
adhesives), is provided with suitable openings such that the
hydrogen recombiner 681 and water pump electrical access port 663
are exposed.
[0132] With reference to FIG. 39, the midplate 655 is then
positioned over the elastomeric layer 657. The midplate 655 has
formed in a surface thereof a channel 727, a static pressure port
671 and a cylindrical depression 831. The channel 727 forms a
portion of the liquid flow path (see FIG. 30) by which the reaction
byproducts are removed from the catalytic reactor 673 to the
rectangular compartment 625 (see FIG. 19) of the chassis 619.
[0133] Referring now to FIG. 40, the catalytic reactor 673 is
positioned such that it is disposed over spring 721 (see FIG. 37).
Also, check valve 675 is disposed in cylindrical depression
831.
[0134] With reference to FIG. 41, the filtration layer 653 is
disposed over the midplate 655. Preferably, the filtration layer
653 comprises thermo-mechanically expanded polytetrafluoroethylene
(PTFE) or other suitable fluoropolymer materials. In some
embodiments, the filtration layer 653 may also serve as a bonding
layer for the assembly, in which case, if it is not suitably tacky
by itself, it may be coated with a suitable adhesive on one or both
sides as appropriate.
[0135] Referring now to FIG. 42, after the filtration layer 653 is
in place, valves 661, 675 and 677 (all of which, in this particular
embodiment, are spring actuated stem valves) are positioned on the
filtration layer 653 over holes 805, 667 and 671, respectively.
FIG. 43 shows a side view of the assembly at this stage of the
process. The use of spring actuated stem valves in this process is
advantageous in that they are self-centering. Referring now to FIG.
44 and FIG. 45 (the later of which is a side view of FIG. 44), the
bottom plate 651 is then placed over the filtration layer 653,
thereby completing the assembly of fluid manifold 605. The
components of the bottom plate 651, such as the hydride/water
interface 633 and port 643, may be integrally molded with the
bottom plate 651 or may be mounted on the bottom plate 651 after
the remainder of the fluid manifold 605 has been assembled.
[0136] Referring again to FIG. 44, it can be seen that, in this
particular embodiment, the hydride/water interface 633 has a
grooved, helical surface 683. The grooves of the helical surface
683, in combination with inlet 841 and outlet 843 defined therein,
form a portion of the fluid flow path depicted in FIG. 30 when the
helical surface 683 is pressed against an opposing hydride surface.
This portion of the fluid flow path is convoluted, thereby
increasing the duration of contact between the fluid and the
hydride and helping to saturate the resulting solution. Saturation
of this solution is beneficial from an energy per unit weight
perspective in that it helps to maximize the amount of hydrogen
generated per unit weight of water. Of course, it will be
appreciated that other hydride/water interfaces of the various
types taught herein may be substituted for the hydride/water
interface 633 depicted in FIG. 44, including, for example, porous
glass fiber materials.
[0137] The hydrogen generator 601 depicted in FIG. 17 has some key
advantages that make it particularly suitable for certain
applications. For example, embodiments of this device can be made
which utilize an active heating element that immediately heats the
catalytic reactor and hydride/water interface zones, thus
increasing hydride solubility and catalytic reactivity and
increasing start-up times (in many such embodiments, startup times
of less than 10 seconds may be achieved). The use of a
self-regulated heater, such as a PTC thermistor, is often
advantageous in such embodiments because it is able to reduce power
consumption to essentially zero once a specified temperature is
obtained (often within the start-up time), since the catalytic
reaction is exothermic and provides the temperature sustaining heat
during operation.
[0138] Similarly, in some embodiments, the hydrogen generator 601
depicted in FIG. 17 offers rapid shutdown (in many embodiments,
shutdown times of less than 10 seconds may be achieved), due to the
presence of the fluid forward pressure regulator valve 661 which is
preferably referenced to the ambient atmosphere with a small
positive bias (typically between 2 and 5 psia), and which rapidly
shuts off fluid flow from the fluid bladder 607 (see FIG. 18) to
the hydride/water interface 633 (see FIG. 21). Rapid and complete
shutdown is also assisted by the use of a catalytic surface that
has a pressure actuated capability to separate the catalytic region
from the hydride solution, immediately stopping catalytically
assisted hydrolysis of the hydride solution.
[0139] Moreover, in some embodiments of hydrogen generator 601,
slow hydrolysis of residual hydride solution and the resulting
increase in hydrogen pressure within hydrogen generator 601 may be
reduced with the hydrogen recombiner 681 (see FIG. 37). Hence, the
hydrogen generator 681 allows for the elimination of such excess
hydrogen gas, while venting only water vapor to the ambient
environment. Similarly, fluid movement to the hydride/water
interface 633 (see FIG. 21) may be restricted by an externally
actuated fluid shutoff valve, and hydrogen gas venting may be
restricted by an externally actuated gas shutoff valve, to
eliminate the possibility of generating or venting hydrogen gas
when hydrogen is not needed.
[0140] The hydrogen generator 601 depicted in FIG. 17 is
illustrated as a stand-alone device. However, it will be
appreciated that this device may be readily integrated with one or
more fuel cells or other such devices. Thus, for example, the fluid
manifold may be modified to include additional layers containing
the necessary functionalities of a fuel cell, or else such
functionalities may be incorporated into one or more of the layers
described herein. Such constructions would be especially
advantageous for disposable fuel cells, such as alkaline fuel
cells. In such an application, any product water formed on the
hydrogen side of the fuel cell could be returned to the
hydride/water interface, thereby reducing the amount of water
required to be stored by the device and/or increasing the amount of
hydride the device can contain. In the case of an alkaline fuel
cell, the fluid manifold may include a filtration laminate on top
of the cathode to filter CO.sub.2 and other contaminants that may
be detrimental to the hydrogen generator or its components.
