Gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope by taking nitrogen as medium

Abstract

The utility model relates to a gas diffusion cascade device for preparing high-abundance nitrogen-15 isotopes by taking nitrogen as a medium. The gas diffusion cascade device comprises a first gas diffusion cascade, a second gas diffusion cascade, a photocatalysis / electro-catalysis device and a high-speed magnetic suspension gas compressor, the first gas diffusion cascade and the second gas diffusion cascade are ladder cascade and respectively comprise a plurality of gas diffusion separation devices; the photocatalysis / electrocatalysis device is positioned between the first gas diffusion cascade and the second gas diffusion cascade; the high-speed magnetic suspension gas compressor is positioned in front of each gas diffusion and separation device in the nitrogen flowing direction; and obtaining the high-abundance nitrogen-15 isotope prepared by taking nitrogen as a medium from the heavy fraction end of the second gas diffusion cascade. The gas diffusion cascade device is high in separation coefficient, large in flow and high in efficiency, the prepared nitrogen-15 isotope abundance is high, and the gas diffusion cascade device is suitable for industrial application.

Description

Technical Field

[0001] The utility model relates to a gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope with nitrogen as a medium, belonging to the technical field of isotope separation. Background Art

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

[0003] Nitrogen-15 isotope has a high abundance requirement in the actual application process, but the natural abundance of nitrogen-15 isotope is low (0.364%), which brings great difficulties 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 output of nitrogen-15 by chemical exchange method is low, while the NO low-temperature rectification method is limited by the disadvantages such as highly toxic NO and extremely easy explosion of nitrogen oxide system. The gas diffusion method separates isotopes by membrane separation, which has the advantages of large flow rate and high reliability. In the early stage, metal porous membranes were widely used in the diffusion separation of uranium isotopes, but they had high costs; while using organic polymer membranes for separation has the advantages of excellent performance and extremely low cost, and has been widely used in industrial manufacturing, but there is still a lack of research on its application in the manufacture of high-abundance nitrogen-15 isotope.

[0004] In addition, due to the great differences in the design and operation of gas diffusion cascades for different gas media and / or different target isotopes, it cannot be taken for granted 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 of the Utility Model

[0005] Problems to be Solved by the Utility Model

[0006] In view of the deficiencies of the prior art, the purpose of the present utility model is to provide a gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope with natural nitrogen as the medium (raw material). The gas diffusion cascade device has a large separation coefficient and a large flow rate, and is suitable for industrial application.

[0007] Solutions for Solving the Problems

[0008] According to intensive research, it is found that by implementing the following technical solutions, the above technical problems can be solved:

[0009] [1] A gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope with nitrogen as the medium, which includes: a first gas diffusion cascade, a second gas diffusion cascade, a photocatalytic / electrocatalytic device, and a high-speed magnetic levitation gas compressor;

[0010] Both the first gas diffusion cascade and the second gas diffusion cascade are stepped cascades, each containing a plurality of gas diffusion separation devices;

[0011] The photocatalytic / electrocatalytic device is located between the first gas diffusion cascade and the second gas diffusion cascade;

[0012] The high-speed magnetic levitation gas compressor is located before each of the gas diffusion separation devices in the nitrogen flow direction;

[0013] High-abundance nitrogen-15 isotope prepared with nitrogen as the medium is obtained from the heavy fraction end of the second gas diffusion cascade.

[0014] [2] The gas diffusion cascade device according to [1], wherein each of the first gas diffusion cascade and the second gas diffusion cascade is composed of a plurality of gas diffusion separation devices connected in series and / or in parallel.

[0015] [3] The gas diffusion cascade device according to [1], wherein a plurality of gas diffusion separation devices are connected in parallel to form a separation stage, and then a plurality of separation stages are connected in series to form the first gas diffusion cascade and the second gas diffusion cascade.

[0016] [4] The gas diffusion cascade device according to any one of [1] to [3], wherein the gas diffusion separation device is a gas diffusion separation device with a basic nitrogen separation coefficient of 1.011 to 1.017 measured by a four-stage total reflux diffusion cascade experiment.

[0017] [5] The gas diffusion cascade device according to [4], wherein the gas diffusion separation device is a gas diffusion separation device with a nitrogen basic separation coefficient of 1.014 to 1.017 obtained by a four-stage total reflux diffusion cascade experiment.

