Catalytic Dehydration Of Glucose Into 5-HMF By Metal-Organic Framework

5-HydroxyMethylfurfural (5-HMF) is an important biomass-based platform chemicals, which can be used to prepare more than 1500 kinds of high value added products. Metal-organic frameworks (MOFs), owing to its adjustable structure and designable catalytic sites, show great potential in catalysis. Most traditional methods for 5-HMF production are complicated and cost-inefficient because they require combination of different catalysts and equipments.In order to overcome this shortcoming, in this dissertation, a bi-functional catalyst MIL-101(Cr)-SO3H containing both Lewis acid and Bronsted acid sites was synthesized to investigate the catalytic glucose dehydration for 5-HMF preparation. It was applied for y-valerolactone-mediated cascade reaction of glucose dehydration with a HMF yield of 46% and selectivity of 47%. In this work, we optimized the reaction conditions, and studied the solvation effect and reaction mechanism. Furthermore, a fixed-bed reactor was also established to explore the potential from an industrial point of view. This paper presents a sustainable and green process for catalytic dehydration of biomass-derived carbohydrate to HMF with a bi-functional metal-organic framework.Firstly, a kind of Cr-terephthalates metal-organic frameworks functionalized with sulfonic acid (-SO3H) groups [denote as MIL-101(Cr)-SO3H], containing Lewis acid site and Br(?)nsted acid site, were synthesized by solvothermal reaction. These catalysts were characterized by analysis techniques including PXRD, EDX, SEM, ICP-AAS, FT-IR, BET surface area analysis et al, Their catalytic performances were investigated on glucose conversion to 5-HMF in different solvents with varied catalysts quantity and get the optimal yield under the reaction conditions:GVL:H2O (9:l,v/v) solution, and equal amount of catalyst and reactant.Secondly, the influence of different reaction solvents on the reaction was investigated, and the reaction mechanism was discussed.The kinetic data of glucose dehydration catalyzed by MIL-101(Cr). H2SO4、MIL-101(Cr)-SO3H show that the Lewis acid site Cr3+ of MIL-101(Cr)-SO3H played a key role in glucose and fructose isomerization. Two glucose molecular contacted with the Cr(III) lewis acid and the hydrogen shift between the Cl and C2 happened, while the Bronsted acid site-SO3H played vital roles in the fructose dehydration. Reaction kinetics suggested that the glucose isomerization in GVL with 10 wt% water follows the second-order kinetics with an apparent activation energy of 100.9 kJ mol-1, with a slight decrease compared to the reaction in water, whose activation energy is 114.0 kJ mol-1. And it made it easier to synthesize the 5-HMF. The product is more stable in GVL with 10 wt% water and it will reduce the possibility of side reaction, resulting in the increased yield of HMF up to 46%. The diffusion rate of the glucose molecular is 200 times larger than glucose isomerization, implying the glucose isomerization becomes the key step in this process.Thirdly, the effect of different ratios of Lewis/Br(?)nsted on the 5-HMF formation was investigated. A series of sulfonic acid functionalized metal-organic frameworks, which contain different ratio of Lewis acid site and Br(?)nsted acid site, were synthesized by solvothermal method at different temperatures for varied reaction times. The kinetic data catalyzed by these catalysts shows that the yield of 5-HMF increased with the increased amount of Br(?)nsted acid, when the ratio of Bransted acid site and Lewis acid site is 1.1, the best HMF selectivity of 47.15% and HMF yield of 46.0% could be obtained at 150℃ after 2 hours.Finally, in order to explore the potential in the industrial application of MIL-101(Cr)-SO3H, the performance of the catalyst was examined in a fixed-bed reactor. It was found that diverse reactants can be catalyzed by MIL-101(Cr)-SO3H into 5-HMF. The MIL-101(Cr)-SO3H was verified effective for catalytic glucose-to-HMF transformation in one-pot, and the catalyst could be recovered and reused for several cycles with remained activity. Further investigation on the consecutive catalytic reaction with this catalyst in a fixed-bed demonstrates that the catalyst is of stable catalytic activity and is able to provide a moderate HMF yield. The MOF-based solid catalyst shows a bright future in the dehydration reaction of biomass-derived carbohydrate into platform chemicals and further studies on its industrial application are necessary and meaningful.