CN108404667B - A method for centrifuging carbon isotopes with iodomethane as a medium - Google Patents

Abstract

A method for centrifugal separation of carbon isotopes using methyl iodide as a medium, comprising: purifying light impurities in the raw material of methyl iodide so that its chemical purity meets the requirements for centrifugal separation of methyl iodide; passing the purified gaseous methyl iodide into a gas centrifuge, Adjust the feed flow rate and the pressure of the fine material nozzle and the lean material nozzle of the gas centrifuge to separate the fine material and the lean material from the fine material nozzle and the lean material nozzle respectively; maintain the supply of methyl iodide and the fine material, The fluid parameters of the lean material are stable. After the gas centrifuge runs continuously until the carbon isotope abundance distribution in it is stable, the fine material and the lean material with stable carbon isotope abundance distribution are collected respectively through the liquid nitrogen cold trap. The method of the invention has low energy consumption and large separation coefficient, and the working medium can be regarded as having no isotope interference other than carbon elements, and is suitable for large-scale production in the form of cascading.

Description

A method for centrifuging carbon isotopes with iodomethane as a medium

technical field

The invention relates to the technical field of isotope separation and preparation, in particular to a method for centrifugally separating carbon isotopes using methyl iodide as a medium.

Background technique

Carbon has two natural stable isotopes: carbon-12 (98.9%) and carbon-13 (1.1%). In recent years, carbon-13 has been widely used in agricultural ecology, drug metabolism, medical diagnosis, etc., especially the carbon-13-enriched urea breath test (UBT) has become the standard for clinical diagnosis of Helicobacter pylori. primary means. The domestic market of carbon-13-enriched urea breath test is in the growth stage, and has the advantages of development potential. Therefore, economical and efficient carbon isotope separation and preparation methods are attracting more and more attention.

The principle of gas centrifugation is to use the centrifugal force field of the gas centrifuge to form different radial pressure distributions of components with different relative molecular masses, so as to realize the relative separation between components, rather than the absolute separation between isotopes. Through the parallel connection and series connection of separation units, a centrifuge separation cascade is formed, and high-abundance products can be obtained. The structure of the gas centrifuge is one feed and two discharges, in which the light components are enriched at the fine material end, and the heavy components are enriched at the lean material end. The effect of gas centrifugation is affected by many aspects, including the physical parameters of the working medium, the structural parameters of the centrifuge, and the parameters of the centrifuge fluid. Due to the particularity of the application of gas centrifuges in uranium enrichment production, some performance parameters are kept secret.

The separation and preparation methods of carbon isotopes mainly include cryogenic rectification, chemical exchange, gas centrifugation, etc. Among them, cryogenic rectification has been industrialized abroad, and the production capacity of carbon-13 enrichment in the world can reach 700kg/a. The main place of origin is the United States. Domestic research on the separation and preparation of carbon isotopes has also been carried out for many years. The Shanghai Research Institute of Chemical Industry is committed to the industrialization of cryogenic distillation; the Department of Engineering Physics of Tsinghua University has successively realized the gas centrifugation of carbon isotopes using n-octane and Freon-11 as working media. separate. In addition, there are no other published literatures about carbon isotope separation and preparation methods at home and abroad. However, the gas centrifugal separation methods of carbon isotopes mentioned above all have the problem of multi-component separation, and the separation coefficient is relatively small. When used in cascade production, it will bring higher equipment costs, and the cascade design process is also more complicated. .

Contents of the invention

In view of this, the main purpose of the present invention is to provide a method for centrifugal separation of carbon isotopes using methyl iodide as a medium, in order to at least partially solve at least one of the above-mentioned technical problems.

To achieve the above object, the technical scheme of the present invention is as follows:

A method for centrifugal separation of carbon isotopes using methyl iodide as a medium, comprising:

Step A: purify the light impurities in the raw material of methyl iodide, so that its chemical purity meets the centrifugal separation requirements of methyl iodide;

Step B: Pass the purified gaseous methyl iodide into the gas centrifuge, adjust the feed flow rate, and the pressure of the fine material nozzle and the lean material nozzle of the gas centrifuge, from the fine material nozzle and the lean material nozzle Separation of fine material and lean material;

Step C: Keep the fluid parameters of methyl iodide feed, concentrate, and lean material stable, and after the gas centrifuge runs continuously until the carbon isotope abundance distribution in it is stable, collect the carbon isotope abundance distribution respectively through a liquid nitrogen cold trap Stable concentrate and lean feed.

Preferably, in step A, the chemical purity of the methyl iodide raw material reaches above 99.5% after purification.

Preferably, in step B, the feed flow rate of the gas centrifuge is 11.5 to 19.5 g/h, the split ratio is 0.4 to 0.6, and the pressures of the fine material nozzle and the lean material nozzle of the gas centrifuge are both 175～300Pa.

Preferably, in step C, the gas centrifuge is operated continuously for more than 1.5 hours, so as to stabilize the carbon isotope abundance distribution in it.

