Method and system for converting hydrogen-containing organic carbon-14 waste gas into carbon-14 labeled urea

Abstract

The invention provides a method and a system for converting hydrogen-containing organic carbon-14 waste gas generated in the nuclear industry field into carbon-14 labeled urea. The method comprises the following steps: (1) purifying air; (2) adsorbing inert gas in the hydrogen-containing waste gas generated by the nuclear power plant by using a retention device; (3) mixing the purified air and the hydrogen-containing waste gas from which the inert gas is removed; (4) conveying the mixed gas to a plasma reactor for catalytic oxidation; and (5) conveying the mixed gas output from the plasma reaction device into an electrolysis device, and finally forming C-14 labeled urea on the surface of the cathode catalyst. The system comprises an optional washing device, a filter, an inert gas retention device, a gas mixing device, a plasma catalysis device, an electrolysis device, a gas circulating pump and a C-14 activity detection device. According to the method disclosed by the invention, a high-pollution organic solvent does not need to be used, and the reaction is carried out at normal temperature and normal pressure, so that the health and safety of workers are effectively ensured.

Description

Technical Field

[0001] The present invention relates to the field of airborne radioactive nuclide capture and resource utilization, and in particular to a method for synthesizing carbon-14 labeled urea and a corresponding synthesis system. Background Art

[0002] Helicobacter pylori is a Gram-negative bacterium that commonly resides in the gastric antrum and duodenum. It can cause chronic gastritis, peptic ulcers, and is closely associated with gastric cancer and other gastric mucosal diseases. Currently, H. pylori infection exceeds 50% of the global population, and reaches 50%-60% in my country. The urea breath test is the gold standard for H. pylori diagnosis, enabling rapid and accurate non-invasive and painless diagnosis of H. pylori infection. This technique uses radioactive carbon-14-labeled urea as the API for diagnostic reagents, offering advantages such as low cost, high quality, safety, and high accuracy. Currently, C-14-labeled urea is primarily synthesized through a series of chemical reactions involving C-14-labeled barium carbonate and an alkali metal amine. This synthesis process requires a long reaction time (approximately 40 hours), and some reaction steps require high temperatures of 300-400°C. Addressing these issues, further solutions are needed.

[0003] On the other hand, atoms of elements such as carbon, nitrogen, and oxygen in the media such as the moderator / coolant, nuclear fuel, and primary circuit materials of nuclear power plant reactors will produce radioactive nuclides such as carbon-14 when bombarded by high-energy neutrons. The gaseous carbon-14 in pressurized water reactors mainly comes from the hydrogen-containing waste gas in the primary circuit during the overhaul of the unit, which mainly includes 14 CO2, 14 CH4 (<1%), H2 (30-80%), N2 (20%~70%) and a small amount of Kr and Xe. 14 The concentration of CH4 is low. At the same time, the weak polarity and high symmetry of CH4 molecules make it difficult to separate them from the mixed gas. Although CH4 can be converted into CO2, which is more easily absorbed by alkaline substances, by thermal catalysis and other methods, the high temperature reaction conditions and the presence of a large amount of H2 greatly increase the complexity and danger of the process. Summary of the Invention

[0004] In response to the difficulties in treating hydrogen-containing waste gas from nuclear power plants, the high rate of Helicobacter pylori infection in the global natural population, and the many shortcomings of commercially available C-14-labeled urea preparation methods, such as complex processes, long time consumption, and involvement of high-temperature steps, the present invention proposes a synthesis method for converting hydrogen-containing waste gas from nuclear power plants into carbon-14-labeled urea and a system for implementing the method.

[0005] According to a first aspect of the present invention, a method is provided for catalytically treating hydrogen-containing waste gas from a nuclear power plant under relatively mild and safe conditions, and further converting the catalytically treated product into C-14-labeled urea with higher market value using an electrochemical method.

[0006] The synthetic method of C-14 labeled urea of ​​the present invention comprises the following steps: S1: Filter the normal air to remove possible SO2 x and particulate matter, thereby achieving clean air; Alternatively, high-purity compressed air or oxygen can be used instead of ordinary air.

[0007] S2: Using a retention device to absorb inert gases from hydrogen-containing waste gas produced by nuclear power plants; The retention device is filled with high-surface-area activated carbon. When hydrogen-containing waste gas flows through the retention device at a velocity of ≥0.1 cm / s, inert gases such as krypton and xenon are adsorbed and retained in the activated carbon's micropores, ultimately completely removing the inert gases from the waste gas. At this point, only hydrogen, methane, carbon dioxide, and nitrogen remain in the waste gas.

