CN2458622Y - Pulse microwave intensified high-voltage low-temp plasma chemical reactor - Google Patents

Abstract

A pulse microwave enhanced high-pressure low-temperature plasma chemical reaction device, characterized in that the device is composed of waveguide-coaxial conversion (1), coaxial cavity (2), and TM ₀₁₀ resonant cavity with reentrant columns (3) connected ; The inner conductor (21) of the coaxial cavity (2) penetrates deep into the TM ₀₁₀ resonant cavity (3), and introduces the plasma excitation voltage through the high voltage introduction structure (22). The utility model can effectively control the plasma, so that the industrialization of plasma chemical synthesis can be realized.

Description

A pulsed microwave enhanced high-pressure low-temperature plasma chemical reaction device

The utility model relates to a chemical reactor, and in particular provides a pulse microwave intensified high-pressure low-temperature plasma chemical reaction device.

Compared with conventional DC arc and high-frequency plasma, microwave plasma has the characteristics of high reactivity, high energy utilization rate, cleanness, no electrode pollution, and high density. It has unique advantages in chemical synthesis and material surface modification. It is suitable for the preparation and treatment of high-purity substances, and the process efficiency is higher. Microwave plasma can be divided into low pressure (less than 760 Torr) and high pressure (greater than 760 Torr) according to its working pressure. Low-pressure microwave plasma has been widely used in thin film deposition, plasma etching and other fields, but negative pressure working conditions are not suitable for industrial applications such as direct conversion of natural gas and purification of toxic and harmful industrial waste gas. In order to meet the needs of large-scale plasma chemical synthesis and the development of new light sources, people have invented a variety of high-pressure microwave plasma excitation technologies in the past 20 years, which can be summarized as follows: (1) capacitive coupling Excitation technology of microwave plasma (CMP); (2) Excitation technology of coaxial surface wave microwave plasma (Surfatron); (3) Excitation technology of waveguide-based surface wave microwave plasma (Surfaguide); (4) TM ₀₁₀ Excitation technology of resonant cavity (MIP) microwave plasma. But from the perspective of chemical reactions, these traditional high-pressure microwave plasma excitation techniques are not suitable for most chemical reactions, because decades of plasma chemistry practice have shown that only when the plasma is in a low-temperature non-equilibrium state , which is most suitable for chemical reactions. Our research group has made some meaningful work in this field. In the accepted patent 00110422.5, a high-pressure microwave plasma excitation device is introduced, which can effectively accumulate microwave energy and enhance field strength. , It can realize the excitation and maintenance of plasma under the condition of no external "ignition", and can operate safely and stably under various conditions of high-pressure protective atmosphere, large gas flow, and high power capacity. However, this microwave plasma generation technology integrates the excitation and maintenance capacity. From the structural point of view, it has extremely high field strength and energy accumulation, and it is easy to make the non-equilibrium low-temperature glow plasma formed in the initial stage of excitation instantaneously. Transition to near-equilibrium high-temperature arc plasma, which is very unfavorable for the preparation of those chemical species that are not stable. Therefore, in order to extend the advantages of low-pressure microwave plasma to high pressure and make the microwave plasma-promoted chemical reaction technology truly qualified for industrial application, it is necessary to find a reliable high-pressure low-temperature microwave plasma excitation and maintenance method.

The purpose of the utility model is to provide a pulse microwave enhanced high-pressure low-temperature plasma chemical reaction device, which can effectively control the plasma, thereby realizing the industrialization of plasma chemical synthesis.

The utility model provides a pulse microwave enhanced high-pressure low-temperature plasma chemical reaction device, which is characterized in that the device consists of a waveguide-coaxial conversion (1), a coaxial cavity (2), and a TM ₀₁₀ resonant cavity with a reentrant column (3) Connection structure; the inner conductor (21) of the coaxial cavity (2) goes deep into the TM ₀₁₀ resonant cavity (3), and introduces the plasma excitation voltage through the high voltage introduction structure (22).

