A method for preparing urea by ultrasonic atomization glow discharge

Abstract

The present invention relates to a method for preparing urea using ultrasonic atomization glow discharge. The method utilizes ultrasonic atomization technology to convert urea raw materials—carbonates and nitrates—into tiny droplets, which are then injected into a vacuum discharge device. Under high vacuum and dielectric barrier discharge conditions, carbonate and nitrate reduction is achieved, ultimately leading to efficient urea synthesis. By optimizing ultrasonic atomization conditions and glow discharge parameters, the method not only improves urea yield and achieves green production, but also enhances urea selectivity and reduces energy consumption and waste emissions. Furthermore, the method also has the functions of carbon capture, carbon neutralization, nitrogen fixation, and environmental pollutant purification, and has the advantages of simple operation, short reaction time, and low equipment investment, thus possessing broad application prospects.

Description

1. Technical Field

[0001] The present invention relates to the field of environmental pollution control and resource recovery technology, specifically a method for preparing urea using a combination of ultrasonic atomization and glow discharge. This method innovatively combines ultrasonic atomization and glow discharge technologies to effectively recover carbonates and nitrates—products of carbon dioxide and nitrogen oxide capture from industrial waste—and synthesizes them into urea, a key industrial chemical product. This method simultaneously achieves multiple environmental goals, including carbon emission reduction, carbon neutrality, and nitrogen fixation, and provides a new technical approach for the clean production of industrial urea. 2. Background Technology

[0002] Since the advent of the industrial age, greenhouse gas emissions, primarily carbon dioxide, have increased rapidly. Rising greenhouse gas concentrations have intensified the atmosphere's ability to block heat from escaping, leading to a stronger greenhouse effect, global warming, and extreme weather events. Consequently, reducing carbon emissions has become a global issue. Carbon capture is an important technology for reducing carbon emissions, effectively separating the large amounts of carbon dioxide found in exhaust gases from power plants, coking plants, and other industrial processes. However, the proper disposal of captured carbon dioxide remains a matter of considerable debate. Underground carbon dioxide storage has been suggested as a possible solution, but there is currently no conclusive evidence that it is completely safe. Marine storage is also more likely to raise a range of marine ecological and safety concerns. Therefore, recycling captured carbon dioxide for reuse is the most economical and safest option.

[0003] Nitrogen pollution is environmental pollution caused by nitrogen-containing compounds. Nitrogen pollution in the air primarily comes from the emission of nitrogen oxides. These nitrogen oxides primarily originate from the combustion of fossil fuels such as coal, oil, and natural gas in industry and domestic use. Nitrogen oxides not only severely impact air quality but also contribute to environmental problems such as acid rain and photochemical smog. Nitrogen pollution in water bodies primarily originates from agriculture, municipal sewage, and industrial wastewater. Excessive use of nitrogen fertilizers in agricultural activities leads to nitrogen loss into water bodies. Municipal sewage and industrial wastewater also contain significant amounts of nitrogen. When nitrogen levels in water exceed certain limits, it can lead to eutrophication, promoting excessive algal growth and causing "algal blooms." Furthermore, nitrates in water bodies can enter the human body through the food chain, posing a potential threat to human health.

[0004] Urea is currently the most widely used fertilizer globally, with a production capacity of approximately 208 million tons. Nitrogen fertilizer currently accounts for 73% of total fertilizer use, with urea accounting for 60% of this consumption. Urea is also a vital chemical raw material, with applications across agriculture, industry, medicine, and food. The mainstream urea synthesis method globally is the CO2-ammonia process, which involves first synthesizing ammonia using the energy-intensive Harper process. Liquid ammonia is then fed to a urea plant, where liquid nitrogen and CO2 enter the synthesis unit at a molar ratio of 2:1. Calculated, producing one ton of urea requires 1.2 tons of anthracite coal, converting it into synthetic ammonia at a cost of approximately 2,938 yuan per ton, bringing the total cost of urea to approximately 2,074 yuan per ton. Due to high production costs and severe overcapacity in urea production, companies face low profits and operational challenges. If urea can be synthesized using industrial waste, such as carbon dioxide / carbonates and nitrogen oxides / nitrates, it can effectively achieve carbon capture, carbon fixation, nitrogen fixation and resource recovery on the one hand, and on the other hand, it can also achieve clean production of urea, reduce secondary pollution and production costs in the urea production process, and achieve the goal of a green circular economy.

