A modification method for increasing the adsorption capacity of activated carbon for radon gas

Abstract

The present invention relates to the technical field of radioactive gas adsorbents, and in particular to a modification method for increasing the adsorption capacity of activated carbon for radon gas. The present invention performs fluorination modification on the activated carbon by pre-reacting the activated carbon in an F2 / N2 mixed gas atmosphere with an F2 volume concentration of 5%, and then reacting in an F2 / N2 mixed gas atmosphere with an F2 volume concentration of 8-15%, so as to increase the adsorption capacity of the activated carbon for radon gas. The present invention provides a modification method for increasing the adsorption capacity of activated carbon for radon gas, and increases the adsorption capacity of activated carbon for radon gas by fluorination modification of the activated carbon. The method of the present invention overcomes the problems in the prior art that the micropore adjustment technology is not highly controllable, the preparation method is complicated, and the selective adsorption capacity of radon gas is limited.

Description

Technical Field

[0001] The invention relates to the technical field of radioactive gas adsorbents, and in particular to a modification method for improving the adsorption capacity of activated carbon for radon gas. Background Art

[0002] In order to adsorb and retain radioactive gases such as radon in underground projects where ventilation is inconvenient, and to prevent radon from being inhaled into the lungs and causing internal irradiation, activated carbon is often used as a radon adsorbent because of its developed micropore distribution. However, the radon dynamic adsorption coefficient of activated carbon currently available on the market is less than 10L / g, which can no longer meet the increasing demand for underground projects. This is mainly because the partial pressure of radon in the air is much lower than the partial pressure of oxygen, nitrogen and other gases, resulting from the competitive adsorption of multiple gas components. Therefore, the development of an adsorbent with high radon adsorption selectivity is the key to increasing the amount of radon adsorption.

[0003] In the 2021 issue 2 of the Journal of Atomic Energy Science and Technology, Volume 55, the article "Liquid Nitrogen Modification Method for Improving the Radon Absorption Efficiency of Activated Carbon" mentioned that the activated carbon was modified four times by continuous liquid nitrogen immersion and evaporation. The radon gas adsorption coefficient of the modified activated carbon increased by 36% compared with the original activated carbon, that is, 4.4L / g before modification and 5.99L / g after modification; in the 2022 issue 19 of the New Journal of Chemistry, the article "High-efficiency radon adsorption by nickelnanoparticles supported on activated carbon" mentioned that the Rn adsorption performance of the Ni / AC composite material was significantly improved by introducing nickel nanoparticles through a two-step process of impregnation and high-temperature reduction. At 25°C and 1 bar, the adsorption coefficient of Ni / AC calcined at 800°C reached 6.56±0.14L / g, which is 48% higher than AC (4.43). The fine and uniform dispersion of nickel nanoparticles, the appropriate chemical state of nickel, and the high content of Ni synergistically promote the adsorption of Rn on Ni / AC.

[0004] In the above two activated carbon modification methods, two strategies are mentioned respectively, namely (1) increasing the micropore volume of the activated carbon adsorbent by the physical liquid nitrogen evaporation phase change method to increase the adsorption amount of radon gas; (2) loading selective adsorption sites for adsorbing radon gas in the micropores of activated carbon to increase the selective adsorption capacity of activated carbon for radon gas. However, the micropore adjustment technology of liquid nitrogen modified evaporation phase change is not highly controllable, and is highly random and empirical. In addition, the increase in micropore volume will also increase the adsorption amount of carbon dioxide, and it does not play a role in the selective adsorption of radon. The loading of nickel ions in the micropores has limited effect on the adsorption of radon gas, and the mechanism of selective adsorption of radon is still unclear.

