Preparation Of Composite Zeolite Catalysts And The Catalytic Performance In Catalytic Pyrolysis Of Biomass

Bio-catalytic pyrolysis of bio-oils with high aromatic content is a research hotspot in the field of biomass pyrolysis.The microporous HZSM-5 catalyst used in the traditional process has a pore size similar to the dynamics diameter of some aromatic molecules,which contributes to the formation of aromatics,but its acidity is stronger.The mesoporous MCM-41 catalyst has rather mild acidity,but larger pore size.This article comprehensively considers the special features of the above two catalysts,and prepares the mesoporous composite molecular sieve HZSM-5/MCM-41.The mesoporous structure promotes the splitting of biomass macromolecules into intermediate molecules and further cracks into in small molecules in the microporous structure,which can effectively increase the content of aromatics in bio-oil and reduce surface coking.In this paper,we use HZSM-5 as a silicon-aluminum source and adopted the post-synthetic method,MCM-41 structure is grown on the surface to obtain a composite molecular sieve.The effects of alkali pre-treatment solution（NaOH solution）concentration,template solution concentration,preparation temperature,different digestion time,and crystallization time on the physicochemical properties of the composite molecular sieve were investigated and studied by means of XRD,nitrogen adsorption desorption,NH₃-TPD,SEM and TEM techniques were used to characterize the composite zeolite catalysts.It was found that the composite molecular sieves prepared under different conditions had different characterizations.We found that the best condition is concentration of alkali pretreatment solution of 2.0 mol/L,template solution mass fraction of 10%,preparation temperature of 110℃,and 24h recrystallization and 24h recrystallization.The structure of HZSM-5 can be detected in the composite molecular sieve,which has an average pore size of 4.89 nm in the mesoporous region,and the characteristic straight channel structure of MCM-41 can be observed in the TEM results.Meanwhile,compared with HZSM-5,The prepared composite molecular sieve has reduced acid sites and is more mild in acidity.The Py-GC/MS non-catalytic pyrolysis experiments at different temperatures show that the relative content of condensable organics is highest at 600℃.The catalytic pyrolysis experiments were conducted under the same temperature conditions.When the mass ratio of biomass material and catalyst is 1:2,the Py-GC/MS experimental results at 600℃show that the pyrolysis product of MCM-41 is dominated by phenols,accounting for 21.62%,and there is no hydrocarbon production.The relative content of hydrocarbons in thep roduct of HZSM-5 catalytic pyrolysis is48.41%.However,the relative content of hydrocarbons in the product obtained by the prepared composite molecular sieve is as high as 64.43%,which is 16.02%higher than that in the HZSM-5,and the proportion of the monocyclic aromatic in the total product was 44.39%,the PAHs accounted for 15.36%.Fluidized bed experimental results are related to reaction temperature,type of catalyst and their arrangement.Non-catalytic pyrolysis experiments of fluidized bed were carried out at different temperatures.It was found that the the highest liquid yield of 43.1%was obtained when the pyrolysis temperature was 550℃.Keep the pyrolysis temperature in 550℃,changing the temperature of the reforming furnace to carry out the HZSM-5 single-component catalytic pyrolysis experiment,the mass ratio of the biomass raw material to the catalyst is 10:4.It was found that the total relative content of aromatics in the water-insoluble phase reached a maximum of 28.49%when reforming temperature is 500℃.Two-stage catalytic pyrolysis experiments of HZSM-5 and MCM-41 were carried out under the same temperature conditions,and the mass ratio of biomass raw material to catalyst was 10:3.5.It was found that the catalytic effect of the mechanical mixing between the two is better than the layered arrangement.The total relative content of aromatics in the water-insoluble phase reached a maximum of 29.43%at a mass ratio of 3:2.Under the same temperate condition,the prepared composite molecular sieve has the most outstanding catalytic effect.The total relative content of aromatics in the water-insoluble phase is the highest,reaching 35.11%.The relative content of single-ring aromatics is 18.83%,and the relative content of polycyclic aromatic hydrocarbons is 16.28%.