CN113998671B - Novel discharge electrode and device and method for preparing hydrogen by reforming methane with microwave liquid-phase plasma - Google Patents

Abstract

The invention discloses a novel discharge electrode and a device and a method for preparing hydrogen by reforming methane with microwave liquid-phase plasma, wherein the discharge electrode comprises: inserting a tungsten rod into the center of the boron nitride tube and fixing, wherein the tungsten rod is higher than the upper end of the boron nitride tube by a certain distance, and sharpening the exposed end of the tungsten rod to facilitate the generation and maintenance of plasma; the device comprises an air inlet system, a microwave plasma reaction system and a product separation system, wherein the air inlet system comprises methane gas, a discharge electrode, a raw material tank and a water pump; the reforming hydrogen production method disclosed by the invention is directly carried out in water, carbon deposition cannot be generated on an electrode, stable operation of plasma can be ensured, the generated carbon source mainly exists in the form of element carbon particles and small molecular carbon, the content is low, and the generated element carbon particles are easily separated by filtration.

Description

A new type of discharge electrode and microwave liquid phase plasma reforming device and method for hydrogen production from methane

technical field

The invention relates to the field of plasma technology, in particular to a novel discharge electrode and a device and method for producing hydrogen from methane reformed by microwave liquid-phase plasma.

Background technique

As a clean energy source, hydrogen has the advantages of high combustion calorific value, and the product is water, which will not cause secondary pollution, so hydrogen is an ideal secondary energy source. Due to its abundant reserves, natural gas is an economical and reasonable choice in the process of hydrogen production from fossil fuels. As the main component of natural gas, methane has been a research hotspot in recent years.

Traditional methane reforming methods for hydrogen production include steam methane reforming, methane dry reforming, methane partial oxidation reforming, methane autothermal reforming, and methane catalytic decomposition. Among them, the methane steam reforming process does not require oxygen, the reaction temperature is high, and the H ₂ /CO ratio is higher than other technologies, so it is more suitable for the production of hydrogen-rich synthesis gas. To overcome the problems of high fuel cost and catalyst deactivation at high temperature, catalyst-free plasma technology has been investigated. At present, the main methods of hydrogen production by plasma methane wet reforming are: dielectric barrier discharge, sliding arc discharge, microwave discharge and spark discharge. But from the current point of view, the above methods of plasma reforming methane to produce hydrogen are all formed by electric discharge in the gas phase. Gas-phase discharge has certain limitations. First, water molecules need to be heated and vaporized, which increases additional energy consumption. Secondly, the plasma density in the gas phase discharge is low, the discharge is unstable, and the hydrogen production efficiency is low. For liquid-phase discharge plasma, compared with gas-phase plasma, it uses liquid as the discharge medium, which has the characteristics of high plasma density, direct mass transfer, and rich active components.

Contents of the invention

The invention provides a new type of discharge electrode and a device and method for producing hydrogen by reforming methane with microwave liquid phase plasma to overcome the problems of low plasma density, unstable discharge, low hydrogen production efficiency and easy carbon deposition in gas phase discharge. .

In order to achieve the above object, technical scheme of the present invention is:

A new type of discharge electrode and microwave liquid-phase plasma reforming methane hydrogen production device, including discharge electrode, raw material tank, water pump, microwave generator, wave guide, sleeve, reactor, vacuum pump, gas collection device and condensing device; Methane gas enters the reactor tangentially from the discharge electrode through the inlet pipeline, and a gas flow meter is arranged on the inlet pipeline;

One end of the waveguide is connected to the microwave generator; the sleeve is vertically fixed to the lower part of the waveguide, and the reactor vertically passes through the upper part of the waveguide and is nested in the sleeve. The discharge electrode is arranged in the casing;

The water pump is arranged in the raw material tank, and the top of the raw material tank is connected with a vacuum pump and a gas collecting device;

A liquid inlet pipeline and a first gas outlet pipeline are arranged between the reactor and the raw material tank, the second gas outlet pipeline connects the raw material tank and the condensing device, and the third gas outlet pipeline connects the condensing device and the gas collection device.

