Micro-channel gas-liquid two-phase discharge nitrogen fixation device

Abstract

The application provides a micro-channel gas-liquid two-phase discharge nitrogen fixation device, which comprises a gas supply system and a liquid supply system, further comprises a micro-fluid chip and a dielectric barrier discharge system, the micro-fluid chip comprises a planar substrate and a transverse channel and a longitudinal channel which are arranged in communication along the planar substrate and are connected with the gas supply system and the liquid supply system respectively, wherein the gas-liquid two-phase forms a two-phase region in the longitudinal channel, and the dielectric barrier discharge system comprises a positive electrode and a negative electrode which are superimposed on the micro-fluid chip along the two-phase region to form an electric field. The micro-channel discharge of the application greatly improves the DBD discharge energy density and promotes the nitrogen dissociation; the micro-channel generates a stable gas-liquid two-phase flow pattern, strengthens the interface reaction and mass transfer between the plasma gas bubble group and the liquid phase, promotes the reaction equilibrium to move to the nitrogen fixation direction, so as to realize the improvement of the plasma nitrogen fixation energy efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nitrogen fixation, and particularly relates to a micro-channel gas-liquid two-phase discharge nitrogen fixation device. BACKGROUND

[0002] Industrial nitrogen fixation product-ammonia (NH3) is an indispensable synthetic raw material for fertilizers and other chemicals. Ammonia is of great interest as a non-carbon carrier in energy storage and conversion. The Haber-Bosch ammonia synthesis nitrogen fixation process has been improved for more than 100 years and has approached its theoretical energy consumption (0.48 MJ / mol), but still accounts for 2% of global energy consumption and emits 1% of global greenhouse gases. Therefore, it is of great significance to find a sustainable alternative route for ammonia synthesis. The theoretical energy consumption of non-thermal plasma (NTP) nitrogen fixation is as low as 0.20 MJ / mol, and the combination of plasma and increasingly cost-effective solar energy can achieve near-zero emissions, which has great potential. The dielectric barrier discharge (DBD) nitrogen fixation method does not require high temperature and high pressure. High-energy electrons generated by atmospheric pressure discharge can promote the occurrence of nitrogen fixation reaction. Currently, the highest energy efficiency of DBD nitrogen fixation without catalyst assistance is less than 5.0 g-NH3 / kWh, but there is still a big gap from the energy efficiency of 200 g-NH3 / kWh for decentralized ammonia synthesis. The reasons for the low energy efficiency of DBD nitrogen fixation are as follows: first, the energy density of DBD discharge is low, and the electron collision dissociation energy threshold of nitrogen molecules is as high as 9.75 eV, and the dissociation of nitrogen becomes the rate-limiting step of nitrogen fixation reaction; second, the plasma reaction is a free radical process, which leads to poor product selectivity, and the synthesis products (ammonia, nitrogen oxides) are prone to decomposition under high electron energy conditions. SUMMARY

[0003] The present application greatly improves the energy density of DBD discharge through micro-channel discharge, promotes the dissociation of nitrogen, and generates stable flow patterns in the micro-channel to strengthen the interface reaction and mass transfer between the plasma bubble group and the liquid phase, thereby promoting the reaction equilibrium to move towards nitrogen fixation, and achieving the improvement of plasma nitrogen fixation energy efficiency.

[0004] To solve the above technical problems, the present application adopts the following technical solutions:

[0005] A micro-channel gas-liquid two-phase discharge nitrogen fixation device, comprising a gas supply system and a liquid supply system, further comprising a microfluidic chip and a dielectric barrier discharge system, the microfluidic chip comprising a planar substrate and a transverse channel and a longitudinal channel arranged in communication along the planar substrate and connected with the gas supply system and the liquid supply system respectively, wherein the gas-liquid two-phase forms a two-phase region in the longitudinal channel, and the dielectric barrier discharge system comprises a positive electrode and a negative electrode superimposed on the microfluidic chip along the two-phase region to form an electric field.

