Catalytic Cracking Of Biomass Pyrolysis Vapor With Zeolites

In order to upgrading the bio-oil,a two-stage fixed bed reactor was used to study the catalytic cracking of pinewood pyrolysis vapor with zeolites.The main content includes three parts as follows.First,the bahaviors of catalytic cracking with six zeolites(MCM-41,Na-MCM-41,HZSM-5,Na-ZSM-5,HY and Na-Y)at 600℃ were comapred.HZSM-5 with moderate strength acids showed the highest selectivity of light aromatic hydrocarbons and olefins;HY with high strength acids showed a violent cracking of bio-oil to produce m ore alkanes and H2 at the expense of reduced bio-oil yield and aggravated coking.Non-acidic and large porous MCM-41 promoted the themal effect on bio-oil.Although all sodium zeolites promoted the CO2 release and inhibited the dehydration,the resualtant effective hydrogen does not transfer to bio-oil but to H2 and CH4.Second,the cracking of pinewood pyrolysis vapor over HZSM-5 at a wide temeperature range were carried out.HZSM-5 exhibited significant effects on catalytic cracking pinewood pyrolysis vapor even at lower temperature(450-600℃),while thermal effects played a dominant role at higher temperature(650-750℃).HZSM-5 degraded most oxygenates and generated a larger amount of light aromatic hydrocarbons and olefins.Due to a preferential deoxygenation and hydrogen transfer by HZSM-5 at 550-600℃,the resultant bio-oils had high yields of 14.5-16.8%,HHVs(high heat values)of 39.1-42.4 MJ kg-1,and energy recoveries of 33-35%.Third,the catalytic performance of HZSM-5 used in iteratively catalytic cracking of pinewood pyrolysis vapor was investigated.It was found that more coke was deposited in the zeolite channels,deactivating the inner and external acid sites as the re-use times increased.The preferential deoxygenation,hydrogen transfer and aromazetion of HZSM-5 were weakened due to the coke deposit,and the resultant bio-oil had a lower HHV.However,HZSM-5 still exhibited a catalytic effect in round fourteenth,when the mass ratio of biomass to catalyst was 4.8.Moreover,the catalytic performance of reactived HZSM-5 was extremely close to the new one.