WO2021184049A1

WO2021184049A1 - Plasma liquid activation device

Info

Publication number: WO2021184049A1
Application number: PCT/VN2020/000013
Authority: WO
Inventors: Do Hoang TUNG; Le Hong MANH; Vu Thi HAO; Viet Pham LONG
Original assignee: Tung Do Hoang
Priority date: 2020-03-11
Filing date: 2020-11-24
Publication date: 2021-09-16

Abstract

The invention relates to a plasma liquid activated device using the Venturi effect combined with the vertical plasma chamber layout for the Venturi effect, water column weight and the water jet pressure generated in the chamber containing continuous water jet, negative-pressure air space, biphasic zone with water bubbles in which two gasandliquid phases are mixed to form and combine a wide variety of plasmas, various forms of plasma-liquid interactions and increase the mixing of active plasmas with liquid through gas bubbles to optimize liquid activation process by plasma. The composition, proportion of reactive oxygen species (ROS) and reactive nitrogen species (RNS) can be controlled by the flow of gas through the slot, the gas composition being supplied, the booster pump pressure, the voltage and power of the high voltage source, as well as the composition and properties of the liquid.

Description

PLASMA LIQUID ACTIVATION DEVICE

FIELD OF INVENTION

This invention relates to a device that forms and combines a variety of plasma types with various forms of plasma-liquid interaction in the same reaction chamber to activate the liquid and control the active substance content in the produced plasma activated liquid.

BACKGROUND OF INVENTION

Plasma activated water (PAW) has been investigated for treatment of bacterial infections for foods, agriculture, and medical applications. Plasma activated liquids (PAL), including PAW, has shown resistance against a wide variety of microorganisms. This bactericidal ability is so effective that it is called "dead water". Besides water, plasma activated buffer solution and cell culture medium have also been researched for cancer treatment In addition to the effect of killing microorganisms and pathogens, PAL also shows the ability to stimulate germination and plant growth. PAL has a good self life, it is able to maintain antibacterial resistance from sereval days to sereval weeks even sereval years, promising immense application potential.

The antibacterial activity of PAW and other plasma treated solutions aremainly produced by reactive oxygen species (ROS) and reactive nitrogen species (RNS). ROS and RNS are generated by plasma-air interactions in the gas phase then dissolved in solution. In addition, the plasma can change the pH of the solution. ROS and RNS combine with the acidity of PAW to act synchronously, forming a powerful oxidizing attack against bacteria. The high degree of susceptibility to PAW of bacterial cells may result from a higher ratio of surface area to volume of proukaiyotic cells compared to eukaryotic cells, resulting in increasing the concentration of the ROS and of the RNS in these cells. With bacteria, ROS and RNS can damage cells through oxidative stress or DNA damage. Research has shown that hydrogen peroxide (H₂O₂) nitrite (NCO₂), nitrate (NO₃ ^") and peroxynitrite (ONOO) are the main agents in the antimicrobial activity of PAW. However, plasma-liquid chemistry is much more complex, especially at the plasma-liquid interface, where many ROS and RNS having strong activity have been produced such as hydroxyl radical (OH.), nitric oxide radical (NO.), superoxide free radical (O₂ ^"), hydroperoxyl radical (HOO.), nitric dioxide radical (N₂O.), singlet oxygen (¹O₂), ozone (O₃). Liquid chemistry initiated by plasma treatment can heavily influence the long-term chemical and antibacterial properties of PAW. Therefore, it is of utmost importance to monitor and control the plasma and liquid chemistry of PAW to achieve the desired collective results for specific applications.

PAW has been produced very simply by treating water with the plasma. To . . form plasma, the medium between the two electrodes must be breakdown. Besides the properties of the medium, the breakdown potential depends on the pressure and the distance between the two electrodes according to Paschen's law described by the formula:

where p is the pressure, d is the electrode distance, γ is the Townsend coefficient and A and B are the experimentally determined constants. Thus, the lower the pressure, the lower the breakdown voltage, the easier it is to form a plasma with a larger electrode distance.

