Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROCHEMICAL GENERATION OF QUATERNARY AMMONIUM COMPOUNDS
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to and the benefit of filing of U.S.
Provisional Patent
Application Serial No. 61/450,735, entitled "Electrochemical Generators for
the Production of
Quaternaryammonium Hypohalites from Quaternaryammonium Halide Salts", filed on
March 9,
2011, the specification of which incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention (Technical Field):
The present invention is related to electrochemical conversion of quaternary
ammonium
halide salts to quaternary ammonium hypohalite salts preferably through the
anodic oxidation of
the halide anions of the quaternary ammonium halide salts.
Background Art:
Note that the following discussion may refer to a number of publications and
references.
Discussion of such publications herein is given for more complete background
of the scientific
principles and is not to be construed as an admission that such publications
are prior art for
patentability determination purposes.
Disinfectants and biocides are used to control microorganisms which may be
present
either in air, on a surface, or in a bulk liquid. Common chemicals that are
used as disinfectants
include alcohols, aldehydes, oxidizing chemicals (including halogens,
hypohalous acids,
hypohalite anions, chloramines, hydrogen peroxide, and ozone), phenols, and
quaternary
ammonium compounds. Some disinfectants, including quaternary ammonium
compounds, can
also serve as surfactant cleaners or corrosion inhibitors. Each of these
chemicals have unique
and specific properties which make them suitable for many applications, but
preferential for
certain applications. Aqueous chlorine is perhaps the most prominent and
universally applied
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biocide. While aqueous chlorine is typically produced either through bubbling
chlorine gas into
water (as in disinfection of potable water) or delivered to a point-of-use in
the form of
concentrated aqueous solutions, it can also be generated electrochemically
from sodium chloride
(salt). Electrolysis of aqueous sodium chloride solutions, and brines
containing other alkali metal
halide salts, has long been used in the production of halogen, hypohalous
acid, and hypochlorite
solutions. Typically, dimensionally stable anodes are used in the electrolytic
production of
halogen solution that can be used for disinfection, sanitization, cleaning and
other applications.
Quaternary ammonium halide salts are a commonly used alternative biocide to
aqueous
halogen solutions in non-drinking water applications. The general chemical
structure of a
quaternary ammonium halide salt is NR4X, where N is a central nitrogen atom, R
denotes an
organic hydrocarbon functional group, and X represents a halide (Cr, Br, or
I). Examples of
quaternary ammonium halides commonly used for disinfection and sanitization
include:
benzalkonium chloride (N-alkyl-N-benzyl-N-dimethylammonium chloride where the
alkyl chain
contains between 8 and 18 carbon atoms), benzethonium chloride, centrimonium
chloride or
bromide (cetyltrimethylammonium chloride or bromide), cetylpyridium chloride,
dequalinium, and
didecyldimethylammonium chloride. The quaternary ammonium cation is the main
active
component, capable of killing microorganisms by perforating the cell membrane.
Quaternary
ammonium cations are environmentally stable, providing a long-lived residual
disinfection
capability in a given application. Quaternary ammonium halide compounds are
often used to
disinfect surfaces, especially in the medical, food, and beverage industries.
Quaternary
ammonium compounds are also used for disinfection and sanitization in other
applications,
including but not limited to treatment of oil/gas drilling hydraulic
fracturing or process waters, as
components of antibacterial consumer products, and treatment of cooling tower
water. They are
also used as corrosion inhibitors of iron and steel in acidic solutions or as
part of an important part
of a corrosion inhibition formulation.
Combinations of aqueous chlorine and/or mixed oxidant solution and quaternary
ammonium salts, effectively producing quaternary ammonium hypohalite salts,
may be used to
enhance the germicidal properties of a disinfecting or sanitizing solution.
However, the combined
solution typically degrades quickly. It is believed the organic portion of the
compound will react
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with the hypohalite portion, decreasing the efficacy of the overall
combination for disinfection and
sanitization, thereby adversely affecting stability of the compounds and
solutions. Thus, a method
by which quaternary ammonium hypohalite compounds can be generated on-site and
on-demand
is desirable, so the biocides may be produced just before use, particularly
since the precursors
(for example a halogen salt or brine and quaternary ammonium salts) are highly
stable and can
be stored for long periods of time. There are no known processes by which
quaternary
ammonium cations and either hypohalite anions or halogens with enhanced
antimicrobial activity
combinations can be made from quaternary ammonium halide salts at the point of
use.
Electrochemical oxidation of halide ions is one such method by which
quaternary
ammonium hypohalite compounds can be produced on-site and on-demand.
Electrochemical
production of aqueous solutions of halogens (chlorine, bromine, or iodine)
from the respective
halide ions through electrochemical oxidation of the halide is a well known
technology. However,
electrochemistry may also destroy (through oxidation or reduction processes at
electrode
surfaces) organic compounds dissolved in water, such as aqueous solutions of
quaternary
ammonium compounds. Thus it is advantageous to develop a process for
electrochemical
oxidizing such compounds, either alone or in combination with additional
alkali halide
components, without destroying them, in order to produce quaternary ammonium
hypohalite
compounds that can act as an effective disinfectant, sanitizer, cleaner,
surfactant, and/or
corrosion inhibitor.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
An embodiment of the present invention is a method for producing a solution,
the method
comprising electrolyzing a first solution comprising a quaternary ammonium
compound in solution
and producing a second solution comprising a quaternary ammonium hypohalite in
solution. The
quaternary ammonium compound preferably comprises a quaternary ammonium
halide. The first
solution optionally further comprises a halide salt, preferably an alkali
metal halide salt, in
solution. The first solution optionally comprises a compound selected from the
group consisting
of surfactant, organic surfactant, colorant, perfume, disinfectant, germicide,
and biocide. The
second solution preferably further comprises an additional oxidant species,
optionally selected
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from the group consisting of halide based oxidant, halogen, hydrogen peroxide,
ozone, chlorine
dioxide, and combinations thereof. The combination of the quaternary ammonium
hypohalite and
the additional oxidant species in the second solution preferably substantially
increases the
disinfection efficacy of the second solution over an unelectrolyzed solution
comprising the
quaternary ammonium hypohalite and the additional oxidant species mixed
together in solution.