[0141] Moreover, the principles described herein may be applied to
the packaging of hydrogen generators. For example, a hydrogen
recombiner of the type described herein for eliminating residual
hydrogen gas may be utilized to eliminate residual hydrogen gas
that may accumulate in the packaging of hydrogen generators,
especially if the hydrogen generators stored for a significant
period of time. As a specific, non-limiting example, multiple
hydrogen generators may be stored in a plastic bag, and the plastic
bag may itself be equipped with a hydrogen recombiner. As a further
specific, non-limiting example, a hydrogen recombiner may also be
incorporated into blister packaging used for individual hydrogen
generators or devices that incorporate them.
A. Heating Elements
[0142] In the various catalytic reactors disclosed herein, it is
preferred to heat the liquid reactant in the presence of the
catalyst since, at least when sodium borohydride is used as the
hydrogen-containing material, the hydrogen generation reaction is
typically catalyzed with greater efficiency at higher temperature
levels. Moreover, the distribution of byproducts at higher
temperatures (e.g., around 90.degree. C.) will typically be
centered around lower hydration states than is the case when the
hydrogen generation reaction occurs at lower temperatures. It will
be appreciated that, in various embodiments, suitable heating may
be implemented by heating the liquid, the catalyst, or both. In
some embodiments, heating may also be utilized as a solubility
enhancer for the hydrogen-containing material.
[0143] In the case of hydrogen generators that are to be used in
conjunction with fuel cells in laptop computers or handheld
electronic devices, the dimensions of the catalytic reactor will
frequently be sufficiently small such that flash heating of the
liquid reactant can be economically performed in the presence of
the catalyst, using techniques similar to those developed for
thermal inkjet printers. Such flash heating can be utilized to
generate discrete bubbles of hydrogen gas that span the diameter of
the fluid flow through the reactor, and that can be readily
adsorbed from the fluid flow in the reactor through a
hydrogen-permeable membrane. Hence, flash heating can serve the
simultaneous purposes of improving the efficiency of the hydrogen
generation reaction, reducing the amount of water consumed by
reaction byproducts, and facilitating the separation of hydrogen
gas from reaction byproducts and unreacted materials. Moreover, the
generation of bubbles via flash heating may be used in the devices
and methodologies described herein, either alone or in combination
with other such mechanisms as piezoelectric actuators, to push (or
pull) liquid reactants or other materials through the reaction zone
and through other parts of the device.
[0144] In one such embodiment, the catalytic reactor may be
fabricated with a series of tiny electrically-heated chambers that
may be constructed, for example, by photolithography. In use, the
reactor runs a pulse of current through the heating elements, which
rapidly heats the liquid reactant in the vicinity of the catalyst.
This results in the formation of a bubble of hydrogen which, as it
is adsorbed through the adjacent hydrogen-permeable membrane, sucks
a further portion of liquid reactant into the catalytic reactor.
Hence, the flash heater acts as an effective pumping mechanism
while hydrogen is being generated, and further provides a
convenient means by which the rate of hydrogen evolution may be
scaled up or down in accordance with demand.
[0145] It will be appreciated that the flash heating methods
described above may be implemented in a variety of ways. For
example, a positive temperature coefficient thermistor may be
provided which is integrated with, or which controls, the heating
devices. Such a thermistor may be designed with an electrical
resistance that is low at room temperature, but becomes very high
at some desired strike temperature. Hence, the thermistor will
efficiently heat the liquid reactants up to the strike temperature,
and will then effectively shut off.
[0146] In some embodiments, the electronic circuitry controlling
the catalytic reactor may be incorporated into the hydrogen
generator. In other embodiments, some, or the bulk of, this
circuitry may be integrated into a hydrogen fuel cell that is
coupled to the hydrogen generator, or into the host device. This
later type of embodiment may be particularly advantageous in
applications where it is desired to fashion the hydrogen generator
as a disposable device. The electronic circuitry may also comprise
various piezoelectric pumps which may be used to control the flow
of reactants through the hydrogen generator.
[0147] The electronic circuitry may further include sensors which
are adapted, for example, to sense changes in the volume of
components of the hydrogen generator due, for example, to the
accumulation of hydrogen gas. It will be appreciated that such
circuitry may be utilized to monitor the status of the hydrogen
generator, and/or to control the hydrogen evolution reaction in
accordance with the existing demand for hydrogen.
B. Housing Materials
[0148] Various materials may be used in the housings of the
hydrogen generators described herein. Preferably, the housing
comprises aluminum, due to the unique combination of strength,
light weight, and relative chemical inertness. However, it will be
appreciated that the housing could also be constructed from various
other materials, including various metals (such as magnesium, tin,
titanium, and their alloys) and various metal alloys, including
steel. The housing may also comprise various polymeric materials,
including polyethylene, polypropylene, PVC, nylon, graphite, and
various glasses. If the housing comprises a metal such as aluminum,
the interior of the housing is preferably coated with a protective
layer of a suitable material, such as an epoxy resin, which is
inert to the reactants and the products and byproducts of the
hydrolysis reaction. The housing, or portions thereof, may also be
thermally insulated.
C. Hydrides, Borohydrides and Boranes
[0149] Various hydrides, or combinations of hydrides, that produce
hydrogen upon contacting water at temperatures that are desired
within the hydrogen generator may be used in the devices and
methodologies described herein. Salt-like and covalent hydrides of
light metals, especially those metals found in Groups I and II, and
even some metals found in Group III, of the Periodic Table are
useful and include, for example, hydrides of lithium, sodium,
potassium, rubidium, cesium, magnesium, beryllium, calcium,
aluminum or combinations thereof. Preferred hydrides include, for
example, borohydrides, alanates, or combinations thereof.
[0150] As shown in TABLE 1 and TABLE 2 below, the hydrides of many
of the light metals appearing in the first, second and third groups
of the periodic table contain a significant amount of hydrogen on a
weight percent basis and release their hydrogen by a hydrolysis
reaction upon the addition of water. The hydrolysis reactions that
proceed to an oxide and hydrogen (see TABLE 2) provide the highest
hydrogen yield, but may not be useful for generating hydrogen in a
lightweight hydrogen generator that operates at ambient conditions
because these reactions tend to proceed only at high temperatures.
