Low temperature plasma gas phase chemical reactor using venturi

Abstract

The application provides a low-temperature plasma gas phase chemical reaction device using a venturi, one end of a quartz tube is provided with a venturi unit, the head of the venturi comprises a first cylindrical structure and a second cylindrical structure, the outer circle diameter of the second cylindrical structure is larger than that of the first cylindrical structure, the second cylindrical structure is located at the left end of the head of the venturi and is attached to the inner wall of the quartz tube, the first cylindrical structure is inserted into the hole of the tail of the venturi and is attached to the hole, there is a gap between the hole and the inner wall of the hole, a small hole vertically penetrating the head of the venturi is arranged at the position close to the tail of the venturi, the one end of the quartz tube close to the head of the venturi is provided with an air inlet pipe, the other end is provided with an air outlet pipe, and a stainless steel mesh is located behind the tail of the venturi. The plasma gas phase chemical reaction is carried out through dielectric barrier discharge, the gas backflow generated by the venturi accelerates the gas flow rate in the local area, the gas pressure is reduced, the plasma discharge is facilitated, and the energy efficiency of the reaction is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of gas synthesis and conversion, and relates to a low-temperature plasma gas-phase chemical reaction device using a Venturi tube. BACKGROUND

[0002] With the increasingly severe climate and environmental problems in the world today, limiting the emission of CO2 and other gases and pollutants is one of the primary tasks. The synthetic ammonia industry, which consumes 2% of the global electricity every year and accounts for 1% to 2% of the total greenhouse gas emissions, is the first to be affected. The traditional industrial synthesis of ammonia adopts the Haber-Bosch method, which requires high temperature, high pressure, and the action of iron-based catalysts to convert nitrogen and hydrogen into ammonia. This not only increases the cost, but also may cause the catalyst to be deactivated under high temperature conditions. In addition, the use of non-renewable energy sources such as natural gas as the main raw material results in huge energy consumption, high cost, and a large amount of pollution emissions, hindering the achievement of energy saving and emission reduction targets. In addition to limiting emissions, using gas conversion to "turn waste into treasure" is also an effective way to alleviate climate and environmental problems. However, traditional thermal catalytic reduction of CO2 requires high temperature conditions and catalysts, which increases the operating cost of the equipment and also has the problems of coking and catalyst deactivation, and cannot well solve the problem of CO2 dissociation. Therefore, in the field of gas synthesis and conversion, these traditional methods generally have the problems of high energy consumption, high cost, low efficiency, and serious pollution emissions. Therefore, in order to reduce the cost and energy consumption of traditional gas synthesis and conversion industry and reduce the emission of pollutants, it is urgent to develop a method for the synthesis and conversion of gases with mild reaction conditions, clean reaction process, low energy consumption, and high energy utilization efficiency.

[0003] Under this background, low-temperature plasma technology, as a new type of efficient molecular activation method, can activate gases under relatively mild conditions. This technology can generate a large number of high-energy electrons under atmospheric pressure. Subsequently, these high-energy electrons will collide with gas molecules, causing excitation, ionization, and dissociation, producing a large number of ions, free radicals, active atoms and molecules, and ultraviolet photons. The electron temperature in the system is as high as 10 4 -10 5 K, which is 2-3 orders of magnitude higher than the temperature of the background gas. The excited species, ions, or free radicals will rapidly further react to produce new molecules. In the fields of CO2 decomposition, CO2 hydrogenation, CH4 dry reforming, and ammonia synthesis, low-temperature plasma technology has broad application prospects.

[0004] The method and device for ammonia production by dielectric barrier discharge combined with catalyst in patent CN201910719287.6 combine dielectric barrier discharge with catalyst, which reduces energy consumption, but has the problems of low raw material gas conversion rate and low ammonia production.

[0005] The new efficient reaction device for ammonia production by low-temperature plasma combined with catalyst in patent CN202111105419.X uses a spiral electrode, which causes distortion of the electric field and makes the discharge uneven, resulting in unstable reaction.

[0006] The device and method for ammonia production in patent CN202011312571.0 allow dielectric barrier discharge to interact with plasma generated by microwave discharge, but there are short-lived species in the active particles after microwave discharge plasma treatment, which are lost in large quantities before reaching the dielectric barrier discharge plasma region, which is not conducive to the continuous reaction.

[0007] The self-heating type carbon dioxide catalytic hydrogenation to methane reactor in patent CN202011434050.2 uses the reaction heat of the methanation reaction to preheat the reaction raw materials, but the overall reaction is still mainly thermal catalysis, which requires higher equipment, and there are still problems such as coking and catalyst deactivation.