The second solution preferably does not substantially comprise a halide salt.
Another embodiment of the present invention is a method of producing a
solution, the
method comprising electrolyzing a first solution comprising a first quaternary
ammonium
compound in solution and a second component and producing a second solution
comprising a
second quaternary ammonium compound in solution and a second compound. The
second
component optionally comprises ammonia or an ammonium salt and the second
compound
comprises a haloamine. Alternatively, the second component comprises a
chlorite salt and the
second compound comprises chlorine dioxide. Alternatively, the second
component comprises
dissolved oxygen at a greater concentration than a naturally occurring
dissolved oxygen
concentration of the first solution and the second compound comprises hydrogen
peroxide. In
this case the electrolyzing step is preferably performed in a divided
electrolytic cell and the
second quaternary ammonium compound and hydrogen peroxide is produced in the
cathodic
compartment of the divided electrolytic cell. If the first solution comprises
a quaternary
ammonium halide or a halide salt, the second solution preferably further
comprises a quaternary
ammonium hypohalite produced in the anodic compartment of the divided
electrolytic cell.
Another embodiment of the present invention is a device for dispensing the
solution
produced in any of claims 1-16, the device comprising a flow through
electrolytic cell comprising
an anode and a cathode and a spray nozzle for dispensing the solution. The
device may
optionally comprise a spray bottle configuration, wherein electrolysis of the
solution is activated by
a user squeezing a trigger. The device may alternatively comprise a hand
washing station,
wherein electrolysis of the solution is activated by a user moving a lever or
a user placing at least
one hand under the device.
Another embodiment of the present invention is a device for dispensing wipes
comprising
a solution, the device comprising a supply of wipes comprising a quaternary
ammonium
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compound, an anode, and a cathode, wherein the wipes are disposable between
the anode the
said cathode, at which time the quaternary ammonium compound is electrolyzed.
The anode
may optionally comprise a drum anode and the cathode may optionally comprise a
drum cathode.
Alternatively, the anode and cathode comprise flat plates, and the device
further comprises a
mechanism for pressing a wipe between the anode and the cathode. The wipes
preferably
comprise a compound selected from the group consisting of quaternary ammonium
halide, halide
salt, surfactant, organic surfactant, colorant, perfume, disinfectant,
germicide, and biocide.
Another embodiment of the present invention is a method for on demand
generation of a
quaternary ammonium hypohalite solution, the method comprising signaling a
desired amount of
a first solution comprising a quaternary ammonium hypohalite in solution to be
produced; mixing a
second solution comprising a quaternary ammonium compound in solution with a
third solution
comprising a halogen solution, the amounts of the second solution and third
solution
corresponding to the desired amount of the third solution; producing the
desired amount of the
third solution; and dispensing the desired solution immediately or prior to
significant degradation
of the third solution. The halogen solution preferably comprises a compound
selected from the
group consisting of bleach, hypochlorous acid, hypobromous acid, hypoiodous
acid, hypochlorite,
hypobromite, hypoiodite, and hypohalite.
Objects, advantages, novel features, and further scope of applicability of the
present
invention will be set forth in part in the detailed description to follow,
taken in conjunction with the
accompanying drawings, and in part will become apparent to those skilled in
the art upon
examination of the following, or may be learned by practice of the invention.
The objects and
advantages of the invention may be realized and attained by means of the
instrumentalities and
combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated into and form a part of the
specification, illustrate an embodiment of the present invention and, together
with the description,
serve to explain the principles of the invention. The drawings are only for
the purpose of
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illustrating various embodiments of the invention and are not to be construed
as limiting the
invention. In the drawings:
FIG. 1 is a schematic drawing showing an electrochemical process by which a
quaternary
ammonium halide salt is converted to a quaternary ammonium hypohalite salt.
FIG. 2 is a schematic drawing of an embodiment of a batch electrochemical cell
for the
conversion of quaternary ammonium halide salts to quaternary ammonium
hypohalite salts.
FIG. 3 is a schematic drawing of an embodiment of a flow through generator
system for
the conversion of quaternary ammonium halide salts to quaternary ammonium
hypohalite salts.
FIG. 4 is a schematic drawing of an embodiment of a flow-through
electrochemical cell for
the conversion of quaternary ammonium halide salts to quaternary ammonium
hypohalite salts.
FIG. 5 is a schematic drawing of an embodiment of the invention for use as
part of a
surface disinfection delivery system.
FIG. 6 is a schematic drawing showing an embodiment of the invention used to
electrolyze a solution of quaternary ammonium halide salts to produce a
solution that is then used
for hand sanitization.
FIG. 7 is a schematic drawing of showing an embodiment of the invention used
to
electrolyze quaternary ammonium halide salts that are incorporated into wipes
that are
subsequently used to disinfect or sanitize surfaces.
