Research On Catalytic Pyrolysis Of Biomass To Advanced Liquid Fuel

Considering that biomass energy is the only carbon-based renewable energy.It is of great significance to convert biomass energy into carbon-based liquid bio-fuel in order to replace or partly replace the consumption of traditional fossil fuels.The process of “biomass fast pyrolysis and supercritical upgrading” has the disadvantage of complex equipment and stable oxygenated organic liquid fuel.In this paper,biomass catalytic pyrolysis was used to simplify the subsequent upgrading process,and the target products were directionally regulated to non-oxygenated hydrocarbon liquid fuels.In order to achieve this goal,this paper combines experimental research with density functional theory.Firstly,catalytic pyrolysis of biomass cellulose,hemicellulose and lignin and directional regulation of products were achieved.Secondly,the effects of catalyst and pyrolysis conditions on the three components were studied by setting different catalysts and pyrolysis parameters.The similarities and differences of catalytic pyrolysis among the three components were pointed out.Finally,the reaction pathways of the three components in catalytic pyrolysis were obtained.On the basis of catalytic pyrolysis and directional regulation of three major components,the catalytic pyrolysis was completed by using actual biomass as raw material.Subsequently,the metal bifunctional catalytic active sites were introduced to study the effects of different metal active sites on the target products.Finally,with chromium as the representative,the loading of metal active center amount was changed,the acidity and pore size of catalyst were adjusted,the hydrocarbon yield was further improved,and the process energy conversion was increased.The results of catalytic pyrolysis of cellulose,hemicellulose and lignin showed that: The pyrolysis products of the three components can be directionally regulated as hydrocarbon fuels without oxygen,such as alkanes,alkenes,monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons.HZSM-5 series catalysts produce the most C1-C4 alkanes,olefins and C6-C10 monocyclic and polycyclic aromatic hydrocarbons due to excellent acidic active sites and appropriate pore structure.With the increase of Si/Al ratio,the yield of target products of HZSM-5 series catalysts decreases gradually.HY is not suitable for directional conversion of pyrolysis products to alkanes,olefins and aromatic hydrocarbons.Because of its large pore structure,H? has high selectivity for PAHs.Higher catalyst to feedstock ratio can effectively promote the catalytic deoxidation reaction of pyrolysis intermediates,and then promote the formation of non-oxygenated hydrocarbon products.The increase of pyrolysis temperature promotes the production of alkanes and alkenes,and ultimately leads to the increase of the yield of monocyclic and polycyclic aromatic hydrocarbons.When the temperature rises further,for cellulose and hemicellulose higher than 650? and for lignin higher than 600?,monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons may further react with alkenes to form PAHs.It can be observed that the yield of anthracene continues to increase at 700?,resulting in carbon deposition.The heating rate has a great influence on the catalytic pyrolysis of cellulose and lignin.Flash pyrolysis can effectively increase the yield of monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons.There was no significant difference in the heating rate of hemicellulose above 100K/s.The catalytic pyrolysis mechanism of cellulose and hemicellulose can be divided into four stages,namely,pyrolysis stage-deoxygenation of pyrolysis products to produce non-oxygenated small molecules stage-cyclization and polymaerization stage of non-oxygenated small molecules-secondary cyclization of monocyclic aromatic hydrocarbons to produce polycyclic aromatic hydrocarbons stage.For lignin catalytic pyrolysis,based on the experimental results of lignin catalytic pyrolysis and density functional theory,taking DMPD as a typical lignin dimer as the research object,two reaction pathways,Route 1 "small molecule deoxygenation and polymerization" and Route 2 "benzene ring direct deoxygenation",were compared.It was considered that Route 1 was the main reaction pathway in lignin catalytic pyrolysis,while Route 2 was the secondary one.The effects of reaction parameters,average pore size of catalyst and small molecular hydrocarbons on the two reaction pathways were discussed.The optimum conditions for cellulose catalytic pyrolysis are: HZSM-5(23),catalyst feed ratio of 5:1,pyrolysis temperature of 650? and heating rate of 10 000 K/s.The highest yields of C1-C4 alkanes,alkenes and total gaseous hydrocarbons are 0.592%,1.451% and 2.043%,respectively.The yields of monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons were 9.895% and 12.907%,respectively.The total yield of aromatic hydrocarbons was 22.802%.The optimum conditions fo hemicellulose catalytic pyrolysis are: HZSM-5(23)is used as catalyst,the ratio of catalyst raw material is 5:1,the pyrolysis temperature is 650?,and the heating rate is 10 000 K/s.The highest yields of C1-C4 alkanes,alkenes and total gaseous hydrocarbons are 0.793%,1.709% and 2.501%,respectively.The yields of monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons were 12.964% and 19.807%,respectively.The total yield of aromatic hydrocarbons was 32.771%.The optimum conditions for lignin catalytic pyrolysis are: HZSM-5(23),catalyst feed ratio of 5:1,pyrolysis temperature of 600? and heating rate of 10 000 K/s.The highest yields of C1-C4 alkanes,alkenes and total gaseous hydrocarbons are 1.55%,1.79% and3.34%,respectively.The yields of monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons were 5.750%and 1.882%,respectively.The total yield of aromatic hydrocarbons was 7.631%.In the process of catalytic pyrolysis of three biomass components,faster heating rate and higher catalyst feed ratio are needed.The inflection point of pyrolysis temperature,methane yield and selectivity of monocyclic aromatic hydrocarbons(MAHs)and polycyclic aromatic hydrocarbons(PAHs)are different for three major components of biomass.The experimental results of actual biomass showed that lignocellulose biomass from agricultural and forestry wastes can be converted into hydrocarbon liquids by catalytic pyrolysis.Compared with the weighted yield and actual yield,it was found that the catalytic pyrolysis of actual biomass significantly increased yield of monocyclic aromatic hydrocarbons and decreased yield of polycyclic aromatic hydrocarbons on the basis of slightly decreasing total aromatic hydrocarbon yield.Then the effects of different metal modified catalysts on the catalytic pyrolysis of biomass were studied.The results show that 5% Cr/HZSM-5 is the only metal modified catalyst higher than HZSM-5(23).The 5% Ga/HZSM-5,5% Sn/HZSM-5 and 5% Pt/HZSM-5 are slightly lower than HZSM-5(23),but the yield of monocyclic aromatic hydrocarbons is slightly higher than that of HZSM-5(23),while the yield of polycyclic aromatic hydrocarbons is slightly lower,which indicates that the above metal modified catalyst also has good reactivity and certain potential.Then the effects of different loads of Cr/HZSM-5 on the catalytic pyrolysis of biomass were studied.The results show that the selectivity of monocyclic aromatic hydrocarbons can be effectively improved and polycyclic aromatic hydrocarbons can be reduced by a very small amount of Cr metal modification.According to the final calculation,the biomass catalytic pyrolysis is 22.92% for a large number of non-oxygen hydrocarbon liquid fuels.If the gaseous hydrocarbons produced by catalytic pyrolysis are taken into account,the energy conversion can be further increased to 32.75%.