U.S. patent application number 10/845971 was filed with the patent office on 2009-12-31 for hydrogen generator.
Invention is credited to Alan Cisar, Eric Clarke, Brad Fiebig, Oliver J. Murphy, Carlos Salinas.
Application Number | 20090324452 10/845971 |
Document ID | / |
Family ID | 34061901 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090324452 |
Kind Code |
A1 |
Salinas; Carlos ; et
al. |
December 31, 2009 |
HYDROGEN GENERATOR
Abstract
An apparatus and method apply water to a hydrogen-containing
composition, such as a hydride, in the presence of a catalyst that
promotes hydrolysis to generate hydrogen in a controlled manner.
The amount of catalyst used can be carefully tailored so that the
reaction rate is limited by the amount of catalyst present (passive
control) or it can be sufficiently large so that the reaction is
controlled by the rate of water addition (active control).
Inventors: |
Salinas; Carlos; (Bryan,
TX) ; Cisar; Alan; (Cypress, TX) ; Clarke;
Eric; (College Station, TX) ; Murphy; Oliver J.;
(Bryan, TX) ; Fiebig; Brad; (Seguin, TX) |
Correspondence
Address: |
FORTKORT & HOUSTON P.C.
9442 N. CAPITAL OF TEXAS HIGHWAY, ARBORETUM PLAZA ONE, SUITE 500
AUSTIN
TX
78759
US
|
Family ID: |
34061901 |
Appl. No.: |
10/845971 |
Filed: |
May 14, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60470319 |
May 14, 2003 |
|
|
|
Current U.S.
Class: |
422/162 ;
422/211 |
Current CPC
Class: |
B01J 4/02 20130101; Y02E
60/36 20130101; B01J 4/001 20130101; C01B 3/065 20130101; Y02E
60/362 20130101 |
Class at
Publication: |
422/162 ;
422/211 |
International
Class: |
B01J 8/00 20060101
B01J008/00; C01B 6/00 20060101 C01B006/00 |
Goverment Interests
[0002] This invention was made with Government support under
DAAH01-00-C-R178 awarded by the U.S. Army Aviation and Missile
Command. The Government has certain rights in this invention.
Claims
1. A hydrogen generator, comprising: a reaction chamber for
containing a hydrogen-containing composition comprising a hydride
and a catalyst, the hydrogen-containing composition having a set
catalyst concentration to provide an expected rate of hydrogen gas
generation upon adding an aqueous solution into the reaction
chamber; wherein the set catalyst concentration is between about
0.1 wt % and about 15 wt % active element or elements of the
catalyst, based on the total amount of hydrogen-containing
composition and the active element or elements in the catalyst.
2. The hydrogen generator of claim 1, further comprising: means
coupled to an inlet port of the reaction chamber for adding the
aqueous solution all at once into the reaction chamber.
3. The hydrogen generator of claim 2, wherein the means for adding
the aqueous solution is detachably coupled to the inlet port.
4. The hydrogen generator of claim 2, wherein the inlet port
comprises a first fluid control device for controlling flow through
the inlet port.
5. The hydrogen generator of claim 1, further comprising: an outlet
port of the reaction chamber.
6. The hydrogen generator of claim 5, wherein the outlet port
comprises a second fluid control device for controlling flow
through the outlet port.
7. The hydrogen generator of claim 1, wherein the hydride is of a
light metal selected from lithium, sodium, potassium, rubidium,
cesium, magnesium, beryllium, calcium, aluminum or combinations
thereof.
8. The hydrogen generator of claim 1, wherein the hydride comprises
one or more covalent hydrides.
9. The hydrogen generator of claim 8, wherein the covalent hydride
is a borohydride, an alanate, or combinations thereof.
10. The hydrogen generator of claim 1, wherein the catalyst
comprises one or more precious metals.
11. The hydrogen generator of claim 1, wherein the catalyst
comprises ruthenium.
12. The hydrogen generator of claim 1, wherein the catalyst is
ruthenium, ruthenium chloride, or combinations thereof.
13. The hydrogen generator of claim 1, wherein the catalyst is
cobalt, nickel, tungsten carbide or combinations thereof.
14. The hydrogen generator of claim 1, wherein the catalyst
comprises one or more transition metals.
15. The hydrogen generator of claim 1, wherein the catalyst form is
selected from powders, blacks, salts of the active metal, oxides,
mixed oxides, organometallic compounds or combinations thereof.
16. The hydrogen generator of claim 1, wherein the catalyst is in a
form of an active metal, an oxide, mixed oxides or combinations
thereof, the hydrogen generator further comprises a support for
supporting the catalyst on a surface of the support.
17. (canceled)
18. The hydrogen generator of claim 1, wherein the set catalyst
concentration is between about 0.3 wt % and about 7 wt % active
element or elements of the catalyst, based on the total amount of
hydrogen-containing composition and the active element or elements
in the catalyst.
19. The hydrogen generator of claim 1, wherein the
hydrogen-containing composition is in a form of one or more
pellets.
20. The hydrogen generator of claim 1, wherein the
hydrogen-containing composition is pellets, granules, powder,
tablets or combinations thereof.
21. The hydrogen generator of claim 1, wherein the
hydrogen-containing composition further comprises a wicking
agent.
22. The hydrogen generator of claim 21, wherein the wicking agent
comprises a hydrophilic organic material.
23. The hydrogen generator of claim 21, wherein the wicking agent
is selected from cellulose fibers, polyester, polyacrylamide or
combinations thereof.
24. The hydrogen generator of claim 21, wherein the
hydrogen-containing composition comprises at least 0.5 wt % wicking
agent.
25. The hydrogen generator of claim 1, wherein the aqueous solution
comprises at least 51% water.
26. The hydrogen generator of claim 25, wherein the aqueous
solution further comprises an antifoam agent.
27. The hydrogen generator of claim 26, wherein the antifoam agent
is a surfactant, a glycol, a polyol or combinations thereof.
28. The hydrogen generator of claim 25, wherein the aqueous
solution further comprises an acid.
29. The hydrogen generator of claim 28, wherein the acid is
selected from mineral acids, carboxylic acids, sulfonic acids,
phosphoric acids or combinations thereof.
30. The hydrogen generator of claim 6, wherein the second fluid
control device is a check valve, a ball valve, a gate valve, a
globe valve, a needle valve or combinations thereof.
31. The hydrogen generator of claim 30, wherein the second fluid
control device further comprises one or more actuators, the
hydrogen generator further comprising a controller in communication
with the one or more actuators via electronic or pneumatic
means.
32. The hydrogen generator of claim 4, wherein the first fluid
control device is a check valve, a ball valve, a gate valve, a
globe valve, a needle valve or combinations thereof.
33. The hydrogen generator of claim 32, wherein the first fluid
control device further comprises one or more actuators, the
hydrogen generator further comprising a controller in communication
with the one or more actuators via electronic or pneumatic
means.
34. The hydrogen generator of claim 5, further comprising: a fluid
separation device for removing liquid from generated hydrogen gas,
wherein the hydrogen gas flows through the fluid separation device
to the outlet port.
35. The hydrogen generator of claim 1, wherein the
hydrogen-containing composition is supported by a porous
substrate.
36. The hydrogen generator of claim 35, wherein the porous
substrate is a foam.
37. The hydrogen generator of claim 36, wherein the foam is
metal.
38. The hydrogen generator of claim 36, wherein the foam is of a
material selected from aluminum, nickel, copper, titanium, silver,
stainless steel or carbon.
39. The hydrogen generator of claim 1, wherein a surface of the
substrate is treated to increase a hydrophilic nature of the
surface.
40. The hydrogen generator of claim 35, wherein pores of the porous
substrate contain the hydrogen-containing composition.
41. The hydrogen generator of claim 35, wherein the porous
substrate is a metal.
42-147. (canceled)
148. The hydrogen generator of claim 1, wherein said hydrogen
generator is a passively controlled hydrogen generator.
149. (canceled)
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/470,319, filed May 14, 2003.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates generally to the generation of
hydrogen gas, such as for use in a fuel cell.
[0005] 2. Background of the Related Art
[0006] A fuel cell is an energy conversion device that efficiently
converts the stored chemical energy of a fuel into electrical
energy. A proton exchange membrane (PEM) fuel cell is a particular
type of fuel cell that generates electricity through two
electrochemical reactions that occur at the proton exchange
membrane/catalyst interfaces at relatively low temperatures
(typically<80.degree. C.). A necessary step in the operation of
such fuel cells is the electrochemical oxidation of a fuel,
typically hydrogen gas, to produce water. Therefore, finding a
convenient source of hydrogen is necessary for the operation of a
fuel cell.
[0007] The hydrides of some of the lighter metallic elements have
been considered as a source of hydrogen for a fuel cell because
they possess high concentrations of hydrogen that can be released
by hydrolysis. Table 1 lists a number of hydrides of elements from
the first and second groups of the periodic table that are useful
for hydrogen generation, although the list is not meant to be
exhaustive of all hydrides suitable for use in a hydrogen
generator. The hydrides in Table 1 are divided into groups of
salt-like hydrides and covalent hydrides. Table 1 provides the
hydrogen content of each of the neat compounds as well as the
hydrogen content of each of the compounds with sufficient water to
hydrolyze the neat compound to hydrogen and oxide products, and
with sufficient water to hydrolyze the neat compound to hydrogen
and hydroxide products.
TABLE-US-00001 TABLE 1 Hydrogen Content of Metal Hydrides Wt %
H.sub.2 With Double Compound Neat Stoichiometric H.sub.2O
Stoichiometric 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
[0008] The hydrides of the salt-like group continue to react and
generate water as long as water is present. In some cases, the
reaction products may form a "blocking layer" that slows or stops
the reaction by blocking access of the water to the hydride.
However, by breaking up or dispersing the blocking layer, the water
can again contact the hydride and the reaction immediately returns
to its initial rate. By contrast, some of the covalent hydrides
react with water only to a limited extent, forming metastable
solutions. Fortunately, the decomposition of these hydrides can be
accelerated with catalysts so that, in the presence of catalysts,
these covalent hydrides react similarly to the salt-like
hydrides.
[0009] Some examples of hydrolysis reactions of light metal
hydrides are shown in Table 2. The hydrogen yields shown in Table 2
are based upon the total mass of the hydrides and the water
required for hydrolysis but do not take into account the mass of
the hydrogen generator container. When considering the hydrogen
yield from a complete hydrogen generator system, the mass of the
container must also be taken into account. However, the container
for a hydrogen generator that operates at low pressure can be quite
light and therefore, the yields from a light weight hydrogen
generator may approach the yields shown in Table 2. Table 2
provides the hydrogen yield for the stoichiometric amounts of
reactants and the hydrogen yield from the reaction with twice the
stoichiometric amount of water supplied.
[0010] The reactions shown in Table 2 include two or three
hydrolysis possibilities for each of four metal hydrides. The first
set of reactions show the ideal case, where the product is hydrogen
and a metal oxide (e.g., MBO.sub.2). These reactions generally
occur only at elevated temperatures. The second set of reactions
show the reaction producing a metal hydroxide (e.g., MB(OH).sub.4)
although extra water beyond the amount listed in the first column
is generally required to achieve complete hydrolysis, even to the
hydroxide. The third set of reactions show the expected result from
the hydrolysis of these compounds to the stable hydroxide hydrates
as the products. The hydroxide hydrate is often the
thermodynamically favored product. The effect of this
thermodynamics is readily apparent from the comparison, for
example, of Equation 10 with Equation 4. (See Table 2).