FIG. 8 is a schematic drawing showing an embodiment of the invention whereby a
solution of quaternary ammonium hypohalite is produced through the combination
of an aqueous
solution of halogen and an aqueous solution of quaternary ammonium halides.
FIG. 9 shows how the solution resulting from the electrolysis of a quaternary
ammonium
halide salt results in the formation of a product that reacts with diethyl-p-
phenylene diamine
(DPD) to produce a magenta color.
FIGS. 10a and 10b show the foaming that sometimes occurs during the
electrolysis of a
quaternary ammonium halide solution or a quaternary ammonium halide/alkali
metal halide
solution.
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FIG. 11 is a graph showing the enhanced microbial inactivation achieved by a
solution of
a quaternary ammonium hypochlorite compound produced through the electrolysis
of the
corresponding quaternary ammonium chloride compound.
FIG. 12 is a graph showing the differences between quaternary ammonium
hypohalite
compounds prepared by electrolysis of a quaternary ammonium halide compound
and the mixing
solutions of a quaternary ammonium halide compound with an alkali (or
alkaline) metal
hypochlorite compound.
FIG. 13 is a graph illustrating the impact of solution pH on the inactivation
of B. globigii
spores using electrolyzed solutions of cetyltrimethylammonium chloride (CTAC).
FIG. 14 is a graph illustrating inactivation efficacies for an electrolyzed
mixture of CTAC
and sodium chloride at different free available chlorine (FAC) concentrations.
FIG. 15 is a graph illustrating the inactivation efficacy of unelectrolyzed,
electrolyzed, and
electrolyzed/quenched tetramethylammonium chloride (TMAC) solutions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(BEST MODES FOR CARRYING OUT THE INVENTION)
Embodiments of the present invention are unique electrochemical cells and
processes by
which quaternary ammonium halide salts are preferably dissolved into solution
and converted,
preferably electrochemically, into quaternary ammonium hypohalite salts in
solution, preferably in
bulk, such as part of a delivery system (for example, a spray bottle) or as
part of a dispensing system
whereby quaternary ammonium halide salts absorbed onto wipes can be dispensed
as quaternary
ammonium hypohalite salts. Other blends between quaternary ammonium cations
and halogen
based disinfectants (such as diatomic halogens, hypohalous acids, or
hypohalite anions) may be
produced. By choosing an appropriate quaternary ammonium halide salt, a
corresponding
quaternary ammonium hypohalite salt solution can be formed that has one or
more desired
properties, such as corrosion inhibition, scale formation inhibition,
surfactant, or cleaning properties.
In an embodiment of the present invention, an aqueous solution comprising
dissolved
quaternary ammonium salts is electrolyzed, which converts the halide component
of the
quaternary ammonium salt to the corresponding halogen. The halogen dissolves
in the aqueous
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solution producing hypohalous acid and hypohalite anion. The general
electrochemical reaction
can be described by the simplified equation:
NR4 X- + H20 ¨> NR4 X0- + H2
where N R4+ is the quaternary ammonium ion containing a central nitrogen atom
connected to
four hydrocarbon functional groups (denoted R), X- is a halide ion (eg. Cl-,
Br, or I-), and X0- is a
hypohalite ion (e.g. C10-, Br0-, or 10-). Examples of quaternary ammonium
compounds that could
be utilized in this process include, but are not limited to, benzalkonium
chloride,
didecyldimethylammonium chloride, cetyltrimethylammonium chloride,
octyltrimethylammonium
chloride, tetramethylammonium chloride, tetraethylammonium chloride,
tetrapropylammonium
chloride, tetrabutylammonium chloride, cetylpyridinium chloride, benzalkonium
bromide,
didecyldimethylammonium bromide, cetyltrimethylammonium bromide,
octyltrimethylammonium
bromide, tetramethylammonium bromide, tetraethylammonium bromide,
tetrapropylammonium
bromide, tetrabutylammonium bromide, cetylpyridinium bromide, benzalkonium
iodide,
didecyldimethylammonium iodide, cetyltrimethylammonium iodide,
octyltrimethylammonium
iodide, tetramethylammonium iodide, tetraethylammonium iodide,
tetrapropylammonium iodide,
tetrabutylammonium iodide, and cetylpyridinium iodide. Polymeric quaternary
ammonium
compounds, for example, but not limited to, the polyquaternium polymers, can
also be used as
the quaternaryammonium halide source in these reactions.
Embodiments of the present invention utilize an electrochemical process by
which a
quaternary ammonium halide salt is converted to a quaternary ammonium
hypohalite salt; one
such process is shown in FIG. 1. In aqueous solution, halide anions 14 of
quaternary ammonium
halide salt 10 partially separate from, but are still associated with,
quaternary ammonium cations
16. When the electrochemical cell is energized, the halide anions 14 are
oxidized to halogen 22 at
the surface of the anode plates 18. Halogen 22 then dissolves in water to
yield hypohalous acid
24 and hydrohalic acid 26. On the surface of cathode 20, water molecules 28
are converted to
hydrogen gas 30 and hydroxide anions 32. Hypohalous acid 24, hydrohalic acid
26, hydroxide
ions 32, and quaternary ammonium cations 16 preferably associate to form a
quaternary
ammonium hypohalite salt 12.