Further, the discharge electrode includes an electrode, a boron nitride base and a boron nitride side wall tube, the electrode is arranged in the boron nitride side wall tube, and the electrode/boron nitride side wall tube is fixed on the boron nitride side wall tube on a boron base.

Further, the height of the electrode is greater than that of the boron nitride side wall tube, and the relative distance between the electrode and the boron nitride side wall tube can be adjusted through the boron nitride base.

Further, the top of the electrode is sharpened, and several symmetrical hole structures are provided on the boron nitride base to ensure that methane gas flows into the reactor evenly.

Further, the boron nitride side wall tube is designed in the shape of a bullet at one end close to the electrode, so that the inflowing methane molecules are concentrated at the tip of the discharge electrode.

Further, the electrodes are any one of tungsten rods, copper rods, and stainless steel rods.

The reforming methane hydrogen production method based on the novel discharge electrode and the microwave liquid phase plasma reforming methane hydrogen production device comprises the following steps:

S1: Inject methane gas and the aqueous solution in the raw material tank into the reactor and mix them thoroughly;

S2: Using a vacuum pump to depressurize the reactor and the raw material tank;

S3: Start the microwave generator to generate plasma at the tip of the electrode;

S4: The plasma acts on methane and aqueous solution to generate hydrogen, which is collected and analyzed after being cooled by the raw material tank and condensing device.

Further, in the step S1, the feed flow rate of the methane gas is 0.1L/min-5.0L/min, the internal pressure of the reactor is 5-10kPa, and the aqueous solution is injected into the reactor The volume is 150-500 mL.

Further, in the step S1, the aqueous solution is one or more of deionized water, sodium chloride aqueous solution, acidic aqueous solution, alkaline aqueous solution, and alcoholic aqueous solution.

Further, in the step S1, preferably, the aqueous solution is one or more of deionized water, sodium chloride aqueous solution, acidic aqueous solution, alkaline aqueous solution, oxidizing aqueous solution, reducing aqueous solution, and alcoholic aqueous solution kind.

Further, in the step S3, the microwave input power is 600-1200W.

Further, in the step S1, one or more of nitrogen, argon, helium, and carbon dioxide may also be added to the methane gas as an auxiliary gas.

The novel discharge electrode and the device and method for producing hydrogen by reforming methane with microwave liquid-phase plasma disclosed in the present invention carry out the reaction of producing hydrogen by reforming methane in a microwave liquid-phase discharge plasma system directly in an aqueous solution without evaporation, thereby Save energy and simplify equipment. The highly active particles generated by the plasma at the electrode end can initiate the methane reforming hydrogen production reaction under mild conditions without adding a catalyst, which avoids the problem of limited use time of the catalyst. It has the advantages of high methane conversion rate, fast reaction time, and convenient operation, and is more suitable for decentralized small-scale hydrogen production. In addition, the reforming hydrogen production method disclosed in the present invention does not generate carbon deposits on the electrodes, and can ensure the stable operation of the plasma. The generated carbon sources mainly exist in the form of elemental carbon particles and small molecular carbon. For the hydrocarbons in the gas-phase products of microwave liquid-phase plasma, only _C2 compounds were detected, and the content was low. Under high power conditions, almost no hydrocarbons are produced, and the resulting elemental carbon particles are easily separated by filtration.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 is the structure schematic diagram of the direct coupling microwave liquid phase plasma methane reforming hydrogen production device of the present invention;

Fig. 2 is the structural representation of discharge electrode of the present invention;

Fig. 3 is the flow chart of the method for producing hydrogen by directly coupling microwave liquid phase plasma methane reforming of the present invention;

Fig. 4 is a gas phase product diagram of the present invention after being detected and discharged by TCD in gas chromatography.

