U.S. patent application number 12/243457 was filed with the patent office on 2010-04-01 for electrolytic device for generation of ph-controlled hypohalous acid aqueous solutions for disinfectant applications.
Invention is credited to Wilfred J. Hemker, Daniel A. Scherson, Jackson W. Wegelin.
Application Number | 20100078331 12/243457 |
Document ID | / |
Family ID | 41168648 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100078331 |
Kind Code |
A1 |
Scherson; Daniel A. ; et
al. |
April 1, 2010 |
ELECTROLYTIC DEVICE FOR GENERATION OF pH-CONTROLLED HYPOHALOUS ACID
AQUEOUS SOLUTIONS FOR DISINFECTANT APPLICATIONS
Abstract
An electrolytic device for the generation of hypohalous acid in
aqueous solutions includes at least a single liquid chamber for
receiving an aqueous solution containing halide ions therein, the
single liquid chamber having an exterior wall and a solid anode
contained within to provide for the oxidation of the halide ions,
which, in turn, provides for the formation of hypohalous acid in
aqueous solution, and a gas permeable cathode forming a portion of
the exterior wall of the single liquid chamber, the cathode
providing for the reduction of oxygen to provide hydroxyl ions in
solution within the single liquid chamber to mix with the products
generated at the anode. An embodiment of the electrolytic device
including an anolyte chamber and a catholyte chamber separated by
an ionomeric membrane is also described, whereby the anolyte
chamber further includes an outlet including a pH control for
determining and regulating the pH of the exiting anolyte effluent
to between about 4 and 9. The product is suitable for disinfectant
applications including as a hand sanitizer.
Inventors: |
Scherson; Daniel A.;
(Beachwood, OH) ; Wegelin; Jackson W.; (Stow,
OH) ; Hemker; Wilfred J.; (Akron, OH) |
Correspondence
Address: |
RENNER KENNER GREIVE BOBAK TAYLOR & WEBER
FIRST NATIONAL TOWER FOURTH FLOOR, 106 S. MAIN STREET
AKRON
OH
44308
US
|
Family ID: |
41168648 |
Appl. No.: |
12/243457 |
Filed: |
October 1, 2008 |
Current U.S.
Class: |
205/335 ;
204/237; 204/252 |
Current CPC
Class: |
C25B 1/26 20130101; C25B
1/24 20130101; C25B 9/00 20130101; C25B 15/08 20130101; C02F 1/4674
20130101; C25B 15/02 20130101 |
Class at
Publication: |
205/335 ;
204/252; 204/237 |
International
Class: |
C25B 15/02 20060101
C25B015/02; C25B 9/08 20060101 C25B009/08; C25B 15/08 20060101
C25B015/08 |
Claims
1. An electrolytic device for the generation of hypohalous acid in
aqueous solutions, the device comprising: a single liquid chamber
having an inlet for receiving an aqueous solution containing halide
ions therein, the single liquid chamber having an exterior wall and
a solid anode contained within the single liquid chamber providing
for the oxidation of the halide ions to provide an aqueous solution
of hypohalous acid; and a gas permeable cathode forming at least a
portion of the exterior wall of the single liquid chamber, the
cathode providing for the reduction of oxygen to provide hydroxyl
ions in solution within the single liquid chamber to mix with the
hypohalous acid produced at the anode, the cathode having a
hydrophobic surface for receiving oxygen from outside the single
liquid chamber and a hydrophilic surface in contact with the
electrolyte solution allowing for reduction of dioxygen.
2. The electrolytic device as claimed in claim 1, wherein the
single liquid chamber further includes an outlet including a pH
control device for determining the pH of the exiting mixed
effluent.
3. The electrolytic device as claimed in claim 1, wherein the
hypohalous acid is hypochlorous acid and the halide ions are
chloride ions.
4. The electrolytic device as claimed in claim 1, further including
a gas compartment for providing oxygen to the gas permeable
cathode, wherein the gas compartment is defined by at least one
exterior wall that encloses the portion of the exterior wall of the
single liquid chamber composed of the gas permeable cathode within
the gas compartment.
5. The electrolytic device as claimed in claim 4, wherein the gas
compartment includes an inlet for receiving oxygen into the gas
compartment.
6. The electrolytic device as claimed in claim 1, wherein the solid
anode is a dimensionally stable anode.
7. The electrolytic device as claimed in claim 1, wherein the gas
permeable cathode is a gas diffusion electrode.
8. The electrolytic device as claimed in claim 2, wherein the pH
control for determining the pH is a pH meter and sensor.
9. An electrolytic device for the generation of hypohalous acid in
aqueous solutions, the device comprising: an anolyte chamber having
an inlet for receiving an aqueous solution containing halide ions
therein, the anolyte chamber having an exterior wall and a solid
anode contained within the anolyte chamber providing for the
oxidation of the halide ions to provide an anolyte effluent of
hypohalous acid in aqueous solution; a catholyte chamber having an
inlet for receiving an aqueous electrolyte, wherein the catholyte
chamber is defined by at least one exterior wall or portion thereof
comprising a gas permeable cathode, the cathode having a
hydrophobic surface for receiving oxygen from outside the catholyte
chamber and a hydrophilic surface allowing for reduction of
dioxygen; and an ionomeric membrane for partitioning the anolyte
chamber from the catholyte chamber; wherein the anolyte chamber
further includes an outlet including a pH control for determining
and regulating the pH of the exiting anolyte effluent to between
about 4 and 9.
10. The electrolytic device as claimed in claim 9, wherein the
catholyte chamber includes reacted catholyte effluent therein.
11. The electrolytic device as claimed in claim 10, wherein
catholyte chamber includes an outlet for releasing any reacted
catholyte effluent remaining in the catholyte chamber to mix with
the exiting anolyte effluent.
12. The electrolytic device as claimed in claim 11, wherein the pH
control for regulating the pH includes a valve and a recirculator
for recirculating the flow of the exiting mixed anolyte and
catholyte effluents back into the anolyte chamber when the mixed
anolyte and catholyte effluents have a pH that is greater than
9.
13. The electrolytic device as claimed in claim 9, further
including an inlet valve for releasing a buffering agent into the
anolyte chamber of aqueous solution containing halide ions.