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There are a variety of solution compositions and operational conditions which
can be
employed for this invention. The quaternary ammonium halide salt used can be a
singular salt or
a mixture containing one or more quaternary ammonium moieties combined with
one or more
halide anions. Similarly, the counterions for the quaternary ammonium cations
could be chloride,
bromide, or iodide. In addition to the quaternary ammonium compound, the
solution used in this
electrolysis process may comprise additional halides such as alkali metal
halide salts, which
increase halogen, hypohalous acid, and hypohalite ion production capacity. In
this case, the feed
salts include, but are not limited to, sodium chloride, sodium bromide, sodium
iodide, potassium
chloride, potassium bromide, and potassium iodide. For example, NaCI and a
quaternary
ammonium halide salt can be electrolyzed simultaneously, producing a combined
biocidal
solution comprising quaternary ammonium hypohalite salt and one or more
chlorine based
oxidants. Moreover, the solution used during the electrolytic process
described herein may
comprise other germicidal components in addition to the quaternary ammonium
cations, such as
additional germicidal agents, colorants, and perfume components.
Halides, surfactants (e.g. linear alkyl benzene sulfonates), and/or other
germicidal
compounds such as biocides may optionally be dissolved with the quaternary
ammonium halide into
solution (such as a brine) prior to electrolysis. If a halide such as an
alkali metal halide salt (e.g.
NaCI) is added, then any quaternary ammonium compound, not just a quaternary
ammonium halide,
may be used, since the halide salt can contribute the halide to the solution.
Embodiments of the
present invention also encompass methods to control or tune the concentrations
of different
disinfectants or surfactants, thereby controlling synergy for a specific
disinfection or cleaning
application.
Other compounds may be added to the solution or brine used to feed the
electrochemical
cell. If ammonia or an ammonium salt (such as ammonium chloride, ammonium
sulfate,
ammonium bromide, ammonium iodide, etc) is added, solutions are produced that
comprise both
quaternary ammonium compound(s) and haloamine(s) such as monochloramine,
dichloramine,
trichloramine, monobromamine, dibromamine, tribromamine, monoiodamine,
diiodamine, or
triiodamine. If a chlorite (C102-) salt (such as sodium chlorite) is added,
solutions are produced
that comprise both quaternary ammonium compound(s) and chlorine dioxide. If
the solution being
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fed into the electrochemical cell contains increased dissolved oxygen,
solutions are produced that
comprise both quaternary ammonium compound(s) and hydrogen peroxide. In this
case it is
preferable that the electrolytic cell is divided (i.e. the cathodic and anodic
compartments are
separate). The quaternary ammonium compound and hydrogen peroxide will be
produced in the
cathodic compartment. Additionally, quaternary ammonium hypohalites may
simultaneously be
produced on the anodic compartment of such a cell (if the feed stream
comprises a quaternary
ammonium halide and/or a halide salt).
One embodiment of the present invention is a batch electrochemical cell as
depicted in
FIG. 2. Here, the electrochemical cell preferably comprises one primary anode
40, one primary
cathode 42, and any number of intermediate electrodes 44. This cell is
immersed into a container
46 which contains aqueous solution 48 that comprises a single quaternary
ammonium halide salt
or multiple quaternary ammonium salts, optionally in combination with various
alkali metal halide
salts and/or other inorganic and organic biocides, dissolved in water. The
cell is then energized
by power supply 50 through electrical connections 52 to produce a solution of
the desired
quaternary ammonium hypohalite salt.
Another embodiment of the present invention is a flow through electrochemical
cell as
depicted in FIG. 3. Initial solution tank 60 contains the aqueous solution 62
to be electrolyzed. In
practice, this solution may comprise any variety of organic quaternary
ammonium cations, halide
anions, added alkali metal halides, surfactants and/or other disinfectants.
Solution 62 is then
transferred preferably using pump 64 through pipe 66 to generator assembly 68
and into
electrochemical cell 70. Generator assembly 68 preferably comprises other
operational and
control features such as power supply 72, operations system controls 74, and
operational display
and user interface 76. After the solution is electrolyzed and halide ions have
been converted to
halogen, hypohalous acid, and hypohalite species, the generated solution
leaves generator 68
through pipe 78 and is disposed in tank 80, where it collects as the product
solution 82. Product
solution 82 may optionally be transferred using pump 84 and pipe 86 to meet
the needs of the
desired application.
Details of an embodiment of electrochemical cell 70 are given in FIG. 4. In
this cell, the
incoming solution 90, which may comprise various quaternary ammonium cations,
halide anions,
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alkali metal cations, surfactants, and/or other germicidal agents, enters cell
housing 92. Inside of
cell housing 92 is the electrochemical cell which preferably comprises primary
anode 94, primary
cathode 96, and intermediate plates 98. The product stream 100 then leaves
cell housing 92.
Practical operation of all types of cells will vary depending on a number of
factors, such
as the chemical nature of the quaternary ammonium halide salt, the
concentration of all halide
salts in solution, the desired level of halogen, hypohalous acid, and
hypohalite ion in the product,
the type of halide ion to be oxidized, and the presence of additional
germicidal agents. Cell
operational parameters that may be varied include, but are not limited to,
cell voltage, electrode
spacing, cell current, solution flow rate, and/or cell operating temperature.
Additionally, other
factors involved in cell construction may vary depending on the operating
conditions, including but
not limited to the spacing of the electrodes, the nature of the coating on the
anode surfaces,
and/or the nature of the coating on the cathode surfaces.
