核壳型介-微孔分子筛催化热解木质纤维素类废物转化为高品位生物油的机理研究

The catalytic fast pyrolysis (CFP) of biomass is one of the most promising utilization technologies to produce valuable liquid fuels. However, the biomass CFP has not been taken up commercialization. One of the biggest obstacles is the deactivation of catalysts by coke deposition, which significantly impact the production of desired aromatic hydrocarbons. Because the product distribution in biomass CFP is largely dependent on the choice of zeolite catalysts, in this project, we will investigate the application of micro/mesoporous core-shell zeolites as catalysts in the CFP of lignocelluosic biomass. Firstly, a series of micro/mesoporous core-shell zeolites will be designed with tunable hierarchical channels and acidity. During biomass CFP, the characteristics, generation features, and distributions of constituents in bio-oil will be studied, and the conversion route from biomass to bio-oil will be constructed. Later, the effects of the well-connected micro/mesopores and gradient-distrubuted acidity on the pyrolysis path of biomass will be investigated. This, plus with the study of coke deposited on catalyst, will be integrated for the interpretation of the pyrolysis mechanism of biomass. Based on the integrated reaction path from biomass, the theoretical regulatory mechanism towards the desired aromatic hydrocarbons will be constructed, and the catalyst can be further tuned to realize the inductive effect. Hopefully, the coke formation will be prohibited and the quality of bio-oil will be significantly improved. This study will lay a solid foundation for the conversion of lignocellulosic biomass to high grade bio-oil.

生物质催化热解可将固体生物质转化为高值液体燃料，实现生物质废物的资源化利用。然而，生物质热解过程中结焦非常严重，限制了生物质原料向目标产物的高效转化，成为生物质催化热解大规模应用的瓶颈。本项目拟以沸石催化剂的优化改性为切入点，构建系列核壳型介-微孔复合分子筛催化剂，可控调变其多级孔道结构和核/壳酸分布，在最优热解条件下探索油相产物中主要成分的产物特征、生成特性及分布规律，探索生物质催化热解的主要反应路径。揭示催化剂联通性良好的表面介-微孔孔道与外弱内强的梯度酸分布对生物质热解历程的影响，结合积碳的特性和形成机理，完整阐述木质纤维素类生物质废物的催化热解机理。在此基础上明确特定高值目标产物(如烃类)的理论调控机制，通过进一步优化催化剂实现目标产物的定向诱导调控，在提高生物油品位的同时抑制结焦，为木质纤维素类生物质废物定向转化为高品质生物油的资源化利用提供更多的理论依据。

针对当前木质纤维素类生物质废物热解制备的生物油品位低、烃类化合物选择性差的问题，本项目以传统催化剂的优化改性为突破口，构筑系列介-微孔核壳复合分子筛并证实其在生物质废物能源转化的高效催化作用，同时阐明了分子筛催化剂的结构与生物油品位间的构效关系。本项目按要求完成了相关研究任务，在以下几个方面取得了创新性的成果：（1）集成多种催化剂构筑双床催化热解工艺，系统研究了金属氧化物、无机盐、分子筛作为第一床催化剂时与ZSM-5第二床催化剂的组合效果。研究证实多级催化热解的设计可有效提高生物质的转化率，且分子筛（如SBA-15,Beta）+ZSM-5的梯级孔催化剂组合可同时提高生物油的产量及烃类选择性；（2）设计合成系列核壳型介-微孔复合分子筛ZSM-5@SBA-15,并在多种固定床热解装置中证实：相较于传统的ZSM-5沸石，核壳型催化剂可显著减少焦的形成并将生物油中烃类产量提高3.1倍。（3）基于ZSM-5@SBA-15的外壳厚度和核/壳酸分布对热解产物的影响，结合催化剂表征结果，揭示了生物质在核壳型催化剂上的主要反应路径，并得出热解催化剂的设计需满足：减少外表面酸位点的同时保留微孔内酸位点、增强表面介孔与微孔的联通性。（4）设计合成满足如上结构特征的中空分子筛催化剂（ZSM-5和ZSM-11)，并在玉米秸秆的催化热解中验证了分子筛结构与生物油品位间的构效关系。以上研究成果为生物质催化热解催化剂的设计和优化提供了实验依据，也为木质纤维素类生物质废物定向转化为高品质生物油的资源化利用提供更多的理论依据。