[0006] Preferably, the transverse channel and the longitudinal channel are arranged in orthogonal communication on the planar substrate.

[0007] Preferably, the positive electrode, the microfluidic chip, and the negative electrode are stacked, and a dielectric layer is stacked between the positive electrode and the microfluidic chip, and between the negative electrode and the microfluidic chip.

[0008] Preferably, the transverse channel and the longitudinal channel are arranged in a cross shape. The two ends of the transverse channel are connected to the liquid supply system, and the longitudinal channel is connected to the gas supply system. Gas enters from one end of the longitudinal channel and exits from the other end.

[0009] Preferably, the positive electrode and the negative electrode are embedded on opposite sides of the longitudinal channel of the microfluidic chip, and a dielectric layer is provided on the side of the positive electrode and the negative electrode away from the microfluidic chip.

[0010] Preferably, the transverse channel and the longitudinal channel are arranged in a T-shape orthogonal. The transverse channel is connected to the gas supply system, and the longitudinal channel is connected to the liquid supply system. Liquid enters from one end of the longitudinal channel and exits from the other end.

[0011] Preferably, the dielectric barrier discharge system further includes a power supply connected to the positive electrode. The power supply is a high-voltage sinusoidal AC power supply or a pulsed output power supply, and its peak output voltage is 0.5 to 10 kV, and its frequency is adjustable to 1 to 20 kV.

[0012] Preferably, both the gas supply system and the liquid supply system are delivered using an injection pump or a peristaltic pump. The gas supply components of the gas supply system are nitrogen, air, a mixture of nitrogen and hydrogen, or a mixture of nitrogen and methane. The liquid supply components of the liquid supply system are water, an acid solution, or a salt solution.

[0013] Preferably, the microfluidic chip material is an insulating medium, and the dielectric constant of the microfluidic chip material is 2-5, and the light transmittance is >80%. The microfluidic chip is polydimethylsiloxane, UV-curable adhesive, plexiglass, or quartz glass.

[0014] Preferably, the positive and negative electrodes are cadmium, tin, lead, indium, indium tin oxide, or nano-silver conductive films.

[0015] As can be seen from the above technical solutions, the present invention has the following beneficial effects: In the present invention, both the gas supply system and the liquid supply system use injection pumps for stable delivery. The supplied gas and liquid flow along the transverse and longitudinal channels, respectively, forming a two-phase flow channel in the longitudinal channel. The dielectric barrier discharge system discharges in the gas phase region to generate products such as ammonia and nitrogen oxides, which are absorbed by the liquid phase. The discharge in the gas-liquid two-phase region enhances the nitrogen fixation reaction. The transverse and longitudinal channels of the microfluidic structure have dimensions of 50–500 μm. The micro-gap and ultra-large specific surface area can enhance the plasma discharge energy and the reaction and transfer between the gas and liquid phases, solving the problems of low energy density and low product selectivity of conventional dielectric barrier discharge nitrogen fixation routes, and improving the energy efficiency of plasma nitrogen fixation. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the present invention;

[0017] Figure 2 This is a schematic diagram of one embodiment of the connection between the microfluidic chip and the dielectric barrier discharge system of the present invention;

[0018] Figure 3 for Figure 2 Schematic diagram of section AA;

[0019] Figure 4 This is a schematic diagram of another embodiment of the connection between the microfluidic chip and the dielectric barrier discharge system of the present invention;

[0020] Figure 5 for Figure 4 Schematic diagram of the BB section;

[0021] Figure 6 The diagram illustrates the nitrogen fixation efficiency of the nitrogen fixation device of the present invention under different discharge voltages.