14. The electrolytic device as claimed in claim 9, wherein the pH
of the mixed anolyte and catholyte effluents is regulated between
about 5 and 8.
15. A method for the generation of hypohalous acid comprising:
oxidizing halide ions in the presence of water within a single
liquid chamber to form an aqueous solution of hypohalous acid;
feeding oxygen through a gas permeable cathode to reduce the oxygen
in the presence of water to form hydroxyl ions, wherein the gas
permeable cathode forms at least a portion of an exterior wall of
the single liquid chamber; mixing the solution containing hydroxyl
ions in an amount sufficient to complete the electrical circuit
within the device and to produce hypohalous acid; determining the
pH of the hypohalous acid to ensure that the pH is between about 4
and 9; and removing the hypohalous acid.
16. The method of claim 15, wherein the step of determining the pH
of the hypohalous acid includes the use of a pH meter.
17. The method of claim 15, wherein the step of feeding oxygen to
the gas permeable cathode includes delivering oxygen from a gas
compartment, wherein the portion of the exterior wall of the single
liquid chamber comprised of the gas permeable cathode is included
in the gas compartment.
18. A method for the generation of hypohalous acid comprising:
oxidizing halide ions in the presence of water within an anolyte
chamber to form an anolyte effluent containing hypohalous acid;
feeding oxygen through a gas permeable cathode to reduce the oxygen
in the presence of water to form a catholyte effluent containing
hydroxyl ions, wherein the gas permeable cathode forms at least a
portion of an exterior wall of a catholyte chamber; mixing the
solution containing the hydroxyl ions in an amount sufficient to
complete the electrical circuit within the device to produce
hypohalous acid; controlling the pH of the hypohalous acid to
ensure that the pH is between about 4 and 9; and removing the
hypohalous acid.
19. The method of claim 18, wherein the step of controlling the pH
of the hypohalous acid further includes the steps of determining
the pH of the hypohalous acid and regulating the pH of the
hypohalous acid.
20. The method of claim 19, wherein the step of determining the pH
of the hypohalous acid includes the use of a pH meter and
sensor.
21. The method of claim 19, wherein the step of regulating the pH
of the hypohalous acid further includes mixing the exiting anolyte
and catholyte effluents in an amount sufficient to increase the pH
of the hypohalous acid to ensure that the pH is between about 4 and
9.
22. The method of claim 21, further comprising the step of
determining the pH of the hypohalous acid after mixing the exiting
anolyte and catholyte effluents, wherein the step includes the use
of a pH meter.
23. The method of claim 21, wherein the step of regulating the pH
of the hypohalous acid further includes recirculating the flow of
the hypohalous acid back to the anolyte chamber if the pH of the
hypohalous acid is below 4 or above 9.
24. The method of claim 23, further comprising the step of
determining the pH of the hypohalous acid after recirculating the
flow of the hypohalous acid back to the anolyte chamber, wherein
the step includes the use of a pH meter and sensor.
25. The method of claim 18, wherein the step of feeding oxygen to
the gas permeable cathode includes delivering oxygen from a gas
compartment, wherein the portion of the exterior wall of the
catholyte chamber comprised of the gas permeable cathode is
included in the gas compartment.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for forming
hypohalous acid and further relates to at least a single liquid
chamber electrolytic device for generation of pH-controlled
hypohalous acid aqueous solutions for disinfectant applications.
This method and device has the advantage whereby the pH of the
solution is regulated and optimized. Such a method and device is
particularly useful for preparing hypochlorous acid. Specifically,
the resultant effluent exiting the device, which may be HClO in
aqueous solution, is suitable for use in hand sanitizers.
BACKGROUND OF THE INVENTION
[0002] Others have attempted to produce hypohalous acids using a
variety of methods. For example, one method of producing
low-chloride aqueous solutions of hypochlorous acid (HClO) includes
spraying fine droplets of aqueous alkali metal hydroxides or
alkaline earth metal hydroxides in a reactor dryer with chlorine
gas to make hypochlorous acid gas and solid metal chloride.
Creating the spray of fine droplets requires high pressures, and
thus, a high energy input. The hypochlorous acid gas is then
condensed along with the water vapor, requiring refrigeration
equipment to achieve condensing temperatures, to produce
concentrated hypochlorous acid. Disadvantages of this process
include difficulty in handling the solid salt, high chlorine
ratios, and energy inefficiency.
[0003] Another process which shares the aforementioned
disadvantages for making aqueous hypochlorous acid includes
spraying a solution of alkali metal hydroxide into a chlorine
atmosphere resulting in HClO vaporization and a dry solid salt.
With this process, aqueous HClO solution is produced by absorption
of the HClO in water as opposed to the condensation of the HClO and
water vapor.
[0004] Still another process uses an organic solvent to extract
HClO from a brine solution. This process suffers from a need to
further remove the HClO from the organic solvent to produce an
aqueous HClO solution, a need to remove residual solvent from the
brine solution, and undesirable reactions of HClO with the organic
solvent.
[0005] Despite the several known processes for producing
hypochlorous acid, there remains a need for a quick, safe, and
efficient process for producing hypochlorous acid solutions
suitable for disinfectant applications. Therefore, methods which do
not require handling of solid salt by-products or chlorine gas
input have been sought, as have more energy efficient methods been
desired which do not require large heating/cooling cycles or high
pressure on the liquid feed.
[0006] One method for producing hypochlorous acid solutions
suitable for use as a disinfectant in food processing describes
controlling the hypochlorite/hypochlorous acid balance of a stream
by mixing liquid acid with a pressurized carrier stream which has
been chlorinated by the addition of a chlorination agent. By
decreasing the pH of the liquid stream, the relative ratio of
hypochlorous acid to hypochlorite of the liquid stream is
increased. This process allowed for the manipulation of the
pressurized streams in order to produce specific concentrations of
hypochlorous acid providing greater control over the reaction
process; however this process necessitates the introduction of a
gaseous species other than air at preferred elevated
temperatures.
