JP5924606B2 - Organic synthesis method - Google Patents

Description

  The present invention relates to an organic matter synthesis method and treatment method using submerged plasma, and a submerged plasma apparatus that can be used in these methods.

  “Liquid plasma” is non-equilibrium plasma in contact with a liquid. The in-liquid plasma is formed by partially ionizing the gas by discharge in the gas in contact with the liquid. A gas that forms plasma by electric discharge may be introduced into a space in contact with the surface (liquid level) of the liquid, or may be introduced as bubbles in the liquid. Electrons, ions, atoms, and molecules in the plasma in liquid can act on the liquid or the substance in the liquid through the gas-liquid interface and cause various chemical reactions.

  Development of technology to form plasma in liquid and improve water quality and waste liquid treatment is in progress. A practical purpose of such submerged plasma technology is, for example, decomposition or sterilization of hardly decomposable organic substances in an aqueous solution. Difficult organic substances such as dioxins that cannot be decomposed by ozone can be decomposed by hydroxy radicals (.OH) formed by the reaction between plasma and water. This is called an accelerated oxidation method, and other methods using ultraviolet rays, methods using hydrogen peroxide, and the like are known.

  Discharges that generate plasma in liquid are roughly classified into direct current or low frequency discharges and high frequency or microwave discharges. Examples of the former include underwater streamers by DC pulse discharge, arc discharge (see Non-Patent Document 1), and dielectric barrier discharge (see Patent Documents 1, 2, and 3). In the case of dielectric barrier discharge, a gas is interposed between the electrodes, and discharge plasma is induced in the gas. The devices disclosed in Patent Documents 1, 2, and 3 each have a structure in which a two-phase region composed of bubbles and water is sandwiched between electrodes. Examples of the latter include RF discharge and microwave discharge. Again, bubbles are used. Bubbles introduced or generated in the liquid absorb electromagnetic wave energy to generate plasma (see Non-Patent Documents 2 and 3). Non-patent document 2 reviews the overall underwater discharge technology. For reference, the entire disclosure of Non-Patent Documents 1 to 3 is incorporated herein by reference.

JP 2010-137212 A JP 2004-268003 A JP 2009-11001 A

“Water Purification by Plasma: Which Reactors are Most Energy Efficient?” By Muhammad Arif Malik, Plasma Chem Plasma process (2010) 30: 21-30. “Formation of Underwater Plasma and Its Characteristics” (Yasuoka Yasuoka et al., J. Plasma Fusion Res. Vol. 84, No. 10 (2008) 666-673) Published by Cambridge University Press, PLASMA CHEMISTRY Alexander Fridman 2008

  The present invention provides a method for more efficiently performing the decomposition and sterilization of a hardly decomposable organic substance in an aqueous solution by using an in-liquid plasma, an in-liquid plasma apparatus that can be used in such a method, and an in-liquid plasma. It is a main object to provide a method for synthesizing an organic substance by the above and a submerged plasma apparatus that can be used in such a method.