[0018] [6] The gas diffusion cascade device according to any one of [1] to [3], wherein the total number of stages of the first gas diffusion cascade is 800 to 900 stages, and the feed stage is located at a position 700 to 800 stages away from the heavy fraction end; the heavy fraction flow rate of the first gas diffusion cascade is 0.00005 to 0.1 times the feed flow rate.

[0019] [7] The gas diffusion cascade device according to [6], wherein the total number of stages of the first gas diffusion cascade is 830 to 860 stages, and the feed stage is located at a position 740 to 770 stages away from the heavy fraction end; the heavy fraction flow rate of the first gas diffusion cascade is 0.0001 to 0.001 times the feed flow rate.

[0020] [8] The gas diffusion cascade device according to any one of [1] to [3], wherein the total number of stages of the second gas diffusion cascade is 90 to 200 stages, and the feed stage is located at a position 90 to 130 stages away from the heavy fraction end; the heavy fraction flow rate of the second gas diffusion cascade is 0.005 to 1 times the feed flow rate.

[0021] [9] The gas diffusion cascade device according to [8], wherein the total number of stages of the second gas diffusion cascade is 90 to 130 stages, and the feed stage is located at a position 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.

[0022] Effects of the Utility Model

[0023] In the present utility model, nitrogen-15 isotope can be separated by gas diffusion method on a gas diffusion cascade with high separation coefficient, large flow rate, and suitable for industrial application.

[0024] Specifically, nitrogen as the separation medium has a small relative molecular mass and a relatively large gas diffusion separation coefficient. Nitrogen is inexpensive, easy to obtain, and has stable physical and chemical properties. The gas diffusion separation process is a physical separation process without introducing other impurities. Moreover, the high-speed magnetic levitation compressor can effectively compress light gases. Therefore, the present utility model has the advantages of large flow rate, high efficiency, and high abundance of the prepared nitrogen-15 isotope (up to more than 90%) due to the adoption of a gas diffusion cascade, the use of a high-speed magnetic levitation compressor to effectively compress light gases, and the adoption of nitrogen with a relatively large separation coefficient as the separation medium.

[0025] On the basis described above, the present utility model can adjust the target isotope abundance by flexibly adjusting the length (number of stages) and flow rate (heavy fraction flow rate, total flow rate, etc.) of the gas diffusion cascade. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the principle for preparing high-abundance nitrogen-15 isotope by the gas diffusion cascade device according to the embodiment of the present utility model.

[0027] Figure 2 It is a schematic diagram of the series and parallel cascade connection forms of the gas diffusion separation device according to the embodiment of the present utility model.

[0028] Figure 3 It is a schematic diagram of the gas transmembrane principle inside a single-stage single separator (gas diffusion separation device) according to the embodiment of the present utility model.

[0029] Figure 4 It is a distribution diagram of the molar percentages of components at each stage in the first gas diffusion cascade according to the embodiment of the present utility model.

[0030] Figure 5 It is a distribution diagram of the molar percentages of components at each stage in the second gas diffusion cascade according to the embodiment of the present utility model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The following will detail various exemplary embodiments, features, and aspects of the present utility model. The special word "exemplary" here means "serving as an example, embodiment, or illustration". Any embodiment described as "exemplary" here does not have to be construed as superior or better than other embodiments.

[0032] In addition, for better illustration of the present utility model, numerous specific details are given in the following detailed description of the embodiments. Those skilled in the art should understand that the present utility model can still be implemented without some of these specific details. In other instances, methods, means, equipment, and steps well-known to those skilled in the art are not described in detail to highlight the gist of the present utility model.

[0033] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values and numerical ranges appearing in the present utility model should be understood to include the inevitable systematic errors or design constraints in industrial production that are approximately equal to the corresponding values. Examples of parameters with specific values can be provided herein, but these parameters do not necessarily have to be exactly equal to the corresponding values.

[0034] In this specification, the directional terms mentioned in the embodiments, such as "up", "down", "front", "back", "left", "right", etc., are only references to the directions in the drawings and are not used to limit the protection scope of the present utility model.

[0035] In this specification, the meaning expressed by "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0036] In this specification, "some specific / preferred embodiments", "some other specific / preferred embodiments", "embodiments", etc. mentioned refer to specific elements (such as features, structures, properties, and / or characteristics) related to the embodiment, which are included in at least one of the embodiments described herein, and may or may not exist in other embodiments. Additionally, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0037] In this specification, the numerical range expressed by "numerical value A to numerical value B" refers to a range that includes the endpoint numerical values A and B.