TABLE-US-00002 TABLE 2 Hydrogen Yield from the Hydrolysis of Metal
Hydrides Hydrogen Yield Reaction (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 + 10 6.30
3.70 LiOH.cndot.H.sub.2O + 8 H.sub.2 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
[0011] Each of the reactions shown in Table 2 has both advantages
and disadvantages as a source of hydrogen. The hydrolysis of
lithium borohydride (LiBH.sub.4) to an oxide, as shown in Equation
1, produces the highest yield of hydrogen of any of the reactions
shown, but only proceeds at high temperature. The hydrolysis of
NaBH.sub.4 produces nearly as much hydrogen (Equation 3), but uses
a less costly starting material. At lower temperature, the
hydrolysis reaction of NaBH.sub.4 as shown in Equation 7 dominates,
but one of the reaction products, NaB(OH).sub.4, is very basic.
Since the BH.sub.4.sup.- ion is normally stable towards hydrolysis
at high pH, the rate of hydrolysis and the resultant hydrogen
generation is reduced by several orders of magnitude in a high pH
system.
[0012] However, in U.S. Pat. No. 6,534,033 and U.S. Patent
Application Pub. No. US 2003/0009942, Amendola, et al. disclosed
that a ruthenium catalyst catalyzes the decomposition of
BH.sub.4.sup.- to hydrogen and borate even in a high pH system
having added NaOH. Amendola disclosed that an aqueous solution of
NaBH.sub.4 pumped over a catalyst bed produced a controlled
hydrogen gas flow. The disclosed catalyst was 5% Ru on an
unspecified ion exchange resin. The generation of gas was stopped
by stopping the flow of the aqueous solution and restarted by
restoring the flow.
[0013] In U.S. Patent Application Publication No. 2003/0014917,
Rusta-Sallehy, et al. disclosed a system to generate hydrogen by
using a chemical hydride in solution and contacting the solution
with a catalyst to generate hydrogen. The disclosed process
required that the borohydride be present as a solution and also
required a pump. Both Rusta-Sallehy and Amendola disclosed systems
that used sodium borohydride solutions to generate hydrogen but
both have several significant limitations. The solutions required a
substantial excess of vater that decreased the mass yield of
hydrogen. The processes also required pumps, which add to the
weight and complexity of the systems. In addition, the aqueous
solution is not completely stable. Even under basic conditions, the
borohydride gradually hydrolyzes, thereby limiting the shelf-life
of the chemical hydride solution.
[0014] The hydrolysis of lithium hydride (LiH) also has a high
yield if it proceeds to completion as shown in Table 2, but the
stability of lithium hydroxide hydrate makes it the stable end
product, with a lower hydrogen yield, as shown in Equation 9. As
reported in Proc. 39.sup.th Power Sources Conf., 184-187 (2000),
Breault and Rolfe have shown that when this reaction is carried out
in a water starved mode, the reaction proceeds to a mixture of
Li.sub.2O and LiOH, with a hydrogen yield of over 8 wt %. However,
this water-starved condition was achieved by injecting water
throughout the mass of hydride in a slow, controlled manner using a
complex mechanical control system, thereby substantially reducing
the wt % yield of hydrogen from the generator system.
[0015] Storing sodium borohydride as a solution for use as a
hydrogen source has been disclosed by Tsang in U.S. Patent
Application Pub. 2003/0228505. Tsang disclosed metering an aqueous
sodium borohydride solution over a ruthenium supported catalyst to
generate hydrogen. To overcome the limitations of both reactivity
and stability, Tsang disclosed storing the sodium borohydride prior
to use in a solution having 5-40 wt % alkali hydroxide or alkaline
metal hydroxide. At these very high pH levels, Tsang disclosed that
sodium borohydride may be stored in solution for at least 6 to 12
months since the high pH renders the borohydride essentially
non-reactive even in the presence of catalyst.
[0016] Tsang further disclosed mixing the high pH solution with
water just before passing the solution over the supported catalyst
in the hydrogen generator. Mixing with water brought the
concentration of the high pH borohydride solution into the
"reactive" range, which Tsang disclosed is less than about 10 wt %
strong base. While Tsang disclosed the desirability of having high
concentrations of borohydride in the solution passing over the
supported catalyst, the final mixed solution was disclosed as being
between 5 and 15 wt %. Tsang noted that the maximum solubility of
sodium borohydride in water at room temperature is about 55 wt %.
Tsang further disclosed that the best mode practice was to meter
the two solutions with two different pumps and mix the solutions
just upstream of the supported catalyst. The system and methods
disclosed by Tsang do not address or solve the problems of making a
light weight hydrogen generator because the two required pumps and
the hydroxide necessary for storing the borohydride solution add
significant weight to the disclosed hydrogen generator.
[0017] Weight is a characteristic of electrochemical cells
generally, and fuel cells in particular, that limit their use.
Therefore, significant efforts have been directed at providing
lightweight components for electrochemical cells and
electrochemical cell systems, such as fuel cell systems.
Accordingly, there is a need for a lightweight generator of
hydrogen gas for fueling fuel cells. It would be desirable to
provide a hydrogen generator that is lightweight and portable, and
adaptable for a variety of uses, including but not limited to PEM
fuel cells. It would be further desirable to provide a hydrogen
generator and related method that efficiently produces high quality
hydrogen gas. It would be further desirable to have a hydrogen
generator that can be accurately and easily controlled.
SUMMARY OF THE INVENTION
[0018] The present invention provides hydrogen generators and
methods for controlling hydrogen generation. The present invention
further provides compositions for storing hydrogen for later
release and methods of making the blended composition. The rate of
hydrogen generation may be actively controlled by varying the rate
that water is added to the hydrogen-containing composition or
passively controlled by modifying the hydrogen-containing
composition so that an expected hydrogen generation rate is
initiated upon adding all the water at one time.
[0019] One embodiment of a passively controlled hydrogen generator
comprises a reaction chamber for containing a hydrogen-containing
composition comprising a hydride and a catalyst. The
hydrogen-containing composition has a set catalyst concentration to
provide the expected or set rate of hydrogen gas generation desired
upon adding an aqueous solution into the reaction chamber. Means
are coupled, preferably detachably coupled, to an inlet port of the
reaction chamber for adding the aqueous solution all at once into
the reaction chamber.
[0020] The passively controlled hydrogen generator includes an
outlet port from the reaction chamber for produced hydrogen to exit
the generator. Both the inlet port and the outlet port of the
reaction chamber may comprise fluid control devices such as, for
example, a check valve, a ball valve, a gate valve, a globe valve,
a needle valve 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.
[0021] Generally, any hydride or combinations of hydrides that
produce hydrogen upon contacting water at temperatures that are
desired within the hydrogen generator are useful for the present
invention. Salt-like and covalent hydrides of light metals,
especially those metals found in Groups I and II and even 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.
[0022] Useful catalysts for the hydrogen-containing composition
include one of 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 is a preferred catalyst. The
catalyst form may be selected from powders, blacks, salts of the
active metal, oxides, mixed oxides, organometallic compounds or
combinations thereof. For those catalysts having a form of an
active metal, an oxide, mixed oxides or combinations thereof, the
hydrogen generator may further comprise a support for supporting
the catalyst on a surface of the support.
[0023] Catalyst concentrations in the hydrogen-containing
composition may range widely. For some applications, the set
catalyst concentration may range between about 0.1 wt % and about
20 wt % active metals based on the total amount of hydride and the
active element or elements in the catalyst. Preferably the set
catalyst concentration may range from between about 0.1 wt % and
about 15 wt % and more preferably, between about 0.3 wt % and about
7 wt %.
[0024] The hydrogen-containing composition may take the form of one
or more pellets or the form of pellets, granules, powder, tablets
or combinations thereof. The hydrogen-containing compositions may
further comprise a wicking agent such as a hydrophilic organic
material. The wicking agent may further be selected from cellulose
fibers, polyester, polyacrylamide or combinations thereof. The
hydrogen-containing composition may comprise at least 0.5 wt %
wicking agent.
[0025] The aqueous solution comprises at least 51% water. The
aqueous solution may further comprise an antifoam agent such as a
surfactant, a glycol, a polyol or combinations thereof and may
further comprise an acid, such as mineral acids, carboxylic acids,
sulfonic acids, phosphoric acids or combinations thereof. Even
though an antifoam agent may be a component of the aqueous
solution, the hydrogen generator may further comprise a fluid
separation device for removing liquid from generated hydrogen gas,
wherein the hydrogen gas flows through the fluid separation device
to the outlet port.
[0026] In some embodiments, the hydrogen-containing composition is
supported on a porous substrate, such as a foam. The foam may be
metal such as, for example, aluminum, nickel, copper, titanium,
silver, or stainless steel or may also be made of carbon. The
surface of the substrate may be treated to increase a hydrophilic
nature of the surface and further, pores of the porous substrate
may be used to hold the hydrogen-containing composition.
[0027] In another embodiment of a passively controlled hydrogen
generator, the hydrogen generator comprises a reaction chamber for
containing a porous substrate, wherein the porous substrate
supports a mixture comprising a hydride and a catalyst, the mixture
having a set catalyst concentration to provide an expected rate of
hydrogen gas generation upon adding an aqueous solution into the
reaction chamber. Preferred hydrides include those of a light metal
selected from lithium, sodium, potassium, rubidium, cesium,
magnesium, beryllium, calcium, aluminum or combinations thereof.
Any of the hydrides and catalysts discussed above are suitable for
use with a porous substrate in a passively controlled hydrogen
generator.
[0028] The porous substrate may be made of a metal or of carbon. A
preferred porous substrate is a foam made, for example, of
aluminum, nickel, copper, titanium, silver, stainless steel or
carbon. The surface of the substrate may be treated to increase a
hydrophilic nature of the surface. At least a portion of the
catalyst may be blended with the hydride and placed in the pores of
the porous substrate. Furthermore, at least a portion of the
catalyst may be applied to a surface of the porous substrate. Any
catalyst applied to the surface of the porous substrate contributes
to the overall mixture of catalyst and hydride.
[0029] Another embodiment of the present invention includes an
actively controlled hydrogen generator comprising a reaction
chamber for holding a hydrogen-containing composition comprising a
hydride and a reservoir comprising an outlet port in fluid
communication with a reaction chamber inlet. The hydrogen generator
further comprises means for adjusting a flow rate of an aqueous
solution from the reservoir into the reaction chamber to control a
hydrogen gas generation rate. In addition to the inlet port, the
reaction chamber further comprises an outlet port for the produced
hydrogen to exit the hydrogen generator.
[0030] The outlet port and the inlet port may further comprise a
first and a second fluid control device for controlling flow
through the outlet and inlet ports respectively. These fluid
control devices may be a check valve, a gate valve, a ball valve, a
needle valve, or combinations thereof. Furthermore, the fluid
control devices may include one or more actuators and the hydrogen
generator may further comprise a controller in communication with
the one or more actuators via electric or pneumatic means.
[0031] Generally, any hydride or combinations of hydrides that
produce hydrogen upon contacting water at temperatures that are
desired within the hydrogen generator are useful for the present
invention. Salt-like and covalent hydrides of light metals,
especially those metals found in Groups I and II and even 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. The hydride may be either a salt-like hydride
or a covalent hydride or combinations thereof.
[0032] The hydrogen-containing composition may further comprise a
catalyst that may be blended or otherwise mixed with the hydride.
The catalyst may be one or more transition metals. Catalysts
suitable for the passively controlled hydrogen generator discussed
above, both in type and form, are useful for the actively
controlled embodiments of the present invention. The catalyst
concentration in the hydrogen-containing composition may range
between about 5 wt % and about 20 wt % active element or elements
of the catalyst and preferably, between about 6 wt % and about 12
wt % active element or elements of the catalyst. Wicking agents may
be added to the hydrogen-containing composition as discussed above.
The aqueous solution suitable for the passively controlled hydrogen
generator is equally useful for the actively controlled hydrogen
generator. Furthermore, the porous substrate suitable for
supporting the hydrogen-containing composition of the passively
controlled hydrogen generator is suitable for use with the actively
controlled hydrogen generator.
