Method for preparing high-abundance nitrogen-15 isotope with nitrogen as medium and gas diffusion cascade device

Abstract

This invention relates to a method and a gas diffusion cascade apparatus for preparing high-abundance nitrogen-15 isotopes using nitrogen as a medium. The method includes: feeding naturally abundant nitrogen into a first gas diffusion cascade, and then... (The sentence is incomplete and requires more context to translate accurately.) 15 N 14 Nitrogen gas with a molar percentage higher than 90% is fed into the photocatalytic / electrocatalytic device for reforming, resulting in... 15 N 15 Nitrogen gas with a molar percentage of N exceeding 55% is then fed into the second gas diffusion cascade, where it is obtained at the heavy fraction end of the second gas diffusion cascade. 15 N 15 Nitrogen gas with a molar percentage of N greater than 90% is used as a raw material to prepare high-abundance nitrogen-15 isotopes. This method has a high separation coefficient, high flow rate, high efficiency, and produces nitrogen-15 isotopes with high abundance, making it suitable for industrial applications.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing high-abundance nitrogen-15 isotope in a nitrogen medium and a gas diffusion cascade device, and belongs to the technical field of isotope separation. BACKGROUND

[0002] Stable isotopes are widely used and currently play an important role in many fields such as medical treatment, biology, agriculture, environment, industrial manufacturing, scientific research and the like. Nitrogen element has two stable isotopes in nature, namely nitrogen-14 (99.636%) and nitrogen-15 (0.364%). Nitrogen-15 isotope can be applied in many aspects such as medical field, agricultural research, chemical research, environment and food safety. Nitrogen-15 isotope can be used for labeling drugs to study the mechanism of corresponding drugs, help to carry out pathological diagnosis and study human nitrogen balance and metabolic process and the like. Nitrogen-15 isotope can also be used for labeling nitrogen-containing bases in DNA to play a key role in genetic engineering research. Meanwhile, nitrogen-15 isotope can also be used for labeling various compounds to study the absorption of nitrogen by plants, the loss of nitrogen in soil, the application effect, absorption and utilization of nitrogen fertilizer and the like. Nitrogen-15 isotope is also widely used in reaction mechanism, catalysis theory and molecular structure research in chemical research, and can be used as a tracer atom to help understand the process and mechanism of chemical reaction and promote the development of chemical science. Nitrogen-15 isotope can also be applied to analysis of atmospheric particulate matter sources, traceability of food and agricultural products and the like.

[0003] Nitrogen-15 isotope has a high abundance requirement in actual application, but the natural abundance of nitrogen-15 isotope is low (0.364%), which brings great difficulty to the preparation of nitrogen-15 isotope. At present, the main methods for preparing nitrogen-15 isotope are chemical exchange method (NO / HNO3 system) and NO low-temperature rectification method. The production yield of nitrogen-15 produced by the chemical exchange method is low, and the NO low-temperature rectification method is limited by the toxicity of NO and the explosion of nitrogen oxide system. The gas diffusion method separates isotopes by membrane separation, has the advantages of large flow and high reliability, and early metal porous membranes are widely used in uranium isotope diffusion separation, but have high cost. The separation using organic polymer membranes has excellent performance and extremely low cost, and has been widely used in industrial manufacturing, but the application in the preparation of high-abundance nitrogen-15 isotope is still lacking.

[0004] In addition, since the design and operation of the gas diffusion cascade are quite different for different gas media and / or different target isotopes, it cannot be assumed that the gas diffusion cascade for a certain gas medium and / or a certain target isotope can be applied to another gas medium and / or another target isotope. SUMMARY

[0005] The problem to be solved by the invention

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for preparing high-abundance nitrogen-15 isotope using natural nitrogen as medium (raw material), which has a large separation factor and a large flow rate and is suitable for industrial application.

[0007] The purpose of the present application is also to provide a gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope using natural nitrogen as medium (raw material), which has a large separation factor and a large flow rate and is suitable for industrial application.

