基于硅铝前驱体结构设计和分形特征对合成斜发沸石的导向作用及其骨架外平衡阳离子对CH4/N2的选择性吸附扩散机制

In order to achieve efficient recovery of CH4 from low quality coal bed gas, adsorbent is one of the key factors. This project demonstrates the influences of structure properties of the obtained clinoptilolite zeolite and its balance cation performances in the presence of external skeletons on the selective adsorption and diffusion behaviors for CH4-N2 mixed gas, which aims at improving the efficient separation of CH4/N2 on the following aspects: the structure design of sol, fractal feature of precursor, and hydrothermal synthesis technique. Firstly, the directing-structure-agents (DSA) with stable and highly active species are obtained by adjusting composition of aluminosilicate sol and various parameters. Then, the growth process of precursor can be controlled by introduction of the selected silane coupling agents onto the initial synthesis system and using DSA as seed. Particularly, the fractal structure evolutions of the sol species during induced period and subsequent nucleation stage are studied by small-angle X-ray scattering (SAXS) technology in combination with other characterization methods. These results are very useful to further understand the crystallization mechanism and thereafter generate purity clinoptilolite zeolite via hydrothermal synthesis. Meanwhile, according to the characteristics of "selectivity" and "polarity", the binary or ternary cation exchange system are designed and selected to prepare the multiple ion-exchanged clinoptilolites, in which the thermodynamics and kinetics are evaluated. Finally, the effects of cationic type, number and its position and distribution in the presence of different channel on the CH4/N2 separation are emphasized, the relevance mechanism of adsorption-diffusion behaviors is proposed, and therefore the structure-performance relationship are elucidated. These results provide important theoretical principle and experimental guidance for the exploration of high-performance adsorbent and development of related potential application.

为实现低浓度煤层气中CH4的高效回收，吸附剂是关键。本项目从溶胶结构设计、前驱体分形解析以及水热合成技术三方面论述斜发沸石的结构性能及其骨架外多种平衡阳离子对CH4-N2混合气体选择性吸附和扩散行为的影响规律，旨在提高CH4/N2吸附分离效率。通过调整配比和工艺参数获得稳定的高活性结构导向剂，并以此为晶种，同时在合成体系中引入硅烷偶联剂控制前驱体的生长过程，采用SXAS技术并结合其他表征方法跟踪溶胶粒子在诱导期和成核阶段的分形结构演变过程，阐明晶化机理，通过水热途径合成高纯相斜发沸石。基于“择性”和“极性”特点，从热力学和动力学角度出发设计和选择二元或三元阳离子交换体系，从而制备出多元离子型斜发沸石。重点研究其骨架外平衡阳离子类型，数量及其在不同孔道中的位置和分布对CH4/N2吸附扩散性能的作用机制，揭示构效关系，为开发高性能吸附剂以及寻求在相关领域中的应用提供重要的理论依据和实验指导。

为实现低浓度煤层气中CH4的高效回收，吸附剂是关键。本项目从溶胶结构设计、前驱体分形解析以及水热合成技术三方面论述斜发沸石的结构性能及其骨架外多种平衡阳离子对CH4，N2，CO2和O2等气体分子选择性吸附和扩散行为的影响规律，旨在提高吸附分离效率。研究内容主要分为“前驱体聚集态结构设计与分形特征演变规律”和“多种离子共存与吸附分离性能”两部分。阐述了斜发沸石溶胶-凝胶水热晶化过程中分形结构及其溶胶粒子尺寸和形貌的演变规律，揭示了溶剂化界面层厚度的形成过程，提出硅铝酸根离子所形成的溶胶-凝胶在水热晶化过程中从初级结构单元的无定形态到次级结构单元，最后组装成三维空间结构的生长机制。 采用晶种法在醇-水体系中合成出具有球型、柱状及花状等不同形貌和尺寸的斜发沸石，发现诱导期是合成高纯相斜发沸石的控制步骤，且醇溶剂随着碳链长度的增加，对于诱导期的促进作用逐步减弱，但是对于生长期具有明显的抑制作用。基于“择性”和“极性”特点，从热力学和动力学角度出发深入考察了二元或三元阳离子（Li+， Fe3+，Cs+，K+，Na+，Rb+，Ba2+，Cu2+，Mg2+，Ni2+，Co3+，Ca2+，Sr2+等）交换性能，结果表明其交换过程主要受热力学因素影响，交换机理则倾向于拟二阶动力学模型和粒子内部扩散机制。探索了上述交换离子类型，数量及其在不同孔道中的位置和分布对CH4，N2，CO2和O2等气体分子的吸附与分离性能的作用规律。结果表明Sr2+或Cs+交换样品表现出良好的N2/CH4分离性能；Li+或Na+交换样品则表现出良好的CO2/CH4和N2/O2分离性能。这些构效关系为开发高性能吸附剂以及寻求在相关领域中的应用提供了重要的理论依据和实验指导。.在本项目资助下，发表学术论文30篇；授权中国发明专利7项；培养17名硕士生和4名博士生顺利毕业；7人次参加国内外2个学术会议。