Study On Catalytic Pyrolysis Characteristics Of Eucalyptus Based On Zinc-Iron Modified HZSM-5

Biomass is a rich source of renewable carbon and has the potential to replace fossil energy.Its efficient use is of great significance for protecting the global environment,diversifying energy sources and improving energy security.The bio-oil obtained by biomass pyrolysis technology can be converted into industrial raw materials for producing gasoline,diesel and aviation kerosene by hydrorefining,forming a substitute effect on crude oil.However,bio-oil defects such as high oxygen content,high water content,acidity,and low calorific value need to be improved.Catalytic pyrolysis technology is beneficial to the production of high quality bio-oil,which is one of the ways to beneficially convert biomass into high-value products.In this paper,the catalyst for biomass catalytic pyrolysis was modified and modified.A zeolite molecular sieve catalyst(HZSM-5)was modified with different ratios and loadings using zinc and iron.The effects of modified HZSM-5 catalyst on woody bio-oil were studied by thermogravimetric analysis and rapid pyrolysis-chromatography-mass spectrometry(PY-GC/MS).Through characterization experiments,it was found that the specific surface area and pore volume of the modified HZSM-5 catalyst decreased slightly(5.7%-29.3%,0.8%-25.2%)and the average pore diameter increased slightly compared with the original HZSM-5.(2.2%-18.6%).The structure of the modified HZSM-5 molecular sieve was not destroyed in the wet impregnation,and the metal oxide was well dispersed.The number of acidic sites decreases as the metal loading is introduced.The multi-case thermogravimetric experiments show that the pyrolysis of eucalyptus can be roughly divided into three stages: dehydration baking,rapid devolatilization and continuous slight devolatilization.The peak weight loss rate and peak temperature of the rapid devolatilization stage varied greatly with the catalysts.The lowest peak temperature(356.7 °C)and the maximum weight loss rate(-12.17%/min)appeared with HZSM-5 and 1Zn4 Fe.The catalytic pyrolysis characteristics of the three modified catalysts of 5Fe,5Zn and 1Zn4 Fe are better than those of untreated HZSM-5.In the range of conversion ? = 0.3-0.7,the average activation energy of eucalyptus was effectively reduced under the catalyst of 5%-metal HZSM-5.It was found by PY-GC/MS experiments that the peak area of the product at 600 °C was the largest,and the peak area of beneficial products such as phenols,alcohols,and furans reached the maximum at 600°C.In the presence of HZSM-5,the peak area of aromatic hydrocarbons continued to rise rapidly with the residence time,and the peak area of phenols and aldehydes decreased first and then increased;the peak areas of acids,sugars,furans and other substances increased first and then cut back.The modified HZSM-5 is advantageous for promoting the reduction of the amount of acid and ketone.Three modified catalysts,2.5Zn&Fe,1Zn4 Fe and 2Zn8 Fe,effectively promoted the formation of monocyclic aromatic hydrocarbons.The peak area of benzene,toluene and xylene in the 1Zn4 Fe group exceeded that of the HZSM-5 group,which was beneficial to increase the product value.The Zn-Fe co-modified catalyst exhibited better activity than the Zn or Fe modified HZSM-5 in the process of adding some monocyclic aromatic hydrocarbons.Iron loading tends to exacerbate the coking of the catalyst in pyrolysis,and zinc exhibits a mitigating effect on coking because it weakens the acid strength.