Research On Catalytic Fast Pyrolysis Of Rice Husk Over Hierarchical Micro-mesoporous Composite Molecular Catalyst Prepared High Quality Bio-oil Based On Deoxygenation And Hydrogenation Techniques

As the economy develops,the massive consumption of fossil energy causes environmental and resource problems.The search for and development of low-cost and high-efficiency fossil fuel alternatives is getting more and more attention.As a kind of renewable energy,biomass energy converted into bio-oil by pyrolysis is one of the important ways to alleviate the serious energy and environmental problems.However,bio-oil has undesirable properties that prevent it from being used as transportation fuel,including high viscosity,chemical instability,low heating value,and corrosiveness.Deoxygenation and hydrogenation are needed to optimize the quality of the bio-oil in the process of catalytic fast pyrolysis of biomass.This thesis studied catalytic fast pyrolysis of rice husk,especially from the perspective of"deoxygenation and hydrogenation".For the“deoxygenation”:the HZSM-5catalyst is modified with organic base solution.On this basis,dating mesoporous molecular sieve catalyst MCM-41 as the shell on the surface of HZSM-5 modified by organic base,and hierarchical micro-mesoporous composite molecular catalyst was prepared.Microwave assisted catalytic fast pyrolysis(MACFP)of rice husk were carried out;Meanwhile,for the“hydrogenation”:cince biomass itself is a hydrogen-deficient raw material,it can provide a hydrogen source(waste greenhouse plastic films,WGPFs)to rice husks and produce a synergistic effect to optimize the quality of bio-oil.Moreover,the catalytic hydropyrolysis of biomass based on the H₂ active atmosphere provides new ideas for the hydrogenation and deoxygenation of bio-oil.The organic alkaline solution was used to modify HZSM-5,and the catalyst was characterized by X-ray diffraction,transmission electron microscopy,N₂adsorption-desorption and temperature-programmed ammonia adsorption-desorption.The results showed that mesoporous structure appeared on the HZSM-5.This modification was removing some of the strong acidic sites on the outer surface and retaining the weak acidic sites on the inside of HZSM-5.In MACFP of rice husk over HZSM-5 modified by TPAOH solution at 550°C,the highest liquid yield(41.5wt.%)was obtained.As the concentration of TPAOH modified solution increases,the relative content of hydrocarbons including benzene,toluene,ethylbenzene and xylene(BTEX)increases and reaches the maximum(45.9%)when using 2.0mol/L TPAOH modified HZSM-5 catalyst(HT-2.0).The organic base TPAOH modified HZSM-5 effectively reduced coke production.Because of the disadvantage of random disorder on the surface of organic base modified HZSM-5 catalyst,CTAB template was used as a precursor of MCM-41,and the organic base modified HZSM-5 catalyst was constructed a second time.Hierarchical micro-mesoporous composite molecular catalyst was prepared,which was"core-shell"structure.The highest hydrocarbon yield(60.5%)was obtained for a catalyst modified by a 2.0 mol/L TPAOH solution,with 10wt.%of CTAB(MCM-41 precursor),as well as with digestion and crystallization at 110°C for 24h.The shell of MCM-41 in mesoporous composite molecular sieve catalyst has an important influence on the selectivity of monocyclic aromatic hydrocarbons.The low coating and excessive assembly of mesoporous catalysts will lead to a decrease in the selectivity to aromatic hydrocarbons.The lower crystallization temperature reduces the formation of MCM-41 catalyst on the surface of HZMS-5.Moreover,the high crystallization temperature destroys the structure of HZSM-5.The low-coated mesoporous molecular sieve reduces the initial cracking of polycyclic aromatic hydrocarbons,which results in the condensation of macromolecules on the surface of HZSM-5 to form coke.On the other hand,too much mesoporous catalyst relatively reduces the number of catalytic active sites on the microporous catalyst,thereby reducing catalyst activity.Combining microwave heating and fluidized bed reactor technology,a microwave fluidized bed was built to further improve the efficiency of CFP of biomass.Compared the difference between the MACFP of rice husks in a fluidized bed and a fixed bed,the liquid phase yield using a microwave fluidized bed increased significantly.The relative content of hydrocarbons(67.6%)is significantly higher than that in the fixed-bed pyrolysis products(60.5%).The increase of catalyst will promote the decarbonylation and decarboxylation reactions,thereby producing more hydrocarbon compounds.Additionally,too much catalyst do not lead to higher monocyclic aromatic hydrocarbon selectivity.The relative content of hydrocarbons was reduced from 67.6%to 58.3%after four catalyst regenerations.With the increase of regeneration times,the meso-microporous composite molecular sieve catalyst has high reusability and good anti-coke ability.It offers possibilities for future mass production use.High H/C_eff materials(polyhydrogen feedstock)to assist biomass catalytic pyrolysis is an effective method to increase the total feedstock H/C_eff.The catalytic fast co-pyrolysis of rice husk and waste greenhouse plastic films was carried out to enhance the hydrodeoxygenation and deoxygenation.Compared with products from fast co-pyrolysis are mostly long-chain aliphatic hydrocarbons,the hydrocarbon products from co-CFP processing are aromatics and short-chain aliphatics.When the mass ratio of rice husk to waste greenhouse plastic films is1:1.5,the relative content of hydrocarbons reaches a maximum(71.1%).In the microwave fluidized bed experiment.The hydrogen supply of the multi-hydrogen feedstock slows down the process of deep dehydrogenation and coking of the precursors.When the mass ratio of RH to WGPFs is 1:1.5 using microwave fluidized bed,the relative content of hydrocarbons is significantly improved compared to rice husk alone catalytic pyrolysis,the value is 76.9%.In order to further hydrogenation,the new idea of catalytic hydropyrolysis(CHP)of rice husk was carried out.The coke yield from catalytic hydropyrolysis of rice husk was reduced2.3wt.%compared with CFP.The presence of hydrogen reduces the coking reaction and increases the production of gaseous hydrocarbon products.In CHP process,decarbonylation and decarboxylation reactions are enhanced.The relative content of hydrocarbons is higher than that from CFP.The higher pressure can increase the catalytic activity,promote the dehydration of intermediate oxygen-containing compounds to generate hydrocarbons,and reduce the formation of coke.High temperature in CHP will improve the cracking of coke and macromolecular transition aromatics,resulting in high selectivity to methane and light olefins.In addition,quantum chemical simulation of guaiacol,an important part of rice husk lignin,was carried out,and the reaction path of hydrogen pyrolysis was expounded in terms of mechanism.