Therefore, the most useful reactions for a lightweight hydrogen
generator that operates at ambient conditions are those reactions
that proceed to hydrogen and a hydroxide. Both the salt-like
hydrides and the covalent hydrides are useful compounds for
hydrogen production because both proceed to yield the hydroxide and
hydrogen. TABLE-US-00001 TABLE 1 Hydrogen Content of Metal Hydrides
Wt % H.sub.2 With Stoichiometric Double Stoichiometric Compound
Neat H.sub.2O H.sub.2O Salt-like Hydrides LiH 12.68 11.89 7.76 NaH
4.20 6.11 4.80 KH 2.51 4.10 3.47 RbH 1.17 2.11 1.93 CsH 0.75 1.41
1.33 MgH.sub.2 7.66 9.09 6.47 CaH.sub.2 4.79 6.71 5.16 Covalent
Hydrides LiBH.sub.4 18.51 13.95 8.59 Na BH.sub.4 10.66 10.92 7.34 K
BH.sub.4 7.47 8.96 6.40 Mg (BH.sub.4).sub.2 11.94 12.79 8.14 Ca
(BH.sub.4).sub.2 11.56 11.37 7.54 LiAlH.sub.4 10.62 10.90 7.33
NaAlH.sub.4 7.47 8.96 6.40 KAlH.sub.4 5.75 7.60 5.67
Li.sub.3AlH.sub.6 11.23 11.21 7.47 Na.sub.3AlH.sub.6 5.93 7.75
5.76
[0151] TABLE-US-00002 TABLE 2 Hydrogen Yield from the Hydrolysis of
Metal Hydrides Reaction Hydrogen Yield (wt %) Equation
Stoichiometric Double No. Water Water Reaction to Oxide LiBH.sub.4
+ 2 H.sub.2O .fwdarw. LiBO.sub.2 + 4 H.sub.2 1 13.95 8.59 2 LiH +
H.sub.2O .fwdarw. Li.sub.2O + 2 H.sub.2 2 11.89 7.76 NaBH.sub.4 + 2
H.sub.2O .fwdarw. NaBO.sub.2 + 4 H.sub.2 3 10.92 7.34 LiAlH.sub.4 +
2 H.sub.2O .fwdarw. LiAlO.sub.2 + 4 H.sub.2 4 10.90 7.33 Reaction
to Hydroxide LiBH.sub.4 + 4 H.sub.2O .fwdarw. LiB(OH).sub.4 + 4
H.sub.2 5 8.59 4.86 LiH + H.sub.2O .fwdarw. LiOH + H.sub.2 6 7.76
4.58 NaBH.sub.4 + 4 H.sub.2O .fwdarw. NaB(OH).sub.4 + 4 H.sub.2 7
7.34 4.43 LiAlH.sub.4 + 4 H.sub.2O .fwdarw. LiAl(OH).sub.4 + 4
H.sub.2 8 7.33 4.43 Reaction to Hydrate Complex LiH + 2 H.sub.2O
.fwdarw. LiOH.cndot.H.sub.2O + H.sub.2 9 4.58 2.52 2 LiAlH.sub.4 +
10 H.sub.2O .fwdarw. LiAl.sub.2(OH).sub.7.cndot.H.sub.2O +
LiOH.cndot.H.sub.2O + 8 H.sub.2 10 6.30 3.70 NaBH.sub.4 + 6
H.sub.2O .fwdarw. NaBO.sub.2.cndot.4 H.sub.2O + 4 H.sub.2 11 5.49
3.15
[0152] The salt-like hydrides, such as LiH, NaH, and MgH.sub.2, are
generally not soluble in most common solvents under near ambient
conditions. Many of these compounds are only stable as solids, and
decompose when heated, rather than melting congruently. These
compounds tend to react spontaneously with water to produce
hydrogen, and continue to react as long as there is contact between
the water and the salt-like hydride. In some cases the reaction
products may form a blocking layer that slows or stops the
reaction, but breaking up or dispersing the blocking layer or
removing it from the reaction zone immediately returns the reaction
to its initial rate as the water can again contact the unreacted
hydride. Methods for controlling the hydrogen production from the
salt-like compounds generally include controlling the rate of water
addition.
[0153] The covalent hydrides shown in TABLE 1 are comprised of a
covalently bonded hydride anion, e.g., BH.sub.4.sup.-,
AlH.sub.4.sup.-, and a simple cation, e.g., Na.sup.+, Li.sup.+.
These compounds are frequently soluble in high dielectric solvents,
although some decomposition may occur. For example, NaBH.sub.4
promptly reacts with water at neutral or acidic pH but is
kinetically quite slow at alkaline pH. When NaBH.sub.4 is added to
neutral pH water, the reaction proceeds but, because the product is
alkaline, the reaction slows to a near stop as the pH of the water
rises and a metastable solution is formed. In fact, a basic
solution of NaBH.sub.4 is stable for months at temperatures below
5.degree. C.
[0154] Some of the covalent hydrides, such as LiAlH.sub.4, react
very similarly to the salt-like hydrides and react with water in a
hydrolysis reaction as long as water remains in contact with the
hydrides. Others covalent hydrides react similarly to NaBH.sub.4
and KBH.sub.4 and only react with water to a limited extent,
forming metastable solutions. However, in the presence of
catalysts, these metastable solutions continue to react and
generate hydrogen.
[0155] Using a catalyst to drive the hydrolysis reaction of the
covalent hydrides to completion is advantageous because the weight
percent of hydrogen available in the covalent hydrides is generally
higher than that available in the salt-like hydrides, as shown in
TABLE 1. Therefore, the covalent hydrides are preferred as a
hydrogen source in some embodiments of a hydrogen generator because
of their higher hydrogen content as a weight percent of the total
mass of the generator.