There are many methods of liquid activation by plasma such as (Figure 1): direct plasma - plasma formed inside the liquid or at the surface of the liquid; indirect plasma - forming a gas plasma outside a liquid and then mixing the plasma products into the liquid. Besides, the plasma itself used to activate the liquid can be as diverse as: the rmalplasma or non-thermal plasma. Each type of plasmas or interactions between plasma and liquid has its own advantages. For example, thethermal plasma will produce more RNS, while the non-thermal plasma will produce more ROS. Furthermore, since plasma exists in the gas phase, in order to increase the active substance content from plasma into liquid, it is extremely necessary to optimize the heterophasic mixing process between gas and liquid phases.

Thus, in order to activate the liquid by plasma we need to form plasma and interactthe same with the liquid that needs to be activated. In order to increase activation efficiency, it is necessary to combine a variety of plasmas, various forms of plasma liquid interactions, and good mixing plasma products with fluids.

As described in the US Patent No. US9023214, to form plasma in the fluid, the invention uses a very high pressure of water (about 100 atm) to be sprayed through a nozzle with a small pore size of 0.8 mm to give a Venturi effect to reduce the pressure in the chamber to 0.1 atm and to form a gaseous liquid biphasic system. However, since the entire chamber is in the biphasic state, in order to activate the plasma the full distance between the two electrodes must be breakdown, the present invention requires a voltage of at least 10 kV (due to the large p.d). The plasma generated in this solution is glow discharge (GD), so the immediate disinfection efficiency is high but the water activation efficiency is not high due to only one type of plasma (GD) and oneplasma liquid interaction (direct - DP) form.

Patent Document No. WO2016096751A associates two types of plasmas (thermal plasma and non-thermal plasma) to increase the efficiency of water activation. In this invention, two different types of plasma can be produced in the same reaction chamber or in two different reaction chambers. The plasma- liquid interaction type in the present invention is directinteraction, the product is mixed by water vortex. Furthermore, since the plasma chamber in this invention is at atmospheric pressure, the plasma has a high temperature which causes the liquid to heat up quickly and often requires a heat sink. In addition to rapidly increasing the liquid temperature, the thermal plasma at atmospheric pressure also produces more nitrates and nitrites and destroys hydroperoxides resulting in PAW produced by this method contains very high content of nitrate (about 1 g/liter) and nitrite content (several hundred mg/liter), but the content of peroxinitrite and hydroperoxide is low (a few mg/liter). hi addition, the mixing of the phases together using the Venturi effect has been used for a long time, with numerous inventions of gas-liquid mixer configurations using the Venturi effect.

SUMMARY OF INVENTION

Therefore, it is an objective of the present invention to provide a technical solution to combine and control a variety of plasmas and various forms of plasma-liquid interactions in the same reaction chamber to increase the active substance content in the plasma activated liquid, and at the same time combine the use of the Venturi effect to efficiently mix plasma product into liquid.

To achieve the above objective, the present invention provides a plasma liquid activated device comprising a hollow cylindrical plasma chamber which arranged in the vertical position, the plasma chamber air tightly connected with two electrodes one of which is disposed on the upper side and the other is disposed on the bottom side.The upper electrode has aninjection needle shape, the lower electrode is hollow cylinder, so that liquid sprayed from the upper electrode downward can flow therethrough. On die wall of the plasma chamber is provided witiia gas intake to control the pressure in the chamber, or change the gas composition in the chamber.

Due to the Venturi effect, when the liquid at high pressure is sprayed through the injection needle-shaped electrode to the lower electrode, negative- pressure is generated in the chamber. Since the plasma chamber is arranged vertically, the weight of the liquid column and the repulsion of the liquid jetfrom the nozzle help maintain the sufficiently large negative-pressure space in the chamber where only moderate liquid pressure is required (from 3 atm - 30 atm).

