U.S. patent application number 11/232008 was filed with the patent office on 2006-02-02 for system for hydrogen generation.
Invention is credited to Richard M. Mohring, Michael Strizki.
Application Number | 20060021279 11/232008 |
Document ID | / |
Family ID | 31886703 |
Filed Date | 2006-02-02 |
United States Patent
Application |
20060021279 |
Kind Code |
A1 |
Mohring; Richard M. ; et
al. |
February 2, 2006 |
System for hydrogen generation
Abstract
The present invention relates to an improvement in a system for
the generation of hydrogen by contacting an aqueous solution of a
metal hydride salt with a hydrogen generation catalyst. In
particular, the present invention relates to the incorporation
within the system of a recycle line of water condensed from the
fluid product to the feed line to be contacted with the catalyst.
The internal recycle line permits the use of a more concentrated
solution of metal hydride as it is diluted by the recycle line
prior to contact with the catalyst.
Inventors: |
Mohring; Richard M.; (East
Brunswick, NJ) ; Strizki; Michael; (Hopewell,
NJ) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
2101 L Street, NW
Washington
DC
20037
US
|
Family ID: |
31886703 |
Appl. No.: |
11/232008 |
Filed: |
September 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10223871 |
Aug 20, 2002 |
|
|
|
11232008 |
Sep 22, 2005 |
|
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Current U.S.
Class: |
48/61 |
Current CPC
Class: |
Y02E 60/36 20130101;
C01B 3/065 20130101; B01J 8/0278 20130101; Y02P 20/584 20151101;
B01J 7/02 20130101; Y02E 60/362 20130101 |
Class at
Publication: |
048/061 |
International
Class: |
B01J 7/00 20060101
B01J007/00 |
Claims
1-18. (canceled)
19. A method of generating hydrogen, comprising: providing an
aqueous composition containing at least one metal hydride;
contacting the metal hydride with a hydrogen generation catalyst to
generate a fluid product stream comprising hydrogen, water and a
metal salt; and mixing at least part of the water of the fluid
product stream with the metal hydride prior to contacting the metal
hydride with the catalyst.
20. The method of claim 19, wherein the metal hydride is provided
in the form of an aqueous solution.
21. The method of claim 19, further comprising separating the fluid
product stream into a gaseous product comprising hydrogen and water
vapor, and a liquid product comprising water and the metal
salt.
22. The method of claim 21, further comprising condensing water
from the gaseous product recovering the condensed water.
23. The method of claim 22, further comprising combining the
condensed water with the metal hydride composition prior to
contacting the metal hydride with the hydrogen generation
catalyst.
24. The method of claim 22, further comprising providing a pump for
withdrawing the condensed water from a condensate recovery zone and
introducing it into a mixing zone.
25. The method of claim 19, further comprising withdrawing the
aqueous composition containing a metal hydride from a fuel supply
reservoir before contacting with the catalyst.
26. The method of claim 25, wherein the withdrawing is conducted
using a fuel pump.
27. The method of claim 26, wherein the fuel pump is located
upstream of a mixing zone for mixing at least part of the water of
the fluid product stream with the aqueous composition containing a
metal hydride.
28. The method of claim 27, wherein the mixing zone is located in
fluid communication with the fuel pump and the hydrogen generation
catalyst.
29. The method of claim 28, further comprising providing a valve
upstream of the mixing zone and permitting alternative flow of the
metal hydride composition and condensed water from a condensate
zone into the mixing zone.
30. The method of claim 24, wherein the concentration of metal
hydride in the fuel supply reservoir is above the maximum
solubility of the hydride and a portion thereof is in
suspension.
31. The method of claim 30, wherein sufficient condensed water is
added to the mixing zone so that all of the metal hydride is in
solution when it contacts the hydrogen generation catalyst.
32. The method of claim 30, further comprising maintaining
uniformity of the suspension.
33. The method of claim 19, further comprising providing a
sufficient amount of an alkaline stabilizing agent to the aqueous
composition containing a metal hydride to provide a pH thereof at
about 7.
34. The method of claim 33, wherein the alkaline stabilizing agent
is an hydroxide.