In the figure, 1. Methane gas, 2. Intake pipeline, 3. Gas flow meter, 4. Discharge electrode, 5. Reactor, 6. Liquid inlet pipeline, 7. First gas outlet pipeline, 8. Raw material tank, 9. Waveguide, 10. Sleeve, 11. Second gas outlet pipeline, 12. Microwave generator, 13. Water pump, 14. Gas collection device, 15. Vacuum pump, 16. Condenser device, 17. Third gas outlet pipe Road, 4-1, boron nitride side wall tube, 4-2, electrode, 4-3, boron nitride base.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings 1-4 in the embodiments of the present invention. Obviously, the described The embodiments are some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

As shown in Figures 1 and 2, a new type of discharge electrode and a microwave liquid phase plasma reforming device for methane hydrogen production, including a discharge electrode 4, a raw material tank 8, a water pump 13, a microwave generator 12, a waveguide 9, a casing 10, Reactor 5, vacuum pump 15, gas collecting device 14 and condensing device 16; methane gas 1 enters in the described reactor 5 from the discharge electrode 4 through the inlet pipeline 2, and the gas flow rate is set on the inlet pipeline 2 3; one end of the waveguide 9 is connected to the microwave generator 12; the sleeve 10 is vertically fixed on the lower part of the waveguide 9, and the reactor 5 vertically passes through and embedded in the upper part of the waveguide 9 Set in the casing 10, the discharge electrode 4 is set in the casing 10; the water pump 13 is set in the raw material tank 8, and the top of the raw material tank 8 is connected with a vacuum pump 15 and a collector. A gas device 14; a liquid inlet pipeline 6 and a first gas outlet pipeline 7 are arranged between the reactor 5 and the raw material tank 8, the second gas outlet pipeline 11 connects the raw material tank 8 and the condensing device 16, and the third gas outlet The gas pipeline 17 connects the condensing device 16 and the gas collecting device 14 . In this embodiment, the waveguide 9 is a rectangular waveguide, the sleeve is a metal sleeve, one end of the air inlet pipeline 2 is connected to the gas flow meter 3, and the other end is connected to the discharge electrode 4. Into the reactor 5, the upper part of the reactor 5 is connected to the liquid inlet pipe 6 and the first gas outlet pipe 7, and the other end of the liquid inlet pipe 6 is connected to the first gas outlet pipe 7. In the raw material tank 8, the lower part of the reactor 5 vertically passes through the rectangular waveguide 9, the metal sleeve 10 is vertically fixed on the lower part of the rectangular waveguide 9, and the discharge electrode 4 is placed in the The metal casing 10 is fully immersed in the liquid, one end of the rectangular waveguide 9 is connected to the microwave generator 12, the top of the raw material tank 8 is connected to the dry vacuum pump 15 and the gas outlet pipe 11, and the outlet The gas pipeline is connected with the condensing device.

Further, the discharge electrode 4 includes an electrode 4-2, a boron nitride base 4-3 and a boron nitride side wall tube 4-1, and the electrode 4-2 is arranged on the boron nitride side wall tube 4- 1, and fixed on the boron nitride base 4-3. In this embodiment, preferably, the electrode 4-2 is a tungsten rod, and the discharge electrode 4 is composed of a tungsten rod 4-2, a boron nitride side wall tube 4-1 and a boron nitride base 4-3 , insert the tungsten rod 4-2 into the center of the boron nitride side wall tube 4-1 and fix it by the boron nitride base 4-3, the distance between the tungsten rod 4-2 and the The upper end of the boron nitride side wall tube 4-1 is at a certain distance, and the exposed end of the tungsten rod 4-2 is sharpened, which is beneficial to the generation and maintenance of plasma. The methane gas is transported through the gas pipeline and output from the gap between the tungsten rod 4-2 and the boron nitride side wall tube 4-1, and quickly reaches near the tip of the electrode, where plasma is generated at the tip of the electrode.

