Study On The Mechanism Of Biomass Catalytic Pyrolysis To Produce High Selectivity Light Olefins

Nowadays,biomass were selected as the raw material for the production of light olefins,and the conversion of biomass to light olefins has received more and more attentions,which is of great significance in increasing light olefin demand markets.However,the process of biomass catalytic pyrolysis to light olefins were complex,the production of light olefins was obviously affected by the composition of biomass,the limitation of reaction conditions and the type of catalysts,also there were few studies on the generation of light olefins via such parameters and the mechanism was not clearly.In this study,the catalytic pyrolysis processes of biomass,three components and the intermediate products were carried out.While the effect of catalysts physical and chemical structure on the formation of light olefins was also studied,which were essential to the better understanding of the intricate process for the conversion from biomass to light olefins.Moreover,the conversion of biomass and hydrogen-rich liquid reactants catalytic pyrolysis for the production of light olefins were performed,which could made it possible for the regulation of light olefins.Firstly,the effect of different catalysts?CaO,MCM-41,ZSM-5 and SAPO-34?on the generation of light olefins were studied,and found that the highest yield of light olefins was obtained by ZSM-5 catalyst?4.38%C-mol?.In order to decreased the coke formation during ZSM-5 catalytic pyrolysis process,MCM-41 and CaO were used to crack the macromolecular compounds into small-oxygenates,and further ZSM-5 or SAPO-34convert these products into light olefins were also studied.While the yield of light olefins increased by the addition of CaO and MCM-41,and CaO shown a higher effect than MCM-41.Secondary,in order to increase the carbon yield of light olefins,Ce,Al,Mg,Cu,La and Fe were used to modified ZSM-5 catalysts,and the relationship between light olefins selectivity and acid sites distribution was explored.The results shown that the total acidity and the medium acid sites increased,accompanying by the increase of light olefins.While the highest yields were obtained by Cu?7.64%C-mol?and Ce?7.42%C-mol?,Fe modified ZSM-5 produced a yield of 6.98%C-mol,and obtained a highest C₃H₆ selectivity.Also,the correlation between C₂H₄ and medium acid sites was the largest,while C₃H₆ with weak acid sites and C₄H₈ with strong acid sites were the highest.In order to obtain more C₃H₆,and Fe/ZSM-5 was cheap and easier to get,Fe/ZSM-5catalyst was selected to perform the conversion of biomass to light olefins.The effects of in-situ and ex-situ process,temperature,Fe loading,catalyst to feed ratio and gas flow rate on the olefins carbon yield and selectivity of biomass and three components were explored.The results showed that maximum carbon yield of light olefins?6.98%C-mol?was obtained at the pyrolysis temperature of 600 ^oC,catalyst to feed ratio of 2,gas flow rate of100 ml/min,and 3 wt%Fe/ZSM-5 for cellulose ex-situ process.And the total yield of light olefins followed the decreasing order of cellulose,hemicelluloses and lignin.Based on the optimum reaction conditions,the conversion of six intermediate products of acetic acid,ethanol,acetone,guaiacol,furfural and furan were selected,and further identify the reaction mechanisms for the generation of light olefins from biomass to three omponents,and intermediate products.While in non-catalysts and with-catalysts pyrolysis process,the carbon yield of light olefins decreased in the order of ethanol,acetone,guaiacol,acetic acid,furan and furfural,the carbon yields of light olefins obtained from ethanol pyrolysis were the highest,while was up to 74.56%C-mol in non-catalysts process and45.35%C-mol in with-catalysts process.Finally,the yield of light olefins from biomass catalytic pyrolysis was much lower,and the conversion of biomass and hydrogen-rich liquid reactants?acetic acid,ethanol,acetone?catalytic pyrolysis for the production of light olefins were performed.The results showed that light olefins and the total yield of light olefins with aromatic increased during mixed catalytic pyrolysis when comparing with cellulose catalytic pyrolysis,and the higher ratio of H/Ceff,the more generation of light olefins.Also,the lowest C₂H₄ and C₃H₆ selectivity was obtained by cellulose co-pyrolysis with ethanol and acetone,ethanol can easily convert to C₂H₄ by degradation,and acetone can produce more C₃H₆,these light olefins will go on diene synthesis reaction to react with furan products from cellulose pyrolysis,and formed more aromatic,in this case the selectivity decreased.