U.S. patent application number 11/322539 was filed with the patent office on 2006-05-18 for in situ generation of hydrogen peroxide.
Invention is credited to Jason T. Corradi, Anil R. Oroskar, Rusty M. Pittman, Gavin P. Towler, Kurt M. Vanden Bussche.
Application Number | 20060102492 11/322539 |
Document ID | / |
Family ID | 36385065 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060102492 |
Kind Code |
A1 |
Corradi; Jason T. ; et
al. |
May 18, 2006 |
In situ generation of hydrogen peroxide
Abstract
A device is disclosed for the generation of hydrogen peroxide.
The device produces hydrogen peroxide on an as-needed basis through
the use of electrolysis of water, wherein the hydrogen and oxygen
are mixed in the electrolyzer, and the hydrogen and oxygen mixture
in water are reacted in a reactor to produce hydrogen peroxide.
Inventors: |
Corradi; Jason T.;
(Arlington Heights, IL) ; Vanden Bussche; Kurt M.;
(Lake in the Hills, IL) ; Oroskar; Anil R.;
(Oakbrook, IL) ; Towler; Gavin P.; (Barrington,
IL) ; Pittman; Rusty M.; (New York, IL) |
Correspondence
Address: |
JOHN G TOLOMEI, PATENT DEPARTMENT;UOP LLC
25 EAST ALGONQUIN ROAD
P O BOX 5017
DES PLAINES
IL
60017-5017
US
|
Family ID: |
36385065 |
Appl. No.: |
11/322539 |
Filed: |
December 30, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10370174 |
Feb 19, 2003 |
|
|
|
11322539 |
Dec 30, 2005 |
|
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Current U.S.
Class: |
205/466 |
Current CPC
Class: |
C01B 15/029
20130101 |
Class at
Publication: |
205/466 |
International
Class: |
C25B 1/30 20060101
C25B001/30 |
Claims
1. A process for the production of hydrogen peroxide comprising the
steps of: flowing water over electrodes in a electrolyzer
generating an aqueous product with hydrogen and oxygen dissolved
therein; and flowing the aqueous product over a reactor comprised
of a catalyst on a support.
2. The process of claim 1 where the catalyst comprises at least one
metal selected from the group consisting of Pt, Pd, Ru, Rh, Ir, Os,
Au, and mixtures thereof.
3. The process of claim 1 wherein the hydrogen peroxide is used for
bleaching, disinfecting or oxidizing.
4. The process of claim 1 using an apparatus comprising: a housing
having a water inlet port and a hydrogen peroxide outlet port; an
electrolyzer disposed within the housing and in fluid communication
with the water inlet port for generating hydrogen and oxygen,
wherein the electrolyzer comprises a plurality of electrodes
separated by spacers and wherein the spacers separate the
electrodes to form a gap of less than 400 micrometers; and a
reactor for producing hydrogen peroxide disposed within the housing
and between the electrolyzer and the hydrogen peroxide outlet
port.
5. The process of claim 1 wherein the power to the electrolyzer
generating an aqueous solution with hydrogen and oxygen is
controlled by a controller.
6. The process of claim 1 wherein the water flow is controlled by a
controlled system to provide hydrogen peroxide on an intermittent
basis.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Division of copending application Ser.
No. 10/370,174 filed Feb. 19, 2003, the contents of which are
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a device and process for
producing hydrogen peroxide directly from water for use in
appliances.
BACKGROUND OF THE INVENTION
[0003] Currently the most widely practiced industrial scale
production method for hydrogen peroxide is an indirect reaction of
hydrogen and oxygen employing alkylanthraquinone as the working
material. In a first catalytic hydrogenation step, the
alkylanthraquinone, dissolved in a working solution comprising
organic solvents (e.g. di-isobutylcarbinol and methyl naphthalene),
is converted to alkylanthrahydroquinone. In a separate
autooxidation step, this reduced compound is oxidized to regenerate
the alkylanthraquinone and yield hydrogen peroxide. Subsequent
separation by aqueous extraction, refining, and concentration
operations are then employed to give a merchant grade product.
[0004] Overall, this indirect route to H.sub.2O.sub.2 formation,
whereby a carrier medium is reduced and then oxidized, adds
complexity and requires high installation and operating costs. One
notable drawback is the significant solubility of the
alkylanthraquinone in the aqueous extraction medium used to
separate the hydrogen peroxide product. This promotes loss of
working solution and leads to contamination of the hydrogen
peroxide product with organic species that, when the hydrogen
peroxide is concentrated to levels suitable for transport, are
reactive with it. A second problem relates to the solubility of the
aqueous extraction solution in the alkylanthraquinone working
solution. When wet working solution is separated from the aqueous
phase for recycle to the indirect oxidation stage, residual aqueous
phase "pockets" within the organic solution provide regions for
hydrogen peroxide product to concentrate to the extent of becoming
hazardous. A third problem relates to the usage and recovery of an
organic compound when small amounts of hydrogen peroxide are needed
without the organic contamination in an aqueous stream.