Further, the height of the electrode 4-2 is greater than the height of the boron nitride side wall tube 4-1, and the relative distance between the electrode 4-2 and the boron nitride side wall tube 4-1 It can be adjusted through the base 4-3. Further, the top of the electrode 4-2 is sharpened, and several symmetrical hole structures are provided on the base 4-3. Further, the electrodes 4-2 are one or more of tungsten rods, copper rods, and stainless steel rods. In this embodiment, the boron nitride side wall tube 4-1 is designed in the shape of a bullet near the discharge end of the tungsten rod 4-2, which is conducive to the accumulation of methane near the discharge electrode after the input of methane gas, and improves the discharge of methane. Conversion rate; the boron nitride base 4-3 is designed as a symmetrical porous structure so that methane gas can be uniformly input into the reactor.

As shown in Figure 3, the reforming methane hydrogen production method based on the novel discharge electrode and the microwave liquid phase plasma reforming methane hydrogen production device includes the following steps:

Step 11: inject the methane gas and the aqueous solution in the raw material tank through the water pump into the reactor respectively through the discharge electrode, and mix thoroughly;

Step 22: using a dry vacuum pump to depressurize the reactor and the raw material tank;

Step 33: start the microwave generator device, and generate plasma at the tip of the discharge electrode;

Step 44: the high-energy particles produced by the liquid phase discharge act on the methane and the aqueous solution to generate hydrogen gas due to the generation of plasma;

Step 55: The hydrogen gas is collected and analyzed after being cooled by the raw material tank and the condensing device.

Wherein, the aqueous solution is one or more of deionized water, sodium chloride aqueous solution, acidic aqueous solution, alkaline aqueous solution, oxidizing aqueous solution, reducing aqueous solution, and alcoholic aqueous solution. In this embodiment, preferably, the aqueous solution is deionized water.

In addition, in order to increase the conversion rate of methane, an auxiliary gas may be added in the present application, wherein the auxiliary gas includes one or more of nitrogen, argon, helium, and carbon dioxide. There are two ways for the auxiliary gas to enter the reactor, one is to enter the reactor tangentially from the discharge electrode like methane gas, and the other is to enter from the upper part of the reactor through the liquid inlet pipe. .

Example 1:

Use a dry vacuum pump to keep the internal pressure of the reactor at 10kPa, adjust the gas flowmeter to keep the methane inlet flow at 0.90L/min, adjust the relative distance between the discharge end of the tungsten rod and the boron nitride side wall tube to 10mm, and use the method of removing Ionized water is used as an aqueous solution, and the volume of deionized water in the reactor is kept at 220mL by the liquid inlet pump, so that the water temperature of the deionized water is kept at 25°C, and the microwave generator is started to make the microwave input power 900W. The high-energy particles act on methane and aqueous solution to generate hydrogen gas. After discharge, the product hydrogen gas is collected through the gas collection device, and the collected product is analyzed and determined by gas chromatography.

Analysis of experimental results: As shown in the gas chromatogram in Figure 4, it can be seen from the figure that the discharge products include: hydrogen, carbon monoxide, carbon dioxide, and _C2 compounds. It was found that the conversion rate of methane was 93.5%; the flow rate of hydrogen was 1.50L/min; the selectivity of hydrogen was 65.8%; the selectivity of carbon was 55.8%; the energy efficiency of hydrogen production was 1.24mmol/kJ; In the examples, no visible carbon deposition was produced.

Example 2:

The difference from Example 1 is only that the microwave input power is 1200W, and the rest of the experimental steps and experimental parameters are the same as those in Example 1.

Analysis of the experimental results: the methane conversion rate is 94.9%; the hydrogen flow rate is 1.93L/min; the hydrogen selectivity is 75.1%, the carbon selectivity is 68.8%; the hydrogen production energy efficiency is 1.20mol/kJ.

Example 3:

The only difference from Example 1 is that the aqueous solution used is a sodium chloride solution, wherein the conductivity of the sodium chloride solution is 3300 μs/cm, and the rest of the experimental steps and experimental parameters are the same as those in Example 1.