[0033] The actively controlled hydrogen generator may further
comprise a fluid separation device for removing liquid from
generated hydrogen gas, wherein the hydrogen gas flows through the
fluid separation device to the outlet port.
[0034] In one embodiment, the means for adjusting a flow rate of
the aqueous solution into the reaction chamber comprises a plunger
slideably disposed within the reservoir for pressurizing the
aqueous solution and may further comprise a gas source in fluid
communication with a gas side of the plunger. The gas source may be
an electrolyzer in fluid communication with the gas side of the
plunger. A controller may be utilized for adjusting an electrical
current flowing from a power source to the electrolyzer in response
to a hydrogen generation demand.
[0035] The hydrogen generator may further comprise a water chamber
for containing the aqueous solution reservoir which may be, for
example, an inflatable bladder. The means for adjusting a flow rate
of the aqueous solution may then comprise a gas source in fluid
communication with an interior of the water chamber. The gas source
may be an electrolyzer for controllably generating the gas for
delivery to the interior of the water chamber. The means for
adjusting a flow rate of the aqueous solution may further comprise
a controller for adjusting an electrical current flowing from a
power source to the electrolyzer. The electrolyzer may obtain
electrolyzer water either from the interior of the water chamber or
the interior of the inflatable bladder.
[0036] The present invention further comprises a method for a
hydrogen-containing composition, comprising dissolving a hydride
and a catalyst in a solvent, evaporating the solvent, and
recovering the hydrogen-containing composition as a solid. The
hydride may be a covalent hydride. The covalent hydride maybe of a
light metal selected, for example, from lithium, sodium, potassium,
rubidium, cesium, magnesium, beryllium, calcium, aluminum or
combinations thereof. Preferred hydrides include a borohydride, an
alanate, or combinations thereof.
[0037] The catalyst may be one or more transition metals, such as
one or more precious metals or ruthenium, ruthenium chloride or
combinations thereof. Preferred catalysts include cobalt
acetylacetonate, nickel acetylacetonate, ruthenium acetylacetonate,
platinum acetylacetonate or combinations thereof because of their
solubility in an organic solvent.
[0038] The solvent is non-reactive with the hydride and is
typically organic. Preferable solvents include, for example,
tetrahydrofuran, ethylene glycol ethers, anhydrous ammonia,
substituted amines, pyridine or combinations thereof.
[0039] Another method for a hydrogen-containing composition of the
present invention includes dissolving a hydride in a solvent to
form a solution, suspending a catalyst throughout the solution,
evaporating the solvent, and recovering the hydrogen-containing
composition as a solid. Preferably, the catalyst is in a form of a
powder. The hydride may be a covalent hydride and is typically
selected from hydrides of light metal selected from lithium,
sodium, potassium, rubidium, cesium, magnesium, beryllium, calcium,
aluminum or combinations thereof.
[0040] The catalyst may be selected from one or more transition
metals. Preferred catalysts include ruthenium, ruthenium chloride,
or combinations thereof. Preferred solvents include, for example,
tetrahydrofuran, ethylene glycol ethers, anhydrous ammonia,
substituted amines, pyridine or combinations thereof.
[0041] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of a preferred embodiment of the invention, as
illustrated in the accompanying drawings wherein like reference
numbers represent like parts of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] So that the above recited features and advantages of the
present invention can be understood in detail, a more particular
description of the invention, briefly summarized above, may be had
by reference to the embodiments thereof that are illustrated in the
appended drawings. It is to be noted, however, that the appended
drawings illustrate only typical embodiments of this invention and
are therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0043] FIG. 1 is a schematic of a passively controlled hydrogen
generator.
[0044] FIG. 2 is a cross-sectional view of an actively controlled
hydrogen generator.
[0045] FIG. 3 is a cross-sectional view of an actively controlled
hydrogen generator having an electrolyzer mounted on a bladder.
[0046] FIG. 4 is a schematic drawing of a hydrogen generator
utilizing a hydrogen-fed electrochemical liquid pump.
[0047] FIGS. 5A-B are drawings of a bottom view and a
cross-sectional view of a hydrogen generator.
[0048] FIG. 6 is a cross-sectional view of a containment system for
a hydrogen generator.
[0049] FIG. 7 is a schematic of an apparatus for quantitatively
measuring the rate of hydrolysis of catalyzed hydride
compositions.
[0050] FIG. 8 is a graph of the rate of hydrogen evolution for
NiCl.sub.2 catalyzed NaBH.sub.4 pellets as a function of catalyst
content.
[0051] FIG. 9 is a graph indicating the hydrolysis rate of mixed
lithium and sodium borohydride pellets (total salt=103.1 mmol)
containing 2.60 wt % Ru on Alumina.
[0052] FIG. 10 is a graph indicating hydrolysis rates for mixtures
of LiBH.sub.4 and NaBH.sub.4 pellets containing different
concentrations of Ru on Alumina in 5/8 inch tube.
[0053] FIG. 11 is a graph indicating the influence of 50 ppm
"C-2245" antifoam Agent (New London) on the hydrolysis of 25 mole %
LiBH.sub.4 and 75 mole % NaBH.sub.4.
[0054] FIG. 12 is a graph indicating the reproducibility of
hydrolysis rates obtained for 5.14 wt % Ru on Alumina in 82 mmol
borohydride (2.839 g) present as 20 mole % LiBH.sub.4 and 80 mole %
NaBH.sub.4.
[0055] FIG. 13 is a graph indicating the variation in the rate of
hydrogen evolution with catalyst content (Ru on Alumina) for 113.4
mmol borohydride (3.926 g) as 20 mole % LiBH.sub.4 and 80 mole %
NaBH.sub.4.
[0056] FIG. 14 is a graph indicating the hydrogen evolution rate
with continuous drop-wise addition of 50 ppm C-2245 antifoam
solution using a syringe pump (20.3 mL solution/hour) to deliver it
to 161 mmol of sodium borohydride in the form of pellets, crushed
granules, or free powder.
[0057] FIG. 15 is a graph indicating the reproducibility of five
hydrolysis runs for 178 mmol sodium borohydride (6.733 g) with 8.17
wt % ruthenium chloride (550 mg) and for delivery of antifoam
solution at 0.374 mL/min for 60 min at an ambient temperature of
21.degree. C. and 5 wt % wicking material.
[0058] FIG. 16 is a graph indicating the reproducibility of five
hydrolysis runs for 178 mmol sodium borohydride at 15.degree.
C.
[0059] FIG. 17 is a graph indicating the reproducibility of
hydrogen gas generation using a polyetherimide (PEI) packet
generator.
[0060] FIG. 18 is a graph demonstrating that the rate of hydrogen
generation can be prolonged by reducing the rate of delivery for
the aqueous hydrolysis solution after an initial reaction
initiation period.
[0061] FIG. 19 is a graph indicating the temperature dependence for
averaged rates of hydrolysis for 178 mmol sodium borohydride with
8.17 wt % ruthenium chloride catalyst.
[0062] FIG. 20 is a graph demonstrating that frequent changes in
the rate of addition of the antifoam solution result in rapid
responses of hydrogen generation rate when the solution is combined
with borohydride pellets.
DETAILED DESCRIPTION
[0063] The present invention provides a hydrogen generator and
methods for controlling hydrogen generation. The present invention
further provides compositions for storing hydrogen for later
release and methods of making the blended composition. The rate of
hydrogen generation may be controlled by either varying the rate
that water is added to the composition or by modifying the
composition so that an expected hydrogen generation rate is
initiated upon adding all the water at one time.
[0064] As shown in Table 1 and Table 2 above, 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 are not useful for generating hydrogen in a
lightweight hydrogen generator that operates at ambient conditions
because these reactions 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.
[0065] The salt-like hydrides, e.g., LiH, NaH, MgH.sub.2, are
generally not soluble in any normal molecular solvent under near
ambient conditions and many are only stable as solids, decomposing
when heated rather than melting congruently. These compounds 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 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.
[0066] 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.
[0067] 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.
[0068] Using a catalyst to drive the hydration reaction of the
covalent hydrides to completion by forming hydrates and hydrogen is
advantageous because the weight percent of hydrogen available in
the covalent hydrates 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.
[0069] Generally, any hydride or combinations of hydrides that
produce hydrogen upon contacting water at temperatures that are
desired within the hydrogen generator are useful for the present
invention. Salt-like and covalent hydrides of light metals are
useful and include, for example, hydrides of lithium, sodium,
potassium, rubidium, cesium, magnesium, beryllium, calcium,
aluminum or combinations thereof.
[0070] Examples of catalysts that are useful for the decomposition
of covalent hydrides such as borohydrides include precious metals
such as ruthenium, platinum, palladium, gold, silver, iridium,
rhodium and osmium. Other transition metals are also useful
catalysts, such as cobalt and nickel, and one or more of the
transition metals (Groups IB-VIII of the Periodic Table) may be
selected as a useful catalyst. Examples of other useful catalysts
include metallic compounds such as tungsten carbide. All of these
examples of catalytic materials are useful in a variety of forms,
including powders, blacks, salts of the active metal, oxides, mixed
oxides, compounds formed by chelation, organometallic compounds,
supported metals, and supported oxides. Supported catalysts include
those having an active metal that is supported on the surface of an
inactive or slightly active support, such as Al.sub.2O.sub.3,
carbon, SiO.sub.2, etc. Catalysts may also be used in the form of a
solid solution with an expensive active metal diluted with a less
expensive but inactive one. Whether blended with a hydride or
applied to the surface of a substrate, all of these forms of
catalyst are useful in accordance with the present invention.
[0071] As shown above in Table 2, the hydrolysis reaction of the
borohydride ion may proceed to the hydroxide or to complex
hydrates. The hydrate NaBO.sub.2.2H.sub.2O is the stable form of
sodium borate above 54.degree. C., but below this temperature, the
stable form is the tetrahydride, NaBO.sub.2.4H.sub.2O. The sodium
borate produced by the reaction is basic, so in the absence of a
catalyst the reaction is self-limiting.
[0072] Ruthenium is an effective catalyst for the hydrolysis of
BH.sub.4.sup.-, most likely in a reduced form as shown in equation
12:
Ru(OH).sub.3+ 3/2H.sub.2.fwdarw.Ru.sup.0+3H.sub.2O (12)
While not limiting the invention, the active form of ruthenium in
the hydrolysis reaction is most likely the reduced form because the
use of reduced ruthenium produces an immediate and vigorous
reaction, with no further increase in rate. However, catalysts
containing oxidized ruthenium species, such as ruthenium chloride,
show an initial reaction that accelerates with time. The
acceleration occurs as the ruthenium chloride is reduced, thereby
providing the reduced ruthenium as a catalyst for the reaction.
[0073] The present invention provides methods for forming
hydrogen-containing compositions comprising at least one hydride
and further comprising catalyst. The catalyst may be mixed with one
or more hydrides for use in hydrogen generators. Preferably the
hydrides and catalyst form a blend. A blend is a mixture of
components that are thoroughly mixed and intermingled. One method
of forming a blend of the catalyst and hydride includes grinding
the hydride together with the catalyst to form granules or a fine
powder. The blend may be packaged for use as granules or a powder
or alternatively, the powder may be pressed into pellets, tablets,
or granules. Mixtures in any form are, however, also suitable for
use in a hydrogen generator.