[0156] The devices and methodologies described herein may use solid
chemical hydrides as the hydrogen-containing material which is
combined with water in a manner that facilitates a hydrolysis
reaction to generate hydrogen gas. Preferably, these chemical
hydrides include alkali metal borohydrides, alkali metal hydrides,
metal borohydrides, and metal hydrides, including, but not limited
to, sodium borohydride NaBH.sub.4 (sometimes designated NBH),
sodium hydride (NaH), lithium borohydride (LiBH.sub.4), lithium
hydride (LiH), calcium hydride (CaH.sub.2), calcium borohydride
(Ca(BH.sub.4).sub.2), magnesium borohydride (MgBH.sub.4), potassium
borohydride (KBH.sub.4), and aluminum borohydride
(Al(BH.sub.4).sub.3).
[0157] Another class of materials that may be useful in the devices
and methodologies described herein are chemical hydrides with
empirical formula B.sub.xN.sub.xH.sub.y and various compounds of
the general formula B.sub.xN.sub.yH.sub.z. Specific examples of
these materials include aminoboranes such as ammonia borane
(H.sub.3BNH.sub.3), diborane diammoniate,
H.sub.2B(NH.sub.3).sub.2BH.sub.4, poly-(aminoborane), borazine
(B.sub.3N.sub.3H.sub.6), morpholine borane, borane-tetrahydrofuran
complex, diborane, and the like. In some applications, hydrazine
and its derivatives may also be useful, especially in applications
where the toxicity of many hydrazine compounds is trumped by other
considerations.
[0158] Various hydrogen gas-generating formulations may be prepared
using these or other aminoboranes (or their derivatives). In some
cases, the aminoboranes may be mixed and ball milled together with
a reactive heat-generating compound, such as LiAlH.sub.4, or with a
mixture, such as NaBH.sub.4 and Fe.sub.2O.sub.3. Upon ignition, the
heat-generating compound in the mixture undergoes an exothermic
reaction, and the energy released by this reaction pyrolyzes the
aminoborane(s), thus forming boron nitride (BN) and H.sub.2 gas. A
heating wire, comprising nichrome or other suitable materials, may
be used to initiate a self-sustaining reaction within these
compositions.
[0159] In some embodiments of the devices and methodologies
described herein, salt hydrates may be utilized as the
water-generating material. The use of such materials can be
advantageous in some applications due in part to the large amounts
of thermal energy per unit weight that can be consumed by the
dehydration reaction these materials. Materials other than hydrate
salts may be used in place of, or in addition to, these materials
in the various devices and methodologies disclosed herein. For
example, materials that undergo condensation reactions (especially
dehydration condensation reactions), either by themselves or by
reacting with other materials, may be used. One example of such a
material includes materials that undergo condensation
polymerization reactions. Another example of such a material are
materials that undergo dehydration reactions, either through
intramolecular or intermolecular processes. For example, carboxylic
acids and polycarboxylic acids that undergo dehydration reactions
to form the corresponding ester, ether, or acetate, either through
an intermolecular reaction or through an intramolecular reaction,
may be utilized in some embodiments as the water-generating
material. A further advantage of this type of material is that the
dehydration product may contain no hydration states, or fewer
hydration states, than the starting material, thus increasing the
total amount of water liberated by the reaction.
[0160] A further class of materials that may be used in this
capacity include sterically hindered hydrates that exhibit
rotational isomerism. These materials are capable of undergoing
rotation about the axis of a central bond (this will frequently be
a boron carbon bond, a nitrogen-nitrogen bond, or a carbon-carbon
bond, but may occur around other bonds as well) to transition
between at least a first and second isomeric state. The material is
provided in a first state in which it is an n-hydrate material at
temperature T.sub.1. However, upon exposure to heat, it undergoes a
dehydration reaction, and also undergoes rotation about the bond to
transition to a second isomeric state in which it is a k-hydrate
material at T.sub.1, wherein n>k. This may be, for example,
because of a change in symmetry of the second state compared to the
first state, or because of the presence of hydrogen bonding or
other phenomenon which interfere with the ability of water
molecules to bind to the material (hydrogen bonding and other such
phenomenon may also be utilized advantageously to keep the material
in the second isomeric state after rotation about the axis has
occurred). As a result of this reaction, the hydrate loses water
irreversibly or semi-irreversibly.
[0161] A similar phenomenon may be used with the
hydrogen-generating material itself. That is, the
hydrogen-generating material may be designed so that, when it
undergoes the hydrogen evolution reaction, the heat evolved causes
the resulting byproduct to assume (preferably irreversibly) a
second rotational isomeric state in which it binds to a reduced
amount of water, as compared to the rotational isomers of the
byproduct. The heat adsorbed by the change in isomeric states may
serve as a further aid in controlling the overall heat generated by
the hydrogen generator. In some embodiments, rotational isomers may
be used as a heat adsorbing means, even without respect to their
possible hydration states.
[0162] In some embodiments of the devices, methodologies and
compositions described herein, steric hindrance can be utilized as
a mechanism to prevent the hydrogen-generating material from
undergoing a hydration reaction, as, for example, by occluding
binding sites for water molecules in the reaction byproduct. In
these embodiments, various substituted hydrides, borohydrides,
boranes, aminoboranes, hydrazines, and the like may be utilized as
the sterically hindered reactant, with the choice of substituents
depending in part on the stereochemistry of the system. These
materials offer the potential advantage of consuming most, if not
all, of the water present in the system in the hydrogen-generation
reaction, whether that water is present as free water molecules or
water of crystallization.
