SYSTEM AND METHOD FOR PRODUCING A HYPOCHLOROUS ACID-BASED DISINFECTANT SOLUTION

Description

TECHNICAL FIELD

The invention relates to a system for producing a disinfectant solution containing hypochlorous acid. The invention also relates to a method using this system.

The field of the invention is that of the manufacture and design of apparatus and systems for the electrochemical production of hypochlorous acid. The invention finds a particular application in the field of disinfection of, for example, but not limited to, water, air, hard or soft surfaces, plant, animal or human surfaces, surfaces of medical devices.

BACKGROUND

Hypochlorous acid (CAS No. 7790-92-3) is a weak inorganic acid of formula HOCl. It partially dissociates in water to produce the hypochlorite ion (OCl⁻) according to the reaction of equation 1:

In aqueous solution, the distribution of the two chlorine species (HOCl/OCl⁻) depends on the pH of water as indicated in appended FIG. 1.

As can be seen from FIG. 1, hypochlorous acid is the predominant species at pH<7.6 and the hypochlorite form becomes predominant at pH>7.6 (alkaline pH). At pH values below 3.5, gaseous chlorine begins to form. To maintain the hypochlorous acid solution (HOCl) in a stable form, maximise its antimicrobial activities and minimise unwanted by-products, the pH should preferably be kept between 3.5 and 7.5.

Hypochlorous acid (HOCl) is also a major bactericidal compound in innate immunity. It is naturally produced in mammals by white blood cells to fight infections. It has germicidal properties against a wide range of microorganisms (bacteria, viruses, fungi, etc.). Compared to sodium hypochlorite (main component of bleach) which is often used as a sterilising agent, hypochlorous acid would be 80 to 120 times more effective while being less irritating to the skin.

Hypochlorous acid has numerous uses such as in water treatment, hygiene and food safety, sanitation of all types of surfaces, objects or food, as well as in pharmacy and medicine, in particular for wound care and skin disinfection. Note that hypochlorous acid is authorised by the US Food and Drug Administration (FDA) as a biocidal product. In addition, the European Commission approved, in July 2021, the active chlorine released from hypochlorous acid (EC n°: 232-232-5) as an active substance in biocidal products used for human hygiene. The recent outbreak of the new Covid-19 coronavirus has not only resulted in a shortage of alcohol-based disinfection products on the market, but has also demonstrated the importance of hypochlorous acid in disinfecting places likely to be contaminated by the Covid-19 coronavirus. Accordingly, there is a growing demand for hypochlorous acid-based disinfectant solutions in a wide range of application sectors (for example, water treatment, food processing, cosmetics, medicine, etc.).

Various systems and methods for preparing disinfectant solutions containing hypochlorous acid have been provided in prior art. Among known systems and methods, mention may be made of, by way of examples:

• • hydrolysis of gaseous chlorine according to the reaction of equation 2 below,
  • acidification of hypochlorite ion according to the reaction of equation 3 below,
  • electrolysis of an aqueous sodium chloride solution according to the reactions of equations 4-6 below.

The method according to equation 2 is fast and efficient for preparing disinfectant solutions containing hypochlorous acid, however, it is hardly used due to the risks inherent in handling of gaseous chlorine and the hazards associated with its storage.

The method according to equation 3 consists in acidifying an aqueous solution of a hypochlorite salt such as calcium or sodium hypochlorite, with an aqueous solution of an acidifier such as hydrochloric acid to obtain a disinfectant solution containing hypochlorous acid. However, this method requires very precise adjustment of pH and temperature during the acidification process to prevent or reduce generation of toxic gaseous chlorine. Furthermore, this method requires the manufacture, transport and storage of hypochlorite salts and acidic products which are corrosive chemicals.

The method according to the reaction of equations 4-6 is most widely used for the production of disinfectant solutions containing hypochlorous acid. This method does not generally require the presence in water of chemicals other than alkali chloride such as sodium or potassium chloride. In particular, this method consists in supplying a tank or enclosure provided with an electrolytic cell including electrodes among which at least one anode and at least one cathode, with an aqueous solution containing a certain proportion of alkali chloride, especially sodium chloride, electrolysing this aqueous solution in order to produce an aqueous hypochlorous acid solution, then transferring, for example by pumping, this hypochlorous acid solution into another enclosure or tank to be diluted therein with water to obtain a disinfectant solution containing hypochlorous acid. It should be noted that the reaction of equation 4 (oxidation of chloride ions) takes place at the at least one anode and leads to formation of gaseous chlorine and that of equation 5 (reduction of water) takes place at the at least one cathode and leads to generation of dihydrogen.

As a reminder, electrolytic cells involved in known methods exist in two categories:

• • The first category includes split cells that use membranes to maintain complete separation of the anode and cathode products in the cells, thus, the gaseous chlorine produced at each anode according to the equation dissolves in water to form hypochlorous acid according to the reaction of equation 2 mentioned above.
  • The second category includes non-split cells that do not use membranes. In this case, gaseous chlorine generated at each anode may react directly with the hydroxide anion produced at each cathode to form hypochlorite ions according to the reaction of equation 6, which hypochlorite ions may be in equilibrium with the hypochlorous acid according to the reaction of equation 1 mentioned above.

Electrolysis methods and systems of prior art all have one or more of the following drawbacks:

• • The disinfectant solutions produced are generally contaminated with large amounts of chloride salt and/or are highly diluted and/or low in hypochlorous acid (<3 ppm).
  • They usually involve large facilities and/or are relatively complex and therefore expensive.
  • They do not meet the need of the user who desires the possibility to adapt the production of the disinfectant solution according to the desired concentration of hypochlorous acid. As discussed above, the applications for using the disinfectant solution are numerous, it is of course desirable to leave the user the possibility of choosing the concentration of hypochlorous acid that is best suited to the disinfection operation to be performed.

The objective of the invention is that of addressing all or some of the aforementioned drawbacks. Another objective of the invention is to provide a system or method for producing a hypochlorous acid-based disinfectant solution that leaves a user the possibility of obtaining said disinfectant solution with the concentration of hypochlorous acid that is most suited for the desired use thereof. Another objective still of the invention is to provide such a system or method that is simple in its design, easily feasible and easy to implement, on a small or large scale and that is inexpensive. Another object of the invention is to provide such a system or method that allows the user to effectively monitor the production of said disinfectant solution

SUMMARY

The solution provided by the invention is a system for producing a disinfectant solution containing hypochlorous acid. This system is remarkable in that it includes:

• • a dilution tank dedicated to the preparation of the disinfectant solution, which tank includes a water inlet for filling said tank with water,
  • at least one electrolyser disposed below the dilution tank, and including:
    • an electrolysis enclosure storing alkali chloride in solid form,
    • at least one set of electrodes comprising at least one anode and at least one cathode arranged in the electrolysis enclosure,
    • a duct for fluidically communicating the electrolysis enclosure and the dilution tank.

This system is further remarkable in that said duct is arranged such that filling the dilution tank with water results in filling the electrolysis enclosure with water, to prepare an aqueous solution containing chloride ions by dissolving part of the alkali chloride stored in said enclosure, and such that when said aqueous solution is electrolysed in the electrolysis enclosure using the set of electrodes to produce hypochlorous acid, at least part of the hypochlorous acid can migrate from said enclosure to said tank, and can dilute in water present in said tank in order to form the disinfectant solution.

The system for producing a disinfectant solution containing hypochlorous acid according to the present invention has many advantages, especially being simple in design, easily feasible, easy to implement, on a small or large scale and inexpensive. Furthermore, the system according to the present invention allows a user to obtain the disinfectant solution with the concentration of hypochlorous acid that is most suited for the desired use thereof. Indeed, the user can adjust this system so that the disinfectant solution is concentrated in hypochlorous acid with the desired free chlorine content (for example, 5 ppm, 100 ppm, 250 ppm, 1500 ppm, 3000 ppm, or more than 3000 ppm). For this, he/she has different ways at its disposal to adjust the system, for example he/she can increase the number of electrolysers and/or the number of sets of electrodes per electrolyser and/or the number of electrodes per sets of electrodes. It should be noted that the system according to the present invention does not comprise any transfer means, for example of the pump type, to transfer the hypochlorous acid (and/or hypochlorite ions) generated in the electrolysis enclosure from the latter to the dilution tank in which the hypochlorous acid has to be mixed with water to form the disinfectant solution. It should also be noted that before electrolysis, the dilution tank disposed above the electrolysis enclosure contained water, and that after electrolysis this water has been replaced by the disinfectant solution.