[0005] Therefore, providing an activated carbon modification method that can both increase the adsorption amount of radon gas and improve the selective adsorption of radon gas is of great significance to the technical field of radioactive gas adsorbents. Summary of the invention

[0006] Based on the above content, the present invention provides a modification method for improving the adsorption capacity of radon gas by activated carbon.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention is a method for preparing fluorinated modified activated carbon, comprising the following steps:

[0009] The activated carbon is first pre-reacted in an F2 / N2 mixed gas atmosphere with an F2 volume concentration of 5%, and then reacted in an F2 / N2 mixed gas atmosphere with an F2 volume concentration of 8-15% to obtain the fluorinated modified activated carbon.

[0010] The second technical solution of the present invention is a fluorinated modified activated carbon prepared according to the above-mentioned preparation method.

[0011] The third technical solution of the present invention is the application of the above-mentioned fluorinated modified activated carbon in the adsorption of radon gas.

[0012] A fourth technical solution of the present invention is a modification method for increasing the adsorption capacity of activated carbon for radon gas, wherein the activated carbon is fluorinated by using the above-mentioned preparation method of fluorinated modified activated carbon to increase the adsorption capacity of activated carbon for radon gas.

[0013] The present invention discloses the following technical effects:

[0014] The preparation method of the fluorinated modified activated carbon of the present invention has high micropore adjustment stability, and can complete the adjustment of micropores and adsorption site loading at one time. The present invention utilizes the abundant micropore volume in the range of 0.5-0.9 nm to provide a sufficiently large adsorption retention space, and the adsorption sites on the surface of the activated carbon cooperate to increase the selective adsorption amount of radon gas by the activated carbon. The fluorinated modified activated carbon prepared by the method of the present invention has a high radon gas adsorption coefficient.

[0015] The present invention provides a modification method for improving the adsorption capacity of activated carbon for radon gas, and improves the adsorption capacity of activated carbon for radon gas by fluorination modification of activated carbon. The method of the present invention overcomes the problems of low controllability of micropore adjustment technology, complex preparation method, and limited improvement of selective adsorption capacity of radon gas in the prior art. DETAILED DESCRIPTION

[0016] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0017] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0018] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0019] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0020] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0021] One of the technical solutions of the present invention is a method for preparing fluorinated modified activated carbon, comprising the following steps:

[0022] The activated carbon is first pre-reacted in an F2 / N2 mixed gas atmosphere with an F2 volume concentration of 5%, and then reacted in an F2 / N2 mixed gas atmosphere with an F2 volume concentration of 8-15% to obtain the fluorinated modified activated carbon.

[0023] In some embodiments of the present invention, the temperature of the pre-reaction is 25° C. and the time is 1 hour.

[0024] In the present invention, the pre-reaction time refers to the time for introducing F2 / N2 mixed gas with a F2 volume concentration of 5%.

[0025] In some embodiments of the present invention, the flow rate of the F2 / N2 mixed gas with an F2 volume concentration of 5% during the pre-reaction is 6 L / h.

[0026] In some embodiments of the present invention, the reaction temperature is 25° C. and the reaction time is 20 minutes.

[0027] In the present invention, the reaction time refers to the time for the reaction to take place after the target amount of fluorine gas is fully charged into the reaction furnace.

[0028] In some embodiments of the present invention, the flow rate of the F2 / N2 mixed gas with an F2 volume concentration of 8-15% during the reaction is 6 L / h.

[0029] The present invention uses F2 / N2 mixed gas with a volume concentration of 5% F2 to pre-react activated carbon for two main purposes: one is to undergo a replacement reaction with the functional groups and metal impurities on the surface of the activated carbon to eliminate their interference with the fluorine atom loading, and the other is to ensure the smoothness of the micropores to facilitate the effect of the subsequent fluorine atom loading reaction, and to properly pre-load the fluorine atoms. If the F2 volume concentration of the pre-reaction F2 / N2 mixed gas is too high, or the same as the volume concentration of the reaction, the functional groups and metal impurities are not pre-replaced and the micropores are not ensured to be smooth, then the high-concentration fluorine gas will gather between the mesopores and micropores, and the excessive reaction with the carbon atoms in the skeleton structure will directly destroy the micropore channel structure of the activated carbon, and ultimately reduce the radon gas adsorption effect of the fluorinated carbon. If the volume concentration of the F2 / N2 mixed gas of the pre-reaction and reaction is too low, it is not possible to fully guarantee the effect of the pre-reaction in eliminating functional groups and metal impurities to keep the micropores smooth, and it is not possible to ensure that the reaction fully obtains the expected fluorine-carbon ratio.