[0005] Considerably more simple and economical than the
alkylanthraquinone route is the direct synthesis of hydrogen
peroxide from gaseous hydrogen and oxygen feed streams. This
process is disclosed in U.S. Pat. No. 4,832,938 B1 and other
references, but attempts at commercialization have led to
industrial accidents resulting from the inherent explosion hazards
of this process. Namely, explosive concentrations of hydrogen in an
oxygen-hydrogen gaseous mixture at normal temperature and pressure
are from 4.7-93.9% by volume. Thus the range is extremely
broad.
[0006] It is also known that dilution of the gaseous mixture with
an inert gas like nitrogen scarcely changes the lower limit
concentrations, on an inert gas-free basis, of the two gases.
Within normal ranges of pressure variation (1-200 atmospheres) and
temperature variation (0-100.degree. C.) the explosive range is
known to undergo little change. Furthermore, even when these
reactants are brought together in a ratio that, in the homogeneous
condition, would be outside the flammability envelope, the
establishment of homogeneity from pure components necessarily
involves at least a temporary passage through the flammability
envelope. For these reasons, the explosion risks associated with
the direct contacting of hydrogen and oxygen are not easily
mitigated.
[0007] In the area of directly contacting hydrogen and oxygen, some
efforts have also been made to contain the reaction in a liquid
phase. For example, U.S. Pat. No. 5,925,588 B1 discloses the use of
a catalyst having a modified hydrophobic/hydrophilic support to
provide optimum performance in an aqueous liquid phase. Also, U.S.
Pat. No. 6,042,804 B1 discloses dispersing minute bubbles of
hydrogen and oxygen into a rapidly flowing acidic aqueous liquid
medium containing a catalyst. Unfortunately, however, the hydrogen
and oxygen reactants are only slightly soluble in the aqueous
reaction solvents disclosed in these references.
[0008] Other references, namely U.S. Pat. No. 4,336,240 B1 and U.S.
Pat. No. 4,347,231 B1 disclose two-phase reaction systems with a
homogeneous catalyst dissolved in an organic phase. As mentioned in
the former of these two references, homogeneous catalyst systems in
general suffer from drawbacks that are a deterrent to their
commercial use. The adverse characteristics include poor catalyst
stability under reaction conditions, limited catalyst solubility in
the reaction medium, and low reaction rates for the production of
hydrogen peroxide. In addition, a gaseous H.sub.2/O.sub.2
containing environment above the two-phase liquid reaction system
maintains the equilibrium concentrations of these reactants
dissolved in the liquid phase. Therefore, this gaseous atmosphere
above the reaction liquid must necessarily be outside the
flammability envelope, thus greatly restricting the range of
potential reactant mole ratios in the liquid phase.
[0009] It would be useful to have a device and process for making
hydrogen peroxide in a convenient manner, on an as-needed basis,
without the need of extra chemicals, and without generating a waste
product stream.
SUMMARY OF THE INVENTION
[0010] The present invention is for making hydrogen peroxide in
solution for use in an appliance. The invention comprises a housing
having a water inlet port and hydrogen peroxide outlet port. An
electrolyzer is situated within the housing and is positioned near
the water inlet port. The invention further includes a reactor
situated within the housing and positioned between the electrolyzer
and the hydrogen peroxide outlet port. The invention generates the
hydrogen peroxide as needed, and removes the need for storage or
direct handling of the hydrogen peroxide.
[0011] In an alternate embodiment the invention further comprises
an oxygen inlet port for delivering oxygen to the reactor. The
oxygen inlet port is preferably positioned between the electrolyzer
and the reactor.
[0012] In one embodiment the electrolyzer comprises a plurality of
electrodes separated by separators, wherein the electrodes are
separated by a gap less than 400 micrometers and preferably by a
gap of about 200 micrometers. The invention also comprises a
reactor, where the reactor includes an appropriate catalyst on a
support for reacting the hydrogen and oxygen in a liquid phase to
form an aqueous hydrogen peroxide solution.
[0013] In another embodiment, the invention comprises a housing
with an inlet port and an outlet port. The invention includes an
electrolyzer positioned near the inlet port for decomposing a
portion of water admitted through the inlet port. The electrolyzer
comprises a plurality of electrodes oriented to allow the water
entering the housing to flow freely over the electrodes. The
invention includes a reactor comprised of a catalyst on a support,
wherein the catalyst is selected from platinum, palladium
ruthenium, rhodium, iridium, osmium and gold. The invention further
includes a control system for supplying the electrical power to the
electrolyzer when hydrogen peroxide is needed.
[0014] Other objects, advantages and applications of the present
invention will become apparent after a detailed description of the
invention.