Other advantageous characteristics of the invention are listed below. Each of these characteristics may be considered alone or in combination with the remarkable characteristics defined above, and may be the subject, where appropriate, of one or more divisional patent applications:

Advantageously, electrolysis of the aqueous solution in the electrolysis enclosure is adjusted to generate the formation of gas bubbles, such that said bubbles create turbulences capable of forcing migration of the at least part of the hypochlorous acid from the electrolysis enclosure to the dilution tank through the duct.

The at least one electrolyser may be one or two or three or more electrolysers.

The at least one set of electrodes may be one or two or more sets of electrodes.

Preferably, the at least one set of electrodes further comprises a plurality of bipolar electrodes interposed between an anode and a cathode of the at least one set of electrodes.

Preferably, the at least one anode, the at least one cathode, and the plurality of bipolar electrodes of the at least one set of electrodes are all in the form of planar, parallel plates evenly spaced from one another.

In an alternative embodiment, the at least one set of electrodes comprises a plurality of anodes and a plurality of cathodes, which pluralities of anodes and cathodes are in the form of planar plates arranged in parallel rows of alternating polarity.

The electrolysis enclosure of the at least one electrolyser may have a capacity of at least 10 litres.

The dilution tank may further comprise means for breaking (or reducing the size of) the gaseous chlorine bubbles which may come from the electrolysis enclosure of the at least one electrolyser in order to promote dissolution of the gaseous chlorine in water, said means for breaking said gaseous chlorine bubbles being arranged at the bottom of the dilution tank at least facing the duct fluidically communicating the electrolysis enclosure and the dilution tank.

The means for breaking the gas bubbles may consist of at least one planar plate having perforations the diameter of which is sufficient to reduce the size of the gas bubbles to dimensions promoting dissolution of chlorine in water.

Preferably, the perforations of the at least one plate have a diameter of less than 5 mm, preferably less than 1 mm.

In particular, the means for breaking the gas bubbles consist of several planar perforated plates, these plates are superimposed such that the perforations of one plate are offset with respect to the perforations of another plate adjacent to it

Advantageously, the system according to the present invention further comprises a measurement device including:

• • a sensor adapted to measure the free chlorine content in the disinfectant solution being formed in the dilution tank,
  • a display adapted to display the free chlorine content measured by the free chlorine sensor.

Typically, the system according to the present invention further comprises regulation means for regulating the pH of the disinfectant solution being formed in the dilution tank.

Advantageously, the system according to the present invention further comprises a control unit operatively connected to the device for measuring the free chlorine content, which control unit is adapted to compare the free chlorine content measured by the sensor and a threshold value of the free chlorine content, and interrupt electrolysis when the free chlorine content measured by the sensor is equal to or greater than the threshold value of the free chlorine content.

In particular, the threshold value of the free chlorine content is set to a maximum value selected in a range of 5 ppm to 3000 ppm, in particular in a range of 10 ppm to 1500 ppm.

In practice, the dilution tank has a water inlet which is connected to a water source by a water feed circuit including, in the direction of the dilution tank, a solenoid valve and a circulation pump.

In practice still, the dilution tank has an outlet for collecting the disinfectant solution, which collection outlet is connected to a tapping provided on the water feed circuit between the solenoid valve and the circulation pump such that the collection line forms, with the pump and the part of the water feed circuit located after this pump, a recirculation loop which is configured to circulate the disinfectant solution from the collection outlet to the water inlet.

Preferably, the free chlorine measurement device is placed on the recirculation loop, in particular on the collection line, so as to make it possible to perform continuous measurements on the disinfectant solution.

The aqueous solution to be electrolysed may have a pH of 3 to 8, preferably a pH of 6 to 8.

According to another aspect, the present invention relates to a method for producing a disinfectant solution containing hypochlorous acid. This method is remarkable in that it includes:

• • a) a step of providing a system according to the present invention;
  • b) a step of filling the dilution tank of said system with water, and wherein filling the dilution tank with water results in filling the electrolysis enclosure of the at least one electrolyser of said system by the duct fluidically communicating said electrolysis enclosure and said dilution tank, in order to prepare an aqueous solution containing chloride ions by dissolving part of the alkali chloride stored in said electrolysis enclosure;
  • c) a step of applying electrical current to the electrodes of the at least one set of electrodes of said at least one electrolyser to electrolyse the aqueous solution containing chloride ions in said enclosure in order to produce hypochlorous acid, and wherein at least part of the hypochlorous acid migrates from said enclosure to said dilution tank through said duct, the at least part of hypochlorous acid having migrated diluting in water present in said dilution tank in order to form the disinfectant solution;
  • d) a step of measuring the free chlorine content of the disinfectant solution being formed in said dilution tank;
  • e) a step of interrupting electrolysis when the free chlorine content measured in step d) reaches a desired free chlorine content value for the disinfectant solution;
  • f) optionally, a step of measuring the free chlorine content by a sensor capable of measuring the free chlorine content of the disinfectant solution being formed in said dilution tank;
  • g) optionally, interrupting electrolysis provided in step e) is handled by a control unit adapted to compare the free chlorine content measured by the sensor in step f) and a threshold value of the free chlorine content and to interrupt electrolysis when the free chlorine content measured by the sensor is equal to or greater than the threshold value of the free chlorine content;
  • h) optionally, a step of measuring at least one intrinsic parameter of the disinfectant solution being formed in the dilution tank, which intrinsic parameter is chosen from the list of parameters comprising pH, temperature, conductivity, and hardness;
  • i) optionally, a step of regulating the pH of the disinfectant solution being formed in the dilution tank.

In particular embodiments, the current voltage applied to the electrodes, in step c) of the method, is between 1 and 15 volts, preferably between 2 and 10 volts.

Advantageously, the disinfectant solution containing the hypochlorous acid has a pH of about 5.1 to about 6.9, preferably a pH of about 6.5.

Preferably, in the optional step g) of the method, the threshold value of the free chlorine content is set to a maximum value selected in a range of 5 ppm to 3000 ppm, in particular in a range of 10 ppm to 1500 ppm.

BRIEF DESCRIPTION OF THE FIGURES

Further advantages and characteristics of the invention will more clearly appear upon reading the following description of preferred embodiments, with reference to the appended drawings, made as indicating and non-limiting examples, and in which:

FIG. 1 is an illustration of dissociation curves of hypochlorous acid in water as a function of pH;

FIG. 2 is a schematic representation of a system for producing a disinfectant solution according to the invention equipped with a dilution tank and an electrolyser;

FIG. 3 is a schematic representation of another system for producing a disinfectant solution according to the invention equipped with a dilution tank and two electrolysers;

FIG. 4 is a photographic representation of a system for producing a disinfectant solution according to the invention equipped with a dilution tank and three electrolysers;

FIG. 5 is a perspective view of an example electrolyser suitable for the present invention;

FIG. 6 is a perspective view of an example hollow tube that can serve as a support element for a set of electrodes of the system according to the invention;

FIG. 7 is a perspective view of an example set of electrodes suitable for the present invention;

FIG. 8 is a schematic representation of the system of FIG. 2 further equipped with a device for measuring the free chlorine content;

FIG. 9 is a schematic representation of the system of FIG. 8 further equipped with a control unit;

FIG. 10 is a schematic representation of the system of FIG. 9 according to a first alternative, the system being further equipped with a recirculation loop and the dilution tank of which is provided with level detectors;

FIG. 11 is a schematic representation of the system of FIG. 9 according to another alternative embodiment, the system being further equipped with another form of recirculation loop and the dilution tank of which is provided with level detectors;

FIG. 12 is a schematic representation of an example dilution tank of the system of the invention according to an alternative embodiment, wherein the dilution tank is provided with a tubular gauge.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present description is given by way of non-limiting example, each characteristic set out only in one embodiment can be extended to the other embodiments. Similarly, one or more characteristic(s) set out only in one embodiment can be combined with one or more other characteristic(s) set out only in another embodiment.

The present description is given by way of non-limiting example, each characteristic set out only in one embodiment can be extended to the other embodiments. Similarly, one or more characteristic(s) set out only in one embodiment can be combined with one or more other characteristic(s) set out only in another embodiment. It should be noted from now on that the appended figures are very simplified, the elements represented therein are therefore not necessarily to scale with respect to one another or from one figure to another. Each reference retains the same meaning from one figure to another.

The present invention first pertains to a system for producing a hypochlorous acid-based disinfectant solution, preferably a disinfectant solution containing hypochlorous acid with a free chlorine content greater than 5 ppm. This system can be used by users to produce the disinfectant solution on a small scale, on-site or on-demand, or on an industrial scale.

By “ppm”, it should be understood part per million. It should be noted that in the case of an aqueous solution, a concentration of 1 ppm can be expressed as follows, 1 ppm=1 mg/kg≈1 mg/L.