[0008] The solution to the problem

[0009] According to the inventor's intensive research, it is found that the above technical problems can be solved by implementing the following technical solutions:

[0010] [1] A method for preparing high-abundance nitrogen-15 isotope using nitrogen as medium, comprising the following steps: feeding natural-abundance nitrogen raw material into a first gas diffusion cascade, then feeding the nitrogen gas with a mole percentage higher than 90% obtained at the heavy fraction end of the first gas diffusion cascade into a photocatalysis / electrocatalysis device for reforming, obtaining nitrogen gas with a mole percentage higher than 55%, then feeding the nitrogen gas into a second gas diffusion cascade, obtaining nitrogen gas with a mole percentage higher than 90% at the heavy fraction end of the second gas diffusion cascade, and using the nitrogen gas as raw material for preparing high-abundance nitrogen-15 isotope; wherein the first gas diffusion cascade and the second gas diffusion cascade are both step cascades, each comprising a plurality of gas diffusion separation devices; and a high-speed magnetic suspension gas compressor is used to compress the nitrogen gas before entering the gas diffusion separation devices in each gas diffusion cascade. 15 N 14 N 15 N 15 N 15 N 15 N

[0011] [2] The method according to [1], wherein the first gas diffusion cascade and the second gas diffusion cascade are each composed of a plurality of gas diffusion separation devices connected in series and / or in parallel; preferably, a plurality of gas diffusion separation devices are connected in parallel to form a separation stage, and a plurality of separation stages are connected in series to form a gas diffusion cascade.

[0012] [3] The method according to [1] or [2], wherein the gas diffusion separation device is a gas diffusion separation device with a basic full separation factor of nitrogen gas of 1.011-1.017 measured by a four-stage full reflux diffusion cascade experiment.

[0013] [4] The method according to any one of [1] to [3], wherein the gas diffusion separation device is a gas diffusion separation device with a basic full separation coefficient of nitrogen gas of 1.014 to 1.017 as measured by a four-stage full reflux diffusion cascade experiment.

[0014] [5] The method according to any one of [1] to [4], wherein the first gas diffusion cascade has a total number of stages of 800 to 900, preferably 830 to 860, wherein the feed stage is located at a position of 700 to 800 stages, preferably 740 to 770 stages, from the heavy fraction end; and the heavy fraction flow rate of the first gas diffusion cascade is 0.00005 to 0.1 times, preferably 0.0001 to 0.001 times, of the feed flow rate.

[0015] [6] The method according to any one of [1] to [5], wherein the second gas diffusion cascade has a total number of stages of 90 to 200, preferably 90 to 130, wherein the feed stage is located at a position of 90 to 130 stages, preferably 90 to 110 stages, from the heavy fraction end; and the heavy fraction flow rate of the second gas diffusion cascade is 0.005 to 1 times, preferably 0.005 to 0.1 times, of the feed flow rate.

[0016] [7] The method according to any one of [1] to [6], wherein the single-stage pressure ratio of the nitrogen gas before and after the gas diffusion separation device is not less than 3.5, preferably not less than 5.0, after being compressed by the high-speed magnetic suspension gas compressor.

[0017] [8] The method according to any one of [1] to [7], wherein the purity of the nitrogen gas of natural abundance is higher than 99.9%.

[0018] [9] A gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope with nitrogen as a medium, characterized in that it comprises:

[0019] a first gas diffusion cascade, a second gas diffusion cascade, a photocatalysis / electrocatalysis device, and a high-speed magnetic suspension gas compressor;

[0020] the first gas diffusion cascade and the second gas diffusion cascade are both step cascades, each comprising a plurality of gas diffusion separation devices;

[0021] the photocatalysis / electrocatalysis device is located between the first gas diffusion cascade and the second gas diffusion cascade;

[0022] the high-speed magnetic suspension gas compressor is located before each of the gas diffusion separation devices in the nitrogen flow direction;

[0023] high-abundance nitrogen-15 isotope prepared with nitrogen as a medium is obtained from the heavy fraction end of the second gas diffusion cascade.

