Method for producing isotopes through multi-stage low-temperature rectification and production system

Abstract

The invention discloses a method and a production system for producing isotopes through multi-stage low-temperature rectification, and belongs to the technical field of low-temperature rectification. A rectification device comprising at least three stages of rectification towers is adopted, the natural abundance of 13C of 1.1% is enriched step by step to 13C of which the abundance exceeds 99%, and the amount of 13C required by the liquid holdup of each stage of tower is also gradually increased. In order to solve the problem of long trial production period of carbon isotope production based on CO low-temperature rectification, raw material gas is simultaneously introduced into each stage of rectification tower for tower filling and enrichment, the quantity of the raw material gas which is more than the design quantity in the preceding stage is transferred to the last stage, and after the last stage meets the design requirement, after the bottom discharged material of the last stage is treated, all the towers are subjected to system total reflux for 24-72 hours, and the carbon isotope is obtained. And after balance is reached, formal production is carried out.

Description

Technical Field

[0001] The present application relates to the technical field of cryogenic distillation, and more particularly, to a method and a production system for producing isotopes by multi-stage cryogenic distillation. Background Art

[0002] 13 As a tracer atom, C is widely used in fields such as medicine, organic chemistry, life sciences, agronomy, environmental science, geological science, and energy science. In particular 13 C-urea has great advantages in the breath test for detecting Helicobacter pylori. 13 The production methods of C include cryogenic distillation method, chemical exchange method, laser method, centrifugal method, thermal diffusion method, gas diffusion method, etc. At present, the industrial production method is mainly the cryogenic distillation method using CO as a raw material.

[0003] The CO cryogenic distillation method utilizes the slight difference in the relative volatility of isotope molecules. Through multiple gas-liquid phase exchange equilibriums on the surface of the packing, the heavy components gradually accumulate towards the bottom of the tower due to their lower relative volatility, while the light components are concentrated at the top of the tower due to their higher relative volatility. The commonly used CO cryogenic distillation production process includes the first-stage distillation, the second-stage distillation, the same-molecule isotope exchange, and the third-stage distillation. Since the production of 13 C has the characteristics of low temperature (-196°C), low separation coefficient (about 1.0076), high number of theoretical plates (about more than 3000), small flow rate (from several g / h to several hundred g / h), long and thin distillation tower (up to several hundred meters high and only dozens of centimeters in tower diameter), difficult equipment manufacturing and installation, and high requirements for instrument control technology, it is one of the relatively difficult separation systems. Moreover, due to the small carbon isotope separation coefficient, a relatively long distillation tower is required, the liquid holdup in the tower is relatively large, the product extraction rate is very low, and the flow rate of the distillation tower becomes smaller and smaller towards the back. If a CO product with an abundance of 99% 13 is used as the seed accelerator, the cost is huge (it requires a cost of hundreds of millions of yuan and there is a certain risk of failure), and it takes up to 2 years of trial production cycle to feed natural abundance into the distillation equilibrium. Therefore, how to shorten the trial production time is a relatively major issue. Summary of the Invention

[0004] Based on the above deficiencies, the present application provides a method and a production system for producing isotopes by multi-stage cryogenic distillation to improve the problem of long trial production cycle in related technologies.

[0005] The present application is implemented as follows:

[0006] In a first aspect, an example of the present application provides a method for producing isotopes by multi-stage rectification, including a trial production step and a continuous production step. Among them, the trial production step includes: using a rectification device including at least three-stage rectification towers, introducing the raw material gas into each stage of the rectification tower at a set flow rate for enrichment. Set the design value of the abundance of the bottom product of each stage of the rectification tower, and the design values of the multi-stage rectification towers increase gradually. In the pre-stage rectification towers before the last stage rectification tower, after the abundance of the bottom product of each pre-stage rectification tower reaches the target value, continuously introduce the bottom product into the last stage rectification tower until the abundance of the bottom product of the pre-stage rectification tower decreases to the design value, and stop transporting to the last stage rectification tower; until the abundance of the bottom product of the last stage rectification tower reaches the design value. The target value of each pre-stage rectification tower is higher than the design value. The target value of the pre-stage rectification tower is lower than the design value of the last stage rectification tower.

[0007] The continuous production step includes: suspending the transportation of the raw material gas to each stage of the rectification tower after the first stage rectification tower. Among any two adjacent stages of rectification towers, input the bottom product of the previous stage rectification tower into the next stage rectification tower for enrichment, and extract the isotope product from the last stage rectification tower.

[0008] Before continuously producing isotopes by step-by-step rectification using at least three-stage rectification towers, in the trial production stage, the traditional method is to transport the raw material gas to the first stage rectification tower. Wait until the rectification product enriched in the first stage rectification tower reaches the design requirements (for example, the abundance of 13 C at the bottom reaches 8% - 10%), then continuously extract a certain flow rate of the first-stage rectification product from the first stage rectification tower, and transport the first-stage rectification product to the second stage rectification tower until the rectification product enriched in the second stage rectification tower reaches the design requirements (for example, the abundance of 13 C at the bottom reaches 50% - 85%), and so on, until the rectification product in the last stage rectification tower reaches the design requirements, and then extract the final high-abundance product from the last stage rectification tower for continuous production. The traditional trial production cycle is the superposition of the trial production times of each stage of the rectification tower, and the trial production cycle is relatively long.

