Method for synthesizing nitric acid through low-temperature plasma coupling photo-Fenton advanced oxidation technology

Abstract

The invention belongs to the field of catalytic synthesis, and provides a method for synthesizing nitric acid by a low-temperature plasma coupling photo-Fenton advanced oxidation technology. According to the invention, under an environmental condition, nitrogen and oxygen in the air form active excited state particles and steady-state oxynitride which are in non-thermodynamic equilibrium under the action of dielectric barrier discharge, and when the active particles and the oxynitride pass through a photo-Fenton oxidation system, the active excited state particles and the steady-state oxynitride are oxidized; the active free radicals produced by the photo-Fenton reaction are further oxidized and converted into a product nitric acid. Compared with the prior art, harsh high-temperature and high-pressure reaction conditions are avoided, the method has the advantages of high efficiency, mild reaction conditions and low energy consumption, gas-phase reactants can be continuously supplied, inexhaustible air is used as a raw material, the product nitric acid with a high additional value is synthesized, and the method is suitable for industrial production. Meanwhile, a new direction is created for industrial production of nitric acid and utilization of energy resources.

Description

Technical Field

[0001] The invention belongs to the field of catalytic synthesis and relates to a method for synthesizing nitric acid by using a low-temperature plasma coupled photo-Fenton advanced oxidation technology. Background Art

[0002] Nitric acid is one of the most important components in the current chemical industry and is widely used in the production of agricultural nitrogen fertilizers, fuels, explosives, medicines, etc. In the industrial field, nitric acid is mainly prepared in two steps. First, nitrogen and hydrogen are converted to ammonia using an iron-based catalyst under high temperature and high pressure conditions of 400-500°C and 10-30MPa using the HB method. Subsequently, the mixed gas of ammonia and air is subjected to an ammonia oxidation reaction at a high temperature of 760-840°C under the action of a platinum-rhodium alloy catalyst through the Ostwald process to produce nitric acid. However, this process not only consumes a huge amount of energy, but also emits a large amount of greenhouse gases, causing environmental pollution.

[0003] In recent years, photocatalytic nitrogen fixation driven by renewable energy and solar energy has become a research hotspot in the field of nitrogen fixation because of its advantages of mild reaction conditions, clean and sustainable energy, and environmental friendliness. It can achieve nitrogen fixation at room temperature and pressure. However, the dissociation of the nitrogen-nitrogen triple bond (bond energy: 941 kJ / mol) in nitrogen molecules is extremely difficult, which greatly limits the nitrogen conversion efficiency of photocatalytic nitrogen fixation. The photo-Fenton oxidation process is an advanced oxidation technology that combines photocatalysis and Fenton reaction, and is often used to treat refractory organic wastewater. Its principle is to introduce ultraviolet light or visible light on the basis of Fenton reaction to stimulate the production of more hydroxyl radicals (·OH), thereby improving the oxidation efficiency and the removal effect of organic matter. Hydroxyl radicals are strong oxidants in nature, second only to fluorine. Its standard redox potential is as high as 2.80V, which enables it to oxidize most organic and inorganic compounds. In addition, inspired by lightning nitrogen fixation in nature, the use of plasma, especially non-thermal plasma with low energy input, is believed to be able to achieve effective nitrogen activation. According to the article "Plasma Technology: An Emerging Technology for Energy Storage" published by A. Bogaerts et al. in the journal ACS Energy Lett in 2018, the theoretical energy consumption limit of plasma-based nitrogen fixation is more than 2.5 times lower than that of the Haber-Bosch process. However, plasma nitrogen fixation often has disadvantages such as difficult to control product selectivity, high energy consumption, and low energy utilization. Therefore, it is reasonable to expect that the synergistic effect of photo-Fenton advanced oxidation technology and non-thermal plasma multi-energy field coupling can achieve efficient and highly selective conversion of nitrogen and oxygen, the main components of air, into nitric acid under ambient conditions.

