多功能石墨烯催化纤维素双相连续反应一锅法合成二甲基呋喃的研究

Converting readly available and renewable cheap cellulose to high quality biofuel dimethylfuran (DMF) has the potential to reduce societal dependence on fossil-carbon based energy. For this multi-step chemical reaction, however, processes involving a number of catalysts and multi complicated conversion and separation steps will have poor overall economics and viability. Therefore, development of effective multifunctional catalysts and facilitation of the multi-step conversion processes is the key of this cellulosic biofuel production.In this project, some new research ideas and methods are proposed for the reaction taking advantages of the new carbon nano material, graphene. Effective graphene-based multifunctional catalysts will be designed and developed for the purpose of the integration of multiple catalytic functions and the improvement in the catalytic performance of the catalysts. Furthermore, a biphasic continuous conversion system is to be established based on the hydrophilicity or hydrophobicity of the catalysts, the feed and the intermediates of each reaction step, and also on the basis of the higher solubility of H2 in the polar solvent than in the non-polar solvent, in which the continuous reactions from "cellulose → glucose → fructose → HMF" in the hydrophilic phase to "HMF → DMF" in the hydrophobic phase are carried out. The research results will generate previous information for the improvement of multifunctional catalysts and the optimization of complex reaction systems, and will also provide a possibility to realize the one-pot conversion of cellulose to DMF.

采用丰富廉价的可再生资源纤维素合成性能优良的生物燃料2,5-二甲基呋喃(DMF)有利于减轻人类对化石燃料的依赖性。然而，对于这个涉及多个催化功能和多个转化步骤的反应，复杂的催化剂体系和繁琐的制备工艺大大降低了规模化生产的可操作性和经济效益。因此开发出多功能固体催化剂和简化反应流程是其研究的重点。本项目拟充分发挥新型碳纳米材料石墨烯的优势，为该反应构建环境友好石墨烯催化剂，实现催化剂多项功能一体化和各步催化反应的高效转化，并进一步利用催化剂、反应物和各步中间产物亲水性/疏水性的差异以及氢气在极性/非极性溶剂中溶解度的差异，建立从亲水相到疏水相连续催化转化的反应体系，实现从亲水相"纤维素→葡萄糖→果糖→5-羟甲基糠醛（HMF）"到疏水相"HMF→DMF"的连续反应。研究结果为构建复杂反应体系催化剂和简化反应流程提供理论依据，为提高纤维素制DMF催化反应性能和实现其一锅法转化提供可能。

本项目针对高浓度葡萄糖转化中5-羟甲基糠醛（5-HMF）收率低、5-HMF产物难从反应溶剂中分离和合成2,5-二甲基呋喃(DMF)类生物燃料时能耗高收率低的问题，开展了应用基础探究。首先研究了高浓度葡萄糖在含有CrCl3催化剂的1-丁基-3-甲基咪唑氯化盐离子液体([BMIM]Cl)中转化成5-HMF 的反应。研究发现，增加 [BMIM]Cl/CrCl3 反应体系中葡萄糖的浓度会导致 5-HMF 的收率降低。采用有机溶剂和水对离子液体进行调制，以乙二醇二甲醚（GDE）为萃取相、以溶解了一定量GDE和水的[BMIM]Cl/CrCl3为反应相, 所调制的“离子液体——GDE——水”三元双相溶剂体系在高浓度葡萄糖转化中取得了很好的效果。在[BMIM]Cl-GDE-H2O 三元双相体系中，高浓度葡萄糖（占离子液体80 wt%）在CrCl3催化作用下生成5-HMF 的收率达到 64.5 mol%，该值约为纯[BMIM]Cl溶剂体系收率的2倍。此外，所生成的5-HMF约有56%被萃取到GDE相中。GDE 在该溶剂体系发挥了多种功能: 作为氢键受体它对5-HMF体现出很高的萃取能力；在反应过程离子液体相中的GDE不断地鼓泡，显著提高了5-HMF在相际间的传质速率，同时GDE还降低了离子液体相的黏度。此外，适量的水在离子液体相中会促进5-HMF的萃取，同时也降低了离子液体相的黏度。为了提高5-HMF萃取率，还开展了助剂调制促进5-HMF萃取分离的研究。通过分析甲基异丁基酮（MIBK）对[BMIM]Cl中5-HMF、糠醛、糠醇的萃取特性，发现5-HMF与[BMIM]Cl之间的氢键作用是导致5-HMF难被萃取的主要原因。尝试了用其他氢键授体，如乙醇，来替代5-HMF与[BMIM]Cl 成键，从而减缓离子液体对5-HMF的束缚，方便萃取。例如, 当用乙醇作为萃取助剂， MIBK从离子液体萃取5-HMF的分配系数提高了10倍。另外，我还首次研究了5-HMF与异丁烯的醚化反应，开发了温和条件下高效制备生物燃油添加剂的合成路线。研究成果在Green Chemistry，Industrial & Engineering Chemistry Research，Catalysis Science & Technology和RSC Advance 期刊上发表了5篇论文。