[0005] Dielectric barrier discharge (DBD) is a high-voltage discharge phenomenon between two electrodes separated by an insulating dielectric barrier. The dielectric barrier covers the electrodes. When an AC voltage is applied across the electrodes, it breaks down the gas, generating a glow discharge. DBD is used to generate a relatively large volume of diffuse plasma and abundant excimer ultraviolet radiation at atmospheric pressure. Furthermore, glow discharge generates a large number of free radicals, such as hydroxyl radicals and singlet oxygen. These are chemically active and readily react with other atoms, molecules, or other free radicals to form stable atoms or molecules. Consequently, they can also induce redox reactions between carbon dioxide / carbonates and nitrogen oxides / nitrates, generating organic intermediates.

[0006] Using any 2-3 of the keywords "carbonate", "nitrate", "dielectric barrier discharge" (DBD) and "urea" as keywords, we searched for journal articles, conference papers and invention patents, but did not find any relevant information. Currently, there are only reports on the electrochemical synthesis of urea. For example, He Nihan et al. (2022) used a nano-confinement strategy to synthesize a porous Cu2O catalyst with a nanocavity structure, achieving the electrocatalytic reaction of low-concentration NO3 - Urea was efficiently prepared by coupling with CO2, with a urea yield of 29.2 mmol / h at a potential of -1.3 V (vs. RHE). -1 g -1, the Faraday efficiency reached 9.43%; Ma Xiaomin et al. (2021) prepared a core-shell structured Cu-Zn nanowire electrocatalyst with NO3 - The electrochemical urea synthesis activity of the electrochemical urea was investigated using CO2 as raw material. The results showed that the optimized urea yield and Faradaic efficiency could reach 7.29 μmol cm -2 h -1 Other research approaches are similar, but the biggest problem with this technology is that CO2 and nitrate are in the gas and liquid phases, respectively. This heterogeneous reaction severely reduces production efficiency. In addition, all of the above reactions must be carried out in a dual-chamber electrochemical reactor, and the continuously rising pH value in the cathode chamber will severely inhibit the reaction efficiency. 3. Summary of the Invention

[0007] The present invention is made in light of the problems existing in the prior art, and its purpose is to provide a method for producing urea using ultrasonic atomization glow discharge. This method utilizes ultrasonic atomization technology to convert urea raw materials—carbonates and nitrates—into tiny droplets, which are injected into a vacuum discharge device. Under high vacuum and dielectric barrier discharge conditions, carbonate and nitrate ions are reduced, ultimately leading to efficient urea synthesis. By optimizing ultrasonic atomization conditions and glow discharge parameters, this method not only improves urea yield but also enhances selectivity, reduces energy consumption and waste emissions. Furthermore, this method also has the functions of carbon capture and concentration, and purification of environmental pollutants. It has the advantages of simple operation, short reaction time, and low equipment investment, and has broad application prospects.

[0008] In order to achieve the above object, the technical solution of the present invention is a method for preparing urea by ultrasonic atomization glow discharge, and its specific implementation process includes the following steps:

[0009] Step 1: Evacuate the vacuum discharge device to a pressure of 0.1-1.0 Pa and maintain it for 10 minutes, and introduce cooling circulating water to maintain the temperature of the reaction zone not exceeding 150°C;

[0010] Step 2: preparing an aqueous solution containing 0.1-0.25 mol / L carbonate and 0.1-0.2 g / L isooctyl succinate sulfonic acid as a carbon source;

[0011] Step 3: Prepare an acetonitrile-water solution containing 0.01-0.05 mol / L nitrate and 0.1-0.2 g / L polyoxyethylene ether as a nitrogen source;

[0012] Step 4: Control the resonant frequency of the piezoelectric ceramic atomizer to generate submicron droplets of the carbon source and nitrogen source solutions, and inject them into the vacuum discharge device under the suction effect of the negative pressure of the vacuum discharge device;

[0013] Step 5: Applying an AC voltage of 1000 to 5000 V between the flat electrodes in the vacuum discharge device using a high-voltage power supply, with the high-voltage power supply outputting for 3 seconds and pausing for 1 second to activate the glow discharge and create disturbances in the reactor cavity to prevent deposition of the reaction solution;

[0014] Step 6: Under high voltage excitation, a stable and strong continuous glow reaction is formed between the flat electrodes for 5 to 30 minutes;

[0015] Step 7: After the reaction is completed, the atomized droplets containing urea are extracted from the vacuum discharge device.

