A plasma generator and its medium applied to volatile organic waste gas treatment

Abstract

The application discloses a plasma generator applied to volatile organic waste gas treatment and a medium thereof, and the device comprises, from outside to inside, an outer electrode, an outer electrode medium layer, an inner electrode medium layer and an inner electrode. Meanwhile, the application relates to an improvement on a preparation method of the electrode medium layer, and the preparation method is as follows: a suspension emulsion (TiO2-PDMS) is prepared by taking polydimethylsiloxane as raw material, taking ethanol as solvent and adding titanium dioxide nanoparticles; quartz is used as the outer electrode medium layer, and TiO2-PDMS is coated on the inner surface of the quartz; a hydrophobic coating layer with catalytic activity is prepared by using a plasma-induced crosslinking method; in addition, ceramic is used as the inner electrode medium layer, is immersed in a manganese nitrate solution and is then prepared into a Mn2O3 / ceramic medium layer by using a thermal decomposition method; and the application has the characteristics of plasma-catalysis module integration, can reduce air flow resistance and has better energy utilization rate.

Description

Technical Field

[0001] This invention relates to the field of plasma generator technology, and in particular to a plasma generator and its medium for treating volatile organic waste gas. Background Technology

[0002] The emission of volatile organic compounds (VOCs) is one of the main factors causing air pollution. Prolonged exposure to VOCs can easily lead to various adverse reactions such as dizziness and nausea, which has attracted widespread attention. In recent years, the removal of VOCs using low-temperature plasma technology has become a research hotspot. Low-temperature plasma technology has advantages such as simple process, simultaneous removal of multiple pollutants, and small footprint, and is considered an effective method for treating gaseous organic pollutants.

[0003] In order to achieve a high mineralization rate of pollutants and reduce ozone emissions during the removal of VOCs using low-temperature plasma technology, low-temperature plasma synergistic catalysis technology is often used to treat organic pollutants. At present, this technology has become a research hotspot and has made some progress.

[0004] Patent CN 112915783 discloses a process for the deep oxidation of gaseous pollutants using a dielectric barrier discharge synergistically with an N-type semiconductor catalyst. By introducing an N-type semiconductor catalyst during the discharge process, excess high-energy electrons from the plasma discharge can be effectively utilized for excitation, forming electrons and holes, and further generating highly oxidizing active free radicals for utilization, thereby improving the energy utilization efficiency of the plasma discharge process. Specifically, this involves attaching WO3, CdS, Fe3O4, and In2O3 to the surface of glass beads and filling the space created by the dielectric barrier discharge for plasma-synergistic catalytic treatment of VOCs.

[0005] The patent with publication number CN 112495378 discloses a method for preparing a low-temperature plasma-supported catalyst. The method involves attaching αMnO2 modified with noble metal nanoparticles (Au, Pt) to a porous carbon cloth support using a special aluminum sol as an adhesive to prepare a supported catalyst, which is then covered on a mesh metal electrode for direct use in the treatment of odorous gases.

[0006] Based on the relative positions of plasma and catalyst, plasma-co-catalyst technology can be divided into catalyst-embedded and catalyst-external types. In the case of an embedded catalytic device, the catalyst is placed in the plasma discharge region, which leads to high airflow resistance and easy adsorption of by-products and carbon deposition, resulting in catalyst deactivation. To solve these problems, some researchers have made the catalyst into a thin film and loaded it on the surface of the electrode. Although this can reduce resistance, the catalyst is prone to falling off over time. At the same time, the intermediate products adsorbed on the catalyst surface will reduce the catalytic performance. In the case of an external catalytic device, the catalyst is placed at the back end of the plasma. It can effectively utilize the long-lived substances generated by the reaction (such as ozone) to decompose into active oxygen on the catalyst surface to further degrade pollutants. However, this device cannot effectively utilize the short-lived substances and photons generated in the plasma, resulting in low energy utilization. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and to propose a plasma generator and its medium for the treatment of volatile organic waste gas.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A plasma generator for treating volatile organic waste gas includes, from the outside to the inside, an outer electrode, an outer electrode dielectric layer, an inner electrode dielectric layer, and an inner electrode. The outer electrode is a stainless steel wire mesh, and the outer electrode dielectric layer is a quartz tube loaded with TiO2-PDMS. The stainless steel wire mesh is tightly wrapped around the outside of the quartz tube without leaving any gaps. The inner electrode is a stainless steel cylindrical electrode, and the inner electrode dielectric layer is a ceramic tube loaded with Mn2O3. The stainless steel cylindrical electrode is tightly inserted into the ceramic tube without leaving any gaps.