[0008] The methane dry reforming device in patent CN202021093161.7 uses a plasma reactor, but the reactor structure is too simple, the reaction time of the raw material gas in the plasma reactor is short, and there are problems of low raw material conversion rate, low target product yield, and low selectivity. SUMMARY

[0009] 1. The technical problem to be solved:

[0010] How to improve the raw material conversion rate and target product yield and selectivity in gas phase chemical reactions under plasma conditions.

[0011] 2. Technical solution:

[0012] In order to solve the above problems, the application provides a low-temperature plasma gas phase chemical device using a venturi, which comprises a high-voltage electrode, a ground electrode and a quartz tube, the high-voltage electrode is a metal rod, which extends into the quartz tube, the ground electrode is a stainless steel mesh, which is wound outside the quartz tube, a discharge area is generated in the quartz tube between the high-voltage electrode and the ground electrode, one end of the quartz tube is provided with a venturi unit, the venturi unit comprises a venturi head and a venturi tail, the venturi head comprises a first cylindrical structure and a second cylindrical structure, the outer diameter of the second cylindrical structure is larger than that of the first cylindrical structure, the second cylindrical structure is located at the left end of the venturi head and is attached to the inner wall of the quartz tube, the first cylindrical structure is inserted into a hole of the venturi tail and is attached to the hole, there is a gap between the hole and the inner wall of the hole, a small hole vertically penetrating the venturi head is arranged at the position close to the venturi tail of the venturi head, the quartz tube is provided with an air inlet pipe at the end close to the venturi head and an air outlet pipe at the other end, and the stainless steel mesh is located behind the venturi tail.

[0013] A sealing gasket is arranged at the position where the second cylindrical structure is attached to the quartz tube.

[0014] The first cylindrical structure and the second cylindrical structure are coaxial with the high-voltage electrode and the quartz tube.

[0015] The material of the venturi unit is quartz or polytetrafluoroethylene.

[0016] The diameter of the high-voltage electrode is 3-5 mm, the outer diameter of the quartz tube is 10-12 mm, the inner diameter of the quartz tube is 7-9 mm, the length of the discharge gap is 2-3 mm, the length of the ground electrode is 8-10 cm, the inner diameter of the air outlet pipe and the air inlet pipe is 3-4 mm, and the outer diameter of the air outlet pipe and the air inlet pipe is 5-6 mm.

[0017] The inner diameter of the small hole is 1-2 mm, the outer diameter of the first cylindrical structure is 3-5 mm, and the outer diameter of the second cylindrical structure is 7-9 mm. The width of the gap is 0.4-0.6 mm, the diameter of the hole is 3-5 mm, and the maximum diameter of the inner wall of the hole is 7-8 mm.

[0018] The reactant raw gas enters the quartz tube from the air inlet pipe.

[0019] 3. Beneficial effects:

[0020] The device uses dielectric barrier discharge structure and venturi as main body, carries out gas phase chemical reaction through dielectric barrier discharge, and the unreacted raw gas and the intermediate product which is not completely reacted can return to plasma area through the gas backflow generated by venturi, which prolongs the reaction time, is beneficial to the generation of active species, improves the utilization rate of raw gas and the yield and selectivity of target product. If the discharge area is filled with catalyst, the gas backflow can also prolong the reaction time between each active species and the catalyst, increase the probability of adsorption of each active species by the catalyst, and improve the reaction probability between each active species, thereby improving the synergistic catalytic efficiency, raw material conversion rate and the yield and selectivity of target product. In addition, the gas backflow generated by the venturi accelerates the gas flow rate in the local area and reduces the gas pressure, which is beneficial to plasma discharge and improves the energy efficiency of the reaction. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic diagram of the structure of the reaction device.

[0022] Figure 2 is a schematic diagram of the structure of the venturi head.

[0023] Figure 3 is a schematic diagram of the structure of the venturi tail.

[0024] Figure 4 is a schematic diagram of the structure of the venturi.

[0025] BRIEF DESCRIPTION OF DRAWINGS: 1. High voltage electrode; 4. Quartz tube; 5. Sealing gasket; 6. Venturi head; 7. Venturi tail; 8. Ground electrode; 9. Gas outlet pipe; 10. Gas inlet pipe; 101. Small hole; 102. First cylindrical structure; 103. Second cylindrical structure; 201. Gap; 202. Hole; 203. Hole inner wall. DETAILED DESCRIPTION

[0026] The application will be described in detail below in conjunction with the drawings and examples.

[0027] As shown in Figure 1 , a low-temperature plasma gas phase chemical reaction device using a venturi includes a high-voltage electrode 1, a ground electrode 8 and a quartz tube 4, the high-voltage electrode 1 is a metal rod, which extends into the quartz tube 4, the ground electrode 8 is a stainless steel mesh, which is wound outside the quartz tube 4, and a discharge area is generated in the quartz tube 4 between the high-voltage electrode 1 and the ground electrode 8. The stainless steel mesh is located behind the venturi tail 7. One end of the quartz tube 4 is provided with a venturi unit. The quartz tube 4 is provided with a gas inlet pipe 10 at one end near the venturi head, and is provided with a gas outlet pipe 9 at the other end,

[0028] As shown in Figure 4 , the venturi unit includes a venturi head 6 and a venturi tail 7.