35. The method of claim 33, wherein the cation portion of the
alkaline stabilizing agent is the same as the cation portion of the
metal hydride.
36. The method of claim 35, wherein the cation is a sodium ion.
37. The method of claim 33, wherein the alkaline stabilizing agent
is sodium hydroxide and the metal hydride is sodium
borohydride.
38. The method of claim 19, further comprising providing a
containment system for the catalyst.
39. The method of claim 38, wherein the containment system
comprises a cylinder having the catalyst therein.
40. The method of claim 19, wherein the hydrogen generation
catalyst comprises a transition metal selected from the group
consisting of ruthenium, iron, cobalt, nickel, copper, manganese,
rhodium, rhenium, platinum, palladium, chromium, silver, osmium,
iridium, borides thereof, alloys thereof, and mixtures thereof.
41. The method of claim 19, wherein the metal hydride is selected
from the group consisting of sodium borohydride, lithium
borohydride, potassium borohydride, ammonium borohydride, and
mixtures thereof.
42. The method of claim 19, wherein the catalyst is a supported
catalyst.
43. A method of generating hydrogen, comprising: providing a fuel
supply reservoir containing an aqueous solution of at least one
metal hydride; withdrawing the aqueous solution from the reservoir
and contacting the aqueous solution with a hydrogen generation
catalyst to generate a fluid product stream comprising hydrogen,
water and a salt of the metal; separating the fluid stream into a
gaseous product comprising hydrogen and water vapor, and a liquid
product comprising water and the metal salt; recovering at least
part of the water vapor to obtain recovered water; and mixing the
recovered water with the aqueous solution of metal hydride prior to
contacting the catalyst.
44. The method of claim 43, wherein mixing is conducted in a
separate mixing zone prior to contacting the metal hydride with the
hydrogen generation catalyst.
45. The method of claim 43, wherein withdrawing the solution from
said fuel supply reservoir is conducted with a fuel pump.
46. The method of claim 45, wherein the fuel pump is located
upstream of the mixing zone.
47. The method of claim 43, wherein the mixing zone is located in
fluid communication with the fuel pump and the hydrogen generation
catalyst.
48. The method of claim 43, further comprising providing a pump for
withdrawing the recovered water from a recovery zone and
introducing it into the mixing zone.
49. The method of claim 43, further comprising providing a valve
upstream of the mixing zone for permitting alternative flow of the
metal hydride solution and the recovered water into the mixing
zone.
50. The method of claim 43, wherein the concentration of the metal
hydride in the fuel supply reservoir is above the maximum
solubility of the hydride and a portion thereof is in
suspension.
51. The method of claim 50, further comprising adding sufficient
recovered water to the mixing zone so that all of the metal hydride
is in solution when it contacts the hydrogen generation
catalyst.
52. The method of claim 50, further comprising agitating the fuel
supply to maintain uniformity of the suspension.
53. The method of claim 50, further comprising providing a
sufficient amount of an alkaline stabilizing agent to the aqueous
solution of metal hydride to provide a pH thereof at about 7.
54. The method of claim 53, wherein the alkaline stabilizing agent
is an hydroxide.
55. The method of claim 53, wherein the cation portion of the
alkaline stabilizing agent is the same as the cation portion of the
metal hydride.
56. The method of claim 55, wherein the cation is a sodium ion.
57. The method of claim 53, wherein the alkaline stabilizing agent
is sodium hydroxide and the metal hydride is sodium
borohydride.
58. The method of claim 43, further comprising providing a
containment system for the catalyst.
59. The method of claim 58, wherein the containment system
comprises a cylinder having the catalyst therein.
60. The method of claim 43, wherein the hydrogen generation
catalyst comprises a transition metal selected from the group
consisting of ruthenium, iron, cobalt, nickel, copper, manganese,
rhodium, rhenium, platinum, palladium, chromium, silver, osmium,
iridium, borides thereof, alloys thereof, and mixtures thereof.
61. The method of claim 43, wherein the metal hydride is selected
from the group consisting of sodium borohydride, lithium
borohydride, potassium borohydride, ammonium borohydride, and
mixtures thereof.
