| With the fossil fuels depleting,people were eager to find available alternative energy sources.Biomass energy is clean and has a wide distribution,the bio-oil can be obtained by the rapid pyrolysis of biomass,but the crude bio-oil has bad quality,it can't be used as fuel and should be upgraded.The most commonly used method to improve the quality of bio-oil is on-line catalytic pyrolysis,and the commonly used catalyst is HZSM-5.However,the macromolecules in the biomass pyrolysis gas could block the pores of HZSM-5 with small pore size,and leading to the catalyst inactivation.But by using the MCM-41 with large pore size can crack the macromolecules into small molecules.In this paper,the rape straw was used as biomass materials,the MCM-41 and HZSM-5 were uniformly mixed in different proportions,the mixed catalysts were used to the on-line catalytic pyrolysis of rape straw.The paper also studied the effect of catalyst mixing ratios on the improvement of quality of bio-oil.The main contents of the work were as follows:The HZSM-5 and MCM-41 all with Si/Al ratio of 50 were uniformly mixed in different proportions.The mixed catalysts were used to catalyze the rape straw pyrolysis vapors.The effects of mixing ratios on the physical and chemical properties of organic phase and the yield of product were studied.The results showed that the yields of the solid phase obtained by the mixed catalysts were all about 25%.When the content of MCM-41 in the mixed catalyst was less than 50%,the yields of gas phase increased to 45.9%,the yield of liquid phase gradually decreased to 29.5%,and the yield of organic phase gradually decreased to 17%,respectively,in addition,the density of the bio-oil organic phase gradually decreased to 0.94 g/cm~3 and the kinematic viscosity gradually decreased to 5.06 mm~2/s,respectively,the pH value gradually increased to 5.41 and the calorific value gradually increased to 34.31 kJ/mol,respectively,with the increase of MCM-41 content.When the content of MCM-41 was over 50%,the yield of gas phase,liquid phase,organic phase and the physicochemical property of the bio-oil all showed opposite trend of change with the increase of content of MCM-41(compared to the content of MCM-41 less than 50%).The compositions of bio-oil organic phase obtained by different mixed catalysts were qualitatively analyzed,the results showed that there were several kinds of functional groups in the bio-oil organic phase,and they corresponded to several organic species,including phenols alcohols,carboxylic acids,aldoketones,and hydrocarbons.The compositions of bio-oil organic phase were semi-quantitatively analyzed.The results showed that with the increase of MCM-41 content,the content of hydrocarbon in the organic phase increased first,and then decreased,the content of carbonyl(aldehydes and ketones)substance decreased first,and then increased,so as the stability of bio-oil.When HZSM-5 and MCM-41 were uniformly mixed in the ratio of 1:1,the content of hydrocarbon was higher,which was 53.83%,the content of carbonyls was lower,which was 6.35%.The change of composition of coke on the deactivated catalysts,the coking rate,the type of coke and the physical properties of the deactivated catalysts with different mixing ratios were analyzed.The results showed that,all the coke on the deactivated catalysts were composed of varieties of organic compounds,including phenol alcohols,aldoketones,carboxylic acids and hydrocarbons.With the increase of MCM-41 content in the mixed catalysts,the coking rate on the deactivated mixed catalysts gradually decreased first,and then tended to be stable,remaining at 13.43%.And when the content of MCM-41 was less than 50%,the mixed catalysts contained more amorphous coke,while the change rates of pore volume and the specific surface area of the deactivated mixed catalysts decreased continuously.When the content of MCM-41 exceeded 50%,the mixed catalysts contained graphite coke only,and the activity of mixed catalysts tended to be stable. |
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