The present invention provides an organic substance synthesis method, a submerged plasma apparatus, a submerged plasma treatment method, and a liquid purification system described in at least the following items.
[Item 1]
Forming a plasma by discharge of a gas containing carbon dioxide gas in contact with water, and generating an organic substance containing formic acid or diformyl peroxide in the water by contact between the plasma and the water;
An organic compound synthesis method comprising:
[Item 2]
Item 2. The organic material synthesis method according to Item 1, wherein the discharge is a dielectric barrier discharge.
[Item 3]
Item 3. The organic compound synthesis method according to Item 1 or 2, wherein the organic material includes performic acid.
[Item 4]
The method for synthesizing an organic substance according to any one of items 1 to 3, using a submerged plasma device,
The submerged plasma device is:
A first electrode;
A solid dielectric layer in contact with the first electrode;
A discharge chamber having an internal space for receiving the first electrode and the solid dielectric layer;
A second electrode disposed opposite to the first electrode through the solid dielectric layer and arranged to separate the internal space of the discharge chamber from water, the gas phase positioned on the internal space side A second electrode having a surface and a liquid phase surface located on the water side and having a plurality of through-holes connecting the gas phase surface and the liquid phase surface;
A gas introduction device that supplies carbon dioxide gas into the internal space of the discharge chamber and forms an interface between the carbon dioxide gas and the water in each through hole in the second electrode;
4. The organic matter synthesis method according to any one of items 1 to 3, wherein the organic matter is generated in the water by the discharge of the carbon dioxide gas.
[Item 5]
A submerged plasma apparatus for performing dielectric barrier discharge,
A first electrode;
A solid dielectric layer in contact with the first electrode;
A discharge chamber having an internal space for receiving the first electrode and the solid dielectric layer;
A second electrode disposed opposite to the first electrode through the solid dielectric layer and arranged to separate the internal space of the discharge chamber from the liquid, the gas phase positioned on the internal space side A second electrode having a surface and a liquid phase surface located on the liquid side, and having a plurality of through holes connecting the gas phase surface and the liquid phase surface;
A gas introduction device for supplying a gas into the internal space of the discharge chamber and forming an interface between the gas and the liquid in each through-hole in the second electrode;
A submerged plasma apparatus.
[Item 6]
6. The in-liquid plasma apparatus according to item 5, wherein each of the first electrode and the second electrode has a flat plate shape.
[Item 7]
Item 7. The submerged plasma device according to Item 5 or 6, wherein an opening size of each of the plurality of through holes is smaller than an interelectrode distance defined by the first electrode and the second electrode.
[Item 8]
8. The in-liquid plasma device according to any one of items 5 to 7, wherein an opening size of each of the plurality of through holes is smaller than 0.5 mm.
[Item 9]
9. The in-liquid plasma device according to any one of items 5 to 8, further comprising an electric circuit configured to apply a voltage between the first electrode and the second electrode to perform dielectric barrier discharge.
[Item 10]
10. The in-liquid plasma apparatus according to any one of items 5 to 9, further comprising a tank that at least temporarily stores the liquid in a stationary or fluid state and contacts the liquid with the liquid phase surface of the second electrode.
[Item 11]
11. The in-liquid plasma device according to any one of items 5 to 10, wherein the discharge chamber has an opening for discharging a part of the gas introduced into the liquid by the gas introduction device into the liquid.
[Item 12]
12. The in-liquid plasma apparatus according to any one of items 5 to 11, wherein the liquid is water.
[Item 13]
The gas introduction device is configured to supply carbon dioxide gas as the gas into the discharge chamber,
Item 13. The in-liquid plasma apparatus according to Item 12, wherein an organic substance containing formic acid or diformyl peroxide is generated in the water by the discharge of the carbon dioxide gas.
[Item 14]
A submerged plasma processing method of processing a liquid using the submerged plasma apparatus according to any one of items 5 to 13,
Bringing a liquid into contact with the liquid phase surface of the second electrode;
Supplying a gas into the internal space of the discharge chamber by the gas introduction device, and forming an interface between the gas and the liquid in each through hole in the second electrode;
Performing a dielectric barrier discharge by applying a voltage between the first electrode and the second electrode, and generating the gaseous plasma in the discharge chamber by the dielectric barrier discharge;
In-liquid plasma treatment method.
[Item 15]
The in-liquid plasma processing method according to item 14, wherein bringing the liquid into contact with the liquid phase surface of the second electrode includes disposing the reaction chamber of the in-liquid plasma apparatus inside the liquid.
[Item 16]
A submerged dielectric barrier discharge plasma apparatus capable of discharging in a liquid,
An electrode coated with a dielectric;
An electrode having a plurality of through holes;
An electrode support substrate for supporting the dielectric-coated electrode;
A pressure adjusting chamber,
The electrode covered with the dielectric and the electrode having the plurality of through holes are arranged to face each other, and the opening diameter of the through hole is an electrode between the electrode covered with the dielectric and the electrode having the plurality of through holes. A submerged dielectric barrier discharge plasma apparatus, wherein a gas inlet is provided in the electrode support substrate, and the pressure adjusting chamber is connected to the gas inlet.
[Item 17]
Item 17. The liquid dielectric according to Item 16, wherein the electrode having the plurality of through holes is formed of one or more materials selected from the group consisting of an aluminum alloy, stainless steel, a nickel alloy, and a titanium alloy. Barrier discharge plasma device.
[Item 18]
The electrode having a plurality of through holes is formed of one or more materials selected from the group consisting of aluminum alloy, stainless steel, nickel alloy, and titanium alloy on a plastic resin or ceramic material provided with a plurality of through holes. Item 17. The submerged dielectric barrier discharge plasma apparatus according to Item 16, wherein the conductive thin film is coated.
[Item 19]
Item 17. The submerged dielectric barrier discharge plasma apparatus according to Item 16, wherein the electrode having the plurality of through holes includes a silicon substrate that has been finely processed to have through holes.
[Item 20]
The through-hole provided in the electrode having the plurality of through-holes according to any one of items 16 to 19, wherein an opening diameter on a side facing the electrode covered with the dielectric is larger than an opening diameter on the other side. Submerged dielectric barrier discharge plasma device.
[Item 21]
Item 17. The submerged dielectric barrier discharge plasma apparatus according to Item 16, wherein the electrode having the plurality of through holes includes a porous material.
[Item 22]
The submerged dielectric barrier discharge plasma according to any of items 16 to 21, wherein the dielectric-coated electrode is formed of ferritic stainless steel or martensitic stainless steel and is coated with soda lime glass. apparatus.
[Item 23]
23. The liquid dielectric barrier discharge plasma apparatus according to any one of items 16 to 22, wherein the pressure adjustment chamber has a pressure adjustment mechanism.
[Item 24]
From the item 16, further comprising a gas introduction pipe for introducing gas into the pressure adjusting chamber, an electrode covered with the dielectric, and a power supply wiring for supplying power to the electrode having the plurality of through holes 24. A submerged dielectric barrier discharge plasma apparatus according to any one of the above.
[Item 25]
Item 25. A liquid purification system comprising the submerged dielectric barrier discharge plasma device according to any one of items 16 to 24, a gas supply device, and a high-voltage power source.

  According to an embodiment of the present invention, there are provided an organic matter synthesis method and other treatment methods using in-liquid plasma. The embodiments of the present invention also provide a novel in-liquid plasma device that can be used in these methods.

