Preparation Of Monocyclic Aromatic Hydrocarbons From Lignocellulose Biomass By Catalytic Pyrolysis Based On Ni/ZSM-5

In order to explore the optimal path to realize the resource utilization of lignocellulosic biomass,the theory and method of catalytic pyrolysis of nickel modified ZSM-5 to prepare lignocellulosic monocyclic aromatic hydrocarbons are studied in this thesis.By modifying ZSM-5 with nickel and conducting catalytic pyrolysis experiments using lignocellulose as raw materials,this thesis optimizes the type of raw materials,the silicon aluminum ratio of the carrier,and the metal loading capacity,and further explores the structure activity relationship and the formation mechanism of monocyclic aromatic hydrocarbons of the nickel modified ZSM-5 catalyst.The specific results are as follows:Firstly,the optimal methods for preparing monocyclic aromatic hydrocarbons from lignocellulose using various commercial metal catalysts are studied.By using different metal catalysts（Pt/C,Rh/C,Ru/C,Pd/C,Ni/Si O₂-Al₂O₃）to conduct catalytic pyrolysis experiments on four biomass types（wheat straw,rape straw,poplar sawdust,and bamboo powder）,the distribution of pyrolysis products is investigated.The experiment shows that wheat straw is the best raw material for the preparation of biomass based monocyclic aromatic hydrocarbons among the selected materials.In addition,commercial metal catalysts significantly increase the relative content of aromatic hydrocarbons and phenols in the product,with 65wt%Ni/Si O₂-Al₂O₃ exhibiting better catalytic performance for aromatic hydrocarbon production,resulting in a relative content of aromatic hydrocarbons in the product of catalytic pyrolysis of wheat straw reaching 31%.Secondly,the optimal method for preparing high content monocyclic aromatic hydrocarbons by catalytic pyrolysis of Ni O/ZSM-5 is studied.The effects of zeolite silicon aluminum molar ratio（Si/Al=18,50,85,300,470）and Ni loading（5,10,15,20,25 wt%）on the catalytic performance of ZSM-5 modified with nickel by impregnation are studied.Ni O/ZSM-5 reduces phenolic products,and the relative content of aromatic hydrocarbons decreases with increasing Si/Al,first increases and then decreases with increasing metal loading.10wt%Ni O/ZSM-5（Si/Al=18）increases the aromatic hydrocarbons in wheat straw pyrolysis products to 67.29%and 44.68%for monocyclic aromatic hydrocarbons;15wt%Ni O/ZSM-5（Si/Al=18）increases the aromatic hydrocarbons in lignin pyrolysis products to 82.23%and69.88%for monocyclic aromatic hydrocarbons.Finally,the conversion mechanism of lignin based monocyclic aromatic hydrocarbons over reduced Ni/ZSM-5 catalysts is studied.The effect of catalyst morphology on lignin pyrolysis products is studied using lignin as pyrolysis material.Ni/ZSM-5 catalysts exhibit higher selectivity for monocyclic aromatic hydrocarbons,especially Benzene-Toluene-Xylene,in lignin pyrolysis products.After nickel modification of ZSM-5,one is to increase the effective hydrogenation sites on the carrier,thereby strengthening the hydrogenation saturation reaction of pyrolysis volatiles on ZSM-5.The second is to promote the removal of oxygen containing groups from the benzene ring,generating more small molecular compounds such as phenol and alkylphenol that are easily converted to aromatic hydrocarbons by ZSM-5 catalysis,while inhibiting further cyclization and polymerization reactions of monocyclic aromatic hydrocarbons.