[0074] Another method for producing a catalyst-hydride blend
includes dissolving the catalyst and the hydride in a solvent to
produce a solution and then evaporating the solvent to produce the
catalyst-hydride blend. Examples of hydrides that may be used in
this method include, but are not limited to, sodium borohydride,
potassium borohydride, lithium borohydride and combinations
thereof. Blended hydride compositions have properties that are a
combination of the properties of the two pure materials. For
example, lithium borohydride (LiBH.sub.4) has a formula weight that
is 42% less than that of NaBH.sub.4 but produces the same volume of
hydrogen per mole of reactant. Even when the amount of water
required to stoichiometrically hydrolyze it to LiB(OH).sub.4 is
included, the combined mass is nearly 14% less. This weight
advantage can be realized in a lightweight hydrogen generator
either by using the lithium salt in place of the sodium salt or by
using blends of LiBH.sub.4 and NaBH.sub.4
[0075] The solvent used in this method for producing a
catalyst-hydride blend is preferably selected from solvents that
are non-reactive with the hydride and that also solvate the
catalyst or catalyst precursor, whichever is used. A catalyst
precursor, such as RuCl.sub.3, transforms into a catalyst, such as
reduced ruthenium, in the presence of water and the hydride. Many
of the useful solvents are organic and include, but are not limited
to, tetrahydrofuran (THF), ethylene glycol ethers, anhydrous
ammonia, substituted amines, pyridine and combinations thereof. The
hydrides are dissolved in the solvent in concentrations up to and
including their saturation level and preferably, at their
saturation level. Catalyst concentrations range between about 0.1
wt % and about 20 wt % active metal based on the total amount of
hydride and the active element or elements in the catalyst.
Preferred concentration may range between about 0.3 wt % and about
12 wt % or more preferably, between about 0.4 wt % and about 9 wt
%.
[0076] Although any of the catalysts previously mentioned may be
used in this solvent method for producing a catalyst-hydride blend,
catalysts in the form of organic complexes of catalytically active
metals are preferred because these materials are highly soluble in
organic solvents. Examples of such materials include cobalt
acetylacetonate, nickel acetylacetonate, ruthenium acetylacetonate,
platinum acetylacetonate and combinations thereof.
[0077] In the solvent method of producing a catalyst-hydride blend,
the step of evaporating the solvent may include using a rotary
evaporator to remove the solvent. Using a rotary evaporator is
useful for making small batches of a catalyst-hydride blend for
laboratory use, but is not preferred for larger batches because
there is a risk of producing non-uniform mixtures of the catalyst
and hydride. Flash drying or spray drying is preferred for the step
of drying the solvent for production of larger batches. In flash
drying, the solvent is heated to a temperature far above its
boiling point but kept as a liquid under pressure. When the
pressure is released, immediate vaporization occurs resulting in
the formation of a fine, uniform powder that is the
catalyst-hydride blend. In spray drying a mist of the solution is
sprayed into a stream of heated air where the solvent evaporates
and the solids are collected. Alternate methods of evaporating the
solvent are also useful as known to those having ordinary skill in
the art. Such alternate methods include, for example, drying the
solution on a heated roll. The blend may be packaged for use as a
powder or alternatively, the powder may be pressed into pellets,
tablets, or granules.
[0078] The present invention further provides a method useful for
producing a catalyst-hydride blend of non-soluble catalysts with a
soluble hydride. The method includes dissolving the hydride in a
solution to form a saturated hydride solution as discussed above
and dispersing or suspending a catalyst in the form of a fine
powder throughout the solution. Any of the catalysts discussed
previously may be dispersed as a fine powder throughout the
solution. One preferred catalyst useful in this method is
ruthenium, which may be used in forms such as ruthenium black,
ruthenium on a support, ruthenium chloride and combinations
thereof. As before, the hydrides are dissolved in the solvent in
concentrations up to and including their saturation level and
preferably, at their saturation level. Catalyst concentrations
range between about 0.1 wt % and about 20 wt % active metal based
on the total amount of hydride and the active element or elements
in the catalyst. Preferred concentration may range between about
0.3 wt % and about 12 wt % or more preferably, between about 0.4 wt
% and about 9 wt %.
[0079] The method further includes the step of evaporating the
solution containing the dispersed catalyst powder by known drying
means, such as spray drying, drying the solution on a heated roll,
flash drying or drying in a rotary evaporator. After the solvent
has been evaporated, each of the dry particles is coated relatively
evenly with a coating of the hydride. The blend may be packaged for
use as a powder or alternatively, the powder may be pressed into
pellets, tablets, or granules.
[0080] The methods of the present invention that provide blends or
mixtures of a covalent hydride and a catalyst are useful because
the resulting blends or mixtures react with water to generate
hydrogen in the same manner as do the salt-like hydrides; i.e., the
mixed composition continues to produce hydrogen as long as water is
available for reaction. Therefore, when a covalent hydride is mixed
with a catalyst, the rate of the hydration reaction that produces
hydrogen can be controlled by the rate of water addition. It should
be noted that some covalent hydrides, such as LiAlH.sub.4, do
produce hydrogen as long as water is available for reaction without
being mixed with a catalyst.
[0081] The amount of catalyst added to the catalyst-hydride blend
or mixture is important because the concentration of catalyst in
the blend or mixture can control the hydration reaction rate and
therefore, the rate of hydrogen generation. For example, if only a
small amount of catalyst is added to the blend or mixture, then the
diffusion rate of the hydride to the catalyst controls the rate of
reaction, not the rate of water addition. With diffusion rate
controlling the rate of reaction, the hydration reaction can be
gradual, which results in a gradual release of hydrogen.
[0082] The hydration 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. Adding a wicking
agent within the pellets or granules of the hydrogen-containing
composition that contains the hydride 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 composition
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 variations in the
quantity of wicking material added to the hydrogen-containing
composition 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.
[0083] The present invention further provides supporting composites
that include catalysts, metal hydrides and/or wicking agents
disposed in and/or on foams or other porous structures. One
embodiment of the present invention includes filling the pores of a
porous substrate, such as a foam, with a hydrogen-containing
composition. Foams can be useful for conducting heat out of the
reaction mass, for keeping the hydrogen-containing composition as a
solid mass, for supporting the catalyst, and, with proper surface
treatment, for delivering water into the core of the reaction mass.
A wide variety of foams or other porous substrates, both metallic
and nonmetallic, may be used.
[0084] In one embodiment, the hydrogen-containing composition is
disposed on a porous foam having good thermal conductivity to help
dissipate the heat of reaction. Some examples of suitable foams
include aluminum, nickel, copper, titanium, silver, stainless
steel, and carbon.
[0085] For example, nickel foam can be rendered much more
hydrophilic than the original metal surface by oxidizing the
surface of nickel foam. The hydrophilic surface aids the
distribution of water throughout the mass of the
hydrogen-containing composition that is contained within the pores
of the foam. Optionally, either separately or in combination with a
hydrophilic surface treatment, wicking materials may be added to
the hydrogen-containing composition before filling the pores of the
foam, such as by assembling the hydride with a hydrophilic binder
or blending the hydride with a wicking agent or other hydrophilic
material. In any of these variations or their combination, or other
methods known to those having ordinary skill in the art, the
objective is to provide means for distributing the water throughout
the reaction mass to produce a smooth, even hydrolysis
reaction.
[0086] The catalyst can be blended or mixed with the hydride before
placing the hydrogen-containing composition into the pores of the
porous material or the catalyst may be applied to the surface of
the porous material prior to loading the hydride. When sufficient
catalyst is blended with the hydride, the hydration reaction is
best controlled through the rate of water addition as a hydrogen
generator having active hydrogen generation control. Alternatively,
the catalyst may be applied to the surface of the foam or other
porous material to reduce the degree of intimate contact and
thereby limit the hydration reaction to the rate of diffusion of
the hydride to the catalyst as for a hydrogen generator having
passive hydrogen generation control. The catalyst can be applied to
the porous material by a variety of means including, for example,
painting a solution or suspension onto the surface of the substrate
and by plating a metallic catalyst onto a conductive support.
Optionally, a smaller amount of catalyst may also be blended with
the hydride packed into the pores of the porous substrate with or
without applying additional catalyst to the surface of the porous
substrate to control the hydration reaction by the rate of
diffusion of the hydride to the catalyst.
[0087] In another embodiment of the present invention, the finely
ground hydride is dispersed in an inert organic liquid to provide a
fluid mixture. By dispersing a hydride throughout a saturated
solution of the same or a different hydride, fluid mixtures can be
produced having extremely high concentrations of the hydrides.
Water may be mixed with or mixed into the dispersion to evolve
hydrogen. A catalyst may also be placed in solution as disclosed
above with the dispersed hydride.
[0088] A variety of solvents are useful for dissolving hydrides in
low to moderate concentrations and for dispersing additional
hydride to provide a fluid mixture. Examples of such solvents
include tetrahydrofuran (THF), ethylene glycol ethers,
iso-propanol, monoethanolamine, ethylenediamine, ethylamine, other
mono- and di-substituted amines, dimethylformamide (DMF),
dimethylacetamide, dimethylsulfoxide (DMSO), and pyridine for
sodium borohydride, diethyl ether for lithium borohydride, and
diethyl ether, THF and other ethers for lithium aluminum
hydride.
[0089] If the hydride reacts promptly with the water, such as
LiAlH.sub.4 or LiBH.sub.4, stirring water into the dispersion leads
to an immediate and quantitative release of hydrogen. If the
supporting solvent is hydrophobic, the reaction is relatively slow
in the absence of mixing.
[0090] The present invention further provides embodiments of a
hydrogen generator having passive control of the rate of hydrogen
generation from a metal hydride. Controlling the hydrogen
generation rate through the rate of diffusion of the hydride to the
water is passive control. Therefore, setting factors that affect
the diffusion rate provides a hydrogen generator that generates an
expected and desired amount of hydrogen.
[0091] It is typical for all or most of the water to be added to
the hydrogen-containing composition all at once in a passively
controlled hydrogen generator. For example, the water addition may
be batch or semi-batch, although it may also be continuous. The
rate of reaction is passively controlled at a rate determined by
factors that include the amount of water added, the amount of
catalyst used, the catalyst activity, the amount of hydride used
and the form of the hydrogen-containing composition contained
within the hydrogen generator, e.g., pellets, granules, tablets or
powder with or without wicking agents. Since the hydride reacts by
diffusing to the catalyst, the rate of hydrogen generation can be
reduced by providing less catalyst available for reaction. The
passive hydrogen generator provides a very simple system that lends
itself to applications where size and weight of the hydrogen
generator system are critical factors.
[0092] Catalyst concentrations in the hydrogen-containing
composition for a passively controlled hydrogen generator may range
widely. For some applications, the set catalyst concentration may
range between about 0.1 wt % and about 20 wt % active metal based
on the total amount of hydride and the active element or elements
in the catalyst. Preferably the set catalyst concentration may
range from between about 0.1 wt % and about 15 wt % and more
preferably, between about 0.3 wt % and about 7 wt %.
[0093] The exact shape of a hydrogen generator based on passive
control is quite flexible making it possible to tailor the form of
the device to the application. A wide range of materials can be
used to fabricate the generators, with the specific materials
mentioned herein only serving as examples. For example, the
hydrogen generator may be formed of an alkaline resistant polymer,
metal, carbon, graphite or combinations thereof. Examples of
configurations of the hydrogen generator include tubular, box-like
or bag-like containers.
[0094] Some embodiments of a passively controlled hydrogen
generator of the present invention include a reaction chamber for
containing the hydrogen-containing composition to be mixed with
water, a fluid separation device that prevents entrained liquid
from exiting the reaction chamber with the generated hydrogen, and
a means for adding water or an aqueous solution to the hydride. The
fluid separation device is preferably made of a material that
resists wetting under extremely alkaline conditions to permit the
hydrogen to escape. Liquid free hydrogen gas can be produced even
from the alkaline borohydride solution by using an oleophobic
barrier such as PREVENTS, manufactured by W. L. Gore &
Associates, Inc., Newark, Del.
