微波下纤维素催化转化的原位红外研究

Diminishing petroleum reserves and growing concerns about global climate change necessitate the development of fuel production pathways based on renewable resources. The conversion of biomass to liquid fuel and chemicals is an effective way to solve energy crisis and to eliminate environment pollution. The research about the pyrolysis of biomass with microwave did not yet probe the reaction nature in the viewpoint of atom or molecule. The results of our prophase test showed that the main composition of liquid product of pyrolysis of biomass by catalysts with microwave is furfural (above 80%). In this project we design a pathway to get gasoline or diesel from cellulose via the intermediate 5-hydroxymethylfurfural with the synergistic effect of catalysts and microwave. We design and set up a new kind of in situ microwave reaction infrared spectrophotmeter cell. Using this in situ cell, active center and surface absorption specie of catalysts, reaction intermediate specie and structure will be investigated by in situ infrared spectroscopy. We shall systematically investigate the micro mechanism of cellulose for catalytic pyrolysis with microwave by means of in situ infrared spectroscopy, vector network analyzer and XPS. The project mainly study on the relationships among reactant molecular structure-dielectric-reaction properties, especially on the synergistic effect between microwave and catalysts in order to provide theoretical basis for molecular tailoring in the conversion of biomass. Using the optimal parameters of test for microwave reaction tube, position in stove, the size of raw, the feed rate, and the gas rate in project, we shall design and build a small movable microwave reactor to solve the problem of biomass centralized treatment.

通过生物质转化有望解决石油能源短缺和环境污染两大世界难题。已有生物质微波裂解的报道，但均没能从原子、分子水平上探索该反应的本质。已有研究结果表明，纤维素在适当条件下可生成重要的平台化合物5-羟甲基糠醛（HMF）,HMF是制备下游生物质燃料和化学品的重要中间体。故此，我们拟以纤维素裂解为探针反应，探索在微波与催化剂协同作用下，经由如HMF等中间化合物制备汽油、柴油高品质液体燃料途径。本课题设计并组装微波原位红外反应池，原位探测催化剂活性中心、催化剂表面吸附态结构、反应中间物种及结构等信息，并结合矢量网络分析仪、XPS等表征手段，从微观角度详细研究纤维素微波催化裂解的反应机理，重点阐述结构-介电耗散-性能之间的关系，特别是微波与催化剂之间的协同效应，为实现生物质选择性转化提供理论依据。

为研究纤维素转化为5-HMF机理，探索其反应的内在规律，设计并组装了微波原位红外反应器，并通过GC-MS，紫外、高效液相色谱等对反应进行表征，寻找绿色、廉价的生物质转化路线，以达到制备高品质液体燃料的目的。所做工作和结果如下：..（1）通过对磁控管发射微波进行分流，达到对微波功率的控制的目的，解决样品很快变黑及反应与收集信号同步的问题。..（2）提出基于Origin的Gaussian拟合法对紫外分光光度计测定5-羟甲基糠醛（5-HMF）和糠醛（FUR）混合物吸收峰进行分峰拟合，使低廉的紫外分光光度计可用于定量分析5-HMF和FUR混合物。..（3）纤维素转化新体系筛选：.在离子液体中纤维素转化成5-HMF有较好的产率。但使用离子液体，其合成过程复杂，价格昂贵，分离产物技术困难，并且对环境的污染严重。.本项目组遵循绿色、可持续发展的原则选择反应体系。.氯化锌溶液：ZnCl2价格便宜，污染小，配制其水溶液简单、方便。实验发现微波下，ZnCl2浓溶液中，纤维素可有效转化成5-HMF。..（4）纤维素转化反应研究：.1）以脱脂棉为纤维素原料：.a) ZnCl2水溶液中SnCl4催化反应：.在70 wt% ZnCl2水溶液中，优化条件下，SnCl4为催化剂的产率达39.4%。与无催化剂的ZnCl2溶液体系相比，5- HMF的产率明显提高。且HCl有助催化作用。..b）ZnCl2溶液和DMAc有机溶剂混合体系，SnCl4催化下5-HMF产率为44.3%，表明有机溶剂对生成5-HMF有利。..2）稻壳为原料.稻壳在氯化锌溶剂，氯化镍催化剂，在微波下转化为5-HMF，产率15.8 %，比脱脂棉原料的5-HMF产率低。.为提高5-HMF产率，须对稻壳进行预处理。研究发现，用稀碱溶液对稻壳进行预处理，5-HMF产率有明显提高。..（5）LiBr水与DMAc混合溶剂体系：.在本反应体系下，经优化工艺条件，5-HMF产率高达58.4 %，已与离子液体体系相近；且无FUR生成。如加入合适催化剂，5-HMF产率将进一步提高，值得下一步研究。..（6）反应机理研究：.本课题纤维素转化反应体系中，FUR是由5-HMF进一步反应产生的。