[0022] In the diagram: 10, gas supply system; 20, liquid supply system; 30, microfluidic chip; 310, lateral channel; 320, longitudinal channel; 410, positive electrode; 420, negative electrode; 50, dielectric layer. Detailed Implementation

[0023] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] Reference Figure 1A microchannel gas-liquid two-phase discharge nitrogen fixation device includes a gas supply system 10, a liquid supply system 20, a microfluidic chip 30, and a dielectric barrier discharge system. The microfluidic chip includes a planar substrate and a microfluidic channel structure. The microfluidic channel structure includes a transverse channel 310 and a longitudinal channel 320 that are connected along the planar substrate and respectively connected to the gas supply system and the liquid supply system. The gas and liquid phases form a two-phase region in the longitudinal channel. The dielectric barrier discharge system includes a positive electrode 410 and a negative electrode 420 that are stacked along the two-phase region to form an electric field. In use, both the gas supply system and the liquid supply system are stably delivered by injection pumps. The supplied gas and liquid flow along the transverse channel and the longitudinal channel respectively, forming a two-phase flow channel in the longitudinal channel. The dielectric barrier discharge system discharges in the gas phase region to generate products such as ammonia and nitrogen oxides, which are absorbed by the liquid phase. The discharge in the gas-liquid two-phase region enhances the nitrogen fixation reaction. The transverse and longitudinal channels of the microfluidic structure have dimensions of 50–500 μm. The micro gaps and ultra-large specific surface area can enhance the plasma discharge energy and the reaction and transfer between the gas and liquid phases, solving the problems of low energy density and low product selectivity of conventional dielectric barrier discharge nitrogen fixation routes, and improving the energy efficiency of plasma nitrogen fixation.

[0025] The nitrogen fixation device of the present invention has a simple structure, is easy to scale up in parallel to realize distributed nitrogen fixation production, has fast start-up and shutdown, high efficiency, and can realize the function of energy storage and power regulation when combined with green electricity.

[0026] As a preferred technical solution of the present invention, the transverse channel 310 and the longitudinal channel 320 are orthogonally connected and arranged on the planar substrate, that is, the transverse channel and the longitudinal channel are vertically distributed along the planar substrate. The gas and liquid phases enter the microfluidic chip through their respective channels, and the gas and liquid phases can merge in the longitudinal channel to form a gas-liquid two-phase flow channel. In this way, ammonia and nitrogen oxides are generated by discharge in the gas phase region, and nitrogen fixation reaction is enhanced by discharge in the gas-liquid two-phase region. It should be noted that the transverse channel and the longitudinal channel are not limited to the aforementioned orthogonal connection arrangement. The transverse channel and the longitudinal channel can also be arranged at a certain angle, such as being distributed in a Y-shape along the planar substrate.

[0027] Furthermore, such as Figure 2As shown, the transverse and longitudinal channels are arranged in a cross-shaped orthogonal configuration. The two ends of the transverse channel are connected to the liquid supply system, and the longitudinal channel is connected to the gas supply system. Gas enters from one end of the longitudinal channel and exits from the other end. The positive electrode, microfluidic chip, and negative electrode are stacked in a sandwich structure. A dielectric layer 50 is stacked between the positive electrode and the microfluidic chip, and between the negative electrode and the microfluidic chip. The positive and negative electrodes are in close contact with the dielectric layer. The presence of the dielectric layer can suppress the development of discharge current and form a high electron temperature, making the gas temperature close to room temperature plasma. In this way, the plasma bubble clusters undergo interfacial reactions and mass transfer with the liquid phase in the channel between the dielectric layer and the microfluidic chip. Since the channel of the microfluidic chip can generate a stable gas-liquid two-phase flow pattern, it promotes the reaction equilibrium to shift towards nitrogen fixation, thereby improving the plasma nitrogen fixation efficiency.