[0004] With the rapid development of industry and the continuous growth of population, the demand for important chemical products such as nitric acid is increasing. It is of great practical significance to realize the one-step conversion of inexhaustible air into nitric acid. Inspired by the nitrogen fixation in nature, a plasma-coupled photo-Fenton advanced oxidation method for synthesizing nitric acid (HNO 3 ). Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art. From the perspective of innovation in nitric acid production process and clean energy conservation, a method for synthesizing nitric acid by using an efficient and highly selective plasma-coupled photo-Fenton advanced oxidation technology is proposed. A low-temperature dielectric barrier discharge plasma array is used to achieve efficient activation of air molecules, and a series-coupled photo-Fenton oxidation system is used to efficiently convert active air molecules and synthesize nitric acid, which is expected to be further expanded to practical applications in the fields of industry, agriculture, and medicine.

[0006] The technical solution of the present invention:

[0007] A method for synthesizing nitric acid by low-temperature plasma coupled photo-Fenton advanced oxidation technology comprises the following steps:

[0008] Low temperature plasma coupled photo-Fenton advanced oxidation technology catalyzes the synthesis of nitric acid from air Figure 1 As shown, the system includes a plasma oxidation system 1, a gas phase circulation system 2, a photo-Fenton oxidation system 3 and a liquid phase circulation system 4. The plasma oxidation system 1 is used to activate air molecules to generate NO x Mixed gas (NO, N 2 O、NO 2 、N 2 O 3 、N 2 O 4 、N 2 O 5 ) and excited species (N*, N 2 *), the gas phase circulation system 2 inputs the mixed gas and excited species into the photo-Fenton oxidation system 3, and the active free radicals generated by the photo-Fenton catalyst and hydrogen peroxide under light conditions are further oxidized to NO x Mixed gas (NO, N 2 O、NO 2 、N 2 O 3 、N 2 O 4 、N 2 O 5 ) and excited species (N*, N 2*), the unreacted residual gas is input into the plasma oxidation system 1 again through the gas phase circulation system 2 for continuous oxidation, and at the same time, the reaction liquid in the photo-Fenton oxidation system 3 is continuously pumped out through the liquid phase circulation system 4, and is further mixed with the gas product activated by the plasma oxidation system 1 and then input into the photo-Fenton oxidation system 3 again for oxidation, forming a continuous cyclic oxidation process of the whole system. After the reaction is completed, the reaction liquid in the photo-Fenton oxidation system 3 is collected and nitric acid is obtained through further filtration and separation.

[0009] Furthermore, the plasma oxidation system 1 is mainly composed of a plasma generator 1.2, a plasma reactor 1.1 and a plasma oscilloscope 1.3, and the plasma reactor 1.1 is mainly composed of a quartz tube, an electrode rod made of stainless steel or brass and a copper wire, wherein the electrode rod made of stainless steel or brass and the copper wire are used as a high-voltage electrode and a grounding electrode, respectively.

[0010] Furthermore, the power of the plasma generator 1.2 in the above plasma oxidation system 1 is detected in real time by a plasma oscilloscope 1.3, and the power range is 50 to 200W.

[0011] Furthermore, the gas phase circulation system 2 uses a circulating gas pump 2.1 with an adjustable flow rate to input the reaction gas from the gas bag 2.2 into the plasma oxidation system 1 to generate NO x Mixed gases and excited species (N*, N 2 *), and then input it into the photo-Fenton oxidation system 3. After part of the gas products are oxidized and absorbed in the photo-Fenton oxidation system 3, the remaining gas is circulated and input into the plasma oxidation system 1 for the next round of oxidation reaction, forming a continuous cyclic oxidation process.

[0012] Furthermore, the flow rate of the circulating air pump 2.1 in the gas phase circulating system 2 is in the range of 0.1 to 15 L / min.

[0013] Furthermore, the photo-Fenton oxidation system 3 is mainly composed of a photo-Fenton reaction cell 3.1 and a xenon lamp or LED lamp 3.2; wherein the optical power range of the xenon lamp or LED lamp 3.2 is 1W to 10W.

[0014] Furthermore, the catalyst used in the above-mentioned photo-Fenton oxidation system 3 is a composite photo-Fenton catalyst, using any one or more metals among Pt, Fe, Co, Au, Ag, Cu, Ru and carriers ZSM-5, Al 2 O 3 、TiO 2 , WO 3 、MoS 2The catalyst is prepared by one or more methods including impregnation, ball milling and hydrothermal method. In the photo-Fenton reaction tank 3.1, a hydrogen peroxide solution is irradiated by a xenon lamp or an LED lamp to generate more active free radicals, thereby further oxidizing and absorbing the gas activated by the plasma oxidation system 1. At the same time, the reaction liquid is sampled and tested to achieve real-time monitoring of the reaction product.

