A pulse-modulated microwave plasma nitrogen fixation system and method

Abstract

This invention provides a pulse-modulated microwave plasma nitrogen fixation system and method. The device includes a solid-state microwave power supply and a reactor. The reactor includes a needle-emitting electrode fixed on a brass integrated reaction chamber. The bottom of the reaction chamber is connected to a quartz tube. A plasma jet region is provided in the quartz tube, and a pressure sensor is installed in the plasma jet region. A vacuum pump is connected to the bottom of the quartz tube to draw the product to a product analysis section for real-time product concentration analysis, obtaining the yield at the current pulse modulation frequency. The corresponding current pulse modulation frequency f is then used to determine the yield. curr The total flow rate F and pressure P of the reacting gases are input into a large-scale intelligent analysis data model to analyze the pulse modulation frequency for the next step, and then output to a solid-state microwave power supply. This invention utilizes pulse-modulated microwave plasma to promote the reaction of N2 and O2 to generate nitrogen oxides, and has built a complete system covering synthesis and product detection. This system provides a scientific basis and technical support for optimizing reaction parameters and further improving yield.

Description

Technical Field

[0001] This invention belongs to the field of plasma technology applications and relates to a pulse-modulated microwave plasma nitrogen fixation system and nitrogen fixation method. Background Technology

[0002] Nitrogen is an essential component of proteins, nucleic acids, and other cellular components that make up life on Earth. Globally, nitrogen exists primarily in the atmosphere as nitrogen gas, but this source cannot be directly utilized by organisms. Therefore, converting nitrogen gas into simpler nitrogen compounds, such as ammonia or nitrogen oxides, through nitrogen fixation is crucial. In traditional industry, artificial nitrogen fixation is mainly achieved through the Hubble process. Although this method has achieved significant yields in industrial applications, it relies on fossil fuels for energy supply under high temperature and pressure conditions, accounting for 1%–2% of global energy consumption and accompanied by substantial carbon dioxide emissions. Furthermore, the synthesis of some nitrogen oxides depends on high-temperature and high-pressure ammonia oxidation methods (such as the Ostwald process) or arc discharge methods. For example, high-temperature and high-pressure processes require large amounts of energy to maintain the reaction temperature (typically exceeding 800°C) and are prone to generating byproducts (such as N₂O), increasing the cost of subsequent separation and purification. Arc discharge methods, on the other hand, suffer from limitations such as poor plasma stability, rapid electrode material wear, and high equipment maintenance costs.

[0003] Against the backdrop of national dual carbon emissions and the severe situation of rapid global population growth and greenhouse gas emissions, a zero-emission low-temperature nitrogen fixation technology has become a hot topic of cutting-edge research worldwide, and plasma technology, as an environmentally friendly nitrogen fixation technology, is considered to be the next generation of key nitrogen fixation technology.

[0004] High-energy electrons, active free radicals, and excited-state species in plasma can effectively break the strong chemical bonds between N2 and O2 (e.g., the N≡N bond dissociation energy is as high as 941 kJ / mol), thus enabling the synthesis of nitrogen oxides under relatively mild conditions. Among these, microwave plasma is considered a promising route for nitrogen oxide synthesis due to its advantages such as high energy density and strong reaction controllability. However, traditional microwave plasma technology often uses continuous wave mode, and its energy input method can easily lead to excessively high temperatures in the reaction zone, triggering reverse reactions under thermodynamic equilibrium constraints (e.g., the decomposition of NO into N2 and O2). Simultaneously, excessively high electron density may exacerbate ineffective collisions between molecules, reducing energy utilization efficiency. Furthermore, traditional plasma synthesis processes require high-power driving power supplies; in industrial production, high power means high energy consumption, significantly increasing the cost of nitrogen fixation. Meanwhile, existing plasma technologies also suffer from poor plasma stability control. This instability leads to uneven electron density and temperature distribution, fluctuations in the generation rate of active particles (such as excited-state N and O atoms), directly affecting the dissociation efficiency of nitrogen (N2) and oxygen (O2), and reducing reaction rate and product yield.