[0030] Similarly, when the flow rate of F2 / N2 mixed gas is limited to 6L / h, it is to control the total amount of F2 introduced into the activated carbon per unit time to prevent F2 from agglomerating and destroying the microporous structure of the activated carbon. When the flow rate is too low, the reaction time is too long, reducing the modification efficiency.

[0031] In some embodiments of the present invention, the ratio of the total amount of fluorine gas introduced during the pre-reaction and the reaction to the number of fluorine-carbon atoms in the activated carbon is 0.3.

[0032] The reason why the fluorine-carbon atomic ratio is limited to 0.3 is that when the fluorine-carbon ratio is lower than 0.3, the amount of fluorine atoms loaded on the activated carbon is insufficient, that is, the number of strong adsorption sites is insufficient, and thus the amount of radon gas adsorbed by the activated carbon is not significantly increased; when the fluorine-carbon ratio is higher than 0.3, the fluorine gas has obviously destroyed the microporous structure of the activated carbon, and the adsorption amount is significantly reduced.

[0033] In some embodiments of the present invention, the micropore volume of the activated carbon is not less than 0.3 cm 3 / g, pore size is 0.8-1.2nm.

[0034] The fluorination modification of the present invention will cause the pore wall of the activated carbon to increase by about 0.2-0.3nm, so the present invention limits the pore size of the initial activated carbon to 0.8-1.2nm. After fluorination modification, fluorinated modified activated carbon with a pore size of 0.5-0.9nm can be obtained.

[0035] The present invention can load fluorine atoms on the activated carbon to form strong radon gas adsorption sites by fluorination modification of the activated carbon, and improve the adsorption amount of radon gas by the activated carbon through the two aspects of pore size and adsorption sites.

[0036] The second technical solution of the present invention is a fluorinated modified activated carbon prepared according to the above preparation method. The micropore volume of the fluorinated modified activated carbon is not less than 0.3 cm 3 / g, pore size is 0.5-0.9nm.

[0037] The third technical solution of the present invention is the application of the above-mentioned fluorinated modified activated carbon in the adsorption of radon gas.

[0038] A fourth technical solution of the present invention is a modification method for increasing the adsorption capacity of activated carbon for radon gas, wherein the activated carbon is fluorinated by using the above-mentioned preparation method of fluorinated modified activated carbon to increase the adsorption capacity of activated carbon for radon gas.

[0039] Unless otherwise specified, the raw materials used in the embodiments of the present invention can be obtained through commercial sources.

[0040] The micropore volume of the activated carbon used in the embodiment of the present invention exceeds 0.3-0.5cm 3 / g, pore size 0.8-1.2nm.

[0041] The present invention is further described below by way of examples.

[0042] Example 1

[0043] The activated carbon (A) is placed in a rotary fluorination reactor and sealed, the furnace tube is turned on and rotated, and the atmosphere is replaced with nitrogen (N2) for 1 hour, then the valve of the reactor outlet pipe is closed, and a 5% volume concentration of F2 / N2 mixed gas (B1, i.e., F2 accounts for 5% of the volume of the mixed gas) is introduced, and the B1 mixed gas is introduced at a rate of 6L / h for 1 hour. Thereafter, a 15% volume concentration of F2 / N2 mixed gas (B2, i.e., F2 accounts for 15% of the volume of the mixed gas) is prepared according to the target fluorine content in the B1+B2 mixed gas, i.e., the fluorine-carbon atomic ratio (F / C) is 0.3, and finally the F2 / N2 mixed gas (B2) is controlled by a mass flow controller (Mass Flow Controller, MFC) to be introduced into the reactor at a rate of 6L / h until the target fluorine gas volume is fully charged into the reactor. Close the inlet valve, continue to rotate for 20 minutes, then open the outlet valve to release the pressure (the present invention has no special requirements for the rotation rate, rotation can accelerate the reaction speed, when the rotation rate is 0, the present invention can also be achieved by extending the reaction time), and introduce N2 to replace the atmosphere and unload the material. The final pore size range is 0.5-0.9nm and the micropore volume exceeds 0.3cm 3 / g of fluorinated modified activated carbon (C).