BRIEF DESCRIPTION OF THE FIGURES
[0015] The description herein makes reference to the accompanying
drawings wherein like parts throughout the several views and
wherein;
[0016] FIG. 1 is a diagram of the present invention;
[0017] FIG. 2 is a general schematic for the generalized
invention;
[0018] FIG. 3 is an electrode array for the present invention;
[0019] FIG. 4 is a diagram of the electrodes for the
electrolyzer;
[0020] FIG. 5 is the electrode array in a preferred
configuration;
[0021] FIG. 6 is a design of an electrode for use in the
electrolyzer; and
[0022] FIG. 7 is a configuration of a plate comprising an electrode
and catalyst region.
DETAILED DESCRIPTION OF THE INVENTION
[0023] There are numerous applications where a bleaching agent is
helpful, such as, for example the removal of stains from clothing
or sink basins and the use of bleach for disinfecting.
Conventionally, the use of bleach in an environment such as a
personal residence requires the purchase of the bleach. The bleach
must be stored in a container, and the user must be aware of the
amount on hand available for use. The bleach can also be used for
disinfectant purposes, such as a periodic application of bleach to
a garbage disposal. The use in a garbage disposal can remove
bacteria that are creating unpleasant odors as a result of growth
in the garbage disposal. One such bleaching agent is hydrogen
peroxide. However, hydrogen peroxide requires storage in a suitable
container to prevent breakdown from UV light, such as using a brown
plastic container. Hydrogen peroxide also will degrade over time,
rendering a solution ineffective if allowed to sit for too long a
time.
[0024] The present invention provides for the production of an
aqueous hydrogen peroxide solution in-line or as a parallel stream
to a regular water line. The solution is produced on an as-needed
basis without the need to add chemicals when affixed to a water
pipe. The invention includes an electrolyzer for dissociating water
directed from a water line. The gases produced from the
electrolyzer, hydrogen and oxygen, are directed to a reactor in
fluid communication with the electrolyzer with water flowing over
an appropriate catalyst for the oxidation of hydrogen to hydrogen
peroxide. FIG. 1 is a diagram of the present invention. A self
contained hydrogen peroxide unit 10 of the present invention
includes a housing 12, an electrolyzer 14 and a hydrogen peroxide
reactor 16. The hydrogen peroxide unit 10 has an inlet 20 for water
and an outlet 22 for a hydrogen peroxide solution. The electrolyzer
14 is situated within the housing 12 and proximate to the inlet 20
for water. The hydrogen peroxide reactor 16 is situated within the
housing 12 and disposed between the electrolyzer 14 and the outlet
22. The electrolyzer 14 includes at least two electrodes 18 as
shown in FIG. 3. The electrodes 18 are oriented to promote the flow
of water over the electrodes 18. The electrolyzer 14 dissociates
the water into hydrogen and oxygen gases. The hydrogen and oxygen
flow over the reactor 16. Preferably the hydrogen and oxygen are
dissolved in the water flowing over the electrodes 18 and the water
flows over the reactor 16. The hydrogen and oxygen react in the
presence of a catalyst for hydrogen peroxide in the aqueous phase.
The hydrogen peroxide solution flows out of the outlet 22 ready for
application. While specific configurations may differ, the
orientation is such that the flow path of the water through the
apparatus enters through the water inlet 20, flows over the
electrodes 18 of the electrolyzer 14, through the reactor 16, and
out the outlet 22. Additional oxygen, if desired, usually in the
form of air, may be directed to the reactor 16 through an optional
independent air inlet 26. The air inlet 26 is preferably positioned
between the electrolyzer 14 and the reactor 16.
[0025] The outlet 22 can connect to any appropriate conduit that
directs the hydrogen peroxide solution to a desired destination. It
would be useful to have almost instant generation of hydrogen
peroxide when needed for the purpose of bleaching, sanitizing,
washing, disinfecting, or providing a convenient oxidizing agent
for chemical processing. The present invention provides the ability
to quickly generate hydrogen peroxide as needed without the
problems associated with storage or waste disposal, and to deliver
the hydrogen peroxide to a desired destination. A desired
destination can be directing the hydrogen peroxide solution for use
as a bleaching agent, as an antiseptic agent, or as a disinfectant
agent, or to a device that will use a bleaching or disinfectant
agent. A desired destination may include, but is not limited to a
washing machine, a dishwasher, a spa, a pool, a hot tub, a faucet,
a garbage disposal, an air conditioner, a refrigerator, a freezer,
a humidifier, a dehumidifier, a toilet, a urinal and a bidet. The
apparatus of the present invention can also be used with
agricultural or farm machinery, such as, for example, milking
machines, and food processing equipment. This provides the ability
to periodically disinfect equipment where the growth of germs and
molds can be expected.
