U.S. patent application number 13/071346 was filed with the patent office on 2011-09-29 for method and system for electrochemical hydrogen generation.
This patent application is currently assigned to RASIRC. Invention is credited to Daniel Alvarez, JR., Jeffrey J. Spiegelman.
Application Number | 20110233069 13/071346 |
Document ID | / |
Family ID | 44655103 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110233069 |
Kind Code |
A1 |
Spiegelman; Jeffrey J. ; et
al. |
September 29, 2011 |
METHOD AND SYSTEM FOR ELECTROCHEMICAL HYDROGEN GENERATION
Abstract
An apparatus, a system and a method for electrochemical
generation of hydrogen are disclosed. The apparatus may include a
cathode, a polymer electrolyte membrane surrounding the cathode and
a housing surrounding the polymer electrolyte membrane. The housing
may include an anode electrically connected to the cathode. The
system for electrochemical generation of hydrogen may include a
water purifier in fluid communication with a hydrogen generating
unit, an electrolyte source in fluid communication with the
hydrogen generation unit and a power source electrically connected
to the hydrogen generating unit. The method may include passing
water and electrolyte into the hydrogen generation unit and
applying a voltage between the anode and the cathode to generate
hydrogen gas.
Inventors: |
Spiegelman; Jeffrey J.; (Del
Mar, CA) ; Alvarez, JR.; Daniel; (Oceanside,
CA) |
Assignee: |
RASIRC
San Diego
CA
|
Family ID: |
44655103 |
Appl. No.: |
13/071346 |
Filed: |
March 24, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61317014 |
Mar 24, 2010 |
|
|
|
Current U.S.
Class: |
205/638 ;
204/237; 204/260; 204/263 |
Current CPC
Class: |
C25B 1/04 20130101; C25B
9/19 20210101; C25B 9/00 20130101; Y02E 60/36 20130101; C25B 15/08
20130101 |
Class at
Publication: |
205/638 ;
204/260; 204/263; 204/237 |
International
Class: |
C25B 1/04 20060101
C25B001/04; C25B 9/00 20060101 C25B009/00; C25B 15/08 20060101
C25B015/08 |
Claims
1. An electrochemical cell for generation of hydrogen, comprising:
a cathode; a polymer electrolyte membrane surrounding the cathode;
and a housing surrounding the polymer electrolyte membrane, wherein
the housing comprises an anode, and wherein the anode is
electrically connected to the cathode.
2. The electrochemical cell of claim 1, comprising an anode
compartment positioned between an anode side of the polymer
electrolyte membrane and the housing.
3. The electrochemical cell of claim 2 further comprising an inlet
port in fluid communication with the anode compartment and
configured to allow water flow into the anode compartment.
4. The electrochemical cell of claim 1, wherein the cathode and the
polymer electrolyte membrane surrounding the cathode comprises a
plurality of rod-shaped cathode-electrolyte membrane structures
arranged in a radial configuration.
5. The electrochemical cell of claim 4, wherein the polymer
electrolyte membrane comprises a first seal on a first end and a
second seal on a second end.
6. The electrochemical cell of claim 1, wherein the housing is
configured to contain an electrolyte, and wherein the electrolyte
comprises hydroxide ions.
7. The electrochemical cell of claim 6, wherein the electrolyte
further comprises aqueous halide salt.
8. The electrochemical cell of claim 1, wherein the cathode
comprises a first metal.
9. The electrochemical cell of claim 8, wherein the first metal is
selected from the group consisting of nickel and nickel alloys of
Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti or Zr.
10. The electrochemical cell of claim 1, wherein the anode
comprises a second metal.
11. The electrochemical cell of claim 10, wherein the second metal
is selected from the group consisting of austenitic stainless
steels, duplex stainless steels, nickel and nickel alloys of Pt,
Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti or Zr.
12. The electrochemical cell of claim 1, wherein the polymer
electrolyte membrane is selected from the group consisting of a
perfluorinated ionomer and a copolymer of ethylene and a vinyl
monomer containing an acid group or salts thereof
13. The electrochemical cell of claim 12, wherein the
perfluorinated ionomer is selected from the group consisting of
perfluorosulfonic acid/tetrafluoroethylene copolymers and
perfluorocarboxylic acid/tetrafluoroethylene copolymer.
14. The electrochemical cell of claim 1, wherein the polymer
electrolyte membrane comprises an anionic exchange membrane.
15. The electrochemical cell of claim 1 further comprising a
plurality of cathode-polymer electrolyte membrane structures
positioned within the housing.
16. The electrochemical cell of claim 1, wherein the cathode is
porous, wherein the cathode comprises a cathode tube, and wherein
the electrochemical cell further includes a cathode compartment
including an interior space of the cathode tube.
17. The electrochemical cell of claim 1, wherein the cathode is
non-porous and wherein the electrochemical cell further comprises a
cathode compartment located between the cathode and the polymer
electrolyte membrane.
18. A system for generation of hydrogen, comprising: a water
purifier in fluid communication with an electrochemical cell of
claim 1; an electrolyte source in fluid communication with the
electrochemical cell; and a power source electrically connected
with the electrochemical cell.
19. The system of claim 18, wherein the electrochemical cell
further comprises an electrolyte circulation system configured to
introduce, circulate and/or flush electrolyte solution from the
electrochemical cell.
20. A method of generating hydrogen, comprising: introducing water
and hydroxide ions into the electrochemical cell of claim 1;
applying a voltage between the anode and the cathode; and
collecting hydrogen gas.
21. The method of claim 20, wherein the collected water saturated
hydrogen gas has a purity greater than approximately 99.999
mol%.
22. The method of claim 20, wherein the collected water saturated
hydrogen gas has a purity has a purity greater than approximately
99.9999 mol%.
23. The method of claim 20, wherein the cathode and the polymer
electrolyte membrane surrounding the cathode comprises one or more
rod-shaped cathode-electrolyte membrane structures arranged in a
radial configuration, wherein the hydrogen gas is collected at a
pressure of from about 30 psig to about 60 psig, and wherein the
polymer electrolyte membrane comprises a first seal on a first end
and a second seal on a second end.