It is sectional drawing which shows typically the basic composition of the in-liquid plasma apparatus 1000 of embodiment of this invention. It is a top view of the plasma apparatus 1000 in a liquid. It is sectional drawing which shows the distance D between electrodes. 4 is a cross-sectional view showing an example in which the in-liquid discharge plasma apparatus 1000 includes a liquid tank 300. FIG. 4 is a cross-sectional view showing a state where a liquid 302 is stored in a liquid tank 300. FIG. It is sectional drawing which shows typically the main structures of the in-liquid plasma apparatus 1100 in the modification of embodiment of this invention. It is sectional drawing which shows typically the main structures of the in-liquid plasma apparatus 1200 in the other modification of embodiment of this invention. (A) is a top view illustrating an arrangement example of the through holes 202 in the second electrode 200, and (b) is a cross-sectional view illustrating an example in which a solid dielectric layer 212 that covers the second electrode 200 is provided. It is a figure which shows a liquid dielectric barrier discharge plasma apparatus. It is a figure which shows a part of electrode part of the dielectric barrier discharge plasma apparatus in a liquid. It is a figure which shows the structure of the electrode which has a some through-hole. It is a figure which shows the structure of the electrode which has a some through-hole. It is a figure which shows the structure of the electrode coat | covered with the dielectric material. It is a figure which shows the state currently used in the liquid. It is a figure which shows the state currently used in piping. It is a figure which shows a high voltage generation circuit. It is a figure which shows a methylene blue pigment decomposition result. It is a figure which shows the emission spectroscopy result of the underwater plasma. It is a figure which shows the structure of the electrode which has several through-holes using a porous material. It is a figure which shows the structure of the electrode which has a some through-hole using the silicon substrate which performed the microfabrication so that it may have a through-hole. It is a figure which shows the result of having analyzed the standard sample of formic acid with the high performance liquid chromatograph, and shows retention time and UV spectrum. It is a figure which shows the result of having analyzed the standard sample containing a formic acid with a high performance liquid chromatograph, and shows retention time and UV spectrum. It is a figure which shows the result of having analyzed with the high performance liquid chromatograph about the sample whose discharge time is 5 minutes, and shows holding time and UV spectrum. It is a figure which shows the result of having analyzed with the high performance liquid chromatograph about the sample whose discharge time is 20 minutes, and shows retention time and UV spectrum. Matrix-assisted laser desorption / ionization of a standard aqueous solution containing performic acid. The results of mass spectrometry by time-of-flight mass spectrometry, (a) is the result of measurement in positive mode, and (b) is the result of measurement in negative mode. is there. Matrix-assisted laser desorption / ionization of a sample having a discharge time of 20 minutes is a result of mass spectrometry by time-of-flight mass spectrometry, (a) is a measurement result by positive mode, and (b) is a measurement result by negative mode. It is. It is a difference spectrum between a UV spectrum of a sample having a discharge time of 1 minute and a UV spectrum of a sample having a discharge time of 20 minutes. It is a graph which shows the relationship between the production amount of a formic acid, and the flow volume of a carbon dioxide gas. It is a graph which shows the relationship between the production amount of a formic acid and the aperture ratio of the through-hole of an electrode.

  Hereinafter, with reference to the drawings, a submerged plasma apparatus according to an embodiment of the present invention, a treatment method using the submerged plasma apparatus, and an organic substance synthesis method will be described. However, the embodiments of the present invention are not limited to those illustrated. .

<Basic configuration of submerged plasma device>
An in-liquid plasma apparatus according to an embodiment of the present invention is a plasma apparatus that performs dielectric barrier discharge. As will be described later, this apparatus is suitably used for the synthesis of organic substances. However, the use of this submerged plasma device is not limited to the synthesis of organic substances.

  First, with reference to FIG. 1 and FIG. 2, the basic structure of the in-liquid plasma apparatus 1000 in a certain aspect is demonstrated. FIG. 1 is a cross-sectional view schematically showing the basic configuration of the in-liquid plasma apparatus 1000. FIG. 2 is a top view of the in-liquid plasma apparatus 1000.

  A submerged plasma apparatus 1000 shown in FIG. 1 includes a discharge chamber 116 having an internal space 114, a first electrode 100 located in the internal space 114 of the discharge chamber 116, and a second electrode 200 facing the first electrode. I have. A solid dielectric layer 112 that is in contact with the first electrode 100 exists between the first electrode 100 and the second electrode 200. Accordingly, the second electrode 200 faces the first electrode 100 with the solid dielectric layer 112 interposed therebetween. There is a space (gap) for discharge between the second electrode 200 and the solid dielectric layer 112. The solid dielectric layer 112 only needs to cover the surface of the first electrode 100.

  The first electrode 100 and the second electrode 200 are each formed from a conductive material such as metal. On the other hand, the discharge chamber 116 is formed of an insulating material.

  The second electrode 200 is disposed so as to separate the inside of the discharge chamber 116 from a liquid (not shown). The second electrode 200 has a liquid phase surface 200 a located outside the discharge chamber 116 and a gas phase surface 200 b located on the inner space 114 side of the discharge chamber 116, and the liquid phase surface 200 a and the gas phase It has a plurality of through holes 202 that connect the surface 200b. FIG. 2 shows 72 through holes 202 arranged in 8 rows and 9 columns as an example only, but the arrangement and the number of through holes 202 are not limited to this example. The arrangement of the through holes 202 may be regular or irregular. The opening sizes of the plurality of through holes 202 may be different depending on the position of the second electrode 200.

  Please refer to FIG. FIG. 3 is a cross-sectional view showing the distance D between the electrodes. The interelectrode distance D is defined by the first electrode 100 and the second electrode 200. Strictly speaking, the interelectrode distance D is a distance from the gas phase surface 200b of the second electrode 200 to the surface of the solid dielectric layer 112. In the drawings, the size ratio of the first electrode 100, the solid dielectric layer 112, and the second electrode 200 does not necessarily reflect the actual size ratio. Typically, the thickness of the solid dielectric layer 112 is smaller than the thickness of the first electrode 100. For this reason, the interelectrode distance D is substantially equal to the distance between the first electrode 100 and the second electrode 200.

  The opening size S of each of the plurality of through holes 202 is smaller than the interelectrode distance D. The opening size S of each through hole 202 can typically be set to a value smaller than 0.5 mm. The cross section of the through hole 202 in a plane perpendicular to the direction in which the through hole 202 extends does not need to have a circular shape. Further, the plurality of through holes 202 need not have the same or similar shapes.

  Refer to FIG. 1 again. The in-liquid plasma apparatus 1000 includes a gas introduction device 120 that supplies a gas for discharge into the discharge chamber 116. The gas introducing device 120 in this example can supply gas to the internal space 114 of the discharge chamber 116 via at least one tube 118. The gas introduction device 120 can operate so as to form an interface between gas and liquid (gas-liquid interface) inside each through hole 202 in the second electrode 200. The gas pressure in the internal space 114 of the discharge chamber 116 can be appropriately adjusted according to the pressure of the liquid with respect to the second electrode 200.