[0005] Furthermore, even if the gas flow rate and pressure are maintained during the reaction, there are still various unavoidable fluctuations and hidden changes in reality, which leads to the technical problem that a single fixed pulse modulation frequency cannot achieve the best yield. Summary of the Invention

[0006] Traditional nitrogen fixation synthesis methods are typically energy-intensive, unstable, and have low yields. To address these technical challenges and achieve green and efficient nitrogen fixation, this invention proposes a pulsed-modulated microwave plasma nitrogen fixation system and method. This system utilizes pulsed-modulated microwave plasma to promote the reaction of N2 and O2 to generate nitrogen oxides. A complete system covering synthesis and product detection is constructed, providing a scientific basis and technical support for optimizing reaction parameters and further improving yield. Pulsed-modulated microwave plasma technology is used to react nitrogen and oxygen to generate nitrogen oxides under discharge conditions. The generated plasma maintains good stability under low power conditions. By introducing pulse modulation technology, microwave energy is injected into the reaction system in intermittent high-power pulses. The relaxation time during the pulse-off phase reduces the overall temperature of the reaction zone, suppressing the reverse reaction process. Simultaneously, by adjusting relevant reaction parameters such as pulse modulation frequency, duty cycle, and power, the electron energy distribution and active particle concentration in the plasma can be precisely controlled, optimizing the N2 / O2 dissociation and recombination pathway. This achieves efficient and highly selective synthesis of nitrogen oxides under low energy consumption conditions. Furthermore, this invention achieves low-power synthesis of nitrogen oxides by adding a catalyst and introducing rare gas for ignition, while significantly improving the yield. An external magnetic field, a gas flow rate control device, and a vacuum pump at the bottom of the quartz tube are added to the plasma jet region to create a low-pressure zone at the tail to ensure the stability of the generated plasma. In addition, the pulse modulation frequency is updated and iterated using a smart data large model to improve the yield. This method significantly improves the yield of nitrogen oxides while achieving green nitrogen fixation.

[0007] The technical solution of the present invention is as follows:

[0008] A pulse-modulated microwave plasma nitrogen fixation system includes an input section, a reactor, a product analysis section, and a large-scale intelligent analysis data model.

[0009] The input section includes a solid-state microwave power supply, a nitrogen cylinder, an oxygen cylinder, a rare gas cylinder, and a mass flow controller. Nitrogen, oxygen, and rare gases are each fed into the reactor via a mass flow controller. The pulse modulation frequency of the solid-state microwave power supply is 25kHz-100kHz.

[0010] The reactor includes a needle-emitting electrode, which is fixed to a one-piece brass reaction chamber via a knob on a hollow brass rod. The position of the needle tip in the reaction chamber is changed by adjusting the knob. The one-piece design of the reaction chamber prevents gas leakage. Microwave power is connected to the needle-emitting electrode via an SMA connector. The bottom of the reaction chamber is connected to a quartz tube to collect gas. A plasma jet region and a low-pressure region at the tail are provided in the quartz tube. The low-pressure region at the tail significantly enhances the stability of the plasma generated at the tube opening. A pressure sensor is provided in the plasma jet region. A vacuum pump is connected to the bottom of the quartz tube to draw the product from the quartz tube to the product analysis section.

[0011] The product analysis section includes a Fourier transform infrared spectrometer and a computer connected to the Fourier transform infrared spectrometer, which analyzes the collected products (nitrogen oxides NO). x The sample is fed into a Fourier transform infrared spectrometer, and then a computer is used to perform real-time product concentration analysis to obtain the concentration at the current pulse modulation frequency f. curr The product synthesis (yield) situation is described below, and then the corresponding current pulse modulation frequency f is obtained. curr The total flow rate F and pressure P of the reactant gas are input into a pre-set intelligent data model in the computer to analyze the pulse modulation frequency for the next step, and then output to the solid-state microwave power supply.