[0095] The hydrogen generator may further include a conduit,
passage or other means to deliver the hydrogen to a fuel cell. In
one preferred embodiment, the means for adding the water to the
reactor can be removed after the water addition to reduce the
weight of the generator while it is operating. The
hydrogen-containing composition can be in any form including, for
example, powders, granules, pellets and tablets. Pellets are a
preferred form because they simplify handling when loading the
generator.
[0096] The means for adding water or aqueous solution to the
reaction chamber includes means that provide water from a
pressurized water system, means that provide water from a gravity
feed system and means that provide for pouring water into the
reaction chamber. Pressurized water systems include, for example,
pumps, syringes, and gas pressurized water systems. Gravity feed
systems include bags, tanks or other vessels of water that are
positioned above the reaction chamber.
[0097] In a passively controlled hydrogen generator, the total
amount of water added is between 100% and about 400% of the
stoichiometric amount required to produce a desired amount of
hydrogen. Preferably, the amount of water added is between about
125% and about 250% of stoichiometric amount.
[0098] In a preferred embodiment, an antifoam agent is added to the
water to make an aqueous solution that is added to the hydride,
because the generation of hydrogen during the hydration reaction
typically creates foaming. By adding an antifoam agent to the
reactant water, the size and weight of the hydrogen generator can
be minimized because less volume is required for disengagement of
the gas from the liquid/solids. Polyglycol anti-foam 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.
[0099] Because the hydration reaction proceeds at a faster rate at
lower pH, an acid may be added to the reaction chamber, for example
by premixing acid into the reactant water. Acids suitable for use
include, for example, mineral acids, carboxylic acids, sulfonic
acids and phosphoric acids.
[0100] FIG. 1 is a schematic of a passively controlled hydrogen
generator in accordance with the present invention that may be made
as a lightweight, single-use, disposable device. The passively
controlled hydrogen generator 10 includes a reaction chamber 11
containing pellets 14 of a hydrogen-containing composition. An
external water source, shown as syringe 17, is threadedly (or
otherwise detachably) attached to the reaction chamber 11 at a
water inlet port 15. A check valve 16 prevents generated hydrogen
from escaping through the water inlet port 15. A measured amount of
water treated with an antifoam agent is injected into the reaction
chamber 11 from the syringe 17. The syringe may then be removed so
that it does not add to the weight or size of the hydrogen
generator. When the aqueous solution contacts the pellets 14, the
hydration reaction starts to generate hydrogen gas. The hydrogen
gas exits the reaction chamber 11 through the hydrogen exit nozzle
12 after passing through a fluid separator 13 to remove entrained
liquid from the hydrogen.
[0101] The present invention further provides embodiments of a
hydrogen generator having active control of the hydrogen generation
rate from a hydrogen-containing composition. In a hydrogen
generator having active control, the rate of the addition of water
or an aqueous solution controls the hydrogen generation rate. In
one embodiment of an actively controlled hydrogen generator, the
hydrogen generator comprises a reaction chamber for holding a
hydrogen-containing composition comprising a hydride; and an
aqueous solution reservoir comprising an outlet port in fluid
communication with a reaction chamber inlet port. The hydrogen
generator further comprises means for adjusting the flow rate of an
aqueous solution from the reservoir into the reaction chamber to
control the hydrogen gas generation rate.
[0102] The hydrogen-containing composition for an actively
controlled hydrogen generator comprises a hydride selected from
salt-like hydrides, covalent hydrides that act like a salt-like
hydride, covalent hydrides that are blended with an excess amount
of catalyst to ensure that the hydration reaction proceeds quickly
and smoothly or combinations thereof. Preferred embodiments of a
hydrogen generator having active control of the hydrogen generation
rate include adding excess catalyst to the catalyst-hydride blend
to ensure that the hydration reaction is not limited by the rate of
diffusion of the hydrate to the catalyst. However, in some
applications it may be desirable to lessen the reactivity of the
hydrogen-containing composition by reducing the catalyst
concentration of the composition while still controlling the
overall hydrogen generation through the rate of water addition.
[0103] Typical catalyst concentrations in the mixture of the one or
more hydrides and catalyst in the hydrogen-containing component of
an actively controlled hydrogen generator range between about 1 wt
% and about 25 wt %, preferably between about 5 wt % and about 20
wt %, and more preferably between about 6 wt % and about 12 wt %,
with weight percent being based upon the active component or
components of the catalyst. The shape and the materials of
construction for an actively controlled hydrogen generator are
similar to those of the passively controlled hydrogen generator as
discussed above.
[0104] The hydrogen generator, whether actively or passively
controlled, may include more than one reaction chamber and/or more
than one water chamber for some applications. Each reaction chamber
comprises an inlet port for admission of water or an aqueous
solution into the reaction chamber and an outlet port for the
release of the generated hydrogen gas. The inlet port and the
outlet port may each further include a fluid control device
selected from, for example, a check valve, a ball valve, a globe
valve, a needle valve or combinations thereof. Each of these valves
may be manually operated or automatically operated as, for example,
a solenoid valve, a pneumatically actuated valve, or an
electrically actuated valve by means other than a solenoid. These
valves may operate to limit the flow of a fluid through the ports
to a single direction, to control or release pressure in the
reaction chamber or to admit or vent fluids to/from the reaction
chamber. A controller, including a computer, microchip-based
controller or other device known to those having ordinary skill in
the art, may actuate one or more of these fluid control devices to
control pressures, levels, flows and temperatures to a setpoint or
to move one of these fluid control devices to a predetermined open
or closed position according to an operating program.
[0105] In an actively controlled hydrogen generator of the present
invention, it is useful to initially wet the pellets at a high flow
rate of the aqueous solution. If the pellets of catalyst-hydride
blend are initially wetted at a high initial flow rate of 1.5 to 4
times the normal rate, the overall duration of the hydrolysis
reaction is prolonged. This initial wetting period may extend for
at least 30 minutes and preferably, between about 5 minutes and
about 20 minutes.
[0106] In one embodiment of an actively controlled hydrogen
generator, the means for adjusting a flow rate of an aqueous
solution to the hydride includes an electrolyzer for generating
hydrogen to pressure the water or aqueous solution from a
reservoir. The reservoir may be, for example, an inflatable
bladder, a chamber having a plunger disposed therein, or a chamber
that may be pressurized. As is well known by those having ordinary
skill in the art, an electrolyzer is an electrochemical cell having
an anode and a cathode that are separated by a proton exchange
membrane and having a power source that provides a current through
the cell. The electrolyzer produces hydrogen and oxygen from a
water feed according to the reaction shown in Equation 13:
##STR00001##
[0107] An electrolyzer can generate enough hydrogen to force the
reactant water out of the reservoir and into the reaction chamber
by, for example, applying pressure to the water chamber. Water may
be supplied to the electrolyzer from the water chamber or from an
alternative source. Water may be supplied to the electrolyzer from,
for example, a water capsule within the electrolyzer or through
conduits from the water chamber or from an alternative source. The
power source may be, for example, a fuel cell that is operated from
hydrogen produced by the hydrogen generator or one or more
batteries.
[0108] In one embodiment of the present invention, the water
chamber contains an inflatable bladder reservoir with water both
inside and outside of the bladder. The reactant water inside the
bladder supplies the reaction chamber with reactant water for the
hydrolysis reaction and the electrolyzer water outside the bladder
supplies electrolyzer water to feed a small electrolyzer mounted in
the shell of the water chamber. The cathode of the electrolyzer
faces the water chamber and produces the hydrogen used to
pressurize the water chamber. The electrolyzer water from the water
chamber diffuses through the proton exchange membrane to the anode
side of the electrolyzer provide the water to the anode side as
necessary to produce hydrogen and oxygen as shown in Equation 13.
The oxygen produced at the anode is vented to the atmosphere. A
controller can increase the current flowing through the
electrolytic cell to increase the rate of hydrogen vented to the
water chamber, thereby increasing the flow rate of the reactant
water from the bladder as the water chamber pressure increases.
Preferably, the electrolyzer cathode is exposed through the floor
of the water chamber to maintain fluid communication with the
electrolyzer water.
[0109] Hydrogen and/or oxygen gases generated by an electrolyzer
can be vented to the water chamber, thereby increasing the pressure
in the water chamber. The pressure increase in the water chamber
caused by the delivery of the gas generated by the electrolyzer
applies an increasing pressure to the outside of the inflatable
bladder in proportion to the volume of the delivered gas from the
electrolyzer. Applying the increased pressure to the bladder forces
the reactant water from the bladder and into the reaction chamber.
By increasing the current to the electrolyzer, hydrogen and oxygen
are produced at a higher rate by the electrolyzer, thereby forcing
reactant water from the bladder and into the reaction chamber at a
higher rate. In some embodiments, as disclosed above, the oxygen
produced by the electrolyzer is vented to the atmosphere. In some
embodiments, the electrolysis gases pressurize the water chamber
and force reactant water from the water chamber into the reaction
chamber without an inflatable bladder. Alternatively, a plunger may
be disposed within the water chamber instead of an inflatable
bladder and gases produced by an electrolyzer or from alternative
sources may pressurize a gas side of the plunger to push reactant
water from the water chamber into the reaction chamber.
[0110] Electrolyzing a small amount of liquid water produces a
relatively large volume of hydrogen gas. Each millimole of
electrolyzer water (18 mg) generates 24.5 mL of hydrogen gas.
Allowing for a slight over pressure to deliver the water, this
volume of hydrogen is sufficient to deliver about 20 mL of reactant
water to the reaction chamber. This amount of water or aqueous
solution delivered to the hydrogen-containing composition in the
reaction chamber can react with, for example, a borohydride salt
(such as NaBH.sub.4) to generate up to 12 L of hydrogen. Since the
rate of electrolyzing the electrolyzer water is controlled by the
current flowing to the electrolyzer, controlling the current to the
electrolyzer controls the rate of reactant water injection into the
reaction chamber, thereby actively controlling the rate of hydrogen
generation.
[0111] In another embodiment of an actively controlled hydrogen
generator, the means for adjusting a flow rate of an aqueous
solution to the reaction chamber includes an electrolyzer mounted
in the wall of the inflatable bladder that contains the water or an
aqueous solution for injection into the reaction chamber. In this
embodiment, by moving the electrolyzer from the shell of the
generator to the wall of the bladder and by sealing the water
chamber that contains the inflatable bladder, the need for a
separate water supply for the electrolyzer is eliminated and both
the hydrogen and the oxygen that is generated by the electrolyzer
can be used to force water from the bladder into the reaction
chamber.
[0112] Another means for adjusting a flow rate of an aqueous
solution to the reaction chamber in accordance with the present
invention includes the use of a hydrogen fed electrochemical pump
that pumps water from the water chamber into the reaction chamber.
Electrochemical oxygen and hydrogen pumps are well known to those
having ordinary skill in the art and are described in several
United States patents, including U.S. Pat. Nos. 5,938,640,
4,902,278, 4,886,514, and 4,522,698, which are hereby fully
incorporated by reference. The electrochemically driven fluid
dispensers disclosed in these patents have an electrochemical cell
in which porous gas diffusion electrodes are joined respectively to
the opposite surfaces of an ion exchange membrane containing water
and functioning as an electrolyte. The electrochemically driven
fluid dispenser uses a phenomenon such that when hydrogen is
supplied to an anode of the electrochemical cell and a DC current
is imposed between the anode and the cathode, the hydrogen becomes
hydrogen ions at the anode. When the produced hydrogen ions reacn
the cathode through the ion exchange membrane, an electrochemical
reaction arises to generate gaseous hydrogen. Since the net effect
of these processes is transport of hydrogen from one side of the
membrane to the other, this cell is also called hydrogen pump. The
hydrogen generated and pressurized at the cathode is used as a
driving source for pushing a piston, a diaphragm, or the like. The
power savings produced by the lower operating potential of a
hydrogen pump, .about.0.1 V, compared to an electrolyzer,
.about.1.6-1.8 V, is significant. Preferably, an alternating
current drives the hydrogen pump with the frequency determining the
liquid flow rate.