[0038] The gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope with nitrogen as the medium of the present utility model includes: a first gas diffusion cascade, a second gas diffusion cascade, a photocatalytic / electrocatalytic device, and a high-speed magnetic levitation gas compressor; both the first gas diffusion cascade and the second gas diffusion cascade are stepped cascades, each containing a plurality of gas diffusion separation devices; the photocatalytic / electrocatalytic device is located between the first gas diffusion cascade and the second gas diffusion cascade; the high-speed magnetic levitation gas compressor is located before each of the gas diffusion separation devices in the nitrogen flow direction; high-abundance nitrogen-15 isotope prepared with nitrogen as the medium is obtained from the heavy fraction end of the second gas diffusion cascade.

[0039] By adopting the above gas diffusion cascade device, the present utility model provides a gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope with nitrogen as the medium (raw material), which has a large separation coefficient and a large flow rate, and is suitable for industrial application.

[0040] Figure 1 It is a schematic diagram of the principle for preparing high-abundance nitrogen-15 isotope by the gas diffusion cascade device according to the embodiments of the present utility model.

[0041] In the embodiments of the present utility model, 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, and a specific example of the specific series and parallel connection composition method is as Figure 2 shown.

[0042] The separation of the working medium by the gas diffusion separation device is a relative separation, not an absolute separation. Usually, the final product required abundance cannot be obtained only through a single separation stage. Therefore, often such as Figure 2The connection mode of multiple separation stages connected in series forms a gas diffusion cascade. Among them, each separation stage can be composed of multiple gas diffusion separation devices connected in parallel inside. Figure 2 Inside each separation stage, there is also a parallel form of multiple gas diffusion separation devices. 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, thereby forming a gas diffusion cascade, which can achieve a gradual increase in the target isotope abundance and finally reach the required product abundance; the parallel connection of multiple gas diffusion separation devices can increase the flow rate of a single stage to reach the production volume required for industrial production. During the parallel connection of the above gas diffusion separation devices, each gas diffusion separation device is not interfered by other machines in the same separation stage in terms of hydraulic parameters, so it is convenient to carry out scale-up design in principle.

[0043] Each gas diffusion separation device is separated based on the isotope separation effect of nitrogen passing through a porous organic membrane. Figure 3 It is a schematic diagram of the gas passing through the membrane principle inside a single-stage single separator (i.e., a gas diffusion separation device) according to an embodiment of the present invention. Among them, 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.

[0044] In some preferred embodiments, the porous organic membrane of the present invention can be a polypropylene membrane, etc.

[0045] In some preferred embodiments, the basic overall separation coefficient of nitrogen obtained by the four-stage total reflux diffusion cascade experiment of the gas diffusion separation device of the present invention is 1.011 - 1.017.

[0046] In some more preferred embodiments, the basic overall separation coefficient of nitrogen obtained by the four-stage total reflux diffusion cascade experiment of the gas diffusion separation device of the present invention is 1.014 - 1.017.

[0047] In some preferred embodiments, the gas diffusion cascade of the present invention is composed of gas diffusion separation devices with a basic overall separation coefficient of nitrogen of 1.011 - 1.017 obtained by the four-stage total reflux diffusion cascade experiment: multiple gas diffusion separation devices are connected in parallel to form a separation stage, and then multiple said separation stages are connected in series.

[0048] In some more preferred embodiments, the gas diffusion cascade of the present invention is composed of gas diffusion separation devices with a basic overall separation coefficient of nitrogen of 1.014 - 1.017 obtained by the four-stage total reflux diffusion cascade experiment: multiple gas diffusion separation devices are connected in parallel to form a separation stage, and then multiple said separation stages are connected in series.

[0049] In the present utility model, the measurement of the basic separation coefficient of nitrogen for the four-stage total reflux diffusion cascade experiment is carried out by a common mass spectrometry method in the art, and the specific implementation means is not limited. The definition of the basic separation coefficient is the separation coefficient corresponding to the difference in unit molar mass.

[0050] In the present utility model, there is no particular limitation on the total number of stages of the gas diffusion cascade, and it can be appropriately adjusted according to actual needs.

