TNU-9分子筛催化苯-甲醇烷基化的择型与构效关系研究

Benzene alkylation with methanol to produce value-added products, such as toluene and xylenes, is a considerable process to reduce benzene content in gasoline and mitigate the corresponding environmental effect. Promoting the xylene yields, especially of the para-xylene is crucial to the overall economy of the process. In view that 10 member ring molecular sieves have exhibited superior shape selectivity in benzene alkylation with methanol, we propose to explore TUN structured zeolite catalyst with additional mesoporosity. A main difference between TNU-9 and ZSM-5 is related to the size of cavities formed by channel intersections, in TNU-9 the 10-ring channels expand into a 12-ring in the intersection, thus forming a larger cavity, giving rise to a variety of volumes in which reactions may proceed. Thus in this proposal, we will consider this novel zeolite material which contains many of the features of interest in catalyst development. The hierarchical porous TUN zeolite will be synthesized via silane assisted self-assembly approach. We will conduct a series of experimental and theoretical studies to determine the reaction mechanism and understand the shape selectivity. Through comparison of kinetic models between conventional microporous and hierarchical porous zeolitic catalysts, the diffusion-reaction interplay will be clarified. Moreover, further experiments will be conducted to verify the model and optimize the conditions for the catalytic benzene methylation reaction.

TNU-9分子筛结构的十元环孔道网络对反应物和产物分子具有择形作用，交叉处的十二元环状空腔则为双分子反应中的大体积过渡态分子提供了生成空间，在催化过程中显示出与ZSM-5截然不同的独特择形机制和产物选择性。针对催化苯-甲醇烷基化反应中对二甲苯选择性受热力学平衡限制，本项目拟以苯-甲醇烷基化高选择性地获得对二甲苯为目标，通过硅烷自组装法定向设计多级孔TNU-9分子筛，研究在此分子筛上苯与甲醇烷基化反应的动力学。并结合外表面修饰技术提高对二甲苯选择性。理解分子筛结构对产物分布的影响机制并据此设计新的高效催化体系，是提高对二甲苯收率的关键。通过理论模拟与实验相结合，在明确反应机理和择形机制的基础上，建立动力学方程；进而基于多级孔道TNU-9分子筛的择形机制和传质特点，通过对比动力学参数加以量化，明确其中的传质和反应速率与产物分布的规律。利用动力学模型指导设计具有高活性和选择性的催化体系。

苯-甲醇经过催化烷基化制备高附加值的甲苯、二甲苯，对于降低汽油中的苯含量、缓解对二甲苯供不应求的现状具有重要现实意义。反应过程中，提高对二甲苯的收率对于全局经济性至关重要。针对催化苯-甲醇烷基化反应中对二甲苯选择性受热力学平衡限制进行课题研究。在TNU-9合成方面，实现纳米级分子筛及多级孔分子筛的可控化合成，将TNU-9分子筛应用于苯-甲醇烷基化反应中进行考评，苯转化率可达54%，甲苯-二甲苯选择性94%。通过调变有机模板剂配比，实现铝落位可控化ZSM-5分子筛合成。通过苯-甲醇烷基化反应机理研究，获得了不同铝落位分子筛对提高对二甲苯选择性的择型效应。研究结果：“多级结构分子筛催化剂及其工业应用”获2020年上海市科学技术发明二等奖，并在国内外杂志上发表论文16篇。