[0015] Furthermore, the liquid phase circulation system 4 uses a circulating peristaltic pump with adjustable pump speed to extract the reaction liquid from the photo-Fenton oxidation system 3 and to combine with the N generated by the plasma oxidation system 1 to activate the air molecules. 2 *、NO x After the gases are mixed, they are input into the photo-Fenton oxidation system 3 again to carry out the next round of oxidation reaction, forming a continuous cycle of oxidation process.

[0016] Furthermore, the rotation speed range of the circulating peristaltic pump of the liquid phase circulation system 4 is 10 to 200 rpm.

[0017] Furthermore, during the reaction process, the reaction gas and the reaction liquid are continuously circulated and the oxidation reaction is continuously performed. After reacting for 2 hours, the reaction liquid is collected and then subjected to a simple filtering operation to obtain a nitric acid solution.

[0018] Furthermore, the detection method of the product nitric acid uses anion chromatography for qualitative and quantitative testing.

[0019] Beneficial effects of the present invention:

[0020] (1) Efficient nitrogen fixation: Low-temperature plasma is used to activate air or nitrogen molecules, and then the active gas molecules are fully converted through photo-Fenton advanced oxidation technology. Compared with the efficiency of catalyst-driven low-temperature plasma air or photocatalytic synthesis of nitric acid reported in the literature, the nitric acid production rate is significantly improved.

[0021] (2) Mild reaction conditions: The present invention realizes the reaction of the main component of air N at room temperature and pressure by coupling multiple energy fields and merging multiple phases. 2 and O 2 The conversion effectively avoids the harsh conditions such as high temperature and high pressure required for traditional air main component conversion.

[0022] (3) Low energy consumption: Due to the coupling of multiple energy fields such as low-temperature plasma and photo-Fenton advanced oxidation technology, the energy consumption of the present invention is relatively small. The energy of low-temperature plasma is mainly used to activate air molecules, while photo-Fenton advanced oxidation technology uses solar energy or other low-energy light sources, greatly reducing energy costs.

[0023] (4) Opening up new directions: This invention opens up new directions for industrial production of nitric acid and energy resource utilization. By combining low-temperature plasma and photo-Fenton advanced oxidation technology, it provides a new solution for the field of nitrogen fixation and is expected to promote the development of related industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the experimental setup for the method of synthesizing nitric acid using low-temperature plasma coupled photo-Fenton advanced oxidation technology in this technical solution.

[0025] Figure 2 This is a diagram of the efficiency of synthesizing nitric acid when adding hydrogen peroxide solutions of different concentrations in Example 1 of the present invention.

[0026] Figure 3 This is a diagram of the efficiency of synthesizing nitric acid for catalysts with different platinum contents in Example 2 of the present invention.

[0027] Figure 4 This is an efficiency diagram for synthesizing nitric acid using pure photo-Fenton, pure plasma and plasma-coupled photo-Fenton advanced oxidation technologies in Example 3 of the present invention.

[0028] In the figure: 1 is a plasma oxidation system, 1.1 a plasma reactor, 1.2 a plasma generator, 1.3 a plasma oscilloscope, 2 is a gas phase circulation system, 2.1 a circulation air pump, 2.2 an air bag, 3 is a photo-Fenton oxidation system, 3.1 a photo-Fenton reaction cell, 3.2 is a xenon lamp or an LED lamp, and 4 is a liquid phase circulation system. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0030] A method for synthesizing nitric acid by low-temperature plasma coupled photo-Fenton advanced oxidation technology can improve the defects of harsh reaction conditions, large pollutant gas emissions, and high energy consumption in the process of synthesizing nitric acid by traditional nitrogen fixation technology. On the basis of no greenhouse gas emissions in the whole process, it realizes the efficient and highly selective conversion of inexhaustible air in one step and the preparation of nitric acid. The present invention solves the problems of harsh process flow, huge energy consumption and pollutant emissions of traditional technology, improves the defects of slow product generation rate, poor selectivity, and low efficiency in the current clean nitrogen fixation process, so that high-concentration, high-value-added chemicals can be directly recovered or connected to downstream chemical synthesis processes after simple filtration operations, and has the advantages of low energy consumption, clean and pollution-free, high product selectivity, and easy separation and purification.