[0163] Still another class of materials useful as a source of
stored moisture are polymer hydrates. These compounds include (but
are not limited to) polycarboxylic acids, polyacrylamides, and
other polymeric materials with functional groups capable of binding
to water. Both classes of compounds can act to solidify, or gel,
large quantities of water. Unlike inorganic hydrates, these
materials lack both a crystalline structure (i.e., they are
amorphous) and a sharp melting or dehydration temperature. Both
give up their water over a broad temperature range. The use of
compounds such as these in a reactor of the type described above
can produce a gradual release of water. In some embodiments, the
rate of release may increase with any increase in temperature.
[0164] Some of these compounds, notably polyacrylimides, have
another useful feature, namely, that their affinity for water tends
to vary inversely with the ionic strength of the solution they are
in contact with. This means that a saturated polymer in contact
with a dilute ionic solution will release water into the solution
as its ion concentration increases. If a solid hydride is brought
into contact with a polymer saturated with respect to pure water,
the increase in ionic concentration in the solution brought about
by the hydrolysis reaction will cause the polymer to release
additional water.
D. Catalysts
[0165] As noted above, in some instances, a catalyst may be
required to initiate the hydrolysis reaction of the chemical
hydride with water. Useful catalysts for this purpose include one
or more of the transition metals found in Groups IB-VIII of the
Periodic Table. The catalyst may comprise one or more of the
precious metals and/or may include cobalt, nickel, tungsten carbide
or combinations thereof. Ruthenium, ruthenium chloride and
combinations thereof are preferred catalysts.
[0166] Various organic pigments may also be useful in catalyzing
the hydrolysis reaction. Some non-limiting examples of these
materials include pyranthrenedione, indanthrene Gold Orange,
ditridecyl-3,4,9,10-perylenetetracarboxylic diimide, indanthrene
black, dimethoxy violanthrone, quinacridone, 1,4-di-keto-pyrrolo
(3,4 C) pyrrole, indanthrene yellow, copper phthalocyanine,
3,4,9,10, perylenetetracarboxylic dianhydride, isoviolanthrone,
perylenetetracarboxylic diimide, and perylene diimide. These
materials, most of which are not metal based, may offer
environmental or cost advantages in certain applications.
[0167] The catalysts used in the devices and methodologies
disclosed herein may be present as powders, blacks, salts of the
active metal, oxides, mixed oxides, organometallic compounds, or
combinations of the foregoing. For those catalysts that are active
metals, oxides, mixed oxides or combinations thereof, the hydrogen
generator may further comprise a support for supporting the
catalyst on a surface thereof.
[0168] The catalyst can be incorporated into the hydrolysis
reaction in a variety of ways, including, but not limited to: (i)
mixing the catalyst with the hydrogen-containing material first,
and then adding water to the hydrogen-containing material/catalyst
mixture; (ii) mixing the catalyst with the reactant water first,
and then adding this solution/mixture to the hydrogen-containing
material; or (iii) combining the hydrogen-containing material with
water in the presence of a porous structure that is made of, or
contains, a catalyst. The hydrogen generating devices described
herein can be adapted to support one or more of these methods for
incorporating catalyst into a reactor.
[0169] Catalyst concentrations in the hydrogen-generating
compositions described herein may vary widely. For some
applications, the set catalyst concentration may range between
about 0.1 wt % to about 20 wt % active metals based on the total
amount of hydride and on the active element or elements in the
catalyst. Preferably, the set catalyst concentration may range from
between about 0.1 wt % to about 15 wt %, and more preferably,
between about 0.3 wt % to about 7 wt %.
E. Reaction Interface
[0170] Various materials may be used in the reaction interface in
the hydrogen generators described herein. Preferably, the reaction
interface is sufficiently porous to permit the egress of spent
hydrogen-containing material (e.g., sodium borate and its hydrates)
through the interface, but has sufficient strength to withstand the
pressure exerted on it by the compression mechanism within the
dispenser. The reaction interface also preferably exhibits
sufficient wicking action so that water applied to it will be
evenly distributed across its surface.
[0171] In some embodiments, this interface may contain multiple
components. For example, the interface may contain a first layer of
a porous material, such as screening or plastic or wire mesh or
foam, and a second layer of a porous wicking agent. In other
embodiments, these elements may be combined (for example, a
suitable wicking agent may be deposited on the surfaces of a wire
or plastic mesh or foam, or the mesh itself may have wicking
characteristics). Specific, non-limiting examples of foams that may
be used in the reaction interface include aluminum, nickel, copper,
titanium, silver, stainless steel, and carbon foams. The surface of
the foam may be treated to increase a hydrophilic nature of the
surface. Cellular concrete may also be used in the reaction
interface.
[0172] The temperature of the reaction interface is an important
consideration in many of the embodiments of the devices and
methodologies disclosed herein, and hence, various heating elements
and temperature monitoring or temperature control devices may be
utilized to maintain the reaction interface at a desired
temperature. For example, when sodium borohydride is utilized as
the hydrogen-containing material, the sodium borate reaction
byproduct can exist in various hydration states, and the population
of each of these states is a function of temperature. Thus, at
40.degree. C., the tetrahydrate species is the principal reaction
product, while at 60.degree. C., the dihydrate species is the
principal reaction product, and at 100.degree. C., the monohydrate
species is the principal reaction product. From a weight penalty
standpoint, it is preferable that the reaction interface be
maintained at a temperature that will favor the formation of
anhydrous or lower hydrate species, since this will require less
water to evolve a given volume of hydrogen gas. Moreover, the
resulting system will, in many cases, be less prone to the
condensation issues described herein, even if no desiccant is
employed in the hydrogen gas stream.
[0173] The use of chelating agents for the reaction byproducts may
also be useful in the devices and methodologies described herein.
For example, when sodium borohydride is used as the
hydrogen-containing material, a chelating agent may be added to the
sodium borohydride, or to the water or other liquid it is reacted
with. Such a material binds the sodium borate reaction byproduct
and, by occupying ligand sites, prevents or minimizes the formation
of hydrates, especially higher order hydrates. Hence, chelating
agents may be advantageously used in some instances to reduce the
weight penalty associated with the system. Chelating agents,
surfactants and other such materials may also be used in the
devices and methodologies described herein as solubility enhancing
agents.