[0012] The construction of the intelligent analysis data model is as follows:

[0013] First, data preparation for building the big data model is performed using the aforementioned input, reactor, and product analysis components. Under atmospheric pressure and a nitrogen-to-oxygen ratio of 1:1, the pressure range fluctuates within approximately 1000 Pa above and below one atmosphere. Twenty reference points are selected, spaced 100 Pa apart. Similarly, 20 reference points are also selected at equal intervals for the total flow rate of the reactant gas, ranging from 0 to v L / min (not reaching 0, where v is the maximum value). These 20 reference points correspond to 20 sets of data (P, F). Under each set of (P, F) conditions, starting from the initial pulse modulation frequency, 20 different adjustment values ​​Δf are attempted, where Δf = n500Hz, n (n = 0, 1, 2…). The input feature X is defined as containing the following parameter—the current pulse modulation frequency f. curr The total flow rate of the reacting gas is F, and the pressure is P. The output label Y represents the adjusted yield change ΔYield. Define the comprehensive scoring formula: Score=α·ΔYield - β·∣Δf∣ Here, coefficient α represents the proportion of contribution of unit yield change to the total score, and β represents the proportion of contribution of unit frequency adjustment absolute value to the total score. Since the goal is to find the modulation frequency corresponding to higher yields, α=1 and β=0.1 are set for each group (P, F, f). curr Select the Δf with the highest score;

[0014] Next, we begin building the model, starting by reading the pressure P, total flow rate of the reacting gas L, and current pulse modulation frequency f from the historical database. curr The output is the adjustment amount Δf for the next step. next We selected the RandomForestRegressor model, with the following requirements: use an ensemble of 100 decision trees; limit the maximum depth of a single tree to prevent overfitting; each node must have at least 5 samples before it can split; and use a fixed random seed to ensure reproducible results. Finally, we defined the trained model as model.predict().

[0015] The rare gas is pre-introduced into the reactor; the output power of the solid-state microwave power supply is 0-200W. The rare gas has three main functions: First, it acts as an ignition source. Due to its relatively low ionization energy, pre-introducing the rare gas before nitrogen and oxygen makes its atoms more easily ionized by the electric field, generating initial free electrons. These free electrons, accelerated by the electric field, further collide with other gas molecules (such as nitrogen or oxygen), initiating a chain ionization reaction. This facilitates plasma formation while reducing the power required for the reaction. Second, the added rare gas dilutes the concentration of the reactant gases, reducing the risk of localized arcing and significantly enhancing plasma stability. Finally, after the rare gas is introduced, the partial pressure of the main reactant gases (N2 / O2) decreases, the gas density decreases, and the mean free path of electron collisions decreases. l e As the electric field increases, the electron's time in the electric field increases, resulting in more complete accumulation of kinetic energy. Furthermore, according to the Penning ionization effect, rare gases will form metastable excited states during discharge, such as Ar. * It has an excited state energy level higher than the ionization energy of nitrogen gas. When it collides with nitrogen molecules, it triggers Penning ionization, which enhances the ionization process of nitrogen gas and thus improves the generation efficiency of nitrogen oxides in the plasma.

[0016] The reaction chamber adopts an inclined swirling gas structure, and ventilation branches are opened on the inner wall of the reaction chamber. The angle of the ventilation branches is distributed clockwise at an angle of 0°-15° with the tangent of the inner diameter, so as to ensure the stability of the gas introduced and thus maintain the stability of plasma generation.

[0017] The duty cycle of the solid-state microwave power supply is 0%-100%.

[0018] There are 4-6 ventilation branches, evenly distributed.

[0019] The lower part of the reaction chamber is designed as an inverted trapezoid to enhance the local electric field and increase the discharge.

[0020] Adding a porous rectifier to the plasma jet region, along with an electromagnet (radial magnetic field) placed on the outer side of the corresponding quartz tube, and a heat insulation layer placed between the electromagnet and the quartz tube, significantly contributes to both plasma stability and nitrogen oxide yield. Firstly, the added radial magnetic field confines the plasma, extending the residence time of electrons and increasing the collision frequency with gas molecules, thus improving the yield. Furthermore, this radial magnetic field effectively suppresses electron diffusion, resulting in a more uniform plasma distribution and ensuring plasma stability. Secondly, the porous rectifier in this region breaks up large-scale eddies, transforming turbulence into laminar or quasi-laminar flow, which also effectively maintains the stability of the generated plasma.

[0021] The porous rectifier is constructed by stacking at least two layers of stainless steel porous plates; the electromagnet is connected to a programmable power supply via an SMA connector.

[0022] The plasma jet region and the tail low-pressure region also include a catalyst-supported section, wherein a catalyst is added to the catalyst-supported section, and the catalyst is a metal-supported catalyst.