[0007] Electrolytic cells have been utilized in prior inventions as
related to production of acidic liquids. One such described
invention provides an electrolytic cell and process for the
production of hydrogen peroxide solution and hypohalide by
electrolysis, whereby hypohalide and hydrogen peroxide are produced
in the anode chamber and the cathode chamber, respectively. The
invention specifically relates to a seawater treatment method where
both the desired products hydrogen peroxide and hypochlorous acid
are reintroduced into the seawater to efficiently treat the water.
However, the invention necessitates the use of a dual chamber
device, and hydrogen peroxide would not be suitable for a daily
hand sanitizing formulation.
[0008] Electrochemical devices have also been used previously to
produce strong acid sterilizing liquids. One such device for use in
water treatment facilities utilizes an apparatus for generating and
dispensing a strong acid sterilizing liquid which contains
hypochlorous acid at low concentrations and whose pH is 3 or less.
In that apparatus, salt water is passed through a channel formed
between a positive electrode plate and a negative electrode plate
disposed to face opposite surfaces of a barrier membrane in which
DC voltage is applied between the electrodes to electrolyze the
salt water. The barrier membrane prevents the mixing of the
products at the positive electrode and the products at the negative
electrode. Acid liquid containing hypochlorous acid can be obtained
by taking the aqueous solution flowing through the space between
the barrier membrane and the positive electrode out of the
electrolytic cell.
[0009] In another method directed toward obtaining a low pH aqueous
acid solution, also using a two-chamber-type electrolytic cell
device, a strong acid water containing a reduced amount of chloride
for use in sterilization is produced whereby chloride ions are
oxidized at the anode. With this apparatus, as with the previously
described invention, the end product is desired to have a pH less
than 3 and therefore is not suitable for a daily hand sanitizing
formulation.
[0010] Chlorination is long known as a method for killing
undesirable microorganisms. Chlorine may be provided in multiple
forms including chlorine gas (Cl.sub.2), a relatively cheap and
highly effective antimicrobial agent; however, it is also a highly
toxic and corrosive gas. Hypochlorites, such as NaOCl or
Ca(OCl).sub.2, are a much safer alternative, but are considerably
more expensive than gaseous chlorine. Finally, hypochlorite
solutions (i.e., bleach) may also be utilized; however, these are
rarely used in large scale applications because they are bulky and
hazardous. Regardless of the chlorine source, hypochlorous acid
(HClO) and the hypochlorite ion (OCl.sup.-) are the final desirable
antimicrobial products. In any application for a hand sanitizer,
however, hypochlorous acid is preferred for safe use in contact
with human skin.
[0011] Beyond safety, the bactericidal activity of an aqueous
solution of hypochlorous acid needs to be considered, particularly
for use in disinfectant applications. The composition of an aqueous
solution of hypochlorous acid varies with the pH of the solution
because the form of chlorine compounds dissolved in the aqueous
solution varies with pH. At low pH, typically above pH 3, HClO is
the predominant form, while at high pH, typically above pH 8,
OCl.sup.- predominates. The HClO form is about 80 times more
effective than OCl.sup.- for killing microorganisms because HClO
crosses cell membranes easier than the hypochlorite ion.
[0012] When the pH of an aqueous solution of hypochlorous acid is 8
or more, or the aqueous solution of hypochlorous acid is alkaline,
hypochlorous acid ions (ClO.sup.-) having fairly low bactericidal
activity are mainly present in the aqueous solution. Thus, the
bactericidal activity of an alkaline aqueous solution of
hypochlorous acid is fairly low.
[0013] When the pH of aqueous solution of hypochlorous acid is 7 or
less, or the aqueous solution of hypochlorous acid is acidic, the
amount of hypochlorous acid (HClO) having a bactericidal activity
10 to 100 times larger than that of hypochlorite ions is larger
than the amount of hypochlorite ions. Thus, the bactericidal
activity of an acidic aqueous solution of hypochlorous acid is
high.
[0014] When the pH of an aqueous solution of hypochlorous acid is
between 3 and 5.5, substantially 100% of the chlorine compound
dissolved in the aqueous solution is hypochlorous acid. Thus, the
bactericidal activity of the aqueous solution of hypochlorous acid
becomes even higher.
[0015] When the pH of an aqueous solution of hypochlorous acid is 3
or less, a part of the chlorine compound dissolved in the aqueous
solution becomes chlorine gas (Cl.sub.2) having yet higher
bactericidal activity than that of hypochlorous acid. Thus, the
bactericidal activity of the aqueous solution of hypochlorous acid
becomes even higher. However, human skin may be damaged by
application of acid sterilizing liquid of such a low pH.
[0016] It would be desirable to control the pH of the chlorinated
solution to increase the antimicrobial effectiveness of the
chlorination process and also to ensure safety for uses such as
hand sanitizer. Previous processes and systems for adjusting the pH
of a water stream have been described. These processes include
using carbon dioxide by injection into water by a direct gas feed,
or bubbler; or in another method for injecting carbon dioxide into
water by aspirating the carbon dioxide into a stream of water using
a Venturi-type eductor. It is, however, difficult to control the
efficiency of the carbon dioxide gas usage and these processes are
inherently inefficient.
SUMMARY OF THE INVENTION
[0017] In the present device, an aqueous solution containing halide
ions is introduced into an electrolytic device for generation of
pH-controlled hypohalous acid aqueous solutions, whereby at least a
single liquid chamber may be utilized in which reactions are taking
place at the interface between the each of the electrodes and the
electrolyte solution to produce an effluent of HClO in aqueous
solution. As reactions are taking place in the presence of excess
water, the reactions occurring in the single liquid chamber release
an effluent which may be monitored for pH, a desired pH range
between about 4 and 9. This method and device has an advantage in
that storage of gaseous species, such as chlorine gas, is not
needed. Also, the source electrolyte is economical and safe for
handling, while the end product may be directly used for
disinfectant purposes at a controlled pH level suitable for use as
a hand sanitizer without irritation or damage.
[0018] More specifically, the present invention provides an
electrolytic device for the generation of hypohalous acid in
aqueous solutions, the device comprising: a single liquid chamber
having an inlet for receiving an aqueous solution containing halide
ions, the single liquid chamber having an exterior wall and a solid
anode contained within the single liquid chamber providing for the
oxidation of the halide ions to provide an aqueous solution of
hypohalous acid; and a gas permeable cathode forming at least a
portion of the exterior wall of the single liquid chamber, the
cathode providing for the reduction of oxygen to provide hydroxyl
ions within the single liquid chamber to mix with the hypohalous
acid produced at the anode, the cathode having a hydrophobic
surface for receiving oxygen from outside the single liquid chamber
and a hydrophilic surface in contact with the electrolyte solution
allowing for reduction of dioxygen.