24. The method of claim 20, wherein the cathode and the polymer
electrolyte membrane surrounding the cathode comprises one or more
rod-shaped cathode-electrolyte membrane structures arranged in a
radial configuration, wherein the hydrogen gas is collected at a
pressure of from about 200 psig to about 500 psig, and wherein the
polymer electrolyte membrane comprises a first seal on a first end
and a second seal on a second end.
25. The method of claim 20, wherein the cathode and the polymer
electrolyte membrane surrounding the cathode comprises one or more
rod-shaped cathode-electrolyte membrane structures arranged in a
radial configuration, wherein the hydrogen gas is collected at a
pressure of from about 1000 psig to about 3000 psig, and wherein
the polymer electrolyte membrane comprises a first seal on a first
end and a second seal on a second end.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional application No. 61/317,014, filed
on Mar. 24, 2010, the disclosure of which is hereby expressly
incorporated by reference in its entirety and is hereby expressly
made a portion of this application.
FIELD OF THE INVENTION
[0002] The present disclosure relates to a method and system for
the generation of hydrogen. Various methods, features and system
configurations are discussed.
BACKGROUND OF THE INVENTION
[0003] A water electrolyzer is an energy conversion device where
water and electricity are used as fuel in order to produce hydrogen
and oxygen. This energy breaks bonds between hydrogen and oxygen
atoms with the use of a catalyst (Eq.1).
H.sub.2O+electrical current.fwdarw.H.sub.2+1/2O.sub.2 (Eq. 1)
[0004] Several applications exist for low flow water electrolyzers.
These include, continuous supply of H.sub.2 to gas chromatographs
and other analytical instrumentation, materials processing,
chemical synthesis, smelting, heavy hydrogen production and weld
gas applications.
[0005] New hydrogen generation technologies are being driven by the
move towards the use of hydrogen as an energy carrier. It is
envisioned that hydrogen may replace petroleum based fuels in
automobiles and electrical generators. A primary objective is the
use of sustainable energy sources in combination with water
electrolyzers to produce hydrogen fuel. For this to be economically
viable, highly energy efficient, low cost hydrogen generator
systems are needed.
[0006] Aside from hydrogen fuel stations and electrical generation
plants, several other applications exist for hydrogen production at
moderate to large scales. These include, on-site ultra-high purity
(UHP) hydrogen production for silicon epitaxy, hydrogen for
metalorganic chemical vapor deposition (MOCVD) of compound
semiconductors, hydrogen for solar cell manufacturing, and hydrogen
cooling gas for power plant generators, food processing and home
heating. For on-site ultra-high purity hydrogen production, a
purity of 99.9995% H.sub.2 is obtained. Such systems are operated
at a pressurization of 200-450 psig, with high system durability,
low temperature operation, and nominal space requirements as
desirable attributes.
[0007] Several electrochemical hydrogen generation technologies are
known, such as described in the teachings of U.S. Pat. Nos.
6,613,215, 6,685,821, 6,939,449 and 7,270,908, which are each
hereby incorporated by reference for this purpose and in their
entireties. Current literature indicates that alkaline based
electrolyzers are the most efficient. These systems utilize a
potassium hydroxide electrolyte where the reaction chemistry is
initiated by reaction of hydroxide ion at the anode followed by
hydrogen production at the cathode (Equations 2-3).
Anode 4OH.sup.+.fwdarw.O.sub.2+2H.sub.2O+4e.sup.- (Eq. 1)
Cathode 2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH.sup.- (Eq. 2)
[0008] Though these systems look very promising, many practical
problems have been encountered in attempts to implement this
technology. Current polymer electrolyte membrane (PEM) and alkaline
system designs lack durability and are prone to mechanical failure.
This in part is due to the vast number of mechanical parts
contained in these systems. These include, tightly compressed
bipolar plates, catalyst materials in the form of thin sheets,
water maintenance systems, fragile graphite pads, membrane support
screens, cell frames, flow field management systems and compression
maintenance systems. The requirement for many of these parts and
sub-systems can be attributed to the inefficient flat plate design.
The use of a membrane as the primary electrolyte for PEM
electrolyzers places undue burden on the entire system. In
addition, these cells suffer from high material cost including
platinum or palladium catalysts which are required to lower
activation barriers and speed up reaction kinetics. In general, a
flat plate design makes scale up difficult due to size, weight and
number of seals. This leads to frequent field failures and poor
reliability. Moreover, flat plate designs are not cost effective
for scale up to high hydrogen production rates.
[0009] A cost model published by the National Renewable Energy
Laboratory (NREL) (NREL/MP-560-36734), which is hereby incorporated
by reference in its entirety, shows that capital equipment costs
are very significant for small to midsize H.sub.2 generators for
vehicle re-fueling applications. Neighborhood re-fueling stations
servicing 5-50 cars are estimated to require H.sub.2 generation at
a rate of 100 slm. Small re-fueling stations (small forecourt) are
estimated to require H.sub.2 generation at 1000 slm. Most
significant are the capital equipment costs associated with these
applications where it is estimated that 73% of the cost of produced
hydrogen for the neighborhood refueling station is associated with
capital costs. Moreover, 55% of the cost of produced hydrogen is
associated with capital equipment for the small refueling station
(small forecourt). System energy efficiencies range from 56% for
PEM systems to 73% for potassium hydroxide (KOH) bipolar stack
systems. Though there is room for improvement on system energy
efficiency, greater improvement is needed for the reduction of
capital equipment costs with respect to volumes of produced
hydrogen for these applications. One must also consider the
durability of these systems, where PEM stacks are estimated to last
5 years, and KOH bipolar stacks are estimated to have a 7 year
lifetime. In the NREL model, material costs such as KOH are
insignificant relative to electricity and capital equipment.
SUMMARY OF CERTAIN INVENTIVE ASPECTS
[0010] There is a need for energy efficient, low cost hydrogen
generation systems which are amenable to high hydrogen flux. The
systems, methods and devices described herein, each may have
several aspects, no single one of which is solely responsible for
its desirable attributes. Without limiting the scope of this
disclosure as expressed by the claims which follow, more prominent
features will now be discussed briefly. After considering this
discussion, and particularly after reading the section entitled
"Detailed Description of Certain Inventive Embodiments" one of
ordinary skill in the art, informed by the disclosure herein, will
understand how the features of this technology provide advantages
that include durable electrochemical hydrogen generation. In
particular, technology needs exist for durable electrochemical
systems with a reduced number of sub-system operations and lower
maintenance requirements. Resulting designs should be more cost
effective per volume of produced hydrogen, more energy efficient,
more durable and/or more reliable that current hydrogen generator
technologies.