[0024] Effects of the invention

[0025] In the present application, the nitrogen-15 isotope can be separated by using the gas diffusion method with nitrogen as the medium on the gas diffusion cascade, and the separation coefficient is high, the flow is large, and it is suitable for industrial application.

[0026] Specifically, the nitrogen as the separation medium has a small relative molecular mass, and the gas diffusion separation coefficient is relatively large. The nitrogen is cheap, easy to obtain, and has stable physical and chemical properties. The gas diffusion separation process is a physical separation process, and does not introduce other impurities. Moreover, the high-speed magnetic suspension compressor can effectively compress light gas. Therefore, the method of the present application has the advantages of large flow, high efficiency, high abundance of the prepared nitrogen-15 isotope (which can reach more than 90%), and the like, because the gas diffusion cascade is used, the high-speed magnetic suspension compressor is used to effectively compress light gas, and the nitrogen with a relatively large separation coefficient is used as the separation medium.

[0027] On the basis of the above, the present application can adjust the target isotope abundance by flexibly adjusting the length (number of stages) and flow (heavy fraction flow, total flow, etc.) of the gas diffusion cascade. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The figure is a schematic diagram of the principle of preparing high-abundance nitrogen-15 isotope by the gas diffusion cascade according to the embodiment of the present application.

[0029] Figure 2 The figure is a schematic diagram of the series and parallel cascade connection form of the gas diffusion separation device string according to the embodiment of the present application.

[0030] Figure 3 The figure is a schematic diagram of the gas membrane passing principle in a single-stage single separator (gas diffusion separation device) according to the embodiment of the present application.

[0031] Figure 4 The figure is a component molar percentage distribution diagram of each stage in the first gas diffusion cascade according to the embodiment of the present application.

[0032] Figure 5 The figure is a component molar percentage distribution diagram of each stage in the second gas diffusion cascade according to the embodiment of the present application. DETAILED DESCRIPTION

[0033] Various exemplary embodiments, features, and aspects of the present application will be described in detail below. The word "exemplary" used herein means "serving as an example, an embodiment, or illustrative". Any embodiment described herein as "exemplary" is not necessarily to be construed as being superior to or preferable over other embodiments.

[0034] In addition, for a better understanding of the present application, numerous specific details are set forth in the following detailed description. One skilled in the art will understand that the application can be practiced without certain specific details. In other instances, well-known methods, apparatuses, devices and steps have not been described in detail since they can be readily understood by persons skilled in the art.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The meaning of "a", "an", and "the" includes plural references. The meaning of "in" includes "in" and "on." The use of "including", "comprising", or "having" means that there are no numerical limitations to the number of objects or steps. The use of "at least" means "greater than or equal to." The use of "or" means "and / or" unless otherwise stated.

[0036] In the specification and embodiments, the directional terms such as "upper", "lower", "front", "back", "left", "right" and the like are used with reference to the directions of the accompanying drawings, and are not intended to limit the scope of protection of the present application.

[0037] In the specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0038] In the specification, "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", and the like refer to the specific elements (e.g., features, structures, properties, and / or characteristics) described in relation to the embodiments, which are included in at least one embodiment described herein, and can be present in other embodiments or can not be present in other embodiments. In addition, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0039] In the specification, the numerical range represented by "numerical value A to numerical value B" means a range including the end point values A and B.

