Promoted Production Of Hydrocarbons In The Catalytic Pyrolysis Of Rape Straw Over Core-shell HZSM-5@MCM-41 Catalysts

Recently,the focus of the researchers are the increasing severe energy supply situation and the deterioration of the ecological environment.Bio-oil produced by biomass pyrolysis can partially replace fossil fuels and can meet the requirements of sustainable development and green chemistry.Due to its low calorific value,high viscosity,strong corrosiveness and poor stability,pyrolysis oil cannot be used directly.Therefore,the pyrolysis oil needs to be catalytically upgraded.The micropores in the zeolite molecular sieve HZSM-5 are beneficial to the production of aromatic compounds in the process of catalytic pyrolysis of biomass,but can cause coke to be deposited on the catalyst.In this paper,rape straw was used as the matrials to study a series of problems in the application of micro-mesoporous composite catalyst HZSM-5@MCM-41 in the experiment of biomass catalytic pyrolysis.First,using cetyltrimethylammonium bromide（CTAB）as a mesoporous template,a core-shell catalyst HZSM-5@MCM-41 with different mesoporosities was prepared,and the effect of the addition amount of the template on the surface physics of the catalyst was determined.And then,the influence of characteristics,the structure-activity relationship between the mesoporosity of the core-shell catalyst and the composition of the bio-oil was explored,the core-shell catalyst was prepared with the optimal template agent addition amount.And on this basis,the HZSM-5@MCM-41 The best kinetic parameters of the catalytic upgrading test,comparing the yield of the target product hydrocarbons in the bio-oil under different test conditions,and exploring the influence of different test conditions on the product composition.Finally,the HZSM-5@MCM-41 A study on the loading modification of metal lanthanum（La）was carried out,and the catalytic properties of HZSM-5@MCM-41 with different loading positions of metal La were explored,and TG and hydrofluoric acid destruction-dichloromethane extraction（HF-CH₂CL₂）were used.With other analytical methods,the amount of coke and coke composition on the catalyst after use were determined,the formation mechanism of coke was preliminarily investigated,and the service life of the catalyst was determined by the regeneration-recycling method.The specific research content is as follows:（1）Using commercial HZSM-5 as the core and cetyltrimethylammonium bromide（CTAB）as the template,the core-shell catalyst HZSM-5@MCM-41 was prepared by the hydrothermal recrystallization method.In the preparation process of the catalyst,the input mass ratio of CTAB and HZSM-5 can be changed,and core-shell catalysts with different mesoporosities can be obtained.Characterization methods such as TEM,BET,NH₃-TPD,and XRD are used to perform surface physics on each core-shell catalyst.The results show that,compared with HZSM-5,the core-shell catalyst modified with CTAB as a template has a certain degree of increase in mesoporous pores;when the mass ratio（THR）of the added CTAB to HZSM-5 original powder is1,HZSM-5@MCM-41（THR=1）has the highest mesopore volume ratio（71.8 wt%）,the external specific surface area reaches 450.5 m²/g,and the strong acid site content reaches the highest value of 26.0μmol/g.This improvement promotes the cleavage of loose oxygen-containing compounds and inhibits the polymerization reaction on the surface of the core HZSM-5,thereby producing more aromatic compounds.With the increase in the amount of template agent,the yield of liquid phase products continues to increase,but the yield of target hydrocarbons first increases and then decreases;when HZSM-5@MCM-41（1）is used as a catalyst,the production of hydrocarbons.The maximum reaches 11.43wt%,which is about 1.5 times that of HZSM-5 catalyzed.In addition,the total yield of hydrocarbons is positively correlated with the mesoporosity of the catalyst.（2）Using HZSM-5@MCM-41（THR=1）as the catalyst,the influence of factors such as pyrolysis temperature,catalytic temperature,catalyst and biomass mass ratio on the product composition was investigated.The results show that,compared with HZSM-5 for catalysis,when the core-shell catalyst HZSM-5@MCM-41 is used,the influence of the pyrolysis temperature and the mass ratio of catalyst to biomass varies greatly.When the pyrolysis temperature is 450°C,The yield of hydrocarbons reaches 10 wt%.With the increase of temperature,the yield of hydrocarbons reaches the highest（11.43 wt%）at 500°C.When the temperature rises to 600°C,the primary cracking of pyrolysis gas becomes more sufficient,thereby generating more short-chain intermediates,leading to an increase in the yield of gas phase products.When using HZSM-5,a higher pyrolysis temperature（550°C）is required to promote the pyrolysis of biomass pyrolysis gas.When using a core-shell catalyst,its mesoporous pores can achieve the function of pre-cracking,so the optimal pyrolysis temperature shifts to the low temperature zone.The catalytic temperature and the mass ratio of catalyst to biomass directly affect the pyrolysis of biomass pyrolysis gas.The degree of reaction,deoxygenation reaction,aromatization reaction,the optimal catalytic temperature,and the mass ratio of catalyst to biomass are 550°C and 1:2,respectively.（3）In order to improve the acid distribution of the core-shell catalyst HZSM-5@MCM-41,the metal La was loaded on the core HZSM-5 and the shell MCM-41 respectively,and the metal was loaded on the micropores and mesopores respectively.The results show that by loading metal La on the micropores,the relative peak area ratio of hydrocarbons can be increased,and the focus is on conversion to low-carbon hydrocarbons（C₇H₈）.While loading metal La on the mesopores,the yield of bio-oil can be improved,and the yield of the target product hydrocarbons also increases.As the ratio of oxygenated compounds increases,the flammability of bio-oil decreases.Therefore,it is more beneficial to improve the quality of bio-oil after the metal is loaded on the micropores to generate the mesopores.At this time,the yield of the target product monocyclic aromatic hydrocarbon was 10.47wt%,which was only 1.13%lower than when it was first used.After the fourth use,the yield of the target product has been significantly reduced compared with the previous one.The yield is 7.59wt%,which is still higher than the hydrocarbon yield of the microporous HZSM-5 catalyst,so the core-shell catalyst has a higher regeneration-cycle service life.