[0011] In a first aspect, an electrochemical cell for generation of
hydrogen includes, for example, a cathode, a polymer electrolyte
membrane surrounding the cathode and a housing surrounding the
polymer electrolyte membrane.
[0012] In some embodiments, the housing comprises an anode and the
anode is electrically connected to the cathode. In some
embodiments, an anode compartment is formed between an anode side
of the polymer electrolyte membrane and the housing. In some
embodiments, the electrochemical cell further includes, for
example, an inlet port in fluid communication with the anode
compartment and configured to allow water flow into the anode
compartment. In some embodiments, a cathode compartment is formed
between a cathode side of the polymer electrolyte membrane and the
cathode. In some embodiments, the cathode includes a first metal.
In some embodiments, the first metal is selected from the group
including Ni, nickel alloys, which may include, for example, Pt,
Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti, or Zr. In some
embodiments, the anode includes a second metal. In some
embodiments, the second metal is selected from the group including
austenitic stainless steels or duplex stainless steels, Ni or
nickel alloys, wherein the nickel alloys further include Pt, Pd,
Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti, Zr or alloys
thereof. In some embodiments, the polymer electrolyte membrane is
formed of perfluorinated ionomer, a copolymer of ethylene and a
vinyl monomer containing an acid group or salts thereof,
perfluorosulfonic acid/tetrafluoroethylene copolymers or
perfluorocarboxylic acid/tetrafluoroethylene copolymer. In some
embodiments, the electrochemical cell further includes, for
example, a plurality of cathode-polymer electrolyte membrane
structures within the housing.
[0013] In another aspect, a system for generation of hydrogen
includes, for example, a water purifier in fluid communication with
an electrochemical cell, an electrolyte source in fluid
communication with the electrochemical cell and a power source
electrically connected with the electrochemical cell.
[0014] In another aspect, a method of generating hydrogen includes,
for example, providing an electrochemical cell, introducing water
and hydroxide ions into the electrochemical cell, applying a
voltage between the anode and the cathode and collecting hydrogen
gas.
[0015] In a first aspect, an electrochemical cell for generation of
hydrogen includes, for example, a cathode, a polymer electrolyte
membrane surrounding the cathode, and a housing surrounding the
polymer electrolyte membrane.
[0016] In some embodiments of the first aspect, the housing
includes an anode. In some embodiments of the first aspect, the
anode is electrically connected to the cathode. Some embodiments of
the first aspect further include an anode compartment positioned
between an anode side of the polymer electrolyte membrane and the
housing. Some embodiments of the first aspect further include an
inlet port in fluid communication with the anode compartment and
configured to allow water flow into the anode compartment. In some
embodiments of the first aspect, the cathode and the polymer
electrolyte membrane surrounding the cathode includes a plurality
of rod-shaped cathode-electrolyte membrane structures arranged in a
radial configuration. In some embodiments of the first aspect, the
polymer electrolyte membrane includes a first seal on a first end
and a second seal on a second end. In some embodiments of the first
aspect, the housing is configured to contain an electrolyte, and
wherein the electrolyte includes hydroxide ions. In some
embodiments of the first aspect, the electrolyte further includes
aqueous halide salt. In some embodiments of the first aspect, the
cathode includes a first metal. In some embodiments of the first
aspect, the first metal is selected from the group consisting of
nickel and nickel alloys of Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os,
Ir, Zn, Co, Ti or Zr. In some embodiments of the first aspect, the
anode includes a second metal. In some embodiments of the first
aspect, the second metal is selected from the group consisting of
austenitic stainless steels, duplex stainless steels, nickel and
nickel alloys of Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co,
Ti or Zr. In some embodiments of the first aspect, the polymer
electrolyte membrane is selected from the group consisting of a
perfluorinated ionomer and a copolymer of ethylene and a vinyl
monomer containing an acid group or salts thereof. In some
embodiments of the first aspect, the perfluorinated ionomer is
selected from the group consisting of perfluorosulfonic
acid/tetrafluoroethylene copolymers and perfluorocarboxylic
acid/tetrafluoroethylene copolymer. In some embodiments of the
first aspect, the polymer electrolyte membrane includes an anionic
exchange membrane. Some embodiments of the first aspect further
include a plurality of cathode-polymer electrolyte membrane
structures positioned within the housing. In some embodiments of
the first aspect, the cathode is porous. In some embodiments of the
first aspect, the cathode includes a cathode tube, and wherein the
electrochemical cell further includes a cathode compartment
including an interior space of the cathode tube. In some
embodiments of the first aspect, the cathode is non-porous and
wherein the electrochemical cell further includes a cathode
compartment located between the cathode and the polymer electrolyte
membrane.
[0017] In a second aspect, a system for generation of hydrogen
includes, for example, a water purifier in fluid communication with
an electrochemical cell of the first aspect, an electrolyte source
in fluid communication with the electrochemical cell, and a power
source electrically connected with the electrochemical cell.
[0018] In some embodiments of the second aspect, the
electrochemical cell further includes an electrolyte circulation
system configured to introduce, circulate and/or flush electrolyte
solution from the electrochemical cell.
[0019] In a third aspect, a method of generating hydrogen includes,
for example, introducing water and hydroxide ions into the
electrochemical cell of the first aspect, applying a voltage
between the anode and the cathode, and collecting hydrogen gas.
[0020] In some embodiments of the third aspect, the collected water
saturated hydrogen gas has a purity greater than approximately
99.999 mol%. In some embodiments of the third aspect, the collected
water saturated hydrogen gas has a purity greater than
approximately 99.9999 mol%. In some embodiments of the third
aspect, the cathode and the polymer electrolyte membrane
surrounding the cathode includes a plurality of rod-shaped
cathode-electrolyte membrane structures arranged in a radial
configuration. In some embodiments of the third aspect, the
hydrogen gas is collected at a pressure of from about 30 psig to
about 60 psig. In some embodiments of the third aspect, the
hydrogen gas is collected at a pressure of from about 200 psig to
about 500 psig. In some embodiments of the third aspect, the
hydrogen gas is collected at a pressure of from about 1000 psig to
about 3000 psig. In some embodiments of the third aspect, the
polymer electrolyte membrane includes a first seal on a first end
and a second seal on a second end.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The foregoing and other features of the present disclosure
will become more fully apparent from the following description and
appended claims, taken in conjunction with the accompanying
drawings. Understanding that these drawings depict only several
embodiments in accordance with the disclosure and are, therefore,
not to be considered limiting of its scope, the disclosure will be
described with additional specificity and detail through use of the
accompanying drawings.