An embodiment of the present invention is a cell combined in a solution
delivery system
such as the spray bottle shown in FIG. 5. Solution housing 110 is filled with
solution 112 which
comprises quaternary ammonium cations, alkali metal cations, halide anions,
surfactants, and/or
other germicidal agents. This solution is drawn through tube 114, preferably
as a result of the
pumping mechanism of trigger 116, and enters head housing 118. Inside of head
housing 118 is
flow-though electrochemical cell 120 (similar to the one described in FIG. 4)
where the halide ions
in solution are converted to halogens, hypohalous acids, and hypohalite
anions, thus producing a
quaternary ammonium hypohalite salt solution, which exits head housing 118
through nozzle 122
as a spray 124. Similar embodiments of this invention may comprise a spray
bottle that is
connected to a small batch cell or flow-through cell type generator which
fills the spray bottle
housing with the electrolyzed solution.
An embodiment of the present invention is a hand wash station as shown in FIG.
6. This
embodiment consists of housing 130 which contains a reservoir of solution 132
that comprises
quaternary ammonium cations, alkali metal cations, halide anions, surfactants,
and/or other
germicidal agents. Solution 132 is pumped through the action of mechanism 134
by way of tube
136 through electrolytic cell 138, where the halides are converted to
halogens, hypohalous acids,
and hypohalite ions to produce a quaternary ammonium hypohalite salt solution
140, which is
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then dispensed through nozzle 142. Solution 132 may optionally comprise a
liquid, gel, foam, or
other medium that can be pumped through cell 136 to undergo electrolysis prior
to dispensing. A
similar embodiment of the present invention comprises an electrochemical
generation system
attached to a janitorial bucket that produces quaternary ammonium hypohalite
solution to be used
for cleaning floors.
An alternative embodiment of the invention is a cell capable of oxidizing the
halide
component of quaternary ammonium halide salts impregnated onto wipes used for
sanitizing
various surfaces, as shown in FIG. 7. Device housing 150 holds a supply of
wipes 152 that have
been impregnated or saturated with quaternary ammonium halide salts. Other
germicidal agents
may optionally or additionally be incorporated into the matrix of these wipes.
Wipes 152 are then
dispensed from housing 150 by passing through drum electrodes consisting of
anode drum 154
and cathode drum 156. As wipes 152 pass through drum electrodes 154 and 156,
electrolysis of
the impregnated halide anions occur, thereby producing quaternary ammonium
hypohalite salts
on electrolyzed wipes 158 that can be used for disinfection and sanitization
of various surfaces.
Possible variations on this embodiment of the present invention include, but
are not limited to,
drum electrodes where a single drum contains anodic and cathodic regions that
are separated by
non-electrolyzed regions, a similar device that manually dispenses
electrolyzed wipes, a similar
device that automatically dispenses electrolyzed wipes, and a similar device
in which wipes are
electrolyzed by placing them between two electrodes that are pressed together.
Another embodiment of the present invention is a device that can combine
separate
aqueous solutions of quaternary ammonium halide salts and halogen(s) to
provide the quaternary
ammonium hypohalite solution without the use of electrolysis. One example of
such a device is
illustrated in FIG. 8. Here, tank 160 contains aqueous quaternary ammonium
halide salt solution
162, which is preferably pumped from tank 160 with pump 164 along tube 166.
Similarly, tank 168
contains aqueous halogen solution (for example, but not limited to, bleach,
hypochlorous acid,
hypobromous acid, hypoiodous acid, hypochlorite, hypobromite, hypoiodite, or
any hypohalite)
170, which is preferably pumped from tank 168 with pump 172 along tube 174.
Pumps 164 and
172 are connected to control box 176 through connections 178. Control box 176
is used to control
the relative amounts of aqueous quaternary ammonium halide salt solution 162
and aqueous
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halogen solution 170 to be combined. These solutions are preferably combined
in a mixing
element (such as a tank) 180 and are further transferred along tube 182 as
quaternary
ammonium hypohalite solution 184 which is stored in tank 186. Quaternary
ammonium hypohalite
solution 184 can then be dispensed from tank 186 through the action of pump
188 to be
transferred along tube 190. Possible variations on this embodiment include,
but are not limited to,
a device that can combine more than two solutions in combinations of aqueous
quaternary
ammonium halide salts or aqueous halogens, additional chemical dosing pumps to
alter the final
solution pH or other characteristics, and devices that do not contain an
intermediate storage
capability. In the latter embodiment, the solution containing quaternary
ammonium hypohalite
salts is preferably dispensed immediately after solution combination. Because
this system uses
stable chemicals in an on site generation process to produce the quaternary
ammonium
hypohalite solution on demand, degradation of the final product is no longer
an issue.
Electrochemical processes such as the ones described herein may produce
products that
are substantively different than a process whereby two components are simply
mixed together. In
the case of quaternary ammonium hypohalite salts, the comparative processes
are the physical
combination of an aqueous solution of an alkali metal hypohalite with an
aqueous solution of a
quaternary ammonium halide without electrolysis, and the electrochemical
oxidation of the halide
portion of a quaternary ammonium halide salt. One major distinction between
these processes is
that the physical combination of the two individual components also produces a
quantity of
undesirable alkali metal halide salt, as is illustrated with the following
chemical equation:
NR4X + MOCI NR4OCI + MX
Here, NR4X is the quaternary ammonium halide salt, MOCI is the metal
hypohalide, NR4OCI is
the quaternary ammonium hypohalite compound that is the intended product of
the chemical
reaction, and MX is the alkali metal halide byproduct, such as NaCI.
Comparatively, the
electrochemical process involves only the oxidation of the halide component of
the quaternary
ammonium halide salt, and therefore, essentially no excess alkali metal halide
is present in the
resulting disinfection solution. This distinction is critical in a number of
applications, and expressly
so in the case of surface disinfection. The extra salts produced through
physical combinations of
a quaternary ammonium halide salt and an alkali metal hypohalite can lead to
the excessive
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formation of residual solids on the surface to be cleared, thus necessitating
a secondary cleaning
step or agent to be used to remove the excess salts. Moreover, alkali metal
halide salts are well
known to be corrosive agents against stainless steels as well as other
materials, and therefore
limiting the exposure of corrosion-susceptible materials is a critical factor
in the selection of
surface disinfectants.