[0009] Since the extraction flow rate of the rectification product of the previous stage rectification tower is much smaller than its feed flow rate, the feed flow rate of the next stage rectification tower is much smaller than that of the previous stage rectification tower, and so on. The feed amount of the multi-stage rectification towers decreases gradually, and the design values of the rectification products enriched in the multi-stage rectification towers increase gradually. Therefore, the feed flow rate of the last stage rectification tower is the smallest, and the last stage 13The amount of C is the largest, so the trial production period of the last-stage rectification column is the longest. Therefore, in the production method provided in this application, during the trial production stage, feed gas is directly supplied to each rectification column at a large flow rate simultaneously, and the enrichment process with a large flow rate is carried out in each rectification column simultaneously. Moreover, after the abundance of the bottom product of each pre-stage rectification column before the last-stage rectification column reaches its target value, the excess product will be directly transported to the last-stage rectification column until the abundance of the bottom product of the pre-stage rectification column is reduced to the design value of this stage of rectification column, and then the supply to the last-stage rectification column is stopped. This is equivalent to multiple rectification columns simultaneously enriching to the last-stage rectification column, and the feed flow rate of the last-stage rectification column is always for large-flow enrichment. Eventually, the trial production period of the entire rectification device is no longer the superposition of the trial production periods of each rectification column. The trial production period of the last-stage rectification column is the trial production period of the entire rectification device. Therefore, the trial production period of the entire rectification device can be shortened. After the trial production is completed, only feed gas is supplied to the first-stage rectification column, and the bottom product of the previous-stage rectification column is transported to the next-stage rectification column, and so on. Through step-by-step enrichment, high-abundance isotope products are continuously extracted from the last-stage rectification column to achieve continuous production.

[0010] Combined with the first aspect, in an optional implementation manner of this application, the feed gas is a CO feed gas with natural abundance, and the isotope product is 13 CO.

[0011] In the above implementation process, using CO with natural abundance as the feed gas and adopting the isotope production method provided in the embodiments of this application can, while obtaining the high-abundance isotope product 13 CO, also shorten the trial production period in the production process, improve production efficiency, and reduce production energy consumption.

[0012] Combined with the first aspect, in an optional implementation manner of this application, in the rectification device, the number of cascaded rectification columns is three, including a first-stage rectification column, a second-stage rectification column, and a third-stage rectification column. In the trial production step, the first design value of the first-stage rectification column is 8% - 10%, the second design value of the second-stage rectification column is 75% - 90%, and the third design value of the third-stage rectification column is not less than 99%.

[0013] In the above implementation process, compared with the trial production method of step-by-step enrichment of three rectification columns in the traditional method, in the embodiments of this application, when producing 13 CO using a rectification device with a cascaded number of three rectification columns, the CO feed gas with natural abundance is supplied to the first-stage rectification column, the second-stage rectification column, and the third-stage rectification column simultaneously. Before the enrichment in the first-stage rectification column and the second-stage rectification column reaches the target value, the third-stage rectification column is also carrying out large-flow enrichment. Therefore, the trial production period of the entire rectification device can be shortened. Moreover, the 13The CO is continuously fed into the third-stage rectification column until the abundance of the bottom product of the first-stage rectification column is reduced to the first design value of 8%-10%, and then the discharging is stopped. This can improve the enrichment efficiency of the third-stage rectification column. At the same time, the 13 CO with a high enrichment at the bottom of the second-stage rectification column is continuously fed into the third-stage rectification column until the abundance of the bottom product of the second-stage rectification column is reduced to the second design value of 75%-90%, and then the discharging is stopped. This is equivalent to the simultaneous enrichment of the first-stage rectification column and the second-stage rectification column into the third-stage rectification column, improving the 13 abundance of CO in the feed raw materials of the third-stage rectification column, thereby accelerating the enrichment efficiency of the third-stage rectification column and shortening the trial production cycle.

[0014] Combined with the first aspect, in an optional implementation manner of the present application, in the trial production step, the bottom product of the third-stage rectification column is subjected to homomolecular isotope exchange and then fed into the third-stage rectification column for enrichment. The reaction formula of the homomolecular isotope exchange is as follows: 12 C 18 O + 13 C 16 O → 13 C 18 O + 12 C 16 O.

[0015] In the above implementation process, a part of the bottom product of the third-stage rectification column 12 C 18 O and 13 C 16 O are subjected to homomolecular isotope exchange, and can form 13 C 18 O and 12 C 16 O. 13 C 18 O and 12 C 16 O are re-fed into the third-stage rectification column for enrichment. 13 C 18 O, as a heavier component, makes 12 C 18 O be enriched and discharged at the top of the column. Therefore, the abundance of 18 O in the isotope product can be reduced through top discharge.

[0016] In combination with the first aspect, in an alternative embodiment of the present application, during the pilot production step, after the abundance of the bottom product of the first rectification column reaches the first target value of the first rectification column, the bottom product of the first rectification column is continuously fed into the third rectification column until the abundance of the bottom product of the first rectification column decreases to the first design value of the first rectification column, and the feeding to the third rectification column is stopped. And / or, after the abundance of the bottom product of the second rectification column reaches the second target value of the second rectification column, the bottom product of the second rectification column is continuously fed into the third rectification column until the abundance of the bottom product of the second rectification column decreases to the second design value of the second rectification column, and the feeding to the third rectification column is stopped.

[0017] In the above implementation process, after converting the excess products in the first rectification column and the second rectification column to the third rectification column, the abundances of the bottom products of the first rectification column and the second rectification column will gradually decrease. When the abundances of the bottom products of the first rectification column and the second rectification column decrease to their respective design values, the feeding to the last rectification column is stopped to meet the pilot production requirements of the first rectification column and the second rectification column.

[0018] In combination with the first aspect, in an alternative embodiment of the present application, during the pilot production step, the set flow rate is 100 g / h to 1000 g / h.

[0019] In the above implementation process, during the pilot production stage, a CO raw material gas with a flow rate of 100 g / h to 1000 g / h is fed into the first rectification column, the second rectification column, and the third rectification column simultaneously, enabling the first rectification column, the second rectification column, and the third rectification column to perform large-flow enrichment simultaneously, which can further shorten the pilot production cycle of the entire rectification device.