[0022] FIG. 1 depicts a single radial oriented aqueous alkaline
electrochemical cell in the form of a membrane tube assembly.
Electrical leads are omitted for clarity.
[0023] FIG. 2 depicts a vertical cross section of an array of
several cathode-electrolyte membrane assemblies.
[0024] FIG. 3 depicts a bundled array with several
cathode-electrolyte membrane assemblies where the outer housing is
omitted for clarity.
[0025] FIG. 4 depicts an electrochemical hydrogen generation
system.
DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS
[0026] The illustrative embodiments described in the detailed
description, drawings, and claims are not meant to be limiting. The
teachings herein can be applied in a multitude of different ways,
including for example, as defined and covered by the claims. It
should be apparent that the aspects herein may be embodied in a
wide variety of forms and that any specific structure, function, or
both being disclosed herein is merely representative. Based on the
teachings herein one skilled in the art should appreciate that an
aspect disclosed herein may be implemented independently of any
other aspect and that two or more of these aspects may be combined
in various ways. For example, a system or apparatus may be
implemented or a method may be practiced by one of skill in the art
using any reasonable number or combination of the aspects set forth
herein. In addition, such a system or apparatus may be implemented
or such a method may be practiced using other structure,
functionality, or structure and functionality in addition to or
other than one or more of the aspects set forth herein. Other
embodiments may be utilized, and other changes may be made, without
departing from the spirit or scope of the subject matter presented
here. It will be readily understood that the aspects of the present
disclosure, as generally described herein, and illustrated in the
Figures, can be arranged, substituted, combined, and designed in a
wide variety of different configurations, all of which are
explicitly contemplated and made part of this disclosure. It is to
be understood that the disclosed embodiments are not limited to the
examples described below, as other embodiments may fall within
disclosure and the claims.
[0027] Some embodiments disclosed herein relate to an apparatus for
generation of hydrogen. For example, FIG. 1 depicts one embodiment
of an apparatus for generation of hydrogen. The apparatus includes
a radial orientation, wherein an inner cathode is surrounded by a
polymeric electrolyte membrane. In some embodiments, the inner
cathode includes a directional seal through which product hydrogen
may exit the apparatus. The inner cathode and the polymeric
electrolyte membrane are contained within an outer housing. In some
embodiments, the outer housing is configured to contain both
apparatus components and aqueous solution within the apparatus.
[0028] In some embodiments, the inner cathode includes an inner
cathode compartment formed of a porous metal membrane electrode. In
some embodiments, the inner cathode electrode is constructed of a
metal resistant to attack by hydroxide (OH.sup.+) ions in the
presence of applied voltage. In some embodiments, the metal
includes sintered Ni or other sintered nickel alloy. In some
embodiments, the metal includes austenitic stainless steel, duplex
stainless steel, Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co,
Ti, Zr or other metals that may be configured to improve cathode
efficiency for reduction of water to hydrogen gas and hydroxide
ions. In some embodiments, the sintered metal membrane is
configured to serve as the cathode as well as a porous passageway
for product hydrogen gas to exit the apparatus. Porous metal
membranes of this type are routinely used in the semiconductor
industry as sintered metal filters or diffusers. Examples of porous
metal membranes are available from Mott Corporation, Farmington,
Conn., which membranes are formed of sintered Ni or sintered
stainless steel with a porosity of from about 0.5 .mu.m to about
100 .mu.m.
[0029] A space between the inner cathode electrode and the polymer
electrolyte membrane may contain, for example, potassium hydroxide
or other Bronsted-Lowry base. This provides the primary electrolyte
for the apparatus and facilitates water and hydroxide transfer
across the polymeric electrolyte membrane. In some embodiments, the
Bronsted-Lowry base includes Group I or Group II metal hydroxides.
In some embodiments, the Bronsted-Lowry base includes a combination
of Bronsted-Lowry bases. In some embodiments, the Bronsted-Lowry
base is present in a concentration of less than about 0.1
moles/Liter. In some embodiments, the Bronsted-Lowry base is
present in a concentration of from about 0.1 moles/Liter to about
5.0 moles/Liter.
[0030] In some embodiments, the electrolyte membrane includes
materials that do not degrade when exposed to the Bronsted-Lowry
base and an applied voltage. In some embodiments, the electrolyte
membrane is formed of a perfluorinated ionomer. In some
embodiments, the electrolyte membrane is formed of a copolymer of
ethylene and a vinyl monomer containing an acid group or salts
thereof. In some embodiments, the perfluorinated ionomer includes,
but is not limited to, perfluorosulfonic acid/tetrafluoroethylene
copolymers ("PFSA-TFE copolymer") or perfluorocarboxylic
acid/tetrafluoroethylene copolymer ("PFCA-TFE copolymer"). Some
perfluorinated ionomers useful in embodiments of the present
disclosure include commercially available NAFION.RTM. (E.I. du Pont
de Nemours & Company), FLEMION.RTM. (Asahi Glass Company, Ltd),
and ACIPLEX.RTM. (Asahi Chemical Industry Company). Some
perfluorinated ionomers useful in embodiments of the present
disclosure have a thickness of from about 1/32 inch to about 1/8
inch.
[0031] In some embodiments, the polymer ionomer membrane is in salt
form, where protons have been replaced by metal or non-metal
cations. In this form, the polymer membrane substituents contain
anionic groups. In the case where potassium hydroxide is used as
the primary electrolyte in the apparatus, the polymer ionomer
membrane contains potassium cations (K.sup.+). In some embodiments,
the polymer ionomer membrane may include, for example, an anion
exchange membrane. Membranes of this type are known for rapid anion
exchange and transport properties which encompass hydroxide
(OH.sup.-) ions. The ionic polymer membrane also may be configured
to serve as a gas separator and water transfer agent and an
additional electrolyte. In some embodiments, the ionic polymer
membrane is a Nafion.RTM. membrane made by DuPont.TM.. It is a
cationic exchange membrane. In some embodiments, in which an
anionic exchange membrane is used, the cation is incorporated into
the polymer and the anion is floating around. These are typically
non-coordinating anions. Commercially available ionomer membranes
may be obtained, for example, from Rohm and Haas Company, E.I. du
Pont de Nemours & Company and/or Dow Chemical Company.