  In the example shown in FIG. 1, the first electrode 100 and the second electrode 200 are both flat and form a parallel plate electrode structure. However, the shape of the first electrode 100 and the second electrode 200 is not limited to a flat plate shape. The first electrode 100 and the second electrode 200 do not need to be parallel. The second electrode 200 shown in FIG. 2 has a generally disk shape, but may be rectangular or may have other shapes. When the first electrode 100 is seen through from the direction perpendicular to the upper surface (liquid phase surface 200a) of the second electrode 200, the contour of the second electrode 200 may be the same as or different from the contour of the first electrode 100. May be. In FIG. 1, the first electrode 100 is illustrated smaller than the second electrode 200, but the magnitude relationship between the first electrode 100 and the second electrode 200 may be arbitrary.

  As shown in FIG. 1, the first electrode 100 and the second electrode 200 are connected to an electric circuit 400 via a first electric conductor 402 and a second electric conductor 404, respectively. The electric circuit 400 may be a high voltage circuit including a booster circuit, for example. The electric circuit 400 may be connected to a power source such as a commercial power system, a generator, or a storage battery. The electric circuit 400 is configured to apply a voltage between the first electrode 100 and the second electrode 200 to perform dielectric barrier discharge inside the discharge chamber 116.

  Reference is now made to FIGS. FIG. 4 shows an example in which the submerged discharge plasma apparatus 1000 includes a liquid tank 300. FIG. 5 shows a state where the liquid 302 is stored in the liquid tank 300. Thus, the liquid tank 300 is configured to at least temporarily store the liquid 302 in a stationary or fluid state. The upper surface (liquid surface) 304 of the liquid 302 is in contact with the atmosphere and receives atmospheric pressure. The gas introduced into the internal space 114 of the discharge chamber 116 is in contact with the liquid 302 inside each through hole 202 of the second electrode 200 to form a contact surface 204. Therefore, the gas pressure in the internal space 114 of the discharge chamber 116 has a value corresponding to the total value of the atmospheric pressure and the water pressure. When the gas is intermittently or continuously supplied to the internal space 114 of the discharge chamber 116, a part of the gas is released from the internal space 114 of the discharge chamber 116 into the liquid 302. A part of such gas can be released into the liquid 302 from any of the plurality of through holes 202 in the second electrode 200. Thus, the pressure of the gas in the internal space 114 of the discharge chamber 116 can be balanced with the pressure of the liquid 302.

  The discharge chamber 116 may have an opening that discharges part of the gas introduced into the internal space 114 by the gas introduction device 120 into the liquid 302.

  FIG. 6 is a cross-sectional view schematically showing the main configuration of an in-liquid plasma device 1100 according to a modification of the embodiment of the present invention. The submerged plasma device 1100 has the same basic configuration as that of the submerged plasma device 1000. Constituent elements having the same function are denoted by the same reference numerals, and description thereof will not be repeated.

  A submerged plasma apparatus 1100 shown in FIG. 6 includes an insulating support 250 that supports the first electrode 100. The insulating support 250 has a concave portion that forms a space for discharge and a convex portion that defines a distance D between the electrodes. The second electrode 200 is supported by the convex portion.

  The insulating support 250 is disposed on the conductive base 420. The conductive base 420 is electrically connected to the second electrode 200 via a conductor 404 a provided inside the insulating support 250. The conductive base 420 is connected to the conductor 404b. In such a configuration example, the surface of the conductor 402 is covered with an insulating layer in order to ensure insulation between the conductor 402 and the conductive base 420. A dielectric barrier discharge can be performed by applying a voltage to the conductor 402 and the conductor 404b.

  FIG. 7 is a cross-sectional view schematically showing the main configuration of an in-liquid plasma apparatus 1200 according to another modification of the embodiment of the present invention. This submerged plasma apparatus 1200 differs from the submerged plasma apparatus 1100 shown in FIG. 6 in that it includes an internal space 114 having at least a substantially flat bottom surface. The bottom surface of the internal space 114 is formed by the top surface of the dielectric layer 112 that covers the first electrode 100. The dielectric layer 112 in this example has a portion that is expanded laterally outward from the outer peripheral side surface of the first electrode 100. In this portion, the dielectric layer 112 is relatively thick. A tube 118 for supplying a gas for discharge to the internal space 114 passes through a portion of the dielectric layer 112 where the first electrode 100 does not exist.

  The in-liquid plasma apparatus 1200 includes a discharge pipe 119 and a valve 122 that can discharge liquid and / or gas that has entered the internal space 114 from the internal space 114 to the outside. The liquid 302 supplied into the liquid tank 300 may enter the internal space 114 before or during the start of discharge. When gas is supplied to the internal space 114 via the pipe 118, the liquid 302 in the internal space 114 can be discharged via the discharge pipe 119 by opening the valve 122. By using such a discharge pipe 119, the inside of the internal space 114 can be filled with gas, so that it is easy to stably perform discharge. In addition, the reaction product formed in the internal space 114 can be taken out to the outside in a gas phase.

  As described above, the internal pressure of the internal space 114 can be adjusted by the flow rate of the gas supplied from the gas introduction device 120 to the internal space 114. As described above, the gas pressure in the internal space 114 has a value corresponding to the total value of the atmospheric pressure and the water pressure. For this reason, if the pressurization with respect to the liquid 302 is added, the upper limit of the pressure of the gas in the internal space 114 can be raised.

  FIG. 8A is a top view illustrating another arrangement example of the through holes 202 in the second electrode 200. The width of the contact surface 204 between the gas and the liquid 302 is proportional to the aperture ratio of the through hole 202 in the second electrode 200 (see FIG. 29). If the through holes 202 are arranged in a honeycomb shape, it is easy to increase the aperture ratio while maintaining the mechanical strength of the second electrode 200.

  FIG. 8B is a cross-sectional view showing an example in which a solid dielectric layer 212 covering the second electrode 200 is provided. As shown in FIG. 8B, a solid dielectric layer 212 may be provided so as to cover a portion of the second electrode 200 that contributes to the discharge. The solid dielectric layer 212 is formed so as to expose a part of the second electrode 200 in order to obtain conduction between the second electrode 200 and water.

<Liquid plasma device>
Hereinafter, embodiments of the in-liquid plasma apparatus will be described in detail.