[0020] In combination with the first aspect, in an alternative embodiment of the present application, during the continuous production step, the feed rate of the first rectification column is 100 g / h to 500 g / h. The feed rate of the second rectification column is 30 g / h to 200 g / h. The feed rate of the third rectification column is 5 g / h to 50 g / h.

[0021] In the above implementation process, after each rectification column reaches 13 the C abundance design value, the pilot production ends, and the feeding of the large-flow raw material gas to the second rectification column and the third rectification column can be stopped. After all rectification columns perform total reflux for a certain period of time, it is switched to the production mode. In the production mode, a raw material gas with a flow rate of 100 g / h to 500 g / h is fed into the first rectification column, the bottom product of the first rectification column is continuously fed to the second rectification column at a flow rate of 30 g / h to 200 g / h, and the bottom product of the second rectification column is continuously fed to the third rectification column at a flow rate of 5 g / h to 10 g / h. Through step-by-step enrichment, high-abundance 13 CO products are finally continuously extracted from the third rectification column.

[0022] In combination with the first aspect, in an alternative embodiment of the present application, in the continuous production step, the bottom product of the secondary distillation column is subjected to homomolecular isotope exchange and then fed into the tertiary distillation column for enrichment. The reaction formula for homomolecular isotope exchange is as follows: 12 C 18 O+ 13 C 16 O→ 13 C 18 O+ 12 C 16 O.

[0023] In the above implementation process, by subjecting a part of the bottom product of the secondary distillation column to homomolecular isotope exchange and then transporting it to the tertiary distillation column, it is possible to reduce the 12 C 18 O's impact on the abundance of 13 CO product, enabling 12 C 18 O to be discharged from the top of the column, thereby increasing the abundance of the bottom product 13 CO.

[0024] In the second aspect, an example of the present application provides a production system for implementing the production method provided in the first aspect, including a raw material gas delivery pipe and a distillation device. The distillation device includes at least three distillation columns, and each distillation column has a feed inlet, a product discharge outlet, and a waste discharge outlet. The feed inlet of each distillation column can be selectively connected to the raw material gas delivery pipe. The product discharge outlet of each distillation column located before the last distillation column can be selectively connected to the feed inlet of the last distillation column through the raw material gas delivery pipe. Among any two adjacent distillation columns, the product discharge outlet of the previous distillation column can be selectively connected to the feed inlet of the subsequent distillation column through the first pipeline.

[0025] In the above implementation process, when using the production system provided in the embodiments of the present application for isotope production, during the trial production stage, the raw material gas delivery pipe is simultaneously connected to each distillation column, and a certain flow rate of raw material gas is directly fed into each distillation column simultaneously, enabling each distillation column to perform high-flow enrichment simultaneously. After the abundance of the bottom product of the previous distillation column before the last distillation column reaches the target value, the excess bottom product is continuously withdrawn from the product discharge outlet of this distillation column and directly transported through the raw material gas delivery pipe to the last distillation column until the abundance of the bottom product of this distillation column is reduced to its design value, and then the feeding to the last distillation column is stopped. In this way, after the bottom product in the last distillation column reaches the target value, all distillation columns can be subjected to total reflux for 24 to 72 hours and then switched to the production mode. During the production mode, the raw material gas delivery pipe feeds raw materials into the first distillation column, and the product discharge outlet of the previous distillation column is connected to the feed inlet of the subsequent distillation column through the first pipeline for step-by-step enrichment to achieve continuous production.

[0026] Combined with the second aspect, in an alternative embodiment of the present application, the number of cascaded distillation columns of the distillation device is three, including a first-stage distillation column, a second-stage distillation column, and a third-stage distillation column. A homomolecular isotope exchanger is provided between the second-stage distillation column and the third-stage distillation column. The product discharge port of the second-stage distillation column is optionally connected to the homomolecular isotope exchanger through a second pipeline, and the homomolecular isotope exchanger is optionally connected to the feed port of the third-stage distillation column through a first pipeline. And / or, the product discharge port of the third-stage distillation column is optionally connected to the homomolecular isotope exchanger through a third pipeline.

[0027] In the above implementation process, when using the above production system for isotope production, during the trial production stage, a part of the bottom product of the third-stage distillation column can be transported through the third pipeline to the homomolecular isotope exchanger for homomolecular isotope exchange, and then returned to the third-stage distillation column for enrichment, which can improve the efficiency of the third-stage distillation column and shorten the trial production cycle. Moreover, during continuous production, a part of the bottom product of the second-stage distillation column can be transported through the second pipeline to the homomolecular isotope exchanger for homomolecular isotope exchange, and then transported to the third-stage distillation column for enrichment, improving the efficiency of the third-stage distillation column and increasing the product abundance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0029] Figure 1 It is a schematic diagram of the production system provided by the embodiment of the present application.

[0030] Icons: 1 - Production system; 11 - Supervisor; 12 - First branch pipe; 13 - Second branch pipe; 14 - Third branch pipe; 15 - Fourth branch pipe; 21 - First - stage rectification column; 211 - First condenser; 212 - First reboiler; 213 - First product discharge port; 214 - First waste discharge port; 215 - First feed port; 22 - Second - stage rectification column; 221 - Second condenser; 222 - Second reboiler; 223 - Second product discharge port; 224 - Second waste discharge port; 225 - Second feed port; 23 - Third - stage rectification column; 231 - Third condenser; 232 - Third reboiler; 233 - Third product discharge port; 234 - Third waste discharge port; 235 - Third feed port; 24 - Isotope exchanger of the same molecule; 31 - Fifth branch pipe; 32 - Sixth branch pipe; 33 - Second pipeline; 34 - Third pipeline; 341 - First pipe section; 342 - Second pipe section; 41 - First switching valve; 42 - Second switching valve; 43 - Third switching valve; 44 - Fourth switching valve; 45 - Fifth switching valve; 46 - Sixth switching valve; 47 - Seventh switching valve; 48 - Eighth switching valve; 49 - Ninth switching valve; 50 - Tenth switching valve; 51 - Eleventh switching valve. Detailed implementation mode