[0028] Furthermore, such as Figure 4 As shown, the horizontal and vertical channels are not limited to the aforementioned cross-shaped arrangement, but can also be arranged orthogonally in a T-shape on the planar substrate. In this case, the horizontal channel is connected to the gas supply system, and the vertical channel is connected to the liquid supply system. Liquid enters from one end of the vertical channel and exits from the other end. At the same time, the positive and negative electrodes are embedded on both sides of the vertical channel of the microfluidic chip, and a dielectric layer is provided on the side of the positive and negative electrodes away from the microfluidic chip. In this case, the positive and negative electrodes are sandwiched between the microfluidic chips, and plasma bubble clusters carry out interfacial reactions and mass transfer between the microfluidic chip, the positive electrode, and the negative electrode. In this case, the dielectric layer is set between the microfluidic chip and the electrode.

[0029] As a preferred technical solution of the present invention, the dielectric barrier discharge system further includes a power supply connected to the positive electrode. Specifically, the power supply is a high-voltage sinusoidal AC power supply or a pulsed output power supply, and its peak output voltage is 0.5-10kV, and the frequency is adjustable to 1-20kV. When the transverse channel and the longitudinal channel are arranged in a cross orthogonal configuration, and the positive electrode, the microfluidic chip, and the negative electrode are stacked, the positive and negative terminals of the power supply are connected to the outermost positive and negative electrodes, respectively. When the transverse channel and the longitudinal channel are arranged in a T-shape orthogonal configuration, and the positive and negative electrodes are embedded on both sides of the longitudinal channel of the microfluidic chip, the positive and negative terminals of the power supply are connected to the positive and negative electrodes inside the microfluidic chip, respectively. In this way, the plasma bubble clusters can carry out interfacial reactions and mass transfer within the channel.

[0030] As a preferred technical solution of the present invention, both the gas supply system and the liquid supply system are delivered using an injection pump. Specifically, the gas supply components of the gas supply system are nitrogen, air, a mixture of nitrogen and hydrogen, or a mixture of nitrogen and methane. The liquid supply components of the liquid supply system are water, acid solution, or salt solution. Of course, in addition to using an injection pump to deliver the gas and liquid, a peristaltic pump can also be used for delivery, and no further restrictions are imposed here.

[0031] Furthermore, the microfluidic chip material is an insulating material with a dielectric constant of 2-5 and a light transmittance of >80%. The microfluidic chip is made of polydimethylsiloxane (PDMS), UV-curable adhesive (NOA81), plexiglass (PMMA), or quartz glass.

[0032] Furthermore, the electrode materials for the positive and negative electrodes are low-melting-point metals such as cadmium, tin, lead, indium, indium tin oxide (ITO), or nano-silver conductive films.

[0033] This invention also provides a microchannel gas-liquid two-phase discharge nitrogen fixation method, comprising the following steps:

[0034] S1: Adjust the flow rate of the syringe pump to regulate the gas and liquid velocity in the regulating channel to produce a stable flow pattern;

[0035] S2: Adjust the discharge voltage and discharge frequency to generate a stable dielectric barrier discharge in the gas or gas-liquid two-phase region, and to cause a nitrogen fixation reaction in the gas-liquid two-phase region.

[0036] S3: After continuous reaction, samples are taken at regular intervals, and the concentrations of ammonium ions and nitrate ions in the product are detected by ultraviolet-visible spectrophotometry.

[0037] The nitrogen fixation device of the present invention will be described in detail below through specific embodiments.

[0038] Example 1:

[0039] Reference Figure 3 A microchannel gas-liquid two-phase discharge nitrogen fixation device includes a gas supply system 10, a liquid supply system 20, a microfluidic chip 30, and a dielectric barrier discharge system. The microfluidic chip includes a planar substrate and a microfluidic channel structure. The microfluidic channel structure includes a transverse channel and a longitudinal channel connected along the planar substrate and respectively connected to the gas supply system and the liquid supply system. The gas and liquid phases form a two-phase region in the longitudinal channel. The dielectric barrier discharge system includes positive and negative electrodes formed by stacking microfluidic chips along the two-phase region to create an electric field. Both the gas supply system 10 and the liquid supply system 20 use syringe pumps with a flow rate of 10–1000 mL / h for stable delivery. The gas supply component is air, and the liquid supply component is deionized water.