[0032] The inner portion of the polymeric membrane is generally
positioned in close proximity to the inner cathode electrode. In
some embodiments, the inner portion of the polymeric membrane
contacts the cathode electrode. As mentioned above, in some
embodiments the cathode is formed of a porous metal or of fused
metal particles or of a sintered metal where many small particles
are fused together with spaces between. The pores or spaces between
the metal particles are generally of a diameter from about 0.1
.mu.m to about 100 .mu.m. The diameter of the cathode is preferably
from about 1/16 to about 1/2 inch. In some embodiments, the cathode
is formed in a tube-like structure. In other embodiments, the
cathode is formed in a rod-shaped or helical shaped structure.
[0033] In operation, as soon as hydroxide ions migrate across the
polymer membrane, hydroxide ions contact the sintered metal. In the
presence of the applied voltage the hydroxide ions combine to
become water and hydrogen gas. This process is described more fully
below with regard to systems and methods of generating hydrogen.
Thus, fitting the polymer membrane around a porous sintered metal
tube structure with as close contact as possible can reduce
distance an ion has to travel, and thus, increase productivity of
the apparatus.
[0034] The porous metal cathode may be connected to a solid tube,
which serves as an outlet for hydrogen to exit the cell via a
directional seal. The directional seal is a one-way pre-loaded
seal. It can be a spring loaded or weighted to have a pressure on
the seal so it is configured to open only at a specific pressure.
In some embodiments, the directional seal is similar to a pressure
release valve. Mechanical means may be used to open the directional
seal in a single direction at a specific force--to release pressure
from a high pressure region to a low pressure region. Some types of
directional seals useful for embodiments of the present disclosure
can be purchased from Swagelok.TM. or Valin.TM..
[0035] As illustrated in FIG. 1, the outer housing comprises an
outer anode shell. In some embodiments, the anode shell is formed
of a metal. In some embodiments, the metal is configured to be
resistant to attack by hydroxide (OH.sup.-) ions in the presence of
applied voltage. In some embodiments, the metal is configured to
improve anode efficiency for oxidation of hydroxide ions to oxygen
gas and water. The metal may include Ni or nickel alloys. In some
embodiments, the metal includes, austenitic stainless steels,
duplex stainless steels, Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir,
Zn, Co, Ti, Zr, alloys of any of these metals or some combination
thereof. In some embodiments, the anode shell is formed of a
conductive polymer. In some embodiments, the outer housing is
formed of a non-metal material, such as plastic.
[0036] The anode is electrically connected to the cathode through
an electrical wire or other suitable electrically conductive
material. Electrical conducting material may include, for example,
a wire, trace, conducting member, etc. In operation, a voltage may
be applied across the electrical conducting material from about
-1.0 V to about -3.5 V. At the applied voltage, water reacts at the
cathode to form H.sub.2 gas and to reform hydroxide ions
(OH.sup.-).
[0037] The embodiment of the apparatus depicted in FIG. 1 is an
aqueous alkaline electrochemical cell. Thus, the base of the
apparatus includes an inlet configured for water entering the outer
housing and the top of the apparatus includes an outlet configured
for oxygen gas generated during operation of the apparatus to exit
the outer housing. During operation, build up of excess oxygen gas
may occur on the anode side of the membrane. This gas can be
periodically or continuously vented through an outlet port. The
outlet for oxygen gas may include a pressure sensitive valve or
transducer. The pressure sensitive valve or transducer may be
configured to allow oxygen gas to be released at specific
pressures. As discussed further below, the oxygen gas may be
released based upon the pressure of the product hydrogen on the
other side of the polymeric membrane. Additionally, the inner
cathode includes an outlet for hydrogen gas generated during
operation of the apparatus.
[0038] In some embodiments, the water flowing into the apparatus
via the inlet is pre-purified in a water purifier as described
further below with regard to FIG. 4.
[0039] As noted above, the outer housing may be configured to
contain aqueous hydroxide ion (OH.sup.-). In some embodiments, the
outer housing is configured to contain an aqueous inorganic salt
mixed with hydroxide ions. The space between the polymer membrane
and the outer housing may include, for example, potassium hydroxide
or other Bronsted-Lowry bases. In some embodiments, the outer
housing is configured to contain an aqueous halide salt mixed with
hydroxide ions. This provides the primary electrolyte to facilitate
oxidation of hydroxide ion to water and O.sub.2 gas.
[0040] The build up of oxygen gas pressure can be advantageous when
producing high pressure hydrogen gas product. Further, in certain
instances it may be advantageous to allow oxygen gas pressure
build-up in the anode compartment to facilitate water transport
across the polymeric membrane. The radial design of the
electrochemical cell is configured to allow continuous maintenance
of high operating pressures with inner components, (such as the
polymer electrolyte membrane), which are not required to have the
same thickness as the outer wall. Pressure build-up of product
hydrogen can be balanced with oxygen pressure in the anode
compartment. Differential pressure across the membrane separator
(polymer electrolyte membrane) is reduced or even minimized and
high pressure on the outer wall of up to about 10,000 psig can be
achieved. In certain embodiments, the differential pressure between
the anode side of the polymer electrolyte membrane and the cathode
side of the polymer electrolyte membrane is approximately 5 psig or
less. In other words, pressure at center cathode is approximately
the same as pressure on the outer housing so the polymer
electrolyte membrane does not collapse.
