Manufacturing method of nanobubble solution

Abstract

To provide a manufacturing method of nanobubble solution that exists in a solution for an extended period and keeps applying active effects and functions such as bactericidal effect to creatures in the solution.SOLUTION: A method includes the steps of: generating fine bubbles including a gas in a solution of water or a polar solvent; controlling a hydrogen ion concentration and a redox potential of the solution; applying physical stimulation to the fine bubbles so as to quickly shrink the fine bubbles and generate nanobubbles; and transmitting the solution containing the fine bubbles and the nanobubbles by using a reverse osmosis membrane. The hydrogen ion concentration is 5.5-10.0 and the redox potential is -900 mV to +900 mV.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for producing a nanobubble solution that has potential usefulness in all technical fields, and in particular, imparts special functions to water, thereby making the usefulness apparent. [Background technology]

[0002] Bubbles with a diameter of 50 μm or less (microbubbles, also called microbubbles) are known to have different properties from normal bubbles, and are used in a variety of fields. In recent years, bubbles with a diameter even smaller than microbubbles (bubbles with a diameter of less than 1 μm, hereafter referred to as nanobubbles (also called ultrafine bubbles, but will be referred to as "nanobubbles" in this application)) are said to have excellent effects from an engineering perspective, and have been attracting attention.

[0003] However, it was not until around the beginning of the 2000s that a method for artificially generating nanobubbles was established. Until then, nanobubbles only existed momentarily when tiny air bubbles naturally disappeared or were crushed. In addition, there was technology to stabilize nanobubbles at a diameter of about 1 μm or less by using surfactants or organic matter. However, because these were enclosed in a strong shell of surfactants or organic matter, they were isolated from the surrounding water and did not have the same functions as nanobubbles, such as an activating effect on living organisms or a bactericidal effect.

[0004] Here, the inventors of the present application have disclosed a method for artificially generating nanobubbles and stabilizing the generated nanobubbles in, for example, Japanese Patent No. 4144669 (Patent Document 1). The method described in Patent Document 1 involves first generating minute air bubbles (microbubbles) with a diameter of 10 to 50 μm in an aqueous solution containing electrolyte ions of iron, manganese, calcium, sodium, magnesium, and minerals, and prepared so that the electrical conductivity is 300 μS / cm or more, and then applying a physical stimulus (ultrasonic irradiation, discharge, high-frequency irradiation, flowing (circulating) the aqueous solution containing the microbubbles in a container and passing it through an orifice or a porous plate (punching plate) having a single or multiple holes) to the microbubbles to crush them, thereby producing nanobubbles with a diameter of 50 to 500 nm, and further stabilizing the shape of the nanobubbles for one month due to the influence of the electrolyte ions.

[0005] Furthermore, based on the knowledge of the invention according to Patent Document 1, the inventors of the present application have disclosed a method for producing an aqueous solution of nanobubbles in which gas is contained within the nanobubbles, such as oxygen nanobubble water (Patent Publication No. 4080440, hereinafter referred to as "Patent Document 2"), nitrogen nanobubble water (Patent Publication No. 4921332, hereinafter referred to as "Patent Document 3"), and carbon dioxide nanobubble water (Patent Publication No. 4921333, hereinafter referred to as "Patent Document 4"). In the invention described in Patent Document 2, it has been found that oxygen nanobubbles are generated in an aqueous solution prepared to have an electrical conductivity of 3 mS / cm or more, and that the particle size of the nanobubbles is maintained for about one month. In Patent Documents 3 and 4, it has been found that nitrogen or carbon dioxide nanobubbles are generated in an aqueous solution prepared to have an electrical conductivity of 100 μS / cm or more (300 μS / cm or less), and that the particle size of the nanobubbles is maintained for about one month. Furthermore, Patent Documents 1 to 4 verify the stabilization of particle size, and Patent Document 2 in particular finds that freshwater fish and saltwater fish can coexist when the salinity concentration of oxygen nanobubble water is maintained at 0.9 to 1.5%, and that providing oxygen nanobubble water for drinking at chicken breeding sites improves resistance to infectious diseases and significantly reduces the use of antibiotics.