[0019] Further, the present invention provides an electrolytic
device for the generation of hypohalous acid in aqueous solutions,
the device comprising: an anolyte chamber having an inlet for
receiving an aqueous solution containing halide ions, the anolyte
chamber having an exterior wall and a solid anode contained within
the anolyte chamber providing for the oxidation of the halide ions
to provide an anolyte effluent of hypohalous acid in aqueous
solution; a catholyte chamber having an inlet for receiving an
aqueous electrolyte, wherein the catholyte chamber is defined by at
least one exterior wall or portion thereof comprising a gas
permeable cathode, the cathode having a hydrophobic surface for
receiving oxygen from outside the catholyte chamber and a
hydrophilic surface allowing for reduction of dioxygen; and an
ionomeric membrane for partitioning the anolyte chamber from the
catholyte chamber; wherein the anolyte chamber further includes an
outlet including a pH control for determining and regulating the pH
of the exiting anolyte effluent to between about 4 and 9.
[0020] The present invention further provides a method for the
generation of hypohalous acid comprising: oxidizing halide ions in
the presence of water within a single liquid chamber to form an
aqueous solution of hypohalous acid; feeding oxygen through a gas
permeable cathode to reduce the oxygen in the presence of water to
form hydroxyl ions, wherein the gas permeable cathode forms at
least a portion of the exterior wall of the single liquid chamber;
mixing the solution containing the hydroxyl ions in an amount
sufficient to complete the electrical circuit within the device and
to produce hypohalous acid; determining the pH of the hypohalous
acid to ensure that the pH is between about 4 and 9; and removing
the hypohalous acid.
[0021] In addition, the present invention further provides a method
for the generation of hypohalous acid comprising: oxidizing halide
ions in the presence of water within an anolyte chamber to form an
anolyte effluent containing hypohalous acid; feeding oxygen through
a gas permeable cathode to reduce the oxygen in the presence of
water to form a catholyte effluent containing hydroxyl ions,
wherein the gas permeable cathode forms at least a portion of an
exterior wall of a catholyte chamber; mixing the hydroxyl ions in
an amount sufficient to complete the electrical circuit within the
device to produce hypohalous acid; controlling the pH of the
hypohalous acid to ensure that the pH is between about 4 and 9; and
removing the hypohalous acid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] By way of example and to make the description more clear,
reference is made to the accompanying drawings in which:
[0023] FIG. 1A is a schematic diagram illustrating the electrolytic
device employable in the process of the invention; and
[0024] FIG. 1B is a schematic diagram of the gas diffusion
electrode used in the electrolytic device employable in the process
of the invention; and
[0025] FIG. 2 is a cross-sectional view of the device describing
one embodiment including a single liquid chamber, a gas
compartment, and a pH control; and
[0026] FIG. 3 is a three-dimensional representation of an
alternative embodiment of FIG. 2 whereby the gas compartment
encircles the single liquid chamber;
[0027] FIG. 4 is a three-dimensional representation of another
alternative embodiment of FIG. 2 whereby the single liquid chamber
encircles the gas compartment; and
[0028] FIG. 5 is a cross-sectional view of an alternative
embodiment of the invention in which the dual chamber device
includes an anolyte chamber and a catholyte chamber, wherein the
gas permeable cathode serves as at least a portion of the exterior
wall of the catholyte chamber; the device further includes a
recirculator and a pH control.
PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION
[0029] Examples of the process of the invention for the production
of hypohalous acid in aqueous solution will be described
hereinafter, but the invention should not be construed as being
limited thereto. One embodiment of the invention provides an
electrolytic device 1 for the production of pH-regulated hypohalous
acid aqueous solutions in a single liquid chamber as shown in
schematic diagram FIG. 1A. In the electrolytic device 1 for use in
the process of the invention, operation of the electrosynthetic
reactor relies on the use of a DC constant current power supply
connected to the gas diffusion electrode 2 to induce reduction of
dioxygen to water and to the anode 3 to promote oxidation of
chloride ion to generate, for example, HClO. In this electrolytic
cell, electricity is consumed to produce chemicals. In FIG. 1B, the
gas diffusion electrode 2, also known interchangeably here within
as a gas permeable cathode, which acts as a current collector, has
a hydrophobic surface 4 which faces air, or some gaseous source of
oxygen, on the outside to prevent liquid from filtering through the
structure. The gas diffusion electrode 2 further has a hydrophilic
surface 5 which faces the electrolyte and allows for the
electrocatalytic surface, where the actual reduction of dioxygen
occurs, to form.
[0030] One representative form of an electrolytic device for the
generation of hypohalous acid is shown in the cross-sectional view
of FIG. 2 and is denoted by the numeral 10. Electrolytic device 10
includes a single liquid chamber 12 and a gas compartment 14. In
the invention, a halide ion source in aqueous solution, such as
NaCl solution or seawater, preferably freed of organic material
thereby avoiding the oxidation reaction of organic material in the
single liquid chamber, is supplied to the electrolytic cell single
liquid chamber 12 by way of a gravity feed container or pump 16
through an inlet 18 for receiving aqueous solutions containing
halide ions. The gravity feed container 16 may be made of any
material, such as plastic or glass, which is non-reactive with the
buffered or unbuffered solution to be fed through the
electrosynthetic reactor. Valve 40 regulates flow through inlet 18
feeding into the single liquid chamber 12.
[0031] The single liquid chamber 12 has a single liquid chamber
exterior wall 32 and a solid anode 20 contained within the single
liquid chamber 12 providing for the oxidation of the halide ions to
produce hypohalous acid in aqueous solution. Alternatively, the
solid anode 20 could be the wall, or a portion thereof, of the
container, as it is not necessary that the anode be immersed fully
in the electrolyte.
[0032] The solid anode 20 used in the invention may be, for
example, a dimensionally stable anode (DSA), commercially available
from a supplier such as De Nora Tech.
