Classifications

• • A—HUMAN NECESSITIES
  • A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
  • A47L—DOMESTIC WASHING OR CLEANING; SUCTION CLEANERS IN GENERAL
  • A47L15/00—Washing or rinsing machines for crockery or tableware
• • A—HUMAN NECESSITIES
  • A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
  • A47L—DOMESTIC WASHING OR CLEANING; SUCTION CLEANERS IN GENERAL
  • A47L15/00—Washing or rinsing machines for crockery or tableware
  • A47L15/0002—Washing processes, i.e. machine working principles characterised by phases or operational steps
• • A—HUMAN NECESSITIES
  • A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
  • A47L—DOMESTIC WASHING OR CLEANING; SUCTION CLEANERS IN GENERAL
  • A47L15/00—Washing or rinsing machines for crockery or tableware
  • A47L15/42—Details
  • A47L15/4236—Arrangements to sterilize or disinfect dishes or washing liquids
  • A47L15/4238—Arrangements to sterilize or disinfect dishes or washing liquids by using electrolytic cells
• • A—HUMAN NECESSITIES
  • A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
  • A47L—DOMESTIC WASHING OR CLEANING; SUCTION CLEANERS IN GENERAL
  • A47L15/00—Washing or rinsing machines for crockery or tableware
  • A47L15/42—Details
  • A47L15/46—Devices for the automatic control of the different phases of cleaning ; Controlling devices
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L2/00—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
  • A61L2/16—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor using chemical substances
  • A61L2/18—Liquid substances or solutions comprising solids or dissolved gases
  • A61L2/186—Peroxide solutions
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D3/00—Other compounding ingredients of detergent compositions covered in group C11D1/00
  • C11D3/39—Organic or inorganic per-compounds
  • C11D3/3947—Liquid compositions
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/28—Per-compounds
  • C25B1/30—Peroxides
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/02—Process control or regulation
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
• • A—HUMAN NECESSITIES
  • A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
  • A47L—DOMESTIC WASHING OR CLEANING; SUCTION CLEANERS IN GENERAL
  • A47L2601/00—Washing methods characterised by the use of a particular treatment
  • A47L2601/06—Electrolysed water
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L2202/00—Aspects relating to methods or apparatus for disinfecting or sterilising materials or objects
  • A61L2202/10—Apparatus features
  • A61L2202/11—Apparatus for generating biocidal substances, e.g. vaporisers, UV lamps

Definitions

• This invention relates to apparatus for, and methods of, producing hydrogen peroxide by means of electrolytic cells, and especially to such apparatus arranged to produce hydrogen peroxide in, for example, an automatic dishwasher.
• detergents are employed to produce a wash liquid for use on dirty items placed in the dishwasher for washing.
• such detergents can decompose to produce pollutants when the wash liquid is released to the environment.
• a problem which may be encountered with hydrogen peroxide is that it is unstable and is not capable of being stored for long periods without decomposing. These properties reduce the attractiveness of utilising hydrogen peroxide, particularly in a domestic environment where it may be used relatively infrequently and/or in small amounts.
• the invention provides apparatus for producing hydrogen peroxide comprising an electrolytic cell arranged to generate hydrogen peroxide, a reservoir for storing hydrogen peroxide generated by the cell and a controller arranged ' to activate the cell and introduce stored hydrogen peroxide from the reservoir to the cell.
• the invention permits the concentration of a store of hydrogen peroxide to be topped up as required, by introducing the stored hydrogen peroxide as the electrolyte in the cell. This counteracts the natural decay of the stored hydrogen peroxide.
• the controller is arranged to monitor the length of time that the stored hydrogen peroxide has been in the reservoir, and to activate the electrolytic cell for a predetermined period in dependence on the length of time of storage.
• the pH of the hydrogen peroxide is controlled so that it is below a predetermined value. It has been found that hydrogen peroxide having a low pH, close to neutral, decays much slower than hydrogen peroxide having a more strongly alkaline pH.
• the invention is particularly suitable for application in an automatic dishwasher.
• the topping up of the concentration of the hydrogen peroxide may be done during a pre-wash step.
• Figure 1 is a schematic drawing of an electrolytic cell
• Figure 2 is a schematic diagram of a system for controlling the conductivity of the cell of Figure 1;
• Figure 3 is a graph showing change in current in the cell of Figure I;
• Figure 4 is a graph showing change in concentration of hydrogen peroxide in the cell of Figure 1;
• Figure 5 is a graph showing a typical rate of decay of hydrogen peroxide
• Figure 6 is a graph showing 3 change in concentration of hydrogen peroxide in the cell of Figure 1 for different initial concentrations
• Figure 7 is a schematic diagram of a system constructed in accordance with the invention for storing and replenishing hydrogen peroxide in the cell of Figure 1;
• Figure 8 is partly cut-away perspective view of the cabinet of an appliance incorporating the cell of Figure 1 and the systems of Figures 2 and 7.
