纳米晶原位自组装合成多级孔SAPO-34/天然硅铝矿物复合材料的研究

SAPO-34 is considered an effective catalyst of the methanol to olefin (MTO) process, the most important non-oil alternative way to fill the worldwide supply-demand gap for light olefins. However, commercial SAPO-34 based catalysts have two drawbacks: (1) the exclusively presence of micropores in conventional SAPO-34, which favors the selectivity to light olefins including ethylene and propylene, but imposes severe limitations for mass transfer and thereby gives rise to rapid deactivation; (2) their preparation via the spraying-drying of the mixture of pre-synthesized SAPO-34 powder and a binder (usually alumina sol), which causes the formation of excessive acid sites and the blockage of micropores in SAPO-34 because of the involvement of the alumina binder and consequently gives rise to the depressed selectivity to olefins and the decreased accessibility of active sites in SAPO-34; and (3) their semi-synthesis nature, which gives the resulting catalyst with weaker interaction between SAPO-34 and the binder and thus poorer resistance to attrition and lower stability to steaming at high temperature. Herein we combine in situ synthesis with the nanocrystalline self-assembly technique to prepare hierarchical SAPO-34/aluminosilicate composites directly from activated aluminosilicate microspheres such as kaolin microspheres, without employing any mesopore template or mesopore-generating agents such as organosilanes. The effects of chemical composition, phase structure and the activation methods of aluminosilicate microspheres as well as the synthesis conditions on the physicochemical properties including pore structure, morphology and acidity of the resultant SAPO-34 composites will be investigated. The mechanism of the formation of nanocrystalline and its in-situ assembly on the surface of the aluminosilicate microspheres will be investigated and the hydrothermal stability and the selectivity of light olefins of the resulted SAPO-34/aluminosilicate composites as MTO catalysts will be evaluated.

甲醇制低碳烯烃(MTO)是由煤或天然气经甲醇制取乙烯、丙烯等的重要过程，其关键是开发具有高低碳烯烃选择性、优异水热稳定性和良好抗磨损性能的催化剂。本项目针对目前SAPO-34基MTO催化剂存在的SAPO-34分子筛孔径较小、结焦失活快以及采用“半合成”方法所得催化剂孔道结构不合理等问题，拟将原位晶化技术与纳米晶自组装技术相结合，发展高岭土等天然硅铝矿物微球的可控活化方法，揭示SAPO-34/天然硅铝矿物复合材料制备过程中纳米晶的形成和自组装机理，以可控活化的天然硅铝矿物微球作为基质和SAPO-34分子筛合成的硅铝源，在不添加介孔模板剂、不使用有机硅烷的条件下，制备出具有大-介-微多级孔道结构的SAPO-34/天然硅铝矿物复合材料，为新一代MTO催化剂的设计制备提供理论基础和技术源头。

甲醇制烯烃(MTO)是由煤或天然气出发经过甲醇或二甲醚制备乙烯、丙烯等低碳烯烃的可以替代石油路线的最可行的方法。项目针对目前工业上MTO催化剂所用的SAPO-34分子筛只具有微孔结构、导致其极易失活且目前都是采用 “半合成”方法制备易造成粘结剂堵塞分子筛孔道，基质与分子筛孔道不连通等弊端，(1)首先选取两种具有不同硅铝比的高岭土微球，分别考察了焙烧温度对两种高岭土微球组成、结构及活化效果的影响，并以两种焙烧高岭土微球为原料合成了SAPO-34@kaolin复合催化材料，研究了高岭土微球硅铝比和焙烧温度对所制备的复合材料中SAPO-34分子筛含量及孔结构的影响，获得了可控活化高岭土微球的方法；(2)针对上述原位合成产物中SAPO-34含量低、粒径大且一般仅具有微孔结构的问题，提出将介孔SAPO-34分子筛的合成与原位纳米晶组装技术相结合，在原位合成SAPO-34的凝胶中引入表面活性剂CTAB和TPOAC，成功制备了SAPO-34含量高、晶粒小且具梯级孔的SAPO-34@高岭土微球复合材料，并阐明了纳米晶自组装及多级孔产生的机理：在原位晶化过程中，CTA+与带负电的KMS发生静电相互作用，抑制了活性硅铝物种从高岭土微球向液相中的溶解，有效促进了SAPO-34在高岭土微球上的原位生长，抑制了非原位产物的形成，且CTA+通过静电作用吸附在带负电的SAPO-34前驱体表面，抑制了SAPO-34分子筛晶粒的生长；而TPOAC的无机硅端与磷酸、活性铝和模板剂相互作用，促进SAPO-34分子筛前驱体的生成，而有机端则导向SAPO-34分子筛中介孔结构的形成，同时TPOAC通过静电作用吸附在SAPO-34分子筛前驱体表面，进而进一步抑制SAPO-34分子筛晶粒的生长，并形成介孔结构；所得梯级孔SAPO-34@高岭土微球复合材料用于MTO催化剂，其双烯选择性高达84.3%，催化寿命长达340 min，展现出良好的工业应用前景；(3)有机融合ZSM-5分子筛的晶种辅助合成法与SAPO-34分子筛的原位合成方法，成功制备出兼具MFI和CHA拓扑结构的SAPO-34/ZSM-5@高岭土微球复合材料, 并且通过调变复合材料中SAPO-34和ZSM-5的质量比，可以调变其用于MTO反应的反应路径，从而调变MTO反应的产物分布。