[0010] The plasma waste gas treatment device of the present invention forms a double-barrier medium with an outer electrode dielectric layer and an inner electrode dielectric layer. Gas passes through the gaps in the medium and is ionized under the action of an electric field to generate plasma. Since pollutants do not come into contact with the electrodes, electrode corrosion can be effectively prevented, extending the service life of the system.

[0011] The specific preparation steps of the electrode dielectric layer of this invention are as follows:

[0012] S1. Pretreatment of the carrier: The quartz and ceramic tubes are ultrasonically cleaned and then dried in an oven.

[0013] S2. Dissolve an appropriate amount of PDMS in ethanol to prepare a PDMS ethanol solution. Add TiO2 nanoparticles and sonicate until a uniformly mixed TiO2-PDMS composite emulsion is formed;

[0014] S3. Combine the outer electrode, the outer electrode dielectric layer, the inner electrode and the inner electrode dielectric layer into a dielectric barrier discharge generating device, and introduce air to discharge, and treat the inner surface of the quartz tube under the action of plasma.

[0015] S4. After the discharge is complete, take out the quartz tube and uniformly coat the prepared TiO2-PDMS composite emulsion on the inner surface of the quartz tube, and repeat step (3) to introduce air for discharge treatment.

[0016] S5. Dissolve an appropriate amount of manganese nitrate in deionized water to obtain a manganese nitrate solution, and immerse the pretreated ceramic tube in the manganese nitrate solution for a period of time.

[0017] S6. Heat the ceramic tube along with the solvent and gradually evaporate the solvent. After all the manganese nitrate in the solution has been transferred to the ceramic tube, remove the ceramic tube, put it in an oven to dry the moisture, and continue to calcine it in a muffle furnace until the Mn2O3 / ceramic composite electrode dielectric layer is formed.

[0018] Preferably, in step S2, the ratio of PDMS to ethanol is 1:20 g / L, and the ratio of added TiO2 to ethanol is 1:1 g / L. The ultrasonic treatment time is 10 min.

[0019] Preferably, in step S3, the plasma power supply is a high-frequency high-voltage AC power supply with an output voltage of 0-30kV, a frequency selection range of 1kHz-100kHz, and a maximum power of 500W.

[0020] Preferably, in step S3, the dielectric barrier discharge generating device is a tubular electrode structure with inner and outer electrodes arranged coaxially and the gap between the electrodes is 5-10 mm.

[0021] Preferably, in step S3, the discharge duration is 5 minutes.

[0022] Preferably, in step S4, the coating method is the dip-coating method, and the dip-coating is performed 1-3 times. After each dip, wait for a period of time for the solvent ethanol to evaporate before dipping again, until the inner surface of the quartz tube is uniformly coated with TiO2-PDMS.

[0023] Preferably, in step S4, the discharge duration is 10 minutes.

[0024] Preferably, in step S5, the concentration of the prepared manganese nitrate solution is 5%, the amount of deionized water used is three times the mass of the ceramic tube, and the reaction impregnation time is 24 hours.

[0025] Preferably, in step S6, the heating method is water bath heating, and the oven temperature is set to 120 degrees Celsius.

[0026] Preferably, in step S6, the muffle furnace adopts a programmed heating step, with an initial temperature of 50 degrees and a heating rate of 10 degrees per minute to raise the temperature to 550 degrees. Then, it is held at 550 degrees for 3 hours and taken out after cooling to obtain the Mn2O3 / ceramic composite medium layer.

[0027] The present invention also provides the application of plasma electrode discharge with catalytic coating in VOCs treatment.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] Plasma etching can generate more hydroxyl groups on the quartz surface. After coating with PDMS, a plasma-induced cross-linking reaction can silanize the quartz surface, giving it excellent hydrophobic properties and reducing the adsorption of intermediate products after VOCs plasma degradation.

[0030] The preparation of thin films by blending nano-TiO2 with PDMS and forming a transparent coating on the quartz surface can increase light transmittance and make full use of the ultraviolet light generated during plasma discharge to excite the photocatalytic degradation of TiO2, thereby improving the VOCs treatment rate. Attached Figure Description

[0031] To illustrate the technical solutions in the embodiments of the present invention or the prior art more specifically and intuitively, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0032] Figure 1 This is a schematic diagram of the discharge electrode structure of the plasma generator used in the treatment of volatile organic compounds according to the present invention;

[0033] Figure 2 This is a top cross-sectional view of the discharge electrode of the plasma generator used in the treatment of volatile organic compounds according to the present invention.

