ZSM-22 分子筛中 Al 落位对费托油品临氢异构性能的影响

The Fischer-Tropsch synthesis technology for the production of liquid fuels from syngas is of great significance for reducing the dependence on foreign oil, achieving clean coal utilization and reducing environmental pollution. The Fischer-Tropsch synthetic oil has a low octane number and low temperature fluidity, and must be treated by isomerization to achieve oil quality upgrade. ZSM-22 molecular sieves show excellent application prospects in the long-chain alkane isomerization reaction, and the skeleton Al atom position is the key factor determining the activity, selectivity and stability of the catalyst. Therefore, it is a very meaningful work to study the relationship between the Al fall position and the physicochemical properties and catalytic properties of ZSM-22 molecular sieves. The project intends to firstly clarify the controllable synthetic route of different Al-ZSM-22 molecular sieves, reveal the key factors affecting the skeleton Al, and determine the existence of Al species through a series of characterization methods, and combine the detailed acid results to find out The intrinsic relationship between the Al position and the acidity of the molecular sieve; the structure-activity relationship between the molecular sieve Al separation and the isomerization performance is established, and the regulation mechanism of the skeleton Al and the acidic distribution of the isomerization product in the ZSM-22 molecular sieve is revealed. To provide a theoretical basis for the further development of Fischer-Tropsch oil isomerization catalysts with industrial application prospects.

由合成气出发生产液体燃料的费托合成技术，对于降低对外石油依存度、实现煤炭清洁利用、减少环境污染具有重要意义。而费托合成油品辛烷值较低、低温流动性较差，须经异构化处理以实现油品品质升级。ZSM-22分子筛在长链烷烃异构反应中表现出优异的应用前景，而骨架Al原子落位是决定催化剂活性、选择性和稳定性的关键因素。因此深入研究Al落位与ZSM-22分子筛理化性质以及催化性能的关系，实现异构催化剂的理性设计是一项十分有意义的工作。本项目拟首先探明不同Al落位ZSM-22分子筛的可控合成路线，揭示影响骨架Al落位的关键因素；并通过一系列表征手段明确Al物种的存在状态，结合详细的酸性结果探明Al落位与分子筛酸性之间的内在联系；建立分子筛Al落位与异构化性能之间的构效关系，揭示ZSM-22分子筛中骨架Al落位及酸性对异构产物分布的调控机制，为进一步研发具有工业应用前景的费托油品异构催化剂提供理论基础。

异构化技术是以直链烷烃为主的费托油品实现品质升级和广泛应用的重要途径。具有一维孔道和适宜酸性的ZSM-22分子筛在费托油品异构化领域展示出广阔的应用前景，而其骨架Al原子落位不仅是影响分子筛孔道和酸性的关键因素，而且与其异构化活性、选择性和稳定性密切相关。本项目基于前期积累的ZSM-5分子筛Al落位调控经验，系统地考察了各关键参数（如硅源、铝源、溶剂等）对ZSM-22分子筛中Al落位的具体影响，结果表明，合成体系的极性及其与硅源、铝源的匹配对骨架Al落位的影响最为显著；结合结构解析和酸性结果认为，合成体系极性降低促进Al物种分布在十元环孔道的T1+T2+T3位，表现为外表面和孔口Brønsted酸位减少，微孔内Brønsted酸位增加；而当合成体系与硅、铝源极性相近时，Al物种倾向落位于非十元环的T4位，表现为较多的外表面Brønsted酸位。在异构化催化剂中，外表面的骨架Al易与Pt物种产生强相互作用，抑制了后者在焙烧、还原中聚集，显著改善了Pt金属分散度。长链烷烃异构化结果表明，ZSM-22分子筛孔口和外表面的酸性位减少，且Pt金属高度分散是异构性能提升、产物分布优化的关键。通过在线取样-离线分析路线深入探究了ZSM-22分子筛的晶化过程，认为Al物种在成核初期已与硅氧四面体形成五元环初级结构单元；随着晶化时间延长，该结构单元相结合形成具有十元环孔道的分子筛晶体；当晶化时间进一步增加，各晶体以外表面Al物种为结合点相互融合，最终形成针状ZSM-22分子筛晶体材料。根据以上研究结论，本项目针对ZSM-22分子筛独特的Al落位，结合对其结构、孔道和金属Pt的理性调控，形成耦合效应，实现了正构烷烃异构化反应性能的大幅提升和产物分布的进一步优化；且将合成经验和路线推广至Beta等分子筛的制备中，为针对性地设计、调控分子筛基催化剂提供了新思路。本项目的实施从更加系统、基础的角度深入探究了Al落位对ZSM-22分子筛异构化性能的作用机理，为开发具有工业应用前景的费托油品异构催化剂奠定了基础。