• FIG. 1 illustrates an electrolytic cell, indicated generally by the reference numeral 1. This is purely a schematic drawing and none of the features are shown to scale. Only one cell 1 is illustrated in this drawing for clarity, but in practice a plurality of such cells would be connected in series.
• the cell 1 comprises two chambers 2, 3, partitioned by an ion-exchange membrane 4 into an anode chamber 2 having an anode 5 and a cathode chamber 3 having a cathode 6.
• the cell 1 also includes an air chamber 7.
• the cathode 6 is a carbon cloth type of electrode that divides the cathode chamber 3 from the air chamber 7.
• a pump 8 is provided in order to pump air from the surroundings into the air chamber 7, so that it is held in the chamber 7 under pressure.
• the pressure causes the air to be forced into the carbon-cloth cathode 6, so as to provide oxygen to the cathode.
• Oxygen is necessary to produce hydrogen peroxide in the cathode chamber 3.
• the anode 5 and cathode 6 are connected to a power source in the form of DC power supply 9. This may be derived from an electrical mains supply, suitably transformed and rectified to produce a DC supply 9 of an appropriate current and voltage.
• the electrolytic cell 1 is activated by applying electrical potential across the anode 5 and cathode 6 to force an internal chemical reaction between ions in the chambers 2, 3 and the electrodes. If the ions are positively charged cations they flow toward the cathode 6 and are reduced. If the ions are negatively charged anions they flow to the anode 5 and are oxidized.
• This reaction comprises the cathodic reduction of oxygen from the air chamber 7 by means of hydrogen ions and electrons which were generated in the anode chamber 2 and which migrate into the cathode chamber 3 via the membrane 4. By controlling this reaction, hydrogen peroxide is produced in the cathode chamber 3.
• the chambers 2, 3, of the cell 1 have different respective electrolytes in them.
• the electrolyte associated with the cathode chamber 3 is called the catholyte 10.
• the electrolyte associated with the anode chamber 2 is known as the anolyte 11.
• the catholyte 10 comprises a solution of sodium chloride.
• Such dishwashers typically have a chamber in which dishwasher salt is stored.
• this salt has been used to maintain the efficiency of the water softener in the dishwasher.
• This store of salt and the supply of water from the local water mains provide a convenient source of sodium chloride solution.
• a suitable anolyte 11 is a solution of a metal sulphate salt, such as sodium sulphate.
• Softened tap water may also be employed as an anolyte.
• the anode 5 is not consumed by the electrochemical reactions in the anode chamber.
• a suitable anode material is a mesh of titanium oxide coated with indium oxide.
• Conventional electrolytic cells have had to employ anode materials that minimise the generation of chlorine gas, for example platinum. Platinum is costly, much more so than indium oxide based anodes. With this apparatus, the anolyte is selected so that chlorine is not produced at the anode, permitting the use of these cheaper materials.
• iridium oxide based anodes have a lower electrical resistance than those of platinum, which improves the rate of production of hydrogen peroxide.
• the ion exchange membrane 4 permits electrical contact between the electrolytes 10, 11 in the respective chambers 2, 3, but does not permit the electrolytes to mix.
• the electrolytic cell 1 is very small, of the order of a few centimetres wide. Therefore, a typical cell can only produce small volumes of hydrogen peroxide. Greater yields can be achieved by employing a plurality of such cells connected in series.
• a further measure for improving yield is to circulate the catholyte 10 between the cell and a reservoir of catholyte held in a catholyte storage tank 12, which is shown in Figure 2.
• the catholyte storage tank 12 has a capacity of several litres, typically approximately five litres.
• hydrogen peroxide is produced in the cathode chamber 3, and this hydrogen peroxide is pumped, by means of catholyte pump 13, into the catholyte tank 12, to be replaced by more catholyte.
• the concentration of hydrogen peroxide in the catholyte gradually increases.
• a five- litre batch of hydrogen peroxide solution of a desired concentration can be produced. In typical domestic and light industrial applications, it has been found that a concentration of approximately 0.35% is adequate for most purposes.
• an anolyte storage tank 14 for containing a reservoir of anolyte 11.
• the anolyte tank 14 has a lower capacity, of typically approximately one litre.
• a pump 15 is employed to circulate anolyte 11 between the anode chamber 2 and the anolyte storage tank 14, in order to supply a fresh batch of ions to the cell 1.
• the anolyte 11 is not used up.
• the anolyte 11 only needs to be replenished by water from the main supply 16 occasionally, in order to replace anolyte that may have evaporated from the storage tank 14.