[0113] In one preferred embodiment of the present invention, the
hydrogen produced by the hydrogen generator is saturated with water
and feeds a fuel cell. The fuel cell also produces water as a
product of the reaction of hydrogen and oxygen. This water flows
out of the fuel cell with the air from the cathode and the excess
(unconsumed) hydrogen from the anode. The water from both of these
water sources can be recovered as condensate and stored in a water
reservoir until needed for the hydration reaction of the metal
hydride in the hydrogen generator. This recovered water may be
pumped into the reaction chamber by a hydrogen electrochemical
liquid pump. An electrochemical pump can consistently provide
accurate pumping of water at micro-flow rates without the need for
a bladder and at significantly lower power than the
electrolyzer.
[0114] In both the passively controlled and the actively controlled
hydrogen generator, while the pelletized form of the hydride or
catalyst-hydride blend is preferred, it is not required. The
pelletized form is typically easier to handle but powdered forms
and granular forms have also been tested and found to be
effective.
[0115] One limitation of a metal hydride hydrogen generator is that
if the hydration reaction is stopped by depriving the reactor of
water, the reaction does not instantly stop but instead, slows to a
stop as the water in the reactor is consumed, thereby allowing the
formation of a salt crust on the surface of the hydride. Restarting
the reactor requires either that the salt crust be mechanically
broken up or that sufficient water be supplied to at least
partially dissolve it. It has sometimes been possible to restart a
hydrogen generator with a smaller excess of water, but this is
generally a slow process.
[0116] However, in the presence of a ruthenium catalyst, an aqueous
solution of ethylene glycol promptly and vigorously reacts and
dissolves the crust, such as a sodium borate crust formed on the
surface of a partially reacted sodium borohydride mass when it is
starved of water or aqueous solution. When the ethylene glycol
solution is introduced to a partially reacted metal hydride mass,
the crust is quickly broken down and the reaction renewed with the
copious generation of hydrogen from the decomposition of the
borohydride.
[0117] In another embodiment of the present invention, a pressure
resistant shell used on the hydrogen generator permits the head
space of the generator to serve as a storage volume for hydrogen,
making it in effect a chemical capacitor. When the generator is
turned down and the hydrogen delivery doesn't drop as fast as the
demand, excess gas is stored in the head space. When demand
increases faster than the generator can ramp up, this gas supplies
the demand. Operating the system so that the head space is always
pressurized with stored hydrogen ensures that hydrogen is available
as required to respond to spikes in power demand. A means for
over-pressure release, such as a pressure safety valve or rupture
disk, is required for any pressure vessel and some or all of the
hydrogen contained within the reactor chamber may be vented through
the release means if necessary to avoid rupturing the
generator.
[0118] FIG. 2 is a cross-sectional view of an actively controlled
hydrogen generator. The hydrogen generator 20 includes a reaction
chamber 21 containing pellets 26 of a hydrogen-containing
composition. A barrier 22 separates a water chamber 24 from the
reaction chamber 21. The water chamber 24 contains an inflatable
bladder 23 that is filled with reactant water or an aqueous
reactant solution containing an antifoam agent and/or optionally,
an acid. The reactant water that is contained within the bladder 23
can be pressured into the reaction chamber 21 through the inlet
nozzle 32. A check valve 31 mounted on the inlet nozzle 32 prevents
the contents of the reaction chamber 21 from flowing into the
bladder 23.
[0119] The water chamber 24 further contains electrolyzer water
that surrounds the bladder 23 and that is fed to the electrolyzer
25 mounted in the shell of the hydrogen generator 20 with the
cathode 25a of the electrolyzer 25 in fluid communication with the
water chamber 24. The electrolyzer water from the water chamber 24
is converted into hydrogen and oxygen by the electrolyzer 25. The
oxygen is vented from the anode 25b of the electrolyzer 25 and the
hydrogen produced at the cathode 25a pressurizes the water chamber
24, exerting pressure on the outer surface of the bladder 23 and
causing reaction water to be pressured from the bladder 23 into the
reaction chamber 21. The electrolyzer water required for
electrolysis at the anode 25b diffuses through the proton exchange
membrane 25c from the water chamber 24. The greater the rate of
hydrogen production from the electrolyzer 25, the greater will be
the rate of pressure increase in the water chamber 24 and
therefore, the rate of water pressured into the reaction chamber 21
from the bladder 23. A controller 33 controls the amount of current
from the power source (not shown) to the electrolyzer 25 to control
the rate of hydrogen generation from the electrolyzer 25 and
ultimately, controls the rate of hydrogen generation from the
hydrogen generator 20. The power source may be a fuel cell, such as
one operating from the hydrogen produced by the hydrogen generator
20, or one or more batteries.
[0120] Hydrogen generated from the hydrolysis reaction of the
reaction water from the bladder 23 contacting the pellets 26 of the
hydrogen-containing composition passes through a fluid separator 29
to remove any entrained water and then passes out the hydrogen
outlet 27. A check valve 28 on the hydrogen outlet 27 prevents
contents of a fuel cell (not pictured) from back-flowing into the
hydrogen generator 20.
[0121] FIG. 3 is a cross-sectional view of an actively controlled
hydrogen generator having an electrolyzer mounted on a bladder. In
this embodiment, a hydrogen generator 40 includes two water
chambers 24 with each water chamber holding an inflatable bladder
23 filled with reactant water. The water chambers 24 are separated
from the reaction chamber 21 with barriers 22. In this embodiment,
an electrolyzer 25 is mounted on the each of the bladders 23. As
current is increased from the power supply (not shown) by the
controller 33, the electrolyzers 25 increase the amount of hydrogen
and oxygen that they produce and pressurize both the sealed water
chambers 24 and the interior of the bladders 23. As the pressures
in the water chambers 24 and the bladders 23 increase, the water
flowing from the bladders 23 into the reaction chamber 21 also
increases. The oxygen produced at the anode 25b vents to the water
chambers 24 and the hydrogen produced at the cathode 25a vents to
the interior of the bladder 23.
[0122] The pellets 26 of the hydrogen-containing composition begin
to hydrolyze and generate hydrogen upon contact with the water. The
hydrogen passes through the fluid separators 29 to remove any
entrained water and the hydrogen may then be delivered to a fuel
cell (not shown). The fluid separators 29 may be, for example, GORE
PREVENTS.TM. barriers mounted on a sheet of polyetherimide or
polyethylene as described in Example 15.
[0123] FIG. 4 is a schematic drawing of a hydrogen generator 50
utilizing a hydrogen-fed electrochemical liquid pump 51 in
accordance with the present invention. In this embodiment, water or
an aqueous solution 52 is held within the water chamber 24 and the
reaction chamber 21 holds pellets 26 of the hydrogen-containing
composition comprising hydride or a catalyst-hydride blend.
Hydrogen produced from the hydrolysis reaction in the reaction
chamber 21 passes to the fuel cell 54 as fuel. The hydrogen stream
55 leaving the reaction chamber 21 is saturated with water. The
fuel cell 54 generates electricity from the fuel supplied and also
produces water at the anode (not shown). Excess hydrogen, the water
produced at the anode, and the water that saturated the hydrogen
stream 55 exit the fuel cell in an excess hydrogen/water return
line 53. The excess hydrogen/water return line 53 delivers the
water and hydrogen to the water chamber 24. A hydrogen-fed
electrochemical liquid pump 51 pumps the water from the water
chamber 24 to the reaction chamber 21 as necessary for hydrogen
production through the hydrolysis of the pellets 26. Check valves
58 prevent reverse flow through the pump 51. A controller 56
controls the rate of pumping by the pump 51 and thereby controls
the rate of hydrogen generation from the generator 50.
[0124] The electrochemical pump 51 comprises an elastic diaphragm
59 and a membrane and electrode assembly (MEA) 57 comprising a
proton exchange membrane disposed between two platinum catalyst gas
diffusion electrodes as known to those having ordinary skill in the
art. Hydrogen from the head space of the water chamber 24 is driven
across the MEA 57 in alternating directions as the polarity is
reversed across the MEA 57. The hydrogen movement causes the
elastic diaphragm 59 to move in a pumping motion. The controller 56
adjusts both the current and the frequency of polarity reversals
across the MEA 57 to drive the electrochemical pump 51. The power
source for the controlled current to the pump 51 is preferably the
fuel cell 54.
[0125] FIGS. 5A-B are drawings of a bottom view and a
cross-sectional view of an embodiment of a lightweight hydrogen
generator. The cross-section view has been rotated to show the top
of the hydrogen generator at the top of the drawing for ease of
viewing. In this embodiment of a hydrogen generator 60, a balsa
wood frame 61 supports a covering of polyetherimide (PEI) sheets 63
(FIG. 5B) forming the top 63a and bottom 63b of the hydrogen
generator 60. Electrolyzers 25 are attached to the PEI sheet
forming the bottom 63b and are in fluid communication with the
water chambers 24 in the same manner as shown in FIG. 2.
Lightweight foam 64 with a large open volume fraction is shown as
an option and serves to prevent the pellets 26 from shifting prior
to use. Fluid separators 29, such as GORE PREVENTS, are attached to
a PEI sheet 63c to provide separation of entrained liquids from the
hydrogen gas product. The hydrogen gas exits through the hydrogen
exit 62.
[0126] FIG. 6 is a cross-sectional view of a containment system for
a hydrogen generator in accordance with the present invention. The
containment system 70 provides separation of the
catalyst-hydride/hydrolysis products 77, generated hydrogen 72, and
water 78 from the ambient surroundings. The container may take any
shape and be made of any materials including, but not limited to,
alkaline resistant polymer, metal, carbon, graphite, or
combinations thereof. At least one water inlet 76 and at least one
hydrogen outlet 74 are provided. Ancillary components of the system
for removal of hydrogen and introduction of water can be attached
to the openings 74, 76 utilizing attachment mechanisms such as
threaded ports, crimping, welding, gluing, interference fit, or
snapping mechanisms. The containment system 70 further includes a
liquid-gas separator 73 that provides separation of the generated
hydrogen 72 from the remaining hydrolysis product 77. The separator
73 may take any shape and be made of, for example, expanded PTFE,
other polymers with nanometer scale pores, or materials that
readily diffuse hydrogen such as silicone or palladium.
Example 1
Hydride Pellet Production
[0127] The hydride is frequently prepared as pellets. For each
compound to be tested in this form, pellets were produced both neat
and with predetermined amounts of catalyst blended with the
hydride. For catalyzed pellets, the catalyst was blended with the
hydride by grinding the components together. Pellets were
standardized with a diameter of 13 mm and a height of .about.1 cm.
The exact height of a pellet varied, as variations in additives and
pressing conditions altered the final density. The pellets were
produced using a standard pellet die (Graseby Specac) with a 12 ton
press (Carver).
[0128] The effect on the density of lithium hydride pellets caused
by varying the pressure exerted by the press is shown in Table 3.
The accuracy of the pressures shown is about .+-.500 psi.
TABLE-US-00003 TABLE 3 Pressure (psi) Density (g/mL) Fraction of
Theoretical 5,000 0.530 68.0% 10,000 0.551 70.7% 15,000 0.577 74.0%
20,000 0.609 78.1% 25,000 0.649 83.3% 30,000 0.659 84.5%
[0129] All of the pellets showed good integrity and were easily
handled after removal from the die. The results show that the
density of the pellets varied smoothly with the applied pressure
over the range examined.