[0033] The gas permeable cathode 22 forms a portion of the single
liquid chamber exterior wall 32 and provides for the reduction of
oxygen to provide hydroxyl ions in solution within the single
liquid chamber which will then mix with the products of the anode.
The cathode, having a hydrophobic surface for receiving oxygen from
outside the single liquid chamber 12 and a hydrophilic surface
allowing for reduction of dioxygen, used for this invention may be,
for example, a gas diffusion electrode (GDE), commercially
available from various suppliers including BASF Fuel Cell, Inc.,
containing high area carbon and high area Pt (platinum) as the
electrocatalyst. The use of an electrocatalyst is desired to reduce
the overall power consumption of the electrolytic device by
reducing the overvoltage required to reduce dioxygen to water.
Other electrocatalysts, such as certain metals and oxides including
species derived from the pyrolysis of certain organic materials,
may be used as well, and are generally to be used in porous form.
Alternatively, the catalyst may be supported on a plate, metal
gauge, sintered powder or sintered metal fiber of a
corrosion-resistant material such as stainless steel, zirconium,
silver and carbon. By forming a hydrophobic sheet on the side of
the cathode opposite the single liquid chamber, access of gas to
the reactive surface can be enhanced.
[0034] In one alternative, the exterior of the single liquid
chamber 12 as defined by the gas permeable cathode 22 may be
exposed to atmospheric air. In another embodiment, as shown in FIG.
2, the electrolytic device 10 may further include an oxygen source
24 for providing oxygen to the gas permeable cathode 22 through a
gas compartment 14. The oxygen source 24 may be air, a commercially
available oxygen cylinder, oxygen produced by the electrolysis of
water in a separately installed electrolytic cell, or oxygen
obtained by concentrating air by a PSA (pressure swing adsorption)
device; and this oxygen source 24 may also include a pump to force
the oxygen toward the hydrophobic surface of the gas permeable
cathode. The gas compartment 14 further includes an inlet 26 for
receiving oxygen through gas compartment exterior wall 30; whereby
the gas compartment 14 has at least one gas compartment exterior
wall 30 that encloses the portion of the single liquid chamber
exterior wall comprised of the gas permeable cathode 22. An outlet
46 enables any overpressure of oxygen or air to leave the
system.
[0035] Within the single liquid chamber, the products of the
reactions at the interfaces between the solid anode 20 and the gas
permeable cathode 22 combine to yield an exiting effluent hereby
also referred to as a mixed effluent.
[0036] In an example whereby the hypohalous acid produced is
hypochlorous acid, and the halide ions are chloride ions, anodic
oxidation takes place in the single liquid chamber 12 to produce
HClO via the oxidation of chloride ion:
Cl.sup.-+H.sub.2O.fwdarw.HClO+2e.sup.-+H.sup.+
While in the presence of water, the chlorine gas Cl.sub.2 (which
forms first) instantaneously transforms to HClO yielding results
corresponding to the above reaction. The gas permeable cathode 22
is responsible for the reduction of dioxygen to water according to
this equation:
O.sub.2+2H.sub.2O+4e.sup.-.fwdarw.4OH.sup.-
The electrochemical reactions occur at or near the interfaces
between the electrodes and the electrolyte solution, not in the
aqueous stream. The products are all water soluble.
[0037] The single liquid chamber 12 further includes an outlet 28,
through which the exiting mixed effluent leaves the single liquid
chamber 12 through single liquid chamber exterior wall 32,
thereafter, the exiting effluent passes through a pH sensing
electrode or pH meter, denoted in FIG. 2 as 34, for determining the
pH of the exited mixed effluent; the desirable pH range for use as
a hand sanitizer is between about 4 and 9. It may be appreciated
that an error-sensing feedback device, or servo, may also be
included to further aid in regulating the pH. The pH meter for
measuring the pH incorporates a valve 36, which may be an
electrically actuated valve, which then directs the exit stream out
for use as product when the effluent solution has a pH between
about 4 and 9.
[0038] In the embodiment as depicted in FIG. 2 and utilizing a
single liquid chamber, it is possible to manage or control pH by
altering the current applied by the DC constant current power
supply to the circuit or, alternatively, by adding a buffering
agent to adjust the pH of the electrolyte solution halide feed as
necessary.
[0039] Another representative form of an electrolytic device for
the generation of hypohalous acid in the present invention is shown
in the three-dimensional view of FIG. 3 and denoted by the numeral
100. The electrolytic device is similarly equipped as is the single
liquid chamber device of FIG. 2; however FIG. 3 demonstrates the
configuration of the gas compartment 114 as is possible with a
cylindrical gas compartment exterior wall 130. The single liquid
chamber 112 may also be cylindrical and is contained within the gas
compartment 114. The single liquid chamber 112 of the electrolytic
cell 100 has a solid anode 120 and a single liquid chamber exterior
wall 132, which may also serve as the interior wall of gas
compartment 114. The single liquid chamber exterior wall 132
encloses the single liquid chamber 112, leaving an opening for the
gas permeable cathode 122 to serve as a portion of the single
liquid chamber exterior wall 132. As the solid anode 120 need not
be entirely immersed in the electrolyte contained within the single
liquid chamber 112, the solid anode 120 may alternatively serve as
a portion of the wall as defined by single liquid chamber 112,
provided the anode is not placed at the same position in which the
gas permeable cathode 122 is located.
[0040] As with the embodiment described in FIG. 2, the electrolytic
device in FIG. 3 has a gravity feed container or pump 116 and an
inlet 118 for feeding halide ions in aqueous solution into the
single liquid chamber 112. A valve 140 further regulates flow from
the gravity feed container or pump 116 into the single liquid
chamber 112. The mixed effluent exits the single liquid chamber
through single liquid chamber exterior wall 132 passing through an
outlet 128 which leads the exit stream through a pH sensing device
or pH meter, denoted as 134 in FIG. 3, for determination of pH.
Further, an error-sensing feedback device, or servo, may also be
included. A valve 136 thereby directs the fluid out of the system
for use as end product if desired pH range between about 4 and 9 is
attained. The gas compartment 114 has a gas compartment exterior
wall 130 which may serve to enclose the electrolytic device 100. An
inlet 126 feeds oxygen from an oxygen source 124 into the gas
compartment 114 for reactions to occur at or near the interface
with the gas permeable cathode 122; an outlet 146 allows for
release of any overpressure of air or oxygen as necessary.