[0023] Metal-supported catalysts are obtained by immersing a pretreated support in a metal salt solution via ion exchange, followed by washing, drying, and calcination activation.

[0024] The carrier includes ZSM-5 molecular sieve; the metal includes copper, with a metal loading of 2-5 wt%.

[0025] The rare gas includes argon.

[0026] The present invention also provides a nitrogen fixation method, wherein the nitrogen fixation system comprises the following steps:

[0027] S1 Adjust the solid-state microwave power supply parameters to drive the discharge;

[0028] S2 ignites a rare gas in the reaction chamber, generating primary free electrons. Then, the flow rate of the rare gas is slowly reduced to a value greater than 0 and not higher than 0.5 L / min by a gas flow controller. At the same time, the flow rates of nitrogen and oxygen are gradually increased and finally adjusted to 1 L / min-5 L / min respectively. The ratio of nitrogen to oxygen is adjusted to 1:1, and the total flow rate of the nitrogen and oxygen reaction gases is less than v.

[0029] The plasma generated by S3 enters the product analysis section through the plasma jet region, the catalyst-supported section, and the tail low-pressure region;

[0030] S4 performs real-time monitoring of the product and uses a smart data big model to update and iterate the pulse modulation frequency.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) Compared with traditional synthesis methods or electric arc methods, the present invention adopts pulse-modulated microwave plasma technology with a pulse modulation frequency of 25kHz-100kHz. Microwave energy is released in a concentrated manner in the form of short pulses, which significantly improves the efficiency of electron energy utilization.

[0033] (2) Based on pulse modulation, the pulse modulation frequency can be controlled in real time by constructing an "intelligent data analysis big model". This overcomes the problem that the pressure and gas flow rate will inevitably change during the reaction process, which will lead to the inability to obtain the best yield with a single fixed modulation frequency. The real-time modulation frequency can better match the molecular vibrations of N2 and O2, and can better optimize the reaction path to achieve the goal of efficient synthesis of nitrogen oxides.

[0034] (3) Under the synergistic effect of the introduced rare gas and the added catalyst, nitrogen oxides can be synthesized at a lower power while significantly improving their yield;

[0035] (4) Regarding the stability of the generated plasma, by adding a magnetic field to the jet region, adding a pump to the bottom of the quartz tube to create a low-pressure region at the tail, and using a gas flow rate control device, the plasma generated by microwave excitation has good stability, which provides a guarantee for the efficient synthesis of nitrogen oxides in the future.

[0036] (5) It is equipped with a complete system from discharge reaction to product analysis, which provides a guarantee for further improving yield and reducing energy consumption. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a pulse-modulated microwave plasma nitrogen fixation system;

[0038] Figure 2 This is a schematic diagram of the reactor;

[0039] Figure 3 This is a schematic diagram of the reactor cross-section;

[0040] Figure 4 This is a schematic diagram of the cross-section of the reactor's vent.

[0041] In the diagram: 1. Solid-state microwave power supply; 2. Programmable power supply; 3. Fourier transform infrared spectrometer; 4. Computer; 5. Porous rectifier; 6. Mass flow controller; 7. Nitrogen cylinder; 8. Insulation layer; 9. Electromagnet; 10. Plasma jet zone; 11. Catalyst loading section; 12. Oxygen cylinder; 13. Rare gas cylinder; 14. Quartz tube; 15. Low-pressure zone at the tail end; 16. Needle emission electrode; 17. Brass hollow rod; 18. SMA connector; 19. Vent branch pipe; 20. Reaction chamber; 21. Knob; 22. Sealing ring; 23. Vacuum pump; 24. Pressure sensor. Detailed Implementation

[0042] Example

[0043] like Figure 1-4 As shown, a pulse-modulated microwave plasma nitrogen fixation system includes an input section, a reactor, a product analysis section, and a large-scale intelligent analysis data model.

[0044] The input section includes a solid-state microwave power supply 1 with adjustable power, duty cycle, and pulse modulation frequency; a nitrogen cylinder 7; an oxygen cylinder 12; a rare gas cylinder 13; and a mass flow controller 6. Nitrogen, oxygen, and rare gas are each fed into a separate reactor via a single flow path controlled by the mass flow controller 6. The rare gas is argon. The solid-state microwave power supply 1 has a pulse modulation frequency of 25kHz-100kHz, an output power of 0-200W, and a duty cycle of 0%-100%.