The system object of the invention comprises:

• • at least one electrolyser 100, and
  • a dilution tank 300 dedicated to the preparation of the disinfectant solution.

By “at least one electrolyser”, it should be understood one electrolyser (see FIG. 2), two electrolysers (see FIG. 3), three electrolysers (see FIG. 4) or more. Therefore, for the sake of simplification, only the case of the system with a single electrolyser, represented in FIG. 2, will be discussed in the remainder of the description, but the system and method according to the present invention works similarly with two, three or more electrolysers, and, advantageously, with high performance in the production of hypochlorous acid and disinfectant solutions containing it.

Furthermore, the electrolyser 100 implemented includes an electrolysis enclosure 110 equipped with at least one set of electrodes 120.

By “at least one set of electrodes”, it should be understood one set of electrodes (see for example FIG. 2), two or more sets of electrodes (see FIG. 5). Here too, for the sake of simplification, only the case of the electrolyser with a single set of electrodes, represented in FIG. 2, will be discussed in the remainder of the description, but the system and method according to the present invention works similarly with two or more sets of electrodes, and, advantageously, with high performance in the production of hypochlorous acid and disinfectant solutions containing it.

On the other hand, as will be described hereinafter, the dilution tank 300 of the system is provided with at least one bottom outlet 303. In principle, each at least one bottom outlet 303 is to be used with an electrolyser 100. The dilution tank 300 may be provided with two, three or more bottom outlets 303 but only one bottom outlet 303 of which is connected to an electrolyser 100. For example, in relation to FIG. 2, a single electrolyser 100 equips the system according to the invention, and the dilution tank 300 is represented with a single bottom outlet 303. However, the dilution tank 300 can be a tank with several bottom outlets in which the unused bottom outlets can be closed by a suitable closing means (for example, plug, tap, shut-off valve, etc.).

Electrolyser 100

The set(s) of electrodes 120 of the at least one electrolyser 100, are each to be supplied with electricity by an energy source 101 producing electrical current. This can be direct and/or pulsed current.

Referring to FIG. 2, the electrolyser 100 comprises an electrolysis enclosure 110 storing alkali chloride in solid form, and generally having an upper opening 111, which can be sealingly closed by a removable cover 130.

The alkali chloride stored in solid form in the electrolysis enclosure 110 is to be mixed with water in this enclosure 110 in order to produce the aqueous solution containing chloride ions, electrolysis of which makes it possible to obtain hypochlorous acid.

By “alkali chloride”, it is meant, according to the present invention, sodium chloride, potassium chloride and a mixture thereof. For the sake of simplification, only the case of sodium chloride will be discussed in the remainder of the description, but the system and method according to the present invention applies to all types of alkali chloride.

By “solid form”, it is meant, according to the present invention, any solid form having a weight of about 5 g to 30 g. Preferably, the solid form of alkali chloride such as sodium chloride is chosen from pellets and tablets. The advantages of using alkali chloride in solid form will be discussed later.

The enclosure 110 may be made of any suitable material being electrically insulating and resistant to corrosion by the aqueous solution containing the alkali chloride such as sodium chloride as well as by the products generated during electrolysis. Preferably, the enclosure 110 is made of glass or rigid plastic, preferably transparent, for example, polyvinyl chloride (PVC), glass-fibre reinforced polypropylene (GFRP), acrylonitrile butadiene styrene (ABS) or polycarbonate (PC). It is clear, however, that this list is not exhaustive. The use of a transparent material, glass or plastic, makes it possible to perform visual inspection of the inner components of the cell 110 and to observe electrolysis during normal operations.

In practice, the enclosure 110 has the shape of a cylinder with a circular section that extends along the vertical direction. Its height varies for example from 15 cm to 150 cm or more than 150 cm, and its diameter varies for example from 10 cm to 80 cm, or more than 80 cm. The shapes and dimensions described for the enclosure 110 are given only by way of example, as the latter may have any other shape (for example, parallelepiped or cylinder with an oval section, or other shape) and suitable dimensions, best suited to the use for which the enclosure 110 and the system according to the invention are intended. Furthermore, the enclosure 110 can have any shape generated by a straight line that moves in parallel to an axis, bearing on two fixed planes. Thus, the circular section of a cylindrical enclosure can be truncated to have a planar part 112 over almost its entire height as illustrated in FIG. 5.

As represented in FIGS. 2 and 8 to 12, the electrolysis enclosure 110 of the system according to the invention is provided with a set of electrodes 120, which is to be connected to the energy source 101 producing electrical current. It can be reminded here that the invention is not limited to this embodiment and that two, three or even more sets of electrodes 120 can equip the electrolysis enclosure 110. The number of sets of electrodes 120 to be used can be chosen according to the desired overall performance (for example, production time of the disinfectant solution containing hypochlorous acid). Indeed, the Applicant was able to find that with a system according to the invention comprising a single electrolysis enclosure 110, the more the number of sets of electrodes increases, the more the production time of the disinfectant solution having a given free chlorine content is reduced. This is highlighted in [Table 1] of the examples and which shows the effect of the number of sets of electrodes 120 per electrolyser 100 on the production time of the disinfectant solution according to the present invention.

The set(s) of electrodes 120 each comprise at least one anode and one cathode (not represented). It is reminded here that, according to well-known definitions of those skilled in the art, it should be understood: by “anode” a positive electrode, which will be the seat of the oxidation reaction of equation No. 4 (2Cl⁻_(aq)Cl_2(g)+2e⁻) mentioned above, and by “cathode” a negative electrode, which will be the seat of the reduction reaction of equation No. 5 (2H₂O_(l)+2e⁻H_2(g)+2OH⁻_(aq)) mentioned above.

The electrodes of the (at least one) set of electrodes 120 may be made of titanium, of titanium coated with a catalytic coating containing metal oxides, such as titanium oxide, ruthenium oxide, iridium oxide and tin oxide; of titanium alloy; of Hastelloy® alloy (nickel-chromium-molybdenum alloy) or of any other corrosion-resistant metal or alloy. By way of example, such a catalytic coating may consist of 45 to 55% titanium oxides, 25 to 30% ruthenium oxide and 20 to 20% iridium. The electrodes may have a planar plate type form or other suitable forms best suited to the use for which the (at least) one set of electrodes 120 is intended within the scope of the present invention. Preferably, the electrodes of the (at least) one set of electrodes 120 are in the form of planar plates made with a sufficient thickness (for example, 1 mm to 4 mm) to be rigid. These planar plates can have a width ranging for example from 25 mm to 100 mm and a length sufficient to be able to insert the (at least) one set of electrodes 120 in the diametrical direction into the enclosure 110 and so that the electrodes of the at least one set of electrodes 120 are at least partially disposed inside the enclosure 110. By way of example, for an enclosure of 25 cm in diameter, the planar plates may have a width of less than 25 cm, for example a length of between 15 cm and 24 cm. In particular, the inter-electrode space is between 0.1 cm and 1.2 cm, preferably between 0.1 cm and 0.5 cm. It should be noted that the closer the electrodes are to each other, the greater the contact/exchange area per unit of volume and therefore the less voltage needed. Indeed, as the distance increases, the energy requirement to pass the electrical current (carried by the ions) through the aqueous solution containing chloride ions increases. Increasing the distance increases the electrical resistance and therefore, for an identical amperage, the voltage has to be increased (Ohm's law).

In particular embodiments of the invention, not represented, there are two electrodes of the (at least) one set of electrodes 120, among which one anode and one cathode, which anode and cathode are in the form of planar plates parallel to each other, and are sufficiently spaced apart from one another, for example by 0.1 cm and 1.2 cm, preferably between 0.1 cm and 0.5 cm.

In other particular embodiments of the invention, not represented, a set of electrodes 120 may comprise two or more anodes and two or more cathodes, which anodes and cathodes are in the form of planar plates parallel to each other, and are alternated in the set of electrodes 120 and fairly spaced apart from one another, for example by 0.1 cm and 1.2 cm, preferably between 0.1 cm and 0.5 cm.

Preferably, the (at least) one set of electrodes 120 further comprises one or more bipolar electrodes arranged between an anode and a cathode of the (at least) one set of electrodes 120.

By the term “bipolar electrode”, it is meant, according to the present invention, an electrode being at an intermediate potential between a higher potential electrode and another lower potential electrode, such that said electrode acts simultaneously as an anode on the part facing the lower potential electrode and as a cathode on the part facing the other. In the case of planar electrodes, reactions of the anodic type occur on one face and cathodic type on the other face.