[0041] It is also possible, as with the device in FIG. 2, that
alternatively the device shown in FIG. 3 may be exposed to
atmospheric air rather than to utilize a gas compartment for
introducing oxygen to the gas permeable cathode. Also, as with the
single liquid chamber electrolytic cell of FIG. 2, pH of the mixed
effluent may best be controlled or optimized by adjusting the
current applied by the DC constant current power supply to the
circuit, or alternatively by adding a buffering agent to adjust the
pH of the electrolyte solution halide feed as necessary.
[0042] FIG. 4 is further an alternate representative form of an
electrolytic device, denoted as device 200, for the generation of
hypohalous acid in the present invention and is shown in the
three-dimensional view. The electrolytic device is similarly
configured as is the single liquid chamber device of FIG. 3;
however FIG. 4 demonstrates the positioning of the gas compartment
214 as the internal cylinder as is possible using the gas permeable
cathode 222 as the external wall of the gas compartment. The single
liquid chamber 212 may also be cylindrical and may encircle the gas
compartment 214; thereby the solid anode 220 forms the single
liquid chamber exterior wall while the gas permeable cathode 222
serves as the interior wall of single liquid chamber.
[0043] As with the embodiment described in FIG. 3, the electrolytic
device of FIG. 4 has a gravity feed container or pump 216 and an
inlet 218 for feeding halide ions in aqueous solution into the
single liquid chamber 212. A valve 240 further regulates flow from
the gravity feed container or pump 216 into the single liquid
chamber 212. The mixed effluent exits the single liquid chamber
through the bottom face of single liquid chamber exterior wall 232
passing through an outlet 246 which leads the exit stream through a
pH sensing device or pH meter 234, for determination of pH. An
error-sensing feedback device, or servo, may also be included. A
valve 236 thereby directs the fluid out of the system for use as
end product if desired pH range between about 4 and 9 is attained.
The gas compartment 214 has a gas compartment exterior wall 230 at
top and bottom face and an inlet 226 which feeds oxygen from an
oxygen source 224 into the gas compartment 214 for reactions to
occur at or near the interface with the gas permeable cathode 222;
an outlet 228 allows for release of any overpressure of air or
oxygen as necessary.
[0044] As with the single liquid chamber electrolytic cell devices
of FIGS. 2 and 3, pH of the mixed effluent may best be controlled
or optimized by adjusting the current applied by the DC constant
current power supply to the circuit, or alternatively by adding a
buffering agent to adjust the pH of the electrolyte solution halide
feed as necessary.
[0045] FIG. 5 further describes another representative form of an
electrolytic device 300 for the generation of hypohalous acid;
whereby this dual chamber device has an anolyte chamber and a
catholyte chamber. The cell has an exterior wall 350, wherein the
gas permeable cathode 322 is positioned as at least a portion of
the exterior wall of the catholyte chamber 314. The electrolytic
device 300 has an anolyte chamber 312 which has an inlet 318 for
receiving an aqueous solution of halide ions therein. As shown in
this embodiment, the anolyte chamber 312 has a solid anode 320
contained within the anolyte chamber providing for the oxidation of
the halide ions to produce an anolyte effluent of hypohalous acid
in aqueous solution. The solid anode 320 may be placed within the
anolyte chamber as shown or alternatively serve as an impermeable
wall, or portion thereof, of the anolyte chamber, as it is not
necessary that the anode be fully immersed in the electrolyte.
However, the solid anode 320 cannot form the part of the anolyte
chamber wall that separates the anolyte chamber 312 from the
catholyte chamber 214.
[0046] In this dual chamber configuration, the gas permeable
cathode 322 can be positioned such that the catholyte chamber 314
has at least one wall that includes at least, in part, the gas
permeable cathode 322. The cathode has a hydrophobic surface for
receiving oxygen from outside the catholyte chamber 314 and a
hydrophilic surface allowing for reduction of dioxygen and for
maintaining the aqueous-based catholyte effluent within the
catholyte chamber 314 of the electrolytic device 300.
[0047] Furthermore, the cell as shown in FIG. 5 has an ionomeric
membrane 344 to partition the two liquid chambers, i.e., the
anolyte chamber 312 and the catholyte chamber 314. The membrane may
be a neutral membrane or an ion exchange membrane. The ionomeric
membrane 344 may be an ion exchange membrane made of synthetic
polymer, such as Nafion.RTM. available from DuPont, or
alternatively a non ionomeric membrane of very fine porosity
available from various sources, to prevent facile mixing of the
anolyte and catholyte solutions. The Nafion membrane utilized in
the present embodiment allows the sodium cations (Na.sup.+) to
transfer from the anolyte chamber to the catholyte chamber with
minimal electrical resistance, while minimizing back transfer of
anions such as OH-- from the catholyte chamber. The use of
ionomeric membrane 344 separating the anolyte chamber 312 and the
catholyte chamber 314 makes it possible to prevent mixing of the
liquids and also for the hypohalous acid to reach the cathode.
While in operation, the anolyte chamber of the invention should
contain, in addition to the reactant chloride, HClO and not any
significant amount of the reduction products of dioxygen, i.e.,
catholyte effluent, that are produced in the catholyte chamber.
[0048] Separate inlets for feeding into the anolyte chamber 312 and
catholyte chamber 314 are maintained by inlet 318 and inlet 326
respectively. While there are many ways to accomplish feeding the
cell, it may be viewed as depicted in FIG. 5 that the gravity feed
container or pump 316 introducing aqueous NaCl or halide ion
containing solution to the anolyte chamber 312 could further
include a source 324 for providing liquid water or another aqueous
solution to the catholyte chamber 314. In this manner, the flow of
liquids fed to the device may be managed by a valve 352 to regulate
input to either the anolyte chamber 312 or catholyte chamber 314
separately.