  FIG. 9 is a sectional structural view of the in-liquid plasma device 1 according to the embodiment of the present invention. The discharge part 10 is a space sandwiched between the electrode 2 covered with a dielectric and the electrode 3 having a plurality of through holes, and the gap length is 1 mm or less. “Gap length” is the distance from the surface of the dielectric in the electrode 2 to the surface of the electrode 3. This distance is equal to the interelectrode distance D described above. The gap length can be set to 0.5 mm ± 0.1 mm, for example.

  The confidentiality of the space surrounded by the electrode support substrate 18 and the electrode 3 having a plurality of through holes is maintained by the O-ring 17. A gas that is a raw material of plasma is guided to the pressure adjustment chamber 12 by the gas introduction tube 7 and is introduced into the discharge unit 10 from the gas introduction port 8 provided in the electrode support substrate 18. After this gas becomes plasma gas in the discharge part 10, it is discharged | emitted in the liquid from the through-hole 9 provided in the electrode 3 which has a several through-hole. At this time, the plasma comes into contact with the liquid through the through hole 9. Stopping the intrusion of the liquid into the discharge unit 10 can be achieved by adjusting the gas pressure by the pressure adjusting mechanism 11. By providing the pressure adjusting chamber 12, the adjustment becomes easier.

  It is important to keep the liquid level in the through-hole 9 and prevent the liquid from entering the discharge part 10. When the liquid enters the discharge part 10 and wets the electrode surface, an electric field is not generated in the bubble 20 due to electrostatic shielding if the liquid has conductivity. As shown in FIG. 10, even if a bubble 20 is generated in a part between the electrodes and a discharge occurs, the other counter electrode surface is short-circuited with the conductive liquid, so that the load capacity increases and the power supply capacity increases. . In the in-liquid plasma apparatus in this embodiment, pressure adjustment is indispensable in order to prevent intrusion of liquid.

  In order to prevent the liquid from entering the discharge part 10, it is effective to appropriately determine the opening diameter of the through hole 9. As a result of repeated experiments, it was found that it is reasonable that the opening diameter of the through-hole 9 is equal to or less than the distance between the electrodes.

  FIG. 11 shows a cross-sectional view of the electrode 3 having a plurality of through holes in the present embodiment. The electrode 3 can be used while being grounded. Since the electrode 3 having a plurality of through-holes has openings, it is desirable that the electrode 3 be made of a metal material that is conductive, has good thermal conductivity, good corrosion resistance, and good workability. Specifically, aluminum alloy, stainless steel, nickel alloy, titanium alloy, or the like can be used. It is also possible to use composite materials. Specifically, a plastic resin or ceramic plate provided with a hole and coated with a conductive thin film can be used.

  In the apparatus 1 of the present embodiment, if the opening diameter of the through hole of the electrode 3 is too small, there is a concern that liquid may enter due to surface tension. In order to prevent this, as shown in FIG. 12, it is effective to incline the side wall so that the diameter of the through hole 9 increases from the liquid phase surface 32 toward the gas phase surface 31. This is also effective in reducing pressure loss.

  FIG. 13 shows a cross-sectional structure of the electrode 2 covered with a dielectric in the present embodiment. A high voltage can be applied to the electrode 2. The electrode 2 has a metal part 34 and a dielectric part 33 and is connected to the power supply wiring 4.

  It is desirable that the portion (solid dielectric layer) located on the discharge surface 35 side of the dielectric portion 33 is as thin as possible so that the voltage applied to the discharge portion 10 is increased. The thickness of the solid dielectric layer is determined in consideration of the dielectric strength of the dielectric portion 33, the controllability of the thickness, the mechanical strength, and the ease of processing. The portion located on the support surface 36 side of the dielectric portion 33 is desirably thick in order to reduce the load capacity and avoid application of a high voltage to the electrode support substrate 18.

  The material of the metal part 34 preferably has a small difference in thermal expansion coefficient with the material of the dielectric part 33. Further, it is practically beneficial that the adhesiveness with the dielectric portion 33 is good, the processing is easy, and the connection to the power supply wiring 4 by the processing is possible. As a result of the experimental study, it was found that epoxy resin, borosilicate glass or soda lime glass can be suitably used as the material of the dielectric portion 33. Moreover, as a material of the metal part 34, a 42 alloy (iron alloy containing 42 mass% nickel), a ferritic stainless steel (SUS403 series), or a martensitic stainless steel (SUS410 series) plate can be used. . The dielectric portion 33 can be formed by thermocompression bonding to the metal portion 34. In a specific example of the embodiment of the present invention, the dielectric thickness on the discharge surface 35 side was 0.1 mm, and the dielectric thickness on the support surface side 36 was 2 mm. Moreover, the thickness of the metal part 34 (stainless steel plate) was 0.1 mm. In addition, ceramics may be used as a dielectric, and a semiconductor may be used as a conductive material instead of metal. These formations may be performed using film formation techniques such as plating, CVD, vapor deposition, thermal oxidation, and printing.

  The electrode support substrate 18 and the side wall 15 preferably exhibit good electrical insulation even when a high voltage is applied between the electrode 2 and the electrode 3. The electrode support substrate 18 and the side wall 15 can be formed of a resin with good processability. Ceramics may be used. In particular, the electrode support substrate 18 is required to have resistance to plasma. In consideration of the temperature rise of the electrode 2 covered with the dielectric due to electric discharge, the electrode support substrate 18 can be formed of a material having good heat resistance.

  When the submerged plasma apparatus of this embodiment is used for water treatment, it is desirable that the electrode support base 18 is not deformed at a temperature of 100 ° C. Specifically, the electrode support substrate 18 can be formed from a fluorine resin, a polyacetal resin, a polyphenylene sulfide resin, or the like.

