Experimental Research On Catalytic Fast Pyrolysis Of Cellulose

Fast pyrolysis technology can convert biomass resources into high quality liquid fuel or bio-oil.Because the crude bio-oil obtained by direct pyrolysis of biomass has the disadvantages of complex composition,strong acidity,high oxygen content,poor stability and so on.So in order to reduce the technical difficulty of subsequent crude bio-oil refining process and improving the quality of bio-oil from the source of biomass pyrolysis,Catalytic Fast Pyrolysis?CFP?process emerges as the times require.CFP is based on the fast pyrolysis process of biomass,adding catalysts in its thermochemical reaction process to achieve efficient enrichment of specific race products in bio-oil.In order to investigate the reaction mechanism of biomass components in catalytic pyrolysis process,this study selected cellulose as the research object.The structure and properties of the catalyst were characterized by NH3-TPD,BET and XRD methods,while using TG-FTIR and Py-GC/MS as the experimental instrument to research the reaction law of cellulose under the catalytic of metal oxides and modified zeolite molecular sieves,focusing on the rule of cellulose directed pyrolysis to produce high-value chemicals and aromatic hydrocarbons.Finally,get the optimization of the catalyst formula and achieve the purpose of the directional pyrolysis conversion of cellulose.Al₂O₃,MgO,Ga₂O₃ and CeO₂ were selected as catalysts to investigate the reaction law of cellulose under the catalysis of metal oxide.First,the pyrolysis behavior of cellulose after adding different metal oxides was studied by TG-FTIR.It was found that the maximum weight loss rate of cellulose decreased,the initial decomposition temperature moved forward and the coke yield increased with the addition of metal oxides.In the four metal oxides,Al₂O₃ has the best comprehensive deoxygenation effect,while transition metal oxides make the temperature range of deoxygenation reaction narrow,but the removal efficiency is relatively low.Then the distribution of cellulose pyrolysis products after the addition of different metal oxides was analyzed by Py-GC/MS.The results show that Al₂O₃ has good selectivity for furan products.MgO promotes the formation of small molecular products.Transition metal oxides increase the total yield of the dehydrated sugar product.Alkali treatment of HZSM-5 zeolite was carried out to explore the influence of alkali treatment process on the yield and distribution of aromatic hydrocarbons in cellulose pyrolysis products,and to find the best alkali treatment concentration.The results of BET characterization showed that the specific surface area of the HZSM-5 zeolite catalyst decreased,the pore volume and the pore size increased.A suitable low concentration alkali solution can be used to make mesoporous structure on the surface of HZSM-5 zeolite molecular sieve.TG/DTG data shows that the alkali treatment process can make the pyrolysis reaction ahead of schedule and inhibit the formation of coke,CO and CO₂,but it has almost no effect on temperature of the maximum reaction rate.Py-GC/MS data show that the proper alkali treatment process can effectively improve the selectivity of monocyclic aromatic hydrocarbons?MAHs?and reduce the selectivity of polycyclic aromatic hydrocarbons?PAHs?.HZSM-5-0.3M zeolite catalyst improved the yield of total aromatic hydrocarbons yield and increased the selectivity of Benzene-Toluene-Xylene?BTX?.Further modification of HZSM-5-0.3M molecular sieve used the method of loading the active metal component?Fe2O3,CeO₂,Ga₂O₃?.Study on the effect of active metal components on the formation of aromatic hydrocarbons,especially the selectivity of monocyclic aromatic hydrocarbons in cellulose pyrolysis products.The load of the active component of metal leads to the reduction of the specific surface area of the molecular sieve,and the pore volume and pore size also change.The temperature of the maximum reaction rate of cellulose was delayed after the loading of metal active components,while had different effects in the maximum reaction rate.Fe2O3 slightly increased the reaction rate,while CeO₂ and Ga₂O₃ slightly reduced the maximum reaction rate.The load of the active component of metal changes the anti-carbon deposition ability of the molecular sieve.Compared with the HZSM-5-0.3M molecular sieve,the loading of Ga₂O₃ further improves the selectivity of MAHs while the yield of aromatic hydrocarbons is further increased.However,the loading of Fe2O3 and CeO₂ improves the selectivity of aromatic hydrocarbons but decreases the yield of aromatic hydrocarbons and increases the by-products.