[0026] In an alternate embodiment, a general configuration of the
invention is shown in FIG. 2. The hydrogen peroxide unit 10
includes an electrolyzer 14, an optional mixer 19 for creating a
hydrogen/oxygen mixture, and a hydrogen peroxide reactor 16. The
unit 10 has an inlet 20 for water. The inlet 20 splits into two
conduits 28 and 30, where one conduit 28 directs water to the
electrolyzer 14, and the second conduit 30 directs water to the
reactor 16. The electrolyzer 14 generates hydrogen and oxygen as
gases. The electrolyzer 14 has a conduit 32 for hydrogen and a
conduit 34 for oxygen, which directs the hydrogen and oxygen to the
mixer 19. The mixer 19 includes inlet ports for the hydrogen and
oxygen. The hydrogen conduits 32 is in fluid communication with the
hydrogen inlet port, and the oxygen conduit 34 is in fluid
communication with the oxygen inlet port. Optionally, the mixer 19
includes at least one inlet port 36 for the addition of oxygen to
the hydrogen and oxygen to increase the ratio of oxygen to hydrogen
in the mixer 19. The inlet port 36 may optionally be in the oxygen
conduit 34, as shown in FIG. 2, or be an additional inlet port (not
shown) to the mixer 19. The inlet port for oxygen can alternately
be used as an inlet port for air to achieve the increase in oxygen
to hydrogen ratio. The mixer 19 includes an outlet port 40 in fluid
communication with the reactor 16. The outlet port 40 carries the
hydrogen/oxygen mixture to the reactor 16. The reactor 16 includes
a product outlet port in fluid communication with a product conduit
22 for directing the hydrogen peroxide solution to a desired
destination. Alternately, the unit 10 includes a conduit 42 for
diverting some of the hydrogen produced from the electrolyzer 14 to
an alternate destination, such as, for example, a combustor to
generate heat. Optionally, an inlet port 38 for oxygen, or air, can
carry additional oxygen, or air, to the reactor 16 downstream of
the mixer 19. The inlet port 38 may enter a conduit carrying the
hydrogen and oxygen mixture, as shown, or may be on the inlet side
of the reactor 16. The electrolyzer:
[0027] The electrolyzer is a convenient device for using ordinary
tap water and converting a portion of the tap water into hydrogen
and oxygen gases through the application of energy. A preferred
embodiment includes an electrolyzer using electrical power. The use
of an electrolyzer is a convenient method and device for generating
the reactants, hydrogen and oxygen, as needed. There is no need to
provide other chemicals, or provide for storage of the reactants,
and therefore there is no waste of the hydrogen peroxide
produced.
[0028] The electrolyzer used for water splitting is a clean method
of producing hydrogen. The standard free energy, enthalpy, and
entropy of water are, respectively, G=237.19 kJ/mol (56.69
kcal/mol), H=285.85 kJ/mol (68.32 kcal/mol), and S=70.08 J/(molK)
(16.72cal/(molK)). The value for the free energy is equivalent to
an electromotive force of 1.23 V, which is the minimum voltage
needed to get the reaction to proceed at conditions of standard
temperature and pressure. The total energy required for the
reaction to proceed is the enthalpy, and can be a combination of
electrical energy and heat. Because G=H-TS and S is positive, the
electrical work needed (G) can be reduced by operating at higher
temperatures. This is a shifting of the energy load from electrical
energy to heat with increasing operating temperatures. This is
desirable because the production of heat is generally less
expensive than electricity.
[0029] The electrolyzer has a cell wherein water is admitted.
Within the cell are two electrodes having different polarities, and
current can flow from one electrode to the other through the water
within the cell. When electrical current is passing through the
cell, the water is decomposed and hydrogen is generated at one
electrode and oxygen is generated at the other electrode. The
electrolyzer can employ one of three types of processes: an aqueous
alkaline system; a solid polymer electrolyte (SPE); or a high
temperature steam electrolysis with temperatures in the range of
about 700.degree. C. to about 1000.degree. C. However, for
processes where the hydrogen and oxygen do not need to be
separated, the electrolyzer merely requires electrodes in
water.
[0030] The aqueous alkaline system is a traditional process and
employs an ionic compound added to the water to improve the
conductivity through the cell. The aqueous electrolyte systems
typically employ a barrier porous to the liquid phase but blocking
gas generated at the electrodes which enables the collection of the
oxygen and hydrogen gases separately and prevents mixing. The
electrolyzer can be a tank type or a filter press type. The tank
type has a plurality of individual cells connected in parallel.
This permits the use of one power source using low voltage. The
current necessary is proportional to the number of cells, and in
turn the transformers and rectifiers are sized accordingly. The
filter press type has a plurality of cells connected in series.
This is called a bipolar arrangement and the voltage required is
proportional to the number of cells for the unit. The units are run
at a pressure from about 100 kPa (0 psig) to about 600 kPa (72.4
psig). Running at higher pressure allows for smaller lines and is
an efficient method of compressing the gases. The electrolyzer is
operated at a temperature from about 0.degree. C. to about
60.degree. C., and preferably from about 25.degree. C. to about
40.degree. C. Heating the water reduces some of the electrolyzer
power requirements. A typical ionic compound used in the cell is
potassium hydroxide, KOH.
[0031] An alternate electrolyzer uses a solid polymer electrolyte
(SPE) for improving the conductivity through the cell. An example
of a solid polymer electrolyte useable in an electrolyzer is a
polysulfonated fluoroionomer. Polysulfonated fluoroionomers are
available commercially, for example, NAFION.TM. is made by E. I.