The bipolar electrode(s) may be made of any corrosion-resistant metal or alloy as for the other electrodes of the at least one set of electrodes 120. Furthermore, the bipolar electrode(s) may also have a shape substantially similar or identical to that of the anode and the cathode of the (at least one) set of electrodes 120. Preferably, the anode, the cathode and the bipolar electrode(s) are all in the form of planar, parallel plates evenly spaced from one another, for example from 0.1 cm to 1 cm. The number of bipolar electrodes per set of electrodes 120 may for example range from 1 to 20, in particular from 2 to 18, for example may be equal to 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or 17.

It should be reminded that, per set of electrodes 120, the number of anode(s) may be equal to one or more and the number of cathodes may be equal to one or more.

Bipolar electrodes are well known in the art (JP2004237165A, EP0065889A1, WO2012172118A1).

Preferably, the at least one set of electrodes is of the non-split type (non

In particular embodiments, not represented, the electrolyser 100 or the system according to the invention may also comprise at least one switch or an electrical control circuit usable to periodically reverse, for example every 90 min with a pause time of 5 min, the polarities of the electrodes of the at least one set of electrodes, such that the electric current flows, between the electrodes, in one direction, and then in the opposite direction (bipolar operation). The purpose of polarity reversal of the electrodes is to eliminate or prevent buildup of deposits (for example, calcium deposits) on the electrode surfaces during operation. This leads to improved operation of the electrodes and prolonged lifetime thereof. Upon polarity reversal, a pause time after depolarisation and repolarisation of the electrodes of 5 min is optimal, this makes it possible to avoid the formation of short circuits between the electrodes of the at least one set of electrodes 120. These short circuits can gradually deteriorate these electrodes. Polarity reversal of electrodes and pause time can be controlled for the control unit 600 which will be described in more detail later.

Advantageously, the (at least one) set of electrodes 120 is configured or adapted to be inserted, removably and sealingly, into the electrolysis enclosure 110 through a respective opening 114, provided to this end in a wall of the electrolysis enclosure 110, and so that, in use, the electrodes of said (at least one) set of electrodes 120 are at least partially immersed in the saline aqueous solution to be electrolysed. Holding in position the set(s) of electrodes 120 in the wall of the enclosure 110 can be carried out by any means suitable for those skilled in the art, especially by insertion with twist and lock or by screwing onto the wall through which the (at least one) set of electrodes 120 is inserted. The opening 114 of the wall 112 has, for example, a diameter of about 90 mm.

In particular embodiments (not represented), the (at least one) set of electrodes 120 is in the form of or is disposed in a cylindrical or parallelepipedal housing, insertable into the electrolysis enclosure 110 and having suitable peripheral openings or piercings such that, in operation, the electrodes of the (at least one) set of electrodes are in contact with the aqueous solution to be electrolysed, on the one hand, and the alkali chloride such as sodium chloride, in solid form, cannot become embedded between the electrodes of the (at least one) set of electrodes (120) and cause short circuits in the electrolyser 100, on the other hand.

In a particular embodiment, especially set forth in FIG. 5, the electrolysis enclosure 110 is provided with elongated hollow tubes 121, with a horizontal axis, each disposed in the enclosure 110. Each of these hollow tubes 121 serves as a support element for a set of electrodes 120 and is designed to facilitate the insertion of the set of electrodes 120 into the enclosure 110, on the one hand, and the removal of the set of electrodes 120 from the enclosure 110, on the other hand, for example when it is desired to perform control operations on the electrodes and/or replacement thereof. In practice, the elongated hollow tubes 121 each have peripheral piercings provided so that, in use, the electrodes of the (at least) one set of electrodes 120 inserted into the respective hollow tube 121, are in contact with the saline aqueous solution to be electrolysed. The purpose of such peripheral piercings is also to prevent alkali chloride such as sodium chloride, in solid form, from becoming embedded between the electrodes of the (at least one) set of electrodes (120) and causing short circuits in the electrolyser. The elongated hollow tubes may be made of a material substantially identical or similar to that constituting the enclosure 110. Their peripheral piercings may have a diameter of 10 mm or less.

FIG. 6 shows an elongated hollow tube 121 the end of which that is intended to be fastened into the wall 112 of the enclosure 100, has an external thread 119 provided for fastening by screwing a set of electrodes 120 provided with a counter-thread (not represented). Of course, other fastening means or techniques than those described with reference to FIG. 6 may be provided to ensure the reversible and watertight fastening of a set of electrodes 120 into an elongated hollow tube 121.

With regard to the arrangement of the (at least one) set of electrodes 120 in the electrolysis enclosure 110, reference may be made to patent application WO2012172118A1 in the name of the Applicant.

Generally speaking, referring to FIGS. 2, 3, 8 to 12, the enclosure 110 has a cover 130 thereabove. This is configured or adapted to sealingly close the upper opening 111 of said enclosure 110. This cover 130 is removable so as to allow the alkali chloride in solid form to be loaded into the enclosure 110, on the one hand, and to allow easy access inside the enclosure 110, especially in order to be able to carry out operations for emptying and/or cleaning the enclosure 110, on the other hand. The cover 130 is made of a material substantially similar or identical to that of the enclosure 110, especially PVC, ABS or PC.

The cover 130 can be fastened to the enclosure by screwing. In FIG. 5, the upper part of the enclosure 110 has an external thread 113 provided for fastening by screwing the cover 130 provided with a counter-thread (not represented). Of course, other fastening means or techniques than those described with reference to FIG. 5 may be provided to ensure reversible closure of the enclosure 110. As an example of these other means or techniques, mention may be made of those commonly used in the field of opening and closing systems for pressure cookers.

Furthermore, the cover 130 can be equipped with a suitable seal (not represented), for example of elastomer, for performing or enhancing sealing between the enclosure 110 and the cover 130.

In FIGS. 2 to 5, and 8 to 12, the cover 130 is provided with a duct 200 (called the communication duct). This is to enable fluidic communication between the inside and outside of the electrolysis enclosure 110. The communication duct 200 may be used for filling the electrolysis enclosure 110 with water for dissolving alkali chloride that is already loaded therein in solid form (via the upper opening 111) in order to form the aqueous solution containing chloride ions to be electrolysed. The communication duct 200 also allows the displacement of the hydrogen gas, of at least part of hypochlorous acid and, where appropriate, of the gaseous chlorine generated in the enclosure 110 during the electrolysis reaction from this enclosure 110 to the dilution tank 300 dedicated to the preparation of the disinfectant solution as this will be described in more detail below.

This communication duct 200 is made of a material substantially similar or identical to that of the enclosure 110 or the cover 130, especially PVC, ABS or PC. It preferably has the shape of a cylindrical tube with a circular base. In use, it opens by its lower end into the enclosure 110 through a cover aperture 131 arranged in the removable cover 130. The free upper end of this communication duct 200 is to be connected to the dilution tank 300 as will be described below.

Such a communication duct 200 can be made as one-piece with the cover 130 or be sealingly fixedly added, for example by means of a rubber sealing ring (not illustrated) into this cover 130.

In particular embodiments of the invention (not represented), the electrolysis enclosure may further comprise, at its lower part, an outlet aperture for emptying thereof. This outlet aperture may for example be closed by any suitable plugging means, for example by a plug, a tap or the like.

An example of an electrolyser that can be used with the system according to the present invention is described in patent application WO2012172118A1 in the name of the Applicant, or is marketed by the latter under the trademark name CHLOR′IN (https://www.chlor-in.com/concept-chlor-in-p3.php).

In the appended figures, the duct 200 is a straight and vertical or substantially straight and vertical duct, but it can be contemplated to provide an inclined duct, or a helical-shaped, vertical or inclined duct.

Dilution Tank

The system according to the present invention further includes a dilution tank 300 in which the disinfectant solution will be prepared by dilution of the hypochlorous acid coming from the at least one electrolyser in water provided by the water source S.

The tank 300 is to be placed above the at least one electrolyser 100. The number of electrolysers may be 1, 2, or 3 or more as indicated above. As can be seen in FIGS. 2, 3 and 4, this tank 300 is placed above, respectively, 1, 2 and 3 electrolysers 100. The number of electrolysers 100 is chosen according to the desired overall performance (for example, production time of the disinfectant solution containing hypochlorous acid, desired hypochlorous acid content for the disinfectant solution). Indeed, the Applicant has been able to find that for a dilution tank 300 of a given volume of water, the more electrolysers there are, the more the disinfectant solution is obtained with a given concentration of hypochlorous acid in a shorter time. This is highlighted in [Table 1] of the examples set forth before, and which shows the effect of the number of electrolysers 120 on the production time of the disinfectant solution according to the present invention.

The tank 300 according to the invention has, at its upper part, a water inlet 302 and, at its bottom 305, at least one bottom outlet (or aperture) 303 (one bottom outlet per electrolyser).