[0016] The above technical solution is further defined as follows: the vacuum discharge device described in step 1 is a reactor capable of realizing dielectric barrier glow discharge, and is composed of (1) an air inlet, (2) a gas outlet, (3) a shell, (4) a vacuum pump, (5) a stop valve, (6) a silicone insulating pad, (7) a dielectric barrier layer, (8) a cooling water flow channel, (9) a plasma passage, (10) a high-voltage power supply, and (11) a flat electrode.

[0017] The above technical solution is further limited to the following: the carbonate in step 2 is one of sodium carbonate, potassium carbonate, and ammonium carbonate;

[0018] The above technical solution is further defined as follows: the nitrate in step 3 is one of sodium nitrate, potassium nitrate, and ammonium nitrate; and the volume ratio of acetonitrile to water in the acetonitrile-water solution is 1:10 to 1:100.

[0019] The above technical solution is further defined as follows: during the injection of submicron droplets in step 4, the system vacuum degree should be maintained at no more than 5 Pa during the reaction.

[0020] The benefits of the present invention are: first, the method fully realizes the recovery and resource utilization of industrial pollutants carbon dioxide and nitrogen oxides; second, the ultrasonic atomization of this technology makes the reactants fully refined, increases the reaction area, and improves the reaction rate. The glow discharge provides sufficient energy for the reaction and promotes the reaction; compared with the traditional urea production process, this method has obvious advantages in energy consumption and waste emissions. The combination of ultrasonic atomization and glow discharge makes the reaction process more gentle and reduces energy consumption. At the same time, the method reduces the generation of harmful by-products and reduces pollution to the environment; because the method adopts advanced ultrasonic atomization and glow discharge technology, it can achieve efficient production on a smaller equipment scale, thereby reducing equipment investment and production costs; by precisely controlling the reaction conditions and optimizing the process flow, the method can produce high-purity urea products to meet the application needs of different fields. IV. Description of the Figures

[0021] In order to more clearly illustrate the specific embodiments of the present invention, the following briefly describes the drawings used in the description of the specific embodiments. Figure 1 Schematic diagram of the structure of the vacuum discharge device of the present invention, wherein the reference numerals are explained as follows:

[0022] 1-air inlet, 2-gas outlet, 3-housing, 4-vacuum pump, 5-stop valve, 6-silicone insulating pad, 7-dielectric barrier, 8-cooling water flow channel, 9-plasma path, 10-high voltage power supply, 11-plate electrode;

[0023] Figure 2 This is a heat map of urea yield under different carbonic acid and nitrogen source conditions. V. Specific Implementation Methods

[0024] The present invention is described in detail below with reference to the accompanying drawings and embodiments:

[0025] Example 1: First, the vacuum discharge device ( Figure 1 ) was evacuated to a pressure of 0.1 Pa and maintained for 10 minutes, cooling circulating water was introduced to maintain the temperature of the reaction zone at no more than 150° C., an aqueous solution containing 0.1 mol / L sodium carbonate and 0.1 g / L isooctyl succinate sulfonic acid was prepared as a carbon source, an acetonitrile-water solution containing 0.01 mol / L ammonium nitrate and 0.1 g / L polyoxyethylene ether (volume ratio, acetonitrile: water = 1:100) was prepared as a nitrogen source, the resonant frequency of the piezoelectric ceramic was controlled to 100 KHz, and submicron droplets of the carbon source and nitrogen source solutions were generated. The vacuum discharge device was suctioned under the negative pressure. Under the control of the mass flow meter, the vacuum discharge device is slowly injected to maintain the vacuum degree in the cavity not higher than 5Pa. A high-voltage power supply is used to apply an AC voltage of 1000V between the flat electrodes in the vacuum discharge device. The high-voltage power supply is output for 3 seconds and paused for 1 second every time to activate the glow discharge to form a disturbance in the reactor cavity to avoid the deposition of the reaction liquid. Under the high-voltage electric excitation, a stable and strong continuous glow reaction is formed between the flat electrodes for 5 minutes. After the reaction is completed, the atomized droplets containing urea are extracted from the vacuum discharge device. The urea yield achieved at this time is 12.7% (calculated as carbonate, which can be Figure 2 (obtained by China Inspection).