Dupont in Wilmington, Del. Electrolyzers using an SPE in the form
of a polymer sheet have the electrodes in electrical contact with
the polymer sheet. The hydrogen ion (H.sup.+) is produced at the
anode and migrates through the SPE to the cathode to produce
H.sub.2. The hydroxyl ions (OH.sup.-) produce oxygen at the anode.
These units have low internal resistance and can operate at higher
temperatures than the aqueous alkaline units.
[0032] For the typical direct current electrolyzer, the electrodes
are separated to direct the different generated gases into separate
receiving devices. The gases are collected, and each gas is
separately directed to the mixer for mixing to form a stable
mixture to be reacted upon contact with the catalyst. Each gas
enters at least one inlet port to the mixer, wherein the gases are
mixed and the mixture is directed to an outlet port in fluid
communication with the conduit supply end. The appropriate ratio of
oxygen to hydrogen is made by either adding additional oxygen from
air, or by diverting some of the hydrogen for an alternate use.
[0033] The reason for decomposing water for later reaction is that
electrolysis is a safe and convenient way for generating hydrogen
in relatively small amounts as needed. The hydrogen is then reacted
with oxygen to produce hydrogen peroxide in water with no other
products.
[0034] In a preferred embodiment, there is no need to separate the
hydrogen and oxygen as they are generated. The electrolyzer can be
at least two of electrodes 18 positioned within the housing 12. The
electrode 18 can generate the gases and allow the hydrogen and
oxygen to commingle and form a mixture, provided the spacing
between the electrodes 18 is a gap of less than about 400
micrometers with the gap preferably about 200 micrometers. The gap
between the electrodes 18 can be set by placing spacers 44 between
the electrodes 18.
[0035] Preferably, the spacers 44 are objects having a long and
thin structure such as a wire, with a circular, square, or
rectangular cross section. The electrodes 18 are plate-like
structures having a first dimension, or length, a second dimension,
or width, and a third dimension, or thickness. For purposes of
discussion the electrodes are oriented such that the length is in
the direction of flow of water over the plates and the width is the
direction transverse to the direction of flow. The spacers have a
length equal to or greater than the length of the electrodes and a
thickness of less than about 400 micrometers but preferably about
200 micrometers, wherein the thickness is the dimension of the
spacer creating the gap between the plates.
[0036] The spacers can be made of any electrically non-conductive
material, including but not limited to ceramics and plastics. One
embodiment for an electrode array is shown in FIG. 3. The spacers
44 are sandwiched between electrodes 18 having a plate like
configuration. The spacers 44 are disposed along the length of the
electrodes 18 between adjacent electrodes 18. The spacers 44 form
channels between the electrodes 18. One method of forming the
structure comprising the electrodes 18 and spacers 44 is to form a
sheet of a non-conductive material, such as a plastic, having a
thickness less than 400 micrometers, and a length greater than the
length of the electrodes 18. Slits are cut in the nonconductive
spacer sheet having a length equal to or greater than the length of
an electrode, with a width between 200 micrometers and 2 mm. The
spacing between the spacers 44 or width of the slits, is largely
dependent on the geometric configuration. The spacers 44 are to
prevent shorting of the electrodes 18. For planar electrodes the
width of the slits can be large, but for electrodes in a spiral, or
cylindrical configuration the width of the slits will be small, and
can vary as the radius of the spiral increases. For example, the
spacers will be closer together near the mandrel for a pair of
spiral wound electrodes, with a greater distance between
neighboring spacers as the electrodes are wound with increasing
radius. The spacers 44 may be formed using methods known in the
art, including extrusion, or molding in a preformed shape.
[0037] The electrodes 18 and sheets of non-conductive material used
for spacers are stacked in an alternating sequence with the ends of
the slits extending to at least the ends of the electrodes 18,
creating a layered structure of alternating spacers 44 and
electrodes wherein channels are created between the spacers 44
along the length of the electrodes 18.
[0038] Alternatively, instead of creating a stack of electrodes 18
as in FIG. 4, two electrodes can be rolled into a coil shape as
shown in FIG. 5 with spacers 44 used to maintain the electrode
separation. When forming a pair of electrode sheets 18 into a coil,
spacers 44 are positioned between the electrodes 18 and along one
of the outer faces of the electrodes 18. A mandrel 46 is affixed to
the edge of the electrodes 18. The mandrel 46 can be made of any
non-conductive material. The electrodes 18 are wrapped around the
mandrel 46, forming a substantially cylindrically shaped object.
Each electrode 18 has an electrical lead for attaching to an
electrical power source. In another alternative (not shown) the
electrodes 18 comprise a plurality of concentric tubes having
increasing diameters. This provides a set of nested tubes with a
gap between each pair of tubes of less than 400 micrometers.
[0039] It is preferable that the decomposition of water occurs over
the whole electrode. The electric field will concentrate lines of
the electric field at sharp edges or sharp points on the electrode.
