核壳结构ZSM-5/MCM-35分子筛的可控合成及其对MTP反应空间限域效应研究

Methanol to propylene (MTP) is one of the important ways to obtain propylene from non-petroleum route. However, due to the intrinsic pore structure and abundant acid sites in external surface of the ZSM-5 catalyst, this process still has some disadvantages, such as low propylene yield and short catalyst lifetime. In this proposal, the core-shell ZSM-5/MCM-35 zeolite with pure silica MCM-35 shell will be prepared by using secondary growth method. The spatially confined effect of core-shell ZSM-5/MCM-35 zeolite will dramatically change the products distribution in MTP reaction to enhance the yield of propylene, meanwhile, the introduction of MCM-35 shell can shut down the secondary reaction of the products by covering the acid sites in external surface of core ZSM-5 to extend the catalyst lifetime. The control principle of the coverage degree and the thickness of the MCM-35 shell will be revealed by optimizing the synthesis conditions. The spatially confined effect of core-shell ZSM-5/MCM-35 zeolite on the products distribution in MTP reaction will be systematically studied by analyzing the results of the micro-reactor evaluation and the characterization of the zeolite to explore the structure-activity relationship. A detailed study of the carbon deposition behavior and reaction regeneration performance of the zeolite will be conducted. The results obtained in this project will lay a theoretical foundation for developing new MTP catalyst with excellent performance.

甲醇制丙烯（MTP）是从非石油路线获得丙烯的重要途径之一，然而，由于ZSM-5催化剂本征孔道结构和过多外表面酸性位的原因，该过程仍存在丙烯的收率较低和催化剂寿命较短的问题。本项目拟采用二次生长法在ZSM-5分子筛的表面构建纯硅MCM-35壳层结构，制备核壳ZSM-5/MCM-35分子筛，在MTP反应中实现对反应产物空间限域择形，提高丙烯收率，同时覆盖ZSM-5分子筛的外表面酸性位，防止产物通过二次反应在分子筛外表面产生积碳，延长催化剂寿命。通过控制合成条件，探究壳层在核相上包覆度和厚度的调控规律；通过微反评价和色谱产物分析，结合分子筛的表征测试结果，研究核壳分子筛纯硅MCM-35壳层的空间限域效应对MTP产物分布的影响规律，探明构效关系；研究积碳失活行为以及反应再生性能；为设计性能更加优异的MTP催化剂奠定理论基础。

甲醇转化制丙烯（MTP）反应过程因其原料甲醇可以由合成气制备得到，而合成气又可广泛地从煤、生物质、天然气和固体废物中获到，被认为是具有前景的非石油路线制烯烃工艺过程之一。但该过程仍存在丙烯的收率较低和催化剂寿命较短的问题。从甲醇制烯烃的反应机理角度入手进行分析，甲醇在分子筛的活性中心上生成小的烯烃分子后，由于ZSM-5分子筛本征孔道结构和过多的外表面酸性位的原因，满足烯烃分子可以继续发生聚合反应以及芳构化反应的条件，使得烯烃尤其是丙烯的选择性大大降低。本研究在ZSM-5分子筛的外表面通过二次生长法覆盖一层纯硅的MCM-35分子筛制备出核壳ZSM-5/MCM-35分子筛，实现了ZSM-5表面酸性位的覆盖，有利于抑制在外表面上发生的副反应，防止催化剂过快积炭失活，而且MCM-35的较小的孔道将起到明显的空间限域作用，有利于低碳烯烃选择性的提高。本项目首先分别制备了高硅铝比和小晶粒核相ZSM-5分子筛；并探索了半纤维素改性的ZSM-5分子筛的合成制备；合成制备出了壳层MCM-35壳层分子筛，进而采用二次生长法制备核壳ZSM-5/MCM-35分子筛，考察了制备条件对所制备核壳分子筛的物化性质的影响，进而在固定床反应器上评价其MTP催化反应性能，实验结果表明核壳ZSM-5/MCM-35分子筛比核相ZSM-5分子筛具有更长的反应寿命以及更高的丙烯性选择性，这为设计性能更加优异的MTP催化剂奠定了理论基础。