[0008] S3: The clean air obtained in S1 and the hydrogen-containing waste gas from which the inert gas has been removed in S2 are fully mixed in a volume ratio of ≥1:1.

[0009] S4: transporting the uniformly mixed gas in S3 to a plasma reactor (power ≥ 20 W) for catalytic oxidation; Specifically, oxygen and nitrogen in the air and methane and hydrogen in the exhaust gas react on the catalyst surface under the action of plasma to generate nitrogen oxides, 14 CO, 14 CO2 and water.

[0010] In this process, H2 is oxidized to water. 14 CH4 is oxidized to 14 CO2 / 14 CO (depending on the reaction conditions and gas ratio); N2 and O2 are converted into NO, N2O, NO2, etc. (depending on the reaction conditions and gas ratio) under the action of plasma; The chemical reaction process that occurs in the plasma reactor is as follows: 2H2 + O2 → 2H2O (elimination of H2) 14 CH4+ 2O2→ 14 CO2 + 2H2O (to achieve 14 CH4 14 CO2 conversion) 14 CH4+ 3 / 2O2→ 14 CO + 2H2O (to achieve 14 CH4 14 CO conversion) N2 + O2 → NO x (Realize the conversion of N2 and O2 to NO x conversion) In this step, you can 14 The conversion rate of CH4, N2, H2, etc. adjusts the power of the plasma, the type and amount of the catalyst arranged in the plasma device, so as to improve the conversion efficiency of the above substrates.

[0011] When the gas flow rate, the ratio of each substrate in the gas, and the type and amount of catalyst are constant, the substrate conversion rate is related to the plasma power. In this case, the substrate conversion rate can be improved by increasing the plasma power. The plasma power is adjusted according to the flow rate of the mixed gas to be processed, with a minimum power of ≥20 W.

[0012] When other reaction conditions remain unchanged, the type and amount of catalyst have a significant impact on substrate conversion. When substrate conversion is low, it can be improved by increasing the catalyst surface area, introducing highly reactive heteroatoms, or increasing the catalyst dosage.

[0013] S5: The mixed gas output from the plasma reaction device is transported to the electrolysis device. In the electrolysis device, 14 CO2, 14 Carbon-containing molecules such as CO will undergo a co-reduction reaction with nitrogen-containing molecules such as NO, N2O, and NO2 on the surface of the cathode catalyst, and will eventually be converted into C-14-labeled urea on the catalyst surface.

[0014] Specifically, 14 CO2 or 14 The mixed gas of CO and nitrogen-containing small molecular compounds (NO, N2O, NO2) is transported to the cathode side of the electrolysis device at a certain flow rate for co-reduction reaction. During the electrolysis process, nitrogen oxides and 14 CO, 14 CO2 and other substances are co-reduced to C-14 labeled urea on the surface of the cathode catalyst. 14 The activity of C is monitored in real time by the instrument. When the activity is greater than the specified limit, the reacted gas is pumped back to the cathode side of the electrolysis device for a cyclic reaction until the gas is 14 The activity of C is less than the specified limit (1 Bq / L).

[0015] Preferably, the resulting mixed gas is delivered to the cathode surface of the electrolysis device at a flow rate of ≥1 mL / min. To optimize urea selectivity, it's important to choose the right catalyst and cathode potential. The inventors found that copper nanocatalysts exhibit high selectivity for urea in the potential range of -0.5 V to -1.2 V vs. RHE, with the highest selectivity reaching 42.5%.

[0016] The reaction process in the electrolysis device is as follows: The reaction on the cathode catalyst surface (CO x is the abbreviation of CO and CO2, N z O y is the abbreviation of three nitrogen oxides NO, NO2 and N2O): 14 CO x + N z O y + H + → NH2 14 CONH2 + H2O Reactions occurring on the anode catalyst surface 2H2O → O2 + 2H + Protons generated on the anode catalyst surface (H + ) diffuses to the cathode catalyst surface under the traction of the electric field, and finally 14 CO x With N z O y Co-reduced to NH2 14 CONH2.