The high-voltage introduction structure (22) of the utility model is a composite structure of inductance and capacitance, which is composed of a conductive shell (224), two capacitor sheets (221) (223) and an inductance coil (222), and the coaxial inner conductor (21 ) is first connected with a capacitor (221), the capacitor (221) and the outer conductor of the coaxial line form a capacitor I, and the capacitor II is formed between the conductive shell (224) and the capacitor (223), and the capacitor ( 221) is connected to the capacitor sheet (223) through the inductance coil (222). Since the outer conductor of the coaxial line is connected to the conductive shell (224) of the high-voltage introduction structure, the capacitor I and the capacitor II are connected in series on the circuit, and then connected to the capacitor II. Inductors connected in parallel.

In principle, the capacitance and inductance should be as large as possible. To ensure that the capacitance is as large as possible, it can be achieved by increasing the capacitance area, reducing the distance between the capacitors and filling the capacitors with a medium; increasing Inductance can be achieved by increasing the number of turns of the inductor coil and placing a magnetic medium in the inductor coil. In the embodiment of this patent, reducing the capacitive gap is limited by the high voltage connected to it. As the gap is reduced, the high voltage can easily break down the capacitor, resulting in the failure of the anti-current structure. Usually, capacitors need to use dielectric isolation, and these dielectrics can be nylon, tetrafluoroethylene, high-purity alumina, magnesium oxide, mica and other materials. The number of turns of the inductance coil can be appropriately increased or decreased according to the needs. The basis for judgment is to measure the leakage energy of the microwave during the debugging process, and to reduce the number of inductance coils as much as possible while ensuring that the leakage energy is less than 10 microwatts/square centimeter. The gap between capacitors is determined according to the breakdown voltage of the selected dielectric material. When the dielectric material is high-purity alumina, the capacitance gap is 0.2-2 mm, and the number of turns of the inductor coil is 5-20 turns; the dielectric is tetrafluoroethylene For ethylene, the gap is 0.2-1.0 mm, and the number of turns of the induction coil is 10-30 turns; when the medium is magnesium oxide, the gap is 1.0-3.0 mm, and the number of turns of the induction coil is 5-30 turns; when the medium is nylon, The gap is 1.5-4.0 mm, and the number of turns of the induction coil is 20-60 turns.

The utility model has the following characteristics: 1. The high-voltage introduction structure (doubling as an anti-flow structure), not only seals the electromagnetic field, avoids the leakage of microwave energy, but also successfully introduces high voltage into the microwave cavity. 2. Using waveguide-coaxial conversion followed by magnetic coupling structure, microwave energy can be simply and efficiently fed into the coaxial cavity. 3. The waveguide-to-coaxial conversion adopts gate flow structure, which can not only effectively transmit microwave energy into the coaxial cavity, but also make the coupling degree adjustable, so as to improve the utilization rate of microwave energy. 4. The high voltage method used in "arc striking" can be DC, AC, or radio frequency high voltage. 5. Using pulsed microwaves to modulate the conventional high-voltage mercerized plasma, on the one hand, it greatly increases the effective area (volume) of the plasma, and at the same time enhances the activity of the plasma; on the other hand, it can effectively control the plasma parameters and prevent the plasma The sudden change from the non-equilibrium state to the equilibrium state has successfully obtained the low-temperature plasma in the non-equilibrium state, and also greatly improved the utilization rate of microwave energy. 6. Since the whole device adopts coaxial cavity and coaxial line transmission and has a wide frequency band, the design concept of this device can be suitable for meter wave, decimeter wave and centimeter wave (such as 2450MHz, 915MHz, 314MHz, etc.). 7. The device can work stably when the working pressure is 1.0-1.8 atm. 8. This device can be applied to gas-phase chemical reactions (such as direct conversion of natural gas to ethylene and acetylene, purification of toxic and harmful industrial waste gases, etc.), chemical vapor deposition (such as deposition of diamond films, etc.).