[0031] The experimental device of the method for synthesizing nitric acid by low-temperature plasma coupled photo-Fenton advanced oxidation technology in this technical scheme is as follows Figure 1 shown.

[0032] Example 1

[0033] The photo-Fenton coupled photo-Fenton air oxidation method was used to produce nitric acid:

[0034] Step Ⅰ: Weigh 0.1g of commercial nano-TiO 2 Catalyst, 0.54 mL 4.7 mg / mL H 2 PtCl 6 Solution, 18mL deionized water and 2mL ethanol, shake evenly, ultrasonically disperse for 10 minutes, place on a stirring table and stir until the solvent is completely volatilized, grind it and put it in a porcelain boat, transfer it to a muffle furnace, heat it to 500℃ at 10℃ / min, calcine for 4 hours, cool it down, filter and wash it with deionized water and ethanol alternately, transfer it to an 80℃ oven, and dry it overnight. 0.5% Pt / TiO 2 catalyst.

[0035] Step II: prepare 10, 30, 50, and 100 mmol / L hydrogen peroxide solutions, weigh 20 mg of the above catalyst and place it in 20 mL of deionized water, and ultrasonically disperse it for 5 minutes.

[0036] Step III: Add 50 mL of deionized water, 20 mL of hydrogen peroxide solution and 20 mL of catalyst dispersion solution into the photo-Fenton oxidation system 3, and seal the device.

[0037] Step IV: After purging the plasma oxidation system 1 and the photo-Fenton oxidation system 3 pipelines with an argon gas bag for 5 minutes, a synthetic air bag was connected, and the gas phase circulation system 2 was turned on to circulate synthetic air into the dielectric barrier discharge plasma reaction tube at a flow rate of 3L / min. At the same time, the liquid phase circulation system 4 was turned on at a speed of 150rpm.

[0038] Step V: Connect the high-voltage transmission line and the low-voltage transmission line, turn on the high-voltage power supply, rotate the high-voltage power supply knob to adjust the power to 50W, turn on the xenon lamp, and adjust the light power to 4W. The nitrogen and oxygen species and excited state species activated by the discharge of the plasma oxidation system 1 are input into the photo-Fenton oxidation system 3 through the pipeline under the action of the gas phase circulation system 2, and are further oxidized by the active free radicals generated by the photo-Fenton reaction.

[0039] Step VI: After 2 hours of reaction, 0.5 mL of the reaction solution was taken with a sampling needle, diluted 50 times, and then tested with anion chromatography. Figure 2 shown.

[0040] Example 2

[0041] Step I: Preparation of photo-Fenton catalysts with different Pt contents: Weigh 0.1 g of commercial TiO 2Catalyst, 0.54mL, 1.08mL, 1.64mL and 2.16mL 4.7 mg / mL H 2 PtCl 6 Solution, 18mL deionized water and 2mL ethanol, shake evenly, ultrasonically disperse for 10 minutes, place on a stirring table and stir and immerse until the solvent is completely volatilized, grind it and put it in a porcelain boat, transfer it to a muffle furnace, heat it to 500℃ at 10℃ / min, calcine for 4 hours, cool it and wash it with deionized water and ethanol alternately, transfer it to an 80℃ oven, and dry it overnight. Pt / TiO with theoretical platinum metal loading of 0.5%, 1.0%, 1.5% and 2% were obtained. 2 catalyst.

[0042] Step II: Prepare 50 mmol / L hydrogen peroxide solution, weigh 20 mg of the above catalysts and place them in 20 mL of deionized water, and ultrasonically disperse them for 5 minutes.

[0043] Step III: Add 50 mL of deionized water, 20 mL of hydrogen peroxide solution and 20 mL of catalyst dispersion solution into the photo-Fenton oxidation system 3, and seal the device.

[0044] Step IV: After purging the plasma oxidation system 1 and the photo-Fenton oxidation system 3 pipelines with an argon gas bag for 5 minutes, a synthetic air bag was connected, and the gas phase circulation system 2 was turned on to circulate synthetic air into the dielectric barrier discharge plasma reaction tube at a flow rate of 3L / min. At the same time, the liquid phase circulation system 4 was turned on at a speed of 150rpm.