[0006] The group of the inventors of the present application also disclosed an invention relating to water for living organisms containing ozone nanobubbles in Japanese Patent No. 5829790 (hereinafter referred to as "Patent Document 5"). The invention described in Patent Document 5 involves generating ozone-containing microbubbles (ozone microbubbles) in two types of raw water with the same or different salt concentrations, and collapsing the microbubbles by applying the above-mentioned physical stimulus to generate ozone nanobubbles, and then removing excess salt and minerals from the same or two types of raw water containing the ozone nanobubbles using a reverse osmosis membrane, thereby obtaining the desired water for living organisms.

[0007] On the other hand, other aqueous solutions containing nanobubbles or methods for producing the same are disclosed in, for example, Japanese Patent No. 6214091 (hereinafter referred to as "Patent Document 6"), Japanese Patent No. 7169016 (hereinafter referred to as "Patent Document 7"), and Japanese Patent No. 7144053 (hereinafter referred to as "Patent Document 8"). The invention described in Patent Document 6 has discovered that nanobubbles can be stabilized by setting the salt concentration to 0.5% or more without depending on electrical conductivity, i.e., electrolyte ions or minerals. The invention described in Patent Document 7 provides active oxygen water containing ultrafine bubbles (nanobubbles), transition metal ions, hydrogen peroxide, hydroxyl radicals, hypochlorous acid, and triplet oxygen by using transition metals, iron, or copper ions to set the oxidation-reduction potential to 770 mV to 950 mV and the pH to 5.5 to 6.8. Furthermore, the invention described in Patent Document 8 provides hydrogen nanobubble water for use in producing fish paste products, which can be stored in a suitable container (e.g., a plastic tank) for up to six months by adding at least one electrolyte ion selected from iron ions, calcium ions, sodium ions, and potassium ions so that the hydrogen ion concentration is pH 7.5 to 8.9, the reduction potential is -800 mV to -300 mV, and the electrical conductivity is 50 to 300 μS / cm. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 4144669 [Patent Document 2] Patent No. 4080440 [Patent Document 3] Patent No. 4921332 [Patent Document 4] Patent No. 4921333 [Patent Document 5] Patent No. 5829790 [Patent Document 6] Patent No. 6214091 [Patent Document 7] Patent No. 7169016 [Patent Document 8] Patent No. 7144053 DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0009] However, the inventions described in Patent Documents 1 to 4 and 6 disclose only examples that focus on the production of nanobubbles containing gas and the stabilization of the nanobubbles. In addition, Patent Document 2 describes in the examples that freshwater fish and saltwater fish coexist as mentioned above, and that providing oxygen nanobubble water for drinking at chicken breeding sites improves resistance to infectious diseases and significantly reduces the use of antibiotics, but does not provide any objective data, and application to all fields is still under consideration.

[0010] One application of nanobubbles produced based on the inventions described in Patent Documents 1 to 4 is the invention described in Patent Document 5. However, although the invention described in Patent Document 5 has been devised to remove excess salt and minerals using a reverse osmosis membrane, the only example of ozone nanobubble water for use in living organisms is a test to suppress bacteria that cause periodontitis, and it is unclear whether it would be harmful to the human body if consumed.

[0011] In addition, Patent Documents 7 and 8 respectively describe activated oxygen water for sterilization purposes and hydrogen nanobubble water for the production of fish paste products for sterilization and improving the aesthetics of fish paste products, so it was unclear whether they would be effective when used on the human body.

[0012] The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a method for producing a nanobubble solution that exists in a solution for a long period of time and continues to impart functions such as an activating effect and a bactericidal effect on a living body to the solution. [Means for solving the problem]

[0013] The above object of the present invention is achieved by a method comprising the steps of generating microbubbles containing a gas in a solution of water or a polar solvent, adjusting the hydrogen ion concentration and redox potential of the solution, applying a physical stimulus to the microbubbles to rapidly shrink the microbubbles to generate nanobubbles, and passing the microbubbles and the solution containing the nanobubbles through a reverse osmosis membrane, wherein the hydrogen ion concentration is 5.5 to 10.0 and the redox potential is -900 mV to +900 mV.