  In the present embodiment, the upper plate 14 is connected to the electrode 3 through the side wall 15. More specifically, the upper plate 14 and the electrode 3 are coupled by a metal bolt / nut 19 that passes through the through hole of the side wall 15. In such a case, the upper plate 14 can be formed of an insulating material such as resin or ceramics. When the upper plate 14 is fixed to the side wall 15 by an insulating coupling method instead of using the metal bolts and nuts 19, the upper plate 14 can be formed of a metal material such as an aluminum alloy or stainless steel.

  FIG. 14 is a diagram showing an embodiment of an in-liquid plasma processing system including an in-liquid plasma apparatus according to the present invention.

  The liquid to be processed 21 is filled in the liquid processing tank 26 in which the in-liquid plasma apparatus 1 is mounted. Gas is sent from the gas supply device 24 to the device 1 through the gas introduction pipe 7. Plasma is generated in the apparatus 1, the plasma comes into contact with the liquid 21, and plasma reaction products such as the generated active species are bubbled 20 and sent out into the liquid 21. The bubble 20 floats and diffuses in the liquid 21, passes through the filter 27, and is discharged to the outside. The filter 27 is provided to capture harmful substances in the exhaust gas.

  The discharging power is supplied from the high-voltage power supply 25 to the device 1 through the power supply wiring 4 and the power supply wiring 5. The power source may be a commercial power source 29 or a solar cell 30. When this processing system is installed outdoors and continuous operation is desired, power supply by the solar cell 30 provided with an auxiliary power supply is reasonable. When performing the liquid treatment using ozone, the gas supply device 24 may be a blower pump or an oxygen supply device. The filter 27 can be an ozonolysis filter.

  In FIG. 15, the form which uses the in-liquid plasma apparatus 1 in a local field is shown. The submerged plasma device 1 is inserted into the pipe 28. In this embodiment, electric power and gas serving as a plasma raw material are fed from the power supply wiring 4, the power supply wiring 5, and the gas introduction pipe 7, and the liquid 21 is subjected to plasma processing. As shown in the figure, the in-liquid plasma apparatus 1 can be installed at a specific point such as a liquid retention site.

<Examples of water treatment>
The dye methylene blue was decolorized using the apparatus 1 of FIG. FIG. 16 shows the configuration of the high voltage drive circuit used in this example. The oscillation circuit is a Wien bridge circuit, and the oscillation frequency and gain are adjusted with a variable resistor. The oscillation frequency used in this example was 26 kHz. The size of the metal part of the electrode 2 covered with the dielectric was 2 cm × 2 cm, the discharge surface side dielectric thickness was 1 mm, the support substrate side dielectric thickness was 2 mm, and the dielectric electrode capacitance was 20 pF. Ferritic stainless steel was used as the metal part, and a soda lime glass plate was used as the dielectric part.

  The distance between the electrodes was 0.5 mm. The electrode support substrate 18, the upper plate 14, and the side wall 15 were produced using a polyacetal resin plate. The power source used was a rectified commercial 100 VAC, and the winding ratio of the high voltage transformer was 1:28. The discharge voltage was 2.8 kV and the apparent power was 10 W. An air pump having a discharge rate of 3500 cc / min was used as the gas supply device 24.

  Using these, the whole was constructed as shown in FIG. 14, and the dye methylene blue was decolorized. FIG. 17 shows the change with time of the spectral transmission characteristics of the treatment liquid. The methylene blue decomposition energy efficiency calculated from this result was 0.180 g / kWh. The chemical reaction was caused by the action of oxidizing active species generated by the discharge plasma. The obtained efficiency is about 2 to 3 times higher than the result of the reported pulse corona discharge (see Non-Patent Document 3). FIG. 18 shows the results of emission spectroscopy of underwater plasma measured in the present example in comparison with atmospheric plasma. In the discharge in water, the generation of hydroxy radicals is clearly observed.

  When the submerged plasma apparatus in this embodiment is used for ozone treatment, energy efficiency can be improved as compared with the conventional ozone treatment apparatus. Hereinafter, this point will be described.

The amount of ozone derived from the following chemical reaction formula (I) is 1.25 g / kWh.
3/2 O ₂ → O ₃ ΔH = 1.5 eV (I)

  Conventionally, the amount of ozone generated by dielectric barrier discharge using oxygen as a raw material is about 0.05 g / kWh to 0.07 g / kWh. The energy efficiency was 4% to 6%. When air is used as a raw material, this efficiency is 2% to 3%. The reason is that nitrogen in the air contributes to the three-body reaction.

  The greatest cause of the low energy efficiency of conventional ozone treatment equipment is due to the reaction mechanism. Referring to the results of theory and experiment, it can be expected that the theoretical efficiency is up to 30% (see Non-Patent Document 3). However, the efficiency of an actual ozone treatment apparatus in practical use is lower than the theoretical efficiency. This is because ozone decomposes and disappears during transportation from the production field to the reaction field. The main factor is the decomposition of ozone molecules due to collision with the transport pipe wall and other particles, and further the promotion of decomposition due to temperature rise. In a practical system, additional power loads such as a gas circulation pump and a cooler are further increased, and the energy efficiency of the system is further reduced. When energy efficiency decreases, the equipment becomes large and practical application is limited to large plants.

  When the submerged plasma apparatus according to the present embodiment is used, it is possible to reduce the power supply capacity and expand the plasma reaction region. The dielectric breakdown electric field strength of water is 1 MV / cm or more. In order to generate streamer discharge in water by DC pulse discharge, it is necessary to supply a voltage of 20 kV or more even if the electric field concentration effect is used. In order to widen the discharge reaction region, it is necessary to enlarge the electrode area. Therefore, the power source capacity is large and the apparatus is large.

