Study On In Situ Catalytic Conversion Of Biomass Fast Pyrolysis Vapors

Pyrolysis oil is usually obtained by biomass being pyrolyzed into pyrolysis vapors which are condensed into liquid bio-oil through a one-step or multi-step condensing process. Crude bio-oil obtained this way can not be directly used by internal combustion engines due to its poor quality. Catalytic conversion is often carried out to help improve the oil quality.However,such heating-cooling-reheating technique causes an increase in energy consumption during bio-oil production process.More improtantly,previous researches indicate that some components of the biomass fast pyrolysis vapors recombine to form more stable molecules over the condensing process,which makes it more challenging for subsequent catalytic upgradation.If biomass fast pyrolysis vapors are catalytically converted prior to condensation,it is possible to save energy and improve bio-oil quality at the same time with a single action.Based on this idea,in this paper,investigation of in situ catalytic conversion of biomass fast pyrolysis vapors was carried out,aiming at enhancing oil properties by partially solving existing problems of traditional bio-oil such as high oxygen content,low heating value,instability,strong acidity and corrosivity,etc.We studied the effects of different zeolites,a series of HZSM-5 zeolites with different Si/Al ratios and HZSM-5 supported transition metal oxides catalysts on the in situ catalytic conversion of biomass fast pyrolysis vapors and various kinds of characterizing techniques were employed to explain catalysts’performance. The principal results are as follows:Experiments on in situ catalytic conversion of biomass fast pyrolysis vapors using HZSM-5,USY-1,H-beta zeolites were carried out.The effects of different zeolites on carbon deposits,liquid oil yield and distribution of bio-oil components were investigated. According to the results,in terms of the amount of carbon deposits produced on the catalysts, USY-1>H-beta>HZSM-5.Liquid oil yield dropped slightly after introduction of zeolite catalysts,with HZSM-5 achieving the highest bio-oil yield.Moreover,the variety and contents of bio-oil components underwent an obvious change.Results showed that HZSM-5 displayed much better catalytic performance than the other zeolites,which was demonstrated by a great increase in hydrocarbons,an evident increase in light phenols but a substantial decrease in heavy phenols and sugars.The catalytic performance of HZSM-5 zeolites is mainly influenced by its acid sites,especially Bronsted acid sites which are majorly responsible for the deoxygenation in catalytic fast pyrolysis.Therefore,the influence of HZSM-5 zeolites with different acidity (Si/Al ratio:30,75,100,300) on in situ catalytic conversion of biomass fast pyrolytic products was investigated. It was found that HZSM-5 zeolites with relatively strong acidity presented a great capability of deoxygenation, which was demonstrated by the fact that the yield of hydrocarbons,mainly aromatics increased substantially and light phenols yield increased to a great extent while heavy phenols yield decreased evidently.In addition,the catalytic capability of deoxygenation of HZSM-5 zeolites decreased greatly with increasing Si/Al ratios.Experiments on in situ catalytic conversion of biomass fast pyrolysis vapors using HZSM-5 (Si/Al=30) zeolites supported a series of transition metal oxides (Fe,Co,Ni,Cu,Zn) catalysts showed that after introduction of transition metal oxides,contents of acids and ketones in the catalysis oil decreased a lot,resulting in lower acidity and higher stability.However,contents of hydrocarbons and light phenols also dropped substantially, which was probably caused by decreased capability of deoxygenation due to loaded active components covering acid sites of HZSM-5 zeolites.HZSM-5 zeolites loaded with iron oxide exhibited the best capability of deoxygenation among all the HZSM-5 supported transition metal oxides catalysts.Expected assumptions were validated by investigating the effects of different zeolites,a series of HZSM-5 zeolites with different Si/Al ratios and HZSM-5 supported transition metal oxides catalysts on the in situ catalytic conversion of biomass fast pyrolysis vapors. It is of important referential value to future in-situ catalytic ugradation of bio-oil.