The pressurized liquid jetoutput from the injection needle-shaped electrode causes spraying with a continuous liquid core in the middle of the surrounding liquid bubblezone. If the distance between the two electrodes is suitable so that the water core is not in contact with the lower electrode, the space between the two electrodes can be divided into three main zones:

- Continuous liquid jet zone;

- Negative-pressure air spatial zone;

- Gas-liquid multi-phase zone in which two liquid and gas phases are mixed. The pressure in the plasma chamber, the continuous liquid jet length, the negative-pressure space size can be changed by varying the water pressure, die needle hole size and the air flow into the chamber through a needle valve on the gas intake.

When the upper electrode is connected to a high voltage source and the lower electrode is grounded, the voltage difference between zones will appear. There are at least 5 zones with voltage differences:

- The zone between die high voltage electrode and the liquid jet;

- The zone between the liquid jet and the biphasic zone surface;

- The zone between the liquid jet and the ground electrode;

- The zone between the high voltage electrode and the chamber wall (which get wet due to splashing liquid);

- The zone between the liquid jetand the chamber wall.

Although the pressure in the chamber is low, but according to Paschen's law, with the distance between the two electrodes according to the invention ranging from 2cm to 8cm, if these voltage difference zones are not present, the hreakdownwould not happen with the voltage in the rangefromabout 6 - 8 kV. However, in each of these voltage difference zones, there are always distances satisfying Paschen's law, so breakdown phenomenon easily occurs especially between high voltage electrode and liquid jet The environment in the plasma chamber at this breakdown contains a lot of free charge, so the breakdown between the liquid jetand the liquid-gas multi-phase zone, the liquid jet and the chamber wall, between the high voltage electrode and the chamber wall (indirect non-thermal plasma) have been easily occurred and a plasma spark between two electrodes (indirect thermal plasma)have been formed. In addition, electrolysis process also occurs between the liquid jet and the ground electrode.

The active substances ROS and RNS are generated from both direct and indirect plasmas, both non-thermal and thermal plasmas, and also from the electrolysis processes. These products are dispersed into gas bubbles to help to increase the contact area and contact time of ROS and RNS with liquid optimizing the liquid activation process by plasma.

BRIEF DESCRIPTION OF THE DRAWINGS d Figure 1 shows the plasma configurations and the forms of plasma-liquid interactions to activate the liquid;

Figure 2 shows a plasma liquid activated device, comprising a plasma chamber, a storage tank, a gas regulating system, a liquid regulating system, and a high voltage power source;

Figure 3 show the plasma chamber incorporating a variety of plasmas and various forms of plasma-liquid interactions;

Figure 4 illustrates the dependence of ROS and RNS speciesin PAW on gas flow;

Figure 5 shows the inhibition effect of oral bacteria of PAW;

Figure 6 shows the teeth cleaning and whitening effect of PAW.

DETAILED DESCRIPTION OF THE INVENTION

The invention proposes a plasma liquid activated device using the Venturry effect combined with a liquid column weight and liquid jet pressure to form a negative-pressure chamber with different spatial zones to combine a variety of plasmas, multiple forms of plasma-liquid interactions and enhances the mixing of active plasma with liquid through gas bubbles to optimize the liquid activation process by the plasma.

The plasma liquid activated deviceaccording to the invention comprising five parts:

- Plasma chamber;

- High voltage power source;

- Gas regulation and supply unit;

- Liquid tank;

- Liquid regulation system.

The plasma chamber comprising two electrode system with a metal injection needle-shapedhigh voltage electrode 11 airtightly connected to an electrode holder base 21 made of insulating material, the holder base having a gas intake slot 22. The holder base 21 is also air tightly connected to an . insulation pipe 23, which is also airtightly connected to aground electrode 12. The ground electrode 12 is airtightly connected to a cylindrical tube 24 plugged in a tank 33 to hold the liquid column ejected from the injection needle-shaped electrode 11 to form a dynamic wall of a negative-pressurechamber 43.

