Research On Product Regulation During Catalytic Fast Pyrolysis And Online Upgrading Process Of Lignocellulosic Biomass Into Liquid Fuels

Lignocellulosic biomass has a main role in biomass resources in China,which has a large number of aromatic ring structures.Converting lignocellulosic biomass into aromatic hydrocarbons through thermochemical transformation can improve the utilization rate of biomass components.Novel metal modified micro-mesoporous composite zeolite catalysts were designed and applied to the in-situ and ex-situ catalytic fast pyrolysis(CFP)of biomass into liquid fuels in this investigation.The regulation mechanism of the key parameters of catalysts on products was proposed.In the study of in-situ CFP reaction,aimed at lignin which is difficult to transform among the three components of biomass,the residue of biomass under enzymatic hydrolysis(enzymatic hydrolysis lignin,EL)was chosen as raw material.At the same time,through a series of experiments,the prepared new modified zeolite catalysts were screened to clarify the regulation mechanism of modification means on the products.The application of metal modification combined with core-shell zeolite catalysts in in-situ CFP of EL mainly investigated the relationship between catalyst design(coating sequence,metal type,loading position,etc.)and liquid products."Coating mesopore first and loading metal later" retained the acid site advantages of core-shell structure catalysts and promoted the deoxygenation and aromatization reactions.The incorporation of single metal into microporous core and mesoporous shell was screened.The same metal introduced into different positions of core-shell structure(microporous core,mesoporous shell)had different regulation effects on the products.Combined with the optimal design,the formation of double-layer metal modified core-shell structure catalysts improved the yield of monocylic aromatic hydrocarbons(MAHs)to 9.37 wt.%and inhibited the generation of polycyclic aromatic hydrocarbons(PAHs)and phenols.The application of metal modification combined with micro-mesoporous zeolite catalysts in in-situ CFP of EL mainly investigated the relationship between the three key parameters of catalysts(pore structure,interaction between metal phase and support,synergistic stability between bimetallic active sites)and the products.The formation of micro-mesoporous composite structure increased the mesoporous specific surface area and pore volume of catalysts,improved the diffusion rate of reactants macromolecules,and decreased the selectivity of PAHs and oxygenates.The interaction between the metal phase and zeolite decreased the strength of strong acid sites but increased the proportion,which promoted the formation of the MAHs(13.15 wt.%)and improved the conversion rate of phenolic substances.The synergistic and stabilizing effect of bimetallic active sites promoted the formation of graphite carbon with low degree of order,and the adverse effect on the catalyst was weakened.Ni Mo/AZM catalyst had the best carbon deposition resistance and thermal stability.In the study of ex-situ CFP reaction,poplar wood was selected as the raw material for the catalytic conversion of biomass to liquid fuel.Using better modified catalysts,the mass yield and selectivity of the target product were improved,and the oxygen content was reduced.The mechanism of carbon deposition and deactivation characteristics of catalyst in the process of online upgrading were investigated.The reaction route and catalyst selection were further adjusted to delay catalyst deactivation.Micro-mesoporous zeolite catalysts decreased the selectivity of oxygenates in liquid phase and increased the mass yield of MAHs significantly.CO and CO2 dominated the gas phase products,decarboxylation and decarbonylation occurred simultaneously in the deoxygenation reactions,and graphite carbon with high degree of order dominated the solid phase products.Under the action of Ni Mo bimetallic modified zeolite catalysts,the mass yield of MAHs in liquid phase was increased to2.21 times that of HZSM-5,and the DTG curve of solid phase product showed two carbon accumulation peaks,which inhibited the formation of high order graphite carbon and delayed the deactivation of catalyst.When hydroxyapatite(HAP)was introduced into the front end of the modified zeolite,the acid in the liquid phase products decreased and ketones increased,and the mass yield of MAHs was further increased to 2.67 times that of HZSM-5.The proportion of CO2 in the gas phase products increased,the gas deoxygenation rate increased,and the carbon deposition decreased greatly,which mitigated the deactivation of the modified zeolites.Raman spectra showed that the carbon deposition had aromatic C-O bond and C=C bond vibration,and the carbon deposition was derived from the polymerization of aromatic hydrocarbons and oxygenates and the excessive cyclization of MAHs.Realtime monitoring results of gas products showed that when the biomass/catalyst ratio reached 1,the selectivity of COx decreased significantly,which was characterized by the decrease of deoxygenation performance of the catalysts,and the deactivation began.AZM and Ni Mo/AZM catalysts with composite pore structure had relatively small selectivity fluctuation of gas products and possessed higher stability in 0-40 min of biomass feeding,which still maintained high catalytic activity in 30-40 min of reaction time,prolonging the span life with a better catalytic performance.In order to further delay the deactivation of the modified catalyst,clay catalysts with basic sites were introduced into the fast pyrolysis stage of biomass to reduce the selectivity of carboxylic acids in the pyrolysis vapors,thus forming a coupled route of in-situ CFP and ex-situ CFP and alleviating the deactivation of catalysts accumulated by coke.Furthermore,Aspen Plus software was adopted to calculate the input and output information of material and energy streams for ‘in-situ CFP coupled with ex-situ CFP’ and ‘ex-situ CFP’ route.The latter had higher energy efficiency,but the former could produce aromatics with higher energy.From the perspective of preparing highlevel liquid fuels,‘in-situ CFP coupled with ex-situ CFP’ route had greater advantages.