Studies on conversion of biomass-based materials into HMF-derived chemicals
Date of Issue2017-02-23
School of Chemical and Biomedical Engineering
The demand for energy and resources of the world now outstrips the earth’s ability to meet. With the decreasing of fossil fuel resource and serious environmental pollution caused by the overuse of fossil fuel, biomass energy has attracted more and more attention. As an important solution to the shortage of energy and resources, biorefinery can integrate biomass conversion process to produce energy and chemical building blocks for a diverse range of applications. Among the various renewable building blocks, 5-hydroxymethylfurfural(HMF) plays an important role due to its rich chemistry and potential availability. It can be obtained from monosaccharides such as fructose, glucose, as well as cellulose directly. Moreover, HMF can also be used to produce many valuable molecules such as levulinic acid, dihydroxymethylfuran, 2,5-furandicarboxylic acid, 2,5-diformylfuran (DFF) and 5-hydroxy-4-keto-2-pentenoic acid. Here, the catalytic transformation of fructose to HMF and its derivates are the study focus. Considering the separation of products and reuse of catalysts, heterogeneous reaction system with carbon-based solid catalysts was designed and applied in the conversion of fructose to HMF and DFF. Dehydration of monosaccharides is the main method for the manufacture of HMF. Carbon spheres bearing high stability, low cost and abundant strong protonic acid sites were used as catalyst. The carbon spheres were prepared through a facile hydrothermal method with glucose as the carbon precursor. And then sulfonation treatment was used to increase the amount and strength of the acid sites on the surface of the carbon spheres. The carbon spheres based solid acid showed excellent performance in the dehydration of fructose to HMF. The influences of acid site density, reaction time, solvents, catalysts amount, temperature and mole ratio of catalyst to substrate were investigated. Under optimized conditions, 90% yield of HMF was obtained with 100% fructose conversion in only 1.5h at 160oC. DFF, which is an important monomer for industry can be synthesized by the selective oxidation of hydroxyl group of HMF. Vanadium-embedded mesoporous carbon microspheres were synthesized and applied in the aerobic oxidation of HMF to DFF, showing almost 100% selectivity towards DFF. The catalytic activity of the initially prepared vanadium-embedded carbon solid spheres is not ideal due to the limit contact chance between the reactant and the active site. However, after the introduction of mesoporous structure into the carbon sphere, the activity of the catalyst increased remarkably. But there was a slight decrease of the catalytic activity during the recycling test due to the leaching of the active sites. Based on the successful synthesis of HMF and DFF through dehydration of fructose and selective oxidation of HMF respectively, molybdenum trioxide supported on carbon spheres were prepared and used as bifunctional catalysts for the one-pot and one-step conversion of fructose to DFF. The catalysts were prepared with a similar method as the vanadium-embedded carbon spheres. Different after-treatment methods were used to modify the physiochemical properties of the catalyst in order to achieve the best DFF yield. As a result, 77% DFF yield and 100% fructose conversion can be obtained under optimized conditions. The component, morphology and structural properties of the catalysts were characterized by many techniques such as X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, Element analysis, X-ray absorption near edge structure, Thermo gravimetric analyzer and so on. Different reaction conditions were investigated to reach the highest yield of target product. In addition, the reusability of the catalysts was also tested.