[0049] In the dual chamber embodiment of the invention as shown in
FIG. 5, and whereby the hypohalous acid produced is hypochlorous
acid, and the halide ions are chloride ions, anodic oxidation takes
place in the anolyte chamber 312 to produce HClO via the oxidation
of chloride ion:
Cl.sup.-+H.sub.2O.fwdarw.+HClO+2e.sup.-+H.sup.+
While in the presence of water, chlorine gas Cl.sub.2 (which forms
first) instantaneously transforms to HClO yielding results
corresponding to the above reaction. Sodium cations (Na.sup.+) may
pass from the anolyte chamber 312 through the membrane 344 into the
catholyte chamber 314. The hydrophilic side of the gas permeable
cathode 322 in the catholyte chamber 314 is responsible for the
reduction of dioxygen to water according to this equation:
O.sub.2+2H.sub.2O+4e.sup.-.fwdarw.4OH.sup.-
The electrochemical reactions occur at or near the interfaces
between the electrodes and the electrolyte solution, not in the
aqueous stream. The products are all water soluble. In this dual
liquid chamber device, the sodium cations may migrate through the
membrane 344 from the anolyte chamber 312 to the catholyte chamber
314 with minimal electrical resistance. In the catholyte chamber
314, the sodium cations and hydroxyl groups remain as such
dissolved in water to yield the catholyte effluent.
[0050] In an alternative cylindrical embodiment not shown, drawn
similarly to the single chamber device concept shown in FIG. 3, the
anolyte chamber of the dual chamber device may have an exterior
wall, corresponding to the wall 132 as described in FIG. 3, that is
formed completely or substantially of the membrane. In such a
cylindrical configuration of the dual chamber device, the gas
permeable cathode may act as an exterior catholyte chamber wall, or
a portion thereof, which would correspond similarly to the wall 130
as described in FIG. 3.
[0051] In the embodiment of the invention as depicted in FIG. 5,
the anolyte chamber 312 and catholyte chamber 314 further include
outlets 328 and 356, respectively, to progress the anolyte and
catholyte effluents through as desired to the exit stream at a
controlled pH. Control of pH may be accomplished by regulating the
volume of catholyte effluent introduced to the exit stream
utilizing valve 348 which will be discussed further below. The pH
may be measured by a pH sensing device or pH meter 334 for
determining pH, while valve 348 may be adjusted for regulating the
pH of the exiting anolyte effluent to between about 4 and 9.
[0052] The catholyte chamber 314 may contain unreacted aqueous
solution, e.g., water and/or reacted catholyte. The electrolytic
device further includes an outlet 346 for releasing reacted
catholyte effluent remaining in the catholyte chamber 314. It will
be appreciated that any reacted catholyte effluent will be alkaline
in nature. A valve 348 regulates flow of the catholyte effluent
through outlet 346 exiting from the catholyte chamber; thereafter
the exiting catholyte is mixed with the exiting anolyte effluent to
form a mixed effluent of higher pH than of the anolyte effluent
alone. The mixed effluent may be measured with pH sensing device or
pH meter 334. The pH control, which may also include a computer
controlled servo, makes it possible to regulate the flow of the
exiting liquid which passes through valve 336 to be in the desired
range of pH between about 4 and 9. In practice, the pH meter 334
placed at the exit stream measures the pH of the exiting effluent.
If the exiting effluent is too acidic, valve 348 may be opened to
allow catholyte to flow also, thereby, introducing the alkaline
solution to the exit stream. Repeated adjustments to regulate the
catholyte effluent flow to combine with the effluent of the anolyte
released may be made as necessary until the exiting solution
reaches the desired pH range between about 4 and 9.
[0053] Further, the pH may be controlled by recirculating the
anolyte or the mixed anolyte and catholyte effluent through a
recirculator 338 back into inlet 318 for reintroduction into the
anolyte chamber 312. As depicted in FIG. 5, the recirculator 338
has a valve 354 which allows the flow of the exiting anolyte
effluent or mixed anolyte and catholyte effluent to be redirected
back into the anolyte chamber 312 when the anolyte effluent or
mixed anolyte and catholyte effluent has a pH that is greater than
9; or the flow may be redirected back into the anolyte chamber when
the exiting anolyte effluent or mixed anolyte and catholyte
effluent have a pH that is less than 4. In other words, to control
pH, recirculating catholyte-containing effluent, or OH in aqueous
solution, back into the anolyte chamber increases pH (to 5, to 6,
to 7, up to 8). Alternatively, pH control may be achieved by
recirculating exiting anolyte effluent back into the electrolyte
within the anolyte chamber to decrease pH. Thereby attainment of
the desired pH within the hypohalous acid solution end product may
be in these ranges: preferred between 4-9; more preferred between
5-8; more preferred between 5-6; pKa of HClO is 7.5 pH. To further
control pH, the electrolytic device may allow for a buffering agent
to be released through inlet valve 318 into the anolyte chamber of
aqueous solution containing halide ions. Also, as with the single
liquid chamber design discussed previously, pH control of the dual
chamber device may also be attained by optimizing current to the
circuit as applied by the DC constant current power.
[0054] Whereas FIG. 5 depicts a device open to atmospheric air to
provide air to the gas permeable cathode 322 from outside of the
inventive cell, it may be alternatively possible to have a gas
compartment to feed air or oxygen to the gas permeable cathode 322
similarly as described in FIGS. 2 and 3. The oxygen source may
include a pump to force the oxygen toward the hydrophobic surface
of the gas permeable cathode 322.
[0055] In all embodiments, the electrolytic cell 10, 100, 200, 300
is preferably made of a glass lining material, carbon, or
corrosion-resistant titanium, stainless steel or PTFE resin from
the standpoint of durability and stability.
[0056] Examples of the process of the invention for the production
of HClO solution will be described hereinafter, but the invention
should not be construed as being limited thereto.
EXAMPLE 1
[0057] As shown experimentally in the laboratory of the assignee,
one embodiment of a single liquid chamber device of the type
described in FIG. 1 of the current invention delivers, as desired,
HClO solutions of concentrations in the range 80-240 ppm chlorine
at pH 5.9-7.8 as shown in Table 1. The operation of the
electrosynthetic reactor relies on the use of a DC constant current
power supply connected to the GDE cathode (E-Tek ELAT.RTM. GDE
LT250EW; 10 cm.times.10 cm) to induce reduction of dioxygen to
water and the oxidation of chloride ion at the DSA anode to
generate HClO. Prior to connecting and turning on the power supply,
the electrosynthetic reactor is filled with either buffered or
unbuffered NaCl solution from the gravity feed container and the
flow rate adjusted with a manual valve to 2-12 ml per minute. Both
the HClO concentrations, as well as the pH of the effluent
solution, are measured by conventional instrumentation and methods
at various time intervals during continuous operation, as a
function of the flow rate, applied current and other relevant
parameters.