[0040] The manufacturing method of the present application for preparing high-abundance nitrogen-15 isotope using nitrogen as a medium includes the following steps: supplying natural-abundance nitrogen raw material into a first gas diffusion cascade, then supplying the nitrogen gas with a molar percentage higher than 90% obtained at the heavy fraction end of the first gas diffusion cascade into a photocatalytic / electrocatalytic device for reforming, obtaining nitrogen gas with a molar percentage higher than 90%, 15 N 14 N 15 N 15 15 N 15 ​Nitrogen gas with a molar percentage of N greater than 90% can be used as a raw material to prepare high-abundance nitrogen-15 isotopes; wherein, the first gas diffusion cascade and the second gas diffusion cascade are both step cascades, each containing multiple gas diffusion separation devices; a high-speed magnetic levitation gas compressor is used to compress the nitrogen gas before it enters the gas diffusion separation device in each of the gas diffusion cascades.

[0041] By employing the above method, this invention provides a method for preparing high-abundance nitrogen-15 isotopes using nitrogen as a medium (raw material). This method has a large separation coefficient and a large flow rate, making it suitable for industrial applications.

[0042] Figure 1 This is a schematic diagram illustrating the principle of gas diffusion cascade preparation of high-abundance nitrogen-15 isotopes according to an embodiment of the present invention.

[0043] In an embodiment of the present invention, the first gas diffusion cascade and the second gas diffusion cascade are each composed of multiple gas diffusion separation devices connected in series and / or in parallel. An example of their specific series or parallel configuration is... Figure 2 As shown.

[0044] Gas diffusion separation devices achieve relative, rather than absolute, separation of the working medium. A single separation stage is usually insufficient to obtain the desired abundance of the final product; therefore, alternative methods are often employed. Figure 2 The multiple separation stages shown are connected in series to form a gas diffusion cascade. Each separation stage can consist of multiple gas diffusion separation devices connected in parallel. Figure 2 Each separation stage contains multiple gas diffusion separation devices connected in parallel. In some preferred embodiments, multiple gas diffusion separation devices are connected in parallel to form a separation stage, and then multiple separation stages are connected in series to form a gas diffusion cascade. This allows for a gradual increase in the abundance of the target isotope, ultimately achieving the required product abundance. The parallel connection of multiple gas diffusion separation devices increases the flow rate of a single stage, achieving the output required for industrial production. In the process of connecting the gas diffusion separation devices in parallel, each gas diffusion separation device is not affected by the hydraulic parameters of other machines in the same separation stage, thus facilitating scale-up design for production in principle.

[0045] Each gas diffusion separation device performs separation based on the isotope separation effect of nitrogen passing through a porous organic membrane. Figure 3 This is a schematic diagram of the gas membrane principle in a single-stage single separator (gas diffusion separation device) according to an embodiment of the present invention, wherein G and C represent the feed flow rate and feed abundance, G' and C' represent the light fraction flow rate and light fraction abundance, and G” and C” represent the heavy fraction flow rate and heavy fraction abundance.

[0046] In some preferred embodiments, the porous organic membrane of the present application can be a polypropylene membrane or the like.

[0047] In some preferred embodiments, the gas diffusion separation device of the present application has a basic full separation coefficient of nitrogen of 1.011-1.017 as measured by a four-stage full reflux diffusion cascade experiment.

[0048] In some more preferred embodiments, the gas diffusion separation device of the present application has a basic full separation coefficient of nitrogen of 1.014-1.017 as measured by a four-stage full reflux diffusion cascade experiment.

[0049] In some preferred embodiments, the gas diffusion cascade of the present application is composed of gas diffusion separation devices having a basic full separation coefficient of nitrogen of 1.011-1.017 as measured by a four-stage full reflux diffusion cascade experiment: a plurality of gas diffusion separation devices are connected in parallel to form a separation stage, and a plurality of the separation stages are connected in series.

[0050] In some more preferred embodiments, the gas diffusion cascade of the present application is composed of gas diffusion separation devices having a basic full separation coefficient of nitrogen of 1.014-1.017 as measured by a four-stage full reflux diffusion cascade experiment: a plurality of gas diffusion separation devices are connected in parallel to form a separation stage, and a plurality of the separation stages are connected in series.