Another difference between simple combination of quaternary ammonium halide
salts
with alkali (or alkaline) metal hypochlorite and the electrochemical
production of quaternary
ammonium hypochlorite compounds is that the electrolysis process may produce
other oxidative
species beyond just the aqueous halogen, which species can demonstrate
synergistic inactivation
properties. Electrochemical cells exist, for example, that can produce a mixed
oxidant solution,
comprised primarily of aqueous chlorine but also having other oxidative
species, that has been
shown to be more effective at inactivating a wide range of microorganisms.
Similarly, an
electrochemical cell designed to produce quaternary ammonium hypochlorite
compounds may
also produce other oxidant species, resulting in a disinfecting solution that
is more effective for
microbial inactivation than simply physically mixing the two corresponding
components together.
Example 1
An aqueous solution of benzalkonium chloride was prepared by dissolving 10
grams of
benzalkonium chloride in 1000 mL of deionized water to give a 1% (10,000 mg/L)
solution. 200
mL of this solution was transferred to a 250 mL beaker, and a three electrode
cell was immersed
in the solution. The cell was then energized to 12 volts for 20 minutes.
During this time, extensive
bubbling was observed on the cathodic electrodes, producing a foam above the
surface of the
solution (similar to that shown in FIGS. 10a and 10b). After 20 minutes, a
sample of the
electrolyzed solution was withdrawn and the free available chlorine (FAC)
content of the solution
was determined to be 332 mg/L using the diethyl-p-phenylene diamine (DPD)
method.
Example 2
An aqueous solution of cetyltrimethylammonium chloride was prepared by adding
20 mL
of a 25% by weight cetyltrimethylammonium solution to 1000 mL of deionized
water to give a
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0.5% (5,000 mg/L) solution. 200 mL of this solution was transferred to a 250
mL beaker, and a
three electrode cell was immersed in the solution. The cell was then energized
to 12 volts for 60
minutes. During this time, extensive bubbling was observed on the cathodic
electrodes, producing
a foam above the surface of the solution (similar to that shown in FIGS. 10a
and 10b). After 60
minutes, a sample of the electrolyzed solution was withdrawn and the free
available chlorine
content of the solution was determined to be 360 mg/L using the DPD method.
Example 3
A solution containing 100 mg/L benzalkonium chloride and 5,000 mg/L sodium
chloride
was prepared by dissolving 0.1 g benzalkonium chloride and 5 g sodium chloride
in 1000 mL
deionized water. 200 mL of this solution was transferred to a 250 mL beaker,
and a three
electrode cell was immersed in the solution. The cell was then energized to 12
volts for 20
minutes. During this time, extensive bubbling was observed on the cathodic
electrodes, producing
a foam above the surface of the solution (similar to that shown FIGS. 10a and
10b). After 20
minutes, a sample of the electrolyzed solution was withdrawn and the free
available chlorine
content of the solution was determined to be 3,000 mg/L using the DPD method.
Example 4
A solution containing 100 mg/L cetyltrimethylammonium chloride and 1,000 mg/L
sodium
chloride was prepared by dissolving 0.4 mL of a 25% cetyltrimethylammonium
chloride solution
and 1 g sodium chloride in 1000 mL deionized water. 200 mL of this solution
was transferred to a
250 mL beaker, and a three electrode cell was immersed in the solution. The
cell was then
energized to 12 volts for 20 minutes. During this time, extensive bubbling was
observed on the
cathodic electrodes, producing a foam above the surface of the solution
(similar to that shown in
FIGS. 10a and 10b. After 20 minutes, a sample of the electrolyzed solution was
withdrawn and
the free available chlorine content of the solution was determined to be 850
mg/L using the DPD
method.
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Example 5
FIG. 9 shows how the solution resulting from the electrolysis of a quaternary
ammonium
halide salt results in the formation of a product that reacts with DPD to
produce a magenta color.
In the example, the reaction was the electrolysis of a 1`)/0 benzalkonium
chloride solution in
deionized water. This solution was electrolyzed for 5 minutes with 12 volts
applied to the cell. The
magenta color is consistent with the presence of free available chlorine
resulting for the oxidation
of the chloride associated with the benzalkonium cation at the anode of the
cell.
Example 6
FIGS. 10a and 10b are photographs showing the foaming that sometimes occurs
during
the electrolysis of a quaternary ammonium halide solution or a quaternary
ammonium
halide/alkali metal halide solution. In these photographs, the solution being
electrolyzed is a 100
mg/L benzalkonium chloride and 20 g/L sodium chloride solution, and the
electrolysis is at 12
volts applied to the cell. Similar results were observed during electrolysis
of brines comprised of
cetyltrimethylammonium chloride, octyltrimethylammonium chloride, or
didecyldimethylammonium
chloride, either alone combined with sodium chloride. Solutions of
tetraalkylammonium chlorides
(such as tetramethylammonium chloride, tetraethylammonium chloride,
tetrapropylammonium
chloride, and tetrabutylammonium chloride), either alone or in sodium chloride
based brines,
produced chlorine when electrolyzed but the production of foam during
electrolysis was
minimized.
