| Bio-oils has some negative properties such as high acidity,water content,oxygen content,and,poor stability together with low heating value.High-quality bio-oil can be obtained by catalytic reforming of biomass pyrolysis volatiles,especially large amount of light aromatic hydrocarbons can be obtained by using selective zeolite catalysts.Light aromatics are important chemical raw materials,but at present they are mainly derived from fossil fuels such as petroleum and coal tar.The production of light aromatics from biomass is an important method to realize their sustainable production.However,the mechanism of biomass conversion to aromatics is not clear,and the yield and selectivity of aromatics need to be further improved.We have conducted the following research to achieve high quality oils containing a large amount of light aromatics and investigate the mechanism of the catalytic reaction process:Promising technology for the conversion of cellulose to aromatics by catalytic fast pyrolysis(CFP)was investigated using five zeolite catalysts,i.e.,5A,SAPO-34,HY,BETA and HZSM-5(Z5).The relationship between the porosity and acidity of different zeolites with product selectivity was studied.The results showed that both the acidity and pore size of the zeolite significantly affected the production of aromatics and coke,especially the bio-oil composition.The bio-oils obtained over 5A or SAPO-34(small pore<5.5 nm)have relatively high oxygen content.The benzene,toluene,ethylbenzene,xylenes and naphthalene(BTEXN)carbon yields over weak acidic zeolites of HY and BETA are only 6.5% and 9.0%,respectively.Due to the appropriate pore size distribution and acid position,Z5 gave the highest BTEXN carbon yield of 21.1%.Moreover,the coke deposited on the spent zeolites was analyzed by temperature programmed oxidation.Furthermore,three possible mechanisms that the acid sites catalyze vapor towards non-condensable gases,aromatics and coke were also studied.Z5 achieved satisfactory deoxygenation and aromatic production simultaneously,made it a potential catalyst for producing light aromatics from reforming the biomass pyrolytic vapors.Secondly,in order to further reduce the carbon deposition yield and increase the aromatic yield,the pore structure of Z5 and the accessible active sites are further modified.Hence,we propose a method for modifying Z5 with leaching agent HF and loading Ni,and their performance for catalytic fast pyrolysis(CFP)of cellulose was investigated in a drop tube quartz reactor.After modifying Z5 with 0.5 mol/L HF(0.5F-Z5),an excellent light aromatics yield was obtained.This is mainly attributed to the enhancement in the small mesopores(2-10 nm)and the decrease of Br?nsted acid sites.Simultaneously,the loading of 1 wt% Ni produced more BTEXN than 0.5F-Z5,due to the improvement in deoxidation/hydrogenation reactions.The highest BTEXN yield(31.3%)was obtained over 1 wt%Ni-0.5mol/LHF-Z5,which increased by 44.9% compared to the parent Z5.In addition,the reaction routes over different active centers and acid-catalyzed reactions were analyzed,based upon the composition of bio-oils and catalyst characterization.Finally,in order to obtain high-quality bio-oil and improve the selectivity of light aromatic hydrocarbons in tar,the metal Pt with hydrogen dealkylation performance is used for bifunctional catalysis.Direct loading of Pt onto Z5 showed a marked increase in BTEXN selectivity,with the selectivity of 0.2Pt-Z5 reaching the highest value(87.4%).This is attributed to the synergistic effect of Pt binding to the acidic sites,resulting in enhanced hydrogen dealkylation.However,Pt loading to FZ5 shows a sharp increase in benzene yield,which is mainly due to the fact that the formation of small mesopores in the catalyst contributes to Pt exerting a more powerful catalytic effect. |
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