[0045] Step V: Connect the high-voltage transmission line and the low-voltage transmission line, turn on the high-voltage power supply, rotate the high-voltage power supply knob to adjust the power to 50W, turn on the xenon lamp, and adjust the light power to 4W. The nitrogen and oxygen species and excited state species activated by the discharge of the plasma oxidation system 1 are input into the photo-Fenton oxidation system 3 through the pipeline under the action of the gas phase circulation system 2, and are further oxidized by the active free radicals generated by the photo-Fenton reaction.

[0046] Step VI: After 2 hours of reaction, 0.5 mL of the reaction solution was taken with a sampling needle, diluted 50 times, and then tested with anion chromatography. Figure 3 shown.

[0047] Example 3

[0048] Step I: Preparation of different metals Fe, Co, Au, Ag, Cu, Ru and different carriers ZSM-5, Al 2 O 3 , WO 3 、MoS 2 Composite photo-Fenton catalyst: weigh 0.4g ZSM-5, Al 2 O3 , WO 3 、MoS 2 Six portions of each of the four supported catalysts were weighed and 57.8 mg Fe(NO 3 ) 3 9H 2 O, 39.5 mg Co(NO 3 ) 2 6H 2 O, 8 mg HAuCl 4 ·3H 2 O, 12.5 mg AgNO 3 、30.40mg Cu(NO 3 ) 2 ·3H 2 O and 8 mg RuCl 3 ·3H 2 O, 18mL deionized water and 2mL ethanol, shake evenly, ultrasonically disperse for 30 minutes, place on a stirring table and stir and immerse until the solvent is completely volatilized, grind it into a porcelain boat, transfer it to a muffle furnace, heat it to 500℃ at 10℃ / min, calcine for 4 hours, cool it down, filter and wash it with deionized water and ethanol alternately, transfer it to an 80℃ oven, and dry it overnight. M / ZSM-5 and M / Al with a theoretical platinum metal loading of 2% were obtained. 2 O 3 、M / WO 3 、M / MoS 2 (M represents any one of metals Fe, Co, Au, Ag, Cu, and Ru) catalyst.

[0049] Step II: Prepare 50 mmol / L hydrogen peroxide solution, weigh 20 mg of the above catalysts and place them in 20 mL of deionized water, and ultrasonically disperse them for 5 minutes.

[0050] Step III: Add 50 mL of deionized water, 20 mL of hydrogen peroxide solution and 20 mL of catalyst dispersion solution into the photo-Fenton oxidation system 3, and seal the device.

[0051] Step IV: After purging the plasma oxidation system 1 and the photo-Fenton oxidation system 3 pipelines with an argon gas bag for 5 minutes, a synthetic air bag was connected, and the gas phase circulation system 2 was turned on to circulate synthetic air into the dielectric barrier discharge plasma reaction tube at a flow rate of 3L / min. At the same time, the liquid phase circulation system 4 was turned on at a speed of 150rpm.

[0052] Step V: Connect the high-voltage transmission line and the low-voltage transmission line, turn on the high-voltage power supply, rotate the high-voltage power supply knob to adjust the power to 50W, turn on the xenon lamp, and adjust the light power to 4W. The nitrogen and oxygen species and excited state species activated by the discharge of the plasma oxidation system 1 are input into the photo-Fenton oxidation system 3 through the pipeline under the action of the gas phase circulation system 2, and are further oxidized by the active free radicals generated by the photo-Fenton reaction.

[0053] Step VI: After reacting for 2 hours, 0.5 mL of the reaction solution was taken using a sampling needle, diluted 50 times, and then tested by anion chromatography.

[0054] Example 4

[0055] By comparing pure photo-Fenton driven air oxidation, pure plasma driven air oxidation and plasma coupled photo-Fenton driven air oxidation experiments, the advantages of this coupled system are confirmed.

[0056] 1) Pure light-Fenton driven air oxidation:

[0057] Step I: Weigh 20 mg of the catalyst prepared in Example 1 and place it in 20 mL of deionized water, disperse it ultrasonically for 5 minutes, and prepare a 50 mmol / L hydrogen peroxide solution.

