应用于生物质/甲醇耦合热解制轻质芳烃的多级孔ZSM-5的构筑与调控机理

Producing BTX (benzene, toluene and xylenes) through catalytic fast pyrolysis of biomass is one of the most promising technologies for achieving value-added utilization of biomass resources.Three critical problems facing catalytic fast pyrolysis of biomass are low yield of BTX, low selectivity to xylenes and significant coking resulting in the rapid deactivation of the catalyst. In order to address these challenges, constructing hierarchical ZSM-5 zeolite with microporous/mesoporous structure is proposed for selectivity tuning in coupling catalytic pyrolysis of biomass and methanol towards BTX production. The obtianed ZSM-5 is subsequently modified by metal species for preparing metal(or lewis acid)/ZSM-5 bifunctional catalyst. These catalysts could strengthen the MTO(methanol-to-olefins) reactions, the Diels-Alder reactions of furans and olefins, and the alkylation reaction of toulene and methanol for enhancing BTX yield, the selecitivity to xylenes and the suppression of coke formation.The effect of preparation method of hierarchical ZSM-5 (hydrothermal synthesis, pretreatment using alkali or acid and pretreatment using steam), metal species and method of modificaton on its specific surface area, pore structure, surface acidity, and its subsequent impact on BTX yield and selectivity in coupling catalytic pyrolysis of biomass and methanol, are systematically analyzed. Combined with its reaction kinetic and mechanistic insight, the relationships between catalyst structure and its catalytic performance are established and discussed. These studies can provide theoretical basis for effecitve converting biomass into aromatic production.

通过生物质催化快速热解制备苯、甲苯和二甲苯等轻质芳烃是实现生物质高值化利用的重要途径。针对目前生物质催化热解存在的关键问题：轻质芳烃收率低、催化剂易积碳失活和二甲苯选择性低，本申请基于生物质/甲醇耦合催化热解体系，构筑具有合理微孔/介孔分布的多级孔ZSM-5分子筛，并对分子筛进行改性，获得金属（或Lewis酸）/多级孔ZSM-5双功能催化剂，强化耦合热解中甲醇制烯烃、生物质热解中间产物呋喃衍生物与烯烃的Diels-Alder加成、以及甲苯甲醇烷基化等一系列反应，以提高轻质芳烃收率和二甲苯选择性并抑制积炭的产生。系统考察多级孔ZSM-5的构筑方法（直接水热合成、酸碱预处理和水热预处理）、改性物种和改性方法与其比表面积、孔结构和内外表面酸性等因素对生物质甲醇耦合热解产物分布的影响，结合反应动力学和反应机理研究，建立催化剂构效关系，为实现生物质高效制取轻质芳烃提供理论基础。

生物质是通过非石油路线制取芳香烃的重要途径。针对生物质单独催化热解存在的轻质芳香烃收率低和积碳严重等关键问题，本项目提出生物质和甲醇耦合热解的反应体系，通过耦合热解协同作用机制指导构建高效金属和多级孔ZSM-5分子筛催化剂，以实现生物质高效催制取轻质芳香烃。本项目首先利用有机酸预处理对生物质三组分（纤维素、木质素和半纤维素）进行分离和解耦热解研究，发现有机酸可以实现三组分的高效解离，解离组分的解耦热解可以实现定向制取左旋葡聚糖和苯酚类化合物，并基于此提出了生物质解耦热解机理，为深入了解生物质三组分催化热解机理提供了理论基础；系统研究了生物质三组分在ZSM-5分子筛上催化热解制取轻质芳烃的机理，提出生物基呋喃是半纤维素和纤维素组分催化热解的重要中间产物；探讨了烘焙预处理对生物质三组分催化热解制取芳香烃的影响规律；以生物基呋喃作为生物质的模型化合物和甲醇进行耦合催化热解，通过系统研究揭示了耦合催化热解的协同作用机制；最后构建了不同金属改性双功能ZSM-5催化剂和不同碱预处理得到的多级孔ZSM-5分子筛催化剂，通过催化剂构效关系的研究提出具有Lewis酸性的金属活性位及Brønsted酸活性位双功能多级孔ZSM-5催化剂是设计高效生物质和甲醇耦合催化热解催化剂的关键。本研究为生物质催化热解制取芳香烃提供了坚实的理论基础和技术支撑，对于未来生物质的高效和高值化利用具有重要意义。