重油分子定向裂化核壳多级孔沸石催化剂的构建及性能研究

Processing heavy feedstocks containing bulky molecules offer new challenges to FCC catalyst. To meet the demands on the catalyst for processing heavier feedstocks, the focus of this project is to design and prepare a novel hierachical core-shell zeolite material, such as Y@ZSM-5, which has a microsphere core consisting of aggregates of zeolite Y nanocrystals with intracrystalline mesopores and a shell consisting of zeolite ZSM-5 (or Beta) nanocrystals with intracrystalline mesopores. The core-shell structure of zeolites is beneficial to diffusion of product molecules for preventing side-reaction, compared with their phisical mixture of Y and ZSM-5 zeolites. And both the reduction of particle size of zeolite and the generation of mesopore inner zeolite crystals will circumvent the limitation imposed by the small pore sizes of zeolites on the accessibility of the active sites and diffusion to larger molecules, and make them applicable for catalysis involving large molecules. Furthermore, the detailed and in-depth studies about how to control the mesoporous/macroporous structure, core-shell structure and corresponding acidity etc. of the catalysts in an extensive range through changing the synthesis technology and conditions, to accomplish the goal that the structure and the performance of catalysts should be adjusted and elected according to the composition of raw feedstocks and expected product distribution. Moreover, the adsorption, diffusion and catalytic cracking of typical larger hydrocarbon molecules on various Y@ZSM-5(or Beta) core-shell catalysts with different structure and properties will be investigated in detail, and establish the relationship between the structure and composition of catalysts with their properties of adsorption, diffusion and catalytic cracking for different reaction molecules to clarify the promotion mechanism about the generation of mesopores inner zeolite crystals, reduction of particle size and core-shell structure on the accessibility of the active sites and diffusion of large molecules by a reasonable hierachical pore-structure. Above studies and corresponding results will open a novel mode for designing and preparing the effective catalysts for catalytic cracking of heavy feedstocks, offer the basic data and academic foundation for the application of catalysts, and therefore facilitate the development of refining industry.

项目针对重油催化裂化反应对催化剂的特殊要求，本着功能性导向的设计思路，构筑一种以Y@ZSM-5为模式的具有核壳结构的多级孔沸石催化剂，核由具有晶内中孔的纳米Y沸石聚集而成的微球，壳由生长于微球表面的中孔ZSM-5或Beta纳米沸石粒子组成。其目的在于通过沸石晶粒纳米化和晶内中孔双重功效解决微孔沸石活性位对大分子可接近性和扩散的限制问题，以及通过核壳化形成中孔/大孔解决两沸石间的扩散问题；完成在全尺度上对沸石催化剂的多级孔结构、核壳结构和酸性的有效调控，根据反应原料组成以及对产品分布的要求从头设计和合成催化剂；选择具有代表性的模型重油大分子研究其在催化剂中的扩散、吸附与裂化规律，在构建与催化剂孔结构和组成之间关系的基础上，揭示沸石晶内中孔、纳米化和核壳多级孔结构对反应分子的可接近性、扩散和催化裂化的内在联系，指导重油催化裂化催化剂的定向设计与制备，并为其实际应用提供完善的基础数据和理论依据。

项目针对原油重质化对FCC催化剂带来的巨大挑战——重油或者超重油中的油品分子尺寸大于裂解催化剂的主要活性组元即Y和ZSM-5沸石的微孔孔道，本着功能性导向设计思路，构建了多种核壳结构的多级孔沸石催化剂：核由具有因碱蚀形成的晶内中孔的Y、ZSM-5或Beta等沸石或沸石聚集体构成，壳由生长在聚集体表面的SAPO-34、Y、Beta或ZSM-5等沸石因空间限制导致的纳米晶粒构成。通过沸石晶粒的纳米化或多孔结构的引入以及增大的外表面积等多重功效解决了微孔沸石活性位对大分子可接近性和扩散的限制问题，以及通过核壳化形成贯穿于核壳之间的中孔/大孔解决两沸石间的扩散以及反应分子在双活性中心之间的不确定的传输途径和传输方向等问题。实现了在全尺度上对沸石催化剂的多级孔结构、核壳结构和酸性位的有效调控，并用以指导重油催化裂化催化剂的设计与制备——利用核壳多级沸石外表面具有相似的活性中心和开放的空间，确保将重油或超重油中的大分子预裂解成小分子，这些小分子随即可进入核相具有特定限域空间（微孔），并在微孔孔道中较强酸性位的作用下进行二次裂解；选择正辛烷、异丙苯、三异丙苯等具有不同动力学尺寸的分子研究其在催化剂中的扩散、吸附与裂解规律，在构建与催化剂孔结构、酸性位和组成之间关系的基础上，揭示了沸石晶内中孔、纳米化和核壳多孔结构对反应分子的可接近性、扩散和催化裂化的内在联系，并结合在芳香烃的苄基化大分子反应中的催化行为，揭示了构建的多级孔沸石催化剂在大分子反应中应用的可能性及其优越性，其研究成果为多级孔核壳沸石的制备和应用奠定了基础。