F. Control Devices
[0174] As previously noted, the hydrogen generators described
herein include an inlet into the reaction chamber for the
introduction of fluid therein, and an outlet from the reaction
chamber for the evolved hydrogen and reaction byproducts to exit
the generator. Both the inlet and the outlet of the reaction
chamber may comprise various fluid control devices such as, for
example, check valves, ball valves, gate valves, globe valves,
needle valves, pumps, or combinations thereof. These control
devices may further comprise one or more pneumatic or electric
actuators and the hydrogen generator may further include a
controller in electric or pneumatic communication with one or more
of these actuators for controlling the open or closed position of
the fluid control devices. Suitable circuitry, chips, and/or
displays may also be provided for control purposes.
[0175] It will further be appreciated that various types of
thermistors and piezoelectric devices may be utilized in the
hydrogen generators described herein, both to control the manner
and conditions under which reactants are exposed to catalyst, and
to control the overall flow of fluids and gases through the
hydrogen generator. In some embodiments, these elements and/or the
hydrogen generator as a whole may be fabricated as MEMS devices
using fabrication techniques that are well known to the
semiconductor arts.
G. Antifoaming Agents
[0176] In some embodiments of the devices and methodologies
disclosed herein, an antifoaming agent is added to the water that
is introduced into the reaction chamber. The use of an antifoaming
agent may be advantageous in some applications or embodiments,
since the generation of hydrogen during the hydration reaction
frequently causes foaming. Hence, by adding an antifoaming agent to
the reactant water, the size and weight of the hydrogen generator
can be minimized, since less volume is required for disengagement
of the gas from the liquid/solids. Polyglycol anti-foaming agents
offer efficient distribution in aqueous systems and are tolerant of
the alkaline pH conditions found in hydrolyzing borohydride
solutions. Other antifoam agents may include surfactants, glycols,
polyols and other agents known to those having ordinary skill in
the art.
H. pH Adjusting Agents
[0177] Various pH adjusting agents may be used in the devices and
methodologies disclosed herein. The use of these agents is
advantageous in that the hydration reaction typically proceeds at a
faster rate at lower pHs. Hence, the addition of a suitable acid to
the fluid mix entering the reaction chamber, as by premixing the
acid into the reactant water, may accelerate the evolution of
hydrogen gas. Indeed, in some cases, the use of a suitable acid
eliminates the need for a catalyst.
[0178] Some non-limiting examples of acids that may be suitable for
this purpose include, for example, boric acid, mineral acids,
carboxylic acids, sulfonic acids and phosphoric acids. The use of
boric acid is particularly desirable in some applications, since it
aids recycling by avoiding the addition to the reaction byproduct
mixture of additional heteroatoms, as would be the case, for
example, with sulfuric acid or phosphoric acid. Moreover, boric
acid is a solid and can be readily mixed with the
hydrogen-containing material if desired; by contrast, other pH
adjusting agents must be added to the aqueous solution or other
material being reacted with the hydrogen-containing material.
[0179] In some embodiments, cation exchange resin materials may
also be used as pH adjusting agents. These materials may be added
to the hydrogen containing material in acid form and as high
surface area powders.
[0180] In other embodiments, carboxylic acids and the like may be
used as the pH adjusting agent. These materials may be advantageous
in certain applications because they frequently exist in various
hydration states, and hence provide additional water to the system.
Moreover, some carboxylic acids are capable of undergoing
condensation reactions, with the addition of heat, to evolve water.
Hence, these materials can aid both with thermal control and by
contributing water to the system.
[0181] While it may be desirable in some applications of the
systems and methodologies disclosed herein to utilize a pH
adjusting agent to lower the pH of a hydrogen-generating
composition or of a liquid medium that is to be reacted with it, in
other applications, the use of a pH adjusting agent may be utilized
to increase the pH of the hydrogen-generating composition or the
liquid medium with which it reacts. For example, while many
hydrogen-generating compositions achieve a higher rate of hydrogen
evolution at lower pHs, and while this is desirable in some
situations, in other situations, as when it is necessary to
transport the hydrogen-generating composition, a high rate of
hydrogen evolution may be disadvantageous. In these situations, a
pH adjusting agent may be utilized to render the composition more
alkaline upon exposure of the material to water or moisture, hence
making the composition less reactive and safer to handle.
[0182] Some non-limiting examples of alkaline pH adjusting agents
include, without limitation, various metal hydroxides, including
lithium hydroxide, sodium hydroxide, potassium hydroxide, RbOH,
CsOH, ammonium hydroxide, N(CH.sub.3).sub.4OH, NR.sub.4OH,
NR.sup.a.sub.xR.sup.b.sub.(4-x)OH, and
NR.sup.aR.sup.bR.sup.cR.sup.dOH compounds, wherein R.sup.a,
R.sup.b, R.sup.c and R.sup.d can each independently be hydrogen,
alkyl, or aryl groups; various metal oxides, such as Li.sub.2O,
Na.sub.2O, K.sub.2O, Rb.sub.2O, Cs.sub.2O; various organic and
metal amines; and the like.
I. Delayed Release Compositions
[0183] Various delayed-release compositions may be utilized in the
hydrogen-generating materials described herein. Such materials,
which may be utilized, for example, to control the reactivity of
the hydrogen-generating materials, include, without limitation,
slow-release coatings, micro-encapsulations, and/or
slowly-dissolving polymer carriers. For example, in some
applications, it may be desirable to render the hydrogen-generating
composition initially unreactive to water or moisture so that the
composition will be safer for handling and transportation. In one
particular type of embodiment, this may be accomplished by
providing the composition in the form of pellets, granules, or
other discrete units whose surfaces are coated with one or more
layers of a material or materials that prevent, delay or control
the reaction of the composition with moisture, water, or one or
more liquid reactants.