[0051] In the present application, the four-stage full reflux diffusion cascade experiment for measuring the basic full separation coefficient of nitrogen is performed by a mass spectrometry method commonly used in the art, and the specific implementation approach is not limited. The basic full separation coefficient is defined as the separation coefficient corresponding to the difference in unit molar mass.

[0052] In the present application, the total stage number of the gas diffusion cascade is not particularly limited and can be appropriately adjusted according to actual needs.

[0053] In some preferred embodiments, the total stage number of the first gas diffusion cascade is 800-900 stages, and more preferably, the total stage number of the first gas diffusion cascade is 830-860 stages, such as 835, 840, 845, 850, 855 stages, etc.

[0054] In some preferred embodiments, the total stage number of the second gas diffusion cascade is 90-200 stages, and more preferably, the total stage number of the second gas diffusion cascade is 90-130 stages, such as 95, 100, 105, 110, 115, 120, 125 stages, etc.

[0055] In the present application, the first gas diffusion cascade and the second gas diffusion cascade both comprise a feed stage, and the position of the feed stage is not particularly limited and can be appropriately adjusted according to actual needs.

[0056] In some preferred embodiments, the feed stage in the first gas diffusion cascade is located at a position 700-800 stages away from the heavy end, more preferably at a position 740-770 stages away from the heavy end, such as at a position 745, 750, 755, 760, 765 stages away from the heavy end, and the like.

[0057] In some preferred embodiments, the feed stage in the second gas diffusion cascade is located at a position 90-130 stages away from the heavy end, more preferably at a position 90-110 stages away from the heavy end, such as at a position 95, 100, 105 stages away from the heavy end, and the like.

[0058] In the present application, the heavy end flow rate of the gas diffusion cascade is not particularly limited and can be appropriately adjusted according to actual needs.

[0059] In some preferred embodiments, the heavy end flow rate of the first gas diffusion cascade is 0.00005-0.1 times the feed flow rate of the feed stage, more preferably 0.0001-0.001 times, such as 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0008 times, and the like.

[0060] In some preferred embodiments, the heavy end flow rate of the second gas diffusion cascade is 0.005-1 times the feed flow rate of the feed stage, more preferably 0.005-0.1 times, such as 0.006, 0.008, 0.009, 0.01, 0.011, 0.012, 0.015, 0.02, 0.05, 0.08 times, and the like.

[0061] In the present application, the total flow rate of the gas diffusion cascade is not particularly limited and can be appropriately adjusted according to actual needs.

[0062] In some preferred embodiments, the total flow rate of the first gas diffusion cascade is 8000000-10000000 times the feed flow rate of the feed stage, more preferably 9000000-10000000 times, such as 8500000, 9200000, 9300000, 9500000, 9800000 times, and the like.

[0063] In some preferred embodiments, the total flow rate of the second gas diffusion cascade is 50000-70000 times the feed flow rate of the feed stage, more preferably 50000-60000 times, such as 52000, 54000, 56000, 58000 times, and the like.

[0064] In some preferred embodiments, the purity of the natural abundance nitrogen gas is higher than 99.9%. The natural abundance nitrogen gas can be a commercially available product.

[0065] In some preferred embodiments, the high-speed magnetic levitation compressor used in the present application is preferably a high-speed magnetic levitation compressor that can be used under negative pressure conditions, such as the high-speed magnetic levitation compressor for negative pressure conditions described in CN209510664U (the content of this patent is incorporated herein by reference in its entirety).

[0066] In addition, the high-speed magnetic levitation gas compressor is located before each gas diffusion separation device in the direction of nitrogen gas flow. In some preferred embodiments, one or more (e.g., 2-4) high-speed magnetic levitation compressors can be present before each gas diffusion separation device.

[0067] In other preferred embodiments, the single-stage pressure ratio of the nitrogen gas before and after (i.e., before and after passing through the membrane) the gas diffusion separation device after being compressed by the high-speed magnetic levitation compressor is at least 3.5, and more preferably 5.0 or more.