The water inlet 302 is dedicated to the input of water into the dilution tank 300. It is to be connected to a water supply source “S” such as for example a tap or a municipal water pipe, or other.

In practice, water to be added to the dilution tank 300 is tap water, but it is obviously possible to use natural source water, distilled water, or deionised or filtered water.

Therefore, in a particular embodiment (not represented), the system according to the present invention may further comprise a water filter arranged between the water supply source S and the water inlet 302 of the dilution tank 300. The purpose of this water filter is to remove, or at least reduce, any organic compounds (or organic pollutants) that may be present and that could interact with chlorine, among other electrolysis products of sodium chloride-saturated water. The water filter may be of any type known to those skilled in the art, such as for example a particle filter (cartridge filter, microfiltration membrane, sand); an activated carbon filter; an ultrafiltration membrane; a membrane switch or a gaseous filtration membrane.

The bottom outlet 303 of the dilution tank 300 is configured or adapted to connect to the communication duct 200 of the electrolyser 100 in order to allow fluidic communication between this dilution tank 300 and the inside of the electrolysis enclosure 110 of this electrolyser 100.

The bottom outlet 303 may be connected to the communication duct 200 of the electrolyser 100, for example, by any type of suitable sealed quick coupling known to those skilled in the art (see, for example, U.S. Pat. No. 5,580,099A; US20190063652A1; EP0829671A2, US20180252347A1).

By “bottom outlet 303”, it is meant a bottom aperture of the tank 300 or a suitable bottom duct inserted into said bottom aperture of the tank 300, which bottom duct can be added and mounted to the dilution tank 300 so as to be able to be permanently, or dismountably, fastened thereto.

The dilution tank 300 may have any shape (for example, parallelepipedal or cylindrical with an oval section, or other shape) and suitable dimensions, best suited to the use for which the enclosure 110 and the system according to the invention are intended. In practice, the tank 300 has the shape of a square or rectangular parallelepiped. The volume of the dilution tank 300 may range from 1 litre to 500 litres or more. Of course, the invention is not limited to these shapes or dimensions for the dilution tank 300.

In practice, the dilution tank 300 is made of a material substantially similar or identical to that of the enclosure 110, especially PVC, ABS or PC. It is preferably protected from ambient light, for example by an auxiliary device for protection against ambient light (not represented). This auxiliary device may take the form of a box or cabinet with walls made of opaque material, for example, but not limited to, wood, opaque plastic (for example, PVC, HDPE), opaque glass, metal (for example, stainless steel).

In particular embodiments of the invention (not represented), the dilution tank 300 may further comprise, at its lower part, an outlet aperture for dispensing the disinfectant solution or emptying the tank 300. This outlet aperture can be closed, for example, by means of a tap or connected by means of connection means (for example, pipe) to a storage tank capable of receiving the disinfectant solution or to a flexible hose for dispensing the latter.

In particular embodiments of the invention (not represented), the dilution tank 300 may further comprise means for breaking the gaseous chlorine bubbles that may come from the electrolysis enclosure 110 of the at least one electrolyser 100 in order to promote dissolution of gaseous chlorine in water, said means for breaking said gaseous chlorine bubbles being arranged at the bottom of the dilution tank 300 at least facing the duct 200 fluidically communicating said electrolysis enclosure and the dilution tank 300. The means for breaking the gas bubbles may consist of at least one planar plate having perforations the diameter of which is sufficient to reduce the size of the gas bubbles to dimensions promoting dissolution of chlorine in water. Preferably, the perforations of the at least one plate have a diameter of less than 5 mm, preferably less than 1 mm. Preferably, the means for breaking the gas bubbles consist of several planar perforated plates. These plates are generally superimposed such that the perforations of one plate are offset from the perforations of another plate adjacent to it.

In an alternative, not represented, the means for breaking the gas bubbles consist of a strainer of stainless metal or plastic (for example, PVC) and with meshes the size of which is less than 5 mm, preferably less than 1 mm.

USE of the system according to the invention.

The system according to the present invention can be assembled in the manner described below, which can be easily deduced from the previous explanations in relation especially to FIG. 1, and without this description of the assembly or use of the system according to the invention having to be interpreted in a limiting sense.

Step 1: it starts with the electrolysis enclosure 110, which in practice is already provided with the (at least) one set of electrodes 120. The electrolysis enclosure is loaded with alkali chloride such as sodium chloride in solid form. It may be indicated that the amount of alkali chloride such as sodium chloride to be loaded into the electrolysis enclosure has to be sufficient to prepare an aqueous solution in which part of the alkali chloride such as sodium chloride is dissolved, for example a brine or an aqueous solution saturated with this alkali chloride. It is reminded here that in the case of sodium chloride, it has a solubility of about 357 g per litre of water at 0° C. In a particular example, about 25 kg of sodium chloride in the form of tablets of about 15 g are loaded into an electrolysis enclosure with a capacity of about 40 litres. It can also be indicated that sodium chloride in the form of tablets of about 15 g is available under the brand name AXAL® PRO from K+S Minerals and Agriculture GmbH, located in Germany. As an alternative to the particular example described herein, potassium chloride or a mixture of sodium chloride and potassium chloride may be used to prepare the aqueous solution to be electrolysed.

Step 2: the electrolysis enclosure 110 is then closed by its removable cover 130.

Step 3: the electrolysis enclosure 110 loaded with alkali chloride such as sodium chloride is placed, and closed by its cover 130, under the dilution tank 300. In relation to the aforementioned particular example, a dilution tank of 260 litres is chosen for at least one electrolysis enclosure the capacity of which is about 40 litres.

Step 4: the duct 200 of the electrolyser 100 is connected to the corresponding bottom outlet 303 of the dilution tank 300. The connection may be made by any suitable sealed quick coupling means known to those skilled in the art, as mentioned above. Now, the dilution tank 300 and the electrolysis enclosure 110 of the electrolyser 100 are in fluidic communication with each other.

Step 5: the dilution tank 300 is connected to the water supply source S, where appropriate, via a suitable water filter as mentioned above.

Step 6: water is input into the dilution tank 300 until the latter and also the electrolysis enclosure 110 are filled, the latter being filled with water via the bottom outlet 303 of the dilution tank 300 and the duct 200 of the electrolysis enclosure 110 to which this bottom outlet 303 is connected. Mention may be made here of the advantage of using alkali chloride, such as sodium chloride, in solid form which is that, when filling the electrolysis enclosure 110, the alkali chloride salt remains at the bottom of the latter.

Step 7: sufficient time is waited for to enable formation of chloride ions in water, by dissolving at least part of the alkali chloride, such as sodium chloride. In practice, this waiting time is about 5 min to 1 h.

Step 8: Once the complete system is mounted, the at least one electrolyser is supplied with electricity by the energy source 101 in order to start electrolysis itself.

In practice, the electrical current supplying the electrodes of the at least one set of electrodes 120 (or electrodes of the at least one electrolyser 100) is direct current. Alternatively, electrolysis according to the invention can be conducted with pulsed current.

Electrolysis in the electrolysis enclosure 110 is generally conducted at a pH of about 6-8, under a voltage of between 1V to 15 V, preferably between 2 and 10 V.

The direct (and/or pulsed) current used may have a current density of between 0.1 A/dm² and 10 A/dm², or even above 10 A/dm². Preferably, electrolysis is conducted with direct (and/or pulsed) current having a current density between 0.1 A/dm² and 5 A/dm².

After an electrolysis period sufficient to obtain a disinfectant solution containing hypochlorous acid with the desired free chlorine content, electrolysis is interrupted (the latter point will be discussed in more detail later).

During electrolysis, at least part of the chloride ions present in the aqueous solution contained in the electrolysis enclosure is oxidised at the at least one anode of the electrolyser to generate chlorine (Cl_2(g)) following the reaction of equation 4 mentioned above. Chlorine thus generated instantly reacts with water present in the aqueous solution to produce hypochlorous acid (HOCl_(aq)) and hydrochloric acid (HCl_(aq)) following the reversible reaction of equation 2 mentioned above. In parallel to the oxidation reaction of the chloride ions, there is a reduction of water, at the at least one cathode of the electrolyser, into gaseous hydrogen (H_2(g) and hydroxide ions (OH⁻) following the reaction of equation 5 mentioned above. Thus, basically, electrolysis of the aqueous solution containing alkali chloride such as sodium chloride, at a pH of 6 to 8 (pH of the tap water), leads to the formation of chlorine products (gaseous chlorine, hypochlorous acid and/or hypochlorite ions) and gaseous hydrogen, within the electrolysis enclosure 110. But, this is in fluid communication with the dilution tank 300, which is filled with water.