62. The method of claim 43, wherein the catalyst is a supported
catalyst.
Description
[0001] The present invention relates to a system for generating
hydrogen gas. In particular, the present invention relates to a
hydrogen generation system including a stabilized metal hydride
solution and a catalyst system.
BACKGROUND OF THE INVENTION
[0002] Hydrogen is a "clean fuel" because it can be reacted with
oxygen in hydrogen-consuming devices, such as a fuel cell or
combustion engine, to produce energy and water. Virtually no other
reaction byproducts are produced in the exhaust. As a result, the
use of hydrogen as a fuel effectively solves many environmental
problems associated with the use of petroleum based fuels. Safe and
efficient storage of hydrogen gas is, therefore, essential for many
applications that can use hydrogen. In particular, minimizing
volume and weight of the hydrogen storage systems are important
factors in mobile applications.
[0003] Several methods of storing hydrogen currently exist but are
either inadequate or impractical for wide-spread consumer
applications. For example, hydrogen can be stored in liquid form at
very low temperatures. However, liquid hydrogen is neither safe nor
practical for most consumer applications. Moreover., the energy
consumed in liquefying hydrogen gas is about 60% of the energy
available from the resulting hydrogen.
[0004] As a result of these and other disadvantages of hydrogen
storage and transportation, the art has turned to fuel cells and
systems for the generation of hydrogen. Such systems are known, for
example Amendola et al, Abstracts ACS National Meeting, August,
1999, pages 864-868, describe such a system that is suitable for
use in motor vehicles that is based on the catalyst generation of
hydrogen from an aqueous metal hydride solution. In accordance with
the present invention, an improvement in the operation of such
systems is provided.
SUMMARY OF THE INVENTION
[0005] There is provided an improvement in a hydrogen generation
system including a metal hydride solution and a catalyst that
activates the reaction of the metal hydride with water to produce
hydrogen gas. The system includes a means for condensing water
vapor from the hydrogen product flow. The system is improved in
accordance with the present invention by recycling a portion of the
condensate water into the feed line to mix with and dilute the
metal hydride fuel solution before it is contacted with the
catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The advantages of the present invention will be further
understood from the following detailed description when considered
with the accompanying drawings wherein:
[0007] FIG. 1 is a block diagram of a conventional system for the
generation of hydrogen from a metal hydride solution.
[0008] FIG. 2 is a block diagram of the improved system of the
present invention.
[0009] FIG. 3 is a block diagram of an alternative embodiment of
the improved system of the present invention.
[0010] FIG. 4 is a block diagram of a still further embodiment of
the improved system of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The system for the generation of hydrogen in accordance with
the present invention is comprised of an aqueous metal hydride
solution fuel and a catalyst for promoting the reaction of the
metal hydride to produce hydrogen, a byproduct salt of the metal
and water in the form of water vapor. This system has been
demonstrated to produce hydrogen safely and efficiently for use in
a hydrogen fuel cell that possesses many advantages over
conventional fuel systems, such as gasoline engines.
[0012] A conventional system for hydrogen generation from an
aqueous metal hydride solution is shown in block diagram in FIG. 1.
Aqueous metal hydride solution is withdrawn from a reservoir 1
through a conduit line 3 by a fuel pump 5 into a catalyst chamber
or compartment 7 where it undergoes reaction to form a fluid
product stream comprising hydrogen, a salt of the metal and water.
The product stream is withdrawn through conduit line 9 into a gas
liquid separator 11 where the byproduct salt is withdrawn as a
solution through conduit line 13 and the gaseous hydrogen product
mixture is withdrawn through conduit line 15. The system is
completely inorganic and produces a high quality energy source
without polluting emissions. The system is likewise readily
controllable since hydrogen is only produced when the solution
contacts the catalyst.