[0017] To improve 14 CO x The conversion rate and utilization rate of the gaseous 14 CO x Monitoring device implementation 14 CO x Real-time monitoring of activity; when the gas output from the electrolysis device 14 CO x When the activity of the electrolytic device is greater than 1 Bq / L (refer to GB 27742-2011), the single-pass conversion rate can be increased by increasing the cathode voltage or reducing the input flow rate, thereby achieving 14 CO x Target activity less than 1 Bq / L.

[0018] S6: Separate and purify the C-14 labeled urea generated in S5 to obtain high-purity C-14 labeled urea (H2N-14 CO-NH2).

[0019] According to a second aspect of the present invention, a system for executing the above method is provided.

[0020] Specifically, the system includes: an optional water washing device and a filter; an inert gas retention device, a gas mixing device, a plasma catalytic device, an electrolysis device, a gas circulation pump, and a C-14 activity detection device.

[0021] Beneficial Effects: This invention utilizes plasma catalytic oxidation technology to safely convert hydrogen-containing nuclear power plant waste gas diluted with air or oxygen into the raw material required for the synthesis of C-14-labeled urea. Finally, using electrocatalytic co-reduction at room temperature and pressure, this raw material is converted into C-14-labeled urea, a highly valuable and market-demand product. The disclosed technology achieves two goals with one stone; furthermore, the method does not require the use of highly polluting organic solvents, effectively ensuring the health and safety of workers. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 . Schematic diagram of the process for converting hydrogen-containing waste gas into urea; Figure 2 Schematic diagram of the electrolysis device.

[0023] Figure 3 This is an optical photograph of the C-14 labeled urea product solution after reaction with the color developing reagent. The red color represents the presence of urea product in the solution. DETAILED DESCRIPTION

[0024] To make the technical solutions and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of this application. Obviously, the described embodiments are exemplary embodiments of this application. Based on the described embodiments of this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0025] (1) Preparation of C-14 labeled urea

[0026] First, ordinary air is washed with water and purified through a high-efficiency filter at a flow rate of 100 L / min to remove any sulfur oxides and dust particles that may be present, thereby obtaining clean air. Simultaneously, hydrogen-containing waste gas from the nuclear power plant is passed through retention device 1 at a flow rate of 2 L / min for purification to remove inert gases such as krypton and xenon. The inert gases are adsorbed in the micropores of the activated carbon in the retention device, thereby obtaining hydrogen-containing waste gas from which the inert gases have been removed.

[0027] The clean air and the hydrogen-containing waste gas from which the inert gas has been removed are fully mixed in a gas mixing device 2 at a volume ratio of 1:1. The resulting mixed gas is then transported to a plasma catalytic device 3 at a flow rate of 100 mL / min. The mixed gas is completely converted into the reaction substrates (nitrogen oxides, 14 CO and 14 CO2).

[0028] The reaction substrate required for urea synthesis is transported to the cathode chamber of the electrolysis device 4 at a flow rate of ≥1 mL / min. At this time, nitrogen oxides and 14 CO and 14 CO2 is co-reduced to C-14 labeled urea on the surface of the catalyst (preferably copper nanocatalyst).

[0029] In the electrolysis device, the working electrode is a copper-based nanocatalyst, in which nitrogen oxides and C-14 label CO x A co-reduction reaction was achieved on the surface of the material to generate C-14 labeled urea, and the working electrode area was 1×1 cm 2 The applied potential range is -0.5 V ~ -1.2 V vs. RHE; the reference electrode is an Ag / AgCl electrode. By connecting the reference electrode and the working electrode, the working electrode potential can be accurately read and controlled; the diaphragm is a cation exchange membrane. The H generated at the anode + It can pass through the diaphragm under the traction of the electric field, thereby realizing the conduction of current in the electrolyte and the H + The counter electrode is an iridium oxide electrode with catalytic water decomposition, and the counter electrode area is 1×1 cm 2 The applied potential range is 2 V~3 V vs. RHE, and water molecules are decomposed into oxygen and H on the electrode surface. + , oxygen is directly exhausted, and H + Under the traction of the electric field, it diffuses to the surface of the working electrode and participates in the generation of C-14 labeled urea.

[0030] Arranged at the end of the electrolysis device 14 CO x Monitoring devices (gas chromatography, gas chromatography-mass spectrometry, etc.) can be used to detect the presence of 14 CO x Real-time monitoring of activity: When the exhaust gas 14 CO x When the activity of the tail gas is ≤1 Bq / L, the tail gas can be directly discharged; when the tail gas 14 CO x When the activity of the gas is greater than 1 Bq / L, start the gas circulation pump to pump the tail gas of the electrolysis device back to the electrolytic cell for electrolysis until the tail gas is14 CO x The activity of the liquid should be ≤1 Bq / L before emptying.