Preferably, in step C, it also includes the step of performing mass spectrometry analysis on the fine material and the lean material to obtain the separation coefficient: adjust the ion source parameters of the gas mass spectrometer, and use (CH ₃ I) ⁺ ion groups as the analysis object , so as to accurately analyze the carbon isotope content of fine material and lean material to calculate the separation system.

Preferably, the gas centrifuge is a single machine or a cascade machine.

Based on the above-mentioned technical scheme, the beneficial effects of the present invention are as follows:

(1) The present invention uses methyl iodide as the working medium, which can be regarded as having no isotope interference other than carbon elements and avoiding complex multi-component separation problems. It has advantages in cascade design and optimization of centrifugal separation production, and has strong technical feasibility and a certain economy.

(2) Using methyl iodide as the working medium, by reasonably adjusting the working parameters of the gas centrifuge such as pressure and flow, the separation coefficient of the single machine can reach 1.11, which is suitable for large-scale production in the form of cascading, and the obtained lean material and raw material are only in the The difference in abundance does not affect its continuous use as a chemical reagent recovery, so the market application value of this method has certain advantages.

(3) The carbon isotope separation method of the present invention has lower energy consumption than the current industrialized production method of carbon isotope, that is, cryogenic distillation.

Description of drawings

Fig. 1 is a schematic diagram of the system structure of an embodiment of the present invention using methyl iodide as a medium for centrifuging carbon isotopes;

Fig. 2 is the method flowchart of the embodiment of the present invention using methyl iodide as a medium for centrifuging carbon isotopes;

Fig. 3 is the result of mass spectrometry analysis of the separation of methyl iodide by a single machine in Example 1 of the present invention.

In the above drawings, the meanings of reference signs are as follows:

1-gas centrifuge; 2-lean material tank; 3-fine material tank; 4-liquid nitrogen cold trap; 5-sampler; 6-gas mass spectrometer; 7-vacuum pump.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

For the separation of carbon isotopes by gas centrifugation, the working medium is one of the key elements. The working medium of gas centrifugation should generally meet the following three conditions:

1) It remains stable at temperatures below 300°C and does not decompose;

2) The relative molecular mass is not less than 70;

3) At room temperature, the saturated vapor pressure is not less than 665Pa.

Methyl iodide (CH ₃ I ) has a relative molecular mass of 141.94, is difficult to pyrolyze, and has a saturated vapor pressure of about 50kPa at room temperature, meeting the requirements of gas centrifugation for the working medium. Stable and mature technology, which is also the advantage of choosing it as a working medium.

The present invention proposes a method for centrifuging carbon isotopes with methyl iodide as a medium. Since the natural stable isotope of iodine is only iodine-127, and the natural abundance of deuterium isotope of hydrogen is extremely low (0.0115%), it can be completely determined by the working medium methyl iodide For binary separation, the two components are ¹² CH ₃ I and ¹³ CH ₃ I, respectively, and the corresponding relative molecular masses are 142 and 143, which avoids the problem of introducing multi-component separation, and also achieves a good carbon isotope separation effect.

This method can be realized by using the existing gas centrifugal separation system. The structure of the gas centrifugal separation system is shown in Figure 1, including a gas centrifuge 1, a feeding and retrieving unit, a lean material tank 2, a fine material tank 3, and a liquid nitrogen cold trap 4. Reclaimer 5 and vacuum pump 7, wherein:

The structure of the gas centrifuge 1 is a conventional structure in this technical field. The methyl iodide is delivered to the gas separator 1 through the supply and take-off unit for carbon isotope separation. The material unit is transported to the lean material tank 2 and the fine material tank 3. The lean material tank 2 and the fine material tank 3 are set in the liquid nitrogen cold trap 4 to cool and collect the fine material and the lean material. The vacuum pump 7 is connected to the supply and extraction The material unit is used to maintain the air partial pressure of the supply and reclaim unit within a certain range.

Fig. 2 is a flowchart of a method for centrifuging carbon isotopes using methyl iodide as a medium according to an embodiment of the present invention. As shown in Figure 2, the present invention provides a method for centrifuging carbon isotopes with methyl iodide as a medium, including:

Step A: purify the light impurities in the raw material of methyl iodide, so that its chemical purity meets the centrifugal separation requirements of methyl iodide;

Wherein, light impurity is a professional term in this field, refers to the impurity that the molecular weight of relative to working medium is much smaller, for example molecular weight is the impurity below 50% of working medium molecular weight; Much smaller impurities are mainly air and water vapor. For natural methyl iodide raw materials, that is, methyl iodide raw materials in natural abundance, liquid nitrogen and "liquid nitrogen-absolute ethanol" mixtures can be used as coolants, using methyl iodide and methyl iodide The difference in saturated vapor pressure of light impurities is purified to make its chemical purity reach more than 99.5%, so as to meet the requirements of gas centrifugal separation.