[0013] The metal hydride fuel component of the system illustrated
in FIG. 1 and in the subject improved system is a complex metal
hydride having the general formula MBH.sub.4 wherein M is a
positive ion selected from those of an alkali metal, such as
sodium, potassium or lithium, certain organic groups and ammonium,
B is a negative ion of a metal selected from Group 13 (formally
Group IIIA) of the Periodic Table, such as boron, aluminum and
gallium, and H is hydrogen. Examples of suitable metal hydrides,
without intended limitation, include NaBH.sub.4, LiBH.sub.4,
NH.sub.4BH.sub.4, LiAlH.sub.4, NaGaH.sub.4 and the like. These
metal hydrides may be utilized in mixtures, but are preferably
utilized individually. Preferred for such systems in accordance
with the present invention are borohydrides, especially sodium
borohydride (NaBH.sub.4), lithium borohydride (LiBH.sub.4),
potassium borohydride (KBH.sub.4), ammonium borohydride
(NH.sub.4BH.sub.4), quaternary ammonium borohydrides and the like,
including mixtures thereof A borohydride, such as illustrated
above, will react with water to produce hydrogen gas and a borate
in accordance with the following chemical reaction:
BH.sub.4.sup.-+2H.sub.2O=BO.sub.2.sup.-+4H.sub.2 This reaction
takes place very slowly in the absence of a catalyst. It has
further been found that the solution of metal hydride salt is
stable without appreciable generation of hydrogen at alkaline pH.
The salt formed in the reaction, borate in the instance of a metal
borohydride, is non-toxic and environmentally safe. In addition,
borate can be regenerated into borohydride for future use. It is
important to note that all of the hydrogen atoms present in
borohydride and water are converted to hydrogen gas, and that half
of the hydrogen atoms in the hydrogen gas produced by the reaction
given above actually come form the water.
[0014] In general, the various borohydride salts are soluble in
water up to about 35%, lithium borohydride has only about 7%
solubility, potassium borohydride about 19% and sodium borohydride
about 35%. It will be appreciated that sodium borohydride is
preferred for the practice of the present invention due to its
comparatively high solubility. Where the concentration of the metal
hydride in the fuel system exceeds the maximum solubility of the
particular salt utilized, it will be in the form of a slurry or
suspension. This is acceptable provided that only a minor portion
of the metal hydride is not in solution and the fuel system
includes a means of maintaining the uniformity of the slurry or
suspension withdrawn to be exposed to the catalyst. As will be
detailed below, the present invention is advantageous in that a
slurry of the fuel borohydride may be utilized for greater economy
of operation.
[0015] Since two molecules of water are consumed for each
borohydride molecule during the reaction illustrated above, the
product stream containing the borate salt is more concentrated than
the borohydride fuel mixture. Stoichiometrically, twice as many
water molecules as borohydride molecules are required to sustain a
constant rate of reaction. In practice, water in excess of even
that requirement is necessary for the efficient conversion of the
sodium borohydride to hydrogen.
[0016] This excess water has heretofore been provided in two ways:
charging the initial metal hydride solution with excess water, i.e.
starting with a dilute solution, or adding more water from a
separate source during or after the reaction. The second
alternative is clearly preferable for reasons of economy since
utilizing a dilute fuel solution would substantially increase the
size of the fuel tank 3 in FIG. 1. It has been proposed in
co-pending application Ser. No. 09/479,362 to utilize a separate
source of water from the hydrogen-consuming device, e.g. a fuel
cell, combustion engine or a gas turbine. Since these devices
consume hydrogen, a main by-product is water and it is proposed to
utilize some of this water to maintain a constant rate of reaction
in the subject hydrogen generators. However, such use still
represents a source of water external to the system. It is often
the case that such water is utilized in a humidification loop to
maintain the membrane in a proton exchange membrane (PEM) fuel cell
and is not available for recycle to other parts of the system.
[0017] The concept of recycling water from the device, e.g. a fuel
cell, has been proposed as well in U.S. Patent Application
Publication No. US 2002/0025462, published Feb. 28, 2002. The
disclosed system includes a condenser to remove water from the
hydrogen gas stream by radiative cooling as well. Further,
MacCarley, Symposium on Alternative Fuel Resources, Santa Monica,
Calif., March, 1976, pages 315-320, in discussing hydrogen systems
for automotive application describes condenser loops for the
removal of water from the generated hydrogen gas stream. However,
the paper does not specifically mention the recycling of water and
gives no detail as to how or where the recycling would be carried
out. As will be shown below, the present invention improves on this
concept by providing a recycle of water within the hydrogen
generator itself thereby significantly enhancing the economies of
its operation.