Example 7
FIG. 11 is a graph showing the enhanced microbial inactivation achieved by a
solution of
a quaternary ammonium hypochlorite compound produced through the electrolysis
of the
corresponding quaternary ammonium chloride compound. Here, an aqueous solution
of
cetyltrimethylammonium chloride (CTAC) at a concentration of 250 mg/L was
divided into two
portions. One portion was passed through an electrochemical cell operating at
an applied cell
voltage of 12 V. After electrolysis the concentration of free available
chlorine, measured using the
DPD methodology, was determined to be 6.8 mg/L. A sample of this solution was
then mixed with
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sodium thiosulfate, which was used to quench the free available chlorine but
does not react with
the quaternary ammonium component of the solution. Similarly, a solution of
sodium hypochlorite
was prepared by the dilution of commercial bleach to have a free available
chlorine concentration
of 6.5 mg/L. All four solutions (6.5 mg/L FAC sodium hypochlorite, 250 mg/L
unelectrolyzed
CTAC, 250 mg/L electrolyzed CTAC, and 250 mg/L electrolyzed and quenched CTAC)
were then
used to inactivate a suspension of Bacillus globigii spores. After a five
minute contact time with
the B. globigii spores, the resulting solutions were enumerated for viable
spore counts (colony
forming units (CFU)) using the dilution plate method. Briefly, specific
volumes of the solution are
spread onto agar plates and allowed to incubate at 35 C for 24 hours, after
which, the number of
surviving spores are quantified in terms of log reduction from the initial
spore concentration.
Results from this experiment are given in FIG. 11, where it is clear that the
electrolyzed solution
of 250 mg/L CTAC exhibited the highest degree of spore inactivation. Further,
the inactivation
was synergistic, not additive, indicating that the freshly produced quaternary
ammonium
hypohalite is important for efficacy. Additionally, the solutions of
unelectrolyzed and
electrolyzed/quenched 250 mg/L CTAC produced approximately the same degree of
B. globigii
inactivation, indicating that the quaternary ammonium functionality of the
molecule was
unaffected due to the electrolysis process.
Example 8
The differences between quaternary ammonium hypohalite compounds prepared by
electrolysis of a quaternary ammonium halide compound and the mixing solutions
of a quaternary
ammonium halide compound with an alkali (or alkaline) metal hypochlorite
compound were
examined. Here, a 500 mg/L CTAC solution was electrolyzed as described above,
producing a
solution with a measured FAC of 32 mg/L. Similarly, a solution containing 500
mg/L CTAC and
31.2 mg/L FAC was prepared by combining CTAC and commercial bleach solutions.
As a control,
a 500 mg/L CTAC solution was prepared without either electrolysis or added
bleach. All three
solutions were then used to inactivation B. Globigii spores with a contact
time of 2, 5, and 10
minutes, and the results from this test are shown in FIG. 12. As can be seen,
the un-electrolyzed
(with no bleach added) 500 mg/L CTAC solution resulted in a 1.25-1.29 log
inactivation of B.
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Globigii spores, depending on contact time. In the case of CTAC mixed with
bleach, slightly
higher spore log inactivations were observed, with a maximum log inactivation
of 1.86 found for
the 10 min contact time. Electrolyzed CTAC, however, produced much higher log
inactivation,
with a maximum log inactivation of 3.87 observed for the 10 minute contact
time. The differences
between the disinfectant produced by electrolysis and the one produced through
the combination
of CTAC and bleach may possibly be related to the cogeneration of oxidants
other than free
available chlorine species, which then work with both the quaternary ammonium
and FAC
components of the solution to produce a significant enhancement of microbial
inactivation
efficacy.
Example 9
FIG. 13 illustrates the impact of solution pH on the inactivation of B.
globigii spores using
electrolyzed solutions of CTAC. It is well known that pH has a dramatic impact
on the ability of
free chlorine to inactivation microorganisms. This is due to the fact that
hypochlorous acid (HOCI)
is more effective at inactivating microorganisms than the hypochlorite (C10-)
anion. The relative
amount of these species present in solution is pH dependent: when the pH is
below 7.5, HOCI is
the major species; when the pH is higher than 7.5, CIO- predominates.
Therefore, aqueous
chlorine solutions are more effective disinfectants when the pH is lower than
7.5. To test the
impact of pH on quaternary ammonium hypochlorite compounds, a solution
containing 250 mg/L
CTAC was electrolyzed and divided up into several portions. The pH of these
portioned solutions
of CTAC was then adjusted to between 6.5 and 9, and these solutions were used
to inactivate a
suspension of B. globigii spores. A similar variable pH series of solutions
was prepared from
unelectrolyzed CTAC also at 250 mg/L, and these solutions were also used to
inactivate B.
globigii spores. As can be seen in FIG. 12, pH had very little impact on the
inaction efficacy of
electrolyzed CTAC, a surprising result given what is known about the
disinfection actions of
aqueous chlorine and other aqueous halogen solutions. These data indicate that
the quaternary
ammonium hypohalite product resulting from the electrolysis may be stabilized
in a beneficial
fashion that would not be possible without the electrolysis step.