The hydrogen gas, and where appropriate, part of the chlorine gas, generated in the electrolysis enclosure 110 therefore follows the duct 220 of the latter, then the bottom outlet 303 of the dilution tank 300 and then passes through the dilution tank 300 containing water to be discharged into the atmosphere.

On the other hand, water contained in the dilution tank 300 and the aqueous solution contained in the electrolysis enclosure 110 together form a system that has an automatic tendency to make the concentrations of the chemical species (In this case: water, hypochlorous acid and/or hypochlorite ions and chloride ions) composing it, homogeneous. This phenomenon of “irreversible” displacement of chemical species that tends to homogenise the composition of the system corresponds to what is called chemical “diffusion” in chemistry-physics.

Thus, in this case, the hypochlorous acid and/or hypochlorite ions as well as the chloride ions therefore tend to move (or migrate) from the aqueous solution from the electrolysis enclosure 110 to the dilution tank 300 and, conversely, water tends to move (or migrate) from the dilution tank 300 to the electrolysis enclosure 110.

It should be noted that chemical diffusion is a phenomenon which, in principle, occurs very slowly if no agitation accelerates it.

But, it is to the credit of the author of the present invention to have found that, despite this highly unfavourable prejudice, it is possible to produce a disinfectant solution the free chlorine content (hypochlorous acid and/or hypochlorite ions) of which can reach 1000 ppm or even more than 1000 ppm in acceptable times, in industrial practice, for example less than 12 h, by disposing the dilution tank 300 above the electrolysis enclosure 110, connecting them fluidically, and using the movement of bubbles of hydrogen gas and, where appropriate, chlorine gas, generated in the aqueous solution of the electrolysis enclosure 110. Indeed, this movement of gas bubbles generates tiny vortices that promote displacement or diffusion of at least some of the molecules of hypochlorous acid and/or hypochlorite ions (or chlorine product) of the concentrated medium which is represented in this case by the aqueous solution contained in the electrolysis enclosure 110 towards the least concentrated medium which is represented in this case by water of the dilution tank 300.

Furthermore, it is possible to adjust electrolysis so as to generate the formation of gas bubbles, especially hydrogen gas, such that these bubbles create turbulences capable of forcing migration of the at least part of the hypochlorous acid from the electrolysis enclosure 110 to the dilution tank 301. For this, the author of the present invention has shown that increasing the number of electrodes per set of electrodes 120 and/or the number of sets of electrodes per electrolyser makes it possible to promote generation of such gas bubbles and to reduce the production time of a disinfectant solution containing hypochlorous acid to a given or desired free chlorine content.

Furthermore, the author of the present invention has surprisingly and unexpectedly found that the disinfectant solutions obtained by virtue of the system according to the present invention may possibly contain alkali chloride such as sodium chloride, but in very low contents, less than 1 ppm, which is very advantageous in a method or system for producing disinfectant solutions.

Back to the notion of “sufficient electrolysis period” mentioned above. In fact, the present invention leaves the choice to the user of the system for producing the disinfectant solution comprising the hypochlorous acid to determine himself/herself the free chlorine content that is best suited to the disinfection operation that he/she intends to perform, for example disinfection of air, disinfection of hard or soft surfaces, disinfection of medical devices, disinfection of skin, disinfection of skin cuts, disinfection of plants (for example, salads, fruits, vegetables, vines, plants), disinfection of animal farm buildings, etc.

Therefore, to obtain the disinfectant solution with a given free chlorine content that is suitable for the desired use thereof, the user can monitor, during the production process, the free chlorine content of water contained in the dilution tank 300. In addition, when the free chlorine content value is as desired, the user can interrupt electrolysis in the electrolyser(s).

“Free chlorine” refers to hypochlorous acid (HOCl) and hypochlorite ions (OCl⁻).

To monitor the change over time in the production of the disinfectant solution containing the hypochlorous acid, the user may collect samples of disinfectant solution being formed in the dilution tank 300 and analyse these samples to determine their free chlorine content. Sample collection and analysis can be carried out on an ad hoc basis or in-line, preferably in-line.

Ad hoc determination of the free chlorine content of the disinfectant solution can be carried out according to conventional analysis methods known to the person skilled in the art: colorimetric assay, acid-base titration, amperometric assay, spectrophotometric analysis (see for example, WO2013121294A1), oxidation-reduction potential (ORP) assay.

Preferably, as illustrated in FIGS. 8 to 12, the system according to the present invention further comprises a measurement device 400 including:

• • a sensor 411 adapted to measure the free chlorine content in the disinfectant solution being formed in the dilution tank 300,
  • a display 412 adapted to display the free chlorine content measured by the sensor 411.

The threshold value of the free chlorine content corresponds to a maximum chosen value, that the free chlorine content of the disinfectant solution being formed in the dilution tank 300 should not exceed. It is set by the user, for example, to a value greater than or equal to 5 ppm. It is generally chosen in a range between 5 ppm and 3000 ppm, in particular between 10 ppm and 1500 ppm. It should be reminded that the system according to the present invention could be adjusted, if necessary, for example so as to obtain a hypochlorous acid-concentrated disinfectant solution with a free chlorine content equal to or greater than 3000 ppm, in particular a free chlorine content equal to or less than 10000 ppm

The measurement device 400 with its sensor 411 and its display 412 may be of a known type and commercially available. It may be connected to a measurement tapping located below the level of the disinfectant solution present in the dilution tank as illustrated in FIG. 8, or in practice, be placed on a recirculation loop 450, as represented in FIGS. 9 to 12.

By virtue of its sensor 411, the measurement device 400 allows continuous measurement of the free chlorine content of the disinfectant solution present in the dilution tank, thus having real-time monitoring of the production of this disinfectant solution. Continuous display of the free chlorine content measured by the sensor 411 allows the user to monitor, in real time, the production of the disinfectant solution containing the hypochlorous acid and to decide to interrupt electrolysis at any time when he/she considers that the disinfectant solution has a sufficiently high free chlorine content for the intended use thereof.

In order to automate monitoring of the production of the disinfectant solution, the system according to the present invention may further comprise a control unit, designated by reference 600 in FIGS. 9 to 12. This control unit 600 is operatively connected to the measurement device 400 and is adapted to compare the free chlorine content measured by the sensor 411 and a threshold value of the free chlorine content and to interrupt electrolysis when the free chlorine content measured by the sensor 411 is equal to or greater than the threshold value of the free chlorine content.

The threshold value of the free chlorine content corresponds to a maximum chosen value, that the free chlorine content of the disinfectant solution being formed in the dilution tank 300 should not exceed. This threshold (or maximum) value may be selected in a range of free chlorine content greater than or equal to 5 ppm, in particular in a range ranging from 5 ppm to 3000 ppm, for example, a range from 10 ppm to 1500 ppm.

Furthermore, the disinfectant solution being formed in the dilution tank 300 generally has a pH greater than 3 and less than 8, in particular from 4 to 7.5. It is preferably maintained or regulated in a pH range of 5 to 7, preferably at a pH of about 5.1 to about 6.9, in particular at a pH of about 6.5.

It should be noted that in the various applications (for example, disinfection of air, plant, animal or human surfaces, medical devices, etc.) for which the disinfectant solution produced by the system according to the present invention is suitable, a pH of 5.1 to 6.9, in particular, a pH of about 6.5 may be considered optimal.

Therefore, preferably, the system according to the present invention further includes a pH probe 413 for measuring or determining the pH of the disinfectant solution present in the dilution tank 300. This pH probe may be of a known type and commercially available. It may be connected to a measurement tapping located below the level of the disinfectant solution present in the dilution tank 300 as illustrated in FIG. 8, or in practice, be placed on a recirculation loop 450 (represented in FIGS. 9 to 12). Alternatively, not represented, the pH probe may be disposed immersed into the dilution tank 300 (for example, use of a digital pH meter with a remote probe, available under Ref. 2201LM from MOINEAU Instruments, France).

In practice, the pH probe 413 is included in the measurement device 400 comprising the sensor 411, which measurement device 400 can further be configured to display, by virtue of the display 412, the value of the pH measured by the pH probe 413 in addition to the value of the free chlorine content measured by the sensor 411.

The system according to the present invention may further comprise a pH regulation device (not represented) connected to receive a signal from the pH probe 413 and being adapted to inject a pH adjusting agent into the dilution tank in response to the signal from the pH probe 413.

By “pH-correcting agent”, it is meant any acidic aqueous solution or any basic aqueous solution which does not alter the chemico-physical characteristics of the hypochlorous acid. Preferably, the pH adjusting agent is in the form of an aqueous solution containing an acid, preferably chosen from inorganic acids such as boric acid, hydrochloric acid, phosphoric acid and sulfuric acid and/or organic acids such as acetic acid, citric acid, ascorbic acid and propionic acid.