Analysis of the experimental results: the methane conversion rate is 75.63%; the hydrogen flow rate is 2.21L/min; the hydrogen selectivity is 74.36%, the carbon selectivity is 74.03%; the hydrogen production energy efficiency is 1.82mmol/kJ.

Example 4:

The difference from Example 1 is that nitrogen is purged before the discharge test, and the rest of the experimental steps and parameters are the same as those in Example 1.

Analysis of the experimental results: the methane conversion rate is 89.16%; the hydrogen flow rate is 1.77L/min; the hydrogen selectivity is 75.0%, the carbon selectivity is 66.5%; the hydrogen production energy efficiency is 1.65mmol/kJ.

Example 5:

The difference from Example 1 is only that an appropriate amount of phosphoric acid is added to deionized water to adjust the pH to 3.37, and the rest of the experimental steps and experimental parameters are the same as those in Example 1.

Analysis of the experimental results: the methane conversion rate is 91.56%; the hydrogen flow rate is 1.87L/min; the hydrogen selectivity is 76.0%, the carbon selectivity is 68.0%; the hydrogen production energy efficiency is 1.54mmol/kJ.

Embodiment 6:

The difference from Example 1 is only that an appropriate amount of oxidizing substance-sodium persulfate is added to the deionized water, and the rest of the experimental steps and experimental parameters are the same as those in Example 1.

Analysis of the experimental results: the methane conversion rate is 94.12%; the hydrogen flow rate is 1.96L/min; the hydrogen selectivity is 76.3%, the carbon selectivity is 71.6%; the hydrogen production energy efficiency is 1.62mmol/kJ.

Comparative example 1 (dielectric barrier discharge plasma)

Wet gas-phase methane reforming experiments were carried out in a tunable ferroelectric packed bed dielectric barrier discharge reactor, the discharge conditions were: CH ₄ : H ₂ O = 2:1, CH ₄ flow rate 4.5 cm ³ /min, H ₂ The flow rate of O is 9.0cm ³ /min; the discharge frequency is 500Hz, the distance between electrodes is 3mm, and the size of the ferroelectric core is 0.5-2mm.

Analysis of experimental results: the conversion rate of methane is 15.9%; the energy efficiency of hydrogen production is 0.19mmol/kJ.

Comparative example 2 (DC spark discharge plasma)

The methane reforming experiment was carried out in the DC spark discharge reaction system. The discharge conditions were as follows: CH ₄ flow rate was 50mL/min, discharge current was 10mA, discharge voltage was 2kV, and discharge power was 20W.

Analysis of the experimental results: the methane conversion rate is 44.41%, the hydrogen production flow rate is 43.62mL/min, and the hydrogen selectivity is 98.21%.

Comparative example 3 (sliding arc discharge plasma)

The combined reforming of water vapor and _CH4 and _CO2 was studied in a slip arc discharge plasma reactor. The applied power was 80 W, the total flow rate of CH ₄ and CO ₂ was kept constant at 360 SCCM, and the ratio of CH ₄ /CO ₂ /H ₂ O was 1/1.5/0.58.

Analysis of the experimental results: the methane conversion rate is 55%, the carbon dioxide conversion rate is 43%, the hydrogen flow rate is 1.93L/min, the hydrogen selectivity is 65.2%, and the carbon selectivity is 32.9%.

Table 1: The experimental result parameter of embodiment and comparative example

As can be seen from Table 1, compared with the methane reforming performance of the gas-phase discharge in the comparative example, the methane reforming of the liquid-phase discharge in the embodiment not only ensures a higher methane conversion rate, but also obtains a relatively high conversion rate. Good hydrogen production efficiency.