[0031] The implementation scheme of the present application will be described in detail below in combination with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0032] The application of stable isotopes is becoming more and more extensive. The separation methods include thermal diffusion method, gas diffusion method, centrifugal separation method, laser method, chemical exchange method, ion exchange method and rectification method. However, at present, only the low - temperature rectification method is suitable for industrial applications. Stable isotopes 13 C, 18 O, 15 N, 10 B are mostly obtained by low - temperature rectification of CO, NO, BF3. The low - temperature rectification for separating stable isotopes utilizes the slight difference in the relative volatility of isotope molecules. Through multiple gas - liquid phase exchange equilibriums on the surface of the packing, the heavier components gradually accumulate towards the bottom of the column due to their lower relative volatility, while the lighter components are concentrated at the top of the column due to their higher relative volatility. Low - temperature rectification often has the characteristic of a small separation coefficient. To increase the abundance of isotope products, it is necessary to increase the height of the vertical cascade column, which has extremely high construction difficulty. Therefore, currently, multi - stage rectification columns are usually used for step - by - step rectification.

[0033] Using CO low - temperature rectification to produce stable isotopes 13C as an example, it usually needs to be distilled at the first stage, distilled at the second stage, isotope exchange of the same molecule and distilled at the third stage. The first stage distillation is mainly to enrich from natural abundance to 8% to 10%. 13 C. Secondary distillation continues to enrich to 75% to 90% 13 C. Then the isotope recombination transformation is carried out. 12 C 18 O is partially converted into 13 C 18 O. Finally, the third stage distillation is carried out to continue enriching to more than 99%. 13 C.

[0034] However, the current three-stage cryogenic distillation method for CO production 13 In the case of CO, the trial production period is relatively long during the trial production phase before continuous production.

[0035] For example, the current three-stage cryogenic distillation method for CO production 13 The trial production process of CO includes: transporting the raw gas CO to the primary distillation tower, and after the primary distillation tower is filled, continue to introduce the raw gas, open the top exhaust port of the primary distillation tower, the top exhaust flow is consistent with the raw gas intake, and the light components are discharged through the top during multiple gas-liquid exchanges. 13 CO is enriched at the bottom of the primary distillation tower. 13 After the abundance of CO reaches the designed value (eg, 8% to 10%), part of the primary distillation product is continuously extracted from the bottom of the primary distillation tower at a second flow rate.

[0036] The primary distillation product is continuously conveyed to the secondary distillation tower at the second flow rate. After the secondary distillation tower is completely filled, the primary distillation product is continued to be introduced, and the top exhaust port of the secondary distillation tower is opened. The top discharge flow rate of the secondary distillation tower is consistent with the second flow rate. During multiple gas-liquid exchanges, the light components are discharged through the top of the secondary distillation tower. 13 CO is enriched at the bottom of the secondary distillation tower. 13 After the abundance of CO reaches the designed value (eg, 75% to 90%), part of the secondary distillation product is continuously extracted from the bottom of the secondary distillation tower at a third flow rate.

[0037] The secondary distillation product is continuously conveyed to the tertiary distillation tower at the third flow rate. After the tertiary distillation tower is completely filled, the secondary distillation product is continued to be introduced, and the top exhaust port of the tertiary distillation tower is opened. The top discharge flow rate of the tertiary distillation tower is consistent with the third flow rate. In the process of multiple gas-liquid exchanges, the light component is discharged through the top of the tertiary distillation tower. 13 CO is enriched at the bottom of the three-stage distillation tower. 13After the abundance of CO reaches the target value (e.g., 75% - 90%), the trial production ends, and continuous production can be carried out.

[0038] The inventors believe through research that the main reasons for the relatively long trial production cycle in the existing trial production process mainly include:

[0039] (1) The current trial production cycle is the sum of the trial production cycles of the primary distillation column, the secondary distillation column, and the tertiary distillation column. During the trial production process of the primary distillation column, the secondary distillation column and the tertiary distillation column are always in a shutdown state, resulting in a waste of time.

[0040] (2) In the current trial production plan, the feed rate of the secondary distillation column is the product discharge rate of the primary distillation column, and the feed rate of the tertiary distillation column is the product discharge rate of the secondary distillation column. The feed flow rates of the secondary distillation column and the tertiary distillation column are significantly reduced, and it takes a longer time to fill the tower. Moreover, the feed flow rates of the secondary distillation column and the tertiary distillation column are small, and large-flow enrichment cannot be carried out, resulting in low enrichment efficiency.

[0041] The inventors believe that during the trial production process of packing and enriching the primary distillation column, raw material gas with the same flow rate is simultaneously fed into the secondary distillation column and the tertiary distillation column. While enriching the primary distillation column, the secondary distillation column and the tertiary distillation column can also be enriched.

[0042] Moreover, the inventors believe that since the 13 most CO is required in the tertiary distillation column, after the primary distillation column meets the design requirements, if the excess 13 CO product of the primary distillation column is directly transported to the tertiary distillation column, before the secondary distillation column reaches the design requirements for enrichment, for the tertiary distillation column, it is equivalent to the primary distillation column and the tertiary distillation column simultaneously enriching the tertiary distillation column. After the secondary distillation column reaches the design requirements, if the excess 13 CO product in the secondary distillation column is further directly transported to the tertiary distillation column, at this time it is equivalent to the three distillation columns simultaneously enriching the tertiary distillation column, which can further shorten the trial production cycle of the tertiary distillation column. After the trial production of the tertiary distillation column ends, the trial production process of the entire distillation device ends, and continuous production can be carried out. Therefore, the trial production cycle of the tertiary distillation column is equivalent to the trial production cycle of the entire distillation device, thereby being able to shorten the entire trial production cycle. Moreover, large-flow enrichment can be carried out in both the secondary distillation column and the tertiary distillation column.

