基于锂同位素分离的大环聚醚接枝聚砜/非织造基复合膜色谱多尺度结构调控与关联机制

Lithium isotopic separation is a chanllenge to be solved during the development of the 4th generation fission type reactor (i.e.molten salt reactor) in the world. Liquid - liquid extraction method for lithium isotopic separation has same disadvanges such as backmixing,reverse extraction difficulty etc.. Herein, according to the special selectivity of macrocyclic polyethers and their derivant to lithium isotopic separation(6Li/7Li) including ion-dipole and size effect, the aim of the present project proposal is to prepare macrocyclic polyethers grafted polysulfone/non woven fabric composited membranes and design ion-exchange membrane chromatograph so as efficiently to separation lithium isotopic by solid-liquid elution chromatography method. The key works focus on the preparation of a series of polyethers with various ether bonds and anchor groups and macrocyclic polyethers grafted polysulfone polymers, the internal relationship between the structure of the polymers and lithium isotopic separation effect. The next step is to prepare macrocyclic polyethers grafted polymers/non-woven composited membrane via wet phase inversion, explore the controlable method of microporous structure of composied membrane and the relationship of the microporous structure and lithium isotopic separation effect. Finally, a platform of membrane chromatograph would be established and used to study the effet of composited membrane, the size of the chromatograph column and the processing parameters etc. on lithium isotopic separation factor and enrichment effect, and illuminate the linkage mechanism of ion diffusion, adsorption and desorption, investigate the kinetics of lithium isotopic separation by membrane chromatograp, obtain the regulation and control method of multi-scale structural microcyclic polyethers grafted polymer/non woven fabric composited membrane chromatograph so as to provide a new method for high-perform lithium isotopic separation.

锂同位素分离是国际上发展第四代核裂变反应堆即钍基熔盐堆必须解决的技术难题。针对液-液萃取锂同位素分离存在返混、反萃困难等问题，基于大环聚醚及其衍生物对锂同位素的络合能力（离子-偶极）和选择性（尺寸效应），本项目提出制备大环聚醚接枝聚砜复合膜，设计离子交换膜色谱系统，采用固-液淋洗色谱法实现锂同位素的高效分离。着重合成具有反应官能团的大环聚醚化合物，制备大环聚醚接枝聚砜膜材料，探索聚合物分子结构与同位素分离效应的关系。采用浸没沉淀相转化法制备大环聚醚接枝聚砜/非织造基复合膜，探索膜微孔结构调控方法，阐释其与同位素分离效应的内在联系。建立膜色谱同位素分离评价平台，研究复合膜、色谱柱尺寸及过程参数对分离因子、富集效应、实际级联数等的影响规律，揭示其与离子扩散、吸附及脱附之间的联动机制，探索膜色谱同位素锂分离动力学，获得大环聚醚接枝聚砜复合膜色谱多尺度结构的调控方法，为同位素高效分离提供新方法。

锂的两种同位素在核能方面均具有重要应用，冠醚化合物由于其荷电效应和尺寸效应具有良好的锂同位素分离性能。本项目设计合成了氨基苯并15-冠-5接枝聚砜(PSF-g-AB15C5)、单氮杂苯并15-冠-5（PSF-g-NB15C5），壳聚糖接枝冠醚（CTS-g-FB15C5）三种冠醚接枝聚合物材料，并分别采用响应面优化合成条件，优化条件下三种聚合物材料冠醚固载量分别为0.813mmol/g，0.654 mmol/g，4.93mmol/g。.以氯甲基化聚砜和氨基苯并15-冠-5为原料，利用两者亲核取代反应和交联反应，首次提出在低聚合物固含量下通过反应-控制相转化成膜方法制备PSF-g-AB15C5聚合物膜。通过调控接枝反应和交联反应程度调控铸膜液粘度，实现对聚合物膜形貌调控。结果表明，随反应程度增加，反应溶液（铸膜液）粘度逐渐增大，制备相转化时分相速率变缓，膜断面由指状孔变为海绵状孔结构。当冠醚固载量为0.52 mmol/g，凝固浴为30% （v/v）乙醇水溶液时，制备的聚合物膜平均孔径76.8nm，孔隙率80.4%，纯水通量为1870 L/m2·h。所制备聚合物膜锂同位素分离因子为可达1.055。.以PSF-g-NB15C5为膜材料，PVP-K30为致孔剂，非织造布为支撑体，DMF为溶剂，水为凝固浴成膜，采用浸没沉淀相转化法制备PSF-g-NB15C5 /NWF复合膜。同时，以CTS-g-FB15C5、PVA为原料，以乙酸水溶液为溶剂，饱和硫酸钠为凝固浴制备CTS-g-FB15C5/PVA复合膜。两种聚合物膜对锂离子吸附均属于化学吸附，且为可逆放热反应。两种聚合物膜对锂离子分离因子分别为1.052和1.046，均大于工业化最低要求1.03。.以PSF-g-AB15C5为膜材料，采用层层装填法构建膜色谱柱，采用淋洗放分离锂同位素。特别是设计制备多级级联膜色谱系统，对两种锂同位素分别富集分离。结果发现，20层膜色谱器分离因子为1.01429，单级分离后7Li丰度提升0.06%，6Li丰度提升0.04%。经五级淋洗后，7Li丰度提升了0.19%，6Li丰度提升了0.17%。进一步制备80层膜色谱器，经五级分离色谱柱前端表现为7Li富集，丰度提升了0.24%，达92.65%；后端表现为6Li富集，丰度提升了0.22%，达7.8%。总之，多级膜色谱法为锂同位素分离提供了一种新的绿色