Example 2
Evaluation of Hydrogen Evolution from Hydride Pellets
[0130] An apparatus for evaluating both neat and hydride-catalyst
compositions for use in passively controlled generators is shown in
FIG. 7. The hydride is shown as a pellet 26, which is a preferred
form for the hydride because it is easily handled. A measured
amount of water was injected into the flask 82 at the start of the
experiment. Typically two to five grams of hydride were used in
each reaction. The amount of water added was determined by the
amount of hydride, the amount of water required to
stoichiometrically hydrolyze it, and the stoichiometry being
tested. As hydrogen was generated, the gas stream exited the flask
82, passed through a drying tube 85, and exited through a mass flow
monitor 83 and vent 84. The drying tube 85 removed most, if not
all, of the water in the gas stream. It is important that the dew
point of the gas passing through the mass flow 83 is significantly
below ambient to avoid condensate in the instrument, which could
substantially reduce the accuracy of the measurements. The rate of
gas generation was monitored as a function of time and integrated
to determine the total volume of gas generated.
[0131] Baseline, or uncatalyzed, pellets were hydrolyzed and the
results examined. All of the initial tests were carried out using
twice the amount of water required to stoichiometrically hydrolyze
the hydride to a hydroxide. The uncatalyzed NaBH.sub.4 pellets
showed an initial burst of hydrogen when water was added. This
burst was .ltoreq.250 mL/min and never lasted more than a few
seconds. After the initial burst of activity, the hydrolysis rate
dropped rapidly to below the threshold for measurement and remained
there until the experiments were terminated. The appearance of
these pellets changed little over the course of the experiment,
remaining as white cylindrical pellets resting in a pool of the
solution formed by the initial reaction. A drop in rate was
expected because the BH.sub.4.sup.- ion is stable in basic
solution, and the sodium borate formed by the hydrolysis reaction
is basic.
[0132] LiH pellets showed an initial burst of hydrogen following
the addition of water. After the initial burst, the rate of
hydrogen generation rapidly dropped. Within a minute or two the
rate had fallen to below the 10 mL/min that represents the lowest
flow that could be reliably measured by the equipment. Short bursts
of hydrogen generation occurred intermittently and were correlated
with cracks appearing in the pellet. The experiment was terminated
after about an hour. In all cases, the pellet was only partially
consumed (sodium borohydride partially reacted) when the experiment
terminated and free water remained. The amount of force used to
fabricate the pellets had no apparent effect on their hydrolysis.
Pellets compacted with a load of about 6,000 pounds showed
essentially the same hydrogen evolution pattern as pellets
compacted at 1,000 pounds.
Example 3
Hydride Pellets with Wicking Agents
[0133] LiH pellets were separately formed with four different
wicking agents that included two sources of cellulose fibers,
(paper and cotton), modified polyester having a surface treatment
to enhance water transport along the surface without absorption
into the fiber, and polyacrylamide, the active component of
disposable diapers. In each case, the wicking material was included
with the LiH in the die for pressing.
[0134] The pellets were hydrolyzed as described in Example 2. The
fiber-containing pellets hydrolyzed quantitatively, unlike the
results of Example 2. However, the reaction was quite rapid,
lasting no more than a few minutes in any of the cases. The rate of
hydrogen generation peaked in excess of 1.5 L per minute and then
decreased to about 100 mL per minute within 5 minutes. The entire
reaction was over in about 45 minutes.
[0135] In the presence of a ground paper wick or a polyacrylamide
wick mixed into the hydrogen-containing composition at 1.1 to 11.1
wt %, the reaction time was reduced to about 20 minutes with a
quantitative evolution of gas. The rate of hydrolysis of LiH
pellets was not influenced by the quantity of wick present.
Example 4
Catalyzed Hydride Pellets
[0136] Using the same apparatus as described in Example 2,
hydrolysis of catalyzed pellets containing RuCl.sub.3 followed a
substantially different course than the uncatalyzed pellets. The
same ratio of water to hydride (twice stoichiometric) was used. It
was added to the chamber containing a catalyzed pellet in a single
addition and the same small initial puff of hydrogen gas was
observed. Following an initial decline, the rate of hydrogen
generation gradually began to climb. Unlike the uncatalyzed
pellets, these pellets quickly dissolved in the water to produce a
clear solution that effervesced with hydrogen. The climb in the
rate of hydrogen production continued for 20 to 35 minutes after
which the rate of gas generation accelerated rapidly. This rapid
rise was followed by a similarly rapid fall. For the pellets with 1
wt % RuCl.sub.3, the area under the curve corresponded to 100% of
the calculated amount of hydrogen expected, i.e., quantitative
hydrolysis of the hydride. This demonstrated the effectiveness of
Ru as a catalyst for the hydrolysis of BH.sub.4.sup.-.
Example 5
Hydride Pellets Containing Resin-supported Catalyst
[0137] Pellets were also produced using Ru on ion exchange resin as
the catalyst. Dowex 50W was converted from the acid form to the
ruthenium form by equilibration with an aqueous solution of
RuCl.sub.3 and dried. After drying, the resin was ground and mixed
with NaBH.sub.4. When water was added to the flask of the apparatus
as described in Example 2, the rate of hydrogen generation rapidly
exceeded the 1 L/min maximum rate of the mass flow monitor. Adding
the water slowly demonstrated that the hydrolysis was quantitative.
Based upon the manufacturers' ion exchange capacity, a pellet made
with 5 wt % of the fully loaded ion exchange resin is 0.625 wt %
Ru. This compares to loadings of 1 wt % Ru for the reduced Ru
catalysts and about 0.6 wt % Ru for RuCl.sub.3. The activity of the
resin-supported catalyst was moderated by reducing the amount of
catalyst used. Pellets with 1 wt % Ru on resin produced hydrogen at
a significantly reduced rate, while still achieving quantitative
hydrolysis.
Example 6
Reduced Ruthenium as Active Species
[0138] The active Ru species was identified by producing and
hydrolyzing a series of pellets produced with different forms of
ruthenium, including ruthenium chloride and three forms of reduced
Ru: Ru black, 20 wt % Ru on a carbon support, and 40 wt % Ru on a
carbon support. These pellets were tested using the apparatus
described in Example 2. All four were effective for the
quantitative hydrolysis of BH.sub.4.sup.- but only the three
reduced ruthenium catalysts produced an immediate and steady
hydrolysis on addition of water. By contrast, testing the pellets
having RuCl.sub.3 catalyst resulted in a delay of the hydrolysis
reaction upon the addition of the water. These results indicate
that the active species for the hydration of hydrides is reduced
Ru. This conclusion also explains the results observed when using
the RuCl.sub.3 catalyst; the gradual formation and accumulation of
Ru.sup.0 produced by the reduction of the RuCl.sub.3 led to an
increase in the number of available reaction sites having the
reduced ruthenium, thereby causing an increase in the reaction rate
that continued until all of the BH.sub.4.sup.- was consumed. In
general, all of the reduced forms of Ru were observed to be quite
active.
Example 7
Nickel Chloride and Cobalt Chloride Catalysts
[0139] Given the effectiveness of RuCl.sub.3, the equivalent
chlorides were tested for nickel and cobalt as well. Anhydrous
NiCl.sub.2 and CoCl.sub.2 were obtained and blended with sodium
borohydride by grinding and then fabricated into pellets for
hydrolysis as described in Example 1.
[0140] Using the apparatus described in Example 2, it was
determined that CoCl.sub.2 is an effective catalyst for hydrolyzing
BH.sub.4.sup.-, but within a narrow useful range. Concentrations of
1.5 wt % and less produce a very slow hydrolysis reaction, while
concentrations over 2 wt % produce a rapid, vigorous, quantitative
hydrolysis.
[0141] NiCl.sub.2 appears to have a wider range of useful
compositions, although more catalyst is required than when using
CoCl.sub.2 as shown in FIG. 8. At all compositions above 5 wt % the
hydrogen evolution rate exhibits two maxima. The first maximum is
the result of acid generation as the deliquescent anhydrous
NiCl.sub.2 is hydrolyzed as shown in Equation 14.
NiCl.sub.2+2H.sub.2O.fwdarw.Ni(OH).sub.2+2HCl (14)
[0142] The second maximum is the result of temperature effects as
the temperature of the mixture increases and the reaction
accelerates. It should be noted that when non-precious metal
catalysts are used, the quantities of catalyst required are
substantially greater than with precious metal catalysts. Using
non-precious metals produces a small, but measurable reduction in
the hydrogen yield as a function of reactant mass.
Example 8
Ratios of Lithium and Sodium Borohydrides
[0143] Using the apparatus described in Example 2, pellets having
different mole ratios of LiBH.sub.4 and NaBH.sub.4 were hydrolyzed
with a constant fraction of supported ruthenium as the catalyst.
The results are shown in FIG. 9, with total borohydride salts of
103.1 mmol for each of the pellets. Greater than 30 mol %
LiBH.sub.4 appeared to be excessive for achieving a steady rate of
generation of hydrogen gas when the catalyst was fixed at 2.60 wt
%. From these results it's clear that a blend of 30 mol %
LiBH.sub.4 and 70 mol % NaBH.sub.4 with 2.60 wt % supported Ru as a
catalyst produces a smooth, steady, quantitative hydrolysis.
Example 9
Catalyst Requirements at Varying Lithium Borohydride Fractions
[0144] Different formulations of lithium and sodium borohydride
salts were blended and pressed into pellets with a ruthenium
catalyst supported on alumina at varying weight fractions. These
pellets were then tested in the apparatus described in Example 2
with the results shown in FIG. 10. Each of the curves indicates
that quantitative amounts of hydrogen gas can be obtained under
these conditions. The three curves show that increasing the mole
fraction of LiBH.sub.4 in the mixture reduces the amount of
catalyst required.
Example 10
Antifoam Agents in the Hydrolysis Water
[0145] Polyglycol anti-foam agents offer efficient distribution in
aqueous systems and tolerance of alkaline pH conditions that are
found in hydrolyzing borohydride solutions. A sample of a
polyglycol anti-foam agent was obtained from the Dow Chemical
Company (Midland, Mich.). It was blended with the water used for
hydrolysis and tested. Good foam control was obtained for the
hydrolysis of the hydride when using 50 ppm of "Polyglycol".
[0146] "Antifoam BB" was obtained from RBP Chemicals (Midland,
Mich.) as an organic defoaming surfactant, and was added to water
at a 50 ppm concentration. The solution was used to hydrolyze mixed
borohydride pellets having 25 mole % LiBH.sub.4 and 75 mole %
NaBH.sub.4 blended with ruthenium supported on alumina at
concentrations ranging from about 3.6 wt % to about 4.3 wt %. This
agent tended to promote the rate of hydrogen gas evolution and it
may contain organic wetting agents. Its foam control was poor.
[0147] New London Chemicals (Midland, Mich.) produces a blended
anti-foaming agent (C-2245) with good alkaline stability that is
described as containing polyglycol and other organic compounds. The
use of "C-2245", added to water at a 50 ppm concentration, produces
a good stabilizing effect on foam production in reactors containing
mixed lithium and sodium borohydride pellets, and provided
satisfactory hydrogen evolution rates for the period of 60 minutes.
FIG. 11 shows the influence of 50 ppm "C-2245" on the hydrolysis of
pellets containing 25 mole % LiBH.sub.4 and 75 mole % NaBH.sub.4
when the wt % of Ru on Alumina is varied from 3.59 wt % to 4.30 wt
% in catalyst. Excellent foam control was obtained for pellets
containing 4.01 wt % Ru on Alumina and satisfactory foam control
was obtained for 4.30 wt % catalyst.
Example 11
Varying Catalyst Proportions in Blend
[0148] Pellets having quantities of borohydride salt and
proportions of catalyst were continuously changed in succession and
tested the apparatus described in Example 2 until the combination
of 82 mmol borohydride and 5.14 wt % Ru on Alumina was arrived at.