[0026] Example 2: First, the vacuum discharge device was evacuated to a pressure of 1.0 Pa and maintained for 10 minutes. Cooling circulating water was introduced to maintain the temperature of the reaction zone at no more than 150° C. An aqueous solution containing 0.25 mol / L potassium carbonate and 0.2 g / L isooctyl succinate sulfonic acid was prepared as a carbon source, and an acetonitrile-water solution containing 0.05 mol / L ammonium nitrate and 0.2 g / L polyoxyethylene ether (volume ratio, acetonitrile: water = 1:10) was prepared as a nitrogen source. The resonant frequency of the piezoelectric ceramic was controlled to 100 kHz to generate submicron droplets of the carbon source and nitrogen source solutions. Under the suction effect of the high pressure, under the control of the mass flow meter, the vacuum discharge device is slowly injected to maintain the vacuum degree in the cavity not higher than 5 Pa. A high-voltage power supply is used to apply an AC voltage of 5000 V between the flat electrodes in the vacuum discharge device. The high-voltage power supply is output for 3 seconds and paused for 1 second every time to activate the glow discharge to form a disturbance in the reactor cavity to avoid the deposition of the reaction liquid. Under the high-voltage electric excitation, a stable and strong continuous glow reaction is formed between the flat electrodes for 30 minutes. After the reaction is completed, the atomized droplets containing urea are extracted from the vacuum discharge device. The urea yield achieved at this time is 25.7% (calculated as carbonate, which can be Figure 2 (obtained by China Inspection).

[0027] Example 3: First, the vacuum discharge device was evacuated to a pressure of 0.25 Pa and maintained for 10 minutes. Cooling circulating water was introduced to maintain the temperature of the reaction zone at no more than 150° C. An aqueous solution containing 0.15 mol / L sodium carbonate and 0.15 g / L isooctyl succinate sulfonic acid was prepared as a carbon source, and an acetonitrile-water solution containing 0.02 mol / L potassium nitrate and 0.15 g / L polyoxyethylene ether (volume ratio, acetonitrile: water = 1:20) was prepared as a nitrogen source. The resonant frequency of the piezoelectric ceramic was controlled to 100 kHz to generate submicron droplets of the carbon source and nitrogen source solutions. Under the suction effect of negative pressure, under the control of the mass flow meter, the vacuum discharge device is slowly injected to maintain the vacuum degree in the cavity not higher than 5Pa. A high-voltage power supply is used to apply an AC voltage of 2000V between the flat electrodes in the vacuum discharge device. The high-voltage power supply is output for 3 seconds and paused for 1 second to activate the glow discharge to form a disturbance in the reactor cavity to avoid the deposition of the reaction liquid. Under the high-voltage electric excitation, a stable and strong continuous glow reaction is formed between the flat electrodes for 20 minutes. After the reaction is completed, the atomized droplets containing urea are extracted from the vacuum discharge device. The urea yield achieved at this time is 33.6% (calculated as carbonate, which can be Figure 2 (obtained by China Inspection).

[0028] Example 4: First, the vacuum discharge device was evacuated to a pressure of 0.2 Pa and maintained for 10 minutes. Cooling circulating water was introduced to maintain the temperature of the reaction zone at no more than 150° C. An aqueous solution containing 0.2 mol / L of ammonium carbonate and 0.1 g / L of isooctyl succinate sulfonic acid was prepared as a carbon source, and an acetonitrile-water solution containing 0.03 mol / L of ammonium nitrate and 0.12 g / L of polyoxyethylene ether (volume ratio, acetonitrile: water = 1:30) was prepared as a nitrogen source. The resonant frequency of the piezoelectric ceramic was controlled to 100 kHz to generate submicron droplets of the carbon source and nitrogen source solutions. Under the suction effect of the high pressure, under the control of the mass flow meter, the vacuum discharge device is slowly injected to maintain the vacuum degree in the cavity not higher than 5Pa. A high-voltage power supply is used to apply an AC voltage of 2500V between the flat electrodes in the vacuum discharge device. The high-voltage power supply is output for 3 seconds and paused for 1 second every time to activate the glow discharge to form a disturbance in the reactor cavity to avoid the deposition of the reaction liquid. Under the high-voltage electric excitation, a stable and strong continuous glow reaction is formed between the flat electrodes for 10 minutes. After the reaction is completed, the atomized droplets containing urea are extracted from the vacuum discharge device. The urea yield achieved at this time is 32.6% (calculated as carbonate, which can be Figure 2 (obtained by China Inspection).