In one embodiment the electrolyzer comprises electrodes having a
textured surface wherein the textured surface has a distribution of
localized peaks. The localized peaks provide for smaller bubbles
that more rapidly transfer the gas to the liquid phase. An example
of such a textured electrode is shown in FIG. 6, wherein the
electrode comprises an array of pyramid shapes 60 having peaks 62.
The localized peaks 62 can be formed using standard geometrical
shapes such as, but not limited to, cones, pyramids, and other
prismatic shapes. The water is decomposed preferentially at the
peaks 62, and minute gas bubbles are generated. In addition the
shapes provide for easier detachment of the gas bubbles into the
water flowing over the electrode 18. This provides for smaller
bubbles and more rapid dissolution of the gases into the water.
[0040] The volume of gases to be reacted is easily controlled by
the amount of electrical power supplied to the electrolyzer.
Details of an electrolyzer are well known in the art, as
demonstrated in U.S. Pat. No. 6,036,827, and which is incorporated
by reference in its entirety. The electrical power supplied to the
electrolyzer is of sufficient quantity to dissociate water at a
rate between 0.01 milligrams/min. to about 10 grams/min.
Optionally, a control system is incorporated in the electrolyzer to
provide an upper limit on the amount of electrical power used by
the electrolyzer, including, but not limited to, a fuse for
shutting off power to the electrolyzer.
[0041] When the water used in the electrolyzer is from a source of
hard water, the water will need to be softened first. The hardness,
especially the iron ion content will have an adverse effect on the
operation of the electrolyzer.
The Mixer:
[0042] The gases from the electrolyzer optionally, are mixed in a
mixer. The mixer has at least one first supply tube having a first
supply tube receiving end for receiving a first fluid stream and a
discharge end opposite the receiving end; at least one second
supply tube having a second supply tube receiving end for receiving
a second fluid stream and a discharge end opposite the receiving
end; a mixing chamber in fluid communication with the first and
second supply tube discharge ends; and a mixing chamber outlet for
discharging a mixed stream of the first and second fluid streams
from the mixing chamber. In a preferred embodiment of the mixer,
the mixing chamber of the mixer is in fluid communication with a
plurality of first supply tubes discharge ends, and in fluid
communication with a plurality of second supply tube discharge
ends. The plurality of first and second supply tube discharge ends
are arrayed in an interdigitated pattern on the mixing chamber.
This provides for a layering of the gases upon entry to the mixing
chamber and rapid diffusional mixing within the chamber
[0043] The mixer can be any type of mixer for mixing gases.
However, the constraints on the mixer are that mixing chambers and
channels need to be sized to keep the volumes of mixtures of
hydrogen and oxygen stable, that is keep the volumes below cell
sizes wherein ignition and propagation of a combustion reaction
between hydrogen and oxygen can occur. In a preferred embodiment of
the mixer described above, the discharge ends of the supply tubes
have an inner diameter of less than 0.02 cm. and the mixing chamber
has an inner diameter of less than 0.02 cm.
[0044] Another possible mixer design includes a packed bed. The
mixer has a plurality of supply tube discharge ends in fluid
communication with the mixing chamber. The mixing chamber is a
packed bed of inert material providing a series of intertwined
channels having channel diameters of less than 0.02 cm.
[0045] One possible mixer design includes a mixing unit, as
described in U.S. patent application Ser. No. 09/850,470, filed on
May 7, 2001, which is incorporated by reference in its entirety.
The mixing unit provides a mixing chamber with a plurality of
supply tubes arranged about the mixing chamber perimeter. The
supply tubes open into the mixing chamber in such a manner that
particular fluids introduced at defined flow rates will form a
fluid spiral flowing concentrically inward. This vortex formation
extends the fluid residence time within the mixing chamber
considerably, thereby improving mixing characteristics.
Establishment of the desired helical and inward fluid flow path is
primarily a function of both the angle of fluid introduction into
the mixing chamber and the fluid kinetic energy. Fluids introduced
radially, or, in the case of a cylindrical mixing chamber, directly
toward its center, will not assume a helical flow path unless acted
upon by another fluid with sufficient kinetic energy in the
tangential direction. The present mixer achieves exceptional mixing
by introducing the first and second fluids to be mixed both
tangentially and radially. In one embodiment, the tangential fluid
kinetic energy components are adequate to bend the radial flow
components so that they assume the overall helical flow pattern
with a sufficient number of windings to allow effective mixing.
Since one fluid is introduced tangentially and another radially, it
is preferred that the ratio of fluid kinetic energy of the
tangentially flowing fluid to that of the radially flowing fluid is
greater than about 0.5 to provide the desired helical and inward
flow pattern. The supply tubes can include additional tubes for the
addition of air to the mixture to control the ratio of oxygen to
hydrogen in the gas mixture. The mixing chamber is sized to be less
than about 0.02 cm. in internal diameter.