[0044] The fluorinated modified activated carbon prepared in this embodiment has a rich pore size distribution that matches the diameter of radon atoms. The larger the pore size range, the greater the adsorption capacity of radon gas. At the same time, the fluorinated modified activated carbon microporous surface is loaded with suitable F atoms, that is, a stable CF chemical bond is formed in the activated carbon micropores, and F can react with radon atoms, and F atoms form an effective adsorption site for capturing and retaining radon atoms. The combined effect of these two conditions (pore size distribution and adsorption sites formed by F atoms) improves the adsorption coefficient of activated carbon to radon gas, as well as the selective adsorption capacity.

[0045] The dynamic adsorption coefficient of radon gas of the fluorinated modified activated carbon prepared in Example 1 and the unmodified activated carbon used was tested. The test conditions were: the activated carbon before and after modification was loaded in a fixed bed, and the radon concentration of the radon-containing air at the inlet of the carbon bed was fixed at 23000 Bq / m 3 , the other components remain unchanged, RAD7 radon detector is used to measure the change of radon concentration at the outlet of carbon bed, and the corresponding dynamic adsorption coefficient is calculated by taking the half-penetration time after the penetration curve is obtained. The results show that the dynamic adsorption coefficient of radon gas of unmodified activated carbon under (25℃, 1atm) is 1.8L / g, and the dynamic adsorption coefficient of radon gas of fluorinated modified activated carbon under (25℃, 1atm) is 8.2L / g, which is about 4.5 times higher.

[0046] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing fluorinated modified activated carbon, characterized in that: The following steps are involved: The activated carbon is first pre-reacted in an F2 / N2 mixed gas atmosphere with an F2 volume concentration of 5%, and then reacted in an F2 / N2 mixed gas atmosphere with an F2 volume concentration of 8-15% to obtain the fluorinated modified activated carbon.

2. The method for preparing fluorinated modified activated carbon according to claim 1, characterized in that: The temperature of the pre-reaction is 25° C. and the time is 1 hour.

3. The method for preparing fluorinated modified activated carbon according to claim 1, characterized in that: During the pre-reaction, the F2 volume concentration is 5%, and the flow rate of the F2 / N2 mixed gas is 6 L / h.

4. The method for preparing fluorinated modified activated carbon according to claim 1, characterized in that: The reaction temperature was 25°C and the reaction time was 20 minutes.

5. The method for preparing fluorinated modified activated carbon according to claim 1, characterized in that: During the reaction, the volume concentration of F2 is 8-15%, and the flow rate of the F2 / N2 mixed gas is 6 L / h.

6. The method for preparing fluorinated modified activated carbon according to claim 1, characterized in that: The ratio of the number of fluorine atoms in the activated carbon to the number of fluorine atoms in the fluorine gas introduced during the pre-reaction and the reaction is 0.

3.

7. The method for preparing fluorinated modified activated carbon according to claim 1, characterized in that: The micropore volume of the activated carbon is not less than 0.3 cm 3 / g, pore size is 0.8-1.2nm.

8. The fluorinated modified activated carbon prepared according to the preparation method according to any one of claims 1 to 7.

9. Use of the fluorinated modified activated carbon as claimed in claim 8 in adsorbing radon gas.

10. A modification method for increasing the adsorption capacity of activated carbon for radon gas, characterized in that: The activated carbon is fluorinated and modified by the preparation method of fluorinated modified activated carbon according to any one of claims 1 to 7, so as to increase the adsorption capacity of the activated carbon for radon gas.