Hydrolysis Of Hemicellulose And Cellulose To Sugars Over Hierarchical HUSY Zeolites

With the gradual consumption of fossil resources, utilization of renewable resources to replace fossil resources has attracted more and more attention. Abundant and sustainable plant biomass is one of the main alternative resources. However, the efficient utilization of cellulose and hemicellulose, which are the major components of biomass, is an urgent problem. Sugars produced from the hydrolysis of hemicellulose and cellulose are the key platform molecules of biomass transformation processes which can be further converted to biofuels and other high-value added chemicals. Consequently, hydrolysis of cellulose and hemicellulose to sugars is an important direction in biomass conversion currently.Zeolites are a kind of porous solid materials with high surface area, which have been widely used in petrochemical industries due to their unique shape-selective effects and high thermal stability. However, their small micropores impose severe mass transfer limitations on macromolecules, so currently their applications in biomass conversion are scarce. This thesis studied the hydrolysis of hemicellulose and cellulose catalyzed by the conventional HUSY and hierarchical HUSY zeolites. In view of the big molecular size and the mechanism of acid-catalyzed hydrolysis of hemicellulose and cellulose, the pore structure and the acidity of HUSY zeolites were modified. In order to facilitate mass transfer, acid treatment was adopted to obtain hierarchical HUSY zeolites by introducing a large amount of mesopores into commercial HUSY zeolites. On the other hand, acidic properties were strengthened by grafting sulfonic acid groups onto the hierarchical HUSY zeolites.Firstly, the influence of the acid concentration, the treatment time and temperature on preparation of hierarchical HUSY zeolites was investigated. And XRD, XRF, FTIR, NH3-TPD, and N2 physisorption were employed to characterize the parent and hierarchical HUSY zeolites. The results indicated that acid treatment was effective to introduce mesopores into HUSY zeolites, moreover the acid concentration for treatment had a significant effect on the properties of the obtained hierarchical HUSY zeolites. The catalytic activity of hierarchical HUSY zeolites was tested in hydrolysis of hemicellulose. The maximum yield of TRS was achieved over the hierarchical HUSY zeolite obtained by treatment of HUSY zeolite with 0.2 M oxalic acid at 85℃for 4 h. And with this catalyst the yield of TRS could be further increased to 61.3%under the reaction conditions of 140℃,6 h, and mcataiyst/mhemicellulose/mwater=1:1:100. Subsequently, the strong acid sites were incorporated to the hierarchical HUSY zeolites by sulfonation, and the sulfonated catalyst was also used to hydrolyze hemicellulose. It was found that the yield of TRS was further improved to 78%under the reaction conditions of 140℃,9h, matalyst/mhemicellulose/mwater=1:2:200. Finally, the sulfonated hierarchical HUSY zeolites were used to catalyze hydrolysis of cellulose which was notoriously resistant to hydrolysis. The results also indicated that mesopores and strong acidity facilitated the enhancement of cellulose conversion and the yield of TRS.