The Reactor:
[0046] In one embodiment, the reactor 16 in the present invention
is a trickle bed reactor. The reactor comprises at least one inlet
port for admitting hydrogen and oxygen to the reactor. The inlet
port can provide for admitting water to the reactor, or in an
alternative, a separate inlet port is provided for admitting water
to the reactor. The reactor includes a chamber for holding a
catalyst on a support material, referred to as the catalyst bed. In
the reactor, water flows over the catalyst bed with a sufficient
volume to form a liquid layer over the surface of the catalyst. The
hydrogen and oxygen flow through the reactor and dissolve in the
aqueous phase. The hydrogen in solution is oxidized on the surface
of the catalyst bed to form hydrogen peroxide in the aqueous phase.
The aqueous solution of hydrogen peroxide exits the reactor 16
through an outlet port. The outlet port is in fluid communication
with a conduit 34 for directing the hydrogen peroxide solution to a
desired destination. A desired destination can be as stated above.
The reactor is sized to produce a hydrogen peroxide solution of
less than about 5 mol. %.
[0047] In one embodiment, the catalyst comprises at least one
catalytic metal. The catalytic metal is any metal suitable to carry
out the oxidation of hydrogen to hydrogen peroxide. Metals suitable
for the catalyst include, but are not limited to, platinum (Pt),
palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir), osmium
(Os), gold (Au), and mixtures thereof. Preferably the catalytic
metal is selected from platinum, palladium, and a mixture thereof.
The catalyst while comprising at least one of the aforementioned
metals, can also include a promoter metal selected from the group
consisting of iron (Fe), cobalt (Co), Nickel (Ni), ruthenium,
rhodium, palladium, and mixtures thereof.
[0048] The catalytic metals are preferably deposited on a support.
The support is any appropriate inert porous material which provides
a sufficiently large wettable surface area for the oxidation of
hydrogen. Materials suitable for the support include, but are not
limited to, carbon, carbon in the form of charcoal, silica,
alumina, titania, zirconia, silicon carbide, silica-alumina,
diatomaceous earth, clay, molecular sieves, and mixtures thereof.
The catalyst is deposited on the support by processes know to those
skilled in the art. Typical techniques include chemical vapor
disposition, impregnation, etc., and are well known in the art.
Molecular sieves suitable for catalysts include, but are not
limited to, zeolites such as H-ZSM-5 having a silica to alumina
ratio of 6, and H-ferrierite having a silica to alumina ratio of
3.25. A preferable support is carbon. The support may be formed in
a wide variety of shapes including, for example, extrudates,
spheres, pills and the like, which are produced by methods known in
the art.
[0049] In the case of a carbon substrate, the catalyst bed is
prepared by creating a porous carbon substrate, the substrate can
be created by pyrolysis of heavy hydrocarbons, polymers, etc. The
metal catalyst is deposited on the carbon substrate by processes
known to those skilled in the art. Typical techniques are chemical
vapor deposition, impregnation, etc. and are well known in the
art.
[0050] For a catalyst comprised of a Pt and/or Pd metal on a silica
or inorganic metal oxide support, the catalyst is prepared by
spray-drying a mixture of a colloidal support material and a
compound of the Pt and/or Pd metal. When both the Pt and Pd are
present, a preferred atomic ratio of Pt:Pd is from 0.01 to 0.1 with
a more preferred ratio of about 0.05.
[0051] In an alternative embodiment the catalytic metal is
deposited on a sheet of material, or the catalytic metal is
deposited on a support, such as a molecular sieve, and the
catalytic metal and support are deposited on a sheet. Materials
suitable for the sheet include, but are not limited to, polymers
such as polyethylene, polypropylene, polystyrene,
polytetrafluoroethylene, also known as TEFLON.TM., or a TEFLON
related polymer, or mixtures thereof The reactor comprises a
plurality of sheets in a stack with spacers separating the sheets.
Preferably the gap provided by the spacers between the sheets is
less than 400 micrometers. Optionally, the sheet is wound in a
spiral wound with spacers to create gaps between sections of the
sheet. The sheets can also be formed as nested concentric tubular
structures, with spacers forming gas between adjacent tubes.
Alternately, the material used for spacers can be a corrugated
structure that is perforated to allow the movement of ions between
the electrodes. The size and distribution of perforation chosen
based on criteria, such as for example flow of fluid and
fabrication consideration.
[0052] In another alternative embodiment, the catalytic metal is
deposited on a porous matrix comprised of fibers, or the catalytic
metal is deposited on a support and the catalytic metal and support
are deposited on a porous matrix. The porous matrix is a porous mat
or layers of porous mats comprised of fibers. The fibers are made
from natural or artificial materials such as plastics. Suitable
materials include, but are not limited to, cellulosic fibers,
cellulose acetate, nylon, polyester, cotton, natural fibrous
materials, fibers made from plastics such as polyethylene or
polypropylene, and mixtures thereof.