[0045] The reactor is 35-45mm long. A 1mm diameter needle-emitting electrode 16 is fixed to a brass integrated reaction chamber 20 by a knob 21 via a brass hollow rod 17. The position of the electrode 16 within the chamber is adjusted by the knob 21. The reaction chamber 20 is 31mm long (1 / 4 of the microwave wavelength) and is encased in an aluminum alloy shell. The microwave power is connected to the needle-emitting electrode 16 via an SMA connector 18. The gas enters the reaction chamber 20 through six ventilation branches 19 located on the inner wall of the reaction chamber 20 at a 15-degree angle to the tangent of the inner diameter of the chamber. The ventilation branches 19 are evenly distributed in a clockwise direction to ensure that the gas entering the reaction chamber 20 is in a vortex state. The lower part of the reaction chamber 20 is designed as an inverted trapezoid to strengthen the local electric field and enhance the discharge. A quartz tube 14 is connected to the bottom of the reaction chamber 20 to collect gas. The quartz tube 14 contains three reaction units: a plasma jet zone 10 (generating a plasma jet at the tip of the needle emission electrode 16), a catalyst loading section 11, and a low-pressure tail zone 15. A porous rectifier 5 is added to the plasma jet zone 10; its structure consists of two layers of stainless steel porous plates stacked together, with a pore size of 1 mm and a spacing of 1.5 mm. An electromagnet 9 is installed outside the quartz tube corresponding to the plasma jet zone 10 to confine the plasma. A heat insulation layer 8 is placed between the electromagnet 9 and the quartz tube 14. The electromagnet 9 is connected to a programmable power supply 2 via an SMA connector. A Cu-ZSM-5 catalyst is added to the catalyst loading section 11, with a Cu loading of 2-5 wt%. The ZSM-5 molecular sieve enhances product selectivity and high-temperature resistance, while the loaded copper enhances the oxidation reaction. The catalyst can significantly increase the product yield. A vacuum pump 23 is connected to the end of the low-pressure tail zone 15 to draw the product into the product analysis section.

[0046] The product analysis section includes a Fourier transform infrared spectrometer (Nico-let is10; Thermo Scientific, Madison, WI) and a computer 4 connected to the Fourier transform infrared spectrometer 3, and the product (NO) x The sample was drawn into the Fourier transform infrared spectrometer 3, and then the product concentration was analyzed in real time by the computer 4 to obtain the concentration at the current pulse modulation frequency f. curr The yield at the given time, and then the corresponding current pulse modulation frequency f. curr The total flow rate F and pressure P of the reacting gas are input into a pre-set intelligent data model in the computer to analyze how to adjust the pulse modulation frequency in the next step, and then output to the solid-state microwave power supply 1.

[0047] The construction of the intelligent data big model includes the following steps:

[0048] First, data preparation for building a big data model is carried out using the aforementioned input section, reactor (catalyst-free section), and product analysis section. Under atmospheric pressure and a nitrogen-to-oxygen ratio of 1:1, the pressure range fluctuates within approximately 1000 Pa above and below one atmosphere, with 20 reference points spaced 100 Pa apart. Similarly, 20 reference points are also taken at equal intervals between the total flow rate of the reactant gas (0-1.5 L / min, not 0). These 20 reference points correspond to 20 sets of data (P, F). Under each set of (P, F) conditions, starting from the initial pulse modulation frequency of 25 kHz, 20 different adjustment values ​​Δf = Δf = n500 Hz, where n (n = 0, 1, 2…) are tried. The input feature X is defined as containing the following parameter—the current pulse modulation frequency f. curr The total flow rate of the reacting gas is F, and the gas pressure is P. The output label Y represents the adjusted yield change ΔYield. Define the comprehensive scoring formula: Score= a·ΔYield - β·∣Δf∣ Here, coefficient α represents the proportion of contribution of unit yield change to the total score, and β represents the proportion of contribution of unit frequency adjustment absolute value to the total score. Since the goal is to find the modulation frequency corresponding to higher yields, α=1 and β=0.1 are set for each group (P, F, f). curr Select the Δf with the highest score;

[0049] Next, the model construction begins. First, the pressure P, total flow rate of the reacting gas F, and current pulse modulation frequency f are read from the historical database. curr The output is the adjustment amount Δf for the next step. next We selected the RandomForestRegressor model, with the following requirements: use an ensemble of 100 decision trees; limit the maximum depth of a single tree to prevent overfitting; each node must have at least 5 samples before it can split; and use a fixed random seed to ensure reproducible results. Finally, we defined the trained model as model.predict().