[0043] Based on this, the embodiments of the present application provide a method for producing isotopes by multi-stage distillation, including:

[0044] S1. Pilot production steps: Using a distillation device including at least three distillation columns, feed the raw material gas into each distillation column at a set flow rate for enrichment; set the design value of the abundance of the bottom product of each distillation column, and the design values of multiple distillation columns increase step by step; in the pre-stage distillation columns before the last distillation column, after the abundance of the bottom product of each pre-stage distillation column reaches the target value, continuously feed the bottom product into the last distillation column until the abundance of the bottom product of the pre-stage distillation column decreases to the design value, and stop feeding into the last distillation column; until the distillation product of the last distillation column reaches the target product abundance. The target value of each pre-stage distillation column is higher than the design value; the target value of the pre-stage distillation column is lower than the design value of the last distillation column.

[0045] Each distillation column 13 After the C amount meets the requirements, each distillation column performs total reflux for 24 - 72 hours and then switches to the production mode.

[0046] S2. Continuous production steps: Feed the raw material gas into the first distillation column. In any two adjacent distillation columns, feed the bottom product of the previous distillation column into the next distillation column for enrichment, and extract the isotope product from the last distillation column.

[0047] When producing isotopes according to the production method provided in the embodiments of the present application, in the pilot production steps before continuous production, by using the method of simultaneously feeding the raw material gas into each distillation column, the enrichment time can be shortened, and the shutdown waiting time of the distillation columns at the back end can be reduced. Moreover, during the enrichment process of the previous distillation column, the distillation columns at the back end are also enriching simultaneously. During the same time of pilot production of the front distillation column, there will be 13 more CO in the entire distillation device. After all the distillation columns before the last distillation column meet the requirements, it is equivalent to multiple distillation columns enriching the last distillation column simultaneously, which can shorten the pilot production cycle of the last distillation column. In addition, the feed flow rate of the subsequent distillation column does not have to be limited by the discharge amount of the previous distillation column, and each distillation column can perform high-flow enrichment, which can also further shorten the enrichment time. Therefore, by using the production method provided in the embodiments of the present application, the pilot production cycle during multi-stage low-temperature distillation can be minimized to the greatest extent.

[0048] For example, when producing high-abundance 13 CO using a three-stage distillation device, the following steps can be referred to:

[0049] (1) Provide the raw material gas:

[0050] The fed raw material CO needs to be purified, with a purity of 99.999%, 13 the C abundance is not less than 1.1% (natural abundance 1.1%), and the purity of CO2 and H2O impurities is controlled below 10 ppm to prevent pipeline blockage.

[0051] (2) Pilot production steps:

[0052] a. Nitrogen purging and replacement are carried out on the first-stage rectification column, the second-stage rectification column, and the third-stage rectification column simultaneously to reduce the moisture content in each rectification column.

[0053] As an example, the purging pressure can be controlled at 1.5 bar to 3 bar, and the nitrogen flow rate is controlled not to be lower than 20 m / s to form a turbulent flow, which can better carry out nitrogen replacement at the dead corners inside the tower. Check with a target plate and measure the moisture content. When the moisture content is less than 10 ppm, stop the replacement.

[0054] b. Use a vacuum pump to evacuate each rectification column.

[0055] As an example, the vacuum degree inside each rectification column is controlled not to be lower than 5 Pa.

[0056] c. Purified CO feed gas is introduced into each rectification column simultaneously. When the pressure of the tower is 1 bar to 2 bar, liquid nitrogen is put into the condenser of the rectification column to cool the tower; continue to introduce the feed gas until the bottom temperature of the rectification column is lower than -100 °C to -150 °C. CO is input into the reboiler at the bottom of the first-stage rectification column, and continue to introduce the feed gas to complete the process of filling the towers of each stage.

[0057] Continue to introduce the feed gas into the rectification columns of each stage. The exhaust is opened at the top of each rectification column, and the exhaust flow rate is equal to the feed flow rate. During the gas-liquid exchange process, the light components 12 CO is discharged through the top, and the CO at the bottom 13 is enriched. Regularly measure the abundances of C at the top and bottom 13 using a mass spectrometry instrument, with a measurement frequency of once every 1 day to 15 days.

[0058] As an example, the feed flow rate of the CO feed gas for each rectification column can be 100 g / h to 1000 g / h. For example, the feed flow rate of the feed gas can be one of 100 g / h, 200 g / h, 300 g / h, 400 g / h, 500 g / h, 600 g / h, 700 g / h, 800 g / h, 900 g / h, or 1000 g / h, or within the range between any two of them.

[0059] d. After the enrichment of 13 CO in the first-stage rectification column reaches the first target value, the excess 13 CO product at the bottom of the first-stage rectification column is directly transported to the third-stage rectification column until the abundance of the bottom product of the first-stage rectification column is reduced to the first design value, and then stop transporting to the third-stage rectification column. At this time, due to the first-stage rectification column transporting the rectification product to the third-stage rectification column, the third-stage rectification column is equivalent to carrying out enrichment with two rectification columns simultaneously.

[0060] As an example, the first design value of the primary distillation tower is 8% to 10%, and the first target value may be greater than 10%. It is understood that the first target value needs to be lower than the design value of the tertiary distillation tower.

[0061] As an example, the first design value may be one of 8%, 9% or 10%, or a range between any two of them.

[0062] As an example, the first target value may be 15% to 95%. For example, the first target value may be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% or a range between any two thereof.

[0063] As an example, the first target value may be 20% to 70%.

[0064] As an example, the primary distillation column will have excess 13 When the CO product is directly transported to the tertiary distillation tower, the primary distillation tower can be fully refluxed and then return to normal mode.