[0014] Furthermore, the above object of the present invention is more effectively achieved by the gas contained in the microbubbles and nanobubbles being any one of ozone, oxygen, nitrogen, hydrogen, carbon dioxide, and nitric oxide, or by further comprising a step of passing the solution containing the microbubbles and nanobubbles through a membrane filter, or by the nanobubble solution having an electric conductivity of 50 to 300 μS / cm, or by the nanobubble solution having a salinity of 0.9 to 2.0%. Effect of the Invention

[0015] According to the method for producing a nanobubble solution of the present invention, it is possible to produce nanobubbles with a bubble diameter of 50 to 200 nm in a solution and have them remain stable for more than six months. Furthermore, a solution containing nanobubbles can have a physiological activation effect on living organisms, a killing effect or a growth inhibition effect on microorganisms such as bacteria and viruses, and a chemical reaction action with organic or inorganic substances, depending on the properties of the gas contained in the nanobubbles. [Brief description of the drawings]

[0016] [Figure 1] 1 shows a particle size frequency distribution of nanobubbles produced by the method for producing a nanobubble solution according to the present invention (the average distribution is about 140 nm and the standard deviation is about 30 nm). [Diagram 2] FIG. 1 is a graph showing the relationship between the surface potential of microbubbles and the pH of an aqueous solution. [Diagram 3] FIG. 13 is a graph showing an increase in zeta potential accompanying the shrinkage of microbubbles. [Figure 4] FIG. 1 is a schematic diagram showing the mechanism by which nanobubbles exist stably. [Diagram 5] FIG. 1 is a side view of an apparatus for generating nanobubbles by generating a vortex flow. [Figure 6] 1 is a flowchart of a method for producing a nanobubble solution according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The properties of nanobubbles and the method for producing a nanobubble solution according to the present invention will be described in detail below. For convenience of explanation, the case of an aqueous solution will be described, but the present invention is not limited thereto.

[0018] First, the properties of nanobubbles will be described.

[0019] Generally, nanobubbles have a particle diameter of 50 to 500 nm, as shown in the particle size distribution in Figure 1. Nanobubbles produced by the nanobubble production method according to the present invention continue to exist in an aqueous solution for a long period of time, for example, one month or more. There is no particular limitation on the method of storing an aqueous solution containing nanobubbles, and the nanobubbles will not disappear for one month or more even if stored in a normal container.

[0020] As a physical property of microbubbles (here referring to microbubbles with a diameter of 50 μm or less), as shown in Figure 2, microbubbles in an aqueous solution have a surface electric potential that depends on the pH of the solution. This is because the hydrogen bond network of water at the gas-liquid interface requires more hydrogen ions and hydroxide ions as its constituent factors. This charge maintains an equilibrium condition with the surrounding water, so it is a constant value regardless of the bubble diameter. In addition, electrostatic force is generated due to the charge on the surface, so ions with an opposite charge are attracted to the vicinity of the gas-liquid interface.

[0021] The charge of a microbubble is kept in equilibrium, but if the microbubble is shrunk in a short time, the charge will concentrate. Figure 3 shows the change in surface charge when the bubble diameter is shrunk from 25 μm to about 5 μm in 10 seconds, indicating that the original equilibrium condition is deviated and the charge will concentrate. If the shrinking speed is further increased and the bubble diameter is further reduced, the amount of charge per unit area will increase inversely proportional to the square of the bubble diameter.

[0022] Since microbubbles are surrounded by a gas-liquid interface, the inside of the microbubbles is self-pressurized due to the effect of surface tension. The pressure increase inside a microbubble relative to the environmental pressure can be theoretically predicted by the Young-Laplace equation. (Number 1) ΔP=4σ / D

[0023] Here, ΔP is the degree of pressure rise, σ is the surface tension, and D is the bubble diameter. In the case of distilled water at room temperature, a microbubble with a diameter of 10 μm would experience a pressure rise of approximately 0.3 atmospheres, and a microbubble with a diameter of 1 μm would experience a pressure rise of approximately 3 atmospheres. The gas inside the self-pressurized microbubbles dissolves in water according to Henry's law. This causes the bubble diameter to gradually shrink, and since the internal pressure increases as the bubble diameter shrinks, the rate at which the bubble diameter shrinks accelerates. As a result, bubbles with a diameter of 1 μm or less are completely dissolved almost instantly. In other words, nanobubbles only exist for an extremely short time.