[0034] In the figure: 1. Inner electrode; 2. Inner electrode dielectric layer; 3. Outer electrode dielectric layer; 4. Outer electrode; 5. Catalytic coating; 6. Discharge cavity. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0036] like Figure 1 and Figure 2As shown, the plasma generator for treating volatile organic compounds disclosed in this invention is coaxially configured from the outside in as an outer electrode 4, an outer electrode dielectric layer 3, an inner electrode dielectric layer 2, and an inner electrode 1. The outer electrode 4 is a stainless steel wire mesh with a width of 150 mm and a pore size of 400 mesh, and is connected to the high-voltage electrode of the plasma power supply. The outer electrode dielectric layer 3 is a quartz glass tube with a catalytic coating 5, which is TiO2-PDMS. The inner electrode dielectric layer 2 is a ceramic tube loaded with a catalyst, which is manganese trioxide. The inner electrode 1 is a stainless steel rod connected to the ground electrode. A discharge cavity 6 is formed between the outer electrode dielectric layer 3 and the inner electrode dielectric layer 2. Waste gas flows through the cavity and is treated under the action of plasma. The gap of the discharge cavity 6 is 5-10 mm.

[0037] Example 1, Fabrication of the external electrode dielectric layer:

[0038] SA1. Take a quartz tube (300mm in length, 26mm in outer diameter, and 1.5mm in thickness), and ultrasonically wash it with anhydrous ethanol and pure water for 10 minutes in sequence, and then dry it in an oven for later use.

[0039] SA2. Weigh 20g of PDMS into a beaker and add 1L of ethanol to dissolve it. Weigh 1g of nano-titanium dioxide and dissolve it in the ethanol solution, then sonicate it for 10min to form a uniformly mixed TiO2-PDMS composite emulsion and transfer it to a 1L graduated cylinder for later use.

[0040] SA3. A quartz tube is used as the external electrode, and a ceramic tube as the internal electrode. Discharge is performed under the drive of a plasma power supply. The discharge power is 50W, and air is introduced as the working gas. The discharge duration is 5 minutes.

[0041] SA4. After the discharge is complete, remove the quartz tube and seal the outer surface with adhesive tape to prevent the solution from seeping in. Then, immerse the quartz tube in TiO2-PDMS solution for a while and remove it. After the ethanol solution evaporates, immerse it in the solution again. Repeat this process 3 times until the inner wall of the quartz tube is evenly coated.

[0042] SA5. Again, using the quartz tube as the external electrode and the ceramic tube as the internal electrode, discharge is performed under the drive of the plasma power supply. The discharge power is 50W, and air is introduced as the working gas. The discharge duration is 10 minutes.

[0043] SA6, after discharge, is removed to obtain the TiO2-PDMS external electrode catalytic medium layer.

[0044] Example 2, Fabrication of the internal electrode dielectric layer:

[0045] SB1. Take a ceramic tube (300mm in length, 13mm in outer diameter, and 1.5mm in wall thickness), and ultrasonically wash it with anhydrous ethanol and pure water for 10 minutes in sequence, and then dry it in an oven for later use.

[0046] SB2. Weigh 15g of manganese nitrate tetrahydrate and dissolve it in 300mL of deionized water to form a manganese nitrate solution. Place the ceramic tube into the manganese nitrate solution and immerse it for 24 hours.

[0047] SB3. The manganese nitrate solution containing the ceramic tube is continuously evaporated in a water bath until the solution is completely evaporated and the manganese nitrate has completely permeated into the ceramic tube.

[0048] SB4. Place the ceramic tube in an oven at 120 degrees Celsius to dry, then place it in a muffle furnace and heat it to 550 degrees Celsius for 3 hours. After cooling, remove the tube to obtain the Mn2O3 / ceramic composite catalytic inner electrode dielectric layer.

[0049] Example 3, Plasma Generator:

[0050] (1) Wrap the prepared external electrode quartz dielectric layer with stainless steel wire mesh. The width of the stainless steel wire mesh is 150 mm and the mesh density is 400 mesh. The wire mesh is completely attached to the surface of the quartz tube without leaving any gaps.

[0051] (2) Insert the prepared inner electrode ceramic dielectric layer into a stainless steel rod. The stainless steel rod is 300 mm long and 10 mm in diameter. The stainless steel rod is completely attached to the inner wall of the ceramic without leaving any gaps.

[0052] (3) The plasma generator is a sleeve-type structure. It includes a stainless steel wire mesh external electrode, a quartz dielectric layer, a stainless steel rod and a ceramic tube dielectric layer. The stainless steel wire mesh is connected to the high-voltage terminal of the power supply, and the stainless steel rod is grounded.