[0050] The nitrogen fixation method using the aforementioned nitrogen fixation system includes the following steps:

[0051] Step 1: Catalyst Preparation: First, the ZSM-5 molecular sieve is pretreated by calcining it at 500℃ for 2 hours to remove adsorbed water and impurities and activate the pore structure. A copper nitrate solution with a concentration of 0.05-0.2 mol / L is prepared to achieve a copper loading of 2-5 wt% on the molecular sieve, and the pH is adjusted to 4-5 to avoid damaging the zeolite structure. The pretreated ZSM-5 is then mixed with the copper salt solution at a solid-liquid ratio of kg / m³. 3The mixture was stirred at a 1:10 ratio; the molecular sieve after ion exchange was washed repeatedly with deionized water until the conductivity of the washing filtrate stabilized, then dried at approximately 100°C for 7 hours; finally, it was calcined in air at 500°C for 2 hours, so that copper exists in either the oxidized state (CuO) or the ionic state (Cu). 2+ It is stably dispersed in molecular sieves.

[0052] Step 2: Experimental System Setup: After passing through the gas mass flow controller 6, the three gas streams are merged into one stream and connected to the ventilation branch pipe 19. The solid-state microwave power supply 1 is connected to the SMA connector 18 of the reaction chamber 20, ensuring the connection is secure. An electromagnet is installed outside the plasma jet region 10 and connected to a programmable power supply 2, controlling the applied magnetic field strength to 0.05T. A porous rectifier 5 is added to the plasma jet region 10 to stabilize the airflow. A vacuum pump at the bottom of the quartz tube is used to transport the product into the infrared spectrometer for subsequent component analysis.

[0053] Step 3: Experiment Start-up: Adjust the solid-state microwave power supply parameters to drive the discharge under the conditions of 90W output power, 25kHz pulse modulation frequency, and 50% duty cycle. First, ignite the gas by introducing 2L / min of argon gas. After generating primary free electrons, slowly reduce the argon gas flow rate to 0.5L / min using the mass flow controller 6, while gradually increasing the flow rates of nitrogen and oxygen. Finally, adjust the flow rates of nitrogen and oxygen to 0.5L / min respectively, and ensure that the ratio of nitrogen to oxygen is 1:1.

[0054] Step 5: Real-time Product Analysis: Start the computer and Fourier transform infrared spectrometer. Before each product detection, purge the gas cell with nitrogen to clean internal impurities. After ensuring the gas cell is full of nitrogen, collect background spectra before introducing the product gas for comparison with the product spectra. When detecting the product, pass the collected product gas through a drying tube to remove moisture before introducing it into the gas cell, as water vapor has strong absorption in the infrared band and will interfere with product detection. Ensure the reaction gas is injected into the gas cell slowly (avoiding turbulence). After the gas stabilizes (2 minutes after introducing the reaction gas), begin data acquisition to obtain the current pulse modulation frequency f. curr The yield at (25kHz) corresponds to the pressure P, the total flow rate of the reactant gas F, and the current pulse modulation frequency f. curr The intelligent data model is input into the computer, and the impact of the current pulse modulation frequency on the yield is analyzed using the model. The iterative update frequency given after the analysis is then input into the solid-state microwave power supply 1 to achieve real-time control of the modulation frequency.

[0055] The specific process for using this model for iterative iteration is as follows: Real-time parameters of the current plasma region pressure P are obtained through sensors, and the pressure P, total flow rate of the reacting gas F, and current pulse modulation frequency f are used to... curr As input for the next step. P, F, f curr Encapsulated as a two-dimensional array [P, F, f] curr Call the `predict()` method of the trained random forest regression model (model), inputting the current state data. The model returns the predicted adjustment Δf. next .