[0041] Generally, instrumentation included in the apparatus
depicted in FIG. 1 is operated at pressures of from about 30 psig
to about 750 psig, but may be operated at pressures up to about
3000 psig. In some embodiments, the apparatus depicted in FIG. 1 is
operated at pressures of up to and including about 10, 20, 30, 40,
50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500,
550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1250, 1500,
1750, 2000, 2250, 2500, 2750, 3000, 3250, 3500, 3750, 4000, 4250,
4500, 4750, 5000 psig or any number in between. The apparatus is
configured to be sealed in a manner that separates inlet gases from
outlet gases and only allows for water and hydroxide (OFF)
transport through the membrane. For use at pressures above 750
psig, for example, from about 1000 psig to about 3000 psig the
outer housing may be formed with a thickness of from about 1/2 to
about 1 inch stainless steel. The anode electrode may be formed of
an insert or a sleeve to line the inside of the outer housing. The
insert or sleeve may be configured to provide support to the outer
housing.
[0042] In some embodiments, the electrochemical hydrogen generation
device includes, for example, a bundled array of
cathode-electrolyte membrane assemblies positioned substantially
parallel with respect to each other. FIG. 2 depicts a vertical
cross section of an array of several cathode-electrolyte membrane
assemblies. Electrical leads are omitted for clarity. FIG. 3
depicts a bundled array with several cathode-electrolyte membrane
assemblies where the outer housing is omitted for clarity. These
types of designs can maximize hydrogen generation in a nominal
amount of space. Each bundled array of cathode-electrolyte membrane
assemblies increases surface area, and thus, is configured to have
a small system footprint. In some embodiments, a bundle includes,
for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 24, 32, 40, 48, 56, 64 or more cathode-electrolyte
membrane assemblies. In some embodiments, a bundle includes 8
cathode-electrolyte membrane assemblies. In some embodiments, a
bundle includes 16 cathode-electrolyte membrane assemblies. In some
embodiments, end caps on each cathode-electrolyte membrane assembly
are each from about 2 inches to about 3 inches in diameter.
[0043] The radial design of the electrochemical cells depicted in
FIG. 1 coupled with the membrane bundles depicted in FIGS. 2 and 3
are configured to allow for a maximum output of hydrogen production
with a minimal amount of space. Current devices and systems known
in the art for producing hydrogen rely on bipolar plates, which
cannot be configured for efficient high throughput production of
hydrogen.
[0044] Some embodiments disclosed herein relate to systems for
generation of hydrogen. FIG. 4 depicts an electrochemical hydrogen
generating system. In the system of FIG. 4, process water passes
through a water purifier. The water purifier may be configured to
remove contaminants from the process water that could corrode or
otherwise contaminate electrodes. For example, the water purifier
may be configured to remove sulfur or phosphorus or CO.sub.2 from
the process water.
[0045] The water purifier is in fluid communication with a feed
water storage tank. The high purity water exiting the water
purifier may then be stored in the feed water storage tank for
later use in generation of hydrogen. The feed water storage tank
may be formed of materials configured to prevent introduction of
contaminants into the high purity water. The materials may include,
for example, high purity plastics, stainless steel, Ni or Ni alloy,
and/or quartz. In some embodiments, the water purifier or the feed
water storage tank may include, for example, a mechanical pump
configured to deliver the high purity water under pressure to the
hydrogen generation unit.
[0046] In some embodiments, an electrolyte mixing tank is placed
upstream of and in fluid communication with the hydrogen generation
unit. Illustrated in FIG. 4 is a type of electrolyte mixing tank, a
KOH mixing tank. Although the KOH making tank holds aqueous
potassium hydroxide, it will be understood by one of ordinary skill
in the art, that any suitable aqueous inorganic salt, including,
for example, aqueous halide/hydroxide salt mixtures can be made and
used in the system. In some embodiments, the resulting electrolyte
solution from the KOH mixing tank is provided together with the
high purity water flowing from the feed water storage tank. The
resulting mixture of electrolyte solution and high purity water
then flows into the hydrogen generation unit. In other embodiments,
the hydrogen generation unit contains addition ports where
controlled amounts of electrolyte and water may be introduced and
subsequently mixed to form a dissolved electrolyte solution. In
some embodiments, a concentration gradient may exist in the mixed
electrolyte solution.
[0047] The hydrogen generation unit is electrically connected to a
power supply. In some embodiments, the power source includes an
electrical outlet attached to a grid or an electrochemical battery
with stored energy. In some embodiments, the power source includes
a sustainable energy such as solar, wind or hydroelectric power. In
some embodiments, the hydrogen generation unit is electrically
connected to a power supply by a wire, trace, conducting member or
the like. In some embodiments, the wire is formed of Ni, Cu or Au.
In some embodiments, the wire includes electrical leads formed of
Ni or Ni alloys such as Ni-Al or Ni-Zn. In some embodiments, the
electrical wires are positioned on the outside of the
electrochemical cell apparatus and thus do not contact corrosive
materials. In some embodiments, a voltmeter or potentiometer is
electrically connected to the electrical wire.
[0048] In some embodiments, the hydrogen generation unit includes
an aqueous alkaline electrochemical cell with a radial orientation.
In some embodiments, the hydrogen generation unit may include, for
example, an apparatus depicted in at least one of FIGS. 1-3.
[0049] In the embodiment of FIG. 4, the hydrogen generation unit
includes an electrolysis module, an electrolyte circulation and a
hydrogen gas dryer/purifier. In some embodiments, the hydrogen
generation unit includes a metal membrane hydrogen purifier. In
some embodiments, the hydrogen generation unit includes a hydrogen
purifier containing metal in a reduced oxidation state. In some
embodiments, the hydrogen generation unit includes an electrolyte
circulation system. The electrolyte circulation system may be
configured to introduce, circulate and/or flush electrolyte
solution from the hydrogen generation apparatus.
[0050] The hydrogen generation unit illustrated in FIG. 4 is in
fluid communication with a compressor. In operation, greater than
99% pure hydrogen generated in the hydrogen generation unit may
flow from the hydrogen generation unit into the compressor. The
compressor specifications are defined by intended hydrogen usage,
where compression up to about 3000 psig may be used. In some
embodiments, compression up to about 3250, 3500, 3750, 4000, 4250,
4500, 4750, 5000, 6000, 7000, 8000, 9000, 10,000 psig or any number
in between may be used. In some embodiments, the compressor is
formed of explosion proof, high purity materials. In some
embodiments, the compressor is free of oil or grease. In some
embodiments the compressor includes high purity seals. In some
embodiments, the high purity seals are formed of Teflon or other
high elastomeric materials. In some embodiments, the high purity
seals include metal to metal seals. As further illustrated in FIG.