[0018] The metal hydride solution utilized as the fuel for the
system is stabilized against decomposition by being at an alkaline
pH, i.e. a pH of at least above pH 7. This is carried out by the
addition of a suitable alkaline stabilizing agent, preferably a
hydroxide, most preferably an alkali metal hydroxide. It is
particularly preferred that the cation portion of the alkaline
stabilizing agent be the same as the cation of the metal hydride
salt. For example, if the metal borohydride is sodium borohydride,
the alkaline stabilizing agent would be sodium hydroxide, both of
which are preferred in the practice of the present invention. The
concentration of the alkaline stabilizing agent is typically
greater than about 0.1 molar, preferably greater than 1.0 molar or
about 4% by weight. The alkaline stabilizing agent is typically
added to the water prior to the addition of the borohydride
thereto. Sodium hydroxide is a particularly preferred stabilizing
agent due to its high solubility in water (about 44%) which allows
stability of the solution without adversely affecting the
solubility of the metal borohydride. The presence of the alkaline
stabilizing agent prevents premature reaction and degradation of
the metal hydride salt before it contacts the catalyst.
[0019] The catalyst in the subject system is present in a
containment means so that it can be separated from the reacted
metal hydride solution which, in the instance of a sodium
borohydride fuel mixture, would contain a mixture of NaBO.sub.2 and
NaBH.sub.4. Containment may be any physical, chemical, electrical
and/or magnetic means of securing the catalyst. Containment systems
are preferably a tube or cylinder retaining the catalyst between
mesh or porous ends such that the solution can flow through during
the reaction and the product liquid/gas mixture is withdrawn from
the downstream end. Other similar means will be readily apparent to
those of ordinary skill in the art.
[0020] The catalyst can also be attached or bound to a suitable
substrate, i.e. a supported catalyst, and thereby be contained in
that the substrate is held in place while the solution of metal
hydride passes over it. Thus, hydrogen production can be controlled
by either contacting or separating the bound catalyst from the
metal hydride solution. An example of such a catalyst is one
entrapped by physical or chemical means onto and/or within a porous
or nonporous substrate. Nonlimiting examples of porous substrates
include ceramics and ion exchange resins. Nonlimiting examples of
nonporous substrates include metallic meshes, fibers and fibrous
materials. The preparation of such supported catalysts is taught,
for example in copending application Ser. No. 09/999,226, the
disclosure of which is incorporated herein by reference.
[0021] Preferably, the catalyst facilitates both aspects of the
reaction of the metal hydride and water, i.e. the availability of a
hydrogen site and the ability to assist in the hydrolysis
mechanism. Metal hydride solutions are complex systems having
multi-step reduction mechanisms. For example, borohydride has four
hydrogens and an eight-electron reduction mechanism. Thus, once a
single hydrogen atom is removed from a borohydride molecule, the
remaining moiety is unstable and will react with water to release
the remaining hydrogen atoms. Catalysts that are useful in the
system of the invention include, without intended limitation,
transition metals, transition metal borides, alloys of these
materials and mixtures thereof.
[0022] Suitable transition metal catalysts for the generation of
hydrogen from a metal hydride solution are known in the art and
include metals from Group 1B to Group VIIIB of the Periodic Table,
or compounds made from these metals. Representative examples of
these metals include, without intended limitation, transition
metals represented by the copper group, zinc group, scandium group,
titanium group, vanadium group, chromium group, manganese group,
iron group, cobalt group and nickel group. These catalyst metals
aid in the reaction by adsorbing hydrogen on their surface in the
form of the protonic H.sup.+. Examples of useful catalyst metals
include, without intended limitation, ruthenium, iron, cobalt,
nickel, copper, manganese, rhodium, rhenium, platinum, palladium,
chromium, silver, osmium, iridium borides thereof, alloys thereof
and mixtures thereof. Ruthenium, rhodium and cobalt are
preferred.