[0024] In contrast, in the method for producing nanobubbles according to the present invention, microbubbles with a diameter of 10 to 50 μm are rapidly shrunk by physical stimulation. When electrolytes such as iron, manganese, calcium, sodium, magnesium ions, and other mineral ions are mixed in the aqueous solution containing the microbubbles so that the electrical conductivity of the aqueous solution is about 50 to 300 μS / cm, the electrostatic repulsive force of these electrolytes inhibits the shrinkage of the bubbles. This electrostatic repulsive force is an electrostatic force acting between ions of the same sign present on the opposite sides of a spherical microbubble as the curvature of the sphere increases with shrinkage of the microbubble. Since the shrunk microbubbles are pressurized, the tendency for the microbubbles to shrink becomes stronger as the microbubbles shrink, but when the bubble diameter becomes smaller than 500 nm, this electrostatic repulsive force becomes apparent and the shrinkage of the bubbles stops.

[0025] When electrolytes such as iron, manganese, calcium, sodium, magnesium ions, and mineral ions are mixed into the aqueous solution so that the electrical conductivity is about 50 to 300 μS / cm, the electrostatic repulsive force becomes strong enough that the bubbles stabilize by balancing the shrinking force and the repulsive force. The bubble diameter when stabilized (nanobubble diameter) varies depending on the concentration and type of electrolyte ions, but is 50 to 500 nm, as shown in Figure 1.

[0026] Nanobubbles are characterized by not only maintaining a pressurized gas inside them, but also by the formation of an extremely strong electric field due to the concentrated surface charge. This strong electric field has a powerful effect on the gas inside the bubbles and the surrounding aqueous solution, resulting in physiological activation effects, bactericidal effects, chemical reactivity, etc.

[0027] The mechanism by which nanobubbles remain stable is shown in Figure 4. In the case of nanobubbles, an extremely high concentration of electric charge is concentrated at the gas-liquid interface, preventing the sphere (air bubble) from shrinking due to the electrostatic repulsive force acting between the charges on the opposite sides of the sphere. In addition, the concentrated high electric field forms an inorganic shell mainly composed of electrolyte ions such as iron around the bubble, which prevents the internal gas from dissipating. Since this shell is different from the shells of surfactants and organic matter, the shell itself easily collapses due to the deviation of the electric charge around the bubble that occurs when nanobubbles come into contact with other substances such as bacteria. When the shell collapses, the gas contained inside is easily released into the aqueous solution.

[0028] Next, the method for producing nanobubbles will be described with reference to drawings and flow charts.

[0029] Fig. 5 is a side view of an apparatus using compression, expansion, and vortex flow to produce nanobubbles. The apparatus shown in Fig. 5 produces microbubbles using a microbubble generator 3, a water intake 31, and a microbubble-containing aqueous solution outlet 32, and sends the microbubbles into a container 1. A circulation pump 4 for partially circulating the aqueous solution containing microbubbles in the container 1 is connected to the container 1, and an orifice (or punched plate) 2 having a large number of holes is connected to a pipe (circulation pipe) in which the circulation pump 4 is installed, and is connected to the container 1. The aqueous solution containing microbubbles in the container 1 is caused to flow through the circulation pipe by the circulation pump 4, and passes through the orifice (or punched plate) 2, causing compression, expansion, and vortex flow.

[0030] 6 is a flow chart showing a method for producing a nanobubble solution. Note that the production method according to the present invention will be described taking an aqueous solution as an example.

[0031] First, microbubbles are generated in a container 1 containing water containing electrolyte ions by using a microbubble generator 3 (step S1).

[0032] Here, the water containing electrolyte ions is referred to, but the state of the water does not matter, such as pure water, seawater, brackish water, or the undiluted liquid (aqueous solution) of wastewater from industrial or agricultural drainage. Incidentally, although an aqueous solution is described in this embodiment, microbubbles and nanobubbles can also be produced in a solution mainly made of a protic polar solvent such as alcohol (e.g., ethanol, methanol, 2-propanol) or aprotic polar solvent such as acetone or tetrahydrofuran, and also in a solution mainly made of a polar solvent other than organic acid.