[0065] e. To be enriched in the secondary distillation tower 13 After CO reaches the second target value, the excess CO at the bottom of the secondary distillation tower is 13 The CO product is directly transported to the tertiary distillation tower until the abundance of the bottom product of the secondary distillation tower decreases to the second design value, and the transportation to the tertiary distillation tower is stopped. Since the distillation products of the primary distillation tower and the secondary distillation tower are both transported to the tertiary distillation tower, it is equivalent to using three distillation towers to enrich the tertiary distillation tower at the same time, which can speed up the enrichment efficiency of the tertiary distillation tower and further shorten the trial production period of the tertiary distillation tower.

[0066] As an example, the second design value of the secondary distillation tower may be 75% to 90%, and the second target value may be greater than 90%. It is understood that the second target value needs to be lower than the design value of the tertiary distillation tower.

[0067] As an example, the second design value may be one of 75%, 80%, 85% or 90%, or a range between any two of them.

[0068] As an example, the second target value may be 91% to 95%.For example, the second target value may be in the range of 91%, 92%, 93%, 94% or 95%, or any two thereof.

[0069] As an example, the secondary distillation column will be redundant 13 When the CO product is directly transported to the tertiary distillation tower, the secondary distillation tower can be fully refluxed and then return to normal mode.

[0070] Further, in some embodiments, a part of the bottom product of the three-stage rectification column can be withdrawn, subjected to isotopic exchange of the same molecule, and then fed into the three-stage rectification column for re-rectification.

[0071] The reaction formula of the isotopic exchange of the same molecule is as follows: 12 C 18 O+ 13 C 16 O→ 13 C 18 O+ 12 C 16 O.

[0072] Subjecting a part of the rectification product of the three-stage rectification column 12 C 18 O and 13 C 16 O to isotopic exchange of the same molecule can form 13 C 18 O and 12 C 16 O. Feeding 13 C 18 O and 12 C 16 O back to the three-stage rectification column for enrichment, 13 C 18 O as the heavier component, so that 12 C 18 O will be enriched and discharged from the top of the column, and the abundance of 18 O in the isotopic product can be reduced through top discharge, and the enrichment efficiency of the three-stage rectification column and the abundance of the rectification product can be improved.

[0073] f. After the enrichment of 13 CO in the three-stage rectification column reaches the third design value, the trial production period ends.

[0074] As an example, the third design value of the three-stage rectification column is not less than 99%.

[0075] (3) Continuous production steps:

[0076] Suspend feeding the raw material gas to the second-stage rectification column and the three-stage rectification column, and keep feeding the raw material gas to the first-stage rectification column. Connect the product discharge port at the bottom of the first-stage rectification column to the feed port of the second-stage rectification column, connect the product discharge port at the bottom of the second-stage rectification column to the feed port of the three-stage rectification column, and continuously withdraw the isotopic product 13 CO from the bottom of the three-stage rectification column.

[0077] As an example, in the continuous production step, the feed rate of the first distillation tower can be set to 100g / h~500g / h; the feed rate of the second distillation tower is 30g / h~200g / h; the feed rate of the third distillation tower is 5g / h~50g / h.

[0078] Furthermore, in some embodiments, in the continuous production process, the bottom product of the secondary distillation tower can be subjected to isotope exchange with the same molecule and then introduced into the tertiary distillation tower for enrichment. The reaction formula of isotope exchange with the same molecule is as follows: 12 C 18 O+ 13 C 16 O→ 13 C 18 O+ 12 C 16 O. The bottom product of the secondary distillation tower is isotopically exchanged with the molecular weight before being transported to the tertiary distillation tower, which can reduce the 12 C 18 O pair 13 The influence of CO product abundance makes 12 C 18 O can be discharged from the top of the tower, increasing the bottom product 13 The abundance of CO.

[0079] The above examples do not mean that the production method provided in the embodiments of the present application is only applicable to 13 C isotope enrichment can also be used to enrich stable isotopes 18 O. 15 N. 10 B is enriched. As an example, NO is used as the raw gas. 15 As an example, BF3 is used as the raw gas to carry out 10 Enrichment of BF3.

[0080] Furthermore, the present application embodiment provides a production system 1 for implementing the above production method, see Figure 1 , including raw gas transmission pipe and distillation device.

[0081] The distillation device includes at least three distillation towers, each of which has a feed inlet, a product outlet and a waste outlet. The feed inlet of each distillation tower can be selectively connected to the raw gas delivery pipe through a second pipeline. The product outlet of each distillation tower before the last distillation tower can be selectively connected to the feed inlet of the last distillation tower through a second pipeline. In any two adjacent distillation towers, the product outlet of the first distillation tower can be selectively connected to the feed inlet of the next distillation tower through a first pipeline.

[0082] For example, the rectification device includes a first-stage rectification column 21, a second-stage rectification column 22, and a third-stage rectification column 23. A first condenser 211 is provided at the top of the first-stage rectification column 21, a first reboiler 212 is provided at the bottom, a first product discharge port 213 is provided at the bottom, a first waste discharge port 214 is provided at the top, and a first feed port 215 is provided in the middle of the column. A second condenser 221 is provided at the top of the second-stage rectification column 22, a second reboiler 222 is provided at the bottom, a second product discharge port 223 is provided at the bottom, a second waste discharge port 224 is provided at the top, and a second feed port 225 is provided in the middle of the column. A third condenser 231 is provided at the top of the third-stage rectification column 23, a third reboiler 232 is provided at the bottom, a third product discharge port 233 is provided at the bottom, a third waste discharge port 234 is provided at the top, and a third feed port 235 is provided in the middle of the column.