[0184] One particular example of a delayed release composition that
may be used with the hydrogen generating compositions described
herein is ethyl cellulose. This material is an excellent
film-forming material with strong adhesion that is insoluble in
water and that can be used to create a moisture-impermeable barrier
over the surfaces of a hydrogen-generating material. It may be used
in conjunction with plasticizers such as phthalates, phosphates,
glycerides, and esters of higher fatty acids and amides to create
films of sufficient flexibility. Ethyl cellulose may be used alone
or in combination with water soluble materials such as methyl
cellulose as a barrier to delay the reaction of hydrogen-generating
materials with water or with other liquid reactions or solutions.
Ethyl cellulose coatings may be applied by spray coating or from
solutions of appropriate solvents such as cyclohexane.
[0185] In some embodiments, ethyl cellulose based films or other
suitable materials may be used to form a protective film over
hydrogen-generating materials that render these materials safer for
shipping and handling. At the point of use, the coated
hydrogen-generating material may then be reacted with water or with
other liquid reactants or solutions in a controlled or time delayed
manner.
[0186] In some embodiments, this reaction may be facilitated
through the addition of suitable amounts of appropriate solvents
and/or surfactants to the liquid reactants or solutions that
facilitate the removal of the coating. In the case of ethyl
cellulose, for example, if the hydrogen-generating material is
being reacted with water or an aqueous solution, suitable amounts
of such solvents as ethanol, methanol, acetone, chloroform, ethyl
lactate, methyl salicylate, toluene, methylene chloride, or various
mixtures of the foregoing may be added to the water or aqueous
solution to facilitate the removal of, or the generation of
openings in, the coating, thereby allowing the hydrogen-generating
material to react. The concentration of these solvents may be
manipulated to achieve a desired rate of reaction or to permit the
onset of the reaction in a desired time frame.
[0187] Alternatively or in combination with the foregoing approach,
the coating may be formulated with a sufficient amount of a water
soluble material such as methyl cellulose to permit the
hydrogen-generating material to react at a desire to rate, or in a
desired timeframe, upon exposure to water or to the aqueous
solution. It will be appreciated that wide variations of release
rates or release patterns can be achieved by varying polymer ratios
and coating weights.
[0188] In other embodiments, a protective coating or coatings may
be applied to pellets, granules, or particles of a
hydrogen-generating material to render the material safer for
handling and transportation. At the point of use, this coating or
coatings may then be stripped with a suitable solvent prior to use
of the hydrogen-generating material. Since the total amount of
coating applied to the hydrogen-generating material may be quite
small, and since the complete removal of this coating from the
surfaces of the hydrogen-generating material may not be necessary
to render the material suitably reactive to water or to other
reagents, in many instances the amount of solvent required to
render the material suitably reactive may be quite small.
[0189] In still other embodiments, coating removal may be achieved
at the point of use through mechanical or physical means. For
example, the coated particles of the hydrogen generating material
may be subjected to mechanical stress so as to rupture the coating,
thereby exposing a portion of the underlying hydrogen-generating
material for reaction (in such embodiments, the coating may be made
sufficiently brittle so that it is frangible). This can be
achieved, for example, by grinding or abrading the particles,
subjecting the particles to pressure or sound waves, heating the
particles (e.g., so as to induce thermal stress in the coating or
to melt or soften the coating), irradiating the particles, or the
like.
[0190] In some embodiments, the hydrogen-generating composition may
be mixed with water-generating materials of the type described
herein, and the aforementioned mechanical or physical means may be
utilized to induce the evolution of water from the water-generating
material. The resulting evolution of hydrogen gas may then rupture
or cause perforations or disruptions in the coating, thereby
exposing a portion of the hydrogen-generating material for further
reaction.
[0191] In one specific embodiment, a container of the
hydrogen-containing material may be provided which is equipped with
a pull tab. When the tab is pulled, the associated mechanical
action causes the coating on a portion of the particles to be
stripped or ruptured, thereby rendering this portion of the
particles available for immediate reaction with water or another
suitable liquid medium. The remaining particles can be engineered
with a timed release profile that is suitable for the particular
application.
[0192] In other embodiments, the hydrogen-generating composition
may be provided with, or interspersed with, conductive filaments or
another suitably conductive medium that can generate localized
heating of the particles through ohmic resistance. At the point of
use, a suitable electric current can be passed through the
conductive medium to melt or rupture a portion of the coating on
some of the particles. In such embodiments, the coating may
comprise a material such as a hydrocarbon wax that has a suitably
low melting or softening temperature.
[0193] In further embodiments, multiple coatings schemes or
compositions may be utilized to produce a plurality of species of
coated hydrogen-generating materials that have different reaction
rates, or that react in different timeframes, with respect to a
given liquid reagent. For example, in one possible embodiment, a
plurality of particles species M.sub.1, . . . , M.sub.n, wherein
n.gtoreq.2, may be created that have respective coatings C.sub.1, .
. . , C.sub.n, wherein, for i=1 to n, coating C.sub.i allows a
percentage p.sub.i of the hydrogen generating material in particle
species M.sub.i to react with water or another liquid reagent
within t.sub.i minutes. The species M.sub.1, . . . , M.sub.n may
then be mixed in various relative proportions, concentrations or
weight percentages such that the resulting mixture has a desired
hydrogen generation profile as a function of time.
[0194] As noted above, in some embodiments, multiple coatings may
be utilized that have different chemical or physical properties.
For example, in some embodiments, a modified release coating may be
used as an external coating, and a stabilizing coating may be used
as an interior coating. In such embodiments, the stabilising coat
may act as a physical barrier between the hydrogen-generating
material and the modified release coating.