[0056] A safety constraint is applied to the model to limit the adjustment range and prevent system instability caused by sudden frequency changes. The maximum allowable adjustment step size is set to ±1kHz (500Hz in this embodiment), and a numerical clipping function is used to limit the predicted Δf within a safe range.

[0057] Update the pulse modulation frequency and send the adjusted frequency to solid-state microwave power supply 1. Calculate the new frequency f. new =f curr +Δf next (In this embodiment f) new (The frequency is set to 100kHz), and the device control function is called to send a frequency setting command to the solid-state microwave power supply 1. This process requires a communication protocol (such as Ethernet) to connect to the solid-state microwave power supply 1 to ensure that the command is executed correctly.

[0058] The above feedback process enables real-time pulse control, overcoming the limitations of traditional fixed pulse modes.

[0059] The following explanation uses two sets of specific parameters:

[0060] First, the parameters for the first set of experiments were as follows: the total flow rate of the reactant gas was 1.5 L / min, the duty cycle was 50%, the copper catalyst loading was 2 wt%, and the power supply output was 90 W. The pulse modulation frequency was adjusted to 25 kHz. In the second set of experiments, real-time pulse modulation was used, and the pulse modulation frequency was updated and iterated to 100 kHz using a "smart data model." Finally, a control group was added, without pulse modulation. The results showed that at 25 kHz, the nitrogen oxide yield was 4.2% and the energy consumption was 2.2 MJ / mol; in the system with real-time pulse modulation, the nitrogen oxide yield was 7.1% and the energy consumption was 1.4 MJ / mol; while in the group without pulse modulation, the nitrogen oxide yield was 3.3% and the energy consumption was 2.9 MJ / mol.

[0061] Secondly, the copper loading in the catalyst molecular sieve was set to 4 wt%, and the other parameters were kept consistent with the first group of experiments. The nitrogen oxide yield was 5.7% and the energy consumption was 1.56 MJ / mol.

Claims

1. A pulse-modulated microwave plasma nitrogen fixation system, characterized in that: This includes the input section, reactor, product analysis section, and intelligent analysis data model; The input section includes a solid-state microwave power supply (1), a nitrogen cylinder (7), an oxygen cylinder (12), a rare gas cylinder (13), and a mass flow controller (6). Nitrogen, oxygen, and rare gas are respectively fed into the reactor via the mass flow controller (6). The pulse modulation frequency of the solid-state microwave power supply is 25kHz-100kHz. The reactor includes a needle emission electrode (16), which is fixed to a brass integrated reaction chamber (20) by a knob on a brass hollow rod, and the position of the needle tip in the reaction chamber (20) is changed by adjusting the knob; microwave power is connected to the needle emission electrode (16) via an SMA connector (18); the bottom of the reaction chamber (20) is connected to a quartz tube (14) to collect gas, and a plasma jet zone (10) and a tail low-pressure zone (15) are provided in the quartz tube (14); a pressure sensor (24) is provided in the plasma jet zone (10), and a vacuum pump (23) is connected to the bottom of the quartz tube (14) to draw the product from the quartz tube (14) to the product analysis section; The product analysis section includes a Fourier transform infrared spectrometer (3) and a computer (4) connected to the Fourier transform infrared spectrometer (3). The collected products are fed into the Fourier transform infrared spectrometer (3), and then the computer (4) performs real-time product concentration analysis to obtain the current pulse modulation frequency f. curr The product synthesis situation is as follows, and then the corresponding current pulse modulation frequency f is calculated. curr The total flow rate F and pressure P of the reaction gas are input into the intelligent data big model set in the computer (4) to analyze the pulse modulation frequency of the next step, and then output to the solid-state microwave power supply (1). The construction of the intelligent analysis data model is as follows: First, data preparation for building the big data model is performed using the input section, reactor, and product analysis section mentioned above. Under atmospheric pressure and a nitrogen-to-oxygen ratio of 1:1, the pressure P fluctuates within 1000 Pa above and below one atmosphere, with 20 reference points spaced 100 Pa apart. Similarly, 20 reference points are also taken at equal intervals between 0 and v L / min for the total flow rate of the reactant gas. These 20 reference points correspond to 20 sets of data (P, F). Under each set of (P, F) conditions, starting from the initial pulse modulation frequency, 20 different adjustment values ​​Δf are tried, where Δf = n × 500 Hz, n = 0, 1, 2… The input feature X is defined as containing the following parameter—the current pulse modulation frequency f. curr Given the total flow rate F and pressure P of the reacting gases, and the output label Y, the adjusted yield change is ΔYield. Define the comprehensive scoring formula: Score = α·ΔYield - β·∣Δf∣ Here, coefficient α represents the proportion of contribution of unit yield change to the total score, and β represents the proportion of contribution of unit frequency adjustment absolute value to the total score. Since the goal is to find the modulation frequency corresponding to higher yields, α=1 and β=0.1 are set for each group (P, F, f). curr Select the Δf with the highest score; Secondly, the model is constructed by first reading the pressure P, the total flow rate of the reacting gas F, and the current pulse modulation frequency f from the historical database. curr The output is the adjustment amount Δf for the next step. next We selected a random forest regressor model with the following requirements: use an ensemble of 100 decision trees; limit the maximum depth of a single tree to prevent overfitting; each node must have at least 5 samples before it can split; and use a fixed random seed to ensure reproducible results. Finally, we defined the trained model as model.predict(). A catalyst loading section (11) is provided between the plasma jet region (10) and the tail low-pressure region (15), and a catalyst is added to the catalyst loading section (11). The catalyst is a metal-supported catalyst.