In a word, the utility model combines the conventional high-voltage mercerizing plasma structure with the microwave structure, uses microwaves to strengthen and expand the conventional mercerizing plasma, and effectively enlarges the volume of the conventional mercerizing plasma, and at the same time controls the volume of the plasma through microwave pulse modulation. parameters, providing a practical way for plasma chemical synthesis.

Describe the utility model in detail below by embodiment.

Accompanying drawing 1 is the structure diagram of pulse microwave enhanced high-pressure low-temperature plasma chemical reaction device,

Accompanying drawing 2 is a schematic diagram of a waveguide-coaxial conversion magnetic coupling structure,

Accompanying drawing 3 waveguide-coaxial conversion gate structural schematic diagram,

Accompanying drawing 4 is a schematic diagram of a high-voltage introduction structure,

Attachment 5 is a schematic diagram of the resonant cavity structure of TM ₀₁₀ .

Example 1

As shown in the figure, the pulse microwave-enhanced low-temperature plasma excitation device for chemical reaction is mainly composed of three parts: waveguide→coaxial microwave introduction structure, 50Hz AC high voltage introduction structure, and TM ₀₁₀ resonant cavity with reentrant column. Figure 1 is a schematic structural view of the device.

The microwave introduction structure adopts the waveguide-coaxial conversion, which transitions the microwave from the rectangular waveguide to the coaxial transmission, and couples the microwave into the TM ₀₁₀ cavity. This device adopts magnetic coupling structure and gate flow structure to realize waveguide-coaxial conversion. The size of the inner and outer conductors of coaxial transmission can be enlarged or reduced according to needs, but at this time there must be a transition section to ensure the impedance matching of the transmission line . Fig. 2 and Fig. 3 are structural schematic diagrams of the magnetic coupling structure and the gate current structure respectively.

50Hz AC high voltage introduction structure: Introduce 50Hz AC high voltage to excite filamentary glow plasma inside the coaxial line, which is the basic starting point of this device. The introduction of high-voltage lines into the microwave cavity must adopt an effective anti-flow structure, that is, it can not only introduce the external high voltage into the cavity, but also cut off the microwave so that it will not lead out of the cavity. This device uses the combination of inductance coil and capacitor to form a high-impedance structure, and its structural schematic diagram is shown in Figure 4.

The TM ₀₁₀ resonant cavity with re-entrant column can effectively accumulate energy. The conductor in the coaxial line extends into the TM ₀₁₀ resonant cavity for a certain length, and the re-entrant column at the rear end extends into the cavity to determine the length of the resonant cavity. Resonant frequency. Its structural diagram is shown in Figure 5.

The working principle of the whole device is as follows: the waveguide→coaxial conversion structure transmits the microwave energy into the coaxial cavity, and then transmits the microwave to the TM ₀₁₀ resonant cavity through the coaxial line. When AC high voltage is applied to the inner conductor of the coaxial line, and Add pulsed microwaves. At this time, by adjusting the length of the reentry column at the rear end of the TM ₀₁₀ resonant cavity protruding into the cavity so that the resonant frequency is the same as the frequency of the microwave source, plasma can be formed at the end of the inner conductor. Since the inner conductor of the coaxial line is in the central axis position in the TM ₀₁₀ resonant cavity, the field strength around it is radially symmetrically distributed, so the plasma formed at its end is also in a radiative state. If the reaction gas around the inner conductor Confined, the energy of the plasma can be effectively used to promote chemical reactions. Because this device adopts high-voltage "ignition" and pulse microwave intensification, the plasma can be stably in a low-temperature plasma far from the equilibrium state. When the plasma area is confined, the reaction gas can fully flow through the plasma activation area, so it is very It is suitable for gas-phase chemical reactions (such as direct conversion of natural gas, purification treatment of toxic and harmful industrial waste gases, etc.), and can also be used for chemical vapor deposition (such as using natural gas to deposit diamond films).