[0033] As for the electrolyte ions, as described above, electrolytes such as iron, manganese, calcium, sodium, potassium, magnesium ions, and mineral ions are preferable. Instead of these electrolytes, salt (sodium chloride) may be used. Concentrations of these ions and salts are preferably about 50 to 300 μS / cm in terms of electrical conductivity, and 0.9 to 2.0% in terms of salt. If the concentration is below the lower limit of these ranges, the nanobubbles are not stabilized. If the concentration is above the upper limit of these ranges, the stability of the nanobubbles is not affected, but depending on the application of the nanobubble aqueous solution or solution produced by the present invention, the salt or electrolyte ions may hinder the application in some cases.

[0034] Incidentally, the electrolyte ions or salt (sodium chloride) should be approximately 50 to 300 μS / cm (electrical conductivity) and 0.9 to 2.0% (salt) by the end of production, so in step S1, they are added so that they are at least twice the upper limit of these numerical ranges.

[0035] Moreover, the gas that can be contained in the microbubbles and thus the nanobubbles can be oxygen, ozone, nitrogen, carbon dioxide, hydrogen, nitric oxide, etc. For example, if the gas to be contained is oxygen or ozone, it is possible to more effectively improve the physiological activation effect on living organisms, the killing effect on microorganisms such as bacteria and viruses, and the growth inhibition effect, etc. In addition, in the stage of containing a gas in step S1, the gas is generated by a gas supplier (not shown) connected to the microbubble generator 3 when the microbubbles are generated. Incidentally, the microbubble generator 3 may be a known one.

[0036] Next, the water containing the microbubbles generated in step S1 is adjusted to pH (hydrogen ion concentration) = 5.5 to 10.0 (step S2). As described above, microbubbles in an aqueous solution (or a solution of a polar solvent) have a surface potential that depends on the pH of the aqueous solution. This is because the hydrogen bond network of water at the gas-liquid interface requires more hydrogen ions and hydroxide ions as its constituent factors. This charge is a constant value regardless of the bubble diameter because it maintains an equilibrium condition with the surrounding water. In addition, electrostatic force acts due to the charge on the surface, so ions with the opposite charge are attracted to the vicinity of the gas-liquid interface.

[0037] If the pH of the water is less than 5.5, the water will not be stabilized, regardless of the gas contained in the nanobubbles. Even if the pH is 10.0 or more, the stabilization is not significantly affected. As for the adjustment of the pH, the pH may be kept within the range of 5.5 to 10.0 by adding the electrolyte ions described above, but it may also be adjusted using any appropriate pH adjuster.

[0038] In step S2, the redox potential of the water containing microbubbles is preferably set to -900mV to +900mV. This range of redox potential is proportional to the above-mentioned pH and contribution to nanobubble stabilization, and outside this potential range, nanobubbles become difficult to stabilize. The redox potential is mostly adjusted by adding electrolyte ions.

[0039] Next, the circulation pump 4 is operated to partially circulate the aqueous solution containing the microbubbles (step S3). The aqueous solution containing the microbubbles is pushed out by the circulation pump 4, and compression, expansion, and vortex flow occur in the piping before and after passing through the orifice (or punching plate) 2. The microbubbles are compressed and expanded when passing through, and the charged microbubbles generate eddy currents due to the vortex flow generated in the piping, causing the microbubbles to rapidly shrink and collapse, and to stabilize as nanobubbles. The order of the circulation pump 4 and the orifice (or punching plate) 2 in the flow path may be reversed. The zeta potential at this time is between -150 mV and +150 mV.

[0040] The average particle size of nanobubbles is 50 to 550 nm, the mode diameter (the most frequent particle size) is 90 to 150 nm, and the particle concentration is 1.20 × 10 8 ~5.50×10 9 Each is preferably in units / mL.

[0041] First, if the average particle size, mode diameter, and particle concentration are below the numerical limit ranges, sterilization cannot be maintained, and the same is true if the average particle size, mode diameter, and particle concentration are above the numerical limit ranges.

[0042] 5, a single orifice (or punched plate) 2 may be provided, and the circulation pump 4 may be omitted as necessary. In that case, it is also possible to utilize the driving force of the microbubble generator 3 on the aqueous solution or the flow of the aqueous solution due to the difference in height.