[0068] In the present application, the photocatalytic / electrocatalytic reaction device is located between the first gas diffusion cascade and the second gas diffusion cascade. As for the photocatalytic / electrocatalytic reaction device, the present application does not make any particular limitation as long as it can 15 N 14 N with a molar percentage higher than 90% is subjected to reforming (catalysis) to obtain 15 N 15 N with a molar percentage higher than 55% can meet the requirements of the present application. In some preferred embodiments, the photocatalytic / electrocatalytic reaction device of the present application uses a catalyst containing iron or ruthenium as the main component.

[0069] The method for preparing high-abundance nitrogen-15 isotope using nitrogen as the medium provided by the present application is described in detail below in combination with Figure 4 、 Figure 5 and specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be obtained by purchase on the market.

[0070] Natural abundance nitrogen gas with a chemical purity higher than 99.9% is supplied into the first gas diffusion cascade, and then the 15 N 14 N with a molar percentage higher than 90% is subjected to catalytic reforming (photocatalysis / electrocatalysis) to obtain 15 N 15 N with a molar percentage higher than 55% is supplied into the second gas diffusion cascade, and then the 15 N 15The nitrogen gas with a mole percentage of more than 90% can be used as a raw material to prepare high-abundance nitrogen-15 isotope.

[0071] Based on the isotope separation effect of nitrogen gas through the porous organic membrane, the effective compression of the nitrogen gas is realized by using a high-speed magnetic suspension gas compressor, and the production and preparation of nitrogen-15 isotope are realized by using the gas diffusion method. The specific implementation is as follows.

[0072] Embodiment

[0073] The gas diffusion cascade is composed of gas diffusion separation devices with a basic total separation coefficient of 1.014 in series and parallel, and the structure is shown in Figure 2 The porous organic membrane in the gas diffusion separation device is a polypropylene membrane, and the catalyst in the catalyst device in the middle of the first gas diffusion cascade and the second gas diffusion cascade contains a catalyst with iron or ruthenium as the main component. The total stage number of the first gas diffusion cascade is 844, the feed stage is located at a position 757 stages away from the heavy fraction end, and the heavy fraction end obtains 15 N 14 The mole percentage of N is 90.37%, the feed flow is 3333 times the heavy fraction flow (i.e. the heavy fraction flow is 0.0003 times the feed flow), the total flow of the first gas diffusion cascade is 9390000 times the feed flow, and the mole percentage distribution of each component at each stage in the first gas diffusion cascade is shown in Figure 4 The total stage number of the second gas diffusion cascade is 110, the feed stage is located at a position 101 stages away from the heavy fraction end, and the heavy fraction end obtains 15 N 15 The mole percentage of N is 90.82%, the feed flow is 100 times the heavy fraction flow (i.e. the heavy fraction flow is 0.01 times the feed flow), the total flow of the second gas diffusion cascade is 54500 times the feed flow, and the mole percentage distribution of each component at each stage in the second gas diffusion cascade is shown in Figure 5 .

[0074] As can be seen from the above embodiment, the method for preparing high-abundance nitrogen-15 isotope by using nitrogen gas as a medium provided by the application has the advantages of large flow and high efficiency, and can be used to prepare high-abundance nitrogen-15 isotope. At the same time, the gas diffusion separation process is a physical separation process, and does not introduce other impurities, so that the prepared nitrogen-15 isotope has high abundance and can reach more than 90%. The method is suitable for industrial application when used for the preparation of high-abundance nitrogen-15 isotope.

[0075] Having described various embodiments of the application, it is to be understood that the above description is meant not to limit and not to encompass all of the possible embodiments covered by the claims. Many modifications and variations of this application can be apparent to those of ordinary skill in the art without departing from the spirit and scope of the described embodiments. It is intended that the scope of the application should only be limited by the appended claims.