[0029] As shown in Figure 2 The first cylindrical structure 102 and the second cylindrical structure 103 are included in the Venturi head 6, the outer diameter of the second cylindrical structure 103 is larger than that of the first cylindrical structure 102, and the second cylindrical structure 103 is located at the left end of the Venturi head 6 and is attached to the inner wall of the quartz tube 4.

[0030] As shown in Figure 3 The first cylindrical structure 102 is inserted into the hole 202 of the Venturi tail 7, and there is a gap 201 between the hole 202 and the hole inner wall 203. The Venturi head 6 is provided with a small hole 101 vertically penetrating the Venturi head 6 near the Venturi tail 7,

[0031] In one embodiment, the first cylindrical structure 101 and the second cylindrical structure 103 are coaxial with the high-voltage electrode 1 and the quartz tube 4.

[0032] In one embodiment, the material of the Venturi unit is quartz or polytetrafluoroethylene.

[0033] In one embodiment, the diameter of the high-voltage electrode 1 is 4 mm, the outer diameter of the quartz tube 4 is 10 mm, the inner diameter is 8 mm, the length of the discharge gap is 2 mm, the length of the ground electrode 8 is 10 cm, the inner diameter of the gas outlet pipe 9 and the gas inlet pipe 10 is 4 mm, and the outer diameter is 6 mm.

[0034] In one embodiment, the inner diameter of the small hole 101 in the Venturi head 6 is 1.6 mm, the outer diameter of the cylindrical structure 102 is 5 mm, and the outer diameter of the cylindrical structure 103 is 8 mm. The width of the gap 201 in the Venturi tail 7 is 0.5 mm, the diameter of the hole 202 is 5 mm, and the maximum diameter of the hole copper inner wall 203 is 7.8 mm.

[0035] In one embodiment, hydrogen and nitrogen are used as raw materials for ammonia synthesis, the mixed raw gas of hydrogen and nitrogen enters the quartz tube 4 from the gas inlet pipe 10, and then enters the plasma discharge area through the Venturi head 6 and the Venturi tail 7 for reaction. The Venturi unit can make the gas flow rate in the pipe experience a slow-fast-slow process, and utilize the Bernoulli principle and the Venturi effect to form a low-pressure area near the area with the shortest diameter of the Venturi, i.e. the small hole 101, so that the fluid near the small hole 101 is sucked into the Venturi. Since the second cylindrical structure 103 of the Venturi head 6 is attached to the inner wall of the quartz tube 4, and there is a sealing gasket 5, the fluid sucked by the small hole 101 can only be provided by the gas near the right side of the small hole 101. Therefore, the Venturi unit can form a gas backflow near the end gas outlet, and the backflow path is the first cylindrical structure 102-in the discharge gap-gap 201-small hole 101-the first cylindrical structure 102.

[0036] The gas backflow can make N2 and H2 that failed to dissociate or failed to completely dissociate re-enter the discharge region, prolong their residence time in the discharge region, facilitate the generation of active species N* and H*, and improve the utilization rate of raw gas. The gas backflow can make intermediate products NH* and NH2* of the ammonia synthesis reaction re-enter the discharge region, prolong the residence time of each active species in the reaction region, and increase the reaction probability between each active species. In the plasma discharge region, a catalyst can be added for synergistic catalysis. The gas backflow can also prolong the reaction time between each active species N*, H*, NH*, and NH2* and the catalyst, increase the probability of adsorption of each active species by the catalyst, and improve the reaction probability between each active species. In this way, the conversion rate of N2 and H2 and the yield of NH3 can be improved.

[0037] Since the gas outlet of the Venturi tail 7 is next to the discharge region, the gas backflow generated near the region can drive the gas flow in the discharge region, so that the gas flow rate in the local discharge region is slightly higher than that in the discharge region without the Venturi. According to Bernoulli's principle, the faster the gas flow rate, the lower the gas pressure, which makes the gas pressure in the local discharge region lower than that without the Venturi. The reduction in gas pressure prolongs the mean free path, so that the charged particles can prolong the acceleration time in the presence of an electric field, increase the energy of the charged particles when colliding with gas molecules, facilitate the dissociation of gas molecules, and facilitate the discharge, thereby reducing the voltage threshold required for the discharge, and further reducing the energy input and improving the energy efficiency.

[0038] The device belongs to a structural innovation device and is suitable for various reactions between plasma and gas, and has certain universality. It can be used for CO2 decomposition: CO2 gas is introduced, and CO2 is decomposed into CO and O2 under the action of plasma.