[0043] Here, it is stated that "compression, expansion and vortex flow occur in the piping before and after passing through the orifice (or punching plate) 2," which corresponds to the "physical stimulus" given to the microbubbles in Patent Documents 1 to 4. In the present invention, the "physical stimulus" has the same meaning.

[0044] Physical stimulation may utilize compression, expansion, and vortex flow in the piping before and after passing through an orifice (or punched plate) as described above, or may utilize the compression, expansion, and vortex flow that occur when the solution flows by discharging a voltage of 2000 to 3000 V to microbubbles in the solution using a discharge generator, or irradiating microbubbles in the solution with ultrasonic waves at a transmission frequency of 20 kHz to 1 MHz using an ultrasonic transmitter, or by operating a rotor attached to a container containing the solution at 500 to 10,000 rpm to cause the solution to flow.

[0045] Of the devices used for this physical stimulation, the discharge generator, ultrasonic transmitter, or rotor may be appropriately installed within the container 1.

[0046] Furthermore, in the case of physical stimulation using discharge, using ultrasonic irradiation, or using a rotor to flow an aqueous solution and utilizing the compression, expansion, and vortex currents that occur during the flow, if the rotation speed of the rotor is smaller than the respective numerical ranges, microbubbles will be crushed and nanobubbles will not be obtained sufficiently, whereas if the rotation speed is larger than the respective numerical ranges, there is either not much improvement in efficiency or, particularly in the case of discharge, there is a high possibility that excessive discharge will occur.

[0047] At the end of step S3, nanobubbles with a diameter of 50 to 500 nm are produced. After step S3, the water containing the nanobubbles is passed through a reverse osmosis membrane (step S4). The purpose of step S4 is to remove excess electrolyte ions and salt so that the aqueous solution finally has an electrical conductivity of about 50 to 300 μS / cm and a salinity of 0.9 to 2.0%.

[0048] In step S4, either batch processing or sequential processing may be used. Note that, at the point in time when the nanobubble-containing water is passed through the reverse osmosis membrane in step S4, the method for producing the nanobubble solution of the present invention is fully established, and a nanobubble solution that can be stored for about six months or more is obtained, but the nanobubble-containing water may be passed through a membrane filter (step S5).

[0049] Although the embodiment of the method for producing nanobubbles according to the present invention has been described above, the present invention is not limited to this as long as it does not deviate from the matters described in the specification and the like. [Industrial Applicability]

[0050] According to the method for producing a solution containing nanobubbles produced by the present invention, the solution can be used for sterilization or disinfection of animals (including humans) or in public health, or for use in cosmetics and in cultivating agricultural crops without using fertilizer, depending on the microbubbles in the solution and the gas contained in the nanobubbles. [Explanation of symbols]

[0051] 1 container 2 Orifice (punched plate) 3. Microbubble generator 31 Water Intake 32 Microbubble-containing aqueous solution outlet 4 Circulation pump

Claims

1. A step of generating microbubbles containing a gas in a solution of water or a polar solvent; adjusting the hydrogen ion concentration and redox potential of the solution; A step of applying a physical stimulus to the microbubbles to rapidly shrink the microbubbles and generate nanobubbles; and The method includes a step of passing the solution containing the microbubbles and the nanobubbles through a reverse osmosis membrane, The method for producing a nanobubble solution, wherein the hydrogen ion concentration is 5.5 to 10.0, and the oxidation-reduction potential is −900 mV to +900 mV.

2. 2. The method for producing a nanobubble solution according to claim 1, wherein the gas contained in the microbubbles and the nanobubbles is any one of ozone, oxygen, nitrogen, hydrogen, carbon dioxide, and nitric oxide.

3. 3. The method for producing a nanobubble solution according to claim 1, further comprising a step of passing the solution containing the microbubbles and the nanobubbles through a membrane filter.

4. 3. The method for producing a nanobubble solution according to claim 1, wherein the nanobubble solution has an electric conductivity of 50 to 300 μS / cm.

5. 3. The method for producing a nanobubble solution according to claim 1, wherein the nanobubble solution has a salt content of 0.9 to 2.0%.

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