Typically, the pH regulation device also comprises a dosing pump capable of injecting, into the disinfectant solution, a dose of the pH adjusting agent.

The pH regulation device (dosing pump connected to the pH adjusting agent tank) may be of a known type and commercially available. Its dosing pump may be connected to the dilution tank 300 (embodiment not represented) or be arranged at any location of a recirculation loop, such as the loop 450 represented in FIGS. 9 to 12.

In practice, the pH probe 413 measures the pH value of the disinfectant solution present in the dilution tank, continuously or periodically, for example every 10 minutes. If the pH value measured by the probe 413 is higher, respectively lower, than a setpoint value, generally set in a pH range of 5 to 7, preferably, a pH range of about 5.1 to about 6.9, in particular at a pH of about 6.5, the dosing pump of the pH regulation device injects a dose of pH adjusting agent so as to decrease, respectively increase the pH of the disinfectant solution until a pH equal to the setpoint value is obtained.

The pH regulation device is generally disposed in proximity to the pH probe 413 which may be included in the measurement device 400 as discussed above.

Measurement and regulation of the pH of the disinfectant solution can be automated as for measurement of the free chlorine content, and this by using the control unit 600 set forth above.

In practice, as represented in FIGS. 10 to 12, the water inlet 302 of the dilution tank 300 is connected to the water source S by a water feed circuit 420 including, in the direction of the dilution tank 300, a valve, preferably a solenoid valve 440 or 441, and a pump 430.

In order to homogenise the disinfectant solution in the dilution tank 300 and performing measurements in particular of pH and the free chlorine content of the disinfectant solution, the system according to the present invention may further comprise an outer recirculation loop, designated by reference 450 in FIG. 10.

This recirculation loop 450 can be formed by a line for collecting at least part of the disinfectant solution, designated by reference 410 in FIGS. 10 to 11, and part of the water feed circuit 420, the collection line 410 being connected, on the one hand, to a collection outlet 307 provided on the dilution tank 300 and, on the other hand, to a tapping, designated by reference 421, located on the water feed circuit 420 between the solenoid valve 440 and the pump 430. This is provided for pumping and circulating at least part (or a fraction) of the disinfectant solution into the circulation loop 450, from the collection outlet 307 to the water inlet 302 of the dilution tank 300.

According to a possible alternative, represented in FIG. 11, the two-way solenoid valve 440 is replaced by a three-way solenoid valve 441 a first way 441a of which is connected to the water source S, a second way 441b of which is connected to the inlet of the pump 430 and a third way 441c of which is connected to the collection line 410, the third way 441c replacing the tapping 421 used in the previous embodiment. Closing the first way 441a and opening the second and third ways 441b and 441c of the solenoid valve 441 makes it possible to form a recirculation loop 450′ equivalent to the recirculation loop 450 previously set forth.

In practice, as represented in FIGS. 10 to 12, the collection outlet 307 is provided in the lower part, on a wall or on the base, of the dilution tank 300 and the water inlet 302 is provided in the upper part of the dilution tank 300. Of course, this configuration can be reversed. The collection outlet 307 is then disposed in the upper part of the dilution tank 300 and the water inlet 302 in the lower part of the dilution tank.

As discussed above, the measurement sensors or probes (pH and free chlorine level), and the means for regulating the pH of the disinfectant solution can be arranged at such a recirculation loop 450 or 450′. This allows the user to have real-time information about the parameters of the disinfectant solution and thus optimally monitor the production of the disinfectant solution at the concentration wanted by the user.

Preferably, the solenoid valve 440 or 441 and the pump 430 are controlled by the control unit 600.

Preferably, the dilution tank 300 is fitted with disinfectant solution level detectors for the purpose of optimising the operation of the recirculation loop 450 or 450′ and the system of the present invention.

In particular embodiments, represented in FIGS. 10 to 11, three level detectors are placed in the dilution tank 300, namely a low level detector N₁, a high level detector N₂ and an intermediate level detector N₃ located between the low level detectors N₁ and high level detectors N₂.

In another embodiment, represented in FIG. 12, the dilution tank 300 is equipped with a tubular gauge 310 which is placed on the external wall (or one of the walls) of the dilution tank 300 being arranged vertically in parallel to the latter. As can be seen in this FIG. 12, the tube 310 has a lower end 311 fluidically connected to an opening 306 in the lower part of the dilution tank 300 and an upper end 312 fluidically connected to an opening 308 in the upper part of the dilution tank. Furthermore, a low level detector N₁′ is placed at the opening 306 of the dilution tank 300 (or at the lower end 311), a high level detector N₂′ is placed at the opening 308 of the dilution tank 300 (or at the upper end 312), and an intermediate level detector N₃′ located between the low level detectors N₁′ and high level detectors N₂′.

The different level detectors N₁, N₂ and N₃ (or N₁′, N₂′, and N₃′) are to be connected to the control unit 600 which can be configured to control, for example:

• • filling the dilution tank 300 with water in response to a low level signal from the low level detector N₁ (or N₁′),
  • interrupting filling the dilution tank 300 with water, and then circulating the disinfectant solution in the circulation loop 450 (or 450′) in response to a high level signal from the high level detector N₂ (or N₂′), or
  • switching on the measurement device 400 to start measuring the free chlorine content of the contents of the dilution tank 300, in response to an intermediate level signal from the intermediate level detector N₃ (or Ns′).

In practice, for filling the dilution tank 300 with water, the low level detector N₁ (or N₁′) detects that the water or disinfectant solution level in the dilution tank 300 is equal to or less than a predetermined minimum level, it outputs a low level signal that the control unit 600 receives. The latter then controls the solenoid valve 440 (or 441) to open the water feed circuit 420 to allow the water supply of the dilution tank 300. In the particular case of the solenoid valve 441, the control unit 600 will control it to open the ways 441a and 441b and close the way 441c.

Regarding interruption of filling and circulation of disinfectant solution in the circulation loop, when the high level detector N₂ (or N₂′) detects that the water or disinfectant solution level in the dilution tank is equal to or higher than a predetermined maximum level, it sends a high level signal to the control unit 600. The latter then controls the solenoid valve 440 to close (or the solenoid valve 441 to close its way 441a and open its ways 441b and 441c) and the pump 430 to start sucking a part of the disinfectant solution out of the dilution tank 300 so that this part of disinfectant solution circulates in the recirculation loop 450 (or 450′) in the direction of the water inlet 302 of the dilution tank 300.

The system according to the present invention may comprise forced operation and automatic operation.

With reference to FIGS. 10 to 12, the control unit 600 can comprise a user interface 601, of the type including buttons, for example for selecting the forced operation or automatic operation, for adjusting the threshold values in particular of the pH and the free chlorine content, for managing the production of the disinfectant solution (use of one or more electrolysers and/or sets of electrodes). The user interface 601 can also make it possible to control, via the control unit 600, various elements of the system according to the present invention, for example,

• • Switching on or off the energy source 101 supplying electrical current to the set(s) of electrodes 120 of the at least one electrolyser 100, and/or
  • Switching on or off at least one electrolyser 100, and/or
  • Switching on or off the measurement device 400, and/or
  • Opening or closing the solenoid valve 440, and/or
  • Switching on or off the pump 430, and/or
  • Switching on or off the pH regulation device, and/or
  • Reversing the polarity of the electrodes of the set(s) of electrodes 120 and, where appropriate, the pause time between each polarity reversal.

The user interface 601 can still allow the user to sequentially inquire about the operating state of the system, about the production of the disinfectant solution containing the hypochlorous acid, and in particular about the pH value measured by the pH probe 413, about the value of the free chlorine level measured by the sensor 411, or about the operating times of the electrolyser(s) 100 recorded by the control unit 600 over time.

During forced operation, the control unit 600 only controls interruption of electrical current supply to the electrolyser(s) 100 when the free chlorine content desired for the disinfectant solution is reached or exceeded.

During automatic operation, the control unit 600 manages the production of the disinfectant solution containing the hypochlorous acid, for example, by allowing or prohibiting electrical current supply to one or more electrolysers 100, when there are several thereof, and/or electrical current supply to one or more electrodes 120, when there are several thereof, by the electrolyser 100.

The control unit 600 can continuously monitor the production of the disinfectant solution in the dilution tank and control switch off of the electrolyser(s) 100, when there are several thereof, by cutting electrical current supply to the corresponding set(s) of electrodes, in the case where the free chlorine content measured by the sensor 411 exceeds the value of the pre-recorded threshold.

