Synthesis Of Acid-Base Bifunctional Catalyst And Its Application In Pyrolysis Of Cellulose

Biomass is a promising carbon-based alternative energy source and sustainable chemical feedstock and its exploitation and utilization is widely concerned. Catalytic pyrolysis is an efficient technique, the acid-base bifunctional catalyst is good for pyrolysis of biomass into different chemicals selectively, the interaction of acid sites and base sites were weakened when the catalyst was prepared into core-shell tape.In this thesis, K₂CO₃/MgO-SiO₂ solid base catalysts were prepared by impregnation with different calcination temperatures and amount of loaded K₂CO₃, then mesoporous shells coated on the solid bases by hydrothermal synthesis, ZnCl₂ doped to change the acidity, Zn-MS@K₂CO₃/MgO-SiO₂ acid-base bifunctional catalysts were prepared. The structure and propertier of solid base and acid-base bifunctional catalysts were studied by FT-IR, XRD, SEM, BET, Hammett indicator method and temperature programmed method. And effect of solid bases and acid-base bifunctional catalysts on dynamics of cellulose pyrolysis were investigated.The main conclusions are as follows:K₂CO₃/MgO-SiO₂ solid base catalyst are nanospheres whose diameters from 150 nm to 250 nm range. The basic K₂CO₃ made mesoporous silica grains decreased.When the amount of K₂CO₃ increases, the specific surface area of solid base is decreased. The diameter of Zn-MS@ K₂CO₃ /MgO-SiO₂ bifunctional acid-base catalyst is about 500 nm. There are two factors can affect specific surface area of acid-base bifunctional catalyst.When the amount of K₂CO₃ loaded is larger, the cotent of Zn doped is more, the impact on the structure of the mesoporous silica is greater and the specific surface area has been reduced accordingly.Hammett indicator method and temperature programmed desorption method show that K₂CO₃/MgO-SiO₂ solid base and acid-base bifunctional catalyst Zn-MS @ K₂CO₃/MgO-SiO₂ inner core are weak bases,with the calcination temperature and the amount of K₂CO₃ loaded increases, the total alkalinity increases first and then decreases. When the calcination temperature is 550 ℃ and the amount of K₂CO₃ loaded is 25%, the total alkalinity of solid base catalyst reaches up to 4.22 mmol/g and the acid-base bifunctional catalyst reaches up to 2.57 mmol/g. When the ratio Si/Zn of shell layer is 20, change the amount of K₂CO₃ loaded inner layer,the total amount of acid in the shell layer reaches down to 0.410 mmol/g; And the amount of K₂CO₃ loaded is 25%, change the ratio Si/Zn of shell layer, the total amount of acid in the shell layer reaches up to 0.545mmol/g.When doping amount of Zn,acid-base bifunctional catalysts can produce clear weak acid centers and a small amount of strong acid sites.Under the condition of solid base and acid-base bifunctional catalyst, the weight loss percentage and temperature of cellulose pyrolysis decrease. The minimum weight loss percentage reached to 74.34%.The two kinds of catalysts show certain selectivity to hydroxyl-acetol and the catalytic activity acid-base bifunctional catalyst is better,the maximum content of acetol reached to 49.9%. According to the dynamic experiment of pyrolyse cellulose, the total alkalinity was greater, pyrolysis reaction activation energy of cellulose pyrolysis was lower, the pyrolysis reaction activation energy reached minimum value of 142.7kJ·mol^-1. The main process of cellulose pyrolysis satisfied the first- order reaction kenetics model.