Step B: Pass the purified gaseous methyl iodide into the gas centrifuge, adjust the feed flow rate, and the pressure of the fine material nozzle and the lean material nozzle of the gas centrifuge, from the fine material nozzle and the lean material nozzle Separation of fine material and lean material;

As an example, the gas centrifuge 1 used in the present invention is a gas centrifuge in stand-alone form, and a feeding orifice is arranged in the feeding and reclaiming unit, which is connected to the gas centrifuge 1 through a pipeline, and iodine can be adjusted through the feeding orifice. Methane is fed into the gas centrifuge 1 at a feed flow rate of 11.5-19.5g/h; a valve is also installed on the pipeline connecting the supply and take-off unit with the gas centrifuge, and the split ratio is adjusted to 0.4-0.6 through the valve. The pressure at the outlet and the lean material nozzle is 175-300Pa, under which conditions a higher separation factor of carbon isotopes can be guaranteed.

During the separation process, the vacuum pump 7 is used to maintain the air partial pressure of the feeding and retrieving unit within 2 Pa, and the fine material and lean material are collected respectively through a liquid nitrogen cold trap.

Step C: Maintain the stability of the fluid parameters of methyl iodide feedstock, fine material, and lean material. After the gas centrifuge continues to run until the carbon isotope abundance distribution is stable, obtain concentrated/depleted carbon isotope-containing fine material and lean material. material.

As preferably, after the fluid parameters of methyl iodide supply and concentrated material and lean material are stabilized, the gas centrifuge is operated for more than 1.5 hours, so that the carbon isotope distribution in it is stable;

This step also includes the step of sampling the fine material and the lean material and using a gas mass spectrometer for mass spectrometry analysis to calculate the separation factor. Wherein, the step of performing mass spectrometry analysis on the fine material and lean material includes: adjusting the ion source parameters of the gas mass spectrometer, using (CH ₃ I) ⁺ ion groups as the analysis object, so as to analyze the carbon content of the fine material and lean material. Accurate analysis of isotope content.

Below enumerate specific embodiment technical scheme of the present invention is further described:

Example 1

By adjusting the feeding orifice, the purified gaseous methyl iodide is fed into the single-machine gas centrifuge at a feeding flow rate of about 15g/h, and the pressure of the fine and lean material nozzles of the centrifuge is adjusted through the valve of the feeding and retrieving unit. At about 230Pa, the split ratio is 0.5. After the fluid parameters of the methyl iodide supply and the fine material and lean material reach a steady state, the gas centrifuge must run continuously and stably for more than 1.5 hours, and then simultaneously separate the fine material tank and the lean material tank. A liquid nitrogen cold trap is used to collect materials, and a vacuum pump is used to maintain the air partial pressure of the feeding and reclaiming unit within 2Pa during the separation process.

The separation coefficient is obtained through sample analysis, and its calculation formula is: γ=[C _p /(1-C _p )]/[C _w /(1-C _w )], where γ is the separation coefficient, and C _p is the The abundance of carbon-12, _Cw is the abundance of carbon-12 in the lean material. The results of the centrifugation of the single machine in this embodiment are shown in FIG. 3 , and the separation coefficient of the single machine was calculated to be 1.11 according to the results of the mass spectrometry analysis. In the prior art, the single-machine separation coefficient for separating carbon isotopes with n-octane as a medium is 1.08, and the single-machine separation coefficient for separating carbon isotopes with Freon as a medium is 1.08. In comparison, the present invention uses methyl iodide as a medium for centrifugal separation of carbon isotopes The effectiveness of the method is suitable for large-scale production in cascaded form.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

Claims (6)

1. A method for centrifugal separation of carbon isotopes, characterized in that, comprising: Step A: purify the light impurities in the raw material of methyl iodide, so that its chemical purity meets the centrifugal separation requirements of methyl iodide; Step B: Pass the purified gaseous methyl iodide as a medium into the gas centrifuge, adjust the feed flow rate, and the pressure of the fine material nozzle and the lean material nozzle of the gas centrifuge, from the fine material nozzle and the lean material The nozzle separates fine material and lean material respectively; Step C: Keep the fluid parameters of methyl iodide feed, concentrate, and lean material stable, and after the gas centrifuge runs continuously until the carbon isotope abundance distribution in it is stable, collect the carbon isotope abundance distribution respectively through a liquid nitrogen cold trap Stable concentrate and lean feed. 2. The method according to claim 1, characterized in that, in step A, the chemical purity of the methyl iodide raw material reaches more than 99.5% after purification. 3. The method according to claim 1, characterized in that, in step B, the feed flow rate of the gas centrifuge is 11.5 to 19.5g/h, the split ratio is 0.4 to 0.6, and the precision of the gas centrifuge is The pressures of the material nozzle and the lean material nozzle are both 175-300Pa. 4. The method according to claim 1, characterized in that, in step C, the gas centrifuge is continuously operated for more than 1.5 hours, so that the carbon isotope abundance distribution in it is stable. 5. method according to claim 1, is characterized in that, in step C, also comprises the step of carrying out mass spectrometry to described fine material and lean material to obtain separation factor: the ion source parameter of adjustment gas mass spectrometer, with ( CH ₃ I) ⁺ ion group is the analysis object, so that the carbon isotope content of fine material and lean material can be accurately analyzed to calculate the separation coefficient. 6. The method according to claim 1, characterized in that, the gas centrifuge is a single machine or a cascade machine.