Claims

1. A method for preparing high-abundance nitrogen-15 isotopes using nitrogen as a medium, characterized in that, Includes the following steps: The natural abundance nitrogen feedstock is supplied into the first gas diffusion cascade, and then the nitrogen obtained at the heavy fraction end of the first gas diffusion cascade is supplied into the second gas diffusion cascade 15 N 14 N with a molar percentage higher than 90% is supplied into the photocatalytic / electrocatalytic device for reforming, and the nitrogen obtained at the heavy fraction end of the photocatalytic / electrocatalytic device is supplied into the second gas diffusion cascade 15 N 15 N with a molar percentage higher than 55% is supplied into the second gas diffusion cascade, and the nitrogen obtained at the heavy fraction end of the second gas diffusion cascade is supplied into the third gas diffusion cascade 15 N 15 N with a molar percentage higher than 90% is used as a feedstock to prepare high abundance nitrogen-15 isotope; wherein the first gas diffusion cascade and the second gas diffusion cascade are both step cascades, each comprising a plurality of gas diffusion separation devices; a high-speed magnetic suspension gas compressor is used to compress the nitrogen gas before entering the gas diffusion separation devices in each of the gas diffusion cascades.

2. The method according to claim 1, characterized in that, The first gas diffusion cascade and the second gas diffusion cascade are each composed of multiple gas diffusion separation devices connected in series and / or in parallel.

3. The method according to claim 2, characterized in that, Multiple gas diffusion separation devices are connected in parallel to form a separation stage, and then multiple separation stages are connected in series to form a gas diffusion cascade.

4. The method according to any one of claims 1 to 3, characterized in that, The gas diffusion separation device is a gas diffusion separation device with a nitrogen basic separation coefficient of 1.011~1.017 obtained by measuring through a four-stage full reflux diffusion cascade experiment.

5. The method according to any one of claims 1 to 3, characterized in that, The gas diffusion separation device is a gas diffusion separation device with a nitrogen basic separation coefficient of 1.014~1.017 obtained by measuring through a four-stage full reflux diffusion cascade experiment.

6. The method according to any one of claims 1 to 3, characterized in that, The first gas diffusion cascade has a total of 800 to 900 stages, with the feed stage located 700 to 800 stages away from the heavy fraction end; The flow rate of the heavy fraction in the first gas diffusion cascade is 0.00005 to 0.1 times the feed flow rate.

7. The method according to claim 6, characterized in that, The first gas diffusion cascade has a total of 830 to 860 stages, with the feed stage located 740 to 770 stages away from the heavy fraction end; The flow rate of the heavy fraction in the first gas diffusion cascade is 0.0001 to 0.001 times the feed flow rate.

8. The method according to any one of claims 1 to 3, characterized in that, The second gas diffusion cascade has a total of 90 to 200 stages, with the feed stage located 90 to 130 stages away from the heavy fraction end; The flow rate of the heavy distillate fraction in the second gas diffusion cascade is 0.005 to 1 times the feed flow rate.

9. The method according to claim 8, characterized in that, The second gas diffusion cascade has a total of 90 to 130 stages, with the feed stage located 90 to 110 stages away from the heavy fraction end; the heavy fraction flow rate of the second gas diffusion cascade is 0.005 to 0.1 times the feed flow rate.

10. The method according to any one of claims 1 to 3, characterized in that, After being compressed by the high-speed magnetic levitation gas compressor, the single-stage pressure ratio of the nitrogen gas before and after passing through the gas diffusion separation device is not less than 3.

5.

11. The method according to claim 10, characterized in that, After being compressed by the high-speed magnetic levitation gas compressor, the single-stage pressure ratio of the nitrogen gas before and after passing through the gas diffusion separation device is not less than 5.

0.

12. The method according to any one of claims 1 to 3, characterized in that, The purity of the naturally abundant nitrogen gas is higher than 99.9%.

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