[0083] As an example, please continue to refer to Figure 1 , the raw material gas delivery pipe includes a main pipe 11 and a first branch pipe 12, a second branch pipe 13, a third branch pipe 14, and a fourth branch pipe 15 connected to the main pipe. A first switching valve 41 is provided at the first branch pipe 12, a second switching valve 42 is provided at the second branch pipe 13, and a third switching valve 43 is provided at the third branch pipe 14. The first branch pipe 12 is connected to the first feed port 215 of the first-stage rectification column 21, the second branch pipe 13 is connected to the second feed port 225 of the second-stage rectification column 22, and the third branch pipe 14 is connected to the third feed port 235 of the third-stage rectification column 23.

[0084] As an example, please continue to refer to Figure 1 , the first pipeline includes a fifth branch pipe 31 connecting the first product discharge port 213 and the second feed port 225, and a sixth branch pipe 32 connecting the second product discharge port 223 and the third feed port 235. Fourth and fifth switching valves 44 and 45 are provided at both ends of the fifth branch pipe 31, and the second branch pipe 13 is connected to the rear end of the fifth switching valve 45 of the fifth branch pipe 31. The feed end of the fourth branch pipe 15 is connected to the rear end of the fourth switching valve 44 of the fifth branch pipe 31 and is located in front of the fifth switching valve 45; the discharge end of the fourth branch pipe 15 is connected to the main pipe 11 and is located behind the second branch pipe 13. A sixth switching valve 46 is provided at the fourth branch pipe 15 near the feed end of the fifth branch pipe 31. An eleventh switching valve 51 is provided at the sixth branch pipe 32.

[0085] Furthermore, please continue to refer to Figure 1, the production system 1 is also provided with a homomolecular isotope exchanger 24. The homomolecular isotope exchanger 24 can be selectively connected to the third feed port 235 of the third-stage rectification column 23 through the second pipeline 33. As an example, the homomolecular isotope exchanger 24 is arranged between the sixth branch pipe 32 and the second pipeline 33. A seventh switching valve 47 is arranged at the second pipeline 33. The third branch pipe 14 is connected to the second pipeline 33, and the gas outlet end of the third branch pipe 14 is located at the rear end of the seventh switching valve 47.

[0086] Furthermore, the third product discharge port 233 can be selectively connected to the homomolecular isotope exchanger 24 through the third pipeline 34. As an example, the third pipeline 34 includes a first pipe section 341 and a second pipe section 342. The feed end of the first pipe section 341 is connected to the third product discharge port 233, and the discharge end is connected to the rear end of the eleventh switching valve 51 of the sixth branch pipe 32. The feed end of the second pipe section 342 is connected to the rear end of the eleventh switching valve 51 of the sixth branch pipe 32, and the discharge end is connected to the third branch pipe 14. And an eighth switching valve 48 and a ninth switching valve 49 are respectively arranged at the feed end and the discharge end of the second pipe section 342. A tenth switching valve 50 is arranged at the feed end of the first pipe section 341. The above-mentioned switching valves are all selected as one-way valves.

[0087] When using the above production system 1 for isotope production, taking the production of 13 CO as an example, before the trial production stage, all the switching valves are kept closed. In the trial production stage, nitrogen can be first filled into the first-stage rectification column 21, the second-stage rectification column 22 and the third-stage rectification column 23 for replacement. When the moisture content in each rectification column is detected to be less than 10 ppm, the replacement is stopped. Then, a vacuum pump is used to evacuate each rectification column. Then, the first switching valve 41, the second switching valve 42 and the third switching valve 43 are opened, and the CO raw material in the raw material gas pipeline is transported to the first-stage rectification column 21, the second-stage rectification column 22 and the third-stage rectification column 23. After the filling of each rectification column is completed, the waste product discharge ports at the tops of each rectification column are opened. During the gas-liquid exchange process, the light component 12 CO is discharged through the top, and the 13 CO at the bottom of the column is enriched. The abundances of 13 C at the top and the bottom are measured regularly with a mass spectrometer, and the measurement frequency is once every 1 day - 15 days.

[0088] When the abundance of 13 C at the bottom of the first-stage rectification column 21 reaches the first target value, the fourth switching valve 44 and the sixth switching valve 46 are opened, so that a part of the 13The CO product can be discharged through the first product outlet 213, flow into the fourth branch pipe 15 through the fifth branch pipe 31, then flow into the main pipe 11 from the fourth branch pipe 15, flow into the third branch pipe 14 from the main pipe 11, flow into the second pipeline 33 from the third branch pipe 14, and finally flow into the third-stage rectification tower 23 through the third feed inlet 235 for enrichment. When the abundance of the bottom product of the first-stage rectification tower 21 decreases to the first design value of 8% - 10%, close the fourth switch valve 44 and the sixth switch valve 46 to stop transporting to the third-stage rectification tower 23.

[0089] When the abundance of 13 C at the bottom of the second-stage rectification tower 22 reaches the second target value, open the eleventh switch valve 51, the eighth switch valve 48, and the ninth switch valve 49, so that a part of the 13 CO product at the bottom of the second-stage rectification tower 22 can be discharged through the second product outlet 223, flow into the third branch pipe 14 through the sixth branch pipe 32 and the second pipe section 342, then flow into the second pipeline 33 from the third branch pipe 14, and finally flow into the third-stage rectification tower 23 through the third feed inlet 235 for enrichment. When the abundance of the bottom product of the second-stage rectification tower 22 decreases to the second design value of 75% - 90%, close the eleventh switch valve 51, the eighth switch valve 48, and the ninth switch valve 49 to stop transporting to the third-stage rectification tower 23.

[0090] Furthermore, the switch valve at the third product outlet 233 of the third-stage rectification tower 23 can be opened, the tenth switch valve 50 and the seventh switch valve 47 can be opened, and at the same time the eighth switch valve 48 and the ninth switch valve 49 can be closed. Part of the product at the bottom of the third-stage rectification tower 23 is transported into the sixth branch pipe 32 through the first pipe section 341, then enters the homomolecular isotope exchanger 24 for homomolecular isotope exchange, and then flows into the third-stage rectification tower 23 through the second pipeline 33.