4, the hydrogen compressor is in fluid communication with a
hydrogen storage unit. In operation, the hydrogen compressed in the
compressor may be delivered to the hydrogen storage unit for
storage until use. In some embodiments, the storage vessel is
constructed of materials to prevent contamination of product
hydrogen. In some embodiments, the materials include, for example,
high purity plastics, stainless steel, Ni or Ni alloys. In general,
the hydrogen storage units for storing high pressure hydrogen (up
to about 10,000 psig) are formed of stainless steel.
[0051] Some embodiments disclosed herein relate to methods of
electrochemical generation of hydrogen. In one embodiment, a method
includes, for example, providing aqueous hydroxide ion (OH.sup.-)
within an outer anode compartment bounded by a first side of an
electrolyte membrane and a housing comprising an anode, providing a
cathode on a second side of the electrolyte membrane, and providing
a voltage potential between the anode and the cathode so water
reacts at the cathode to form H.sub.2 gas and to reform hydroxide
ions, so hydroxide ions migrate from the cathode side of the
electrolyte membrane to the anode side of the electrolyte membrane
and so water and oxygen gas are generated in the anode
compartment.
[0052] In some embodiments, water is pre-purified prior to
introduction to the electrochemical hydrogen generator. In some
embodiments, the water is purified using ion exchange resins. In
some embodiments, the water is purified using reverse osmosis. In
some embodiments, the water is purified using distillation. In some
embodiments, the water is purified to remove materials that would
otherwise contaminate electrodes in the apparatus. In some
embodiments, the water is purified to remove sulfur. In some
embodiments, the water is purified to remove phosphorus. In some
embodiments, the water is purified to remove CO.sub.2 or other
gaseous contaminants. Gaseous contaminants may include nitrogen,
oxygen or CO. In some embodiments, the water is purified to remove
metal containing species, silica, silicates, acids, halogen
containing species, refractory compounds and/or organic compounds.
In some embodiments, acceptable contaminant levels following
purification are less than about 1 ppm. In some embodiments,
acceptable contaminant levels following purification are less than
about 1 ppb. In some embodiments, acceptable contaminant levels
following purification are less than about 1 ppt.
[0053] Water is provided to the anode and/or cathode compartment to
replenish water consumed during operation of the electrochemical
cell. In some embodiments, the water is periodically added to the
anode or cathode compartment through an inlet port. In some
embodiments, the water is continuously added to the anode or
cathode compartment through an inlet port. The water flowing
through the inlet port is subsequently converted to hydrogen and
oxygen by the electrochemical cell. In some embodiments, a water
purifier or a feed water storage tank mechanically increases the
pressure of the high purity water. The high purity water may be
delivered from either the water purifier or the feed water storage
tank to the hydrogen generation unit. In some embodiments, the
water flows into the apparatus from the water purifier. The water
in the purifier may be degassed prior to introduction into the
hydrogen generating apparatus. Water may be delivered to the
apparatus at pressure to facilitate production of high pressure
product hydrogen. In some embodiments, water is delivered at up to
approximately 100 psig. Water may be delivered at up to
approximately 50,60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160,
170, 180, 190, 200 psig or any number in between.
[0054] In some embodiments, water and electrolyte are circulated
continuously through the anode and cathode compartments to aid in
removing gas bubbles and/or to prevent dry spots from forming on
the membrane surface. Ultrasound may be used to remove gas bubbles
and/or to prevent dry spots from forming on the membrane surface.
In some embodiments, water and electrolyte are flushed out of the
anode and cathode compartments to remove unwanted residues, scales
or soluble contaminants. These solutions may be replaced with fresh
water and/or electrolyte solution. Depending on the purity of the
inlet water, flushing may be infrequent.
[0055] Oxygen gas may be released from the apparatus at specific
pressures by a pressure sensitive valve. During operation of the
electrochemical cell, the pressure of the oxygen gas remains
roughly equivalent to the pressure of the product hydrogen. The
pressure of the product hydrogen and the pressure of the oxygen may
be maintained at from about 60 psig to about 3000 psig. In some
embodiments, the pressure of the oxygen and the product hydrogen is
maintained at from about 300 psig to about 500 psig. In some
embodiments, oxygen pressure on the anode side of the electrolyte
membrane is allowed to build up in a controlled fashion to balance
pressure build up of product hydrogen on the cathode side of the
electrolyte membrane. In some embodiments, oxygen pressure is
within approximately 5 psig of hydrogen pressure. In some
embodiments, oxygen pressure is equal to hydrogen pressure.
[0056] In some embodiments, product hydrogen may exit out of the
cathode compartment through a solid tube which is mechanically
connected to the porous metal cathode. The solid tube fluidly
connects to a directional seal which is configured to allow the
product hydrogen to exit the hydrogen generating apparatus. The
product hydrogen may be delivered at a pressure of from about 30
psig to about 60 psig. The product hydrogen may be delivered at a
pressure of from about 200 psig to about 500 psig. The product
hydrogen may be delivered at a pressure of from about 1000 psig to
about 3000 psig. In some embodiments, the product hydrogen is
delivered at a pressure of up to about 10,000 psig. In some
embodiments, the hydrogen gas is produced at high pressure and then
stored at high pressure. In some embodiments the hydrogen gas is
produced at lower pressure, and then, mechanical means are used to
compress the product hydrogen to higher pressure for storage.
[0057] The product hydrogen may be compressed by mechanical or
other methods after exiting the apparatus. In some embodiments,
product hydrogen is directed from the electrochemical cell to a
hydrogen drier or a purification unit. In some embodiments, the
hydrogen drier may include, for example, a polymer membrane
dehumidification device. In some embodiments, the hydrogen drier
includes, for example, molecular sieves, silica, alumina, zeolites,
or other water adsorbing materials.
[0058] In some embodiments, the purity of the product hydrogen is
approximately 99.999 mol% or more. In some embodiments, the purity
of the product hydrogen is approximately 99.9999 mol% or more. In
some embodiments, the purity of the product hydrogen is
approximately 99.99999 mol% or more. Water vapor may be removed
from the product hydrogen with a membrane drying device level of
less than 10 ppm. Water vapor may be removed from the product
hydrogen with an adsorbent-based drier to a level of less than 100
ppb. In some embodiments, gaseous contaminants are removed from the
product hydrogen with a gas purifier to give a total contaminant
level of less than 100 ppb.
