In-Situ Catalytic Upgrading Of Rape Straw Pyrolysis Vapors For Refined Bio-Oil Over La Modified Hierarchical Porous HZSM-5 Catalysts

Biomass,as a kind of renewable energy with abundant reserves,is the best choice for replacing fossil energy in fuel and chemical industry with the growth of global energy demand and the challenges brought by the environment and sustainable development.The technology for pyrolysis of biomass to prepare bio-oil has several advantages,such as low invested cost,easy handling and industrial production,and the catalytic pyrolysis of biomass by HZSM-5 can further improve the quality of bio-oil.In this paper,rape straw was selected as biomass material,and the microporous HZSM-5 catalyst was reamed by Na₂CO₃ solution,and then the HZSM-5 catalyst was modified by metal La impregnation.Using these catalysts,in-situ upgrading for production of bio-oil from the rape straw vacuum pyrolysis vapors was performed,and the pyrolysis product bio-oil was collected.The specific research is as follows:?1?For the microporous structure and properties of HZSM-5 catalyst,the HZSM-5zeolites were treated by Na₂CO₃ solution with different concentration.The structure and properties of the HZSM-5 catalysts before and after modification were characterized by XRD,BET,SEM-EDS and Py-FTIR,respectively.The results showed that after treatment with Na₂CO₃ solution,the mesoporous pore volume and outer surface area of the molecular sieve were increased,while the MFI structure of HZSM-5 is retained and the molecular sieve acid distribution is changed.With the increase of Na₂CO₃ concentration,the yield of bio-oil organic phase and kinematic viscosity of the organic oil decreased,while the content of the oxygenated compounds and the carbonyl compounds decreased first and then increased.The calorific value of the bio-oil organic phase obtained from modified HZSM-5?after 3 mol/L Na₂CO₃ treatment,3M-HZSM-5?catalyst reached 34.7MJ/Kg and the content of hydrocarbons can be up to 46.27%.The oxygenated compounds and the carbonyl compounds of the bio-oil organic phase decreased by 27.6%and 41.7%compared with that of unmodified.?2?In order to improve the acid distribution of HZSM-5 catalyst,the hierarchical HZSM-5 was modified with different loadings of La by impregnation.After the HZSM-5zeolite was pretreated with 3 mol/L Na₂CO₃ solution,and then the hierarchical HZSM-5was modified with different loadings of La by impregnation.The results show that the modification of La retains the micro/meso-porous pore and MFI structure of the catalyst,but changes the acid distribution of the zeolite.With the increase of loadings of La,the yield,density,kinematic viscosity and oxygen content of bio-oil organic phase decreased first and then increased,while the content of oxygenated compounds and carbonyl compounds showed the same tendency as well.The hierarchical porous HZSM-5?La loading were 5wt%,5%La/3M-HZSM-5?catalyst had a better effect on improving the quality of bio-oil,the hydrocarbon content and the high heating value of the bio-oil organic phase reached 49.86%and 37.7MJ/Kg.Meanwhile,the oxygenated compounds and the carbonyl compounds decreased by 32.43%and 57.03%,respectively.?3?The coking HZSM-5 catalyst before and after modification was collected,and the catalytic stability and anti-coking performance of the modified catalyst were analyzed by SEM and TG/DTG.The coked catalyst obtained after 120 minutes of use was analyzed.The yield of coke of different catalysts were as follows:HZSM-5>3M-HZSM-5>5%La/3M-HZSM-5.After 5%La/3M-HZSM-5 catalyst was used,the coke content of the catalyst was only 11.05%,and the regenerative capacity of the coked catalyst is improved.?4?Based on the analysis of the product and the characterization of the catalyst,the reaction mechanism of catalytic pyrolysis of biomass rapeseed straw to prepare hydrocarbon products was studied:?a?the pyrolysis of rape straw biomass into oxygenated organic compounds;?b?the oxygenated organic compounds are pyrolyzed into macromolecular intermediates on the catalyst surface and mesopores;?c?the macromolecular intermediate continues to crack at the acidic site of the catalyst to form some small molecular hydrocarbon fragments;?d?the hydrocarbon fragments undergo reforming,aromatization,isomerization at the active sites in the pores of the catalyst to ultimately form hydrocarbon compounds,particularly aromatic hydrocarbon products.