Studies Of Lewis-br（?）nsted Acid For Synergistic Catalytic Conversion Of C₆（mono-/poly-）Saccharide To Alkyl Levulinate

Biomass is a rich and renewable resource that can be used as raw material for production of a variety of high value-added chemicals.Levulinate esters have applications in the fields of food,fuel additives,chemicals,medicine.It is an important route for the preparation of levulinate esters from biomass-derived carbohydrates.The direct alcoholysis of C₆ sugar to levulinate esters has the advantages of short reaction process and simple separation,which has abstracted much attention recently.In this paper,we firstly studied the conversion of glucose to levulinate esters.According to the reaction mechanism of glucose conversion to levulinate ester,the synergistic Lewis/Br?nsted acididy is needed,so a bifunctional hierarchical Sn-Al-Beta catalyst with strong L/B acidity was prepared.The obtained samples were characterized by XRD,N₂ physical adsorption,TEM,XPS,FT-IR and UV-vis DRS.The incorporation of Sn enhanced the L acidity.Hydrothermal treatment by tetraethylammonium hydroxide increased the porosity of the samples.The incorporation of Sn resulted in higher catalytic activity in glucose isomerization,and the mesopores of the samples promoted the utilization of the active site of the catalyst.49%yield of levulinate esters was obtained over Sn-Al-Beta-0.5 for the conversion of glucose at a temperature of 180℃ for 5 h.Its activity is significantly higher than Al-Beta zeolites.Cellulose is a linear polysaccharide formed by linking glucose monomers throughβ-1,4 glycosidic bonds,from which methyl levulinate can be directly prepared.Depolymerization of cellulose into glucose is a key step and a main obstacle for this route.In the second part of the thesis,the oxidation-depolymerization strategy was adopted for the depolymerization of cellulose.The acid site generated by oxidation promoted the depolymerization of cellulose to glucose.Meanwhile,Al₂（SO₄）₃·18H₂O was used for the catalyzing of the conversion sugar to levulinate esters.The effects of microcrystalline cellulose oxidation conditions and alcoholysis reaction conditions on the formation of methy levulinate were studied.52%yield of MLE was obtained for microcrystalline cellulose that was oxidized at 200℃ for 10 h with Al₂（SO₄）₃·18H₂O as the catalyst at 180°C for 3 h.