To sum up, the novel discharge electrode and microwave liquid-phase plasma reforming methane hydrogen production device provided by this application are simple in structure and easy to operate, and the entire reaction process can be directly carried out in aqueous solution to save energy consumption, and , which can realize high-efficiency discharge in a wide range of working pressures and in different kinds of aqueous solutions. Using the above-mentioned device to produce hydrogen by plasma reforming methane can effectively solve the problems that the existing reforming hydrogen production process needs to be carried out under high temperature and high pressure, and carbon deposits are easily generated, resulting in unstable discharge.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims (7)

1. A device for producing hydrogen from methane by microwave liquid-phase plasma reforming, characterized in that it includes a discharge electrode (4), a raw material tank (8), a water pump (13), a microwave generator (12), a waveguide (9 ), casing (10), reactor (5), vacuum pump (15), gas collecting device (14) and condensing device (16); methane gas (1) tangentially discharges from the The electrode (4) enters the reactor (5), and the gas flow meter (3) is arranged on the gas inlet line (2); One end of the waveguide (9) is connected to the microwave generator (12); the sleeve (10) is vertically fixed on the lower part of the waveguide (9), and the reactor (5) (9) The upper part passes through vertically and is nested in the sleeve (10), and the discharge electrode (4) is arranged in the sleeve (10) and completely immersed in the liquid; The water pump (13) is set in the raw material tank (8), and the top of the raw material tank (8) is connected with a vacuum pump (15) and a gas collecting device (14); A liquid inlet pipeline (6) and a first gas outlet pipeline (7) are provided between the reactor (5) and the raw material tank (8), and a second gas outlet pipeline (11) is connected to the raw material tank ( 8) and the condensing device (16), the third outlet pipeline (17) connects the condensing device and the gas collecting device (14); The discharge electrode (4) includes an electrode (4-2), a boron nitride base (4-3) and a boron nitride side wall tube (4-1), and the electrode (4-2) is set on the nitrogen The boron nitride side wall tube (4-1), and the electrode (4-2) is fixed on the boron nitride base (4-3); The height of the electrode (4-2) is greater than the height of the boron nitride side wall tube (4-1), and the electrode (4-2) and the boron nitride side wall tube (4-1) The relative distance between them can be adjusted through the boron nitride base (4-3); The top of the electrode (4-2) is sharpened, and the boron nitride base (4-3) is provided with several symmetrical hole structures to ensure that methane gas flows evenly into the reactor (5). 2. The device for reforming methane to hydrogen with microwave liquid phase plasma according to claim 1, characterized in that the electrode (4-2) is any one of a tungsten rod, a copper rod, and a stainless steel rod. 3. The method for producing hydrogen by reforming methane based on the device for producing hydrogen by microwave liquid-phase plasma reforming methane according to any one of claims 1-2, characterized in that it comprises the following steps: S1: Inject methane gas (1) and the aqueous solution in the raw material tank (8) into the reactor (5) and mix them thoroughly; S2: Use a vacuum pump (15) to depressurize the reactor (5) and raw material tank (8); S3: start the microwave generator (12) to generate plasma at the tip of the electrode (4-2); S4: The plasma acts on methane and aqueous solution to generate hydrogen, which is collected and analyzed after being cooled by the raw material tank (8) and the condensing device (16). 4. A method for producing hydrogen by microwave liquid-phase plasma reforming methane according to claim 3, characterized in that, in the step S1, the feed flow rate of the methane gas is 0.1L/min-5.0L /min, the internal pressure of the reactor is 5-10kPa, and the volume of the aqueous solution injected into the reactor is 150-500mL. 5. a kind of microwave liquid-phase plasma reforming method for methane hydrogen production according to claim 3 is characterized in that, in described step S1, described aqueous solution is deionized water, sodium chloride aqueous solution, acidic aqueous solution, One or more of alkaline aqueous solution and alcoholic aqueous solution. 6 . The method for producing hydrogen by microwave liquid-phase plasma reforming methane according to claim 3 , characterized in that, in the step S3 , the microwave input power of the microwave generator ( 12 ) is 600-1200W. 7. The method for producing hydrogen from a kind of microwave liquid-phase plasma reforming methane according to claim 3, characterized in that, in the step S1, nitrogen, argon, helium, One or more of carbon dioxide is used as auxiliary gas.

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