[0023] The catalysts preferably have high surface area, i.e. they
have small average particle sizes, for example an average diameter
of less than about 100 microns, preferably less than about 50
microns, most preferably less than about 25 microns. The chemical
reaction of metal hydrides in water in the presence of the catalyst
follows zero order kinetics at all concentrations of metal hydride
measured, i.e. the volume of hydrogen gas generated is linear with
time. It is, therefore, believed that the reaction rate depends
primarily on the surface area of the catalyst. In addition to metal
particles having very small average particle size, larger
particles, e.g. agglomerates may be utilized provided that they
have sufficient porosity to possess the requisite surface area.
[0024] In the system improved upon in accordance with the present
invention, the generation of hydrogen can be controlled by
regulating contact of the solution with the catalyst because little
hydrogen will be generated from the stabilized solution in its
absence. Control can be effected. for example, by regulating the
flow of solution to the catalyst, or by withdrawing the catalyst
from the solution to cease production. It has been found that
hydrogen generation is increased with increases in temperature and
is fairly constant at a given temperature until the metal hydride
solution is almost exhausted. It will be appreciated by those of
ordinary skill in the art that the desired rate of reaction can be
obtained and controlled by factors including regulation of the
temperature, the concentration of the alkaline stabilizing agent,
the selection of a catalyst, the surface area of the catalyst and
the like.
[0025] Several methods are available to contact the stabilized
metal hydride solution with the catalyst system. When hydrogen is
required, the solution can be pumped to a chamber containing the
catalyst or the catalyst can be moved into a tank containing the
solution. The metal hydride solution can be pumped either in
batches or continuously. The instantaneous demand for hydrogen can
be met with a small buffer tank, not illustrated, that always
contains a supply of available hydrogen gas. The hydrogen gas from
this tank can be utilized to meet immediate demand and the
resultant pressure drop can trigger the system to produce more
hydrogen gas, thereby maintaining a constant supply of hydrogen
available to the hydrogen-consuming device.
[0026] As illustrated by FIG. 2, the conventional system shown in
FIG. 1 is improved upon in accordance with the present invention by
the addition of a recycle stream of condensate water to the feed
into the catalyst chamber 7. In FIG. 2, structures that are the
same as shown in FIG. 1 have like numbering. In FIG. 2, the gaseous
product stream of hydrogen and water in the form of steam exiting
gas/liquid separator 11 through conduit line 15 is cooled in a
condenser/heat exchanger 17 and caused to pass into a separation
and recovery zone 21 through conduit line 19. In condensate
recovery zone 19, the pressure is reduced so that the hydrogen
product with some residual water vapor separates from liquid water
and is withdrawn through product conduit line 23. It is not
necessary to effect a total separation of the water in the product
gas since, as discussed above, it is beneficial to have some water
vapor therein. The recovered water is caused to flow through
conduit line 25 to a control unit 27 that may be a valve or simply
an orifice to restrict flow, and then via conduit line 29 to mixing
zone 31 where it is mixed in the desired proportion with the
incoming metal hydride fuel supply to form a diluted fuel mixture
that is fed into catalyst chamber 7 by pump 5 as described with
reference to FIG. 1.
[0027] There are several advantages realized by the recycle system
illustrated in FIG. 2. The most important of these is probably the
economy of being able to store and utilize a concentrated metal
hydride solution fuel supply. This allows the use of a smaller fuel
reservoir without sacrificing the duration of hydrogen generation
between refueling the system. It is possible as mentioned above to
utilize a metal hydride fuel supply of such concentration that a
minor portion of the metal hydride is not in solution resulting in
a suspension or slurry. It is also possible to utilize a solution
containing the maximum concentration of metal hydride with the
possibility that, with environmental changes, a portion thereof may
come out of solution. If a minor portion of the metal hydride is
not in solution be design or due to environmental changes, the
amount of water admitted to mixing zone 31 by control means 27
would be increased such that complete solubilization thereof and
the desired dilution are both achieved prior to introduction of the
fuel solution to catalyst chamber 7. It would also be preferable to
have in conjunction with fuel supply 1, a mixing means, not shown,
such as a mechanical stirrer or turbulence agitator that would
assure that the slurry provided from the fuel supply 1 is
substantially uniform.
