Experimental Study On Preparation Of Bio-oil With Highly Selective Aromatics By Catalytic Pyrolysis Of Biomass

Compared with fossil fuels,biomass energy has attracted widespread attention due to its characteristics which were rich in resources,renewable,environmentally friendly and so on.Among the many biomass energy utilization technologies,the biomass pyrolysis liquefaction which could obtain the high value-added chemical raw materials or alternative products of fossil fuels was oncerned a lot.However,there are some negative properties of bio-oil such as complex components,the high oxygen and water contents,high viscosity,and low energy density,so its quality promotion research is imperative.Rapid catalytic pyrolysis can convert biomass into aromatic hydrocarbons,including toluene,xylene,naphthalene and other gasoline raw materials and chemical materials,is one of the most promising technologies of biomass high-quality utilization.In this article,the fast catalytic pyrolysis of cellulose and hemicellulose and the on-line catalytic upgrading of biomass were carried out from the modified catalyst preparation,then the experimental verification of biomass catalytic pyrolysis for preparing high quality bio-oil was concerned.The catalytic mechanism in pyrolysis progress of aromatic hydrocarbons was discussed and a new method on preparation of bio-oil with high selective aromatics and the auxiliary pretreatment of raw materials was explored.The research work in this paper includes the following aspects:The biomass directly pyrolysis,catalytic pyrolysis under HZSM-5 and acid treatment were carried out.It indicate that: the HZSM-5 with different Si/Al ratio was used in the pyrolysis reaction,the yield of liquid decreased,and the highest relative content of aromatics in bio-oil was 14.33%.With the increase of Si/Al ratio,the catalytic effect was weakened.With the increase of C/B(catalysts/biomass)of HZSM-5(25),the yield of bio-oil gradually decreased,and the aromatics content increased significantly.The condition of 8%-HCl+HZSM-5 facilitated the simplification of the oil components,and the relative content of the hydrocarbons increased to 21.15%.In order to further improve the catalytic performance and increase the yield and selectivity of aromatics,the modification of HZSM-5 by Fe,Zr and Co was studied.The results showed that after modfication the distribution was more concentrated.The lattice diffraction peaks of HZSM-5 were observed in all the catalysts.And the specific surface area,pore volume and average pore diameter of the modified catalysts all decreased,and the arrangement is more compact and tidy.The metal modification contributes to the increase of the acid sites of the HZSM-5 catalysts,thereby increasing the reactivity during the pyrolysis process.In this regard,the effect of Fe is superior to that of Zr and Co.With the increase of the Fe loading,the center signal intensity of the strong acid was increasing.Catalytic pyrolysis of cellulose and hemicellulose as the representative model of biomass samples under various catalysts was carried out.For cellulose on-line pyrolysis,with the increase of Fe and Zr loading,the relative content of aromatics increased,mainly contained the increase of naphthalene and xylene.With the introduction of the catalytic reforming for the cellulose pyrolysis steam,the content of aromatics increased significantly,and 4FeHZSM-5 and 4ZrHZSM-5 were more effective,the contents were up to 33.13% and 30.07%,respectively.Higher contents of aromatics were obtained in hemicellulose on-line catalytic pyrolysis.Under the Fe-based catalysts,the selectivity of 2-methyl-naphthalene was the best.The selectivity of the main aromatics procucts changed little under the Zr-based catalysts,and the selectivity of xylene was the best under the Co-based catalysts.The relative content of aromatics raised up to 68.15%(4Fe/HZSM-5)in the fast catalytic pyrolysis of hemicellulose,and the content of 2-methyl-naphthalene was the highest.Meanwhile,the main formation mechanism of aromatic hydrocarbons in the cellulose and hemicellulose pyrolysis process was also discussed,which could provide the theoretical guidance for the preparation of highly selective aromatic hydrocarbon bio-oil by biomass pyrolysis.The on-line catalytic pyrolysis of biomass feedstocks was carried out.The results showd that: Fe-based catalysts could comprehensively promote the increase of aromatics content,and the selectivity of 1-methyl-naphthalene increased.Zr-based catalysts promoted the content of aromatic hydrocarbons as well as the content of ketones and furan compounds increased.With the increase of Zr loading,the selectivity of toluene and xylene raised,while the selectivity of naphthalene was decreased.Co-based catalysts have no effect on improving the total content of aromatics,but the content and selectivity of toluene and xylene were increased with the increase of Co loading.The relative contents of aromatics in the pyrolysis oil of four biomass feedstocks reached a high level,were 40.52%(Pine),38.60%(Cypress),34.67%(Cotton)and 35.18%(Canola)respectively under 4Fe/HZSM-5 catalysts.Finally,the verification experiments were carried out to produce high quality bio-oil by fast pyrolysis under the condition of continuous feeding of biomass.It was found that the introduction of the three metal components further reduced the liquid yield compared to the HZSM-5 catalysis.4Fe/HZSM-5 was especially beneficial to the formation of naphthalene and its derivatives at the same time of increasing the content of various aromatic hydrocarbon components.With the increase of Fe loading,the yield of bio-oil decreased,and the relative contents of aromatics components in the bio-oil showed an increasing trend.Under HCl-P and NaBH4-P conditions,the relative content of aromatics increased significantly,up to 54.46%,and the catalytic effect of 4Fe/HZSM-5 was further verified.Moreover,a new method of preparation of high quality bio-oil based on the combination of the pretreatment and catalytic pyrolysis was proposed.The recearch supplied a good exploration for biomass catalytic pyrolysis based on the preparation of highly selective aromatic hydrocarbon bio-oil,which provided a reference for the improvement of biomass pyrolysis liquefaction process.