[0053] In an alternative embodiment, the reactor is a fixed bed
reactor wherein the fixed bed comprises a catalyst as described
above. The fixed bed reactor is filled with water and the hydrogen
and oxygen gases are bubbled through the reactor. The gases are
preferably mixed, and dissolve in the water. The hydrogen is
oxygenated in the aqueous phase forming a hydrogen peroxide
solution. The solution is drawn off the reactor through a reactor
outlet port.
[0054] The reactor design can be a concurrent flow reactor, as in
the trickle bed, wherein the gas mixture flows in the same general
direction as the water stream, or the design can be a
countercurrent flow wherein the gas mixture bubbles upward against
a downward flow of the water stream.
[0055] One preferred embodiment of the invention comprises at least
two plates, wherein each plate comprises an electrode and a
substrate coated with catalyst. An example of such a plate 48 is
shown in FIG. 7. The plate 48 can be a rigid or flexible material.
The plate 48 is comprised of three regions: an electrode 18, an
electrically insulating region 50, and a catalyst region 52.
[0056] In one embodiment the plate 48 comprises an electrically
non-conductive substrate, having a front surface and rear surface
for the electrode region 18, a conductive material is deposited on
the front surface and the back surface; the electrically insulating
region 50 remains untreated; and the catalyst region 52 is coated
with a catalyst.
[0057] The electrolyzer 14 and reactor 16 are formed by stacking a
plurality of plates 48 with spacers 44 to separate the plates 48.
The spacers 44 are sized to separate the plates between about 100
micrometers and about 400 micrometers, and are oriented to provide
channels from the electrolyzer 14 to the reactor 16.
[0058] Alternately, the electrolyzer 14 and reactor 16 comprises
two plates 48. The plates 48 are separated by spacers 44 with
spacers 44 positioned along the outer surface of one of the plates
48. A mandrel 46 is attached along one of the edges of the plates
48 that runs from the electrode region 18 to the catalyst region
52. The plates 48 are wrapped around the mandrel 46 forming a
generally cylindrically shaped object comprising the electrolyzer
electrode 18 and the reactor 16, having channels for water to flow
from the electrode 18 to the reactor 16.
[0059] Other reactor alternatives include non-fixed bed reactors.
An example of a non-fixed bed reactor includes a stirred tank
reactor, either using a continuous or batch process. The stirred
tank reactor includes a water inlet port in fluid communication
with a reaction chamber for admitting water to the chamber. The
reaction chamber comprises a reservoir for holding a catalyst on a
support in a slurry comprising an aqueous solution and the catalyst
on a support. The slurry is stirred with an impeller to mix the
slurry keeping the solution well mixed with the catalyst. A gas
inlet port is in fluid communication with the chamber for admitting
the gas to the chamber. The gas inlet port can force the gas
mixture into the solution through a sparger for creating a
dispersion of small gas bubbles, or any other appropriate mechanism
for distributing the gas in the solution. An aqueous solution of
hydrogen peroxide is drawn from the reaction chamber through a
product outlet port. The stirred tank reactor includes a screen
positioned across the product outlet port for filtering the solid
catalyst particles and preventing the catalyst particles from being
swept out of the reaction chamber with the product solution. An
alternative design can include a separation unit for separating the
solid catalyst particles from the solution, and reinjecting the
catalyst particles into the reaction chamber.
[0060] An alternate method of preparing the catalyst is by mixing
silica with a concentrated solution of metal compounds forming a
paste. The paste is filtered and dried under conditions supporting
a slow crystallization of the catalyst bearing silica. The
conditions include a reducing environment under hydrogen at a
temperature between about 250.degree. C. and about 400.degree. C.
The paste is treated with an acidic solution containing a bromide
compound in a concentration from about 2 mg/l to about 20 mg/l, and
bromine at a concentration from about 0.05 to about 2% by weight,
and is treated at a temperature from about 10.degree. C. to about
80.degree. C. The paste is subsequently filtered and dried at a
temperature from about 100.degree. C. to about 140.degree. C.
[0061] In a preferred embodiment, the apparatus 10 includes an
electrolyzer 14 and reactor 16, without a mixer 19. The preferred
design of the electrolyzer 14 provides mixing and dissolution of
the hydrogen and oxygen in the water prior to flowing the aqueous
solution over the reactor catalyst, removing the need for a mixer
19, and reducing cost of building; the apparatus 10.
[0062] The invention, optionally, further comprises a sensor
disposed downstream of the reactor 16. The sensor detects the
presence of hydrogen peroxide and provides feedback to control the
power delivered to the electrolyzer 14. Potential sensors include
spectroscopic methods, such as ultraviolet or infrared
spectroscopic techniques; and potentiometric methods. Sensors for
detecting hydrogen peroxide are known in the art, such as
demonstrated, for example, in U.S. Pat. No. 6,129,831, which is
incorporated by reference.
[0063] While the invention has been described with what are
presently considered the preferred embodiments, it is to be
understood that the invention is not limited to the disclosed
embodiments, but is intended to cover various modifications and
equivalent arrangements included with the scope of the appended
claims.
* * * * *