2. The pulse-modulated microwave plasma nitrogen fixation system as described in claim 1, characterized in that: The rare gas is introduced into the reactor beforehand; the output power of the solid-state microwave power supply (1) is 0-200W.

3. The pulse-modulated microwave plasma nitrogen fixation system as described in claim 1, characterized in that: The reaction chamber (20) adopts an inclined swirling structure, and ventilation branches (19) are opened on the inner wall of the reaction chamber (20). The angle of the ventilation branches is 0-15° with the tangent of the inner diameter and distributed in a clockwise direction.

4. The pulse-modulated microwave plasma nitrogen fixation system as described in claim 1, characterized in that: The lower part of the reaction chamber (20) is an inverted trapezoid.

5. The pulse-modulated microwave plasma nitrogen fixation system as described in claim 1, characterized in that: A porous rectifier (5) is added to the plasma jet region (10), and an electromagnet (9) is provided on the outside of the quartz tube (14) corresponding to the plasma jet region (10), and a heat insulation layer (8) is placed between the electromagnet (9) and the quartz tube (14).

6. The pulse-modulated microwave plasma nitrogen fixation system as described in claim 5, characterized in that: The structure of the porous rectifier (5) is at least two layers of stainless steel porous plates stacked together; the electromagnet (9) is connected to the programmable power supply (2) through an SMA connector.

7. The pulse-modulated microwave plasma nitrogen fixation system as described in claim 1, characterized in that: The support includes ZSM-5 molecular sieve; the metal includes copper, with a metal loading of 2-5 wt%.

8. The pulse-modulated microwave plasma nitrogen fixation system as described in claim 1, characterized in that: The duty cycle of the solid-state microwave power supply (1) is 0%-100%.

9. A nitrogen fixation method, characterized in that: The nitrogen fixation system according to claim 1 includes the following steps: S1 adjusts the parameters of the solid-state microwave power supply (1) to drive the discharge; S2 introduces rare gas into the reaction chamber (20) for ignition. After generating primary free electrons, the flow rate of rare gas is slowly reduced by the mass flow controller (6) to be greater than 0 and not less than 0.5 L / min. At the same time, the flow rates of nitrogen and oxygen are gradually opened and increased. Finally, the flow rates of nitrogen and oxygen are adjusted to 1 L / min-5 L / min respectively, and the ratio of nitrogen to oxygen is adjusted to 1:

1. The total flow rate of the reaction gas of nitrogen and oxygen is less than v. The plasma generated by S3 enters the product analysis section through the plasma jet zone (10), the catalyst support section (11), and the tail low-pressure zone (15); S4 performs real-time monitoring of the product and uses a smart data big model to update and iterate the pulse modulation frequency.

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