The high voltage power source5 used in this invention can be either a DC power source or an AC power source or a switching source with a peak voltage of a least 6kV

The gas regulation and supply unit including a piping system and flow regulation valves 6.

The tank 33 is of a suitable size for the required solution activation capacity.

The liquid regulation system includesa booster pump 31 that can compress liquid to a minimum pressure of 3 aim, an elbow, piping system and effervescent unit 32.

Parts of the device are connected together as shown in Figure 2 so that the plasma chamber is disposed vertically with the injection needle-shaped electrode 11 on the upper side and the tube 24 partially submerged in the tank

33.

When the booster pump 31 is initiated, liquid 34 from the tank 33 is air- bubble separated with effervescent unit 32 and sucked up and compressed to a pressure above at least 3 amt and then flown into injection needle-shaped electrode llto spray downwards to form a liquid jet having high pressure and speed which has been pumped into the chamber 43. The liquid jet 41 exits the injection needle-shaped electrode 11 causing a Venturi effect forming negative . pressure in the chamber 43. The initial water jetis continuous, then gas bubbles are formed at the end of the liquid jet forming liquid column 42 having a high bubble density and low conductivity and breakdown potential.

The pressure in chamber 43, the density of gas bubbles and the size of the liquid column 42 can be varied by the pressure of the booster pump 31, the gas flow through the slot 22, and the length of the liquid-nonimmersed portion of tiie tube 24. When the injection needle-shaped electrode is connected to the high voltage power source (Figure 3), the ground electrode 12 is grounded, breakdowns71 and 74 respectively occur easily between the high voltage electrode 11 and the water jet41, between the liquid jet 41 and the gas bubble layer 42 which are direct non-thermal plasmas due to the low air pressure in the chamber. The environment in the plasma chamber at this time contains a lot of free charges, so it easily occurs breakdowns 76, 73 and 75 between the liquid jet 41 and the wall of the chamber 23 (direct non-thermal plasma), the high voltage electrode 11 with the chamber wall 23 (indirect non-thermal plasma) and forms a direct spark discharged between two electrodes 11 and 12 (indirect thermal plasma). In addition, electrolysis process 72 also occurs between the liquid jet 41 and the ground electrode 12.

ROS and RNS are produced from the combination of direct plasma and indirect plasma, both non-thermal plasma and thermal plasma, and also from the electrolysis processes. These products are dispersed into gas bubbles to increase the contact area and contact time of ROS and RNS with liquid optimizing the liquid activation process by plasma.

The composition and ratio of ROS and RNS can be controlled by the gas flow through tiie slot 22, the composition and flow of the gas supplied through the flow regulation valves 6, the pressure of the water generated by the booster pump 31, tiie voltage and capacity of high voltage power source 5, as well as the composition and properties of the liquid 34.

Example a. Change the concentration of the active substance by changing the plasma condition

Figure 4 shows the concentration of ROS and RNS generated by the device according to the invention and the ability to change the concentrations of ROS and KNS by changing the gas flow from 0.2 to 1.6liters /min . b. The killing effect of PAW on oral bacteria

To test the ability to kill oral bacteria, sample of microorganisms in the oral cavity was collected by using a sterilized cotton swab spreaded on the surface of the tongue and teeth. Cotton swab containing oral microbiological sample is immediately placed into the vial containing 10 ml of distilled water and undo: ultrasonic vibrations for 10s to homogenize the sample. Then, two halves of the sterilized cotton swab are dipped in the homogeneous microbiological solution forf 10 seconds and then removed. One half of thecotton swabis soaked in distilled water for 30 seconds, the other is soaked in PAW for 30 seconds. After soaking the two cotton swabs were removed and placed into two vials which containing accordingly marked culture mediums. P is a vial of cotton swab soaked in PAW and C is a control vial of cotton swab soaked in distilled water. These two sample vials were incubated in an incubator for 24 hours. The results as shown in Figure 5 show that the microbial control vial grows to form colonies that cause cloudiness of the culture medium. At the same time 30 second soaking in PAW inhibited microorganisms so that they could not grow after 24 hours and the solution in the P vial is still transparent

