改性多级孔分子筛材料对气体中CH3I的去除作用

Removal of CH3I in Gas by Modified Hierarchical Molecular Sieve Materials

  • 摘要: 乏燃料溶解会释放出大量高温高湿的放射性废气,这些气体不仅含有大量放射性物质(如放射性碘),还可能含有氮氧化物,使气体呈酸性。酸性废气增加了处理过程的复杂性,同时会腐蚀吸附材料、降低吸附效率并缩短使用寿命。为降低高温高湿环境对吸附过程的影响,本研究探讨了疏水改性多级孔载银分子筛在模拟乏燃料溶解尾气条件下对碘甲烷(CH3I)的去除性能。首先,利用氢氟酸(HF)对ZSM-5分子筛进行刻蚀处理,以引入多级孔结构。然后,通过浸渍法将银引入经刻蚀处理的ZSM-5分子筛中,并采用苯基三乙氧基硅烷对载银分子筛进行疏水改性。最后,利用自行设计的气体吸附装置,在模拟乏燃料溶解尾气条件下,对改性材料的CH3I吸附能力进行评估。实验结果表明,HF处理显著提高了沸石的比表面积和孔径,使其能容纳更多的银离子。疏水改性分子筛对CH3I的去除性能均明显优于未改性分子筛。研究表明,经过疏水改性的载银分子筛在吸附含CH3I的气态放射性碘方面具有应用潜力。

     

    Abstract: During the dissolution process of spent nuclear fuel, significant amounts of high-temperature and high-humidity radioactive off-gas are generated. These gases not only contain substantial radioactive substances, such as radioactive iodine, but may also include nitrogen oxides, rendering the gases acidic. The acidic nature of these off-gases complicates their treatment and induces corrosion in adsorbent materials, potentially diminishing their adsorption efficiency and reducing their service life. The performance of hydrophobically modified hierarchical porous silver-loaded zeolites for methyl iodide (CH3I) removal was explored in this study. Their effectiveness under high-temperature and high-humidity conditions was specifically examined. To create a hierarchical porous structure, ZSM-5 zeolite was first chemically treated with hydrofluoric acid (HF). This etching process significantly increased the specific surface area of the zeolite, and created additional pore sites and active centers, thereby enhancing its adsorption capacity for targeted substances. Silver ions were then introduced into the etched ZSM-5 zeolite using an impregnation technique. To further improve its adsorption performance in high-humidity environments, the silver-loaded zeolite was modified with phenyltriethoxysilane to impart hydrophobic properties. The incorporation of hydrophobic groups effectively minimizes moisture interference, thereby improving the stability and durability of the zeolite in humid conditions. This process yields a series of zeolite materials with adjustable hydrophobic characteristics. The adsorption performance of these materials was systematically evaluated using a gas adsorption apparatus, with a focus on their ability to remove CH3I from simulated spent nuclear fuel dissolution off-gases. The results reveal that HF treatment and silver loading significantly increase the specific surface area and pore sites of the zeolite, enabling it to accommodate more silver ions and achieve a notably higher adsorption capacity compared to untreated ZSM-5 zeolite. Furthermore, hydrophobically modified zeolites exhibite superior CH3I removal performance relative to unmodified zeolites, demonstrating that hydrophobic modification enhances moisture resistance and significantly improves CH3I removal efficiency. Moreover, it is found that retaining a certain amount of fluoride ions could improve the adsorption capacity of silver-loaded zeolite by charge transfer with iodide ions during the adsorption process, which results in the presence of I in the form of \mathrmI_3^- or \mathrmI_5^- , and improves the binding capacity of silver and iodine. This study highlights that optimized hydrophobically modified silver-loaded zeolites offer significant potential for the filtration of radioactive iodine-containing gases. These findings present a promising new pathway for the development of advanced adsorbent materials for spent nuclear fuel dissolution off-gas treatment systems.

     

/

返回文章
返回