[0051] In some preferred embodiments, the total number of stages of the first gas diffusion cascade is 800 - 900 stages, and more preferably, the total number of stages of the first gas diffusion cascade is 830 - 860 stages, such as 835, 840, 845, 850, 855 stages, etc.

[0052] In some preferred embodiments, the total number of stages of the second gas diffusion cascade is 90 - 200 stages, and more preferably, the total number of stages of the second gas diffusion cascade is 90 - 130 stages, such as 95, 100, 105, 110, 115, 120, 125 stages, etc.

[0053] In the present utility model, both the first gas diffusion cascade and the second gas diffusion cascade include a feed stage, and there is no particular limitation on the position of the feed stage, and it can be appropriately adjusted according to actual needs.

[0054] 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 fraction end, and more preferably at a position 740 - 770 stages away from the heavy fraction end, such as positions 745, 750, 755, 760, 765 stages, etc.

[0055] 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 fraction end, and more preferably at a position 90 - 110 stages away from the heavy fraction end, such as positions 95, 100, 105 stages, etc.

[0056] In the present utility model, there is no particular limitation on the heavy fraction flow rate of the gas diffusion cascade, and it can be appropriately adjusted according to actual needs.

[0057] In some preferred embodiments, the heavy fraction flow rate of the first gas diffusion cascade is 0.00005 - 0.1 times the feed flow rate of the feed stage, and more preferably 0.0001 - 0.001 times, such as 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0008 times, etc.

[0058] In some preferred embodiments, the flow rate of the heavy fraction of the second gas diffusion cascade is 0.005 to 1 times, more preferably 0.005 to 0.1 times, of the feed flow rate of the feed stage, such as 0.006, 0.008, 0.009, 0.01, 0.011, 0.012, 0.015, 0.02, 0.05, 0.08 times, etc.

[0059] In the present utility model, there is no particular limitation on the total flow rate of the gas diffusion cascade, and it can be appropriately adjusted according to actual needs.

[0060] In some preferred embodiments, the total flow rate of the first gas diffusion cascade is 8,000,000 to 10,000,000 times, more preferably 9,000,000 to 10,000,000 times, of the feed flow rate of the feed stage, such as 8,500,000, 9,200,000, 9,300,000, 9,500,000, 9,800,000 times, etc.

[0061] In some preferred embodiments, the total flow rate of the second gas diffusion cascade is 50,000 to 70,000 times, more preferably 50,000 to 60,000 times, of the feed flow rate of the feed stage, such as 52,000, 54,000, 56,000, 58,000 times, etc.

[0062] In some preferred embodiments, the purity of natural abundance nitrogen gas is higher than 99.9%. Natural abundance nitrogen gas can be a commercially available product.

[0063] In some preferred embodiments, the high-speed magnetic levitation compressor used in the present utility model is preferably a high-speed magnetic levitation compressor that can be used under negative pressure conditions. For example, the high-speed magnetic levitation compressor used under negative pressure conditions described in CN209510664U (the content of this patent is incorporated herein by reference in its entirety).

[0064] In addition, the high-speed magnetic levitation gas compressor is located in front of each of the gas diffusion separation devices in the nitrogen flow direction. In some preferred embodiments, one or more (such as 2 to 4) high-speed magnetic levitation compressors may be present in front of each gas diffusion separation device.

[0065] In some other preferred embodiments, after being compressed by the high-speed magnetic levitation compressor, the single-stage pressure ratio of the nitrogen gas before and after passing through the gas diffusion separation device (i.e., before and after passing through the membrane) is at least 3.5, more preferably 5.0 or more.

[0066] In the present utility model, the photocatalytic / electrocatalytic reaction device is located between the first gas diffusion cascade and the second gas diffusion cascade. For the photocatalytic / electrocatalytic reaction device, the present utility model does not make any particular limitation as long as it can 15 N14 Nitrogen with an N molar percentage higher than 90% is reformed (catalyzed) to obtain 15 N 15 Nitrogen with an N molar percentage higher than 55% can meet the requirements of the present invention. In some preferred embodiments, the photocatalytic / electrocatalytic reaction device of the present invention uses a catalyst containing iron or ruthenium as the main component.