This experiment showed that with 30 second contact, PAW has a remarkable inhibitory effect on oral bacteria. c. Effect of disinfecting and stimulating plant culture sample

Acacia seeds are sensitive to disinfectants and easily lose ability to germinate, so testing on a successful sample of Acacia seeds has the conditions for immediate application and can be extended to other types of samples. Dried acacia seeds are cleanedby shaking in 70% alcohol for 60 seconds, then shaking inl% Javel aqueous solutionfor 20 minutes. PAW can be used alone or in combination with Javel as shown in Table 1. Afterward, rinse the same with sterile distilled water, soak in water or in PAW for 1 hour (formula 2 and 3, Table 1) and sown on agar medium. Monitoring the seed infection and germination rate.

Table 1: Method of treating acacia seedswith PAW separately or in combination with Javel. Control method was a sterilization method with 1% Javel for 20 minutes

The results in Table 2 show that using PAW in combination with Javel (formula 3) significantly reduced the rate ofinfoctcd samples, from over 10% to 1.75%, thus the free radicals ofPAW support OCV ions of Javel water in lolling bacteria and fimgi on the sur&ce of acacia seeds, compared with the control •ample using Javel 1% (10-11%).

•. s . ·· . * ·· ·

• It is · noted that seeds after sterilization Witi · i Javel were aoalce · ·d*·· f'pr * 1 horn in

PAW (formula 2), foe germination rate of seeds increased significantly, from 17% to 32%.

PAW has foe effect of surface disinfection for acacia seeds when combined with Javdsolution. Especially PAW increases foe germination rate when soaking sterilized acacia seeds for 1 hour in PAW. This result initially opens up foe prospect of using PAW as a sample disinfectant and stimulating seed gpnwimtinn mhitinn

Table 2: Effects ofPAW on infection rate and gemmation rate of acacia seeds. The experiment was repeated 3 times.

d. Oral cleaning and whitening effect

The tester had dentins that were discolored by Tetracycline and drank coffee frequently in the morning. Therefore, in addition to the dark color of the teeth, the teeth also smell and quickly form plaque. Previously, tester had dental checkcvery six months to have tartar removal. Three months after foe tartar was taken, the tester started using 25ml of PAW to gargle for about 30 seconds each time, twice a day after brushing in the evening and in the morning.

Figure 6 shows the results of the color showing the tester's teeth whitening gradually over time using PAW to gargle, showing the ability of PAW to remove color. Especially the odor has completely disappeared Plaque not only was not formed more but tends to thin.

Claims

1. A plasma liquid activated device using the Venturi effect through a hollowcylindrical plasma chamber arranged in the vertical direction, the device comprising: the hollow cylindrical plasma chamber has a needle-shaped high voltage electrode (11) on the upper side, a hollow cylindrical ground electrode (12) on the bottom side, these two electrodes are air tightly connected each other through a base (21), a tube (23) and the tube (24) are all made of insulating material, the base (21) including air intake slot (22) for adjusting pressure; in which this device operates as follows: a) spraying the compressed solution to a minimum of 3 atm pressure from the injection needle-shaped electrode downwards; b) the gas flow is adjusted so that the pressure in the plasma chamber and the size of the negative-pressure space can change so that the space in the plasma chamber is divided into three main zones: continuous water jet zone, negative-pressure air zone and biphasic zone with water bubbles in which two gas and liquid phases are mixed; c) when the two electrodes are connected to a sufficiently high voltage power source (> 6 kV), it will form multiple voltage difference zones and a variety of plasmas with various forms of plasma-liquid interactions; d. plasma water is formed by combining both heat-equilibrium plasma and heat-unbalanced plasma, direct plasma, indirect plasma and electrolysis in the same reaction chamber.