[0040] The transverse and longitudinal channels are arranged in a cross-shaped orthogonal configuration. The two ends of the transverse channel are connected to the liquid supply system, and the longitudinal channel is connected to the gas supply system. Gas enters from one end of the longitudinal channel and exits from the other end. The positive electrode, microfluidic chip, and negative electrode are stacked in a sandwich-like structure. The electrodes cover the gas phase region and the gas-liquid two-phase region of the microfluidic chip, respectively.

[0041] The microfluidic chip is made of PDMS material and is fabricated by standard photolithography and casting method. The cross-shaped channel formed by the horizontal and vertical channels is 40mm long in both the horizontal and vertical directions. An elliptical discharge region with a major axis of 10mm and a minor axis of 6mm is expanded in the vertical channel. The center of the ellipse is 10mm away from the intersection of the cross and the channel cross section is a rectangle of 0.1mm×0.2mm.

[0042] The positive and negative electrodes of the dielectric barrier discharge system are made of transparent ITO glass with a thickness of 0.3 mm. The glass serves as the dielectric layer with a thickness of 0.2 mm. The power supply for the dielectric barrier discharge system is a high-voltage sinusoidal AC power supply or a pulsed output power supply with a peak output voltage of 0.5–10 kV and a frequency adjustable from 1 to 20 kHz.

[0043] Example 2:

[0044] Reference Figure 5 A microchannel gas-liquid two-phase discharge nitrogen fixation device includes a gas supply system 10, a liquid supply system 20, a microfluidic chip 30, and a dielectric barrier discharge system. The microfluidic chip includes a planar substrate and a microfluidic channel structure. The microfluidic channel structure includes a transverse channel and a longitudinal channel connected along the planar substrate and respectively connected to the gas supply system and the liquid supply system. The gas and liquid phases form a two-phase region in the longitudinal channel. The dielectric barrier discharge system includes positive and negative electrodes formed by stacking microfluidic chips along the two-phase region to create an electric field. Both the gas supply system 10 and the liquid supply system 20 use syringe pumps with a flow rate of 10–1000 mL / h for stable delivery. The gas supply component is air, and the liquid supply component is deionized water.

[0045] The transverse and longitudinal channels are arranged in a T-shape orthogonally on the planar substrate. The transverse channel is connected to the gas supply system, and the longitudinal channel is connected to the liquid supply system. The liquid enters from one end of the longitudinal channel and exits from the other end. At the same time, the positive and negative electrodes are arranged parallel to the microfluidic channel structure. Specifically, they are embedded on both sides of the longitudinal channel of the microfluidic chip. The electrodes are only distributed on both sides of the gas-liquid two-phase region.

[0046] The microfluidic chip is made of PMMA (polymethyl methacrylate) and is machined into a T-shaped structure. The horizontal channel length of the T-shaped structure is 40 mm, the vertical channel length is 40 mm, and the channel cross-section is a rectangle of 0.3 mm × 0.6 mm.

[0047] The positive and negative electrodes of the dielectric barrier discharge system are made of copper and are distributed in parallel at a distance of 0.2 mm from both sides of the transverse channel. The length of the electrodes is 60 mm. The glass is used as the dielectric layer with a thickness of 0.2 mm. The power supply of the dielectric barrier discharge system is a high-voltage sinusoidal AC power supply or a pulsed output power supply with a peak output voltage of 0.5 to 10 kV and a frequency adjustable from 1 to 20 kHz.

[0048] Down Figure 6 To determine the nitrogen fixation yield and energy efficiency of the nitrogen fixation device under different discharge voltages, the following... Figure 6 It can be seen that the nitrogen fixation yield and energy efficiency are highest when the discharge voltage is 200V, that is, the nitrogen fixation energy efficiency is the highest, and it can reach up to 12gN / kWh. This is because increasing the discharge voltage can accelerate the nitrogen fixation rate of the product and reduce energy consumption. However, if the voltage is further increased, the DBD discharge changes from filament discharge to arc discharge. The discharge is uneven and some energy will be converted into heat energy, which leads to a decrease in synthesis efficiency.