Discharging is facilitated by introducing bubbles into the water. In the case of dielectric barrier discharge, the starting voltage can be reduced, but for this purpose it is preferable to keep the distance between the electrodes short. Dielectric barrier discharge is considered a stable streamer corona discharge. The necessary discharge start voltage is lower than the value (Vs) given by the following equation (1) of Paschen's equation.
Vs = Bpd / ln (Appd / ln (1 + 1 / γ)) (1)
A, B: constant p: pressure γ: γ coefficient d: discharge gap length

  However, according to the conventional submerged dielectric barrier discharge, a two-phase mixed region of bubbles and liquid exists between the electrodes. As a result, the load capacity increases. Moreover, it is necessary to form a two-phase flow with external power. On the other hand, when high frequency discharge is performed, Vs decreases due to charge trapping in the bubbles. However, the absorption of high-frequency power by plasma increases, and the power source capacity increases.

According to the embodiment of the in-liquid plasma device according to the present invention, at least one of the following effects can be obtained.
1) A discharge plasma is stably and constantly generated in a dielectric barrier discharge in liquid.
2) The plasma can stably contact the liquid.
3) It is possible to reduce the size and weight and to reduce power consumption.

<Modification>
FIGS. 19 and 20 show the structures of the electrode 3 having a plurality of through holes, each of which includes a porous material and a silicon substrate that has been finely processed so as to have through holes. In any structure, good discharge characteristics were obtained. In the case of the porous material, good discharge was realized in any of bulk, powder, and fiber. In this case, if each material is non-conductive, the liquid to be treated which is an electrolyte ensures conductivity and becomes an electrode.

  In one aspect, the submerged plasma device according to the present invention includes an electrode coated with a dielectric, an electrode having a plurality of through holes, an electrode support substrate that supports the electrode coated with the dielectric, and a pressure adjustment chamber. A dielectric barrier discharge plasma apparatus in liquid. In this aspect, the electrode covered with the dielectric and the electrode having the plurality of through holes are disposed to face each other. A gas inlet is provided in the electrode support substrate. The pressure adjustment chamber is connected to the gas introduction port. The pressure adjustment chamber may have a pressure adjustment mechanism. You may provide the gas introduction pipe | tube for introducing gas into the said pressure regulation chamber, and the electric power feeding wiring for supplying electric power to one of electrodes.

  A liquid purification system according to an embodiment of the present invention includes the above-described submerged dielectric barrier discharge plasma apparatus, a gas supply apparatus, and a high-voltage power supply.

[Synthesis of organic substances]
An attempt was made to synthesize organic substances from carbon dioxide and water using the in-liquid discharge plasma apparatus 1000 shown in FIG. So far, there is no report that organic substances have been synthesized by submerged discharge plasma.

  As shown in FIG. 5, carbon dioxide gas is supplied at 1 L (liter) / minute from the gas introduction device 120 with water stored as the liquid 302 in the liquid tank 300 using the submerged discharge plasma device 1000. While, power of 20 W (AC 100 V, 0.2 A) was applied to generate discharge plasma in water. As a result, it was confirmed that at least one organic substance selected from the group consisting of formic acid, diformyl peroxide and formic acid was produced in water.

A high performance liquid chromatograph (manufactured by Shimadzu Corporation, LC-10) was used for identification of organic substances generated in water. Develosil RPAQEUS-AR-5 (manufactured by Nomura Chemical) was used for the column, 50 mM phosphate buffer (pH 2.4) was used for the mobile phase, and the oven temperature was 40 ° C. As a standard sample of formic acid, an aqueous solution in which Wako Pure Chemical (88%) was diluted 1000 times was used. Since performic acid is not commercially available, R.I. Gehr, D.H. Chen,
and M.M. A formic acid aqueous solution prepared by the method described in Moreau, Water Science and Technology, 59 (1), 89-96, (2009) was used as a standard sample. The above aqueous solution containing formic acid is a mixed aqueous solution of formic acid, hydrogen peroxide, sulfuric acid and formic acid. The initial concentration of each component contained in this mixed aqueous solution (concentration when no formic acid is generated) is formic acid ( 9.9M), hydrogen peroxide (4.7M), and sulfuric acid (0.77M), and it is estimated that about 20% of the formic acid is converted to performic acid.

  The measurement results (retention time (retention time) and UV spectrum) of the above standard sample are shown in FIGS. Based on the results of these standard samples, organic substances generated by the underwater discharge plasma were identified.

  The measurement results for the sample with a discharge time of 5 minutes and the sample with a discharge time of 20 minutes are shown in FIGS.

  As apparent from FIGS. 23 and 24, formic acid (PFA) is generated by the underwater discharge plasma, and the amount of formic acid generated increases with the discharge time. Further, an organic substance having a shorter retention time than performic acid and showing strong UV absorption at 191 nm is generated, and the amount of the organic substance generated increases with the discharge time.

  In order to identify organic substances having absorption at 191 nm, the mass was determined by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry. For mass spectrometry, MALDI TOF-MS manufactured by Shimadzu Corporation was used, and measurement was performed in both negative and positive modes. As the matrix material, DHBA (2,5-Dihydroxybenzoic acid) was used. As the sample, an aqueous solution containing performic acid used as the standard sample above and a sample having a discharge time of 20 minutes were used. The measurement results are shown in FIG. 25 and FIG.

  FIG. 25 shows the results for a standard aqueous solution containing performic acid. FIG. 25 (a) shows the measurement results in the positive mode, and FIG. 25 (b) shows the measurement results in the negative mode. FIG. 26 shows the results for a sample with a discharge time of 20 minutes, FIG. 26 (a) shows the measurement results in the positive mode, and FIG. 26 (b) shows the measurement results in the negative mode.

As a result, the organic substance having absorption at 191 nm is considered to be diformyl peroxide. The molecular weight of diformyl peroxide (HOC-O-O-COH) is M = 90. It is not clear whether m / z = 89.4 is attributed to an ion with a molecular weight of M = 90 or an ion with an amount of M = 89 having lost one proton. M / z = 60.5 belongs to an ion having a mass of 61, m / z = 60.5 is HOCOO ⁻ , m / z = 59.5 is OCOO ⁻ , and m / z = 61.5 Corresponds to the parent molecular ion.