TABLE-US-00001 TABLE 1 Hypochlorous Acid Generation in Electrolytic
Cell NaCl Sol. Flow Rate, Trial # ml/min DC Volts DC mA [Cl] ppm pH
5.0 g/L NaCl in pH 5.7, 10 mM Phosphate Buffer 393-89-1 8 3 120 80
6.2 393-89-2 7 3 120 105 5.9 393-89-3 a) 6 3.5 190 185 5.9 393-89-4
a) 6 3.5 170 195 5.9 393-89-5 b) 10 3.9 250 160 6.2 393-89-6 b) 8
3.9 240 190 6.1 393-89-7 8.5 4.9 400 230 6.2 393-89-8 7.5 4.9 380
225 6.2 5.0 g/L NaCl in Deionized Water 393-89-9 7 3.9 270 170 6.5
393-89-10 10 3.9 250 170 8 393-89-11 c) 10.5 4.6 340 240 6
393-89-12 c) 10.5 4.6 320 190 7.2 393-89-13 c) 11 5 390 210 7.8
[0058] In the present device, a method for the generation of
hypohalous acid comprising oxidizing halide ions in the presence of
water within a single liquid chamber to form an anolyte effluent is
achieved. On the cathode side, oxygen is being fed through, or in
the case of utilizing a pump being forced through, a gas permeable
cathode to reduce the oxygen in the presence of water to form
hydroxyl groups. In this device the gas permeable cathode forms at
least a portion of an exterior wall of the single liquid chamber.
The step of mixing the hydroxyl groups in an amount sufficient to
complete the electrolyte circuit within the device to produce
hypohalous acid is achieved. The pH may be determined by a pH meter
and the hypohalous acid may be removed from the electrolytic
device. Control of pH may be attained by adjusting the current to
the circuit as applied by the DC constant current power or by
adding a buffering agent to the halide aqueous feed. Desired range
for use as hand sanitizer is pH between about 4 and 9. The step of
feeding oxygen to the gas permeable cathode may include delivering
oxygen from a gas compartment, wherein the portion of the exterior
wall of the single liquid chamber comprised of the gas permeable
cathode is included in the gas compartment. Alternatively, the step
of feeding oxygen to the gas permeable cathode may include exposing
the hydrophobic exterior of the gas permeable cathode to
atmospheric air.
[0059] A method of this invention utilizing a two liquid chamber
electrolytic device for the generation of pH-controlled hypohalous
acid aqueous solutions, such as HClO in aqueous solution, is
achieved. The method includes, on the anode side, oxidizing halide
ions in the presence of water within an anolyte chamber to form an
anolyte effluent containing hypohalous acid. On the cathode side,
oxygen is fed through a gas permeable cathode to reduce the oxygen
in the presence of water to form a catholyte effluent containing
hydroxyl groups, wherein the gas permeable cathode forms at least a
portion of an exterior wall of a catholyte chamber. The hydroxyl
groups are mixed in an amount sufficient to complete the
electrolyte circuit within the device to produce hypohalous acid.
This device allows for controlling pH of the hypohalous acid to
ensure that the pH is between about 4 and 9. Determining the pH of
the hypohalous acid may include use of a pH meter. The hypohalous
acid may be removed from the electrolytic device.
[0060] The pH may be further controlled and regulated in the two
liquid chamber electrolytic device, for example, by mixing the
exiting anolyte and catholyte effluents in an amount sufficient to
increase the pH of the hypohalous acid to ensure that the pH is
between about 4 and 9. The method further comprises the step of
determining the pH after mixing the exiting anolyte and catholyte
effluents, wherein the step includes the use of a pH meter. This
method is advantageous in that the pH of the hypohalous acid
produced may be controlled to ensure that the pH is between about 4
and 9 before removing the hypohalous acid for use as end
product.
[0061] Regulating the pH of the hypohalous acid produced by the two
liquid chamber electrolytic device may further be accomplished by
recirculating the flow of the hypohalous acid back into the anolyte
chamber if the pH of the hypohalous acid is above pH 9; wherein the
method further comprises the step of determining the pH of the
hypohalous acid after recirculating the flow of the hypohalous acid
back to the anolyte chamber, wherein the step includes the use of a
pH meter.
[0062] In another embodiment, it will be appreciated that the user
could also regulate the pH of the hypohalous acid produced by the
dual liquid chamber of the electrolytic device if the pH is below 4
alternatively by (1) recirculating the flow of the hypohalous acid
back to the anolyte chamber where the input from the feed may also
be altered of buffered or (2) closing off the valve 354 shown in
FIG. 5 until the pH increases sufficiently above pH 4.
[0063] The step of feeding oxygen to the gas permeable cathode may
include delivering oxygen from a gas compartment, wherein the
portion of the exterior wall of the catholyte chamber comprised of
the gas permeable cathode is included in the gas compartment.
Alternatively, the step of feeding oxygen to the gas permeable
cathode may include exposing the hydrophobic exterior of the gas
permeable cathode to atmospheric air.
[0064] The method and device of this invention further has the
advantage in that storage of gaseous species, such as chlorine gas,
is not needed. Also, the source electrolyte is economical and safe
for handling, while the end product may be directly used for
disinfectant purposes at a controlled pH level suitable for use as
a hand sanitizer without irritation or damage to human skin.
[0065] In light of the foregoing, it should thus be evident that
the process of the present invention, providing a device and method
for producing hypohalous acid in aqueous solution with controlled
pH, substantially improves the art. While, in accordance with the
patent statutes, only the preferred embodiments of the present
invention have been described in detail hereinabove, the present
invention is not to be limited thereto or thereby. Rather, the
scope of the invention shall include all modifications and
variations that fall within the scope of the attached claims.
* * * * *