[0028] It will be appreciated that the amount of the metal hydride
salt that is not in solution in the fuel supply concentrate is
limited by the configuration, of the system, the amount of water
that can be added thereto through conduit 29, the time available to
affect solubilization thereof and the like. Typically, the fuel
supply will contain no more than about 5% of undissolved metal
hydride.
[0029] A second advantage of the recycle system provided in
accordance with the present invention is that the addition of water
from the recycle line maintains a dilute fuel feed thereby
significantly reducing the possibility of the system becoming
clogged as a result of the water being used up to the point where
there is insufficient water exiting the catalyst chamber 7 to
maintain the product salt, a borate in the case of the fuel being a
metal borohydride, in solution. Precipitation of the product salt
in the catalyst chamber itself or in any of the associated
downstream apparatus of piping will render the system ineffective
until disassembled and cleaned. Such a problem can be very
significant in terms of the use of such systems as an alternate
power source for vehicles.
[0030] A further advantage of the system of the invention is that
the water exiting the condensate recovery tank 21 is at a
significantly lower temperature than in the catalyst chamber 7,
hence it functions as an aid in controlling the temperature of the
reaction, which is exothermic. This added control of system
operating temperature is also significant in the contemplated use
of the system to power vehicles. More important, however, is the
fact that the regulating capacity of the system assures a
substantially constant flow of product hydrogen, a commercially
significant advantage. A still further advantage of the system of
the invention is the fact that the recycle system is internal of
the system. i.e. it can be within the system itself so that there
is no need for external apparatus such as tanks and/or conduits to
introduce water from an external source.
[0031] Another embodiment of the improved system according to the
present invention is shown in FIG. 3, wherein like structures have
like numbering. In FIG. 3, the metering of the diluted fuel into
the mixing zone 31 is effected by the fuel pump 5 that is located
upstream of mixing zone 31 and by a second pump, condensate pump
33, also located upstream of mixing zone 5. Regulation of these two
pumps produces the proper feed into mixing zone 5 so that the
desired dilution is achieved.
[0032] In a further embodiment of the present invention shown in
FIG. 4, wherein similar structures have like numbering, the mixing
zone 31 is upstream of fuel pump 5. Flow of condensate water and
concentrated fuel mixture into mixing zone 5 is regulated by a
three-way valve 35, such as a toggle valve, that controls the
amounts of each feed by alternating flow thereof into the mixing
zone 5. In each instance, control of the proper dilution of the
fuel mixture that enters the catalyst chamber 7 is effect by
conventional sensing apparatus, not shown, that feeds information
into computer means, not shown, that in turn regulates the amount
of each component of the fuel mixture introduced into the mixing
zone 5 through conduit line 37. Such apparatus as well as the
placement and use thereof to establish the proper dilution of the
fuel mixture to be introduced into the mixing zone 5 is considered
to be within the skill of the art.
[0033] The following example further describes and demonstrates the
improved operation of the subject system according to the present
invention. The example is given solely for the illustration
purposes and is not to be construed as a limitation of the present
invention.
EXAMPLE
[0034] A hydrogen generation test system according to FIG. 2 was
constructed to bench test the improved system of the invention. The
mixing zone 5 was a static inline tube mixer consisting of tubing
containing a twisted piece of metal. The fuel supply concentrate
tank 1 contained a 30% aqueous solution of sodium borohydride that
was passed into the system at a flow rate of approximately 850
mL/min. The condensate recycle was fed into the mixing zone 31 at a
flow rate of approximately 300 mL/min. In spite of fluctuations in
liquid flow rates caused by pressure variations within the system,
the ratio of fuel concentrate to condensate was kept nearly
constant so as to maintain a nearly constant dilute effective fuel
concentration. The effective concentration of fuel solution
introduced into the catalyst chamber 7 for a test run was
approximately 22%. Both effective rate of hydrogen generation and
conversion of the sodium borohydride fuel solution for the system
were constant over the run. It will be appreciated that the ability
of the improved system accordance with the present invention to
control the variables necessary to maintain a constant product flow
is significant for such uses as the powering of vehicles.
* * * * *