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Example 10
As an example of the differences between quaternary ammonium hypochlorite
solutions
that are produced through the combination of a solution containing quaternary
ammonium halide
compounds with a solution containing an alkali (or alkaline) metal
hypochlorite as compared to
the direct electrolysis of a quaternary ammonium halide compound, solutions
based on CTAC
were prepared by combining CTAC (150 mg/L) and sodium hypochlorite (variable
FAC
concentration between 1 and 50 mg/L FAC). Similarly, CTAC (167 mg/L) was
electrolyzed in an
electrochemical cell, producing a solution that had a FAC concentration of 4.2
mg/L. Alone, CTAC
at 167 mg/L was able to achieve a 0.90 0.14 log inactivation of B. globigii
spores while that same
solution, after electrolysis, achieved a 2.93 0.19 log inactivation of B.
globigii spores. In
comparison, the mixed CTAC and bleach solutions had lower log inactivation of
B. globigii spores
until the FAC concentration was at least 20 mg/L, and at that concentration,
the solution was only
able to achieve a log inactivation of 1.23 0.17. Similar results were observed
when comparing
other concentrations of mixed and electrolyzed solutions using other CTAC
concentrations as well
as other quaternary ammonium compounds. Enhanced spore inactivation associated
with
quaternary ammonium hypochlorite produced through electrolysis as opposed to
quaternary
ammonium produced through blending the individual components is consistent
with the presence
of other oxidizing biocides, possibly including hydrogen peroxide.
Example 11
In some applications of the present disclosure, it may be necessary to vary
the relative
amounts of FAC and quaternary ammonium components in a produced quaternary
ammonium
hypochlorite solution. This can be readily achievable using the present
invention by blending an
alkali metal halide salt with a quaternary ammonium halide compound to produce
a mixed brine
that is then electrolyzed. In one specific example, CTAC was blended with
sodium chloride to
produce a series of brines with varying concentration of CTAC, with the
concentration of sodium
chloride being constant at 20 g/L. Here the concentration of CTAC in the
brines was set to be 50,
100, 500, 1000, and 5000 mg/L. These solutions were then electrolyzed, and FAC
concentrations
of the electrolyzed solutions was found to be 4550, 4000, 3000, 2650, and 1600
mg/L
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respectively. These solutions were then diluted so that the FAC concentration
was either 5 or 10
mg/L, resulting in an equivalent cetyltrimethylammonioum concentration of
0.06, 0.13, 0.83, 1.9,
and 16 mg/L for the 5 mg/L FAC solutions and 0.11, 0.25, 1.67, 3.78, and 31
mg/L for the 10
mg/L FAC solutions respectively. These solutions were then used to inactivate
B. globigii spores
and the results of this test are shown in FIG. 14 and TABLE 1.
NaCI CTAC FAC Electrolysis solution diluted
Electrolysis solution diluted
concentration concentration concentration to a FAC
concentration of to a FAC concentration of
in the brine in the brine of the 5 mg/L 10 mg/L
(g/L) (mg/L) electrolyzed Quaternary Log
Quaternary Log
CTAC/NaCI ammonium inactivation ammonium inactivation
brine (mg/L) concentration concentration
(mg/L) (mg/L)
20 50 4550 0.06 1.17 0.11 3.5
20 100 4000 0.13 1.18 0.25 3.5
20 500 3000 0.83 1.16 1.67 3.5
20 1000 2650 1.9 1.18 3.78 3.5
20 5000 1600 16 1.51 31 3.5
TABLE 1
As can be seen, the log inactivation of solutions based on a 5 mg/L FAC
concentration
were typically around 1.1 with the highest log inactivation of 1.51 seen with
an equivalent
cetyltrimethylammonioum concentration of 16 mg/L. However, when the FAC
concentration was
10 mg/L, all solutions independent of cetyltrimethylammonioum concentration
demonstrated a log
inactivation of 3.5 (the maximum observable under this test design).
Unelectrolyzed CTAC
solutions under similar concentrations and exposure times typically resulted
in log inactivation of
around 0.27-0.30 while FAC alone solutions under these conditions typically
result in a log
inactivation of less than 1. This data indicates that it is possible to
achieve a biocide of the desired
strength by choosing the appropriate blend ratio of a quaternary ammonium
halide compound
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with an alkali metal halide salt into the brine used for electrolysis.
Moreover, these results are
surprising in that only small amounts of CTAC were necessary to achieve the
synergistic
disinfection in the electrolyzed quaternary ammonium hypochlorite compound
solution. Other
concentrations of CTAC, as well as other concentrations of sodium chloride and
other quaternary
ammonium compounds, produced similar results with the main difference being
actual ratios of
quaternary ammonium compound to FAC in the produced solutions, which showed
differing
inactivation efficacy depending on the chemical nature of the quaternary
ammonium compound.
Example 12
For some quaternary ammonium halide compounds, electroxidation of the halide
component of the compounds can install an unexpected biocidal capability. One
example is the
case of tetramethylammonium chloride (TMAC), a quaternary ammonium compound
that is not
traditionally effective as a microbiocide. When a 500 mg/L TMAC solution was
electrolyzed,
thereby producing tetramethylammonium hypochlorite, and the unelectrolyzed,
electrolyzed, and
electrolyzed/quenched TMAC solutions were then used to inactivate B. globigii
spores. FIG. 15
shows the results of these inactivation tests. The unelectrolyzed and
electrolyzed/quenched
TMAC solutions both produced about a 0.27 and 0.36 log inactivation with
contact times of 2 and
5 minutes, respectively. These observations are consistent with the low
biocidal efficacy of TMAC
in the quaternary ammonium chloride form. However, electrolyzed TMAC resulted
in a 3.6 log
inactivation independent of exposure time.
Although the invention has been described in detail with particular reference
to these
preferred embodiments, other embodiments can achieve the same results.
Variations and
modifications of the present invention will be obvious to those skilled in the
art and it is intended
to cover all such modifications and equivalents. The entire disclosures of all
patents and
publications cited above are hereby incorporated by reference.
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