[0039] It can also be used for CO2 hydrogenation: CO2 and H2 are introduced, and CH4, CO, alcohols and acids are generated by reaction under the action of plasma. It can also be used for CO2 reforming CH4: CO2 and CH4 are introduced, and hydrocarbon compounds, CO and H2 are generated by reaction under the action of plasma.

[0040] The operation method of the device is taken as an example of introducing H2 and N2: after the system is built, N2 and H2 are introduced into the reactor, the power supply is turned on to adjust the input voltage to a predetermined value to generate plasma; after the discharge is stable, a gas chromatograph is used to detect the composition of the reaction gas; ammonia in the tail gas can be absorbed in deionized water, and unreacted N2 and H2 are discharged to the outside by the fume hood; after the experiment is completed, the instrument power is turned off, the H2 source is turned off first, and then the N2 source is turned off after all the H2 in the reactor is discharged.

Claims

1. A low-temperature plasma gas-phase chemical reaction device utilizing a Venturi tube, comprising a high-voltage electrode (1), a ground electrode (8), and a quartz tube (4), wherein the high-voltage electrode (1) is a metal rod extending into the quartz tube (4), the ground electrode (8) is a stainless steel mesh wound around the outside of the quartz tube (4), and a discharge region is generated within the quartz tube (4) between the high-voltage electrode (1) and the ground electrode (8), characterized in that: One end of the quartz tube (4) is provided with a Venturi tube unit, which includes a Venturi tube head (6) and a Venturi tube tail (7). The Venturi tube head (6) includes a first cylindrical structure (102) and a second cylindrical structure (103). The outer diameter of the second cylindrical structure (103) is larger than that of the first cylindrical structure (102). The second cylindrical structure (103) is located at the left end of the Venturi tube head (6) and fits against the inner wall of the quartz tube (4). The Venturi tube tail (7) has a hole (202). The outside of the hole (202) has The inner wall of the hole (203) has a gap (201) between the hole (202) and the inner wall of the hole (203). The first cylindrical structure (102) is inserted into the hole (202) of the tail of the venturi tube (7) and connected to the hole (202). The head of the venturi tube (6) is provided with a small hole (101) that penetrates the head of the venturi tube (6) vertically near the tail of the venturi tube (7). The quartz tube (4) is provided with an air inlet pipe (10) at one end near the head of the venturi tube and an air outlet pipe (9) at the other end. The stainless steel mesh is located behind the tail of the venturi tube (7).

2. The low-temperature plasma gas-phase chemical reaction apparatus utilizing a Venturi tube as described in claim 1, characterized in that: A sealing gasket (5) is provided at the joint between the second cylindrical structure (103) and the quartz tube (4) for sealing.

3. The low-temperature plasma gas-phase chemical reaction apparatus utilizing a Venturi tube as described in claim 1, characterized in that: The first cylindrical structure (102) and the second cylindrical structure (103) are coaxial with the high voltage electrode (1) and the quartz tube (4).

4. The low-temperature plasma gas-phase chemical reaction apparatus utilizing a Venturi tube as described in any one of claims 1-3, characterized in that: The venturi unit is made of quartz or polytetrafluoroethylene.

5. The low-temperature plasma gas-phase chemical reaction apparatus utilizing a Venturi tube as described in any one of claims 1-3, characterized in that: The high-voltage electrode (1) has a diameter of 3-5 mm, the outer diameter of the quartz tube (4) is 10-12 mm, the inner diameter is 7-9 mm, the discharge gap length is 2-3 mm, the ground electrode (8) has a length of 8-10 cm, and the inner diameter of the exhaust pipe (9) and the intake pipe (10) is 3-4 mm and the outer diameter is 5-6 mm.

6. The low-temperature plasma gas-phase chemical reaction apparatus utilizing a Venturi tube as described in any one of claims 1-3, characterized in that: The inner diameter of the small hole (101) is 1-2 mm, the outer diameter of the first cylindrical structure (102) is 3-5 mm, the outer diameter of the second cylindrical structure (103) is 7-9 mm, the width of the gap (201) is 0.4-0.6 mm, the diameter of the hole (202) is 3-5 mm, and the maximum diameter of the inner wall (203) of the hole is 7-8 mm.

7. The low-temperature plasma gas-phase chemical reaction apparatus utilizing a Venturi tube as described in any one of claims 1-3, characterized in that: The mixed raw material gas enters the quartz tube (4) from the inlet pipe (10).

8. The low-temperature plasma gas reaction apparatus utilizing a Venturi tube as described in any one of claims 1-3, characterized in that: It can be used for CO2 decomposition; it can be used for CO2 hydrogenation to produce CH4, CO, alcohols and acids; it can be used for CO2 reforming of CH4 to produce hydrocarbons, CO and H2; it can be used for N2 and H2 to synthesize ammonia.

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