[0058] Step II: Add 50 mL of deionized water, 20 mL of hydrogen peroxide solution and 20 mL of catalyst dispersion solution into the photo-Fenton oxidation system 3, and seal the device.

[0059] Step III: After purging the pipeline of the photo-Fenton oxidation system 3 with an argon bag for 5 minutes, a synthetic air bag was connected, and the gas phase circulation system 2 was turned on to circulate synthetic air into the photo-Fenton oxidation system 3 at a flow rate of 3 L / min. At the same time, the liquid phase circulation system 4 was turned on at a rotation speed of 150 rpm.

[0060] Step IV: Turn on the xenon lamp and adjust the light power to 4W.

[0061] Step V: After 2 hours of reaction, 0.5 mL of the reaction solution was taken with a sampling needle, diluted 50 times, and then tested with anion chromatography. Figure 4 shown.

[0062] 2) Pure plasma driven air oxidation:

[0063] Step Ⅰ: Add only 90 mL of deionized water to the photo-Fenton reaction cell 3.1 to absorb NO x Gas, sealing device.

[0064] Step II: After purging the plasma oxidation system 1 and the photo-Fenton reaction pool 3.1 pipeline with an argon gas bag for 5 minutes, connect the synthetic air bag, start the gas phase circulation system 2, and circulate the synthetic air into the dielectric barrier discharge plasma reaction tube at a flow rate of 3L / min. At the same time, start the liquid phase circulation system 4 at a speed of 150rpm.

[0065] Step III: Connect the high-voltage transmission line and the low-voltage transmission line, turn on the high-voltage power supply, and rotate the high-voltage power supply knob to adjust the power to 50 W. The nitrogen and oxygen species and excited state species activated by the plasma oxidation system 1 are input into the deionized water in the photo-Fenton reaction cell 3.1 through the pipeline under the action of the gas phase circulation system 2 for absorption treatment.

[0066] Step IV: After 2 hours of reaction, 0.5 mL of the reaction solution was taken with a sampling needle, diluted 50 times, and then tested with anion chromatography. Figure 4 shown.

[0067] 3) Plasma-coupled photo-Fenton air oxidation:

[0068] Step I: Weigh 20 mg of the catalyst prepared in Example 1 and place it in 20 mL of deionized water, disperse it ultrasonically for 5 minutes, and prepare a 50 mmol / L hydrogen peroxide solution.

[0069] Step II: Add 50 mL of deionized water, 20 mL of hydrogen peroxide solution and 20 mL of catalyst dispersion solution into the photo-Fenton oxidation system 3, and seal the device.

[0070] Step III: After purging the plasma oxidation system 1 and the photo-Fenton oxidation system 3 pipelines with an argon gas bag for 5 minutes, a synthetic air bag was connected, and the gas phase circulation system 2 was turned on to circulate synthetic air into the dielectric barrier discharge plasma reaction tube at a flow rate of 3L / min. At the same time, the liquid phase circulation system 4 was turned on at a speed of 150rpm.

[0071] Step IV: Connect the high-voltage transmission line and the low-voltage transmission line, turn on the high-voltage power supply, rotate the high-voltage power supply knob to adjust the power to 50W, turn on the xenon lamp, and adjust the light power to 4W. The nitrogen and oxygen species and excited state species activated by the discharge of the plasma oxidation system 1 are input into the photo-Fenton oxidation system 3 through the pipeline under the action of the gas phase circulation system 2, and are further oxidized by the active free radicals generated by the photo-Fenton reaction.

[0072] Step V: After 2 hours of reaction, 0.5 mL of the reaction solution was taken with a sampling needle, diluted 50 times, and then tested with anion chromatography. Figure 4 shown.

[0073] The results of Example 4 clearly show that the low-temperature plasma coupled photo-Fenton advanced oxidation technology proposed in the present invention shows excellent efficiency in synthesizing nitric acid, which is significantly higher than the efficiency of pure photo-Fenton oxidation technology and pure low-temperature plasma oxidation technology in synthesizing nitric acid. Moreover, through this multi-energy field coupling technology, the selectivity of the product nitric acid can be close to 100%. This means that under the conditions of low energy consumption and normal temperature and pressure, with the help of renewable energy, it is successfully achieved to convert the inexhaustible nitrogen (N2) in the air into 2 ) and oxygen (O 2 ) is converted into a high-value-added chemical with high selectivity - nitric acid (HNO 3 ).