[0031] Finally, C-14 labeled urea was obtained. 12 CO2, so in order to achieve the national requirement of ≥98% radiochemical purity in C-14 labeled urea products, it is necessary to strictly control the volume ratio of hydrogen-containing waste gas from which inert gases have been removed and clean air. Here, a 1:1 ratio is selected for the synthesis of C-14 labeled urea products, and ultimately a yield of 1 mg / min and a radiochemical purity of 98% are achieved at a cathode voltage of -1 V vs. RHE.

[0032] After the electrolysis is completed, the urea color reaction is realized by the condensation reaction between urea and diacetyl monoxime. The reaction between the two will generate a red compound, indicating the successful preparation of urea (such as Figure 3 shown).

[0033] (2) System for executing the above method

[0034] The present invention also provides a system for performing the above method, which includes: an optional water washing device and a filter; an inert gas retention device, a gas mixing device, a plasma catalytic device, an electrolysis device, a gas circulation pump, and a C-14 activity detection device.

[0035] like Figure 2 As shown, the air is washed by the water washing device and then filtered through the filter. The hydrogen-containing waste gas is removed from the inert gas in the retention device 1. Then, the air and the hydrogen-containing waste gas are fully mixed in the gas mixing device 2. Then, the resulting mixed gas is completely converted into the reaction substrate required for urea synthesis in the plasma catalytic device 3. The reaction substrate required for urea synthesis is transported to the cathode chamber in the electrolysis device 4. At this time, nitrogen oxides and 14 CO and 14 CO2 is co-reduced to C-14 labeled urea crude product on the surface of the catalyst (the electrolysis device 4 is connected to a gas circulation pump. 14 CO x When the activity is greater than a predetermined value, the gas circulation pump is started to pump the tail gas of the electrolysis device back to the electrolytic cell for electrolysis), separation and purification are carried out to finally obtain the desired C-14 labeled urea.

Claims

1. A method for synthesizing C-14 labeled urea using hydrogen-containing waste gas generated by a nuclear power plant, the method comprising the following steps: S1: Filtering normal air to remove possible SOx and particulate matter in the normal air, thereby obtaining clean air; S2: Using a retention device to absorb inert gases from hydrogen-containing waste gas produced by nuclear power plants; S3: fully mixing the clean air obtained in S1 and the hydrogen-containing waste gas from which the inert gas has been removed in S2 at a volume ratio of ≥1:1; S4: transporting the uniformly mixed gas in S3 to the plasma reactor for catalytic oxidation; S5: The mixed gas output from the plasma reaction device is transported to the electrolysis device. In the electrolysis device, 14 CO2, 14 Carbon-containing molecules such as CO will undergo a co-reduction reaction with nitrogen-containing molecules such as NO, N2O, and NO2 on the surface of the cathode catalyst, and will eventually be converted into C-14-labeled urea on the catalyst surface; S6: Separate and purify the C-14 labeled urea generated in S5 to obtain high-purity C-14 labeled urea (H2N- 14 CO-NH2).

2. The method according to claim 1, wherein In S1, as an alternative, high-purity compressed air or oxygen can be used instead of ordinary air.

3. The method according to claim 1, wherein In S2, the retention device is filled with activated carbon with a high specific surface area; the hydrogen-containing waste gas flows through the retention device at a flow rate of ≥0.1 cm / s.

4. The method according to claim 1, wherein In S4, the power of the plasma is adjusted according to the flow rate of the mixed gas to be processed, and the minimum power is ≥20 W.

5. The method according to claim 1, wherein In S5, the post-reaction gas is monitored in real time. 14 When the activity of C is greater than the specified limit, the reacted gas is pumped back to the cathode side of the electrolysis device for cyclic reaction until the gas 14 The activity of C is less than the specified limit.

6. The method according to claim 1, wherein in S5, the catalyst is a copper nanocatalyst, and the cathode potential is in the range of -0.5 V to -1.2 V vs. RHE potential.

7. A system for performing the method according to any one of claims 1 to 6, the system comprising: Optional water washing device and filter; Inert gas retention device, gas mixing device, plasma catalysis device, electrolysis device, gas circulation pump, C-14 activity detection device.

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