FIG. 12 shows that the 5.14 wt % loading of catalyst in 82 mmol of
borohydride salt can reliably produce suitable rates of hydrogen
gas production, in excess of the 65 mL/min target set for these
experiments, with an average standard deviation of 3.2 mL/min and
with excellent reproducibility. The total reaction mass for each of
these tests was 13.1 g, yielding a hydrogen generation of 6.0 wt
%.
Example 12
Catalyst Proportions
[0149] Pellets were made and tested in the apparatus described in
Example 2. The pellets were made up of about 113.4 mmol of mixed
borohydride salts having 20 mole % LiBH.sub.4 and 80 mole %
NaBH.sub.4. Ru on alumina catalyst was blended with the mixed
borohydride salts before the pellets were formed. Each batch of
pellets had a different level of ruthenium supported on the
alumina, ranging from 4.99 wt % to 4.48 wt %. The water added to
the flask in the testing apparatus was held constant at 10.1 g of
water containing 50 ppm C-2245 antifoam. The best proportion of
catalyst for this reactant mass was found to be 4.99 wt %, as shown
in FIG. 13.
Example 13
Hydrogen Production Rates with Active Control
[0150] Achieving a target delivery rate of 240 mL of hydrogen gas
per minute for an hour (14.4 L/hr) requires 161 mmol of sodium
borohydride storage material and 20.3 mL of aqueous antifoam
solution. All of tested blends contained a sufficient amount of
catalyst to insure a prompt reaction so that the rate of water
addition determined the rate of hydrogen generation and not the
rate of diffusion of the hydride to the catalyst. These
compositions are, therefore, intended for use in an actively
controlled hydrogen generator.
[0151] To determine the effect of the form of the hydride on the
process several variations were tested: pellets, crushed granules,
and free powder. The hydrogen evolution rate was controlled by
using a syringe pump (20.3 mL solution/hour) to deliver the drop
wise addition of water having 50 ppm C-2245 antifoam. Ruthenium
chloride was present as catalyst at about 8.2 wt %. As shown in
FIG. 14, a target rate of 240 mL H.sub.2/minute can be maintained
for about 50 minutes using most of these combinations but the rates
tended to be erratic with a significant excess of hydrogen produced
in the early stages of the reaction when water was poorly
distributed in the developing alkaline foam and crust.
[0152] Furthermore, the observed rates indicated that the
granulated and powder forms of solid borohydride performed better
than the pellet forms owing to better transfer of water in the
hydrolyzing solids. The inclusion of plain paper wicking laid out
on the bottom of the floor of the tubular reactor smoothed the
rates for the case of granules and fresh powder by increasing the
distribution of water within the crust, but did not improve rates
for the pellet forms.
Example 14
Temperature Effects
[0153] Satisfactory rates of hydrogen gas generation have been
obtained for the hydrolysis of 178 mmol quantities of sodium
borohydride powder when ruthenium chloride catalyst is present in
excess and the rate of reaction is controlled by metering the
reagent aqueous antifoam solution via a syringe pump for 60-63
minutes. Slight scatter is evident for runs obtained at 21.degree.
C. with an average standard deviation of 30.6 mL/min of hydrogen
gas per minute as shown in FIG. 15. The five runs shown in FIG. 15
were run under conditions including 178 mmol of sodium borohydride
with 8.17 wt % ruthenium chloride with delivery of the aqueous
solution at 0.374 mL/min for 60 minutes at an ambient temperature
of 21.degree. C. and 5 wt % wicking material. The rates were steady
and the average useful duration of hydrolysis reaction was 55
minutes.
[0154] The same tests were run at 15.degree. C., holding all other
variables constant, with the results shown in FIG. 16. Scatter is
significant for the runs at 15.degree. C. (average standard
deviation=37.7 mL/min) because the wetting front was sometimes
stalled in progressing along the length of the tube despite the
presence of a wick.
Example 15
A PEI Hydrogen Generator
[0155] A packet hydrogen generator comprising a flexible bag having
a mass of 7.7 g, measuring about 31/2 in..times.6 in. and made of
three sheets of polyetherimide (PEI) was constructed for testing.
The sheets were bonded together with high temperature Bemis hot
melt adhesive. Two GORE PREVENTS.TM. barriers were mounted on the
middle PEI sheet with polypropylene backing or alternatively, with
nickel foam backing. The inlet check valve and exit barb were
mounted to the upper sheet. Fuel supplied to the hydrogen generator
comprised a blend of 178 mmol of sodium borohydride (6.73 g) and
8.17 wt % ruthenium chloride catalyst formed into pellets. The
pellets were inserted between the middle and lower PEI sheets and
sealed either just prior to initiating the hydrolysis reaction, or
at the time of fabrication of the bag. Water with antifoam additive
was introduced via the centrally located check valve from an
overhead position at a rate of 0.374 mL/min at 21.degree. C.
[0156] FIG. 17 shows that the average standard deviation for three
runs was 25.4 mL/min H.sub.2 with the flow remaining well above the
240 mL/min target for over 50 minutes. The brief spike in the rate
at the onset of the hydrolysis reaction is actually useful, as it
insures that the fuel cell is rapidly purged of air or inert gas.
Quantitative amounts of hydrogen gas are thereby obtained,
especially when the pellets are clustered near the antifoam
solution inlet valve.
Example 16
Effect of Pre-Wetting the Pellets
[0157] The rate of hydrogen generation can be prolonged through
reducing the rate of delivery for the aqueous hydrolysis solution
after an initial reaction initiation period. These tests were
conducted using the apparatus described in Example 2 modified by
adding a syringe pump to inject water into the flask in a slow
controlled manner so that the hydrogen generation rate was actively
controlled by the rate of water addition. The pelletized fuel
comprised 178 mmol sodium borohydride blended with 8.17 wt %
ruthenium chloride.
[0158] For the hydrolysis reaction with pellets, preferably a
preadsorption or wetting period is provided to ensure a steady rate
of prolonged hydrolysis of the sodium borohydride pellets. The rate
of the water/defoamer solution was is 0.374 mL/min during an
initial preadsorption period.
[0159] The results provided in FIG. 18 show that the minimum
preadsorption time can be as little as 5 minutes with an ensuing
steady flow of hydrogen gas that can extend for an additional 110
minutes. If the pellets are wetted at an initial rate of 0.374
mL/min for 5 to 20 minutes, the overall duration of the hydrolysis
reaction may be prolonged by a shift in delivery rate to as little
as 0.15 mL/min. A target flow of 120 mL H.sub.2 per minute is met
or exceeded for a duration of about two hours when the solution
delivery rate thereafter is slowed to as little as 0.15 mL/min. The
initial surge of water serves to rapidly wet a substantial amount
of the hydride, which promotes a stable reaction thereafter. The
initial surge of hydrogen is useful for insuring that the fuel cell
is quickly purged of inert gases that may have been present in
storage.
[0160] The results of varying the temperature under these
conditions are shown in FIG. 19. It is apparent that the average
hydrolysis rates appear in a cluster over the temperature range
from 15.degree. C. to 30.degree. C., but that the average rate
obtained at 10.degree. C. falls below this cluster. It may be seen
from these results that the actively controlled hydrogen generator
is useful over a wide temperature range.
Example 17
Effect of Changes in the Feed Rate of the Aqueous Solution
[0161] Rates of hydrogen generation may also be varied in response
to rapid changes in the flow of the aqueous solution containing an
antifoam agent where it is important for the fuel cell to follow a
varying load demand. FIG. 20 shows the profile of response of the
generator to frequent changes in rate of delivery of antifoam
solution to the generator bag. For cycling between an energy demand
requiring 270 mL H.sub.2 per minute and a lower level energy demand
requiring 120 mL H.sub.2/min, the packet style generator will
perform reliably and at repeated rates for about an hour. Although
performance for the high demand portion of the cycle falls off with
time, the low demand performance is virtually invariant. The
generator tends to respond to changes in rate of aqueous solution
within 20 to 40 seconds. The values of the aqueous solution
delivery rates shown in FIG. 20 are expressed in units of mL/min.
The size of the packet generator was 31/2 in by 5 in. Water with 50
ppm "C-2245" antifoam agent was delivered by a variable speed
syringe pump and hydrogen flow was monitored (after drying) with a
hydrogen mass flow monitor. The ambient temperature was about
22.degree. C.
Example 18
Preparation of a Blend of Catalyzed Hydride
[0162] A quantity of tetrahydrofuran (THF) is rigorously dried by
stirring with freshly dried 3A molecular sieve for sixteen hours in
a closed flask. The solvent is allowed to remain in contact with
the sieves until used. The flask of THF is transferred into a glove
bag, with the other ingredients for the mixture, and the bag
thoroughly purged with dry argon.
[0163] Under the inert atmosphere of the glove bag, 200 mL of the
solvent is filtered into a round bottomed flask, 30 g of sodium
borohydride added, and the mixture stirred until the borohydride
dissolved. While the borohydride dissolves, an additional 30 mL of
THF is filtered and placed in a small Erlenmeyer flask along with
0.5 g of ruthenium acetylacetonate
(Ru(C.sub.5H.sub.7O.sub.2).sub.3). The flask is swirled by hand
until a clear solution is produced. The two solutions are combined
and the flask stoppered for removal from the glove bag.
[0164] The flask containing the solution is connected to a rotary
evaporator with a condenser cooled to below 10.degree. C. and
evacuated. The flask is rotated and heated with a warm water bath
until all of the solvent evaporates. The flask with the dried
material is returned to the glove box bag, the bag purged, and the
material placed in a tightly sealed bottle until ready for use.
Example 19
Preparation of a Blend of Catalyzed Hydride Using Ammonia
[0165] This process is carried out in a sealed system for
protection from noxious fumes. A quantity of anhydrous ammonia is
rigorously dried by stirring under pressure at ambient temperature
with sodium and the vessel with the ammonia connected via a common
manifold with the other vessels used in this process. Quantities of
104 g of sodium borohydride and 2 g of cobalt acetylacetonate
(Co(C.sub.5H.sub.7O.sub.2).sub.3) are weighed into separate
containers and connected to the manifold so that the
Co(C.sub.5H.sub.7O.sub.2).sub.3 could be mixed with the sodium
borohydride after both are dissolved in the ammonia.
[0166] The borohydride container is cooled with a dry ice-acetone
bath and the container of ammonia slightly opened. Sufficient
ammonia is distilled into the container to supply 100 g of solvent.
The container is closed, allowed to warm, and the borohydride
dissolved. Sufficient ammonia is distilled into the
Co(C.sub.5H.sub.7O.sub.2).sub.3 container to provide 20 g of
solvent. The container is closed, allowed to warm, and the
Co(C.sub.5H.sub.7O.sub.2).sub.3 dissolved. The two solutions are
then mixed together.
[0167] The container of mixed ingredients is sealed, disconnected
from the manifold and connected, via an atomizing nozzle, to a
large, evacuable chamber in an orientation that allows the solution
to be sprayed into the chamber as a liquid. The chamber is
evacuated and the vacuum pump left running to maintain a dynamic
vacuum. The solution is gradually sprayed into the chamber where
the ammonia flashes off as a vapor, leaving a solid blend of sodium
borohydride and Co(C.sub.5H.sub.7O.sub.2).sub.3. The mixture of
solids is collected at the bottom and the gas removed from the
top.
[0168] It will be understood from the foregoing description that
various modifications and changes may be made in the preferred and
alternative embodiments of the present invention without departing
from its true spirit. This description is intended for purposes of
illustration only and should not be construed in a limiting sense.
The scope of this invention should be determined only by the
language of the claims that follow.
* * * * *