芳烃异构化中烷基的定向转移与分子筛催化剂结构精准调控

The transalkylation of aromatics is an important reaction for the production of aromatic-based bulk chemicals. The key problem always perplexes the catalysis field is how to control the catalysts structure for the directed transalkylation and achieve higher selectivity for the target products. This project aims at the isomerization of dimethylnaphthalene (DMN) to produce the high-end polyester monomer 2,6-DMN. The nano co-crystalline zeolite containing the MTW-type 12-membered ring, which show excellent selectivity for 2,6-DMN, would be created in experiments. The density functional theory calculations will also be performed for the investigation into the crystallization process, grain boundary structure and acid properties of the zeolites. The thermodynamic parameters and kinetic mechanisms for the ion-exchanged zeolites catalyzed isomerization of DMN will be calculated for guiding the ion-exchange experiments. Silanes will be used for the decoration of the zeolites surface and the opening to prohibit the reverse reaction of the DMN isomerization reaction. The modulation mechanism of the zeolites acidity and pore structure will be elucidated. The reaction pressure and temperature conditions will be predicted on the basis of theoretical calculation, for guiding the evaluation of the prepared catalysts with fixed-bed reactor. The relationships among the preparation methods, structures, and catalytic performances of the zeolites catalysts will be found on the basis of comprehensive analysis of the experimental and theoretical results. The matching principles of the acidity and pore structure for the DMN isomerization to 2,6-DMN will be elucidated. This project will provide theoretical support for the developments of industrial catalysts for the directed transalkylation of alkylnaphthalenes, and lay foundations for the value-added utilization of byproducts of coal conversion and petrochemical industry.

芳烃烷基转移反应是制备芳基大宗化学品的重要反应，如何通过调控催化剂结构使烷基定向转移生成目标产物，实现更高催化选择性始终是催化界面临的关键问题。本项目以二甲基萘（DMN）异构化制高端聚酯单体2,6-DMN为目标反应，创制对2,6-DMN有优异择形性的含MTW结构12元环纳米共晶分子筛，结合密度泛函理论计算，研究分子筛晶化机制、晶界结构及酸性特征等；计算离子改性分子筛催化目标反应的热力学参数及动力学机理，指导分子筛改性实验，并采用硅烷对分子筛外表面和孔口进行修饰以抑制拟异构化副反应，阐明分子筛酸性与孔道结构的调变机制；基于理论模拟推算适宜的反应压力与温度条件指导固定床反应器上催化剂评价，以期构建分子筛催化剂制备方法-结构-性能之间的关系，提出适宜DMN异构化反应的分子筛酸性与孔结构匹配原则，为开发萘系芳烃烷基转移的工业催化剂提供理论支撑，为煤转化及石油化工副产化学品的增值利用奠定基础。

2,6-二甲基萘（2,6-DMN）是重要高端聚酯单体，目前由于2,6-DMN的生产技术导致的其产能不足，严重影响了下游聚酯产业的发展。目前制备催化2,6-DMN主要难点在于目标产物选择性低，原因在于二甲基萘有十种同分异构体，导致其较难实现高效择形的催化反应；本项目研究2,6-DMN高效择形催化剂，通过理论模拟的方法研究分子筛活性位的微观结构、金属离子改性对酸性位的影响，萘系分子在分子筛中的扩散能垒等，发现金属离子掺入分子筛骨架会影响骨架稳定性，分子筛骨架中金属离子的半径是影响分子筛稳定性的关键因素；金离子改性对分子筛能将分子筛的B酸改成L酸，并有利于活化反应分子，比较萘系分子在一系列分子筛孔道中的扩散能垒发现SAPO-11分子筛孔道对2,6-DMN有较好的择形效果。实验上创制纳米共晶分子筛，利用共晶分子筛优于单相分子筛的特有的的酸性和孔道结构，并通过离子改性、硅沉积等技术，并在分子水平调控纳米共晶分子筛催化剂的活性位和孔道结构，发现共晶分子筛的择形效果优于单相的分子筛，金属离子改性对提催化高活性和择形效果有利；硅沉积能提高择形效果，但是会降低原料转化率。优选的分子筛催化性能在反应7 h时2,6-DMN选择性可以达到46%，2,6-/2,7-DMN比可达到2.04；本项目为开发2,6-DMN制备的工业催化剂提供理论和基础数据支撑。