[0091] When the abundance of 13 C at the bottom of the third-stage rectification tower 23 reaches the third design, close the second switch valve 42, the third switch valve 43, the sixth switch valve 46, and the tenth switch valve 50, and at the same time open the fifth switch valve 45 to suspend the transportation of the CO raw material gas to the second-stage rectification tower 22 and the third-stage rectification tower 23. Transport the first-stage rectification product at the bottom of the first-stage rectification tower 21 to the second-stage rectification tower 22, transport the second-stage rectification product at the bottom of the second-stage rectification tower 22 to the homomolecular isotope exchanger 24, and after homomolecular isotope exchange, transport it to the third-stage rectification tower 23 for enrichment, and discharge the high-abundance isotope product 13 CO from the third product outlet 233.

[0092] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various modifications and changes can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for producing isotopes by multi-stage distillation, characterized in that: include: Trial production steps: using a distillation device comprising at least three distillation towers, and simultaneously passing the raw gas into each distillation tower at a set flow rate for enrichment; The design value of the abundance of the bottom product of each stage of the distillation tower is set, and the design value of the multi-stage distillation tower increases step by step; in the front-stage distillation tower located before the last stage of the distillation tower, after the abundance of the bottom product of each stage of the front-stage distillation tower reaches the target value, the bottom product is continuously introduced into the last stage of the distillation tower until the abundance of the bottom product of the front-stage distillation tower decreases to the design value, and the transportation to the last stage of the distillation tower is stopped; until the abundance of the bottom product of the last stage of the distillation tower reaches the design value; the target value of each stage of the front-stage distillation tower is higher than the design value; the target value of the front-stage distillation tower is lower than the design value of the last stage of the distillation tower; Continuous production steps: suspending the supply of the raw gas to each distillation tower after the first distillation tower; in any two adjacent distillation towers, inputting the bottom product of the previous distillation tower into the next distillation tower for enrichment, and extracting the isotope product from the last distillation tower.

2. The method according to claim 1, characterized in that The raw gas is naturally abundant CO raw gas, and the isotope product is 13 CO.

3. The method according to claim 2, characterized in that In the distillation device, the distillation tower has three cascade stages, including a primary distillation tower, a secondary distillation tower and a tertiary distillation tower; In the trial production step, the first design value of the primary distillation tower is 8% to 10%, the second design value of the secondary distillation tower is 75% to 90%, and the third design value of the tertiary distillation tower is not less than 99%.

4. The method according to claim 3, characterized in that In the trial production step, the bottom product of the three-stage distillation tower is subjected to molecular isotope exchange and then introduced into the three-stage distillation tower again for enrichment; The reaction formula for the isotopic exchange of the same molecule is as follows: 12 C 18 O+ 13 C 16 O→ 13 C 18 O+ 12 C 16 O.

5. The method according to claim 3, characterized in that: In the trial production step, after the abundance of the bottom product of the first distillation tower reaches the first target value of the first distillation tower, the bottom product of the first distillation tower is continuously passed into the third-stage distillation tower until the abundance of the bottom product of the first distillation tower decreases to the first design value of the first distillation tower, and the delivery to the third-stage distillation tower is stopped; and / or, after the abundance of the bottom product of the secondary distillation tower reaches the second target value of the secondary distillation tower, the bottom product of the secondary distillation tower is continuously passed into the tertiary distillation tower until the abundance of the bottom product of the secondary distillation tower decreases to the second design value of the secondary distillation tower, and the delivery to the tertiary distillation tower is stopped; Optionally, the first target value is 15% to 95%; Optionally, the second target value is 91% to 95%.

6. The method according to claim 3, characterized in that In the trial production step, the set flow rate is 100g / h to 1000g / h.

7. The method according to claim 6, characterized in that In the continuous production step, the feed amount of the primary distillation tower is 100 g / h to 500 g / h; the feed amount of the secondary distillation tower is 30 g / h to 200 g / h; and the feed amount of the tertiary distillation tower is 5 g / h to 50 g / h.

8. The method according to claim 7, characterized in that In the continuous production step, the bottom product of the secondary distillation tower is subjected to molecular isotope exchange and then introduced into the tertiary distillation tower for enrichment; The reaction formula for the isotopic exchange of the same molecule is as follows: 12 C 18 O+ 13 C 16 O→ 13 C 18 O+ 12 C 16 O.

9. A production system for implementing the method according to any one of claims 1 to 8, characterized in that: include: A raw gas delivery pipe and a distillation device; the distillation device comprises at least three distillation towers, each of which has a feed inlet, a product outlet and a waste outlet; The feed inlet of each distillation tower can be selectively connected to the raw gas delivery pipe; The product outlet of each stage of the distillation tower before the last stage of the distillation tower can be selectively connected to the feed inlet of the last stage of the distillation tower through the raw gas delivery pipe; In any two adjacent distillation towers, the product outlet of the previous distillation tower can be selectively connected to the feed inlet of the next distillation tower through a first pipeline.

10. The production system according to claim 9, characterized in that: The distillation device has three cascaded distillation towers, including a first-stage distillation tower, a second-stage distillation tower and a third-stage distillation tower; an isotope exchanger of the same molecule is provided between the second-stage distillation tower and the third-stage distillation tower; The product outlet of the second-stage distillation tower can be selectively connected to the isotope exchanger of the same molecule through a second pipeline, and the isotope exchanger of the same molecule can be selectively connected to the feed inlet of the third-stage distillation tower through the first pipeline; And / or, the product outlet of the third-stage distillation tower can be optionally connected to the isomolecular isotope exchanger through a third pipeline.

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