Study On Dual Catalytic Reforming Of Biomass To Produce Upgraded Bio-oil

Biomass,which is one of the most prevailing renewable energy,owns the advantages of wide distribution,abundant reserves,and strong regeneration.In addition,compared to some other renewables,biomass is the only“Carbon Resource”energy,indicating it could be used to produce heat,power,fuel,and high value-added chemicals.However,the quality of bio-oil deserved from pyrolysis is so poor that it could not be used as fuel.Therefore,upgrading process is needed regarding the target of obtaining upgraded bio-fuel.In this study,a series of experiments were conducted to improve the quality of bio-oil,which include the modification of HZSM-5 to enhance the catalytic performance,the use of metal oxides and HZSM-5 to co-catalyze bamboo sawdust?BS?,the synthesis of advanced mesoporous metal oxides,the utilization of a tandem bubbling fluidized bed/fixed bed reactor to catalytic upgrading the biomass pyrolytic products.Moreover,the computational fluid dynamics?CFD?simulation of biomass pyrolysis also was carried out.An integrated modified HZSM-5 was prepared by sodium hydroxide leaching and followed by hydrothermal process in series,and the co-modified zeolites were then used to conduct the catalytic fast pyrolysis?CFP?of BS and waste oils to investigate whether an enhanced production of aromatics could be obtained.X-ray diffraction,N₂adsorption-desorption,TEM and NH₃-TPD were utilized to characterize the modified zeolites.Experimental results indicated that the crystal structure of HZSM-5 was largely damaged as alkali treatment time was 6h,and a micro-mesopore hierarchical system was created inside the zeolites.Simultaneously,the strong acid sites decreased with the increment of modification time,while the weak acid sites performed an opposite inclination.During the CFP of BS using the co-modified zeolites,the relative content of aromatic hydrocarbons increased from 18.23%to 31.88%as the modification time increased from 0 to 2h.In addition,regarding the distribution of aromatic hydrocarbons,it was observed that the relative content of benzene,toluene,and xylenes?BTX?increased at first and then decreased within the studied modification time,with toluene and xylenes being the dominated products.Regarding the synergistic catalytic performance between metal oxides and HZSM-5 during the CFP of BS,compared to HZSM-5,MgO exhibited pronounced deacidification via ketonization and aldol condensation reactions as the minimum content of acids?2.12%?and the maximum content of ketones?28.81%?could be obtained.Furthermore,given the selectivity of phenols,MgO not only spurred the increase of overall phenols content,but also facilitated the selectivity of light phenols like phenol and 4-methyl-phenol.With respect to the co-CFP of BS and waste lubricating oil?WLO?,a HZSM-5/MgO mass ratio of 3:2 largely accelerated the formation of aromatics via Diels-Alder reaction.Simultaneously,the WLO percentage played a vital role in hydrocarbons?i.e.aromatics+olefins&alkanes?,and the maximum content?70.31%?could be attained at the percentage of 60%as a function of significant activation of hydrocarbon pool.Simultaneously,a use of dual catalytic stage of CaO and HZSM-5 significantly facilitated the contents of aromatics and olefins,as well as remarkably inhibited the formation of undesirables like acids,and a maximum content of hydrocarbons could be reached at HZSM-5 to CaO mass ratio of3:2.Additionally,a series of metal oxides including ZrO₂/?-Al₂O₃,CeO₂/?-Al₂O₃,and ZrO₂-CeO₂/?-Al₂O₃ were synthesized and employed to conduct CFP of BS to produce hydrocarbon precursors such as ketones and furans.The use of metal oxides enhanced the formation of ketones and monoaromatic hydrocarbons compared to catalyst-free trial.Among the metal oxides,ZrO₂-CeO₂/?-Al₂O₃ exhibited the most significant ketonization and aldol condensation activities yielding the highest concentration of linear and cyclic ketones.In addition,non-acidic oxygenates such as furfural,acetol,butanedial,2,3-dihydrobenzofuran and methyl acetate,were efficiently converted into hydrocarbon precursors over metal oxides.A dual catalytic bed system integrating ZrO₂-CeO₂/?