[0029] Example 5: First, the vacuum discharge device was evacuated to a pressure of 0.8 Pa and maintained for 10 minutes. Cooling circulating water was introduced to maintain the temperature of the reaction zone at no more than 150°C. An aqueous solution containing 0.23 mol / L of sodium carbonate and 0.125 g / L of isooctyl succinate sulfonic acid was prepared as a carbon source. An acetonitrile-water solution containing 0.025 mol / L of sodium nitrate and 0.125 g / L of polyoxyethylene ether (volume ratio, acetonitrile: water = 1:50) was prepared as a nitrogen source. The resonant frequency of the piezoelectric ceramic was controlled to 100 kHz to generate submicron droplets of the carbon source and nitrogen source solutions. Under the suction effect of negative pressure, under the control of the mass flow meter, slowly inject into the vacuum discharge device, maintain the vacuum degree in the cavity not higher than 5Pa, apply 3000V AC voltage between the flat electrodes in the vacuum discharge device with a high-voltage power supply, and pause for 1 second every 3 seconds of output of the high-voltage power supply to activate the glow discharge to form disturbance in the reactor cavity to avoid the deposition of the reaction liquid. Under the high-voltage electric excitation, a stable and strong continuous glow reaction is formed between the flat electrodes for 15 minutes. After the reaction is completed, the atomized droplets containing urea are extracted from the vacuum discharge device. The urea yield achieved at this time is 60.2% (calculated as carbonate, which can be Figure 2 (obtained by China Inspection).

[0030] The specific embodiments described above are only used to specifically illustrate the spirit of the present invention, and the scope of protection of the present invention is not limited thereto. For those skilled in the art, it is of course possible to easily make other embodiments by changing, replacing or modifying the technical contents disclosed in this specification, and these other embodiments should all be included in the scope of protection of the present invention.

Claims

1. A method for preparing urea by ultrasonic atomization glow discharge, characterized in that: The method comprises the following steps: Step 1: Evacuate the vacuum discharge device to a pressure of 0.1 to 1.0 Pa and maintain it for 10 minutes, and introduce cooling circulating water to maintain the temperature of the reaction zone not exceeding 150° C.; the vacuum discharge device is a reactor that can realize dielectric barrier glow discharge, and is composed of (1) an air inlet, (2) a gas outlet, (3) a shell, (4) a vacuum pump, (5) a stop valve, (6) a silicone insulating pad, (7) a dielectric barrier layer, (8) a cooling water flow channel, (9) a plasma path, (10) a high-voltage power supply, and (11) a flat electrode; Step 2: preparing an aqueous solution containing 0.1-0.25 mol / L carbonate and 0.1-0.2 g / L isooctyl succinate sulfonic acid as a carbon source; the carbonate is one of sodium carbonate, potassium carbonate, and ammonium carbonate; Step 3: preparing an acetonitrile-water solution containing 0.01-0.05 mol / L nitrate and 0.1-0.2 g / L polyoxyethylene ether as a nitrogen source; the nitrate is one of sodium nitrate, potassium nitrate, and ammonium nitrate; Step 4: Control the resonant frequency of the piezoelectric ceramic atomizer to generate submicron droplets of the carbon source and nitrogen source solutions, and inject them into the vacuum discharge device under the suction effect of the negative pressure of the vacuum discharge device; Step 5: Applying an AC voltage of 1000 to 5000 V between the flat electrodes in the vacuum discharge device using a high-voltage power supply, with the high-voltage power supply outputting for 3 seconds and pausing for 1 second to activate the glow discharge and create disturbances in the reactor cavity to prevent deposition of the reaction solution; Step 6: Under high voltage excitation, a stable and strong continuous glow reaction is formed between the flat electrodes for 5 to 30 minutes; Step 7: After the reaction is completed, the atomized droplets containing urea are extracted from the vacuum discharge device.

2. The method for preparing urea by ultrasonic atomization glow discharge according to claim 1, wherein: The volume ratio of acetonitrile to water in the acetonitrile-water solution described in step 3 is 1:10 to 1:

100.

3. The method for preparing urea by ultrasonic atomization glow discharge according to claim 1, wherein: During the injection of submicron droplets in step 4, the system vacuum should be maintained at no more than 5 Pa during the reaction.

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