The reaction for forming diformyl peroxide is 2HOC-O-OH (formic acid) → HOC-O-O-COH + H ₂ O + 1 / 2O ₂
It is thought that.

  Next, the amount of formic acid produced was estimated. FIG. 27 shows the difference spectrum between the UV spectrum of the sample with a discharge time of 1 minute and the UV spectrum of the sample with a discharge time of 20 minutes.

  The difference spectrum shown in FIG. 27 almost coincides with the UV spectrum of formic acid. Therefore, the amount of formic acid produced was estimated assuming that this difference spectrum is attributed to the formic acid produced in 19 minutes.

  The absorbance at the absorption maximum in the difference spectrum of FIG. 27 is 0.025, and assuming that the molar extinction coefficient of formic acid is 50, the concentration of formic acid in 500 mL is 0.5 mM. The amount can be estimated to be 0.25 mmol. When converted into the amount produced per minute, it becomes 0.013 mmol. Since the supplied power is about 20 W, it is 1.2 kJ per minute. As a result, the energy efficiency is 0.011 mmol / kJ.

  With reference to FIG. 28 and FIG. 29, the relationship between the production amount of formic acid, the flow rate of carbon dioxide gas, and the aperture ratio of the through holes of the electrodes will be described. In the experiment, the submerged discharge plasma apparatus 1000 shown in FIG. 4 was used as before.

  From the graph showing the relationship between the amount of formic acid produced and the flow rate of carbon dioxide gas shown in FIG. 28, when the flow rate of carbon dioxide gas is at least between 0.5 L / min and 0.75 L / min, It can be seen that if the flow rate is increased, the amount of formic acid produced increases, but if the flow rate is increased to at least 1 L / min or higher, the amount of formic acid produced decreases. That is, it can be seen that the flow rate of carbon dioxide gas has a suitable range according to the aperture ratio of the through holes of the electrodes. In this case, the aperture ratio refers to the ratio of the total cross-sectional area of the through holes that effectively connect the gas phase surface and the liquid phase surface to the discharge area. That is, the through hole which is a gas escape hole is not included in the opening.

  From the graph showing the relationship between the amount of formic acid produced and the aperture ratio of the electrode through-hole shown in FIG. 29, the aperture ratio of the through-hole 202 in the second electrode 200 included in the submerged discharge plasma apparatus 1000 shown in FIG. It can be seen that when the aperture ratio is smaller than 0.35, the amount of formic acid produced decreases substantially in proportion to the aperture ratio. Therefore, it can be said that a higher opening ratio is preferable from the viewpoint of the amount of produced formic acid.

  As described above, organic substances could be synthesized from only carbon dioxide and water by underwater discharge plasma. Using this synthesis process, carbon dioxide, which is said to cause global warming, can be immobilized. Further, no method for synthesizing pure formic acid has been found, and it can be an effective method for synthesizing formic acid. Because formic acid has a strong oxidizing power, it is used for cleaving disulfide bonds in proteins. It is also used in oxidation reactions such as epoxidation and hydroxylation in organic synthesis. In the medical and food industries, bactericidal power is used.

  The submerged plasma apparatus in the embodiment of the present invention can be used to subject a reaction product formed by non-equilibrium plasma to a chemical reaction to newly synthesize, modify, or decompose a substance. The submerged plasma device is characterized in that the generated plasma is adjacent to the material to be processed by the plasma. Specifically, the in-liquid plasma apparatus according to the embodiment of the present invention can be used for sterilization treatment in water purification plants, drinking water, food factories, semiconductor factories, liquid crystal factories, fish tanks, aquariums, and the like. It can also be used for the decomposition of organic substances in contaminated water treatment, the treatment of factory waste liquids, and the synthesis of materials in solution.

  In addition, the electrode structure with which the in-liquid plasma apparatus by embodiment of this invention is provided can also be used for plasma processing in gas. Examples include remote plasma CVD in which a plasma region and a reaction region are separated, and remote plasma surface treatment. Such an electrode structure can also be used as an air purifier that decomposes pollutants in the atmosphere.

  According to the in-liquid plasma apparatus according to the embodiment of the present invention, the power capacity required for the operation can be reduced, and a reduction in size and weight can be realized. Thereby, it becomes easy to cope with processing in a local field. In addition, it is easy to construct a processing system according to the processing amount and environment. As a consumer device, it will be possible to use in-liquid plasma technology.

DESCRIPTION OF SYMBOLS 100 1st electrode 112 Solid dielectric layer 114 Internal space 116 Discharge chamber 118 Tube 120 Gas introduction apparatus 200 2nd electrode 200a Liquid phase surface 200b Gas phase surface 202 Through-hole 204 Contact surface 300 Liquid tank 302 Liquid 304 Liquid surface 400 Electric circuit 402 First electric conductor 404 Second electric conductor 1000 Submerged plasma apparatus

Claims (3)

Forming a plasma in contact with water by discharge of a gas containing carbon dioxide gas without containing water, and an organic substance containing formic acid or diformyl peroxide in the water by contact between the plasma and the water Generating,
An organic compound synthesis method using a submerged plasma apparatus,
The submerged plasma device is:
A first electrode;
A solid dielectric layer in contact with the first electrode;
A discharge chamber having an internal space for receiving the first electrode and the solid dielectric layer;
A second electrode made of metal, facing the first electrode through the solid dielectric layer and arranged to separate the internal space of the discharge chamber from water, A gas phase surface located on the side, a liquid phase surface located on the water side, and a second electrode having a plurality of through holes connecting the gas phase surface and the liquid phase surface,
With the interface between the gas containing carbon dioxide gas and the water formed in each through hole in the second electrode,
A method for synthesizing an organic substance, wherein the organic substance is generated in the water by discharging a gas containing the carbon dioxide gas .   The organic material synthesis method according to claim 1, wherein the discharge is a dielectric barrier discharge.   The organic matter synthesis method according to claim 1, wherein the organic matter includes performic acid.

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