-Al₂O₃ and HZSM-5 significantly facilitated the production of aromatic hydrocarbons compared to pure HZSM-5 catalytic run.The use of ZrO₂-CeO₂/?-Al₂O₃mixed with HZSM-5 mode maximized the formation of xylenes,while ZrO₂-CeO₂/?-Al₂O₃ mixed with BS catalytic trial increased the concentration of benzene,toluene,and alkylbenzenes.CFP of BS and co-pyrolysis of bamboo sawdust and waste tire?WT?were conducted by a tandem bubbling fluidized bed/fixed bed reactor.Effect of pyrolysis and catalyst temperatures on product yield was studied.In addition,synergistic effect of HZSM-5 and base catalysts?including CaO,MgO,and SrO?for the promotion of aromatic hydrocarbons was revealed.Experimental results illustrated that both pyrolytic and catalytic reactor temperatures played pivotal roles in the yield of bio-oil,and the optimal pyrolysis and catalytic reactor temperatures were 550 ^o C and 500 ^o C,respectively.Ex-situ catalytic trial decreased the yield of bio-oil compared to in-situ run,while it facilitated the formation of phenol and alkylphenols.Mixed catalytic upgrading modes exhibited more significant aromatization and deoxygenation activities than sequential ones.In particular,ex-situ run using CaO mixed with HZSM-5increased the concentration of aromatic hydrocarbons to 31.34%,which was¹1.48%higher than that derived from CaO and HZSM-5 sequentially processed mode.The dominated products in alkylphenols were cresol isomers and ethylphenols,and compared to sequential cases,mixed catalytic upgrading trials promoted the relative selectivity of phenol.Synergistic effect of base catalysts and HZSM-5 contributed to the production of monocyclic aromatic hydrocarbons,and CaO mixed with HZSM-5mode showed the most prominent synergistic effect for the enhanced relative selectivity to xylenes and toluene.Co-CFP of BS with WT over pure HZSM-5 increased the yields of bio-oil and char,while the gas yield decreased with the increasing of waste tire percentage in the feedstock blends.The product distribution of bio-oil obtained from co-CFP of BS and WT over pure HZSM-5 was dominated by aromatic hydrocarbons,and the relative concentration increased from 26.71 to 71.50%as the WT percentage elevated from 0 to 60 wt%.Co-CFP of BS and WT using HZSM-5 mixed with MgO mode produced higher yield of bio-oil than the sequential mode when HZSM-5/MgO mass ratio was raised from 1:4 to 1:1.However,sequential mode was proved to be more effective in the promotion of aromatic hydrocarbons than the mixed mode at higher HZSM-5 proportion.A positive additive effect for alkylbenzenes was found when the sequential mode was used at varying HZSM-5/MgO mass ratios.Regarding the olefins,C10 olefins were main products,and limonene selectivity increased at first and then decreased with the highest selectivity of 38.87%occurring at HZSM-5/MgO of 2:3 in the mixed mode case.The additive effect of HZSM-5 and MgO indicated that both the mixed and sequential modes inhibited the formation of polycyclic aromatic hydrocarbons with the most significant additive effect obtained at HZSM-5/MgO mass ratio of 1:1 using the mixed mode.Finally,co-modified HZSM-5 also was used to conduct the dual catalytic co-pyrolysis experiments and it was found that compared to fresh HZSM-5,the use of 2AH-Z5 and 4AH-Z5 increased the yield of bio-oil from29.71%to 33.54%,32.73%,respectively.Moreover,the formation of toluene and xylenes also was enhanced with relative content increasing to 26.66%and 9.39%,respectively.Based on pyrolysis experiments,the CFD simulation of BS pyrolysis using ANSYS also was conducted.The Euler-Euler model was employed to simulate the pyrolysis process.Experimental results indicated that the steady status could be reached when the simulation time was increased to 240s.The simulated yield of bio-oil and bio-char tended to increase with the increasing of pyrolysis temperature,and the highest yield could be attained at 550 ^o C.The errors of simulation results and experiments regarding the yields of pyrolytic products were within the reasonable range,and simulated bio-oil yield was lower than the experimental one.