• a reservoir 17 of metal salt solution is provided and is controlled so as to dose the catholyte 10 with this salt solution in order to bring the conductivity level of the cell quickly to the desired level, ha this embodiment, the metal salt solution held in the reservoir 17 is a solution of sodium chloride, that is to say brine.
• a current sensor 18 is arranged to detect electrical current passing through the cell 1. This current is indicative of the conductivity of the cell 1.
• the current sensor 18 comprises a current transducer that produces a signal indicative of the current strength to a controller incorporating a processor 19.
• the processor 19 periodically compares the signal with a predetermined current value and controls a pump 20 connected to the reservoir 17 of brine in dependence on this difference between measured and predetermined current values. If the current detected by the sensor 18 is below a predetermined value, the processor is arranged to activate the brine pump so as to dispense a volume of brine. Brine from the reservoir 17 enters a static mixer 21, which forces the brine to mix with catholyte being pumped from the catholyte tank 12 into the electrolytic cell 1. The combination of liquids exiting the static mixer 21 then enters the cell 1 and effects an immediate change in its conductivity.
• Figure 3 is a graph showing the change in current detected at the transducer during a typical conductivity control process.
• the predetermined current level was set to 16 Amps.
• the conductivity of the cell increases sharply, so that the cell reaches the required current level in a matter of minutes.
• This level of current is maintained throughout the process of producing a batch of hydrogen peroxide, with relatively little deviation in current level.
• the processor 19 may be arranged to record the conductivity data for monitoring of the system. Abnormal changes in conductivity may be indicative of a fault in the equipment and so the data can be employed to help alert a user or a technician to problems.
• Figure 4 shows the rate of production of hydrogen peroxide by the cell 1 as the catholyte 10 is recirculated between the catholyte tank 12 and the cell. The rate of production is steady and the hydrogen peroxide comes up to the required concentration within two hours.
• the catholyte tank 12 is arranged to store a batch of hydrogen peroxide produced by the cell.
• hydrogen peroxide is known to decay over a period of a few days, Thus, if the batch of hydrogen peroxide is not used within this time, it will degrade and become unusable.
• the concentration of hydrogen peroxide stored in the catholyte tank 12 is topped up whenever a batch of hydrogen peroxide is required, by energising the electrolytic cell 1 and circulating the contents of the catholyte tank 12 through the cell, until the hydrogen peroxide thus produced reaches the required concentration.
• the processor 19 is arranged to monitor the length of time that the stored hydrogen peroxide has been held in the tank 12.
• Figure 5 is a graph showing a typical decay rate for hydrogen peroxide. For example, if the hydrogen peroxide has been stored for five days, it will have decayed such that its concentration is reduced from approximately 0.4% to approximately 0.225%.
• the processor 19 is arranged to activate the electrolytic cell 1 in order to bring the concentration back up to a predetermined level.
• Figure 6 is a graph showing the change in hydrogen peroxide concentration over time as the cell is activated at different initial concentrations.
• the processor determines by a simple algorithm how long it will take the cell 1 to refresh the hydrogen peroxide, so as to produce a batch of a predetermined concentration.
• the dishwasher 22 comprises an insulated outer cabinet 23 containing a tub 24, the front wall of which is pivotable about its bottom edge to provide a door 25 to give access to the tub.
• the dishes, other crockery, cutlery and utensils forming the load are placed in racks in the tub.
• One rack 26 is shown in Figure 8 in the upper portion of the tub 24.
• another rack is provided in the lower portion of the tub 24.
• Water is sprayed over the dishes from jets 27, 28 driven by a centrifugal pump which is in turn powered by an electric motor. The pump and motor are not visible in this drawing.
• the electrolytic cell 1, the storage tanks 12, 14 and parts of the hydrogen peroxide-producing apparatus may be housed in convenient locations in the appliance, for example in a compartment under the cabinet or in partitions in the sidewalls.
• the door 25 is opened and the dishes etc forming the load of the machine are inserted into the rack.
• User-operable controls 29 are provided on a front panel 30 and are operated to start the washing operation.
• the machine fills with water and a heating element 31 is activated.
• the electric motor is operated and the pump drives hot water to the spray jets 27, 28 to start a pre-wash step.
• the tub of the dishwasher is indicated at 24 and is connected to the domestic main water supply 16.
• the controller incorporating the processor 19 is not shown in this drawing. The controller is arranged to control the pumps, valves and the electrolytic cell in the dishwasher.
