锂同位素分离膜化学交换膜材料的结构与性能调控研究

Separation of lithium isotope using the Membrane Chemical Exchange (MCE) technology is novel both in isotope separation and membrane fields. This proposal aims to provide a basis for lithium isotope separation via MCE. We will focus on the development of a new type of solvent resistant membrane prepared by a semicrystalline polymer and the mass transport resistance of the membrane, the external boundary layer and the chemical exchange. The solid-liquid phase separation behavior of poly(ethylene vinyl alcohol, EVAL) in demixing process will be understood and utilized to manipulate the membrane structure. The thermodynamic and kinetic behavior of the membrane solution in demixing will be systematically investigated. Both solid-liquid and liquid-liquid phase separation will be evaluated in relation to the membrane structure and diffusion performance. A dual-temperature coagulation bath approach will be used to control the membrane morphology via controlling the demixing of the polymers in solution. Effect of hydrophobic silica nanoparticles on the solvent exchange rate and demixing process will be investigated as well. The lithium transport model based on a stable operation will be used for comparing the mass transport resistance of the membrane in relating to the chemical exchange reaction and external concentration polarization. The results and fundamental understanding in this proposal will pave a foundation for membrane chemical exchange for the lithium isotope separation.

本项目旨在建立锂同位素分离的膜化学交换基本理论，探索新型膜化学交换技术的核心耐溶剂膜材料的结构和性能的关系，解决半结晶高分子相分离对膜结构的调控机理以及膜化学交换传质阻力模型的关键科学问题。项目研究以聚乙烯-乙烯醇（EVAL）共聚物为关键材料，采用浸没沉淀法，通过相分离热力学和动力学的系统研究，得到成膜过程中固-液相分离和液-液相分离行为对孔结构构建关系, 为调控孔结构提供理论依据；采用双温度凝胶浴，研究高分子结晶行为对非对称膜结构生成过程的影响机制；研究疏水二氧化硅纳米材料对支撑层溶剂交换速率的影响，调控非对称膜材料的支撑层孔结构的形成。项目还将针对膜化学交换的特殊性，建立稳态传质模型，定量分析膜化学交换过程中各段传质的阻力，为优化各个传质过程提供量化依据。本项目研究成果将为同位素分离膜化学交换技术提供高性能的膜材料, 奠定膜化学交换锂同位素富集和分离的理论基础.

项目研究了锂同位素分离的膜化学交换技术的核心问题，包括耐溶剂膜材料的结构和性能优化，膜化学交换的基本原理和过程模拟，并进行实验室的验证。我们提出了针对半结晶高分子膜材料的结构控制的二级相分离基本理论，通过固-液相分离和液-液相分离的动力学差异来调控膜孔从不连通的指状孔向连通纳米结构的海绵状孔的转变，优化了膜的扩散传质性能。系统研究了偶氮萘酚同位素分离萃取体系(HA体系)在锂同位素中富集的基本理论，描述了化学交换模型和富集锂同位素的多级理论。最后在实验室建立了多级同位素富集系统，第一次采用膜化学交换技术将Li7的丰度从92.5%富集到93%，验证膜化学交换在同位素分离中的可行性。过程模拟验证膜化学交换技术具备较好的同位素分离工业化应用前景。本项目工作为膜化学交换多级富集锂同位素提供了材料和理论依据。