The control unit 600 can continuously monitor the production of the disinfectant solution in the dilution tank and control switch off of the electrolyser(s) 100, when there are several thereof, by cutting electrical power supply to the corresponding set(s) of electrodes, in the case where the pH probe has measured a pH outside the pH threshold range previously recorded and where the control unit 600 has detected an anomaly in the operation of the pH regulation device, for example the latter is no longer able or available to inject the pH adjustment agent to bring the pH back into the desired pH range.

In particular embodiments, not represented, the system according to the present invention may further comprise a system for remotely transmitting information 603 and/or a system for storing all the information of the system according to the invention:

• • the production percentage,
  • the pH value measured of the disinfectant solution,
  • the value measured of the free chlorine content of the disinfectant solution,
  • the values of the thresholds set, especially for pH and free chlorine content,
  • the operating time of the system according to the present invention, to determine when to change the at least one set of electrodes 120,
  • the polarity reversal period of the at least one set of electrodes 120,
  • the occurrence of each power cut,
  • automatic operation or forced operation,
  • triggering diagnostics.

This information can be recorded at least three times a day over 30 days repeatedly. However, it may be preferable to retain the information on the diagnosis of the system according to the invention, the occurrence of power cuts.

The control unit 600 is preferably provided with a screen 602 of the Liquid Crystal Display 82 or LCD type, communicating information on the operation of the system according to the invention to the user.

For further information regarding the control unit 600 (its characteristics and uses), it may be useful to refer to patent application WO2012172118A1 in the name of the applicant.

In short, the system according to the present invention can operate in manual and/or semi-automatic and/or automatic mode, to monitor the production of disinfectant solutions containing hypochlorous acid at free chlorine contents desired by the user.

Therefore, the present invention also relates to a method for producing the disinfectant solution. This method according to the invention includes:

• • a step a) in which a system according to the present invention is provided;
  • a step b) in which the dilution tank 300 and the electrolysis enclosure 110 are filled with water in accordance with the present invention;
  • a step c) in which electrical current is applied to the electrodes of the at least one set of electrodes 120 of the at least one electrolyser 100 to electrolyse the aqueous solution containing chloride ions in the enclosure 110 in order to produce hypochlorous acid, and in which at least part of the hypochlorous acid migrates from said enclosure 110 to said dilution tank 300 through the duct 200, the at least part of hypochlorous acid having migrated diluting in water present in said dilution tank 300 in order to form the disinfectant solution;
  • a step d) in which the free chlorine content of the disinfectant solution being formed in the dilution tank 300 is measured;
  • a step e) in which electrolysis is interrupted when the free chlorine content measured in step d) reaches a desired free chlorine content value for the disinfectant solution.

By desired free chlorine content value, it should be understood the free chlorine content value wanted or selected by the user and that he/she considers it to be sufficiently high for the desired use of the disinfectant solution containing the hypochlorous acid.

The method according to the present invention may further include a step f) in which the free chlorine content is measured by the sensor 411 capable of measuring the free chlorine content of the disinfectant solution being formed in said dilution tank.

The method according to the present invention may further include a step g) in which interrupting electrolysis provided in step e) is handled by the control unit 600 adapted to compare the free chlorine content measured by the sensor 411 in step f) and a threshold value of the free chlorine content and to interrupt electrolysis when the free chlorine content measured by the sensor 411 is equal to or greater than the threshold value of the free chlorine content. Preferably, this threshold value of the free chlorine content is set to a maximum value selected in a range of 5 ppm to 3000 ppm, in particular in a range of 10 ppm to 1500 ppm.

The method according to the present invention may further include a step h) in which at least one intrinsic parameter of the disinfectant solution being formed in the dilution tank 300 is measured, which intrinsic parameter can be chosen from the list of parameters comprising pH, temperature, conductivity, and hardness.

The method according to the present invention may further include a step g) in which the pH of the disinfectant solution being formed in the dilution tank 300 is regulated.

Preferably, in step c), the current voltage applied to the electrodes is between 1 and 15 volts, preferably between 2 and 10 volts.

Advantageously, the disinfectant solution containing the hypochlorous acid has a pH of about 5.1 to about 6.9, preferably a pH of about 6.5. These pH ranges are optimal for the applications for which the disinfectant solutions produced according to the present invention are intended.

The various elements (dilution tank, electrolyser(s), communication duct, piping, wiring, measurement means (pH, free chlorine content) and regulation means, control unit, etc.) of the system according to the present invention may be arranged into a compact assembly of low overall size, which is transportable and ready to be installed and used for the production of hypochlorous acid-based disinfectant solution.

In practice, the entire system according to the present invention is carried by a vertical support structure able to support at least the dilution tank 300 and the at least one electrolyser 100 (and its electrolysis enclosure 110) and ensuring the rigidity thereof. This vertical support structure can, for example, be of the type including a frame delimiting a space dedicated to the production of the disinfectant solution according to the invention and in which are disposed:

• • a first compartment mounted to the frame and in which the at least one electrolyser 100, and, where appropriate, the circulation pump 430, can be disposed;
  • a second compartment disposed above the first compartment and in which the dilution tank 300 can be placed, this second compartment having, in its lower part, at least one lower opening, in order to be able to place, through this at least one lower opening, the respective communication duct 200 of the at least one electrolyser,
  • the external walls of the first compartment PC1 and/or of the second compartment PC2 serving as a support for the other elements of the system according to the present invention such as the power supply source 101, the water feed pipe, the electrical cable(s), and where appropriate, the control unit 600, the solenoid valve 440 (or 441), and other components/elements considered to fall within the scope of the present invention.

Of course, the invention is not limited to this form for mounting the system of the present invention. In particular, it may be provided a form of frame comprising two opposite parallel side walls (or two pairs of opposite side posts), an upper horizontal plate provided to support the tank 300, and a lower horizontal plate (or base or pedestal) provided to support the at least one electrolyser 100 and, where applicable, the pump 430, the upper and lower plates being fixedly connected to the opposite side walls (or to the pairs of opposite side posts) and the upper plate having at least one lower opening, for placing the respective communication duct 200 of the at least one electrolyser.

An example system according to the present invention assembled in the form of a compact assembly is shown in the photograph of FIG. 4.

Furthermore, one or more characteristic(s) set out only in one embodiment can be combined with one or more other characteristic(s) set out only in another embodiment. Similarly, one or more characteristic(s) set out only in one embodiment can be extended to the other embodiments, even though this or these characteristic(s) are described only in combination with other characteristics:

• • The electrolysis enclosure 110 or its cover 130 may be provided with a pressure gauge to monitor the pressure in this electrolysis enclosure 110,
  • The dilution tank 300 may be fitted with a cover or a ceiling having an opening for discharging gases (gaseous hydrogen and, where applicable, chlorine),
  • The electrodes of the at least one set of electrodes 120 may be solid or perforated,
  • The electrolysis enclosure(s) 100 may be mounted to a pedestal or base,
  • The support structure provided to support the system according to the present invention may be equipped with rolling means such as castors in order to facilitate the movement of said entire system.

EXAMPLES

Various tests for the production of a disinfectant solution containing hypochlorous acid with a free chlorine content of 250 ppm have been carried out under the following operating conditions:

• • Dilution tank 300=260 litres,
  • electrolysis enclosure=40 litres,
  • Set(s) of electrodes=per set of electrodes, 7 planar plates disposed in parallel rows of alternating polarity. The plates are 210 mm long and 55 mm wide and are of titanium, coated with titanium oxide, ruthenium oxide and iridium oxide,
  • Ambient temperature (about 25° C.),
  • The disinfectant solution has been maintained at pH=6.5,
  • Voltage applied=between 4 and 6 volts,
  • Amperage=between 15 and 30 amps.

	TABLE 1
	Number of	Number of set of	Production time (in
	electrolysers	electrodes	hours)

Test 1	1	1	7 to 9
Test 2	2	1	5 to 7
Test 3	3	1	3 to 5
Test 4	1	2	5 to 7
Test 5	2	2	3 to 4
Test 6	3	2	2 to 3

It appears from this table that for the production of a disinfectant solution containing hypochlorous acid at a given free chlorine content, the more the number of electrolysers and/or sets of electrodes increases, the shorter the production time of said disinfectant solution is.

The invention is not limited to the only embodiments described. Furthermore, in the claims, any reference sign between brackets should not be interpreted as a limitation of the claim. Besides, the use of the verb “to have”, “to comprise” or “to include” and of their conjugated forms does not exclude the presence of elements or steps other than those stated in a claim. Of course, one or more characteristic(s) set out only in one embodiment can be combined with one or more other characteristic(s) set out only in another embodiment. Furthermore, one or more characteristics and/or steps set out only in one embodiment can be extended to other embodiments.