• a flow diverter 32 directs water from a water softener 33 connected inline with the water mains 16 directly into the wash sump for the dishwasher. This initialises the pre-wash step, which is employed to rinse particles of food and other dirt from the items in the tub 24 to be washed. Whilst the pre-wash step is taking place, the peroxide solution which had been stored in the catholyte tank 12 is pumped through the electrolytic cell 1, which is energised by means of the transformed and rectified power supply derived from the electric mains supply. Thus, the process of generating hydrogen peroxide does not start from scratch, but instead starts from the residual concentration remaining in the stored solution. This continues until a batch of hydrogen peroxide of the required concentration is produced, at which point the dishwasher is arranged to start its main wash step.
• a drain valve 34 connected to the catholyte tank 12 is activated, so that the batch of hydrogen peroxide contained therein is dispensed into the wash tub 24 of the dishwasher 22.
• the hydrogen peroxide serves as a detergent for cleaning items in the tub 24. It has been found that hydrogen peroxide is particularly suitable for washing items of glassware, which may become scratched and clouded by exposure to conventional detergents. A further advantage of hydrogen peroxide is that it decays into oxygen and water and so does not contribute to pollution when released into the environment.
• the catholyte tank 12 is replenished with fresh softened water from the water mains supply 16.
• the process of hydrogen peroxide production is restarted afresh until a batch of hydrogen peroxide of the required concentration is produced.
• This batch is then stored in the catholyte tank 12 until the dishwasher is operated again, at which point the processor 19 determines the length of time that the peroxide has been in storage and thereby calculates the time that the cell 1 needs to run to replace the decayed hydrogen peroxide. This time; may be communicated to a user of the dishwasher by means of, for example, a visual display on the control panel 30.
• the tub 24 is emptied via a drain pump 35 and re-filled with fresh water, which is heated in order to rinse the load. After the rinse, the tub again drains.
• the drying step includes a short blast of high-speed airflow, to force residual water out of recesses in the dishes, such as the upturned bases of mugs. This may be followed by a period of slower- flowing air arranged to dry the dishes. The air may be heated.
• a further measure which may be implemented to reduce the time taken to refresh a batch of hydrogen peroxide involves reducing its rate of decay. By reducing the rate of decay, a batch of hydrogen peroxide stored for a long period will have a higher residual concentration than was achievable hitherto. This may be effected by controlling the pH of the catholyte. It has been found that a pH of less than 8.5 gives a batch of hydrogen peroxide with a slower decay rate.
• the graph of Figure 5 shows a typical decay for hydrogen peroxide at a pH of 8.11. It takes approximately five days for the concentration to reduce from approximately 0.4% to approximately 0.225%. However, if the pH is greater than 8.5, this rate of decay is much quicker.
• a batch of hydrogen peroxide produced at a pH of 8.64 at the cathode takes half a day to decay from a concentration of 0.4% to 0.225%.
• pH of the catholyte may be controlled by controlling the pH of the anolyte, since any change in pH of the catholyte produces a proportional change in the pH of the anolyte.
• the preferred value of the pH of the anolyte is between 1 and 2. This may be achieved by using a solution of sodium sulphate as the anolyte. Alternatively, softened water may be employed. During activation of the electrolytic cell 1, the anolyte is not used up, but there will naturally be a small amount of loss due to, for example, evaporation.
• anolyte tank valve 36 arranged to divert water from the mains supply 16 to the anolyte tank 14. If a larger amount of water is required, this is added in small amounts, to allow the pH of the anolyte 11 to stabilise between doses of water.
• Further stability in the pH of the anolyte 11 may be achieved by limiting exposure of the anolyte to air by, for example, making the anolyte tank 14 airtight, so that the anolyte does not need to be topped up so frequently.
• the invention has been described with reference to an automatic dishwasher employing hydrogen peroxide for dishwashing.
• the invention has a multitude of applications.
• the invention may be employed for other cleaning operations, such as in floor cleaning appliances and particularly carpet cleaners.
• the hydrogen peroxide would be heated, which is thought to increase its bleaching effect.
• Hydrogen peroxide has a sterilising effect, and so the invention could be employed both domestically and industrially to sterilise instruments, work surfaces, to treat injuries and infections and as a handwash dispenser. Further applications of the invention will be apparent to the skilled person.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Inorganic Chemistry (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Automation & Control Theory (AREA)
• Epidemiology (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Wood Science & Technology (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

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• 2006
  • 2006-04-11 GB GB0607277A patent/GB2437956A/en not_active Withdrawn
• 2007
  • 2007-04-02 WO PCT/GB2007/001219 patent/WO2007128961A2/en active Application Filing
  • 2007-04-02 EP EP07732269A patent/EP2004878A2/en not_active Withdrawn
  • 2007-04-02 US US12/295,244 patent/US20090272654A1/en not_active Abandoned
  • 2007-04-02 CN CN2007800180939A patent/CN101448980B/zh not_active Expired - Fee Related
  • 2007-04-10 TW TW096112399A patent/TW200806573A/zh unknown

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