[0074] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any modification and change made to the present invention within the protection scope of the claims of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for synthesizing nitric acid by low-temperature plasma coupled photo-Fenton advanced oxidation technology, characterized in that: The following steps are involved: The system for catalyzing the synthesis of nitric acid from air by plasma-coupled photo-Fenton advanced oxidation technology comprises a plasma oxidation system (1), a gas phase circulation system (2), a photo-Fenton oxidation system (3) and a liquid phase circulation system (4). The plasma oxidation system (1) is used to activate air to generate NO x The gas phase circulation system (2) inputs the mixed gas and excited species into the photo-Fenton oxidation system (3), and further oxidizes part of NO by using the active free radicals generated by the photo-Fenton catalyst and hydrogen peroxide under light conditions. x The mixed gas and excited species, and the unreacted residual gas are inputted into the plasma oxidation system (1) again through the gas phase circulation system (2) for continuous oxidation. At the same time, the reaction liquid in the photo-Fenton oxidation system (3) is continuously pumped out through the liquid phase circulation system (4), further mixed with the gas product activated by the plasma oxidation system (1), and then inputted into the photo-Fenton oxidation system (3) for oxidation again, thereby forming a continuous cyclic oxidation process of the whole system. After the reaction is completed, the reaction liquid in the photo-Fenton oxidation system (3) is collected and further filtered and separated to obtain nitric acid.

2. The method according to claim 1, characterized in that The plasma oxidation system (1) is mainly composed of a plasma generator (1.2), a plasma reactor (1.1) and a plasma oscilloscope (1.3), wherein the plasma reactor (1.1) is mainly composed of a quartz tube, an electrode rod made of stainless steel or brass and a copper wire, wherein the electrode rod made of stainless steel or brass and the copper wire are used as a high-voltage electrode and a grounding electrode respectively.

3. The method according to claim 1, characterized in that The gas phase circulation system (2) uses a circulating gas pump (2.1) with adjustable flow rate to input the reaction gas from the gas bag (2.2) into the plasma oxidation system (1) to generate NO x The mixed gas and excited species are then input into the photo-Fenton oxidation system (3). After part of the gas products are oxidized and absorbed in the photo-Fenton oxidation system (3), the remaining gas is circulated and input into the plasma oxidation system (1) again for the next round of oxidation reaction, forming a continuous cyclic oxidation process.

4. The method according to claim 1, characterized in that The photo-Fenton oxidation system (3) is mainly composed of a photo-Fenton reaction pool (3.1) and a xenon lamp or an LED lamp (3.2); wherein the optical power range of the xenon lamp or the LED lamp (3.2) is 1W to 10W.

5. The method according to claim 4, characterized in that The catalyst used in the photo-Fenton oxidation system (3) is a composite photo-Fenton catalyst, which is made by compounding any one or more metals among Pt, Fe, Co, Au, Ag, Cu, and Ru with carriers ZSM-5, Al2O3, TiO2, WO3, and MoS2, and preparing the catalyst by one or more methods among impregnation, ball milling, and hydrothermal method; in the photo-Fenton reaction pool (3.1), in the presence of hydrogen peroxide solution, it is irradiated by a xenon lamp or an LED lamp (3.2), thereby generating more active free radicals, and further oxidizing and absorbing the gas activated by the plasma oxidation system (1).

6. The method according to claim 1, characterized in that The liquid phase circulation system (4) uses a circulating peristaltic pump with adjustable pump speed to extract the reaction liquid from the photo-Fenton oxidation system (3) and catalyze the activation of NO generated by air molecules with the plasma oxidation system (1). x After the mixed gas and excited species are mixed, they are input into the photo-Fenton oxidation system (3) again to carry out the next round of oxidation reaction, forming a continuous cyclic oxidation process.

7. The method according to claim 1, characterized in that During the reaction process, the reaction gas and the reaction liquid circulate continuously to continuously carry out the oxidation reaction. After reacting for 2 hours, the reaction liquid is collected and then subjected to a simple filtration operation to obtain a nitric acid solution.

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