[0067] The following combines Figure 4 、 Figure 5 and specific examples to detail the method for preparing high-abundance nitrogen-15 isotope using nitrogen as a medium provided by the present invention. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention. For those not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0068] Natural abundance nitrogen with a chemical purity higher than 99.9% is fed into the first gas diffusion cascade, and then the 15 N 14 Nitrogen with an N molar percentage higher than 90% is catalytically reformed (photocatalytic / electrocatalytic) to obtain 15 N 15 Nitrogen with an N molar percentage higher than 55% is fed into the second gas diffusion cascade after being obtained, and 15 N 15 Nitrogen with an N molar percentage higher than 90% can be used as a raw material to prepare high-abundance nitrogen-15 isotope.

[0069] Based on the isotope separation effect of nitrogen passing through a porous organic membrane, a high-speed magnetic levitation gas compressor is used to effectively compress nitrogen gas, and the gas diffusion method is used for the production and preparation of nitrogen-15 isotope. Specific examples are as follows.

[0070] Example

[0071] The gas diffusion cascade is composed of series and parallel connections of gas diffusion separation devices with a nitrogen basic separation factor of 1.014. Its structure is as Figure 2 shown, where the porous organic membrane in the gas diffusion separation device is a polypropylene membrane, and the catalytic device between the first gas diffusion cascade and the second gas diffusion cascade contains a catalyst with iron or ruthenium as the main component. The total number of stages of the first gas diffusion cascade is 844, the feed stage is located at the 757th stage from the heavy fraction end, and the 15 N 14The molar percentage of N is 90.37%, the feed flow rate is 3333 times the heavy fraction flow rate (i.e., the heavy fraction flow rate is 0.0003 times the feed flow rate), the total flow rate of the first gas diffusion cascade is 9390000 times the feed flow rate, and the molar percentage distribution of each component in each stage of the first gas diffusion cascade is as Figure 4 shown. The total number of stages of the second gas diffusion cascade is 110, the feed stage is located at the 101st stage from the heavy fraction end, and the 15 N 15 The molar percentage of N is 90.82%, the feed flow rate is 100 times the heavy fraction flow rate (i.e., the heavy fraction flow rate is 0.01 times the feed flow rate), the total flow rate of the second gas diffusion cascade is 54500 times the feed flow rate, and the molar percentage distribution of each component in each stage of the second gas diffusion cascade is as Figure 5 shown.

[0072] As can be seen from the above embodiments, the gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope with nitrogen as the medium provided by the present utility model has the advantages of large flow rate and high efficiency, and can be used for preparing high-abundance nitrogen-15 isotope. At the same time, the gas diffusion separation process is a physical separation process, without introducing other impurities, and the prepared nitrogen-15 isotope has a high abundance, which can reach more than 90%. Using this gas diffusion cascade device for the preparation of high-abundance nitrogen-15 isotope is suitable for industrial applications.

[0073] The various embodiments of the present utility model have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A gas diffusion cascade device for preparing high-abundance nitrogen-15 isotope with nitrogen as the medium, characterized in that, Comprising: A first gas diffusion cascade, a second gas diffusion cascade, a photocatalytic / electrocatalytic device, and a high-speed magnetic levitation gas compressor; Both the first gas diffusion cascade and the second gas diffusion cascade are stepped cascades, each comprising a plurality of gas diffusion separation devices; The photocatalytic / electrocatalytic device is located between the first gas diffusion cascade and the second gas diffusion cascade; The high-speed magnetic levitation gas compressor is located before each of the gas diffusion separation devices in the nitrogen flow direction; High-abundance nitrogen-15 isotope prepared with nitrogen as the medium is obtained from the heavy fraction end of the second gas diffusion cascade.

2. The gas diffusion cascade device according to claim 1, characterized in that, 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.

3. The gas diffusion cascade device according to claim 1, wherein A plurality of gas diffusion separation devices are connected in parallel to form a separation stage, and then a plurality of separation stages are connected in series to form the first gas diffusion cascade and the second gas diffusion cascade.

4. The gas diffusion cascade device 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 total separation coefficient of 1.011 - 1.017 obtained through a four-stage total reflux diffusion cascade experiment.

5. The gas diffusion cascade device according to claim 4, wherein The gas diffusion separation device is a gas diffusion separation device with a nitrogen basic total separation coefficient of 1.014 - 1.017 obtained through a four-stage total reflux diffusion cascade experiment.

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

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

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

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

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