Experimental Study On Pyrolysis Of Lignocellulose On Hierarchical Pore Structure Zeolites And Dispersed Nickel Catalysts

Lignocellulosic biomass is a renewable resource widely available in nature.Pyrolysis of lignocellulose into bio-oil,which is an effective way to utilise biomass resources.However,pyrolysed liquid bio-oil has the disadvantages of high oxygen content,low calorific value and high acidity,and therefore cannot be used directly.Catalytic fast pyrolysis（CFP）is an effective way to improve the quality of bio-oil.In this study,the catalytic fast pyrolysis of cellulose and lignin,the main two components of biomass,were studied respectively.Nickel nitrate was loaded onto the cellulose by impregnation method to prepare a dispersion catalyst with active components in close contact with raw materials.Thermogravimetric analysis was used to investigate the thermal degradation of cellulose.The results showed that the loading of 1wt.%Nickel catalyst could reduce the thermal decomposition temperature of cellulose by 40℃.Due to the formation of cokes,the yield of liquid product pyrolyzed by the nickel-supported cellulose dispersed catalyst decreased.As the nickel loading increased,there was no further reduction in carbon deposition was observed.The structural composition of lignin is more complex than that of cellulose and hemicellulose,the strong thermal stability,of which makes it harder to pyrolyze.First,the fast catalytic pyrolysis of lignin with Hβ,HZSM-5 and USY zeolite catalysts was discussed.Results showed that with different zeolites as catalyst,the yield of lignin fast catalytic pyrolysis liquid products was HZSM-5>Hβ>USY in descending order,and the selectivity of oxygenates in the product was HZSM-5>USY>Hβ.With Hβzeolite as the catalyst,the yield of liquid product higher was higher and the effect of deoxidation was better.In the process of biomass pyrolysis,the fine pores in the microporous zeolites make the larger molecules have mass transfer resistance.In order to improve the mass transfer performance,Hβand HZSM-5 zeolites with hierarchical pore structure were prepared by the"post-treatment"desilication method under alkaline condition.Treatments under different alkaline conditions（Na₂CO₃,TMAOH/NaOH and NaOH）can increase the number of mesopores in while keeping their micropores structure from being destroyed.The yield of lignin-pyrolyzed liquid product increased slightly on HZSM-5 with hierarchical pore structure,while the selectivity of oxygenates in the product decreased from 27%to 5%,and the deoxygenation effect was significantly improved.The yield of lignin-pyrolyzed liquid product increased by 50%on the Hβwith hierarchical pore structure while still maintaining a good deoxygenation effect.The effect of the concentration of NaOH solution on the desilication of Hβwith Si-Al ratio of 22 and 40 was alslo investigated.When Hβzeolite with a silica to alumina ratio of 22 was treated with NaOH n with a concentration of 0.1⁰.5mol/L,the number of mesopores increased,the basic structure of the microporous structure basically unchanged.However For the group where the Hβzeolite with a silica to alumina ratio of 40was treated with 0.1 mol/L NaOH solution,the number of mesopores increased,but the crystallinity was only 30%.As the NaOH concentration increased,the crystallinity decreased.When the concentration of NaOH was too high,these would be execeeding desiliconization such asβ22-D1.0,β40-D0.5 andβ40-D1.0 obtained by NaOH treatment,where the framework of the zeolites was collapsed and the structure was completely destroyed.Meanwhile,the selectivity of oxygenates in the product was 78%,12%and 81%respectively.the deoxidation effect was also poor.