[0053] Example 4

[0054] This device was used to treat VOCs. The simulated waste gas contained toluene with a concentration of 800 mg / m3. The background gas was air, the gas flow rate was 20 L / min, the energy density of the reaction input was 60 J / L, and the reaction lasted for 30 min. The final toluene removal rate was 94%, the selectivity of carbon monoxide and carbon dioxide was 36% and 24%, respectively, and the ozone concentration measured at the outlet was 23 ppm. After the reaction, the quartz medium layer was removed and observed to find that only a small amount of yellowish-brown substance was attached to the inner wall, and the attachment area was relatively scattered.

[0055] Comparative Example 1

[0056] The difference from Example 4 is that an uncoated TiO2-PDMS quartz dielectric layer was used instead, while the other steps and conditions were the same. The final toluene removal rate was 78%, and the selectivity for carbon monoxide and carbon dioxide was 17% and 11%, respectively. The ozone concentration measured at the outlet was 41 ppm. After the reaction was completed, the quartz tube was removed and observed to have a large amount of yellowish-brown substance adhering to the inner wall throughout the discharge area.

[0057] Comparative Example 2

[0058] The difference from Example 4 is that the inner electrode dielectric layer is replaced by a ceramic tube, while the other steps and conditions are the same. The final toluene removal rate is 83%, the selectivity of carbon monoxide and carbon dioxide is 28% and 19% respectively, and the ozone concentration measured at the outlet is 126 ppm.

[0059] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A plasma generator for treating volatile organic waste gas, comprising, from the outside to the inside, an outer electrode, an outer electrode dielectric layer, an inner electrode dielectric layer, and an inner electrode, characterized in that, The outer electrode is a stainless steel wire mesh, and the outer electrode dielectric layer is a quartz tube loaded with TiO2-PDMS. The stainless steel wire mesh is tightly wrapped around the outside of the quartz tube without leaving any gaps. The inner electrode is a stainless steel cylindrical electrode, and the inner electrode dielectric layer is a ceramic tube loaded with Mn2O3. The stainless steel cylindrical electrode is tightly inserted into the ceramic tube without leaving any gaps.

2. A plasma generator for treating volatile organic waste gas according to claim 1, characterized in that, The outer electrode, outer electrode dielectric layer, inner electrode dielectric layer, and inner electrode are coaxially arranged, and the discharge gap between the outer electrode dielectric layer and the inner electrode dielectric layer is 5-10 mm.

3. A method for fabricating the dielectric layer of the external electrode of a plasma generator as described in claim 1, characterized in that, The specific operating steps are as follows: SA1. Dissolve an appropriate amount of PDMS in ethanol to prepare a PDMS ethanol solution, add TiO2 nanoparticles and sonicate until a uniformly mixed TiO2-PDMS composite emulsion is formed. SA2. Clean the quartz glass tube, dry it, and then put it into the plasma generator for a period of time before taking it out. SA3. Immediately after the discharge treatment, the inner surface of the quartz tube is coated with a TiO2-PDMS composite emulsion. Then, the quartz tube is placed in the plasma generator again for discharge treatment. After the treatment, the residual solvent on the surface is wiped off.

4. The method for fabricating the dielectric layer of the external electrode of a plasma generator according to claim 3, characterized in that, In step SA1, the ratio of polydimethylsiloxane to ethanol is 1:20 g / L, the ratio of added TiO2 to ethanol is 1:1 g / L, and the ultrasonic treatment time is 10 min.

5. The method for fabricating the dielectric layer of the external electrode of a plasma generator according to claim 3, characterized in that, In step SA2, the plasma generator discharge voltage is 10kV, the processing time is 5min, and the carrier gas is air.

6. The method for fabricating the dielectric layer of the external electrode of a plasma generator according to claim 3, characterized in that, The SA3 coating method described above uses an immersion-lift method, with 1-3 immersion-lift cycles and a discharge treatment time of 10 minutes. The carrier gas used is air.

7. A method for fabricating an inner electrode dielectric layer in a plasma generator, used to prepare the inner electrode dielectric layer of the plasma generator as described in claim 1, characterized in that, The specific steps are as follows: SB1. Dissolve an appropriate amount of manganese nitrate in deionized water to obtain a solution, and immerse the ceramic tube in the manganese nitrate solution for a period of time. SB2. Evaporate the solvent along with the ceramic tube at 100 degrees Celsius. After all the manganese nitrate in the water has been transferred to the ceramic tube, remove it, dry it in an oven, and calcine it in a muffle furnace until a Mn2O3 / ceramic composite catalytic electrode is formed.

8. A plasma generator and its medium for treating volatile organic waste gas according to claim 7, characterized in that, In step SB1, the concentration of manganese nitrate solution is 5%, the amount of deionized water used is three times the mass of the ceramic tube, and the reaction impregnation time is 24 hours.

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