[0049] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A microchannel gas-liquid two-phase discharge nitrogen fixation device, comprising a gas supply system (10) and a liquid supply system (20), characterized in that, It also includes a microfluidic chip (30) and a dielectric barrier discharge system. The microfluidic chip includes a planar substrate and a transverse channel and a longitudinal channel that are connected along the planar substrate and respectively connected to a gas supply system and a liquid supply system. Gas forms a gas phase region in the upper part of the longitudinal channel, and gas and liquid form a two-phase region in the lower part of the longitudinal channel. The dielectric barrier discharge system includes a positive electrode and a negative electrode that are stacked along the two-phase region to form an electric field. The positive electrode, the microfluidic chip, and the negative electrode are stacked, with the positive and negative electrodes covering the gas phase region and the gas-liquid two-phase region of the microfluidic chip, and a dielectric layer (50) is stacked between the positive electrode and the microfluidic chip and between the negative electrode and the microfluidic chip. The transverse channel and the longitudinal channel are arranged in a cross shape. The two ends of the transverse channel are connected to the liquid supply system, and the longitudinal channel is connected to the gas supply system. Gas enters from one end of the longitudinal channel and exits from the other end. Both the gas supply system and the liquid supply system use injection pumps for stable delivery. The supplied gas and liquid flow along the transverse and longitudinal channels respectively, forming a two-phase flow channel in the longitudinal channel. The dielectric barrier discharge system discharges in the gas phase region to generate ammonia and nitrogen oxides, which are absorbed by the liquid phase. It also discharges in the gas-liquid two-phase region to enhance the nitrogen fixation reaction.

2. The microchannel gas-liquid two-phase discharge nitrogen fixation device according to claim 1, characterized in that, The transverse and longitudinal channels are orthogonally connected and arranged on the planar base.

3. The microchannel gas-liquid two-phase discharge nitrogen fixation device according to claim 2, characterized in that, The positive and negative electrodes are embedded on opposite sides of the longitudinal channel of the microfluidic chip, and a dielectric layer (50) is provided on the side of the positive and negative electrodes away from the microfluidic chip.

4. The microchannel gas-liquid two-phase discharge nitrogen fixation device according to claim 3, characterized in that, The transverse channel and the longitudinal channel are arranged in a T-shape. The transverse channel is connected to the gas supply system, and the longitudinal channel is connected to the liquid supply system. Liquid enters from one end of the longitudinal channel and exits from the other end.

5. The microchannel gas-liquid two-phase discharge nitrogen fixation device according to claim 1 or 4, characterized in that, The dielectric barrier discharge system also includes a power supply connected to the positive electrode. The power supply is a high-voltage sinusoidal AC power supply or a pulsed output power supply, and its peak output voltage is 0.5 to 10 kV, and its frequency is adjustable from 1 to 20 kV.

6. The microchannel gas-liquid two-phase discharge nitrogen fixation device according to claim 5, characterized in that, The gas supply system consists of nitrogen, air, a mixture of nitrogen and hydrogen, or a mixture of nitrogen and methane; the liquid supply system consists of water, an acid solution, or a salt solution.

7. The microchannel gas-liquid two-phase discharge nitrogen fixation device according to claim 5, characterized in that, The microfluidic chip is made of an insulating medium, and the dielectric constant of the microfluidic chip material is 2-5, and the light transmittance is >80%. The microfluidic chip is made of polydimethylsiloxane, UV-curable adhesive, plexiglass, or quartz glass.

8. The microchannel gas-liquid two-phase discharge nitrogen fixation device according to claim 5, characterized in that, The positive and negative electrodes are cadmium, tin, lead, indium, indium tin oxide, or nano-silver conductive films.

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