For microwaves with a working frequency of 2450MHz, the size of the reaction device is as follows: d ₁ =4～10mm,

d ₂ =6～14mm, d ₃ =20～36mm, d ₄ =30～50mm, l ₁ =4～16mm, l ₂ =2～8mm,

d ₅ =14～30mm, d ₆ =20～36mm, d ₇ =34～40mm, d ₈ =44～60,

d ₉ =36～60mm, d ₁₀ =90～120mm Among them, the supporting frame (and sealing window) in Figure 2 is poly

Tetrafluoroethylene, waveguide-to-coaxial conversion adopts magnetic coupling structure.

Embodiment 2 In Embodiment 1, if the inner conductor support frame of the waveguide-coaxial conversion structure (doubling as a sealing window)

When it is boron nitride, d ₁ =4-10mm, d ₄ =45-80mm.

Embodiment 3 In Embodiment 1, if the inner conductor support frame of the waveguide-to-coaxial conversion structure (doubling as a sealing window)

When it is alumina, d ₁ =4~10mm, d ₄ =100~176mm.

Example 4 In Example 1, if the high-voltage introduction part only uses the capacitor plate as the anti-current structure to cut off the microwave,

That is to remove the inductance coil, d ₈ =60 ~ 90mm.

Embodiment 5 In Embodiment 1, if the waveguide-to-coaxial conversion adopts a gate flow structure, the dimensions of the device are as follows:

d ₁ ′=20～40mm, d ₂ ′=10～20mm, d ₃ ′=20～46mm, d ₄ ′=70～100mm.

Claims (6)

1. A pulse microwave enhanced high-pressure low-temperature plasma chemical reaction device, characterized in that: the device consists of a waveguide-coaxial conversion (1), a coaxial cavity (2), and a TM ₀₁₀ resonant cavity with a reentrant column (3) Connection structure: the inner conductor (21) of the coaxial cavity (2) penetrates deep into the _TM010 resonant cavity (3), and introduces the plasma excitation voltage through the high voltage introduction structure (22). 2. The pulse microwave enhanced high-pressure low-temperature plasma chemical reaction device according to claim 1, characterized in that: the high-voltage introduction structure (22) is a composite structure of inductance and capacitance, consisting of a conductive shell (224), two capacitor plates ( 221) (223) and inductance coil (222), and one end of the inner conductor (21) of the coaxial line is first connected with a capacitor (221), and the capacitor (221) and the outer conductor of the coaxial line form a capacitor I, Capacitor II is formed between the conductive casing (224) and the capacitor sheet (223), and the capacitor sheet (221) and the capacitor sheet (223) are connected through the inductance coil (222). (224) are connected, thereby forming a structure on the circuit in which capacitor I is connected in series with capacitor II, and then connected in parallel with inductance. 3. The pulse microwave enhanced high-pressure low-temperature plasma chemical reaction device according to claim 2, characterized in that: when high-purity alumina is selected as the capacitor dielectric material, the capacitor gap is 0.2-2 mm, and the number of turns of the inductance coil is 5 -20 turns. 4. The pulse microwave enhanced high-pressure low-temperature plasma chemical reaction device according to claim 2, characterized in that: when the capacitor medium is tetrafluoroethylene, the gap is 0.2-1.0 mm, and the number of turns of the inductance coil is 10-30 turns . 5. The pulse microwave enhanced high-pressure low-temperature plasma chemical reaction device according to claim 2, characterized in that: when the capacitor medium is magnesium oxide, the gap is 1.0-3.0 mm, and the number of turns of the inductance coil is 5-30. 6. The pulse microwave intensified high-pressure low-temperature plasma chemical reaction device according to claim 2, characterized in that: when the capacitor medium is nylon, the gap is 1.5-4.0 mm, and the number of turns of the inductance coil is 20-60.

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