[0195] For example, the stabilising coat may act to slow migration
of moisture or solvent between the modified release coating and the
hydrogen-generating material. While the stabilising coat will
preferably keep the hydrogen-generating separated from the modified
release coating during storage, the stabilising coating will
preferably not interfere significantly with the rate of release or
reaction of the hydrogen-generating material, and therefore may be
semi-permeable or even soluble in water or in the liquid medium
that the hydrogen-generating material is to be reacted with. Hence,
the stabilizing coat may be utilized to keep migration of
hydrogen-generating materials to a minimum such that their
interaction with coating materials is reduced or prevented, while
still allowing for release of hydrogen-generating materials in an
aqueous environment.
[0196] The stabilizing coat may be any suitable material which
creates an inert barrier between the hydrogen-generating material
and the modified release coating, and may be water soluble, water
swellable or water permeable polymeric or monomeric materials.
Examples of such materials include, but are not limited to,
hydroxypropylmethyl cellulose, hydroxypropyl cellulose, polyvinyl
pyrrolidone, polyethylene glycol or methacrylate based polymers.
Preferably the stabilising coat includes a water-soluble polymer
that does not interfere with the release of the hydrogen-generating
material.
[0197] The modified release coating may also be any suitable
coating material, or combination of coating materials, that will
provide the desired modified release profile. For example, coatings
such as enteric coatings, semi-enteric coatings, delayed release
coatings or pulsed release coatings may be desired. In particular,
coatings may be utilized that provide an appropriate lag in release
prior to the rapid release at a rate essentially equivalent to
immediate release of the hydrogen-containing material.
[0198] In particular, materials such as hydroxypropylmethyl
cellulose phthalate of varying grades, methacrylate based polymers
and hydroxypropylmethyl cellulose acetate succinate may be utilized
in various applications. It is also possible to use a mixture of
enteric polymers to produce the modified release coating, or to use
a mixture of enteric polymer with a water permeable, water
swellable or water-soluble material. Suitable water-soluble or
water permeable materials include but are not limited to
hydroxypropylmethyl cellulose, hydroxypropyl cellulose, polyvinyl
pyrrolidone, polyethylene glycol or mixtures thereof.
[0199] Another class of delayed release coatings that may be
utilized in some embodiments of the compositions, systems and
methodologies described herein are basic materials, such as metal
hydroxides or metal or organic amines, including the materials
described herein as pH adjusting agents. In the case of
hydrogen-generating materials that react with water or aqueous
solutions, coatings of these materials on the exterior surfaces of
the hydrogen-generating materials can be used to render the
hydrogen-generating material essentially unreactive (or reactive at
a very slow rate) to moisture or to relatively small amounts of
water by rendering the effective pH at the reaction interface
(e.g., at the surface of the hydrogen-generating material)
sufficiently alkaline. On the other hand, if the amount of coating
material is sufficiently small, at the point of use, the amount of
water or liquid medium that the hydrogen-generating material is
exposed to may be sufficiently large to solvate the alkaline
material without significantly affecting the pH of the resulting
solution. So long as the coating is selected such that solvation
occurs fast enough, the presence of such a coating can be made to
have little or no effect on the reactivity of the particles of the
hydrogen-generating material at the point of use.
J. Wicking Agents
[0200] As previously noted, the hydrolysis reaction of a hydride
cannot proceed if water is unable to reach the hydride. When
pellets of some hydrides, such as LiH, react with water, a layer of
insoluble reaction products is formed that blocks further contact
of the water with the hydride. The blockage can slow down or stop
the reaction.
[0201] The devices and methodologies disclosed herein overcome this
problem by providing a means for expelling such insoluble products
from the reaction zone. However, in some cases, the addition of a
wicking agent within the pellets or granules of the hydride or
borohydride improves the water distribution through the pellet or
granule and ensures that the hydration reaction quickly proceeds to
completion. Both salt-like hydrides and covalent hydrides benefit
from an effective dispersion of water throughout the hydride.
Useful wicking materials include, for example, cellulose fibers
like paper and cotton, modified polyester materials having a
surface treatment to enhance water transport along the surface
without absorption into the fiber, and polyacrylamide, the active
component of disposable diapers. The wicking agents may be added to
the hydrogen-containing material in any effective amount,
preferably in amounts between about 0.5 wt % and about 15 wt % and
most preferably, between about 1 wt % and about 2 wt %. It should
be noted, however, that, in some applications, variations in the
quantity of wicking material added to the hydrogen-containing
material do not seem to be significant; i.e., a small amount of
wicking material is essentially as effective as a large amount of
wicking material.
[0202] In some embodiments, one or more wicking agents may be used
to create a conduit in which at least a portion of the excess water
which may be present in the hydrogen generation reaction byproducts
may be returned to another part of the hydrogen generator so that
it may be further utilized in the generation of hydrogen gas. Such
wicking agents may be disposed, for example, downstream from the
catalytic reactor, and may be in fluidic contact with a water
reservoir or with the catalytic reactor itself.
K. Liquid Reactants
[0203] While the devices and methodologies described herein have
frequently been explained in reference to the use of water as a
reactant with the hydride, borohydride, borane, or other hydrogen
containing material, it will be appreciated that various other
materials may be used in place of, or in addition to, water. For
example, various alcohols may be reacted with the
hydrogen-containing material. Of these, low molecular weight
alcohols, such as methanol, ethanol, normal and iso-propanol,
normal, iso- and secondary-butanol, ethylene glycol, propylene
glycol, butylene glycol, and mixtures thereof, are especially
preferred. The alcohols may be used either alone or as aqueous
solutions of varying concentrations. Liquid reactants containing
alcohol may be particularly useful in low temperature applications
where the liquid reactant may be subjected to freezing. Various
liquid reactants containing ammonia or other hydrogen containing
materials may also be used.
[0204] The above description of the present invention is
illustrative, and is not intended to be limiting. It will thus be
appreciated that various additions, substitutions and modifications
may be made to the above described embodiments without departing
from the scope of the present invention. Accordingly, the scope of
the present invention should be construed in reference to the
appended claims.
* * * * *