[0059] In some embodiments, oxygen by-product exits out of a gas
port in fluid communication with the outer anode compartment. The
purity of the oxygen by-product may be approximately 99.9999 mol%
or more. In some embodiments, the oxygen gas is vented to air. In
some embodiments, the oxygen gas is collected for subsequent
use.
[0060] The product hydrogen may contain less than about 1% water
vapor. The product hydrogen may contain from about 1% to about 0.1%
water vapor. The product hydrogen may contain from about 0.1% to
about 1 ppm water vapor. The product hydrogen may contain less than
about 1 ppm water vapor. The product hydrogen may contain less than
about 1 ppb water vapor.
[0061] In the case that water vapor needs to be removed from the
product hydrogen for high purity applications, several known
methods of moisture removal from hydrogen are readily available.
For example, water vapor can be removed through use of at least one
of a molecular sieve, a membrane dryer from RASIRC.TM., or a
membrane dryer from Perma Pure, LLC.
[0062] All references cited herein are incorporated herein by
reference in their entireties. To the extent publications and
patents or patent applications incorporated by reference contradict
the disclosure contained in the specification, the specification is
intended to supersede and/or take precedence over any such
contradictory material.
[0063] Unless otherwise defined, all terms (including technical and
scientific terms) are to be given their ordinary and customary
meaning to a person of ordinary skill in the art, and are not to be
limited to a special or customized meaning unless expressly so
defined herein.
[0064] Terms and phrases used in this application, and variations
thereof, especially in the appended claims, unless otherwise
expressly stated, should be construed as open ended as opposed to
limiting. As examples of the foregoing, the term `including` should
be read to mean `including, without limitation,` `including but not
limited to,` or the like; the term `comprising` as used herein is
synonymous with `including,` `containing,` or `characterized by,`
and is inclusive or open-ended and does not exclude additional,
unrecited elements or method steps; the term `having` should be
interpreted as `having at least;` the term `includes` should be
interpreted as `includes but is not limited to;` the term `example`
is used to provide exemplary instances of the item in discussion,
not an exhaustive or limiting list thereof; adjectives such as
`known`, `normal`, `standard`, and terms of similar meaning should
not be construed as limiting the item described to a given time
period or to an item available as of a given time, but instead
should be read to encompass known, normal, or standard technologies
that may be available or known now or at any time in the future;
and use of terms like `preferably,` `preferred,` `desired,` or
`desirable,` and words of similar meaning should not be understood
as implying that certain features are critical, essential, or even
important to the structure or function of the invention, but
instead as merely intended to highlight alternative or additional
features that may or may not be utilized in a particular embodiment
of the invention. Likewise, a group of items linked with the
conjunction `and` should not be read as requiring that each and
every one of those items be present in the grouping, but rather
should be read as `and/of` unless expressly stated otherwise.
Similarly, a group of items linked with the conjunction `or` should
not be read as requiring mutual exclusivity among that group, but
rather should be read as `and/of` unless expressly stated
otherwise.
[0065] With respect to the use of substantially any plural and/or
singular terms herein, those having skill in the art can translate
from the plural to the singular and/or from the singular to the
plural as is appropriate to the context and/or application. The
various singular/plural permutations may be expressly set forth
herein for sake of clarity.
[0066] It will be further understood by those within the art that
if a specific number of an introduced claim recitation is intended,
such an intent will be explicitly recited in the claim, and in the
absence of such recitation no such intent is present. For example,
as an aid to understanding, the following appended claims may
contain usage of the introductory phrases "at least one" and "one
or more" to introduce claim recitations. However, the use of such
phrases should not be construed to imply that the introduction of a
claim recitation by the indefinite articles "a" or "an" limits any
particular claim containing such introduced claim recitation to
embodiments containing only one such recitation, even when the same
claim includes the introductory phrases "one or more" or "at least
one" and indefinite articles such as "a" or "an" (e.g., "a" and/or
"an" should typically be interpreted to mean "at least one" or "one
or more"); the same holds true for the use of definite articles
used to introduce claim recitations. In addition, even if a
specific number of an introduced claim recitation is explicitly
recited, those skilled in the art will recognize that such
recitation should typically be interpreted to mean at least the
recited number (e.g., the bare recitation of "two recitations,"
without other modifiers, typically means at least two recitations,
or two or more recitations). Furthermore, in those instances where
a convention analogous to "at least one of A, B, and C, etc." is
used, in general such a construction is intended in the sense one
having skill in the art would understand the convention (e.g., "a
system having at least one of A, B, and C" would include but not be
limited to systems that have A alone, B alone, C alone, A and B
together, A and C together, B and C together, and/or A, B, and C
together, etc.). In those instances where a convention analogous to
"at least one of A, B, or C, etc." is used, in general such a
construction is intended in the sense one having skill in the art
would understand the convention (e.g., "a system having at least
one of A, B, or C" would include but not be limited to systems that
have A alone, B alone, C alone, A and B together, A and C together,
B and C together, and/or A, B, and C together, etc.). It will be
further understood by those within the art that virtually any
disjunctive word and/or phrase presenting two or more alternative
terms, whether in the description, claims, or drawings, should be
understood to contemplate the possibilities of including one of the
terms, either of the terms, or both terms. For example, the phrase
"A or B" will be understood to include the possibilities of "A" or
"B" or "A and B."
[0067] All numbers expressing quantities of ingredients, reaction
conditions, and so forth used in the specification are to be
understood as being modified in all instances by the term `about.`
Accordingly, unless indicated to the contrary, the numerical
parameters set forth herein are approximations that may vary
depending upon the desired properties sought to be obtained. At the
very least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of any claims in any
application claiming priority to the present application, each
numerical parameter should be construed in light of the number of
significant digits and ordinary rounding approaches.
[0068] Furthermore, although the foregoing has been described in
some detail by way of illustrations and examples for purposes of
clarity and understanding, it is apparent to those skilled in the
art that certain changes and modifications may be practiced.
Therefore, the description and examples should not be construed as
limiting the scope of the invention to the specific embodiments and
examples described herein, but rather to also cover all
modification and alternatives coming with the true scope and spirit
of the invention.
* * * * *